Author name code: hauschildt ADS astronomy entries on 2022-09-14 author:"Hauschildt, Peter H." ------------------------------------------------------------------------ Title: EMISSA (Exploring millimetre indicators of solar-stellar activity). II. Towards a robust indicator of stellar activity Authors: Mohan, A.; Wedemeyer, S.; Hauschildt, P. H.; Pandit, S.; Saberi, M. Bibcode: 2022A&A...664L...9M Altcode: 2022arXiv220804217M Context. An activity indicator, which can provide a robust quantitative mapping between the stellar activity and the physical properties of its atmosphere, is important in exploring the evolution of the observed active phenomena across main-sequence stars of different spectral types. Common activity indicators do provide qualitative correlations with physical properties such as Teff and the rotation period, among others. However, due to the large variability in their values, even for a single star, defining robust quantitative mappings between activity and physical properties is difficult. Millimetre (mm) wavelengths probe the different atmospheric layers within the stellar chromosphere, providing a tomographic view of the atmospheric dynamics.
Aims: The project aims to define a robust activity indicator by characterising mm brightness temperature spectra (TB(ν)) of the cool main-sequence stars (Teff ∼ 5000-7000 K) compiled by Paper I in this series. The sample contains 13 stars, including the Sun.
Methods: We derived the mm TB(ν) spectral indices (αmm) for cool stars, including the Sun, based on observations in the 30-1000 GHz range. The derived values for αmm are explored as a function of various physical parameters and empirical power-law functions were derived. We also compared αmm estimates with other activity indicators.
Results: Despite the estimation errors, αmm values could distinguish the cool stars well, unlike common activity indicators. The low estimation errors on the derived trends of αmm vs. physical parameters suggest that αmm could be a robust activity indicator.
Conclusions: We note that αmm, which is linked to chromospheric thermal stratification and activity in cool stars, can well distinguish and physically characterise the stars more robustly than common activity indicators. We emphasise the need for multi-frequency data across the mm band for stars, with a range of physical parameters and gathered at multiple epochs during their activity cycles. This will help to explore αmm in a statistically robust manner and to study the emergence of chromospheric heating on the main sequence. Title: Solar/Stellar atmospheric tomography with mm - cm data: Initial catalogue of main sequence stars and results Authors: Mohan, Atul; Wedemeyer, Sven; Pandit, Sneha; Saberi, Maryam; Hauschildt, Peter Bibcode: 2022cosp...44.2495M Altcode: Millimeter - Centimeter (10 - 1000 GHz) bands are particularly sensitive to emission from various outer atmospheric layers of main sequence stars, with shorter wavelengths probing deeper layers. This makes the study of mm - cm spectra (S$_{obs}$) a unique tool to study the vertical atmospheric stratification of these stars as a function of various physical parameters. A major challenge in the field of mm astronomy had been the lack of a sensitive interferometer which can not only detect the faint $\sim$ 10 - 100 $\mu$Jy level atmospheric fluxes robustly from these stars, but also provide enough spatial resolution needed to distinguish any emission from companion stars and stellar disks. With the advent of the Atacama Large Millimeter/Sub-millimeter array, the aforementioned hurdles have been overcome to a great extent for at least the stars within a distance of 10\,pc.\\ In this work, we gathered the archival data of main sequence stars robustly detected with ALMA, and additionally reported 10 - 80 GHz fluxes if any, from other modern interferometric arrays like ATCA, JVLA etc. The data for the Sun were also gathered and the disk-averaged fluxes were recorded to get the sun-as-a-star spectrum. The resulting sample comprises of 12 main sequence stars plus the sun-as-a-star covering an effective temperature (T$_{eff}$) range of 3000 - 10000 K. We compared their observed fluxes against respective purely photospheric model fluxes obtained using the PHOENIX code (S$_{model}$) and obtained the upper atmospheric excess energy spectrum ($\Delta$S/S$_{model}$ = S$_{obs}$/S$_{model}$ - 1 ). We find evidence for a stratified atmosphere which gets progressively hotter with height in cool stars (T$_{eff}$ < 7000 K). The spectral index of the observed mm-cm brightness spectrum, was characterised for every star in the sample with sufficient data. The steepness was found to decrease with T$_{eff}$, possibly hinting at steeper thermal gradients in cooler stars. This study demonstrates the potential of mm - cm band diagnostics to perform atmospheric tomography in cool stars and that long duration light curves for these stars can be powerful tools for studying the dynamics across different layers. This calls for the need to have dedicated long duration surveys of nearby cool stars in mm - cm bands assisted by state of the art modelling to better understand the nature of atmospheric stratification and dynamics in cool stars as a function of stellar type. Title: OPTAB: Public code for generating gas opacity tables for radiation hydrodynamics simulations Authors: Hirose, Shigenobu; Hauschildt, Peter; Minoshima, Takashi; Tomida, Kengo; Sano, Takayoshi Bibcode: 2022A&A...659A..87H Altcode: 2021arXiv211205689H We have developed a public code, OPTAB, that outputs Rosseland, Planck, and two-temperature Planck mean gas opacity tables for radiation hydrodynamics simulations in astrophysics. The code is developed for modern high-performance computing, being written in Fortran 90 and using Message Passing Interface and Hierarchical Data Format, Version 5. The purpose of this work is to provide a platform on which users can generate opacity tables for their own research purposes. Therefore, the code has been designed so that a user can easily modify, change, or add opacity sources in addition to those already implemented, which include bremsstrahlung, photoionization, Rayleigh scattering, line absorption, and collision-induced absorption. In this paper, we provide details of the opacity calculations in our code and present validation tests to evaluate the performance of our code. Title: EMISSA (Exploring Millimeter Indicators of Solar-Stellar Activity). I. The initial millimeter-centimeter main-sequence star sample Authors: Mohan, A.; Wedemeyer, S.; Pandit, S.; Saberi, M.; Hauschildt, P. H. Bibcode: 2021A&A...655A.113M Altcode: 2021arXiv211013339M Context. Due to their wide wavelength coverage across the millimeter to centimeter (mm-cm) range and their increased sensitivity, modern interferometric arrays facilitate observations of the thermal and non-thermal radiation that is emitted from different layers in the outer atmospheres of stars.
Aims: We study the spectral energy distribution (Sobs(ν)) of main-sequence stars based on archival observations in the mm-cm range with the aim to study their atmospheric stratification as a function of stellar type.
Methods: The main-sequence stars with significant detection in mm bands were identified in the ALMA Science Archive. These data were then complemented with spectral flux data in the extreme ultraviolet to cm range as compiled from various catalogues and observatory archives. We compared the resultant Sobs(ν) of each star with a photospheric emission model (Smod(ν)) calculated with the PHOENIX code. The departures of Sobs(ν) from Smod(ν) were quantified in terms of a spectral flux excess parameter (ΔS∕Smod) and studied as a function of stellar type.
Results: The initial sample consists of 12 main-sequence stars across a broad range of spectral types from A1 to M3.5 and the Sun-as-a-star as reference. The stars with Teff = 3000-7000 K (F-M type) showed a systematically higher Sobs(ν) than Smod(ν) in the mm-cm range. Their ΔS∕Smod exhibits a monotonic rise with decreasing frequency. The steepness of this rise is higher for cooler stars in the Teff = 3000-7000 K range, although the single fully convective star (Teff ~ 3000 K) in the sample deviates from this trend. Meanwhile, Sobs(ν) of the A-type stars agrees with Smod(ν) within errors.
Conclusions: The systematically high ΔS∕Smod in F-M stars indicates hotter upper atmospheric layers, that is, a chromosphere and corona in these stars, like for the Sun. The mm-cm ΔS∕Smod spectrum offers a way to estimate the efficiency of the heating mechanisms across various outer atmospheric layers in main-sequence stars, and thereby to understand their structure and activity. We emphasise the need for dedicated surveys of main-sequence stars in the mm-cm range. Title: A comparison between X-shooter spectra and PHOENIX models across the HR-diagram Authors: Lançon, A.; Gonneau, A.; Verro, K.; Prugniel, P.; Arentsen, A.; Trager, S. C.; Peletier, R.; Chen, Y. -P.; Coelho, P.; Falcón-Barroso, J.; Hauschildt, P.; Husser, T. -O.; Jain, R.; Lyubenova, M.; Martins, L.; Sánchez Blázquez, P.; Vazdekis, A. Bibcode: 2021A&A...649A..97L Altcode: 2020arXiv201209129L
Aims: The path towards robust near-infrared extensions of stellar population models involves the confrontation between empirical and synthetic stellar spectral libraries across the wavelength ranges of photospheric emission. Indeed, the theory of stellar emission enters all population synthesis models, even when this is only implicit in the association of fundamental stellar parameters with empirical spectral library stars. With its near-ultraviolet to near-infrared coverage, the X-shooter Spectral Library (XSL) allows us to examine to what extent models succeed in reproducing stellar energy distributions (SEDs) and stellar absorption line spectra simultaneously.
Methods: As a first example, this study compares the stellar spectra of XSL with those of the Göttingen Spectral Library, which are based on the PHOENIX synthesis code. The comparison was carried out both separately in the three arms of the X-shooter spectrograph known as UVB, VIS and NIR, and jointly across the whole spectrum. We did not discard the continuum in these comparisons; only reddening was allowed to modify the SEDs of the models.
Results: When adopting the stellar parameters published with data release DR2 of XSL, we find that the SEDs of the models are consistent with those of the data at temperatures above 5000 K. Below 5000 K, there are significant discrepancies in the SEDs. When leaving the stellar parameters free to adjust, satisfactory representations of the SEDs are obtained down to about 4000 K. However, in particular below 5000 K and in the UVB spectral range, strong local residuals associated with intermediate resolution spectral features are then seen; the necessity of a compromise between reproducing the line spectra and reproducing the SEDs leads to dispersion between the parameters favored by various spectral ranges. We describe the main trends observed and we point out localized offsets between the parameters preferred in this global fit to the SEDs and the parameters in DR2. These depend in a complex way on the position in the Hertzsprung-Russell diagram (HRD). We estimate the effect of the offsets on bolometric corrections as a function of position in the HRD and use this for a brief discussion of their impact on the studies of stellar populations. A review of the literature shows that comparable discrepancies are mentioned in studies using other theoretical and empirical libraries. Title: A 3D radiative transfer framework: XII. Many-core, vector and GPU methods Authors: Hauschildt, P. H.; Baron, E. Bibcode: 2021A&C....3500450H Altcode: 2021arXiv210201734H 3D detailed radiative transfer is computationally taxing, since the solution of the radiative transfer equation involves traversing the six dimensional phase space of the 3D domain. With modern supercomputers the hardware available for wallclock speedup is rapidly changing, mostly in response to requirements to minimize the cost of electrical power. Given the variety of modern computing architectures, we aim to develop and adapt algorithms for different computing architectures to improve performance on a wide variety of platforms. We implemented the main time consuming kernels for solving 3D radiative transfer problems for vastly different computing architectures using MPI, OpenMP, OpenACC and vector algorithms. Adapted algorithms lead to massively improved speed for all architectures, making extremely large model calculations easily feasible. These calculations would have previously been considered impossible or prohibitively expensive. Efficient use of modern computing devices is entirely feasible, but unfortunately requires the implementation of specialized algorithms for them. Title: Probing Spectral Formation of Type Ia Supernovae using PHOENIX Authors: DerKacy, J.; Baron, E.; Branch, D.; Hoeflich, P.; Hauschildt, P.; Brown, P.; Wang, L. Bibcode: 2021AAS...23730906D Altcode: Radiative transfer simulations of Type Ia supernova spectra provide the opportunity to compare theoretical models to observations, and to probe the impact of individual physical variations on spectral formation. I will discuss recent work using the generalized stellar atmospheres code PHOENIX probing the UV spectra of SN 2011fe, including the first known detections of C IV and Si IV in a UV supernova spectrum. The impact of other spectral formation mechanisms on the UV are also addressed, including photoionization edges, line blanketing by iron group elements, and spectral temperature dependencies. Additionally I will discuss work in progress focusing on understanding the origins of why a subset of broad-lined Ia spectra appear to be Doppler-shifted versions of core-normal spectra. Title: Studying the atmosphere of the close binary star system AADor with PHOENIX/3D Authors: Prodoehl, F.; Hauschildt, P. Bibcode: 2021AAS...23743806P Altcode: Synthetic spectra from model atmospheres are frequently used in the analysis of observed spectroscopic and photometric data. For the most part, the models are sufficiently detailed to test the current theoretical understanding of stellar and sub-stellar mass objects at various stages in their evolution. However, the vast majority of model atmospheres are constructed under the assumption that the nearest stellar neighbor is so far away that it can be safely ignored. This assumption, while safe for most stars, fails for many short period binaries. A number of binary systems have orbital separations small enough so that one of the binary members is significantly heated by its companion. In order for synthetic spectra to be useful in such cases, the standard "isolated" modeling approach must be replaced by one that includes the effects of irradiation. The AADor system is an excellent example of a well-studied non-mass transferring post-common envelope binary system. Its members are a sdOB-type primary and an extremely low mass secondary. We investigate how several PHOENIX/1D models combined to a 1.5D model can represent the AA Dor secondary and compare these results to a PHOENIX/3D model that is able to include 3D effects like transverse radiation and transmission of light close to the terminator. Title: Time series of optical spectra of Nova V659 Sct Authors: Jack, Dennis; Schröder, Klaus-Peter; Eenens, Philippe; Wolter, Uwe; González-Pérez, José Nicolás.; Schmitt, Jürgen H. M. M.; Hauschildt, Peter H. Bibcode: 2020AN....341..781J Altcode: 2020arXiv200614052J With our robotic 1.2 m TIGRE telescope, we were able to obtain eight optical spectra with intermediate resolution (R ≈ 20,000) of the Nova V659 Sct during different phases of its outburst. We present a list of the lines found in the Nova spectra. The most common features are H I, O I, Na I, Fe II, and Ca II. Studying the spectral evolution of the strong features, we found that the absorption features move to higher expansion velocities before disappearing, and the emission features show (different) asymmetries. Because of the intermediate spectral resolution, we identified and analyzed the interstellar medium absorption features present in the spectra. We detected atomic absorption features of Na I and Ca II. The sodium D lines show more complex substructures with three main absorption features at a velocity of around -10, 30, and 85 km s-1. We identified several diffuse interstellar bands (DIBs) in the Nova V659 Sct spectra and determined their velocities and equivalent widths. Title: Ultraviolet Line Identifications and Spectral Formation Near Max Light in Type Ia Supernova 2011fe Authors: DerKacy, James M.; Baron, E.; Branch, David; Hoeflich, Peter; Hauschildt, Peter; Brown, Peter J.; Wang, Lifan Bibcode: 2020ApJ...901...86D Altcode: 2020arXiv200804402D We present ultraviolet line identifications of near maximum-light Hubble Space Telescope observations of SN 2011fe using synthetic spectra generated from both SYNOW and PHOENIX. We find the spectrum to be dominated by blends of iron group elements Fe, Co, and Ni (as expected due to heavy line blanketing by these elements in the UV) and for the first time identify lines from C IV and Si IV in a supernova spectrum. We also find that classical delayed detonation models of SNe Ia are able to accurately reproduce the flux levels of SN 2011fe in the UV. Further analysis reveals that photionization edges play an important role in feature formation in the far-UV, and that temperature variations in the outer layers of the ejecta significantly alter the Fe III/Fe II ratio producing large flux changes in the far-UV and velocity shifts in mid-UV features. SN 2011fe is the best observed core-normal SNe Ia; therefore analysis of its UV spectra shows the power of UV spectra in discriminating between different metallicities and progenitor scenarios of SNe Ia, due to the fact that the UV probes the outermost layers of the SN Ia, which are most sensitive to metallicity and progenitor variations. Title: The CARMENES search for exoplanets around M dwarfs. The He I infrared triplet lines in PHOENIX models of M 2-3 V stars Authors: Hintz, D.; Fuhrmeister, B.; Czesla, S.; Schmitt, J. H. M. M.; Schweitzer, A.; Nagel, E.; Johnson, E. N.; Caballero, J. A.; Zechmeister, M.; Jeffers, S. V.; Reiners, A.; Ribas, I.; Amado, P. J.; Quirrenbach, A.; Anglada-Escudé, G.; Bauer, F. F.; Béjar, V. J. S.; Cortés-Contreras, M.; Dreizler, S.; Galadí-Enríquez, D.; Guenther, E. W.; Hauschildt, P. H.; Kaminski, A.; Kürster, M.; Lafarga, M.; López del Fresno, M.; Montes, D.; Morales, J. C. Bibcode: 2020A&A...638A.115H Altcode: 2020arXiv200506246H The He I infrared (IR) line at a vacuum wavelength of 10 833 Å is a diagnostic for the investigation of atmospheres of stars and planets orbiting them. For the first time, we study the behavior of the He I IR line in a set of chromospheric models for M-dwarf stars, whose much denser chromospheres may favor collisions for the level population over photoionization and recombination, which are believed to be dominant in solar-type stars. For this purpose, we use published PHOENIX models for stars of spectral types M2 V and M3 V and also compute new series of models with different levels of activity following an ansatz developed for the case of the Sun. We perform a detailed analysis of the behavior of the He I IR line within these models. We evaluate the line in relation to other chromospheric lines and also the influence of the extreme ultraviolet (EUV) radiation field. The analysis of the He I IR line strengths as a function of the respective EUV radiation field strengths suggests that the mechanism of photoionization and recombination is necessary to form the line for inactive models, while collisions start to play a role in our most active models. Moreover, the published model set, which is optimized in the ranges of the Na I D2, Hα, and the bluest Ca II IR triplet line, gives an adequate prediction of the He I IR line for most stars of the stellar sample. Because especially the most inactive stars with weak He I IR lines are fit worst by our models, it seems that our assumption of a 100% filling factor of a single inactive component no longer holds for these stars. Title: VizieR Online Data Catalog: GJ 3512 radial velocity and light curves (Morales+, 2019) Authors: Morales, J. C.; Mustill, A. J.; Ribas, I.; Davies, M. B.; Reiners, A.; Bauer, F. F.; Kossakowski, D.; Herrero, E.; Rodriguez, E.; Lopez-Gonzalez, M. J.; Rodriguez-Lopez, C.; Bejar, V. J. S.; Gonzalez-Cuesta, L.; Luque, R.; Palle, E.; Perger, M.; Baroch, D.; Johansen, A.; Klahr, H.; Mordasini, C.; Anglada-Escude, G.; Caballero, J. A.; Cortes-Contreras, M.; Dreizler, S.; Lafarga, M.; Nagel, E.; Passegger, V. M.; Reffert, S.; Rosich, A.; Schweitzer, A.; Tal-Or, L.; Trifonov, T.; Zechmeister, M.; Quirrenbach, A.; Amado, P. J.; Guenther, E. W.; Hagen, H. -J.; Henning, T.; Jeffers, S. V.; Kaminski, A.; Kurster, M.; Montes, D.; Seifert, W.; Abellan, F. J.; Abril, M.; Aceituno, J.; Aceituno, F. J.; Alonso-Floriano, F. J.; Ammler-von Eiff, M.; Antona, R.; Arroyo-Torres, B.; Azzaro, M.; Barrado, D.; Becerril-Jarque, S.; Benitez, D.; Berdinas, Z. M.; Bergond, G.; Brinkmoller, M.; Del Burgo, C.; Burn, R.; Calvo-Ortega, R.; Cano, J.; Cardenas, M. C.; Cardona Guillen, C.; Carro, J.; Casal, E.; Casanova, V.; Casasayas-Barris, N.; Chaturvedi, P.; Cifuentes, C.; Claret, A.; Colome, J.; Czesla, S.; Diez-Alonso, E.; Dorda, R.; Emsenhuber, A.; Fernandez, M.; Fernandez-Martin, A.; Ferro, I. M.; Fuhrmeister, B.; Galadi-Enriquez, D.; Gallardo Cava, I.; Garcia Vargas, M. L.; Garcia-Piquer, A.; Gesa, L.; Gonzalez-Alvarez, E.; Gonzalez Hernandez, J. I.; Gonzalez-Peinado, R.; Guardia, J.; Guijarro, A.; de Guindos, E.; Hatzes, A. P.; Hauschildt, P. H.; Hedrosa, R. P.; Hermelo, I.; Hernandez Arabi, R.; Hernandez, Otero F.; Hintz, D.; Holgado, G.; Huber, A.; Huke, P.; Johnson, E. N.; de Juan, E.; Kehr, M.; Kemmer, J.; Kim, M.; Kluter, J.; Klutsch, A.; Labarga, F.; Labiche, N.; Lalitha, S.; Lampon, M.; Lara, L. M.; Launhardt, R.; Lazaro, F. J.; Lizon, J. -L.; Llamas, M.; Lodieu, N.; Lopez Del Fresno, M.; Lopez Salas, J. F.; Lopez-Santiago, J.; Magan Madinabeitia, H.; Mall, U.; Mancini, L.; Mandel, H.; Marfil, E.; Marin Molina, J. A.; Martin, E. L.; Martin-Fernandez, P.; Martin-Ruiz, S.; Martinez-Rodriguez, H.; Marvin, C. J.; Mirabet, E.; Moya, A.; Naranjo, V.; Nelson, R. P.; Nortmann, L.; Nowak, G.; Ofir, A.; Pascual, J.; Pavlov, A.; Pedraz, S.; Perez Medialde, A. D.; Perez-Calpena, A.; Perryman, M. A. C.; Rabaza, O.; Ramon Ballesta, A.; Rebolo, R.; Redondo, P.; Rix, H. -W.; Rodler, F.; Rodriguez Trinidad, A.; Sabotta, S.; Sadegi, S.; Salz, M.; Sanchez-Blanco, E.; Sanchez Carrasco, M. A.; Sanchez-Lopez, A.; Sanz-Forcada, J.; Sarkis, P.; Sarmiento, L. F.; Schafer, S.; Schlecker, M.; Schmitt, J. H. M. M.; Schofer, P.; Solano, E.; Sota, A.; Stahl, O.; Stock, S.; Stuber, T.; Sturmer, J.; Suarez, J. C.; Tabernero, H. M.; Tulloch, S. M.; Veredas, G.; Vico-Linares, J. I.; Vilardell, F.; Wagner, K.; Winkler, J.; Wolthoff, V.; Yan, F.; Zapatero Osorio, M. R. Bibcode: 2020yCatp021036502M Altcode: These tables list the radial velocities measured with the visual (VIS) and near-infrared (NIR) channels of the CARMENES spectrograph (Quirrenbach et al. 2018SPIE10702E..0WQ), and the stellar activity indices computed with SERVAL (Zechmeister et al. 2018A&A...609A..12Z). Photometry obtained from the Montsec, Sierra Nevada, and las Cumbres observatories is also listed here as used in the paper.

(4 data files). Title: The CARMENES search for exoplanets around M dwarfs. Photospheric parameters of target stars from high-resolution spectroscopy. II. Simultaneous multi-wavelength range modeling of activity insensitive lines (Corrigendum) Authors: Passegger, V. M.; Schweitzer, A.; Shulyak, D.; Nagel, E.; Hauschildt, P. H.; Reiners, A.; Amado, P. J.; Caballero, J. A.; Cortés-Contreras, M.; Domínguez-Fernández, A. J.; Quirrenbach, A.; Ribas, I.; Azzaro, M.; Anglada-Escudé, G.; Bauer, F. F.; Béjar, V. J. S.; Dreizler, S.; Guenther, E. W.; Henning, T.; Jeffers, S. V.; Kaminski, A.; Kürster, M.; Lafarga, M.; Martín, E. L.; Montes, D.; Morales, J. C.; Schmitt, J. H. M. M.; Zechmeister, M. Bibcode: 2020A&A...634C...2P Altcode: No abstract at ADS Title: Ultraviolet Line Identifications in Near Max Light Spectra of Type Ia Supernova 2011fe Authors: DerKacy, J. M.; Baron, E.; Branch, D.; Hoeflich, P.; Hauschildt, P. Bibcode: 2020AAS...23527627D Altcode: We present ultraviolet line identifications of near maximum-light HST observations of SN 2011fe using synthetic spectra generated from both SYNOW and PHOENIX. We find the spectrum to be dominated by blends of iron group elements Fe, Co, and Ni (as expected due to the heavy line blanketing caused by these elements in the UV) and selected ions of intermediate mass elements, including C IV, Si IV, and Mg II. We also examine the abundances of these highly ionized IME species and their distribution in velocity space. Additionally, we find that classical DDT models of Type Ia supernovae are able to accurately reproduce the flux levels of SN 2011fe in the UV. Since SN 2011fe is the best observed core-normal SNe Ia, analysis of UV spectra shows strong promise in discriminating between different metallicities and progenitor scenarios of Type Ia supernovae. This is due to the fact that the UV probes the outermost layers of the Type Ia supernova, which are most sensitive to metallicity and progenitor variations. Title: Predicting the Extreme Ultraviolet Radiation Environment of Exoplanets around Low-mass Stars: GJ 832, GJ 176, and GJ 436 Authors: Peacock, Sarah; Barman, Travis; Shkolnik, Evgenya L.; Hauschildt, Peter H.; Baron, E.; Fuhrmeister, Birgit Bibcode: 2019ApJ...886...77P Altcode: 2019arXiv191008053P Correct estimates of stellar extreme ultraviolet (EUV; 100-1170 Å) flux are important for studying the photochemistry and stability of exoplanet atmospheres, as EUV radiation ionizes hydrogen and contributes to the heating, expansion, and potential escape of a planet’s upper atmosphere. Contamination from interstellar hydrogen makes observing EUV emission from M stars particularly difficult, and impossible past 100 pc, and necessitates other means to predict the flux in this wavelength regime. We present EUV-infrared (100 Å-5.5 μm) synthetic spectra computed with the PHOENIX atmospheric code of three early M dwarf planet hosts: GJ 832 (M1.5 V), GJ 176 (M2.5 V), and GJ 436 (M3.5 V). These one-dimensional, semi-empirical, non-local thermodynamic equilibrium models include simple temperature prescriptions for the stellar chromosphere and transition region, from where ultraviolet (100-3008 Å) fluxes originate. We guide our models with Hubble Space Telescope far- and near-UV spectra and discuss the ability to constrain these models using Galaxy Evolution Explorer UV photometry. Our models closely reproduce the observations and predict the unobservable EUV spectrum at a wavelength resolution of <0.1 Å. The temperature profiles that best reproduce the observations for all three stars are described by nearly the same set of parameters, suggesting that early M-type stars may have similar thermal structures in their upper atmospheres. With an impending UV observation gap and the scarcity of observed EUV spectra for stars less luminous and more distant than the Sun, upper atmosphere models such as these are important for providing realistic spectra across short wavelengths and for advancing our understanding of the effects of radiation on planets orbiting M stars. Title: A giant exoplanet orbiting a very-low-mass star challenges planet formation models Authors: Morales, J. C.; Mustill, A. J.; Ribas, I.; Davies, M. B.; Reiners, A.; Bauer, F. F.; Kossakowski, D.; Herrero, E.; Rodríguez, E.; López-González, M. J.; Rodríguez-López, C.; Béjar, V. J. S.; González-Cuesta, L.; Luque, R.; Pallé, E.; Perger, M.; Baroch, D.; Johansen, A.; Klahr, H.; Mordasini, C.; Anglada-Escudé, G.; Caballero, J. A.; Cortés-Contreras, M.; Dreizler, S.; Lafarga, M.; Nagel, E.; Passegger, V. M.; Reffert, S.; Rosich, A.; Schweitzer, A.; Tal-Or, L.; Trifonov, T.; Zechmeister, M.; Quirrenbach, A.; Amado, P. J.; Guenther, E. W.; Hagen, H. -J.; Henning, T.; Jeffers, S. V.; Kaminski, A.; Kürster, M.; Montes, D.; Seifert, W.; Abellán, F. J.; Abril, M.; Aceituno, J.; Aceituno, F. J.; Alonso-Floriano, F. J.; Ammler-von Eiff, M.; Antona, R.; Arroyo-Torres, B.; Azzaro, M.; Barrado, D.; Becerril-Jarque, S.; Benítez, D.; Berdiñas, Z. M.; Bergond, G.; Brinkmöller, M.; del Burgo, C.; Burn, R.; Calvo-Ortega, R.; Cano, J.; Cárdenas, M. C.; Cardona Guillén, C.; Carro, J.; Casal, E.; Casanova, V.; Casasayas-Barris, N.; Chaturvedi, P.; Cifuentes, C.; Claret, A.; Colomé, J.; Czesla, S.; Díez-Alonso, E.; Dorda, R.; Emsenhuber, A.; Fernández, M.; Fernández-Martín, A.; Ferro, I. M.; Fuhrmeister, B.; Galadí-Enríquez, D.; Gallardo Cava, I.; García Vargas, M. L.; Garcia-Piquer, A.; Gesa, L.; González-Álvarez, E.; González Hernández, J. I.; González-Peinado, R.; Guàrdia, J.; Guijarro, A.; de Guindos, E.; Hatzes, A. P.; Hauschildt, P. H.; Hedrosa, R. P.; Hermelo, I.; Hernández Arabi, R.; Hernández Otero, F.; Hintz, D.; Holgado, G.; Huber, A.; Huke, P.; Johnson, E. N.; de Juan, E.; Kehr, M.; Kemmer, J.; Kim, M.; Klüter, J.; Klutsch, A.; Labarga, F.; Labiche, N.; Lalitha, S.; Lampón, M.; Lara, L. M.; Launhardt, R.; Lázaro, F. J.; Lizon, J. -L.; Llamas, M.; Lodieu, N.; López del Fresno, M.; López Salas, J. F.; López-Santiago, J.; Magán Madinabeitia, H.; Mall, U.; Mancini, L.; Mandel, H.; Marfil, E.; Marín Molina, J. A.; Martín, E. L.; Martín-Fernández, P.; Martín-Ruiz, S.; Martínez-Rodríguez, H.; Marvin, C. J.; Mirabet, E.; Moya, A.; Naranjo, V.; Nelson, R. P.; Nortmann, L.; Nowak, G.; Ofir, A.; Pascual, J.; Pavlov, A.; Pedraz, S.; Pérez Medialdea, D.; Pérez-Calpena, A.; Perryman, M. A. C.; Rabaza, O.; Ramón Ballesta, A.; Rebolo, R.; Redondo, P.; Rix, H. -W.; Rodler, F.; Rodríguez Trinidad, A.; Sabotta, S.; Sadegi, S.; Salz, M.; Sánchez-Blanco, E.; Sánchez Carrasco, M. A.; Sánchez-López, A.; Sanz-Forcada, J.; Sarkis, P.; Sarmiento, L. F.; Schäfer, S.; Schlecker, M.; Schmitt, J. H. M. M.; Schöfer, P.; Solano, E.; Sota, A.; Stahl, O.; Stock, S.; Stuber, T.; Stürmer, J.; Suárez, J. C.; Tabernero, H. M.; Tulloch, S. M.; Veredas, G.; Vico-Linares, J. I.; Vilardell, F.; Wagner, K.; Winkler, J.; Wolthoff, V.; Yan, F.; Zapatero Osorio, M. R. Bibcode: 2019Sci...365.1441M Altcode: 2019arXiv190912174M Surveys have shown that super-Earth and Neptune-mass exoplanets are more frequent than gas giants around low-mass stars, as predicted by the core accretion theory of planet formation. We report the discovery of a giant planet around the very-low-mass star GJ 3512, as determined by optical and near-infrared radial-velocity observations. The planet has a minimum mass of 0.46 Jupiter masses, very high for such a small host star, and an eccentric 204-day orbit. Dynamical models show that the high eccentricity is most likely due to planet-planet interactions. We use simulations to demonstrate that the GJ 3512 planetary system challenges generally accepted formation theories, and that it puts constraints on the planet accretion and migration rates. Disk instabilities may be more efficient in forming planets than previously thought. Title: Endeavours towards precise M-dwarf properties: Activity robust multi-line modeling in the visual and near-infrared Authors: Passegger, Vera Maria; Schweitzer, Andreas; Shulyak, Denis; Nagel, Evangelos; Hauschildt, Peter H.; Reiners, Ansgar; Amado, Pedro J.; Caballero, José A.; Cortés-Contreras, Miriam; Domínguez-Fernández, Alejandro J.; Montes, David; Quirrenbach, Andreas; Ribas, Ignasi Bibcode: 2019ESS.....433301P Altcode: A precise characterisation of planet-hosting stars is very important to derive and constrain the physical properties of orbiting planets. The CARMENES instrument, which is searching for habitable planets around M dwarfs, provides us with high-resolution spectra in the visual (0.52-0.96 μm) and near-infrared wavelength range (0.96-1.71 μm). We fit the most recent PHOENIX-SESAM stellar atmosphere models simultaneously to both wavelength ranges to determine effective temperature, surface gravity, and metallicity for 282 M dwarfs. With these temperatures we also derive stellar masses and radii using luminosities and Gaia DR2 parallaxes. Although stellar activity is widely unconsidered in stellar parameter determination, we show the importance of taking into account this property by carefully selecting magnetically insensitive lines, especially for the near-infrared wavelength range. For the first time, we directly compare stellar parameters such as effective temperature, surface gravity, and metallicity derived from multiple wavelength ranges for the same spectra. We recommend using a combination of the visual and near-infrared wavelength ranges for parameter determination in order to maximise the amount of spectral information and minimise possible effects due to model imperfections. Title: The CARMENES search for exoplanets around M dwarfs. Photospheric parameters of target stars from high-resolution spectroscopy. II. Simultaneous multiwavelength range modeling of activity insensitive lines Authors: Passegger, V. M.; Schweitzer, A.; Shulyak, D.; Nagel, E.; Hauschildt, P. H.; Reiners, A.; Amado, P. J.; Caballero, J. A.; Cortés-Contreras, M.; Domínguez-Fernández, A. J.; Quirrenbach, A.; Ribas, I.; Azzaro, M.; Anglada-Escudé, G.; Bauer, F. F.; Béjar, V. J. S.; Dreizler, S.; Guenther, E. W.; Henning, T.; Jeffers, S. V.; Kaminski, A.; Kürster, M.; Lafarga, M.; Martín, E. L.; Montes, D.; Morales, J. C.; Schmitt, J. H. M. M.; Zechmeister, M. Bibcode: 2019A&A...627A.161P Altcode: 2019arXiv190700807P We present precise photospheric parameters of 282 M dwarfs determined from fitting the most recent version of PHOENIX models to high-resolution CARMENES spectra in the visible (0.52-0.96 μm) and NIR wavelength range (0.96-1.71 μm). With its aim to search for habitable planets around M dwarfs, several planets of different masses have been detected. The characterization of the target sample is important for the ability to derive and constrain the physical properties of any planetary systems that are detected. As a continuation of previous work in this context, we derived the fundamental stellar parameters effective temperature, surface gravity, and metallicity of the CARMENES M-dwarf targets from PHOENIX model fits using a χ2 method. We calculated updated PHOENIX stellar atmosphere models that include a new equation of state to especially account for spectral features of low-temperature stellar atmospheres as well as new atomic and molecular line lists. We show the importance of selecting magnetically insensitive lines for fitting to avoid effects of stellar activity in the line profiles. For the first time, we directly compare stellar parameters derived from multiwavelength range spectra, simultaneously observed for the same star. In comparison with literature values we show that fundamental parameters derived from visible spectra and visible and NIR spectra combined are in better agreement than those derived from the same spectra in the NIR alone.

Full Tables B.1 and B.2 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/627/A161 Title: The CARMENES search for exoplanets around M dwarfs. Two temperate Earth-mass planet candidates around Teegarden's Star Authors: Zechmeister, M.; Dreizler, S.; Ribas, I.; Reiners, A.; Caballero, J. A.; Bauer, F. F.; Béjar, V. J. S.; González-Cuesta, L.; Herrero, E.; Lalitha, S.; López-González, M. J.; Luque, R.; Morales, J. C.; Pallé, E.; Rodríguez, E.; Rodríguez López, C.; Tal-Or, L.; Anglada-Escudé, G.; Quirrenbach, A.; Amado, P. J.; Abril, M.; Aceituno, F. J.; Aceituno, J.; Alonso-Floriano, F. J.; Ammler-von Eiff, M.; Antona Jiménez, R.; Anwand-Heerwart, H.; Arroyo-Torres, B.; Azzaro, M.; Baroch, D.; Barrado, D.; Becerril, S.; Benítez, D.; Berdiñas, Z. M.; Bergond, G.; Bluhm, P.; Brinkmöller, M.; del Burgo, C.; Calvo Ortega, R.; Cano, J.; Cardona Guillén, C.; Carro, J.; Cárdenas Vázquez, M. C.; Casal, E.; Casasayas-Barris, N.; Casanova, V.; Chaturvedi, P.; Cifuentes, C.; Claret, A.; Colomé, J.; Cortés-Contreras, M.; Czesla, S.; Díez-Alonso, E.; Dorda, R.; Fernández, M.; Fernández-Martín, A.; Fuhrmeister, B.; Fukui, A.; Galadí-Enríquez, D.; Gallardo Cava, I.; Garcia de la Fuente, J.; Garcia-Piquer, A.; García Vargas, M. L.; Gesa, L.; Góngora Rueda, J.; González-Álvarez, E.; González Hernández, J. I.; González-Peinado, R.; Grözinger, U.; Guàrdia, J.; Guijarro, A.; de Guindos, E.; Hatzes, A. P.; Hauschildt, P. H.; Hedrosa, R. P.; Helmling, J.; Henning, T.; Hermelo, I.; Hernández Arabi, R.; Hernández Castaño, L.; Hernández Otero, F.; Hintz, D.; Huke, P.; Huber, A.; Jeffers, S. V.; Johnson, E. N.; de Juan, E.; Kaminski, A.; Kemmer, J.; Kim, M.; Klahr, H.; Klein, R.; Klüter, J.; Klutsch, A.; Kossakowski, D.; Kürster, M.; Labarga, F.; Lafarga, M.; Llamas, M.; Lampón, M.; Lara, L. M.; Launhardt, R.; Lázaro, F. J.; Lodieu, N.; López del Fresno, M.; López-Puertas, M.; López Salas, J. F.; López-Santiago, J.; Magán Madinabeitia, H.; Mall, U.; Mancini, L.; Mandel, H.; Marfil, E.; Marín Molina, J. A.; Maroto Fernández, D.; Martín, E. L.; Martín-Fernández, P.; Martín-Ruiz, S.; Marvin, C. J.; Mirabet, E.; Montañés-Rodríguez, P.; Montes, D.; Moreno-Raya, M. E.; Nagel, E.; Naranjo, V.; Narita, N.; Nortmann, L.; Nowak, G.; Ofir, A.; Oshagh, M.; Panduro, J.; Parviainen, H.; Pascual, J.; Passegger, V. M.; Pavlov, A.; Pedraz, S.; Pérez-Calpena, A.; Pérez Medialdea, D.; Perger, M.; Perryman, M. A. C.; Rabaza, O.; Ramón Ballesta, A.; Rebolo, R.; Redondo, P.; Reffert, S.; Reinhardt, S.; Rhode, P.; Rix, H. -W.; Rodler, F.; Rodríguez Trinidad, A.; Rosich, A.; Sadegi, S.; Sánchez-Blanco, E.; Sánchez Carrasco, M. A.; Sánchez-López, A.; Sanz-Forcada, J.; Sarkis, P.; Sarmiento, L. F.; Schäfer, S.; Schmitt, J. H. M. M.; Schöfer, P.; Schweitzer, A.; Seifert, W.; Shulyak, D.; Solano, E.; Sota, A.; Stahl, O.; Stock, S.; Strachan, J. B. P.; Stuber, T.; Stürmer, J.; Suárez, J. C.; Tabernero, H. M.; Tala Pinto, M.; Trifonov, T.; Veredas, G.; Vico Linares, J. I.; Vilardell, F.; Wagner, K.; Wolthoff, V.; Xu, W.; Yan, F.; Zapatero Osorio, M. R. Bibcode: 2019A&A...627A..49Z Altcode: 2019arXiv190607196Z Context. Teegarden's Star is the brightest and one of the nearest ultra-cool dwarfs in the solar neighbourhood. For its late spectral type (M7.0 V), the star shows relatively little activity and is a prime target for near-infrared radial velocity surveys such as CARMENES.
Aims: As part of the CARMENES search for exoplanets around M dwarfs, we obtained more than 200 radial-velocity measurements of Teegarden's Star and analysed them for planetary signals.
Methods: We find periodic variability in the radial velocities of Teegarden's Star. We also studied photometric measurements to rule out stellar brightness variations mimicking planetary signals.
Results: We find evidence for two planet candidates, each with 1.1 M⊕ minimum mass, orbiting at periods of 4.91 and 11.4 d, respectively. No evidence for planetary transits could be found in archival and follow-up photometry. Small photometric variability is suggestive of slow rotation and old age.
Conclusions: The two planets are among the lowest-mass planets discovered so far, and they are the first Earth-mass planets around an ultra-cool dwarf for which the masses have been determined using radial velocities.

Tables D.1 and D.2 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/627/A49 Title: VizieR Online Data Catalog: CARMENES stars multi wavelength measurements (Passegger+, 2019) Authors: Passegger, V. M.; Schweitzer, A.; Shulyak, D.; Nagel, E.; Hauschildt, P. H.; Reiners, A.; Amado, P. J.; Caballero, J. A.; Cortes-Contreras, M.; Dominguez-Fernandez, A. J.; Quirrenbach, A.; Ribas, I.; Azarro, M.; Anglada-Escude, G.; Bauer, F. F.; Bejar, V. J. S.; Dreizler, S.; Guenther, E. W.; Henning, T.; Jeffers, S. V.; Kaminski, A.; Kuerster, M.; Lafarga, M.; Martin, E. L.; Montes, D.; Morales, J. C.; Schmidt, J. H. M. M.; Zechmeister, M. Bibcode: 2019yCat..36270161P Altcode: We present basic photospheric parameters of 282 M dwarfs within the CARMENES survey in the visible and near-infrared wavelength ranges. In table_b1 we provide Carmencita identifier (Karmn), Simbad name, equatorial coordinates, spectral type, rotational velocity, assumed age, and an activity flag for each star in our sample. In table_b2 we give effective temperature, surface gravity and [Fe/H] for each star in different wavelength ranges (VIS+NIR, NIR, and VIS), together with their errors.

(2 data files). Title: A massively non-LTE model atmosphere for Sirius A Authors: Aufdenberg, Jason P.; Acosta, Allison; Hauschildt, Peter Bibcode: 2019AAS...23410802A Altcode: Elemental abundances in the atmosphere of Sirius A reveal a history of nucleosynthesis. Sirius A has tightly constrained fundamental parameters due to its orbit with Sirius B, a measured interferometric diameter, and a precise parallax. Its slow rotation and apparent lack of atmospheric convection suggest one-dimensional model atmospheres should be a good approximation. Recent abundance analyses of Sirius A from Landstreet (2011) and Cowley et al. (2016) have employed local thermodynamic equilibrium (LTE) models in comparison to high-resolution spectra from the Hubble Space Telescope Imaging Spectrograph (HST/STIS), the Goddard High Resolution Spectrograph (GHRS), and the Very Large Telescope Ultraviolet Visible Echelle Spectrograph (VLT/UVES). In order to perform an abundance analysis for Sirius A that does not assume LTE, we have employed the PHOENIX model atmosphere code to compute 1-D non-LTE models and spectra. These models treat 194 species, 34976 levels and 600676 transitions in non-LTE for several ions of all elements from hydrogen to lead except Se, Br, Kr, Sb, Te, I, Xe, Pt, Au, Tc, and Pm to further constrain Sirius A's elemental abundances.

We have thus far compared our non-LTE abundance results with literature values for 30 elements and find six elements (N, Na, Cu, Mo, Ba, Os) have abundances which differ by more than 2 standard deviations ( 0.6 dex or more) from literature values. These results appear to differ from previous work for three reasons: (1) the latest oscillator strengths from Kurucz (2014) may differ significantly (2 to 10 times) from earlier values for specific lines and (2) non-LTE models show enhanced ionization of trace species relative to LTE which depletes these species and elevates the abundance needed to match the observed spectrum, and (3) non-LTE departure coefficient values for specific lines may different significantly from unity. We also find our model for Sirius A provides a good match to the observed spectral energy distribution in absolute units between 100 nm to 1 cm based on recent observations obtained by White et al. (2019) with ALMA, GBT, and the VLA. Title: VizieR Online Data Catalog: Teegarden's Star RV and Hα curves (Zechmeister+, 2019) Authors: Zechmeister, M.; Dreizler, M.; Ribas, I.; Reiners, A.; Caballero, J. A.; Bauer, F. F.; Bejar, V. J. S.; Gonzalez-Cuesta, L.; Herrero, E.; Lalitha, S.; Lopez-Gonzalez, M. J.; Luque, R.; Morales, J. C.; Palle, E.; Rodriguez, E.; Rodriguez Lopez, C.; Tal-Or, L.; Anglada-Escude, G.; Quirrenbach, A.; Amado, P. J.; Abril, M.; Aceituno, F. J.; Aceituno, J.; Alonso-Floriano, F. J.; Ammler-von Eiff, M.; Antona Jimenez, R.; Anwand-Heerwart, H.; Arroyo-Torres, B.; Azzaro, M.; Baroch, D.; Barrado, D.; Becerril, S.; Benitez, D.; Berdinas, Z. M.; Bergond, G.; Bluhm, P.; Brinkmoeller, M.; Del Burgo, C.; Calvo Ortega, R.; Cano, J.; Cardona Guillen, C.; Carro, J.; Cardenas Vazquez, M. C.; Casal, E.; Casasayas-Barris, N.; Casanova, V.; Chaturvedi, P.; Cifuentes, C.; Claret, A.; Colome, J.; Cortes-Contreras, M.; Czesla, S.; Diez-Alonso, E.; Dorda, R.; Fernandez, M.; Fernandez-Martin, A.; Fuhrmeister, B.; Fukui, A.; Galadi-Enriquez, D.; Gallardo Cava, I.; Garcia de La Fuente, J.; Garcia-Piquer, A.; Garcia Vargas, M. L.; Gesa, L.; Gongora Rueda, J.; Gonzalez-Alvarez, E.; Gonzalez Hernandez, J. I.; Gonzalez-Peinado, R.; Groezinger, U.; Guardia, J.; Guijarro, A.; de Guindos, E.; Hatzes, A. P.; Hauschildt, P. H.; Hedrosa, R. P.; Helmling, J.; Henning, T.; Hermelo, I.; Hernandez Arabi, R.; Hernandez Castano, L.; Hernandez, Otero F.; Hintz, D.; Huke, P.; Huber, A.; Jeffers, S. V.; Johnson, E. N.; de Juan, E.; Kaminski, A.; Kemmer, J.; Kim, M.; Klahr, H.; Klein, R.; Klueter, J.; Klutsch, A.; Kossakowski, D.; Kuerster, M.; Labarga, F.; Lafarga, M.; Llamas, M.; Lampon, M.; Lara, L. M.; Launhardt, R.; Lazaro, F. J.; Lodieu, N.; Lopez Del Fresno, M.; Lopez-Puertas, M.; Lopez Salas, J. F.; Lopez-Santiago, J.; Magan Madinabeitia, H.; Mall, U.; Mancini, L.; Mandel, H.; Marfil, E.; Marin Molina, J. A.; Maroto Fernandez, D.; Martin, E. L.; Martin-Fernandez, P.; Martin-Ruiz, S.; Marvin, C. J.; Mirabet, E.; Montanes-Rodriguez, P.; Montes, D.; Moreno-Raya, M. E.; Nagel, E.; Naranjo, V.; Narita, N.; Nortmann, L.; Nowak, G.; Ofir, A.; Oshagh, M.; Panduro, J.; Parviainen, H.; Pascual, J.; Passegger, V. M.; Pavlov, A.; Pedraz, S.; Perez-Calpena, A.; Perez Medialdea, D.; Perger, M.; Perryman, M. A. C.; Rabaza, O.; Ramon Ballesta, A.; Rebolo, R.; Redondo, P.; Reffert, S.; Reinhardt, S.; Rhode, P.; Rix, H. -W.; Rodler, F.; Rodriguez Trinidad, A.; Rosich, A.; Sadegi, S.; Sanchez-Blanco, E.; Sanchez Carrasco, M. A.; Sanchez-Lopez, A.; Sanz-Forcada, J.; Sarkis, P.; Sarmiento, L. F.; Schaefer, S.; Schmitt, J. H. M. M.; Schoefer, P.; Schweitzer, A.; Seifert, W.; Shulyak, D.; Solano, E.; Sota, A.; Stahl, O.; Stock, S.; Strachan, J. B. P.; Stuber, T.; Stuermer, J.; Suarez, J. C.; Tabernero, H. M.; Tala Pinto, M.; Trifonov, T.; Veredas, G.; Vico Linares, J. I.; Vilardell, F.; Wagner, K.; Wolthoff, V.; Xu, W.; Yan, F.; Zapatero Osorio, M. R. Bibcode: 2019yCat..36270049Z Altcode: Time series for radial velocities and activity indicators of Teegarden's Star from CARMENES VIS and NIR spectrograph are presented. See Zechmeister et al. (2017A&A...609A..12Z) for a detailed description of the parameters.

(2 data files). Title: The MESAS Project: Long-wavelength Follow-up Observations of Sirius A Authors: White, Jacob Aaron; Aufdenberg, J.; Boley, A. C.; Devlin, M.; Dicker, S.; Hauschildt, P.; Hughes, A. G.; Hughes, A. M.; Mason, B.; Matthews, B.; Moór, A.; Mroczkowski, T.; Romero, C.; Sievers, J.; Stanchfield, S.; Tapia, F.; Wilner, D. Bibcode: 2019ApJ...875...55W Altcode: 2019arXiv190303481W Modeling the submillimeter to centimeter emission of stars is challenging due to a lack of sensitive observations at these long wavelengths. We launched an ongoing campaign to obtain new observations entitled Measuring the Emission of Stellar Atmospheres at Submillimeter/millimeter wavelengths (MESAS). Here we present Atacama Large Millimeter/submillimeter Array, Green Bank Telescope, and Very Large Array observations of Sirius A, the closest main-sequence A-type star, that span from 1.4 to 9.0 mm. These observations complement our previous millimeter data on Sirius A and are entirely consistent with the PHOENIX stellar atmosphere models constructed to explain them. We note that accurate models of long-wavelength emission from stars are essential not only to understand fundamental stellar processes, but also to determine the presence of dusty debris in spatially unresolved observations of circumstellar disks. Title: The CARMENES search for exoplanets around M dwarfs. Chromospheric modeling of M 2-3 V stars with PHOENIX Authors: Hintz, D.; Fuhrmeister, B.; Czesla, S.; Schmitt, J. H. M. M.; Johnson, E. N.; Schweitzer, A.; Caballero, J. A.; Zechmeister, M.; Jeffers, S. V.; Reiners, A.; Ribas, I.; Amado, P. J.; Quirrenbach, A.; Anglada-Escudé, G.; Bauer, F. F.; Béjar, V. J. S.; Cortés-Contreras, M.; Dreizler, S.; Galadí-Enríquez, D.; Guenther, E. W.; Hauschildt, P. H.; Kaminski, A.; Kürster, M.; Lafarga, M.; López del Fresno, M.; Montes, D.; Morales, J. C.; Passegger, V. M.; Seifert, W. Bibcode: 2019A&A...623A.136H Altcode: 2019arXiv190203992H Chromospheric modeling of observed differences in stellar activity lines is imperative to fully understand the upper atmospheres of late-type stars. We present one-dimensional parametrized chromosphere models computed with the atmosphere code PHOENIX using an underlying photosphere of 3500 K. The aim of this work is to model chromospheric lines of a sample of 50 M2-3 dwarfs observed in the framework of the CARMENES, the Calar Alto high-Resolution search for M dwarfs with Exo-earths with Near-infrared and optical Echelle Spectrographs, exoplanet survey. The spectral comparison between observed data and models is performed in the chromospheric lines of Na I D2, Hα, and the bluest Ca II infrared triplet line to obtain best-fit models for each star in the sample. We find that for inactive stars a single model with a VAL C-like temperature structure is sufficient to describe simultaneously all three lines adequately. Active stars are rather modeled by a combination of an inactive and an active model, also giving the filling factors of inactive and active regions. Moreover, the fitting of linear combinations on variable stars yields relationships between filling factors and activity states, indicating that more active phases are coupled to a larger portion of active regions on the surface of the star. Title: Predicting the Extreme Ultraviolet Radiation Environment of Exoplanets around Low-mass Stars: The TRAPPIST-1 System Authors: Peacock, Sarah; Barman, Travis; Shkolnik, Evgenya L.; Hauschildt, Peter H.; Baron, E. Bibcode: 2019ApJ...871..235P Altcode: 2018arXiv181206159P The high energy radiation environment around M dwarf stars strongly impacts the characteristics of close-in exoplanet atmospheres, but these wavelengths are difficult to observe due to geocoronal and interstellar contamination. On account of these observational restrictions, a stellar atmosphere model may be used to compute the stellar extreme ultraviolet (EUV; 100-912 Å) spectrum. We construct semiempirical nonlocal thermodynamic equilibrium model spectra of the ultracool M8 star TRAPPIST-1 that span EUV to infrared wavelengths (100 Å-2.5 μm) using the atmosphere code PHOENIX. These upper atmosphere models contain prescriptions for the chromosphere and transition region and include newly added partial frequency redistribution capabilities. In the absence of broadband UV spectral observations, we constrain our models using Hubble Space Telescope Lyman α observations from TRAPPIST-1 and Galaxy Evolution Explorer UV photometric detections from a set of old M8 stars (>1 Gyr). We find that calibrating the models using both data sets separately yield similar far-ultraviolet and NUV fluxes, and EUV fluxes that range from (1.32-17.4) × 10-14 ergs s-1 cm-2. The results from these models demonstrate that the EUV emission is very sensitive to the temperature structure in the transition region. Our lower activity models predict EUV fluxes similar to previously published estimates derived from semiempirical scaling relationships, while the highest activity model predicts EUV fluxes a factor of 10 higher. Results from this study support the idea that the TRAPPIST-1 habitable zone planets likely do not have much liquid water on their surfaces due to the elevated levels of high energy radiation emitted by the host star. Title: Stellar Emission as a Source of Flux Bias in Debris Disks Authors: White, J. A.; Aufdenberg, J.; Boley, A. C.; Hauschildt, P.; Hughes, A. M.; Matthews, B.; Moór, A.; Wilner, D. J. Bibcode: 2018ASPC..517..171W Altcode: Our understanding of stellar atmospheres and our ability to infer architectures of extrasolar planetary systems rely on understanding the emission of stars at sub-millimeter to centimeter wavelengths. In this chapter we describe how unconstrained stellar emission can interfere with the accurate characterization of circumstellar debris. The ngVLA is the only facility with the sensitivity that allows for the observations of a broad range of stellar spectral types in a feasible amount of time. The observations will enable the building and testing of accurate models of stellar emission, which in turn are required for evaluating both the occurrence and abundance of debris over the proposed wavelength range of the ngVLA. Title: Science with an ngVLA: Stellar Emission as a Source of Flux Bias in Debris Disks Authors: White, Jacob Aaron; Aufdenberg, Jason; Boley, Aaron C.; Hauschildt, Peter; Hughes, A. Meredith; Matthews, Brenda; Moór, Attila; Wilner, David J. Bibcode: 2018arXiv181006565W Altcode: Our understanding of stellar atmospheres and our ability to infer architectures of extrasolar planetary systems rely on understanding the emission of stars at submillimeter to centimeter wavelengths. In this chapter we describe how unconstrained stellar emission can interfere with the accurate characterization of circumstellar debris. The ngVLA is the only facility with the sensitivity that allows for the observations of a broad range of stellar spectral types in a feasible amount of time. The observations will enable the building and testing of accurate models of stellar emission, which in turn are required for evaluating both the occurrence and abundance of debris over the proposed wavelength range of the ngVLA Title: CARMENES: high-resolution spectra and precise radial velocities in the red and infrared Authors: Quirrenbach, A.; Amado, P. J.; Ribas, I.; Reiners, A.; Caballero, J. A.; Seifert, W.; Aceituno, J.; Azzaro, M.; Baroch, D.; Barrado, D.; Bauer, F.; Becerril, S.; Bèjar, V. J. S.; Benítez, D.; Brinkmöller, M.; Cardona Guillén, C.; Cifuentes, C.; Colomé, J.; Cortés-Contreras, M.; Czesla, S.; Dreizler, S.; Frölich, K.; Fuhrmeister, B.; Galadí-Enríquez, D.; González Hernández, J. I.; González Peinado, R.; Guenther, E. W.; de Guindos, E.; Hagen, H. -J.; Hatzes, A. P.; Hauschildt, P. H.; Helmling, J.; Henning, Th.; Herbort, O.; Hernández Castaño, L.; Herrero, E.; Hintz, D.; Jeffers, S. V.; Johnson, E. N.; de Juan, E.; Kaminski, A.; Klahr, H.; Kürster, M.; Lafarga, M.; Sairam, L.; Lampón, M.; Lara, L. M.; Launhardt, R.; López del Fresno, M.; López-Puertas, M.; Luque, R.; Mandel, H.; Marfil, E. G.; Martín, E. L.; Martín-Ruiz, S.; Mathar, R. J.; Montes, D.; Morales, J. C.; Nagel, E.; Nortmann, L.; Nowak, G.; Pallé, E.; Passegger, V. -M.; Pavlov, A.; Pedraz, S.; Pérez-Medialdea, D.; Perger, M.; Rebolo, R.; Reffert, S.; Rodríguez, E.; Rodríguez López, C.; Rosich, A.; Sabotta, S.; Sadegi, S.; Salz, M.; Sánchez-López, A.; Sanz-Forcada, J.; Sarkis, P.; Schäfer, S.; Schiller, J.; Schmitt, J. H. M. M.; Schöfer, P.; Schweitzer, A.; Shulyak, D.; Solano, E.; Stahl, O.; Tala Pinto, M.; Trifonov, T.; Zapatero Osorio, M. R.; Yan, F.; Zechmeister, M.; Abellán, F. J.; Abril, M.; Alonso-Floriano, F. J.; Ammler-von Eiff, M.; Anglada-Escudé, G.; Anwand-Heerwart, H.; Arroyo-Torres, B.; Berdiñas, Z. M.; Bergondy, G.; Blümcke, M.; del Burgo, C.; Cano, J.; Carro, J.; Cárdenas, M. C.; Casal, E.; Claret, A.; Díez-Alonso, E.; Doellinger, M.; Dorda, R.; Feiz, C.; Fernández, M.; Ferro, I. M.; Gaisné, G.; Gallardo, I.; Gálvez-Ortiz, M. C.; García-Piquer, A.; García-Vargas, M. L.; Garrido, R.; Gesa, L.; Gómez Galera, V.; González-Álvarez, E.; González-Cuesta, L.; Grohnert, S.; Grözinger, U.; Guàrdia, J.; Guijarro, A.; Hedrosa, R. P.; Hermann, D.; Hermelo, I.; Hernández Arabí, R.; Hernández Hernando, F.; Hidalgo, D.; Holgado, G.; Huber, A.; Huber, K.; Huke, P.; Kehr, M.; Kim, M.; Klein, R.; Klüter, J.; Klutsch, A.; Labarga, F.; Labiche, N.; Lamert, A.; Laun, W.; Lázaro, F. J.; Lemke, U.; Lenzen, R.; Llamas, M.; Lizon, J. -L.; Lodieu, N.; López González, M. J.; López-Morales, M.; López Salas, J. F.; López-Santiago, J.; Magán Madinabeitia, H.; Mall, U.; Mancini, L.; Marín Molina, J. A.; Martínez-Rodríguez, H.; Maroto Fernández, D.; Marvin, C. J.; Mirabet, E.; Moreno-Raya, M. E.; Moya, A.; Mundt, R.; Naranjo, V.; Panduro, J.; Pascual, J.; Pérez-Calpena, A.; Perryman, M. A. C.; Pluto, M.; Ramón, A.; Redondo, P.; Reinhart, S.; Rhode, P.; Rix, H. -W.; Rodler, F.; Rohloff, R. -R.; Sánchez-Blanco, E.; Sánchez Carrasco, M. A.; Sarmiento, L. F.; Schmidt, C.; Storz, C.; Strachan, J. B. P.; Stürmer, J.; Suárez, J. C.; Tabernero, H. M.; Tal-Or, L.; Tulloch, S. M.; Ulbrich, R. -G.; Veredas, G.; Vico Linares, J. L.; Vidal-Dasilva, M.; Vilardell, F.; Wagner, K.; Winkler, J.; Wolthoff, V.; Xu, W.; Zhao, Z. Bibcode: 2018SPIE10702E..0WQ Altcode: The design and construction of CARMENES has been presented at previous SPIE conferences. It is a next-generation radial-velocity instrument at the 3.5m telescope of the Calar Alto Observatory, which was built by a consortium of eleven Spanish and German institutions. CARMENES consists of two separate échelle spectrographs covering the wavelength range from 0.52 to 1.71μm at a spec-tral resolution of R < 80,000, fed by fibers from the Cassegrain focus of the telescope. CARMENES saw "First Light" on Nov 9, 2015. During the commissioning and initial operation phases, we established basic performance data such as throughput and spectral resolution. We found that our hollow-cathode lamps are suitable for precise wavelength calibration, but their spectra contain a number of lines of neon or argon that are so bright that the lamps cannot be used in simultaneous exposures with stars. We have therefore adopted a calibration procedure that uses simultaneous star / Fabry Pérot etalon exposures in combination with a cross-calibration between the etalons and hollow-cathode lamps during daytime. With this strategy it has been possible to achieve 1-2 m/s precision in the visible and 5-10 m/s precision in the near-IR; further improvements are expected from ongoing work on temperature control, calibration procedures and data reduction. Comparing the RV precision achieved in different wavelength bands, we find a "sweet spot" between 0.7 and 0.8μm, where deep TiO bands provide rich RV information in mid-M dwarfs. This is in contrast to our pre-survey models, which predicted comparatively better performance in the near-IR around 1μm, and explains in part why our near-IR RVs do not reach the same precision level as those taken with the visible spectrograph. We are now conducting a large survey of 340 nearby M dwarfs (with an average distance of only 12pc), with the goal of finding terrestrial planets in their habitable zones. We have detected the signatures of several previously known or suspected planets and also discovered several new planets. We find that the radial velocity periodograms of many M dwarfs show several significant peaks. The development of robust methods to distinguish planet signatures from activity-induced radial velocity jitter is therefore among our priorities. Due to its large wavelength coverage, the CARMENES survey is generating a unique data set for studies of M star atmospheres, rotation, and activity. The spectra cover important diagnostic lines for activity (H alpha, Na I D1 and D2, and the Ca II infrared triplet), as well as FeH lines, from which the magnetic field can be inferred. Correlating the time series of these features with each other, and with wavelength-dependent radial velocities, provides excellent handles for the discrimination between planetary companions and stellar radial velocity jitter. These data are also generating new insight into the physical properties of M dwarf atmospheres, and the impact of activity and flares on the habitability of M star planets. Title: VizieR Online Data Catalog: 324 CARMENES M dwarfs velocities (Reiners+, 2018) Authors: Reiners, A.; Zechmeister, M.; Caballero, J. A.; Ribas, I.; Morales, J. C.; Jeffers, S. V.; Schofer, P.; Tal-Or, L.; Quirrenbach, A.; Amado, P. J.; Kaminski, A.; Seifert, W.; Abril, M.; Aceituno, J.; Alonso-Floriano, F. J.; Ammler-von Eiff, M.; Antona, R.; Anglada-Escude, G.; Anwand-Heerwart, H.; Arroyo-Torres, B.; Azzaro, M.; Baroch, D.; Barrado, D.; Bauer, F. F.; Becerril, S.; Bejar, V. J. S.; Benitez, D.; Berdinas, Z. M.; Bergond, G.; Blumcke, M.; Brinkmoller, M.; Del Burgo, C.; Cano, J.; Cardenas Vazquez, M. C.; Casal, E.; Cifuentes, C.; Claret, A.; Colome, J.; Cortes-Contreras, M.; Czesla, S.; Diez-Alonso, E.; Dreizler, S.; Feiz, C.; Fernandez, M.; Ferro, I. M.; Fuhrmeister, B.; Galadi-Enriquez, D.; Garcia-Piquer, A.; Garcia Vargas, M. L.; Gesa, L.; Gomez Galera, V.; Gonzalez Hernandez, J. I.; Gonzalez-Peinado, R.; Grozinger, U.; Grohnert, S.; Guardia, J.; Guenther, E. W.; Guijarro, A.; de Guindos, E.; Gutierrez-Soto, J.; Hagen, H. -J.; Hatzes, A. P.; Hauschildt, P. H.; Hedrosa, R. P.; Helmling, J.; Henning, T.; Hermelo, I.; Hernandez Arabi, R.; Hernandez Castano, L.; Hernandez Hernando, F.; Herrero, E.; Huber, A.; Huke, P.; Johnson, E. N.; de Juan, E.; Kim, M.; Klein, R.; Kluter, J.; Klutsch, A.; Kurster, M.; Lafarga, M.; Lamert, A.; Lampon, M.; Lara, L. M.; Laun, W.; Lemke, U.; Lenzen, R.; Launhardt, R.; Lopez Del Fresno, M.; Lopez-Gonzalez, J.; Lopez-Puertas, M.; Lopez Salas, J. F.; Lopez-Santiago, J.; Luque, R.; Magan Madinabeitia, H.; Mall, U.; Mancini, L.; Mandel, H.; Marfil, E.; Marin Molina, J. A.; Maroto Fernandez, D.; Martin, E. L.; Martin-Ruiz, S.; Marvin, C. J.; Mathar, R. J.; Mirabet, E.; Montes, D.; Moreno-Raya, M. E.; Moya, A.; Mundt, R.; Nagel, E.; Naranjo, V.; Nortmann, L.; Nowak, G.; Ofir, A.; Oreiro, R.; Palle, E.; Panduro, J.; Pascual, J.; Passegger, V. M.; Pavlov, A.; Pedraz, S.; Perez-Calpena, A.; Perez Medialdea, D.; Perger, M.; Perryman, M. A. C.; Pluto, M.; Rabaza, O.; Ramon, A.; Rebolo, R.; Redondo, P.; Reffert, S.; Reinhart, S.; Rhode, P.; Rix, H. -W.; Rodler, F.; Rodriguez, E.; Rodriguez-Lopez, C.; Rodriguez Trinidad, A.; Rohloff, R. -R.; Rosich, A.; Sadegi, S.; Sanchez-Blanco, E.; Sanchez Carrasco, M. A.; Sanchez-Lopez, A.; Sanz-Forcada, J.; Sarkis, P.; Sarmiento, L. F.; Schafer, S.; Schmitt, J. H. M. M.; Schiller, J.; Schweitzer, A.; Solano, E.; Stahl, O.; Strachan, J. B. P.; Sturmer, J.; Suarez, J. C.; Tabernero, H. M.; Tala, M.; Trifonov, T.; Tulloch, S. M.; Ulbrich, R. G.; Veredas, G.; Vico Linares, J. I.; Vilardell, F.; Wagner, K.; Winkler, J.; Wolthoff, V.; Xu, W.; Yan, F.; Zapatero Osorio, M. R. Bibcode: 2018yCat..36120049R Altcode: As part of the GTO agreement, we provide early access to one CARMENES spectrum for each of our sample targets (Table B.1). They can be downloaded from the CARMENES GTO Data Archive (Caballero et al., 2016, in Observatory Operations: Strategies, Processes, and Systems VI, Proc. SPIE, 9910, 99100E) (http://carmenes.cab.inta-csic.es)

(1 data file). Title: MESAS: Measuring the Emission of Stellar Atmospheres at Submillimeter/millimeter Wavelengths Authors: White, Jacob Aaron; Aufdenberg, Jason; Boley, A. C.; Hauschildt, Peter; Hughes, Meredith; Matthews, Brenda; Wilner, David Bibcode: 2018ApJ...859..102W Altcode: 2018arXiv180410206W In the early stages of planet formation, small dust grains grow to become millimeter-sized particles in debris disks around stars. These disks can in principle be characterized by their emission at submillimeter and millimeter wavelengths. Determining both the occurrence and abundance of debris in unresolved circumstellar disks of A-type main-sequence stars requires that the stellar photospheric emission be accurately modeled. To better constrain the photospheric emission for such systems, we present observations of Sirius A, an A-type star with no known debris, from the James Clerk Maxwell Telescope, Submillimeter Array, and Jansky Very Large Array at 0.45, 0.85, 0.88, 1.3, 6.7, and 9.0 mm. We use these observations to inform a PHOENIX model of Sirius A’s atmosphere. We find the model provides a good match to these data and can be used as a template for the submillimeter/millimeter emission of other early A-type stars where unresolved debris may be present. The observations are part of an ongoing observational campaign entitled Measuring the Emission of Stellar Atmospheres at Submillimeter/millimeter wavelengths. Title: Convection Enhances Magnetic Turbulence in AM CVn Accretion Disks Authors: Coleman, Matthew S. B.; Blaes, Omer; Hirose, Shigenobu; Hauschildt, Peter H. Bibcode: 2018ApJ...857...52C Altcode: 2018arXiv180304381C We present the results of local, vertically stratified, radiation magnetohydrodynamic shearing-box simulations of magnetorotational instability (MRI) turbulence for a (hydrogen poor) composition applicable to accretion disks in AM CVn type systems. Many of these accreting white dwarf systems are helium analogs of dwarf novae (DNe). We utilize frequency-integrated opacity and equation-of-state tables appropriate for this regime to accurately portray the relevant thermodynamics. We find bistability of thermal equilibria in the effective-temperature, surface-mass-density plane typically associated with disk instabilities. Along this equilibrium curve (i.e., the S-curve), we find that the stress to thermal pressure ratio α varied with peak values of ∼0.15 near the tip of the upper branch. Similar to DNe, we found enhancement of α near the tip of the upper branch caused by convection; this increase in α occurred despite our choice of zero net vertical magnetic flux. Two notable differences we find between DN and AM CVn accretion disk simulations are that AM CVn disks are capable of exhibiting persistent convection in outburst, and ideal MHD is valid throughout quiescence for AM CVns. In contrast, DNe simulations only show intermittent convection, and nonideal MHD effects are likely important in quiescence. By combining our previous work with these new results, we also find that convective enhancement of the MRI is anticorrelated with mean molecular weight. Title: The CARMENES search for exoplanets around M dwarfs. High-resolution optical and near-infrared spectroscopy of 324 survey stars Authors: Reiners, A.; Zechmeister, M.; Caballero, J. A.; Ribas, I.; Morales, J. C.; Jeffers, S. V.; Schöfer, P.; Tal-Or, L.; Quirrenbach, A.; Amado, P. J.; Kaminski, A.; Seifert, W.; Abril, M.; Aceituno, J.; Alonso-Floriano, F. J.; Ammler-von Eiff, M.; Antona, R.; Anglada-Escudé, G.; Anwand-Heerwart, H.; Arroyo-Torres, B.; Azzaro, M.; Baroch, D.; Barrado, D.; Bauer, F. F.; Becerril, S.; Béjar, V. J. S.; Benítez, D.; Berdinas, Z. M.; Bergond, G.; Blümcke, M.; Brinkmöller, M.; del Burgo, C.; Cano, J.; Cárdenas Vázquez, M. C.; Casal, E.; Cifuentes, C.; Claret, A.; Colomé, J.; Cortés-Contreras, M.; Czesla, S.; Díez-Alonso, E.; Dreizler, S.; Feiz, C.; Fernández, M.; Ferro, I. M.; Fuhrmeister, B.; Galadí-Enríquez, D.; Garcia-Piquer, A.; García Vargas, M. L.; Gesa, L.; Gómez Galera, V.; González Hernández, J. I.; González-Peinado, R.; Grözinger, U.; Grohnert, S.; Guàrdia, J.; Guenther, E. W.; Guijarro, A.; de Guindos, E.; Gutiérrez-Soto, J.; Hagen, H. -J.; Hatzes, A. P.; Hauschildt, P. H.; Hedrosa, R. P.; Helmling, J.; Henning, Th.; Hermelo, I.; Hernández Arabí, R.; Hernández Castaño, L.; Hernández Hernando, F.; Herrero, E.; Huber, A.; Huke, P.; Johnson, E. N.; de Juan, E.; Kim, M.; Klein, R.; Klüter, J.; Klutsch, A.; Kürster, M.; Lafarga, M.; Lamert, A.; Lampón, M.; Lara, L. M.; Laun, W.; Lemke, U.; Lenzen, R.; Launhardt, R.; López del Fresno, M.; López-González, J.; López-Puertas, M.; López Salas, J. F.; López-Santiago, J.; Luque, R.; Magán Madinabeitia, H.; Mall, U.; Mancini, L.; Mandel, H.; Marfil, E.; Marín Molina, J. A.; Maroto Fernández, D.; Martín, E. L.; Martín-Ruiz, S.; Marvin, C. J.; Mathar, R. J.; Mirabet, E.; Montes, D.; Moreno-Raya, M. E.; Moya, A.; Mundt, R.; Nagel, E.; Naranjo, V.; Nortmann, L.; Nowak, G.; Ofir, A.; Oreiro, R.; Pallé, E.; Panduro, J.; Pascual, J.; Passegger, V. M.; Pavlov, A.; Pedraz, S.; Pérez-Calpena, A.; Pérez Medialdea, D.; Perger, M.; Perryman, M. A. C.; Pluto, M.; Rabaza, O.; Ramón, A.; Rebolo, R.; Redondo, P.; Reffert, S.; Reinhart, S.; Rhode, P.; Rix, H. -W.; Rodler, F.; Rodríguez, E.; Rodríguez-López, C.; Rodríguez Trinidad, A.; Rohloff, R. -R.; Rosich, A.; Sadegi, S.; Sánchez-Blanco, E.; Sánchez Carrasco, M. A.; Sánchez-López, A.; Sanz-Forcada, J.; Sarkis, P.; Sarmiento, L. F.; Schäfer, S.; Schmitt, J. H. M. M.; Schiller, J.; Schweitzer, A.; Solano, E.; Stahl, O.; Strachan, J. B. P.; Stürmer, J.; Suárez, J. C.; Tabernero, H. M.; Tala, M.; Trifonov, T.; Tulloch, S. M.; Ulbrich, R. G.; Veredas, G.; Vico Linares, J. I.; Vilardell, F.; Wagner, K.; Winkler, J.; Wolthoff, V.; Xu, W.; Yan, F.; Zapatero Osorio, M. R. Bibcode: 2018A&A...612A..49R Altcode: 2017arXiv171106576R The CARMENES radial velocity (RV) survey is observing 324 M dwarfs to search for any orbiting planets. In this paper, we present the survey sample by publishing one CARMENES spectrum for each M dwarf. These spectra cover the wavelength range 520-1710 nm at a resolution of at least R >80 000, and we measure its RV, Hα emission, and projected rotation velocity. We present an atlas of high-resolution M-dwarf spectra and compare the spectra to atmospheric models. To quantify the RV precision that can be achieved in low-mass stars over the CARMENES wavelength range, we analyze our empirical information on the RV precision from more than 6500 observations. We compare our high-resolution M-dwarf spectra to atmospheric models where we determine the spectroscopic RV information content, Q, and signal-to-noise ratio. We find that for all M-type dwarfs, the highest RV precision can be reached in the wavelength range 700-900 nm. Observations at longer wavelengths are equally precise only at the very latest spectral types (M8 and M9). We demonstrate that in this spectroscopic range, the large amount of absorption features compensates for the intrinsic faintness of an M7 star. To reach an RV precision of 1 m s-1 in very low mass M dwarfs at longer wavelengths likely requires the use of a 10 m class telescope. For spectral types M6 and earlier, the combination of a red visual and a near-infrared spectrograph is ideal to search for low-mass planets and to distinguish between planets and stellar variability. At a 4 m class telescope, an instrument like CARMENES has the potential to push the RV precision well below the typical jitter level of 3-4 m s-1. Title: The CARMENES search for exoplanets around M dwarfs . First visual-channel radial-velocity measurements and orbital parameter updates of seven M-dwarf planetary systems Authors: Trifonov, T.; Kürster, M.; Zechmeister, M.; Tal-Or, L.; Caballero, J. A.; Quirrenbach, A.; Amado, P. J.; Ribas, I.; Reiners, A.; Reffert, S.; Dreizler, S.; Hatzes, A. P.; Kaminski, A.; Launhardt, R.; Henning, Th.; Montes, D.; Béjar, V. J. S.; Mundt, R.; Pavlov, A.; Schmitt, J. H. M. M.; Seifert, W.; Morales, J. C.; Nowak, G.; Jeffers, S. V.; Rodríguez-López, C.; del Burgo, C.; Anglada-Escudé, G.; López-Santiago, J.; Mathar, R. J.; Ammler-von Eiff, M.; Guenther, E. W.; Barrado, D.; González Hernández, J. I.; Mancini, L.; Stürmer, J.; Abril, M.; Aceituno, J.; Alonso-Floriano, F. J.; Antona, R.; Anwand-Heerwart, H.; Arroyo-Torres, B.; Azzaro, M.; Baroch, D.; Bauer, F. F.; Becerril, S.; Benítez, D.; Berdiñas, Z. M.; Bergond, G.; Blümcke, M.; Brinkmöller, M.; Cano, J.; Cárdenas Vázquez, M. C.; Casal, E.; Cifuentes, C.; Claret, A.; Colomé, J.; Cortés-Contreras, M.; Czesla, S.; Díez-Alonso, E.; Feiz, C.; Fernández, M.; Ferro, I. M.; Fuhrmeister, B.; Galadí-Enríquez, D.; Garcia-Piquer, A.; García Vargas, M. L.; Gesa, L.; Gómez Galera, V.; González-Peinado, R.; Grözinger, U.; Grohnert, S.; Guàrdia, J.; Guijarro, A.; de Guindos, E.; Gutiérrez-Soto, J.; Hagen, H. -J.; Hauschildt, P. H.; Hedrosa, R. P.; Helmling, J.; Hermelo, I.; Hernández Arabí, R.; Hernández Castaño, L.; Hernández Hernando, F.; Herrero, E.; Huber, A.; Huke, P.; Johnson, E.; de Juan, E.; Kim, M.; Klein, R.; Klüter, J.; Klutsch, A.; Lafarga, M.; Lampón, M.; Lara, L. M.; Laun, W.; Lemke, U.; Lenzen, R.; López del Fresno, M.; López-González, M. J.; López-Puertas, M.; López Salas, J. F.; Luque, R.; Magán Madinabeitia, H.; Mall, U.; Mandel, H.; Marfil, E.; Marín Molina, J. A.; Maroto Fernández, D.; Martín, E. L.; Martín-Ruiz, S.; Marvin, C. J.; Mirabet, E.; Moya, A.; Moreno-Raya, M. E.; Nagel, E.; Naranjo, V.; Nortmann, L.; Ofir, A.; Oreiro, R.; Pallé, E.; Panduro, J.; Pascual, J.; Passegger, V. M.; Pedraz, S.; Pérez-Calpena, A.; Pérez Medialdea, D.; Perger, M.; Perryman, M. A. C.; Pluto, M.; Rabaza, O.; Ramón, A.; Rebolo, R.; Redondo, P.; Reinhardt, S.; Rhode, P.; Rix, H. -W.; Rodler, F.; Rodríguez, E.; Rodríguez Trinidad, A.; Rohloff, R. -R.; Rosich, A.; Sadegi, S.; Sánchez-Blanco, E.; Sánchez Carrasco, M. A.; Sánchez-López, A.; Sanz-Forcada, J.; Sarkis, P.; Sarmiento, L. F.; Schäfer, S.; Schiller, J.; Schöfer, P.; Schweitzer, A.; Solano, E.; Stahl, O.; Strachan, J. B. P.; Suárez, J. C.; Tabernero, H. M.; Tala, M.; Tulloch, S. M.; Veredas, G.; Vico Linares, J. I.; Vilardell, F.; Wagner, K.; Winkler, J.; Wolthoff, V.; Xu, W.; Yan, F.; Zapatero Osorio, M. R. Bibcode: 2018A&A...609A.117T Altcode: 2017arXiv171001595T Context. The main goal of the CARMENES survey is to find Earth-mass planets around nearby M-dwarf stars. Seven M dwarfs included in the CARMENES sample had been observed before with HIRES and HARPS and either were reported to have one short period planetary companion (GJ 15 A, GJ 176, GJ 436, GJ 536 and GJ 1148) or are multiple planetary systems (GJ 581 and GJ 876).
Aims: We aim to report new precise optical radial velocity measurements for these planet hosts and test the overall capabilities of CARMENES.
Methods: We combined our CARMENES precise Doppler measurements with those available from HIRES and HARPS and derived new orbital parameters for the systems. Bona-fide single planet systems were fitted with a Keplerian model. The multiple planet systems were analyzed using a self-consistent dynamical model and their best fit orbits were tested for long-term stability.
Results: We confirm or provide supportive arguments for planets around all the investigated stars except for GJ 15 A, for which we find that the post-discovery HIRES data and our CARMENES data do not show a signal at 11.4 days. Although we cannot confirm the super-Earth planet GJ 15 Ab, we show evidence for a possible long-period (Pc = 7030-630+970 d) Saturn-mass (mcsini = 51.8M⊕) planet around GJ 15 A. In addition, based on our CARMENES and HIRES data we discover a second planet around GJ 1148, for which we estimate a period Pc = 532.6 days, eccentricity ec = 0.342 and minimum mass mcsini = 68.1M⊕.
Conclusions: The CARMENES optical radial velocities have similar precision and overall scatter when compared to the Doppler measurements conducted with HARPS and HIRES. We conclude that CARMENES is an instrument that is up to the challenge of discovering rocky planets around low-mass stars.

Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programmes 072.C-0488, 072.C-0513, 074.C-0012, 074.C-0364, 075.D-0614, 076.C-0878, 077.C-0364, 077.C-0530, 078.C-0044, 078.C-0833, 079.C-0681, 183.C-0437, 60.A-9036, 082.C-0718, 183.C-0972, 085.C-0019, 087.C-0831, 191.C-0873. The appendix tables are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/609/A117 Title: The CARMENES search for exoplanets around M dwarfs. HD147379 b: A nearby Neptune in the temperate zone of an early-M dwarf Authors: Reiners, A.; Ribas, I.; Zechmeister, M.; Caballero, J. A.; Trifonov, T.; Dreizler, S.; Morales, J. C.; Tal-Or, L.; Lafarga, M.; Quirrenbach, A.; Amado, P. J.; Kaminski, A.; Jeffers, S. V.; Aceituno, J.; Béjar, V. J. S.; Guàrdia, J.; Guenther, E. W.; Hagen, H. -J.; Montes, D.; Passegger, V. M.; Seifert, W.; Schweitzer, A.; Cortés-Contreras, M.; Abril, M.; Alonso-Floriano, F. J.; Ammler-von Eiff, M.; Antona, R.; Anglada-Escudé, G.; Anwand-Heerwart, H.; Arroyo-Torres, B.; Azzaro, M.; Baroch, D.; Barrado, D.; Bauer, F. F.; Becerril, S.; Benítez, D.; Berdiñas, Z. M.; Bergond, G.; Blümcke, M.; Brinkmöller, M.; del Burgo, C.; Cano, J.; Cárdenas Vázquez, M. C.; Casal, E.; Cifuentes, C.; Claret, A.; Colomé, J.; Czesla, S.; Díez-Alonso, E.; Feiz, C.; Fernández, M.; Ferro, I. M.; Fuhrmeister, B.; Galadí-Enríquez, D.; Garcia-Piquer, A.; García Vargas, M. L.; Gesa, L.; Gómez Galera, V.; González Hernández, J. I.; González-Peinado, R.; Grözinger, U.; Grohnert, S.; Guijarro, A.; de Guindos, E.; Gutiérrez-Soto, J.; Hatzes, A. P.; Hauschildt, P. H.; Hedrosa, R. P.; Helmling, J.; Henning, Th.; Hermelo, I.; Hernández Arabí, R.; Hernández Castaño, L.; Hernández Hernando, F.; Herrero, E.; Huber, A.; Huke, P.; Johnson, E. N.; de Juan, E.; Kim, M.; Klein, R.; Klüter, J.; Klutsch, A.; Kürster, M.; Labarga, F.; Lamert, A.; Lampón, M.; Lara, L. M.; Laun, W.; Lemke, U.; Lenzen, R.; Launhardt, R.; López del Fresno, M.; López-González, M. J.; López-Puertas, M.; López Salas, J. F.; López-Santiago, J.; Luque, R.; Magán Madinabeitia, H.; Mall, U.; Mancini, L.; Mandel, H.; Marfil, E.; Marín Molina, J. A.; Maroto Fernández, D.; Martín, E. L.; Martín-Ruiz, S.; Marvin, C. J.; Mathar, R. J.; Mirabet, E.; Moreno-Raya, M. E.; Moya, A.; Mundt, R.; Nagel, E.; Naranjo, V.; Nortmann, L.; Nowak, G.; Ofir, A.; Oreiro, R.; Pallé, E.; Panduro, J.; Pascual, J.; Pavlov, A.; Pedraz, S.; Pérez-Calpena, A.; Pérez Medialdea, D.; Perger, M.; Perryman, M. A. C.; Pluto, M.; Rabaza, O.; Ramón, A.; Rebolo, R.; Redondo, P.; Reffert, S.; Reinhart, S.; Rhode, P.; Rix, H. -W.; Rodler, F.; Rodríguez, E.; Rodríguez-López, C.; Rodríguez Trinidad, A.; Rohloff, R. -R.; Rosich, A.; Sadegi, S.; Sánchez-Blanco, E.; Sánchez Carrasco, M. A.; Sánchez-López, A.; Sanz-Forcada, J.; Sarkis, P.; Sarmiento, L. F.; Schäfer, S.; Schmitt, J. H. M. M.; Schiller, J.; Schöfer, P.; Solano, E.; Stahl, O.; Strachan, J. B. P.; Stürmer, J.; Suárez, J. C.; Tabernero, H. M.; Tala, M.; Tulloch, S. M.; Ulbrich, R. -G.; Veredas, G.; Vico Linares, J. I.; Vilardell, F.; Wagner, K.; Winkler, J.; Wolthoff, V.; Xu, W.; Yan, F.; Zapatero Osorio, M. R. Bibcode: 2018A&A...609L...5R Altcode: 2017arXiv171205797R We report on the first star discovered to host a planet detected by radial velocity (RV) observations obtained within the CARMENES survey for exoplanets around M dwarfs. HD 147379 (V = 8.9 mag, M = 0.58 ± 0.08 M⊙), a bright M0.0 V star at a distance of 10.7 pc, is found to undergo periodic RV variations with a semi-amplitude of K = 5.1 ± 0.4 m s-1 and a period of P = 86.54 ± 0.06 d. The RV signal is found in our CARMENES data, which were taken between 2016 and 2017, and is supported by HIRES/Keck observations that were obtained since 2000. The RV variations are interpreted as resulting from a planet of minimum mass mP sin i = 25 ± 2 M⊕, 1.5 times the mass of Neptune, with an orbital semi-major axis a = 0.32 au and low eccentricity (e < 0.13). HD 147379 b is orbiting inside the temperate zone around the star, where water could exist in liquid form. The RV time-series and various spectroscopic indicators show additional hints of variations at an approximate period of 21.1 d (and its first harmonic), which we attribute to the rotation period of the star.

