Author name code: schmutz ADS astronomy entries on 2022-09-14 author:"Schmutz, Werner" ------------------------------------------------------------------------ Title: Minima Epoches of BF Draconis Observed by the TESS Satellite Authors: Schmutz, Werner Bibcode: 2022RNAAS...6..173S Altcode: The epochs of 80 minima from 2019 to 2022 of the eclipsing binary BF Dra have been measured from photometric fluxes obtained by the TESS satellite with uncertainties of 3 s and 6 s for primary and secondary minima, respectively. There is a clear negative linear trend of the interval length between primary and secondary minima, which confirms previous analyses that the system's orbit has an apsidal motion. It is found that the periastron advances 1.43 ± 0.03 deg/century, i.e., the apsidal period is U = 25,200 ± 500 yr. These values agree with previous estimates within the combined uncertainties but the present uncertainties are lower by a factor of eight. It is also confirmed that the residuals of the TESS-minima have a significant trend relative to a mean long-term apsidal motion signature due to a systematic influence of unknown origin. Title: Data Fusion of Total Solar Irradiance Composite Time Series Using 41 Years of Satellite Measurements Authors: Montillet, Jean-Philippe; Finsterle, Wolfgang; Kermarrec, Gael; Sikonja, Rok; Haberreiter, Margit; Schmutz, Werner; Dudok de Wit, Thierry Bibcode: 2022arXiv220704926M Altcode: Since the late 1970s, successive satellite missions have been monitoring the sun's activity and recording the total solar irradiance (TSI). Some of these measurements have lasted for more than a decade. In order to obtain a seamless record whose duration exceeds that of the individual instruments, the time series have to be merged. Climate models can be better validated using such long TSI time series which can also help to provide stronger constraints on past climate reconstructions (e.g., back to the Maunder minimum). We propose a 3-step method based on data fusion, including a stochastic noise model to take into account short and long-term correlations. Compared with previous products scaled at the nominal TSI value of 1361 W/m2, the difference is below 0.2 W/m2 in terms of solar minima. Next, we model the frequency spectrum of this 41-year TSI composite time series with a Generalized Gauss-Markov model to help describe an observed flattening at high frequencies. It allows us to fit a linear trend into these TSI time series by joint inversion with the stochastic noise model via a maximum-likelihood estimator. Our results show that the amplitude of such trend is $\sim$ -0.004 +/- 0.004 W/(m2yr) for the period 1980 - 2021. These results are compared with the difference of irradiance values estimated from two consecutive solar minima. We conclude that the trend in these composite time series is mostly an artifact due to the colored noise. Title: Solar Noise in 40-year long Total Solar Irradiance Composite Time Series Authors: Montillet, Jean-Philippe; Finsterle, Wolfgang; Kermarrec, Gael; Sikonja, Rok; Haberreiter, Margit; Schmutz, Werner; Dudok de Wit, Thierry Bibcode: 2021AGUFMSH45B2373M Altcode: Since the late 70s, successive satellite missions have been monitoring the suns activity, recording total solar irradiance observations. These measurements provide estimates of the Earths energy imbalance, i.e. the difference of energy absorbed and emitted by our planet. With this amount of TSI data, solar irradiance reconstruction models can be better validated which can also improve studies looking at past climate reconstructions (e.g., Maunder minimum). Various algorithms have been proposed to merge the various TSI measurements recorded over the last 4 decades. We develop a 2-step algorithm based on data fusion, including a stochastic noise model to take into account the short and long-term correlations. We develop a wavelet filter in order to eliminate specific correlations introduced by the data fusion. Comparing with previous products,the mean value difference is below 0.1 W/m2and the discrepancy with the solar minima is mostly below 0.05 W/m2. Next, we model the frequency spectrum of this 40-year TSI composite time series with a Generalized Gauss-Markov model(with white noise) due to an observe flattening at high frequencies. It allows us to fit a linear trend in these TSI time series by joint inversion with the stochastic noise model via a maximum-likelihood estimator. Our results show that the amplitude of such trend is 0.004±0.005 W/(m2.yr). We conclude that the trend in these composite time series is mostly an artifact due to the solar noise. Title: First observations from the SPICE EUV spectrometer on Solar Orbiter Authors: Fludra, A.; Caldwell, M.; Giunta, A.; Grundy, T.; Guest, S.; Leeks, S.; Sidher, S.; Auchère, F.; Carlsson, M.; Hassler, D.; Peter, H.; Aznar Cuadrado, R.; Buchlin, É.; Caminade, S.; DeForest, C.; Fredvik, T.; Haberreiter, M.; Harra, L.; Janvier, M.; Kucera, T.; Müller, D.; Parenti, S.; Schmutz, W.; Schühle, U.; Solanki, S. K.; Teriaca, L.; Thompson, W. T.; Tustain, S.; Williams, D.; Young, P. R.; Chitta, L. P. Bibcode: 2021A&A...656A..38F Altcode: 2021arXiv211011252F
Aims: We present first science observations taken during the commissioning activities of the Spectral Imaging of the Coronal Environment (SPICE) instrument on the ESA/NASA Solar Orbiter mission. SPICE is a high-resolution imaging spectrometer operating at extreme ultraviolet (EUV) wavelengths. In this paper we illustrate the possible types of observations to give prospective users a better understanding of the science capabilities of SPICE.
Methods: We have reviewed the data obtained by SPICE between April and June 2020 and selected representative results obtained with different slits and a range of exposure times between 5 s and 180 s. Standard instrumental corrections have been applied to the raw data.
Results: The paper discusses the first observations of the Sun on different targets and presents an example of the full spectra from the quiet Sun, identifying over 40 spectral lines from neutral hydrogen and ions of carbon, oxygen, nitrogen, neon, sulphur, magnesium, and iron. These lines cover the temperature range between 20 000 K and 1 million K (10 MK in flares), providing slices of the Sun's atmosphere in narrow temperature intervals. We provide a list of count rates for the 23 brightest spectral lines. We show examples of raster images of the quiet Sun in several strong transition region lines, where we have found unusually bright, compact structures in the quiet Sun network, with extreme intensities up to 25 times greater than the average intensity across the image. The lifetimes of these structures can exceed 2.5 hours. We identify them as a transition region signature of coronal bright points and compare their areas and intensity enhancements. We also show the first above-limb measurements with SPICE above the polar limb in C III, O VI, and Ne VIII lines, and far off limb measurements in the equatorial plane in Mg IX, Ne VIII, and O VI lines. We discuss the potential to use abundance diagnostics methods to study the variability of the elemental composition that can be compared with in situ measurements to help confirm the magnetic connection between the spacecraft location and the Sun's surface, and locate the sources of the solar wind.
Conclusions: The SPICE instrument successfully performs measurements of EUV spectra and raster images that will make vital contributions to the scientific success of the Solar Orbiter mission. Title: A journey of exploration to the polar regions of a star: probing the solar poles and the heliosphere from high helio-latitude Authors: Harra, Louise; Andretta, Vincenzo; Appourchaux, Thierry; Baudin, Frédéric; Bellot-Rubio, Luis; Birch, Aaron C.; Boumier, Patrick; Cameron, Robert H.; Carlsson, Matts; Corbard, Thierry; Davies, Jackie; Fazakerley, Andrew; Fineschi, Silvano; Finsterle, Wolfgang; Gizon, Laurent; Harrison, Richard; Hassler, Donald M.; Leibacher, John; Liewer, Paulett; Macdonald, Malcolm; Maksimovic, Milan; Murphy, Neil; Naletto, Giampiero; Nigro, Giuseppina; Owen, Christopher; Martínez-Pillet, Valentín; Rochus, Pierre; Romoli, Marco; Sekii, Takashi; Spadaro, Daniele; Veronig, Astrid; Schmutz, W. Bibcode: 2021ExA...tmp...93H Altcode: 2021arXiv210410876H A mission to view the solar poles from high helio-latitudes (above 60°) will build on the experience of Solar Orbiter as well as a long heritage of successful solar missions and instrumentation (e.g. SOHO Domingo et al. (Solar Phys. 162(1-2), 1-37 1995), STEREO Howard et al. (Space Sci. Rev. 136(1-4), 67-115 2008), Hinode Kosugi et al. (Solar Phys. 243(1), 3-17 2007), Pesnell et al. Solar Phys. 275(1-2), 3-15 2012), but will focus for the first time on the solar poles, enabling scientific investigations that cannot be done by any other mission. One of the major mysteries of the Sun is the solar cycle. The activity cycle of the Sun drives the structure and behaviour of the heliosphere and of course, the driver of space weather. In addition, solar activity and variability provides fluctuating input into the Earth climate models, and these same physical processes are applicable to stellar systems hosting exoplanets. One of the main obstructions to understanding the solar cycle, and hence all solar activity, is our current lack of understanding of the polar regions. In this White Paper, submitted to the European Space Agency in response to the Voyage 2050 call, we describe a mission concept that aims to address this fundamental issue. In parallel, we recognise that viewing the Sun from above the polar regions enables further scientific advantages, beyond those related to the solar cycle, such as unique and powerful studies of coronal mass ejection processes, from a global perspective, and studies of coronal structure and activity in polar regions. Not only will these provide important scientific advances for fundamental stellar physics research, they will feed into our understanding of impacts on the Earth and other planets' space environment. Title: XMM-Newton X-Ray Observations of the Unusual Wolf-Rayet Star WR 66 Authors: Skinner, Stephen L.; Schmutz, Werner; Güdel, Manuel; Zhekov, Svetozar A. Bibcode: 2021RNAAS...5..125S Altcode: We summarize results of an XMM-Newton X-ray observation of the WN8h-type Wolf-Rayet star WR 66 which shows unusual 3.5-4.1 hr optical variations. One possible explanation is a compact companion (cc) which, if present, could give rise to luminous X-ray emission. WR 66 was marginally detected and its inferred X-ray luminosity (Lx) is orders of magnitude below that expected from wind accretion onto a neutron star, but is comparable to that of the WN8h stars WR 16 and WR 124. If luminous X-ray emission from an accreting WR+cc system is present then it is absorbed and escapes detection. Other explanations of the faintly detected X-ray emission of WN8h stars are not ruled out. Title: Data Fusion of Total Solar Irradiance Composite Time Series Using 40 years of Satellite Measurements: First Results Authors: Montillet, Jean-Philippe; Finsterle, Wolfgang; Schmutz, Werner; Haberreiter, Margit; Sikonja, Rok Bibcode: 2021EGUGA..23.4382M Altcode: Since the late 70"s, successive satellite missions have been monitoring the sun"s activity, recording total solar irradiance observations. These measurements are important to estimate the Earth"s energy imbalance, i.e. the difference of energy absorbed and emitted by our planet. Climate modelers need the solar forcing time series in their models in order to study the influence of the Sun on the Earth"s climate. With this amount of TSI data, solar irradiance reconstruction models can be better validated which can also improve studies looking at past climate reconstructions (e.g., Maunder minimum). Various algorithms have been proposed in the last decade to merge the various TSI measurements over the 40 years of recording period. We have developed a new statistical algorithm based on data fusion. The stochastic noise processes of the measurements are modeled via a dual kernel including white and coloured noise. We show our first results and compare it with previous releases (PMOD,ACRIM, ... ). Title: Changes in the Total Solar Irradiance and climatic effects Authors: Schmutz, Werner K. Bibcode: 2021JSWSC..11...40S Altcode: The correlation between the averaged reconstructed March temperature record for Kyoto, Japan, and the reconstructed Total Solar Irradiance (TSI) over 660 years from 1230 to 1890 gives evidence with 98% probability that the Little Ice Age with four cold periods is forced by variations of TSI. If the correlation is restricted to the period 1650-1890, with two cold periods in the 17th and 19th century and for which two independent reconstructed March temperature records are available, the probability of solar forcing increases to 99.99%. As solar irradiance variations have a global effect there has to be a global climatic solar forcing impact. However, by how much global temperature were lower during these minima and with what amplitude TSI was varying is not accurately known. The two quantities, global temperature and TSI, are linked by the energy equilibrium equation for the Earth system. The derivation of this equation with respect to a variation of the solar irradiance has two terms: A direct forcing term, which can be derived analytically and quantified accurately from the Stefan-Boltzmann law, and a second term, describing indirect influences on the surface temperature. If a small TSI variation should force a large temperature variation, then it has to be the second indirect term that strongly amplifies the effect of the direct forcing. The current knowledge is summarized by three statements:<list list-type="dash"><list-item>During the minima periods in the 13th, 15/16th, 17th, and 19th centuries the terrestrial climate was colder by 0.5-1.5 °C; </list-item><list-item>Indirect Top-down and Bottom-up mechanisms do not amplify direct forcing by a large amount, i.e. indirect solar forcing is of the same magnitude (or smaller) as direct solar forcing; </list-item><list-item>The radiative output of the Sun cannot be lower by more than 2 Wm−2 below the measured present-day TSI value during solar cycle minimum. </list-item></list>These three statements contradict each other and it is concluded that at least one is not correct. Which one is a wrong statement is presently not known conclusively. It is argued that it is the third statement and it is speculated that over centennial time scales the Sun might vary its radiance significantly more than observed so far during the last 40 years of space TSI measurements. To produce Maunder minimum type cold climate excursions, a TSI decrease of the order of 10 Wm−2 is advocated. Title: Relative coronal abundance diagnostics with Solar Orbiter/SPICE Authors: Zambrana Prado, N.; Buchlin, E.; Peter, H.; Young, P. R.; Auchere, F.; Carlsson, M.; Fludra, A.; Hassler, D.; Aznar Cuadrado, R.; Caminade, S.; Caldwell, M.; DeForest, C.; Fredvik, T.; Harra, L.; Janvier, M.; Kucera, T. A.; Giunta, A. S.; Grundy, T.; Müller, D.; Parenti, S.; Schmutz, W. K.; Schühle, U.; Sidher, S.; Teriaca, L.; Thompson, W. T.; Williams, D. Bibcode: 2020AGUFMSH038..09Z Altcode: Linking solar activity on the surface and in the corona to the inner heliosphere is one of Solar Orbiter's main goals. Its UV spectrometer SPICE (SPectral Imaging of the Coronal Environment) will provide relative abundance measurements which will be key in this quest as different structures on the Sun have different abundances as a consequence of the FIP (First Ionization Potential) effect. Solar Orbiter's unique combination of remote sensing and in-situ instruments coupled with observation from other missions such as Parker Solar Probe will allow us to compare in-situ and remote sensing composition data. With the addition of modeling, these new results will allow us to trace back the source of heliospheric plasma. As high telemetry will not always be available with SPICE, we have developed a method for measuring relative abundances that is both telemetry efficient and reliable. Unlike methods based on Differential Emission Measure (DEM) inversion, the Linear Combination Ratio (LCR) method does not require a large number of spectral lines. This new method is based on linear combinations of UV spectral lines. The coefficients of the combinations are optimized such that the ratio of two linear combinations of radiances would yield the relative abundance of two elements. We present some abundance diagnostics tested on different combinations of spectral lines observable by SPICE. Title: Dynamics and thermal structure in the quiet Sun seen by SPICE Authors: Peter, H.; Aznar Cuadrado, R.; Schühle, U.; Teriaca, L.; Auchere, F.; Carlsson, M.; Fludra, A.; Hassler, D.; Buchlin, E.; Caminade, S.; Caldwell, M.; DeForest, C.; Fredvik, T.; Harra, L. K.; Janvier, M.; Kucera, T. A.; Giunta, A. S.; Grundy, T.; Müller, D.; Parenti, S.; Schmutz, W. K.; Sidher, S.; Thompson, W. T.; Williams, D.; Young, P. R. Bibcode: 2020AGUFMSH038..03P Altcode: We will present some of the early data of the Spectral Imaging of the Coronal Environment (SPICE) instrument on Solar Orbiter. One of the unique features of SPICE is its capability to record a wide range of wavelengths in the extreme UV with the possibility to record spectral lines giving access to a continuous plasma temperature range from 10.000 K to well above 1 MK. The data taken so far were for commissioning purposes and they can be used for a preliminary evaluation of the science performance of the instrument. Here we will concentrate on sample spectra covering the whole wavelength region and on the early raster maps acquired in bright lines in the quiet Sun close to disk center. Looking at different quiet Sun features we investigate the thermal structure of the atmosphere and flow structures. For this we apply fits to the spectral profiles and check the performance in terms of Doppler shifts and line widths to retrieve the structure of the network in terms of dynamics. While the amount of data available so far is limited, we will have a first look on how quiet Sun plasma responds to heating events. For this, we will compare spectral lines forming at different temperatures recorded at strictly the same time. Title: First Results From SPICE EUV Spectrometer on Solar Orbiter Authors: Fludra, A.; Caldwell, M.; Giunta, A. S.; Grundy, T.; Guest, S.; Sidher, S.; Auchere, F.; Carlsson, M.; Hassler, D.; Peter, H.; Aznar Cuadrado, R.; Buchlin, E.; Caminade, S.; DeForest, C.; Fredvik, T.; Harra, L. K.; Janvier, M.; Kucera, T. A.; Leeks, S.; Mueller, D.; Parenti, S.; Schmutz, W. K.; Schühle, U.; Teriaca, L.; Thompson, W. T.; Tustain, S.; Williams, D.; Young, P. R. Bibcode: 2020AGUFMSH038..02F Altcode: SPICE (Spectral Imaging of Coronal Environment) is one of the remote sensing instruments onboard Solar Orbiter. It is an EUV imaging spectrometer observing the Sun in two wavelength bands: 69.6-79.4 nm and 96.6-105.1 nm. SPICE is capable of recording full spectra in these bands with exposures as short as 1s. SPICE is the only Solar Orbiter instrument that can measure EUV spectra from the disk and low corona of the Sun and record all spectral lines simultaneously. SPICE uses one of three narrow slits, 2"x11', 4''x11', 6''x11', or a wide slit 30''x14'. The primary mirror can be scanned in a direction perpendicular to the slit, allowing raster images of up to 16' in size.