RV data (Table A.1) are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/609/L5 Title: VizieR Online Data Catalog: HD147379 b velocity curve (Reiners+, 2018) Authors: Reiners, A.; Ribas, I.; Zechmeister, M.; Caballero, J. A.; Trifonov, T.; Dreizler, S.; Morales, J. C.; Tal-Or, L.; Lafarga, M.; Quirrenbach, A.; Amado, P. J.; Kaminski, A.; Jeffers, S. V.; Aceituno, J.; Bejar, V. J. S.; Guardia, J.; Guenther, E. W.; Hagen, H. -J.; Montes, D.; Passegger, V. M.; Seifert, W.; Schweitzer, A.; Cortes-Contreras, M.; Abril, M.; Alonso-Floriano, F. J.; Ammler-von Eiff, M.; Antona, R.; Anglada-Escude, G.; Anwand-Heerwart, H.; Arroyo-Torres, B.; Azzaro, M.; Baroch, D.; Barrado, D.; Bauer, F. F.; Becerril, S.; Benitez, D.; Berdinas, Z. M.; Bergond, G.; Bluemcke, M.; Brinkmoeller, M.; Del Burgo, C.; Cano, J.; Cardenas Vazquez, M. C.; Casal, E.; Cifuentes, C.; Claret, A.; Colome, J.; Czesla, S.; Diez-Alonso, E.; Feiz, C.; Fernandez, M.; Ferro, I. M.; Fuhrmeister, B.; Galadi-Enriquez, D.; Garcia-Piquer, A.; Garcia Vargas, M. L.; Gesa, L.; Gomez Galera, V.; Gonzalez Hernandez, J. I.; Gonzalez-Peinado, R.; Groezinger, U.; Grohnert, S.; Guijarro, A.; de Guindos, E.; Gutierrez-Soto, J.; Hatzes, A. P.; Hauschildt, P. H.; Hedrosa, R. P.; Helml!, Ing J.; H Enning, Th.; Hermelo, I.; Hernandez Arabi, R.; Hernandez Castano, L.; Hernandez Hernando, F.; Herrero, E.; Huber, A.; Huke, P.; Johnson, E. N.; de Juan, E.; Kim, M.; Klein, R.; Klueter, J.; Klutsch, A.; Kuerster, M.; Labarga, F.; Lamert, A.; Lampon, M.; Lara, L. M.; Laun, W.; Lemke, U.; Lenzen, R.; Launhardt, R.; Lopez Del Fresno, M.; Lopez-Gonzalez, M. J.; Lopez-Puertas, M.; Lopez Salas, J. F.; Lopez-Santiago, J.; Luque, R.; Magan Madinabeitia, H.; Mall, U.; Mancini, L.; Mandel, H.; Marfil, E.; Marin Molina, J. A.; Maroto Fernandez, D.; Martin, E. L.; Martin-Ruiz, S.; Marvin, C. J.; Mathar, R. J.; Mirabet, E.; Moreno-Raya, M. E.; Moya, A.; Mundt, R.; Nagel, E.; Naranjo, V.; Nortmann, L.; Nowak, G.; Ofir, A.; Oreiro, R.; Palle, E.; Panduro, J.; Pascual, J.; Pavlov, A.; Pedraz, S.; Perez-Calpena, A.; Perez Medialdea, D.; Perger, M.; Perryman, M. A. C.; Pluto, M.; Rabaza, O.; Ramon, A.; Rebolo, R.; Redondo, P.; Reffert, S.; Reinhart, S.; Rhode, P.; Rix, H. -W.; Rodler, F.; Rodriguez, E.; Rodriguez-Lopez, C.; Rodriguez Trinidad, A.; Rohloff, R. -R.; Rosich, A.; ! Sadegi, S.; Sanchez-Blanco, E.; Sanchez Carrasco, M. A.; Sanchez-Lopez, A.; Sanz-Forcada, J.; Sarkis, P.; Sarmiento, L. F.; Schaefer, S.; Schmitt, J. H. M. M.; Schiller, J.; Schoefer, P.; Solano, E.; Stahl, O.; Strachan, J. B. P.; Stuermer, J.; Suarez, J. C.; Tabernero, H. M.; Tala, M.; Tulloch, S. M.; Ulbrich, R. -G.; Veredas, G.; Vico Linares, J. I.; Vilardell, F.; Wagner, K.; Winkler, J.; Wolthoff, V.; Xu, W.; Yan, F.; Zapatero Osorio, M. R. Bibcode: 2017yCat..36099005R Altcode: We analyzed data from the CARMENES VIS channel and HIRES/Keck. The CARMENES measurements were taken in the context of the CARMENES search for exoplanets around M dwarfs. The CARMENES instrument consists of two channels: the VIS channel obtains spectra at a resolution of R=94600 in the wavelength range 520-960nm, while the NIR channel yields spectra of R=80400 covering 960-1710nm. Both channels are calibrated in wavelength with hollow-cathode lamps and use temperature- and pressure-stabilized Fabry-Perot etalons to interpolate the wavelength solution and simultaneously monitor the spectrograph drift during nightly operations (Bauer et al., 2015A&A...581A.117B).

(1 data file). Title: VizieR Online Data Catalog: CARMENES radial velocity curves of 7 M-dwarf (Trifonov+, 2018) Authors: Trifonov, T.; Kuerster, M.; Zechmeister, M.; Tal-Or, L.; Caballero, J. A.; Quirrenbach, A.; Amado, P. J.; Ribas, I.; Reiners, A.; Reffert, S.; Dreizler, S.; Hatzes, A. P.; Kaminski, A.; Launhardt, R.; Henning, T.; Montes, D.; Bejar, V. J. S.; Mundt, R.; Pavlov, A.; Schmitt, J. H. M. M.; Seifert, W.; Morales, J. C.; Nowak, G.; Jeffers, S. V.; Rodriguez-Lopez, C.; Del Burgo, C.; Anglada-Escude, G.; Lopez-Santiago, J.; Mathar, R. J.; Ammler-von Eiff, M.; Guenther, E. W.; Barrado, D.; Gonzalez Hernandez, J. I.; Mancini, L.; Stuermer, J.; Abril, M.; Aceituno, J.; Alonso-Floriano, F. J.; Antona, R.; Anwand-Heerwart, H.; Arroyo-Torres, B.; Azzaro, M.; Baroch, D.; Bauer, F. F.; Becerril, S.; Benitez, D.; Berdinas, Z. M.; Bergond, G.; Bluemcke, M.; Brinkmoeller, M.; Cano, J.; Cardenas Vazquez, M. C.; Casal, E.; Cifuentes, C.; Claret, A.; Colome, J.; Cortes-Contreras, M.; Czesla, S.; Diez-Alonso, E.; Feiz, C.; Fernandez, M.; Ferro, I. M.; Fuhrmeister, B.; Galadi-Enriquez, D.; Garcia-Piquer, A.; Garcia Vargas, M. L.; Gesa, L.; Gomez Galera, V.; Gonzalez-Peinado, R.; Groezinger, U.; Grohnert, S.; Guardia, J.; Guijarro, A.; de Guindos, E.; Gutierrez-Soto, J.; Hagen, H. -J.; Hauschildt, P. H.; Hedrosa, R. P.; Helmling, J.; Hermelo, I.; Hernandez Arabi, R.; Hernandez Castano, L.; Hernandez Hernando, F.; Herrero, E.; Huber, A.; Huke, P.; Johnson, E.; de Juan, E.; Kim, M.; Klein, R.; Klueter, J.; Klutsch, A.; Lafarga, M.; Lampon, M.; Lara, L. M.; Laun, W.; Lemke, U.; Lenzen, R.; Lopez Del Fresno, M.; Lopez-Gonzalez, J.; Lopez-Puertas, M.; Lopez Salas, J. F.; Luque, R.; Magan Madinabeitia, H.; Mall, U.; Mandel, H.; Marfil, E.; Marin Molina, J. A.; Maroto Fernandez, D.; Martin, E. L.; Martin-Ruiz, S.; Marvin, C. J.; Mirabet, E.; Moya, A.; Moreno-Raya, M. E.; Nagel, E.; Naranjo, V.; Nortmann, L.; Ofir, A.; Oreiro, R.; Palle, E.; Panduro, J.; Pascual, J.; Passegger, V. M.; Pedraz, S.; Perez-Calpena, A.; Perez Medialdea, D.; Perger, M.; Perryman, M. A. C.; Pluto, M.; Rabaza, O.; Ramon, A.; Rebolo, R.; Redondo, P.; Reinhardt, S.; Rhode, P.; Rix, H. -W.; Rodler, F.; Rodriguez, E.; Rodriguez Trinidad, A.; Rohlo, R. -R.; Rosich, A.; Sadegi, S.; Sanchez-Blanco, E.; Sanchez Carrasco, M. A.; Sanchez-Lopez, A.; Sanz-Forcada, J.; Sarkis, P.; Sarmiento, L. F.; Schaefer, S.; Schiller, J.; Schoefer, P.; Schweitzer, A.; Solano, E.; Stahl, O.; Strachan, J. B. P.; Suarez, J. C.; Tabernero, H. M.; Tala, M.; Tulloch, S. M.; Veredas, G.; Vico Linares, J. I.; Vilardel, F.; Wagner, K.; Winkler, J.; Woltho, V.; Xu, W.; Yan, F.; Zapatero Osorio, M. R. Bibcode: 2017yCat..36090117T Altcode: The two CARMENES spectrographs are grism cross-dispersed, white pupil, echelle spectrograph working in quasi-Littrow mode using a two-beam, two-slice image slicer. The visible spectrograph covers the wavelength range from 0.52um to 1.05um with 61 orders, a resolving power of R=94600, and a mean sampling of 2.8 pixels per resolution element.

The data presented in this paper were taken during the early phase of operation of the CARMENES visible-light spectrograph.

(8 data files). Title: Optical and ultraviolet spectroscopic analysis of SN 2011fe at late times Authors: Friesen, Brian; Baron, E.; Parrent, Jerod T.; Thomas, R. C.; Branch, David; Nugent, Peter E.; Hauschildt, Peter H.; Foley, Ryan J.; Wright, Darryl E.; Pan, Yen-Chen; Filippenko, Alexei V.; Clubb, Kelsey I.; Silverman, Jeffrey M.; Maeda, Keiichi; Shivvers, Isaac; Kelly, Patrick L.; Cohen, Daniel P.; Rest, Armin; Kasen, Daniel Bibcode: 2017MNRAS.467.2392F Altcode: 2017MNRAS.tmp..243F; 2016arXiv160704784F We present optical spectra of the nearby Type Ia supernova SN 2011fe at 100, 205, 311, 349 and 578 d post-maximum light, as well as an ultraviolet (UV) spectrum obtained with the Hubble Space Telescope at 360 d post-maximum light. We compare these observations with synthetic spectra produced with the radiative transfer code phoenix. The day +100 spectrum can be well fitted with models that neglect collisional and radiative data for forbidden lines. Curiously, including these data and recomputing the fit yields a quite similar spectrum, but with different combinations of lines forming some of the stronger features. At day +205 and later epochs, forbidden lines dominate much of the optical spectrum formation; however, our results indicate that recombination, not collisional excitation, is the most influential physical process driving spectrum formation at these late times. Consequently, our synthetic optical and UV spectra at all epochs presented here are formed almost exclusively through recombination-driven fluorescence. Furthermore, our models suggest that the UV spectrum even as late as day +360 is optically thick and consists of permitted lines from several iron-peak species. These results indicate that the transition to the 'nebular' phase in Type Ia supernovae is complex and highly wavelength dependent. Title: Study of the variability of Nova V5668 Sgr, based on high-resolution spectroscopic monitoring Authors: Jack, D.; Robles Pérez, J. de J.; De Gennaro Aquino, I.; Schröder, K. -P.; Wolter, U.; Eenens, P.; Schmitt, J. H. M. M.; Mittag, M.; Hempelmann, A.; González-Pérez, J. N.; Rauw, G.; Hauschildt, P. H. Bibcode: 2017AN....338...91J Altcode: 2017arXiv170201171J We present results of our dense spectroscopic monitoring of Nova V5668 Sgr. Starting on March 19, 2015, only a few days after its discovery, we have obtained a series of spectra with the Telescopio Internacional en Guanajuato, Robótico y Espectroscópico telescope and its Heidelberg extended range optical spectrograph échelle spectrograph, which offers a resolution of R = 20,000 and covers the optical wavelength range 3,8008,800 Å. We performed a line identification of the discernible features for four spectra, which are representative of the respective phases in the light curve evolution of that nova. We simultaneously analyzed the variations in the visual light curve and the corresponding spectra of Nova V5668 Sgr. We found that, during the declining phases of the nova, the absorption features in all hydrogen and many other lines had shifted to higher expansion velocities of about -2,000 km s-1. Conversely, during the rise toward the following maximum, these observed absorption features had returned to lower expansion velocities. We found that the absorption features of some Fe II lines displayed the same behavior, but in addition disappeared for a few days during some declining phases. Features of several N I lines also disappeared, while new N II lines appeared in the emission for a few days during some of the declining phases of the light curve of Nova V5668 Sgr. The shape of the emission features is changing during the evolution, and shows a clear double-peak structure after the deep minimum. Thanks to the dense spectral monitoring we could observe several interesting developments of the Nova V5668 Sgr. Title: A Parallel Numerical Algorithm To Solve Linear Systems Of Equations Emerging From 3D Radiative Transfer Authors: Wichert, Viktoria; Arkenberg, Mario; Hauschildt, Peter H. Bibcode: 2016csss.confE..32W Altcode: Highly resolved state-of-the-art 3D atmosphere simulations will remain computationally extremely expensive for years to come. In addition to the need for more computing power, rethinking coding practices is necessary. We take a dual approach by introducing especially adapted, parallel numerical methods and correspondingly parallelizing critical code passages. In the following, we present our respective work on PHOENIX/3D.
With new parallel numerical algorithms, there is a big opportunity for improvement when iteratively solving the system of equations emerging from the operator splitting of the radiative transfer equation J = ΛS. The narrow-banded approximate Λ-operator Λ* , which is used in PHOENIX/3D, occurs in each iteration step. By implementing a numerical algorithm which takes advantage of its characteristic traits, the parallel code's efficiency is further
increased and a speed-up in computational time can be achieved. Title: Proceeding On : Parallelisation Of Critical Code Passages In PHOENIX/3D Authors: Arkenberg, Mario; Wichert, Viktoria; Hauschildt, Peter H. Bibcode: 2016csss.confE..31A Altcode: Highly resolved state-of-the-art 3D atmosphere simulations will remain computationally extremely expensive for years to come. In addition to the need for more computing power, rethinking coding practices is necessary. We take a dual approach here, by introducing especially adapted, parallel numerical methods and correspondingly parallelising time critical code passages. In the following, we present our work on PHOENIX/3D.While parallelisation is generally worthwhile, it requires revision of time-consuming subroutines with respect to separability of localised data and variables in order to determine the optimal approach. Of course, the same applies to the code structure. The importance of this ongoing work can be showcased by recently derived benchmark results, which were generated utilis- ing MPI and OpenMP. Furthermore, the need for a careful and thorough choice of an adequate, machine dependent setup is discussed. Title: Direct Imaging discovery of a second planet candidate around the possibly transiting planet host CVSO 30 Authors: Schmidt, T. O. B.; Neuhäuser, R.; Briceño, C.; Vogt, N.; Raetz, St.; Seifahrt, A.; Ginski, C.; Mugrauer, M.; Buder, S.; Adam, C.; Hauschildt, P.; Witte, S.; Helling, Ch.; Schmitt, J. H. M. M. Bibcode: 2016A&A...593A..75S Altcode: 2016arXiv160505315S Context. Direct imaging has developed into a very successful technique for the detection of exoplanets in wide orbits, especially around young stars. Directly imaged planets can be both followed astrometrically on their orbits and observed spectroscopically and thus provide an essential tool for our understanding of the early solar system.
Aims: We surveyed the 25 Ori association for direct-imaging companions. This association has an age of only few million years. Among other targets, we observed CVSO 30, which has recently been identified as the first T Tauri star found to host a transiting planet candidate.
Methods: We report on photometric and spectroscopic high-contrast observations with the Very Large Telescope, the Keck telescopes, and the Calar Alto observatory. They reveal a directly imaged planet candidate close to the young M3 star CVSO 30.
Results: The JHK-band photometry of the newly identified candidate is at better than 1σ consistent with late-type giants, early-T and early-M dwarfs, and free-floating planets. Other hypotheses such as galaxies can be excluded at more than 3.5σ. A lucky imaging z' photometric detection limit z' = 20.5 mag excludes early-M dwarfs and results in less than 10 MJup for CVSO 30 c if bound. We present spectroscopic observations of the wide companion that imply that the only remaining explanation for the object is that it is the first very young (<10 Myr) L - T-type planet bound to a star, meaning that it appears bluer than expected as a result of a decreasing cloud opacity at low effective temperatures. Only a planetary spectral model is consistent with the spectroscopy, and we deduce a best-fit mass of 4-5 Jupiter masses (total range 0.6-10.2 Jupiter masses).
Conclusions: This means that CVSO 30 is the first system in which both a close-in and a wide planet candidate are found to have a common host star. The orbits of the two possible planets could not be more different: they have orbital periods of 10.76 h and about 27 000 yr. The two orbits may have formed during a mutual catastrophic event of planet-planet scattering.

Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under programme IDs 090.C-0448(A), 290.C-5018(B), 092.C-0488(A) and at the Centro Astronómico Hispano-Alemán in programme H15-2.2-002. Title: Phoenix Meets CO5BOLD: 3D NLTE Radiative Transfer Calculations For M-Dwarf Chromospheres Authors: De Gennaro Aquino, Ivan; Hauschildt, Peter H.; Wedemeyer, Sven Bibcode: 2016csss.confE.149D Altcode: M-dwarf atmospheres are phenomenologically so rich that is currently impossible to include all the physical processes in one astrophysical simulation code. 1D models have greatly improved our understanding of the radiative properties of M-dwarf photospheres and important achievements have been obtained in 1D and 3D magneto-hydrodynamic simulations. Using a snapshot from a CO5BOLD M-dwarf simulation as input model, we use the 3D atmosphere code PHOENIX/3D to compute the radiative properties of a M-dwarf photosphere-chromosphere atmosphere with NLTE treatment for several atomic species and background atomic and molecular opacities. Title: CARMENES: an overview six months after first light Authors: Quirrenbach, A.; Amado, P. J.; Caballero, J. A.; Mundt, R.; Reiners, A.; Ribas, I.; Seifert, W.; Abril, M.; Aceituno, J.; Alonso-Floriano, F. J.; Anwand-Heerwart, H.; Azzaro, M.; Bauer, F.; Barrado, D.; Becerril, S.; Bejar, V. J. S.; Benitez, D.; Berdinas, Z. M.; Brinkmöller, M.; Cardenas, M. C.; Casal, E.; Claret, A.; Colomé, J.; Cortes-Contreras, M.; Czesla, S.; Doellinger, M.; Dreizler, S.; Feiz, C.; Fernandez, M.; Ferro, I. M.; Fuhrmeister, B.; Galadi, D.; Gallardo, I.; Gálvez-Ortiz, M. C.; Garcia-Piquer, A.; Garrido, R.; Gesa, L.; Gómez Galera, V.; González Hernández, J. I.; Gonzalez Peinado, R.; Grözinger, U.; Guàrdia, J.; Guenther, E. W.; de Guindos, E.; Hagen, H. -J.; Hatzes, A. P.; Hauschildt, P. H.; Helmling, J.; Henning, T.; Hermann, D.; Hernández Arabi, R.; Hernández Castaño, L.; Hernández Hernando, F.; Herrero, E.; Huber, A.; Huber, K. F.; Huke, P.; Jeffers, S. V.; de Juan, E.; Kaminski, A.; Kehr, M.; Kim, M.; Klein, R.; Klüter, J.; Kürster, M.; Lafarga, M.; Lara, L. M.; Lamert, A.; Laun, W.; Launhardt, R.; Lemke, U.; Lenzen, R.; Llamas, M.; Lopez del Fresno, M.; López-Puertas, M.; López-Santiago, J.; Lopez Salas, J. F.; Magan Madinabeitia, H.; Mall, U.; Mandel, H.; Mancini, L.; Marin Molina, J. A.; Maroto Fernández, D.; Martín, E. L.; Martín-Ruiz, S.; Marvin, C.; Mathar, R. J.; Mirabet, E.; Montes, D.; Morales, J. C.; Morales Muñoz, R.; Nagel, E.; Naranjo, V.; Nowak, G.; Palle, E.; Panduro, J.; Passegger, V. M.; Pavlov, A.; Pedraz, S.; Perez, E.; Pérez-Medialdea, D.; Perger, M.; Pluto, M.; Ramón, A.; Rebolo, R.; Redondo, P.; Reffert, S.; Reinhart, S.; Rhode, P.; Rix, H. -W.; Rodler, F.; Rodríguez, E.; Rodríguez López, C.; Rohloff, R. R.; Rosich, A.; Sanchez Carrasco, M. A.; Sanz-Forcada, J.; Sarkis, P.; Sarmiento, L. F.; Schäfer, S.; Schiller, J.; Schmidt, C.; Schmitt, J. H. M. M.; Schöfer, P.; Schweitzer, A.; Shulyak, D.; Solano, E.; Stahl, O.; Storz, C.; Tabernero, H. M.; Tala, M.; Tal-Or, L.; Ulbrich, R. -G.; Veredas, G.; Vico Linares, J. I.; Vilardell, F.; Wagner, K.; Winkler, J.; Zapatero Osorio, M. -R.; Zechmeister, M.; Ammler-von Eiff, M.; Anglada-Escudé, G.; del Burgo, C.; Garcia-Vargas, M. L.; Klutsch, A.; Lizon, J. -L.; Lopez-Morales, M.; Ofir, A.; Pérez-Calpena, A.; Perryman, M. A. C.; Sánchez-Blanco, E.; Strachan, J. B. P.; Stürmer, J.; Suárez, J. C.; Trifonov, T.; Tulloch, S. M.; Xu, W. Bibcode: 2016SPIE.9908E..12Q Altcode: The CARMENES instrument is a pair of high-resolution (R> 80,000) spectrographs covering the wavelength range from 0.52 to 1.71 μm, optimized for precise radial velocity measurements. It was installed and commissioned at the 3.5m telescope of the Calar Alto observatory in Southern Spain in 2015. The first large science program of CARMENES is a survey of 300 M dwarfs, which started on Jan 1, 2016. We present an overview of all subsystems of CARMENES (front end, fiber system, visible-light spectrograph, near-infrared spectrograph, calibration units, etalons, facility control, interlock system, instrument control system, data reduction pipeline, data flow, and archive), and give an overview of the assembly, integration, verification, and commissioning phases of the project. We show initial results and discuss further plans for the scientific use of CARMENES. Title: An irradiated brown-dwarf companion to an accreting white dwarf Authors: Hernández Santisteban, Juan V.; Knigge, Christian; Littlefair, Stuart P.; Breton, Rene P.; Dhillon, Vikram S.; Gänsicke, Boris T.; Marsh, Thomas R.; Pretorius, Magaretha L.; Southworth, John; Hauschildt, Peter H. Bibcode: 2016Natur.533..366H Altcode: 2016Natur.533..366S; 2016arXiv160507132H Interacting compact binary systems provide a natural laboratory in which to study irradiated substellar objects. As the mass-losing secondary (donor) in these systems makes a transition from the stellar to the substellar regime, it is also irradiated by the primary (compact accretor). The internal and external energy fluxes are both expected to be comparable in these objects, providing access to an unexplored irradiation regime. The atmospheric properties of donors are largely unknown, but could be modified by the irradiation. To constrain models of donor atmospheres, it is necessary to obtain accurate observational estimates of their physical properties (masses, radii, temperatures and albedos). Here we report the spectroscopic detection and characterization of an irradiated substellar donor in an accreting white-dwarf binary system. Our near-infrared observations allow us to determine a model-independent mass estimate for the donor of 0.055 ± 0.008 solar masses and an average spectral type of L1 ± 1, supporting both theoretical predictions and model-dependent observational constraints that suggest that the donor is a brown dwarf. Our time-resolved data also allow us to estimate the average irradiation-induced temperature difference between the dayside and nightside of the substellar donor (57 kelvin) and the maximum difference between the hottest and coolest parts of its surface (200 kelvin). The observations are well described by a simple geometric reprocessing model with a bolometric (Bond) albedo of less than 0.54 at the 2σ confidence level, consistent with high reprocessing efficiency, but poor lateral heat redistribution in the atmosphere of the brown-dwarf donor. These results add to our knowledge of binary evolution, in that the donor has survived the transition from the stellar to the substellar regime, and of substellar atmospheres, in that we have been able to test a regime in which the irradiation and the internal energy of a brown dwarf are comparable. Title: High spectral resolution monitoring of Nova V339 Delphini with TIGRE (Corrigendum) Authors: De Gennaro Aquino, I.; Schröder, K. -P.; Mittag, M.; Wolter, U.; Jack, D.; Eenens, P.; González-Pérez, J. N.; Hempelmann, A.; Schmitt, J. H. M. M.; Hauschildt, P. H.; Rauw, G. Bibcode: 2016A&A...589C...4D Altcode: No abstract at ADS Title: Solar Science with the Atacama Large Millimeter/Submillimeter Array—A New View of Our Sun Authors: Wedemeyer, S.; Bastian, T.; Brajša, R.; Hudson, H.; Fleishman, G.; Loukitcheva, M.; Fleck, B.; Kontar, E. P.; De Pontieu, B.; Yagoubov, P.; Tiwari, S. K.; Soler, R.; Black, J. H.; Antolin, P.; Scullion, E.; Gunár, S.; Labrosse, N.; Ludwig, H. -G.; Benz, A. O.; White, S. M.; Hauschildt, P.; Doyle, J. G.; Nakariakov, V. M.; Ayres, T.; Heinzel, P.; Karlicky, M.; Van Doorsselaere, T.; Gary, D.; Alissandrakis, C. E.; Nindos, A.; Solanki, S. K.; Rouppe van der Voort, L.; Shimojo, M.; Kato, Y.; Zaqarashvili, T.; Perez, E.; Selhorst, C. L.; Barta, M. Bibcode: 2016SSRv..200....1W Altcode: 2015SSRv..tmp..118W; 2015arXiv150406887W The Atacama Large Millimeter/submillimeter Array (ALMA) is a new powerful tool for observing the Sun at high spatial, temporal, and spectral resolution. These capabilities can address a broad range of fundamental scientific questions in solar physics. The radiation observed by ALMA originates mostly from the chromosphere—a complex and dynamic region between the photosphere and corona, which plays a crucial role in the transport of energy and matter and, ultimately, the heating of the outer layers of the solar atmosphere. Based on first solar test observations, strategies for regular solar campaigns are currently being developed. State-of-the-art numerical simulations of the solar atmosphere and modeling of instrumental effects can help constrain and optimize future observing modes for ALMA. Here we present a short technical description of ALMA and an overview of past efforts and future possibilities for solar observations at submillimeter and millimeter wavelengths. In addition, selected numerical simulations and observations at other wavelengths demonstrate ALMA's scientific potential for studying the Sun for a large range of science cases. Title: Center-to-limb variation of intensity and polarization in continuum spectra of FGK stars for spherical atmospheres Authors: Kostogryz, N. M.; Milic, I.; Berdyugina, S. V.; Hauschildt, P. H. Bibcode: 2016A&A...586A..87K Altcode: 2015arXiv151107213K
Aims: One of the necessary parameters needed for the interpretation of the light curves of transiting exoplanets or eclipsing binary stars (as well as interferometric measurements of a star or microlensing events) is how the intensity and polarization of light changes from the center to the limb of a star. Scattering and absorption processes in the stellar atmosphere affect both the center-to-limb variation of intensity (CLVI) and polarization (CLVP). In this paper, we present a study of the CLVI and CLVP in continuum spectra, taking into consideration the different contributions of scattering and absorption opacity for a variety of spectral type stars with spherical atmospheres.
Methods: We solve the radiative transfer equation for polarized light in the presence of a continuum scattering, taking into consideration the spherical model of a stellar atmosphere. To cross-check our results, we developed two independent codes that are based on Feautrier and short characteristics methods, respectively,
Results: We calculate the center-to-limb variation of intensity (CLVI) and polarization (CLVP) in continuum for the Phoenix grid of spherical stellar model atmospheres for a range of effective temperatures (4000-7000 K), gravities (log g = 1.0-5.5), and wavelengths (4000-7000 Å), which are tabulated and available at the CDS. In addition, we present several tests of our codes and compare our calculations for the solar atmosphere with published photometric and polarimetric measurements. We also show that our two codes provide similar results in all considered cases.
Conclusions: For sub-giant and dwarf stars (log g = 3.0-4.5), the lower gravity and lower effective temperature of a star lead to higher limb polarization of the star. For giant and supergiant stars (log g = 1.0-2.5), the highest effective temperature yields the largest polarization. By decreasing the effective temperature of a star down to 4500-5500 K (depending on log g), the limb polarization decreases and reaches a local minimum. It increases again with a corresponding decrease in temperature down to 4000 K. For the most compact dwarf stars (log g = 5.0-5.5), the limb polarization degree shows a maximum for models with effective temperatures in the range 4200-4600 K (depending on log g) and decreases toward higher and lower temperatures.

The intensity and polarization profiles are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/586/A87 Title: M dwarfs and the fraction of high carbon-to-oxygen stars in the solar neighbourhood Authors: Gizis, John E.; Marks, Zachary; Hauschildt, Peter H. Bibcode: 2016MNRAS.455.3824G Altcode: 2015arXiv151006985G We investigate the frequency of high carbon-to-oxygen (C/O = 0.9) M dwarf stars in the solar neighbourhood. Using synthetic spectra, we find that such M dwarfs would have weaker TiO bands relative to hydride features. Similar weakening has already been detected in M-subdwarf (sdM) stars. By comparing to existing spectroscopic surveys of nearby stars, we show that less than one per cent of nearby stars have high carbon-to-oxygen ratios. This limit does not include stars with C/O = 0.9, [m/H] > 0.3, and [C/Fe] > 0.1, which we predict to have low-resolution optical spectra similar to solar metallicity M dwarfs. Title: VizieR Online Data Catalog: Center-to-limb polarization of FGK stars (Kostogryz+, 2016) Authors: Kostogryz, N. M.; Milic, I.; Berdyugina, S. V.; Hauschildt, P. H. Bibcode: 2016yCat..35860087K Altcode: Calculated center-to-limb variations of intensity (limb darkening) for different stellar parameters with spherical atmosphere model approximation. All intensities are normalized to the intensity in the center of stellar disks, therefore, in the centre of the disks (mu=1.0), I(mu)/I(1.0)=1.0. The parameters of spherical Phoenix stellar model atmospheres we considered here are the following: effective temperature is in the range of 4000K-7000K with the step of 100K and for logg=1.0-5.5 with the step of 0.5. All calculations are made for such wavelengths: 4000Å, 4500Å, 5000Å, 6000Å, 7000Å. We also present the position of the stellar limb and calculated stellar radius.

Calculated center-to-limb variations of polarization (CLVP) for different stellar parameters with spherical atmosphere model approximation. All intensities are normalized to the intensity in the center of stellar disks, therefore, in the centre of the disks (mu=1.0), I(mu)/I(1.0)=1.0. The parameters of spherical Phoenix model atmosphere we considered here are the following: effective temperature is in the range of 4000K-7000 K with the step of 100K and for logg=1.0-5.5 with the step of 0.5. All calculations are made for such wavelengths: 4000Å, 4500Å, 5000Å, 6000Å, 7000Å. We also present the position of the stellar limb.

(2 data files). Title: High spectral resolution monitoring of Nova V339 Delphini with TIGRE Authors: De Gennaro Aquino, I.; Schröder, K. -P.; Mittag, M.; Wolter, U.; Jack, D.; Eenens, P.; González-Pérez, J. N.; Hempelmann, A.; Schmitt, J. H. M. M.; Hauschildt, P. H.; Rauw, G. Bibcode: 2015A&A...581A.134D Altcode:
Aims: We investigate the early development of the classical nova V339 Del (Nova Delphini 2013) through high-resolution optical spectroscopy. To study the structure of the ejecta, we focus on the evolution of the absorption and emission features and the changes within the line profiles.
Methods: We obtained spectra with the robotic 1.2 m telescope TIGRE equipped with the HEROS spectrograph (R = 20 000, wavelength coverage from 3800 to 8800 Å). Our data set covers the outburst from 3 until 121 days after discovery.
Results: We provide a qualitative analysis of the spectra, describing the line profiles evolution and providing a rich list of identified lines. During the optically thick phase, we detected several blue-shifted absorption features from s-processed elements, whose origin is unclear. The presence of strong lines from C/O and the absence of Neon features confirm that the nature of the central white dwarf is a CO type. The later "nebular" phase spectra show evidence of the non-spherical, inhomogeneous structure of the ejecta. The detailed evolution of the line profiles and appearance of high ionization species (e.g. N III, O III, He II, [Fe VII]) are direct consequences of the re-ionization of the ejecta during the peak of the soft X-ray emission. Title: Synthetic activity indicators for M-type dwarf stars Authors: Wedemeyer, Sven; Ludwig, Hans-Günter; Hauschildt, Peter; De Gennaro Aquino, Ivan Bibcode: 2015IAUGA..2255174W Altcode: Our understanding of the Sun has been substantially progressed owing to the advances in high-resolution observations during the last decades. These observations guided the development of numerical simulation codes for stellar atmospheres towards unprecedented levels of realism and complexity. Such 3D radiation magnetohydrodynamic (RMHD) codes can be applied and adapted to cooler stars. Here, we present a set of time-dependent 3D RMHD simulations for dwarf stars of spectral type M (representative of AD Leo). "M-dwarfs" are the most abundant stars in our galaxy and known to exhibit mega-flares. Comparisons of M-dwarf models with the Sun as fundamental reference case reveal differences and similarities, which lead to important insights into the structure and dynamics of quiescent "background" atmospheres. The models, which extend from the upper convection zone into the chromosphere, have different initial magnetic field strengths (up to 500G) and topologies, representing regions with different activity levels. The 3D model atmospheres are characterized by a very dynamic and intermittent structure on small spatial and temporal scales, final field strengths reaching a few kG and a wealth of physical processes, which by nature cannot be described by means of 1D static model atmospheres.Synthetic observables, i.e. spectra and intensity images, are calculated by using these models as input for detailed radiative transfer calculations and can be combined into synthetic full stellar disks, thus simulating spatially unresolved observations of M-dwarfs. The considered diagnostics, like, e.g., Halpha, Ca II lines, or the continuum intensity from UV to millimeter wavelengths, sample various properties of the dynamics, thermal and magnetic structure of the photosphere and the chromosphere and thus provide measures of stellar activity, which can be compared to observations. The complicated magnetic field structure and its imprint in synthetic diagnostics may have important implications for the understanding and characterization of stellar activity and with it possibly for the evaluation of planetary habitability around active M-dwarf stars. Title: VLTI/AMBER Studies of the Atmospheric Structure and Fundamental Parameters of Red Giant and Supergiant Stars Authors: Arroyo-Torres, B.; Wittkowski, M.; Marcaide, J. M.; Abellan, F. J.; Chiavassa, A.; Fabregat, J.; Freytag, B.; Guirado, J. C.; Hauschildt, P. H.; Marti-Vidal, I.; Quirrenbach, A.; Scholz, M.; Wood, P. R. Bibcode: 2015ASPC..497...91A Altcode: We present recent near-IR interferometric studies of red giant and supergiant stars, which are aimed at obtaining information on the structure of the atmospheric layers and constraining the fundamental parameters of these objects.

The observed visibilities of six red supergiants (RSGs), and also of one of the five red giants observed, indicate large extensions of the molecular layers, as previously observed for Mira stars. These extensions are not predicted by hydrostatic PHOENIX model atmospheres, hydrodynamical (RHD) simulations of stellar convection, or self-excited pulsation models. All these models based on parameters of RSGs lead to atmospheric structures that are too compact compared to our observations. We discuss how alternative processes might explain the atmospheric extensions for these objects.

As the continuum appears to be largely free of contamination by molecular layers, we can estimate reliable Rosseland angular radii for our stars. Together with distances and bolometric fluxes, we estimate the effective temperatures and luminosities of our targets, locate them in the HR diagram, and compare their positions to recent evolutionary tracks. Title: Search with UVES and X-Shooter for signatures of the low-mass secondary in the post common-envelope binary AA Doradus Authors: Hoyer, D.; Rauch, T.; Werner, K.; Hauschildt, P. H.; Kruk, J. W. Bibcode: 2015A&A...578A.125H Altcode: 2015arXiv150407750H Context. AA Dor is a close, totally eclipsing, post common-envelope binary with an sdOB-type primary star and an extremely low-mass secondary star, located close to the mass limit of stable central hydrogen burning. Within error limits, it may either be a brown dwarf or a late M-type dwarf.
Aims: We aim to extract the secondary's contribution to the phase-dependent composite spectra. The spectrum and identified lines of the secondary decide on its nature.
Methods: In January 2014, we measured the phase-dependent spectrum of AA Dor with X-Shooter over one complete orbital period. Since the secondary's rotation is presumable synchronized with the orbital period, its surface strictly divides into a day and night side. Therefore, we may obtain the spectrum of its cool side during its transit and of its hot, irradiated side close to its occultation. We developed the Virtual Observatory (VO) tool TLISA to search for weak lines of a faint companion in a binary system. We successfully applied it to the observations of AA Dor.
Results: We identified 53 spectral lines of the secondary in the ultraviolet-blue, visual, and near-infrared X-Shooter spectra that are strongest close to its occultation. We identified 57 (20 additional) lines in available Ultraviolet and Visual Echelle Spectrograph (UVES) spectra from 2001. The lines are mostly from C ii-iii and O ii, typical for a low-mass star that is irradiated and heated by the primary. We verified the orbital period of P = 22 597.033201 ± 0.00007 s and determined the orbital velocity K_sec = 232.9+16.6-6.5 km s-1 of the secondary. The mass of the secondary is M_sec = 0.081+0.018-0.010 M_⊙ and, hence, it is not possible to reliably determine a brown dwarf or an M-type dwarf nature. Conclusions: Although we identified many emission lines of the secondary's irradiated surface, the resolution and signal-to-noise ratio of our UVES and X-Shooter spectra are not good enough to extract a good spectrum of the secondary's nonirradiated hemisphere.

Based on observations collected at the European Southern Observatory, Chile, programs 066.D-1800 and 092.C-0692.Based on observations made with the NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer.Figures 2-5, 9, and Appendices are available in electronic form at http://www.aanda.org Title: Identification of the feature that causes the I-band secondary maximum of a Type Ia supernova Authors: Jack, D.; Baron, E.; Hauschildt, P. H. Bibcode: 2015MNRAS.449.3581J Altcode: 2015arXiv150303088J We obtained a time series of spectra covering the secondary maximum in the I band of the bright Type Ia supernova 2014J in M82 with the TIGRE telescope. Comparing the observations with theoretical models calculated with the time dependent extension of the PHOENIX code, we identify the feature that causes the secondary maximum in the I-band light curve. Fe II 3d6(3D)4s-3d6(5D)4p and similar high-excitation transitions produce a blended feature at ∼7500 Å, which causes the rise of the light curve towards the secondary maximum. The series of observed spectra of SN 2014J and archival data of SN 2011fe confirm this conclusion. We further studied the plateau phase of the R-band light curve of SN 2014J and searched for features which contribute to the flux. The theoretical models do not clearly indicate a new feature that may cause the R-band plateau phase. However, Co II features in the range of 6500-7000 Å and the Fe II feature of the I band are clearly seen in the theoretical spectra, but do not appear to provide all of the flux necessary for the R-band plateau. Title: What causes the large extensions of red supergiant atmospheres?. Comparisons of interferometric observations with 1D hydrostatic, 3D convection, and 1D pulsating model atmospheres Authors: Arroyo-Torres, B.; Wittkowski, M.; Chiavassa, A.; Scholz, M.; Freytag, B.; Marcaide, J. M.; Hauschildt, P. H.; Wood, P. R.; Abellan, F. J. Bibcode: 2015A&A...575A..50A Altcode: 2015arXiv150101560A
Aims: This research has two main goals. First, we present the atmospheric structure and the fundamental parameters of three red supergiants (RSGs), increasing the sample of RSGs observed by near-infrared spectro-interferometry. Additionally, we test possible mechanisms that may explain the large observed atmospheric extensions of RSGs.
Methods: We carried out spectro-interferometric observations of the RSGs V602 Car, HD 95687, and HD 183589 in the near-infrared K-band (1.92-2.47 μm) with the VLTI/AMBER instrument at medium spectral resolution (R ~ 1500). To categorize and comprehend the extended atmospheres, we compared our observational results to predictions by available hydrostatic PHOENIX, available 3D convection, and new 1D self-excited pulsation models of RSGs.
Results: Our near-infrared flux spectra of V602 Car, HD 95687, and HD 183589 are well reproduced by the PHOENIX model atmospheres. The continuum visibility values are consistent with a limb-darkened disk as predicted by the PHOENIX models, allowing us to determine the angular diameter and the fundamental parameters of our sources. Nonetheless, in the case of V602 Car and HD 95686, the PHOENIX model visibilities do not predict the large observed extensions of molecular layers, most remarkably in the CO bands. Likewise, the 3D convection models and the 1D pulsation models with typical parameters of RSGs lead to compact atmospheric structures as well, which are similar to the structure of the hydrostatic PHOENIX models. They can also not explain the observed decreases in the visibilities and thus the large atmospheric molecular extensions. The full sample of our RSGs indicates increasing observed atmospheric extensions with increasing luminosity and decreasing surface gravity, and no correlation with effective temperature or variability amplitude.
Conclusions: The location of our RSG sources in the Hertzsprung-Russell diagram is confirmed to be consistent with the red limits of recent evolutionary tracks. The observed extensions of the atmospheric layers of our sample of RSGs are comparable to those of Mira stars. This phenomenon is not predicted by any of the considered model atmospheres including available 3D convection and new 1D pulsation models of RSGs. This confirms that neither convection nor pulsation alone can levitate the molecular atmospheres of RSGs. Our observed correlation of atmospheric extension with luminosity supports a scenario of radiative acceleration on Doppler-shifted molecular lines.

Based on observations made with the VLT Interferometer (VLTI) at Paranal Observatory under programme ID 091.D-0275.Figures 2-6 are available in electronic form at http://www.aanda.org Title: On the atmospheric structure and fundamental parameters of red supergiants Authors: Wittkowski, M.; Arroyo-Torres, B.; Marcaide, J. M.; Abellan, F. J.; Chiavassa, A.; Freytag, B.; Scholz, M.; Wood, P. R.; Hauschildt, P. H. Bibcode: 2015IAUS..307..280W Altcode: We present near-infrared spectro-interferometric studies of red supergiant (RSG) stars using the VLTI/AMBER instrument, which are compared to previously obtained similar observations of AGB stars. Our observations indicate spatially extended atmospheric molecular layers of water vapor and CO, similar as previously observed for Mira stars. Data of VY~CMa indicate that the molecular layers are asymmetric, possibly clumpy. Thanks to the spectro-interferometric capabilities of the VLTI/AMBER instrument, we can isolate continuum bandpasses, estimate fundamental parameters of our sources, locate them in the HR diagram, and compare their positions to recent evolutionary tracks. For the example of VY CMa, this puts it close to evolutionary tracks of initial mass 25-32 M ⊙. Comparisons of our data to hydrostatic model atmospheres, 3d simulations of convection, and 1d dynamic model atmospheres based on self-excited pulsation models indicate that none of these models can presently explain the observed atmospheric extensions for RSGs. The mechanism that levitates the atmospheres of red supergiant is thus a currently unsolved problem. Title: Reproduction of the Wilson-Bappu Effect Using PHOENIX Authors: Olvera, C. M. Guerra; Jack, D.; Shroder, K. -P.; Fuhrmeister, B.; Mittag, M.; Hauschildt, P. Bibcode: 2015csss...18..405O Altcode: We use the versatile PHOENIX atmospheric modeling code in its version, which includes a gravity-scaled chromosphere above the temperature minimum to model the Ca II K emission line profile for solar-type stars, all with T_{eff} = 5780K and same turbulence broadening, only with different surface gravities. Models, which produce the modest emission observed in relatively inactive stars, reproduce the Wilson-Bappu effect (WBE) in absolute terms, i.e. the emission line-widths grow with lower gravity consistent with Δ W ∝ g^{-0.17} in the range of log{g}=5.0 to 3.5. Further modeling is in process to include lower gravities. In the solar case, which we used as a first test, we find the temperature minimum (over height, single component) for a relatively inactive Sun to reach down to 3930 K. The respective PHOENIX model (log{g} = 4.4) matches width and typical flux of the chromospheric Ca II emission of a nearly inactive Sun, as observed with the Hamburg robotic telescope (see Fig. 1). For comparison, the quiet Sun model C of tet{1981ApJS...45..635V} had a temperature minimum of 4170 K. Title: 3D Multi-Level Non-LTE Radiative Transfer for the CO Molecule Authors: Berkner, A.; Schweitzer, A.; Hauschildt, P. H. Bibcode: 2015csss...18..689B Altcode: The photospheres of cool stars are both rich in molecules and an environment where the assumption of LTE can not be upheld under all circumstances. Unfortunately, detailed 3D non-LTE calculations involving molecules are hardly feasible with current computers. For this reason, we present our implementation of the super level technique, in which molecular levels are combined into super levels, to reduce the number of unknowns in the rate equations and, thus, the computational effort and memory requirements involved, and show the results of our first tests against the 1D implementation of the same method. Title: The non-active stellar chromosphere: Ca II basal flux Authors: Pérez Martínez, M. I.; Schröder, K. -P.; Hauschildt, P. Bibcode: 2014MNRAS.445..270P Altcode: We analyse high-resolution, high-s/n European Southern Observatories (ESO)-archive spectra (from UVES, the UV echelle spectrograph) of 76 inactive or modestly active stars of spectral type G to M, main sequence and giants. Using PHOENIX model photospheres with Ca II K lines that match the observed line profiles, we (i) revise the effective temperatures, (ii) obtain a precise surface flux scale for each star and (iii) directly determine the exact surface fluxes of each Ca II K chromospheric emission with respect to the photospheric line profile. We find that our stellar sample exhibits a lower boundary to its chromospheric surface flux distribution with an unprecedented definition. From a subsample of the 25 least active stars, we obtain a simple empirical formula for the basal Ca II flux as a function of effective temperature: log {F^basal_{Ca II(H+K)}} = 7.05(± 0.31) log {T_eff} - 20.86(± 1.15). This is in good agreement with the Mg II basal flux. In a direct comparison with the large body of Mt Wilson S-measurements of the chromospheric Ca II emission and its well-defined cut-off, excellent agreement is achieved as well. A new result, however, is the small scatter of the least active star's fluxes about the basal flux. It is about 25 per cent and equals the residual uncertainties of our approach. At the same time, we do not find any evidence for a gravity dependence within these limits. This strongly confirms the basal flux as a well-defined and universal phenomenon, which characterizes every inactive chromosphere. Title: CARMENES instrument overview Authors: Quirrenbach, A.; Amado, P. J.; Caballero, J. A.; Mundt, R.; Reiners, A.; Ribas, I.; Seifert, W.; Abril, M.; Aceituno, J.; Alonso-Floriano, F. J.; Ammler-von Eiff, M.; Antona Jiménez, R.; Anwand-Heerwart, H.; Azzaro, M.; Bauer, F.; Barrado, D.; Becerril, S.; Béjar, V. J. S.; Benítez, D.; Berdiñas, Z. M.; Cárdenas, M. C.; Casal, E.; Claret, A.; Colomé, J.; Cortés-Contreras, M.; Czesla, S.; Doellinger, M.; Dreizler, S.; Feiz, C.; Fernández, M.; Galadí, D.; Gálvez-Ortiz, M. C.; García-Piquer, A.; García-Vargas, M. L.; Garrido, R.; Gesa, L.; Gómez Galera, V.; González Álvarez, E.; González Hernández, J. I.; Grözinger, U.; Guàrdia, J.; Guenther, E. W.; de Guindos, E.; Gutiérrez-Soto, J.; Hagen, H. -J.; Hatzes, A. P.; Hauschildt, P. H.; Helmling, J.; Henning, T.; Hermann, D.; Hernández Castaño, L.; Herrero, E.; Hidalgo, D.; Holgado, G.; Huber, A.; Huber, K. F.; Jeffers, S.; Joergens, V.; de Juan, E.; Kehr, M.; Klein, R.; Kürster, M.; Lamert, A.; Lalitha, S.; Laun, W.; Lemke, U.; Lenzen, R.; López del Fresno, Mauro; López Martí, B.; López-Santiago, J.; Mall, U.; Mandel, H.; Martín, E. L.; Martín-Ruiz, S.; Martínez-Rodríguez, H.; Marvin, C. J.; Mathar, R. J.; Mirabet, E.; Montes, D.; Morales Muñoz, R.; Moya, A.; Naranjo, V.; Ofir, A.; Oreiro, R.; Pallé, E.; Panduro, J.; Passegger, V. -M.; Pérez-Calpena, A.; Pérez Medialdea, D.; Perger, M.; Pluto, M.; Ramón, A.; Rebolo, R.; Redondo, P.; Reffert, S.; Reinhardt, S.; Rhode, P.; Rix, H. -W.; Rodler, F.; Rodríguez, E.; Rodríguez-López, C.; Rodríguez-Pérez, E.; Rohloff, R. -R.; Rosich, A.; Sánchez-Blanco, E.; Sánchez Carrasco, M. A.; Sanz-Forcada, J.; Sarmiento, L. F.; Schäfer, S.; Schiller, J.; Schmidt, C.; Schmitt, J. H. M. M.; Solano, E.; Stahl, O.; Storz, C.; Stürmer, J.; Suárez, J. C.; Ulbrich, R. G.; Veredas, G.; Wagner, K.; Winkler, J.; Zapatero Osorio, M. R.; Zechmeister, M.; Abellán de Paco, F. J.; Anglada-Escudé, G.; del Burgo, C.; Klutsch, A.; Lizon, J. L.; López-Morales, M.; Morales, J. C.; Perryman, M. A. C.; Tulloch, S. M.; Xu, W. Bibcode: 2014SPIE.9147E..1FQ Altcode: This paper gives an overview of the CARMENES instrument and of the survey that will be carried out with it during the first years of operation. CARMENES (Calar Alto high-Resolution search for M dwarfs with Exoearths with Near-infrared and optical Echelle Spectrographs) is a next-generation radial-velocity instrument under construction for the 3.5m telescope at the Calar Alto Observatory by a consortium of eleven Spanish and German institutions. The scientific goal of the project is conducting a 600-night exoplanet survey targeting ~ 300 M dwarfs with the completed instrument. The CARMENES instrument consists of two separate echelle spectrographs covering the wavelength range from 0.55 to 1.7 μm at a spectral resolution of R = 82,000, fed by fibers from the Cassegrain focus of the telescope. The spectrographs are housed in vacuum tanks providing the temperature-stabilized environments necessary to enable a 1 m/s radial velocity precision employing a simultaneous calibration with an emission-line lamp or with a Fabry-Perot etalon. For mid-M to late-M spectral types, the wavelength range around 1.0 μm (Y band) is the most important wavelength region for radial velocity work. Therefore, the efficiency of CARMENES has been optimized in this range. The CARMENES instrument consists of two spectrographs, one equipped with a 4k x 4k pixel CCD for the range 0.55 - 1.05 μm, and one with two 2k x 2k pixel HgCdTe detectors for the range from 0.95 - 1.7μm. Each spectrograph will be coupled to the 3.5m telescope with two optical fibers, one for the target, and one for calibration light. The front end contains a dichroic beam splitter and an atmospheric dispersion corrector, to feed the light into the fibers leading to the spectrographs. Guiding is performed with a separate camera; on-axis as well as off-axis guiding modes are implemented. Fibers with octagonal cross-section are employed to ensure good stability of the output in the presence of residual guiding errors. The fibers are continually actuated to reduce modal noise. The spectrographs are mounted on benches inside vacuum tanks located in the coudé laboratory of the 3.5m dome. Each vacuum tank is equipped with a temperature stabilization system capable of keeping the temperature constant to within +/-0.01°C over 24 hours. The visible-light spectrograph will be operated near room temperature, while the near-IR spectrograph will be cooled to ~ 140 K. The CARMENES instrument passed its final design review in February 2013. The MAIV phase is currently ongoing. First tests at the telescope are scheduled for early 2015. Completion of the full instrument is planned for the fall of 2015. At least 600 useable nights have been allocated at the Calar Alto 3.5m Telescope for the CARMENES survey in the time frame until 2018. A data base of M stars (dubbed CARMENCITA) has been compiled from which the CARMENES sample can be selected. CARMENCITA contains information on all relevant properties of the potential targets. Dedicated imaging, photometric, and spectroscopic observations are underway to provide crucial data on these stars that are not available in the literature. Title: A 3D radiative transfer framework. XI. Multi-level NLTE Authors: Hauschildt, Peter H.; Baron, Edward Bibcode: 2014A&A...566A..89H Altcode: 2014arXiv1404.4376H Context. Multi-level non-local thermodynamic equilibrium (NLTE) radiation transfer calculations have become standard throughout the stellar atmospheres community and are applied to all types of stars as well as dynamical systems such as novae and supernovae. Nevertheless even today spherically symmetric 1D calculations with full physics are computationally intensive. We show that full physics NLTE calculations can be done with fully 3 dimensional (3D) radiative transfer.
Aims: With modern computational techniques and current massive parallel computational resources, full detailed solution of the multi-level NLTE problem coupled to the solution of the radiative transfer scattering problem can be solved without sacrificing the micro physics description.
Methods: We extend the use of a rate operator developed to solve the coupled NLTE problem in spherically symmetric 1D systems. In order to spread memory among processors we have implemented the NLTE/3D module with a hierarchical domain decomposition method that distributes the NLTE levels, radiative rates, and rate operator data over a group of processes so that each process only holds the data for a fraction of the voxels. Each process in a group holds all the relevant data to participate in the solution of the 3DRT problem so that the 3DRT solution is parallelized within a domain decomposition group.
Results: We solve a spherically symmetric system in 3D spherical coordinates in order to directly compare our well-tested 1D code to the 3D case. We compare three levels of tests: a) a simple H+He test calculation, b) H+He+CNO+Mg, c) H+He+Fe. The last test is computationally large and shows that realistic astrophysical problems are solvable now, but they do require significant computational resources.
Conclusions: With presently available computational resources it is possible to solve the full 3D multi-level problem with the same detailed micro-physics as included in 1D modeling. Title: VLTI/AMBER observations of cold giant stars: atmospheric structures and fundamental parameters Authors: Arroyo-Torres, B.; Martí-Vidal, I.; Marcaide, J. M.; Wittkowski, M.; Guirado, J. C.; Hauschildt, P. H.; Quirrenbach, A.; Fabregat, J. Bibcode: 2014A&A...566A..88A Altcode: 2014arXiv1404.7384A
Aims: The main goal of this research is to determine the angular size and the atmospheric structures of cool giant stars (ɛ Oct, β Peg, NU Pav, ψ Peg, and γ Hya) and to compare them with hydrostatic stellar model atmospheres, to estimate the fundamental parameters, and to obtain a better understanding of the circumstellar environment.
Methods: We conducted spectro-interferometric observations of ɛ Oct, β Peg, NU Pav, and ψ Peg in the near-infrared K band (2.13-2.47 μm), and γ Hya (1.9-2.47 μm) with the VLTI/AMBER instrument at medium spectral resolution (~1500). To obtain the fundamental parameters, we compared our data with hydrostatic atmosphere models (PHOENIX).
Results: We estimated the Rosseland angular diameters of ɛ Oct, β Peg, NU Pav, ψ Peg, and γ Hya to be 11.66±1.50 mas, 16.87±1.00 mas, 13.03±1.75 mas, 6.31±0.35 mas, and 3.78±0.65 mas, respectively. Together with distances and bolometric fluxes (obtained from the literature), we estimated radii, effective temperatures, and luminosities of our targets. In the β Peg visibility, we observed a molecular layer of CO with a size similar to that modeled with PHOENIX. However, there is an additional slope in absorption starting around 2.3 μm. This slope is possibly due to a shell of H2O that is not modeled with PHOENIX (the size of the layer increases to about 5% with respect to the near-continuum level). The visibility of ψ Peg shows a low increase in the CO bands, compatible with the modeling of the PHOENIX model. The visibility data of ɛ Oct, NU Pav, and γ Hya show no increase in molecular bands.
Conclusions: The spectra and visibilities predicted by the PHOENIX atmospheres agree with the spectra and the visibilities observed in our stars (except for β Peg). This indicates that the opacity of the molecular bands is adequately included in the model, and the atmospheres of our targets have an extension similar to the modeled atmospheres. The atmosphere of β Peg is more extended than that predicted by the model. The role of pulsations, if relevant in other cases and unmodeled by PHOENIX, therefore seems negligible for the atmospheric structures of our sample. The targets are located close to the red limits of the evolutionary tracks of the STAREVOL model, corresponding to masses between 1 M⊙ and 3 M⊙. The STAREVOL model fits the position of our stars in the Hertzsprung-Russell (HR) diagram better than the Ekström model does. STAREVOL includes thermohaline mixing, unlike the Ekström model, and complements the latter for intermediate-mass stars.

Based on observations made with the VLT Interferometer (VLTI) at Paranal Observatory under programme ID 089.D-0801.Figures 2-4 are available in electronic form at http://www.aanda.org Title: First spectroscopic observations of the substellar companion of the young debris disk star PZ Telescopii Authors: Schmidt, T. O. B.; Mugrauer, M.; Neuhäuser, R.; Vogt, N.; Witte, S.; Hauschildt, P. H.; Helling, Ch.; Seifahrt, A. Bibcode: 2014A&A...566A..85S Altcode: 2014arXiv1404.2870S Context. In 2010 a substellar companion to the solar analog pre-main sequence star PZ Tel and member of the approximately 12 Myr old β Pic moving group was found by high-contrast direct imaging independently by two teams.
Aims: In order to determine the basic parameters of this companion more precisely and independent of evolutionary models, hence age-independent, we obtained follow-up spectroscopic observations of the primary and companion.
Methods: We used the Spectrograph for INtegral Field Observations in the Near Infrared (SINFONI) at the Very Large Telescope Unit 4/Yepun of ESO's Paranal Observatory in the H + K band and processed the data using the spectral deconvolution technique. The resulting spectrum of the companion was then compared to a grid of Drift-Phoenix synthetic model spectra, a combination of a general-purpose model atmosphere code with a non-equilibrium, stationary cloud and dust model, using a χ2 minimization analysis.
Results: We find a best fitting spectral type of G6.5 for PZ Tel A. The extracted spectrum of the substellar companion, at a spatial position compatible with earlier orbit estimates, yields a temperature Teff = 2500-115+138 K, a visual extinction AV = 0.53-0.53+0.84 mag, a surface gravity of log g = 3.50-0.30+0.51 dex, and a metallicity at the edge of the grid of [M/H] = 0.30-0.30 dex.
Conclusions: We derive a luminosity of log(Lbol/L⊙) = -2.66-0.08+0.06, a radius of R = 2.42-0.34+0.28 RJup, and a mass of M = 7.5-4.3+16.9 MJup for the PZ Tel companion, which is consistent with most earlier estimates using photometry alone. Combining our results with evolutionary models, we find a best-fitting mass of about 21 Jupiter masses at an age corresponding to the recently determined lithium depletion age of 7-2+4 Myr. Hence, the PZ Tel companion is most likely a wide brown dwarf companion in the 12-4+8 Myr old β Pic moving group.

Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under program ID 087.C-0109(A). Title: Characterization of the gaseous companion κ Andromedae b. New Keck and LBTI high-contrast observations Authors: Bonnefoy, M.; Currie, T.; Marleau, G. -D.; Schlieder, J. E.; Wisniewski, J.; Carson, J.; Covey, K. R.; Henning, T.; Biller, B.; Hinz, P.; Klahr, H.; Marsh Boyer, A. N.; Zimmerman, N.; Janson, M.; McElwain, M.; Mordasini, C.; Skemer, A.; Bailey, V.; Defrère, D.; Thalmann, C.; Skrutskie, M.; Allard, F.; Homeier, D.; Tamura, M.; Feldt, M.; Cumming, A.; Grady, C.; Brandner, W.; Helling, C.; Witte, S.; Hauschildt, P.; Kandori, R.; Kuzuhara, M.; Fukagawa, M.; Kwon, J.; Kudo, T.; Hashimoto, J.; Kusakabe, N.; Abe, L.; Brandt, T.; Egner, S.; Guyon, O.; Hayano, Y.; Hayashi, M.; Hayashi, S.; Hodapp, K.; Ishii, M.; Iye, M.; Knapp, G.; Matsuo, T.; Mede, K.; Miyama, M.; Morino, J. -I.; Moro-Martin, A.; Nishimura, T.; Pyo, T.; Serabyn, E.; Suenaga, T.; Suto, H.; Suzuki, R.; Takahashi; Takami, M.; Takato, N.; Terada, H.; Tomono, D.; Turner, E.; Watanabe, M.; Yamada, T.; Takami, H.; Usuda, T. Bibcode: 2014A&A...562A.111B Altcode: 2013arXiv1308.3859B Context. We previously reported the direct detection of a low-mass companion at a projected separation of 55 ± 2 AU around the B9-type star κ Andromedae. The properties of the system (mass ratio, separation) make it a benchmark for understanding the formation and evolution of gas giant planets and brown dwarfs on wide orbits.
Aims: We present new angular differential imaging (ADI) images of the system at 2.146 (Ks), 3.776 (L'), 4.052 (NB_4.05), and 4.78 μm (M') obtained with Keck/NIRC2 and LBTI/LMIRCam, as well as more accurate near-infrared photometry of the star with the MIMIR instrument. We aim to determine the near-infrared spectral energy distribution of the companion and use it to characterize the object.
Methods: We used analysis methods adapted to ADI to extract the companion flux. We compared the photometry of the object to reference young, and old objects and to a set of seven PHOENIX-based atmospheric models of cool objects accounting for the formation of dust. We used evolutionary models to derive mass estimates considering a wide range of plausible initial conditions. Finally, we used dedicated formation models to discuss the possible origin of the companion.
Results: We derive a more accurate J = 15.86 ± 0.21, H = 14.95 ± 0.13, Ks = 14.32 ± 0.09 mag for κ And b. We detect the companion in all our high-contrast observations. We confirm previous contrasts obtained at Ks and L' band. We derive NB_4.05 = 13.0 ± 0.2, and M' = 13.3 ± 0.3 mag and estimate log 10(L/L⊙) = -3.76 ± 0.06. Atmospheric models yield Teff = 1900+100-200 K. They do not set any constraint on the surface gravity. "Hot-start" evolutionary models predict masses of 14+25-2 MJup based on the luminosity and temperature estimates, and when considering a conservative age range for the system (30+120-10 Myr), "warm-start" evolutionary tracks constrain the mass to M ≥ 10MJup.
Conclusions: The mass of κ Andromedae b mostly falls in the brown-dwarf regime, owing to remaining uncertainties in age and in mass-luminosity models. According to the formation models, disk instability in a primordial disk may account for the position and a wide range of plausible masses of κ And b.

The LBT is an international collaboration among institutions in the United States, Italy, and Germany. LBT Corporation partners are: The University of Arizona on behalf of the Arizona university system; Instituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University; The Ohio State University, and The Research Corporation, on behalf of the University of Notre Dame, University of Minnesota, and University of Virginia.Appendices are available in electronic form at http://www.aanda.org Title: The atmospheric structure and fundamental parameters of the red supergiants AH Scorpii, UY Scuti, and KW Sagittarii Authors: Arroyo-Torres, B.; Wittkowski, M.; Marcaide, J. M.; Hauschildt, P. H. Bibcode: 2013A&A...554A..76A Altcode: 2013arXiv1305.6179A
Aims: We present the atmospheric structure and the fundamental properties of the red supergiants (RSGs) AH Sco, UY Sct, and KW Sgr based on VLTI/AMBER observations.
Methods: We carried out spectro-interferometric observations of AH Sco, UY Sct, and KW Sgr in the near-infrared K band (1.92-2.47 μm) with the VLTI/AMBER instrument with spatial and spectral resolutions of 3 milliarcsec and 1500, respectively, and compared the data to a new grid of hydrostatic PHOENIX model atmospheres.
Results: In our visibility data, we observe molecular layers of water and CO in extended atmospheres. For a uniform disk modeling, we observe size increases at the water band centered at 1.9 μm of 10% to 25% and at the CO bandheads at 2.3-2.5 μm of 20%-35% with respect to the near-continuum bandpass at around 2.20 μm. Our near-infrared spectra of AH Sco, UY Sct, and KW Sgr are well reproduced by the PHOENIX model atmospheres. The continuum visibility values are consistent with a limb-darkened disk as predicted by the PHOENIX models. However, the model visibilities do not predict the large observed extensions of the molecular layers. Comparing the continuum visibility values to PHOENIX models, we estimate the Rosseland-mean photospheric angular diameters of AH Sco, UY Sct, and KW Sgr to be 5.81 ± 0.15 mas, 5.48 ± 0.10 mas, and 3.91 ± 0.25 mas, respectively. Together with the distance and the spectro-photometry, we calculate radii of 1411 ± 124 R⊙ for AH Sco, 1708 ± 192 R⊙ for UY Sct, and 1009 ± 142 R⊙ for KW Sgr and effective temperatures of 3682 ± 190 K for AH Sco, 3365 ± 134 K for UY Sct, and 3720 ± 183 K for KW Sgr.
Conclusions: AH Sco, UY Sct, and KW Sgr exhibit extended atmospheric layers of H2O and CO. The PHOENIX atmosphere models predict the spectra and the continuum visibility values, but cannot reproduce the large extensions of the molecular layers. This indicates that the opacities of the molecular bands are included, but that the model atmospheres are too compact compared to the observations. The observed extended layers may be levitated by processes such as pulsation or convection, which are not included in the hydrostatic atmospheric models. The location of the targets in the HR-diagram is confirmed to be close to, and possibly slightly to the right of, the Hayashi limit of recent evolutionary tracks corresponding to masses between about 20 M⊙ and 40 M⊙. Title: A new extensive library of PHOENIX stellar atmospheres and synthetic spectra Authors: Husser, T. -O.; Wende-von Berg, S.; Dreizler, S.; Homeier, D.; Reiners, A.; Barman, T.; Hauschildt, P. H. Bibcode: 2013A&A...553A...6H Altcode: 2013arXiv1303.5632H
Aims: We present a new library of high-resolution synthetic spectra based on the stellar atmosphere code PHOENIX that can be used for a wide range of applications of spectral analysis and stellar parameter synthesis.
Methods: The spherical mode of PHOENIX was used to create model atmospheres and to derive detailed synthetic stellar spectra from them. We present a new self-consistent way of describing micro-turbulence for our model atmospheres.
Results: The synthetic spectra cover the wavelength range from 500 Å to 5.5 μm with resolutions of R = 500 000 in the optical and near IR, R = 100 000 in the IR and Δλ = 0.1 Å in the UV. The parameter space covers 2300 K ≤ Teff ≤ 12 000 K, 0.0 ≤ log g ≤ +6.0, - 4.0 ≤ [Fe/H] ≤ +1.0, and - 0.2 ≤ [α/Fe] ≤ +1.2. The library is a work in progress and we expect to extend it up to Teff = 25 000 K. Title: The atmospheric structure and fundamental parameters of Red Supergiants Authors: Arroyo-Torres, B.; Wittkowski, M.; Marcaide, J. M.; Hauschildt, P. H. Bibcode: 2013EAS....60...93A Altcode: We present studies of the atmospheric structure and fundamental properties of the red supergiants (RSGs) VY CMa, AH Sco, UY Sct, and KW Sgr based on near-infrared K-band interferometry obtained with the VLTI/AMBER instrument with a spectral resolution of 1500. In our visibility data, we observe the presence of molecular layers of water and CO in extended atmospheres. For a uniform disk modeling, we observe size increases in the water band centered at 1.9 μm and in the CO band at 2.3-2.5 μm, with respect to the near-continuum bandpass (2.20-2.25 μm). With our spectral resolution, we obtain diameters in the near-continuum, that are free from contamination by molecular layers. Using PHOENIX atmosphere models, we estimate Rosseland-mean photospheric angular diameters of VY CMa, AH Sco, UY Sct, and KW Sgr of 11.13 ± 0.3mas, 5.81 ± 0.15mas, 5.48 ± 0.10mas, and 3.91 ± 0.25mas, respectively. We estimate radii and effective temperatures, and place the stars in the HR diagram. The PHOENIX atmosphere models predict the spectra and the continuum visibility values, but do not predict the molecular layers visibility well: The model atmosphere is too compact when compared with the observations. This may be caused by pulsation and/or convection, which are not included in the models. Title: The atmospheric structure and fundamental parameters of the red supergiants AH Sco, UY Sct, and KW Sgr Authors: Arroyo-Torres, B.; Wittkowski, M.; Marcaide, J. M.; Hauschildt, P. H. Bibcode: 2013hsa7.conf..516A Altcode: We present the atmospheric structure and the fundamental parameters of the Red Supergiants (RSGs) AH Sco, UY Sct, and KW Sgr. We have carried out spectro-interferometric observations in the near-infrared bands (between 1.9 μm and 2.5 μm) with the VLTI/AMBER instrument in medium resolution. In the visibility data, we detect the presence of molecular layers of water and CO in extended atmospheres. For a uniform disk modelling, we observe size increases in the water band centered at 1.9 μm and in the CO band at 2.3--2.5 μm, with respect to the near-continuun bandpass (2.20-2.25 μm). Our near-infrared spectra of AH Sco, UY Sct, and KW Sgr are well reproduced by the PHOENIX model. However the synthetic visibility amplitudes of the model do not predict the large extensions of the molecular bands. The continuum (2.15-2.25 μm) appears free from contamination by molecular layers. Thus, the continuum fitting to the PHOENIX can be used to estimate the diameter. We estimate the Rosseland-mean photospheric angular diameter of AH Sco, UY Sct, and KW Sgr to be 6.12±0.7 mas, 5.67± 0.55 mas, and 4.07±0.65 mas, respectively (preliminary values). We estimate radii and effective temperatures, and place the stars in the HR diagram. Title: Extracting the Physical Parameters of a Sample of M-dwarfs from High-resolution Near-infrared Spectra Authors: del Burgo, C.; Martín, E. L.; Zapatero Osorio, M. R.; Deshpande, R.; Witte, S.; Helling, C.; Hauschildt, P. H. Bibcode: 2013ASPC..472...53D Altcode: This study is part of an effort to determine the physical and kinematical properties of a sample of 36 nearby late M-dwarfs, with spectral types M5-M9.5. They are the targets of a program to search for exoplanets orbiting around them from the radial velocity method using the near-infrared echelle spectrograph NIRSPEC on the Keck II telescope. Preliminary results about the effective temperature, surface gravity, and rotational broadening of a subsample of nine M-dwarfs are presented. The analysis is based on the comparison of the spectra obtained in the J-band with a high resolving power of 22,000 and stellar atmosphere synthetic models using the PHOENIX and the PHOENIX/DRIFT codes. This study shows that the strong potassium absorption doublet at 12432 and 12522 Å is useful to determine the effective temperature. Our results are of interest for the new generation of near-infrared spectrographs that are being developed to measure radial velocities with unprecedented precisions of a few ms-1, for which accurate theoretical models for comparison are needed. Title: New limb-darkening coefficients for Phoenix/1d model atmospheres. II. Calculations for 5000 K ≤ Teff ≤ 10 000 K Kepler, CoRot, Spitzer, uvby, UBVRIJHK, Sloan, and 2MASS photometric systems Authors: Claret, A.; Hauschildt, P. H.; Witte, S. Bibcode: 2013A&A...552A..16C Altcode:
Aims: We present an extension of our investigations on limb-darkening coefficients computed with spherical symmetrical Phoenix models. The models investigated in this paper cover the range 5000 K ≤ Teff ≤ 10 000 K and complete our previous studies of low effective temperatures computed with the same code.
Methods: The limb-darkening coefficients are computed for the transmission curves of the Kepler, CoRoT, and Spitzer space missions and the Strömgren, Johnson-Cousins, Sloan, and 2MASS passbands. These computations were performed by adopting the least-squares method.
Results: We have used six laws to describe the specific intensity distribution: linear, quadratic, square root, logarithmic, exponential, and a general law with four terms. The computations are presented for the solar chemical composition and cover the range 3.0 ≤ log g ≤ 5.5. The adopted microturbulent velocity and the mixing-length parameter are 2.0 km s-1 and 2.0.

Tables 2-25 are available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/552/A16 Title: 3D radiative transfer effects in parametrized starspots Authors: Berkner, A.; Hauschildt, P. H.; Baron, E. Bibcode: 2013A&A...550A.104B Altcode:
Aims: We use our 3D radiative transfer framework to investigate how the presence of a parametrized starspot affects radiative transfer in stellar atmospheres in general, and molecular CO lines in a stellar spectrum, in particular.
Methods: The equation of state is solved for a given temperature structure including a simple parametrized spot model and the 3D scattering problem for line transfer is solved via an operator splitting technique. The formal solution is based on a full characteristics solution. We have used both a LTE model and a test model with a 2 level atom, simulating a single spectral line in NLTE.
Results: We present the resulting CO band spectra showing both surface resolved and an integrated total emergent flux for the star and compare the umbral, penumbral, and quiet spectrum for a solar type star, which clearly shows the presence of spots as an increased CO line-depth. Furthermore, we show that the opacity structure of the spot has a significantly different angular variation than the quiet plane parallel star and its visible shape is strongly influenced by scattering, where strong scattering disconnects the lateral intensity profile from the temperature profile of the spot.
Conclusions: Even a simple, small scale parametrized model shows significant 3D effects, in both the resolved and in the surface integrated spectrum. The 3D model allows for a much more detailed treatment than simple mixing of spectra with different effective temperatures. Title: VizieR Online Data Catalog: Limb-darkening for CoRoT, Kepler, Spitzer. II. (Claret+, 2013) Authors: Claret, A.; Hauschildt, P. H.; Witte, S. Bibcode: 2013yCat..35520016C Altcode: 2013yCat..35529016C We present an extension of our investigations on limb-darkening coefficients computed with spherical symmetrical PHOENIX models. The models investigated in this paper cover the range 5000K<=Teff<=10000K and complete our previous studies of low effective temperatures computed with the same code.

The limb-darkening coefficients are computed for the transmission curves of the Kepler, CoRoT, and Spitzer space missions and the Stroemgren, Johnson-Cousins, Sloan, and 2MASS passbands. These computations were performed by adopting the least-squares method.

We have used six laws to describe the specific intensity distribution: linear, quadratic, square root, logarithmic, exponential, and a general law with four terms. The computations are presented for the solar chemical composition and cover the range 3.0<=logg<=5.5. The adopted microturbulent velocity and the mixing-length parameter are 2.0km/s and 2.0.

(17 data files). Title: Characterization of 36 late M-dwarfs using spectral energy distributions and near-infrared echelle spectra . Authors: del Burgo, C.; Helling, Ch.; Martín, E. L.; Witte, S.; Zapatero Osorio, M. R.; Hauschildt, P. H. Bibcode: 2013MmSAI..84.1084D Altcode: The aim of the study presented here is to determine the physical and kinematical properties of a sample of 36 nearby M-dwarfs, with spectral types M5-M9.5. Echelle spectra in the J-band were obtained using the NIRSPEC spectrograph on the Keck II telescope, with a resolving power of 22,000, at different epochs. The comparison of the observed spectra with stellar atmosphere models derived from the PHOENIX and the DRIFT-PHOENIX codes, has permitted the determination of the effective temperature (T_{eff }), surface gravity (log g), and rotational broadening (v_rotsin i) of the 36 M-dwarfs, assuming solar-like metallicity. This approach turned out to be quite insensitive to T_{eff } in the spectral type range from M5 to M9.5, which motivated us to use a different method. Thus, 2MASS J, H and K, and WISE W1, W2 and W3 photometry, which covers a wide wavelength range that includes the emission peak of our targets, was compared with the BT-SETTL-PHOENIX code to alternatively derive T_{eff } for every M-dwarf. The so obtained values of T_{eff } are consistent with other near-infrared studies. Our investigation shows some limitations of current theoretical models and methods. Although late M-dwarfs are difficult to model given their intrinsic faintness and atmosphere complexity, a proper characterization of them is necessary to better conduct the next generation of radial velocity surveys, which are aimed at searching for rocky planets around those stars. Title: Time-dependent radiative transfer with PHOENIX (Corrigendum) Authors: Jack, D.; Hauschildt, P. H.; Baron, E. Bibcode: 2013A&A...549C...1J Altcode: No abstract at ADS Title: A 3D radiative transfer framework. X. Arbitrary velocity fields in the comoving frame Authors: Baron, E.; Hauschildt, P. H.; Chen, B.; Knop, S. Bibcode: 2012A&A...548A..67B Altcode: 2012arXiv1210.6679B
Aims: General 3D astrophysical atmospheres will have random velocity fields. We seek to combine the methods we have developed for solving the 1D problem with arbitrary flows to those that we have developed for solving the fully 3D relativistic radiative transfer problem for monotonic flows.
Methods: The methods developed for 3D atmospheres with monotonic flows, solving the fully relativistic problem along curves defined by an affine parameter, are very flexible and can be extended to the case of arbitrary velocity fields in 3D. Simultaneously, the techniques we developed for treating the 1D problem with arbitrary velocity fields are easily adapted to the 3D problem.
Results: The algorithm we present can be used to solve 3D radiative transfer problems that include arbitrary wavelength couplings. We use a quasi-analytic formal solution of the radiative transfer equation that significantly improves the overall computation speed. We show that the approximate lambda operator developed in previous work gives good convergence, even neglecting wavelength coupling. Ng acceleration also gives good results. We present tests that are of similar resolution to what has been presented using Monte-Carlo techniques, thus our methods will be applicable to problems outside of our test setup. Additional domain decomposition parallelization strategies will be explored in future work. Title: New limb-darkening coefficients for PHOENIX/1D model atmospheres. I. Calculations for 1500 K ≤ Teff ≤ 4800 K Kepler, CoRot, Spitzer, uvby, UBVRIJHK, Sloan, and 2MASS photometric systems Authors: Claret, A.; Hauschildt, P. H.; Witte, S. Bibcode: 2012A&A...546A..14C Altcode:
Aims: The knowledge of how the specific intensity is distributed over the stellar disk is crucial for interpreting the light curves of extrasolar transiting planets, double-lined eclipsing binaries, and other astrophysical phenomena. To provide theoretical inputs for light curve modelling codes, we present new calculations of limb-darkening coefficients for the spherically symmetric phoenix models.
Methods: The limb-darkening coefficients were computed by covering the transmission curves of Kepler, CoRoT, and Spitzer space missions, as well as the passbands of the Strömgren, Johnson-Cousins, Sloan, and 2MASS. These computations adopted the least-square method. In addition, we also calculated the linear and bi-parametric approximations by adopting the flux conservation method as an additional tool for estimating the theoretical error bars in the limb-darkening coefficients.
Results: Six laws were used to describe the specific intensity distribution: linear, quadratic, square root, logarithmic, exponential, and a more general one with 4 terms. The computations are presented for the solar chemical composition, with log g varying between 2.5 and 5.5 and effective temperatures between 1500-4800 K. The adopted microturbulent velocity and the mixing-length parameters are 2.0 km s-1 and 2.0, respectively.