We present an overview of the first SPICE data taken on several days during the instrument commissioning carried out by the RAL Space team between 2020 April 21 and 2020 June 14. We also include results from SPICE observations at the first Solar Orbiter perihelion at 0.52AU, taken between June 16-21st. We give examples of full spectra from the quiet Sun near disk centre and provide a list of key spectral lines emitted in a range of temperatures between 10,000 K and over 1 million K, from neutral hydrogen and ions of carbon, oxygen, nitrogen, neon, sulphur and magnesium. We show examples of first raster images in several strong lines, obtained with different slits and a range of exposure times between 5s and 180s. We describe the temperature coverage and density diagnostics, determination of plasma flows, and discuss possible applications to studies of the elemental abundances in the corona. We also show the first off-limb measurements with SPICE, as obtained when the spacecraft pointed at the limb. Title: A New Methodology to Process the Total Solar Irradiance observations Using Machine Learning and Data Fusion Authors: Montillet, J. P.; Finsterle, W.; Schmutz, W. K. Bibcode: 2020AGUFMA237...06M Altcode: Across the last decades, various space missions have measured the total solar irradiance (TSI) such as the Variability of Irradiance and Gravity Oscillations (VIRGO) experiment on the Solar and Heliospheric Observatory (SOHO) starting in 1996. Since the beginning of its recording time, one challenge is to correct the measurements from the degradation of the TSI sensors in space. Various groups have proposed different methodologies to produce a continuous TSI time series (TSI composite) which is essential to monitor the sun activity and its influence on the Earth's climate.

However, the benchmark to test all those solutions is source of a debate in the community. Moreover, the input data for the TSI composite are the degradation-corrected measurements provided by each individual instrument team. Here, we propose a different approach using a machine learning and data fusion algorithm to produce automatically the degradation-corrected TSI time series based on a small number of generic assumptions. The algorithm is applied to the VIRGO/PMO6, VIRGO/DIARAD and PREMOS/PMO6 data. The time series agree between each other in terms of mean value with a difference of ~ 0.14 W/m2 (PREMOS), ~ 0.23 W/m2 (VIRGO) and ~ -0.18 W/m2 (DIARAD). Finally, taking a conservative value of 0.3 W/m2 between our different TSI products, induces a variation of the global mean surface temperature of ~ 0.02 K based on global climate simulations, which is within the uncertainties of simulated global mean surface temperatures, hence not impacting significantly any climate forcing scenarios. Title: Calibrating optical distortions in the Solar Orbiter SPICE spectrograph Authors: Thompson, W. T.; Schühle, U.; Young, P. R.; Auchere, F.; Carlsson, M.; Fludra, A.; Hassler, D.; Peter, H.; Aznar Cuadrado, R.; Buchlin, E.; Caldwell, M.; DeForest, C.; Fredvik, T.; Harra, L. K.; Janvier, M.; Kucera, T. A.; Giunta, A. S.; Grundy, T.; Müller, D.; Parenti, S.; Caminade, S.; Schmutz, W. K.; Teriaca, L.; Williams, D.; Sidher, S. Bibcode: 2020AGUFMSH0360029T Altcode: The Spectral Imaging of the Coronal Environment (SPICE) instrument on Solar Orbiter is a high-resolution imaging spectrometer operating at extreme ultraviolet (EUV) wavelengths from 70.4-79.0 nm and 97.3-104.9 nm. A single-mirror off-axis paraboloid focuses the solar image onto the entrance slit of the spectrometer section. A Toroidal Variable Line Space (TVLS) grating images the entrance slit onto a pair of MCP-intensified APS detectors. Ray-tracing analysis prior to launch showed that the instrument was subject to a number of small image distortions which need to be corrected in the final data product. We compare the ray tracing results with measurements made in flight. Co-alignment with other telescopes on Solar Orbiter will also be examined. Title: First results from the EUI and SPICE observations of Alpha Leo near Solar Orbiter first perihelion Authors: Buchlin, E.; Teriaca, L.; Giunta, A. S.; Grundy, T.; Andretta, V.; Auchere, F.; Peter, H.; Berghmans, D.; Carlsson, M.; Fludra, A.; Harra, L.; Hassler, D.; Long, D.; Rochus, P. L.; Schühle, U.; Aznar Cuadrado, R.; Caldwell, M.; Caminade, S.; DeForest, C.; Fredvik, T.; Gissot, S.; Heerlein, K.; Janvier, M.; Kraaikamp, E.; Kucera, T. A.; Müller, D.; Parenti, S.; Schmutz, W. K.; Sidher, S.; Smith, P.; Stegen, K.; Thompson, W. T.; Verbeeck, C.; Williams, D.; Young, P. R. Bibcode: 2020AGUFMSH0360024B Altcode: On June 16th 2020 Solar Orbiter made a dedicated observing campaign where the spacecraft pointed to the solar limb to allow some of the high resolution instruments to observe the ingress (at the east limb) and later the egress (west limb) of the occultation of the star Alpha Leonis by the solar disk. The star was chosen because its luminosity and early spectral type ensure high and stable flux at wavelengths between 100 and 122 nanometers, a range observed by the High Resolution EUI Lyman alpha telescope (HRI-LYA) and by the long wavelength channel of the SPICE spectrograph. Star observations, when feasible, allow to gather a great deal of information on the instrument performances, such as the radiometric performance and the instrument optical point spread function (PSF).

We report here the first results from the above campaign for the two instruments. Title: First results from combined EUI and SPICE observations of Lyman lines of Hydrogen and He II Authors: Teriaca, L.; Aznar Cuadrado, R.; Giunta, A. S.; Grundy, T.; Parenti, S.; Auchere, F.; Vial, J. C.; Fludra, A.; Berghmans, D.; Carlsson, M.; Harra, L.; Hassler, D.; Long, D.; Peter, H.; Rochus, P. L.; Schühle, U.; Buchlin, E.; Caldwell, M.; Caminade, S.; DeForest, C.; Fredvik, T.; Gissot, S.; Heerlein, K.; Janvier, M.; Kraaikamp, E.; Kucera, T. A.; Mueller, D.; Schmutz, W. K.; Sidher, S.; Smith, P.; Stegen, K.; Thompson, W. T.; Verbeeck, C.; Williams, D.; Young, P. R. Bibcode: 2020AGUFMSH0360003T Altcode: The Solar Orbiter spacecraft carries a powerful set of remote sensing instruments that allow studying the solar atmosphere with unprecedented diagnostic capabilities. Many such diagnostics require the simultaneous usage of more than one instrument. One example of that is the capability, for the first time, to obtain (near) simultaneous spatially resolved observations of the emission from the first three lines of the Lyman series of hydrogen and of He II Lyman alpha. In fact, the SPectral Imaging of the Coronal Environment (SPICE) spectrometer can observe the Lyman beta and gamma lines in its long wavelength (SPICE-LW) channel, the High Resolution Lyman Alpha (HRI-LYA) telescope of the Extreme Ultraviolet Imager (EUI) acquires narrow band images in the Lyman alpha line while the Full Disk Imager (FSI) of EUI can take images dominated by the Lyman alpha line of ionized Helium at 30.4 nm (FSI-304). Being hydrogen and helium the main components of our star, these very bright transitions play an important role in the energy budget of the outer atmosphere via radiative losses and the measurement of their profiles and radiance ratios is a fundamental constraint to any comprehensive modelization effort of the upper solar chromosphere and transition region. Additionally, monitoring their average ratios can serve as a check out for the relative radiometric performance of the two instruments throughout the mission. Although the engineering data acquired so far are far from ideal in terms of time simultaneity (often only within about 1 h) and line coverage (often only Lyman beta was acquired by SPICE and not always near simultaneous images from all three telescopes are available) the analysis we present here still offers a great opportunity to have a first look at the potential of this diagnostic from the two instruments. In fact, we have identified a series of datasets obtained at disk center and at various positions at the solar limb that allow studying the Lyman alpha to beta radiance ratio and their relation to He II 30.4 as a function of the position on the Sun (disk center versus limb and quiet Sun versus coronal holes). Title: The Solar Orbiter SPICE instrument. An extreme UV imaging spectrometer Authors: SPICE Consortium; Anderson, M.; Appourchaux, T.; Auchère, F.; Aznar Cuadrado, R.; Barbay, J.; Baudin, F.; Beardsley, S.; Bocchialini, K.; Borgo, B.; Bruzzi, D.; Buchlin, E.; Burton, G.; Büchel, V.; Caldwell, M.; Caminade, S.; Carlsson, M.; Curdt, W.; Davenne, J.; Davila, J.; Deforest, C. E.; Del Zanna, G.; Drummond, D.; Dubau, J.; Dumesnil, C.; Dunn, G.; Eccleston, P.; Fludra, A.; Fredvik, T.; Gabriel, A.; Giunta, A.; Gottwald, A.; Griffin, D.; Grundy, T.; Guest, S.; Gyo, M.; Haberreiter, M.; Hansteen, V.; Harrison, R.; Hassler, D. M.; Haugan, S. V. H.; Howe, C.; Janvier, M.; Klein, R.; Koller, S.; Kucera, T. A.; Kouliche, D.; Marsch, E.; Marshall, A.; Marshall, G.; Matthews, S. A.; McQuirk, C.; Meining, S.; Mercier, C.; Morris, N.; Morse, T.; Munro, G.; Parenti, S.; Pastor-Santos, C.; Peter, H.; Pfiffner, D.; Phelan, P.; Philippon, A.; Richards, A.; Rogers, K.; Sawyer, C.; Schlatter, P.; Schmutz, W.; Schühle, U.; Shaughnessy, B.; Sidher, S.; Solanki, S. K.; Speight, R.; Spescha, M.; Szwec, N.; Tamiatto, C.; Teriaca, L.; Thompson, W.; Tosh, I.; Tustain, S.; Vial, J. -C.; Walls, B.; Waltham, N.; Wimmer-Schweingruber, R.; Woodward, S.; Young, P.; de Groof, A.; Pacros, A.; Williams, D.; Müller, D. Bibcode: 2020A&A...642A..14S Altcode: 2019arXiv190901183A; 2019arXiv190901183S
Aims: The Spectral Imaging of the Coronal Environment (SPICE) instrument is a high-resolution imaging spectrometer operating at extreme ultraviolet wavelengths. In this paper, we present the concept, design, and pre-launch performance of this facility instrument on the ESA/NASA Solar Orbiter mission.
Methods: The goal of this paper is to give prospective users a better understanding of the possible types of observations, the data acquisition, and the sources that contribute to the instrument's signal.
Results: The paper discusses the science objectives, with a focus on the SPICE-specific aspects, before presenting the instrument's design, including optical, mechanical, thermal, and electronics aspects. This is followed by a characterisation and calibration of the instrument's performance. The paper concludes with descriptions of the operations concept and data processing.
Conclusions: The performance measurements of the various instrument parameters meet the requirements derived from the mission's science objectives. The SPICE instrument is ready to perform measurements that will provide vital contributions to the scientific success of the Solar Orbiter mission. Title: The Solar Orbiter EUI instrument: The Extreme Ultraviolet Imager Authors: Rochus, P.; Auchère, F.; Berghmans, D.; Harra, L.; Schmutz, W.; Schühle, U.; Addison, P.; Appourchaux, T.; Aznar Cuadrado, R.; Baker, D.; Barbay, J.; Bates, D.; BenMoussa, A.; Bergmann, M.; Beurthe, C.; Borgo, B.; Bonte, K.; Bouzit, M.; Bradley, L.; Büchel, V.; Buchlin, E.; Büchner, J.; Cabé, F.; Cadiergues, L.; Chaigneau, M.; Chares, B.; Choque Cortez, C.; Coker, P.; Condamin, M.; Coumar, S.; Curdt, W.; Cutler, J.; Davies, D.; Davison, G.; Defise, J. -M.; Del Zanna, G.; Delmotte, F.; Delouille, V.; Dolla, L.; Dumesnil, C.; Dürig, F.; Enge, R.; François, S.; Fourmond, J. -J.; Gillis, J. -M.; Giordanengo, B.; Gissot, S.; Green, L. M.; Guerreiro, N.; Guilbaud, A.; Gyo, M.; Haberreiter, M.; Hafiz, A.; Hailey, M.; Halain, J. -P.; Hansotte, J.; Hecquet, C.; Heerlein, K.; Hellin, M. -L.; Hemsley, S.; Hermans, A.; Hervier, V.; Hochedez, J. -F.; Houbrechts, Y.; Ihsan, K.; Jacques, L.; Jérôme, A.; Jones, J.; Kahle, M.; Kennedy, T.; Klaproth, M.; Kolleck, M.; Koller, S.; Kotsialos, E.; Kraaikamp, E.; Langer, P.; Lawrenson, A.; Le Clech', J. -C.; Lenaerts, C.; Liebecq, S.; Linder, D.; Long, D. M.; Mampaey, B.; Markiewicz-Innes, D.; Marquet, B.; Marsch, E.; Matthews, S.; Mazy, E.; Mazzoli, A.; Meining, S.; Meltchakov, E.; Mercier, R.; Meyer, S.; Monecke, M.; Monfort, F.; Morinaud, G.; Moron, F.; Mountney, L.; Müller, R.; Nicula, B.; Parenti, S.; Peter, H.; Pfiffner, D.; Philippon, A.; Phillips, I.; Plesseria, J. -Y.; Pylyser, E.; Rabecki, F.; Ravet-Krill, M. -F.; Rebellato, J.; Renotte, E.; Rodriguez, L.; Roose, S.; Rosin, J.; Rossi, L.; Roth, P.; Rouesnel, F.; Roulliay, M.; Rousseau, A.; Ruane, K.; Scanlan, J.; Schlatter, P.; Seaton, D. B.; Silliman, K.; Smit, S.; Smith, P. J.; Solanki, S. K.; Spescha, M.; Spencer, A.; Stegen, K.; Stockman, Y.; Szwec, N.; Tamiatto, C.; Tandy, J.; Teriaca, L.; Theobald, C.; Tychon, I.; van Driel-Gesztelyi, L.; Verbeeck, C.; Vial, J. -C.; Werner, S.; West, M. J.; Westwood, D.; Wiegelmann, T.; Willis, G.; Winter, B.; Zerr, A.; Zhang, X.; Zhukov, A. N. Bibcode: 2020A&A...642A...8R Altcode: Context. The Extreme Ultraviolet Imager (EUI) is part of the remote sensing instrument package of the ESA/NASA Solar Orbiter mission that will explore the inner heliosphere and observe the Sun from vantage points close to the Sun and out of the ecliptic. Solar Orbiter will advance the "connection science" between solar activity and the heliosphere.
Aims: With EUI we aim to improve our understanding of the structure and dynamics of the solar atmosphere, globally as well as at high resolution, and from high solar latitude perspectives.
Methods: The EUI consists of three telescopes, the Full Sun Imager and two High Resolution Imagers, which are optimised to image in Lyman-α and EUV (17.4 nm, 30.4 nm) to provide a coverage from chromosphere up to corona. The EUI is designed to cope with the strong constraints imposed by the Solar Orbiter mission characteristics. Limited telemetry availability is compensated by state-of-the-art image compression, onboard image processing, and event selection. The imposed power limitations and potentially harsh radiation environment necessitate the use of novel CMOS sensors. As the unobstructed field of view of the telescopes needs to protrude through the spacecraft's heat shield, the apertures have been kept as small as possible, without compromising optical performance. This led to a systematic effort to optimise the throughput of every optical element and the reduction of noise levels in the sensor.