Tables 2-25 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/546/A14 Title: A 3D radiative transfer framework. IX. Time dependence Authors: Jack, D.; Hauschildt, P. H.; Baron, E. Bibcode: 2012A&A...546A..39J Altcode: 2012arXiv1209.5788J Context. Time-dependent, 3D radiation transfer calculations are important for the modeling of a variety of objects, from supernovae and novae to simulations of stellar variability and activity. Furthermore, time-dependent calculations can be used to obtain a 3D radiative equilibrium model structure via relaxation in time.
Aims: We extend our 3D radiative transfer framework to include direct time dependence of the radiation field; i.e., the ∂I/∂t terms are fully considered in the solution of radiative transfer problems.
Methods: We build on the framework that we have described in previous papers in this series and develop a subvoxel method for the ∂I/∂t terms.
Results: We test the implementation by comparing the 3D results to our well tested 1D time dependent radiative transfer code in spherical symmetry. A simple 3D test model is also presented.
Conclusions: The 3D time dependent radiative transfer method is now included in our 3D RT framework and in PHOENIX/3D. Title: EChO. Exoplanet characterisation observatory Authors: Tinetti, G.; Beaulieu, J. P.; Henning, T.; Meyer, M.; Micela, G.; Ribas, I.; Stam, D.; Swain, M.; Krause, O.; Ollivier, M.; Pace, E.; Swinyard, B.; Aylward, A.; van Boekel, R.; Coradini, A.; Encrenaz, T.; Snellen, I.; Zapatero-Osorio, M. R.; Bouwman, J.; Cho, J. Y. -K.; Coudé de Foresto, V.; Guillot, T.; Lopez-Morales, M.; Mueller-Wodarg, I.; Palle, E.; Selsis, F.; Sozzetti, A.; Ade, P. A. R.; Achilleos, N.; Adriani, A.; Agnor, C. B.; Afonso, C.; Allende Prieto, C.; Bakos, G.; Barber, R. J.; Barlow, M.; Batista, V.; Bernath, P.; Bézard, B.; Bordé, P.; Brown, L. R.; Cassan, A.; Cavarroc, C.; Ciaravella, A.; Cockell, C.; Coustenis, A.; Danielski, C.; Decin, L.; De Kok, R.; Demangeon, O.; Deroo, P.; Doel, P.; Drossart, P.; Fletcher, L. N.; Focardi, M.; Forget, F.; Fossey, S.; Fouqué, P.; Frith, J.; Galand, M.; Gaulme, P.; González Hernández, J. I.; Grasset, O.; Grassi, D.; Grenfell, J. L.; Griffin, M. J.; Griffith, C. A.; Grözinger, U.; Guedel, M.; Guio, P.; Hainaut, O.; Hargreaves, R.; Hauschildt, P. H.; Heng, K.; Heyrovsky, D.; Hueso, R.; Irwin, P.; Kaltenegger, L.; Kervella, P.; Kipping, D.; Koskinen, T. T.; Kovács, G.; La Barbera, A.; Lammer, H.; Lellouch, E.; Leto, G.; Lopez Morales, M.; Lopez Valverde, M. A.; Lopez-Puertas, M.; Lovis, C.; Maggio, A.; Maillard, J. P.; Maldonado Prado, J.; Marquette, J. B.; Martin-Torres, F. J.; Maxted, P.; Miller, S.; Molinari, S.; Montes, D.; Moro-Martin, A.; Moses, J. I.; Mousis, O.; Nguyen Tuong, N.; Nelson, R.; Orton, G. S.; Pantin, E.; Pascale, E.; Pezzuto, S.; Pinfield, D.; Poretti, E.; Prinja, R.; Prisinzano, L.; Rees, J. M.; Reiners, A.; Samuel, B.; Sánchez-Lavega, A.; Forcada, J. Sanz; Sasselov, D.; Savini, G.; Sicardy, B.; Smith, A.; Stixrude, L.; Strazzulla, G.; Tennyson, J.; Tessenyi, M.; Vasisht, G.; Vinatier, S.; Viti, S.; Waldmann, I.; White, G. J.; Widemann, T.; Wordsworth, R.; Yelle, R.; Yung, Y.; Yurchenko, S. N. Bibcode: 2012ExA....34..311T Altcode: 2012ExA...tmp...35T; 2011arXiv1112.2728T A dedicated mission to investigate exoplanetary atmospheres represents a major milestone in our quest to understand our place in the universe by placing our Solar System in context and by addressing the suitability of planets for the presence of life. EChO—the Exoplanet Characterisation Observatory—is a mission concept specifically geared for this purpose. EChO will provide simultaneous, multi-wavelength spectroscopic observations on a stable platform that will allow very long exposures. The use of passive cooling, few moving parts and well established technology gives a low-risk and potentially long-lived mission. EChO will build on observations by Hubble, Spitzer and ground-based telescopes, which discovered the first molecules and atoms in exoplanetary atmospheres. However, EChO's configuration and specifications are designed to study a number of systems in a consistent manner that will eliminate the ambiguities affecting prior observations. EChO will simultaneously observe a broad enough spectral region—from the visible to the mid-infrared—to constrain from one single spectrum the temperature structure of the atmosphere, the abundances of the major carbon and oxygen bearing species, the expected photochemically-produced species and magnetospheric signatures. The spectral range and resolution are tailored to separate bands belonging to up to 30 molecules and retrieve the composition and temperature structure of planetary atmospheres. The target list for EChO includes planets ranging from Jupiter-sized with equilibrium temperatures T eq up to 2,000 K, to those of a few Earth masses, with T eq u223c 300 K. The list will include planets with no Solar System analog, such as the recently discovered planets GJ1214b, whose density lies between that of terrestrial and gaseous planets, or the rocky-iron planet 55 Cnc e, with day-side temperature close to 3,000 K. As the number of detected exoplanets is growing rapidly each year, and the mass and radius of those detected steadily decreases, the target list will be constantly adjusted to include the most interesting systems. We have baselined a dispersive spectrograph design covering continuously the 0.4-16 μm spectral range in 6 channels (1 in the visible, 5 in the InfraRed), which allows the spectral resolution to be adapted from several tens to several hundreds, depending on the target brightness. The instrument will be mounted behind a 1.5 m class telescope, passively cooled to 50 K, with the instrument structure and optics passively cooled to u223c45 K. EChO will be placed in a grand halo orbit around L2. This orbit, in combination with an optimised thermal shield design, provides a highly stable thermal environment and a high degree of visibility of the sky to observe repeatedly several tens of targets over the year. Both the baseline and alternative designs have been evaluated and no critical items with Technology Readiness Level (TRL) less than 4-5 have been identified. We have also undertaken a first-order cost and development plan analysis and find that EChO is easily compatible with the ESA M-class mission framework. Title: The Exoplanet Characterization Observatory (EChO): performance model EclipseSim and applications Authors: van Boekel, Roy; Benneke, Björn; Heng, Kevin; Hu, Renyu; Madhusudhan, Nikku; Quanz, Sascha; Bétrémieux, Yan; Bouwman, Jeroen; Chen, Guo; Decin, Leen; de Kok, Remco; Glauser, Adrian; Güdel, Manuel; Hauschildt, Peter; Henning, Thomas; Jeffers, Sandra; Jin, Sheng; Kaltenegger, Lisa; Kerschbaum, Franz; Krause, Oliver; Lammer, Helmut; Luntzer, Armin; Meyer, Michael; Miguel, Yamila; Mordasini, Christoph; Ottensamer, Roland; Rank-Lueftinger, Theresa; Reiners, Ansgar; Reinhold, Timo; Schmid, Hans Martin; Snellen, Ignas; Stam, Daphne; Sun, Zhao; Vandenbussche, Bart Bibcode: 2012SPIE.8442E..1FV Altcode: We present EclipseSim, a radiometric model for exoplanet transit spectroscopy that allows easy exploration of the fundamental performance limits of any space-based facility aiming to perform such observations. It includes a library of stellar model atmosphere spectra and can either approximate exoplanet spectra by simplified models, or use any theoretical or observed spectrum, to simulate observations. All calculations are done in a spectrally resolved fashion and the contributions of the various fundamental noise sources are budgeted separately, allowing easy assessment of the dominant noise sources, as a function of wavelength. We apply EclipseSim to the Exoplanet Characterization Observatory (EChO), a proposed mission dedicated to exoplanet transit spectroscopy that is currently in competition for the M3 launch slot of ESA’s cosmic vision programme. We show several case studies on planets with sizes in the super-Earth to Jupiter range, and temperatures ranging from the temperate to the ≍1500K regime, demonstrating the power and versatility of EChO. EclipseSim is publicly available.* Title: VizieR Online Data Catalog: Limb-darkening for CoRoT, Kepler, Spitzer (Claret+, 2012) Authors: Claret, A.; Hauschildt, P. H.; Witte, S. Bibcode: 2012yCat..35460014C Altcode: 2012yCat..35469014C The knowledge of how the specific intensity is distributed over the stellar disk is crucial for interpreting the light curves of extrasolar transiting planets, double-lined eclipsing binaries, and other astrophysical phenomena. To provide theoretical inputs for light curve modelling codes, we present new calculations of limb-darkening coefficients for the spherically symmetric PHOENIX models.

The limb-darkening coefficients were computed by covering the transmission curves of Kepler, CoRoT, and Spitzer space missions, as well as the passbands of the Stromgren, Johnson-Cousins, Sloan, and 2MASS. These computations adopted the least-square method. In addition, we also calculated the linear and bi-parametric approximations by adopting the flux conservation method as an additional tool for estimating the theoretical error bars in the limb-darkening coefficients.

Six laws were used to describe the specific intensity distribution: linear, quadratic, square root, logarithmic, exponential, and a more general one with 4 terms. The computations are presented for the solar chemical composition, with logg varying between 2.5 and 5.5 and effective temperatures between 1500K-4800K. The adopted Microturbulent velocity and the mixing-length parameters are 2.0km/s and 2.0, respectively. Model are for solar metallicity.

(17 data files). Title: CARMENES. I: instrument and survey overview Authors: Quirrenbach, Andreas; Amado, Pedro J.; Seifert, Walter; Sánchez Carrasco, Miguel A.; Mandel, Holger; Caballero, Jose A.; Mundt, Reinhard; Ribas, Ignasi; Reiners, Ansgar; Abril, Miguel; Aceituno, Jesus; Alonso-Floriano, Javier; Ammler-von Eiff, Matthias; Anglada-Escude, Guillem; Antona Jiménez, Regina; Anwand-Heerwart, Heiko; Barrado y Navascués, David; Becerril, Santiago; Bejar, Victor; Benitez, Daniel; Cardenas, Concepcion; Claret, Antonio; Colome, Josep; Cortés-Contreras, Miriam; Czesla, Stefan; del Burgo, Carlos; Doellinger, Michaela; Dorda, R.; Dreizler, Stefan; Feiz, Carmen; Fernandez, Matilde; Galadi, David; Garrido, Rafael; González Hernández, Jonay; Guardia, Josep; Guenther, Eike; de Guindos, Enrique; Gutiérrez-Soto, Juan; Hagen, Hans J.; Hatzes, Artie; Hauschildt, Peter; Helmling, Jens; Henning, Thomas; Herrero, Enrique; Huber, Armin; Huber, Klaus; Jeffers, Sandra; Joergens, Viki; de Juan, Enrique; Kehr, M.; Klutsch, Alexis; Kürster, Martin; Lalitha, S.; Laun, Werner; Lemke, Ulrike; Lenzen, Rainer; Lizon, Jean-Louis; López del Fresno, Mauro; López-Morales, Mercedes; López-Santiago, Javier; Mall, Ulrich; Martin, Eduardo; Martín-Ruiz, Susana; Mirabet, Eduard; Montes, David; Morales, Juan Carlos; Morales Muñoz, Rafael; Moya, Andres; Naranjo, Vianak; Oreiro, Raquel; Pérez Medialdea, David; Pluto, Michael; Rabaza, Ovidio; Ramon, Alejandro; Rebolo, Rafael; Reffert, Sabine; Rhode, Petra; Rix, Hans-Walter; Rodler, Florian; Rodríguez, Eloy; Rodríguez López, Cristina; Rodríguez Pérez, Emilio; Rodriguez Trinidad, A.; Rohloff, Ralf-Reiner; Sánchez-Blanco, Ernesto; Sanz-Forcada, Jorge; Schäfer, Sebastian; Schiller, Jörg; Schmidt, Christof; Schmitt, Jürgen; Solano, Enrique; Stahl, Otmar; Storz, Clemens; Stürmer, Julian; Suarez, Juan Carlos; Thiele, Ulrich; Ulbrich, Rainer; Vidal-Dasilva, Manuela; Wagner, Karl; Winkler, Johannes; Xu, Wenli; Zapatero Osorio, Maria Rosa; Zechmeister, Mathias Bibcode: 2012SPIE.8446E..0RQ Altcode: CARMENES (Calar Alto high-Resolution search for M dwarfs with Exo-earths with Near-infrared and optical Echelle Spectrographs) is a next-generation instrument for the 3.5m telescope at the Calar Alto Observatory, built by a consortium of eleven Spanish and German institutions. The CARMENES instrument consists of two separate échelle spectrographs covering the wavelength range from 0.55 μm to 1.7 μm at a spectral resolution of R = 82, 000, fed by fibers from the Cassegrain focus of the telescope. Both spectrographs are housed in temperature-stabilized vacuum tanks, to enable a long-term 1 m/s radial velocity precision employing a simultaneous calibration with Th-Ne and U-Ne emission line lamps. CARMENES has been optimized for a search for terrestrial planets in the habitable zones (HZs) of low-mass stars, which may well provide our first chance to study environments capable of supporting the development of life outside the Solar System. With its unique combination of optical and near-infrared ´echelle spectrographs, CARMENES will provide better sensitivity for the detection of low-mass planets than any comparable instrument, and a powerful tool for discriminating between genuine planet detections and false positives caused by stellar activity. The CARMENES survey will target 300 M dwarfs in the 2014 to 2018 time frame. Title: VizieR Online Data Catalog: Spectroscopy of very low mass objects (Patience+, 2012) Authors: Patience, J.; King, R. R.; De Rosa, R. J.; Vigan, A.; Witte, S.; Rice, E.; Helling, C.; Hauschildt, P. Bibcode: 2012yCat..35400085P Altcode: 2012yCat..35409085P With a uniform VLT SINFONI data set of nine targets, we have developed an empirical grid of J, H, K spectra of the atmospheres of objects estimated to have very low substellar masses of ~5-20MJup and young ages ranging from ~1-50Myr. Most of the targets are companions, objects which are especially valuable for comparison with atmosphere and evolutionary models, as they present rare cases in which the age is accurately known from the primary. Based on the youth of the sample, all objects are expected to have low surface gravity, and this study investigates the critical early phases of the evolution of substellar objects. The spectra are compared with grids of five different theoretical atmosphere models.

************************************************************************** * * * Sorry, but the author(s) never supplied the tabular material * * announced in the paper * * * ************************************************************************** Title: Fundamental properties and atmospheric structure of the red supergiant VY Canis Majoris based on VLTI/AMBER spectro-interferometry Authors: Wittkowski, M.; Hauschildt, P. H.; Arroyo-Torres, B.; Marcaide, J. M. Bibcode: 2012A&A...540L..12W Altcode: 2012arXiv1203.5194W
Aims: We investigate the atmospheric structure and fundamental properties of the red supergiant VY CMa.
Methods: We obtained near-infrared spectro-interferometric observations of VY CMa with spectral resolutions of 35 and 1500 using the AMBER instrument at the VLTI.
Results: The visibility data indicate the presence of molecular layers of water vapor and CO in the extended atmosphere with an asymmetric morphology. The uniform disk diameter in the water band around 2.0 μm is increased by ~20% compared to the near-continuum bandpass at 2.20-2.25 μm, and in the CO band at 2.3-2.5 μm it is increased by up to ~50%. The closure phases indicate relatively small deviations from point symmetry close to the photospheric layer, and stronger deviations in the extended H2O and CO layers. Making use of the high spatial and spectral resolution, a near-continuum bandpass can be isolated from contamination by molecular and dusty layers, and the Rosseland-mean photospheric angular diameter is estimated to 11.3 ± 0.3 mas based on a PHOENIX atmosphere model. Together with recent high-precision estimates of the distance and spectro-photometry, this estimate corresponds to a radius of 1420 ± 120 R⊙ and an effective temperature of 3490 ± 90 K.
Conclusions: VY CMa exhibits asymmetric, possibly clumpy, atmospheric layers of H2O and CO, which are not co-spatial, within a larger elongated dusty envelope. Our revised fundamental parameters put VY CMa close to the Hayashi limit of recent evolutionary tracks of initial mass 25 M⊙ with rotation or 32 M⊙ without rotation, shortly before evolving blueward in the HR-diagram.

Based on observations made with the VLT Interferometer (VLTI) at Paranal Observatory under programme ID 386.D-0012.Figures 2, 3 and 5 are available in electronic form at http://www.aanda.org Title: Spectroscopy across the brown dwarf/planetary mass boundary. I. Near-infrared JHK spectra Authors: Patience, J.; King, R. R.; De Rosa, R. J.; Vigan, A.; Witte, S.; Rice, E.; Helling, Ch.; Hauschildt, P. Bibcode: 2012A&A...540A..85P Altcode: 2012arXiv1201.3921P With a uniform VLT SINFONI data set of nine targets, we have developed an empirical grid of J, H, K spectra of the atmospheres of objects estimated to have very low substellar masses of ~5-20 MJup and young ages ranging from ~1-50 Myr. Most of the targets are companions, objects which are especially valuable for comparison with atmosphere and evolutionary models, as they present rare cases in which the age is accurately known from the primary. Based on the youth of the sample, all objects are expected to have low surface gravity, and this study investigates the critical early phases of the evolution of substellar objects. The spectra are compared with grids of five different theoretical atmosphere models. This analysis represents the first systematic model comparison with infrared spectra of young brown dwarfs. The fits to the full JHK spectra of each object result in a range of best fit effective temperatures of ± 150-300 K whether or not the full model grid or a subset restricted to lower log (g) values is used. This effective temperature range is significantly larger than the uncertainty typically assigned when using a single model grid. Fits to a single wavelength band can vary by up to 1000 K using the different model grids. Since the overall shape of these spectra is governed more by the temperature than surface gravity, unconstrained model fits did not find matches with low surface gravity or a trend in log (g) with age. This suggests that empirical comparison with spectra of unambiguously young objects targets (such as those presented here) may be the most reliable method to search for indications of low surface gravity and youth. Based on comparison with previous observations, the SINFONI spectra represent a second epoch for the targets 2M0141 and DH Tau B, and the combined data show no variations in the spectral morphology over time. The analysis of two other targets, AB Pic B and CT Cha B, suggests that these objects may have lower temperatures, and consequently lower masses, than previously estimated.

Based on observations obtained at the Paranal Observatory, Chile for ESO programs 279.C-5010(A), 080.C-0590(A), 077.C-0264(A), 078.C-0800(B), & 078.C-0800(A).The spectra are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/540/A85 Title: Modeling the near-UV Band of GK Stars. II. Non-LTE Models Authors: Short, C. Ian; Campbell, Eamonn A.; Pickup, Heather; Hauschildt, Peter H. Bibcode: 2012ApJ...747..143S Altcode: 2012arXiv1201.0910S We present a grid of atmospheric models and synthetic spectral energy distributions (SEDs) for late-type dwarfs and giants of solar and 1/3 solar metallicity with many opacity sources computed in self-consistent non-local thermodynamic equilibrium (NLTE), and compare them to the LTE grid of Short & Hauschildt (Paper I). We describe, for the first time, how the NLTE treatment affects the thermal equilibrium of the atmospheric structure (T(τ) relation) and the SED as a finely sampled function of T eff, log g, and [A/H] among solar metallicity and mildly metal-poor red giants. We compare the computed SEDs to the library of observed spectrophotometry described in Paper I across the entire visible band, and in the blue and red regions of the spectrum separately. We find that for the giants of both metallicities, the NLTE models yield best-fit T eff values that are 30-90 K lower than those provided by LTE models, while providing greater consistency between log g values, and, for Arcturus, T eff values, fitted separately to the blue and red spectral regions. There is marginal evidence that NLTE models give more consistent best-fit T eff values between the red and blue bands for earlier spectral classes among the solar metallicity GK giants than they do for the later classes, but no model fits the blue-band spectrum well for any class. For the two dwarf spectral classes that we are able to study, the effect of NLTE on derived parameters is less significant. We compare our derived T eff values to several other spectroscopic and photometric T eff calibrations for red giants, including one that is less model dependent based on the infrared flux method (IRFM). We find that the NLTE models provide slightly better agreement to the IRFM calibration among the warmer stars in our sample, while giving approximately the same level of agreement for the cooler stars. Title: Near-infrared light curves of type Ia supernovae Authors: Jack, D.; Hauschildt, P. H.; Baron, E. Bibcode: 2012A&A...538A.132J Altcode: 2012arXiv1201.1723J
Aims: With our time-dependent model atmosphere code PHOENIX, our goal is to simulate light curves and spectra of hydrodynamical models of all types of supernovae. In this work, we simulate near-infrared light curves of SNe Ia and confirm the cause of the secondary maximum.
Methods: We apply a simple energy solver to compute the evolution of an SN Ia envelope during the free expansion phase. Included in the solver are energy changes due to expansion, the energy deposition of γ-rays and interaction of radiation with the material.
Results: We computed theoretical light curves of several SN Ia hydrodynamical models in the I, J, H, and K bands and compared them to the observed SN Ia light curves of SN 1999ee and SN 2002bo. By changing a line scattering parameter in time, we obtained quite reasonable fits to the observed near-infrared light curves. This is a strong hint that detailed NLTE effects in IR lines have to be modeled, which will be a future focus of our work.
Conclusions: We found that IR line scattering is very important for the near-infrared SN Ia light curve modeling. In addition, the recombination of Fe III to Fe II and of Co III to Co II is responsible for the secondary maximum in the near-infrared bands. For future work the consideration of NLTE for all lines (including the IR subordinate lines) will be crucial. Title: Dark Matter Powered Stars: Constraints from the Extragalactic Background Light Authors: Maurer, A.; Raue, M.; Kneiske, T.; Horns, D.; Elsässer, D.; Hauschildt, P. H. Bibcode: 2012ApJ...745..166M Altcode: 2012arXiv1201.1305M The existence of predominantly cold non-baryonic dark matter is unambiguously demonstrated by several observations (e.g., structure formation, big bang nucleosynthesis, gravitational lensing, and rotational curves of spiral galaxies). A candidate well motivated by particle physics is a weakly interacting massive particle (WIMP). Self-annihilating WIMPs would affect the stellar evolution especially in the early universe. Stars powered by self-annihilating WIMP dark matter should possess different properties compared with standard stars. While a direct detection of such dark matter powered stars seems very challenging, their cumulative emission might leave an imprint in the diffuse metagalactic radiation fields, in particular in the mid-infrared part of the electromagnetic spectrum. In this work, the possible contributions of dark matter powered stars (dark stars, DSs) to the extragalactic background light (EBL) are calculated. It is shown that existing data and limits of the EBL intensity can already be used to rule out some DS parameter sets. Title: A new extensive library of synthetic stellar spectra from PHOENIX atmospheres and its application to fitting VLT MUSE spectra Authors: Husser, T. -O.; Kamann, S.; Dreizler, S.; Hauschildt, Peter H. Bibcode: 2012ASInC...6...71H Altcode: 2012arXiv1203.1941H We present a new library of synthetic spectra based on the stellar atmosphere code phx. It covers the wavelength range from 500 Å to 55 000 Å with a resolution of R=500 000 in the optical and near IR, R=100 000 in the IR and &Delta&;lambda;=0.1 Å in the UV. The parameter space covers 2 300 K ≤ T_{eff} ≤ 8 000 K, 0.0 ≤ log(g) ≤ +6.0, -4.0 ≤ [Fe/H] ≤ +1.0 and -0.3 ≤ [α/Fe] ≤ +0.8. The library is work-in-progress and going to be extended to at least T_{eff}=25 000 K. We use a new self-consistent way of describing the microturbulence for our model atmospheres. The entire library of synthetic spectra will be available for download. Furthermore we present a method for fitting spectra, especially designed to work with the new 2nd generation VLT instrument muse. We show that we can determine stellar parameters (T_{eff}, log(g), [Fe/H] and [α/Fe]) and even single element abundances. Title: Surface convection: from the Sun to red giant stars Authors: Piau, L.; Kervella, P.; Dib, S.; Hauschildt, P. Bibcode: 2011sf2a.conf..235P Altcode: 2011arXiv1112.1381P We check how the change in surface conditions between the Sun and red giant branch stars changes the characteristic surface convection length scale to be used in models. We investigate the question in the case of the mixing length theory and of the phenomenology of full spectrum of turbulence. For the observational part, we rely on independent measurements of effective temperatures and interferometric radii of nearby red giants. We find that the local red giant branch cannot be explained taking into account the solar calibrated convective length scale. Title: The science of EChO Authors: Tinetti, Giovanna; Cho, James Y. -K.; Griffith, Caitlin A.; Grasset, Olivier; Grenfell, Lee; Guillot, Tristan; Koskinen, Tommi T.; Moses, Julianne I.; Pinfield, David; Tennyson, Jonathan; Tessenyi, Marcell; Wordsworth, Robin; Aylward, Alan; van Boekel, Roy; Coradini, Angioletta; Encrenaz, Therese; Snellen, Ignas; Zapatero-Osorio, Maria R.; Bouwman, Jeroen; Coudé du Foresto, Vincent; Lopez-Morales, Mercedes; Mueller-Wodarg, Ingo; Pallé, Enric; Selsis, Franck; Sozzetti, Alessandro; Beaulieu, Jean-Philippe; Henning, Thomas; Meyer, Michael; Micela, Giuseppina; Ribas, Ignasi; Stam, Daphne; Swain, Mark; Krause, Oliver; Ollivier, Marc; Pace, Emanuele; Swinyard, Bruce; Ade, Peter A. R.; Achilleos, Nick; Adriani, Alberto; Agnor, Craig B.; Afonso, Cristina; Allende Prieto, Carlos; Bakos, Gaspar; Barber, Robert J.; Barlow, Michael; Bernath, Peter; Bézard, Bruno; Bordé, Pascal; Brown, Linda R.; Cassan, Arnaud; Cavarroc, Céline; Ciaravella, Angela; Cockell, Charles; Coustenis, Athéna; Danielski, Camilla; Decin, Leen; De Kok, Remco; Demangeon, Olivier; Deroo, Pieter; Doel, Peter; Drossart, Pierre; Fletcher, Leigh N.; Focardi, Matteo; Forget, Francois; Fossey, Steve; Fouqué, Pascal; Frith, James; Galand, Marina; Gaulme, Patrick; González Hernández, Jonay I.; Grassi, Davide; Griffin, Matt J.; Grözinger, Ulrich; Guedel, Manuel; Guio, Pactrick; Hainaut, Olivier; Hargreaves, Robert; Hauschildt, Peter H.; Heng, Kevin; Heyrovsky, David; Hueso, Ricardo; Irwin, Pat; Kaltenegger, Lisa; Kervella, Patrick; Kipping, David; Kovacs, Geza; La Barbera, Antonino; Lammer, Helmut; Lellouch, Emmanuel; Leto, Giuseppe; Lopez Morales, Mercedes; Valverde, Lopez Miguel A.; Lopez-Puertas, Manuel; Lovi, Christophe; Maggio, Antonio; Maillard, Jean-Pierre; Prado, Jesus Maldonado; Marquette, Jean-Baptiste; Martin-Torres, Francisco J.; Maxted, Pierre; Miller, Steve; Molinari, Sergio; Montes, David; Moro-Martin, Amaya; Mousis, Olivier; Tuong, Napoléon Nguyen; Nelson, Richard; Orton, Glenn S.; Pantin, Eric; Pascale, Enzo; Pezzuto, Stefano; Poretti, Ennio; Prinja, Raman; Prisinzano, Loredana; Réess, Jean-Michel; Reiners, Ansgar; Samuel, Benjamin; Sanz Forcada, Jorge; Sasselov, Dimitar; Savini, Giorgio; Sicardy, Bruno; Smith, Alan; Stixrude, Lars; Strazzulla, Giovanni; Vasisht, Gautam; Vinatier, Sandrine; Viti, Serena; Waldmann, Ingo; White, Glenn J.; Widemann, Thomas; Yelle, Roger; Yung, Yuk; Yurchenko, Sergey Bibcode: 2011IAUS..276..359T Altcode: The science of extra-solar planets is one of the most rapidly changing areas of astrophysics and since 1995 the number of planets known has increased by almost two orders of magnitude. A combination of ground-based surveys and dedicated space missions has resulted in 560-plus planets being detected, and over 1200 that await confirmation. NASA's Kepler mission has opened up the possibility of discovering Earth-like planets in the habitable zone around some of the 100,000 stars it is surveying during its 3 to 4-year lifetime. The new ESA's Gaia mission is expected to discover thousands of new planets around stars within 200 parsecs of the Sun. The key challenge now is moving on from discovery, important though that remains, to characterisation: what are these planets actually like, and why are they as they are?

In the past ten years, we have learned how to obtain the first spectra of exoplanets using transit transmission and emission spectroscopy. With the high stability of Spitzer, Hubble, and large ground-based telescopes the spectra of bright close-in massive planets can be obtained and species like water vapour, methane, carbon monoxide and dioxide have been detected. With transit science came the first tangible remote sensing of these planetary bodies and so one can start to extrapolate from what has been learnt from Solar System probes to what one might plan to learn about their faraway siblings. As we learn more about the atmospheres, surfaces and near-surfaces of these remote bodies, we will begin to build up a clearer picture of their construction, history and suitability for life.

The Exoplanet Characterisation Observatory, EChO, will be the first dedicated mission to investigate the physics and chemistry of Exoplanetary Atmospheres. By characterising spectroscopically more bodies in different environments we will take detailed planetology out of the Solar System and into the Galaxy as a whole.

EChO has now been selected by the European Space Agency to be assessed as one of four M3 mission candidates. Title: CoolGrid: Modeling the Right Half of the Hertzsprung-Russell Diagram Authors: Short, C. I.; Hauschildt, P. H. Bibcode: 2011ASPC..445..173S Altcode: We evaluate the ability of PHOENIX LTE models to fit spectrophotometry throughout the visible and near-UV bands for late-type stars of a wide range of stellar parameters. Title: A 3D radiative transfer framework. VIII. OpenCL implementation Authors: Hauschildt, P. H.; Baron, E. Bibcode: 2011A&A...533A.127H Altcode:
Aims: We discuss an implementation of our 3D radiative transfer (3DRT) framework with the OpenCL paradigm for general GPU computing.
Methods: We implemented the kernel for solving the 3DRT problem in Cartesian coordinates with periodic boundary conditions in the horizontal (x,y) plane, including the construction of the nearest neighbor Λ∗ and the operator splitting step.
Results: We present the results of both a small and a large test case and compare the timing of the 3DRT calculations for serial CPUs and various GPUs.
Conclusions: The latest available GPUs can lead to significant speedups for both small and large grids compared to serial (single core) computations. Title: Detecting planets around very cool dwarfs at near infrared wavelengths with the radial velocity technique Authors: Rodler, F.; Del Burgo, C.; Witte, S.; Helling, Ch.; Hauschildt, P. H.; Martín, E. L.; Álvarez, C.; Deshpande, R. Bibcode: 2011A&A...532A..31R Altcode: 2011arXiv1105.2287R Context. Radial velocity monitoring of very cool dwarfs such as late M- and hot L-dwarfs has become a promising tool in the search for rocky planets as well as follow-up planetary candidates around dwarfs detected by transit surveys. These stars are faint at optical wavelengths, as their spectral flux distribution peaks at near-infrared (NIR) wavelengths. For this reason, it is desirable to measure the radial velocities in this wavelength regime. However, in the NIR very few medium- and high-resolution spectrographs are available at large telescopes. In the near future, high-resolution spectrographs for the NIR will be built, which will allow us to search for rocky planets around cool M-dwarfs and L-dwarfs from radial velocities monitoring.
Aims: We investigate the precision that can be attained in radial velocity measurements of very cool dwarfs in the NIR. The goal is to determine in which atmospheric window of the Earth's atmosphere the highest radial velocity precision can be achieved to help in designing the next generation of NIR high-resolution spectrographs.
Methods: We use stellar atmosphere synthetic models for an M- and an L-dwarf with temperatures of 2200 K and 1800 K, respectively, and a theoretical spectrum of the Earth's transmission in the spectral range from 0.9 to 2.5 μm. We simulate a series of Doppler-shifted spectra observed with different resolving powers and signal-to-noise ratios, and for different rotational broadenings of the dwarf. For different combinations of the input parameters, we recover the radial velocity by means of cross-correlation with a high signal-to-noise ratio template and determine the associate uncertainties.
Results: The highest precision in radial velocity measurements for the cool M-dwarf is found in the Y band around 1.0 μm, while for the L-dwarf it is determined in the J band around 1.25 μm. We note that synthetic models may lack some faint absorption features or underestimate their abundances. In addition, some instrumental/calibration aspects that are not taken into account in our estimations would increase the uncertainties. Title: A 3D radiative transfer framework: XIII. OpenCL implementation Authors: Hauschildt, Peter H.; Baron, E. Bibcode: 2011arXiv1107.5719H Altcode: We discuss an implementation of our 3D radiative transfer (3DRT) framework with the OpenCL paradigm for general GPU computing. We implement the kernel for solving the 3DRT problem in Cartesian coordinates with periodic boundary conditions in the horizontal $(x,y)$ plane, including the construction of the nearest neighbor $\Lstar$ and the operator splitting step. We present the results of a small and a large test case and compare the timing of the 3DRT calculations for serial CPUs and various GPUs. The latest available GPUs can lead to significant speedups for both small and large grids compared to serial (single core) computations. Title: Physical parameters of a sample of M dwarfs from high-resolution near-infrared spectra Authors: Del Burgo, C.; Deshpande, R.; Martín, E. L.; Zapatero Osorio, M. R.; Witte, S.; Helling, Ch.; Hauschildt, P. H. Bibcode: 2011EPJWC..1604006D Altcode: We show preliminary results about the effective temperature, surface gravity, and projected rotational velocity of eleven M dwarfs from the comparison of high-resolution near-infrared spectra with resolving power of ~20,000 and atmosphere synthetic models. Our results are in good agreement with those found in the literature. We find that the haze of observed absorption features (mostly water vapor) is relatively well modeled by the synthetic spectra. Title: Dust in brown dwarfs and extra-solar planets. III. Testing synthetic spectra on observations Authors: Witte, S.; Helling, Ch.; Barman, T.; Heidrich, N.; Hauschildt, P. H. Bibcode: 2011A&A...529A..44W Altcode: Context. This work is concerned with dust formation in ultra-cool atmospheres, encompassing the latest type stars, brown dwarfs, and hot giant exoplanets. Dust represents one of the most important and yet least understood sources of opacity in these types of objects.
Aims: We compare our model spectra with SpeX data in order to draw conclusions about the dust cloud structure and related quantities in ultra-cool atmospheres.
Methods: We use the self-consistent Drift-Phoenix atmosphere code, which features a kinetic dust formation mechanism and accounts for the dust cloud influence on the spectra.
Results: We present fits of our latest model spectra to observations that cover a wide range of our model grid. The results are remarkably good, yielding significant improvement over the older Cond-/Dusty-Phoenix models, especially in the L-dwarf regime. The new models are able to properly reproduce observed spectra, including complicated features such as the molecular band strengths. This raises confidence in the reliability of our dust-modeling approach.
Conclusions: We demonstrate that our code produces excellent results concerning the fitting with observations. This suggests that our dust cloud and atmosphere structures are reasonably accurate. Like all other current cloud models, ours is not able to produce satisfying results for spectral types later than L6 without manually tuning down the amount of dust. Our results show the formation of convective cells within the cloud, which are able to destroy the lower cloud parts. The dust opacity is reduced significantly without the need to tune the dust cloud thickness. There are indications that the cycle of dust accumulation and cloud destruction by convection is time-dependent on rather long timescales. Considering a statistical distribution of locally variable dust clouds over a dwarf's surface can result in a large number of spectral configurations for the same model atmosphere parameters, hence introducing an additional and more or less random degree of freedom to those atmospheres. Without resorting to the model atmosphere parameters, this alone can account for the unusually red and blue objects that have been discovered. Title: Theoretical light curves of type Ia supernovae Authors: Jack, D.; Hauschildt, P. H.; Baron, E. Bibcode: 2011A&A...528A.141J Altcode: 2011arXiv1105.3330J
Aims: We present the first theoretical SN Ia light curves calculated with the time-dependent version of the general purpose model atmosphere code PHOENIX. Our goal is to produce light curves and spectra of hydro models of all types of supernovae.
Methods: We extend our model atmosphere code PHOENIX to calculate type Ia supernovae light curves. A simple solver was implemented which keeps track of energy conservation in the atmosphere during the free expansion phase.
Results: The correct operation of the new additions to PHOENIX were verified in test calculations. Furthermore, we calculated theoretical light curves and compared them to the observed SN Ia light curves of SN 1999ee and SN 2002bo. We obtained LTE as well as NLTE model light curves.
Conclusions: We have verified the correct operation of our extension into the time domain. We have calculated the first SN Ia model light curves using PHOENIX in both LTE and NLTE. For future work the infrared model light curves need to be further investigated. Title: Discovery of an ~23 M Jup Brown Dwarf Orbiting ~700 AU from the Massive Star HIP 78530 in Upper Scorpius Authors: Lafrenière, David; Jayawardhana, Ray; Janson, Markus; Helling, Christiane; Witte, Soeren; Hauschildt, Peter Bibcode: 2011ApJ...730...42L Altcode: 2011arXiv1101.4666L We present the discovery of a substellar companion on a wide orbit around the ~ 2.5 M sun star HIP 78530, which is a member of the 5 Myr old Upper Scorpius association. We have obtained follow-up imaging over two years and show that the companion and primary share common proper motion. We have also obtained JHK spectroscopy of the companion and confirm its low surface gravity, in accordance with the young age of the system. A comparison with DRIFT-PHOENIX synthetic spectra indicates an effective temperature of 2800 ± 200 K and a comparison with template spectra of young and old dwarfs indicates a spectral type of M8 ± 1. The mass of the companion is estimated to be 19-26 M Jup based on its bolometric luminosity and the predictions of evolutionary models. The angular separation of the companion is 4farcs5, which at the distance of the primary star, 156.7 pc, corresponds to a projected separation of ~710 AU. This companion features one of the lowest mass ratios (~0.009) of any known companion at separations greater than 100 AU. Title: Surface convection and red-giant radius measurements Authors: Piau, L.; Kervella, P.; Dib, S.; Hauschildt, P. Bibcode: 2011A&A...526A.100P Altcode: 2010arXiv1010.3649P Phenomenological models of convection adopt characteristic length scales that are chosen to fit solar or stellar observations. We investigate whether changes in these length scales are required between the Sun and low mass stars on the red giant branch (RGB). The question is addressed jointly in the frameworks of the mixing length theory and the full spectrum of turbulence model. For both models, the convective length scale is assumed to be a fixed fraction of the local pressure scale height. We use constraints provided by the observed effective temperatures and linear radii independently. We consider a sample of 38 nearby giants and subgiants for which surface temperatures and luminosities are known accurately and the radii are determined by interferometry to better than 10%. We computed dedicated models for the few cases where the stellar masses were determined by asteroseismological measurements. First we calibrated the solar models. With the same physics, we then computed RGB models for masses between 0.9 M⊙ and 2.5 M⊙ and metallicities ranging from [Fe/H] = -0.34 to solar. The evolution is followed up to 103 L⊙. Special attention is given to the opacities and the non-grey atmosphere models used as boundary conditions for which the model of convection is the same as in the interior. For both the mixing length theory and the full spectrum of turbulence models, the characteristic solar length scale for convection has to be slightly reduced to fit the lower edge of the observed RGB. The corresponding models also agree more closely with the expected mass distribution on the RGB and the seismic constraints. These results are robust regardless of effective temperatures determined spectroscopically or radii determined interferometrically are used. Title: Radiative Trasnfer Calculation Of Light Curves And Spectra For Type Ia Sne Models Authors: De, Soma; Baron, E.; Timmes, F.; Hauschildt, P. Bibcode: 2011AAS...21743424D Altcode: 2011BAAS...4343424D We present calculations of the light curves and spectra from

a suite of Type Ia supernovae models, ranging from

standard single degenerate scenarios to double degenerate

collisions. We use a fully relativistic and time dependent radiative

transfer code PHOENIX for our calculations which is time dependent

in both radiative transfer and rate equation. Simple hydrodynamic

calculation is used to treat conservation of energy of the gas and

the radiation together and also allow different time-scales for gas

and radiation. Between two time steps for the calculation of the

light curve, the correct distribution of total energy change among

gas and radiation is obtained by iteratively solving for the

radiative transfer equation and hence the new temperature in the new

time step. In our work we explore systematic relationships between the

mass of 56ni mass produced, the mass of silicon group elements

produced, the white dwarf metallicity, and the mass of unburned

material Title: A 3D radiative transfer framework . VII. Arbitrary velocity fields in the Eulerian frame Authors: Seelmann, A. M.; Hauschildt, P. H.; Baron, E. Bibcode: 2010A&A...522A.102S Altcode: 2010arXiv1007.3419S
Aims: A solution of the radiative-transfer problem in 3D with arbitrary velocity fields in the Eulerian frame is presented. The method is implemented in our 3D radiative transfer framework and used in the PHOENIX/3D code. It is tested by comparison to our well-tested 1D co-moving frame radiative transfer code, where the treatment of a monotonic velocity field is implemented in the Lagrangian frame. The Eulerian formulation does not need much additional memory and is useable on state-of-the-art computers, even large-scale applications with 1000's of wavelength points are feasible.
Methods: In the Eulerian formulation of the problem, the photon is seen by the atom at a Doppler-shifted wavelength depending on its propagation direction, which leads to a Doppler-shifted absorption and emission. This leads to a different source function and a different Λ^* operator in the radiative transfer equations compared to the static case.
Results: The results of the Eulerian 3D spherical calculations are compared to our well-tested 1D Lagrangian spherical calculations, the agreement is, up to vmax = 1 × 103 km s-1 very good. Test calculation in other geometries are also shown. Title: PHOENIX: A General-purpose State-of-the-art Stellar and Planetary Atmosphere Code Authors: Baron, E.; Chen, Bin; Hauschildt, P. H. Bibcode: 2010ascl.soft10056B Altcode: PHOENIX is a general-purpose state-of-the-art stellar and planetary atmosphere code. It can calculate atmospheres and spectra of stars all across the HR-diagram including main sequence stars, giants, white dwarfs, stars with winds, TTauri stars, novae, supernovae, brown dwarfs and extrasolar giant planets. Title: Studying the Physical Diversity of Late-M Dwarfs with Dynamical Masses Authors: Dupuy, Trent J.; Liu, Michael C.; Bowler, Brendan P.; Cushing, Michael C.; Helling, Christiane; Witte, Soeren; Hauschildt, Peter Bibcode: 2010ApJ...721.1725D Altcode: 2010arXiv1007.4197D We present a systematic study of the physical properties of late-M dwarfs based on high-quality dynamical mass measurements and near-infrared (NIR) spectroscopy. We use astrometry from Keck natural and laser guide star adaptive optics imaging to determine orbits for the late-M binaries LP 349 - 25AB (M7.5+M8), LHS 1901AB (M6.5+M6.5), and Gl 569Bab (M8.5+M9). We find that LP 349 - 25AB (Mtot = 0.120+0.008 -0.007 Msun) is a pair of young brown dwarfs for which Lyon and Tucson evolutionary models jointly predict an age of 140 ± 30 Myr, consistent with the age of the Pleiades. However, at least the primary component seems to defy the empirical Pleiades lithium depletion boundary, implying that the system is in fact older (if the parallax is correct) and that evolutionary models under-predict the component luminosities for this magnetically active binary. We find that LHS 1901AB is a pair of very low-mass stars (Mtot = 0.194+0.025 -0.021 Msun) with evolutionary model-derived ages consistent with the old age (>6 Gyr) implied by its lack of activity. Our improved orbit for Gl 569Bab results in a higher mass for this binary (Mtot = 0.140+0.009 -0.008 Msun) compared to previous work (0.125 ± 0.007 Msun). We use these mass measurements along with our published results for 2MASS J2206 - 2047AB (M8+M8) to test four sets of ultracool model atmospheres currently in use. Fitting these models to our NIR integrated-light spectra provides temperature estimates warmer by ≈250 K than those derived independently from Dusty evolutionary models given the measured masses and luminosities. We propose that model atmospheres are more likely to be the source of this discrepancy, as it would be difficult to explain a uniform temperature offset over such a wide range of masses, ages, and activity levels in the context of evolutionary models. This contrasts with the conclusion of Konopacky et al. that model-predicted masses (given input T eff and L bol) are at fault for differences between theory and observations. In addition, we find an opposite (and smaller) mass discrepancy from what they report when we adopt their model-testing approach: masses are too high rather than too low because our T eff estimates derived from fitting NIR spectra are ≈650 K higher than their values from fitting broadband photometry alone.

Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

Based partly on observations made with ESO Telescopes at the Paranal Observatory under program IDs 073.C-0155, 077.C-0783, and 077.C-0441. Title: Hydrogen recombination with multilevel atoms Authors: de, Soma; Baron, E.; Hauschildt, P. H. Bibcode: 2010MNRAS.407..658D Altcode: 2010arXiv1005.0580D; 2010MNRAS.tmp..936D Hydrogen recombination is one of the most important atomic processes in many astrophysical objects such as Type II supernova (SN II) atmospheres, the high redshift Universe during the cosmological recombination era and HII regions in the interstellar medium. Accurate predictions of the ionization fraction can be quite different from those given by a simple solution if one takes into account many angular momentum substates, non-resonant processes and calculates the rates of all atomic processes from the solution of the radiative transfer equation instead of using a Planck function under the assumption of thermal equilibrium. We use the general-purpose model atmosphere code PHOENIX 1D to compare how the fundamental probabilities such as the photoionization probability, the escape probability and the collisional de-excitation probability are affected by the presence of other metals in the environment, multiple angular momentum substates and non-resonant processes. Our comparisons are based on a model of SN 1999em, SNe Type II, 20 d after its explosion. Title: Modeling the Near-ultraviolet Band of GK Stars. I. Local Thermodynamic Equilibrium Models Authors: Short, C. Ian; Hauschildt, P. H. Bibcode: 2010ApJ...718.1416S Altcode: We present a grid of LTE atmospheric models and synthetic spectra that covers the spectral class range from mid-G to mid-K, and luminosity classes from V to III, that is dense in T eff sampling (ΔT eff = 62.5 K), for stars of solar metallicity and moderately metal-poor scaled solar abundance ([{{A}\over {H}}]=0.0 and -0.5). All models have been computed with two choices of atomic line list: (1) the "big" line lists of Kurucz that best reproduce the broadband solar blue and near-UV f λ level, and (2) the "small" lists of Kurucz & Peytremann that provide the best fit to the high-resolution solar blue and near-UV spectrum. We compare our model spectral energy distributions to a sample of stars carefully selected from the large catalog of uniformly re-calibrated spectrophotometry of Burnashev with the goal of determining how the quality of fit varies with stellar parameters, especially in the historically troublesome blue and near-UV bands. We confirm that our models computed with the "big" line list recover the derived T eff values of the PHOENIX NextGen grid, but find that the models computed with the "small" line list provide greater internal self-consistency among different spectral bands, and closer agreement with the empirical T eff scale of Ramirez & Melendez, but not to the interferometrically derived T eff values of Baines et al. We find no evidence that the near-UV band discrepancy between models and observations for Arcturus (α Boo) reported in two works by Short & Hauschildt is pervasive, and that Arcturus may be peculiar in this regard. Title: Modeling the near-UV band of GK stars, Paper I: LTE models Authors: Short, C. Ian; Hauschildt, Peter Bibcode: 2010arXiv1007.1433S Altcode: We present a grid of LTE atmospheric models and synthetic spectra that cover the spectral class range from mid-G to mid-K, and luminosity classes from V to III, that is dense in Teff sampling (Delta Teff=62.5 K), for stars of solar metallicity and moderately metal poor scaled solar abundance ([A/H]=0.0 and -0.5). All models have been computed with two choices of atomic line list: a) the "big" line lists of Kurucz (1992) that best reproduce the broad-band solar blue and near UV flux level, and b) the "small" lists of Kurucz & Peytremann (1975) that provide the best fit to the high resolution solar blue and near-UV spectrum. We compare our model SEDs to a sample of stars carefully selected from the large catalog of uniformly re-calibrated spectrophotometry of Burnashev (1985) with the goal of determining how the quality of fit varies with stellar parameters, especially in the historically troublesome blue and near-UV bands. We confirm that our models computed with the "big" line list recover the derived Teff values of the PHOENIX NextGen grid, but find that the models computed with the "small" line list provide greater internal self-consistency among different spectral bands, and closer agreement with the empirical Teff scale of Ramirez & Melendez (2005), but not to the interferometrically derived Teff values of Baines et al. (2010). We find no evidence that the near UV band discrepancy between models and observations for Arcturus (alpha Boo) reported by Short & Hauschildt (2003 and 2009) is pervasive, and that Arcturus may be peculiar in this regard. Title: Resolving debris discs in the far-infrared: Early highlights from the DEBRIS survey Authors: Matthews, B. C.; Sibthorpe, B.; Kennedy, G.; Phillips, N.; Churcher, L.; Duchêne, G.; Greaves, J. S.; Lestrade, J. -F.; Moro-Martin, A.; Wyatt, M. C.; Bastien, P.; Biggs, A.; Bouvier, J.; Butner, H. M.; Dent, W. R. F.; di Francesco, J.; Eislöffel, J.; Graham, J.; Harvey, P.; Hauschildt, P.; Holland, W. S.; Horner, J.; Ibar, E.; Ivison, R. J.; Johnstone, D.; Kalas, P.; Kavelaars, J.; Rodriguez, D.; Udry, S.; van der Werf, P.; Wilner, D.; Zuckerman, B. Bibcode: 2010A&A...518L.135M Altcode: 2010arXiv1005.5147D We present results from the earliest observations of DEBRIS, a Herschel key programme to conduct a volume- and flux-limited survey for debris discs in A-type through M-type stars. PACS images (from chop/nod or scan-mode observations) at 100 and 160 μm are presented toward two A-type stars and one F-type star: β Leo, β UMa and η Corvi. All three stars are known disc hosts. Herschel spatially resolves the dust emission around all three stars (marginally, in the case of β UMa), providing new information about discs as close as 11 pc with sizes comparable to that of the Solar System. We have combined these data with existing flux density measurements of the discs to refine the SEDs and derive estimates of the fractional luminosities, temperatures and radii of the discs.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. Title: PHOENIX Spectra of Red Supergiants - Varying the Surface Abundances and the Microturbulence Authors: Lançon, A.; Hauschildt, P. H. Bibcode: 2010ASPC..425...61L Altcode: Based on PHOENIX models, we briefly discuss effects of surface abundances and microturbulence on the near-IR spectra of red supergiant stars. Title: Hydrogen in Type Ib Supernovae Authors: Baron, Eddie; Branch, David; Hauschildt, Peter; Ketchum, Wesley; James, Spencer Bibcode: 2010pese.confE...7B Altcode: No abstract at ADS Title: Multi-wavelength observations of a giant flare on CN Leonis. II. Chromospheric modelling with PHOENIX Authors: Fuhrmeister, B.; Schmitt, J. H. M. M.; Hauschildt, P. H. Bibcode: 2010A&A...511A..83F Altcode:
Aims: In M dwarfs, optical emission lines and continua are sensitive to changing chromospheric conditions, e.g., during flares. To study flare conditions for an observed spectrum, a comparison to synthesised spectra from model atmospheres is needed.
Methods: Using the stellar atmosphere code PHOENIX, we computed a set of 41 1D NLTE parameterised chromospheric models including the photosphere and parts of the transition region. By comparison of a linear combination of the synthesised spectra and a quiescent (observed) chromosphere to observed UVES/VLT spectra of a giant flare of the M 5.5 dwarf CN Leo (Gl406), we find the best-fitting flare model chromosphere.
Results: Our model spectra give a fairly good overall description of the observed continua and emission lines. In the best-fitting model, the temperature minimum is deep in the atmosphere resulting in high electron pressure for the chromospheric flaring area. The inferred chromospheric filling factor of the flare is about 3 percent, which declines during the flare. The photospheric flare filling factor is about 0.3 percent.

Based on observations collected at the European Southern Observatory, Paranal, Chile, 077.D-0011(A) and on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. Title: A 3D radiative transfer framework. VI. PHOENIX/3D example applications Authors: Hauschildt, P. H.; Baron, E. Bibcode: 2010A&A...509A..36H Altcode: 2009arXiv0911.3285H
Aims: We demonstrate the application of our 3D radiative transfer framework in the model atmosphere code PHOENIX for a number of spectrum synthesis calculations for very different conditions.
Methods: The 3DRT framework discussed in the previous papers of this series was added to our general-purpose model atmosphere code PHOENIX/1D and an extended 3D version PHOENIX/3D was created. The PHOENIX/3D code is parallelized via the MPI library using a hierarchical domain decomposition and displays very good strong scaling.
Results: We present the results of several test cases for widely different atmosphere conditions and compare the 3D calculations with equivalent 1D models to assess the internal accuracy of the 3D modeling. In addition, we show the results for a number of parameterized 3D structures.
Conclusions: With presently available computational resources it is possible to solve the full 3D radiative transfer (including scattering) problem with the same micro-physics as included in 1D modeling. Title: Watching dark matter stars burn - possible signatures of Dark Stars in the EBL Authors: Maurer, A.; Raue, M.; Kneiske, T.; Elsaesser, D.; Hauschildt, P.; Horns, D. Bibcode: 2010idm..confE..89M Altcode: 2010PoS...110E..89M No abstract at ADS Title: Cosmic Radiation Fields: Sources in the early Universe Authors: Raue, Martin; Kneiske, Tanja; Horns, Dieter; Elsaesser, Dominik; Hauschildt, Peter Bibcode: 2010crf..work.....R Altcode: 2010PoS...121E....R The workshop "Cosmic Radiation Fields - Sources in the Early Universe" (CRF 2010) focuses on the connection between the extragalactic infrared background and sources in the early universe, in particular stars powered by dark matter burning (Dark Stars; DS). The workshop covers the following topics: the cosmic infrared background, formation of early stars, dark stars, effect of dark matter in the early universe, dark matter halos, primordial star formation rate, and reionization. Further information can be found on the conference webpage: http://www.desy.de/crf2010/. Organizing committee: Tanja Kneiske, Martin Raue, Dominik Elsaesser, Alexander Gewering-Peine, Peter Hausschildt, Dieter Horns, and Andreas Maurer. Title: Constraints on dark matter powered stars from the extragalactic background light Authors: Maurer, A.; Raue, M.; Kneiske, T.; Elsaesser, D.; Hauschildt, P.; Horns, D. Bibcode: 2010tsra.confE.229M Altcode: 2010PoS...123E.229M No abstract at ADS Title: On the hydrogen recombination time in Type II supernova atmospheres Authors: de, Soma; Baron, E.; Hauschildt, P. H. Bibcode: 2010MNRAS.401.2081D Altcode: 2009MNRAS.tmp.1740D; 2009arXiv0910.0552D Non-local thermodynamic equilibrium radiative transfer calculations of differentially expanding supernovae atmospheres are computationally intensive and are almost universally performed in a time-independent snapshot mode, where both the radiative transfer problem and the rate equations are solved assuming the steady-state approximation. The validity of the steady-state approximation in the rate equations has recently been questioned for Type II supernova (SN II) atmospheres after maximum light on to the plateau. We calculate the effective recombination time of hydrogen in SN II using our general purpose model atmosphere code PHOENIX. While we find that the recombination time for the conditions of SNe II at early times is increased over the classical value for the case of a simple hydrogen model atom with energy levels corresponding to just the first two principal quantum numbers, the classical value of the recombination time is recovered in the case of a multilevel hydrogen atom. We also find that the recombination time at most optical depths is smaller in the case of a multilevel atom than for a simple two-level hydrogen atom. We find that time dependence in the rate equations is important in the early epochs of a supernova's lifetime. The changes due to the time-dependent rate equation (at constant input luminosity) are manifested in physical parameters such as the level populations which directly affect the spectra. The Hα profile is affected by the time-dependent rate equations at early times. At later times, time dependence does not significantly modify the level populations and therefore the Hα profile is roughly independent of whether the steady-state or time-dependent approach is used. Title: Time Dependent Radiative Transfer in Cosmic Recombination Epoch Authors: De, Soma; Baron, E.; Hauschildt, P. Bibcode: 2010AAS...21543709D Altcode: 2010BAAS...42..391D The Recmbination Epoch in cosmology (redshift of 800-1300) could be a very useful probe of the early universe and given the potential of high S/N observations from PLANCK we will be able to extract much information if we have a consistent radiative transfer framework that can trace the recombination era as a function of time. One can study a variety of quantities such as subtle effects in the electron fraction, line profiles, etc.

We consider a patch of the early universe during the recombination epoch with a set of spatially separated baryonic mass points moving with a Hubble flow. The density of dark matter and dark energy is embedded in the Hubble constant at each epoch. We treat this as an 1D problem. This patch is treated as a snapshot of the universe at a certain instant of time identified by redshift z and then evolve the system in time over the recombination era. In order to do this correctly, the time for a photon to travel across the whole patch should be smaller than the time interval between two snapshots. We use our very successful atmosphere code PHOENIX with time dependent radiative transfer equation and rate equations for hydrogen, helium and lithium to solve for the radiation field intensity at each radially separated point at each instant of time. All elements are considered to be in NLTE and have multi-level atomic structure. We solve the transfer equation using the short-characteristic approach where the specific intensity at two intersecting points between a characteristic ray and a radial layer represent two different directions of photon propagation at a given point but at two different instants of time. Compton scattering is being implemented in our calculation, it is an important process in the recombination epoch and couples the matter and radiation temperatures. Title: Constraints on dark matter powered stars from the extragalactic background light Authors: Maurer, A.; Raue, M.; Kneiske, T.; Elsaesser, D.; Hauschildt, P.; Horns, D. Bibcode: 2010crf..work...19M Altcode: 2010PoS...121E..19M No abstract at ADS Title: Dust in brown dwarfs and extra-solar planets. II. Cloud formation for cosmologically evolving abundances Authors: Witte, S.; Helling, Ch.; Hauschildt, P. H. Bibcode: 2009A&A...506.1367W Altcode: 2009arXiv0908.3597W Context: Substellar objects have extremely long life spans. The cosmological consequence for older objects are low abundances for heavy elements, which in turn results in a wide distribution of objects over metallicity, hence over age. Within their cool atmosphere, dust clouds become a dominant feature, affecting the opacity and the remaining gas phase abundance of heavy elements.
Aims: We investigate the influence of the stellar metallicity on the dust formation in substellar atmospheres and on the dust cloud structure and its feedback on the atmosphere. This work has implications for the general questions of star formation and of dust formation in the early universe.
Methods: We utilise numerical simulations to solve a set of moment equations to determine the quasi-static dust cloud structure (Drift). These equations model the nucleation, the kinetic growth of composite particles, their evaporation, and the gravitational settling as a stationary dust formation process. Element conservation equations augment this system of equations by including the element replenishment by convective overshooting. The integration with an atmosphere code (Phoenix) allows determination of a consistent (T, p, v_conv)-structure (T - local temperature, p - local pressure, v_conv - convective velocity), hence, to calculate synthetic spectra.
Results: A grid of Drift-Phoenix model atmospheres was calculated for a wide range of metallicity, [M/H] in [ +0.5, -0.0, -0.5, ..., -6.0] , to allow for systematic study of atmospheric cloud structures throughout the evolution of the universe. We find dust clouds in even the most metal-poor ([M/H] = -6.0) atmosphere of brown dwarfs. Only the most massive among the youngest brown dwarfs and giant gas planets can resist dust formation. For very low heavy element abundances, a temperature inversion develops that has a drastic impact on the dust cloud structure.
Conclusions: The combination of metal depletion by dust formation and the uncertainty of interior element abundances makes the modelling of substellar atmospheres an intricate problem in particular for old substellar objects. We furthermore show that the dust-to-gas ratio does not scale linearly with the object's [M/H] for a given effective temperature. The mean grain sizes and the composition of the grains change depending on [M/H], which influences the dust opacity that determines radiative heating and cooling, as well as the spectral appearance. Title: Structure and spectra of irradiated secondaries in close binaries. A model calculation of the pre-cataclysmic variable UU Sagittae Authors: Wawrzyn, A. C.; Barman, T. S.; Günther, H. M.; Hauschildt, P. H.; Exter, K. M. Bibcode: 2009A&A...505..227W Altcode: Context: The standard stellar model atmosphere ignores the influence of external radiation. This assumption, while sufficient for most stars, fails for many short-period binaries.
Aims: In setting up combined model atmospheres for close binaries, we want to constrain the parameters of both components, especially in the case of a hot primary component strongly influencing its cool secondary companion. This situation can be found after common envelope evolution (CEE). The status of both components today allows one to retrace the CEE itself.
Methods: We used our stellar atmosphere code PHOENIX, which includes the effect of irradiation in its radiation transport equation, to investigate the close binary star UU Sge. We combined our calculated spectra of both components, weighted by their visible size, and adjusted the input parameters until reasonable agreement with observations is reached.
Results: We derive a range of 80 000-85 000 K for the effective temperature of the primary (Teff, p) and give a rough estimate for the primary's abundances, particularly the nitrogen enrichment. The heated day-side of the secondary has an apparent “effective” or equilibrium temperature of 24 000-26 000 K, nearly independent of its intrinsic luminosity. It shows an enhancement in nitrogen and carbon.
Conclusions: The evolution of the primary and secondary stars were strongly influenced by the other's presence. Radiation from the primary on the secondary's day-side is still an important factor in understanding the secondary's atmospheric structure. Title: 3D Radiative Transfer with PHOENIX Authors: Baron, E.; Chen, Bin; Hauschildt, Peter H. Bibcode: 2009AIPC.1171..148B Altcode: 2009arXiv0908.4273B Using the methods of general relativity Lindquist derived the radiative transfer equation that is correct to all orders in v/c. Mihalas developed a method of solution for the important case of monotonic velocity fields with spherically symmetry. We have developed the generalized atmosphere code PHOENIX, which in 1-D has used the framework of Mihalas to solve the radiative transfer equation (RTE) in 1-D moving flows. We describe our recent work including 3-D radiation transfer in PHOENIX and particularly including moving flows exactly using a novel affine method. We briefly discuss quantitative spectroscopy in supernovae. Title: 1D and 3D radiative transfer in circumstellar disks Authors: Hügelmeyer, S. D.; Dreizler, S.; Homeier, D.; Hauschildt, P. H.; Barman, T. Bibcode: 2009AIPC.1171...93H Altcode: We present our code for the calculation of the 1D structure and synthetic spectra of accretion disks. The code is an extension of the well-tested stellar atmosphere code PHOENIX and is therefore capable of including large lists of atomic and molecular lines as well as a large set of dust species. We assume the standard accretion disk model for geometrically thin disks and solve the radiative transfer equation in the vertical direction for a number of disk rings with different radii. The combination of these rings yields the total disk spectrum. Comparison to observations of the T Tauri star GQ Lup shows the capability of our code. Additionally, we will show first results of 3D radiative transfer calculations. We plan to investigate the effect of rotating disks on the line profile by means of a two-level atom. Title: Methane line opacities in very cool stellar objects Authors: Hauschildt, P. H.; Warmbier, R.; Schneider, R.; Barman, T. Bibcode: 2009A&A...504..225H Altcode: Aims: We investigate the effects of different line data for methane 12CH4 on the structures of model atmospheres and low resolution synthetic spectra for ultra-cool substellar objects.
Methods: For each set of methane line data we compare the resulting model atmospheres and spectra computed with the general purpose model atmosphere code PHOENIX.
Results: The new HGW methane line data compares well to the HITRAN2004 data. We find the the HITRAN2004 methane lines are in some bands stronger than the HGW lines, resulting in deeper absorption bands in the synthetic spectra.
Conclusions: Title: Time-dependent radiative transfer with PHOENIX Authors: Jack, D.; Hauschildt, P. H.; Baron, E. Bibcode: 2009A&A...502.1043J Altcode: 2009arXiv0907.1441J Aims: We present first results and tests of a time-dependent extension to the general purpose model atmosphere code PHOENIX. We aim to produce light curves and spectra of hydro models for all types of supernovae.
Methods: We extend our model atmosphere code PHOENIX to solve time-dependent non-grey, NLTE, radiative transfer in a special relativistic framework. A simple hydrodynamics solver was implemented to keep track of the energy conservation of the atmosphere during free expansion.
Results: The correct operation of the new additions to PHOENIX were verified in test calculations.
Conclusions: We have shown the correct operation of our extension to time-dependent radiative transfer and will be able to calculate supernova light curves and spectra in future work. Title: Physical parameters of T dwarfs derived from high-resolution near-infrared spectra Authors: Del Burgo, C.; Martín, E. L.; Zapatero Osorio, M. R.; Hauschildt, P. H. Bibcode: 2009A&A...501.1059D Altcode: 2009arXiv0903.4461D Aims: We determine the effective temperature, surface gravity and projected rotational velocity of nine T dwarfs from the comparison of high-resolution near-infrared spectra and synthetic models, and estimate the mass and age of the objects from state-of-the-art models.
Methods: We use the AMES-COND cloudless solar metallicity models provided by the PHOENIX code to match the spectra of nine T-type field dwarfs observed with the near-infrared high-resolution spectrograph NIRSPEC using ten echelle orders to cover part of the J band from 1.147 to 1.347 μm with a resolving power R∼20 000. The projected rotational velocity, effective temperature and surface gravity of the objects are determined based on the minimum root mean square of the differences between the modelled and observed relative fluxes. Estimates of the mass and age of the objects are obtained from effective temperature-surface gravity diagrams, where our results are compared with existing solar metallicity models.
Results: The modelled spectra reproduce quite well the observed features for most of the T dwarfs, with effective temperatures in the range of 922-1009 K, and surface gravities between 104.1 and 104.9 cm s-2. Our results support the assumption of a dust free atmosphere for T dwarfs later than T5, where dust grains form and then gravitationally sediment into the low atmosphere. The modelled spectra do not accurately mimic some individual very strong lines like the K i doublet at 1.2436 and 1.2525 μm. Our modelled spectra does not match well the observed spectra of the two T dwarfs with earlier spectral types, namely SDSSp J125453.90-012247.4 (T2) and 2MASS J05591914-1404488 (T4.5), which is likely due to the presence of condensate clouds that are not incorporated in the models used here. By comparing our results and their uncertainties to evolutionary models, we estimate masses in the interval ≈5-75~MJ for T dwarfs later than T5, which are in good agreement with those found in the literature. We found apparent young ages that are typically between 0.1 and a few Gyr for the same T dwarfs, which is consistent with recent kinematical studies.

Reduced NIRSPEC spectra of the nine T-type dwarfs are available electronically in fits format at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/501/1059 Title: Comoving-frame radiative transfer in arbitrary velocity fields. II. Large scale applications Authors: Knop, S.; Hauschildt, P. H.; Baron, E. Bibcode: 2009A&A...501..813K Altcode: 2009arXiv0909.4264K Aims: A solution of the radiative-transfer problem in arbitrary velocity fields introduced in a previous paper, has limitations in its applicability. For large-scale applications, the methods described also require large memory sets that are commonly not available to state-of-the-art computing hardware. In this work, we modify the algorithm to allow the computation of large-scale problems.
Methods: We reduce the memory footprint via a domain decomposition. By introducing iterative Gauss-Seidel type solvers, we improve the speed of the overall computation. Because of the domain decomposition, the new algorithm requires the use of parallel-computing systems.
Results: The algorithm that we present permits large-scale solutions of radiative-transfer problems that include arbitrary wavelength couplings. In addition, we discover a quasi-analytic formal solution of the radiative transfer that significantly improves the overall computation speed. More importantly, this method ensures that our algorithm can be applied to multi-dimensional Lagrangian radiative-transfer calculations. In multi-dimensional atmospheres, velocity fields are in general chaotic ensuring that the inclusion of arbitrary wavelength couplings are mandatory. Title: Spectral synthesis of circumstellar disks - application to white dwarf debris disks Authors: Hügelmeyer, S. D.; Dreizler, S.; Homeier, D.; Hauschildt, P. Bibcode: 2009JPhCS.172a2060H Altcode: 2009arXiv0905.0329H Gas and dust disks are common objects in the universe and can be found around various objects, e.g. young stars, cataclysmic variables, active galactic nuclei, or white dwarfs. The light that we receive from disks provides us with clues about their composition, temperature, and density. In order to better understand the physical and chemical dynamics of these disks, self-consistent radiative transfer simulations are inevitable. Therefore, we have developed a 1+1D radiative transfer code as an extension to the well-established model atmosphere code PHOENIX. We will show the potential of the application of our code to model the spectra of white dwarf debris disks. Title: A 3D radiative transfer framework. IV. Spherical and cylindrical coordinate systems Authors: Hauschildt, P. H.; Baron, E. Bibcode: 2009A&A...498..981H Altcode: 2009arXiv0903.1949H Aims: We extend our framework for 3D radiative transfer calculations with a non-local operator splitting methods along (full) characteristics to spherical and cylindrical coordinate systems. These coordinate systems are better suited to a number of physical problems than Cartesian coordinates.
Methods: The scattering problem for line transfer is solved via means of an operator splitting (OS) technique. The formal solution is based on a full characteristics method. The approximate Λ operator is constructed considering nearest neighbors exactly. The code is parallelized over both wavelength and solid angle using the MPI library.
Results: We present the results of several test cases with different values of the thermalization parameter for the different coordinate systems. The results are directly compared to 1D plane parallel tests. The 3D results agree very well with the well-tested 1D calculations.
Conclusions: Advances in modern computers will make realistic 3D radiative transfer calculations possible in the near future. Title: Radiative Transfer Calculations In The Context of Cosmological Recombination Authors: De, Soma; Baron, E.; Hauschildt, P. Bibcode: 2009AAS...21441301D Altcode: We present preliminary results of the ionization fractions and hence the CMB power spectrum in the cosmological recombination era by solving both the cosmological rate equations and radiative transfer equations simultaneously. We use our NLTE moving radiative tranfer code PHOENIX and multi-level hydrogen and helium atoms. We work in the comoving frame. Periodic boundary conditions are used and the transfer equation is iterated to solve for the radiation field. Once we have determined the radiation field we solve the energy equation to obtain the matter temperatures which is used to iteratively solve for the ionization fractions from the time dependent rate equations. Title: A 3D radiative transfer framework. V. Homologous flows Authors: Baron, E.; Hauschildt, P. H.; Chen, B. Bibcode: 2009A&A...498..987B Altcode: 2009arXiv0903.2486B Context: Observations and theoretical calculations have shown the importance of non-spherically symmetric structures in supernovae. Thus, the interpretation of observed supernova spectra requires the ability to solve the transfer equation in 3-D moving atmospheres.
Aims: We present an implementation of the solution of the radiative transfer equation in 3-D homologously expanding atmospheres in spherical coordinates. The implementation is exact to all orders in v/c.
Methods: We use the methods that we have developed in previous papers in this series as well as a new affine method that makes use of the fact that photons travel on straight lines. The affine method greatly facilitates delineating the characteristics and can be used in the case of strong-gravitational and arbitrary-velocity fields.
Results: We compare our results in 3-D for spherically symmetric test problems with high velocity fields (up to 87% of the speed of light) and find excellent agreement, when the number of momentum space angles is high. Our well-tested 1-D results are based on methods where the momentum directions vary along the characteristic (co-moving momentum directions). Thus, we are able to verify both the analytic framework and its numerical implementation. Additionally, we have been able to test the parallelization over characteristics. Using 5122 momentum angles we ran the code on 16 384 Opteron processors and achieved excellent scaling.
Conclusions: It is now possible to calculate synthetic spectra from realistic 3D hydro simulations. This should open an era of progress in hydro modeling, similar to that that occurred in the 1980s when 1-D models were confronted with synthetic spectra. Title: Optical and Near-Infrared Spectroscopy of the L Subdwarf SDSS J125637.13-022452.4 Authors: Burgasser, Adam J.; Witte, Soeren; Helling, Christiane; Sanderson, Robyn E.; Bochanski, John J.; Hauschildt, Peter H. Bibcode: 2009ApJ...697..148B Altcode: 2009arXiv0903.1567B Red optical and near-infrared spectroscopy are presented for SDSS J125637.13-022452.4, one of only four L subdwarfs reported to date. These data confirm the low-temperature, metal-poor nature of this source, as indicated by prominent metal-hydride bands, alkali lines, and collision-induced H2 absorption. The optical and near-infrared spectra of SDSS J1256-0224 are similar to those of the sdL4 2MASS J16262034+3925190, and we derive a classification of sdL3.5 based on the preliminary scheme of Burgasser, Cruz, and Kirkpatrick. The kinematics of SDSS J1256-0224 are consistent with membership in the Galactic inner halo, with estimated UVW space velocities indicating a slightly prograde, eccentric, and inclined Galactic orbit (3.5 lsim R lsim 11 kpc; midZ maxmid = 7.5 kpc). Comparison to synthetic spectra computed with the PHOENIX code, including the recent implementation of kinetic condensate formation (DRIFT-PHOENIX), indicates T eff ≈ 2100-2500 K and [M/H] ≈ -1.5 to -1.0 for log g ≈ 5.0-5.5 (cgs), although there are clear discrepancies between model and observed spectra particularly in the red optical region. As such, any conclusions on the role of metallicity in condensate grain and cloud formation are probably premature. Indeed, a shift in the temperature scale of L subdwarfs relative to L dwarfs may obviate the need for modified condensate and grain chemistry in low metallicity atmospheres.

This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile. Title: VizieR Online Data Catalog: Infrared spectra of 9 T dwarfs (del Burgo+, 2009) Authors: Del Burgo, C.; Martin, E. L.; Zapatero-Osorio, M. R.; Hauschildt, P. Bibcode: 2009yCat..35011059D Altcode: High-resolution near-infrared spectra in the J-band of nine T dwarfs were obtained using the Keck II telescope and the NIRSPEC spectrograph.

(2 data files). Title: Radiative transfer in circumstellar disks. I. 1D models for GQ Lupi Authors: Hügelmeyer, S. D.; Dreizler, S.; Hauschildt, P. H.; Seifahrt, A.; Homeier, D.; Barman, T. Bibcode: 2009A&A...498..793H Altcode: 2009arXiv0903.2381H We present a new code for the calculation of the 1D structure and synthetic spectra of accretion disks. The code is an extension of the general purpose stellar atmosphere code PHOENIX and is therefore capable of including extensive lists of atomic and molecular lines as well as dust in the calculations. We assume that the average viscosity can be represented by a critical Reynolds number in a geometrically thin disk and solve the structure and radiative transfer equations for a number of disk rings in the vertical direction. The combination of these rings provides the total disk structure and spectrum. Since the warm inner regions of protoplanetary disks show a rich molecular spectrum, they are well suited for a spectral analysis with our models. In this paper we test our code by comparing our models with high-resolution VLT CRIRES spectra of the T Tauri star GQ Lup. Title: A new formal solution of the radiative transfer in arbitrary velocity fields Authors: Knop, S.; Hauschildt, P. H.; Baron, E. Bibcode: 2009A&A...496..295K Altcode: 2009arXiv0902.1876K Aims: We present a new formal solution of the Lagrangian equation of radiative transfer that is useful in solving the equation of radiative transfer in the presence of arbitrary velocity fields.
Methods: Normally a term due to the inclusion of the wavelength derivative in the Lagrangian equation of radiative transfer is associated with a generalised opacity. In non-monotonic velocity fields, this generalised opacity may become negative. To ensure that the opacity remains positive, this term of the derivative is included in the formal solution of the radiative transfer problem.
Results: The new definition of the generalised opacity allows for a new solution of the equation of radiative transfer in the presence of velocity fields. It is especially useful for arbitrary velocity fields, where it effectively prevents the occurrences of negative generalised opacities and still allows the explicit construction of the Λ-operator of the system needed for an accelerated Λ-iteration. We performed test calculations, where the results of old, established solutions were compared with the new solution. The relative deviations never exceeded 1% and so the new solution is indeed suitable for use in radiative-transfer modelling. Non-monotonic velocity fields along photon paths frequently occur in three-dimensional hydrodynamical models of astrophysical atmospheres. Therefore, the formal solution will be of use for multidimensional radiative transfer and has immediate applications in the modelling of pulsating stars and astrophysical shock fronts. Title: Stellar model atmospheres with abundance stratification Authors: LeBlanc, F.; Monin, D.; Hui-Bon-Hoa, A.; Hauschildt, P. H. Bibcode: 2009A&A...495..937L Altcode: Context: Atomic diffusion is believed to be an important physical process in the atmospheres of several types of stars. Stellar atmospheres, including the stratification of the elements due to diffusion, are then needed to properly compare theoretical results to observations for such stars.
Aims: This paper aims to estimate the effect of vertical abundance stratification on the atmospheric structure of stars and its potential importance regarding observational anomalies for various types of stars.
Methods: Simulations using a modified version of the PHOENIX atmosphere code will be described, while taking vertical abundance stratification into account.
Results: Our results show that large abundance gradients can exist in the atmospheres of Ap and blue horizontal branch stars. Stratification can also lead to relatively large atmospheric structural changes. The effect of elemental stratification on the atmospheric structure might well be able to explain the well-known core-wing anomaly of the Balmer lines observed for cool Ap stars. Title: The Cosmological Evolution of Dust Clouds in Brown Dwarf Atmospheres Authors: Witte, S.; Helling, Ch.; Hauschildt, P. H. Bibcode: 2009AIPC.1094..572W Altcode: 2009csss...15..572W We present our latest DRIFT-PHOENIX model results for dust cloud formation in cool atmospheres and investigate the influence of the metallicity [M/H] on the dust cloud structure on the example of a typical mid-L dwarf (Teff = 2000 K, log (g) = 5.0). Our new dust model simulates the formation of TiO2 seed particles (nucleation) and their subsequent gravitational settling, accompanied by kinetic growth and evaporation of seven solid species on top of these seeds. The gas phase depletion by each of the considered surface reactions and the element replenishment by convective up-mixing are consistently coupled into this mechanism. The result is a stationary cloud structure in phase-non-equilibrium. We observe a comparably low decrease of the dust particle number density and a weak increase of the mean grain size in the lower dust cloud for decreasing metallicities down to [M/H] = -4.0. For even lower metallicities to [M/H] = -6.0, these trends are reversed. Title: Non-LTE Modeling of the Near-Ultraviolet Band of Late-Type Stars Authors: Short, C. Ian; Hauschildt, P. H. Bibcode: 2009ApJ...691.1634S Altcode: 2008arXiv0811.1145S We investigate the ability of both LTE and non-LTE (NLTE) models to fit the near-UV band absolute flux distribution, f λ(λ), and individual spectral line profiles of three standard stars for which high-quality spectrophotometry and high-resolution spectroscopy are available: The Sun (G2 V), Arcturus (K2 III), and Procyon (F5 IV-V). We investigate (1) the effect of the choice of atomic line list on the ability of NLTE models to fit the near-UV band f λ level, (2) the amount of a hypothesized continuous thermal absorption extinction source required to allow NLTE models to fit the observations, and (3) the semiempirical temperature structure, T kin(log τ5000), required to fit the observations with NLTE models and standard continuous near-UV extinction. We find that all models that are computed with high-quality atomic line lists predict too much flux in the near-UV band for Arcturus, but fit the warmer stars well. The variance among independent measurements of the solar irradiance in the near-UV is sufficiently large that we cannot definitely conclude that models predict too much near-UV flux, in contrast to other recent results. We surmise that the inadequacy of current atmospheric models of K giants in the near-UV band is best addressed by hypothesizing that there is still missing continuous thermal extinction, and that the missing near-UV extinction becomes more important with decreasing effective temperature for spectral classes later than early G, suggesting a molecular origin. Title: Ab initio modeling of molecular IR spectra of astrophysical interest: application to CH4 Authors: Warmbier, R.; Schneider, R.; Sharma, A. R.; Braams, B. J.; Bowman, J. M.; Hauschildt, P. H. Bibcode: 2009A&A...495..655W Altcode: Aims: We describe an ab initio-based numerical method of obtaining infrared spectroscopic data (line list) of polyatomic molecules that allows calculation of complete sets of lines for temperatures up to several thousand Kelvin. While the main focus is on completeness and consistency, not spectroscopic accuracy, the approach is in principle “exact” for line positions and, although not exact for line strengths, of sufficient accuracy to be of value, especially in wavelength regions where there are gaps in reliable experimental data.
Methods: Global potential energy and dipole moment hypersurfaces are fitted to the results of ab initio electronic structure calculations. The MULTIMODE software is then used to obtain rovibrational energy levels and dipole transition matrix elements. This information is used to calculate a complete set of Einstein coefficients of spontaneous emission A ij.
Results: The method is applied to obtain a spectroscopic database for methane containing over 1.4 million lines up to an upper state energy of 6200 cm-1 ( ∼ 9000 K). The emission spectrum of CH4 at 1000 K is calculated with the complete set of Einstein coefficients and compared with the one obtained from the HITRAN database. Gaps in the database are realistically filled in by the calculated spectrum.
Conclusions: Consistent and complete databases are important for astrophysical applications. Databases obtained by the method described here fulfill this requirement and are sufficiently accurate for astrophysical applications such as model atmosphere calculations and the corresponding synthetic spectra. Title: Spectral synthesis of inner gaseous protoplanetary disks with PHOENIX Authors: Hügelmeyer, S. D.; Dreizler, S.; Homeier, D.; Hauschildt, P. H.; Barman, T. Bibcode: 2009AIPC.1094..389H Altcode: 2009csss...15..389H The inner gaseous regions of protoplanetary disks are of special interest in the formation and evolution of planets and stars because they are the likely birthplaces of planets and serve as the accretion reservoir for young stars. The study of inner disks may give rise to a better understanding of the dynamics, physical and chemical structure, and gas content of the region. As a first step, we have developed a 1+1D disk radiative transfer package as an extension to the well established multipurpose stellar atmosphere program PHOENIX. The solution of the equations of momentum and energy conservation as well as the radiative transfer equation is adopted for the physical conditions in and the geometry of disks. Irradiation by the central star is treated in detail. Comparison of our models with high-resolution infrared spectra will enable us to constrain the structure, dynamics, and gas content of disks, and thus give new insights on the physical processes governing star and planet formation. Additionally, we present our current construction site: a 3D radiative transfer code for accretion disks. Title: Geometry of irradiated stars Authors: Wawrzyn, A. C.; Günther, H. M.; Barman, T. S.; Hauschildt, P. H. Bibcode: 2009AIPC.1094..973W Altcode: 2009csss...15..973W The physical conditions in a variety of objects (e.g. hot exoplanets and close binaries) are fundamentally influenced by external irradiation. In static cases this leads to the development of zones of different temperatures on the `day-side'. In order to combine spectra from all zones to a full visible circular disk and to obtain a 1.5D spectrum we need to calculate the weight of each patch. In the following we present the geometrical considerations and calculate the observed projected area of constant temperature in an irradiated object for specific re-radiation angles. This allows non-isotropic models to be used. We supply an IDL code to calculate the observed projected area for any patch given the phase and angle between surface and line of sight as well as a proper weighting for each by numerical integration. We end up with a simple approach to upgrade a 1D irradiation model to a quasi 1.5D one. This method can be applied e.g. to irradiated secondaries in close binaries. Title: Medium-resolution infrared integral field spectroscopy of the brown dwarf TWA 5 B Authors: Neuhäuser, Ralph; Schmidt, Tobias O. B.; Seifahrt, Andreas; Bedalov, Ana; Helling, Christiane; Witte, Sören; Hauschildt, Peter Bibcode: 2009AIPC.1094..844N Altcode: 2009csss...15..844N We obtained medium-resolution infrared K-band integral field spectroscopy with VLT/Sinfoni for the brown dwarf TWA 5 B, a companion to the weak-line T Tauri star TWA 5 in the TW Hya association. We compare the final spectrum with theoretical model atmospheres from DRIFT-PHOENIX (Dehn et al. 2007, Helling et al. 2008 ab, Witte 2008) for temperature from 2000 to 3100 K, gravity log g = 3.0, 3.5, and 4.0 (g in cm/s2) and metallicity -0.5, 0.0 (solar), and 0.5; we also varried the extinction towards TWA 5 B while searching for the best-fit model between Av = 0.0 and 15 mag. The best-fitting model spectrum yields the following parameters for TWA 5 B: Effective temperature Teff~=2800 K, metallicity [M/H]~=-0.5 (for metal content M), surface gravity log g~=4.0, and extinction Av = 0.0 mag. From these parameters and the distance towards TWA (~65 pc), we can compute the mass of the brown dwarf to be roughly 25 Jupiter masses, but with large error bars including massive planets and low-mass stars. Given its projected separation from the primary star, ~123 AU, it has certainly more likely formed star-like, i.e. being a brown dwarf companion. Title: Commission 36: Theory of Stellar Atmospheres Authors: Landstreet, John D.; Asplund, Martin; Spite, Monique; Balachandran, Suchitra B.; Berdyugina, Svetlana V.; Hauschildt, Peter H.; Ludwig, Hans G.; Mashonkina, Lyudmila I.; Nagendra, K. N.; Puls, Joachim; Randich, M. Sofia; Tautvaisiene, Grazina Bibcode: 2009IAUTA..27..222L Altcode: Commission 36 covers the whole field of the physics of stellar atmospheres. The scientific activity in this large subject has been very intense during the last triennium and led to the publication of a large number of papers, which makes a complete report quite impractical. We have therefore decided to keep the format of the preceding report: first a list of areas of current research, then Web links for obtaining further information. Title: Importance of Time-dependence in the Rate Equations in SN Type II Atmosphere and Estimation of Recombination Time Authors: De, Soma; Baron, E.; Hauschildt, P. Bibcode: 2009AAS...21349001D Altcode: 2009BAAS...41..465D We address the issue of importance of time dependence in the rate equations in the atomospheres of Type II supernovae on the plateau. Recently, Utrobin and Chugai (2006) argued that time-dependence is required to obtain the correction ionization state. The showed that they could better reproduces the Balmer lines in SN 1987A by including time-dependent rate equations However, there are many degenerate ways to produce stronger Balmer lines on the plateau, for example, using a more complex density structure than just a single power-law. Utrobin and Chugai's argument that the recombination time is long compared to the age of the supernova is based on a two-level hydrogen atom model. However, supernova atmospheres include multilevel atoms and hence more lines and electron donors could affect the ionization state and hence the recombination time. We calculate the recombination time from our radiative transfer code PHOENIX from fundamental principles by just adding up the net continuum transitions for each bound state treated in NLTE. We treat H, He in NLTE to start with and then add other elements such as Fe (which are all present in LTE) into NLTE as we proceed. We compare this recombination time to a typical type II supernova on the plateau to access the importance of time dependence in rate equations. Title: 3-D Radiative Transfer in the Next Decade Authors: Baron, E.; Hauschildt, Peter H. Bibcode: 2009astro2010S..11B Altcode: No abstract at ADS Title: Division VIII / Working Group Supernova Authors: Hillebrandt, Wolfgang; Schmidt, Brian P.; Baron, Edward; Benetti, Stefano; Blinnikov, Sergey I.; Blinnikov, Sergey I.; Branch, David R.; Cappellaro, Enrico; Filippenko, Alexei V.; Fransson, Claes; Garnavich, Peter M.; Green, Daniel W. E.; Goobar, Ariel M.; Hamuy, Mario; Hauschildt, Peter H.; Kirshner, Robert P.; Leibundgut, Bruno; Lennon, Daniel J.; Lentz, Eric J.; Lundqvist, Peter; McGraw, Robert; Mazzali, Paolo A.; Meikle, W. Peter S.; Mezzacappa, Anthony; Niemeyer, Jens C.; Nomoto, Ken'ichi; Pain, Reynald; Panagia, Nino; Patat, Ferdinando; Phillips, Mark M.; Pian, Elena; Pignata, Guiliano; Podsiadlowski, Philipp; Ruiz-Lapuente, María Pilar; Sadler, Elaine M.; Schmidt, Brian P.; Shull, Peter O.; Spyromilio, Jason; Suntzeff, Nicholas B.; Thielemann, Friedrich-Karl; Tout, Christopher; Trimble, Virginia L.; Truran, James W.; Tsvetkov, Dmitry Yu.; Turatto, Massimo; della Valle, Massimo; Van Dyk, Schuyler; Voges, Wolfgang H.; Walton, Nicholas A.; Wang, Lifan; Wheeler, J. Craig; Weiler, Kurt W.; Whitelock, Patricia A.; Woosley, Stanford E.; Yamaoka, Hitoshi; Zhao, Gang Bibcode: 2009IAUTA..27..295H Altcode: The Supernova Working Group was re-established at the IAU XXV General Assembly in Sydney, 21 July 2003, sponsored by Commissions 28 (Galaxies) and 47 (Cosmology). Here we report on some of its activities since 2005. Title: Reflectance spectra of earth-like exoplanets . Authors: Wagner, M.; Hauschildt, P. H. Bibcode: 2009MmSAI..80..667W Altcode: Numerical simulations on irradiated exoplanets provide spectra that contain informations about the temperature- and density structure and chemical composition of the exoplanetary atmosphere. The calculation of cool objects is challenging, because of the much more complex chemistry, i.e. the strong molecular abundances as well as the occurrence of dust formation. In order to create an object with planetary features, such as size, temperature and abundances, the stellar atmosphere code PHOENIX had to be adapted in an appropriate way. Starting with an object of Venus-like parameters in 1D (spherical setup), temperature and optical depth will be reduced to Earth-like values. But in an optically thin atmosphere, what influence might the surface texture have on the combined spectrum? An albedo module has already been embedded to serve the cases of non-angular dependence (e.g. soils, vegetation) and angular dependence, i.e. water surface. The aim is to expand the work to 3D. Title: A comparison of chemistry and dust cloud formation in ultracool dwarf model atmospheres Authors: Helling, Ch.; Ackerman, A.; Allard, F.; Dehn, M.; Hauschildt, P.; Homeier, D.; Lodders, K.; Marley, M.; Rietmeijer, F.; Tsuji, T.; Woitke, P. Bibcode: 2008MNRAS.391.1854H Altcode: 2008arXiv0809.3657H; 2008MNRAS.tmp.1310H The atmospheres of substellar objects contain clouds of oxides, iron, silicates and other refractory condensates. Water clouds are expected in the coolest objects. The opacity of these `dust' clouds strongly affects both the atmospheric temperature-pressure profile and the emergent flux. Thus, any attempt to model the spectra of these atmospheres must incorporate a cloud model. However, the diversity of cloud models in atmospheric simulations is large and it is not always clear how the underlying physics of the various models compare. Likewise, the observational consequences of different modelling approaches can be masked by other model differences, making objective comparisons challenging. In order to clarify the current state of the modelling approaches, this paper compares five different cloud models in two sets of tests. Test case 1 tests the dust cloud models for a prescribed L-, L-T and T-dwarf atmospheric (temperature T, pressure p, convective velocity vconv) structures. Test case 2 compares complete model atmosphere results for given (effective temperature Teff, surface gravity logg). All models agree on the global cloud structure but differ in opacity relevant details such as grain size, amount of dust, dust and gas-phase composition. These models can loosely be grouped into high- and low-altitude cloud models whereas the first appears generally redder in near-infrared colours than the latter. Comparisons of synthetic photometric fluxes translate into a modelling uncertainty in apparent magnitudes for our L-dwarf (T-dwarf) test case of 0.25 <~ Δm <~ 0.875 (0.1 <~ Δm <~ 1.375), taking into account the Two-Micron All Sky Survey, the UKIRT WFCAM, the Spitzer IRAC and VLT VISIR filters with UKIRT WFCAM being the most challenging for the models. Future developments will need closer links with laboratory astrophysics, and a consistent treatment of the cloud chemistry and turbulence. Title: Lithium Depletion of Nearby Young Stellar Associations Authors: Mentuch, Erin; Brandeker, Alexis; van Kerkwijk, Marten H.; Jayawardhana, Ray; Hauschildt, Peter H. Bibcode: 2008ApJ...689.1127M Altcode: 2008arXiv0808.3584M We estimate cluster ages from lithium depletion in five pre-main-sequence groups found within 100 pc of the Sun: the TW Hydrae association, η Chamaeleontis cluster, β Pictoris moving group, Tucanae-Horologium association, and AB Doradus moving group. We determine surface gravities, effective temperatures, and lithium abundances for over 900 spectra through least-squares fitting to model-atmosphere spectra. For each group, we compare the dependence of lithium abundance on temperature with isochrones from pre-main-sequence evolutionary tracks to obtain model-dependent ages. We find that the η Cha cluster and the TW Hydrae association are the youngest, with ages of 12 +/- 6 Myr and 12 +/- 8 Myr, respectively, followed by the β Pic moving group at 21 +/- 9 Myr, the Tucanae-Horologium association at 27 +/- 11 Myr, and the AB Dor moving group at an age of at least 45 Myr (whereby we can only set a lower limit, since the models—unlike real stars—do not show much lithium depletion beyond this age). Here the ordering is robust, but the precise ages depend on our choice of both atmospheric and evolutionary models. As a result, while our ages are consistent with estimates based on Hertzsprung-Russell isochrone fitting and dynamical expansion, they are not yet more precise. Our observations do show that with improved models, much stronger constraints should be feasible, as the intrinsic uncertainties, as measured from the scatter between measurements from different spectra of the same star, are very low: around 10 K in effective temperature, 0.05 dex in surface gravity, and 0.03 dex in lithium abundance. Title: Nova V2362 Cygni (nova Cygni 2006): Spitzer, Swift, and Ground-Based Spectral Evolution Authors: Lynch, David K.; Woodward, Charles E.; Gehrz, Robert; Helton, L. Andrew; Rudy, Richard J.; Russell, Ray W.; Pearson, Richard; Venturini, Catherine C.; Mazuk, S.; Rayner, John; Ness, Jan-Uwe; Starrfield, Sumner; Wagner, R. Mark; Osborne, Julian P.; Page, Kim; Puetter, Richard C.; Perry, R. Brad; Schwarz, Greg; Vanlandingham, Karen; Black, John; Bode, Michael; Evans, Aneurin; Geballe, Thomas; Greenhouse, Matthew; Hauschildt, Peter; Krautter, Joachim; Liller, William; Lyke, James; Truran, Jim; Kerr, T.; Eyres, S. P. S.; Shore, Steven N. Bibcode: 2008AJ....136.1815L Altcode: Nova V2362 Cygni has undergone a number of very unusual changes. Ground-based spectroscopy initially revealed a normal sequence of events: the object faded and its near-infrared emission lines gradually shifted to higher excitation conditions until about day 100 when the optical fading reversed and the object slowly brightened. This was accompanied by a rise in the Swift X-ray telescope flux and a sudden shift in excitation of the visible and IR spectrum back to low levels. The new lower excitation spectrum revealed broad line widths and many P-Cygni profiles, all indicative of the ejection of a second shell. Eventually, dust formed, the X-ray brightness—apparently unaffected by dust formation—peaked and then declined, and the object faded at all wavelengths. The Spitzer dust spectra revealed a number of solid-state emission features that, at this time, are not identified. Title: Multilayered Spectral Formation in Type Ia Supenovae around Maximum Light Authors: Bongard, Sebastien; Baron, E.; Smadja, G.; Branch, David; Hauschildt, Peter H. Bibcode: 2008ApJ...687..456B Altcode: 2008arXiv0806.3287B We use the radiative transfer code PHOENIX to study the line formation of the wavelength region 5000-7000 Å. This is the region where the SN Ia-defining Si II feature occurs. This region is important, since the ratio of the two nearby silicon lines has been shown to correlate with the absolute blue magnitude. We use a grid of LTE synthetic spectral models to investigate the formation of line features in the spectra of SNe Ia. By isolating the main contributors to the spectral formation, we show that the ions that drive the spectral ratio are Fe III, Fe II, Si II, and S II. While the former two strongly dominate the flux transfer, the latter two form in the same physical region inside the supernova. We also show that the naive blackbody that one would derive from a fit to the observed spectrum is very different than the true underlying continuum. Title: Direct evidence of a sub-stellar companion around CT Chamaeleontis Authors: Schmidt, T. O. B.; Neuhäuser, R.; Seifahrt, A.; Vogt, N.; Bedalov, A.; Helling, Ch.; Witte, S.; Hauschildt, P. H. Bibcode: 2008A&A...491..311S Altcode: 2008arXiv0809.2812S Aims: In our ongoing search for close and faint companions around T Tauri stars in the Chamaeleon star-forming region, we here present observations of a new common proper motion companion to the young T-Tauri star and Chamaeleon member CT Cha and discuss its properties in comparison to other young, low-mass objects and to synthetic model spectra from different origins.
Methods: Common proper motion of the companion and CT Cha was confirmed by direct Ks-band imaging data taken with the VLT Adaptive Optics (AO) instrument NACO in February 2006 and March 2007, together with a Hipparcos binary for astrometric calibration. An additional J-band image was taken in March 2007 to obtain color information for a first classification of the companion. Moreover, AO integral field spectroscopy with SINFONI in J, and H+K bands was obtained to deduce physical parameters of the companion, such as temperature and extinction. Relative flux calibration of the bands was achieved using photometry from the NACO imaging data.
Results: We found a very faint (Ks = 14.9 mag, Ks0 = 14.4 mag) object, just ~2.67´´ northwest of CT Cha corresponding to a projected separation of ~440 AU at 165 ± 30 pc. We show that CT Cha A and this faint object form a common proper motion pair and that the companion is by ≥4σ significance not a stationary background object. The near-infrared spectroscopy yields a temperature of 2600 ± 250 K for the companion and an optical extinction of AV = 5.2 ± 0.8 mag, when compared to spectra calculated from Drift-Phoenix model atmospheres. We demonstrate the validity of the model fits by comparison to several other well-known young sub-stellar objects.
Conclusions: We conclude that the CT Cha companion is a very low-mass member of Chamaeleon and very likely a physical companion to CT Cha, as the probability for a by chance alignment is ≤0.01. Due to a prominent Pa-β emission in the J-band, accretion is probably still ongoing onto the CT Cha companion. From temperature and luminosity (log(L_bol/L⊙) = -2.68 ± 0.21), we derive a radius of R = 2.20_-0.60+0.81 RJup. We find a consistent mass of M = 17 ± 6 MJup for the CT Cha companion from both its luminosity and temperature when placed on evolutionary tracks. Hence, the CT Cha companion is most likely a wide brown dwarf companion or possibly even a planetary mass object.