Results: In this paper we review the design of the two elements of the EUI instrument: the Optical Bench System and the Common Electronic Box. Particular attention is also given to the onboard software, the intended operations, the ground software, and the foreseen data products.
Conclusions: The EUI will bring unique science opportunities thanks to its specific design, its viewpoint, and to the planned synergies with the other Solar Orbiter instruments. In particular, we highlight science opportunities brought by the out-of-ecliptic vantage point of the solar poles, the high-resolution imaging of the high chromosphere and corona, and the connection to the outer corona as observed by coronagraphs. Title: The nature of the companion in the Wolf-Rayet system EZ Canis Majoris Authors: Koenigsberger, G.; Schmutz, W. Bibcode: 2020A&A...639A..18K Altcode: 2020arXiv200506028K Context. EZ Canis Majoris is a classical Wolf-Rayet star whose binary nature has been debated for decades. It was recently modeled as an eccentric binary with a periodic brightening at periastron of the emission originating in a shock heated zone near the companion.
Aims: The focus of this paper is to further test the binary model and to constrain the nature of the unseen close companion by searching for emission arising in the shock-heated region.
Methods: We analyze over 400 high resolution International Ultraviolet Explorer spectra obtained between 1983 and 1995 and XMM-Newton observations obtained in 2010. The light curve and radial velocity (RV) variations were fit with the eccentric binary model and the orbital elements were constrained.
Results: We find RV variations in the primary emission lines with a semi-amplitude K1 ∼ 30 km s-1 in 1992 and 1995, and a second set of emissions with an anti-phase RV curve with K2 ∼ 150 km s-1. The simultaneous model fit to the RVs and the light curve yields the orbital elements for each epoch. Adopting a Wolf-Rayet mass M1 ∼ 20 M⊙ leads to M2 ∼ 3-5 M⊙, which implies that the companion could be a late B-type star. The eccentric (e = 0.1) binary model also explains the hard X-ray light curve obtained by XMM-Newton and the fit to these data indicates that the duration of maximum is shorter than the typical exposure times. Conclusions: The anti-phase RV variations of two emission components and the simultaneous fit to the RVs and the light curve are concrete evidence in favor of the binary nature of EZ Canis Majoris. The assumption that the emission from the shock-heated region closely traces the orbit of the companion is less certain, although it is feasible because the companion is significantly heated by the WR radiation field and impacted by the WR wind. Title: First TSI results and status report of the CLARA/NorSat-1 solar absolute radiometer Authors: Walter, Benjamin; Andersen, Bo; Beattie, Alexander; Finsterle, Wolfgang; Kopp, Greg; Pfiffner, Daniel; Schmutz, Werner Bibcode: 2020IAUGA..30..358W Altcode: The Compact Lightweight Absolute Radiometer (CLARA) is orbiting Earth on-board the Norwegian NorSat-1 micro-satellite since 14th of July 2017. The first light total solar irradiance (TSI) measurement result of CLARA is 1360.18 W m-2 for the so far single reliable Channel B. Channel A and C measured significantly lower (higher) TSI values and were found being sensitive to satellite pointing instabilities. These channels most likely suffer from electrical interference between satellite components and CLARA, an effect that is currently under investigation. Problems with the satellite attitude control currently inhibit stable pointing of CLARA to the Sun. Title: Solar disk radius measured by Solar occultation by the Moon using bolometric and photometric instruments on board the PICARD satellite Authors: Thuillier, G.; Zhu, P.; Shapiro, A. I.; Sofia, S.; Tagirov, R.; van Ruymbeke, M.; Perrin, J. -M.; Sukhodolov, T.; Schmutz, W. Bibcode: 2020IAUGA..30..361T Altcode: No abstract at ADS Title: The Solar Orbiter EUI instrument: The Extreme Ultraviolet Imager Authors: Rochus, P. L.; Auchere, F.; Berghmans, D.; Harra, L.; Schmutz, W. K.; Schühle, U. Bibcode: 2019AGUFMSH21D3291R Altcode: The Extreme Ultraviolet Imager (EUI) is part of the remote sensing instrument package of the ESA/NASA Solar Orbiter mission that will explore the inner heliosphere and observe the Sun from vantage points close to the Sun and out-of-the-ecliptic.

EUI aims at improving our understanding of the structure and dynamics of the solar atmosphere. EUI will take images of the solar atmosphere, globally as well as at high resolution, and from high solar latitude perspectives.

EUI consists of 3 telescopes that are optimized to image in Lyman-a and EUV 17.4nm and 30.4 nm to provide a coverage from chromosphere up to corona. EUI is designed to cope with the strong constraints that Solar Orbiter has as a deep space mission. Limited telemetry availability is compensated by state-of-the-art image compression, on board image processing and event selection. The imposed power limitations and potentially harsh radiation environment lead to the usage of novel CMOS sensors. As the unobstructed field of view of the telescopes needs to protrude through the spacecraft heat shield, the apertures were kept as small as possible. This lead to a systematic effort to optimize the throughput of every optical element and the reduction of noise levels in the sensor.

In this paper we review the design of the two elements of the EUI instrument: the Optical Bench System and the Common Electronic Box. Particular attention is also given to the on board software, the intended operations, the ground software and the foreseen data products.

EUI will bring unique science opportunities thanks to its specific design, its viewpoint and thanks to the planned synergies with the other Solar Orbiter instruments. We highlight in particular science opportunities brought by the out-of-ecliptic vantage point of the solar poles, the high resolution imaging of the high chromosphere and corona, and the connection to the outer corona as observed by coronagraphs. Title: Long uninterrupted photometric observations of the Wolf-Rayet star EZ CMa by the Toronto BRITE satellite reveal a very fast apsidal motion Authors: Schmutz, W.; Koenigsberger, G. Bibcode: 2019A&A...624L...3S Altcode: 2019arXiv190309501S Context. The variability of the Wolf-Rayet star EZ CMa has been documented for close to half a century, and a clear periodicity of ∼3.7 days is established. However, all attempts to prove that it is a binary have failed because the photometric, spectroscopic, and polarimetric variations are not coherent over more than a few orbital cycles.
Aims: In this Letter we show that the lack of coherence in the variability can be explained with a very rapid apsidal motion in a binary orbit.
Methods: We measured the times of minima in a recently published exceptionally long photometric light curve obtained by the Toronto BRITE satellite. The apsidal motion and the system eccentricity are determined from the length of the time intervals between these minima, which alternate in their duration, following a pattern that is clearly associated with apsidal motion. These minima are superposed on brightness enhancements of the emission from a shock zone, which occur at about the times of periastron phases.
Results: We determine the orbital periodicity, Pa = 3.63 d, and the period of the apsidal motion, U ≃ 100 d, which together yield an average sidereal period of Ps = 3.77 d. The eccentricity is found to be close to 0.1. The rate of periapsis retreat changes significantly over the period of observation and is determined to be -16° P-1a at the beginning of the observing period and -10° P-1a at the end.
Conclusions: We demonstrate that by introducing a fast apsidal motion, the basic photometric variability is very well explained. The binary nature of EZ CMa is now established. This might imply that other apparently single Wolf-Rayet stars that emit hard X-rays, similar to EZ CMa, are also binaries. Title: High energy processes in Wolf-Rayet stars Authors: Skinner, S. L.; Schmutz, W.; Güdel, M.; Zhekov, S. Bibcode: 2019AN....340...50S Altcode: 2018arXiv181203954S Wolf-Rayet (WR) stars are massive (≥10 M⊙) evolved stars undergoing advanced nuclear burning in their cores, rapidly approaching the end of their lives as supernovae. Their powerful winds enrich the interstellar medium with heavy elements, providing raw material for future generations of stars. We briefly summarize high-energy processes in WR stars, focusing mainly on their X-ray emission. We present new results from Chandra observations of the eclipsing WR + O binary CQ Cep covering a full orbit which stringently test X-ray emission models. Title: The EUI instrument onboard Solar Orbiter: the EUV corona imaged differently Authors: Berghmans, David; Rochus, Pierre; Auchère, Frédéric; Harra, Louise; Schmutz, Werner; Schühle, Udo Bibcode: 2018csc..confE..73B Altcode: The ESA Solar Orbiter mission is designed to determine how the Sun creates and controls the heliosphere. The spacecraft will bring a combination of in situ and remote sensing instruments out of the ecliptic (>30°) and close to the sun (0.3 solar-radii). The launch of Solar Orbiter is expected (not earlier than) Feb 2019. The Extreme Ultraviolet Imager is part of the remote-sensing package of Solar Orbiter, to be operating during 3 ten-day periods of each orbit around the Sun, which last roughly half a year. These 3 periods will correspond to perihelion and maximal solar latitude north and south. The Extreme Ultraviolet Imager is itself a suite of three UV and EUV telescopes that observe the solar atmosphere both globally as well as at very high resolution. The two high-resolution imagers (HRIs) will image the solar atmosphere in the chromospheric Lyman alpha line and the coronal 17nm pass band with a resolution of 0.5 arcsec. From perihelion, this will correspond to a pixel footprint on the solar disc of (110km)^2 . The Full Sun Imager (FSI), working at the 17.4 nm and 30.4 nm EUV passbands, will provide a global view of the solar atmosphere and is therefore an essential building block for the "connection science" of the Solar Orbiter mission. The FSI field of view is large enough (228arcmin) that, even at perihelion and at maximal off-points by Solar Orbiter, the full solar disk remains in the field of view. This large FOV and the FSI's high sensitivity will allow to image the "transition corona" where the topology of streamers and pseudo-streamers fades in the solar wind. Furthermore, FSI will be the first to image all this from out of the ecliptic. In this talk we will give an overview of the EUI instrument. We will focus on the novel aspects of EUI that will allow it to image beyond what previous EUV imagers could show us: EUV imaging from the highest solar latitude, with the widest field-of-view and at highest spatial resolution. Title: From solar to stellar brightness variations. The effect of metallicity Authors: Witzke, V.; Shapiro, A. I.; Solanki, S. K.; Krivova, N. A.; Schmutz, W. Bibcode: 2018A&A...619A.146W Altcode: 2018arXiv180904360W Context. Comparison studies of Sun-like stars with the Sun suggest an anomalously low photometric variability of the Sun compared to Sun-like stars with similar magnetic activity. Comprehensive understanding of stellar variability is needed to find a physical reason for this observation.
Aims: We investigate the effect of metallicity and effective temperature on the photometric brightness change of Sun-like stars seen at different inclinations. The considered range of fundamental stellar parameters is sufficiently small so the stars investigated here still count as Sun-like or even as solar twins.
Methods: To model the brightness change of stars with solar magnetic activity, we extended a well-established model of solar brightness variations based on solar spectra, Spectral And Total Irradiance REconstruction (SATIRE), to stars with different fundamental parameters. For this we calculated stellar spectra for different metallicities and effective temperature using the radiative transfer code ATLAS9.
Results: We show that even a small change (e.g. within the observational error range) of metallicity or effective temperature significantly affects the photometric brightness change compared to the Sun. We find that for Sun-like stars, the amplitude of the brightness variations obtained for Strömgren (b + y)/2 reaches a local minimum for fundamental stellar parameters close to the solar metallicity and effective temperature. Moreover, our results show that the effect of inclination decreases for metallicity values greater than the solar metallicity. Overall, we find that an exact determination of fundamental stellar parameters is crucially important for understanding stellar brightness changes. Title: First Detection of Solar Flare Emission in Mid-ultraviolet Balmer Continuum Authors: Dominique, Marie; Zhukov, Andrei N.; Heinzel, Petr; Dammasch, Ingolf E.; Wauters, Laurence; Dolla, Laurent; Shestov, Sergei; Kretzschmar, Matthieu; Machol, Janet; Lapenta, Giovanni; Schmutz, Werner Bibcode: 2018ApJ...867L..24D Altcode: 2018arXiv181009835D We present the first detection of solar flare emission at mid-ultraviolet wavelengths around 2000 Å by the channel 2 of the Large-Yield RAdiometer (LYRA) on board the PRoject for OnBoard Autonomy 2 mission. The flare (SOL20170906) was also observed in the channel 1 of LYRA centered at the H I Lyα line at 1216 Å, showing a clear non-thermal profile in both channels. The flare radiation in channel 2 is consistent with the hydrogen Balmer continuum emission produced by an optically thin chromospheric slab heated up to 10,000 K. Simultaneous observations in channels 1 and 2 allow the separation of the line emission (primarily from the Lyα line) from the Balmer continuum emission. Together with the recent detection of the Balmer continuum emission in the near-ultraviolet by the Interface Region Imaging Spectrometer, the LYRA observations strengthen the interpretation of broadband flare emission as the hydrogen recombination continua originating in the chromosphere. Title: Revised historical solar irradiance forcing Authors: Egorova, T.; Schmutz, W.; Rozanov, E.; Shapiro, A. I.; Usoskin, I.; Beer, J.; Tagirov, R. V.; Peter, T. Bibcode: 2018A&A...615A..85E Altcode: 2018arXiv180400287E Context. There is no consensus on the amplitude of historical solar forcing. The estimated magnitude of the total solar irradiance (TSI) difference between the Maunder minimum and the present time ranges from 0.1 to 6 W m-2 making the simulation of the past and future climate uncertain. One reason for this disagreement is the applied evolution of the quiet Sun brightness in solar irradiance reconstruction models. This work addresses the role of the quiet Sun model choice and updated solar magnetic activity proxies on the solar forcing reconstruction.
Aims: We aim to establish a plausible range for the solar irradiance variability on decadal to millennial timescales.
Methods: The spectral solar irradiance (SSI) is calculated as a weighted sum of the contributions from sunspot umbra, sunspot penumbra, faculae, and quiet Sun, which are pre-calculated with the NLTE Spectral SYnthesis code (NESSY). We introduce activity belts of the contributions from sunspots and faculae and a new structure model for the quietest state of the Sun. We assume that the brightness of the quiet Sun varies in time proportionally to the secular (22-yr smoothed) variation of the solar modulation potential.
Results: A new reconstruction of the TSI and SSI covering the period 6000 BCE - 2015 CE is presented. The model simulates solar irradiance variability during the satellite era well. The TSI change between the Maunder and recent minima ranges between 3.7 and 4.5 W m-2 depending on the applied solar modulation potential. The implementation of a new quietest Sun model reduces, by approximately a factor of two, the relative solar forcing compared to the largest previous estimation, while the application of an updated solar modulation potential increases the forcing difference between the Maunder minimum and the present by 25-40%. Title: The EUI flight instrument of Solar Orbiter: from optical alignment to end-to-end calibration Authors: Halain, J. -P.; Renotte, E.; Auchère, F.; Berghmans, D.; Delmotte, F.; Harra, L.; Schmutz, W.; Schühle, U.; Aznar Cuadrado, R.; Dumesnil, C.; Gyo, M.; Kennedy, T.; Verbeeck, C.; Barbay, J.; Giordanengo, B.; Gissot, S.; Gottwald, A.; Heerlein, K.; Hellin, M. -L.; Hermans, A.; Hervier, V.; Jacques, L.; Laubis, C.; Mazzoli, A.; Meining, S.; Mercier, R.; Philippon, A.; Roose, S.; Rossi, L.; Scholze, F.; Smith, P.; Teriaca, L.; Zhang, X.; Rochus, P. Bibcode: 2018SPIE10699E..0HH Altcode: The Extreme Ultraviolet Imager (EUI) instrument for the Solar Orbiter mission will image the solar corona in the extreme ultraviolet (17.1 nm and 30.4 nm) and in the vacuum ultraviolet (121.6 nm) spectral ranges. The development of the EUI instrument has been successfully completed with the optical alignment of its three channels' telescope, the thermal and mechanical environmental verification, the electrical and software validations, and an end-toend on-ground calibration of the two-units' flight instrument at the operating wavelengths. The instrument has been delivered and installed on the Solar Orbiter spacecraft, which is now undergoing all preparatory activities before launch. Title: Chandra Observations of the Eclipsing Wolf-Rayet Binary CQ CepOver a Full Orbital Cycle Authors: Skinner, Steve L.; Guedel, Manuel; Schmutz, Werner; Zhekov, Svetozar Bibcode: 2018AAS...23232003S Altcode: We present results of Chandra X-ray observations and simultaneous optical light curves of the short-period (1.64 d) eclipsing WN6+O9 binary system CQ Cep obtained in 2013 and 2017 covering a full binary orbit. Our primary objective was to compare the observed X-ray properties with colliding wind shock theory, which predicts that the hottest shock plasma (T > 20 MK) will form on or near the line-of-centers between the stars. Thus, X-ray variability is expected during eclipses when the hottest plasma is occulted. The X-ray spectrum is strikingly similar to apparently single WN6 stars such as WR 134 and spectral lines reveal plasma over a broad range of temperatures T ~ 4 - 40 MK. Both primary and secondary optical eclipses were clearly detected and provide an accurate orbital period determination (P = 1.6412 d). The X-ray emission remained remarkably steady throughout the orbit and statistical tests give a low probability of variability. The lack of significant X-ray variabililty during eclipses indicates that the X-ray emission is not confined along the line-of-centers but is extended on larger spatial scales, contrary to colliding wind predictions. Title: Small-scale heating events in the solar atmosphere: lifetime, total energy and magnetic properties Authors: Guerreiro, Nuno; Haberreiter, Margit; Hansteen, Viggo; Schmutz, Werner Bibcode: 2018EGUGA..2014516G Altcode: Small-scale heating events (SSHEs) are believed to play a fundamental role in the heating of the solar corona, the pervading redshifts in the transition region, and the acceleration of spicules. We present a method to identify and track SSHEs over their lifetime and apply it to two simulation models. We identify the locations where the energy dissipation is maximum inside the SSHEs volume and we trace the SSHEs by following the spatial and temporal evolution of the maximum energy dissipation inside the SSHEs volume. The method is effective in following the SSHE and allows us to determine their lifetime, total energy and properties of the plasma as well as the magnetic field orientation in the vicinity of the SSHEs. We conclude that the SSHEs that have the potential to heat the corona live less than 4 minutes. Moreover, the typically energy release ranges from 1020 erg to 1024 erg. In addition, the directional change of the magnetic field lines on both sides of the current sheet constituting the SSHEs at the time of the absolute maximum energy dissipation ranges from 5 to 15 degree. This work is very relevant for the interpretation and the potential observational evidence of the SSHEs from upcoming data from the Spectral Imaging of the Coronal Environment instrument (SPICE) and the Extreme UV imager (EUI) onboard the Solar Orbiter Mission. Title: Order out of Randomness: Self-Organization Processes in Astrophysics Authors: Aschwanden, Markus J.; Scholkmann, Felix; Béthune, William; Schmutz, Werner; Abramenko, Valentina; Cheung, Mark C. M.; Müller, Daniel; Benz, Arnold; Chernov, Guennadi; Kritsuk, Alexei G.; Scargle, Jeffrey D.; Melatos, Andrew; Wagoner, Robert V.; Trimble, Virginia; Green, William H. Bibcode: 2018SSRv..214...55A Altcode: 2017arXiv170803394A Self-organization is a property of dissipative nonlinear processes that are governed by a global driving force and a local positive feedback mechanism, which creates regular geometric and/or temporal patterns, and decreases the entropy locally, in contrast to random processes. Here we investigate for the first time a comprehensive number of (17) self-organization processes that operate in planetary physics, solar physics, stellar physics, galactic physics, and cosmology. Self-organizing systems create spontaneous " order out of randomness", during the evolution from an initially disordered system to an ordered quasi-stationary system, mostly by quasi-periodic limit-cycle dynamics, but also by harmonic (mechanical or gyromagnetic) resonances. The global driving force can be due to gravity, electromagnetic forces, mechanical forces (e.g., rotation or differential rotation), thermal pressure, or acceleration of nonthermal particles, while the positive feedback mechanism is often an instability, such as the magneto-rotational (Balbus-Hawley) instability, the convective (Rayleigh-Bénard) instability, turbulence, vortex attraction, magnetic reconnection, plasma condensation, or a loss-cone instability. Physical models of astrophysical self-organization processes require hydrodynamic, magneto-hydrodynamic (MHD), plasma, or N-body simulations. Analytical formulations of self-organizing systems generally involve coupled differential equations with limit-cycle solutions of the Lotka-Volterra or Hopf-bifurcation type. Title: First TSI observations of the new Compact Lightweight Absolute Radiometer (CLARA) Authors: Walter, B.; Finsterle, W.; Koller, S.; Levesque, P. L.; Pfiffner, D.; Schmutz, W. K. Bibcode: 2017AGUFMSH43B2811W Altcode: Continuous and precise Total Solar Irradiance (TSI) measurements are indispensable to evaluate the influence of short- and long-term solar radiative emission variations on the Earth's energy budget. The existence of a potentially long-term trend in the suns activity and whether or not such a trend could be climate effective is still a matter of debate. The Compact Lightweight Absolute Radiometer (CLARA) is one of PMOD/WRC's future contributions to the almost seamless series of space borne TSI measurements since 1978. CLARA is one of three payloads of the Norwegian micro satellite NORSAT-1, along with Langmuir probes for space plasma research and an Automatic Identification System (AIS) receiver to monitor maritime traffic in Norwegian waters. NORSAT-1 was launched July 14th 2017 and the nominal operation of CLARA will start after the instrument commissioning beginning August 21st2017. We present the design, calibration and first TSI observations of CLARA, a new generation of active cavity Electrical Substitution Radiometers (ESR) comprising the latest radiometer developments of PMOD/WRC: i) A three-cavity design for degradation tracking and redundancy, ii) a digital control loop with feed forward system allowing for measurement cadences of 30s, iii) an aperture arrangement to reduce internal scattered light and iv) a new cavity and heatsink design to minimize non-equivalence, size and weight of the instrument. CLARA was end-to-end calibrated against the SI traceable cryogenic radiometer of the TSI Radiometer Facility (TRF) in Boulder (Colorado). The absolute measurement uncertainties for the three SI-traceable TSI detectors of CLARA are 567, 576 and 912 ppm (k = 1). Title: ASPIICS: a giant, white light and emission line coronagraph for the ESA proba-3 formation flight mission Authors: Lamy, P. L.; Vivès, S.; Curdt, W.; Damé, L.; Davila, J.; Defise, J. -M.; Fineschi, S.; Heinzel, P.; Howard, Russel; Kuzin, S.; Schmutz, W.; Tsinganos, K.; Zhukov, A. Bibcode: 2017SPIE10565E..0TL Altcode: Classical externally-occulted coronagraphs are presently limited in their performances by the distance between the external occulter and the front objective. The diffraction fringe from the occulter and the vignetted pupil which degrades the spatial resolution prevent useful observations of the white light corona inside typically 2-2.5 solar radii (Rsun). Formation flying offers and elegant solution to these limitations and allows conceiving giant, externally-occulted coronagraphs using a two-component space system with the external occulter on one spacecraft and the optical instrument on the other spacecraft at a distance of hundred meters [1, 2]. Such an instrument ASPIICS (Association de Satellites Pour l'Imagerie et l'Interférométrie de la Couronne Solaire) has been selected by the European Space Agency (ESA) to fly on its PROBA-3 mission of formation flying demonstration which is presently in phase B (Fig. 1). The classical design of an externally-occulted coronagraph is adapted to the formation flying configuration allowing the detection of the very inner corona as close as 0.04 solar radii from the solar limb. By tuning the position of the occulter spacecraft, it may even be possible to reach the chromosphere and the upper part of the spicules [3]. ASPIICS will perform (i) high spatial resolution imaging of the continuum K+F corona in photometric and polarimetric modes, (ii) high spatial resolution imaging of the E-corona in two coronal emission lines (CEL): Fe XIV and He I D3, and (iii) two-dimensional spectrophotometry of the Fe XIV emission line. ASPIICS will address the question of the coronal heating and the role of waves by characterizing propagating fluctuations (waves and turbulence) in the solar wind acceleration region and by looking for oscillations in the intensity and Doppler shift of spectral lines. The combined imaging and spectral diagnostics capabilities available with ASPIICS will allow mapping the velocity field of the corona both in the sky plane (directly on the images) and along the line-of-sight by measuring the Doppler shifts of emission lines in an effort to determine how the different components of the solar wind, slow and fast are accelerated. With a possible launch in 2014, ASPIICS will observe the corona during the maximum of solar activity, insuring the detection of many Coronal Mass Ejections (CMEs). By rapidly alternating high-resolution imaging and spectroscopy, CMEs will be thoroughly characterized. Title: In-flight performance of the solar UV radiometer LYRA/PROBA-2 Authors: Stockman, Y.; BenMoussa, A.; Dammasch, I.; Defise, J. -M.; Dominique, M.; Halain, J. -P.; Hochedez, J. -F.; Koller, S.; Schmutz, W.; Schühle, U. Bibcode: 2017SPIE10565E..0AS Altcode: LYRA is a solar radiometer, part of the PROBA-2 micro-satellite payload (Fig. 1). The PROBA-2 [1] mission has been launched on 02 November 2009 with a Rockot launcher to a Sun-synchronous orbit at an altitude of 725 km. Its nominal operation duration is two years with possible extension of 2 years. PROBA-2 is a small satellite developed under an ESA General Support Technology Program (GSTP) contract to perform an in-flight demonstration of new space technologies and support a scientific mission for a set of selected instruments [2]. PROBA-2 host 17 technological demonstrators and 4 scientific instruments. The mission is tracked by the ESA Redu Mission Operation Center. One of the four scientific instruments is LYRA that monitors the solar irradiance at a high cadence (> 20 Hz) in four soft X-Ray to VUV large passbands: the "Lyman-Alpha" channel, the "Herzberg" continuum range, the "Aluminium" and "Zirconium" filter channels. The radiometric calibration is traceable to synchrotron source standards [3]. LYRA benefits from wide bandgap detectors based on diamond. It is the first space assessment of these revolutionary UV detectors for astrophysics. Diamond sensors make the instruments radiation-hard and solar-blind (insensitive to the strong solar visible light) and, therefore, visible light blocking filters become superfluous. To correlate the data of this new detector technology, silicon detectors with well known characteristics are also embarked. Due to the strict allocated mass and power budget (5 kg, 5W), and poor priority to the payload needs on such platform, an optimization and a robustness of the instrument was necessary. The first switch-on occured on 16 November 2009. Since then the instrument performances have been monitored and analyzed during the commissioning period. This paper presents the first-light and preliminary performance analysis. Title: LYRA, solar uv radiometer on the technology demonstration platform PROBA-2 Authors: Stockman, Y.; Hochedez, J. -F.; Schmutz, W.; BenMoussa, A.; Defise, J. -M.; Denis, F.; D'Olieslaeger, M.; Dominique, M.; Haenen, K.; Halain, J. -P.; Koller, S.; Koizumi, S.; Mortet, V.; Rochus, P.; Schühle, U.; Soltani, A.; Theissen, A. Bibcode: 2017SPIE10567E..3KS Altcode: LYRA is a solar radiometer part of the PROBA 2 micro satellite payload. LYRA will monitor the solar irradiance in four soft X-Ray - VUV passbands. They have been chosen for their relevance to Solar Physics, Aeronomy and SpaceWeather: 1/ Lyman Alpha channel, 2/ Herzberg continuum range, 3/ Aluminium filter channel (including He II at 30.4 nm) and 4/ Zirconium filter channel. The radiometric calibration is traceable to synchrotron source standards. The stability will be monitored by on-board calibration sources (LEDs), which allow us to distinguish between potential degradations of the detectors and filters. Additionally, a redundancy strategy maximizes the accuracy and the stability of the measurements. LYRA will benefit from wide bandgap detectors based on diamond: it will be the first space assessment of revolutionary UV detectors. Diamond sensors make the instruments radiation-hard and solar-blind (insensitive to visible light) and therefore, make dispensable visible light blocking filters. To correlate the data of this new detector technology, well known technology, such as Si detectors are also embarked. The SWAP EUV imaging telescope will operate next to LYRA on PROBA-2. Together, they will provide a high performance solar monitor for operational space weather nowcasting and research. LYRA demonstrates technologies important for future missions such as the ESA Solar Orbiter. Title: The nature of solar brightness variations Authors: Shapiro, A. I.; Solanki, S. K.; Krivova, N. A.; Cameron, R. H.; Yeo, K. L.; Schmutz, W. K. Bibcode: 2017NatAs...1..612S Altcode: 2017arXiv171104156S Determining the sources of solar brightness variations1,2, often referred to as solar noise3, is important because solar noise limits the detection of solar oscillations3, is one of the drivers of the Earth's climate system4,5 and is a prototype of stellar variability6,7—an important limiting factor for the detection of extrasolar planets. Here, we model the magnetic contribution to solar brightness variability using high-cadence8,9 observations from the Solar Dynamics Observatory (SDO) and the Spectral And Total Irradiance REconstruction (SATIRE)10,11 model. The brightness variations caused by the constantly evolving cellular granulation pattern on the solar surface were computed with the Max Planck Institute for Solar System Research (MPS)/University of Chicago Radiative Magnetohydrodynamics (MURaM)12 code. We found that the surface magnetic field and granulation can together precisely explain solar noise (that is, solar variability excluding oscillations) on timescales from minutes to decades, accounting for all timescales that have so far been resolved or covered by irradiance measurements. We demonstrate that no other sources of variability are required to explain the data. Recent measurements of Sun-like stars by the COnvection ROtation and planetary Transits (CoRoT)13 and Kepler14 missions uncovered brightness variations similar to that of the Sun, but with a much wider variety of patterns15. Our finding that solar brightness variations can be replicated in detail with just two well-known sources will greatly simplify future modelling of existing CoRoT and Kepler as well as anticipated Transiting Exoplanet Survey Satellite16 and PLAnetary Transits and Oscillations of stars (PLATO)17 data. Title: NESSY: NLTE spectral synthesis code for solar and stellar atmospheres Authors: Tagirov, R. V.; Shapiro, A. I.; Schmutz, W. Bibcode: 2017A&A...603A..27T Altcode: Context. Physics-based models of solar and stellar magnetically-driven variability are based on the calculation of synthetic spectra for various surface magnetic features as well as quiet regions, which are a function of their position on the solar or stellar disc. Such calculations are performed with radiative transfer codes tailored for modeling broad spectral intervals.
Aims: We aim to present the NLTE Spectral SYnthesis code (NESSY), which can be used for modeling of the entire (UV-visible-IR and radio) spectra of solar and stellar magnetic features and quiet regions.
Methods: NESSY is a further development of the COde for Solar Irradiance (COSI), in which we have implemented an accelerated Λ-iteration (ALI) scheme for co-moving frame (CMF) line radiation transfer based on a new estimate of the local approximate Λ-operator.
Results: We show that the new version of the code performs substantially faster than the previous one and yields a reliable calculation of the entire solar spectrum. This calculation is in a good agreement with the available observations. Title: Numerical simulations and infrared spectro-interferometry reveal the wind collision region in γ2 Velorum Authors: Lamberts, A.; Millour, F.; Liermann, A.; Dessart, L.; Driebe, T.; Duvert, G.; Finsterle, W.; Girault, V.; Massi, F.; Petrov, R. G.; Schmutz, W.; Weigelt, G.; Chesneau, O. Bibcode: 2017MNRAS.468.2655L Altcode: 2017arXiv170101124L Colliding stellar winds in massive binary systems have been studied through their radio, optical lines and strong X-ray emission for decades. More recently, near-infrared spectro-interferometric observations have become available in a few systems, but isolating the contribution from the individual stars and the wind collision region still remains a challenge. In this paper, we study the colliding wind binary γ2 Velorum and aim at identifying the wind collision zone from infrared interferometric data, which provide unique spatial information to determine the wind properties. Our analysis is based on multi-epoch Very Large Telescope Interferometer/Astronomical Multi-BEam Recombiner (VLTI/AMBER) data that allows us to separate the spectral components of both stars. First, we determine the astrometric solution of the binary and confirm previous distance measurements. We then analyse the spectra of the individual stars, showing that the O star spectrum is peculiar within its class. Then, we perform three-dimensional hydrodynamic simulations of the system from which we extract model images, visibility curves and closure phases that can be directly compared with the observed data. The hydrodynamic simulations reveal the 3D spiral structure of the wind collision region, which results in phase-dependent emission maps. Our model visibility curves and closure phases provide a good match when the wind collision region accounts for 3-10 per cent γ2 Vel's total flux in the near-infrared. The dialogue between hydrodynamic simulations, radiative transfer models and observations allows us to fully exploit the observations. Similar efforts will be crucial to study circumstellar environments with the new generation of VLTI instruments like GRAVITY and MATISSE. Title: Solar disc radius determined from observations made during eclipses with bolometric and photometric instruments on board the PICARD satellite Authors: Thuillier, G.; Zhu, P.; Shapiro, A. I.; Sofia, S.; Tagirov, R.; van Ruymbeke, M.; Perrin, J. -M.; Sukhodolov, T.; Schmutz, W. Bibcode: 2017A&A...603A..28T Altcode: Context. Despite the importance of having an accurate measurement of the solar disc radius, there are large uncertainties of its value due to the use of different measurement techniques and instrument calibration. An item of particular importance is to establish whether the value of the solar disc radius correlates with the solar activity level.