Based on observations made with ESO telescopes at the Paranal Observatory under program IDs 076.C-0292(A), 078.C-0535(A), & 279.C-5010(A).

Color versions of Figs. 4, 6, 8 and 11 are only available in electronic form at http://www.aanda.org Title: A 3D radiative transfer framework. III. Periodic boundary conditions Authors: Hauschildt, P. H.; Baron, E. Bibcode: 2008A&A...490..873H Altcode: 2008arXiv0808.0601H Aims: We present a general method to solve radiative transfer problems including scattering in the continuum as well as in lines in 3D configurations with periodic boundary conditions.
Methods: The scattering problem for line transfer is solved via means of an operator splitting (OS) technique. The formal solution is based on a full characteristics method. The approximate Λ operator is constructed considering nearest neighbors exactly. The code is parallelized over both wavelength and solid angle using the MPI library.
Results: We present the results of several test cases with different values of the thermalization parameter and two choices for the temperature structure. The results are directly compared to 1D plane parallel tests. The 3D results agree very well with the well-tested 1D calculations.
Conclusions: Advances in modern computers will make realistic 3D radiative transfer calculations possible in the near future. Our current code scales to very large numbers of processors, but requires larger memory per processor at high spatial resolution. Title: Irradiated planets Authors: Hauschildt, P. H.; Barman, T.; Baron, E. Bibcode: 2008PhST..130a4033H Altcode: We present models for the spectra emitted by irradiated planets and discuss the numerical methods used in the modeling. In addition, we show results of simple 3D calculations that are designed as a first step toward detailed multi-dimensional models of irradiated planets. Title: High-Accuracy Spectral Lines for Radiation Transport in Stellar Atmospheres Authors: Sharma, Amit R.; Braams, Bastiaan J.; Bowman, Joel M.; Warmbier, Robert; Schneider, Ralf; Hauschildt, Peter H. Bibcode: 2008hitr.confE...5S Altcode: The theory of radiative transfer is an important element for the understanding of the spectral signature and physical structure of stellar atmosphere. PHOENIX1 is a such, very general non-Local Thermodynamic Equilibrium(NLTE) stellar atmosphere computer code which can handle very large model atoms/molecules as well as line blanketing by hundreds of millions of atomic and molecular lines. The code is used to compute model atmospheres and synthetic spectra (solution of the radiative transport equations) for, e.g., novae, supernovae, M and brown dwarfs, O to M giants, white dwarfs and accretion disks in Active Galactic Nuclei (AGN). The radiative transfer in PHOENIX is solved in spherical geometry and includes the effects of special relativity (including advection and aberration) in the modeling. The code includes a large number of NLTE and LTE background spectral lines and solves transport equation for each of the lines. The numerical solution requires many wavelength points which arise in the non-LTE case by balancing all populating and de-populating processes from each molecular level (typically 150,000 to 300,000 points). Typically, HITRAN and GEISA are the computer accessible spectroscopic databases used by such transport codes. However, these spectroscopic databases are far from adequate and complete and there is constant demand for more complete and consistent spectral lines for the existing and newly observed molecules in space. We used the code MULTIMODE2 to obtain eigenvalues and eigenfunctions of the general so-called Watson Hamiltonian using variational methods. The procedure begins with a Hartree form for the wavefunction and then vibrational self-consistent field (VSCF) equations are solved for the given state (usually the ground vibrational state) The Hartree form for the wavefunction in the VSCF method is the representation of the vibrational wavefunction as a product of single-mode wavefunctions. From the converged single mode Hamiltonians a basis of virtual states is obtained and these are used in subsequent virtual space CI calculations. This is very much in the spirit of CI approaches taken in electronic structure theory. The application of this methodology for molecules with more than 4 atoms is made possible by the so-called n-mode representation of the potential3 VSCF method augmented by CI or perturbation theory results in improved vibrational frequencies. These methods can accurately solve the problem of coupled vibrations, which physically arise because the vibrationally excited states of polyatomic molecules exhibit displacements, so large that anharmonicities become important, causing the harmonic modes to mix. Following the (ro-)vibrational state calculations we compute Einstein coefficients and spectral intensities for all allowed transitions. However, a stringent requirement for these calculations is a highly accurate potential energy surface. Ab initio-based, full-dimensional potential energy surfaces (PES) are employed in this work. These potentials are global fits to of the order of 104 electronic energies using a basis of polynomials in Morse-like functions of all the internuclear distances. The polynomial basis is invariant with respect to all permutations of like atoms and, as a result, yield highly compact and accurate representations of the PES. Similar techniques are also employed to represent the dipole moment surface (DMS)4 for a polyatomic molecules in the normal coordinate space using full dimensional permutationally invariant potential energy surface. The VSCF, VCI and PES generation scheme, together, can consistently deliver high accuracy spectral lines for large number of molecules for radiation transport application in astrophysics. Chemically interesting singlet carbocation C2H + 5 , known as the ethyl cation, is of special interest in the field astrophysics, specially in the ionosphere of Titan, due to the recent observations by cassini spacecraft. Ethyl cation exhibits interesting structural minimum and transition state, namely the bridged structure (or non-classical) and the Y-shape (or classical) structure. The calculations performed at the Hartree-Fock level of theory found the classical form to be a real minimum and the bridged structure to be less stable than the classical form. However, as soon as correlation effects are taken into account the classical form turns out to be a first order saddle point and less stable than the non-classical form. In the lower-lying structure, referred to as the _bridgedà® structure (or non-classical structure), one hydrogen forms a bridge with the two carbon nuclei and the other four hydrogen atoms (two hydrogen on each carbon nuclei) are nearly co-planar with the two carbon atoms. Semi-global potential energy surface is developed using the method described above with the electronic structure energy calculated using the fourth order MÜLLER-PLESSET (MP4) perturbation theory with contributions due to single, double, triple and quadruple excitations to the electron correlation energy(MP4(SDTQ)). The dipole moment surface is calculated at the MP2 level of theory. Multimode code is used to calculate the vibrational energies up to 4000 cm-1 . Zero point vibrational energy is further compared with Diffusion Monte Carlo (DMC) calculations. The other most interesting and extensively studied molecule is methane. Adiabatic rotation approximation is used to obtain Hamiltonian for rotating molecule. Ro-vibrational energies, transition matrix elements and Einstein coefficients are calculated for J = 0, 1, 3, 5, 10, 15, 20, 25, 30. The present calculations are in good agreement with the well established HITRAN database for methane. Title: Second XMM/RGS spectrum of V2491 Cyg Authors: Ness, J. -U.; Starrfield, S.; Gonzalez, R.; Kuulkers, E.; Osborne, J. P.; Page, K.; Schwarz, G.; Vanlandingham, K. M.; Drake, J. J.; Hernanz, M.; Sala, G.; Evans, A.; Gehrels, N.; Hauschildt, P.; Krautter, J.; Gehrz, R. D.; Woodward, C. E. Bibcode: 2008ATel.1573....1N Altcode: A second XMM-Newton observation of the nova V2491 Cyg was obtained on 2008 May 30.3, 49.6 days after the recent outburst and 10 days after an earlier one obtained on day 39.9 (Ness et al., ATel #1561). The exposure time in the Reflection Grating Spectrometers (RGS) was 29.8ksec, and the average count rate in the RGS1 was 2.7 counts per second (c/s). The light curve extracted from the RGS1 is less variable than during the first observation. Title: Comparison of cloud models for Brown Dwarfs Authors: Helling, Ch.; Ackerman, A.; Allard, F.; Dehn, M.; Hauschildt, P.; Homeier, D.; Lodders, K.; Marley, M.; Rietmeijer, F.; Tsuji, T.; Woitke, P. Bibcode: 2008IAUS..249..173H Altcode: 2007arXiv0711.3993H; 2007IAUS..249..173H A test case comparison is presented for different dust cloud model approaches applied in brown dwarfs and giant gas planets. We aim to achieve more transparency in evaluating the uncertainty inherent to theoretical modelling. We show in how far model results for characteristic dust quantities vary due to different assumptions. We also demonstrate differences in the spectral energy distributions resulting from our individual cloud modelling in 1D substellar atmosphere simulations. Title: Time-dependent NLTE Rates in Type II Supernovae Authors: De, Soma; Baron, E.; Hauschildt, P. Bibcode: 2008AAS...212.6402D Altcode: 2008BAAS...40..255D It has been suggested that the steady-state approximation for determining NLTE occupation numbers is not sufficient in Type II supernovae and thus the time-dependent rate equations must be solved (Utrobin and Chugai 2005). This is because the recombination time increases due to Lyman alpha trapping causing the recombination time to become comparable to the age of the supernova. The calculations are based on the Sobolev approximation and a simple two-level hydrogen atom. We calculate the recombination time for hydrogen using our general radiative transfer code PHOENIX. We use a known density, temperature and velocity structure consistent with the observed spectrum of SN 1999em, 20 days after maximum light. Since PHOENIX does exact radiative transfer, we can determine whether the approximations of Utrobin and Chugai (2005) hold. We study four different systems: a simple two-level hydrogen atom and a complete multilevel hydrogen atom in both pure hydrogen and solar compositions to explore the relevance of time dependence in the rate equations. Title: Erratum: "Consistent Simulations of Substellar Atmospheres and Nonequilibrium Dust Cloud Formation" (ApJ, 675, L105 [2008]) Authors: Helling, Christiane; Dehn, Matthias; Woitke, Peter; Hauschildt, Peter H. Bibcode: 2008ApJ...677L.157H Altcode: No abstract at ADS Title: The influence of dust formation modelling on Na I and K I line profiles in substellar atmospheres Authors: Johnas, C. M. S.; Helling, Ch.; Dehn, M.; Woitke, P.; Hauschildt, P. H. Bibcode: 2008MNRAS.385L.120J Altcode: 2008arXiv0801.3544J; 2008MNRAS.tmpL..24J We aim to understand the correlation between cloud formation and alkali line formation in substellar atmospheres. We perform line profile calculations for NaI and KI based on the coupling of our kinetic model for the formation and composition of dust grains with 1D radiative transfer calculations in atmosphere models for brown dwarfs and giant gas planets. The NaI and KI line profiles sensibly depend on the way clouds are treated in substellar atmosphere simulations. The kinetic dust formation model results in the highest pseudo-continuum compared to the limiting cases. Title: Consistent Simulations of Substellar Atmospheres and Nonequilibrium Dust Cloud Formation Authors: Helling, Christiane; Dehn, Matthias; Woitke, Peter; Hauschildt, Peter H. Bibcode: 2008ApJ...675L.105H Altcode: 2008arXiv0801.3733H We aim to understand cloud formation in substellar objects. We combined our nonequilibrium, stationary cloud model DRIFT (seed formation, growth, evaporation, gravitational settling, element conservation) with the general-purpose model atmosphere code PHOENIX (radiative transfer, hydrostatic equilibrium, mixing-length theory, chemical equilibrium) in order to consistently calculate cloud formation and radiative transfer with their feedback on convection and gas-phase depletion. We calculate the complete 1D model atmosphere structure and the chemical details of the cloud layers. The DRIFT-PHOENIX models enable the first stellar atmosphere simulation that is based on the actual cloud formation process. The resulting (T, p) -profiles differ considerably from the previous limiting PHOENIX cases DUSTY and COND. A tentative comparison with observations demonstrates that the determination of effective temperatures based on simple cloud models has to be applied with care. Based on our new models, we suggest a mean Teff = 1800 K for the L dwarf twin-binary system DENIS J0205-1159, which is up to 500 K hotter than suggested in the literature. We show transition spectra for gas-giant planets which form dust clouds in their atmospheres and evaluate photometric fluxes for a WASP-1 type system. Title: Atmospheric Properties of Transiting Extrasolar Planets Authors: Barman, T.; Hauschildt, P. Bibcode: 2008ASPC..398..387B Altcode: For a few of the nearby transiting extrasolar planets direct flux measurements have been obtained using the Spitzer Space Telescope. The atmospheric properties of these planets are discussed below along with their agreement and disagreement with theoretical models. Title: The Consistent Modeling of Alkali Lines and Dust Formation in Extreme Exo--Planets Authors: Johnas, C. M. S.; Helling, Ch.; Witte, S.; Dehn, M.; Woitke, P.; Hauschildt, P. H. Bibcode: 2008ASPC..398..393J Altcode: We present the first PHOENIX tep{Hauschildt99} model atmosphere results for extreme exo-planets where we have coupled a detailed modeling of the alkali line profiles tep{Johnas06} with non-equilibrium treatment of the chemically heterogeneous dust clouds (DRIFT) tep{Helling07}. Our investigation of the Na I D and K I lines show strong differences in shape and depth of the line profiles compared to commonly used impact approximated van der Waals profiles and a previously approximative dust treatment in PHOENIX. Such previous attempts of treating dust in phase equilibrium lead to a much stronger element depletion of the atmospheric gas. Consequently, the modelling of dust formation processes does influence the spectral pseudo-continuum which is determined by the resonance absorption wings of the alkali lines. Title: Detailed Spectral Modeling of a Three-dimensional Pulsating Reverse Detonation Model: Too Much Nickel Authors: Baron, E.; Jeffery, David J.; Branch, David; Bravo, Eduardo; García-Senz, Domingo; Hauschildt, Peter H. Bibcode: 2008ApJ...672.1038B Altcode: 2007arXiv0709.4177B We calculate detailed non-LTE synthetic spectra of a pulsating reverse detonation (PRD) model, a novel explosion mechanism for Type Ia supernovae. While the hydro models are calculated in three dimensions, the spectra use an angle-averaged hydro model and thus some of the three-dimensional (3D) details are lost, but the overall average should be a good representation of the average observed spectra. We study the model at three epochs: maximum light, 7 days prior to maximum light, and 5 days after maximum light. At maximum the defining Si II feature is prominent, but there is also a prominent C II feature, not usually observed in normal SNe Ia near maximum. We compare to the early spectrum of SN 2006D, which did show a prominent C II feature, but the fit to the observations is not compelling. Finally, we compare to the postmaximum UV+optical spectrum of SN 1992A. With the broad spectral coverage it is clear that the iron-peak elements on the outside of the model push too much flux to the red and thus the particular PRD realizations studied would be intrinsically far redder than observed SNe Ia. We briefly discuss variations that could improve future PRD models. Title: Direct Detection of Exo-Planets: GQ Lupi Authors: Neuhäuser, Ralph; Guenther, Eike; Hauschildt, Peter Bibcode: 2008poii.conf..539N Altcode: 2008poio.conf..539N No abstract at ADS Title: Commission 36: Theory of Stellar Atmospheres Authors: Spite, Monique; Landstreet, John D.; Asplund, Martin; Ayres, Thomas R.; Balachandran, Suchitra C.; Dravins, Dainis; Hauschildt, Peter H.; Kiselman, Dan; Nagendra, K. N.; Sneden, Christopher; Tautvaišiené, Grazina; Werner, Klaus Bibcode: 2007IAUTB..26..160S Altcode: The business meeting of Commission 36 was held during the General Assembly in Prague on 16 August. It was attended by about 15 members. The issues presented included a review of the work made by members of Commission 36, and the election of the new Organising Committee. We note that a comprehensive report on the activities of the commission during the last triennium has been published in Reports on Astronomy, Transactions IAU Volume XXVIA. The scientific activity of the members of the commission has been very intense, and has led to the publication of a large number of papers. Title: The effects of new Na I D line profiles in cool atmospheres Authors: Johnas, C. M. S.; Hauschildt, P. H.; Schweitzer, A.; Mullamphy, D. F. T.; Peach, G.; Whittingham, I. B. Bibcode: 2007A&A...475.1039J Altcode: No abstract at ADS Title: Spitzer, Swift and Ground-based Spectral Evolution of the Double Thermonuclear Runaway in Nova V2362 Cygni (Nova Cygni 2006) Authors: Lynch, David K.; Woodward, C. E.; Gehrz, R. D.; Helton, L. A.; Rudy, R. J.; Russell, R. W.; Pearson, R.; Venturini, C. C.; Mazuk, S.; Rayner, J.; Ness, J.; Starrfield, S.; Wagner, R. M.; Osborne, J.; Page, K.; Puetter, R. C.; Perry, R. B.; Schwarz, G.; Vanlandingham, K.; Block, J.; Bode, M.; Evans, A.; Geballe, T.; Greenhouse, M.; Hauschildt, P.; Krautter, J.; Liller, W.; Lyke, J.; Truran, J.; Kerr, T.; Eyres, S. P. S.; Shore, S. N. Bibcode: 2007AAS...211.5112L Altcode: 2007BAAS...39..817L Nova V2362 Cygni was apparently the result of a rare type of thermonuclear runaway in which the initial explosion was followed by a second one a few months later. Spitzer and ground-based spectroscopy initially revealed a normal sequence of events until about day 100 when the optical fading reversed and the object slowly brightened. This was accompanied by a rise in the Swift XRT flux and a rejuvenation of the visible and IR spectrum which had previously been moving toward higher excitation. The new lower excitation spectrum revealed broad line widths and many P-Cygni profiles.

Eventually dust formed, the X-Ray brightness peaked and declined and the object faded at all wavelengths. The Spitzer dust spectra revealed a number of solid-state emission features which at this time are not identified. Title: Determination of Element Abundances Authors: Hauschildt, P. H.; Johnas, C. M. S. Bibcode: 2007ASPC..378..111H Altcode: No abstract at ADS Title: Lithium abundances of very low mass members of Chamaeleon I Authors: Johnas, C. M. S.; Guenther, E. W.; Joergens, V.; Schweitzer, A.; Hauschildt, P. H. Bibcode: 2007A&A...475..667J Altcode: Aims:We present the first study of the lithium abundances of very low mass objects in Chamaeleon I close to the hydrogen burning mass limit based on atmospheric models and high-resolution spectroscopic observations. The studied objects, Cha Hα 2, 3, 4, 5, 6 and 8, are very young brown dwarf candidates and very low mass stars on the verge of lithium depletion.
Methods: For this analysis, we have computed a new “GAIA-cond” class model grid over effective temperatures from 2600 K to 3100 K, surface gravities from log(g) = 3.5 to 5.5, and lithium abundances from logɛ = 0.0 to 3.7, for two different line profile setups introduced in previous work. Calculated synthetic spectra are compared with high-resolution UVES / VLT echelle spectra of the objects.
Results: We find good descriptions of the lithium resonance doublet lines at 6708 Å and of the surrounding pseudo-continuum and determine a consistent set of lithium abundances (log(ɛ) = 1.55). However, the derived lithium abundances are lower than the meteoritic one (log(ɛ) = 3.31) and that of higher mass stars in Cha I (log(ɛ) = 3.1/3.4 for LTE-/non-LTE-calculations). By modeling the TiO-line, we demonstrate that veiling does not make the lithium lines appear weaker. We can also rule out that the results are spoiled by the presence of spots.
Conclusions: A possible explanation for these results would be that the objects are either more massive, or much older, than previously thought, so that the lithium depletion has already started. Although the uncertainties of the masses and ages are large, they are not large enough as to explain the observed lithium depletion. Therefore, the most likely explanation is either a lack of understanding of the details of the formation of the lithium line, or a lack of understanding of the internal structure of the very young low-mass objects.

Based on observations obtained at the European Southern Observatory at Paranal, Chile in program 65.L-0629(A,B) and 65.I-0011(A). Title: A high resolution spectral atlas of brown dwarfs Authors: Reiners, A.; Homeier, D.; Hauschildt, P. H.; Allard, F. Bibcode: 2007A&A...473..245R Altcode: 2007arXiv0707.2652R We present a UVES/VLT high resolution atlas of three L dwarfs and one T dwarf system, spectral classes at which most of the objects are brown dwarfs. Our atlas covers the optical region from Hα up to the near infrared at 1 μm. We present spectral details of ultra-cool atmospheres at very high resolution (R ∼ 33 000) and compare the spectra to model calculations. Our comparison shows that molecular features from VO and CaH, and atomic features from Cs and Rb are reasonably well fit by current models. On the other hand, features due to TiO, CrH, and water, and atomic Na and K reveal large discrepancies between model calculations and our observations.

Based on observations

collected at the European Southern Observatory, Paranal, Chile, 077.C-0449. Title: Alkali Line Profiles in Ultra-cool White Dwarfs Authors: Homeier, D.; Allard, N.; Johnas, C. M. S.; Hauschildt, P. H.; Allard, F. Bibcode: 2007ASPC..372..277H Altcode: 2007arXiv0707.4138H We present PHOENIX atmosphere models for metal-rich cool white dwarfs using improved line shapes for the Na I and K I resonance doublets. Profiles for collisional broadening due to H_2 and He based on the adiabatic representation show strong deviations from Van der Waals interaction at short distances. Comparison with observed spectra that show extremely broadened Na I lines indicates that a He-rich atmospheric composition is required to explain the line strengths and spectral energy distributions. Our current synthetic spectra, using an expansion in powers of density to the third order optimised for brown dwarf atmosphere conditions, significantly underestimate the observed absorption in the far wings, even predicting smaller total line strength than a Lorentzian profile. This is shown to be due to the handling of multiple perturber interactions becoming inadequate for the extreme densities of the coolest white dwarfs. The density expansion would have to be extended at least to the 7th order for an accurate treatment of such conditions and might break down altogether in the densest objects. The results of a direct calculation of the unified profile should therefore be used for model atmospheres of cool metal-rich white dwarfs. Qualitative comparison of the full adiabatic profile to the spectrum of WD 2356-209 indicates good agreement with the observed line shape. Observations of the coolest white dwarfs may therefore serve as a laboratory for testing the physics of the deeper atmospheres and interiors of brown dwarfs and giant planets. Title: Steps for solving the radiative transfer equation for arbitrary flows in stationary space-times Authors: Chen, B.; Kantowski, R.; Baron, E.; Knop, S.; Hauschildt, P. H. Bibcode: 2007MNRAS.380..104C Altcode: 2007MNRAS.tmp..669C; 2006astro.ph..3251C We derive the radiative transfer equation for arbitrary stationary relativistic flows in stationary space-times, i.e. for steady-state transfer problems. We show how the standard characteristics method of solution developed by Mihalas and used throughout the radiative transfer community can be adapted to multidimensional applications with isotropic sources. Because the characteristics always coincide with geodesics and can always be specified by constants, direct integration of the characteristics derived from the transfer equation as commonly done in 1D applications is not required. The characteristics are known for a specified metric from the geodesics. We give details in both flat and static spherically symmetric space-times. This work has direct application in 3D simulations of supernovae, gamma-ray bursts, and active galactic nuclei, as well as in modelling neutron star atmospheres. Title: The Influence of Chemi-Ionization and Chemi-Recombination Processes on H Lines in M Dwarf Atmospheres Authors: Mihajlov, Anatolij A.; Jevremović, Darko; Hauschildt, Peter; Dimitrijević, Milan S.; Ignjatović, Ljubinko M.; Allard, France Bibcode: 2007AIPC..938..214M Altcode: Using general stellar atmosphere code PHOENIX, the influence of chemi-ionization and inverse chemi-recombination processes, in H*(n)+H(1s) collisions, on the population of higher levels and consequently on profiles of Hydrogen lines in the atmospheres of late type (M) stars was studied. Obtained results are the first demonstration of the possibility to confirm the considered processes influence by direct observations of stellar spectra. It is demonstrated that it is very important to include chemi-ionization and chemi-recombination processes in modeling of atmospheres of late type stars, especially if one wants to use line profiles for diagnostics of stellar photospheres and lower chromospheres. Title: Comparative study of dust cloud modelling for substellar atmospheres Authors: Helling, Ch.; Ackerman, A. S.; Allard, F.; Dehen, M.; Hauschildt, P.; Hubeny, I.; Homeier, D.; Lodders, K.; Marley, M.; Tsuji, T.; Woitke, P. Bibcode: 2007AN....328..655H Altcode: No abstract at ADS Title: Influence of chemi-ionization and chemi-recombination processes on hydrogen line shapes in M dwarfs Authors: Mihajlov, A. A.; Jevremović, D.; Hauschildt, P.; Dimitrijević, M. S.; Ignjatović, Lj. M.; Alard, F. Bibcode: 2007A&A...471..671M Altcode: Aims:We study the influence of chemi-ionization in H*(n) + H(1s) collisions and inverse chemi-recombination processes on the population of higher levels and consequently on profiles of hydrogen lines in the atmospheres of late type (M) stars.
Methods: Modeling, using general stellar atmosphere code PHOENIX to reveal the importance of the inclusion of such processes.
Results: We demonstrate for the first time observationally detectable effects of these chemi-processes on stellar spectra.
Conclusions: It is very important to include chemi-ionization and chemi-recombination processes in modeling of atmospheres of late type stars, especially if one wants to use line profiles for diagnostics of stellar photospheres and lower chromospheres. Title: Line spectra and profiles for ultracool substellar objects Authors: Johnas, Christine M. S.; Hauschildt, Peter H. Bibcode: 2007AIPC..926..120J Altcode: The pressures in the line forming regions of cool stellar and substellar objects increase dramatically with lower effective temperatures. This causes strong pressure broadening of the few remaining atomic lines, with damping wings more than 0.5 μm wide, dominating the emitted spectrum. Therefore, there is an essential need for reasonably accurate line profiles for these lines under high-pressure conditions. We show the results of model atmosphere calculations using detailed line profiles for a number of alkali resonance lines and discuss the need for additional and improved line profile for stellar and planetary atmosphere simulations. Title: Modelling the Near-IR Spectra of Red Supergiant-dominated Populations Authors: Lançon, Ariane; Gallagher, Jay S.; de Grijs, Richard; Hauschildt, Peter; Ladjal, Djazia; Mouhcine, Mustapha; Smith, Linda J.; Wood, Peter R.; Förster Schreiber, Natascha Bibcode: 2007IAUS..241..152L Altcode: 2007arXiv0704.0401L We report on recent progress in the modelling of the near-IR spectra of young stellar populations, i.e. populations in which red supergiants (RSGs) are dominant. First, we discuss the determination of fundamental parameters of RSGs using fits to their near-IR spectra with new PHOENIX model spectra; RSG-specific surface abundances are accounted for and effects of the microturbulence parameter are explored. New population synthesis predictions are then described and, as an example, it is shown that the spectra of young star clusters in M82 can be reproduced very well from 0.5 to 2.4 micrometers. We warn of remaining uncertainties in cluster ages. Title: Quasi-Molecular K-H[2 ]Absorption As An Alternative To The Resurgence Of CaH Bands In The Spectra Of T-Type Dwarfs: Is The Cloud-Clearing Scheme At Stake? Authors: Allard, F.; Allard, N. F.; Johnas, C. M. S.; Hauschildt, P. H.; Homeier, D.; Kielkopf, J. K.; Spiegelman, F. Bibcode: 2007IAUS..240..332A Altcode: As brown dwarfs cool off with time, their atmospheres become denser and more transparent, allowing the emitted thermal flux to escape from deeper atmospheric layers. Burgasser et al. (2002) have investigated and classified the red spectra of T dwarfs in a spectral sequence where a resurgence of the hydride bands, after disappearing in the M to L spectral transition, occur between the late L to T before disappearing again in the late T dwarfs. CaH for example is identified in mid-T dwarfs at around 0.7μm (Burgassser 2003). The authors explain this resurgence by a cloud-clearing scheme where holes would allow to see the CaH from deeper enriched layers, while it is settled out from the uppermost atmospheric layers seen on the rest of the brown dwarf surface. We present the first synthetic spectra of T dwarfs including a semi-classical modelling of the pressure broadening of alkalis lines (Na I D, Li I, K I, Rb I, and Cs I fundamental resonance doublets) by molecular hydrogen and helium, the most important species in these atmospheres. We compare the models to the T dwarfs red optical spectra of Burgasser et al. (2003) and we find that the 0.7μm feature has been wrongly identified to CaH. In particular, the very strong KI resonance transition doublet at 0.77μm explains by itself this absorption feature by producing a quasi-molecular satellite absorption feature at this wavelength. The strength of this satellite is very sensitive to the density of perturbers in the lower photosphere and to the background opacity provided by the Na I D red wing, which explains naturally both its apparition in late L dwarfs and its vanishing in late T dwarfs. We find in conclusion that no cloud-clearing scheme or non-equilibrium processes is necessary to explain this absorption feature, and the evolution of the red optical spectrum of T dwarfs. And this should teach us caution about these atmospheres often too enthusiastly considered planetary. MHR 3D convection models are nevertheless underway to estimate the likelihood of cloud-clearings in late L and T dwarfs. Title: The SSS Phase of RS Ophiuchi Observed with Chandra and XMM-Newton. I. Data and Preliminary Modeling Authors: Ness, J. -U.; Starrfield, S.; Beardmore, A. P.; Bode, M. F.; Drake, J. J.; Evans, A.; Gehrz, R. D.; Goad, M. R.; Gonzalez-Riestra, R.; Hauschildt, P.; Krautter, J.; O'Brien, T. J.; Osborne, J. P.; Page, K. L.; Schönrich, R. A.; Woodward, C. E. Bibcode: 2007ApJ...665.1334N Altcode: 2007arXiv0705.1206N The phase of supersoft source (SSS) emission of the sixth recorded outburst of the recurrent nova RS Oph was observed on days 39.7 and 66.9 after outburst with Chandra and on day 54.0 with XMM-Newton. A ~35 s period on day 54.0 originates from the SSS emission and not from the shock. We discuss the bound-free absorption by neutral elements in the line of sight, resonance absorption lines plus self-absorbed emission-line components, collisionally excited emission lines from the shock, He-like intersystem lines, and spectral changes during an episode of high-amplitude variability. We find a decrease of the oxygen K-shell absorption edge that can be explained by photoionization of oxygen. The absorption component has average velocities of -1286+/-267 km s-1 on day 39.7 and of -771+/-65 km s-1 on day 66.9. The wavelengths of the emission-line components are at rest wavelengths, as confirmed by measurements of non-self-absorbed He-like intersystem lines. We found collisionally excited emission lines from the radiatively cooling shock at wavelengths shorter than 15 Å that are systematically blueshifted by -526+/-114 km s-1 on day 39.7 and are fading. We found anomalous He-like f/i ratios, which indicates either high densities or significant UV radiation near the plasma where the emission lines are formed. During the phase of strong variability the spectral hardness light curve overlies the total light curve when shifted by 1000 s. This can be explained by photoionization of neutral oxygen in the line of sight if the densities are of order 1010-1011 cm-3. Title: Analyzing SN 2003Z with PHOENIX Authors: Knop, S.; Hauschildt, P. H.; Baron, E.; Dreizler, S. Bibcode: 2007A&A...469.1077K Altcode: 2009arXiv0902.1867K Aims:We present synthetic spectra around maximum for the type II supernova SN 2003Z, which was first detected on January 29.7 2003. Comparison with observed spectra aim at the determination of physical parameters for SN 2003Z.
Methods: Synthetic spectra are calculated with our stellar atmosphere code PHOENIX. It solves the special relativistic equation of radiative transfer, including large NLTE-calculations and line blanketing by design, in 1-dimensional spherical symmetry. The observed spectra were obtained at the 3.5 m telescope at Calar Alto. The TWIN instrument was used so that a spectral range from about 3600 to 7500 Å was covered. The spectra were taken on Feb. 4, 5, 9, and 11, 2003.
Results: The physical parameters of the models give the luminosities, a range of possible velocity profiles for the SN, an estimate of the colour excess, and the observed metalicity.

Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC). Title: A 3D radiative transfer framework. II. Line transfer problems Authors: Baron, E.; Hauschildt, P. H. Bibcode: 2007A&A...468..255B Altcode: 2007astro.ph..3437B Context: Higher resolution telescopes as well as 3D numerical simulations will require the development of detailed 3D radiative transfer calculations. Building upon our previous work we extend our method to include both continuum and line transfer.
Aims: We present a general method to calculate radiative transfer including scattering in the continuum as well as in lines in 3D static atmospheres.
Methods: The scattering problem for line transfer is solved via means of an operator splitting (OS) technique. The formal solution is based on a long-characteristics method. The approximate Λ operator is constructed considering nearest neighbors exactly. The code is parallelized over both wavelength and solid angle using the MPI library.
Results: We present the results of several test cases with different values of the thermalization parameter and two choices for the temperature structure. The results are directly compared to 1D spherical tests. With our current grid setup the interior resolution is much lower in 3D than in 1D, nevertheless the 3D results agree very well with the well-tested 1D calculations. We show that, with relatively simple parallelization, the code scales to very large number of processors which is mandatory for practical applications.
Conclusions: Advances in modern computers will make realistic 3D radiative transfer calculations possible in the near future. Our current code scales to very large numbers of processors, but requires larger memory per processor at high spatial resolution. Title: Near-IR spectra of red supergiants and giants. I. Models with solar and with mixing-induced surface abundance ratios Authors: Lançon, A.; Hauschildt, P. H.; Ladjal, D.; Mouhcine, M. Bibcode: 2007A&A...468..205L Altcode: 2007arXiv0704.2120L Context: It remains difficult to interpret the near-IR emission of young stellar populations. One main reason is our incomplete understanding of the spectra of luminous red stars.
Aims: This work provides a grid of theoretical spectra of red giant and supergiant stars, that extends through optical and near-IR wavelengths. For the first time, models are also provided with modified surface abundances of C, N and O, as a step towards accounting for the changes that occur due to convective dredge-up in red supergiants or may occur at earlier evolutionary stages in the case of rotation. The aims are (i) to assess how well current models reproduce observed spectra, in particular in the near-IR; (ii) to quantify the effects of the abundance changes on the spectra; and (iii) to determine how these changes affect estimates of fundamental stellar parameters.
Methods: Spectra are computed with the model atmosphere code PHOENIX and compared with a homogeneous set of observations. Although the empirical spectra have a resolution of only λ/Δλ ∼ 1000, we emphasize that models must be calculated at high spectral resolution in order to reproduce the shapes of line blends and molecular bands.
Results: Giant star spectra of class III can be fitted extremely well at solar metallicity down to ~3400 K, where difficulties appear in the modelling of near-IR H2O and TiO absorption bands. Luminous giants of class II can be fitted well too, with modified surface abundances preferred in a minority of cases, possibly indicating mixing in excess of standard first dredge-up. Supergiant stars show a larger variety of near-IR spectra, and good fits are currently obtained for about one third of the observations only. Modified surface abundances help reproducing strong CN bands, but do not suffice to resolve the difficulties. The effect of the abundance changes on the estimated Teff depends on the wavelength range of observation and can amount several 100 K.
Conclusions: While theoretical spectra for giant stars are becoming very satisfactory, red supergiants require further work. The model grid must be extended, in particular to larger micro-turbulent velocities. Some observed spectra may call for models with even lower gravities than explored here (and therefore probably stellar winds), and/or with more extreme abundances than predicted by standard non-rotating evolution models. Non-static atmospheres models should also be envisaged.

Selected theoretical spectra (see text) can be retrieved in FITS format at CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5), or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/468/205 Title: Reddening, Abundances, and Line Formation in SNe II Authors: Baron, E.; Branch, David; Hauschildt, Peter H. Bibcode: 2007ApJ...662.1148B Altcode: 2007astro.ph..3068B We present detailed NLTE spectral synthesis models of the Type II supernova 2005cs, which occurred in M51 and for which the explosion time is well determined. We show that previous estimates for the reddening were significantly too high and briefly discuss how this will affect the inferred progenitor mass. We also show that standard CNO-burning-enhanced abundances require far too large an oxygen depletion, although there is evidence for a single optical N II line, and the sodium abundance shows clear evidence for enhancement over solar, both as expected from CNO processing. Finally, we calculate a distance using the SEAM method. Given the broad range of distances to M51 in the literature, the determination of a distance using Cepheid variables would be quite valuable. Title: The influence of convective energy transport on dust formation in brown dwarf atmospheres Authors: Dehn, Matthias; Helling, Christiane; Woitke, Peter; Hauschildt, Peter Bibcode: 2007IAUS..239..227D Altcode: No abstract at ADS Title: The effects of new Na I D line profiles in cool atmospheres Authors: Johnas, C. M. S.; Hauschildt, P. H.; Schweitzer, A.; Mullamphy, D. F. T.; Peach, G.; Whittingham, I. B. Bibcode: 2007A&A...466..323J Altcode: Aims:New Na I D line profiles and their effects on synthetic spectra of cool dwarfs computed with PHOENIX are studied. Sodium is the most abundant alkali in cool dwarf atmospheres and mostly responsible for the shape of the optical spectrum.
Methods: In previous work we have pointed out the importance of atomic hydrogen as a perturber. Here, broadening due to collisions with atomic hydrogen as well as fully quantum mechanically calculated profiles for perturbations by helium are introduced for the Na I resonance line profiles. Furthermore, the effects of the new line profiles are compared to already existing line profile calculations.
Results: We have calculated a number of "GAIA-cond" class model atmospheres and synthetic spectra for effective temperatures from 1100 K to 3000 K considering a gravity of 4.5. The line formation process has been analyzed with the flux contribution function. Due to changes in atmospheric structure, the effects of the line profiles on the synthetic spectra become larger for smaller effective temperatures. The influence of hydrogen as perturber is visible at higher effective temperatures although at the same time the strength of molecular bands increases. Furthermore, the newly introduced fully quantum mechanically calculated He I broadened profiles change the synthetic spectra by reducing the flux and the depths of the sodium absorption lines. Title: Commission 36: Theory of Stellar Atmospheres Authors: Spite, Monique; Landstreet, John; Asplund, M.; Ayres, T.; Balachandran, S.; Dravins, D.; Hauschildt, P.; Kiselman, D.; Nagendra, K. N.; Sneden, C.; Tautvaišiené, G.; Werner, K. Bibcode: 2007IAUTA..26..215S Altcode: Commission 36 covers all the physics of stellar atmospheres. The scientific activity in this large field has been very intense during the last triennium and led to the publication of a large number of papers which makes an exhaustive report practically not feasible. As a consequence we decided to keep the format of the preceding report: first a list of areas of current research, then web links for obtaining further information. Title: General relativistic radiative transfer Authors: Knop, S.; Hauschildt, P. H.; Baron, E. Bibcode: 2007A&A...463..315K Altcode: 2006astro.ph.11938K Aims:We present a general method to calculate radiative transfer including scattering in the continuum as well as in lines in spherically symmetric systems that are influenced by the effects of general relativity (GR). We utilize a comoving wavelength ansatz that allows to resolve spectral lines throughout the atmosphere.
Methods: The used numerical solution is an operator splitting (OS) technique that uses a characteristic formal solution. The bending of photon paths and the wavelength shifts due to the effects of GR are fully taken into account, as is the treatment of image generation in a curved spacetime.
Results: We describe the algorithm we use and demonstrate the effects of GR on the radiative transport of a two level atom line in a neutron star like atmosphere for various combinations of continuous and line scattering coefficients. In addition, we present grey continuum models and discuss the effects of different scattering albedos on the emergent spectra and the determination of effective temperatures and radii of neutron star atmospheres. Title: VizieR Online Data Catalog: Theoretical spectra of red giants and supergiants (Lancon+, 2007) Authors: Lancon, A.; Hauschildt, P. H.; Ladjal, D.; Mouhcine, M. Bibcode: 2007yCat.6125....0L Altcode: Each FITS file in this directory contains a theoretical stellar spectrum. The spherical model atmospheres and the synthetic spectra were computed with PHOENIX version 13.11.00B as described in the article, with an initial wavelength sampling step of 0.01nm in the wavelength range of interest [510nm-2490nm]. The spectra made available here have been smoothed with a Gaussian with a full width at half maximum of 0.2nm. They are resampled with a wavelength step of 0.025nm.

(4 data files). Title: Near-infrared integral-field spectroscopy of the companion to GQ Lupi Authors: Seifahrt, A.; Neuhäuser, R.; Hauschildt, P. H. Bibcode: 2007A&A...463..309S Altcode: 2006astro.ph.12250S Context: The first substellar companion of possibly planetary mass around a normal star, GQ Lup, has been directly imaged (Neuhäuser et al. 2005, A&A, 435, L13). Besides the unknown formation history, the mass of such an object is a criterion to decide about its true nature.
Aims: We aim to determine the physical properties of the GQ Lup companion - effective temperate (T_eff) and surface gravity (log{g}), and thus its mass independently from evolutionary models.
Methods: We use the adaptive optics integral-field spectrograph SINFONI at the VLT for near-infrared spectroscopy from 1.1 to 2.5 μm with a resolution of R = 2500-4000. We compare these spectra with synthetic atmospheric models (GAIA v2.0 cond).
Results: From the complete set of spectra we find a consistent effective temperature and surface gravity of T_eff = 2650 ± 100 K and log{g} = 3.7 ± 0.5 dex. Combined with a slightly revised luminosity of log{L/L⊙} = -2.25 ± 0.24 dex for the companion, we determine a radius of R = 3.50+1.50-1.03 {R_Jup} and thus a mass of 25 {M_Jup}. The uncertainty of this value is rather high. Due to the large uncertainty of the surface gravity, the mass could range from 4 to 155 {M_Jup}. By comparing the paramaters of the companion of GQ Lup to the ones of 2MASS J05352184-0546085, published by Stassun et al. (2006, Nature, 440, 311), we conclude that the companion to GQ Lup A has a mass lower than 36 ± 3 {M_Jup}.

Based on observations collected at the European Southern Observatory, Chile, in programmes 275.C-5033(A) and 077.C-0264(A). Title: VizieR Online Data Catalog: Spectra of red giants and supergiants (Lancon+, 2007) Authors: Lancon, A.; Hauschildt, P. H.; Ladjal, D.; Mouhcine, M. Bibcode: 2007yCat..34680205L Altcode: Each FITS file in this directory contains a theoretical stellar spectrum. The spherical model atmospheres and the synthetic spectra were computed with PHOENIX version 13.11.00B as described in the article, with an initial wavelength sampling step of 0.01nm in the wavelength range of interest [510nm-2490nm]. The spectra made available here have been smoothed with a Gaussian with a full width at half maximum of 0.2nm. They are resampled with a wavelength step of 0.025nm.

(1 data file). Title: The M Dwarf GJ 436 and its Neptune-Mass Planet Authors: Maness, H. L.; Marcy, G. W.; Ford, E. B.; Hauschildt, P. H.; Shreve, A. T.; Basri, G. B.; Butler, R. P.; Vogt, S. S. Bibcode: 2007PASP..119...90M Altcode: 2006astro.ph..8260M We determine stellar parameters for the M dwarf GJ 436, which hosts a Neptune-mass planet. We employ primarily spectral modeling at low and high resolution, examining the agreement between model and observed optical spectra of five comparison stars of type M0-M3. The modeling of high-resolution optical spectra suffers from uncertainties in TiO transitions, affecting the predicted strengths of both atomic and molecular lines in M dwarfs. The determination of Teff, gravity, and metallicity from optical spectra remains at ~10%. As molecules provide opacity both in lines and as an effective continuum, determining molecular transition parameters remains a challenge facing models such as the PHOENIX series, best verified with high resolution and spectrophotometric spectra. Our analysis of GJ 436 yields an effective temperature of Teff = 3350 +/- 300 K and a mass of 0.44 Msolar. New Doppler measurements of GJ 436 with a precision of 3 m s-1 taken during 6 years improve the Keplerian model of the planet, giving it a minimum mass Msini=0.0713MJup = 22.6 M⊕, period P = 2.6439 days, and eccentricity e = 0.16 +/- 0.02. The noncircular orbit contrasts with the tidally circularized orbits of all close-in exoplanets, implying either ongoing pumping of eccentricity by a more distant companion, or a higher Q value for this low-mass planet. The velocities indeed reveal a long-term trend, indicating a possible distant companion. Title: Accurate M Dwarf Metallicities from Spectral Synthesis: A Critical Test of Model Atmospheres Authors: Bean, Jacob L.; Sneden, Christopher; Hauschildt, Peter H.; Johns-Krull, Christopher M.; Benedict, G. Fritz Bibcode: 2006ApJ...652.1604B Altcode: 2006astro.ph..8093B We describe a method for accurately determining M dwarf metallicities with spectral synthesis based on abundance analyses of visual binary stars. We obtained high-resolution, high-signal-to-noise ratio spectra of each component of five visual binary pairs at McDonald Observatory. The spectral types of the components range from F7 to K3 V for the primaries and from M0.5 to M3.5 V for the secondaries. We have determined the metallicities of the primaries differentially with respect to the Sun by fitting synthetic spectra to Fe I line profiles in the observed spectra. In the course of our analysis of the M dwarf secondaries, we have made significant improvements to the PHOENIX cool-star model atmospheres and the spectrum analysis code MOOG. Our analysis yields an rms deviation of 0.11 dex in metallicity values between the binary pairs. We estimate the uncertainties in the derived stellar parameters for the M dwarfs to be 48 K, 0.10 dex, 0.12 dex, 0.15 km s-1, and 0.20 km s-1 for Teff, logg, [M/H], ξ, and η, respectively. Accurate stellar evolutionary models are needed to progress further in the analysis of cool-star spectra; the new model atmospheres warrant recalculation of the evolutionary models. Title: Type Ia Supernova Spectral Line Ratios as Luminosity Indicators: "From Phenomenology to Radiative Transfer and Back Again" Authors: Bongard, Sebastien; Baron, E.; Smadja, G.; Branch, D.; Hauschildt, P. Bibcode: 2006AAS...20920001B Altcode: 2006BAAS...38.1178B Type Ia supernovae have played a crucial role in the discovery of the dark energy, via the measurement of their light curves and the determination of the peak brightness via fitting templates to the observed lightcurve shape. Two spectroscopic indicators (RSi and RCa) are also known to be well correlated with peak luminosity. Since the spectroscopic luminosity indicators are obtained directly from observed spectra, they may emphasize different aspects on the intrinsic scatter and will have different systematic errors than do measurements using photometry. We present new variants of such spectroscopic indicators which are easy to automate and which minimize the effects of noise. Using the radiative transfer code PHOENIX, we isolate the main spectral contributions to the RSi wavelength region and propose an explanation for the counterintuitive correlation of this spectral indicator with luminosity. Based on these results we introduce RSiS, a new spectral indicator which correlation with luminosity is twice as good as RSi. Finally, we quantify the accuracy of the measure of SNeIa peak brightness with these indicators in the context of SNAP/JDEM. Title: Energy transport, overshoot, and mixing in the atmospheres of M-type main- and pre-main-sequence objects Authors: Ludwig, H. -G.; Allard, F.; Hauschildt, P. H. Bibcode: 2006A&A...459..599L Altcode: 2006astro.ph..8264L We constructed hydrodynamical model atmospheres for mid M-type main-, as well as pre-main-sequence (PMS) objects. Despite the complex chemistry encountered in these cool atmospheres a reasonably accurate representation of the radiative transfer is possible, even in the context of time-dependent and three-dimensional models. The models provide detailed information about the morphology of M-type granulation and statistical properties of the convective surface flows. In particular, we determined the efficiency of the convective energy transport, and the efficiency of mixing by convective overshoot. The convective transport efficiency was expressed in terms of an equivalent mixing-length parameter α_MLT in the formulation of mixing-length theory (MLT) given by Mihalas (1978). α_MLT amounts to values around ≈2 for matching the entropy of the deep, adiabatically stratified regions of the convective envelope, and lies between 2.5 and 3.0 for matching the thermal structure of the deep photosphere. For current spectral analysis of PMS objects this implies that MLT models based on α_MLT=2.0 overestimate the effective temperature by 100 K and surface gravities by 0.25 dex. The average thermal structure of the formally convectively stable layers is little affected by convective overshoot and wave heating, i.e., stays close to radiative equilibrium conditions. Our models suggest that the rate of mixing by convective overshoot declines exponentially with geometrical distance to the Schwarzschild stability boundary. It increases at given effective temperature with decreasing gravitational acceleration. Title: Type Ia Supernova Spectral Line Ratios as Luminosity Indicators Authors: Bongard, Sebastien; Baron, E.; Smadja, G.; Branch, David; Hauschildt, Peter H. Bibcode: 2006ApJ...647..513B Altcode: 2005astro.ph.12229B Type Ia supernovae have played a crucial role in the discovery of the dark energy, via the measurement of their light curves and the determination of the peak brightness via fitting templates to the observed light-curve shape. Two spectroscopic indicators are also known to be well correlated with peak luminosity. Since the spectroscopic luminosity indicators are obtained directly from observed spectra, they will have different systematic errors than do measurements using photometry. In addition, these spectroscopic indicators may be useful for studies of effects of evolution or age of the SNe Ia progenitor population. We present several new variants of such spectroscopic indicators that are easy to automate and that minimize the effects of noise. We show that these spectroscopic indicators can be measured by proposed JDEM missions such as SNAP and JEDI. Title: Resolving stellar atmospheres. I. The Hα line and comparisons to microlensing observations Authors: Thurl, C.; Sackett, P. D.; Hauschildt, P. H. Bibcode: 2006A&A...455..315T Altcode: 2006astro.ph..4088T Context: .We present work on {H}α spectral line characteristics in PHOENIX stellar model atmospheres and their comparison to microlensing observations.
Aims: .We examine in detail the {H}α equivalent width (EW) and the line shape characteristics for effective temperatures of 4500 K<T{eff}< 5600 K where {H}α is a strong spectral feature.
Methods: .We find that {H}α EW in models calculated under the assumption of local thermodynamic equilibrium (LTE) is up to 15% smaller than in models without this assumption, non-LTE models (NLTE) and that line shapes vary significantly for the two model types. A comparison with available high quality microlensing data, capable of tracing {H}α absorption across the face of one G5III giant, shows that the LTE model that fits the EW best is about 100 K hotter than and the best-fitting NLTE model has a similar T{eff} as predicted by the spectral type analysis of the observed star but agree within the uncertainties of the observationally derived temperature.
Results: .Neither LTE nor NLTE models fit the line shape well. We suspect unmodelled chromospheric emission. Line shape diagnostics suggest lower gravities than derived for the star and are unacceptable low in the case of the LTE models. We show that EW alone is insufficient for comparison to stellar model atmospheres, but combined with a new shape parameter we define is promising. In stellar parameter ranges where the {H}α line is strong, a NLTE approach of modeling stellar atmospheres is not only beneficial but mandatory.
Title: Spectral Modeling of SNe Ia Near Maximum Light: Probing the Characteristics of Hydrodynamical Models Authors: Baron, E.; Bongard, Sebastien; Branch, David; Hauschildt, Peter H. Bibcode: 2006ApJ...645..480B Altcode: 2006astro.ph..3101B We have performed detailed non-local thermodynamic equilibrium (NLTE) spectral synthesis modeling of two types of one-dimensional hydrodynamical models: the very highly parameterized deflagration model W7, and two delayed-detonation models. We find that, overall, both models do about equally well at fitting well-observed SNe Ia near maximum light. However, the Si II λ6150 feature of W7 is systematically too fast, whereas for the delayed-detonation models it is also somewhat too fast but significantly better than that of W7. We find that a parameterized mixed model does the best job of reproducing the Si II λ6150 line near maximum light, and we study the differences in the models that lead to better fits to normal SNe Ia. We discuss what is required of a hydrodynamical model to fit the spectra of observed SNe Ia near maximum light. Title: Influence of NLTE calculations on the hydrogen lines in chromospheric models Authors: Fuhrmeister, B.; Short, C. I.; Hauschildt, P. H. Bibcode: 2006A&A...452.1083F Altcode: We present extensive NLTE calculations for a semi-empirical solar 1D chromosphere model based on the VAL C model. We report on a significant influence of nitrogen, oxygen, and sulfur on the emergent hydrogen emission with respect to LTE vs. NLTE calculations for these elements. Moreover, we present a model spectrum with 20 light and iron group elements computed in NLTE. We compare this to an observed solar spectrum and to a photospheric model spectrum. We find that the agreement for this model with the data is less good than the original VAL C model especially in the UV. This may imply the need of changes in the chromospheric temperature structure or may point to general problems of static 1D chromospheric models. Title: Broad-band photometric colors and effective temperature calibrations for late-type giants. II. Z < 0.02 Authors: Kučinskas, A.; Hauschildt, P. H.; Brott, I.; Vansevičius, V.; Lindegren, L.; Tanabé, T.; Allard, F. Bibcode: 2006A&A...452.1021K Altcode: 2006astro.ph..3416K We investigate the effects of metallicity on the broad-band photometric colors of late-type giants, and make a comparison of synthetic colors with observed photometric properties of late-type giants over a wide range of effective temperatures (T_eff=3500-4800 K) and gravities (log g=0.0-2.5), at [M/H]=-1.0 and -2.0. The influence of metallicity on the synthetic photometric colors is small at effective temperatures above 3800 K, but the effects grow larger at lower T_eff, due to the changing efficiency of molecule formation which reduces molecular opacities at lower [M/H]. To make a detailed comparison of the synthetic and observed photometric colors of late type giants in the T_eff-color and color-color planes (which is done at two metallicities, [M/H]=-1.0 and -2.0), we derive a set of new T_eff-log g-color relations based on synthetic photometric colors, at [M/H]=-0.5, -1.0, -1.5, and -2.0. These relations are based on the T_eff-log g scales that we derive employing literature data for 178 late-type giants in 10 Galactic globular clusters (with metallicities of the individual stars between [M/H]=-0.7 and -2.5), and synthetic colors produced with the PHOENIX, MARCS and ATLAS stellar atmosphere codes. Combined with the T_eff-log g-color relations at [M/H]=0.0 (Kučinskas et al. 2005), the set of new relations covers metallicities [M/H]=0.0dots-2.0 (Δ[M/H]=0.5), effective temperatures T_eff=3500dots4800 K (Δ T_eff=100 K), and gravities log g=-0.5dots3.0. The new T_eff-log g-color relations are in good agreement with published T_eff-color relations based on observed properties of late-type giants, both at [M/H]=-1.0 and -2.0. The differences in all T_eff-color planes are typically well within 100 K. We find, however, that effective temperatures predicted by the scales based on synthetic colors tend to be slightly higher than those resulting from the T_eff-color relations based on observations, with the offsets up to 100 K. This is clearly seen both at [M/H]=-1.0 and -2.0, especially in the T_eff-(B-V) and T_eff-(V-K) planes. The consistency between T_eff-log g-color scales based on synthetic colors calculated with different stellar atmosphere codes is very good, with typical differences being well within Δ T_eff ∼ 70 K at [M/H]=-1.0 and Δ T_eff ∼ 40 K at [M/H]=-2.0. Title: Non-lte Multi-species Modeling of the Hydrogen Lines in Solar Chromospheric Models Authors: Short, Ian; Fuhrmeister, B.; Hauschildt, P. Bibcode: 2006AAS...208.1103S Altcode: 2006BAAS...38...90S We present extensive non-local thermodynamic equilibrium (Non-LTE) calculations for a semi-empirical one dimensional (1D) solar chromospheric model based on the historically significant VAL C model. We report on the significant influence of nitrogen (N), oxygen (O), and sulfur (S) on the emergent hydrogen (H) continuum and line emission as computed with these elements in LTE and Non-LTE. Moreover, we present a model spectrum with 20 light and iron (Fe) group elements computed in Non-LTE. We compare this to an observed solar spectrum and to a photospheric model spectrum. We find that the agreement for this model with the data is less good than the original VAL C model especially in the UV. This may imply the need for changes in the chromospheric temperature structure or may point to general problems of static 1D chromospheric models. Title: The Photosphere and Stellar Wind of Deneb (A2 Ia) in the Far Ultraviolet Authors: Aufdenberg, J. P.; Morrison, N. D.; Hauschildt, P. H.; Adelman, S. J. Bibcode: 2006ASPC..348..124A Altcode: The A2 Ia-type supergiant star Deneb has been observed by FUSE. A rich absorption spectrum, dominated by Fe II lines, is revealed between 1085Å and 1185Å. The identified lines show no or only small (-25 km s-1) blueward Doppler shifts and no P-Cygni profiles are visible. Apparent emission lines in the spectrum are identified as windows of low opacity and can be reproduced by a PHOENIX hydrostatic model atmosphere. Expanding model atmospheres are needed to reproduce Deneb's excess radio emission and P-Cygni profiles (Hα, Mg II h&k), but, the wind appears largely transparent in the FUSE region. Expanding model atmospheres indicate that enhanced non-LTE ionization of Fe II longrightarrow Fe II can largely hide the wind in the UV and the FUV. Deneb's Wien tail presents a strong challenge to expanding model atmospheres and promises to provide strong constraints on wind's temperature and ionization structure. Title: ToO IRS Observations of Novae Authors: Woodward, Charles; Black, John; Bode, Michael; Evans, Aneuryn; Geballe, Thomas; Gehrz, Robert; Greenhouse, Matthew; Hauschildt, Peter; Helton, Andrew; Krautter, Joachim; Liller, William; Lyke, James; Lynch, David; Rudy, Richard; Salama, Alberto; Schwarz, Greg; Shore, Steve; Starrfield, Sumner; Truran, Jim; Vanlandingham, Karen; Wagner, R. Mark Bibcode: 2006sptz.prop30007W Altcode: Stars are the engines of energy production and chemical evolution in our Universe. They deposit radiative and mechanical energy into their environments and enrich the ambient interstellar medium with elements synthesized in their interiors and dust grains condensed in their atmospheres. Classical novae (CN) contribute to this cycle of chemical enrichment through explosive nucleosynthesis and the violent ejection of material dredged from the white dwarf progenitor and mixed with the accreted surface layers. Using Spitzer (+IRS), we propose a 25.8 hrs no-impact ToO program to study (in temporal detail) the evolutionary stages of CN by targeting 4 Galactic and 2 Magellanic Cloud (MC) novae. Spitzer is a unique facility that enables us to investigate aspects of the CN phenomenon including the in situ formation and astromineralogy of nova dust, the elemental abundances resulting from thermonuclear runaway, the correlation of ejecta masses with progenitor type, the bolometric luminosities of the outburst, and the kinematics and structure of the ejected envelopes. Synoptic, high signal-to-noise IRS spectra permit: 1) determination of the grain size distribution and mineral composition of nova dust; 2) estimation of chemical abundances of nova ejecta from coronal and other emission line spectroscopy; 3) measurement of the density and masses of the ejecta; 4) characterization of the geometry and structure of ejected shells at early stages during which the initial mixing of the chemical abundances can be studied in detail; and 5) exploration of the characteristics of CN in low metallicity systems (MC) at mid- to far-IR wavelengths. Observations of CN with Spitzer will be complemented by extensive ground-based, as well as space-based (e.g., Chandra, Swift, XMM-Newton), DDT and ToO programs led by team CoIs. Title: A 3D radiative transfer framework. I. Non-local operator splitting and continuum scattering problems Authors: Hauschildt, P. H.; Baron, E. Bibcode: 2006A&A...451..273H Altcode: 2006astro.ph..1183H We describe a highly flexible framework to solve 3D radiation transfer problems in scattering dominated environments based on a long characteristics piece-wise parabolic formal solution and an operator splitting method. We find that the linear systems are efficiently solved with iterative solvers such as Gauss-Seidel and Jordan techniques. We use a sphere-in-a-box test model to compare the 3D results to 1D solutions in order to assess the accuracy of the method. We have implemented the method for static media, however, it can be used to solve problems in the Eulerian-frame for media with low velocity fields. Title: NLTE Strontium and Barium in Metal-poor Red Giant Stars Authors: Short, C. I.; Hauschildt, P. H. Bibcode: 2006ApJ...641..494S Altcode: 2006astro.ph..1210S We present atmospheric models of red giant stars of various metallicities, including extremely metal poor (XMP; [Fe/H]<-3.5) models, with many chemical species, including, significantly, the first two ionization stages of strontium (Sr) and barium (Ba), treated in non-local thermodynamic equilibrium (NLTE) with various degrees of realism. We conclude that (1) for all lines that are useful Sr and Ba abundance diagnostics, the magnitude and sense of the computed NLTE effect on the predicted line strength is metallicity dependent, (2) the indirect NLTE effect of overlap between Ba and Sr transitions and transitions of other species that are also treated in NLTE nonnegligibly enhances NLTE abundance corrections for some lines, (3) the indirect NLTE effect of NLTE opacity of other species on the equilibrium structure of the atmospheric model is not significant, (4) the computed NLTE line strengths differ negligibly if collisional b-b and b-f rates are an order of magnitude smaller or larger than those calculated with standard analytic formulae, and (5) the effect of NLTE on the resonance line of Ba II at 4554.03 Å is independent of whether that line is treated with hyperfine splitting. As a result, the derivation of abundances of Ba and Sr for metal-poor red giant stars with LTE modeling that are in the literature should be treated with caution. Title: Early Infrared Spectral Development of V1187 Scorpii (Nova Scorpii 2004 No. 2) Authors: Lynch, D. K.; Woodward, C. E.; Geballe, T. R.; Russell, R. W.; Rudy, R. J.; Venturini, C. C.; Schwarz, G. J.; Gehrz, R. D.; Smith, N.; Lyke, J. E.; Bus, S. J.; Sitko, M. L.; Harrison, T. E.; Fisher, S.; Eyres, S. P.; Evans, A.; Shore, S. N.; Starrfield, S.; Bode, M. F.; Greenhouse, M. A.; Hauschildt, P. H.; Truran, J. W.; Williams, R. E.; Perry, R. Brad; Zamanov, R.; O'Brien, T. J. Bibcode: 2006ApJ...638..987L Altcode: We report on an unprecedented infrared time series of spectra of V1187 Sco, a very fast ONeMg nova. The observations covered a 56 day period (2004 August 6-September 30) starting 2 days after the nova's peak brightness. Time evolution of the spectra revealed changing line strengths and profiles on timescales of less than a day to weeks as the nova evolved from early postmaximum to early coronal phases. When our ground-based optical and Spitzer Space Telescope data were combined, the wavelength coverage of 0.38-36 μm allowed an accurate spectral energy distribution to be derived when it was about 6 weeks after outburst. Developing double structure in the He I lines showed them changing from narrow to broad in only a few days. Using the O I lines in combination with the optical spectra, we derived a reddening of E(B-V)=1.56+/-0.08 and a distance of 4.9+/-0.5 kpc. Modeling of the ejected material strongly suggested that it was geometrically thick with ΔR/R=0.8-0.9 (more of a wind than a shell) and a low filling factor of order a few percent. The line shapes were consistent with a cylindrical jet, bipolar, or spherical Hubble flow expansion with a maximum speed of about -3000 km s-1. The central peak appeared to be more associated with the spherical component, while the two peaks (especially in Hβ) suggested a ring with either a lower velocity component or with its axis inclined to the line of sight. Title: Metal Hydride and Alkali Halide Opacities in Extrasolar Giant Planets and Cool Stellar Atmospheres Authors: Weck, Philippe F.; Stancil, Phillip C.; Kirby, Kate; Schweitzer, Andreas; Hauschildt, Peter H. Bibcode: 2006nla..conf..274W Altcode: The lack of accurate and complete molecular line and continuum opacity data has been a serious limitation to developing atmospheric models of cool stars and Extrasolar Giant Planets (EGPs). We report our recent calculations of molecular opacities resulting from the presence of metal hydrides and alkali halides. The resulting data have been included in the PHOENIX stellar atmosphere code ( tealt*{hau99}). The new models, calculated using spherical geometry for all gravities considered, also incorporate our latest database of nearly 670 million molecular lines, and updated equations of state. Title: Dust in the atmospheres of brown dwarfs and young planets: the effects of gravitational settling and convective overshoot Authors: Homeier, D.; Ludwig, H. -G.; Allard, F.; Hauschildt, P.; Dehn, M. Bibcode: 2006IAUS..232..328H Altcode: Dwarfs of the spectral types late-M, L and T span mass regimes from very-low-mass stars through brown dwarfs down to young planetary objects. They all show massive molecular line-blanketing and the condensation of refractory species with decreasing T_{eff}, leading to changes in chemical equilibrium composition and absorption due to dust grains. The spectral evolution from late-M through L to mid- and late-T classes is now understood as chiefly due to increasing amounts of condensates in the visible photosphere up to mid-L types, and the settling of dust clouds into deeper regions at the transition from L to T, resulting in a depletion of condensable elements in the upper atmosphere. The ensuing photospheric cooling also drives a change in carbon chemistry leading to the hallmark methane absorption features of T dwarfs.Recent observations of brown dwarfs in the L-T spectral sequence and model atmosphere calculations have shown that these changes in spectral features reveal differences in the efficiency of cloud removal that seem to be triggered by an additional parameter besides effective temperature. We present models describing the settling of particle clouds as an equilibrium process between condensation, gravitational sedimentation and convective and turbulent mixing, based on 3D-hydrodynamical simulations for the description of the velocity field. These calculations predict a strong dependence of the settling on gravity, and can therefore explain observed differences between the spectral energy distributions of brown dwarfs of equal luminosity as an effect of different mass. Based on these calculations we would expect even stronger deviations in the colours of young brown dwarfs of very low mass from those commonly observed in the field. Such predictions seem to be in aggreement with the first observations of candidate planetary-mass objects, and would imply that extrasolar planets at very young ages have spectral energy distributions significantly different from previous models. Our models al so predict characteristic time scales for the cloud formation processes that may be compared to observed variability in brown dwarfs. Title: Photometric colors of late-type giants: theory versus observations Authors: Kucinskas, A.; Hauschildt, P. H.; Ludwig, H. -G.; Brott, I.; Vansevicius, V.; Lindegren, L.; Tanabé, T.; Allard, F. Bibcode: 2006IAUS..232..276K Altcode: 2005astro.ph.12354K Late-type giants (i.e., stars on the red and asymptotic giant branches, RGB/AGB, respectively) are dominant contributors to the overall spectral appearance of intermediate age and old stellar populations, especially in the red/near-infrared part of the spectrum. Being intrinsically bright, they are well suited for probing distant/obscured populations, especially those that can not be studied with their fainter members, like main sequence turn-off stars or subgiants. Late-type giants and supergiants will be the only stellar types accessible in intermediate age and old populations beyond the distances of several Mpc with the future 30-50 m class extremely large telescopes (Olsen et al. 2003). Indeed, proper understanding of their observable properties by means of theoretical models is of key importance for studying the evolution of stellar populations and their host galaxies. Title: A Deep Study of the 3C 273 Field in γ-rays Authors: Brott, I.; Kreykenbohm, I.; Lubiński, P.; Produit, N.; Hauschildt, P. H.; Courvoisier, T. J. -L. Bibcode: 2006IAUS..230..459B Altcode: 3C 273 is one of the brightest and best studied quasars. It has been observed for 770 ks with the imager IBIS (FoV 12 deg) on board INTEGRAL. To achieve the best possible S/N the dataset has been screened using several criteria indicating the quality of the data (i.e., number of good time intervals, etc). We describe the necessary tools and methods to analyze data of deep fields. Title: Convection and observable properties of late-type giants Authors: Kucinskas, A.; Ludwig, H. -G.; Hauschildt, P. H. Bibcode: 2006IAUS..232..498K Altcode: 2005astro.ph.12353K We show that contrary to what is expected from 1D stationary model atmospheres, 3D hydrodynamical modeling predicts a considerable influence of convection on the spectral properties of late-type giants. This is due to the fact that convection overshoots into the formally stable outer atmospheric layers producing a notable granulation pattern in the 3D hydrodynamical models, which has a direct influence on the observable spectra and colors. Within the framework of standard 1D model atmospheres the average thermal stratification of the 3D hydro model can not be reproduced with any reasonable choice of the mixing length parameter and formulation of the turbulent pressure. The differences in individual photometric colors - in terms of 3D versus 1D - reach up to ∼0.2 mag, or Δ T_{eff}∼70 K. We discuss the impact of full 3D hydrodynamical models on the interpretation of observable properties of late-type giants, briefly mentioning problems and challenges which need to be solved for bringing these models to a routine use within the astronomical community in 5-10 years from now. Title: Infrared spectra of exoplanet candidate GQ Lup b Authors: Neuhaeuser, R.; Seifahrt, A.; Guenther, E. W.; Mugrauer, M.; Hauschildt, P. Bibcode: 2006epsc.conf...32N Altcode: We have presented evidence that the directly detected companion to GQ Lup could be a planet with mass estimates below 13 Jupiter masses. The companion is clearly co-moving and bound. The mass estimate was via theoretical models for formation and atmosphere, hence model-dependant and uncertain. Originally, we took a K-band spectrum with VLT/NACO with resolution 700 only. Now, we have taken two much better spectra in the H and K bands with VLT/Sinfoni with resolution 4000. We will present and discuss these two spectra regarding temperature and gravity of the companion and, hence, its mass and nature. Title: Early Spectra of Supernovae Authors: Baron, E.; Nugent, Peter E.; Branch, David; Hauschildt, P. H. Bibcode: 2005ASPC..342..351B Altcode: 2004astro.ph..9659B We briefly describe the current version of the PHOENIX code. We then present some results on the modeling of Type II supernovae and show that fits to observations can be obtained, when account is taken for spherically symmetric, line-blanketed, expanding atmospheres. We describe the SEAM method of obtaining distances to supernovae and briefly discuss its future prospects. Title: The low-mass companion of GQ Lup Authors: Guenther, E. W.; Neuhäuser, R.; Wuchterl, G.; Mugrauer, M.; Bedalov, A.; Hauschildt, P. H. Bibcode: 2005AN....326..958G Altcode: 2005astro.ph.10794G Using NACO on the VLT in the imaging mode we have detected an object at a distance of only 0.7 arcsec from GQ Lup. The object turns out to be co-moving. We have taken two K-band spectra with a resolution of \lambda / \Delta \lambda=700. In here, we analyze the spectra in detail. We show that the shape of spectrum is not spoiled by differences in the Strehl ratio in the blue and in the red part, as well as differential refraction. We reanalyze the spectra and derive the spectral type of the companion using classical methods. We find that the object has a spectral type between M9V and L4V, which corresponds to a T_eff between 1600 and 2500 K. Using GAIA-dusty models, we find that the spectral type derivation is robust against different log(g)-values. The T_eff derived from the models is again in the range between 1800 and 2400 K. While the models reproduce nicely the general shape of the spectrum, the 12CO lines in the spectrum have about half the depth as those in the model. We speculate that this difference might be caused by veiling, like in other objects of similar age, and spectral class. We also find that the absolute brightness of the companion matches that of other low-mass free-floating objects of similar age and spectral type. A comparison with the objects in USco observed by Mohanty et al. (\cite{mohanty04b}) shows that the companion of GQ Lup has a lower mass than any of these, as it is of later spectral type, and younger. The same is as true, for the companion of AB Pic. To have a first estimate of the mass of the object we compare the derived T_eff and luminosity with those calculated from evolutionary tracks. We also point out that future instruments, like NAHUAL, will finally allow us to derive the masses of such objects more precisely. Title: Status of the physics of substellar objects Authors: Jones, H. R. A.; Viti, S.; Tennyson, J.; Barber, B.; Harris, G.; Pickering, J. C.; Blackwell-Whitehead, R.; Champion, J. -P.; Allard, F.; Hauschildt, P. H.; Jorgensen, U. G.; Ehrenfreund, P.; Stachowska, E.; Ludwig, H. -G.; Martin, E.; Pavlenko, Ya.; Lyubchik, Yu.; Kurucz, R. L. Bibcode: 2005AN....326..920J Altcode: A full understanding of the properties of substellar objects is one of the major challenges facing astrophysics. Since their discovery in 1995, we have discovered hundreds of brown dwarfs and extrasolar planets. While these discoveries have enabled important comparisons with theory, observational progress has been much more rapid than the theoretical understanding of cool atmospheres. The reliable determination of mass, abundances, gravities and temperatures is not yet possible. The key problem is that substellar objects emit their observable radiation in the infrared region of the spectrum where our knowledge of atomic, molecular and line broadening data is poor. Here we report on the status of PoSSO (Physics of SubStellar Objects). In order to understand brown dwarfs and extrasolar planets increasing more like those in our solar system, we are studying a wide range of processes. Here we give an update on the project and sketch an outline of atoms, molecules and processes requiring study. Title: Broad-band photometric colors and effective temperature calibrations for late-type giants. I. Z = 0.02 Authors: Kučinskas, A.; Hauschildt, P. H.; Ludwig, H. -G.; Brott, I.; Vansevičius, V.; Lindegren, L.; Tanabé, T.; Allard, F. Bibcode: 2005A&A...442..281K Altcode: 2005astro.ph.10434K We present new synthetic broad-band photometric colors for late-type giants based on synthetic spectra calculated with the PHOENIX model atmosphere code. The grid covers effective temperatures T_eff=3000dots 5000 K, gravities log g=-0.5dots{+3.5}, and metallicities [M/H]=+0.5dots{-4.0}. We show that individual broad-band photometric colors are strongly affected by model parameters such as molecular opacities, gravity, microturbulent velocity, and stellar mass. Our exploratory 3D modeling of a prototypical late-type giant shows that convection has a noticeable effect on the photometric colors too, as it alters significantly both the vertical and horizontal thermal structures in the outer atmosphere. The differences between colors calculated with full 3D hydrodynamical and 1D model atmospheres are significant (e.g., Δ(V-K)∼0.2 mag), translating into offsets in effective temperature of up to 70 K. For a sample of 74 late-type giants in the Solar neighborhood, with interferometric effective temperatures and broad-band photometry available in the literature, we compare observed colors with a new PHOENIX grid of synthetic photometric colors, as well as with photometric colors calculated with the MARCS and ATLAS model atmosphere codes. We find good agreement of the new synthetic colors with observations and published T_eff-color and color-color relations, especially in the T_eff-(V-K), T_eff-(J-K) and (J-K)-(V-K) planes. Deviations from the observed trends in the T_eff-color planes are generally within ±100 K for T_eff=3500 to 4800 K. Synthetic colors calculated with different stellar atmosphere models agree to ±100 K, within a large range of effective temperatures and gravities. The comparison of the observed and synthetic spectra of late-type giants shows that discrepancies result from the differences both in the strengths of various spectral lines/bands (especially those of molecular bands, such as TiO, H2O, CO) and the continuum level. Finally, we derive several new T_eff-log g-color relations for late-type giants at solar-metallicity (valid for T_eff=3500 to 4800 K), based both on the observed effective temperatures and colors of the nearby giants, and synthetic colors produced with PHOENIX, MARCS and ATLAS model atmospheres. Title: Quantitative Spectroscopy of Supernovae for Dark Energy Studies Authors: Baron, E.; Branch, David; Jeffery, David; Nugent, Peter; Thomas, Rollin; Bongard, Sebastien; Hauschildt, Peter H.; Kasen, Daniel; Mihalas, Dimitri Bibcode: 2005astro.ph.10166B Altcode: Detailed quantitative spectroscopy of Type Ia supernovae (SNe~Ia) provides crucial information needed to minimize systematic effects in both ongoing SNe Ia observational programs such as the Nearby Supernova Factory, ESSENCE, and the SuperNova Legacy Survey (SNLS) and in proposed JDEM missions such as SNAP, JEDI, and DESTINY. Quantitative spectroscopy is mandatory to quantify and understand the observational strategy of comparing ``like versus like''. It allows us to explore evolutionary effects, from variations in progenitor metallicity to variations in progenitor age, to variations in dust with cosmological epoch. It also allows us to interpret and quantify the effects of asphericity, as well as different amounts of mixing in the thermonuclear explosion. Title: Phase-Dependent Properties of Extrasolar Planet Atmospheres Authors: Barman, Travis S.; Hauschildt, Peter H.; Allard, France Bibcode: 2005ApJ...632.1132B Altcode: 2005astro.ph..7136B Recently the Spitzer Space Telescope observed the transiting extrasolar planets, TrES-1 and HD 209458b. These observations have provided the first estimates of the day-side thermal flux from two extrasolar planets orbiting Sun-like stars. In this paper, synthetic spectra from atmospheric models are compared to these observations. The day-night temperature difference is explored and phase-dependent flux densities are predicted for both planets. For HD 209458b and TrES-1, models with significant day-to-night energy redistribution are required to reproduce the observations. However, the observational error bars are large, and a range of models remains viable. Title: 6Li in the Atmosphere of GJ 117 Authors: Christian, D. J.; Mathioudakis, M.; Jevremović, D.; Hauschildt, P. H.; Baron, E. Bibcode: 2005ApJ...632L.127C Altcode: 2005astro.ph..9247C We present high-resolution VLT UVES observations of the active K dwarf GJ 117. 6Li enhancement has been shown for energetic solar events, one chromospherically active binary, and several dwarf halo stars. Our analysis reveals the detection of 6Li on this source with 6Li/7Li = 0.030 +/- 0.010. We found no significant contribution from other lines, including Ti I, in the Li profile of GJ 117 and a template star of similar spectral type and metallicity. We discuss the possibility for 6Li production by spallation and find it to be consistent with the activity levels of the object. Title: Review on low-mass stars and brown dwarfs Authors: Chabrier, G.; Baraffe, I.; Allard, F.; Hauschildt, P. H. Bibcode: 2005astro.ph..9798C Altcode: In this review, we examine the successes and weaknesses of modern low-mass star and brown dwarf theory.(1) We first focus on the mechanical (equation of state) and thermal (atmosphere) properties and on the evolution. We then examine the current shortcomings of the theory and we discuss recent observational analysis which have suggested discrepancies between models and observations.(2) We then examine the stellar and brown dwarf IMF and suggest that a power-law above the average thermal Jeans mass (about 1 Msol) rolling over a lognormal form below this limit adequately reproduces the observations of field and young cluster stellar and brown dwarf distributions. This yields a reasonably accurate estimate of the stellar and brown dwarf Galactic census. Finally (3) we argue that the combination of turbulence driven fragmentation at large scale and gravity at small scales provides an appealing solution for the general star and brown dwarf formation mechanism. It also provides a physical ground for the aforementioned power-law + lognormal form for the IMF, whereas a series of different power laws lacks such a physical motivation. At last, we argue that the deuterium-burning limit as the distinction between stars and planets has no physical foundation in this modern star formation scheme. Opacity limited fragmentation extending down to a few (< 10) jupiter masses, due to shocks, anisotropy or magnetic fields, provides a much more robust limit, even though difficult to determine accurately. Therefore, the various "direct" detections of exoplanets claimed recently in the literature are most likely regular low-mass brown dwarfs and the direct detection of an extrasolar planet remains for now elusive. Title: PHOENIX model chromospheres of mid- to late-type M dwarfs Authors: Fuhrmeister, B.; Schmitt, J. H. M. M.; Hauschildt, P. H. Bibcode: 2005A&A...439.1137F Altcode: 2005astro.ph..5375F We present semi-empirical model chromospheres computed with the atmosphere code PHOENIX. The models are designed to fit the observed spectra of five mid- to late-type M dwarfs. Next to hydrogen lines from the Balmer series we used various metal lines, e.g. from Fe i, for the comparison between data and models. Our computations show that an NLTE treatment of C, N, O impacts on the hydrogen line formation, while NLTE treatment of less abundant metals such as nickel influences the lines of the considered species itself. For our coolest models we investigated also the influence of dust on the chromospheres and found that dust increases the emission line flux. Moreover we present an (electronically published) emission line list for the spectral range of 3100 to 3900 and 4700 to 6800 Å for a set of 21 M dwarfs and brown dwarfs. The line list includes the detection of the Na i D lines in emission for a L3 dwarf. Title: Modeling CHANDRA Low Energy Transmission Grating Spectrometer Observations of Classical Novae with PHOENIX Authors: Petz, A.; Hauschildt, P. H.; Ness, J. -U.; Starrfield, S. Bibcode: 2005ASPC..330..299P Altcode: 2005astro.ph..1072P We use the PHOENIX code package to model the X-ray spectrum of Nova V4743 Sagittarii observed with the LETGS onboard the Chandra satellite on March 2003. To analyze nova atmospheres and related systems with an underlying nuclear burning envelope at X-ray wavelengths, it was necessary to update the code with new microphysics. We demonstrate that the X-ray emission is dominated by thermal bremsstrahlung and that the hard X-rays are dominated by Fe and N absorption. Preliminary models are calculated assuming solar abundances. It is shown that the models can be used to determine abundances in the nova ejecta by increasing the absorption in the shell and considering more elements in the NLTE calculations. Title: Direct imaging of planets around young stars, the case of GQ Lup b. Authors: Neuhaeuser, R.; Guenther, E.; Mugrauer, M.; Wuchterl, G.; Hauschildt, P. Bibcode: 2005AN....326..630N Altcode: No abstract at ADS Title: Model atmospheres of substellar atmospheres at a young age: influence of gravity and dust. Authors: Homeier, D.; Allard, F.; Ludwig, H. -G.; Hauschildt, P.; Dehn, M. Bibcode: 2005AN....326Q.628H Altcode: No abstract at ADS Title: Determination of stellar shape in microlensing event MOA 2002-BLG-33 Authors: Rattenbury, N. J.; Abe, F.; Bennett, D. P.; Bond, I. A.; Calitz, J. J.; Claret, A.; Cook, K. H.; Furuta, Y.; Gal-Yam, A.; Glicenstein, J. -F.; Hearnshaw, J. B.; Hauschildt, P. H.; Kilmartin, P. M.; Kurata, Y.; Masuda, K.; Maoz, D.; Matsubara, Y.; Meintjes, P. J.; Moniez, M.; Muraki, Y.; Noda, S.; Ofek, E. O.; Okajima, K.; Philpott, L.; Rhie, S. H.; Sako, T.; Sullivan, D. J.; Sumi, T.; Terndrup, D. M.; Tristram, P. J.; Wood, J.; Yanagisawa, T.; Yock, P. C. M. Bibcode: 2005A&A...439..645R Altcode: 2005astro.ph..6013R We report a measurement of the shape of the source star in microlensing event MOA 2002-BLG-33. The lens for this event was a close binary whose centre-of-mass passed almost directly in front of the source star. At this time, the source star was closely bounded on all sides by a caustic of the lens. This allowed the oblateness of the source star to be constrained. We found that a/b = 1.02+0.04-0.02 where a and b are its semi-major and semi-minor axes respectively. The angular resolution of this measurement is approximately 0.04 μ{arcsec}. We also report HST images of the event that confirm a previous identification of the source star as an F8-G2 turn-off main-sequence star. Title: Modelling Alkali Line Absorption and Molecular Bands in Cool DAZs Authors: Homeier, D.; Allard, N.; Allard, F.; Hauschildt, P. H.; Schweitzer, A.; Stencil, P. C.; Weck, P. F. Bibcode: 2005ASPC..334..209H Altcode: 2005astro.ph..1077H Two peculiar stars showing an apparent extremely broadened and strong Na I D absorption have been discovered in surveys for cool white dwarfs by Oppenheimer et al. (2001) and Harris et al. (2003, SDSS). We discuss the nature of these objects using PHOENIX atmosphere models for metal-poor brown dwarfs/very low mass stars, and new white dwarf LTE and NLTE models for hydrogen- and helium-dominated atmospheres with metals. These include complete molecular formation in chemical equilibrium and a model for the alkali resonance line broadening based on the damping profiles of Allard et al. (2003), as well as new molecular line opacities for metal hydrides. First results of our calculations indicate good agreement with a hydrogen-dominated WD atmosphere with a Na abundance roughly consistent with a state of high accretion. We analyse deviations of the abundances of Na, K, Mg and Ca from the cosmic pattern and comment on implications of these results for standard accretion scenarios. Title: Modeling CHANDRA Low Energy Transmission Grating Spectrometer Observations of Classical Novae with PHOENIX Authors: Petz, A.; Hauschildt, P. H.; Ness, J. U.; Starrfield, S. Bibcode: 2005AIPC..774..357P Altcode: We use the PHOENIX code package to model the X-ray spectrum of Nova V4743 Sagittarii observed with the LETGS onboard the Chandra satellite on 19 March 2003. To analyze nova atmospheres and related systems with an underlying nuclear burning envelope at X-ray wavelengths, it was necessary to update the code with new microphysics. We demonstrate that the X-ray emission is dominated by thermal bremsstrahlung and that the hard X-rays are dominated by Fe and N absorption. Preliminary models are calculated assuming solar abundances. It is shown that the models can be used to determine element abundances in the nova ejecta by increasing the absorption in the shell. Title: Hot-Jupiters and hot-Neptunes: A common origin? Authors: Baraffe, I.; Chabrier, G.; Barman, T. S.; Selsis, F.; Allard, F.; Hauschildt, P. H. Bibcode: 2005A&A...436L..47B Altcode: 2005astro.ph..5054B We compare evolutionary models for close-in exoplanets coupling irradiation and evaporation due respectively to the thermal and high energy flux of the parent star with observations of recently discovered new transiting planets. The models provide an overall good agreement with observations, although at the very limit of the quoted error bars of OGLE-TR-10, depending on its age. Using the same general theory, we show that the three recently detected hot-Neptune planets (GJ436, ρ Cancri, μ Ara) may originate from more massive gas giants which have undergone significant evaporation. We thus suggest that hot-Neptunes and hot-Jupiters may share the same origin and evolution history. Our scenario provides testable predictions in terms of the mass-radius relationships of these hot-Neptunes. Title: Direct detection of exo-planets: GQ Lupi Authors: Neuhaeuser, Ralph; Guenther, Eike; Hauschildt, Peter Bibcode: 2005astro.ph..6011N Altcode: We present a comparison of our VLT/NACO K-band spectrum of the GQ Lupi companion with the new GAIA-dusty model atmosphere grid for T=2000 and 2900 K and log g from 0 to 4. Then, we discuss the mass estimate for GQ Lup companion. Title: Probing the Chromospheres of M dwarfs with the IRS Authors: Cushing, Michael; Chabrier, Gilles; Hauschildt, Peter; Liebert, James; Wehrse, Rainer Bibcode: 2005sptz.prop20409C Altcode: Arguable the most effective wavelength region to probe the coolest, outer layers of M dwarf atmospheres is to use mid-infrared spectrophotometry. Here the continuum opacity is very small, though if the atmosphere is not heated from below, the opacity due to water will be very strong. However, if there is any temperature increase above the minimum temperature layer due to a chromosphere or just weak acoustic heating, the water opacity weakens greatly, and a substantial increase in mid-infrared flux is predicted by models. This enhancement would be expected to increase sharply with increasing wavelength, reaching perhaps a 50% difference at 30 microns, and exceeding 60% at 36 microns. We thus propose to observe a set of eleven M1-M6 dwarfs, with and without quiescent H alpha emission. Most of the latter have old disk / halo space velocities. The observations should test the level of "basal" chromospheric-like activity for old stars that should have at most, weak, spun-down dynamos. Title: Detection of red line asymmetries in LHS 2034 Authors: Fuhrmeister, B.; Schmitt, J. H. M. M.; Hauschildt, P. H. Bibcode: 2005A&A...436..677F Altcode: We report very pronounced line asymmetries during a long duration flare on the dM6 star LHS 2034 (AZ Cnc). While all lines of the Balmer series and all strong He i lines show these asymmetries, the metal lines do not. This can be explained with the help of PHOENIX model chromospheres considering the formation depth of the lines involved. Moreover, the asymmetries persist over about one hour changing shape and amplitude. Fitting the asymmetries with an additional broad Gaussian component leads us to the scenario of a series of downward propagating condensations that decelerate due to the higher density of the lower chromosphere. In addition, similar but weaker line asymmetries were found in LHS 2397a. Title: VizieR Online Data Catalog: Late-type giants BVRIJHKL and Teff calibration (Kucinskas+, 2005) Authors: Kucinskas, A.; Hauschildt, P. H.; Ludwig, H. -G.; Brott, I.; Vansevicius, V.; Lindegren, L.; Tanabe, T.; Allard, F. Bibcode: 2005yCat..34420281K Altcode: Table 2 contains synthetic broad-band photometric colors of late-type giants in the Johnson-Cousins-Glass photometric system. Colors are based on the synthetic spectra calculated with the PHOENIX stellar model atmosphere code. Photometric filter definitions used are those from Bessell (1990PASP..102.1181B) for the Johnson-Cousins BVRI bands, and from Bessell & Brett (1988PASP..100.1134B) for the Johnson-Glass JHKL bands.