Aims: The main goal of this work is to measure the solar disc radius in the near-UV, visible, and near-IR regions of the solar spectrum.
Methods: Three instruments on board the PICARD spacecraft, namely the Bolometric Oscillations Sensor (BOS), the PREcision MOnitoring Sensor (PREMOS), and a solar sensor (SES), are used to derive the solar disc radius using the light curves produced when the Sun is occulted by the Moon. Nine eclipses, from 2010 to 2013, resulted in 17 occultations as viewed from the moving satellite. The calculation of the solar disc radius uses a simulation of the light curve taking into account the center-to-limb variation provided by the Non-local thermodynamic Equilibrium Spectral SYnthesis (NESSY) code.
Results: We derive individual values for the solar disc radius for each viewed eclipse. Tests for a systematic variation of the radius with the progression of the solar cycle yield no significant results during the three years of measurements within the uncertainty of our measurements. Therefore, we derive a more precise radius value by averaging these values. At one astronomical unit, we obtain 959.79 arcseconds (arcsec) from the bolometric experiment; from PREMOS measurements, we obtain 959.78 arcsec at 782 nm and 959.76 arcsec at 535 nm. We found 960.07 arcsec at 210 nm, which is a higher value than the other determinations given the photons at this wavelength originate from the upper photosphere and lower chromosphere. We also give a detailed comparison of our results with those previously published using measurements from space-based and ground-based instruments using the Moon angular radius reference, and different methods.
Conclusions: Our results, which use the Moon as an absolute calibration, clearly show the dependence of the solar disc radius with wavelength in UV, visible and near-IR. Beyond the metrological results, solar disc radius measurements will allow the accuracy of models of the solar atmosphere to be tested. Proposed systematic variations of the solar disc radius during the time of observation would be smaller than the uncertainty of our measurement, which amounts to less than 26 milliarcseconds. Title: Small-scale heating events in the solar atmosphere. II. Lifetime, total energy, and magnetic properties Authors: Guerreiro, N.; Haberreiter, M.; Hansteen, V.; Schmutz, W. Bibcode: 2017A&A...603A.103G Altcode: Context. Small-scale heating events (SSHEs) are believed to play a fundamental role in understanding the process responsible for heating of the solar corona, the pervading redshifts in the transition region, and the acceleration of spicules.
Aims: We determine the properties of the SSHEs and the atmospheric response to them in 3D magnetohydrodynamics (3D-MHD) simulations of the solar atmosphere.
Methods: We developed a method for identifying and following SSHEs over their lifetime, and applied it to two simulation models. We identified the locations where the energy dissipation is greatest inside the SSHEs volume, and we traced the SSHEs by following the spatial and temporal evolution of the maximum energy dissipation inside the SSHEs volume.
Results: The method is effective in following the SSHEs. We can determine their lifetime, total energy, and properties of the plasma, as well as the magnetic field orientation in the vicinity of the SSHEs.
Conclusions: We determine that the SSHEs that have the potential to heat the corona live less than 4 min, and typically the energy they release ranges from 1020 to 1024 erg. In addition, the directional change of the field lines on the two sides of the current sheet constituting the SSHEs ranges from 5° to 15° at the moment of the absolute maximum energy dissipation. Title: A new observational solar irradiance composite Authors: Haberreiter, Margit; Schöll, Micha; Dudok de Wit, Thierry; Kretzschmar, Matthieu; Misios, Stergios; Tourpali, Kleareti; Schmutz, Werner Bibcode: 2017JGRA..122.5910H Altcode: Variations in the solar spectral irradiance (SSI) are an important driver of the chemistry, temperature, and dynamics of the Earth's atmosphere and ultimately the Earth's climate. To investigate the detailed response of the Earth's atmosphere to SSI variations, a reliable SSI data set is needed. We present an observational SSI composite data set that is based on 20 instruments and has been built by using probabilistic approach that takes into account the scale-dependent uncertainty of each available SSI observation. We compare the variability of this new composite with available SSI reconstructions and discuss the respective modeled responses in the Earth's atmosphere. As the composite is based on purely statistical means, we consider it as a valuable independent data set. Title: Does the Wolf-Rayet binary CQ Cephei undergo sporadic mass transfer events? Authors: Koenigsberger, Gloria; Schmutz, Werner; Skinner, Stephen L. Bibcode: 2017A&A...601A.121K Altcode: Context. Stellar wind mass-loss in binary systems carries away angular momentum causing a monotonic increase in the orbital period, Ṗ> 0. Despite possessing a significant stellar wind, the eclipsing Wolf-Rayet (WR) binary system CQ Cep does not show the expected monotonic period increase, in fact, it is sometimes reported to display the opposite behavior.
Aims: The objective of this paper is to perform a new analysis of the rate of period change Ṗ and determine the conditions under which Roche-lobe overflow (RLO) mass-transfer combined with wind mass loss can explain the discrepant behavior.
Methods: The historic records of times of light curve minima were reviewed and compared with the theoretical values of Ṗ for cases in which both wind mass-loss and RLO occur simultaneously.
Results: The observational data indicate that Ṗ alternates between positive and negative values on a timescale of years. The negative values (Ṗ -0.6 to -8.5 s yr-1) are significantly larger in absolute value than the positive ones (Ṗ + 0.2 to +1.2 s yr-1). We find that a plausible scenario for CQ Cep is one in which the O star undergoes intense but sporadic RLO events that lead to accretion onto the WR star, at which times Ṗ< 0. At other times, Ṗ> 0 when the WR wind, and possibly material swept up from the O star, carries angular momentum away from the system. A scenario in which the WR star is the mass donor cannot be excluded, but requires that either the WR wind mass-loss rate undergoes large sporadic enhancements or that an additional process that removes angular momentum from the system be present. Title: Modeling of the middle atmosphere response to 27-day solar irradiance variability Authors: Sukhodolov, Timofei; Rozanov, Eugene; Ball, William T.; Peter, Thomas; Schmutz, Werner Bibcode: 2017JASTP.152...50S Altcode: The solar rotational variability (27-day) signal in the Earth's middle atmosphere has been studied for several decades, as it was believed to help in the understanding of the Sun's influence on climate at longer timescales. However, all previous studies have found that this signal is very uncertain, likely due to the influence of the internal variability of the atmosphere. Here, we applied an ensemble modeling approach in order to decrease internal random variations in the modeled time series. Using a chemistry-climate model (CCM), SOCOLv3, we performed two 30-member 3-year long (2003-2005) ensemble runs: with and without a rotational component in input irradiance fluxes. We also performed similar simulations with a 1-D model, in order to demonstrate the system behavior in the absence of any dynamical feedbacks and internal perturbations. For the first time we show a clear connection between the solar rotation and the stratospheric tropical temperature time-series. We show tropical temperature and ozone signal phase lag patterns that are in agreement with those from a 1-D model. Pronounced correlation and signal phase lag patterns allow us to properly estimate ozone and temperature sensitivities to irradiance changes. While ozone sensitivity is found to be in agreement with recent sensitivities reported for the 11-year cycle, temperature sensitivity appears to be at the lowest boundary of previously reported values. Analysis of temperature reanalysis data, separate ensemble members, and modeling results without a rotational component reveals that the atmosphere can produce random internal variations with periods close to 27 days even without solar rotational forcing. These variations are likely related to tropospheric wave-forcing and complicate the extraction of the solar rotational signal from observational time-series of temperature and, to a lesser extent, of ozone. Possible ways of further improving solar rotational signal extraction are discussed. Title: Total Solar Irradiance changes between 2010 and 2014 from the PREcision MOnitor Sensor absolute radiometer (PREMOS/PICARD) Authors: Cessateur, G.; Schmutz, W. K.; Ball, W.; Finsterle, W.; Walter, B. Bibcode: 2016AGUFMSH42B..04C Altcode: The PREMOS/PICARD instrument monitored total solar irradiance (TSI) from July 2010 to April 2014. During this period other TSI instruments showed divergent trends large enough to mask, or exacerbate, a multi-decadal trend in the Sun's output. We present the complete PICARD mission PREMOS TSI time series and provide an inter-comparison with other instruments operating during the same period. Additionally, we present a unique assessment of the backup radiometer degradation during the mission, which provides an additional, robust estimate of the change in TSI from 2011 to 2014; this assessment leads to the conclusion that composites of TSI observations are still too uncertain to estimate TSI between solar cycle minima. Title: Nominal Values for Selected Solar and Planetary Quantities: IAU 2015 Resolution B3 Authors: Prša, Andrej; Harmanec, Petr; Torres, Guillermo; Mamajek, Eric; Asplund, Martin; Capitaine, Nicole; Christensen-Dalsgaard, Jørgen; Depagne, Éric; Haberreiter, Margit; Hekker, Saskia; Hilton, James; Kopp, Greg; Kostov, Veselin; Kurtz, Donald W.; Laskar, Jacques; Mason, Brian D.; Milone, Eugene F.; Montgomery, Michele; Richards, Mercedes; Schmutz, Werner; Schou, Jesper; Stewart, Susan G. Bibcode: 2016AJ....152...41P Altcode: 2016arXiv160509788P In this brief communication we provide the rationale for and the outcome of the International Astronomical Union (IAU) resolution vote at the XXIXth General Assembly in Honolulu, Hawaii, in 2015, on recommended nominal conversion constants for selected solar and planetary properties. The problem addressed by the resolution is a lack of established conversion constants between solar and planetary values and SI units: a missing standard has caused a proliferation of solar values (e.g., solar radius, solar irradiance, solar luminosity, solar effective temperature, and solar mass parameter) in the literature, with cited solar values typically based on best estimates at the time of paper writing. As precision of observations increases, a set of consistent values becomes increasingly important. To address this, an IAU Working Group on Nominal Units for Stellar and Planetary Astronomy formed in 2011, uniting experts from the solar, stellar, planetary, exoplanetary, and fundamental astronomy, as well as from general standards fields to converge on optimal values for nominal conversion constants. The effort resulted in the IAU 2015 Resolution B3, passed at the IAU General Assembly by a large majority. The resolution recommends the use of nominal solar and planetary values, which are by definition exact and are expressed in SI units. These nominal values should be understood as conversion factors only, not as the true solar/planetary properties or current best estimates. Authors and journal editors are urged to join in using the standard values set forth by this resolution in future work and publications to help minimize further confusion. Title: Assessing the beginning to end-of-mission sensitivity change of the PREcision MOnitor Sensor total solar irradiance radiometer (PREMOS/PICARD) Authors: Ball, William T.; Schmutz, Werner; Fehlmann, André; Finsterle, Wolfgang; Walter, Benjamin Bibcode: 2016JSWSC...6A..32B Altcode: The switching of the total solar irradiance (TSI) backup radiometer (PREMOS-B) to a primary role for 2 weeks at the end of the PICARD mission provides a unique opportunity to test the fundamental hypothesis of radiometer experiments in space, which is that the sensitivity change of instruments due to the space environment is identical for the same instrument type as a function of solar-exposure time of the instruments. We verify this hypothesis for the PREMOS TSI radiometers within the PREMOS experiment on the PICARD mission. We confirm that the sensitivity change of the backup instrument, PREMOS-B, is similar to that of the identically-constructed primary radiometer, PREMOS-A. The extended exposure of the backup instrument at the end of the mission allows for the assessment, with an uncertainty estimate, of the sensitivity change of the primary radiometer from the beginning of the PICARD mission compared to the end, and of the degradation of the backup over the mission. We correct six sets of PREMOS-B observations connecting October 2011 with February 2014, using six ratios from simultaneous PREMOS-A and PREMOS-B exposures during the first days of PREMOS-A operation in 2010. These ratios are then used, without indirect estimates or assumptions, to evaluate the stability of SORCE/TIM and SOHO/VIRGO TSI measurements, which have both operated for more than a decade and now show different trends over the time span of the PICARD mission, namely from 2010 to 2014. We find that by February 2014 relative to October 2011 PREMOS-B supports the SORCE/TIM TSI time evolution, which in May 2014 relative to October 2011 is ~0.11 W m-2, or ~84 ppm, higher than SOHO/VIRGO. Such a divergence between SORCE/TIM and SOHO/VIRGO over this period is a significant fraction of the estimated decline of 0.2 W m-2 between the solar minima of 1996 and 2008, and questions the reliability of that estimated trend. Extrapolating the uncertainty indicated by the disagreement of SORCE/TIM and PREMOS with respect to SOHO/VIRGO, we can conclude that it is currently not possible to assess centennial timescale changes in solar irradiance based on any of the presently existing TSI composites. It is imperative to accurately estimate solar irradiance changes from observations in order to extrapolate centennial scale trends important for understanding both long-term solar irradiance changes and the Sun's influence on the Earth's climate. Title: The qualification campaign of the EUI instrument of Solar Orbiter Authors: Halain, J. -P.; Rochus, P.; Renotte, E.; Hermans, A.; Jacques, L.; Mazzoli, A.; Auchère, F.; Berghmans, D.; Harra, L.; Schühle, U.; Schmutz, W.; Aznar Cuadrado, R.; Dumesnil, C.; Gyo, M.; Kennedy, T.; Verbeeck, C.; Smith, P. Bibcode: 2016SPIE.9905E..2XH Altcode: The Extreme Ultraviolet Imager (EUI) instrument is one of the ten scientific instruments on board the Solar Orbiter mission to be launched in October 2018. It will provide full-sun and high-resolution images of the solar corona in the extreme ultraviolet (17.1 nm and 30.4 nm) and in the vacuum ultraviolet (121.6 nm). The validation of the EUI instrument design has been completed with the Assembly, Integration and Test (AIT) of the instrument two-units Qualification Model (QM). Optical, electrical, electro-magnetic compatibility, thermal and mechanical environmental verifications were conducted and are summarized here. The integration and test procedures for the Flight Model (FM) instrument and sub-systems were also verified. Following the Qualification Review, the flight instrument activities were started with the assembly of the flight units. The mechanical and thermal acceptance tests and an end-to-end final calibration in the (E)UV will then be conducted before delivery for integration on the Solar Orbiter Spacecraft by end of 2016. Title: The SPICE Spectral Imager on Solar Orbiter: Linking the Sun to the Heliosphere Authors: Fludra, Andrzej; Haberreiter, Margit; Peter, Hardi; Vial, Jean-Claude; Harrison, Richard; Parenti, Susanna; Innes, Davina; Schmutz, Werner; Buchlin, Eric; Chamberlin, Phillip; Thompson, William; Gabriel, Alan; Morris, Nigel; Caldwell, Martin; Auchere, Frederic; Curdt, Werner; Teriaca, Luca; Hassler, Donald M.; DeForest, Craig; Hansteen, Viggo; Carlsson, Mats; Philippon, Anne; Janvier, Miho; Wimmer-Schweingruber, Robert; Griffin, Douglas; Davila, Joseph; Giunta, Alessandra; Waltham, Nick; Eccleston, Paul; Gottwald, Alexander; Klein, Roman; Hanley, John; Walls, Buddy; Howe, Chris; Schuehle, Udo Bibcode: 2016cosp...41E.607F Altcode: The SPICE (Spectral Imaging of the Coronal Environment) instrument is one of the key remote sensing instruments onboard the upcoming Solar Orbiter Mission. SPICE has been designed to contribute to the science goals of the mission by investigating the source regions of outflows and ejection processes which link the solar surface and corona to the heliosphere. In particular, SPICE will provide quantitative information on the physical state and composition of the solar atmosphere plasma. For example, SPICE will access relative abundances of ions to study the origin and the spatial/temporal variations of the 'First Ionization Potential effect', which are key signatures to trace the solar wind and plasma ejections paths within the heliosphere. Here we will present the instrument and its performance capability to attain the scientific requirements. We will also discuss how different observation modes can be chosen to obtain the best science results during the different orbits of the mission. To maximize the scientific return of the instrument, the SPICE team is working to optimize the instrument operations, and to facilitate the data access and their exploitation. Title: Solar abundances with the SPICE spectral imager on Solar Orbiter Authors: Giunta, Alessandra; Haberreiter, Margit; Peter, Hardi; Vial, Jean-Claude; Harrison, Richard; Parenti, Susanna; Innes, Davina; Schmutz, Werner; Buchlin, Eric; Chamberlin, Phillip; Thompson, William; Bocchialini, Karine; Gabriel, Alan; Morris, Nigel; Caldwell, Martin; Auchere, Frederic; Curdt, Werner; Teriaca, Luca; Hassler, Donald M.; DeForest, Craig; Hansteen, Viggo; Carlsson, Mats; Philippon, Anne; Janvier, Miho; Wimmer-Schweingruber, Robert; Griffin, Douglas; Baudin, Frederic; Davila, Joseph; Fludra, Andrzej; Waltham, Nick; Eccleston, Paul; Gottwald, Alexander; Klein, Roman; Hanley, John; Walls, Buddy; Howe, Chris; Schuehle, Udo; Gyo, Manfred; Pfiffner, Dany Bibcode: 2016cosp...41E.681G Altcode: Elemental composition of the solar atmosphere and in particular abundance bias of low and high First Ionization Potential (FIP) elements are a key tracer of the source regions of the solar wind. These abundances and their spatio-temporal variations, as well as the other plasma parameters , will be derived by the SPICE (Spectral Imaging of the Coronal Environment) EUV spectral imager on the upcoming Solar Orbiter mission. SPICE is designed to provide spectroheliograms (spectral images) using a core set of emission lines arising from ions of both low-FIP and high-FIP elements. These lines are formed over a wide range of temperatures, enabling the analysis of the different layers of the solar atmosphere. SPICE will use these spectroheliograms to produce dynamic composition maps of the solar atmosphere to be compared to in-situ measurements of the solar wind composition of the same elements (i.e. O, Ne, Mg, Fe). This will provide a tool to study the connectivity between the spacecraft (the Heliosphere) and the Sun. We will discuss the SPICE capabilities for such composition measurements. Title: Main results of the PICARD mission Authors: Meftah, M.; Corbard, T.; Hauchecorne, A.; Irbah, A.; Boumier, P.; Chevalier, A.; Schmutz, W.; Ikhlef, R.; Morand, F.; Renaud, C.; Hochedez, J. -F.; Cessateur, G.; Turck-Chièze, S.; Salabert, D.; Rouzé, M.; van Ruymbeke, M.; Zhu, P.; Kholikov, S.; Koller, S.; Conscience, C.; Dewitte, S.; Damé, L.; Djafer, D. Bibcode: 2016SPIE.9904E..0ZM Altcode: PICARD is a mission devoted to solar variability observations through imagery and radiometric measurements. The main goal is to provide data for scientific investigation first in the area of solar physics, and second in the assessment of the influence of the solar variability on the Earth climate variability. PICARD contains a double program with in-space and on-ground measurements. The PICARD spacecraft was launched on June 15, 2010, commissioned in-flight in October of the same year and was retired in April 2014. The PICARD ground-based observatory is operational since May 2011. We shall give a short overview of the PICARD instrumentation. New estimates of the absolute values of the total solar irradiance, of the solar spectral irradiance at typical wavelengths, and of the solar oblateness will be given. We will also report about helioseismic studies. Finally, we will present our current results about solar radius variations after six years of solar observation. Title: Detection and characterization of small-scale heating events in the solar atmosphere from 3D-MHD simulations and their potential role in coronal heating Authors: Guerreiro, Nuno; Haberreiter, Margit; Schmutz, Werner; Hansteen, Viggo Bibcode: 2016cosp...41E.750G Altcode: Aiming at better understanding the mechanism(s) responsible for the coronal heating we focus on analyzing the properties of the magnetically generated small-scale heating events (SSHEs) in the solar atmosphere. We present a comprehensive method to detect and follow SSHEs over time in 3D-MHD simulations of the solar atmosphere. Applying the method we are able to better understand the properties of the SSHEs and how the plasma in their vicinity respond to them. We study the lifetime, energy and spectral signatures and show that the energy flux dissipated by them is enough to heat the corona. Ultimately, these results will be important for the coordinated scientific exploration of SPICE and EUI along with other instruments on board solar orbiter. Title: The origin of Total Solar Irradiance variability on timescales less than a day Authors: Shapiro, Alexander; Krivova, Natalie; Schmutz, Werner; Solanki, Sami K.; Leng Yeo, Kok; Cameron, Robert; Beeck, Benjamin Bibcode: 2016cosp...41E1774S Altcode: Total Solar Irradiance (TSI) varies on timescales from minutes to decades. It is generally accepted that variability on timescales of a day and longer is dominated by solar surface magnetic fields. For shorter time scales, several additional sources of variability have been proposed, including convection and oscillation. However, available simplified and highly parameterised models could not accurately explain the observed variability in high-cadence TSI records. We employed the high-cadence solar imagery from the Helioseismic and Magnetic Imager onboard the Solar Dynamics Observatory and the SATIRE (Spectral And Total Irradiance Reconstruction) model of solar irradiance variability to recreate the magnetic component of TSI variability. The recent 3D simulations of solar near-surface convection with MURAM code have been used to calculate the TSI variability caused by convection. This allowed us to determine the threshold timescale between TSI variability caused by the magnetic field and convection. Our model successfully replicates the TSI measurements by the PICARD/PREMOS radiometer which span the period of July 2010 to February 2014 at 2-minute cadence. Hence, we demonstrate that solar magnetism and convection can account for TSI variability at all timescale it has ever been measured (sans the 5-minute component from p-modes). Title: First light measurements of the Total Solar Irradiance experiment CLARA on NORSAT-1 Authors: Schmutz, Werner Bibcode: 2016cosp...41E1753S Altcode: NORSAT-1 is a Norwegian micro-satellite, which will be launched April 22, 2016. (In the future at the time of writing this abstract.) The satellite carries two scientific instruments and an AIS receiver for performing ship detection from space. One of the scientific instruments is a Compact Light-weight Absolute RAdiometer (CLARA) and the other is a Langmuir Probe instrument comprising four probes mounted on booms. The latter experiment will measure electron density and the platform's floating potential along the orbit. The University of Oslo provides the Langmuir probes. The radiometer experiment CLARA has been built by PMOD/WRC funded through the Swiss PRODEX program. It will measure Total Solar Irradiance with an instrument of novel design that is optimized for minimizing mass and size by still ensuring highest measuring accuracy and thermal stability. The radiometers of CLARA have been fully characterized as well as calibrated at the TRF facility. It is expected that the first light accuracy of the absolute measurement of Total Solar Irradiance will be better than pm0.3 W/m^{2, allowing to probe the current TSI composite for its absolute level. The presentation will give an overview of the CLARA instrument and its calibration. It is expected that at the time of the COSPAR conference the first light TSI value of CLARA/NORSAT-1 is ready for publication. Together with a previous absolute TSI measurements available for July 27, 2010 measured by PREMOS/PICARD the new absolute TSI measurement will be used to test the accuracy of long term TSI trend given by the relative TSI composite. Title: Are solar brightness variations faculae- or spot-dominated? Authors: Shapiro, A. I.; Solanki, S. K.; Krivova, N. A.; Yeo, K. L.; Schmutz, W. K. Bibcode: 2016A&A...589A..46S Altcode: 2016arXiv160204447S Context. Regular spaceborne measurements have revealed that solar brightness varies on multiple timescales, variations on timescales greater than a day being attributed to a surface magnetic field. Independently, ground-based and spaceborne measurements suggest that Sun-like stars show a similar, but significantly broader pattern of photometric variability.
Aims: To understand whether the broader pattern of stellar variations is consistent with the solar paradigm, we assess relative contributions of faculae and spots to solar magnetically-driven brightness variability. We investigate how the solar brightness variability and its facular and spot contributions depend on the wavelength, timescale of variability, and position of the observer relative to the ecliptic plane.
Methods: We performed calculations with the SATIRE model, which returns solar brightness with daily cadence from solar disc area coverages of various magnetic features. We took coverages as seen by an Earth-based observer from full-disc SoHO/MDI and SDO/HMI data and projected them to mimic out-of-ecliptic viewing by an appropriate transformation.
Results: Moving the observer away from the ecliptic plane increases the amplitude of 11-year variability as it would be seen in Strömgren (b + y)/2 photometry, but decreases the amplitude of the rotational brightness variations as it would appear in Kepler and CoRoT passbands. The spot and facular contributions to the 11-year solar variability in the Strömgren (b + y)/2 photometry almost fully compensate each other so that the Sun appears anomalously quiet with respect to its stellar cohort. Such a compensation does not occur on the rotational timescale.
Conclusions: The rotational solar brightness variability as it would appear in the Kepler and CoRoT passbands from the ecliptic plane is spot-dominated, but the relative contribution of faculae increases for out-of-ecliptic viewing so that the apparent brightness variations are faculae-dominated for inclinations less than about I = 45°. Over the course of the 11-year activity cycle, the solar brightness variability is faculae-dominated shortwards of 1.2 μm independently of the inclination. Title: Solar spectral irradiance model validation using Solar Spectral Irradiance and Solar Radius measurements Authors: Thuillier, Gérard; Zhu, Ping; Shapiro, Alexander; Sofia, Sabatino; Tagirov, Rinat; Van Ruymbeke, Michel; Schmutz, Werner Bibcode: 2016EGUGA..18.7407T Altcode: The importance of the reliable solar spectral irradiance (SSI) data for solar and climate physics is now well acknowledged. In particular, the irradiance time series are necessary for most of the current studies concerning climate evolution. However, space instruments are vulnerable to the degradation due to the environment while ground based measurements are limited in wavelength range and need atmospheric effects corrections. This is why SSI modeling is necessary to understand the mechanism of the solar irradiance variability and to provide long and uninterrupted irradiance records to climate and Earth atmosphere scientists. Here we present COSI (COde for Solar Irradiance) model of the SSI variability. The COSI model is based on the Non local thermodynamic Equilibrium Spectral SYnthesis Code (NESSY). We validate NESSY by two independent datasets: - The SSI at solar minimum occurring in 2008, - The radius variation with wavelength and absolute values determined from PREMOS and BOS instruments onboard the PICARD spacecraft. Comparisons between modeling and measured SSI will be shown. However, since SSI measurements have an accuracy estimated between 2 to 3%, the comparison with the solar radius data provides a very important additional constrains on model. For that, 17 partial solar occultations by the Moon are used providing solar radii clearly showing the dependence of the solar radius with wavelength. These results are compared with the NESSY predictions. The agreement between NESSY and observations is within the model and measurements accuracy. Title: Solar irradiance observations with PREMOS filter radiometers on the PICARD mission: In-flight performance and data release Authors: Cessateur, G.; Schmutz, W.; Wehrli, C.; Gröbner, J.; Haberreiter, M.; Kretzschmar, M.; Rozanov, E.; Schöll, M.; Shapiro, A.; Thuillier, G.; Egorova, T.; Finsterle, W.; Fox, N.; Hochedez, J. -F.; Koller, S.; Meftah, M.; Meindl, P.; Nyeki, S.; Pfiffner, D.; Roth, H.; Rouzé, M.; Spescha, M.; Tagirov, R.; Werner, L.; Wyss, J. -U. Bibcode: 2016A&A...588A.126C Altcode: Context. The PREcision Monitoring Sensor (PREMOS) is a solar radiometer on board the French PICARD mission that was launched in June 2010 and decommissioned in April 2014.
Aims: The PREMOS radiometer obtains solar irradiance measurements in specific spectral windows in the UV, visible, and near-infrared. In this paper, the PREMOS data and calibration methods are presented.
Methods: Using back-up channels, the degradation can theoretically be assessed to correct operational channels. However, a strong degradation within all PREMOS channels requires the application of additional methods, namely using back-up channels and assessing the degradation via a proxy-based model.
Results: The corrected Level 3 PREMOS data are then used in different contexts in order to be validated. First, the signature of the p-mode are retrieved from the PREMOS data. The Venus transit allows us to empirically determine the intrinsic noise level within the PREMOS high cadence data for the visible and near-infrared channels. We then compare the PREMOS data directly to other data sets, namely from the SOLar-STellar Irradiance Comparison Experiment (SOLSTICE) and the Solar Irradiance Monitor (SIM) instruments on board the SOlar Radiation and Climate Experiment (SORCE) spacecraft. Regarding the UV channels, we found an excellent correlation over the lifetime of the PREMOS mission. The ratio between SORCE and PREMOS observations is always less than 1%. Regarding the SSI measurements in the visible and near-infrared, a comparison of short-term variations (I.e. 27-day modulation) shows a rather good correlation by taking into consideration the intrinsic noise within both SIM and PREMOS observations. Title: Characterization of small-scale heating events in the solar atmosphere from 3D-MHD simulations and their potential role in coronal heating Authors: Guerreiro, Nuno; Haberreiter, Margit; Hansteen, Viggo; Schmutz, Werner Bibcode: 2016EGUGA..1814407G Altcode: Aiming at better understanding the mechanism(s) responsible for the coronal heating and the ubiquitous redshifts observed in the lower transition region we focus on analyzing the properties of small-scale heating events (SSHEs) in the solar atmosphere. We present a comprehensive method to follow SSHEs over time in 3D-MHD simulations of the solar atmosphere. Applying the method we are able to better understand the properties of the SSHEs and how the plasma in their vicinity respond to them. We present results for the lifetime, energy and spectral signatures of the SSHEs. Ultimately, these results will be important for the coordinated scientific exploration of SPICE and EUI along with other interments on board solar orbiter. ​ Title: Solar Spectral Irradiance Observations from the PICARD/PREMOS Radiometer Authors: Cessateur, G.; Schöll, M.; Schmutz, W. K.; Wehrli, C.; Groebner, J.; Haberreiter, M.; Kretzschmar, M.; Shapiro, A.; Thuillier, G. O.; Finsterle, W.; Fox, N.; Hochedez, J. F.; Koller, S.; Meftah, M.; Nyeki, S.; Pfiffner, D.; Roth, H.; Rouze, M.; Spescha, M.; Tagirov, R.; Werner, L.; Wyss, J. Bibcode: 2015AGUFMSH32A..06C Altcode: Space weather and space climate studies require accurate Solar Spectral Irradiance (SSI) observations. The PREcision Monitoring Sensor (PREMOS) instrument aboard the PICARD satellite acquired solar irradiance measurements in specific spectral windows in the UV, visible and near infrared from October 2010 to March 2014. This contribution aims at presenting the Level 3 data, corrected for non solar features as well as for degradation. These level 3 data has been tested over different scientific cases, such as observations during the Venus transit and the presence of the p-mode signature within high-cadence data. The PREMOS Level 3 data have also been compared to others data sets, namely the SOLSTICE and SIM instruments aboard SORCE, for nearly 3 and half years. An excellent correlation has been found for the UV spectral ranges. We have also found a rather good correlation for visible and near-infrared observations for short-term variations, for which an error of about 200 ppm has been estimated within PREMOS visible and near-infrared observations. The PREMOS data could also be used to address several scientific topics, i.e. for validating semi-empirical models of the solar irradiance. We will emphasize about our new irradiance model, COSIR for Code of Solar Irradiance Reconstruction, which is successful at reproducing the solar modulation as seen in the PREMOS, SoHO/Virgo and SORCE data. Title: Characterisation of small-scale heating events in the solar atmosphere from 3D MHD simulations and their potential role in coronal heating Authors: Haberreiter, M.; Guerreiro, N.; Hansteen, V. H.; Schmutz, W. K. Bibcode: 2015AGUFMSH31C2442H Altcode: The physical mechanism that heats the solar corona is one of the still open science questions in solar physics. One of the proposed mechanism for coronal heating are nanoflares. To investigate their role in coronal heating we study the properties of the small-scale heating events in the solar atmosphere using 3D MHD simulations. We present a method to identify and track these heating events in time which allows us to study their life time, energy, and spectral signatures. These spectal signatures will be compared with available spectrosopic observations obtained with IRIS and SUMER. Ultimately, these results will be important for the coordinated scientific exploitation of SPICE and EUI along with other instruments onboard Solar Orbiter to address the coronal heating problem. Title: Small-scale Heating Events in the Solar Atmosphere. I. Identification, Selection, and Implications for Coronal Heating Authors: Guerreiro, N.; Haberreiter, M.; Hansteen, V.; Schmutz, W. Bibcode: 2015ApJ...813...61G Altcode: We present a comprehensive method to analyze small-scale heating events in detail in a 3D magnetohydrodynamics simulation for quiet-Sun conditions. The method determines the number, volume, and some general geometric properties of the small-scale heating events at different instants in a simulation with a volume of 16 × 8 × 16 Mm3, spanning from the top of the convection zone to the corona. We found that there are about 104 small-scale heating events at any instant above the simulated area of 128 Mm2. They occur mainly at heights between 1.5 and 3.0 Mm. We determine the average value of their projected vertical extent, which ranges from 375 to 519 km over time, and we show that height, volume, and energy distribution of the events at any instant resemble power laws. Finally, we demonstrate that larger heating structures are a combination of much smaller heating events and that small-scale heating events dissipate enough energy to maintain the coronal energetic balance at any instant. Title: Erratum: Erratum to: The Infrared Solar Spectrum Measured by the SOLSPEC Spectrometer Onboard the International Space Station Authors: Thuillier, G.; Harder, J. W.; Shapiro, A.; Woods, T. N.; Perrin, J. -M.; Snow, M.; Sukhodolov, T.; Schmutz, W. Bibcode: 2015SoPh..290.3089T Altcode: 2015SoPh..tmp..150T No abstract at ADS Title: The role of the Fraunhofer lines in solar brightness variability Authors: Shapiro, A. I.; Solanki, S. K.; Krivova, N. A.; Tagirov, R. V.; Schmutz, W. K. Bibcode: 2015A&A...581A.116S Altcode: 2015arXiv150705437S Context. The solar brightness varies on timescales from minutes to decades. A clear identification of the physical processes behind such variations is needed for developing and improving physics-based models of solar brightness variability and reconstructing solar brightness in the past. This is, in turn, important for better understanding the solar-terrestrial and solar-stellar connections.