(1 data file). Title: VizieR Online Data Catalog: PHOENIX model chromospheres of M dwarfs (Fuhrmeister+, 2005) Authors: Fuhrmeister, B.; Schmitt, J. H. M. M.; Hauschildt, P. H. Bibcode: 2005yCat..34391137F Altcode: We present an extensive identification catalog of chromospheric emission lines in the optical range. The data were obtained with ESO's Kueyen telescope equipped with the UVES spectrograph from March, 13th to 16th in 2002. The instrument was operated in dichroic mode (spectral coverage from 3030 to 3880 and from 4580 to 6680{AA}). The data for the stars Prox Cen, UV Ceti and LHS 292 were obtained with the same instrument in winter 2000/2001 with a monochroic setup providing only the blue part of the spectrum. We tabulated measured wavelength, equivalent width (EW) and FWHM for every line and star and also provide the rest wavelength from the Moore catalog which was used for identification (Moore 1972). Few lines were identified with the NIST database. The spectra were all corrected for radial velocity besides Kelu-1, DENIS-P J1058.7-1548 and 2MASSI J1315309-264951. DENIS-P J1058.7-1548 has no detected lines, and therefore no data in the table.

(2 data files). Title: Evidence for a co-moving sub-stellar companion of GQ Lup Authors: Neuhäuser, R.; Guenther, E. W.; Wuchterl, G.; Mugrauer, M.; Bedalov, A.; Hauschildt, P. H. Bibcode: 2005A&A...435L..13N Altcode: 2005astro.ph..3691N We present a companion of the ≤2 Myr young classical T Tauri star GQ Lup in the Lupus star forming region at 140 ± 50 pc from imaging, astrometry, and spectroscopy. With direct K-band imaging using VLT/NACO, we detected an object 6 mag fainter than GQ Lup located 0.7'' west of it. Compared to images obtained 2 to 5 years earlier with Subaru/CIAO and HST/PC, this object shares the proper motion of GQ Lup by 5 and 7σ, respectively, hence it is a co-moving companion. Its K-L' color is consistent with a spectral type early to mid L. Our NACO K-band spectrum yields spectral type M9-L4 with H2O and CO absorption, consistent with the new GAIA-Dusty template spectrum for log g ≃ 2 to 3 and Teff ≃ 2000 K with ~2 Rjup radius at ∼ 140 pc, hence few Jupiter masses. Using the theoretical models from Wuchterl & Tscharnuter (2003), Burrows et al. (1997), and Baraffe et al. (2002), the mass lies between 1 and 42 Jupiter masses. Title: Low-Temperature Opacities Authors: Ferguson, Jason W.; Alexander, David R.; Allard, France; Barman, Travis; Bodnarik, Julia G.; Hauschildt, Peter H.; Heffner-Wong, Amanda; Tamanai, Akemi Bibcode: 2005ApJ...623..585F Altcode: 2005astro.ph..2045F Previous computations of low-temperature Rosseland and Planck mean opacities from Alexander & Ferguson are updated and expanded. The new computations include a more complete equation of state (EOS) with more grain species and updated optical constants. Grains are now explicitly included in thermal equilibrium in the EOS calculation, which allows for a much wider range of grain compositions to be accurately included than was previously the case. The inclusion of high-temperature condensates such as Al2O3 and CaTiO3 significantly affects the total opacity over a narrow range of temperatures before the appearance of the first silicate grains. The new opacity tables are tabulated for temperatures ranging from 30,000 to 500 K with gas densities from 10-4 to 10-19 g cm-3. Comparisons with previous Rosseland mean opacity calculations are discussed. At high temperatures, the agreement with OPAL and Opacity Project is quite good. Comparisons at lower temperatures are more divergent as a result of differences in molecular and grain physics included in different calculations. The computation of Planck mean opacities performed with the opacity sampling method is shown to require a very large number of opacity sampling wavelength points; previously published results obtained with fewer wavelength points are shown to be significantly in error. Methods for requesting or obtaining the new tables are provided. Title: Modeling M-dwarf chromospheres with PHOENIX Authors: Fuhrmeister, B.; Schmitt, J. H. M. M.; Hauschildt, P. H. Bibcode: 2005ESASP.560..559F Altcode: 2005csss...13..559F No abstract at ADS Title: NLTE models of extremely metal poor stars Authors: Short, C. I.; Hauschildt, P. H. Bibcode: 2005ESASP.560..967S Altcode: 2005csss...13..967S No abstract at ADS Title: The 2002 outburst of V838 Mon: as cool as it gets Authors: Starrfield, S.; Wagner, R. M.; Hauschildt, P. H.; Bond, H. E.; Evans, A.; Rushton, M. T.; Munari, U.; Henden, A.; Levay, Z. G.; Panagia, N.; Sparks, W. B.; Corradi, R. L. M. Bibcode: 2005ESASP.560..359S Altcode: 2005csss...13..359S No abstract at ADS Title: Evolutionary stellar population synthesis at high spectral resolution: optical wavelengths Authors: González Delgado, R. M.; Cerviño, M.; Martins, L. P.; Leitherer, C.; Hauschildt, P. H. Bibcode: 2005MNRAS.357..945G Altcode: 2005astro.ph..1204D; 2005MNRAS.tmp...89D; 2005astro.ph..1204G; 2005MNRAS.357..945D We present the single stellar population (SSP) synthesis results of our new synthetic stellar atmosphere models library with a spectral sampling of 0.3 Å, covering the wavelength range from 3000 to 7000 Åfor a wide range of metallicities (twice solar, solar, half solar and 1/10 solar). The stellar library is composed of 1650 spectra computed with the latest improvements in stellar atmospheres. In particular, it incorporates non-local thermodynamic equilibrium (LTE) line-blanketed models for hot (Teff>= 27500 K), and LTE line-blanketed models (Phoenix) for cool (3000 <=Teff<= 4500 K) stars. Because of the high spectral resolution of this library, evolutionary synthesis models can be used to predict the strength of numerous weak absorption lines and the evolution of the profiles of the strongest lines over a wide range of ages. The SSP results have been calculated for ages from 1 Myr to 17 Gyr using the stellar evolutionary tracks provided by the Geneva and Padova groups. For young stellar populations, our results have a very detailed coverage of high-temperature stars with similar results for the Padova and Geneva isochrones. For intermediate and old stellar populations, our results, once degraded to a lower resolution, are similar to the ones obtained by other groups (limitations imposed by the stellar evolutionary physics notwidthstanding). The limitations and advantages of our models for the analysis of integrated populations are described. The full set of the stellar library and the evolutionary models are available for retrieval at the websites http://www.iaa.csic.es/~rosa and http://www.iaa.csic.es/~mcs/sed@, or on request from the first two authors. Title: A high-resolution stellar library for evolutionary population synthesis Authors: Martins, Lucimara P.; González Delgado, Rosa M.; Leitherer, Claus; Cerviño, Miguel; Hauschildt, Peter Bibcode: 2005MNRAS.358...49M Altcode: 2005MNRAS.tmp..133M; 2005astro.ph..1225P; 2005astro.ph..1225M We present a library of 1654 high-resolution stellar spectra, with a sampling of 0.3 Åand covering the wavelength range from 3000 to 7000 Å. The library was computed with the latest improvements in stellar atmospheres, incorporating non-local thermodynamic equilibrium (non-LTE) line-blanketed models for hot, massive (Teff>= 27500K) and line-blanketed models for cool (3000 <=Teff<= 4500K) stars. The total coverage of the grid is 3000 K <=Teff<= 55000 K and -0.5 <= log g<= 5.5, for four chemical abundance values: twice solar, solar, half solar and 1/10 solar. Evolutionary synthesis models using this library are presented in a companion paper. We tested the general behaviour of the library by calculating and comparing equivalent widths of numerous H and HeI lines, and some of the commonly used metallic indices. We also compared the library with the empirical libraries STELIB and Indo-US. The full set of the synthetic stellar spectra is available from our websites (http://www.iaa.csic.es/~rosa and http://www.astro.iag.usp.br/~lucimara/library.htm). Title: Extrasolar planets: atmospheres, spectra, and evolution Authors: Barman, T. S.; Allard, F.; Baraffe, I.; Chabrier, G.; Hauschildt, P. H. Bibcode: 2005ESASP.560..437B Altcode: 2005csss...13..437B No abstract at ADS Title: Modeling of stellar chromospheres: Phoenix vs. Multi Authors: Jevremović, D.; Baron, E.; Hauschildt, P. H. Bibcode: 2005ESASP.560..673J Altcode: 2005csss...13..673J No abstract at ADS Title: Modeling CHANDRA low energy transmission grating spectrometer observations of classical novae with PHOENIX. I. V4743 Sagittarii Authors: Petz, A.; Hauschildt, P. H.; Ness, J. -U.; Starrfield, S. Bibcode: 2005A&A...431..321P Altcode: 2004astro.ph.10370P We use the PHOENIX code package to model the X-ray spectrum of Nova V4743 Sagittarii observed with the LETGS onboard the Chandra satellite 19 March 2003. Our atmosphere models are 1D spherical, expanding, line blanketed, and in full non-local thermodynamic equilibrium. To analyze nova atmospheres and related systems with an underlying nuclear burning envelope at X-ray wavelengths, it was necessary to update the code with new microphysics, as discussed in this paper. We demonstrate that the X-ray emission is dominated by thermal bremsstrahlung and that the hard X-rays are dominated by Fe and N absorption. The best fit to the observation is provided at a temperature of Teff = 5.8 × 105 K, with Lbol = 50 000 L⊙. The models are calculated for solar abundances. It is shown that the models can be used to determine abundances in the nova ejecta. Title: Overview of supernova modeling with PHOENIX Authors: Baron, E.; Hauschildt, Peter H. Bibcode: 2005MSAIS...7...86B Altcode: We discuss the information that can be obtained by comparing detailed NLTE \texttt{PHOENIX} models to observed supernova spectra. We show that the progenitor chemical composition, total reddening of the supernova, and accurate distances can be obtained with synthetic spectra that provide good fits to both the shape of the SED and the spectral lineshapes in the observed spectra. Title: A PHOENIX Model Atmosphere Grid for Gaia Authors: Brott, I.; Hauschildt, P. H. Bibcode: 2005ESASP.576..565B Altcode: 2005tdug.conf..565B; 2005astro.ph..3395B We present the results of a set of model atmospheres and synthetic spectra computed with the PHOENIX code. The models cover a range of effective temperatures (2 700 K ≤ Teff ≤ 10 000 K), gravities (-0.5 ≤ log(g) ≤ 5.5) and metallicities (-4.0 ≤ [Z/H] ≤ +0.5). In addition, variations of alpha elements are considered for each metallicity. The models are computed with a homogeneous set of input data in order to allow for direct relative comparison between the models. For example, all models use a mixing length of l/Hp = 2.0. We provide synthetic spectra with a resolution of 0.2 nm from the UV to the infrared for all models. We give a brief overview of the input physics and show illustrative results. All synthetic spectra are available via ftp. Title: First Steps Towards Modelling a Brown Dwarf Atmosphere Including the Formation of Dust Authors: Dehn, M.; Helling, C.; Woitke, P.; Hauschildt, P. Bibcode: 2005prpl.conf.8158D Altcode: 2005LPICo1286.8158D No abstract at ADS Title: The Deuterium Test for Exo-Planet Candidates Detected Directly Authors: Neuhäuser, Ralph; Seifahrt, Andreas; Hauschildt, Peter; Alves, Joao; Guenther, Eike Bibcode: 2005hris.conf..484N Altcode: In the near future, direct images will be obtained for massive planets orbiting around other stars. Most likely, the first such objects detected directly will have masses near the proposed limit between brown dwarfs and planets, i.e., around 13 Jupiter masses, because the more massive planets are the brightest. Hence, it may be dubious in these first few cases, whether the detected object is a brown dwarf or a real planet. To solve this problem, one can perform the deuterium test, i.e., one can distinguish between a brown dwarf (defined as an object able to fuse all deuterium) and an real planet (defined as an object not being able to fuse any deuterium) by whether or not deuterium can be identified in a spectrum. Any such object, brown dwarf or planet, would have spectral type T, defined as those with strong methane lines in the infrared. We present a model spectrum with the CH3D line at ~ 4.5 μm which can be obtained for such objects with CRIRES at the VLT. Title: Cool stellar atmospheres with PHOENIX . Authors: Hauschildt, P.; Baron, E. Bibcode: 2005MSAIS...7..140H Altcode: We give an overview about the state-of-the-art in cool stellar (and sub-stellar) atmosphere simulations. Recent developments in numerical methods and parallel supercomputers, as well as in the quality of input data such as atomic and molecular line lists have led to substantial improvements in the quality of synthetic spectra when compared to multi-wavelength observations. A wide range of objects from M dwarfs and giants down to substellar objects is considered. We discuss effects such as atomic and molecular NLTE (and) line blanketing, external irradiation, and formation and opacities of dust particles and clouds; each of which affects the structure of the atmospheres and their spectra. Current models can simultaneously fit many of the observed features of a given star with a single model atmosphere, however, a number of problems remain unsolved and will have to be addressed in the future, in particular for very low mass stars and substellar objects. Title: A Non-LTE Line-Blanketed Model of a Solar-Type Star Authors: Short, C. I.; Hauschildt, P. H. Bibcode: 2005ApJ...618..926S Altcode: 2004astro.ph..9693S We present LTE and non-LTE (NLTE) atmospheric models of a star with solar parameters and study the effect of treating many thousands of iron-group lines out of LTE on the computed atmospheric structure, the overall absolute flux distribution, and the moderately high resolution spectrum in the visible and near-UV bands. Our NLTE modeling includes the first two or three ionization stages of 20 chemical elements, up to and including much of the Fe group, and includes about 20,000 Fe I and II lines. We investigate separately the effects of treating the light metals and the Fe-group elements in NLTE. Our main conclusions are that (1) NLTE line-blanketed models with direct multilevel NLTE for many actual transitions give results qualitatively similar to those of the more approximate treatment of L. S. Anderson for both the Fe statistical equilibrium and the atmospheric Tkin structure; (2) models with many Fe lines in NLTE have a Tkin structure that agrees more closely with LTE semiempirical models based on center-to-limb variation and a wide variety of spectra lines, whereas LTE models agree more with semiempirical models based only on an LTE calculation of the Fe I excitation equilibrium; and (3) the NLTE effects of Fe-group elements on the model structure and Fλ distribution are much more important than the NLTE effects of all the light metals combined and serve to substantially increase the violet and near-UV Fλ level as a result of NLTE Fe overionization. These results suggest that there may still be important UV opacity missing from the models. However, the choice of the species and multiplet-dependent van der Waals broadening enhancement also plays a significant role in determining whether LTE or NLTE models provide a close fit to the near-UV flux level. We also find that the rms deviation of the shape of the rectified high-resolution synthetic spectrum from that of the observed spectrum is not significantly affected by the inclusion of NLTE effects. Title: Theoretical Modelling of Late-Type Giant Atmospheres: Preparing for Gaia Authors: Kucinskas, A.; Brott, I.; Hauschildt, P. H.; Ludwig, H. -G.; Lindegren, L.; Tanabé, T.; Vansevicius, V. Bibcode: 2005ESASP.576..591K Altcode: 2005tdug.conf..591K; 2005astro.ph..3208K Late-type giants (RGB/AGB stars) will be important tracers of the Galactic morphology and evolution in the framework of Gaia, as they are intrinsically bright and thus can probe distant stellar populations or those obscured by interstellar extinction. A realistic representation of their atmospheres and spectra with stellar atmosphere models is thus of crucial importance, both for the design and optimization of Gaia instruments, as well as the interpretation of provided astrophysical data. Our analysis of synthetic photometric colours of latetype giants based on PHOENIX, MARCS and ATLAS model atmospheres indicates a general agreement between the current theoretical predictions and observations in the framework of stationary 1-D model atmospheres. Presently available models allow temperature determinations of RGB/AGB stars to an accuracy of ∼ ±100 K. In an exploratory study we try to quantify possible residual systematic effects due to the approximations made in 1-D models using full 3-D hydrodynamical models. We find that differences in broad-band photometric colours calculated with 1-D and 3-D models are significant, translating to the offsets in effective temperature of up to μTeff ∼70 K. Clearly, full 3-D hydrodynamical models will help to alleviate such ambiguities in current theoretical modelling. Additionally, they will allow to study new phenomena, to open qualitatively new windows for stellar astrophysics in the Gaia-era. Title: Direct Imaging of Extra-Solar Planets- The Case of GQ Lupi A and B Authors: Neuhäuser, R.; Mugrauer, M.; Wuchterl, G.; Guenther, E. W.; Bedalov, A.; Hauschildt, P. Bibcode: 2005prpl.conf.8327N Altcode: 2005LPICo1286.8327N No abstract at ADS Title: Spectral Properties of Brown Dwarfs and Hot Jupiters Authors: Homeier, Derek; Allard, France; Hauschildt, Peter; Barman, Travis; Schweitzer, Andreas; Baron, Edward Bibcode: 2005hris.conf..465H Altcode: 2004astro.ph..5438H Brown dwarfs bridge the gap between the stellar and planetary mass regimes. Evolving from conditions very similar to the lowest-mass stars, the atmospheres of older brown dwarfs closely resemble those expected in close-in extrasolar giant planets, and with cooler BDs still being discovered, more and more approach the properties of gas giants at wider separation. Interpreting the spectra of BDs is therefore a crucial step towards understanding and predicting the spectral and thermal properties of EGPs. Title: PoSSO Physics of SubStellar Objects Authors: Jones, Hugh; Viti, Serena; Tennyson, Jonathan; Barber, Bob; Pickering, Juliet; Blackwell-Whitehead, Richard; Champion, Jean-Paul; Allard, France; Hauschildt, Peter; Jørgensen, Uffe; Ehrenfreund, Pascale; Stachowska, Ewa; Ludwig, Hans-Günter; Pavlenko, Yakiv; Lyubchik, Yuri; Kurucz, Robert Bibcode: 2005hris.conf..477J Altcode: A full understanding of the properties of substellar objects is one of the major challenges facing astrophysics. Since their discovery in 1995, we have discovered hundreds of brown dwarfs and extrasolar planets. While these discoveries have enabled important comparisons with theory, observational progress has been much more rapid than the theoretical understanding of cool atmospheres. The determination of mass, abundances, gravities and temperatures is not yet possible. The key problem is that substellar objects emit their observable radiation in the infrared region of the spectrum where our knowledge of atomic, molecular and line broadening data is poor. In order to understand these objects, and extra-solar planets increasing more like those our Solar System, we urge the wider physical chemistry community to engage in this exciting new field. Here we sketch an outline of the atoms, molecules and processes requiring study. Title: Alkali Line Formation in the Atmospheres of Extrasolar Giant Planets Authors: Allard, N. F.; Allard, F.; Machin, L.; Hauschildt, P.; Louis, F.; Loeillet, B.; Kielkopf, J. F.; Pascale, J. Bibcode: 2004ASPC..321..197A Altcode: We present calculations of alkali line profiles and of their formation in the atmospheres of brown dwarfs and extrasolar giant planets. We compare our new theoretical spectra to the near-infrared spectrum of SDSS 1624. Title: Phase-dependent Properties of Extrasolar Giant Planet Atmospheres Authors: Barman, T. S.; Allard, F.; Hauschildt, P. H. Bibcode: 2004ASPC..321..201B Altcode: No abstract at ADS Title: Co-moving frame radiative transfer in spherical media with arbitrary velocity fields Authors: Baron, E.; Hauschildt, P. H. Bibcode: 2004A&A...427..987B Altcode: 2004astro.ph..8212B Recently, with the advances in computational speed and availability there has been a growth in the number and resolution of fully 3D hydrodynamical simulations. However, all of these simulations are purely hydrodynamical and there has been little attempt to include the effects of radiative transfer except in a purely phenomenological manner because the computational cost is too large even for modern supercomputers. While there has been an effort to develop 3D Monte Carlo radiative transfer codes, most of these have been for static atmospheres or have employed the Sobolev approximation, which limits their applicability to studying purely geometric effects such as macroscopic mixing. Also the computational requirements of Monte Carlo methods are such that it is difficult to couple with 3D hydrodynamics. Here, we present an algorithm for calculating 1D spherical radiative transfer in the presence of non-monotonic velocity fields in the co-moving frame. Non-monotonic velocity flows will occur in convective, and Raleigh-Taylor unstable flows, in flows with multiple shocks, and in pulsationally unstable stars such as Mira and Cepheids. This is a first step to developing fully 3D radiative transfer than can be coupled with hydrodynamics. We present the computational method and the results of some test calculations. Title: Spitzer Space Telescope and Coordinated Optical Spectrophotometry of V1187 Scorpii (Nova Scorpii 2004 #2) Authors: Woodward, C. E.; Ruch, G.; Gehrz, R. D.; Humphreys, R. M.; Polomski, E.; Wagner, R. M.; Barlow, M.; Bode, M. F.; Eyres, S.; Evans, A.; Geballe, T. R.; Greenhouse, M. A.; Hauschildt, P.; Krautter, J.; Liller, W.; Lyke, J. E.; Rudy, R.; Salama, A.; Schwarz, G.; Shore, S. N.; Starrfield, S.; Strutskie, M. F.; Truran, J.; Williams, R. E. Bibcode: 2004AAS...205.1923W Altcode: 2004BAAS...36.1374W Classical nova (CN) explosions are thermonuclear runaway (TNR) in the accreted H-rich envelope on the white dwarf (WD) in a cataclysmic variable system. Infrared and optical observations of CN have established their importance for understanding the formation of astrophysical grains, and as contributors to abundance anomalies in the ISM on local scales. Abundance studies of nova ejecta also provide information about nucleosynthesis in the WD progenitor and in the TNR. Here, we present Spitzer Space Telescope IRS spectra of the Galactic Classical nova V1187 Scorpii (Nova Scorpii 2004 #2) as well as coordinated optical spectroscopy and photometry obtained on the MMT 6.5-m and the 2.0-m robotic Liverpool telescopes.

The Spitzer spectra, obtained on 28.40 September 2004 UT as part of our Cycle 1 ToO nova program, exhibit broad ( ∼ 4800 km/s) H-recombination line emission (e.g., HI 6-5, HI 7-6, HI 9-8) as well as forbidden line emission including [Mg VII]5.50 micron, [Mg V]5.61 micron, [Ne II]12.81 micron, and [Ne III]15.55 micron. Of note, the [O IV]25.89 micron line is present in the spectra of V1187 Sco. The high resolution optical spectra, obtained on 2004 September 23.01 UT, show double peaked emission lines with velocity components separated by ∼ 1200 km/s, suggesting that the ejecta of V1187 Sco is distributed in clumps of varying ionization states exhibiting a range of ejection velocities (frequently found in CN). We present a preliminary discussion of line identification, reddening, abundances, as well as a comparison of V1187 Sco to other ONeMg nova. Our Spitzer observations are also supported by complementary ground-based infrared spectra obtain as part of a large collaborative study of this nova (see posters by Lynch et al. and Russell et al.).

This work is supported in part by NASA (JPL/SSC) and the NSF (AST02-05814). Title: Type IIP Supernovae as Cosmological Probes: A Spectral-fitting Expanding Atmosphere Model Distance to SN 1999em Authors: Baron, E.; Nugent, Peter E.; Branch, David; Hauschildt, Peter H. Bibcode: 2004ApJ...616L..91B Altcode: 2004astro.ph.10153B Because of their intrinsic brightness, supernovae make excellent cosmological probes. We describe the spectral-fitting expanding atmosphere method (SEAM) for obtaining distances to Type IIP supernovae (SNe IIP) and present a distance to SN 1999em for which a Cepheid distance exists. Our models give results consistent with the Cepheid distance, even though we have not attempted to tune the underlying hydrodynamical model but have simply chosen the best fits. This is in contradistinction to the expanding photosphere method (EPM), which yields a distance to SN 1999em that is 50% smaller than the Cepheid distance. We emphasize the differences between the SEAM and the EPM. We show that the dilution factors used in the EPM analysis were systematically too small at later epochs. We also show that the EPM blackbody assumption is suspect. Since SNe IIP are visible to redshifts as high as z<~6, with the James Webb Space Telescope, the SEAM may be a valuable probe of the early universe. Title: The Physics of Extrasolar Gaseous Planets : from Theory to Observable Signatures Authors: Chabrier, G.; Allard, F.; Baraffe, I.; Barman, T.; Hauschildt, P. H. Bibcode: 2004ASPC..321..131C Altcode: 2004astro.ph..1608C We review our present understanding of the physical properties of substellar objects, brown dwarfs and irradiated or non-irradiated gaseous exoplanets. This includes a description of their internal properties, mechanical structure and heat content, their atmospheric properties, thermal profile and emergent spectrum, and their evolution, in particular as irradiated companions of a close parent star. The general theory can be used to make predictions in term of detectability for the future observational projects. Special attention is devoted to the evolution of the two presently detected transit planets, HD 209458b and OGLE-TR-56B. For this latter, we present a consistent evolution for its recently revised mass and show that we reproduce the observed radius within its error bars. We briefly discuss differences between brown dwarfs and gaseous planets, both in terms of mass function and formation process. We outline several arguments to show that the minimum mass for deuterium burning, recently adopted officially as the limit to distinguish the two types of objects, is unlikely to play any specific role in star formation, so that such a limit is of purely semantic nature and is not supported by a physical justification. Title: From Very Low Mass Stars to Extrasolar Planets Authors: Allard, France; Barman, Travis S.; Paillet, Jimmy; Baraffe, I.; Chabrier, G.; Hauschildt, P. H. Bibcode: 2004sf2a.conf..193A Altcode: 2004sf2a.confE.265A We have modeled, using the atmosphere code Phoenix, the photosphere structures and spectral distribution of brown dwarfs and of all known Extrasolar Giant Planets (EGPs) to this day. Since EGPs are often brighter, more massive and larger than telluric planets, they will be more readily detected in the future transit surveys (COROT, KEPLER, SIMS, Eddington), and be the most directly observable using current technology (e.g. by nulling interferometry with the GENIE experiment). In this paper we summarize the spectral properties of EGPs as a function of their orbital distance, phase as viewed from the earth, mass and age, and type of primary star. We establish the most favorable observation conditions (i.e. maximum luminosity contrast of the planet to the primary star). We also explore uncertainties tied to the chemical composition of the atmosphere, and the presence of cloud layers, and study constraining cases such as HD209458b, OGLE-TR56b and Jupiter. Title: Non-LTE Models of (Cool) Stellar and Giant Planetary Atmospheres Authors: Schweitzer, Andreas; Hauschildt, Peter H. Bibcode: 2004AIPC..730..111S Altcode: The atmospheres of cool stars, brown dwarfs and extrasolar giant planets are rich with a large mix of molecules producing a complicated spectrum dominated by molecular absorption bands and, consequently, highly non-Planckian shape. Additionally, many discovered extrasolar planets and brown dwarfs are close to a nearby, much hotter, main sequence star. Either of the above two conditions cause large deviations from LTE if the collisional processes are insufficient to restore LTE in the atmospheric layers.

Here we review the general conditions which drive stellar atmospheres in non thermal equilibrium (Non-LTE). Furthermore, we present recent advances in simulating non-LTE effects in cool atmospheres for both non-irradiated and irradiated stars and planets. In non-irradiated atmospheres, the radiative rates are often too small compared to the collisional rates to drive large deviations from LTE. However, irradiated atmospheres show significant non-LTE effects, e.g., in the recently discovered planet HD209458b eclipsing its parent star. Title: Model Atmospheres for Irradiated Stars in Precataclysmic Variables Authors: Barman, Travis S.; Hauschildt, Peter H.; Allard, France Bibcode: 2004ApJ...614..338B Altcode: 2004astro.ph..6599B Model atmospheres have been computed for M dwarfs that are strongly irradiated by nearby hot companions. A variety of primary and secondary spectral types are explored in addition to models specific to four known systems: GD 245, NN Ser, AA Dor, and UU Sge. This work demonstrates that a dramatic temperature inversion is possible on at least one hemisphere of an irradiated M dwarf and that the emergent spectrum will be significantly different from an isolated M dwarf or a blackbody flux distribution. For the first time, synthetic spectra suitable for direct comparison to high-resolution observations of irradiated M dwarfs in non-mass-transferring post-common-envelope binaries are presented. The effects of departures from local thermodynamic equilibrium on the Balmer line profiles are also discussed. Title: Molecular Line Opacity of LiCl in the Mid-Infrared Spectra of Brown Dwarfs Authors: Weck, P. F.; Schweitzer, A.; Kirby, K.; Hauschildt, P. H.; Stancil, P. C. Bibcode: 2004ApJ...613..567W Altcode: 2004astro.ph..6147W We present a complete line list for the X1Σ+ electronic ground state of 7Li35Cl, computed using fully quantum-mechanical techniques. This list includes transition energies and oscillator strengths in the spectral region 0.3-39,640.7cm-1 for all allowed rovibrational transitions in absorption within the electronic ground state. The calculations were performed using an accurate hybrid potential constructed from a spectral inversion fit of experimental data and from recent multireference single- and double-excitation configuration interaction calculations. The line list was incorporated into the stellar atmosphere code PHOENIX to compute spectra for a range of young to old T dwarf models. The possibility of observing a signature of LiCl in absorption near 15.8 μm is addressed and the proposal to use this feature to estimate the total lithium elemental abundance for these cool objects is discussed. Title: Mid-Infrared Spectroscopy of the Coldest Known Brown Dwarf 2MASS 0415-0935: Physical Diagnostics and Spectral Modeling Authors: Burgasser, Adam; Allard, France; Hauschildt, Peter; Homeier, Derek; Kirkpatrick, J. Davy; McLean, Ian Bibcode: 2004sptz.prop.3259B Altcode: We propose to obtain 5-22 micron low-resolution spectroscopy for the coldest known brown dwarf, 2MASS 0415-0935, using the IRS instrument on Spitzer. With an effective temperature of ~700-800 K, this source is a benchmark for the study of low temperature atmospheres and a key starting point for the search for even cooler brown dwarfs. The proposed observations will sample the brightest continuum emission region for this object and resolve many individual molecular features, including the important 10.5 micron band of NH3, the only detectable nitrogen-bearing molecule in a brown dwarf atmosphere and a tracer of atmospheric dynamics. By combining the Spitzer data with high signal-to-noise, moderate resolution optical (0.6-1.0 micron) and near-infrared (1.0-2.4 micron) ground-based data already obtained by our group, and matching to our state-of-the-art spectral models, we will be able to derive the physical properties of this source (temperature, surface gravity, and metallicity), as well as test current opacity models for H2O, CH4, and NH3, critical for modeling and interpreting brown dwarf and planetary atmospheres. The proposed program is a focused experiment for measuring the physical parameters of the coolest brown dwarfs now known and soon to be discovered, and provides a key empirical test of atmosphere models used for both substellar and planetary studies. Title: ToO Observations of Galactic and Magellanic Cloud Classical Novae Authors: Woodward, Charles; Barlow, Michael; Bode, Michael; Evans, Nye; Geballe, Thomas; Gehrz, Robert; Greenhouse, Mattew; Hauschildt, Peter; Krautter, Joachim; Liller, William; Lyke, James; Rudy, Richard; Salama, Alberto; Schwarz, Greg; Shore, Steven; Skrutskie, Michael; Starrfield, Sumner; Truran, James; Wagner, R. Mark; Williams, Robert Bibcode: 2004sptz.prop.2333W Altcode: Stars are the engines of energy production and chemical evolution in our Universe. They deposit radiative and mechanical energy into their environments, and enrich the ambient interstellar medium with elements synthesized in their interiors and dust grains condensed in their atmospheres. Classical novae (CN), a transient phenomenon, contribute to this cycle of chemical enrichment through explosive nucleosynthesis and the violent ejection of material dredged from the white dwarf progenitor and mixed with the accreted surface layers. Using Spitzer (+IRS), we propose a 10.5 hr, no-impact, multi-cycle (2) ToO program to study (in temporal detail) the later evolutionary stages of CN (> 40 days post-outburst) by targeting 4 Galactic and 3 Magellanic Cloud novae. Spitzer is a unique facility that can enable us to investigate aspects of CN phenomenon including: the in situ formation and astromineralogy of dust, the elemental abundances resulting from thermonuclear runaway, the correllation of ejecta masses with progenitor type, the bolometric luminosities of the outburst, and the kinematics and structure of the ejected envelopes. Specifically, our program addresses four research problems in the study of CN evolution: 1)~determination of the grain size distribution and mineral composition of nova dust; 2)~estimation of chemical abundances of nova ejecta from coronal and forbidden emission line spectroscopy; 3)~measurement of the density and masses of the ejecta; and 4)~characterization of the nature of novae in the SMC and LMC at mid- to far-infrared wavelengths. Title: Measuring Fundamental Parameters of Substellar Objects. I. Surface Gravities Authors: Mohanty, Subhanjoy; Basri, Gibor; Jayawardhana, Ray; Allard, France; Hauschildt, Peter; Ardila, David Bibcode: 2004ApJ...609..854M Altcode: 2004astro.ph..3265M We present an analysis of high-resolution optical spectra for a sample of very young, mid- to late-M, low-mass stellar and substellar objects: 11 in the Upper Scorpius association, and two (GG Tau Ba and Bb) in the Taurus star-forming region. Effective temperatures and surface gravities are derived from a multiple-feature spectral analysis using TiO, Na I, and K I, through comparison with the latest synthetic spectra. We show that these spectral diagnostics complement each other, removing degeneracies with temperature and gravity in the behavior of each. In combination, they allow us to determine temperature to within 50 K and gravity to within 0.25 dex, in very cool young objects. Our high-resolution spectral analysis does not require extinction estimates. Moreover, it yields temperatures and gravities independent of theoretical evolutionary models (although our estimates do depend on the synthetic spectral modeling). We find that our gravities for most of the sample agree remarkably well with the isochrone predictions for the likely cluster ages. However, discrepancies appear in our coolest targets: these appear to have significantly lower gravity (by up to 0.75 dex) than our hotter objects, even though our entire sample covers a relatively narrow range in effective temperature (~300 K). This drop in gravity is also implied by intercomparisons of the data alone, without recourse to synthetic spectra. We consider, and argue against, dust opacity, cool stellar spots, or metallicity differences leading to the observed spectral effects; a real decline in gravity is strongly indicated. Such gravity variations are contrary to the predictions of the evolutionary tracks, causing improbably low ages to be inferred from the tracks for our coolest targets. Through a simple consideration of contraction timescales, we quantify the age errors introduced into the tracks through the particular choice of initial conditions and demonstrate that they can be significant for low-mass objects that are only a few megayears old. However, we also find that these errors appear insufficient to explain the magnitude of the age offsets in our lowest gravity targets. We venture that this apparent age offset may arise from evolutionary model uncertainties related to accretion, deuterium burning and/or convection effects. Finally, when combined with photometry and distance information, our technique for deriving surface gravities and effective temperatures provides a way of obtaining masses and radii for substellar objects independent of evolutionary models; radius and mass determinations are presented in Paper II. Title: Probing the atmosphere of the bulge G5III star OGLE-2002-BUL-069 by analysis of microlensed Hα line Authors: Cassan, A.; Beaulieu, J. P.; Brillant, S.; Coutures, C.; Dominik, M.; Donatowicz, J.; Jørgensen, U. G.; Kubas, D.; Albrow, M. D.; Caldwell, J. A. R.; Fouqué, P.; Greenhill, J.; Hill, K.; Horne, K.; Kane, S.; Martin, R.; Menzies, J.; Pollard, K. R.; Sahu, K. C.; Vinter, C.; Wambsganss, J.; Watson, R.; Williams, A.; Fendt, C.; Hauschildt, P.; Heinmueller, J.; Marquette, J. B.; Thurl, C. Bibcode: 2004A&A...419L...1C Altcode: 2004astro.ph..1071C We discuss high-resolution, time-resolved spectra of the caustic exit of the binary microlensing event OGLE 2002-BLG-069 obtained with UVES on the VLT. The source star is a G5III giant in the Galactic Bulge. During such events, the source star is highly magnified, and a strong differential magnification around the caustic resolves its surface. Using an appropriate model stellar atmosphere generated by the PHOENIX v2.6 code we obtain a model light curve for the caustic exit and compare it with a dense set of photometric observations obtained by the PLANET microlensing follow up network. We further compare predicted variations in the Hα equivalent width with those measured from our spectra. While the model and observations agree in the gross features, there are discrepancies suggesting shortcomings in the model, particularly for the Hα line core, where we have detected amplified emission from the stellar chromosphere after the source star's trailing limb exited the caustic. This achievement became possible by the provision of the very efficient OGLE-III Early Warning System, a network of small telescopes capable of nearly-continuous round-the-clock photometric monitoring, on-line data reduction, daily near-real-time modelling in order to predict caustic crossing parameters, and a fast and efficient response of a 8 m class telescope to a ``Target-of-Opportunity'' observation request.

Based on observations made at ESO, 69.D-0261(A), 269.D-5042(A), 169.C-0510(A). Title: The effect of evaporation on the evolution of close-in giant planets Authors: Baraffe, I.; Selsis, F.; Chabrier, G.; Barman, T. S.; Allard, F.; Hauschildt, P. H.; Lammer, H. Bibcode: 2004A&A...419L..13B Altcode: 2004astro.ph..4101B We include the effect of evaporation in our evolutionary calculations of close-in giant planets, based on a recent model for thermal evaporation taking into account the XUV flux of the parent star (Lammer et al. \cite{Lammer2003}). Our analysis leads to the existence of a critical mass for a given orbital distance mcrit(a) below which the evaporation timescale becomes shorter than the thermal timescale of the planet. For planets with initial masses below mcrit, evaporation leads to a rapid expansion of the outer layers and of the total planetary radius, speeding up the evaporation process. Consequently, the planet does not survive as long as estimated by a simple application of mass loss rates without following consistently its evolution. We find out that the transit planet HD 209458b might be in such a dramatic phase, although with an extremely small probability. As a consequence, we predict that, after a certain time, only planets above a value mcrit(a) should be present at an orbital distance a of a star. For planets with initial masses above mcrit, evaporation does not affect the evolution of the radius with time. Title: Improved discretization of the wavelength derivative term in CMF operator splitting numerical radiative transfer Authors: Hauschildt, P. H.; Baron, E. Bibcode: 2004A&A...417..317H Altcode: 2004astro.ph..1164H We describe two separate wavelength discretization schemes that can be used in the numerical solution of the comoving frame radiative transfer equation. We present an improved second order discretization scheme and show that it leads to significantly less numerical diffusion than the previous scheme. We also show that due to the nature of the second order term in some extreme cases it can become numerically unstable. We stabilize the scheme by introducing a mixed discretization scheme and present the results from several test calculations. Title: The Evolution of Irradiated Planets: Application to Transits Authors: Chabrier, G.; Barman, T.; Baraffe, I.; Allard, F.; Hauschildt, P. H. Bibcode: 2004ApJ...603L..53C Altcode: 2004astro.ph..1487C Extending the theory that we derived recently for HD 209458b to different cases of strongly irradiated gaseous exoplanets, we have calculated the consistent evolution of a new transiting planet, OGLE-TR-56b, for its recently revised mass determination. The theory is shown to successfully reproduce the observed radius for the proper age of the system. We also examine the dissipation of kinetic energy at the planet's internal adiabat due to atmospheric winds and place constraints on the efficiency of this process. We show that a fraction ~0.1%-0.5% of the incident flux transformed into thermal energy deposited at the adiabatic level can accommodate the observed radii of both OGLE-TR-56b and HD 209458b. The present theory yields quantitative predictions on the evolution of the emergent spectrum and fundamental properties of hot jupiters. The predictions for radius, luminosity, temperature as a function of the planet's mass, and orbital distance can be used as benchmarks for future detections of transit planets. Title: Examining stellar atmospheres via microlensing Authors: Thurl, C.; Sackett, P. D.; Hauschildt, P. H. Bibcode: 2004AN....325..247T Altcode: Resolving stellar atmospheres of stars other than the Sun has proven very tedious and only possible for the nearest and largest stars. microlensing offers a solution by providing a ``natural'' telescope.

Binary lenses create extended caustic lines in the magnification pattern. As the source star crosses such a caustic, its light curve not only shows a strong peak of distinctive shape, but its surface also experiences a substantial differential magnification and is therefore spatially resolved. As suggested by \cite{schneider, heyrov, heyrov00, hendry, bryce, fields} microlensing gives us the opportunity to examine the atmospheres of stars and to test stellar models against observations. Title: Hunting for the signatures of 3-D explosions with 1-D synthetic spectra Authors: Lentz, E. J.; Baron, E.; Hauschildt, P. H. Bibcode: 2004cetd.conf..173L Altcode: No abstract at ADS Title: 2MASS J0516288+260738: a new low-mass eclipsing binary system. Authors: Schuh, S.; Drechsel, H.; Hauschildt, P.; Handler, G.; Endl, M.; Dreizler, S. Bibcode: 2004ANS...325R..84S Altcode: 2004ANS...325a..84S; 2004ANS...325..P09S No abstract at ADS Title: Probing the atmosphere of a solar-like star by galactic microlensing at high magnification Authors: Abe, F.; Bennett, D. P.; Bond, I. A.; Calitz, J. J.; Claret, A.; Cook, K. H.; Furuta, Y.; Gal-Yam, A.; Glicenstein, J. -F.; Hearnshaw, J. B.; Hauschildt, P. H.; Kent, D.; Kilmartin, P. M.; Kurata, Y.; Masuda, K.; Maoz, D.; Matsubara, Y.; Meintjes, P. J.; Moniez, M.; Muraki, Y.; Noda, S.; Ofek, E. O.; Okajima, K.; Philpott, L.; Rattenbury, N. J.; Rhie, S. H.; Sako, T.; Sullivan, D. J.; Sumi, T.; Terndrup, D. M.; Tristram, P. J.; Yanagisawa, T.; Yock, P. C. M. Bibcode: 2003A&A...411L.493A Altcode: 2003astro.ph.10410A We report a measurement of limb darkening of a solar-like star in the very high magnification microlensing event MOA 2002-BLG-33. A 15 hour deviation from the light curve profile expected for a single lens was monitored intensively in V and I passbands by five telescopes spanning the globe. Our modelling of the light curve showed the lens to be a close binary system whose centre-of-mass passed almost directly in front of the source star. The source star was identified as an F8-G2 main sequence turn-off star. The measured stellar profiles agree with current stellar atmosphere theory to within ~ 4% in two passbands. The effective angular resolution of the measurements is <1 mu as. These are the first limb darkening measurements obtained by microlensing for a Solar-like star. Title: The atmospheres and Evolution of Extrasolar Planets Authors: Barman, T. S.; Allard, F.; Baraffe, I.; Chabrier, G.; Hauschildt, P. H. Bibcode: 2003AAS...203.1701B Altcode: 2003BAAS...35Q1234B Observations of transiting extrasolar giant planet (EGP), HD 209458b, provided the first tests of atmospheric and evolutionary models for the shortest period EGPs. To date, most models fail to reproduce the observed radius of HD 209458b without including mechanisms, such as tidal heating or strong atmospheric circulations, in addition to irradiation by the parent star. Based solely on the observations of HD 209458b it is difficult to say with certainty how crucial these additional heating sources are to the evolution of close-in EGPs. Fortunately, new transiting EGP candidates are being discovered allowing for more robust tests of the theory over a broader parameter space. In this poster, new atmospheric and evolutionary models are presented for a variety of orbital separations, stellar spectral types, and planetary masses. Comparisons are made to the latest EGP transit observations. Title: The limb-darkening for spherically symmetric NextGen model atmospheres: A-G main-sequence and sub-giant stars Authors: Claret, A.; Hauschildt, P. H. Bibcode: 2003A&A...412..241C Altcode: We compute passband-integrated specific intensities for spherically symmetric models generated with the PHOENIX code. The models cover the range 5000 K <=Teff<=10 000 K with surface gravities between 3.5 and 5.5, in steps of 0.5. The adopted mixing-length parameter is 2.0 pressure scale heights, while the microturbulent velocity is 2.0 km s-1. The calculations were carried out for four photometric systems: Strömgren, Johnson, Geneva and Walraven, completing 24 filters. The series introduced by Claret (2000) and a new bi-parametric (exponential) law are shown to be able to describe the intensity distribution of spherical models with acceptable sigma . Simple limb-darkening laws do not produce accurate fits to the computed radiation fields. On the other hand, the concept of ``quasi'' spherical models is introduced and we present the corresponding limb-darkening coefficients for the most commonly adopted limb-darkening laws for the same filters.

Tables 2-17 are only available in electronic form at http://www.edpsciences.org Title: A new model for brown dwarf spectra including accurate unified line shape theory for the Na I and K I resonance line profiles Authors: Allard, N. F.; Allard, F.; Hauschildt, P. H.; Kielkopf, J. F.; Machin, L. Bibcode: 2003A&A...411L.473A Altcode: We present the first brown dwarf atmosphere models based on theoretical calculations of absorption profiles of sodium and potassium perturbed by helium and molecular hydrogen. The synthetic spectra have been compared to previous calculations with Lorentz profiles and the classic van der Waals approximation, and to the observed spectrum of the T dwarf SDSS 1624. The new profiles provide increased opacities in the optical spectra of methane brown dwarfs. However, the potassium and sodium far wings alone cannot explain the missing opacity in the 0.85 to 1.1 mu m range. Title: Alkali Halide Opacity in Brown Dwarf and Cool Stellar Atmospheres: A Study of Lithium Chloride Authors: Kirby, K.; Weck, P. F.; Schweitzer, A.; Stancil, P. C.; Hauschildt, P. H. Bibcode: 2003AAS...203.0605K Altcode: 2003BAAS...35.1212K Recent thermochemical equilibrium calculations have revealed the important role played by lithium chloride in the lithium chemistry of cool dwarf atmospheres (K. Lodders 1999, ApJ 519, 793). Indeed, LiCl appears to be the dominant Li-bearing gas over an extended domain of the (P,T) diagram, typically for temperatures below 1500 K. LiCl has a large dipole moment in its ground electronic state which can give rise to intense rovibrational line spectra. In addition, LiCl can make dipole transitions to several low-lying unbound excited states, causing dissociation of the molecule. For these reasons, LiCl may be a significant source of line and continuum opacity in brown dwarf and cool stellar atmospheres.

In this work, we report calculations of complete lists of line oscillator strengths and photodissociation cross sections for the low-lying electronic states of LiCl. We have performed single- and double-excitation configuration interaction calculations using the ALCHEMY ab initio package (Mc Lean et al. 1991, MOTECC 91, Elsevier, Leiden) and obtained the potential curves and the corresponding dipole transition moment functions between the X 1Σ ^+ ground state and the B 1Σ ^+ and A 1Π excited states.

The resulting line oscillator strengths and molecular photodissociation cross sections have been included in the PHOENIX stellar atmosphere code (Hauschildt & Baron 1999, J. Comput. App. Math. 102, 41). The new models, calculated using spherical geometry for all gravities considered, also incorporate our latest database of nearly 670 million molecular lines, and updated equations of state (EOS).

This work was supported in part by NSF grants AST-9720704 and AST-0086246, NASA grants NAG5-8425, NAG5-9222, and NAG5-10551 as well as NASA/JPL grant 961582. Title: Modelling the Spectra of SN 1998bw from a Jet Powered Explosion Model Authors: Lentz, E. J.; Baron, E.; Hauschildt, P. H. Bibcode: 2003AAS...203.4515L Altcode: 2003BAAS...35.1279L Supernova 1998bw and several other extreme Type Ic supernovae show strong evidence of asymmetry. We have segmented the jet induced model for these objects by Maeda & Nomoto into several slices and modelled each of slices as independent objects. We compare a sequence of early spectra of SN 1998bw to the spectra of these slice and also to a composit spectrum made from all of the segments. Title: 2MASS J0516288+260738: Discovery of the first eclipsing late K + Brown dwarf binary system? Authors: Schuh, S. L.; Handler, G.; Drechsel, H.; Hauschildt, P.; Dreizler, S.; Medupe, R.; Karl, C.; Napiwotzki, R.; Kim, S. -L.; Park, B. -G.; Wood, M. A.; Paparó, M.; Szeidl, B.; Virághalmy, G.; Zsuffa, D.; Hashimoto, O.; Kinugasa, K.; Taguchi, H.; Kambe, E.; Leibowitz, E.; Ibbetson, P.; Lipkin, Y.; Nagel, T.; Göhler, E.; Pretorius, M. L. Bibcode: 2003A&A...410..649S Altcode: 2003astro.ph..8329S We report the discovery of a new eclipsing system less than one arcminute south of the pulsating DB white dwarf KUV 05134+2605. The object could be identified with the point source 2MASS J0516288+260738 published by the Two Micron All Sky Survey. We present and discuss the first light curves as well as some additional colour and spectral information. The eclipse period of the system is 1.29 d, and, assuming this to be identical to the orbital period, the best light curve solution yields a mass ratio of m2/m1=0.11, a radius ratio of r2/r1~ 1 and an inclination of 74o. The spectral anaylsis results in a Teff=4200 K for the primary. On this basis, we suggest that the new system probably consists of a late K + Brown dwarf (which would imply a system considerably younger than ~0.01 Gyr to have r2/r1~ 1), and outline possible future observations.

This paper uses observations made at the Bohyunsan Optical Astronomy Observatory of Korea Astronomy Observatory, at the South African Astronomical Observatory (SAAO), at the 0.9 m telescope at Kitt Peak National Observatory recommissioned by the Southeastern Association for Research in Astronomy (SARA), at Gunma Astronomical Observatory established by Gunma prefecture, Japan, at the Florence and George Wise Observatory, operated by the Tel-Aviv University, Israel and at Piszkésteto, the mountain station of Konkoly Observatory of the Hungarian Academy of Science, Hungary.

This publication makes use of data products from the Two Micron All Sky Survey, a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center / California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation.

The Digitized Sky Survey was produced at the Space Telescope Science Institute under US Government grant NAG W-2166. The images of these surveys are based on photographic data obtained using the Oschin Schmidt Telescope on Palomar Mountain and the UK Schmidt Telescope. The plates were processed into the present compressed digital form with the permission of these institutions. Title: High-Precision Limb-Darkening Measurement of a K3 Giant Using Microlensing Authors: Fields, Dale L.; Albrow, M. D.; An, J.; Beaulieu, J. -P.; Caldwell, J. A. R.; DePoy, D. L.; Dominik, M.; Gaudi, B. S.; Gould, A.; Greenhill, J.; Hill, K.; Jørgensen, U. G.; Kane, S.; Martin, R.; Menzies, J.; Pogge, R. W.; Pollard, K. R.; Sackett, P. D.; Sahu, K. C.; Vermaak, P.; Watson, R.; Williams, A.; Glicenstein, J. -F.; Hauschildt, P. H.; PLANET Collaboration Bibcode: 2003ApJ...596.1305F Altcode: 2003astro.ph..3638F We obtain high-precision limb-darkening measurements in five bands (V, VE, IE, I, and H) for the K3 III (Teff=4200 K, [Fe/H]=+0.3, logg=2.3) source of the Galactic bulge microlensing event EROS BLG-2000-5. These measurements are inconsistent with the predictions of atmospheric models at higher than 10 σ. While the disagreement is present in all bands, it is most apparent in I, IE, and VE, in part because the data are better and in part because the intrinsic disagreement is stronger. We find that when limb-darkening profiles are normalized to have unit total flux, the I-band models for a broad range of temperatures all cross each other at a common point. The solar profile also passes through this point. However, the profile as measured by microlensing does not. We hypothesize that the models have incorporated some aspect of solar physics that is not shared by giant atmospheres. Title: Atmospheric Models of Red Giants with Massive-Scale Non-Local Thermodynamic Equilibrium Authors: Short, C. I.; Hauschildt, P. H. Bibcode: 2003ApJ...596..501S Altcode: 2003astro.ph..6531S We present plane-parallel and spherical LTE and non-LTE (NLTE) atmospheric models of a variety of stellar parameters of the red giant star Arcturus (α Boo, HD 124897, HR 5340) and study their ability to fit the measured absolute flux distribution. Our NLTE models include tens of thousands of the strongest lines in NLTE, and we investigate separately the effects of treating the light metals and the Fe group elements Fe and Ti in NLTE. We find that the NLTE effects of Fe group elements on the model structure and Fλ distribution are much more important than the NLTE effects of all the light metals combined, and serve to substantially increase the violet and near-UV Fλ levels as a result of NLTE Fe overionization. Both the LTE and NLTE models predict significantly more flux in the blue and UV bands than is observed. We find that within the moderately metal-poor metallicity range, the effect of NLTE on the overall UV flux level decreases with decreasing metallicity. These results suggest that there may still be important UV opacity missing from the models. We find that models of solar metallicity giants of spectral type similar to that of Arcturus fit well the observed flux distributions of those stars from the red to the near-UV band. This suggests that the blue and near-UV flux discrepancy is metallicity dependent, increasing with decreasing metallicity. Title: A Chandra Low Energy Transmission Grating Spectrometer Observation of V4743 Sagittarii: A Supersoft X-Ray Source and a Violently Variable Light Curve Authors: Ness, J. -U.; Starrfield, S.; Burwitz, V.; Wichmann, R.; Hauschildt, P.; Drake, J. J.; Wagner, R. M.; Bond, H. E.; Krautter, J.; Orio, M.; Hernanz, M.; Gehrz, R. D.; Woodward, C. E.; Butt, Y.; Mukai, K.; Balman, S.; Truran, J. W. Bibcode: 2003ApJ...594L.127N Altcode: V4743 Sagittarii (Nova Sgr 2002 No. 3) was discovered on 2002 September 20. We obtained a 5 ks ACIS-S spectrum in 2002 November and found that the nova was faint in X-rays. We then obtained a 25 ks Chandra Low Energy Transmission Grating Spectrometer (LETGS) observation on 2003 March 19. By this time, it had evolved into the supersoft X-ray phase exhibiting a continuous spectrum with deep absorption features. The light curve from the observation showed large-amplitude oscillations with a period of 1325 s (22 minutes) followed by a decline in the total count rate after ~13 ks of observations. The count rate dropped from ~40 counts s-1 to practically zero within ~6 ks and stayed low for the rest of the observation (~6 ks). The spectral hardness ratio changed from maxima to minima in correlation with the oscillations and then became significantly softer during the decay. Strong H-like and He-like lines of oxygen, nitrogen, and carbon were found in absorption during the bright phase, indicating temperatures between 1 and 2 MK, but they were shifted in wavelength corresponding to a Doppler velocity of -2400 km s-1. The spectrum obtained after the decline in count rate showed emission lines of C VI, N VI, and N VII, suggesting that we were seeing expanding gas ejected during the outburst, probably originating from CNO-cycled material. An XMM-Newton Target of Opportunity observation, obtained on 2002 April 4 and a later LETGS observation from 2003 July 18 also showed oscillations, but with smaller amplitudes. Title: Analysis of the Flux and Polarization Spectra of the Type Ia Supernova SN 2001el: Exploring the Geometry of the High-Velocity Ejecta Authors: Kasen, Daniel; Nugent, Peter; Wang, Lifan; Howell, D. A.; Wheeler, J. Craig; Höflich, Peter; Baade, Dietrich; Baron, E.; Hauschildt, P. H. Bibcode: 2003ApJ...593..788K Altcode: 2003astro.ph..1312K SN 2001el is the first normal Type Ia supernova to show a strong, intrinsic polarization signal. In addition, during the epochs prior to maximum light, the Ca II IR triplet absorption is seen distinctly and separately at both normal photospheric velocities and at very high velocities. The high-velocity triplet absorption is highly polarized, with a different polarization angle than the rest of the spectrum. The unique observation allows us to construct a relatively detailed picture of the layered geometrical structure of the supernova ejecta: in our interpretation, the ejecta layers near the photosphere (v~10,000 km s-1) obey a nearly axial symmetry, while a detached, high-velocity structure (v~18,000-25,000 km s-1) with high Ca II line opacity deviates from the photospheric axisymmetry. By partially obscuring the underlying photosphere, the high-velocity structure causes a more incomplete cancellation of the polarization of the photospheric light and so gives rise to the polarization peak and rotated polarization angle of the high-velocity IR triplet feature. In an effort to constrain the ejecta geometry, we develop a technique for calculating three-dimensional synthetic polarization spectra and use it to generate polarization profiles for several parameterized configurations. In particular, we examine the case in which the inner ejecta layers are ellipsoidal and the outer, high-velocity structure is one of four possibilities: a spherical shell, an ellipsoidal shell, a clumped shell, or a toroid. The synthetic spectra rule out the spherical shell model, disfavor a toroid, and find a best fit with the clumped shell. We show further that different geometries can be more clearly discriminated if observations are obtained from several different lines of sight. Thus, assuming that the high-velocity structure observed for SN 2001el is a consistent feature of at least a known subset of Type Ia supernovae, future observations and analyses such as these may allow one to put strong constraints on the ejecta geometry and hence on supernova progenitors and explosion mechanisms. Title: Spectral Types of Planetary Host Star Candidates: New Transiting Planets? Authors: Dreizler, S.; Rauch, T.; Hauschildt, P.; Schuh, S. L.; Kley, W.; Werner, K. Bibcode: 2003ANS...324....2D Altcode: 2003ANS...324..A03D; 2003ANS...324b...2D No abstract at ADS Title: News of Effective Temperatures of L Dwarfs Authors: Schweitzer, Andreas; Gizis, John E.; Allard, France; Hauschildt, Peter H. Bibcode: 2003IAUS..211..403S Altcode: In this work we report recent spectral analyses of L dwarfs and our success in measuring Teff and log(g). Using dust filled atmospheres for early L dwarfs and rained out atmospheres for late L dwarfs we could derive Teff of 1400 to 2000 K for L8 to M9.5 dwarfs respectively. We also give an outlook what we can achieve with future models that are improving the fits to intermediate L dwarfs and IR spectra. Title: Evolutionary models for low mass stars and brown dwarfs at young ages Authors: Baraffe, Isabelle; Chabrier, Gilles; Allard, France; Hauschildt, Peter Bibcode: 2003IAUS..211...41B Altcode: We analyse evolutionary tracks at young ages for low mass stars with masses m <e 1.4 M⊙ and brown dwarfs

down to one mass of Jupiter. We analyse current theoretical uncertainties due to initial conditions. Simple tests on initial conditions show the high uncertainties of models at ages ∼<= 1 Myr. Title: Model Atmospheres and Spectra: The Role of Dust Authors: Allard, France; Guillot, Tristan; Ludwig, Hans-Günter; Hauschildt, Peter H.; Schweitzer, Andreas; Alexander, David R.; Ferguson, Jason W. Bibcode: 2003IAUS..211..325A Altcode: Brown dwarf atmospheres form molecules, then high temperature condensates (corundum, titanates, silicates, and iron compounds), and then low temperature condensates (ices) as they cool down over time. These produce large opacities which govern entirely their spectral energy distribution. Just as it is important to know molecular opacities (TiO, H_2O, CH_4, etc.) with accuracy, it is imperative to understand the interplay of processes (e.g. condensation, sedimentation, coagulation, convection) that determines the radial and size distribution of grains. Limiting case models have shown that young, hot brown (L) dwarfs form dust mostly in equilibrium, while at much cooler stages (late T dwarfs) all high temperature condensates have sedimented out of their photospheres. But this process is gradual and all intermediate classes of brown dwarfs can partly be understood in terms of partial sedimentation of dust. With new models accounting for these processes, we describe the effects they may have upon brown dwarf spectral properties. Title: Influence of chemi-ionization and chemi-recombination processes on the population of hydrogen Rydberg states in atmospheres of late type dwarfs Authors: Mihajlov, A. A.; Jevremović, D.; Hauschildt, P.; Dimitrijević, M. S.; Ignjatović, Lj. M.; Alard, F. Bibcode: 2003A&A...403..787M Altcode: We study the influence of a group of chemi-ionization and chemi-recombination processes on the populations of higher states of hydrogen in the layers of a stellar atmosphere. The group of processes includes ionization: H*(n)+H(1s)==> H2++e , H*(n)+H(1s)==> H(1s)+H++e, and inverse recombination: H2++e==> H*(n)+H(1s), H(1s)+H++e==> H*(n)+H(1s), where H*(n) is the hydrogen atom in a state with the principal quantum number n >> 1, and H2+ is the hydrogen molecular ion in a weakly bound rho-vibrational state of the ground state. These processes have been treated within the framework of the semi-classical approximation, developed in several previous papers, and have been included in the general stellar atmosphere code PHOENIX. We present results for an M dwarf atmosphere with Teff = 3800 K and find that the inclusion of chemi-ionization and chemi-recombination processes is significant in the low temperature parts of the atmosphere. Title: Methane and the Spectra of T Dwarfs Authors: Homeier, Derek; Hauschildt, Peter H.; Allard, France Bibcode: 2003IAUS..211..419H Altcode: 2002astro.ph..9171H We have updated our PHOENIX model atmospheres and theoretical spectra for ultracool dwarfs with new opacity data for methane based on line strength predictions with the STDS software. By extending the line list to rotational levels of J = 40 we can significantly improve the shape of the near-IR absorption features of CH_4, and in addition find an enhanced blanketing effect, resulting in up to 50% more flux emerging in the J band than seen in previous models, which may thus contribute to the brightening in J and blue IR colors observed in T dwarfs. Title: OGLE-TR-3: A possible new transiting planet Authors: Dreizler, S.; Hauschildt, P. H.; Kley, W.; Rauch, T.; Schuh, S. L.; Werner, K.; Wolff, B. Bibcode: 2003A&A...402..791D Altcode: 2003astro.ph..3183D Recently, 59 low-luminosity object transits were reported from the Optical Gravitational Lensing Experiment (OGLE). Our follow-up low-resolution spectroscopy of 16 candidates provided two objects, OGLE-TR-3 and OGLE-TR-10, which have companions with radii compatible with those of gas-giant planets. Further high-resolution spectroscopy revealed a very low velocity variation (<500 m s-1) of the host star OGLE-TR-3 which may be caused by its unseen companion. An analysis of the radial velocity and light curve results in M<2.5 MJup, R<1.6 RJup, and an orbital separation of about 5 Rsun, which makes it the planet with the shortest period known. This allows to identify the low-luminosity companion of OGLE-TR-3 as a possible new gas-giant planet. If confirmed, this makes OGLE-TR-3 together with OGLE-TR-56 the first extrasolar planets detected via their transit light curves.

Based on observations collected at the European Southern Observatory, Paranal, Chile (ESO Programme 269.C-5034). Title: Evolutionary models for cool brown dwarfs and extrasolar giant planets. The case of HD 209458 Authors: Baraffe, I.; Chabrier, G.; Barman, T. S.; Allard, F.; Hauschildt, P. H. Bibcode: 2003A&A...402..701B Altcode: 2003astro.ph..2293B We present evolutionary models for cool brown dwarfs and extra-solar giant planets. The models reproduce the main trends of observed methane dwarfs in near-IR color-magnitude diagrams. We also present evolutionary models for irradiated planets, coupling for the first time irradiated atmosphere profiles and inner structures. We focus on HD 209458-like systems and show that irradiation effects can substantially affect the radius of sub-jovian mass giant planets. Irradiation effects, however, cannot alone explain the large observed radius of HD 209458b. Adopting assumptions which optimise irradiation effects and taking into account the extension of the outer atmospheric layers, we still find ~ 20% discrepancy between observed and theoretical radii. An extra source of energy seems to be required to explain the observed value of the first transit planet. Title: Spectrum Modeling of Distorted Stellar Atmospheres and the X-ray Binary V4641 Sgr Authors: Lentz, E. J.; Orosz, J. A.; Hauschildt, P. H. Bibcode: 2003AAS...202.3202L Altcode: 2003BAAS...35..743L We have developed a method to compute synthetic spectra for stars which have rotationally or tidally distorted atmospheres which vary in effective temperature and gravity over their surfaces. The spectra are composited from the specific intensities from high resolution, spherical, non-LTE model atmospheres for each segment of the surface. We consider the effects of tidal distortion on the spectrum of the X-ray binary V4641 Sgr (SAX J1819.3-2525) by comparing the composite model spectrum to portions of an Echelle spectrum of the star. The parameters for the component model atmospheres segments, including effective temperature and gravity and the projected area and velocity, are taken from a model (Orosz et al. 2003) of the star built using broadband filter specific intensities from the same atmosphere models. Title: Spectral Analysis of Ultracool Dwarfs Authors: Homeier, D.; Hauschildt, P. H.; Allard, F. Bibcode: 2003AAS...202.3201H Altcode: 2003BAAS...35..743H Improvements of opacity data for the molecular bands governing the spectral energy distribution of the coolest brown dwarfs have brought about major advances to the modelling of substellar atmospheres. At this point uncertainties in the lines strengths for the most important absorbers in the infrared, H2O and CH4, are becoming secondary to uncertainties in the temperature structure, e. g. related to the distribution of dust, for objects in the T dwarf temperature range. Theoretical spectra generated with these models can set constraints on the temperatures and gravities of ultracool dwarfs independent from age determinations and cooling models. Thus, a quantitative analysis of infrared spectra can serve as a test for evolutionary models and help to identify brown dwarfs in the planetary mass range (PMOs). We present the latest PHOENIX models for effective temperatures 700 K< ∼ T eff< ∼1400 K, discussing the effects of metallicity and gravity on the near infrared absorption bands. The accuracy currently attainable in determining these parameters from low resolution spectral fits or infrared colors alone, and using the additional information available from absolute-flux calibrated spectra, is assessed. Title: Detectability of Mixed Unburnt C+O in Type Ia Supernova Spectra Authors: Baron, E.; Lentz, Eric J.; Hauschildt, Peter H. Bibcode: 2003ApJ...588L..29B Altcode: 2003astro.ph..3627B Motivated by recent three-dimensional calculations of the explosion of Type Ia supernovae via a pure deflagration, we calculate the observed spectra at 15-25 days past maximum light of a parameterized model that has a considerable fraction of unburnt C+O in the central regions. Rather than attempting a self-consistent three-dimensional calculation, which is beyond the scope of current computer codes, we modify the composition structure of the one-dimensional deflagration model W7. In our exploratory parameterized calculations, we find that a central concentration of C+O is not ruled out by observations for the epochs we study. We briefly examine whether nebular phase spectra could be incompatible with observations. Title: The influence of chemical ionization and chemical recombination processes on the plasma parameters in low-temperature layers of stellar atmospheres Authors: Mihajlov, A. A.; Jevremovi', D.; Ignjatovi', M. Lj.; Hauschildt, P.; Dimitrijevi', S. M. Bibcode: 2003A&AT...22..513M Altcode: Available from http://taylorandfrancis.metapress.com/openurl.asp?genre=article&issn=1055-6796&volume=22&issue=4&spage=513 Title: Determination of Primordial Metallicity and Mixing in the Type II-P Supernova 1993W Authors: Baron, E.; Nugent, Peter E.; Branch, David; Hauschildt, Peter H.; Turatto, M.; Cappellaro, E. Bibcode: 2003ApJ...586.1199B Altcode: 2002astro.ph.12071B We present the results of a large grid of synthetic spectra and compare them to early spectroscopic observations of SN 1993W. This supernova was discovered close to its explosion date and, at a recession velocity of 5400 km s-1, is located in the Hubble flow. We focus here on two early spectra that were obtained approximately 5 and 9 days after explosion. We parameterize the outer supernova envelope as a power-law density profile in homologous expansion. In order to extract information on the value of the parameters, a large number of models was required. We show that very early spectra combined with detailed models can provide constraints on the value of the power-law index, the ratio of hydrogen to helium in the surface of the progenitor, the progenitor metallicity, and the amount of radioactive nickel mixed into the outer envelope of the supernova. The spectral fits reproduce the observed spectra exceedingly well. The spectral results combined with the early photometry predict that the explosion date was 4.7+/-0.7 days before the first spectrum was obtained. The ability to obtain the metallicity from early spectra make SNe II-P attractive probes of chemical evolution in the universe, and by showing that we have the ability to pin down the parameters of the progenitor and mixing during the supernova explosion, it is likely to make SNe II-P useful cosmological distance indicators which are at the same time complementary to SNe Ia.

Partially based on observations performed at ESO La Silla. Title: The Early Ultraviolet Evolution of the ONeMg Nova V382 Velorum 1999 Authors: Shore, Steven N.; Schwarz, Greg; Bond, Howard E.; Downes, Ronald A.; Starrfield, Sumner; Evans, A.; Gehrz, Robert D.; Hauschildt, Peter H.; Krautter, Joachim; Woodward, Charles E. Bibcode: 2003AJ....125.1507S Altcode: 2003astro.ph..1415S We present a multiwavelength study of the ONeMg Galactic nova V382 Velorum 1999 using HST/STIS and FUSE ultraviolet spectra and comparisons with published ground-based optical spectra. We find a close match to the basic phenomenology of another well-studied ONeMg nova, V1974 Cygni (Nova Cyg 1992), in particular, to the spectral development through the start of the nebular phase. Following an ``iron curtain'' phase, the nova proceeded through a stage of P Cygni line profiles on all important resonance lines, as in many ONeMg novae and unlike the CO class. Emergent emission lines displayed considerable structure, as seen in V1974 Cyg, indicating fragmentation of the ejecta at the earliest stages of the outburst. Analysis and modeling of our ultraviolet spectra suggest that (4-5)×10-4Msolar of material was ejected and that the distance to the nova is ~=2.5 kpc. Relative to solar values, we find the following abundances: He=1.0, C=0.6+/-0.3, N=17+/-4, O=3.4+/-0.3, Ne=17+/-3, Mg=2.6+/-0.1, Al=21+/-2, and Si=0.5+/-0.3. Finally, we briefly draw comparisons with Nova LMC 2000, another ONeMg nova, for which similar data were obtained with HST and FUSE.

Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract 5-26555. These observations are associated with proposals for programs GO 8540 and GO 8671. Also based on observations made with the NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer. FUSE is operated for NASA by the Johns Hopkins University under NASA contract NAS 5-32985. Title: Testing spherical, expanding, line-blanketed model atmospheres of giant stars with interferometry Authors: Aufdenberg, Jason P.; Hauschildt, Peter H. Bibcode: 2003SPIE.4838..193A Altcode: We show examples of PHOENIX stellar atmosphere model simulations for data obtained by long-baseline optical interferometers. A single spherical, hydrostatic model atmosphere for the M-type giant star γ Sagittae is shown to be in good agreement with interferometric, spectrophotometric, and high-dispersion spectroscopic data sets. In particular we show that the interferometric triple products and wavelength-dependent uniform disk diameters measured by the Navy Prototype Optical Interferometer (NPOI) are well matched by our model. With expanding atmosphere models for the A-type supergiant α Cygni we predict that the center-to-limb intensity profile is sensitive to the mass-loss rate of its stellar wind. For one possible NPOI configuration we show the sensitivity of the squared visibility amplitudes to the model mass-loss rate at spatial frequencies beyond the first null. The importance of hot star photospheric interferometry is discussed. Title: The Molecular Continuum Opacity of 24MgH in Cool Stellar Atmospheres Authors: Weck, P. F.; Schweitzer, A.; Stancil, P. C.; Hauschildt, P. H.; Kirby, K. Bibcode: 2003ApJ...584..459W Altcode: 2002astro.ph..7042W The opacity due to photodissociation of 24MgH in the atmospheres of cool stars is investigated. The lowest two electronic transitions A2Π<--X2Σ+ and B'2Σ+<-- X2Σ+ are considered, where the cross sections for the latter were published previously (Weck, Stancil, & Kirby) and the former are presented in this work. Model atmospheres calculated with the PHOENIX code are used to investigate the effect of the photodissociation opacity on spectra of cool stars. The A2Π<--X2Σ+ photodissociation cross sections are obtained using a combination of ab initio and experimentally derived potential curves and dipole transition moments. Partial cross sections have been evaluated over the accessible wavelength range 1770- 4560 Å for all rotational transitions from the vibrational levels v''=0-11. Assuming a Boltzmann distribution of the rovibrational levels of the X2Σ+ state, LTE photodissociation cross sections are presented for temperatures between 1000 and 5000 K. Shape resonances, arising from rotational predissociation of quasi-bound levels of the A2Π state near threshold, characterize the LTE photodissociation cross sections. A sum rule is proposed as a check on the accuracy of the photodissociation calculations. Title: The Extraordinary X-ray Light Curve of the Classical Nova V1494 Aquilae (1999 No. 2) in Outburst: The Discovery of Pulsations and a ``Burst'' Authors: Drake, Jeremy J.; Wagner, R. Mark; Starrfield, Sumner; Butt, Yousaf; Krautter, Joachim; Bond, H. E.; Della Valle, M.; Gehrz, R. D.; Woodward, Charles E.; Evans, A.; Orio, M.; Hauschildt, P.; Hernanz, M.; Mukai, K.; Truran, J. W. Bibcode: 2003ApJ...584..448D Altcode: 2002astro.ph.10072D V1494 Aql (Nova Aql 1999 No. 2) was discovered on 1999 December 2. We obtained Chandra ACIS-I spectra on 2000 April 15 and June 7 which appear to show only emission lines. Our third observation, on August 6, showed that its spectrum had evolved to that characteristic of a Super Soft X-ray Source. We then obtained Chandra LETG+HRC-S spectra on September 28 (8 ks) and October 1 (17 ks). We analyzed the X-ray light curve of our grating observations and found both a short timescale ``burst'' and oscillations. Neither of these phenomena has previously been seen in the light curve of a nova in outburst. The ``burst'' was a factor of ~10 rise in X-ray counts near the middle of the second observation, and which lasted about 1000 s; it exhibited at least two peaks, in addition to other structure. Our time series analysis of the combined 25 ks observation shows a peak at ~2500 s which is present in independent analyses of both the zeroth-order image and the dispersed spectrum and is not present in similar analyses of grating data for HZ 43 and Sirius B. Further analyses of the V1494 Aql data find other periods present which implies that we are observing nonradial g+ modes from the pulsating, rekindled white dwarf. Title: Brown Dwarfs and Extrasolar Planets Authors: Allard, F.; Baraffe, I.; Chabrier, G.; Barman, T. S.; Hauschildt, P. H. Bibcode: 2003ASPC..294..483A Altcode: Brown dwarfs bridge the gap between the stellar and planetary mass regimes and, as they cool, their atmospheres evolve towards conditions most commonly associated with planets. Despite differences (e.g., formation and proximity to a stellar companion), it is interesting to know just how much of the knowledge gained by studying brown dwarfs can be directly applied when predicting the thermal and spectral properties of extrasolar planets. This paper briefly summarizes the characteristics of brown dwarfs and extrasolar giant planet atmospheres, and discusses the significance of irradiation on the evolution of extrasolar planets. Title: Physics and Chemistry of Molecules and Dust at Low Temperatures Authors: Ferguson, J. W.; Alexander, D. R.; Tamanai, A.; Bodnarik, J.; Hauschildt, P. H.; Allard, F. Bibcode: 2003ASPC..294..539F Altcode: The issues associated with computing the opacity of material at low temperatures are described. The computation of the opacity requires both a thorough knowledge of the chemical state of the material (species populations) and the absorption/scattering behavior of those species. At low temperatures, both of these issues become very complex. For temperatures below 1800K, some materials begin to precipitate out of the gas phase as small solid particles. Because these small grains are very efficient at absorbing and scattering light, they dominate the opacity whenever they exist. The abundance of important molecular and solid absorbers as a function of temperature, pressure, and the chemical composition will be explored. The effects of dust on the computation of stellar atmospheres will be discussed. Title: A New Grid of Atmospheres for Early-Type Stars Authors: Lentz, E. J.; Hauschildt, P. H.; Aufdenberg, J. P.; Baron, E. Bibcode: 2003IAUS..210P.B13L Altcode: No abstract at ADS Title: Model atmospheres of massive zero-metallicity stars Authors: Lentz, Eric J.; Hauschildt, Peter H.; Aufdenberg, Jason P.; Baron, Ed Bibcode: 2003IAUS..212..416L Altcode: We have calculated detailed, fully non-LTE, model atomospheres for massive zero-metal stars. We find the atmospheres of massive primordial stars become unbound due to radiation pressure on lines and continua over a much larger fraction of their evolution than previously expected. Title: Gravity & Mass Measurement in Young Substellar Objects Authors: Mohanty, Subhanjoy; Basri, Gibor; Jayawardhana, Ray; Allard, France; Hauschildt, Peter; Ardila, David Bibcode: 2003IAUJD..20E..29M Altcode: We present an analysis of optical high-resolution spectra of very young ultra-low mass stellar and substellar objects in Upper Scorpius and Taurus. We show that a multi-feature spectral analysis combined with the latest synthetic spectra can yield accurate surface gravities (+/- 0.25 dex) and effective temperatures (+/- 50K). This represents the most stringent observational constraint so far on gravity in young ultra-low mass objects. Combining our gravity and temperature results with observed and synthetic photometry and known cluster distance we also derive masses and radii for our objects. These are the first mass and radii measurements in young ultra-low mass objects that are INDEPENDENT of theoretical evolutionary tracks. We find that two of our faintest targets have planetary mass (~ 6 Jupiters). We also find that significant discrepancies exist between our results and the theoretical tracks for the coolest objects: our derived radii are substantially larger than predicted. Recent studies of M dwarf eclipsing binaries also show the theoretical radii to be underestimations. We conclude that high-resolution spectroscopy is invaluable for guiding the evolutionary modeling of young low-mass stars and brown dwarfs. Title: Spherical and Expanding Model Atmosphere Predictions for Interferometry Authors: Aufdenberg, J. P.; Hauschildt, P. H.; Baron, E. Bibcode: 2003ASPC..288..239A Altcode: 2003sam..conf..239A Direct interferometric measurement of stellar limb-darkening, unambiguously revealed by the shape of the visibility curve a beyond the first null, is presently available for a only a few stars. The vast majority of present day stellar diameter measurements require a theoretical limb-darkening correction to recover the ``true'' diameter and to interpret multi-wavelength uniform disk results. Compilations of theoretical, wavelength dependent, center-to-limb intensity profiles needed for such corrections are almost exclusively derived from plane-parallel model atmospheres and are therefore generally inappropriate for modeling the atmospheres of giant and supergiant stars. In our theoretical studies of the angular sizes of both hot and cool supergiant stars with the general-purpose stellar atmosphere code PHOENIX, we have found significant and testable differences between spherical and plane-parallel model predictions. We show examples of these differences in our studies of 1) the interferometric diameter of the A-type supergiant α Cygni and 2) interferometric diameter ratios at wavelengths inside and adjacent to the 712 nm TiO band for normal M-type giants and supergiants. Title: Parallelization Strategies for ALI Radiative Transfer in Moving Media Authors: Baron, E.; Hauschildt, P. H.; Lowenthal, D. Bibcode: 2003ASPC..288..385B Altcode: 2002astro.ph..7043B; 2003sam..conf..385B We describe the method we have used to parallelize our spherically symmetric special relativistic short characteristics general radiative transfer code PHOENIX. We describe some possible parallelization strategies and show why they would be inefficient. We discuss the multiple parallelization strategy techniques that we have adopted. We briefly discuss generalizing these strategies to full 3-D (spatial) radiation transfer codes. Title: Molecular Absorbers in the Atmospheres of Methane Dwarfs Authors: Homeier, D.; Allard, F.; Hauschildt, P. H.; Boudon, V. Bibcode: 2003IAUS..210P.E56H Altcode: No abstract at ADS Title: Time-Dependent Moment Equation Method for Supernova Lightcurves Authors: Lentz, E. J.; Baron, E.; Hauschildt, P. H. Bibcode: 2003ASPC..288..275L Altcode: 2003sam..conf..275L We have developed a time-dependent solution to the moment equations to solve for the temperature structure and radiation field of objects where the temperature and structure of the object change slowly relative to the radiation field, like supernovae. We have restored the time derivative terms to the transport equation and modified our method for the formal solution and approximate lambda operator. Title: Stellar atmospheres and synthetic spectra for GAIA Authors: Hauschildt, P. H.; Allard, F.; Baron, E.; Aufdenberg, J.; Schweitzer, A. Bibcode: 2003ASPC..298..179H Altcode: 2003gsst.conf..179H No abstract at ADS Title: The Molecular Line Opacity of MgH in Cool Stellar Atmospheres Authors: Weck, P. F.; Schweitzer, A.; Stancil, P. C.; Hauschildt, P. H.; Kirby, K. Bibcode: 2003ApJ...582.1059W Altcode: 2002astro.ph..6219W A new, complete, theoretical rotational and vibrational line list for the A2Π<--X2Σ+ electronic transition in MgH is presented. The list includes transition energies and oscillator strengths for all possible allowed transitions and was computed using the best available theoretical potential energies and dipole transition moment function with the former adjusted to account for experimental data. The A<--X line list as well as new line lists for the B'2Σ+<-- X2Σ+ and the X2Σ+<--X2Σ+ (pure rovibrational) transitions were included in comprehensive stellar atmosphere models for M, L, and T dwarfs and solar-type stars. The resulting spectra, when compared to models lacking MgH, show that MgH provides significant opacity in the visible between 4400 and 5600 Å. Further comparison of the spectra obtained with the current line list to spectra obtained using the line list constructed by Kurucz show that the Kurucz list significantly overestimates the opacity due to MgH, particularly for the bands near 5150 and 4800 Å, with the discrepancy increasing with decreasing effective temperature. Title: Temperature Correction Methods Authors: Hauschildt, P. H.; Barman, T. S.; Baron, E.; Allard, F. Bibcode: 2003ASPC..288..227H Altcode: 2003sam..conf..227H No abstract at ADS Title: The contrast of magnetic elements across the solar spectrum Authors: Steiner, O.; Hauschildt, P. H.; Bruls, J. Bibcode: 2003AN....324..398S Altcode: No abstract at ADS Title: Model Atmosphere Analyses of Post-Common Envelope Stars Authors: Rushton, M. T.; Smalley, B.; Ogley, R. N.; Wood, J. H.; Hauschildt, P.; Bleach, J. N. Bibcode: 2003IAUS..210P.E33R Altcode: 2002astro.ph..8291R Understanding post-common-envelope evolution is important in the studies of close-binary systems. The majority of all interacting binaries with a compact object in their system (e.g. cataclysmic variables, X-ray binaries) are thought to have passed through a common-envelope (CE) phase. Current models of interacting binaries all assume, as a starting point, that there is no significant modification of the secondary star compared with a normal star of similar spectral type. The extent to which the CE significantly alters the composition of the secondary star has yet to be determined. We are studying the M-type secondary in the pre-CV system EG UMa, in order to determine its atmospheric parameters by comparison with synthetic spectra generated using PHOENIX. Absorption lines due to several elements have been used in investigating the stellar parameters of effective temperature, gravity and over elemental abundance. In addition, we are searching for anomalies due to s-process elements (such as Ba, Sr, Rb, Y), which may have been deposited in the atmosphere during the CE stage, and prove that CE evolution has occurred. EG UMa displays strong YO absorption bands, which are normally associated with giants and S stars. These bands may have been formed as a result of an Y-abundance enhancement introduced by the CE, which would be consistent with the observed possible Rb and Sr enrichment. Title: Low Temperature Dust Opacity Authors: Alexander, David R.; Ferguson, Jason W.; Allard, France; Hauschildt, Peter H. Bibcode: 2003asdu.confE.126A Altcode: As temperatures below approximately 1800 K (depending upon the density and composition) are encountered in an astrophysical environment, dust grains become important sources of opacity. Because these small grains are very efficient absorbers and scatterers of light, they dominate the opacity wherever they exist. The thermodynamic and optical properties of these materials will be explored, along with deficiencies in the available laboratory data. Recent results show that even with relatively low abundances, grains such as Al2O3 and CaTiO3 can have a dramatic impact on the structure of stellar, sub-stellar and planetary atmospheres, and on star and planet formation. The effect of dust opacity for temperatures down to 300 K will be discussed. The potential significance of non-equilibrium effects will also be discussed. Title: Methane Opacities in T Dwarf Atmospheres Authors: Homeier, D.; Hauschildt, P. H.; Allard, F. Bibcode: 2003ASPC..288..357H Altcode: 2002astro.ph..9163H; 2003sam..conf..357H We present the current status of PHOENIX model atmospheres for dwarfs of spectral type T, typical for older field brown dwarfs and low-mass brown dwarfs. In comparison to warmer L dwarf atmosphers, the spectral features of these objects can largely be reproduced by treating the influence of dust in the limiting case of complete settling, i. e. neglecting the dust opacity (Cond models). One major challenge in modelling cool brown dwarf atmospheres is the correct treatment of the molecular lines of H2O and CH4. These are the dominant opacity sources in the IR and responsible for the very blue colours of T dwarfs in the near infrared.

Reliable opacity data for these absorbers are thus mandatory for a correct determination of the temperature structure as well as for detailed modelling of the characteristic absorption features in the H and K bands, which are the defining criteria of spectral class T.

Line lists extracted from low temperature atmospheric databases such as HITRAN and GEISA are generally strongly limited to lower-state energies. To overcome these limits, a new list of line-by-line predictions for the methane opacities from the four lowest vibrational states has been computed with the Spherical Top Database System (STDS).

Improvements of these line lists have been achieved thanks to recent successes in the experimental calibration of the molecular parameter describing the vibrational and rotational bands in the spherical top model. This allowed extrapolations to higher rotational states than previously possible. As a result our opacity sampling models now allow a much more complete reproduction of the strong features occuring in the temperature regimes of brown dwarf atmospheres.

A more diffuse background opacity remains due to the extremely high line density from higher vibrational states, which at this time can be described only partly by statistical models. Title: NLTE Calculations of a Na D Doublet in the Atmosphere of the Transiting Planet HD209458b Authors: Barman, T. S.; Hauschildt, P. H.; Schweitzer, A.; Stancil, P. C.; Baron, E.; Allard, F. Bibcode: 2003ASPC..294..467B Altcode: The observation of sodium absorption in the atmosphere of HD209458b, currently the only EGP known to transit its parent star, is the first direct evidence of an EGP atmosphere. We explore the possibility that neutral sodium is not in local thermodynamic equilibrium (LTE) in the outer atmosphere of irradiated EGPs and that the sodium concentration may be underestimated by models that make the LTE assumption. Our results indicate that it may not be necessary to invoke excessive photoionization, low metallicity, or even high altitude clouds to explain the observations. Title: Radiation and Chemi-Ionization/Recombination Processes in Atom-Atom and Ion-Atom Collisions in the Modeling of Low-Temperature Stellar Atmospheres Authors: Mihajlov, A. A.; Ignjatovic, Lj.; Dimitrijevic, M. S.; Jevremovic, D.; Hauschildt, P. Bibcode: 2003IAUS..210P..B2M Altcode: No abstract at ADS Title: Putting Radiation Hydrodynamics into a Detailed Model Atmosphere Calculation Authors: Schweitzer, A.; Hauschildt, P. H. Bibcode: 2003ASPC..288..541S Altcode: 2003sam..conf..541S Non-grey hydrodynamics is still clearly not practicle. However, it is possible to combine a grey radiation hydrodynamics code and a non-grey model atmosphere code to obtain more realistic results. In this presentation we describe our current work in combining the atmosphere code PHOENIX and the radiation hydrodynaimcs code TITAN. We use PHOENIX to tabulate the material functions like the equation of state and the mean opacities. For example, TITAN can then calculate a shock propagating through an atmosphere for which the initial structure is provided by PHOENIX. The resulting atmospheric structures will then be fed back into PHOENIX to calculate high resolution spectra including NLTE treatment. Our goal is to apply this method to obtain high quality spectra of Mira variables as a function of phase. Title: Highlights of Stellar Modeling with PHOENIX Authors: Baron, E.; Hauschildt, P. H.; Allard, F.; Lentz, E. J.; Aufdenberg, J.; Schweitzer, A.; Barman, T. Bibcode: 2003IAUS..210...19B Altcode: 2002astro.ph..9052B We briefly describe the current version of the PHOENIX code. We then present some illustrative results from the modeling of Type Ia and Type II supernovae, hot stars, and irradiated giant planets. Good fits to observations can be obtained, when account is taken for spherically symmetric, line-blanketed, static or expanding atmospheres. Title: Surface Gravity & Mass in Young Brown Dwarfs and Planemos Authors: Mohanty, Subhanjoy; Jayawardhana, Ray; Basri, Gibor; Allard, France; Hauschildt, Peter; Ardila, David Bibcode: 2003ASSL..299..259M Altcode: 2003oils.conf..259M No abstract at ADS Title: Opacities of Molecules and Dust Authors: Alexander, D. R.; Ferguson, J. W.; Tamanai, A.; Bodnarik, J.; Allard, F.; Hauschildt, P. H. Bibcode: 2003ASPC..288..289A Altcode: 2003sam..conf..289A As progressively lower temperatures are encountered in a stellar atmosphere, first molecules and finally dust grains become important sources of opacity. The abundance of important molecular and solid absorbers depends upon temperature, pressure, and the chemical composition in complex ways which require detailed equation of state calculations. Molecular spectra, which usually contain thousands or millions of spectral lines, are usually treated statistically in the opacity sampling method. Because of the size of modern line lists and the computation time required to process them, efficient computation of molecular opacity requires careful selection of the wavelengths and the relevant lines. We will discuss these procedures, and the results obtained for important absorbers such as H2O and TiO.

For temperatures below about 1,800 K, some materials begin to precipitate out of the gas phase as small solid particles. Because these small grains are very efficient absorbers and scatterers of light, they dominate the opacity whenever they exist. The thermodynamic and optical properties of these materials will be explored. Recent results show that even grains with relatively low abundances, such as Al2O 3 and CaTiO3, can have a dramatic impact on the structure of stellar atmospheres. Most atmospheres with Teff < 3,000 K, both giant and dwarf, have grains in their outer layers in sufficient quantity to affect the emergent spectrum. Title: Using Superlevels to Calculate Molecular NLTE Problems Authors: Schweitzer, A.; Hauschildt, P. H.; Baron, E.; Allard, F. Bibcode: 2003ASPC..288..339S Altcode: 2003sam..conf..339S We present the method we use in the atmosphere code PHOENIX to calculate molecular NLTE. It is based on the concept of superlevels. Superlevels consist of many similar levels added together which are assumed to be populated by a relative LTE distribution. This reduces the size of the system of rate equations to be solved tremendously. However, we modified the classical superlevel method and combined it with our dynamical opacity sampling technique which allows us to treat millions of lines. Therefore, we can calculate the transitions with maximum accuracy. We demonstrate the qualities of this method with the examples of CO and TiO. Title: Chemical Equilibrium of Dust at Low Temperature Authors: Ferguson, Jason W.; Alexander, David R.; Allard, France; Hauschildt, Peter H. Bibcode: 2003asdu.confE.127F Altcode: The opacity of material is required whenever the detailed transfer of radiation through a gas is modeled. Computation of the opacity requires both a thorough knowledge of the chemical state of the gas (species populations) and the absorption/scattering behavior of those species. At low temperatures the equation of state (EOS) calculations become particularly complex. Our EOS computations assume chemical equilibrium and include over 600 solid and liquid species with data mainly from the JANAF database. We will present and discuss our EOS computations for gas temperatures from 2000 K to 300 K and a wide range of gas densities, pressures and chemical compositions. Large discontinuities in species abundances are seen when an individual grain species condenses. It has been known for some time that solid silicate and iron particles play important roles in the chemical equilibrium and opacity of a cool gas. Many other condensed species, including Al2 O3, CaTiO3, and even carbon at very low temperature, can play equally important roles. Title: Resolving Stellar Atmospheres with Microlensing Authors: Thurl, Christine; Sackett, Penny D.; Hauschildt, Peter H. Bibcode: 2003IAUJD...9E..28T Altcode: Resolving the stellar surface and determining limb darkening characteristics in stars other than the Sun has proved to be very difficult. Observations have not yet yielded a satisfying picture of stellar surface brightness distributions in distant stars.

During a microlensing event the part of the source star which coincides with the caustic becomes highly magnified. When the trailing end of the star leaves the inside of the caustic the limb - and therefore the stellar atmosphere - contributes much of the measured flux. We use this to measure surface brightness features of the source star and determine limb darkening characteristics.

It has been shown previously that commonly-used limb darkening laws fail to match stellar model atmospheres at the limb of the star (Bryce et al). We examine this in more detail and also address possible implications for the use of microlensing to study stellar atmospheres with broad band and spectroscopic data. Title: Optical Spectroscopy of V838 Monocerotis Authors: Wagner, R. M.; Starrfield, S. G.; Hauschildt, P. H. Bibcode: 2002AAS...201.4002W Altcode: 2002BAAS...34.1161W Optical spectroscopy of V838 Mon was obtained on 2002 Feb. 8 (range 415-675 nm, resolution 0.14 nm) and on Sep. 25 (range 390-750 nm, resolution 0.38 nm) with the 6.5-m MMT of the University of Arizona and the Smithsonian Institution. The Feb. spectrum exhibits strong emission lines of the Balmer series, Fe II, Ba II, Na I D, and weaker features with sharp P Cygni profiles. The width of the emission lines implies an average expansion velocity of about 150 km/s and a terminal velocity of about 350 km/s for a wind or expanding envelope. The spectrum indicates that the progenitor must be a highly evolved object. Preliminary modeling of this spectrum and a HST/STIS UV spectrum obtained a day earlier suggests that the object is deficient in hydrogen and similar in composition to the born-again post-AGB star V4334 Sgr. The Sep. 25th spectrum is composite. Strong TiO and VO bands are seen in the red suggesting a late-M-giant component. At shorter wavelengths, there are strong and narrow absorption lines of the Balmer series and He I (447.1, 587.5 nm). Narrow emission lines arising from [O I] (630.0, 636.3 nm), Mg I (457.1, 516.7 nm), and many other weaker emission and absorption lines are also present. Strong interstellar absorption features of Na I D, 578.0 nm, and perhaps 443.0 nm are present and the equivalent width of 578.0 nm implies E(B-V) = 0.54 mag. The composite spectrum suggests that V838 Mon might be a binary system. These spectra and comparisons with post-AGB stars and eruptive variables such as M31RV and V4332 Sgr will be presented. Title: Numerical simulations of surface convection in a late M-dwarf Authors: Ludwig, H. -G.; Allard, F.; Hauschildt, P. H. Bibcode: 2002A&A...395...99L Altcode: 2002astro.ph..8584L Based on detailed 2D and 3D numerical radiation-hydrodynamics (RHD) simulations of time-dependent compressible convection, we have studied the dynamics and thermal structure of the convective surface layers of a prototypical late-type M-dwarf (Teffapprox 2800 K, log g=5.0, solar chemical composition). The RHD models predict stellar granulation qualitatively similar to the familiar solar pattern. Quantitatively, the granular cells show a convective turn-over time scale of ~100 s, and a horizontal scale of 80 km; the relative intensity contrast of the granular pattern amounts to 1.1%, and root-mean-square vertical velocities reach 240 m s-1 at maximum. Deviations from radiative equilibrium in the higher, formally convectively stable atmospheric layers are found to be insignificant allowing a reliable modeling of the atmosphere with 1D standard model atmospheres. A mixing-length parameter of αMLT = 2.1 provides the best representation of the average thermal structure of the RHD model atmosphere while alternative values are found when fitting the asymptotic entropy encountered in deeper layers of the stellar envelope (αMLT = 1.5), or when matching the vertical velocity (αMLT = 3.5). The close correspondence between RHD and standard model atmospheres implies that presently existing discrepancies between observed and predicted stellar colors in the M-dwarf regime cannot be traced back to an inadequate treatment of convection in the 1D standard models. The RHD models predict a modest extension of the convectively mixed region beyond the formal Schwarzschild stability boundary which provides hints for the distribution of dust grains in cooler (brown dwarf) atmospheres. Title: Molecular Line and Continuum Opacities for Modeling of Extrasolar Giant Planet and Cool Stellar Atmospheres Authors: Weck, P. F.; Stancil, P. C.; Schweitzer, A.; Hauschildt, P. H.; Kirby, K.; Yamaguchi, Y.; Allen, W. Bibcode: 2002nla..work..165W Altcode: The molecular hue and continuum opacities are investigated in the atmospheres of cool stars and Extrasolar Giant Planets (EGPs). Using a combination of ab inito and experimentally derived potential curves and dipole transition moments, accurate data have been calculated for rovibrationally-resolved oscillator strengths and photodissociation cross sections in the B' 2∑+ ← X 2∑+ and A 2II ← X 2∑+ baud systems in MgH. We also report our progress on the study of the electronic structure of LiCl and FeH. Title: Detectability of Hydrogen Mixing in Type Ia Supernova Premaximum Spectra Authors: Lentz, Eric J.; Baron, E.; Hauschildt, Peter H.; Branch, David Bibcode: 2002ApJ...580..374L Altcode: 2002astro.ph..7470L The presence of a small amount of hydrogen is expected in most single-degenerate scenarios for producing a Type Ia supernova (SN Ia). While hydrogen may be detected in very early high-resolution optical spectra, in early radio spectra, and in X-ray spectra, here we examine the possibility of detecting hydrogen in early low-resolution spectra such as those that will be obtained by proposed large-scale searches for nearby SNe Ia. We find that definitive detections will require both very early spectra (less than 5 days after explosion) and perhaps slightly higher amounts of hydrogen than are currently predicted to be mixed into the outer layers of SNe Ia. Thus, the nondetection of hydrogen so far does not in and of itself rule out any current progenitor models. Nevertheless, very early spectra of SNe Ia will provide significant clues to the amount of hydrogen present and hence to the nature of the SN Ia progenitor system. Spectral coverage in both the optical and IR will be required to definitively identify hydrogen in low-resolution spectra. Title: Nova Model Atmopheres Authors: Hauschildt, Peter H.; Schwarz, G.; Short, C. Ian; Baron, E.; Starrfield, S. Bibcode: 2002AIPC..637..249H Altcode: 2002cne..conf..249H We review the basics physics of nova atmospheres and discuss the physics that has to be included for detailed models of their early spectra. We also present NLTE calculations for model atmospheres of novae during outburst. This fully self-consistent NLTE treatment for a number of model atoms includes > 5000 NLTE levels and > 57000 NLTE primary transitions. We discuss the implication of departures from LTE for the strengths of the lines in nova spectra. The new results show that our large set of NLTE lines constitute the majority of the total line blanketing opacity in nova atmospheres. Although we include LTE background lines, their effects are small on the model structures and on the synthetic spectra. We demonstrate that the assumption of LTE leads to incorrect synthetic spectra and that NLTE calculations are required for reliably modeling nova spectra. In addition, we show that detailed NLTE treatment for a number of ionization stages of iron changes the results of previous calculations and improves the fit to observed nova spectra. These new models have also been used to fit the lightcurves of novae during the early phases of the nova outburst. Title: Spectral types of planetary host star candidates: Two new transiting planets? Authors: Dreizler, S.; Rauch, T.; Hauschildt, P.; Schuh, S. L.; Kley, W.; Werner, K. Bibcode: 2002A&A...391L..17D Altcode: 2002astro.ph..7192D Recently, 46 low-luminosity object transits were reported from the Optical Gravitational Lensing Experiment. Our follow-up spectroscopy of the 16 most promising candidates provides a spectral classification of the primary. Together with the radius ratio from the transit measurements, we derived the radii of the low-luminosity companions. This allows to examine the possible sub-stellar nature of these objects. Fourteen of them can be clearly identified as low-mass stars. Two objects, OGLE-TR-03 and OGLE-TR-10 have companions with radii of 0.15 R_sun which is very similar to the radius of the transiting planet HD 209458 B. The planetary nature of these two objects should therefore be confirmed by dynamical mass determinations. Title: Detailed Spectroscopic Analysis of SN 1987A: The Distance to the Large Magellanic Cloud Using the Spectral-fitting Expanding Atmosphere Method Authors: Mitchell, Robert C.; Baron, E.; Branch, David; Hauschildt, Peter H.; Nugent, Peter E.; Lundqvist, Peter; Blinnikov, Sergei; Pun, Chun S. J. Bibcode: 2002ApJ...574..293M Altcode: 2002astro.ph..4012M Supernova 1987A remains the most well studied supernova to date. Observations produced excellent broadband photometric and spectroscopic coverage over a wide wavelength range at all epochs. We model the observed spectra from day 1 to day 81 using a hydrodynamical model. We show that good agreement can be obtained at times up to about 60 days if we allow for extended nickel mixing. Later than about 60 days the observed Balmer lines become stronger than our models can reproduce. We show that this is likely due to a more complicated distribution of gamma rays than we allow for in our spherically symmetric calculations. We present synthetic light curves in UBVRIJHK and a synthetic bolometric light curve. Using this broad baseline of detailed spectroscopic models, we find a distance modulus of μ=18.5+/-0.2 using the spectral-fitting expanding atmosphere method of determining distances to supernovae. We find that the explosion time agrees with that of the neutrino burst and is constrained at 68% confidence to within +/-0.9 days. We argue that the weak Balmer lines of our detailed model calculations cast doubt on the accuracy of the purely photometric expanding photosphere method. We also suggest that Type IIP supernovae will be most useful as distance indicators at early times because of a variety of effects. Title: Spectra and Evolution of Exrasolar Planets Authors: Allard, F.; Baraffe, I.; Chabrier, G.; Barman, T.; Hauschildt, P. H. Bibcode: 2002sf2a.conf..573A Altcode: We have used our general atmosphere code Phoenix to generate radiative equilibrium models of irradiated planets located near a dM6 and a G2 primary. The external radiation, as modeled also by Phoenix, was explicitly included in the solution of the radiative transfer equation. A cool (Teff = 500K) and a hot (Teff = 1000K) planet were modeled at various orbital separations from both the dM6 and the G2 primary. In all scenarios, we compared the effects of the irradiation in two cases: one where dust clouds form and remain suspended in the atmosphere and another where dust clouds form but settle out of the atmosphere. The atmospheric structure and emergent spectrum strongly depend on the presence or absence of dust clouds. Title: Atmospheric analysis of the M/L and M/T dwarf binary systems LHS 102 and Gliese 229 Authors: Leggett, S. K.; Hauschildt, Peter H.; Allard, F.; Geballe, T. R.; Baron, E. Bibcode: 2002MNRAS.332...78L Altcode: 2001astro.ph.12335L We present 0.9-2.5μm spectroscopy with R ~800 and 1.12-1.22μm spectroscopy with R ~5800 for the M dwarfs Gl 229A and LHS 102A, and for the L dwarf LHS 102B. We also report IZJHKL ' photometry for both components of the LHS 102 system, and L ' photometry for Gl 229A. The data are combined with previously published spectroscopy and photometry to produce flux distributions for each component of the kinematically old disc M/L dwarf binary system LHS 102 and the kinematically young disc M/T dwarf binary system Gliese 229. The data are analysed using synthetic spectra generated by the latest `AMES-dusty' and `AMES-cond' models by Allard & Hauschildt. Although the models are not able to reproduce the overall slope of the infrared flux distribution of the L dwarf, most likely because of the treatment of dust in the photosphere, the data for the M dwarfs and the T dwarf are well matched. We find that the Gl 229 system is metal-poor despite having kinematics of the young disc, and that the LHS 102 system has solar metallicity. The observed luminosities and derived temperatures and gravities are consistent with evolutionary model predictions if the Gl 229 system is very young (age~30Myr) with masses (A,B) of (0.38,>~0.007)Msolar , and the LHS 102 system is older, aged 1-10Gyr with masses (A,B) of (0.19,0.07)Msolar . Title: The Spectral Energy Distribution and Mass-Loss Rate of the A-Type Supergiant Deneb Authors: Aufdenberg, J. P.; Hauschildt, P. H.; Baron, E.; Nordgren, T. E.; Burnley, A. W.; Howarth, I. D.; Gordon, K. D.; Stansberry, J. A. Bibcode: 2002ApJ...570..344A Altcode: 2002astro.ph..1218A A stellar wind module has been developed for the PHOENIX stellar atmosphere code for the purpose of computing non-LTE, line-blanketed, expanding atmospheric structures and detailed synthetic spectra of hot luminous stars with winds. We apply the code to observations of Deneb, for which we report the first positive detections of millimeter and centimeter emission (obtained using the Submillimeter Common-User Bolometric Array and the Very Large Array) as well a strong upper limit on the 870 μm flux (using the Heinrich Hertz Telescope). The slope of the radio spectrum shows that the stellar wind is partially ionized. We report a uniform-disk angular diameter measurement θUD=2.40+/-0.06 mas from the Navy Prototype Optical Interferometer (NPOI). The measured bolometric flux and corrected NPOI angular diameter yield an effective temperature of 8600+/-500 K. Least-squares comparisons of synthetic spectral energy distributions from 1220 Å to 3.6 cm with the observations provide estimates for the effective temperature and the mass-loss rate of ~=8400+/-100 K and (8+/-3)×10-7 Msolar yr-1, respectively. This range of mass-loss rates is consistent with that derived from high-dispersion UV spectra when non-LTE metal-line blanketing is considered. We are unable achieve a reasonable fit to a typical Hα P Cygni profile with any model parameters over a reasonable range. This is troubling because the Hα profile is the observational basis for the wind momentum-luminosity relationship. Title: Non-LTE Effects of Na I in the Atmosphere of HD 209458b Authors: Barman, Travis S.; Hauschildt, Peter H.; Schweitzer, Andreas; Stancil, Phillip C.; Baron, E.; Allard, France Bibcode: 2002ApJ...569L..51B Altcode: 2002astro.ph..3139B The recent announcement that sodium absorption has been observed in the atmosphere of HD 209458b, the only extrasolar giant planet (EGP) observed to transit its parent star, is the first direct detection of an EGP atmosphere. We explore the possibility that neutral sodium is not in local thermodynamic equilibrium (LTE) in the outer atmosphere of irradiated EGPs and that the sodium concentration may be underestimated by models that make the LTE assumption. Our results indicate that it may not be necessary to invoke excessive photoionization, low metallicity, or even high-altitude clouds to explain the observations. Title: Effective Temperatures of Late L Dwarfs and the Onset of Methane Signatures Authors: Schweitzer, Andreas; Gizis, John E.; Hauschildt, Peter H.; Allard, France; Howard, Eric M.; Kirkpatrick, J. Davy Bibcode: 2002ApJ...566..435S Altcode: 2001astro.ph.10316S We present a spectral analysis of a sample of late L dwarfs. We use our latest model atmospheres and synthetic spectra and optical and K-band spectra to determine effective temperatures. We derive effective temperatures of 1400-1700 K for L8-L6 dwarfs. The analysis demonstrates that our recent models that rain out the formed dust completely are applicable to optical spectra of late L dwarfs and that more consistent models are needed for intermediate L dwarfs and for infrared spectra. We compare the results for the effective temperatures with the temperatures of the onset of methane formation. Our models predict methane absorption at 3.3 μm to occur at temperatures about 400 K higher than methane absorption at 2.2 μm. This is consistent with our data and previous observations, which show methane absorption at 3.3 μm, but not at 2.2 μm, in late L dwarfs. Title: Evolutionary models for low-mass stars and brown dwarfs: Uncertainties and limits at very young ages Authors: Baraffe, I.; Chabrier, G.; Allard, F.; Hauschildt, P. H. Bibcode: 2002A&A...382..563B Altcode: 2001astro.ph.11385B We analyse pre-Main Sequence evolutionary tracks for low mass stars with masses m <= 1.4 Msun based on the Baraffe et al. (\cite{Bar98}) input physics. We also extend the recent Chabrier et al. (2000) evolutionary models based on dusty atmosphere to young brown dwarfs down to one mass of Jupiter. We analyse current theoretical uncertainties due to molecular line lists, convection and initial conditions. Simple tests on initial conditions show the high uncertainties of models at ages la 1 Myr. We find a significant sensitivity of atmosphere profiles to the treatment of convection at low gravity and Teff < 4000 K, whereas it vanishes as gravity increases. This effect adds another source of uncertainty on evolutionary tracks at very early phases. We show that at low surface gravity (log g <~ 3.5) the common picture of vertical Hayashi lines with constant Teff is oversimplified. The effect of a variation of initial deuterium abundance is studied. We compare our models with evolutionary tracks available in the literature and discuss the main differences. We finally analyse to what extent current observations of young systems provide a good test for pre-Main Sequence tracks. Title: Cool Stellar Atmospheres Authors: Hauschildt, P. H.; Allard, F.; Schweitzer, A.; Baron, E. Bibcode: 2002ASPC..274...95H Altcode: 2002ohds.conf...95H No abstract at ADS Title: Cool stellar atmospheres Authors: Hauschildt, Peter H.; Schweitzer, Andreas; Allard, F.; Ferguson, J. W.; Alexander, D.; Baron, E. Bibcode: 2002ASSL..274...15H Altcode: We give an overview about the state-of-the-art in cool stellar (and sub-stellar) atmosphere simulations. Recent developments in numerical methods and parallel supercomputers, as well as in the quality of input data such as atomic and molecular line lists have led to substantial improvements in the quality of synthetic spectra when compared to multi-wavelength observations. A wide range of ojbects from M dwarfs and giants down to substellar objects is considered. We discuss effects such as atomic and molecular NLTE (and) line blanketing, external irradiation, and formation and opacities of dust particles and clouds; each of which affects the structure of the atmospheres and their spectra. Current models can simultaneously fit many of the observed features of a given star with a single model atmosphere, however, a number of problems remain unsolved and will have to be addressed in the future, in particular for very low mass stars and substellar objects. Title: V838 Monocerotis - a Newly Discovered, Very Peculiar, Slow Nova-Like Object Authors: Rauch, Thomas; Hauschildt, Peter; Asplund, Martin; Gredel, Roland; Käufl, Hans-Ulrich; Kerber, Florian; Rosa, Michael; Starrfield, Sumner G.; Wagner, R. Mark; Williams, Robert E. Bibcode: 2002ASPC..279..345R Altcode: 2002IAUCo.187..345R; 2002esce.conf..345R No abstract at ADS Title: From the Sun to Jupiter: Evolution of Low Mass Stars and Brown Dwarfs down to Planetary Masses Authors: Baraffe, Isabelle; Chabrier, Gilles; Allard, France; Hauschildt, Peter Bibcode: 2002osp..conf...93B Altcode: We present current models for low mass stars and substellar objects down to planetary masses and discuss the success and remaining uncertainties of the theory. We focus on early evolutionary phases during the first ∼ 10 Myr, covering for stars the initial deuterium burning phase to the zero-age Main Sequence. Uncertainties of models at young ages due to the choice of initial conditions are emphasized. Title: Spectral types of planetary host star candidates: new transiting planets ? Authors: Dreizler, S.; Rauch, T.; Hauschildt, P.; Schuh, S. L.; Kley, W.; Werner, K. Bibcode: 2002AGAb...19R...6D Altcode: No abstract at ADS Title: Irradiation of CV secondaries Authors: Barman, T. S.; Hauschildt, P. H.; Allard, F. Bibcode: 2002ASPC..261...49B Altcode: 2002pcvr.conf...49B In many cases, the red secondary star in a cataclysmic variable (CV) system contributes a significant amount to the total near-IR and IR flux. Over the past decade, several CV secondaries have been observed; however, the interpretation of these observations is complicated by the fact that one hemisphere of the secondary is subjected to the intense radiation fields of the primary, accretion disk, and boundary layer. Using our general purpose atmosphere code (PHOENIX), we have modeled the effects of the impinging radiation from a hot white dwarf on the atmosphere of a CV secondary. We will present preliminary results for an average CV system. Title: Radiative accelerations in stellar atmospheres Authors: Hui-Bon-Hoa, A.; LeBlanc, F.; Hauschildt, P. H.; Baron, E. Bibcode: 2002A&A...381..197H Altcode: We present calculations of radiative accelerations obtained with the general purpose model atmosphere code PHOENIX. The accelerations are computed simultaneously for all the elements He-Ga; Kr-Nb; Ba; La, using the opacity sampling method. The calculations are mainly performed with the LTE approximation. Tests are made to evaluate the influence of non-LTE effects and the validity of the radiative flux obtained through the diffusion approximation. It is shown that the abundances supported in the atmospheres of HgMn and He-weak stars are generally consistent with those observed. Title: Rovibrational Photodissociation of MgH for Advanced Stellar Atmosphere Models Authors: Weck, P. F.; Schweitzer, A.; Stancil, P. C.; Hauschildt, P. H.; Kirby, K. Bibcode: 2001AAS...199.9208W Altcode: 2001BAAS...33.1441W For very cool stars (M and later) molecular absorption is the most important opacity source. The lack of accurate and complete molecular data has been a serious limitation to developing atmospheric models of such stars, from which synthetic spectra and important physical parameters, such as surface chemical composition, can be calculated. Models generally include molecular bands with hundreds of millions of spectral lines, but few have considered the effect of molecular photodissociation processes. Photodissociation from a range of vibrational (v) and rotational (R) levels of the ground electronic state of a molecule can provide a significant source of continuum opacity. We have performed extensive calculations of photodissociation cross sections for MgH, using the most accurate available molecular data. Potential curves and transition moments for the low-lying electronic states of MgH (Saxon et al., 1978), as well as the ground state dipole moment function, were used to generate cross sections for photodissociation through the B'-X and A-X transitions and through the X state, itself. Calculations were performed for the full range of rovibrational levels (v,R) in the ground electronic state. These photodissociation cross sections have been included in the PHOENIX stellar atmosphere code. The new models, calculated using spherical geometry for all gravities considered, also incorporate our latest database of nearly 670 million molecular lines, and updated equations of state (EOS). This work was supported in part by NSF grants AST-9720704 and AST-0086246, NASA grants NAG5-8425, NAG5-9222, and NAG5-10551 as well as NASA/JPL grant 961582. Some of the calculations were performed on the IBM SP2 of the UGA UCNS, on the IBM SP ``Blue Horizon'' of the San Diego Supercomputer Center, with support from the NSF, and on the IBM SP of the NERSC with support from the DoE. Title: Diameters of Cool Giant Stars at 712 nm & 754 nm: Theory vs. Observations Authors: Aufdenberg, J. P.; Quirrenbach, A.; Hauschildt, P. H.; Baron, E. Bibcode: 2001AAS...199.9207A Altcode: 2001BAAS...33.1441A As reported by Quirrenbach et al. (2000, IAU Symposium No. 205), the Mark III Interferometer on Mt. Wilson was used to measure the diameters of 47 cool giant stars in two filters centered at 712 nm and at 754 nm. These filters probe the stellar atmosphere in a strong TiO band (712 nm) and in a ``continuum'' band relatively free of TiO absorption (754 nm). The measured diameters are systematically larger at 712 nm than at 754 nm. The diameter ratio increases with decreasing effective temperature, and it is larger for luminosity class I than for luminosity class II and III stars. We have been successful in quantitatively reproducing these trends with the latest set of cool giant models from the general-purpose stellar atmosphere code PHOENIX. Spherical, hydrostatic, massively line-blanketed atmosphere models have been constructed using a depth-impact parameter coordinate system where parallel rays intersect nested shells. From these models, synthetic center-to-limb intensity variations in the 712 nm and 754 nm bands have been extracted. From these synthetic limb profiles, we predict the uniform-disk ratio of the two bands as a function of model effective temperature and surface gravity. With the exception of Mira (o Ceti), the diameter ratios of all of the observed oxygen-rich giants fall within the limits predicted by the models. We find that the computation of the model atmospheres in a spherical geometry, with complete as possible atomic and molecular line blanketing, is required to generate the geometrical extension of the atmosphere and the limb profiles inferred from the observations. Most of the stars have well constrained bolometric flux measurements and IR interferometric angular diameters which provide nearly model-independent effective temperatures. These measured effective temperatures, along with surface gravity estimates, provide a consistency check of the models. JPA is supported by a Harvard-Smithsonian CfA postdoctoral fellowship. This work was supported in part by NSF grants AST-9720704 and AST-0086246, NASA grants NAG5-8425, NAG5-9222, as well as NASA/JPL grant 961582 to the University of Georgia and in part by NSF grants AST-97314508, by NASA grant NAG5-3505 and an IBM SUR grant to the University of Oklahoma. Title: Spectral Analysis of L dwarfs using PHOENIX Authors: Schweitzer, A.; Gizis, J. E.; Hauschildt, P. H.; Allard, F.; Reid, I. N.; Kirkpatrick, J. D. Bibcode: 2001AAS...199.6103S Altcode: 2001BAAS...33.1398S We present a spectroscopic study of L dwarfs using our latest AMES-Cond and AMES-Dusty model atmospheres. These model atmospheres are calculated using the atmosphere code PHOENIX and include dust formation and dust absorption inside the photosphere. Early L dwarfs turn out to have a dust filled photosphere and can be described with the AMES-Dusty models which leave the formed dust completely in the layer in which it forms. The late L dwarfs turn out to have a dust free (rained out) photosphere and can be described with the AMES-Cond models which rain out the formed dust completely. Intermediate L dwarfs, however, cannot be reproduced with either model yet and require unified models which consider the settling of dust to produce a self consistent dust stratification. We derive effective temperatures of 1400 K to 2000 K for L8 to M9.5 dwarfs respectively. As expected for this field sample out of the 2MASS catalog, we derive high values for log(g) of 4.5 and higher. This work was supported in part by NASA ATP grants NAG5-8425, NAG 5-3018 and LTSA grant NAG 5-3619. Some of the calculations were performed on the IBM SP2 of the UGA UCNS, on the IBM SP ``Blue Horizon'' of the San Diego Supercomputer Center, with support from the NSF, and on the IBM SP of the NERSC with support from the DoE. The observations were obtained at the W. M. Keck Observatory, which is operated jointly by the University of California, the California Institute of Technology and NASA. Title: Optical - IR stellar astrophysics: Models vs. Observations Authors: Ferguson, J. W.; Penley, J. J.; Alexander, D. R.; Allard, F.; Hauschildt, P. H. Bibcode: 2001AAS...19913515F Altcode: 2001BAAS...33.1508F Recent observational catalogs by Lancon & Wood (2000, A&AS, 146, 217) and Pickles (1998, PASP, 110, 863) among others include the spectra of dozens of stars covering an unprecedented wavelength range from the optical to near-infrared. These observations include a wide range of stellar temperatures, and many types of stars including some with unusual chemical compositions. Such observations are a vast improvement over previous "optical-only" or "infrared-only" spectra. Having good observations with such a broad wavelength range make it possible to better model the conditions of these stars. Carefully fitting the effects of molecules such as H2O, CO, VO, and TiO in the spectra of these stars is paramount in our effort to better understand these stars. We show the results of PHOENIX (Hauschildt & Baron, 1999, J. Comp. Appl. Math., 102, 41) stellar atmosphere models with recent improvements in the TiO, H2O and a few other minor molecular opacity sources. Models computed with different sources of molecular opacity (H2O for example) show varying degrees of accuracy of fit, although none of the sources given are perfect fits to the observed spectral shape. Comparisons with the observations are made and the resulting effective temperature/spectral class scale is shown. Low temperature astrophysics at Wichita State University is supported by NSF grant No. EPS-9874732 with matching support from the State of Kansas, by a NASA EPSCoR grant NCC5-168 and NASA LTSA grant NAG5-3435. Title: Stellar Atmospheres: Cool Stars Authors: Hauschildt, P. Bibcode: 2001eaa..bookE2765H Altcode: The term `cool stellar atmosphere' is generally applied to the atmospheres of stars with effective temperatures less than that of the Sun. In this spirit, this article describes the basic physics of stellar and substellar atmospheres with effective temperatures below about 5000 K. This category includes two common subclasses: dwarf stars and giant stars. From the point of view of the STELLAR ATMO... Title: Infrared spectroscopy of substellar objects in Orion Authors: Lucas, P. W.; Roche, P. F.; Allard, France; Hauschildt, P. H. Bibcode: 2001MNRAS.326..695L Altcode: 2001astro.ph..5154L We present broad-band spectra of a sample of 21 low-luminosity sources in the Trapezium cluster, with masses in the range 0.008-0.10Msolar (assuming an age of 1Myr). These were selected for low extinction in most cases, and are located west of the brighter nebulosity. The spectra are in the H bandpass (1.4-1.95μm) and K bandpass (1.9-2.5μm) also for most of the brighter sources, with a resolution of 50nm. They were taken with the United Kingdom Infrared Telescope (UKIRT) using the CGS4 spectrometer. Absorption by water vapour bands is detected in all the substellar candidates except one, which is a highly reddened object with strong H2 emission and an anomalously blue (I-J) colour, implying that it is a very young cluster member with circumstellar matter. The observation of prominent water vapour bands confirms the low effective temperatures implied by our (I-J) colour measurements in an earlier paper, and would imply late-M or L spectral types if these were older field dwarfs. However, the profiles of the H-bandpass spectra are very different from those of field dwarfs with similar water absorption strength, demonstrating that they are not foreground or background objects. In addition, the CO absorption bands at 2.3μm and the Nai absorption feature at 2.21μm are very weak for such cool sources. All these features are quite well reproduced by the AMES-Dusty-1999 model atmospheres of Allard et al., and arise from the much lower gravities predicted for the Trapezium sources (3.5<logg<4.0) compared to evolved objects (logg~5.5). This represents a new proof of the substellar status of our sources, independent of the statistical arguments for low contamination, which are re-examined here. The very late spectral types of the planetary mass objects and very low-mass brown dwarfs demonstrate that they are cluster members, since they are too luminous to be field dwarfs in the background. We also present additional UKIRT photometry of a small region in the south of the Trapezium cluster where the extinction and nebular brightness are low, which permitted the detection of objects with 1-Myr masses slightly lower than our previous least massive source at 8MJup. Following a minor update to our previous J-band photometry, due to a new UKIRT filter calibration, there are ~15 planetary mass candidates in the full data set. Title: Irradiated Planets Authors: Barman, Travis S.; Hauschildt, Peter H.; Allard, France Bibcode: 2001ApJ...556..885B Altcode: 2001astro.ph..4262B We have modeled irradiated planets located near a dM5 and a G2 primary star. The impinging radiation field was explicitly included in the solution of the radiative transfer equation and in the computation of the atmospheric structure. We find that large errors in both the thermal and reflected flux will result from models that do not include the impinging radiation in a self-consistent manner. A cool (Teff=500 K) and a hot (Teff=1000 K) planet were modeled at various orbital separations from both the dM5 star and the G2 primary. In all scenarios, we compared the effects of the irradiation in two extreme cases: one where dust clouds form and remain suspended in the atmosphere and another where dust clouds form but completely settle out of the atmosphere. The atmospheric structure and emergent spectrum strongly depend on the presence or absence of dust clouds. We find that in the absence of dust opacity, the impinging radiation significantly alters the innermost layers of an extrasolar giant planet atmosphere and that they are actually brighter in the optical than dusty planets. Our models also indicate that the planet-to-star brightness ratio in the optical will be less that 1×10-5 for objects like τ Bootis, which is consistent with recently reported upper limit values. Title: Non-LTE Synthetic Spectral Fits to the Type Ia Supernova 1994D in NGC 4526 Authors: Lentz, Eric J.; Baron, E.; Branch, David; Hauschildt, Peter H. Bibcode: 2001ApJ...557..266L Altcode: 2001astro.ph..4225L We have fitted the normal, well-observed, Type Ia Supernova (SN Ia) SN 1994D with non-LTE spectra of the deflagration model W7. We find that well before maximum luminosity W7 fits the optical spectra of SN 1994D. After maximum brightness the quality of the fits weakens as the spectrum forms in a core rich in iron-peak elements. We show the basic structure of W7 is likely to be representative of the typical SN Ia. We have shown that like W7, the typical SN Ia has a layer of unburned C+O composition at v>15000 km s-1, followed by layers of C-burned and O-burned material with a density structure similar to W7. We present UVOIR (UBVRIJKH) synthetic photometry and colors and compare with observation. We have computed the distance to the host galaxy, NGC 4526, obtaining a distance modulus of μ=30.8+/-0.3. We discuss further application of this direct measurement of SNe Ia distances. We also discuss some simple modifications to W7 that could improve the quality of the fits to the observations. Title: 56Ni Mixing in the Outer Layers of SN 1987A Authors: Mitchell, Robert C.; Baron, E.; Branch, David; Lundqvist, Peter; Blinnikov, Sergei; Hauschildt, Peter H.; Pun, Chun S. J. Bibcode: 2001ApJ...556..979M Altcode: 2001astro.ph..4148M Supernova 1987A remains the most well observed and well studied supernova to date. Observations have produced excellent broadband photometric and spectroscopic coverage over a wide wavelength range at all epochs. Here we focus on the very early spectroscopic observations. Only recently have numerical models been of sufficient detail to accurately explain the observed spectra. In SN 1987A, good agreement has been found between observed and synthetic spectra for day 1, but by day 4, the predicted Balmer lines become much weaker than the observed lines. We present the results of work based on a radiation-hydrodynamic model by Blinnikov and collaborators. Synthetic non-LTE spectra generated from this model by the general radiation transfer code PHOENIX strongly support the theory that significant mixing of 56Ni into the outer envelope is required to maintain strong Balmer lines. Preliminary results suggest a lower limit to the average nickel mass of 1.0×10-5 Msolar is required above 5000 km s-1 by day 4. PHOENIX models thus have the potential to be a sensitive probe for nickel mixing in the outer layers of a supernova. Title: Grains in the Atmospheres of Red Giant Stars Authors: Ferguson, Jason W.; Alexander, David R.; Allard, France; Hauschildt, Peter H. Bibcode: 2001ApJ...557..798F Altcode: Model atmospheres for cool giant stars are usually computed with detailed equation of state and opacity calculations that include many molecular species. We show that models of oxygen-rich stars with effective temperatures below 3000 K must also include dust grains. The effects of dust condensation in the equation of state and on the opacity must be included to obtain accurate temperature structures and spectra. Title: Analysis of Keck HIRES Spectra of Early L-Type Dwarfs Authors: Schweitzer, Andreas; Gizis, John E.; Hauschildt, Peter H.; Allard, France; Reid, I. Neill Bibcode: 2001ApJ...555..368S Altcode: 2001astro.ph..3402S We present analyses of high- and medium-resolution spectra of early L dwarfs. We have used our latest set of model atmospheres to reproduce and analyze the observed features. We can model the optical flux and atomic line profiles with the best accuracy to date. The models used to reproduce the observations include dust condensation and dust opacities. Compared with previous studies using older models, we find that our dust treatment is much improved. The derived parameters for the objects are well in the expected range for old, very low mass objects. This is also supported by the absence of Li in most of the objects. For the objects showing Li, we can be almost certain they are brown dwarfs. However, a spectral analysis in general, and this one in particular, can only very roughly determine mass and age. Title: The Limiting Effects of Dust in Brown Dwarf Model Atmospheres Authors: Allard, France; Hauschildt, Peter H.; Alexander, David R.; Tamanai, Akemi; Schweitzer, Andreas Bibcode: 2001ApJ...556..357A Altcode: 2001astro.ph..4256A We present opacity sampling model atmospheres, synthetic spectra, and colors for brown dwarfs and very low mass stars in the following two limiting cases of dust grain formation: (1) Inefficient gravitational settling (i.e., the dust is distributed according to the chemical equilibrium predictions) and (2) efficient gravitational settling (i.e., the dust forms and depletes refractory elements from the gas, but their opacity does not affect the thermal structure). The models include the formation of over 600 gas-phase species and 1000 liquids and crystals and the opacities of 30 different types of grains including corundum (Al2O3), the magnesium aluminum spinel MgAl2O4, iron, enstatite (MgSiO3), forsterite (Mg2SiO4), amorphous carbon, SiC, and a number of calcium silicates. The models extend from the beginning of the grain formation regime well into the condensation regime of water ice (Teff=3000-100 K) and encompass the range of logg=2.5-6.0 at solar metallicity. We find that silicate dust grains can form abundantly in the outer atmospheric layers of red and brown dwarfs with a spectral type later than M8. The greenhouse effects of dust opacities provide a natural explanation for the peculiarly red spectroscopic distribution of the latest M dwarfs and young brown dwarfs. The grainless (cond) models, on the other hand, correspond closely to methane brown dwarfs such as Gliese 229B. We also discover that the λλ5891, 5897 Na I D and λλ7687, 7701 K I resonance doublets play a critical role in T dwarfs, in which their red wings define the pseudocontinuum from the I to the Z bandpass. Title: Parallel Implementation of the PHOENIX Generalized Stellar Atmosphere Program. III. A Parallel Algorithm for Direct Opacity Sampling Authors: Hauschildt, Peter H.; Lowenthal, David K.; Baron, E. Bibcode: 2001ApJS..134..323H Altcode: 2001astro.ph..4258H We describe two parallel algorithms for line opacity calculations based on a local file and on a global file approach. The performance and scalability of both approaches is discussed for different test cases and very different parallel computing systems. The results show that a global file approach is more efficient on high-performance parallel supercomputers with dedicated parallel I/O subsystem, whereas the local file approach is very useful on farms of workstations, e.g., cheap PC clusters. Title: Radiative properties of magnetic elements. I. Why are vec G-band bright points bright? Authors: Steiner, O.; Hauschildt, P. H.; Bruls, J. Bibcode: 2001A&A...372L..13S Altcode: Photospheric magnetic elements are most conspicuously visible in high-resolution G-band filtergrams. We show that their enhanced contrast in the G-band is due to a reduction of the CH abundance by dissociation in the deep photospheric layers of the flux tube, where it is hotter than in the surrounding atmosphere. As a consequence, the CH-lines weaken, allowing more of the continuum to ``shine'' through the forest of G-band CH-lines. We suggest that other molecular bands or atomic lines may exhibit a similar behaviour. Title: The Extraordinary CHANDRA Light Curve of V1494 Aql Authors: Starrfield, S.; Drake, J.; Wagner, R. M.; Butt, Y.; Hauschildt, P. H.; Krautter, J.; Gehrz, R. D.; Woodward, C. E.; Della Valle, M.; Orio, M.; Mukai, K.; Hernanz, M.; Truran, J. W.; Evans, A. E. Bibcode: 2001AAS...198.1109S Altcode: 2001BAAS...33Q.804S V1494 Aql (Nova Aql 1999 No. 2) was discovered on 2 December 1999. It reached Vmax ~4 making it the brightest nova in the northern hemisphere since V1500 Cyg erupted in 1975. Our early optical spectra showed that it was an ``Fe II'' class nova (Williams: AJ, 104, 725, 1992). We activated our CHANDRA Target of Opportunity proposal for bright novae in outburst and obtained ACIS-I spectra on 15 April and 7 June 2000 which showed only emission lines. Our third observation on 6 August showed that it had evolved to a sharp ``emission line'' spectrum characteristic of a Super Soft X-ray Source (peak ~ 0.5 keV). We obtained HRC-S+LETG spectra on 28 Sept. (8 ksec) and 1 October (17 ksec). These spectra qualitatively resemble those of CAL 83 obtained with XMM (Paerels, F., et al. 2001, A&A, 365, L308.). More exciting, we have analyzed the light curve of our grating observations and find that there is a factor of 6 rise in counts near the middle of the second observation which lasts about 1000 seconds and has a complex structure. Our time series analyses of these data show a 2500 sec periodicity that is not present in similar analyses of the observations of HZ 43 or Sirius B. An analysis of our HRC-S+LETG observation of V382 Vel (Nova Vel 1999) is in progress and further analyses of these data are underway. We gratefully acknowledge partial support from NASA CHANDRA grants to CFA, OSU, UGA, and ASU. Title: A Galactic Distance Scale Using Type-II Supernovae Authors: Mitchell, R. C.; Baron, E.; Branch, D.; Lundqvist, P.; Blinnikov, S. I.; Hauschildt, P. H.; Pun, C. S. J. Bibcode: 2001AAS...198.3904M Altcode: 2001BAAS...33..839M Supernovae count among the most luminous phenomena in the universe, and as such they have been long sought after to serve as cosmological distance indicators. Type Ia supernova are currently the most favored, since theoretically they are the most uniform in luminosity. Type II supernovae, on the other hand, have a much larger variance in luminosity and therefore cannot provide an accurate distance by photometry alone. The Spectral-fitting Expanding Atmosphere Method (SEAM) calculates the luminosity of a supernova by matching computer models of the object's spectra to observed spectra, a feat that requires excellent radiative-transfer and hydrodynamic models and an equally powerful and accurate code. This study will introduce the program PHOENIX, and use it to examine the SN 1987A hydrodynamic models of Sergei Blinnikov and collaborators from Day 1 to Day 103. We will show that PHOENIX can be used to assess the accuracy of hydrodynamic models of supernovae, and to simulate their spectral evolution with unparalleled detail. With PHOENIX, we will be able to determine the luminosity and distance to Type II supernovae with remarkable precision. This work was supported in part by NSF grant AST-9731450, NASA grant NAG5-3505, and an IBM SUR grant to the University of Oklahoma. Some of the calculations presented in this poster were performed at the San Diego Supercomputer Center (SDSC), supported by the NSF, and at the National Energy Research Supercomputer Center (NERSC), supported by the U.S. DOE. We thank both these institutions for a generous allocation of computer time. Title: Solar Mn I 5432/5395 Å line formation explained Authors: Doyle, J. G.; Jevremović, D.; Short, C. I.; Hauschildt, P. H.; Livingston, W.; Vince, I. Bibcode: 2001A&A...369L..13D Altcode: We present a solution for the long standing problem concerning the ``chromospheric'' behaviour of the Mn i 5395/5432 Å lines in the solar spectrum using multi-line/multi-species NLTE modelling. Using comprehensive spectral line formation modelling, we show that the Mn i lines are very sensitive to optical pumping in a transition which overlaps with Mg ii k. It therefore follows that one has to be careful with the choice of lines as temperature indicators and for the determination of the Mn abundances although on the other hand, due to the formation process of these lines they may be useful as a solar and stellar activity diagnostic. Title: Hα Equivalent Width Variations across the Face of a Microlensed K Giant in the Galactic Bulge Authors: Albrow, M.; An, J.; Beaulieu, J. -P.; Caldwell, J. A. R.; Dominik, M.; Greenhill, J.; Hill, K.; Kane, S.; Martin, R.; Menzies, J.; Pollard, K.; Sackett, P. D.; Sahu, K. C.; Vermaak, P.; Watson, R.; Williams, A.; PLANET Collaboration; Hauschildt, P. H. Bibcode: 2001ApJ...550L.173A Altcode: 2000astro.ph.11380A We present Very Large Telescope FORS1 spectroscopy that temporally resolves the second caustic crossing of the Galactic bulge K giant source of microlensing event EROS 2000-BLG-5, the first time this has been accomplished for several phases of a caustic transit. The ~1 Å Hα equivalent width of the source star increases slightly as the center of the star egresses the caustic and then plummets by 30% during the final limb crossing. These changes are not seen in contemporaneous spectra of control stars in the FORS1 slit but are qualitatively consistent with expectations from stellar atmosphere models as the caustic differentially magnifies different portions of the stellar face of the target. Observations such as these in a variety of stellar lines are equivalent to atmospheric tomography and are expected to provide a direct test of stellar models.

Based on observations at the European Southern Observatory (programs 265.C-5728 and 265.C-5729). Title: Non-LTE Modeling of Nova Cygni 1992 Authors: Short, C. Ian; Hauschildt, Peter H.; Starrfield, S.; Baron, E. Bibcode: 2001ApJ...547.1057S Altcode: 2000astro.ph..9502S We present a grid of nova models that have an extremely large number of species treated in non-LTE and apply it to the analysis of an extensive time series of ultraviolet spectroscopic data for Nova Cygni 1992. We use ultraviolet colors to derive the time development of the effective temperature of the expanding atmosphere during the fireball phase and the first 10 days of the optically thick wind phase. We find that the nova has a pure, optically thick wind spectrum until about 10 days after the explosion. During this interval, we find that synthetic spectra based on our derived temperature sequence agree very well with the observed spectra. We find that a sequence of hydrogen-deficient models provides an equally good fit, provided the model effective temperature is shifted upward by ~1000 K. We find that high-resolution UV spectra of the optically thick wind phase are fit moderately well by the models. We find that a high-resolution spectrum of the fireball phase is better fit by a model with a steep density gradient, similar to that of a supernova, than by a nova model. Title: Infrared Spectra and Spectral Energy Distributions of Late M and L Dwarfs Authors: Leggett, S. K.; Allard, F.; Geballe, T. R.; Hauschildt, P. H.; Schweitzer, Andreas Bibcode: 2001ApJ...548..908L Altcode: 2000astro.ph.10174L We have obtained 1.0-2.5 μm spectra at R~600 of 14 disk dwarfs with spectral types M6-L7. For four of the dwarfs, we have also obtained infrared spectra at R~3000 in several narrow intervals. In addition, we present new L' photometry for four of the dwarfs in the sample, which allows improved determinations of their bolometric luminosities. While obtaining the photometry we resolved the L dwarf Denis-P J0205-1159 into an identical pair of objects separated by 0.35". The spectra together with the published energy distribution for one other L5 dwarf are compared to synthetic spectra generated by upgraded model atmospheres. Good matches are found for 2200 K>=Teff>=1900 K (spectral types around M9-L3), but discrepancies exist at Teff>=2300 K (M8) and Teff<=1800 K (L4-L7). At the higher temperatures the mismatches are due to incompleteness in the water vapor opacity line list. At the lower temperatures the disagreement is probably due to our treatment of dust; we assume a photospheric distribution in equilibrium with the gas phase and neglect any diffusion mechanisms. We derive effective temperatures for the sample from the comparison with synthetic spectra and also by comparing our observed total intrinsic luminosities to structural model calculations (which are mostly independent of the atmosphere but are dependent on the unknown masses and ages of the targets). The two derivations agree to about 200 K except for the faintest object in the sample, where the discrepancy is larger. Agreement with other temperature determinations is also +/-~200 K, except for the L7 dwarf. Title: Radiation-hydrodynamics Simulations of Surface Convection in a Late M-dwarf Authors: Ludwig, Hans-Günter; Hauschildt, Peter Bibcode: 2001AGM....18..P15L Altcode: Based on detailed 2D and 3D numerical radiation hydrodynamics calculations of time-dependent compressible convection, we have studied the dynamics and thermal structure of the convective surface layers of a prototypical late-type M-dwarf at Teff=2800 K, and log g=5.0 with solar chemical composition. The thermal structure of the atmosphere is dominated by molecular absorption, the formation of dust grains is not important for the chosen model parameters. In the multi dimensional models the radiative transfer is treated by a multi-group (4 groups) approach which provides a simplified, nevertheless rather realistic treatment of the complex radiative energy transport. The equation of state includes the important contribution of H2 molecule formation. Our models predict a convective pattern at the surface of an late M-dwarf qualitatively similar to solar granulation. Quantitatively, the convective turn-over timescale amounts to ≈ 100 s, a typical horizontal scale of convective cells to 80 km, and a relative intensity contrast of the granular pattern to 1.1 %. The efficiency of convective energy transport corresponds to an effective mixing-length parameter between 1.5 to 2.1 depending on the thermal property which is represented. The models provide mixing timescales due to atmospheric overshoot which can be extrapolated to lower effective temperatures where dust grains are present and mixed into optically thin layers. Title: X-ray Pulsations and a ``Burst'' in the X-ray Light Curve of Classical Nova V1494 Aql (1999 #2) in Outburst Authors: Krautter, J.; Drake, J.; Starrfield, S.; Wagner, R. M.; Butt, Y.; Bond, H. E.; della Valle, M.; Gehrz, R. D.; Woodward, C. E.; Evans, A. E.; Orio, M.; Hauschildt, P.; Hernanz, M.; Mukai, K.; Truran, J. W. Bibcode: 2001AGM....18S0101K Altcode: 2001AGAb...18....5K Nova V1494 Aql was discovered on Dec. 2, 1999. We activated our CHANDRA T-o-O proposal for bright novae in outburst and obtained ACIS-I spectra on Apr. 15 and Jun. 7, 2000, which showed only emission lines. Our third observation on Aug. 6 found that it had evolved into that characteristic of a Super Soft X-ray source (peak ~ 0.5 keV). We obtained HRC-S+LETG spectra on 28 Sept. (8 ksec) and 1 October (17 ksec). These spectra demonstrated that we were observing the atmosphere of a hot white dwarf which was probably still undergoing nuclear hydrogen burning on top of its surface. We analyzed the light curve of our grating observations and found both a short time scale ``burst'' and periodic variations of the count rate. Neither of these phenomena have ever been seen in the light curve of a nova in outburst. The ``burst'' was a factor of 6 rise in X-ray counts which lasted about 1000 sec and exhibited at least two peaks plus other structure. Our time series analyses of the combined 25 ksec observation showed a peak at 2501.6 sec. Further analysis of the V1494 Aql data found other periods present which implies that we were observing non-radial g modes from the pulsating, rekindled white dwarf. Title: The Physics of Low-mass Stars and Substellar Objects. Galactic Implications (CD-ROM Directory: contribs/chabrier) Authors: Chabrier, G.; Baraffe, I.; Allard, F.; Hauschildt, P. H. Bibcode: 2001ASPC..223...49C Altcode: 2001csss...11...49C No abstract at ADS Title: Effective Temperatures for Very Cool Objects, from Resonance Lines of Cs I and Rb I (CD-ROM Directory: contribs/mohanty) Authors: Mohanty, S.; Basri, G.; Allard, F.; Hauschildt, P. H.; Delfosse, X.; Martín, E. L.; Forveille, T.; Goldman, B. Bibcode: 2001ASPC..223..838M Altcode: 2001csss...11..838M No abstract at ADS Title: Non-LTE Modeling of Nova Cygni 1992 Authors: Short, C. I.; Hauschildt, P. H.; Baron, E. Bibcode: 2001ASPC..231..548S Altcode: 2001gssi.conf..548S No abstract at ADS Title: Multiwavelength analyses of the extraordinary nova LMC 1991* Authors: Schwarz, Greg J.; Shore, S. N.; Starrfield, S.; Hauschildt, Peter H.; Della Valle, M.; Baron, E. Bibcode: 2001MNRAS.320..103S Altcode: LMC 91 was a very fast, classical nova and the brightest nova ever observed in the Large Magellanic Cloud. It was extensively observed during both its early optically thick and its nebular evolution in the optical and UV wavelength regions. We successfully fit all the optically thick spectra using a grid of spherically symmetric, non-LTE, line-blanketed, expanding synthetic spectra created with the model atmosphere code PHOENIX. The emission lines of the nebular spectra have been fitted using an optimization technique for the emission-line luminosities predicted by the photoionization code CLOUDY. Our analyses show the following: the bolometric luminosity was super-Eddington before visual maximum and reached LBolmax~6×105Lsolar, the ejected mass was ~3×10-4Msolar, and nuclear burning on the white dwarf ceased after ~100 days. The elemental abundances (by number) with respect to solar of the ejecta are He/H=0.8+/-0.2, C/H=5-2+2.5, N/H=85-17+22, O/H=6.5-1.5+2.5, and all other elements ~0.1. These abundances were determined from both the optically thick and nebular analyses. The extreme luminosity, high ejected mass, rapid turn-off time, and low metallicity (except for enhanced CNO) represent the extreme values of observational nova parameters and thus present interesting challenges for understanding the nature of the outburst of LMC 91. Title: Pre-Main Sequence Models for Low-Mass Stars and Brown Dwarfs Authors: Baraffe, I.; Chabrier, G.; Allard, F.; Hauschildt, P. Bibcode: 2001ASPC..243..571B Altcode: 2000astro.ph..7157B; 2001fdtl.conf..571B We present evolutionary models for low mass stars and brown dwarfs ($m \le 1.2 \msol$) based on recent improvement of the theory: equation of state, atmosphere models, ... We concentrate on early evolutionary phases from the initial deuterium burning phase to the zero-age Main Sequence. Evolutionary models for young brown dwarfs are also presented. We discuss the uncertainties of the present models. We analyse the difficulties arising when comparing models with observations for very young objects, in particular concerning the problem of reddening. Title: Pre-Main Sequence Models for Low-Mass Stars and Brown Dwarfs Authors: Baraffe, Isabelle; Chabrier, Gilles; Allard, France; Hauschildt, Peter Bibcode: 2001IAUS..200..483B Altcode: We present evolutionary models for young low mass stars (m <=1 msol) based on recent improvement of the theory: equation of state, atmosphere models, etc. We concentrate on early evolutionary phases from the initial deuterium burning phase to the zero-age Main Sequence. Evolutionary models for young brown dwarfs are also presented. We discuss the uncertainties of the present models. We analyse the difficulties arising when comparing models with observations for very young objects, in particular concerning the problem of reddening. Title: Why are G-Band Bright Points Bright? Authors: Steiner, O.; Bruls, J.; Hauschildt, P. H. Bibcode: 2001ASPC..236..453S Altcode: 2001aspt.conf..453S No abstract at ADS Title: Stellar Atmospheres Authors: Hauschildt, P. H.; Allard, F.; Aufdenberg, J.; Barman, T.; Schweitzer, A.; Baron, E. Bibcode: 2001ASPC..239..175H Altcode: 2001mlap.conf..175H No abstract at ADS Title: Cool Stellar Atmospheres Authors: Hauschildt, P.; Allard, France; Barman, Travis; Schweitzer, Andreas; Baron, E.; Leggett, S. K. Bibcode: 2001ASPC..231..427H Altcode: 2001gssi.conf..427H No abstract at ADS Title: Analysis of Type IIn SN 1998S: Effects of Circumstellar Interaction on Observed Spectra Authors: Lentz, Eric J.; Baron, E.; Lundqvist, Peter; Branch, David; Hauschildt, Peter H.; Fransson, Claes; Garnavich, Peter; Bastian, Nate; Filippenko, Alexei V.; Kirshner, R. P.; Challis, P. M.; Jha, S.; Leibundgut, Bruno; McCray, R.; Michael, E.; Panagia, Nino; Phillips, M. M.; Pun, C. S. J.; Schmidt, Brian; Sonneborn, George; Suntzeff, N. B.; Wang, L.; Wheeler, J. C. Bibcode: 2001ApJ...547..406L Altcode: 2000astro.ph.10615L We present spectral analysis of early observations of the Type IIn supernova 1998S using the general non-local thermodynamic equilibrium atmosphere code PHOENIX. We model both the underlying supernova spectrum and the overlying circumstellar interaction region and produce spectra in good agreement with observations. The early spectra are well fitted by lines produced primarily in the circumstellar region itself, and later spectra are due primarily to the supernova ejecta. Intermediate spectra are affected by both regions. A mass-loss rate of order M~0.0001-0.001 Msolar yr-1 is inferred for a wind speed of 100-1000 km s-1. We discuss how future self-consistent models will better clarify the underlying progenitor structure. Title: Irradiated M Dwarfs Authors: Barman, T. S.; Hauschildt, P. H. Bibcode: 2001ASPC..231..447B Altcode: 2001gssi.conf..447B No abstract at ADS Title: Parallel Supercomputing In Stellar Atmosphere Simulations Authors: Hauschildt, Peter H.; Lowenthal, David K.; Baron, E.; Allard, France Bibcode: 2001ASPC..247..303H Altcode: 2001scpp.conf..303H No abstract at ADS Title: Optically Thick Winds of Novae Authors: Aufdenberg, J. P.; Hauschildt, Peter H.; Short, C. Ian; Starrfield, Sumner G. Bibcode: 2001ASPC..231..539A Altcode: 2001gssi.conf..539A No abstract at ADS Title: SN 1984A and Delayed-Detonation Models of Type IA Supernovae Authors: Lentz, Eric J.; Baron, E.; Branch, David; Hauschildt, Peter H. Bibcode: 2001ApJ...547..402L Altcode: 2000astro.ph..7302L SN 1984A shows unusually large expansion velocities in lines from freshly synthesized material, relative to typical Type Ia supernovae (SNe Ia). SN 1984A is an example of a group of SNe Ia which have very large blueshifts of the P Cygni features but otherwise normal spectra. We have modeled several early spectra of SN 1984A with the multipurpose non-LTE (NLTE) model atmosphere and spectrum synthesis code PHOENIX. We have used as input two delayed-detonation models: CS15DD3 (Iwamoto et al.) and DD21c (Höflich, Wheeler, & Thielemann). These models show line-expansion velocities which are larger than that for a typical deflagration model like W7, which we have previously shown to fit the spectra of normal SNe Ia quite well. We find these delayed-detonation models to be reasonable approximations to large absorption feature blueshift SNe Ia, like SN 1984A. Higher densities of newly synthesized intermediate-mass elements at higher velocities, v>15,000 km s-1, are found in delayed-detonation models than in deflagration models. We find that this increase in density at high velocities is responsible for the larger blueshifts in the synthetic spectra. We show that the variations in line width in observed SNe Ia are likely due to density variations in the outer, high-velocity layers of their atmospheres. Title: Preliminary Spectral Analysis of the Type II Supernova 1999EM Authors: Baron, E.; Branch, David; Hauschildt, Peter H.; Filippenko, Alexei V.; Kirshner, R. P.; Challis, P. M.; Jha, S.; Chevalier, R.; Fransson, Claes; Lundqvist, Peter; Garnavich, Peter; Leibundgut, Bruno; McCray, R.; Michael, E.; Panagia, Nino; Phillips, M. M.; Pun, C. S. J.; Schmidt, Brian; Sonneborn, George; Suntzeff, N. B.; Wang, L.; Wheeler, J. C. Bibcode: 2000ApJ...545..444B Altcode: 2000astro.ph.10614B We have calculated fast direct spectral model fits to two early-time spectra of the Type II plateau SN 1999em, using the SYNOW synthetic spectrum code. The first is an extremely early blue optical spectrum and the second a combined Hubble Space Telescope and optical spectrum obtained one week later. Spectroscopically this supernova appears to be a normal Type II, and these fits are in excellent agreement with the observed spectra. Our direct analysis suggests the presence of enhanced nitrogen. We have further studied these spectra with the full non-LTE general model atmosphere code PHOENIX. While we do not find confirmation for enhanced nitrogen (nor do we rule it out), we do require enhanced helium. An even more intriguing possible line identification is complicated Balmer and He I lines, which we show falls naturally out of the detailed calculations with a shallow density gradient. We also show that very early spectra such as those presented here combined with sophisticated spectral modeling allow an independent estimate of the total reddening to the supernova, since when the spectrum is very blue, dereddening leads to changes in the blue flux that cannot be reproduced by altering the ``temperature'' of the emitted radiation. These results are extremely encouraging since they imply that detailed modeling of early spectra can shed light on both the abundances and total extinction of SNe II, the latter improving their utility and reliability as distance indicators. Title: Irradiated Planets Authors: Barman, T. S.; Hauschildt, P. H.; Allard, F. Bibcode: 2000AAS...197.1110B Altcode: 2000BAAS...32.1418B We have used our general atmosphere code PHOENIX (version 10.8) to generate radiative equilibrium models of irradiated planets located near a dM6 and a G2 primary. The external radiation, represented by synthetic spectra from a previous set of PHOENIX model atmospheres, was explicitly included in the solution of the radiative transfer equation. We do not use precomputed, ad hoc, temperature-pressure profiles. A cool ({T eff} = 500 K) and a hot ({T eff} = 1000K) planet were modeled at various orbital separations from both the dM6 and the G2 primary. In all scenarios, we compared the effects of the irradiation in two extreme cases: one where dust clouds form and remain suspended in the atmosphere and another where dust clouds form but completely settle out of the atmosphere. The atmospheric structure and emergent spectrum strongly depend on the presence or absence of dust clouds. Several models have also been computed by solving the spherically symmetric radiative transfer equation instead of assuming plane parallel geometry, as is usually done for EGPs. We find that the plane parallel solution may, in some circumstances, significantly underestimate the flux near the planetary limb and should, therefore, be used with caution. Title: Sphericaly extended, massively non-LTE models of standard red giant stars Authors: Short, C. I.; Hauschildt, Peter Bibcode: 2000AAS...197.4401S Altcode: 2000BAAS...32.1471S We present spherically extended atmospheric models of red giant standard stars with all of the significant atomic opacity treated in direct multi-level non-local thermodynamic equilibrium (NLTE). We compare our synthetic flux distributions to the global energy distribution and to the detailed shape of lines of the CO fundamental band for several stars. Title: Grains in the Atmospheres of Late Type Stars Authors: Alexander, D. R.; Ferguson, J. W.; Allard, France; Hauschildt, P. H. Bibcode: 2000AAS...197.4409A Altcode: 2000BAAS...32.1473A As part of a larger project to compute accurate model atmospheres for cool giant stars (Hauschildt et al, ApJ, 525, 871, 1999), we have used the PHOENIX program to compute models in spherical geometry with a detailed treatment of both the equation of state and the opacity. The equation of state includes atoms, molecules, and the condensation of solid grains in thermodynamic equilibrium. Monochromatic atomic and molecular opacities are included via the opacity sampling technique at 20,000 frequencies. The opacity of 26 grain species is computed using the Mie theory. Despite the very low densities found in red giant atmospheres, we find that models of oxygen-rich stars with effective temperatures below 3000 K include dust grains. The presence of grains in an atmosphere has two important consequences that are potentially observable. First, the temperature of the surface layers of the star is raised by the increased opacity of the grains, compared to a model with identical parameters in which grain condensation is not included. Second, the depletion of TiO molecules from the gas phase, as titanium condenses into CaTiO3, reduces the strength of the visible absorption features of TiO in the emergent spectra of the models. Low temperature astrophysics at Wichita State University is supported by NASA EPSCoR grant NCC5-168 and NASA LTSA grant NAG5-3435. Title: The use of the NextGen model atmospheres for cool giants in a light curve synthesis code Authors: Orosz, J. A.; Hauschildt, P. H. Bibcode: 2000A&A...364..265O Altcode: 2000astro.ph.10114O We have written a light curve synthesis code that makes direct use of model atmosphere specific intensities, in particular the NextGen model atmosphere grid for cool giants (Teff<= 6800 K and log (g)<= 3.5, Hauschildt et al. \cite{hauschildt99}). We point out that these models (computed using spherical geometry) predict a limb darkening behaviour that deviates significantly from a simple linear or two-parameter law (there is less intensity at the limb of the star). The presence of a significantly nonlinear limb darkening law has two main consequences. First, the ellipsoidal light curve computed for a tidally distorted giant using the NextGen intensities is in general different from the light curve computed using the same geometry but with the black body approximation and a one- or two-parameter limb darkening law. In most cases the light curves computed with the NextGen intensities have deeper minima than their black body counterparts. Thus the light curve solutions for binaries with a giant component obtained with models with near linear limb darkening (either black body or plane-parallel model atmosphere intensities) are biased. Observations over a wide wavelength range (i.e. both the optical and infrared) are particularly useful in discriminating between models with nearly linear limb darkening and the NextGen models. Second, we show that rotational broadening kernels for Roche lobe filling (or nearly filling) giants can be significantly different from analytic kernels due to a combination of the nonspherical shape of the star and the radical departure from a simple limb darkening law. As a result, geometrical information inferred from Vrot sin i measurements of cool giants in binary systems are likewise biased. Title: Cosmological Measurements from Type II Supernovae with SNAP Authors: Baron, E.; Branch, D.; Thomas, R.; Hauschildt, P. Bibcode: 2000AAS...197.6108B Altcode: 2000BAAS...32Q1505B We discuss the exciting potential for using Type II supernova spectra and photometry expected to be obtained with the proposed SNAP satellite for determining cosmological parameters. Type II supernovae provide an independent route to obtaining luminosity distances from that of Type Ia supernovae, using most of the same photometry and spectroscopy measurements that will be obtained by SNAP for the Type Ia supernovae. The Type II method will allow us to derive cosmological parameters based on completely different physics from that of the Type Ia supernovae. Since the physics of a Type II supernova atmosphere involves predominantly hydrogen and helium, evolutionary effects (such as metallicity variations) can in fact be determined from comparison of detailed models and observed spectra. Recent advances in computational power allow us to determine the model parameters to higher accuracy than was previously possible. We contrast the constraints on measurement systematics using Type II and Type Ia supernovae as cosmological probes and show that both supernova types should be aggressively pursued. This research has been supported in part by the NSF, NASA, the U.S. DOE, the IBM Corporation, and Research Systems Inc. Title: Deuterium Burning in Substellar Objects Authors: Chabrier, G.; Baraffe, I.; Allard, F.; Hauschildt, P. Bibcode: 2000ApJ...542L.119C Altcode: 2000astro.ph..9174C We consider the depletion of primordial deuterium in the interior of substellar objects as a function of mass, age, and absolute magnitude in several photometric passbands. We characterize potential spectroscopic signatures of deuterium in the lines of deuterated water HDO. These results will serve as a useful, independent diagnostic to characterize the mass and/or the age of young substellar objects and to provide an independent age determination of very young clusters. These results can serve to identify objects at the deuterium-burning limit and to confront the theoretical prediction that D burning is a necessary condition to form starlike objects. Title: Non-LTE Treatment of Molecules in the Photospheres of Cool Stars Authors: Schweitzer, Andreas; Hauschildt, Peter H.; Baron, E. Bibcode: 2000ApJ...541.1004S Altcode: 2000astro.ph..6049S We present a technique to treat systems with very many levels, such as molecules, in non-LTE. This method is based on a superlevel formalism coupled with rate operator splitting. Superlevels consist of many individual levels that are assumed to be in LTE relative to each other. The usage of superlevels reduces the dimensionality of the rate equations dramatically and, thereby, makes the problem computationally more easily treatable. Our superlevel formalism retains maximum accuracy by using direct opacity sampling (dOS) when calculating the radiative transitions and the opacities. We developed this method in order to treat molecules in cool dwarf model calculations in non-LTE. Cool dwarfs have low electron densities and radiation fields that are far from blackbody radiation fields; both properties may disqualify them from the common LTE approximation. Therefore, the most important opacity sources, the molecules, need to be treated in non-LTE. As a case study we applied our method to carbon monoxide. We find that our method gives accurate results since the conditions for the superlevel method are very well met for molecules. Because of very high collisional cross sections with hydrogen and the high densities of H2, the population of CO itself shows no significant deviation from LTE. Title: CHANDRA and HST/STIS Observations of V382 Vel (1999) and V1494 Aql (1999) Authors: Starrfield, S.; Shore, S. N.; Butt, Y.; Drake, J.; Bond, H. E.; Downes, R.; Krautter, J.; Wagner, R. M.; Gehrz, R. D.; Woodward, C. E.; Della Valle, M.; Hauschildt, P. H.; Truran, J. W. Bibcode: 2000HEAD....5.4103S Altcode: 2000BAAS...32R1253S V382 Vel was discovered on May 22, 1999 and reached a Vmax brighter than 3 making it the brightest nova since V1500 Cyg in 1975. We observed it with HST/STIS three times during Summer 1999 and activated our CHANDRA Target of Opportunity program in early Fall 1999. Our first ACIS-I observation was on December 30, 1999 and we obtained an HRC+LETG spectrum on February 14, 2000. This nova is known to be an ONeMg nova and the grating spectrum showed lines of O VII and VIII, N VI and VII, Ne IX and X, and Mg XI plus other lines. We obtained two more ACIS-I spectra, one in April 2000 and one in August 2000. We shall show the results of these observations plus our inferences with respect to the hard component seen in the ROSAT observations of V1974 Cyg (Krautter et al. ApJ, 456, 788, 1996) and other novae. V1494 Aql was discovered in outburst on December 1, 1999 and reached a Vmax of ~5. Our first CHANDRA ACIS - I observation was in April 2000. We obtained 2 more ACIS-I observations in June and August 2000. At this time, an HRC+LETG spectrum is planned for late September 2000. We will also present our available data on this nova. We gratefully acknowledge partial support from NASA, NSF, STScI, CHANDRA, and DOE grants to our various institutions. Title: Evolutionary Models for Very Low-Mass Stars and Brown Dwarfs with Dusty Atmospheres Authors: Chabrier, G.; Baraffe, I.; Allard, F.; Hauschildt, P. Bibcode: 2000ApJ...542..464C Altcode: 2000astro.ph..5557C We present evolutionary calculations for very low-mass stars and brown dwarfs based on synthetic spectra and nongray atmosphere models which include dust formation and opacity, i.e., objects with Teff<~2800 K. The interior of the most massive brown dwarfs is shown to develop a conductive core after ~2 Gyr which slows down their cooling. Comparison is made in optical and infrared color-magnitude diagrams with recent late-M and L dwarf observations. The saturation in optical colors and the very red near-infrared colors of these objects are well explained by the onset of dust formation in the atmosphere. Comparison of the faintest presently observed L dwarfs with these dusty evolutionary models suggests that dynamical processes such as turbulent diffusion and gravitational settling are taking place near the photosphere. As the effective temperature decreases below Teff~1300-1400 K, the colors of these objects move to very blue near-infrared colors, a consequence of the ongoing methane absorption in the infrared. We suggest the possibility of a brown dwarf dearth in J, H, and K color-magnitude diagrams around this temperature. Title: TiO and H2O Absorption Lines in Cool Stellar Atmospheres Authors: Allard, France; Hauschildt, Peter H.; Schwenke, David Bibcode: 2000ApJ...540.1005A Altcode: 2000astro.ph..8465A We compare the structures of model atmospheres and synthetic spectra calculated using different line lists for TiO and water vapor. We discuss the effects of different line list combinations on the model structures and spectra for both dwarf and giant stars. It is shown that recent improvements result in significantly improved spectra, in particular, in the optical where TiO bands are important. The water vapor-dominated near-infrared region remains problematic as the current water line lists do not yet completely reproduce the shapes of the observed spectra. We find that the AMES TiO list provides more opacity in most bands and that the new, smaller oscillator strengths lead to systematically cooler temperatures for early-type M dwarfs than previous models. These effects combine and will help to significantly improve the fits of models to observations in the optical as well as result in improved synthetic photometry of M stars. We show that the Davis, Littleton, & Phillips fel-values for the δ and ϕ bands of TiO best reproduce the observed V-I color indices. Title: Nova in the Large Magellanic Cloud 2000 Authors: Shore, S. N.; Starrfield, S.; Bond, H. E.; Downes, R.; Hauschildt, P. H.; Gehrz, R. D.; Woodward, C. E.; Krautter, J.; Evans, A. N. Bibcode: 2000IAUC.7486....1S Altcode: 2000IAUC.7486Q...1S; 2000IAUC.7486A...1S S. N. Shore, Indiana University, South Bend; S. Starrfield, Arizona State University; H. E. Bond and R. Downes, Space Telescope Science Institute; P. H. Hauschildt, University of Georgia; R. D. Gehrz and C. E. Woodward, University of Minnesota; J. Krautter, Landessternwarte, Heidelberg; and A. N. Evans, Keele University, write: "We observed this nova (cf. IAUC 7457, 7458) with the Hubble Space Telescope's Imaging Spectrograph (STIS) on Aug. 19.7 and Aug. 20.9 UT using the medium-resolution echelle gratings (E140M and E230M). Three spectra were obtained, centered at 142.5, 197.8, and 270.7 nm with resolutions of about 45 000 (E140M) and 30 000 (E230M). Weak iron-peak absorption may still be present, especially from 155.0 to 156.5 nm. The spectrum strongly resembles that of V382 Vel obtained 2 months after visual maximum (IAUC 7261) but with much stronger Ly-alpha and Si III] 189.5-nm and C III] 191.0-nm emission, with Si III]/C III] about 2. Strong C IV P-Cyg absorption is seen with a terminal velocity of 2000 km/s, similar to the FWHM velocity for the emission lines. The following strong emission lines have been detected: C III 107.6-nm, N V 124.0-nm, N III/O III 126.7-nm, O I 130.4-nm, C II 133.4-nm, Si IV/O IV] 140.0- nm, C IV 155.0-nm, He II 164.0-nm, O III] 166.7-nm, N III] 175.0-nm, Si II 181.6-nm, Al III 186.0-nm, Si III] 189.5-nm, C III] 191.0-nm, N II] 214.5-nm, C II 232.1-nm, Al II 267.2-nm, and Mg II 280.0-nm. Unusual features of the spectrum are the absence of N IV] at 148.6 and 171.8 nm and the presence of strong Ly-alpha emission at a time when He II 164.0-nm is also strong, but the Ly-alpha in this nova is stronger due to lower interstellar absorption. Most emission profiles show fine structure consistent with knots of the sort detected in HST spectra of V1974 Cyg and V382 Vel. A strong interstellar absorption line spectrum is present, showing Si II/S II 126.0-nm, Si IV 140.0-nm, C IV 155.0-nm, Al II 167.1-nm, Al III 186.0-nm, and Fe II 260.0-nm with Galactic and LMC components (+250 km/s) clearly resolved. The integrated flux from 115.0 to 312.0 nm was 8.6 x 10**-11 erg cm**-2 s**-1 [or 5.6 x 10**-10 erg cm**-2 s**-1, corrected for LMC reddening with E(B-V) = 0.2]. For a distance of 50 kpc, this corresponds to 4.1 x 10**4 solar luminosities. In view of the similarity of the spectra, these data yield a probable distance for V382 Vel of 3000 pc, assuming its reddening is E(B-V) = 0.2. A further STIS observation is planned for mid-Nov., and continued groundbased monitoring at all wavelengths is urged." Title: Spherically Symmetric Model Atmospheres for Low-Mass Pre-Main-Sequence Stars with Effective Temperatures between 2000 and 6800 K Authors: Allard, France; Hauschildt, Peter H.; Schweitzer, Andreas Bibcode: 2000ApJ...539..366A Altcode: 2000astro.ph..8464A We present a grid of spherically symmetric model atmospheres for young pre-MS stars. This grid spans the parameter range 2000 K<=Teff<=6800 K and 2.0<=logg<=3.5 for M=0.1 Msolar, appropriate for low-mass stars and brown dwarfs. A major improvement is the replacement of TiO and H2O line lists with the newer line list, calculated by the NASA-Ames group, for TiO (about 175 million lines of five isotopes) and for H2O (about 350 million lines in two isotopes). We provide the model structures, spectra, and broadband colors in standard filters in electronic form. Title: A Grid of Non-LTE Model Atmospheres for White Dwarfs in Cataclysmic Variables Authors: Barman, Travis S.; Hauschildt, Peter H.; Short, C. Ian; Baron, E. Bibcode: 2000ApJ...537..946B Altcode: We have calculated a grid of non-LTE (NLTE) line-blanketed model atmospheres for white dwarfs in cataclysmic variable (CV) systems using our stellar atmosphere code PHOENIX. The grid covers the temperature range 20,000-500,000 K for solar abundances and 10-2 and 10-4 solar metal abundance. The effective temperature resolution is 10,000 K in the range 20,000-200,000 K and is 20,000 K in the range 200,000-500,000 K. The models include a large number of NLTE levels for light metals such as CNO and heavy metals such as Ni and Fe. The necessity of using self-consistent NLTE line-blanketed model atmospheres for the analysis of white dwarfs is well known and reaffirmed here. We discuss the importance of metal opacity, especially metals heavier than Ca, in the atmospheres of CV primaries. We also compare our grid to previously published models and discuss the general improvements offered by our models. In addition, a specific model from our grid is compared to a Hubble Space Telescope observation of U Gem and predictions for Far-Ultraviolet Spectroscopic Explorer (FUSE) observations are made. Title: An Effective Temperature Scale for Late-M and L Dwarfs, from Resonance Absorption Lines of Cs I and Rb I Authors: Basri, Gibor; Mohanty, Subhanjoy; Allard, France; Hauschildt, Peter H.; Delfosse, Xavier; Martín, Eduardo L.; Forveille, Thierry; Goldman, Bertrand Bibcode: 2000ApJ...538..363B Altcode: 2000astro.ph..3033B We present Keck HIRES spectra of six late-M dwarfs and 11 L dwarfs. Our goal is to assign effective temperatures to the objects using detailed atmospheric models and fine analysis of the alkali resonance absorption lines of Cs I and Rb I. These yield mutually consistent results (+/-50 K) when we use ``cleared-dust'' models, which account for the removal of refractory species from the molecular states but do not include dust opacities. We find a tendency for the Rb I line to imply a slightly higher temperature, which we ascribe to an incomplete treatment of the overlying molecular opacities. The final Teff we adopt are based on the Cs I fits alone, though the Rb I fits support the Cs I temperature sequence. This work, in combination with results from the infrared, hints that dust in these atmospheres has settled out of the high atmosphere but is present in the deep photosphere. We also derive radial and rotational velocities for all the objects, finding that the previously discovered trend of rapid rotation for very low mass objects is quite pervasive. To improve on our analysis, there is a clear need for better molecular line lists and a more detailed understanding of dust formation and dynamics. Title: Spectral Energy Distributions for Disk and Halo M Dwarfs Authors: Leggett, S. K.; Allard, F.; Dahn, Conard; Hauschildt, P. H.; Kerr, T. H.; Rayner, J. Bibcode: 2000ApJ...535..965L Altcode: 2000astro.ph..1100L We have obtained infrared (1-2.5 μm) spectroscopy for 42 halo and disk dwarfs with spectral types M1-M6.5. These data are compared to synthetic spectra generated by the latest model atmospheres of Allard & Hauschildt. Photospheric parameters metallicity, effective temperature, and radius are determined for the sample.We find good agreement between observation and theory except for known problems due to incomplete molecular data for metal hydrides and H2O. The metal-poor M subdwarfs are well matched by the models, as oxide opacity sources are less important in this case. The derived effective temperatures for the sample range from 3600 to 2600 K; at these temperatures grain formation and extinction are not significant in the photosphere. The derived metallicities range from solar to 1/10 solar. The radii and effective temperatures derived agree well with recent models of low-mass stars. The spectra are available in electronic form upon request. Title: Diffusion in the Atmospheres of Blue Horizontal-Branch Stars Authors: Hui-Bon-Hoa, A.; LeBlanc, F.; Hauschildt, P. H. Bibcode: 2000ApJ...535L..43H Altcode: We investigate the effects of diffusion in the atmospheres of hot horizontal-branch stars using a model atmosphere code including diffusion self-consistently. Equilibrium stratifications (i.e., for which the diffusion velocity equals zero in each layer) are computed for models of effective temperatures between 10,000 and 25,000 K. The stratified models provide much better agreement with many observational features [jump in the (u, u-y) color-magnitude diagram, gaps, lower spectroscopic gravities] in comparison with classical horizontal-branch models. The observed abundance anomalies are also consistent with the amounts that can be supported in the atmospheres. Title: Metallicity Effects in Non-LTE Model Atmospheres of Type IA Supernovae Authors: Lentz, Eric J.; Baron, E.; Branch, David; Hauschildt, Peter H.; Nugent, Peter E. Bibcode: 2000ApJ...530..966L Altcode: 1999astro.ph..6016L We have calculated a grid of photospheric phase atmospheres of Type Ia supernovae (SNe Ia) with metallicities from 10 times to 1/30 the solar metallicity in the C+O layer of the deflagration model, W7. We have modeled the spectra using the multipurpose non-LTE model atmosphere and spectrum synthesis code PHOENIX. We show models for the epochs 7, 10, 15, 20, and 35 days after explosion. When compared to observed spectra obtained at the approximately corresponding epochs, these synthetic spectra fit reasonably well. The spectra show variation in the overall level of the UV continuum with lower fluxes for models with higher metallicity in the unburned C+O layer. This is consistent with the classical surface cooling and line-blocking effect due to metals in the outer layers of C+O. The UV features also move consistently to the blue with higher metallicity, demonstrating that they are forming at shallower and faster layers in the atmosphere. The potentially most useful effect is the blueward movement of the Si II feature at 6150 Å with increasing C+O layer metallicity. We also demonstrate the more complex effects of metallicity variations by modifying the 54Fe content of the incomplete burning zone in W7 at maximum light. We briefly address some shortcomings of the W7 model when compared to observations. Finally, we identify that the split in the Ca H+K feature produced in W7 and observed in some SNe Ia is due to a blending effect of Ca II and Si II and does not necessarily represent a complex abundance or ionization effect in Ca II. Title: Modelling the M-S-C Giants Spectral Sequence Authors: Allard, France; Hauschildt, Peter H.; Alexander, David R.; Cohen, Martin; Augason, Gordon C. Bibcode: 2000IAUS..177..517A Altcode: No abstract at ADS Title: Theoretical Models for Substellar Objects (Contributed Talk) Authors: González, J. -F.; Allard, F.; Baraffe, I.; Chabrier, G.; Hauschildt, P. H. Bibcode: 2000ASPC..219..486G Altcode: 2000dpp..conf..486G No abstract at ADS Title: High Resolution Spectra of L Type Stars and Brown Dwarfs Authors: Basri, G.; Allard, F.; Hauschildt, P.; Mohanty, S. Bibcode: 2000vlms.conf..133B Altcode: No abstract at ADS Title: Model Atmospheres and Spectra of Brown Dwarfs to Giant Planets Authors: Allard, F.; Hauschildt, P. H.; Alexander, D. R.; Ferguson, J. W.; Tamanai, A. Bibcode: 2000ASPC..212..127A Altcode: 2000fgpc.conf..127A No abstract at ADS Title: Evolution of Low-Mass Stars and Substellar Objects. Contribution to the Galactic Mass Budget Authors: Chabrier, G.; Baraffe, I.; Allard, F.; Hauschildt, P. H. Bibcode: 2000fepc.conf..399C Altcode: 1999astro.ph..5210C We briefly summarize our present knowledge of the theory of low-mass stars and substellar objects and their contribution to the Galactic population. Title: Self-consistent model atmospheres including diffusion Authors: Hui-Bon-Hoa, A.; LeBlanc, F.; Hauschildt, P. H. Bibcode: 2000IAUJD...5E..22H Altcode: We present a new development of the multipurpose model atmosphere code PHOENIX which includes self-consistently the effects of diffusion. Following the approach used for the resolution of the radiative tranfer, the radiative accelerations of each element are calculated by the opacity sampling method. The mutual influence of abundance variations among the different elements is therefore considered. We compute equilibrium stratifications (i. e. those for which the diffusion velocity equals zero in each layer) for each element, that is, the amount that can be supported by the radiative accelerations. We will compare our results with observations of Chemically Peculiar stars. In particular, we will show that there is a much better agreement between our models and the photometry of blue Horizontal-Branch (HB) stars in comparison with canonical HB models. Title: The multiple system LHS 1070: a case study for the onset of dust formation in the atmospheres of very low mass stars Authors: Leinert, Christoph; Allard, France; Richichi, Andrea; Hauschildt, Peter H. Bibcode: 2000A&A...353..691L Altcode: LHS 1070 (other common name: GJ 2005) is a nearby multiple system consisting of very low mass red dwarfs. We present the results of WFPC2 photometry and FOS spectroscopy for the three optically resolved components of this system acquired during HST cycle 5. These show (1) absolute brightnesses corresponding to theoretical masses of 0.080-0.083 Msun and 0.079-0.080 Msun for the faint pair, depending mainly on their age and metallicity; (2) a saturation of the optical TiO and VO absorption bands typical of the onset of photospheric dust formation, and (3) emission lines typical of moderate chromospheric activity in only the two most massive components. Li I lines are not seen. But also all other lines of the alkali elements are remakably weak or even absent in the two faint companions B and C. This appears to be an effect of dust formation. Comparison of the observations with model spectra, which account for dust formation and for the resulting opacities, yields good agreement for solar metallicity and effective temperatures and gravities (in log cm/s2) of 2950 K;5.3, 2400 K;5.5 and 2300 K;5.5 for the three components A,B and C, respectively. The existence of a fourth component, recently discovered in this system by HST Fine Guidance Sensor observations (Henry et al. \cite{henry99}), has already been taken into account in the evaluation of the data for the main component. An effective temperature and gravity (in log cm/s2) for the fourth component of 2500 K;5.3 would best be compatible with our data. Then, based on our analysis the three components C, B and D of LHS 1070, in this order, are the faintest stars within 20 pc of the Sun for which dynamical determinations of mass appear possible within a decade. The system LHS 1070 thus has the potential to be the most important source of information for probing the low mass end of the main sequence. Based on observations with the Hubble Space Telescope, with additional observations obtained on the ESO-MPIA 2.2 m telescope on La Silla, Chile. Title: Ni56 Mixing in the Early Expansion Phase of SN 1987A Authors: Mitchell, R. C.; Baron, E.; Branch, D.; Lundqvist, P.; Blinnikov, S. I.; Hauschildt, P. H. Bibcode: 1999AAS...195.4305M Altcode: 1999BAAS...31.1432M Supernova 1987A provided excellent broad-band photometry and spectroscopic coverage over a wide wavelength range. It is particularly well studied in the very early days of a supernova expansion. It is only in recent years that models of the expanding envelope of a supernova have been of sufficient detail to accurately explain the observed spectra. Good agreements have been found between observed and synthetic spectra for day one, but by day four, substantial discrepancies have been observed. Schmutz et al. (1990), using various hydrodynamic models, noted that observed Balmer lines were much stronger than predicted, despite the fact that the photospheric temperature had dropped below the ionization threshold. Takeda (1991), using a pure H/He steady-state envelope model in non-LTE, also noted the weakness of the theoretical Balmer lines. We present the results of work based on a radiation-hydrodynamic model by Blinnikov et al. (1999). Synthetic non-LTE spectra generated from this model by the general radiation transfer code PHOENIX strongly support the theory that significant mixing of Ni56 into the outer envelope is required to maintain strong Balmer lines through day four. Preliminary results suggest an average nickel mass of 10-8 to 10-7 solar masses mixed above the line forming region at day four. Once the entire time series has been successfully modeled, we will be able to calculate an accurate distance to SN 1987A. This work was supported in part by NSF grants AST-9731450 and AST-9417102, NASA grant NAG5-3505, and an IBM SUR grant to the University of Oklahoma. Some of the calculations presented in this poster were performed at the San Diego Supercomputer Center (SDSC), supported by the NSF, and at the National Energy Research Supercomputer Center (NERSC), supported by the U.S. DOE. We thank both these institutions for a generous allocation of computer time. Title: Non-LTE Line-blanketed Stellar Wind Atmosphere Models for the A-supergiant Deneb Authors: Aufdenberg, J. P.; Hauschildt, P. H.; Baron, E. Bibcode: 1999AAS...195.5001A Altcode: 1999BAAS...31.1446A We present non-LTE metal line-blanketed stellar wind atmosphere models and synthetic spectra for comparison with the spectral energy distribution of the A-supergiant Deneb from UV to radio wavelengths. Deneb is alone among A-supergiants in having both a precisely measured angular diameter from the Navy Prototype Optical Interferometer (Nordgren, T. et al., 1999, priv. comm.) and a positive detection at centimeter wavelengths with the Very Large Array (Howarth, I., 1999, priv. comm.). These recent measurements together with our wind atmosphere models considerably improve constraints on Deneb's fundamental stellar and wind parameters. Using the precise angular diameter we are able to use the Barnes-Evans relationship to constrain the reddening toward Deneb independent of any assumptions about its intrinsic colors. Our models treat the hydrostatic inner atmosphere and the extended expanding outer atmosphere as a unified structure and the radiative transfer is solved in the co-moving frame. We present synthetic radio spectra for the partially ionized winds of A-supergiants over a range of mass-loss rates and we find that the standard assumptions regarding the radio spectra of warm supergiants break down for A-supergiants. By simultaneously fitting the UV, optical, IR and radio spectrophotometry we are able to constrain the mass-loss rate and temperature distribution throughout the extended atmosphere. Stability of the deep hydrostatic layers against outward acceleration provides a lower limit on gravitational acceleration in these layers. This work was supported in part by an Arizona State University NASA Space Grant Fellowship and CNRS, NSF, and NASA grants to the University of Georgia. Some calculations were performed on the IBM SP and the SGI Origin 2000 of the UGA UCNS and on the IBM SP at SDSC and on the Cray T3E of the NERSC. Title: The Binary L-Dwarf DENIS-P J0205-1159 Authors: Leggett, S. K.; Allard, F.; Geballe, T. R.; Hauschildt, P. H. Bibcode: 1999AAS...19510902L Altcode: 1999BAAS...31R1533L We report the confirmation of another identical-pair small-separation binary L-dwarf in imaging JHKL' data taken with the TUFTI camera on UKIRT. We place the system in physical context within a sample of nine M9-L7 dwarfs using low (R 600) and medium (R 3000) resolution infrared spectroscopy, obtained with CGS4 on UKIRT, to constrain the most recent models by Allard and Hauschildt. We derive effective temperature, gravity and metallicity. The new models include improved linelists for titanium oxide, iron hydride and water. The effect of dust condensation and extinction is treated in a detailed way using models which include clouds. Metallicity effects are also considered. Title: Nova V382 Velorum: first Hubble Space Telescope spectrum and NLTE atmospheric modeling Authors: Short, C. I.; Hauschildt, P. H.; Shore, S. N.; Starrfield, S.; Baron, E. Bibcode: 1999AAS...195.3606S Altcode: 1999BAAS...31.1420S We present the initial fitting of non-LTE nova models to the first ultraviolet spectra of Nova V382 Velorum taken with the Hubble Space Telescope Imaging Spectrograph. We find a best fit T eff of 19 000 K and that the velocity field is better described by a radiatively driven wind law rather than that of ballistic expansion. We find that by the time that the first HST spectrum was taken at May 31.3 UT, which was eight days after visual maximum, the region around the Mg II hk lines already exhibited strong nebular emission on top of the optically thick envelope spectrum. However, at shorter wavelengths the spectrum still corresponds to the optically thick wind phase of the nova outburst, and we are able to identify the P-Cyg profiles of the Al III λ 1855 and 1863 lines. This work was supported in part by NSF grant AST-9720704, NASA ATP grant NAG 5-3018 and LTSA grant NAG 5-3619 to the University of Georgia. Title: Treatment of molecular non--LTE in cool stellar atmospheres Authors: Schweitzer, A.; Hauschildt, P. Bibcode: 1999AAS...195.5003S Altcode: 1999BAAS...31.1447S We developed a technique to treat huge systems like molecules in non--LTE. This technique is based on the superlevel formalism. Superlevels consist of many individual levels that are assumed to be in LTE. The usage of superlevels reduces the size of the rate equations and the number of rates dramatically and, thereby, makes the problem computationally feasible. Our superlevel formalism retains maximum accuracy by using direct opacity sampling (dOS) when calculating the radiative transitions. We implemented this method in our current model atmospheres for cool dwarfs. Cool dwarfs have low electron densities and a radiation field that is far from a black body. Both properties invalidate the conditions for the common LTE approximation. Therefore, we need to treat the huge molecular systems in non--LTE. As a case study we applied our method on carbon monoxide. We find that our method gives accurate results since the conditions for the superlevel method are very well met for molecules. The test molecule CO shows significant deviations from LTE in the outer regions of cool photospheres. Title: Spectral Models of the Type IC Supernova SN 1994I in M51 Authors: Baron, E.; Branch, David; Hauschildt, Peter H.; Filippenko, Alexei V.; Kirshner, R. P. Bibcode: 1999ApJ...527..739B Altcode: 1999astro.ph..7172B We present detailed non-LTE (NLTE) synthetic spectra for comparison with a time series of observed optical spectra of the Type Ic supernova SN 1994I which occurred in M51. With the exceptions of Si I and S I, we treat the important species in the formation of the spectrum in full NLTE. We present results for both a hydrodynamic model that has been fitted to the light curve and for an illustrative custom-crafted model that is more massive. Both models give reasonable fits to the overall observed spectra; however, neither is able to reproduce all the observed features. Some conspicuous observed features are absent, and some predicted features are unobserved. No model that we have explored is able to reproduce satisfactorily the observed infrared feature near 1 μm on 1994 April 15 (+7 days), which has been attributed to the triplet He I λ10830 transition. The low-mass hydrodynamic model produces an infrared feature with a blend of He I, C I, O I, and Si I-Si II lines, but it predicts a strong unobserved absorption feature near 6100 Å due to Fe III, and the observed feature just blueward of 6000 Å most likely due to Na D is not reproduced. The more massive model does a better job of reproducing the observed infrared line shape, but also predicts the unobserved feature near 6100 Å. The early-time spectrum of the low-mass model is far too blue; thus, a more massive model may be slightly favored. Since the predicted infrared feature is produced by a blend of so many elements, and there is no overwhelming evidence for other helium features such as λ5876, it may be premature to conclude that SNe Ic unambiguously contain helium. Thus, we conclude that pure C + O cores are still viable progenitors for SNe Ic. Title: SN 1984A and Delayed Detonation Models of Type Ia Supernovae Authors: Lentz, E. J.; Baron, E.; Branch, D.; Hauschildt, P. H. Bibcode: 1999AAS...195.3807L Altcode: 1999BAAS...31.1424L Supernova SN 1984A shows unusually large expansion velocities in lines from freshly synthesized material, relative to typical Type Ia supernovae (SNe Ia). SN 1984A represents an extreme example of SNe Ia with large expansion velocities, but otherwise normal spectra. We have modeled several early spectra of SN 1984A with the multi-purpose NLTE model atmosphere and spectrum synthesis code, PHOENIX. We have used as input two delayed detonation models, DD21c (Höflich et al. 1998) and CS15DD3 (Iwamoto et al. 1999). These models show line expansion velocities which are larger than for typical deflagration models like W7 (Nomoto et al. 1984, Thielemann et al. 1986), which we have previously shown to fit normal SNe Ia quite well (Lentz et al. 2000). Higher densities of newly synthesized material from burning at higher velocities are found in delayed detonation models than in deflagration models. We find these delayed detonation models to be reasonable approximations to high expansion velocity SNe Ia like SN 1984A. Even if the explosion mechanism of the delayed detonation models is incorrect, the density of synthesized material at high velocities is of the right magnitude. Title: The NEXTGEN Model Atmosphere Grid. II. Spherically Symmetric Model Atmospheres for Giant Stars with Effective Temperatures between 3000 and 6800 K Authors: Hauschildt, Peter H.; Allard, France; Ferguson, Jason; Baron, E.; Alexander, David R. Bibcode: 1999ApJ...525..871H Altcode: 1999astro.ph..7194H We present the extension of our NextGen model atmosphere grid to the regime of giant stars. The input physics of the models presented here is nearly identical to that of the NextGen dwarf atmosphere models; however, spherical geometry is used self-consistently in the model calculations (including the radiative transfer). We revisit the discussion of the effects of spherical geometry on the structure of the atmospheres and the emitted spectra and discuss the results of non-LTE calculations for a few selected models. Title: Massive Multispecies, Multilevel Non-LTE Model Atmospheres for Novae in Outburst Authors: Short, C. Ian; Hauschildt, Peter H.; Baron, E. Bibcode: 1999ApJ...525..375S Altcode: 1999astro.ph..6238S We have used our PHOENIX multipurpose model atmosphere code to calculate atmospheric models that represent novae in the optically thick wind phases of their outburst. We have improved the treatment of non-local thermodynamic equilibrium (NLTE) effects by expanding the number of elements that are included in the calculations from 15 to 19 and the number of ionization stages from 36 to 87. The code can now treat a total of 10,713 levels and 102,646 lines in NLTE. Al, P, K, and Ni are included for the first time in the NLTE treatment, and most elements now have at least the lowest six ionization stages included in the NLTE calculation. We have investigated the effects of expanded NLTE treatment on the chemical concentration of astrophysically significant species in the atmosphere, the equilibrium structure of the atmosphere, and the emergent flux distribution. Although we have found general qualitative agreement with previous, more limited NLTE models, the expanded NLTE treatment leads to significantly different values for the size of many of the NLTE deviations. In particular, for the hottest model presented here (Teff=35,000 K), for which NLTE effects are largest, we find that the expanded NLTE treatment reduces the NLTE effects for these important variables: H I concentration, pressure structure, and emergent far-UV flux. Moreover, we find that the addition of new NLTE species may greatly affect the concentration of species that were already treated in NLTE, so that, generally, all species that contribute significantly to the e- reservoir or to the total opacity, or whose line spectrum overlaps or interlocks with that of a species of interest, must be treated in NLTE to ensure an accurate result for any particular species. Title: Numerical solution of the expanding stellar atmosphere problem. Authors: Hauschildt, P. H.; Baron, E. Bibcode: 1999JCoAM.109...41H Altcode: 1998astro.ph..8182H The authors discuss numerical methods and algorithms for the solution of NLTE stellar atmosphere problems involving expanding atmospheres, e.g., found in novae, supernovae and stellar winds. They show how a scheme of nested iterations can be used to reduce the high dimension of the problem to a number of problems with smaller dimensions. As examples of these sub-problems, they discuss the numerical solution of the radiative transfer equation for relativistically expanding media with spherical symmetry, the solution of the multi-level nonLTE statistical equilibrium problem for extremely large model atoms, and their temperature correction procedure. Although modern iteration schemes are very efficient, parallel algorithms are essential in making large-scale calculations feasible, therefore they discuss some parallelization schemes that they have developed. Title: Nova Sagittarii 1994 1 (V4332 Sagittarii): The Discovery and Evolution of an Unusual Luminous Red Variable Star Authors: Martini, Paul; Wagner, R. Mark; Tomaney, Austin; Rich, R. Michael; della Valle, M.; Hauschildt, Peter H. Bibcode: 1999AJ....118.1034M Altcode: 1999astro.ph..5016M We report photometry and spectroscopy of the evolution of Nova Sagittarii 1994 1 (V4332 Sagittarii) during outburst. We compare the photometric and spectral evolution of this outburst with known classes of outbursts-including classical novae and outbursts occurring on symbiotic stars-and find this object does not conform to any known class of outburst. The closest match to the behavior of this unusual object is M31 RV, an extremely luminous and red variable object discovered in the bulge of M31 in 1988. However, the temporal behavior and maximum luminosity of the two events differ by several orders of magnitude, requiring substantial intrinsic variation if these two events are members the same type of outburst. Our model of the spectroscopic evolution of this outburst shows that the effective temperature cooled from 4400 to 2300 K over the 3 month span of our observations. In combination with line diagnostics in our later spectra, including [O I] lambda5577 and the dramatic increase in the Hα-to-Hβ ratio, we infer the existence of a cool, dense (N_e~10^8-10^9 cm^-3) envelope that is optically thick in the hydrogen Balmer recombination lines (case C). We suggest that a nuclear event in a single star, in which a slow shock drove the photosphere outward, can power the observed luminosity evolution and the emission spectrum. Title: Barnes-Evans relations for late-type giants and dwarfs Authors: Beuermann, K.; Baraffe, I.; Hauschildt, P. Bibcode: 1999A&A...348..524B Altcode: 1999astro.ph..6350B The visual surface brightness of K/M giants and dwarfs with near-solar metallicity differ slightly in agreement with the gravity effects predicted by recent theoretical models. We show that M-dwarfs display also a metallicity dependence of the surface brightness in the infrared K-band in agreement with theory. Based on these results, we present improved Barnes-Evans type relations and estimate the radii of 60 single or presumed M and K-dwarfs. Title: High-resolution spectroscopy of ROSAT-discovered weak-line T Tauri stars near Lupus Authors: Wichmann, R.; Covino, E.; Alcalá, J. M.; Krautter, J.; Allain, S.; Hauschildt, P. H. Bibcode: 1999MNRAS.307..909W Altcode: We present high-resolution optical echelle spectroscopy for a large fraction of the Li-rich late-type stars recently discovered in the vicinity of the Lupus dark clouds. Our results confirm the high Liilambda6708 equivalent widths previously estimated from medium-resolution spectra, thus adding strength to the conclusion that the large majority of these stars are still in the pre-main-sequence phase of their evolution, contrary to claims from other authors that many of them might be zero-age main-sequence stars. We present a statistical approach to derive a mean distance for the sample, and find that it is consistent with, or slightly lower than, the Hipparcos distance of the Lupus star-forming region. The radial velocities measured for part of these stars are consistent with those observed for the Lupus star-forming region, while stars outside the dark clouds show a mean difference of the order of 3kms^-1. The projected rotational velocities show a lack of slow rotators, which is interpreted as a consequence of the X-ray selection of the sample. The Li-rich stars in Lupus studied in this work yield a fairly `clean' sample of very young stars, while in other star-forming regions a larger fraction of older zero-age main-sequence stars has been found among ROSAT-discovered Li-rich stars. We argue that this fact reflects the relation of these stars with the Gould Belt. Title: On the abundance of lithium in T Coronae Borealis Authors: Shahbaz, T.; Hauschildt, P. H.; Naylor, T.; Ringwald, F. Bibcode: 1999MNRAS.306..675S Altcode: 1999astro.ph..2225S We have obtained high-resolution echelle spectroscopy of the recurrent nova T CrB. We find that the surface lithium abundance in T CrB is significantly enhanced compared with the case of field M giants, where it is not detectable. We offer possible explanations for this in terms of either a delay in the onset of convection in the giant star, enhanced coronal activity caused by star-spots or the enhancement of Li resulting from the nova explosion(s). Title: Model Atmospheres of Hot Luminous Stars with Winds Authors: Aufdenberg, J. P.; Hauschildt, P. H.; Baron, E. Bibcode: 1999AAS...194.1304A Altcode: 1999BAAS...31..845A We present preliminary atmospheric structures and synthetic spectra for hot luminous OB stars with winds. We use the latest version of our multi-purpose stellar atmosphere and radiative transfer code PHOENIX. In these steady-state expanding model atmospheres, we assume a beta-law velocity structure for the wind and solve the spherical co-moving frame radiative transfer equation with full non-LTE metal-line blanketing. In these models the solution of the radiation transfer equation treats both the static photosphere and the expanding wind components as a single structure. The temperature structure is solved for iteratively by satisfying energy conservation. These models provide predictions for the ionization structure within the wind and allow us to calculate synthetic spectra which include the extreme ultraviolet ionizing flux distribution and detailed line profiles. We acknowledge partial support from NASA and NSF grants to our respective institutions. Title: Metallicity Effects in NLTE Model Atmospheres of Type IA Supernovae Authors: Lentz, E. J.; Baron, E.; Branch, D.; Hauschildt, P. H.; Nugent, P. E. Bibcode: 1999AAS...194.8606L Altcode: 1999BAAS...31R.976L We have calculated a grid of photospheric phase atmospheres of Type Ia supernovae (SNe Ia) with metallicities from ten times to one thirtieth the normal metallicity in the C+O layer of the deflagration model, W7 (Nomoto et al. 1984, Thielemann et al. 1986). We have modeled the spectra using the multi-purpose NLTE model-atmosphere and spectrum-synthesis code, PHOENIX. We show models for the epochs 7, 10, 15, 20, and 35 days after explosion. When compared to approximately corresponding spectra observed at epochs -12, -9, -4, 0, and 15 days after peak B magnitude, these synthetic spectra fit reasonably well. The spectra show a consistent variation in the overall level of the UV `contiunuum' with higher fluxes for models with lower metallicity in the unburned C+O layer. The models show higher temperatures in the outer layers of C+O with lower metallicity and less surface cooling from the metals. The UV features also move consistently to the blue with higher metallicity demonstrating that they are forming at shallower and faster layers in the atmosphere. The last, and potentially most useful, effect is the blueward movement of the Si II feature at 6150 Angstroms with increasing C+O layer metallicity. We also demonstrate the more complex effects of modifying the (54) Fe content of the incomplete burning zone in W7 at maximum light. We discuss effects of the results on the use of SNe Ia for cosmology. We briefly address some shortcomings of the W7 model when compared to observations. Title: Period-luminosity-color-radius relationships of Cepheids as a function of metallicity: evolutionary effects Authors: Alibert, Yann; Baraffe, Isabelle; Hauschildt, Peter; Allard, France Bibcode: 1999A&A...344..551A Altcode: 1999astro.ph..1294A Based on consistent evolutionary and pulsation calculations, we analyse the effect of metallicity and of different convection treatments in the stellar models on period-magnitude, -color and -radius relationships. In order to perform an accurate comparison with observations, we have computed grids of atmosphere models and synthetic spectra for different metallicities, covering the range of effective temperatures and gravities relevant for Cepheids. The models are compared to recent observations of galactic and Magellanic Clouds Cepheids. Unprecedented level of agreement is found between models and observations. We show that within the range of metallicity for the Galaxy and the Magellanic Clouds, a change of slope in the period-luminosity (PL) relationship is predicted at low periods, due to the reduction of the blue loop during core He burning. The minimum mass undergoing a blue loop and consequently the critical period at which this change of slope occurs depend on the metallicity Z and on the convection treatment in the stellar models. However, besides this change of slope, we do not find any significant effect of metallicity on period-magnitude relationships from V to K bands, and on period-color relationships in IR colors. We only find a detectable effect of Z on (B-V) colors. These results are not affected by uncertainties inherent in current stellar models, mainly due to convection treatment. Title: On the primordial helium abundance and spectroscopic uncertainties. Authors: Pistinner, S. L.; Hauschildt, P. H.; Eichler, D.; Baron, E. Bibcode: 1999PhR...311..151P Altcode: To assess the uncertainties in primordial helium abundance determination by nebular codes, the authors calculate a grid of OB stellar atmospheres at low metallicities, including both non-local thermodynamic equilibrium (NLTE) and metal line blanketing effects. The more sophisticated stellar atmosphere models one uses can differ from LTE models by as much as 40% in the ratio of He to H-ionizing photons. Title: ISO observations of XX Oph Authors: Evans, A.; Eyres, S. P. S.; Hauschildt, P. H.; Allard, F. Bibcode: 1999ESASP.427..305E Altcode: 1999usis.conf..305E We present ISO SWS and PHOT-P observations of the binary XX Oph. The UIR features seen in ground-based data are confirmed. The near infrared is modelled by a 3400 K log g=3.5 giant, which is likely to be underabundant in carbon. There is an infrared excess at long wavelengths, corresponding to emission by dust having temperature 336 K and β-index 0.4. Title: The NextGen Model Atmosphere Grid for 3000<=Teff<=10,000 K Authors: Hauschildt, Peter H.; Allard, France; Baron, E. Bibcode: 1999ApJ...512..377H Altcode: 1998astro.ph..7286H We present our NextGen Model Atmosphere grid for low-mass stars for effective temperatures larger than 3000 K. These LTE models are calculated with the same basic model assumptions and input physics as the VLMS part of the NextGen grid so that the complete grid can be used, e.g., for consistent stellar evolution calculations and for internally consistent analysis of cool star spectra. This grid is also the starting point for a large grid of detailed NLTE model atmospheres for dwarfs and giants. The models were calculated from 3000 to 10,000 K (in steps of 200 K) for 3.5<=logg<=5.5 (in steps of 0.5) and metallicities of -4.0<=[M/H]<=0.0.

We discuss the results of the model calculations and compare our results to the Kurucz grid. Some comparisons to standard stars like Vega and the Sun are presented and compared with detailed NLTE calculations. Title: Spectroscopy of low-metallicity giant HII regions: a grid of low-metallicity stellar atmospheres Authors: Pistinner, S. L.; Hauschildt, P. H.; Eichler, D.; Baron, E. A. Bibcode: 1999MNRAS.302..684P Altcode: 1998astro.ph.11021P We calculate a grid of spherically symmetric OB stellar atmospheres at low metallicities, including both non-local thermodynamic equilibrium (NLTE) and metal line blanketing effects. This is done to assess the uncertainties in helium abundance determination by nebular codes due to input stellar atmosphere models. The more sophisticated stellar atmosphere models we use can differ from LTE models by as much as 40 per cent in the ratio of He to H ionizing photons. Title: A Grid of White Dwarf NLTE Model Atmospheres Authors: Barman, T. S.; Hauschildt, P. H.; Baron, E.; Short, C. I. Bibcode: 1999AAS...19312410B Altcode: 1999BAAS...31S.669B We have calculated a grid of White Dwarf NLTE line blanketed model atmospheres using the stellar atmosphere code PHOENIX. The grid covers the temperature range 20,000K to 500,000K and is complete for solar abundance, 10-2 and 10-4 solar abundance. The grid has a temperature resolution of 10,000K in the range of 20,000K to 200,000K and a resolution of 20,000K in the range of 200,000K to 500,000K. The models include a large number of NLTE levels and lines for H, He, C, N and O as well as Si, S, and Fe. The necessity of using self-consistent NLTE line blanketed model atmospheres for the analysis of White Dwarfs is well known. Our new grid makes the most detailed state-of-the-art calculations available for both reevaluating current data and for the study of data yet to be acquired(e.g., by AXAF and FUSE). Our models will be useful, for example, in spectral analysis of hot PG 1159 type stars, determining metal abundances in hot DA and DB White Dwarfs, as well as studying the evolution of novae, and cataclysmic variables. Title: Effective Temperature Scales of Red Giants Stars Authors: Alexander, D. R.; Ferguson, J. W.; Wing, R. F.; Johnson, H. R.; Hauschildt, P. H.; Allard, F. Bibcode: 1999IAUS..191...84A Altcode: We have completed a grid of spherically symmetric AGB star atmospheres using the state of the art spectral synthesis code PHOENIX. Models are constructed for stars with masses of 1 Msun and 1.5 Msun, spanning the range 10 to 3,300 Lsun in luminosity and 2,500 to 5,200 K in effective temperature. We find that grains of Al2O 3 and CaTiO3 among other species form in atmospheres cooler than Teff =~ 3,000 K. In the coolest models the grains cause a weakening of the TiO absorption features in the red and near infrared of up to 30% through both a depression of the continuum and a depletion of the TiO number abundance. We use spectrophotometric observations from a number of catalogs to determine effective temperature - spectral class and effective temperature - color relationships. We also compare synthetic colors calculated from our models with observations of M giants on Wing's 8-color narrow-band system of classification photometry. Title: The Properties of Novae in the LMC and Beyond Authors: Starrfield, S.; Vanlandingham, K. M.; Schwarz, G. J.; Hauschildt, P. H.; Shore, S. N.; Sonneborn, G. Bibcode: 1999ASPC..164..131S Altcode: 1999uosa.conf..131S No abstract at ADS Title: A non-local thermodynamic equilibrium spherical line-blanketed stellar atmosphere model of the early B giant beta CMa Authors: Aufdenberg, J. P.; Hauschildt, P. H.; Baron, E. Bibcode: 1999MNRAS.302..599A Altcode: The observed multiwavelength spectrum of the B1II--III star beta CMa is successfully reproduced, including the extreme ultraviolet (EUV) continuum observed by Extreme Ultraviolet Explorer (EUVE), with a non-local thermodynamic equilibrium fully line-blanketed spherical hydrostatic model atmosphere. The available spectrophotometry of beta CMa from 500 A to 25 mu m is best fitted with model parameters T_eff = 24000 K, log g = 3.5 and an angular diameter of theta_LD = 0.565 mas. We find that a neutral interstellar hydrogen column of N(H^0) ~= 2 x 10^18 cm^-2 provides the best agreement between the model EUV flux and that observed by EUVE. We use model atmosphere fits together with Hipparcos distances to calculate radii, luminosities and ionizing fluxes for beta CMa and alpha Vir. An investigation of spherical and plane-parallel models shows that the Lyman continuum predictions are quite sensitive to model geometry and surface gravity between effective temperatures 18 000 and 33 000 K. This result provides an explanation for the reported excesses between the observed EUV fluxes from beta CMa and epsilon CMa and plane-parallel model atmosphere predictions. Title: Model Atmospheres for Novae in Outburst: Summary of Research Authors: Hauschildt, Peter H. Bibcode: 1999STIN...0030685H Altcode: This paper presents a final report and summary of research on Model Atmospheres for Novae in Outburst. Some of the topics include: 1) Detailed NLTE (non-local thermodynamic equilibrium) Model Atmospheres for Novae during Outburst: II. Modeling optical and ultraviolet observations of Nova LMC 1988 #1; 2) A Non-LTE Line-Blanketed Stellar Atmosphere Model of the Early B Giant epsilon CMa; 3) Spectroscopy of Low Metallicity Stellar atmospheres; 4) Infrared Colors at the Stellar/Substellar Boundary; 5) On the abundance of Lithium in T CrB; 6) Numerical Solution of the Expanding Stellar Atmosphere Problem; and 7) The NextGen Model Atmosphere grid for 3000 less than or equal to T eff less than or equal to 10000K. Title: Analyses of the LMC Novae Authors: Vanlandingham, K. M.; Schwarz, G. J.; Starrfield, S.; Hauschildt, P. H.; Shore, S. N.; Sonneborn, G. Bibcode: 1999IAUS..190..391V Altcode: 1998IAUS..190E.141V In the past 10 years, 6 classical novae have been observed in the Large Magellanic Cloud (LMC). We have begun a study of these objects using ultraviolet spectra obtained by IUE and optical spectra from nova surveys. We are using the results of this study to further our understanding of novae and stellar evolution. Our study includes analysis of both the early, optically thick spectra using model atmospheres, and the later nebular spectra using optimization of photoionization codes. By analysing of all the LMC novae in a consistent manner, we can compare their individual results and use their combined properties to calibrate Galactic novae. In addition, our studies can be used to determine the elemental abundances of the nova ejecta, the amount of mass ejected, and the contribution of novae to the ISM abundances. To date we have analyzed Nova LMC 1988#1 and Nova LMC 1990#1, and have obtained preliminary results for Nova LMC 1991. The results of this work are presented in this poster. The metal content of the LMC is known to be sub-solar and varies as a function of location within the cloud. A detailed abundance analysis of the ejecta of the LMC novae provides important information concerning the effect of initial metal abundances on energetics of the nova outburst. Since the distance to the LMC is well known, many important parameters of the outburst, such as the luminosity, can be absolutely determined. Both galactic and extragalactic novae have been proposed as potential standard candles. Recent work by Della Valle & Livio (1995) has improved on the standard relations (e.g., Schmidt 1957; Pfau 1976; Cohen 1985; Livio 1992) by including novae from the LMC and M31. Unfortunately, the dependence of the nova outburst on metallicity has not been well-studied. Recent theoretical work by Starrfield et al. (1998) indicates that the luminosity of the outburst increases with decreasing metal abundances. If there is a dependence of luminosity on metallicity, it will have to be determined before novae can be used as standard candles. Title: Observations of the Polar ST Leonis Minoris during an Extreme Low State: Identification of the Secondary Star Authors: Ciardi, David R.; Howell, Steve B.; Dhillon, V. S.; Wagner, R. Mark; Hauschildt, Peter H.; Allard, France Bibcode: 1999ASPC..157..146C Altcode: 1999mcv..work..146C We present near-infrared (1.85-2.47 micron) spectroscopic observations of the polar ST Leonis Minoris (ST LMi) in an extreme low-state. The near-infrared spectra, showing no emission lines whatsoever, are produced solely by the secondary star. We have fit the average spectrum with a series of stellar atmosphere models and found the secondary star to have an average temperature of 2800 plus or minus 100 K. However, the phase-resolved spectra show a strong variation in the near-infrared spectra as a function of orbital phase, corresponding to a variation in the surface temperature of the star, ranging from about 3100 K to 2700 K. Title: Spectroscopy of L- and M- Dwarfs Authors: Leggett, S. K.; Allard, F. A.; Dahn, C. C.; Hauschildt, P. H.; Rayner, J. Bibcode: 1998AAS...193.9805L Altcode: 1998BAAS...30.1394L We have obtained infrared (1-2.5 microns) spectroscopy for 54 halo and disk stars around the stellar/substellar boundary. These data are combined with optical data where available and compared to synthetic spectra generated by the latest model atmospheres of Allard & Hauschildt. We find good agreement between observation and theory except for known problems in the V and H passbands probably due to incomplete molecular data for TiO, metal hydrides and H_2O. The metal-poor M subdwarfs are well matched by the models as oxide opacity sources are less important in this case. A version of the NextGen-Dusty models which includes homogeneous formation and extinction by dust grains produces a much improved match to the coolest objects in the sample, compared to the grainless models. Photospheric parameters - metallicity, effective temperature, radius - are determined for the sample. We present relationships between bolometric correction and color, and effective temperature and color, as a function of metallicity, and compare the radii and effective temperatures to recent structural models of low mass stars and brown dwarfs. Title: Infrared Colors at the Stellar/Substellar Boundary Authors: Leggett, S. K.; Allard, F.; Hauschildt, P. H. Bibcode: 1998ApJ...509..836L Altcode: 1998astro.ph..7255L We present new infrared JHK photometry for 61 halo and disk stars around the stellar/substellar boundary. We also present new L' photometry for 21 of these stars and for 40 low-mass stars taken from the Leggett photometry compilation. These data are combined with available optical photometry and astrometric data to produce color-color and absolute magnitude-color diagrams; the current sample extends the similar work presented in the 1992 paper into more metal-poor and lower mass regimes. The disk and halo sequences are compared to the predictions of the latest model atmospheres and structural models. We find good agreement between observation and theory except for known problems in the V and H passbands, probably due to incomplete molecular data for TiO, metal hydrides, and H2O. The metal-poor M subdwarfs are well matched by the models since oxide opacity sources are less important in this case. The known extreme M subdwarfs have metallicities about one-hundredth solar, and the coolest subdwarfs have Teff ~ 3000 K with masses ~0.09M/M⊙. The grainless models are not able to reproduce the flux distributions of disk objects with Teff < 2500 K; however, a preliminary version of the NextGen-Dusty models that includes homogeneous formation and extinction by dust grains is able to match the colors of these very cool objects. The least luminous objects in this sample are GD 165B, three DENIS objects--DBD 0205, DBD 1058, and DBD 1228--and Kelu-1. These have Teff ~ 2000 K and are at or below the stellar limit with masses <=0.075M/M⊙. Photometry alone cannot constrain these parameters further since the age is unknown, but published lithium detections for two of these objects (Kelu-1 and DBD 1228) imply that they are young (aged about 1 Gyr) and substellar (mass <= 0.06M/M⊙). Title: The Lyman Continuum of O stars From Hydrostatic Spherical Non-LTE Line-Blanketed Model Atmospheres Authors: Aufdenberg, J. P.; Hauschildt, P. H.; Baron, E. Bibcode: 1998AAS...193.4408A Altcode: 1998BAAS...30.1316A We have used the parallelized version of the stellar atmosphere and radiative transfer code PHOENIX to compute a set of 45 non-local thermodynamic equilibrium (NLTE) stellar atmosphere models and synthetic spectra corresponding to O stars. These hydrostatic models are computed with spherical geometry treating the ~ 5000 levels of H I, He I-II, C I-IV, N I-VI, O I-VI, Mg II, Ca II, Ne I, S II-III, Si II-III and Fe I-III in NLTE. In addition, approximately 5 million background LTE lines are included in the total line-blanketing. For this set of models, we use a solar metal abundance. We compare the ionizing Lyman continuum fluxes from this set of models to published values from LTE plane-parallel static models. We find our non-LTE spherical models consistently predict larger Lyman continuum fluxes relative to earlier models. Our models predict up to 20% more hydrogen ionizing flux and up to 125% more neutral helium ionizing flux compared to earlier models, particularly for model O stars with Teff < 36,000 K. Title: Multiwavelength observations of nova LMC 1991 during pre-maximum Authors: Schwarz, G. J.; Starrfield, S.; Hauschildt, P. H.; Shore, S. N. Bibcode: 1998AAS...19310108S Altcode: 1998BAAS...30R1400S Nova LMC 1991 (hereafter LMC 91) was the intrisically most luminous nova, and one of the fastest (t_3 = 6 +/- 1 days), yet observed. It was discovered on 18.3 April, 1991 (Liller, IAUC 5244) at m_v = 12, although UK Schmidt J (4000 - 5400 Angstroms) plates show that LMC 91 steadily increased in brightness from a possible pre-outburst magnitude of mV ~ 20.5 in early April. It reached m_V(max) ~ 9 on 24 April. The slow rise to maximum was very unusual, showing behavior more closely resembling a slow nova. The combination of the rapid discovery announcement and a very slow pre-maximum rise permitted many IUE and optical observations. The 20.0 April optical spectrum showed strong hydrogen and iron multiplet P Cygni lines; most other novae with pre-maximum spectra (with the exception of DQ Her) show only blue shifted absorption lines. The IUE spectrum on that date, the earliest UV spectrum ever obtained of a nova in outburst, showed the bulk of the flux being emitted below 2300 Angstroms. By 22.8 April, the UV spectral peak had shifted to lambda > 2500 Angstroms and the spectrum was similar to the pre-maximum spectra seen in Nova Cyg 1992. The best agreement between the observations and the synthetic spectra (calculated with spherical, NLTE, line-blanketed PHOENIX model atmospheres) requires a metallicity Z = 0.1Zsun. This is significantly lower metallicity than the canonical LMC value of 1/3 used to successfully model nova LMC 1988 #1 (Schwarz et al. 1998, MNRAS, in press). The extreme brightness and low metallicity of LMC 91 may confirm recent hydrodynamic calculations that metallicity is inversely correlates with luminosity if mixing occurs during the thermonuclear runaway (Starrfield et al. 1998, MNRAS, 296, 502). Title: Spectral Analysis of Circumstellar Wind Interaction in the Type IIn Supernova 1998S Authors: Lentz, E. J.; Baron, E.; Branch, D.; Hauschildt, P. H.; Fransson, C.; Lundqvist, P.; Garnavich, P. M.; Kirshner, R. P.; SINS Team Bibcode: 1998AAS...193.4708L Altcode: 1998BAAS...30.1324L We analyze the effects of circumstellar interaction on spectra of the Type IIn supernova 1998S obtained from the ground and with the HST by the SINS team. The narrow ( ~ 100 - 1000 km s(-1) ) UV and Balmer lines are assumed to come from a thin circumstellar shell, and the broad ( ~ 5000 - 10,000 km s(-1) ), shallow features must have formed in the supernova. We have modeled the spectra using the general NLTE model-atmosphere and spectrum-synthesis code, PHOENIX. We find general agreement between observations and the model results, however, our models fail to reproduce the strong UV excess. The UV excess can be probably be explained by adding inverse Comptonization of the photospheric photons in the hot shocked gas in the interaction region between ejecta and the wind. A large mass loss rate seems to be needed. We have also explored the effects of external illumination from the shocks on the ejecta, and we find this to be important. We predict that SN 1998S will be a strong radio source, and that it should soon turn on at short radio wavelengths. Title: Massive multi-species, multi-level, non-LTE modeling of stellar atmospheres Authors: Short, C. I.; Hauschildt, P. H. Bibcode: 1998AAS...193.4401S Altcode: 1998BAAS...30R1315S We have incorporated into the phoenix model atmosphere code the ability to treat Fe, Ni, and Co up to ionization stage vi, Mg, Ca, and Al up to ionization stage iii, and S and Si up to ionization stage iv, out of local thermodynamic equilibrium (LTE) using a multi-level direct method with large model atoms (~ 400 levels and ~ 7500 transitions in the case of Ni iii). These species are critically important for modeling the time development of Novae spectra. We have also added the ability to similarly treat Cs, Rb, and K, which are important for fitting chromospheric models to M dwarf spectra, and Ba which is important for modeling SNe supernovae. This is an increase from 40 to 85 in the total number of ionization stages among all species treated in non-LTE by phoenix, and provides an unprecedented ability to directly compute multi-species, multi-level non-LTE solutions with a model atmosphere code. The equation of state, and the chemical, thermal, and hydrostatic equilibrium equations are all solved consistently with the non-LTE equilibrium of the species treated in non-LTE. Also, the addition of many new non-LTE species allows us to compute synthetic spectra with self-consistent, massive non-LTE line blanketing due to many atoms and ions. Title: A multiwavelength study of the early evolution of the classical nova LMC 1988 1 Authors: Schwarz, Greg J.; Hauschildt, Peter H.; Starrfield, S.; Whitelock, P. A.; Baron, E.; Sonneborn, G. Bibcode: 1998MNRAS.300..931S Altcode: LMC 1988 1 was a moderately fast, CO, dust-forming classical nova. It was observed extensively in many different wavelength regions during its early evolution. The UV, optical and infrared light curves of LMC 1988 1 are very similar to those of the Galactic Nova V1668 Cyg 1978. As in V1668 Cyg, LMC 1988 1 showed the presence of an optically thin dust shell ~55 d after visual maximum which lasted for about two months. We successfully fit the UV and optical spectra of LMC 1988 1 taken within the first two months of its outburst (when the atmosphere was still optically thick) with synthetic spectra computed using PHOENIX nova model atmospheres. The synthetic spectra reproduce most of the features seen in the observations and provide V-band magnitudes consistent with the observed light curve. From the synthetic spectral fits to the observed data, we find that the bolometric luminosity was approximately constant at (3.0+/-0.3)x10^38ergs^-1 (assuming a distance of 53 kpc to the LMC) during the first 45 d after visual maximum. The fits are improved by increasing the CNO abundances to ~10 times their solar values, implying that the ejecta were enriched in CNO elements. Title: Evolutionary models for solar metallicity low-mass stars: mass-magnitude relationships and color-magnitude diagrams Authors: Baraffe, I.; Chabrier, G.; Allard, F.; Hauschildt, P. H. Bibcode: 1998A&A...337..403B Altcode: 2009A&A...500..551B; 1998astro.ph..5009B We present evolutionary models for low mass stars from 0.075 to 1 M_sun for solar-type metallicities [M/H]= 0 and -0.5. The calculations include the most recent interior physics and the latest generation of non-grey atmosphere models. We provide mass-age-color-magnitude relationships for both metallicities. The mass-M_V and mass-M_K relations are in excellent agreement with the empirical relations derived observationally. The theoretical color-magnitude diagrams are compared with the sequences of globular clusters (47 Tucanae) and open clusters (NGC2420 and NGC2477) observed with the Hubble Space Telescope. Comparison is also made with field star sequences in M_V-(V-I), M_K-(I-K) and M_K-(J-K) diagrams. These comparisons show that the most recent improvements performed in low-mass star atmosphere models yield now reliable stellar models in the near-infrared. These models can be used for metallicity, mass, temperature and luminosity calibrations. Uncertainties still remain, however, in the optical spectral region below T_eff ~ 3700K, where predicted (V-I) colors are too blue by 0.5 mag for a given magnitude. The possible origins for such a discrepancy, most likely a missing source of opacity in the optical and the onset of grain formation are examined in detail. Tables 1 to 3 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html Title: Observations of the Polar ST Leonis Minoris during an Extreme Low State: Identification of the Secondary Star Authors: Ciardi, David R.; Howell, Steve B.; Dhillon, V. S.; Wagner, R. Mark; Hauschildt, Peter H.; Allard, France Bibcode: 1998PASP..110.1007C Altcode: We present near-infrared (1.85-2.47 μm) and optical (4300-5800 Å) spectroscopic observations of the polar ST Leonis Minoris (ST LMi) in an extreme low state. The near-infrared spectrum, showing no emission lines whatsoever, is produced solely by the secondary star. We have fitted the spectrum with a series of stellar atmosphere models and found the secondary star to have a temperature of 2800+/-200 K. Six months later, ST LMi was reobserved in the near-infrared, at which time mass transfer had resumed, and the system was in a high state. Title: The Relative Contributions to the Near-Infrared Emission in Short-Period Cataclysmic Variables Authors: Ciardi, David R.; Howell, Steve B.; Hauschildt, Peter H.; Allard, France Bibcode: 1998ApJ...504..450C Altcode: We present phase-resolved near-infrared broadband photometry of four short-period cataclysmic variables (HU Aqr, WZ Sge, TY Psc, and V592 Cas). Coupled with ultraviolet and optical data obtained from the literature, we have modeled the spectral energy distributions of these four cataclysmic variables, as well as that of the twin of WZ Sge, AL Com. The secondary stars contribute no more than 20%-50% of the near-infrared flux except for the polar HU Aqr, where the secondary contributes ~75% of the near-infrared flux. For the systems located above the orbital period minimum, the temperatures of the secondary stars match those for the expected main-sequence secondary stars. However, our modeling places WZ Sge below the orbital period minimum and shows it containing a secondary star of less than 1700 K--the coldest ``star'' yet identified. Title: VizieR Online Data Catalog: Low-mass stars evolutionary models (Baraffe+ 1998) Authors: Baraffe, I.; Chabrier, G.; Allard, F.; Hauschildt, P. Bibcode: 1998yCat..33370403B Altcode: Physical properties and absolute magnitudes of low-mass stars for different initial metallicity [M/H], helium mass fraction Y and mixing length parameter Lmix: mass (in solar mass), age (in Gyrs) effective temperature (in K), log of gravity (in cgs) and absolute magnitudes. The VRI magnitudes are in the Johnson-Cousins system and the JHK magnitudes in the CIT system. Note that the bolometric magnitude corresponds to M_bol(Sun)=4.64. The lowest mass corresponds to the hydrogen-burning limit. (1 data file). Title: A Spherical Non-LTE Line-blanketed Stellar Atmosphere Model of the Early B Giant epsilon Canis Majoris Authors: Aufdenberg, J. P.; Hauschildt, P. H.; Shore, S. N.; Baron, E. Bibcode: 1998ApJ...498..837A Altcode: 1998astro.ph..2031A We use a spherical non-LTE fully line-blanketed model atmosphere to fit the full multiwavelength spectrum, including the extreme-ultraviolet (EUV) continuum observed by the Extreme Ultraviolet Explorer, of the B2 II star ɛ Canis Majoris (CMa). The available spectrophotometry of ɛ CMa from 350 Å to 25 μm is best fitted with model parameters Teff = 21,750 K, log g = 3.5, and an angular diameter of 0.77 mas. Our best-fit model predicts a hydrogen ionizing flux, q0, of 1.59 × 1021 photons cm-2 s-1 at the star's surface and 2290 photons cm-2 s-1 at the surface of the Local Cloud.

The close agreement between the model and the measured EUV flux from ɛ CMa is a result of the higher temperatures at the formation depths of the H I and He I Lyman continua compared with other models. The realistic model treatment of early B giants with spherical geometry and non-LTE metal line-blanketing results in the prediction of significantly larger EUV fluxes compared with plane-parallel models. We find that our metal line-blanketed spherical models show significantly warmer temperature structures, 1-3 kK at the formation depth of the Lyman continua, and predict stronger EUV fluxes, up to a factor of 5 in the H I Lyman continuum, compared with plane-parallel atmospheres that have identical model parameters. In contrast, we find that spherical and plane-parallel models that do not include metal line blanketing are nearly identical. Our Teff = 21,000 K, log g = 3.2, spherical non-LTE model predicts more than twice as many hydrogen ionizing photons and over 200 times more neutral helium ionizing photons than a standard hydrostatic plane-parallel LTE model with the same stellar parameters.

Our synthetic spectra are in reasonably good agreement with observed continuum and line fluxes from echelle spectra obtained with the Goddard High Resolution Spectrograph. While we find agreement between the absolute UV flux of ɛ CMa as measured by GHRS and our model atmosphere, these fluxes are ~30% higher in the UV than those measured by IUE, OAO 2, and TD-1, in excess of the published errors in the absolute calibration of these data. Title: New Determinations of Abundances for Novae Ejecta Authors: Starrfield, S.; Vanlandingham, K.; Schwarz, G.; Hauschildt, P.; Shore, S. N. Bibcode: 1998AAS...192.0602S Altcode: 1998BAAS...30..823S The nova outburst is a consequence of the accretion of hydrogen rich material onto a white dwarf in a close binary system and both theory and observations show that the accreting material mixes with core material during the outburst. Abundance determinations of nova ejecta shows that the core material is either carbon and oxygen or oxygen, neon, and magnesium. We have determined the ejecta abundances for V838 Her (1991), OS And (1986), V693 CrA (1981), PW Vul (1984), LMC 1988 #1, and LMC 1990 #1 using both optical and ultraviolet data. Our analysis technique uses CLOUDY (Ferland 1996) in combination with an optimization method obtained from high energy physics (MINUIT: James and Roos 1993). Our predicted line fluxes are in excellent agreement with the observations. We are also analyzing spectra obtained early in the outburst, when the expanding shell is optically thick, with stellar atmospheres computed with PHOENIX (Hauschildt et al. 1997, ApJ, 490,803). We will present the results of our studies using both these methods. Our re-analyses of V693 CrA and PW Vul resolved the problems with the previous studies. Title: Parallel Implementation of the PHOENIX Generalized Stellar Atmosphere Program. II. Wavelength Parallelization Authors: Baron, E.; Hauschildt, Peter H. Bibcode: 1998ApJ...495..370B Altcode: 1997astro.ph..9238B We describe an important addition to the parallel implementation of our generalized nonlocal thermodynamic equilibrium (NLTE) stellar atmosphere and radiative transfer computer program PHOENIX. In a previous paper in this series we described data and task parallel algorithms we have developed for radiative transfer, spectral line opacity, and NLTE opacity and rate calculations. These algorithms divided the work spatially or by spectral lines, that is, distributing the radial zones, individual spectral lines, or characteristic rays among different processors and employ, in addition, task parallelism for logically independent functions (such as atomic and molecular line opacities). For finite, monotonic velocity fields, the radiative transfer equation is an initial value problem in wavelength, and hence each wavelength point depends upon the previous one. However, for sophisticated NLTE models of both static and moving atmospheres needed to accurately describe, e.g., novae and supernovae, the number of wavelength points is very large (200,000-300,000) and hence parallelization over wavelength can lead both to considerable speedup in calculation time and the ability to make use of the aggregate memory available on massively parallel supercomputers. Here, we describe an implementation of a pipelined design for the wavelength parallelization of PHOENIX, where the necessary data from the processor working on a previous wavelength point is sent to the processor working on the succeeding wavelength point as soon as it is known. Our implementation uses a MIMD design based on a relatively small number of standard message passing interface (MPI) library calls and is fully portable between serial and parallel computers. Title: Time-resolved Spectroscopy of AL Comae Berenices Authors: Howell, Steve B.; Hauschildt, Peter; Dhillon, V. S. Bibcode: 1998ApJ...494L.223H Altcode: We present time-resolved spectroscopy for AL Com, one of the faintest known tremendous outburst amplitude dwarf novae (TOADs). Using newly produced models for a white dwarf and red secondary, we show that the star AL Com has orbitally phase-resolved broad absorption features of yet unidentified origin and an optically thin accretion disk. Radial velocities measured from the few spectra available show essentially no motion of the white dwarf, leading to a strict upper limit on the secondary mass of <=0.18 Msolar, with a likely value of 0.04-0.09 Msolar. This agrees well with recent theoretical arguments placing the TOADs as post-period minimum cataclysmic variables. Title: Optical and ultraviolet spectral observations of nova LMC 1991 Authors: Schwarz, C. J.; Starrfield, S.; Hauschildt, P. H.; Shore, S. N. Bibcode: 1998ASPC..137..473S Altcode: 1998wsow.conf..473S No abstract at ADS Title: Elemental abundances for nova ejecta Authors: Starrfield, S.; Vanlandingham, K.; Schwarz, G.; Hauschildt, P. H.; Shore, S. N. Bibcode: 1998sese.conf..433S Altcode: No abstract at ADS Title: A Superlevel Method for Molecular NLTE in Cool Atmospheres Authors: Schweitzer, A.; Hauschildt, P. H.; Allard, F. Bibcode: 1998ASPC..134..455S Altcode: 1998bdep.conf..455S No abstract at ADS Title: Spherical Non-LTE Line-Blanketed Stellar-Atmosphere Models of the Early-B Giants epsilon-CMa, beta-CMa, and alpha-Vir Authors: Aufdenberg, J. P.; Hauschildt, P. H.; Baron, E. Bibcode: 1998ASPC..131..127A Altcode: 1998phls.conf..127A No abstract at ADS Title: Optical and Infrared Spectroscopy of CM Draconis Authors: Viti, S.; Jones, H. R. A.; Allard, F.; Schweitzer, A.; Hauschildt, P. Bibcode: 1998HiA....11..441V Altcode: The authors compare observations of the binary system CM Draconis with synthetic spectra. Spectroscopic observations from 0.40 to 2.41 μm, combined with photometry and the accurately known surface gravity enable to estimate the temperature and metallicity using detailed spectra synthesis. They find discrepancies between the analysis of the infrared and optical spectrum while the optical spectral energy distribution (SED) yields a metal-rich solution with Teff = 3000K, the infrared SED yields around 3200K and -0.8 ≤ [M/H] ≤ -0.6 compatible with the high space motion of the system. The low-metallicity characteristics of the infrared SED could be real and is partly supported by the detailed analysis of the atomic lines in the optical region. Although, the known incompleteness of the TiO and H2O line lists in the models may cause substantial systematic errors. Title: Photospheric Dust Grains Formation in Brown Dwarfs Authors: Allard, F.; Alexander, D. R.; Tamanai, A.; Hauschildt, P. H. Bibcode: 1998ASPC..134..438A Altcode: 1998bdep.conf..438A No abstract at ADS Title: The Formation of PAHs in Carbon Star Atmospheres Authors: Ferguson, Jason W.; Alexander, David R.; Johnson, Hollis R.; Allard, France; Hauschildt, Peter H. Bibcode: 1998IAUS..191P.304F Altcode: Polycyclic Aromatic Hydrocarbons (PAHs) have been suggested as the source of the diffuse interstellar bands, and may serve as a link in the formation of grains from complex molecules in atmospheres of carbon-rich stars. If PAHs exist in interstellar clouds, then where do they form? The most obvious answer would seem to be in the atmospheres of carbon stars, where the stellar wind may eject them into the interstellar medium. Cherchneff, Barker & Tielens (1992) and Helling et al. (1996) computed the fraction of carbon contained within PAHs for several carbon-rich stellar atmospheres. Both conclude that PAHs are not significant in stellar photospheres, that they may form in dynamical atmospheres, but that the resident time of the PAHs in those atmosphere may be insufficient for a significant amount of PAHs to form before being ejected. We extend the calculations of Helling et al. to much lower temperatures and higher densities, and investigate whether significant amounts of PAHs form in those outer layers. Even though our models extend to much smaller optical depths than those considered by Helling et al. we find that PAHs never account for more than 1 ppm of the elemental carbon in any static model atmosphere in thermal equilibrium. If it is assumed that grain formation is inhibited by, for example, the passage of shock waves, then PAHs may account for up to 30% of the elemental carbon. Title: ROSAT WTTSs near Lupus: Results of Echelle Spectroscopy Authors: Wichmann, R.; Covino, E.; Krautter, J.; Alcala, J. M.; Allain, S.; Hauschildt, P. Bibcode: 1998AGAb...14..102W Altcode: 1998AGM....14..P07W We have obtained high-resolution echelle spectroscopy for a large fraction of the Li-rich late-type stars recently discovered in and near the Lupus dark clouds by follow-up observations of ROSAT x-ray sources (Krautter et al. 1997, A&AS 123, 329). Our data show that about 90 percent of these stars exhibit Li I \lambda 6708 equivalent widths in excess of zero-age main sequence stars, thus confirming their pre-main sequence nature and supporting their classification as weak-line T Tauri stars (WTTS). Using previously obtained data on rotational periods (Wichmann et al. 1998, A&A 330, 521), we present a statistical approach to determine the mean distance of these stars, and find this distance, within errors, to be consistent with the HIPPARCOS distance of the Lupus star forming region (Wichmann et al. 1997, ESA SP-402). Radial velocities of the ROSAT WTTS are consistent with the radial velocity of the Lupus star forming region, although a small difference of 2--3 km s^{-1} cannot be ruled out. If confirmed, this deviation might yield some insight into the velocity structure of the Gould Belt towards the Lupus star forming region. Title: Optical and ultraviolet spectral observations of nova LMC 1991 Authors: Schwarz, G. J.; Starrfield, S.; Hauschildt, P. H.; Shore, S. N. Bibcode: 1998sese.conf..463S Altcode: No abstract at ADS Title: The Eclipsing Binary System CM Draconis Authors: Viti, S.; Tennyson, J.; Jones, H. R. A.; Schweitzer, A.; Allard, F.; Hauschildt, P. H. Bibcode: 1998ASPC..134..475V Altcode: 1998bdep.conf..475V No abstract at ADS Title: A Comparison of the Infrared Spectra of Two Very Late-type M Dwarfs with Different Gravities Authors: Viti, S.; Tennyson, J.; Jones, H. R. A.; Allard, F.; Hauschildt, P. H. Bibcode: 1998ASPC..134..471V Altcode: 1998bdep.conf..471V No abstract at ADS Title: Observational and Theoretical Studies of the Nova Outburst Authors: Starrfield, S.; Truran, J. W.; Sparks, W. M.; Hauschildt, P. H.; Shore, S. N.; Krautter, J.; Vanlandingham, K.; Schwarz, G. Bibcode: 1998ASPC..137..352S Altcode: 1998wsow.conf..352S No abstract at ADS Title: Model Atmospheres of Very Low Mass Stars and Brown Dwarfs Authors: Allard, F.; Alexander, D. R.; Hauschildt, P. H. Bibcode: 1998ASPC..154...63A Altcode: 1998csss...10...63A We review the current theory of very low mass stars model atmospheres including the coolest known M dwarfs, M subdwarfs, and brown dwarfs, i.e., T_eff <= 5,000 K and -2.0 <= [M/H] <= +0.0. We discuss ongoing efforts to incorporate molecular and grain opacities in cool stellar spectra, as well as the latest progress in deriving the effective temperature scale of M dwarfs. We especially present the latest results of the models related to the search for brown dwarfs. Title: Model Atmospheres for White Dwarfs in Cataclysmic Variables Authors: Hauschildt, Peter H.; Aufdenberg, J.; Starrfield, S.; Baron, E. Bibcode: 1998ASPC..137...96H Altcode: 1998wsow.conf...96H No abstract at ADS Title: The physics of early nova spectra and light curves Authors: Hauschildt, P. H.; Shore, S. N.; Schwarz, G.; Starrfield, S.; Baron, E.; Allard, F. Bibcode: 1998sese.conf..453H Altcode: No abstract at ADS Title: Detailed Non-LTE Model Atmospheres for Novae during Outburst. I. New Theoretical Results Authors: Hauschildt, Peter H.; Shore, Steven N.; Schwarz, Greg J.; Baron, E.; Starrfield, S.; Allard, France Bibcode: 1997ApJ...490..803H Altcode: 1997astro.ph..7104H We present new, detailed non-LTE (NLTE) calculations for model atmospheres of novae during outburst. This fully self-consistent NLTE treatment for a number of model atoms includes 3922 NLTE levels and 47,061 NLTE primary transitions. We discuss the implication of departures from LTE for the strengths of the lines in nova spectra. The new results show that our large set of NLTE lines constitutes the majority of the total line-blanketing opacity in nova atmospheres. Although we include LTE background lines, their effects are small on the model structures and on the synthetic spectra. We demonstrate that the assumption of LTE leads to incorrect synthetic spectra and that NLTE calculations are required for reliably modeling nova spectra. In addition, we show that detailed NLTE treatment for a number of ionization stages of iron changes the results of previous calculations and improves the fit to observed nova spectra. Title: Spherical Non-LTE Line-Blanketed Stellar Atmosphere Models of epsilon CMa, beta CMa, and alpha VIR and the Lyman Continuum in the Early B Giant Stars. Authors: Aufdenberg, J. P.; Sankrit, R.; Hauschildt, P. H.; Baron, E. Bibcode: 1997AAS...191.1201A Altcode: 1997BAAS...29.1227A We model the full multi-wavelength spectrum, including the extreme ultraviolet (EUV) continuum of three early B giants, epsilon CMa, beta CMa, and alpha Vir with spherical, non-LTE, fully line-blanketed, model atmospheres. Comparisons of these models to the spectrophotometric data, along with the HIPPARCOS parallax measurements, provide fundamental stellar parameters for these stars. We find close agreement between the model spectra and the measured EUV fluxes from epsilon CMa and beta CMa. The realistic treatment of early B giant atmospheres, with models including spherical geometry and NLTE metal line blanketing, results in the prediction of larger Lyman continuum fluxes, by up to a factor of two, than existing plane-parallel models for these stars. We present a grid of PHOENIX NLTE model atmospheres of late O and early B stars and provide predictions for the hydrogen and helium ionizing fluxes as a function of effective temperature. The increased EUV flux predicted for B stars has significant implications for our understanding of the ionization of the material surrounding these stars. We present photoionization models of the H II region around alpha Vir, calculated using CLOUDY, with our model atmosphere as the input continuum. The distance to this star and its radius are known and so it is a well constrained system. We find that our model can reproduce the measured extent of the H II region, the Hα surface brightness, the {[S II]}lambda 6716/Hα ratio and the temperature of the region given by Reynolds (1988). We also estimate the amount of the ionizing radiation escaping from the surroundings and therefore available to ionize the diffuse ISM. Title: Spatially Resolved Spectra of V1974 Cygni (Nova Cygni 1992) with the Goddard High Resolution Spectrograph Authors: Shore, Steven N.; Starrfield, Sumner; Ake, T. B., III; Hauschildt, Peter H. Bibcode: 1997ApJ...490..393S Altcode: We report the observation of spatially resolved low-resolution GHRS spectra of the shell of the bright Galactic ONeMg nova Cygni 1992. The spectra were obtained in 1995 September, after the X-ray turnoff of the nova. We have determined the dynamical structure of the ejecta and show the evolution of the ionization within the ejecta. Abundance limits have been found to agree with the published analyses based on earlier IUE data for key species in the ejecta, especially neon. The knot spectrum, obtained with the 0.25" aperture, shows an enhanced Ne/He ratio compared with the 2" aperture observation. These data provide a detailed picture of physical conditions and abundances of the knots and larger scale ejecta that have not previously been available from UV spectra, including those taken before the COSTAR installation and IUE data. The knots were created during the initial stages of the explosion, and the differential mixing that may have resulted can be studied using the spatially resolved spectra. The 1995 spectra were compared with archival Faint Object Spectrograph data from 1994 and previous GHRS spectra from 1992 and 1993. We also obtained high signal-to-noise ratio (S/N) observations of the UV continuum of the hot central star in order to study the physical conditions in the post-thermonuclear runaway envelope. These show that the white dwarf had relaxed to a very low effective temperature, about 20,000 K, and a luminosity of about 30 L⊙, within 2 years after the X-ray turnoff. We also used reprocessed archival IUE spectra to determine the decay time for the ultraviolet continuum flux for this nova, which we find to be about 1.7 years. The current temperature and luminosity do not fall on the white dwarf cooling tracks for any reasonable stellar mass. Title: The effective temperature and metallicity of CM Draconis Authors: Viti, Serena; Jones, Hugh R. A.; Schweitzer, Andreas; Allard, France; Hauschildt, Peter H.; Tennyson, Jonathan; Miller, Steven; Longmore, Andrew J. Bibcode: 1997MNRAS.291..780V Altcode: We compare observations of the binary system CM Draconis with synthetic spectra computed using the stellar atmosphere code phoenix. Spectroscopic observations from 0.40 to 2.41mum, combined with photometry and the accurately known surface gravity, enable us to estimate the temperature and metallicity using detailed spectral synthesis. We find discrepancies between the analysis of the infrared and optical spectra: while the optical spectral energy distribution (SED) yields a metal-rich solution with T_eff=3000K, the infrared SED yields around 3200K with -0.8<= [M/H]<=-0.6, compatible with the high space motion of the system. The low-metallicity characteristics of the infrared SED could be real, and are partly supported by a detailed analysis of the atomic lines in the optical region. Although the known incompleteness of the TiO and H_2O line lists in the models used, as well as problems with the observational data, will cause systematic errors, we suggest that CM Draconis could be a chemically peculiar system in that it cannot be modelled with solar abundances. Title: Evolutionary models for metal-poor low-mass stars. Lower main sequence of globular clusters and halo field stars Authors: Baraffe, I.; Chabrier, G.; Allard, F.; Hauschildt, P. H. Bibcode: 1997A&A...327.1054B Altcode: 1997astro.ph..4144B We have performed evolutionary calculations of very-low-mass stars from 0.08 to 0.8 M_sunl for different metallicites from [M/H]= -2.0 to -1.0 and we have tabulated the mechanical, thermal and photometric characteristics of these models. The calculations include the most recent interior physics and improved non-grey atmosphere models. The models reproduce the entire main sequences of the globular clusters observed with the Hubble Space Telescope over the afore-mentioned range of metallicity. Comparisons are made in the WFPC2 Flight system including the F555, F606 and F814 filters, and in the standard Johnson-Cousins system. We examine the effects of different physical parameters, mixing-length, alpha -enriched elements, helium fraction, as well as the accuracy of the photometric transformations of the HST data into standard systems. We derive mass-effective temperature and mass-magnitude relationships and we compare the results with the ones obtained with different grey-like approximations. These latter are shown to yield inaccurate relations, in particular near the hydrogen-burning limit. We derive new hydrogen-burning minimum masses, and the corresponding absolute magnitudes, for the different metallicities. We predict color-magnitude diagrams in the infrared NICMOS filters, to be used for the next generation of the HST observations, providing mass-magnitudes relationships in these colors down to the brown-dwarf limit. We show that the expected signature of the stellar to substellar transition in color-magnitude diagrams is a severe blueshift in the infrared colors, due to the increasing collision-induced absorption of molecular hydrogen with increasing density and decreasing temperature. At last, we apply these calculations to the observed halo field stars, which yields a precise determination of their metallicity, and thus of their galactic origin. We find no evidence for significant differences between the halo field stars and the globular cluster sequences. Title: Non-Local Thermodynamic Equilibrium Effects of Ti I in M Dwarfs and Giants Authors: Hauschildt, Peter H.; Allard, France; Alexander, David R.; Baron, E. Bibcode: 1997ApJ...488..428H Altcode: We present detailed NLTE Ti I calculations in model atmospheres of cool dwarf and giant stars. A fully self-consistent NLTE treatment for a Ti I model atom with 395 levels and 5279 primary bound-bound transitions is included, and we discuss the implication of departures from LTE in this atom for the strengths of Ti I lines and TiO molecular bands in cool star spectra. We show that in the atmospheric parameter range investigated, LTE is a poor approximation to Ti I line formation, as expected from the low collisional rates in cool stars. The secondary effects of Ti I overionization on the TiO number density and the TiO molecular opacities, however, are found to be negligible in the molecular line-forming region for the relatively small parameter range studied in this paper. Title: Abundance analysis of the slow nova PW Vulpeculae 1984 Authors: Schwarz, Greg J.; Starrfield, Sumner; Shore, Steven N.; Hauschildt, Peter H. Bibcode: 1997MNRAS.290...75S Altcode: 1997astro.ph..5086S We determine the elemental abundances for the ejecta of the slow nova PW Vul 1984. Our technique uses a minimization of the emission-line fits of a photoionization model to available ultraviolet, optical and infrared spectra. We find the following abundances (by number) with respect to solar: He/H=1.0+/-0.4, C/H=7.0^+7_-4, N/H=85^+59_-41 and O/H=6^+7_-2. In addition, there is weak evidence for solar Ne and Mg, and for twice solar Fe. Previous studies of PW Vul by Saizar et al. and Andrea et al. yielded considerable differences in their derived elemental abundances for the ejecta. Our abundances fall in between those found in the previous studies. To explain the discrepant abundances, we analyse in detail the data and methods used to obtain the previous results. The abundances found by Saizar et al. are significantly smaller than our values because of the lower electron temperature used by them in deriving elemental abundances from ion abundances. Andrea et al. used an ionization correction method to obtain their abundances and later verified their results with a photoionization model. Our analysis of their data shows that the absolute fluxes of the optical emission lines used by Andrea et al. are underestimated by 15 per cent, leading to a factor of 2 increase in their derived abundances. We also find that the photoionization model used by Andrea et al. predicts twice as much carbon as the photoionization code we used even when fitting the same data with similar model parameters. Title: Synthetic Spectra of Hydrodynamic Models of Type Ia Supernovae Authors: Nugent, Peter; Baron, E.; Branch, David; Fisher, Adam; Hauschildt, Peter H. Bibcode: 1997ApJ...485..812N Altcode: 1996astro.ph.12044N We present detailed non-LTE synthetic spectra of hydrodynamic supernovae (SNe) Ia models. We make no assumptions about the form of the spectrum at the inner boundary. We calculate both Chandrasekhar-mass deflagration models and sub-Chandrasekhar ``helium detonators.'' Gamma-ray deposition is handled in a simple, accurate manner. We have parameterized the storage of energy, which arises from the time-dependent deposition of radioactive decay energy, in a reasonable manner that spans the expected range. We find that the Chandrasekhar-mass deflagration model W7 of Nomoto, Thielemann, & Yokoi shows good agreement with the observed spectra of SN 1992A and SN 1994D, particularly in the UV, where our models are expected to be most accurate. The sub-Chandrasekhar models do not reproduce the UV deficit observed in normal SNe Ia. They do bear some resemblance to subluminous SNe Ia, but the shapes of the spectra (i.e., the colors) are opposite that of the observed ones, and the intermediate-mass element lines (such as Si II and Ca II) are extremely weak, which seems to be a generic difficulty of the models. Although the sub-Chandrasekhar models have a significant helium abundance (unlike Chandrasekhar-mass models), helium lines are not prominent in the spectra near maximum light and thus do not act as a spectral signature for the progenitor. Title: Parallel Implementation of the PHOENIX Generalized Stellar Atmosphere Program Authors: Hauschildt, Peter H.; Baron, E.; Allard, France Bibcode: 1997ApJ...483..390H Altcode: 1996astro.ph..7087H We describe the parallel implementation of our generalized stellar atmosphere and non-LTE (NLTE) radiative transfer computer program PHOENIX. We discuss the parallel algorithms we have developed for radiative transfer, spectral line opacity, and NLTE opacity and rate calculations. Our implementation uses a multiple instruction-multiple data design based on a relatively small number of MPI library calls. We report the results of test calculations on a number of different parallel computers and discuss the results of scalability tests. Title: Grain Formation in Atmospheres of Cool Dwarfs Authors: Alexander, D. R.; Allard, F.; Tamanai, A.; Hauschildt, P. H. Bibcode: 1997Ap&SS.251..171A Altcode: We have constructed a grid of model atmospheres for cool dwarf stars and brown dwarfs with Teff ≤ 3000 K that includes (i) an equation of state which accounts for over 600 gas phase species and 1000 liquids and solids, and (ii) the opacities of corundum (Al2O3), iron, enstatite (MgSiO3) and forsterite (Mg2SiO4), as well as amorphous carbon and SiC. We confirm earlier findings of Tsuji, Ohnaka & Aoki (1996a) that grains are abundant in the outer photospheric layers of red and brown dwarfs with spectral type later than M8. We identify high temperature condensates including perovskite (CaTiO3) that depletes the photospheres of important absorbers including TiO, and we confirm the disappearance of TiO bands in the observed spectra of cool dwarfs. Title: NLTE effects of Ti~I in M dwarfs and giants Authors: Hauschildt, Peter H.; Allard, France; Alexander, David R.; Baron, E. Bibcode: 1997astro.ph..5063H Altcode: We present detailed NLTE Ti~I calculations in model atmospheres of cool dwarf and giant stars. A fully self-consistent NLTE treatment for a Ti~I model atom with 395 levels and 5279 primary bound-bound transitions is included, and we discuss the implication of departures from LTE in this atom for the strengths of Ti~I lines and TiO molecular bands in cool star spectra. We show that in the atmospheric parameter range investigated, LTE is a poor approximation to Ti~I line formation, as expected from the low collisional rates in cool stars. The secondary effects of Ti~I overionization on the TiO number density and the TiO molecular opacities, however, are found to be negligible in the molecular line forming region for the relatively small parameter range studied in this paper. Title: Brown Dwarfs from the Stellar Perspective Authors: Allard, France; Hauschildt, Peter H. Bibcode: 1997astro.ph..5071A Altcode: In this paper, we review the current theory of very low mass stars model atmospheres including the coolest known M~dwarfs, M~subdwarfs, and brown dwarfs, i.e. T$_{eff} \leq 5,000 $K and $-2.0 \le [M/H] \le +0.0$. We discuss ongoing efforts to incorporate molecular and grain opacities in cool stellar spectra, as well as the latest progress in deriving the effective temperature scale of M~dwarfs. We also present the latest results of the models related to the search for brown dwarfs. Title: The Hubble constant, supernova light curves and spectra, and radiation transport Authors: Branch, David; Baron, E.; Nugent, Peter; Hauschildt, Peter H. Bibcode: 1997PhPl....4.2016B Altcode: As luminous events that can be physically modeled, supernovae provide an attractive route to the value of the Hubble constant. The modeling involves radiation transport through matter undergoing homologous expansion with velocity gradient on the order of 10-6 s-1. For supernovae of type Ia, which are thermonuclear disruptions of mass accreting or coalescing carbon-oxygen white dwarfs, one wants to be able to calculate the light curve (luminosity in some optical passband versus time), which is powered by the radioactivity decay chain 56Ni→56Co→56Fe. For all kinds of supernovae, including those of types II, Ib, and Ic, which result from the gravitational collapse of the cores of massive stars, the goal is to accurately calculate the emergent ultraviolet-optical-infrared spectra, as a function of time. Local-thermodynamic-equilibrium (LTE) light-curve calculations for type Ia supernovae by Höflich and co-workers, and our spectrum calculations based on a fully relativistic non-LTE radiative transfer code, are described. The associated radiative transport needs are discussed. Title: Preliminary results of the ASU/UGA O-star project Authors: Scowen, P. A.; Hauschildt, P. H.; Aufdenberg, J. P.; Sankrit, R. Bibcode: 1997AIPC..393..291S Altcode: 1997sfnf.conf..291S Understanding the physics of the photodissociation regions (PDRs) which occur between the ionized HII regions and the surrounding molecular clouds is critical in assessing the role that primary star formation has on secondary events. It is also pivotal to understanding how HII regions affect their local environment. Modelling of these interfaces, and of the photons that escape to ionize the local ISM, has been hampered by a lack of modern models of the O-star atmospheres. We present preliminary results from a program intended to better model the physics of the extended atmospheres of O stars and thus derive more physically accurate photon fluxes and therefore better estimates of the actual ionization rates. The models include features such as winds, spherical symmetry, accurate and up-to-date opacites, and the effect of metallicity on the extended envelope of material around O stars and the spectra that emerge from them. Title: Model Atmospheres of Very Low Mass Stars and Brown Dwarfs Authors: Allard, France; Hauschildt, Peter H.; Alexander, David R.; Starrfield, Sumner Bibcode: 1997ARA&A..35..137A Altcode: As progressively cooler stellar and substellar objects are discovered, the presence first of molecules and then of condensed particulates greatly complicates the understanding of their physical properties. Accurate model atmospheres that include these processes are the key to establishing their atmospheric parameters. They play a crucial role in determining structural characteristics by setting the surface conditions of model interiors and providing transformations to the various observational planes. They can reveal the spectroscopic properties of brown dwarfs and help establish their detectability. In this paper, we review the current state-of-the-art theory and modeling of the atmospheres of very low mass stars, including the coolest known M dwarfs, M subdwarfs, and brown dwarfs, i.e. T_eff {less than or equal to} 4000 K and -4.0 {less than or equal to} [M/H]} {less than or equal to} +0.0.} We discuss ongoing efforts to incorporate molecular and grain opacities in cool stellar spectra, as well as the latest progress in (a) deriving the effective temperature scale of M dwarfs, (b) reproducing the lower main sequences of metal-poor subdwarfs in the halo and globular clusters, and (c}) results of the models related to the search for brown dwarfs Title: NLTE modeling of SNe Ia near maximum light Authors: Baron, E.; Hauschildt, P. H.; Mezzacappa, A. Bibcode: 1997ASIC..486..627B Altcode: 1997thsu.conf..627B No abstract at ADS Title: Non-LTE model atmosphere analysis of the early ultraviolet spectra of Nova OS Andromedae 1986 Authors: Schwarz, Greg J.; Hauschildt, Peter H.; Starrfield, S.; Baron, E.; Allard, France; Shore, Steven N.; Sonneborn, G. Bibcode: 1997MNRAS.284..669S Altcode: 1996astro.ph..8199S We analyse the early, optically thick, ultraviolet spectra of Nova OS And 1986 using a grid of spherically symmetric, non-LTE, line- blanketed, expanding model atmospheres and synthetic spectra with the following set of parameters: 5000<=T_model<=60000K, solar abundan ces, rho ~r^-3, v_max=2000 km s^-1, L=6x10^4Lsolar, and a statistical or microturbulent velocity of 50 km s^-1. We use the synthetic spectra to estimate the model parameters corresponding to the observed IUE spectra. The fits to the observations are then iteratively improved by changing the parameters of the model atmospheres - in particular, T_model and the abundances - to arrive at the best fits to the optically thick pseudo-continuum and the features found in the IUE spectra. The IUE spectra show two different optically thick sub-phases. The earliest spectra, taken a few days after maximum optical light, show a pseudo-continuum created by overlapping absorption lines. The later observations, taken approximately 3 weeks after maximum light, show the simultaneous presence of allowed, semiforbidden and forbidden lines in the observed spectra. Analysis of these phases indicates that OS And 1986 had solar metallicities, except for Mg which showed evidence of being underabundant by as much as a factor of 10. We determine a distance of 5.1 kpc to OS And 1986, and derive a peak bolometric luminosity of ~5x10^4Lsolar. The computed nova parameters provide insights into the physics of the early outburst and explain the spectra seen by IUE. Lastly, we find evidence in the later observations for large non-LTE effects of Fe ii which, when included, lead to much better agreement with the observations. Title: The Effective Temperature and Metallicity of CM Draconis Authors: Viti, S.; Jones, H. R. A.; Schweitzer, A.; Allard, F.; Hauschildt, P. Bibcode: 1997IAUJD..10E..11V Altcode: We compare observations of the binary system CM Draconis with synthetic spectra computed using the PHOENIX stellar atmosphere code. Spectroscopic observations from 0.40 to 2.41 microns, combined with photometry and the accurately known surface gravity enable us to derive the temperature and metallicity using detailed spectra synthesis as well as the spectral energy distribution. This enables us to obtain the most direct measurement of both metallicity [M/H] and effective temperature (Teff) so far made for the system. Our results imply Teff ~3200K and -0.8 <= [M/H] <= -0.6. The largest uncertainty in this conclusion lies in the lack of reliable molecular data for cool stars, especially for water. Title: Multiwavelength Modeling of Nova Atmospheres Authors: Hauschildt, P. H.; Starrfield, S. Bibcode: 1997nasa.reptV....H Altcode: We have analyzed the early optically thick ultraviolet spectra of Nova OS And 1986 using a grid of spherically symmetric, non-LTE, line-blanketed, expanding model atmospheres and synthetic spectra with the following set of parameters: 5,000 less than or equal to Tmodel less than or equal to 60,000K, solar abundances, (rho)(alpha) r-3, vmax = 2000 km/s, L = 6 x 104 solar luminosity, and a statistical or microturbulent velocity of 50 km/s. We used the synthetic spectra to estimate the model parameters corresponding to the observed IUE spectra. The fits to the observations were then iteratively improved by changing the parameters of the model atmospheres, in particular Tmodel and the abundances, to arrive at the best fits to the optically thick pseudo-continuum and the features found in the IUE spectra. The IUE spectra show two different optically thick subphases. The earliest spectra, taken a few days after maximum optical light, show a pseudo-continuum created by overlapping absorption lines. The later observations, taken approximately 3 weeks after maximum light, show the simultaneous presence of allowed, semi-forbidden, and forbidden lines in the observed spectra. Analysis of these phases indicate that OS And 86 had solar metallicities except for Mg which showed evidence of being underabundant by as much as a factor of 10. We determine a distance of 5.1 kpc to OS And 86 and derive a peak bolometric luminosity of approximately 5 x 104 solar luminosity. The computed nova parameters provide insights into the physics of the early outburst and explain the spectra seen by IUE. Lastly, we find evidence in the later observations for large non-LTE effects of Fe II which, when included, lead to much better agreement with the observations. Title: Analysis of Keck high-resolution spectra of VB 10 Authors: Schweitzer, Andreas; Hauschildt, Peter H.; Allard, France; Basri, G. Bibcode: 1996MNRAS.283..821S Altcode: 1996astro.ph..6150S We use a preliminary version of our `NextGen' grid of cool star model atmospheres to compute synthetic line profiles which fit high-resolution Keck spectra of the cool M dwarf VB10 satisfactorily well. We show that the parameters derived from the Keck data are consistent with the parameters derived from lower resolution spectra with larger wavelength coverage. We discuss the treatment of van der Waals broadening in cool stellar atmospheres that are dominated by molecules (mostly H_2). The line profiles are dominated by van der Waals pressure broadening and are a sensitive indicator for the gravity and metallicity. Therefore the high-resolution Keck spectra are useful for determining the parameters of M dwarfs. There is some ambiguity between the metallicity and gravity. For VB10, we find from the high-resolution spectra that 5.0<logg<5.5 and 0<[M/H]<+0.5 for an adopted fixed effective temperature of 2700 K, which is consistent with recent interior calculations. Title: Non-local thermodynamic equilibrium effects in modelling of supernovae near maximum light. Authors: Baron, E.; Hauschildt, P. H.; Nugent, P.; Branch, D. Bibcode: 1996MNRAS.283..297B Altcode: Supernovae (SNe), with their diversity of compositions, velocities, envelope masses, and interactions, are good testing grounds for probing the importance of non-local thermodynamic equilibrium (NLTE) in expanding atmospheres. In addition to treating H, He, Li I, O I, Ne I, Na I, and Mg II in NLTE, we use a very large model atom of Fe II to test the importance of NLTE processes in both Type Ia and Type II SNe. Since the total number of potential line transitions that one has to include is enormous (≍40 million), approximations and simplifications are required to treat the problem accurately and in finite computer time. With our large Fe II model atom (617 levels and 13,675 primary NLTE line transitions) we are able to test several assumptions for treating the background opacity that are needed to obtain correct UV line blanketing, which determines the shape of near-maximum light supernova spectra. we find that, due to interactions within the multiplets, treating the background lines as pure scattering (thermalization parameter ɛ = 0) is a poor approximation, and that an overall mean value of ɛ ≡ 0.05-0.10 is a far better approximation. This is true even in SNe Ia, where the continuum absorption optical depth at 5000 Å (≡τstd) is ≪1. we also demonstrate that a detailed treatment of NLTE effects is required to determine properly the ionization states of both abundant and trace elements. Title: UV Observations of Three LMC Be-Star/X-ray Binaries Authors: Schmidtke, P. C.; Cowley, A. P.; Hauschildt, P. H.; Ponder, A. L.; McGrath, T. K.; Frattare, L. M.; Franklin, B. E. Bibcode: 1996PASP..108..668S Altcode: This paper describes IUE ultraviolet observations of three Be-star/X-ray binaries in the LMC: CAL 9, CAL E, and RX J0520.5-6932. Because the optical spectra show evidence of an overlying continuum source, ultraviolet spectra were obtained to further investigate its properties, but no UV emission lines are found. The UV spectra have been compared to models indicating that the stellar temperatures are near 30000 K (for log g = 4.0). This is in agreement with the temperatures suggested by the spectral type determined in the optical region. Thus, there is no clear evidence in either the optical or UV regions of the gas being accreted by the unseen compact companion which must give rise to the X-ray emission. Optical photometry shows these systems undergo irregular variations of up to a few tenths of a magnitude. (SECTION: Stars) Title: Synthetic Spectra and Mass Determination of the Brown Dwarf GI 229B Authors: Allard, France; Hauschildt, Peter H.; Baraffe, Isabelle; Chabrier, Gilles Bibcode: 1996ApJ...465L.123A Altcode: We present preliminary nongray model atmospheres and interiors for cool brown dwarfs. The resulting synthetic spectra are compared to available spectroscopic and photometric observations of the coolest brown dwarf yet discovered, Gl 229B (Nakajima et al.). Despite the grainless nature of the present models, we find that the resulting synthetic spectra provide an excellent fit to most of the spectral features of the brown dwarf. We confirm the presence of methane absorption and the substellar nature of Gl 229B. These preliminary models set an upper limit for the effective temperature of 1000 K. We also compute the evolution of brown dwarfs with solar composition and masses from 0.02 to 0.065 Msolar. While uncertainties in the age of the system yield some indeterminateness for the mass of Gl 229B, the most likely solution is m ~ 0.04--0.055 Msolar. In any case, we can set an upper limit m = 0.065 Msolar for a very unlikely age, t = 10 Gyr. Title: Spectral analysis of M dwarfs Authors: Jones, Hugh R. A.; Longmore, Andrew J.; Allard, France; Hauschildt, Peter H. Bibcode: 1996MNRAS.280...77J Altcode: We compare 1.16-1.22 μm spectra of cool low-mass dwarfs with synthetic spectra calculated with a stellar atmosphere code. The synthetic spectra give a representation of the overall spectral features which has not been possible in previous comparisons with cool low-mass dwarf spectra, although the interpretation of the observed spectra is severely hampered by the quality of atomic and molecular input data. The observed spectral region is rich in absorption features of which the strongest are K, Fe, Mg and FeH. Each observed spectrum is compared with a grid of synthetic spectra extending well outside the expected parameter space for M dwarfs. The effective temperatures, metallicities and gravities derived are compared with expectations based on previous work. For the cooler objects the parameters show broad agreement; however, for the hotter objects the poor fit of Fe lines leads to best fits to models with low gravity and metallicity. All features show a strong sensitivity to temperature, especially the K and FeH. Metallicity and gravity effects are relatively smaller. For the hotter stars, Mg and Fe absorption lines are the most useful discriminators between gravity and metallicity. For the cooler objects the complicated dependence of modelled equivalent widths on metallicity and gravity makes it awkward to separate effects due to a single model parameter. The comparisons suggest a similar spread in metallicities to that anticipated, although for our sample neither kinematic motion nor membership of a particular photometric class is, on its own, a reliable indicator of metallicity. Comparison of the observed strong K lines in GD 165B with synthetic spectra indicate that it is relatively metal rich. This result together with an improved measurements of its distance means that within the best available constraints it is likely to be a brown dwarf. Title: Model Atmospheres for Novae and Supernovae Authors: Hauschildt, P. H.; Baron, E.; Allard, F.; Starrfield, Sumner Bibcode: 1996AAS...188.3204H Altcode: 1996BAAS...28..866H The spectra of novae and supernovae form in an environment that (a) is optically thick for lines and continua, (b) has a large radial extension, (c) has very high-speed (and differential) velocity fields, (d) huge temperature gradients, (e) very low densities, and (f) a huge number of spectral lines. Analyzing the thousands of observed spectra of novae and SNe available today in various archives requires very sophisticated numerical techniques. These methods must include a detailed treatment of non-LTE effects for a large number of lines, special relativistic radiative transfer, inclusion of millions of spectral lines, and an equation of state that is capable of handling several hundred species of both atoms and molecules. I will describe how we solve these problems with our general model atmosphere code PHOENIX and describe a few results of general interest, e.g., the influence of non-LTE effects on nova spectra. Title: NLTE Effects in Modeling of Supernovae near Maximum Light Authors: Baron, E.; Hauschildt, P. H.; Nugent, P.; Branch, D. Bibcode: 1996astro.ph..5088B Altcode: Supernovae, with their diversity of compositions, velocities, envelope masses, and interactions are good testing grounds for probing the importance of NLTE in expanding atmospheres. In addition to treating H, He, Li I, O I, Ne I, Na I, and Mg II in NLTE, we use a very large model atom of Fe II to test the importance of NLTE processes in both SNe Ia and II. Since the total number of potential line transitions that one has to include is enormous ($\approx 40$ million), approximations and simplifications are required to treat the problem accurately and in finite computer time. With our large Fe II model atom (617 levels, 13,675 primary NLTE line transitions) we are able to test several assumptions for treating the background opacity that are needed to obtain correct UV line blanketing which determines the shape of near-maximum light supernova spectra. We find that, due to interactions within the multiplets, treating the background lines as pure scattering (thermalization parameter $\epsilon = 0$) is a poor approximation and that an overall mean value of $\epsilon \sim 0.05 - 0.10 $ is a far better approximation. This is true even in SNe Ia, where the continuum absorption optical depth at 5000 Å ($\equiv \tau_{\rm std}$) is $<< 1$. We also demonstrate that a detailed treatment of NLTE effects is required to properly determine the ionization states of both abundant and trace elements. Title: Infrared Spectra of Low-Mass Stars: Toward a Temperature Scale for Red Dwarfs Authors: Leggett, S. K.; Allard, F.; Berriman, Graham; Dahn, Conard C.; Hauschildt, Peter H. Bibcode: 1996ApJS..104..117L Altcode: We present new low-resolution (R ∼ 250)1.0-2.4 μm spectra for 13 red dwarf stars. The sample size is increased to 16 by including other published infrared spectra. New, as well as published, red spectra are presented for 10 of these 16 stars, and new and published VRIJHKLL' photometry is also presented. Both halo and disk stars are included in the sample, which covers a range of spectral type from dM0 to dM6.5. We derive bolometric luminosities and bolometric corrections from the observational data, finding good agreement with earlier results for the disk stars. We fit synthetic spectra generated by Allard & Hauschildt's state-of-the-art model atmospheres to the observed spectra. Although some discrepancies remain between the theoretical and observed spectra, we find that the molecular features give a consistent value for effective temperature across the entire observed wavelength range. The Teff values and radii derived, and their dependency on metallicity, are in agreement with the most recent structural models of low-mass stars, removing the long-standing discrepancy between the observed and calculated locations of such stars in the H-R diagram, at least for stars more massive than 0.1 Msun. Title: The Effects of Fe II Non-LTE on Nova Atmospheres and Spectra Authors: Hauschildt, Peter H.; Baron, E.; Starrfield, Sumner; Allard, France Bibcode: 1996ApJ...462..386H Altcode: 1996astro.ph..1149H The atmospheres of novae at early times in their outbursts are very extended, expanding shells with low densities. Models of these atmospheres show that non-LTE effects are very important and must be included in realistic calculations. We have, therefore, been improving our atmospheric studies by increasing the number of ions treated in non-LTE. One of the most important ions is Fe II, which has a complex structure and numerous lines in the observable spectrum. In this paper we investigate non-LTE effects for Fe II for a wide variety of parameters. We use a detailed Fe II model atom with 617 level and 13,675 primary lines, treated using a rate-operator formalism. We show that the radiative transfer equation in nova atmospheres must be treated with sophisticated numerical methods and that simple approximations, such as the Sobolev method, cannot be used because of the large number of overlapping lines in the comoving frame.