Aims: We estimate the relative contributions of the continuum, molecular, and atomic lines to the solar brightness variations on different timescales.
Methods: Our approach is based on the assumption that variability of the solar brightness on timescales greater than a day is driven by the evolution of the solar surface magnetic field. We calculated the solar brightness variations employing the solar disc area coverage of magnetic features deduced from the MDI/SOHO observations. The brightness contrasts of magnetic features relative to the quiet Sun were calculated with a non-LTE radiative transfer code as functions of disc position and wavelength. By consecutive elimination of molecular and atomic lines from the radiative transfer calculations, we assessed the role of these lines in producing solar brightness variability.
Results: We show that the variations in Fraunhofer lines define the amplitude of the solar brightness variability on timescales greater than a day and even the phase of the total solar irradiance variability over the 11-year cycle. We also demonstrate that molecular lines make substantial contribution to solar brightness variability on the 11-year activity cycle and centennial timescales. In particular, our model indicates that roughly a quarter of the total solar irradiance variability over the 11-year cycle originates in molecular lines. The maximum of the absolute spectral brightness variability on timescales greater than a day is associated with the CN violet system between 380 and 390 nm. Title: The extreme UV imager telescope on-board the Solar Orbiter mission: overview of phase C and D Authors: Halain, J. -P.; Rochus, P.; Renotte, E.; Hermans, A.; Jacques, L.; Auchère, F.; Berghmans, D.; Harra, L.; Schühle, U.; Schmutz, W.; Zhukov, A.; Aznar Cuadrado, R.; Delmotte, F.; Dumesnil, C.; Gyo, M.; Kennedy, T.; Smith, P.; Tandy, J.; Mercier, R.; Verbeeck, C. Bibcode: 2015SPIE.9604E..0GH Altcode: The Solar Orbiter mission is composed of ten scientific instruments dedicated to the observation of the Sun's atmosphere and its heliosphere, taking advantage of an out-of ecliptic orbit and at perihelion reaching a proximity close to 0.28 A.U. On board Solar Orbiter, the Extreme Ultraviolet Imager (EUI) will provide full-Sun image sequences of the solar corona in the extreme ultraviolet (17.1 nm and 30.4 nm), and high-resolution image sequences of the solar disk in the extreme ultraviolet (17.1 nm) and in the vacuum ultraviolet (121.6 nm). The EUI concept uses heritage from previous similar extreme ultraviolet instrument. Additional constraints from the specific orbit (thermal and radiation environment, limited telemetry download) however required dedicated technologies to achieve the scientific objectives of the mission. The development phase C of the instrument and its sub-systems has been successfully completed, including thermomechanical and electrical design validations with the Structural Thermal Model (STM) and the Engineering Model (EM). The instrument STM and EM units have been integrated on the respective spacecraft models and will undergo the system level tests. In parallel, the Phase D has been started with the sub-system qualifications and the flight parts manufacturing. The next steps of the EUI development will be the instrument Qualification Model (QM) integration and qualification tests. The Flight Model (FM) instrument activities will then follow with the acceptance tests and calibration campaigns. Title: The Infrared Solar Spectrum Measured by the SOLSPEC Spectrometer Onboard the International Space Station Authors: Thuillier, G.; Harder, J. W.; Shapiro, A.; Woods, T. N.; Perrin, J. -M.; Snow, M.; Sukhodolov, T.; Schmutz, W. Bibcode: 2015SoPh..290.1581T Altcode: 2015SoPh..tmp...75T A solar spectrum extending from the extreme ultraviolet to the near-infrared is an important input for solar physics, climate research, and atmospheric physics. Ultraviolet measurements have been conducted since the beginning of the space age, but measurements throughout the contiguous visible and infrared (IR) regions are much more sparse. Ageing is a key problem throughout the entire spectral domain, but most of the effort extended to understand degradation was concentrated on the ultraviolet spectral region, and these mechanisms may not be appropriate in the IR. This problem is further complicated by the scarcity of long-term data sets. Onboard the International Space Station, the SOLSPEC spectrometer measured an IR solar spectral irradiance lower than the one given by ATLAS 3, e.g. by about 7 % at 1 700 nm. We here evaluate the consequences of the lower solar spectral irradiance measurements and present a re-analysis of the on-orbit calibration lamp and solar data trend, which lead to a revised spectrum. Title: A Chandra Observation of the Eclipsing Wolf-Rayet Binary CQ Cep Authors: Skinner, Stephen L.; Zhekov, Svetozar A.; Güdel, Manuel; Schmutz, Werner Bibcode: 2015ApJ...799..124S Altcode: 2014arXiv1411.4075S The short-period (1.64 d) near-contact eclipsing WN6+O9 binary system CQ Cep provides an ideal laboratory for testing the predictions of X-ray colliding wind shock theory at close separation where the winds may not have reached terminal speeds before colliding. We present results of a Chandra X-ray observation of CQ Cep spanning ~1 day during which a simultaneous Chandra optical light curve was acquired. Our primary objective was to compare the observed X-ray properties with colliding wind shock theory, which predicts that the hottest shock plasma (T >~ 20 MK) will form on or near the line-of-centers between the stars. The X-ray spectrum is strikingly similar to apparently single WN6 stars such as WR 134 and spectral lines reveal plasma over a broad range of temperatures T ~ 4-40 MK. A deep optical eclipse was seen as the O star passed in front of the Wolf-Rayet star and we determine an orbital period P orb = 1.6412400 d. Somewhat surprisingly, no significant X-ray variability was detected. This implies that the hottest X-ray plasma is not confined to the region between the stars, at odds with the colliding wind picture and suggesting that other X-ray production mechanisms may be at work. Hydrodynamic simulations that account for such effects as radiative cooling and orbital motion will be needed to determine if the new Chandra results can be reconciled with the colliding wind picture. Title: A Chandra Observation of the Eclipsing Wolf-Rayet Binary CQ Cep Authors: Skinner, Steve L.; Zhekov, Svetozar; Guedel, Manuel; Schmutz, Werner Bibcode: 2015AAS...22534412S Altcode: The short-period (1.64 day) near-contact eclipsing WN6+O9 binary system CQ Cep provides an ideal laboratory for testing the predictions of X-ray colliding wind shock theory at close separation where the winds may not have reached terminal speeds before colliding. We present results of a Chandra X-ray observation of CQ Cep spanning one day during which a simultaneous Chandra optical light curve was acquired. Our primary objective was to compare the observed X-ray properties with colliding wind shock theory, which predicts that the hottest shock plasma (T > 20 MK) will form on or near the line-of-centers between the stars. The X-ray spectrum is strikingly similar to apparently single WN6 stars such as WR 134 and spectral lines reveal plasma over a broad range of temperatures T ~ 4 - 40 MK. A deep optical eclipse was seen as the O star passed in front of the Wolf-Rayet star but, surprisingly, no significant X-ray variability was detected. Because of the high inclination orbit, this implies that the hottest X-ray plasma is not confined to the region between the stars, at odds with the colliding wind shock picture. We will summarize the Chandra results in the context of predictions from colliding wind theory. Title: Solar Spectral Irradiance Variability in November/December 2012: Comparison of Observations by Instruments on the International Space Station and Models Authors: Thuillier, G.; Schmidtke, G.; Erhardt, C.; Nikutowski, B.; Shapiro, A. I.; Bolduc, C.; Lean, J.; Krivova, N.; Charbonneau, P.; Cessateur, G.; Haberreiter, M.; Melo, S.; Delouille, V.; Mampaey, B.; Yeo, K. L.; Schmutz, W. Bibcode: 2014SoPh..289.4433T Altcode: 2014SoPh..tmp..120T Onboard the International Space Station (ISS), two instruments are observing the solar spectral irradiance (SSI) at wavelengths from 16 to 2900 nm. Although the ISS platform orientation generally precludes pointing at the Sun more than 10 - 14 days per month, in November/December 2012 a continuous period of measurements was obtained by implementing an ISS `bridging' maneuver. This enabled observations to be made of the solar spectral irradiance (SSI) during a complete solar rotation. We present these measurements, which quantify the impact of active regions on SSI, and compare them with data simultaneously gathered from other platforms, and with models of spectral irradiance variability. Our analysis demonstrates that the instruments onboard the ISS have the capability to measure SSI variations consistent with other instruments in space. A comparison among all available SSI measurements during November-December 2012 in absolute units with reconstructions using solar proxies and observed solar activity features is presented and discussed in terms of accuracy. Title: Variability of Sun-like stars: reproducing observed photometric trends Authors: Shapiro, A. I.; Solanki, S. K.; Krivova, N. A.; Schmutz, W. K.; Ball, W. T.; Knaack, R.; Rozanov, E. V.; Unruh, Y. C. Bibcode: 2014A&A...569A..38S Altcode: 2014arXiv1406.2383S Context. The Sun and stars with low magnetic activity levels become photometrically brighter when their activity increases. Magnetically more active stars display the opposite behavior and become fainter when their activity increases.
Aims: We reproduce the observed photometric trends in stellar variations with a model thattreats stars as hypothetical suns with coverage by magnetic features different from that of the Sun.
Methods: The model attributes the variability of stellar spectra to the imbalance between the contributions from different components of the solar atmosphere, such as dark starspots and bright faculae. A stellar spectrum is calculated from spectra of the individual components by weighting them with corresponding disk-area coverages. The latter are obtained by extrapolating the solar dependences of spot and facular disk-area coverages on chromospheric activity to stars with different levels of mean chromospheric activity.
Results: We find that the contribution by starspots to the variability increases faster with chromospheric activity than the facular contribution. This causes the transition from faculae-dominated variability and direct activity-brightness correlation to spot-dominated variability and inverse activity-brightness correlation with increasing chromospheric activity level. We show that the regime of the variability also depends on the angle between the stellar rotation axis and the line-of-sight and on the latitudinal distribution of active regions on the stellar surface. Our model can be used as a tool for extrapolating the observed photometric variability of the Sun to Sun-like stars at different activity levels, which makes a direct comparison between solar and stellar irradiance data possible.

Appendices are available in electronic form at http://www.aanda.org Title: The extreme UV imager of solar orbiter: from detailed design to flight model Authors: Halain, J. -P.; Rochus, P.; Renotte, E.; Auchère, F.; Berghmans, D.; Harra, L.; Schühle, U.; Schmutz, W.; Zhukov, A.; Aznar Cuadrado, R.; Delmotte, F.; Dumesnil, C.; Gyo, M.; Kennedy, T.; Mercier, R.; Verbeeck, F.; Thome, M.; Heerlein, K.; Hermans, A.; Jacques, L.; Mazzoli, A.; Meining, S.; Rossi, L.; Tandy, J.; Smith, P.; Winter, B. Bibcode: 2014SPIE.9144E..08H Altcode: The Extreme Ultraviolet Imager (EUI) on-board the Solar Orbiter mission will provide full-sun and high-resolution image sequences of the solar atmosphere at selected spectral emission lines in the extreme and vacuum ultraviolet. After the breadboarding and prototyping activities that focused on key technologies, the EUI project has completed the design phase and has started the final manufacturing of the instrument and its validation. The EUI instrument has successfully passed its Critical Design Review (CDR). The process validated the detailed design of the Optical Bench unit and of its sub-units (entrance baffles, doors, mirrors, camera, and filter wheel mechanisms), and of the Electronic Box unit. In the same timeframe, the Structural and Thermal Model (STM) test campaign of the two units have been achieved, and allowed to correlate the associated mathematical models. The lessons learned from STM and the detailed design served as input to release the manufacturing of the Qualification Model (QM) and of the Flight Model (FM). The QM will serve to qualify the instrument units and sub-units, in advance of the FM acceptance tests and final on-ground calibration. Title: The Solar Irradiance Spectrum at Solar Activity Minimum Between Solar Cycles 23 and 24 Authors: Thuillier, G.; Bolsée, D.; Schmidtke, G.; Foujols, T.; Nikutowski, B.; Shapiro, A. I.; Brunner, R.; Weber, M.; Erhardt, C.; Hersé, M.; Gillotay, D.; Peetermans, W.; Decuyper, W.; Pereira, N.; Haberreiter, M.; Mandel, H.; Schmutz, W. Bibcode: 2014SoPh..289.1931T Altcode: On 7 February 2008, the SOLAR payload was placed onboard the International Space Station. It is composed of three instruments, two spectrometers and a radiometer. The two spectrometers allow us to cover the 16 - 2900 nm spectral range. In this article, we first briefly present the instrumentation, its calibration and its performance in orbit. Second, the solar spectrum measured during the transition between Solar Cycles 23 to 24 at the time of the minimum is shown and compared with other data sets. Its accuracy is estimated as a function of wavelength and the solar atmosphere brightness-temperature is calculated and compared with those derived from two theoretical models. Title: Reconstruction of the solar EUV irradiance as observed with PROBA2/LYRA Authors: Haberreiter, Margit; Delouille, Veronique; Del Zanna, Giulio; Ermolli, Ilaria; Kretzschmar, Matthieu; Mampeay, Benjamin; Dominique, Marie; Schmutz, Werner Bibcode: 2014EGUGA..1614449H Altcode: The solar EUV spectrum has important effects on the upper atmosphere of the Earth and any planet. For a detailed investigation of these effects it is important to have a constistent data series of the EUV spectral irradiance available. Here, we present the reconstruction of the solar EUV irradiance based on PSPT and SOHO/EIT images and along with synthetic spectra calculated for six different coronal features representing the brightness variation of the solar atmosphere. The EIT images are segmented with the SPoCA tool which allows to identify the features based on a consistent brightness classification for each feature. With the SOLMOD code we then calculate intensity spectra for 10 nm to 100 nm for each of the coronal feature. Weighting the intensity spectra with the area covered by each of the features yields the temporal variation of the EUV spectrum. The reconstructed time series is then validated against the spectral irradiance as observed with PROBA2/LYRA. This is an important step towards the understanding of the variations of the solar EUV spectrum and ultimately its detailed effect on the Earth's upper atmosphere. Title: Analysis of Different Solar Spectral Irradiance Reconstructions and Their Impact on Solar Heating Rates Authors: Thuillier, G.; Melo, S. M. L.; Lean, J.; Krivova, N. A.; Bolduc, C.; Fomichev, V. I.; Charbonneau, P.; Shapiro, A. I.; Schmutz, W.; Bolsée, D. Bibcode: 2014SoPh..289.1115T Altcode: Proper numerical simulation of the Earth's climate change requires reliable knowledge of solar irradiance and its variability on different time scales, as well as the wavelength dependence of this variability. As new measurements of the solar spectral irradiance have become available, so too have new reconstructions of historical solar irradiance variations, based on different approaches. However, these various solar spectral irradiance reconstructions have not yet been compared in detail to quantify differences in their absolute values, variability, and implications for climate and atmospheric studies. In this paper we quantitatively compare five different reconstructions of solar spectral irradiance changes during the past four centuries, in order to document and analyze their differences. The impact on atmosphere and climate studies is discussed in terms of the calculation of short wave solar heating rates. Title: The PREMOS/PICARD Radiometer: An overview after 3 years of observations Authors: Cessateur, Gaël; Schmutz, Werner; Shapiro, Alexander Bibcode: 2014cosp...40E.469C Altcode: Total and Spectral Solar Irradiance are key input parameters to atmospheric/oceanic and space weather models. We present here spectral solar irradiance data from the radiometer PREMOS onboard the PICARD satellite for three years, which covers covers the solar spectrum from the Ultraviolet to near-infrared. We will also introduce the algorithm COCOSIS (for Combination of COSI Spectra) which allows us to retrieve the solar variability of the irradiance. Our investigation shows that COCOSIS is highly successful at reproducing solar spectral irradiance over rotational periods for most of channels from