Our results show that the formation of the Fe II lines is strongly affected by non-LTE effects. For low effective temperatures, Teff < 20,000 K, the optical Fe II lines are most influenced by non-LTE effects, while for higher Teff the UV lines of Fe II are very strongly affected by non-LTE. The departure coefficients are such that Fe II tends to be overionized in non-LTE when compared to LTE. Therefore, Fe II non-LTE must be included with sophisticated radiative transfer in nova atmosphere models in order to analyze observed nova spectra reliably. Finally, we show that the number of wavelength points required for the Fe II non-LTE model atmosphere calculations can be reduced from 90,000 to about 30,000 without changing the results if we choose a sufficiently dense UV wavelength grid. Title: Preliminary spectral analysis of SN 1994I Authors: Baron, E.; Hauschildt, P. H.; Branch, D.; Kirshner, R. P.; Filippenko, A. V. Bibcode: 1996MNRAS.279..799B Altcode: 1995astro.ph.10070B We present optical spectra of the Type 1c supernova 1994I in M51 and preliminary non-local thermodynamic equilibrium (non-LTE) analysis of the spectra. Our models are not inconsistent with the explosions of C+O cores of massive stars. While we find no direct evidence for helium in the optical spectra, our models cannot rule out small amounts of helium. More than 0.1 M_solar of helium seems unlikely. Title: Synthetic Spectra and Mass Determination of the Brown Dwarf Gl229B Authors: Allard, France; Hauschildt, Peter H.; Baraffe, Isabelle; Chabrier, Gilles Bibcode: 1996astro.ph..3019A Altcode: We present preliminary non-grey model atmospheres and interiors for cool brown dwarfs. The resulting synthetic spectra are compared to available spectroscopic and photometric observations of the coolest brown dwarf yet discovered, Gl229B (Nakajima \etal, 1995). Despite recognized shortcomings of current methane opacities, we find that the model spectra provide an excellent fit to most of the spectral features of the brown dwarf. We confirm the presence of methane absorption and the substellar nature of Gl229B. These preliminary models set an upper limit for the effective temperature of 1000~K. We also compute the evolution of brown dwarfs with solar composition and masses from 0.02 to 0.065 $\msol$. While uncertainties in the age of the system yield some undetermination for the mass of Gl229B, the most likely solution is $m\approx 0.04-0.055 \msol$. In any case, we can set an upper limit $m= 0.065\msol$ for a very unlikely age $t=10$ Gyr. Title: Radiative transfer in the comoving frame Authors: Baron, E.; Hauschildt, P. H.; Mezzacappa, A. Bibcode: 1996MNRAS.278..763B Altcode: We discuss the formulation of the radiative transfer equation in the comoving frame. For characteristic velocities larger than ~2000 km s^-1, the effects of advection on the synthetic spectra are non-negligible, and hence they should be included in model calculations. We show that the time-independent or quasi-static approximation is adequate for most astrophysical problems, e.g., hot stars, novae and supernovae. We examine the use of the Sobolev approximation in modelling moving atmospheres, and find that the number of overlapping lines in the comoving frame make the approximation suspect in models that predict both lines and continua. We also discuss the form of the Rosseland mean opacity in the comoving frame, and derive a formula that is easy to implement in radiation hydrodynamics calculations. Title: Spectrum synthesis of type IA SNe Authors: Hauschildt, P. H.; Baron, E.; Nugent, P.; Branch, D. Bibcode: 1996ASPC...96..175H Altcode: 1996hds..conf..175H No abstract at ADS Title: Water and titanium oxide in late-type M dwarfs Authors: Jones, H. R. A.; Viti, S.; Miller, S.; Tennyson, J.; Allard, F.; Hauschildt, P. Bibcode: 1996ASPC..109..717J Altcode: 1996csss....9..717J No abstract at ADS Title: Pressure broadening in M dwarfs and VB 10 Authors: Schweitzer, A.; Hauschildt, P. H.; Allard, F. Bibcode: 1996ASPC..109..571S Altcode: 1996csss....9..571S No abstract at ADS Title: NLTE model atmospheres for M dwarfs and giants Authors: Hauschildt, P. H.; Allard, F.; Alexander, D. R.; Schweitzer, A.; Baron, F. Bibcode: 1996IAUS..176..539H Altcode: 1996astro.ph..1155H The atmospheres of M stars are dominated by a small number of very strong molecular compounds (H$_2$O, TiO, H$_2$, CO, VO). Most of the hydrogen is locked in molecular H$_2$, most of the carbon in CO; and H$_2$O, TiO and VO opacities define a pseudo-continuum covering the entire flux distribution of these stars. The optical ``continuum'' is due to TiO vibrational bands which are often used as temperature indicators for these stars. These may be the depth of the bands relative to the troughs in between them; or the depth of the VO bands; or of the atomic lines relative to the local ``continuum''; or even the strength of the infrared water bands; all of these depend on the strength of the TiO bands and the amount of flux-redistribution to longer wavelengths exerted by them. Departures from LTE of the Ti I atom, and thus the concentration of the important TiO molecule, could, therefore, have severe and measurable consequences on the atmospheric structure and spectra of these stars. In this paper we discuss NLTE effects of Ti I in fully self-consistent models for a few representative M/Brown dwarf and M giant model atmospheres and spectra. Title: Are novae standard candles? Authors: Pistinner, S.; Shaviv, G.; Hauschildt, P. H.; Starrfield, S. Bibcode: 1996ASSL..208..295P Altcode: 1996cvro.coll..295P; 1996IAUCo.158..295P No abstract at ADS Title: The Hot Winds of Novae Authors: Hauschildt, Peter H.; Starrfield, S.; Baron, E.; Allard, F. Bibcode: 1996aeu..conf..413H Altcode: 1996IAUCo.152..413H No abstract at ADS Title: Water vapour in cool dwarf stars Authors: Jones, Hugh R. A.; Longmore, Andrew J.; Allard, France; Hauschildt, Peter H.; Miller, Steven; Tennyson, Jonathan Bibcode: 1995MNRAS.277..767J Altcode: We present comparisons which show good agreement between observed and synthetic spectra for water vapour transitions in a range of M dwarfs. The observations were made from 2.85 to 3.40 μm where water vapour transitions are strong in cool stars but relatively weak in the Earth's atmosphere, allowing reliable observations to be made. The synthetic spectra were computed using a stellar atmosphere code and include preliminary ab initio calculations for ro-vibrational bands up to J=30. Synthetic spectra indicate that changes in metallicity and gravity have a small effect on the strength of the observed water bands whereas temperature changes produce large differences in strength. Formally, we find similar effective temperatures to those found in previous work. However, since the molecular opacity at the peak of the flux distribution is not well determined, uncertainties in the model atmosphere structure and the effective temperature scale remain. Detailed line profiles can be modelled for atomic lines because their damping constants are known, but they are not known for molecular transitions. Atomic lines computed with Voigt profiles and Van der Waals pressure broadening give an averaged full width half maximum of around 50 km s^-1. For the observed water vapour transitions to match this generation of synthetic spectra we use Gaussian profiles with a full width half maximum of 2 km s^-1 to model the pressure broadening of water vapour transitions. Examination of the model structure indicates that water vapour lines are formed relatively high in the photosphere at pressures about an order of magnitude lower than those of atomic lines. These results strongly suggest that water vapour transitions are not pressure broadened sufficiently to overlap; as previously assumed when modelling molecular transitions in cool dwarfs using the Just Overlapping Line Approximation. The inferred lack of pressure broadening allows flux to escape between water lines, even within a region of strong water vapour absorption, and leads to weaker water band strengths. We demonstrate that this result is likely to explain much of the past discrepancy between observed and theoretical spectra energy distributions for M dwarfs. Title: Evidence for a Spectroscopic Sequence among Type 1a Supernovae Authors: Nugent, Peter; Phillips, Mark; Baron, E.; Branch, David; Hauschildt, Peter Bibcode: 1995ApJ...455L.147N Altcode: 1995astro.ph.10004N In this Letter we present evidence for a spectral sequence among Type Ia supernovae (SN Ia's). The sequence is based on the systematic variation of several features seen in the near-maximum light spectrum. This sequence is analogous to the recently noted photometric sequence among SN Ia's which shows a relationship between the peak brightness of a SN Ia and the shape of its light curve. In addition to the observational evidence we present a partial theoretical explanation for the sequence. This has been achieved by producing a series of non-LTE synthetic spectra in which only the effective temperature is varied. The synthetic sequence nicely reproduces most of the differences seen in the observed one and presumably corresponds to the amount of 56Ni produced in the explosion. Title: An Exploratory Model Atmosphere for the Brown Dwarf Gl229B Authors: Hauschildt, P. H.; Allard, F.; Alexander, D. R. Bibcode: 1995AAS...18710312H Altcode: 1995BAAS...27.1432H We present an exploratory convective model atmosphere and synthetic spectrum for the cool brown dwarf Gl229B recently discovered by Nakajima et al (1995). The model is computed using the multi-purpose stellar atmosphere code Phoenix with a special implementation of condensation rates and grain opacities (Alexander & Ferguson 1994), an H_3(+) line list by Neale & Tennyson (1995), and the combined HITRAN (Rothman et al, 1992) and GEISA (Husson et al, 1992) planetary data bases. The synthetic spectrum is compared to the available spectroscopic and photometric observations of Gl229B. We investigate in particular the effects of grain condensation and opacities, and some alternatives to the incompleteness of the considered CH4 line list. By discussing the inferred structure and spectrum of Gl229B, we provide some insights and guidelines for future studies of this brown dwarf in different spectral ranges. Model atmospheres, synthetic spectra and colors presented here will be made available upon request. This research is partially supported by a NASA LTSA grant to ASU and an NSF grant AST-9217946 to WSU. Title: Hot Water in Cool Stars Authors: Viti, S.; Jones, H. R. A.; Tennyson, J.; Polyansky, O. L.; Miller, S.; Hauschildt, P.; Allard, F. Bibcode: 1995AAS...18710314V Altcode: 1995BAAS...27.1432V We compare high quality data of the infrared water vapour bands for one of the coolest known M dwarfs, TVLM 513-46546 with synthetic spectra from the model atmosphere code sc {PHOENIX}. We show how the use of three different datasets for the water vapour input to the model produces dramatic changes to the synthetic spectra yet none account for the observations. These comparisons underline the urgent need for more accurate data for water vapour. We have calculated a preliminary water linelist computed with parameters suitable for Sunspots. The codes employed calculate quantum mechanically the rotation-vibration energy levels, wavefunctions and associated dipole transition strengths using the sc {DVR3D} program suite. This water linelist improves on the previous one because it uses a better potential and the full symmetry of the water molecule. However, so far the energy levels computed are limited to the ground vibrational state. Using these calculations we have compared our results with linestrengths measured in laboratory experiments performed at a temperature of 1823K and the agreement is very good. We are calculating a more complete water linelist. It will include all energy levels up to 30 000 cm(-1) for angular momentum states up to J=30 and it uses an accurate potential surface. First results from this production are already available. Progress on these projects will be reported at the conference. Title: Non-LTE treatment of Fe II in astrophysical plasmas. Authors: Hauschildt, P. H.; Baron, E. Bibcode: 1995JQSRT..54..987H Altcode: 1996astro.ph..1148H The authors describe their implementation of an extremely detailed model atom of singly ionized iron for NLTE computations in static and moving astrophysical plasmas. The model atom includes 617 levels, 13,675 primary permitted transitions and up to 1.2 million secondary transitions. The authors' approach guarantees that the total iron opacity is included at the correct wavelength with reasonable memory and CPU requirements. They find that the lines saturate the wavelength space, such that special wavelength points inserted along the detailed profile functions may be replaced with a statistical sampling method. The authors describe the results of various test calculations for novae and supernovae. Title: A New Generation of Evolutionary Sequences for Novae Authors: Starrfield, S.; Hauschildt, P.; Truran, J.; Sparks, W.; Wiescher, M. Bibcode: 1995AAS...187.7915S Altcode: 1995BAAS...27.1399S We report on the results of new calculations of Thermonuclear Runaways (TNR) on 1.25Msun and 1.35Msun oxygen-neon-magnesium white dwarfs using an updated version of NOVA. NOVA is a one-dimensional, fully implicit, hydrodynamic stellar evolution code that includes a large nuclear reaction network. The results of our previous studies can be found in Starrfield et al (1992, ApJ, 391, L71) and Politano et al (1995, ApJ, 448, 807). Since those calculations were done, we have updated both the nuclear reaction network and the nuclear reaction rates (see, for example, Van Wormer et al 1994, ApJ, 432, 326 and Herndl et al 1995, Phys. Rev. C, 52, 1078). We now use opacities from the OPAL carbon rich tables. When we are outside the range of validity of the OPAL tables, we continue to use the Iben fit. The new sequences also include boundary layer heating both from the accretion shock and the internal energy of the infalling material (Shaviv and Starrfield 1987, ApJ, 321, L51). Finally, in order to improve the agreement between our theoretical light curves and the observations, we use bolometric corrections obtained from the latest generation of spherical, expanding, Non-LTE, stellar atmospheres for novae (Hauschildt et al 1995a, ApJ, 447, 829; Hauschildt et al 1995b, ApJ, in press). Our first results show that the changes in the reaction rates and the opacities cause quantitative changes with respect to our published studies. For accretion onto the 1.25Msun white dwarf, for example, we find that less mass is ejected and a smaller amount of (26) Al is produced. In addition, the abundances of (31) P and (32) S increase by factors of more than two. The causes are that (1)the OPAL opacities are larger than those given by the Iben fit, which results in less mass being accreted on the white dwarf for the same initial conditions, and (2) the proton-capture reaction rates for some of the intermediate mass nuclei near (26) Al have increased so that the evolution to higher mass nuclei is enhanced. We acknowledge partial support by DOE, NASA, and NSF. Title: M Stars Model Atmospheres: Spectra and Colors Authors: Allard, F.; Lawlor, T.; Alexander, D. R.; Hauschildt, P. H. Bibcode: 1995AAS...18710311A Altcode: 1995BAAS...27.1432A In this paper, we present new pressure-dependent line-by-line LTE model atmospheres for red giants in spherical geometry, computed using the multi-purpose atmospheric code Phoenix, which constitutes an extension of the existing cool dwarf grids of Allard & Hauschildt (1995) to the abundance and gravity regimes of cool M-S-C type giants. Departures from LTE in the Ti I lines is investigated for some selected models across the grid, but only modest NLTE effects are found in the abundance of the important absorber TiO. The combined dwarf and giant grid is compared to observations in the 8-colors Wing photometric sample of cool dwarfs and M-S-C giants of the Large Magellanic Clouds. The Pheonix giant grid is also compared to results obtained with our version of the Atlas9 code. In particular, we investigate the failure of Atlas-family models to reproduce the Violet (2700 to 4000 Angstroms) energy distribution of cool giants. Short & Lester (1994) suggested this may be due to a lack of molecular photo-dissociation opacities of hydrides. We find that Phoenix models computed with opacities similar to our Atlas9 opacities do not show this Violet discrepancy. We explore remaining opacity differences as well as differences in the treatment of radiative transfer. Model atmospheres, synthetic spectra and colors presented here will be made available upon request. This research is partially supported by a grant AST-9217946 from the National Science Foundation. Title: NLTE Modeling of SNe Ia Near Maximum Light Authors: Baron, E.; Hauschildt, P. H.; Mezzacappa, A. Bibcode: 1995astro.ph.11081B Altcode: Modeling the atmospheres of SNe~Ia requires the solution of the NLTE radiative transfer equation. We discuss the formulation of the radiative transfer equation in the co-moving frame. For characteristic velocities larger than about 2000 km/s, the effects of advection on the synthetic spectra are non-negligible, and hence should be included in model calculations. We show that the time-independent or quasi-static approximation is adequate for SNe~Ia near maximum light, as well as for most other astrophysical problems; e.g., hot stars, novae, and other types of supernovae. We examine the use of the Sobolev approximation in modeling moving atmospheres and find that the number of overlapping lines in the co-moving frame make the approximation suspect in models that predict both lines and continua. We briefly discuss the form of the Rosseland mean opacity in the co-moving frame, and present a formula that is easy to implement in radiation hydrodynamics calculations. Title: Some Remarks about Nova Spectroscopy and Photometry Authors: Pistinner, Shlomi; Shaviv, Giora; Hauschildt, Peter H.; Starrfield, Sumner Bibcode: 1995ApJ...451..724P Altcode: In this paper we explore the sensitivity of stellar atmosphere modeling of early nova spectra to the input parameters. Our results identify spectral regions where the continuum spectra are insensitive to the input parameters and certain wave bands where they are sensitive to the input parameters. Thus, we identify the best spectral region for determining elemental abundances, effective temperatures, and luminosities.

We find in some cases that nova atmospheres have a continuum extinction coefficient that is dominated by scattering. The continuum scattering and the resulting continuum extinction are for these cases nearly gray. We apply and extend the small parameter Chandrasekhar expansion and we use the properties of the gray opacity, to study the effects of small residual absorption in the atmosphere. Two cases are treated: the case of a static extended atmosphere and the case of an extended atmosphere in motion. We solve, self-consistently, the transfer equation for these physical conditions. The assumption of radiative equilibrium allows us to also obtain a self-consistent temperature profile which validates our approximation a posteriori.

Using these solutions, we (a) derive conditions for the required signal-to-noise ratio (or the relative accuracy of the observed fluxes) and the required observed frequency range needed to obtain a prescribed accuracy for those nova parameters obtained from a comparison of observed with synthetic spectra; (b) assess and establish the importance of spectroscopic (in contrast to photometric) measurements; (c) show that the use of synthetic spectra is an essential part, in the optically thick phase, of the determination of nova characteristics from the observations; and (d) define a new property continuum similarity and show how and when nova spectra possess this property. We find that the only wavelength region which is not affected by the physical conditions used to arrive at these conclusions is the ultraviolet. Therefore, we conclude that the ultraviolet is the most important wavelength region to use when deriving nova parameters from synthetic spectra. Title: Erratum:``Low Hubble Constant from the Physics of Type Ia Supernovae'' [Phys. Rev. Lett. 75, 394 (1995)] Authors: Nugent, Peter; Branch, David; Baron, E.; Fisher, Adam; Vaughan, Thomas; Hauschildt, Peter H. Bibcode: 1995PhRvL..75.1874N Altcode: No abstract at ADS Title: The Physics of Early Nova Spectra Authors: Hauschildt, Peter H.; Starrfield, Sumner; Shore, Steven N.; Allard, France; Baron, E. Bibcode: 1995ApJ...447..829H Altcode: We discuss the physical effects that are important for the formation of the early spectra of novae. Nova atmospheres are optically thick, fast expanding shells with flat density profiles, leading to geometrically very extended atmospheres. We show that the properties of early nova spectra can be understood in terms of this basic model and discuss some important effects that influence the structure and the emitted spectrum of nova atmospheres, e.g., line blanketing, non-LTE effects, and the velocity field. The proper modeling of nova atmospheres is discussed, and we give some computational details. Title: Low Hubble Constant from the Physics of Type Ia Supernovae Authors: Nugent, Peter; Branch, David; Baron, E.; Fisher, Adam; Vaughan, Thomas; Hauschildt, Peter H. Bibcode: 1995PhRvL..75..394N Altcode: Two physical methods for determining luminosities and distances of type Ia supernovae, the spectral fitting expanding atmosphere method and the 56Ni radioactivity method, depend on the interval between the times of explosion and maximum brightness, but in differing ways. By requiring consistency between the two methods we derive blue and visual absolute magnitudes MB~=MV~=-19.74+/-0.45 mag which, together with the ridge line of type Ia supernovae in the magnitude-redshift diagram, constrain the Hubble constant to be 50+12-10 km s-1 Mpc-1. Title: New Evolutionary Tracks for Very Low Mass Stars Authors: Baraffe, I.; Chabrier, G.; Allard, F.; Hauschildt, P. H. Bibcode: 1995ApJ...446L..35B Altcode: We present new evolutionary calculations for low-mass and very low mass M dwarfs, for a metallicity range -2 ≤ [M/H] ≤ 0, down to the hydrogen-burning minimum mass (0.07 < M/Msun < 0.6). We use the most recent atmosphere models calculated by Allard & Hauschildt (1995), based on synthetic spectra at finite metallicity, and gray atmosphere models based on Alexander & Ferguson (1994) Rosseland opacities.

Comparisons are made with observational results down to the bottom of the main sequence, for different metallicities, in magnitude-color and color-color diagrams. We find excellent agreement between theory and observations over the whole characteristic temperature/luminosity range. This enables us to determine the mass of the faintest objects observed, which is found to be mlim ≍ 0.085 Msun for [M/H] = 0 and -0.5, and mlim = 0.09 Msun for [M/H] = -1.5, for an age of 10 Gyr.

We also examine the effect of the age, the metallicity, and the outer boundary conditions on the evolution. Title: Supernova 1993J: one year later. Authors: Baron, E.; Hauschildt, P. H.; Young, T. R. Bibcode: 1995PhR...256...23B Altcode: Supernova 1993J, a Type IIpec supernova, was discovered on 1993 March 28 in the nearby galaxy M81. The spectra displayed strong Balmer lines establishing its classification as a Type II supernova. About 26 days after explosion the Hα profile became anomalous, signaling the presence of significant amounts of helium. Additionally, the light curve displayed an anomalous double peak. We review the observations and interpretation of SN 1993J through the use of light curve fitting and synthetic spectra. Title: Model Atmospheres for M (Sub)Dwarf Stars. I. The Base Model Grid Authors: Allard, France; Hauschildt, Peter H. Bibcode: 1995ApJ...445..433A Altcode: 1996astro.ph..1150A We have calculated a grid of more than 700 model atmospheres valid for a wide range of parameters encompassing the coolest known M~dwarfs, M~subdwarfs and brown dwarf candidates: $1500\le \teff \le 4000\,$K, $3.5\le \log(g)\le 5.5$, and $-4.0\le { [M/H]}\le +0.5$. Our equation of state includes 105 molecules and up to 27 ionization stages of 39 elements. In the calculations of the base grid of model atmospheres presented here, we include over 300 molecular bands of 4 molecules (TiO, VO, CaH, FeH) in the JOLA approximation, the water opacity of Ludwig (1971), collision induced opacities, b-f and f-f atomic processes, as well as about 2 million spectral lines selected from a list with more than 42 million atomic and 24 million molecular (H$_2$, CH, NH, OH, MgH, SiH, C$_2$, CN, CO, SiO) lines. High-resolution synthetic spectra are obtained using an opacity sampling method. The model atmospheres and spectra are calculated with the generalized stellar atmosphere code PHOENIX, assuming LTE, plane-parallel geometry, energy (radiative plus convective) conservation, and hydrostatic equilibrium. The model spectra give close agreement with observations of M~dwarfs across a wide spectral range from the blue to the near-IR, with one notable exception: the fit to the water bands. We discuss several practical applications of our model grid, e.g., broadband colors derived from the synthetic spectra. In light of current efforts to identify genuine brown dwarfs, we also show how low-resolution spectra of cool dwarfs vary with surface gravity, and how the high-resolution line profile of the Li~I resonance doublet depends on the Li abundance. Title: Non-LTE Spectral Analysis and Model Constraints on SN 1993J Authors: Baron, E.; Hauschildt, P. H.; Branch, D.; Austin, S.; Garnavich, P.; Ann, Hong Bae; Wagner, R. M.; Filippenko, A. V.; Matheson, T.; Liebert, James Bibcode: 1995ApJ...441..170B Altcode: We present non-LTE synthetic spectra for a time series of observations of SN 1993J obtained on 1993 March 30-31, April 7, April 13-15, and June 13 UT. The spectra are dominated by hydrogen Balmer lines; neutral helium lines, which have been nonthermally excited; and Fe II features. The density profile evolves from an extremely steep "brick wall" structure with an equivalent power-law index of about 50 on March 30 to a more typical SN II profile with a power law index of about 10. The early spectra are well fitted by a solar composition of metals, although an enhanced abundance of helium is required in order to fit the neutral helium lines. By June 13, the photosphere has receded deep into the helium layer, although there appears to be a layer of hydrogen at higher velocity. The distance is estimated for each epoch. While consistent results are found for spectra obtained in the month of April, the spread in distances from March to June is quite large. Our value for April is μ = 28.0 +/- 0.3 mag, consistent with the recent Cepheid distance to the host galaxy M81. We also compare our results to other implementations of the expanding photosphere method. Title: Spectrum Synthesis of the Type IA Supernovae SN 1992A and SN 1981B Authors: Nugent, Peter; Baron, E.; Hauschildt, Peter H.; Branch, David Bibcode: 1995ApJ...441L..33N Altcode: We present non-LTE synthetic spectra for the Type Ia supernovae SN 1992A and SN 1981B, near maximum light. At this epoch both supernovae were observed from the UV through the optical. This wide spectral coverage is essential for determining the density structure of a SN Ia. Our fits are in good agreement with observation and provide some insight as to the differences between these supernovae. We also discuss the application of the expanding photosphere method to SNe Ia which gives a distance that is independent of those based on the decay of ^56^Ni and Cepheid variable stars. Title: Ionization and temperature of nova shells. II. The influence of realistic photospheric radiation fields. Authors: Beck, H. K. B.; Hauschildt, P. H.; Gail, H. -P.; Sedlmayr, E. Bibcode: 1995A&A...294..195B Altcode: In order to determine the physical situation preceding the process of dust formation in classical novae we calculate the time dependent ionization and temperature structure of an expanding shell which is exposed to the ionizing radiation of a hot central source. Additionally the energy balance between ionizational heating and cooling processes by electron recombination, gas expansion, collisionally excited forbidden lines of several atoms and free-free radiation of hydrogen is solved. The radiation field of the classical nova is given by a synthetic spectrum calculated on the assumption of spherical symmetry and a time-independent, expanding, non-LTE atmosphere in radiative equilibrium. We show that in novae of slow and moderate speed class complete carbon ionization throughout the nova shell is not possible before day ~50 after the outburst. In the early phases the degree of carbon ionization is significantly lower than in the corresponding blackbody model, thus enabling a complex chemistry to proceed, which may involve fast ion-neutral reactions. Title: The Physics of Early Nova Spectra Authors: Hauschildt, P. H.; Starrfield, S.; Shore, S. N.; Allard, F.; Baron, E. Bibcode: 1995ASSL..205..257H Altcode: 1995cava.conf..257H No abstract at ADS Title: The Outburst of Nova Cassiopeiae 1993 Authors: Starrfield, S.; Hauschildt, P. H.; Shore, S. N.; Gonzales-Riestra, R.; Sonneborn, G.; Allard, F. Bibcode: 1995ASSL..205..267S Altcode: 1995cava.conf..267S No abstract at ADS Title: M (sub) Dwarf Model Atmospheres: The Next Generation Authors: Allard, F.; Hauschildt, P. H. Bibcode: 1995bmsb.conf...32A Altcode: No abstract at ADS Title: Model Atmospheres for the ``Most Abnormal'' DZ White Dwarf Authors: Aannestad, P. A.; Hauschildt, P.; Hammond, G. L.; Allard, F. Bibcode: 1994AAS...185.4602A Altcode: 1994BAAS...26.1382A We present model atmospheres calculations for G165-7, a DZ white dwarf with the most metal lines in its spectrum. The model spectra are fitted to existing ground-based observations from 3200 Angstroms to 10,000 Angstroms , including high resolution MMT data in the region 3700 Angstroms - 4600 Angstroms (Sion et al. ApJS,72,707). We use the plane-parallel, LTE mode of the general computer code PHOENIX 4.9 to compute the model atmospheres and synthetic spectra for G165-7. About 10(5) atomic lines and 10(6) molecular lines are included within the spectral region. The equation of state is solved for 39 elements (with up to 26 ionization stages per element) and 105 molecules. The models include, self consistently, line blanketing of the lines selected from the latest atomic and molecular line list of Kurucz (1993, CD-ROM, 1 and 15) and others. Title: Non-LTE Effects on the Strength of the Lyman Edge in Quasar Accretion Disks Authors: Stoerzer, H.; Hauschildt, P. H.; Allard, F. Bibcode: 1994ApJ...437L..91S Altcode: We have calculated UV/EUV (300 A <= λ <= 1500 A) continuous energy distributions of accretions disks in the centers of active galactic nuclei (AGNs) for disk luminosities in the range 0.1L_Edd <= L_acc_ < 1.0L_Edd_ and central masses ranging from 10^8^ M_sun_ to 10^9^ M_sun_. The vertical gas pressure structure of the disk and the disk height are obtained analytically; the temperature stratification and the resulting continuum radiation fields are calculated numerically. We have included non-LTE effects of both the ionization equilibrium and the level populations of hydrogen and helium. We show that these non-LTE effects reduce the strength of the Lyman edge when compared to the LTE case. In non-LTE we find that the edge can be weakly in emission or absorption for disks seen face-on, depending on the disk parameters. Title: Spectrum Synthesis of the Type IA SNe 1992A and 1981B Authors: Nugent, Peter; Baron, E.; Branch, David; Hauschildt, Peter Bibcode: 1994AAS...185.7902N Altcode: 1994BAAS...26.1444N We present NLTE synthetic spectra for the Type Ia supernovae SN 1992A and SN 1981B, near maximum light. At this epoch both supernovae were observed from the UV through the optical. This wide spectral coverage is essential for determining the density structure of a SN Ia. Our fits are in good agreement with observation and provide some insight as to the differences between these supernovae. We also discuss the application of the expanding photosphere method to SNe Ia which gives a distance that is independent of those based on the decay of (56) Ni and Cepheid variable stars. Title: The early Spectral Evolution of Nova Cassiopeiae 1993 Authors: Hauschildt, Peter H.; Starrfield, Sumner; Shore, Steven N.; Gonzalez-Riestra, Rosario; Sonneborn, George; Allard, France Bibcode: 1994AJ....108.1008H Altcode: In this paper we describe the evolution of Nova Cas 1993 over the first two months of its outburst. We present an ultraviolet light curve that covers the period from announcement to just after dust began forming in the ejecta (1994 Feb. 15) and International Ultraviolet Explorer (IUE) spacecraft constraints forced us to halt our observations. We have used spherical, expanding, Non-local Thermodynamic Equilibrium (NLTE) stellar atmospheres to compute synthetic spectra and have compared the results to combined ultraviolet (low-resolution 1200-3400 A and high-resolution 2400-3300 A) spectra. Our fits show that the effective temperature of the ejecta increased from approx. 8000 to about approx. 16 000 K between 1993 Dec. 12 and 1993 Dec. 26. The temperature then increased more slowly to approx. 24 000 on 1994 Jan. 28. A preliminary abundance analysis shows evidence for hydrogen depletion, as we also found for Nova V1974 Cygni; however we find a larger enhancement of carbon, nitrogen, and oxygen. We also show that the principal mechanism for mass ejection in this nova is a radiation pressure driven wind and that mechanical driving is not necessary. Title: EUV energy distributions of accretion disks in active galactic nuclei. Authors: Storzer, H.; Hauschildt, P. H. Bibcode: 1994A&A...289...45S Altcode: We have calculated UV/EUV (300A<=λ<=1500A) continuous energy distributions of accretion disks in the centers of active galactic nuclei (AGNs) for disk luminosities in the range 0.1xL_Edd_<=L_acc_< 1.0xL_Edd_ and central masses ranging from 10^8^Msun_ to 10^10^Msun_. The vertical gas pressure structure of the disk is obtained analytically, the temperature stratification and the resulting continuum radiation fields are calculated numerically. We show that weak Lyman edges are an intrinsic feature of such disks. The strength of the H I Lyman edge decreases for increasing accretion rate and fixed mass of the central black hole. It increases for increasing central mass and fixed luminosity in terms of the Eddington luminosity. Title: Convergence properties of the accelerated Λ-iteration method for the solution of radaitive transfer problems. Authors: Hauschildt, P. H.; Störzer, H.; Baron, E. Bibcode: 1994JQSRT..51..875H Altcode: The authors investigate the convergence properties and the computational speed of the accelerated Λ-iteration method for the solution of a wide variety of radiative transfer problems. Title: Dust formation in Nova Cassiopeiae 1993 seen by ultraviolet absorption Authors: Shore, S. N.; Starrfield, S.; Gonzalez-Riestrat, R.; Hauschildt, P. H.; Sonneborn, G. Bibcode: 1994Natur.369..539S Altcode: The clouds of gas in interstellar space also contain grains of dust, whose properties and origins have been the focus of debate for decades. Some dust formation has been assumed to take place in novae explosions1-5, as was first implied by the observation of a steep decrease in the amount of light emitted by the nova1,2 DQ Herculis 1934 about 100 days after outburst, presumed to be due to extinction by dust. Here we report observations from the International Ultraviolet Explorer satellite which show directly the onset of dust formation in Nova Cassiopeiae 1993, a classical nova of the same type as DQ Her 1934. The dust formed very quickly- about 70 days after the nova explosion-despite the initially high temperature of the ejecta. Our results suggest that high-energy photons are absorbed efficiently by the gas in the ejecta, lowering the temperature in the gas while it is still dense, and thereby allowing molecules to form and then to condense into dust. Title: Modeling and Interpretation of the Optical and HST UV Spectrum of SN 1993J Authors: Baron, E.; Hauschildt, P. H.; Branch, D. Bibcode: 1994ApJ...426..334B Altcode: We present spherically symmetric, non-LTE, expanding model atmosphere synthetic spectra of SN 1993J and compare them to the ultraviolet and optical spectra obtained simultaneously on 1993 April 15 by the HST and at Lick Observatory. We are able to fit the optical and HST near-UV spectra with a variety of compositions, but find that our best fits are obtained with an enhanced helium abundance (Y = 0.8) and significant nonthermal ionization due to gamma rays produced by the decay of ^56^Ni. We find the effects of X-rays produced by thermal bremsstrahlung in the circumstellar material to have little effect on the spectrum. Our current models are unable to fit the HST far-UV region, predicting too little flux and strong, unseen Fe II features. Title: Non-LTE Modeling of Nova Andromedae 1986 Authors: Schwarz, G.; Hauschildt, P.; Starrfield, S.; Allard, F.; Sonneborn, G.; Shore, S. N. Bibcode: 1994AAS...184.4703S Altcode: 1994BAAS...26..937S We have analyzed the IUE spectra which covers the early optically thick phase of Nova OS And 1986. We use spherically symmetric, non-LTE, line-blanketed, expanding model atmospheres to calculate a grid of co-moving frame, NLTE atmospheres for this nova with the following set of parameters: L=2 times 10(5) L_sun, rho ~ r(-3) , statistical velocity = 50 km s(-1) , 5000 <= T_eff <= 60000K, v_max = 2000 km s(-1) and solar abundances. We then computed observer frame synthetic spectra for each of the model atmospheres in the grid and used them to estimate the model parameters corresponding to the observed IUE spectra. The fit to the observations was iteratively improved by changing the parameters of the model atmospheres, in particular T_eff, v_max, and the abundances. The synthetic spectra give a very good fit to the pseudo-continuum and many of the features found in the IUE spectra. The earliest spectra, approximately 4 and 5 days after maximum light in the optical, are best fit by models with solar abundances for all elements except for carbon and oxygen which have abundances enhanced by a factor of about ten. We can not determine nitrogen abundances due to the lack of strong nitrogen lines in the ultraviolet. The later spectra, taken 19 and 27 days after maximum light, show, simultaneously, allowed, semi-forbidden, and forbidden lines. For these epochs, we can fit the allowed lines and the pseudo-continuum with solar abundances, except for carbon and oxygen which are still required to be enhanced by a about a factor of ten. The semi-forbidden and forbidden lines are formed in the emerging pre-nebula and are not, currently, included in the model atmospheres. We also find evidence for large non-LTE effects of Fe II in the later observations. Title: NLTE Synthetic Spectra of Type IA Supernovae Authors: Nugent, Peter; Baron, E.; Branch, David; Hauschildt, Peter Bibcode: 1994AAS...184.5706N Altcode: 1994BAAS...26..953N An approximate lambda iteration is used to solve the fully relativistic radiation transport equation to all orders in v/c. The NLTE rate equations are solved for MgII, CaII and NaI using an extension of the method of Rybicki and Hummer 1991, simultaneously with the condition of radiative equilibrium. The Kurucz list of 3 million lines is used to select the approximately 300,000 strongest lines with the populations assumed to be in LTE. The model atmospheres are constructed assuming that the velocity profile is homologous and that the density profile follows either a power law or an exponential falloff. Both SNe 1981B and 1992A are fit from the UV through the optical near maximum light producing reasonable agreement with observations. We discuss the application of the expanding photosphere method to SNe Ia which gives a distance that is independent of those based on radioactive nickel decay and Cepheids variable stars. Title: An operator splitting method for atmospheres with shocks Authors: Buchholz, B.; Hauschildt, P. H.; Rammacher, W.; Ulmschneider, P. Bibcode: 1994A&A...285..987B Altcode: We develop a fast operator splitting (OS) method to solve spectral line radiative transfer problems in time-dependent hydrodynamic computations with shock discontinuities, assuming complete redistribution. The convergence properties and the results obtained with our method are compared with results obtained using a modified core-saturation method and with the {LAMBDA}-iteration. We find that our operator splitting method is robust, accurate and fast. Title: The Influence of H 2O Line Blanketing on the Spectra of Cool Dwarf Stars Authors: Allard, F.; Hauschildt, P. H.; Miller, S.; Tennyson, J. Bibcode: 1994ApJ...426L..39A Altcode: We present our initial results of model atmosphere calculations for cool M dwarfs using an opacity sampling method and a new list of H2O lines. We obtain significantly improved fits to the infrared spectrum of the M dwarf VB10 when compared to earlier models. H2O is by far the dominant opacity source in cool stars. To illustrate this, we show the Rosseland mean of the total extinction under various assumptions. Our calculations demonstrate the importance of a good treatment of the water opacities in cool stars and the improvements possible by using up-to-date data for the water line absorption. Title: Analysis of the Early Spectra and Light Curve of SN 1987A Authors: Hauschildt, Peter H.; Ensman, Lisa M. Bibcode: 1994ApJ...424..905H Altcode: Numerical modeling of supernova spectra, light curves, and hydrodynamics requires physical inputs, numerical techniques, approximations, and assumptions which must be thoroughly understood in order to study the details of supernova explosions. Here, we discuss some of these in the context of the early evolution of supernova 1987A. Gray radiation-hydrodynamics is used to calculate the bolometric light curve and the hydrodynamic evolution of the supernova. Synthetic spectra are then obtained for the resulting density and velocity structure. The spectrum calculations are performed using a special-relativistic treatment of the radiative transfer equation in the comoving frame, line blanketing by about 10^5^ spectral lines, and departures from LTE for H I, He I, Mg II, and Ca II. We find that we are able to simultaneously fit the early light curve and spectra reasonably well, using a progenitor model from Arnett (1991a), without fine-tuning the free parameters. Temperature structures and radiative equilibrium, non-LTE effects, homologous expansion, and mean opacities are discussed. Title: Non--LTE Model Atmosphere Analysis of Nova Cygni 1992 Authors: Hauschildt, P. H.; Starrfield, S.; Austin, S.; Wagner, R. M.; Shore, S. N.; Sonneborn, G. Bibcode: 1994ApJ...422..831H Altcode: We use spherically symmetric non-local thermodynamic equilibrium (non-LTE), line-blanketed, expanding model atmospheres to analyze the International Ultraviolet Explorer (IUE) and optical spectra of Nova Cygni 1992 during the early phases of its outburst. We find that the first IUE spectrum obtained just after discovery on 1992 February 20, is best reproduced by a model atmosphere with a steep density gradient and homologous expansion, whereas the IUE and optical spectra obtained on February 24 show an extended, optically thick, wind structure. Therefore, we distinguish two phases of the early evolution of the nova photosphere: the initial, rapid, 'fireball' phase and the subsequent, much longer, optically thick 'wind' phase. The importance of line-blanketing in nova spectra is demonstrated. Our preliminary abundance analysis implies that hydrogen is depleted in the ejecta, corresponding to abundance enhancements of Fe by a factor of approximately 2 and of CNO by more than a factor of 10 when compared to solar abundances. The synthetic spectra reproduce both the observed pseudo-continua as well as most of the observed features from the UV to the optical spectral range and demonstrate the importance of obtaining nearly simultaneous UV and optical spectra for performing accurate analyses of expanding stellar atmospheres (for both novae and supernovae). Title: Nova Cassiopeiae 1993 Authors: Shore, S. N.; Starrfield, S.; Hauschildt, P.; Gonzalez-Riestra, R.; Sonneborn, G. Bibcode: 1994IAUC.5938....1S Altcode: S. N. Shore, Indiana University, South Bend; S. Starrfield and P. Hauschildt, Arizona State University; R. Gonzalez-Riestra, IUE Observatory, Vilspa; and G. Sonneborn, NASA/Goddard Space Flight Center, report: "Observations of Nova Cas 1993 with the IUE Satellite have confirmed the formation of dust (IAUC 5925, 5936) in the nova ejecta during the deep optical decline that is now underway (IAUC 5934). Spectra obtained on Feb. 18.1 and 19.5 UT show that the 120-200-nm portion of the spectrum has declined by more than a factor of ten since Feb. 11.2 UT with virtually no change in the absorption line opacity; the entire wavelength interval has been uniformly depressed. The longer-wavelength portion of the spectrum, 220-340 nm, exhibits depression by more than a factor of 20 in comparison to Feb. 11.5, with a broad peak in the extinction near Mg II 280 nm. The Feb. 18.3 long-wavelength spectra now show the C II 232-nm multiplet in emission, one of the few changes in the line spectrum during the past two weeks. There is no evidence for either enhanced absorption near 220 nm or for a steep short-wavelength rise. Therefore, the observed extinction, from the circumstellar dust that has just formed in the nova ejecta, does not resemble typical interstellar dust. The most likely explanation is that these grains are larger than normal interstellar dust. If the drop in the emitted radiation in the ultraviolet and optical is compensated by an increase in the infrared radiation as expected (cf. Gehrz 1988, Ann. Rev. Astron. Astrophys. 26, 377), the integrated infrared flux longward of 1 micron should reach of order 8*10**-8 erg cm-2 s-1 (based on the ultraviolet flux depression). We have used E(B-V) = 0.5 to correct for the interstellar (not circumstellar) extinction. Before the decline began, the 120-340-nm continuum contained the bulk of the luminosity. The bolometric luminosity of the nova has been constant to within about 10 percent from 1993 Dec. 15 to 1994 Feb. 11. It likely still is, except that it is now hidden by the enhanced extinction produced by the increasingly opaque circumstellar dust." Title: Novae at Maximum Light: They can be Cool! Authors: Hauschildt, P. H.; Starrfleld, S.; Allard, F. Bibcode: 1994ASPC...64..705H Altcode: 1994csss....8..705H No abstract at ADS Title: Nova Cassiopeiae 1993 Authors: Shore, S. N.; Starrfield, S.; Hauschildt, P. H.; Sonneborn, G.; Gonzalez-Riestra, R.; Mikuz, H.; Prudic, J. Bibcode: 1994IAUC.5925....1S Altcode: S. N. Shore, Indiana University, South Bend; S. Starrfield and P. H. Hauschildt, Arizona State University; G. Sonneborn, Goddard Space Flight Center; and R. Gonzalez-Riestra, International Ultraviolet Explorer (IUE) Observatory, Vilspa, report: "Observations of N Cas 1993 have been obtained with the IUE satellite since shortly after the report of its discovery (IAUC 5902). The first spectra (1993 Dec. 12.1 UT) showed the nova at ultraviolet (UV) minimum with most of the opacity coming from overlapping absorption lines from the iron group elements: the 'iron curtain'. We have been obtaining IUE spectra at about 4-day intervals since that time, which reveal that the ejected material has remained in an extremely optically thick shell stage. The wavelength region around 280 nm is a blend of both Fe II and Mg II. This blend displays a pseudo-P-Cyg profile with a broad absorption trough that extends to a velocity of about -1600 km/s. Interstellar Mg II h and k absorption lines are superposed on emission from the nova; they have mean velocities of -35 km/s but extend to nearly -60 km/s. Windows in the Fe II absorption spectrum have recently begun to appear at 158 nm and longer wavelengths, and changes in the spectral energy distribution imply a slowly growing temperature for the ejecta. An ultraviolet rise of a factor of three occurred around Dec. 22, but after that time the nova has remained at nearly constant integrated UV flux (through 1994 Jan. 12). A preliminary upper limit of E(B-V) = 0.6 is derived from the UV-to-optical flux ratio. The interstellar Mg II and Na I lines suggest a distance of 4-6 kpc. We note that the optical light curve is similar to that of a DQ Her-type of nova (Payne-Gaposchkin 1957, The Galactic Novae, p. 13). Such a nova will form an optically-thick dust shell about 60-90 days after maximum light in the optical. Our stellar-atmosphere modeling indicates that the slow spectral evolution is consistent with steady- state ejection over the past month. The optical light curve, the relatively slow UV spectral evolution, the steady state mass ejection, and the detection of CO molecular lines in the infrared (IAUC 5916, 5922) lead us to expect that this nova will also form optically-thick dust (Shore and Starrfield 1994, Sky Telesc., in press); infrared observations will be necessary to confirm this expectation." H. Mikuz, Ljubljana, Slovenia, reports that a prediscovery photograph, taken by J. Prudic (Ljubljana) on 1993 Dec. 4.95 UT with a 58-mm f/2 lens and T-Max 400 film, shows this object at mpv = 8.0 (comparison stars from AAVSO Atlas). Title: On the strength of the Lyman edge in quasar accretion disks. Authors: Störzer, H.; Hauschildt, P. H. Bibcode: 1994AGAb...10..227S Altcode: No abstract at ADS Title: Spectral Analysis of SN 1993J Authors: Baron, E.; Hauschildt, P. H.; Branch, D. Bibcode: 1993AAS...183.3902B Altcode: 1993BAAS...25.1348B We present results of model calculations of synthetic spectra for a time series of observations of the Type IIpec supernova SN 1993 in M81. We find that at very early times the composition was likely to be roughly solar and the atmosphere was rather extended. The structure quickly evolved to be extremely steep with equivalent power-law indices at the ``photosphere'' of N ~ 20-40 and the composition became significantly enhanced in helium with Y ~ 0.8. We find the helium is excited by non-thermal ionization from fast electrons produced by the Comptonization of gamma rays from the decay of ~ 0.1 M_sun of (56) Ni. We find a distance to the supernova consistent with that of the recently determined Cepheid distance. We compare our distance with other published distance determinations. We also discuss discrepancies between our models and the observations. Title: Interpretation of the Early Spectra of SN 1993J in M81 Authors: Baron, E.; Hauschildt, P. H.; Branch, D.; Wagner, R. M.; Austin, S. J.; Filippenko, A. V.; Matheson, T. Bibcode: 1993ApJ...416L..21B Altcode: We present optical spectra obtained on 1993 April 7 and April 13 of the bright supernova SN 1993J in the nearby galaxy M81. The spectra show strong hydrogen Balmer lines with pronounced P Cygni profiles, except for Hα, which is greatly dominated by emission. In order to obtain diagnostics on the velocities, temperatures, densities, and composition of the atmosphere, we present non-local thermodynamic equilibrium (NLTE) synthetic spectrum fits to these observations. For April 7 we find a photospheric velocity of 10,000-11,000 km s^-1^, with a photospheric electron temperature of 7500-8000 K and a radius of 10^15^ cm. On April 13 the photospheric velocity is about 11,000 km s^-1^, the photospheric temperature is about 6500 K, and the radius is ~1.6 x 10^15^ cm. Most of the features of the spectra are well fitted by model atmospheres with solar composition. We find a distance for SN 1993J of 4.0 +/- 0.5 Mpc and the explosion epoch to be UT 1993 March 27.5+/-0.5. Title: Multi-level non-LTE radiative transfer in expanding shells. Authors: Hauschildt, P. H. Bibcode: 1993JQSRT..50..301H Altcode: The author presents a new and general method for the solution of complex multi-level non-LTE radiative transfer problems both in static and moving media. The method is based on the approximate Λ-iteration method and is a direct extension of the scheme devised by Rybicki and Hummer (1991). The author demonstrates that this method is able to treat both active continua and overlapping lines with relatively small amount of computer resources. Some simplified test cases are presented and discussed. Title: Non-LTE Model Atmosphere Studies of Nova Cygni 1992 Authors: Hauschildt, P. H.; Starrfield, S.; Austin, S.; Shore, S.; Wehrse, R.; Shaviv, G. Bibcode: 1993AnIPS..10..109H Altcode: No abstract at ADS Title: Prediction of the 22Na and 26Al Production and γ-RAY Emission from Nova CYG 1992 and Nova HER 1991 Authors: Starrfield, S.; Truran, J. W.; Sparks, W. M.; Shore, S. N.; Sonneborn, G.; Wagner, R. M.; Gonzales-Riestra, R.; Hauschildt, P. H.; Austin, S.; Vanlandingham, K. Bibcode: 1993AnIPS..10..320S Altcode: No abstract at ADS Title: Ultraviolet Studies of Novae in the Large Magellanic Cloud Authors: Starrfield, Sumner; Hauschildt, Peter H.; Shore, Steven N.; Sonneborn, George; Gonzales-Riestra, R.; Sparks, Warren M. Bibcode: 1993LNP...416..181S Altcode: 1993namc.meet..181S We report on the ultraviolet observations of five novae in the Large Magellanic Cloud (LMC). They are LMC 1988 #1, which was a CO nove similar to OS And; LMC 1988 #2, which was an ONeMg nova similar to Nova Her 1991; LNC 1990 #1, which was a very fast ONeMG nova similar to V693 CrA 1981; LMC 1990 #2, which was a recurrent nova similar to U Sco; and LMC 1991 which reached V approximately 9. Title: Spherical Expanding NLTE Model Atmosphere Studies of Nova Cyg 1992 Authors: Hauschildt, P. H.; Starrfield, S.; Austin, S.; Wagner, R. M.; Shore, S. N.; Wehrse, R.; Shaviv, G. Bibcode: 1992AAS...18110012H Altcode: 1992BAAS...24.1280H We show synthetic spectra for Nova Cyg 1992 during the early, optically thick phase of its evolution. The model atmospheres are calulated using the assumptions of a steady state, spherically symmetric wind model for the early envelope. We solve the non-gray special relativistic equations of radiative transfer and radiative equilibrium in the Lagrangian frame. Non-LTE effects are included self-consistently, as is the effect of line blanketing of about 100,000 UV metal lines (the ``iron-curtain''). The models assume a radial density gradient (rho ~ r(-3) ) and self-similar expansion. These follow from hydrodynamical calculation of the nova outburst and from late time observations of Nova Cyg 1992. We show comparisons between our synthetic spectra and observed IUE low and high resolution spectra and medium resolution optical spectra of Nova Cyg 92 and discuss some of the properties of the spectra and the model atmospheres. An especially important generalization from our models is that the pseudo-emission features, resulting from line opacity minima, are sensitive to the velocity gradient in the ejecta. Title: Radiative Equilibrium in Rapidly Expanding Shells Authors: Hauschildt, P. H. Bibcode: 1992ApJ...398..224H Altcode: The equation of radiative equilibrium for rapidly expanding spherical shells including the special relativistic terms is discussed, and a temperature-correction procedure for the solution of this equation is given. The temperature-correction scheme combines a partial linearization approach with the approximate Lambda-operator iteration method. For some test problems, the temperature structures of atmospheres in radiative equilibrium in the Lagrangian frame are calculated. The effects of the velocity field on the temperature stratification and the luminosity are also discussed. We find that the temperature structure of a moving photosphere in radiative equilibrium in the Lagrangian frame differs significantly from that of a static photosphere and that, at least, all first-order terms, in particular the advection and aberration terms, have to be included consistently both in the radiative transfer and the energy equation in studies of supernovae atmospheres and other high-speed radiating flows. Title: Prediction of the 22Na and 26Al Production and γ-Ray Emission from Nova Cyg 1992 and Nova Her 1991 Authors: Starrfield, S.; Truran, J. W.; Sparks, W. M.; Shore, S. N.; Sonneborn, G.; Wagner, R. M.; Gonzalez-Riestra, R.; Hauschildt, P. H.; Austin, S.; Vanlandingham, K. Bibcode: 1992AAS...181.4406S Altcode: 1992BAAS...24.1190S No abstract at ADS Title: Spherically Symmetric, Expanding, Non--LTE Model Atmospheres for Novae during Their Early Stages Authors: Hauschildt, P. H.; Wehrse, R.; Starrfield, S.; Shaviv, G. Bibcode: 1992ApJ...393..307H Altcode: In the continuum and line-blanketed models presented here, nova atmospheres are characterized by a very slow decrease of density with increasing radius. This feature leads to very large geometrical extensions so that there are large temperature differences between the inner and outer parts of the line-forming regions. The theoretical spectra show a large IR excess and a small Balmer jump which may be either in absorption or in emission. For the parameters considered (effective temperature of about 10 exp 4 K, L = 2 x 10 exp 4 solar luminosities, outer boundary density of about 3 x 10 exp -15 g cm exp -3, mass-loss rate of 10 exp -5 solar masses/yr), most lines are in absorption. The effects of changes in the abundances of the heavy elements on the emergent spectra are discussed. The strong unidentified features observed in ultraviolet spectra of novae are found in actuality to be regions of transparency within the Fe 'forest'. Ultraviolet spectra obtained from the IUE archives are displayed, and spectral synthesis of these spectra is done using the theoretical atmospheres. Title: A fast operator perturbation method for the solution of the special relativistic equation of radiative transfer in spherical symmetry. Authors: Hauschildt, P. H. Bibcode: 1992JQSRT..47..433H Altcode: A fast method for the solution of the radiative transfer equation in rapidly moving spherical media, based on an approximate Λ-operator iteration, is described. The method uses the short characteristic method and a tridiagonal approximate Λ-operator to achieve fast convergence. The convergence properties and the CPU time requirements of the method are discussed for the test problem of a two-level atom with background continuum absorption and Thomson scattering. Details of the actual implementation for fast vector and parallel computers are given. The method is accurate and fast enough to be incorporated in radiation-hydrodynamic calculations. Title: Model Atmospheres for Nova during the Early Stages Authors: Hauschildt, P. H.; Wehrse, R.; Starrfield, S.; Shaviv, G. Bibcode: 1992ASPC...29..178H Altcode: 1992cvs..work..178H No abstract at ADS Title: Ultraviolet studies of novae in the large Magellanic cloud Authors: Starrfield, S.; Hauschildt, P. H. Bibcode: 1992STIN...9316181S Altcode: We report on the ultraviolet observations of five novae in the LMC. They are as follows: LMC1988 no. 1, which was a CO nova similar to OS, and LMC 1988 no. 2, which was an ONeMg nova similar to Nova Her 1991; LMC 1990 no. 1, which was a very fast ONeMg nova similar to V693 CrA 1981; LMC 1990 no. 2, which was a recurrent nova similar to U Sco; and LMC 1991 which reached V approximately 9. Title: Solution of the special relativistic equation of radiative transfer in rapidly expanding spherical shells. Authors: Hauschildt, P. H.; Wehrse, R. Bibcode: 1991JQSRT..46...81H Altcode: A new method for the solution of the radiative transfer equation in expanding spherical media based on the Discrete Ordinate Matrix Exponential (DOME) method is describe. The effects of advection and aberration terms on line profiles for scattering dominated shells as observed, e.g., in supernova photospheres are discussed. It is shown that these effects have a large influence on the radiation field in rapidly expanding shells and should therefore be included in model calculations. Title: Model atmospheres for SNe II during early stages. Authors: Best, M.; Hauschildt, P. H.; Wehrse, R.; Shaviv, G. Bibcode: 1991AnPCS..16..397B Altcode: The photospheres of type II supernovae during the coasting phase are characterized by moderate temperatures, large radii, very low densities and high expansions velocities. These properties lead to large geometrical extensions and to electron scattering as the main source of opacity. Therefore these photospheres are very different from those of stars in hydrostatic equilibrium. In this review the authors first describe the input physics for models and essential numerical aspects of the model construction. In particular they stress the central role of an adequate treatment of the radiative transfer equation which should simultaneously take into account the sphericity, a high ratio of scattering to absorption, and relativistic effects. Subsequently they discuss details of the emergent spectra and their relevance for parameter determinations. Finally, model spectra are compared with observations of the brights supernovae SN 1979c and SN 1980k, which seem to be more average examples of type II supernovae than SN 1987A, and possibilities for using these objects for extragalactic distance determinations are investigated. Title: Relativistic effects in supernova photospheres Authors: Hauschildt, P. H.; Best, M.; Wehrse, R. Bibcode: 1991A&A...247L..21H Altcode: The role of relativistic effects in the radiative transfer equation and the condition of radiative equilibrium is studied for supernova photospheres. It is found that these effects change significantly the equilibrium temperature stratification and the emergent spectra so that in abundance determinations errors up to about one order of magnitude may occur if they are neglected. Title: Non-LTE-Modellatmosphären für Novae und Supernovae Title: Non-LTE-Modellatmosphären für Novae und Supernovae Title: Non-LTE model atmospheres for novae and supernovae; Authors: Hauschildt, Peter H. Bibcode: 1991PhDT.......290H Altcode: No abstract at ADS Title: Model atmospheres for SNe II during early stages Authors: Best, Monika; Hauschildt, Peter H.; Wehrse, Rainer; Shaviv, Giora Bibcode: 1991AnPh...16..397B Altcode: The photospheres of type II supernovae during the coasting phase ( ~ 1 week to 1 month after outburst) are characterized by moderate temperatures (Teff ~ 7...12 Ö- 10^3K) , large radii (R ~ 10^13...10^15cm) , very low densities (p ~ 10^-13... 10^-16 gcm-3) and high expansions velocities (up to ~ 30000 km-1 in the outer layers). These properties lead to large geometrical extensions (i.e. the photons can travel a large fraction of the radius without being absorbed) and to electron scattering as the main source of opacity. Therefore these photospheres are very different from those of stars in hydrostatic equilibrium. In this review we first describe the input physics for models and essential numerical aspects of the model construction. In particular we stress the central role of an adequate treatment of the radiative transfer equation which should simultaneously take into account the sphericity, a high ratio of scattering to absorption, and relativistic effects. Subsequently we discuss details of the emergent spectra and their relevance for parameter determinations. Finally, model spectra are compared with observations of the bright supernovae SN 1979C and SN 1980 K, which seem to be more average examples of type II supernovae than SN 1987A, and possibilities for using these objects for extragalactic distance determinations are investigated.

Title: Non-LTE Modellatmosphären für Novae und Supernovae. Authors: Hauschildt, P. Bibcode: 1991nmfn.book.....H Altcode: Contents: 1. Einleitung. 2. Die Zustandsgleichung. 3. Die Absorptions- und Streukoeffizienten. 4. Der Strahlungstransport. 5. Die Modellberechnung. 6. Ergebnisse für Supernovae. 7. Ergebnisse für Novae. Title: Line Formatio in SN II Photospheres Authors: Best, M.; Hauschildt, P. H.; Wehrse, R. Bibcode: 1991ESOC...37..415B Altcode: 1991sos..conf..415B No abstract at ADS Title: Model atmospheres for the early stages of novae in outburst Authors: Wehrse, R.; Hauschildt, P. H.; Shaviv, G.; Starrfield, S. Bibcode: 1990ESASP.310..461W Altcode: 1990eaia.conf..461W No abstract at ADS Title: Model Atmospheres for Novae during the Early Stages Authors: Wehrse, R.; Hauschildt, P. H.; Shaviv, G.; Starrfield, S. Bibcode: 1990LNP...369..264W Altcode: 1990IAUCo.122..264W; 1990pcn..conf..264W Continuum and line blanketing models for the photospheres of novae in the early stages of their outbursts are presented. The expanding envelopes are characterized by a very slow increase of density with decreasing radius which leads to very large geometrical extensions and large temperature differences between the inner and outer parts. The spectra show a large IR excess and a small Balmer jump which may be either in absorption or in emission. For the parameters considered (T eff = 104,1.5 x 104, 2 x 104K, R = 1011 cm, solar composition), most lines are in absorption. The effects of both modifications in the temperature structure (e.g. by heating from shock fronts) and changes in the abundances of the heavy elements on the emergent spectra are briefly discussed. Title: Theoretical models for the continuum and colors of SN 1979C and SN 1980K. Authors: Hauschildt, P. H.; Shaviv, G.; Wehrse, R. Bibcode: 1989A&A...210..262H Altcode: Models for the continuum energy distribution from supernovae of type II are constructed and compared with the recently observed SN 1979 C and SN 1980 K for the coasting phase of their evolution. Fairly good agreement with the observed energy distributions from the UV range down to the IR as well as with colors is found. Using the colors we demonstrate how the distance to the SN can be found. The advantage of this method relative to the classical Baade-Wesselink method is that it needs data only for a single time. Title: An atlas of calculated continuum energy distributions for supernovae of type II Authors: Hauschildt, P. H.; Wehrse, R.; Shaviv, G. Bibcode: 1989A&AS...77..115H Altcode: An atlas of continuum energy distributions in the UV, visible, and near-IR regions has been compiled for type II supernovae. It is assumed that the cooling envelope can be approximated with a sequence of stationary atmospheres, that the level populations follow a Boltzmann distribution for the local temperature throughout the photosphere, and that the strongest source of continuum opacity is electron scattering. Results are presented for models with effective temperatures of between 7000 and 15,000 K. Title: Ultraviolet observations of LMC nova 1988. Authors: Starrfield, S.; Stryker, L. L.; Sonneborn, G.; Sparks, W. M.; Sion, E. M.; Wagner, R. M.; Ferland, G.; Gallagher, J. S.; Wade, R.; Williams, R. E.; Heathcote, S.; Gehrz, R.; Ney, E. P.; Kenyon, S.; Shav, G., IV; Wehrse, R.; Hauschildt, P.; Truran, J. W.; Wu, C. C. Bibcode: 1988ESASP.281a.175S Altcode: 1988uvai....1..175S; 1988IUE88...1..175S; 1988IUES....1..175S The IUE obtained ultraviolet spectra of a nova in an external galaxy. The spectral features do not seem unusual for a nova at maximum but it is hoped to be able to follow it for a long enough time to be able to study the high ionization lines that appear when the density drops to lower values (the nebular stage). A high dispersion spectrum was also obtained to assist in the line identification and to study the line of sight to the LMC 1 deg of arc away from SN 1987A. Title: The analysis of spectra of novae taken near maximum. Authors: Stryker, L. L.; Hestand, J.; Starrfield, S.; Wehrse, R.; Hauschildt, P.; Spies, W.; Baschek, B.; Shaviv, G. Bibcode: 1988ESASP.281a.149S Altcode: 1988IUES....1..149S; 1988IUE88...1..149S; 1988uvai....1..149S A project to analyze ultraviolet spectra of novae obtained at or near maximum optical light is presented. These spectra are characterized by a relatively cool continuum with superimposed permitted emission lines from ions such as Fe II, Mg II, and Si II. Spectra obtained late in the outburst show only emission lines from highly ionized species and in many cases these are forbidden lines. The ultraviolet data will be used with calculations of spherical, expanding, stellar atmospheres for novae to determine elemental abundances by spectral line synthesis. This method is extremely sensitive to the abundances and completely independent of the nebular analyses usually used to obtain novae abundances. Title: Zur Bestimmung von Elementhäufigkeiten aus Supernova II-Spektren. Authors: Hauschildt, P. H.; Wehrse, R. Bibcode: 1988AGAb....1...19H Altcode: No abstract at ADS Title: Calculated Energy Distributions for Type-Ii Supernovae Authors: Hauschildt, P. H.; Spies, W.; Wehrse, R.; Shaviv, G. Bibcode: 1988LNP...305..412H Altcode: 1988IAUCo.108..412H; 1988adse.conf..412H The authors have calculated a large grid of hydrogen-rich supernova photospheres, in which radii, effective temperatures, density profiles, and expansion velocities have been varied. In the quasi-exact radiative transfer, the dilution of the radiation field, and scattering as well as absorption are accurately considered. Good agreement can be obtained with the UV and IR spectra of supernovae 1979C, 1980K, and 1987A as observed during the coasting phase. Potential methods of parameter determinations for SN II are briefly discussed. Title: Model Photospheres and Synthetic Spectra for Supernova Type-Ii Authors: Hauschildt, P.; Spies, W.; Wehrse, R.; Shaviv, G. Bibcode: 1987ESOC...26..433H Altcode: 1987sn...work..433H The UV spectra of recent type II supernovae were calculated theoretically and compared with observation. Two phases in the evolution of SN type II envelopes are distinguished. The first phase is characterized by a high effective temperature and small effects of lines. The second phase is characterized by a low effective temperature and strong line blanketing. Continuum models were fitted to SN 1980K during its first phase of evolution, and good agreement was found. Blanketed models were fitted to SN 1987A. It is shown that blanketed models for the second phase provide good agreement with observations, and that the UV spectra of SN 1987A can be explained by metal abundances that are between those found in the LMC and the sun. The peculiar features in the spectra are due to the combined effect of a large number of Fe group lines in an expanding atmosphere. Title: Synthetic Spectra for Supernovae II Authors: Spies, W.; Hauschildt, P.; Wehrse, R.; Baschek, B.; Shaviv, G. Bibcode: 1987LNP...287..316S Altcode: 1987nuas.proc..316S The results of an attempt to study the spectra of supernova photospheres using detailed photospheric models are reported. The photosphere is calculated assuming a spherical configuration, a density following a power law with exponent 10, the existence of LTE and radiative equilibrium, and expansion velocity increasing proportionally to the radius. The calculated spectra and effective temperature agree well with the observed spectrum of SN 1980 K. Interesting correspondences are found between the UV fluxes of SN 1987 A and the energy distribution of a blanketed model with T(eff) = 8000 K and v(exp) = 15,000 km/s.