PREMOS. Title: The TSI record from PREMOS/PICARD Authors: Schmutz, Werner; Thuillier, Gerard; Finsterle, Wolfgang; Walter, Benjamin; Fehlmann, Andre Bibcode: 2014cosp...40E2931S Altcode: Since the launch of PICARD in 2010 the PMO6 absolute radiometers of the PREMOS experiment had been measuring Total Solar Irradiance. We will present the TSI data record, corrected for sensor degradation, and review the stability of the radiometers during the entire mission. Implications for the uncertainty of Composite Total Solar Irradiance time Series data sets will be discussed. Title: Middle atmosphere heating rate and photolysis response to the uncertainties in spectral solar irradiance data Authors: Sukhodolov, Timofei; Schmutz, Werner; Shapiro, Alexander; Tourpali, Kleareti; Peter, Thomas; Rozanov, Eugene; Bais, Alkiviadis; Telford, Paul Bibcode: 2014cosp...40E3225S Altcode: Solar radiation is the main source of energy for the Earth’s atmosphere and in many respects defines its composition, photochemistry, temperature profile and dynamics. Therefore, the uncertainties in the magnitude and spectral composition of the spectral solar irradiance (SSI) evolution during the declining phase of 23rd solar cycle have substantial implications for the modeling of the middle atmosphere evolution, leading to a pronounced differences in the heating rates and also affecting photolysis rates. To estimate the role of SSI uncertainties we have compared the most important photolysis rates (O2, O3, and NO2) and heating rates calculated with the reference radiation code libRadtran using SSI for June 2004 and February 2009 obtained from two models (NRL, COSI) and one observation data set based on SORCE observations. We have also evaluated the ability of the several photolysis and heating rates calculation methods widely used in atmospheric models to reproduce the absolute values of the photolysis rates and their response to the implied SSI changes. Title: Identification and characterization of small-scale heating events in the solar atmosphere from 3D MHD simulations Authors: Guerreiro, Nuno; Haberreiter, Margit; Schmutz, Werner; Hansteen, Viggo Bibcode: 2014cosp...40E1095G Altcode: We studied the properties of small scale heating events (in the nano and micro-flare regime) in the solar atmosphere using existing 3D MHD simulations. We put forward a method for event identification and categorization. We determine the spatial extend of the events and their frequency and energy distributions. These results aim at improving the understanding of small scale heating events and their role for the heating of the solar corona. Title: Assessment of the spectral solar cycle variations in the visual and near IR from VIRGI/SOHO data Authors: Schmutz, Werner; Haberreiter, Margit; Shapiro, Alexander; Cessateur, Gaël; Wehrli, Christoph; Adams, Wilnelia Bibcode: 2014cosp...40E2929S Altcode: According to Harder et al. (2009) SIM measurements onboard the SORCE satellite reveal a several times higher spectral solar variability in UV than previously estimated. In compensation, to maintain the known amplitude of the Total Solar Irradiance variations, the visual was observed to be in anti-phase. Haigh et al. (2010) has demonstrated that this different-then-thought wavelength dependence has profound implications for the response of the terrestrial climate. In Wehrli et al. (A&A 556, L3 2013) we have presented evidence that annual averages of the VIRGO filter radiometer data in the 500 nm channel are significantly positively correlated with TSI. In this presentation we present an update including the most recent SPM VIRGO radiometer data and give an estimate of the amplitudes of the spectral solar cycle variations in the VIRGO channels. The implication is that the highly significant positive correlation at 500 nm excludes the postulated anti-phase solar cycle variations at this wavelength. Harder et al. (2009) also published large UV variations and this proposal is assessed from the point of view that Total Solar Irradiance Variations are know. It is concluded that large UV amplitudes, as proposed, are not excluded even if the 500 nm variations are in-phase with the solar cycle, given the amplitudes measured in the VIRGO/SOHO channels. Title: CLARA - A compact and light-weight absolute radiometer on the NORSAT-1 mission Authors: Schmutz, Werner; Finsterle, Wolfgang; Walter, Benjamin; Suter, Markus; Andersen, Bo; Osmundsen, Magne Bibcode: 2014cosp...40E2930S Altcode: PMOD/WRC is building the Compact and Light-weight Absolut RAdiometer (CLARA) to fly on the Norwegian Space Centre's (NCS) NORSAT-1 mission. CLARA is based on a new design by PMOD/WRC which minimizes size and weight while improving the radiometric performance. The NORSAT-1 mission is planned to be launched to a polar LEO in Q4 2015 or Q1 2016. NSC intends to extend the initial three-years mission for as long as the platform and payload remain functional. Title: On-Orbit Degradation of Solar Instruments Authors: BenMoussa, A.; Gissot, S.; Schühle, U.; Del Zanna, G.; Auchère, F.; Mekaoui, S.; Jones, A. R.; Walton, D.; Eyles, C. J.; Thuillier, G.; Seaton, D.; Dammasch, I. E.; Cessateur, G.; Meftah, M.; Andretta, V.; Berghmans, D.; Bewsher, D.; Bolsée, D.; Bradley, L.; Brown, D. S.; Chamberlin, P. C.; Dewitte, S.; Didkovsky, L. V.; Dominique, M.; Eparvier, F. G.; Foujols, T.; Gillotay, D.; Giordanengo, B.; Halain, J. P.; Hock, R. A.; Irbah, A.; Jeppesen, C.; Judge, D. L.; Kretzschmar, M.; McMullin, D. R.; Nicula, B.; Schmutz, W.; Ucker, G.; Wieman, S.; Woodraska, D.; Woods, T. N. Bibcode: 2013SoPh..288..389B Altcode: 2013arXiv1304.5488B We present the lessons learned about the degradation observed in several space solar missions, based on contributions at the Workshop about On-Orbit Degradation of Solar and Space Weather Instruments that took place at the Solar Terrestrial Centre of Excellence (Royal Observatory of Belgium) in Brussels on 3 May 2012. The aim of this workshop was to open discussions related to the degradation observed in Sun-observing instruments exposed to the effects of the space environment. This article summarizes the various lessons learned and offers recommendations to reduce or correct expected degradation with the goal of increasing the useful lifespan of future and ongoing space missions. Title: Correlation of spectral solar irradiance with solar activity as measured by VIRGO Authors: Wehrli, C.; Schmutz, W.; Shapiro, A. I. Bibcode: 2013A&A...556L...3W Altcode: 2013arXiv1307.1285W Context. The variability of solar spectral irradiance (SSI) over the rotational period and its trend over the solar activity cycle are important for understanding the Sun-Earth connection as well as for observational constraints for solar models. Recently the Spectral Irradiance Monitor (SIM) experiment on the Solar Radiation and Climate Experiment (SORCE) has published an unexpected negative correlation with total solar irradiance (TSI) of the visible spectral range. It is compensated by a strong and positive variability of the near UV range.
Aims: We aim to verify whether the anti-correlated SIM-trend in the visible can be confirmed by independent observations of the Variability of solar IRadiance and Gravity Oscillations (VIRGO) experiment on the SOlar and Heliospheric Observatory (SOHO) satellite. The challenge of all space experiments measuring solar irradiance are sensitivity changes of their sensors due to exposure to intense UV radiation, which are difficult to assess in orbit.
Methods: We exclude the first six years prior to 2002 where one or more fast processes contributed to instrumental changes and analyse a ten-year timeseries of VIRGO sun photometer data between 2002 and 2012. The variability of SSI is correlated with the variability of the TSI, which is taken as a proxy for solar activity.
Results: Observational evidence indicates that after six years only one single long-term process governs the degradation of the backup sun photometer in VIRGO which is operated once a month. This degradation can be well approximated by a linear function over ten years. The analysis of the residuals from the linear trend yield robust positive correlations of spectral irradiance at 862, 500, and 402 nm with total irradiance. In the analysis of annual averages of these data the positive correlations change into weak negative correlations, but with little statistical significance for the 862 nm and 402 nm data. At 500 nm the annual spectral data are still positively correlated with TSI. The persisting positive correlation at 500 nm is in contradiction to the SIM results.

Appendix A is available in electronic form at http://www.aanda.org Title: The LYRA Instrument Onboard PROBA2: Description and In-Flight Performance Authors: Dominique, M.; Hochedez, J. -F.; Schmutz, W.; Dammasch, I. E.; Shapiro, A. I.; Kretzschmar, M.; Zhukov, A. N.; Gillotay, D.; Stockman, Y.; BenMoussa, A. Bibcode: 2013SoPh..286...21D Altcode: 2013arXiv1302.6525D The Large Yield Radiometer (LYRA) is an XUV-EUV-MUV (soft X-ray to mid-ultraviolet) solar radiometer onboard the European Space Agency Project for On-Board Autonomy 2 (PROBA2) mission, which was launched in November 2009. LYRA acquires solar-irradiance measurements at a high cadence (nominally 20 Hz) in four broad spectral channels, from soft X-ray to MUV, which have been chosen for their relevance to solar physics, space weather, and aeronomy. We briefly review the design of the instrument, give an overview of the data products distributed through the instrument website, and describe how the data are calibrated. We also briefly present a summary of the main fields of research currently under investigation by the LYRA consortium. Title: Impact of a potential 21st century "grand solar minimum" on surface temperatures and stratospheric ozone Authors: Anet, J. G.; Rozanov, E. V.; Muthers, S.; Peter, T.; BröNnimann, S.; Arfeuille, F.; Beer, J.; Shapiro, A. I.; Raible, C. C.; Steinhilber, F.; Schmutz, W. K. Bibcode: 2013GeoRL..40.4420A Altcode: We investigate the effects of a recently proposed 21st century Dalton minimum like decline of solar activity on the evolution of Earth's climate and ozone layer. Three sets of two member ensemble simulations, radiatively forced by a midlevel emission scenario (Intergovernmental Panel on Climate Change RCP4.5), are performed with the atmosphere-ocean chemistry-climate model AOCCM SOCOL3-MPIOM, one with constant solar activity, the other two with reduced solar activity and different strength of the solar irradiance forcing. A future grand solar minimum will reduce the global mean surface warming of 2 K between 1986-2005 and 2081-2100 by 0.2 to 0.3 K. Furthermore, the decrease in solar UV radiation leads to a significant delay of stratospheric ozone recovery by 10 years and longer. Therefore, the effects of a solar activity minimum, should it occur, may interfere with international efforts for the protection of global climate and the ozone layer. Title: Detection of Solar Rotational Variability in the Large Yield RAdiometer (LYRA) 190 - 222 nm Spectral Band Authors: Shapiro, A. V.; Shapiro, A. I.; Dominique, M.; Dammasch, I. E.; Wehrli, C.; Rozanov, E.; Schmutz, W. Bibcode: 2013SoPh..286..289S Altcode: 2012arXiv1205.2377S; 2012SoPh..tmp..121S We analyze the variability of the spectral solar irradiance during the period from 7 January 2010 until 20 January 2010 as measured by the Herzberg channel (190 - 222 nm) of the Large Yield RAdiometer (LYRA) onboard PROBA2. In this period of time, observations by the LYRA nominal unit experienced degradation and the signal produced by the Herzberg channel frequently jumped from one level to another. Both factors significantly complicate the analysis. We present the algorithm that allowed us to extract the solar variability from the LYRA data and compare the results with SORCE/SOLSTICE measurements and with modeling based on the Code for the Solar Irradiance (COSI). Title: Eclipses Observed by Large Yield RAdiometer (LYRA) - A Sensitive Tool to Test Models for the Solar Irradiance Authors: Shapiro, A. I.; Schmutz, W.; Dominique, M.; Shapiro, A. V. Bibcode: 2013SoPh..286..271S Altcode: 2012SoPh..tmp..171S; 2012arXiv1201.6546S We analyze the light curves of the recent solar eclipses measured by the Herzberg channel (200 - 220 nm) of the Large Yield RAdiometer (LYRA) onboard Project for OnBoard Autonomy (PROBA2). The measurements allow us to accurately retrieve the center-to-limb variations (CLV) of the solar brightness. The formation height of the radiation depends on the observing angle, so the examination of the CLV provide information about a broad range of heights in the solar atmosphere. We employ the 1D NLTE radiative transfer COde for Solar Irradiance (COSI) to model the measured light curves and corresponding CLV dependencies. The modeling is used to test and constrain the existing 1D models of the solar atmosphere, e.g. the temperature structure of the photosphere and the treatment of the pseudo-continuum opacities in the Herzberg continuum range. We show that COSI can accurately reproduce not only the irradiance from the entire solar disk, but also the measured CLV. Hence it can be used as a reliable tool for modeling the variability of the spectral solar irradiance. Title: The latitudinal dependence of the solar radiance Authors: Finsterle, Wolfgang; Shapiro, Alexander; Schmutz, Werner; Krivova, Natalie Bibcode: 2013EGUGA..1511672F Altcode: Active regions and sunspots occur predominantly at low to mid heliographic latitudes. Hence, it seems reasonable to assume that the radiant output of the sun is not spherically symmetrical. Due to the relatively small inclination (~7.25°) of the solar rotation axis this asphericity is difficult to detect in integrated disk data taken from an ecliptic-bound vantage point. A histogram analysis of 13 years of VIRGO TSI data revealed a slight north-south asymmetry with maximal deviations of ±4 parts in 10^5. Interestingly, the north-south asymmetry persists even after subtracting the simulated TSI data by Krivova et al. (2003) from the VIRGO TSI measurements. The Krivova time series attributes the TSI to magnetic activity patterns as observed by MDI (sunspots, faculae, and plage). The asymmetry thus seems to be of a different origin, i.e. unrelated to sunspots, faculae, or plage, although smaller magnetic structures might contribute to the asymmetry. We will also investigate a potential asymmetry in the equator-to-pole temperature gradient. At this point we can only speculate if the observed asymmetry is characteristic of solar cycle 23, which is covered by the VIRGO time series, or more fundamental. In any case it would be very interesting to extend the TSI vs. latitude curve towards higher heliographic latitudes. Title: A Collaborative FP7 Effort towards the First European Comprehensive SOLar Irradiance Data Exploitation (SOLID) Authors: Haberreiter, Margit; Dasi, Maria; Delouille, Veronique; Del Zanna, Giulio; Dudok de Wit, Thierry; Ermolli, Ilaria; Kretzschmar, Matthieu; Krivova, Natalie; Mason, Helen; Qahwaji, Rami; Schmutz, Werner; Solanki, Sami; Thuillier, Gerard; Tourpali, Kleareti; Unruh, Yvonne; Verbeeck, Cis; Weber, Mark; Woods, Tom Bibcode: 2013EGUGA..1513079H Altcode: Variations of solar irradiance are the most important natural factor in the terrestrial climate and as such, the time dependent spectral solar irradiance is a crucial input to any climate modelling. There have been previous efforts to compile solar irradiance but it is still uncertain by how much the spectral and total solar irradiance changed on yearly, decadal and longer time scales. Observations of irradiance data exist in numerous disperse data sets. Therefore, it is important to bring together the European expertise in the field to analyse and merge the complete set of European irradiance data, complemented by archive data that include data from non-European missions. We report on the initiation of a collaborative effort to unify representatives from all European solar space experiments and European teams specialized in multi-wavelength solar image processing. It is intended to include the European groups involved in irradiance modelling and reconstruction. They will work with two different state of the art approaches to produce reconstructed spectral and total solar irradiance data as a function of time. These results will be used to bridge gaps in time and wavelength coverage of the observational data. This will allow the proposing SOLID team to reduce the uncertainties in the irradiance time series - an important requirement by the climate community - and to provide uniform data sets of modelled and observed solar irradiance data from the beginning of the space era to the present including proper error and uncertainty estimates. Climate research needs these data sets and therefore, the primary benefit is for the climate community, but the stellar community, planetary, lunar, and ionospheric researchers are also interested in having at their disposition incident radiation of the Sun. The proposing team plans to realize a wide international synergy in solar physics from 7 European countries, and collaborators from the US, complemented by representatives from the climate community, who will accompany their research work with wide dissemination activities. Title: Modeling the variability of Sun-like stars Authors: Shapiro, Alexander; Knaack, Reto; Krivova, Natalie; Schmutz, Werner; Solanki, Sami; Unruh, Yvonne Bibcode: 2013EGUGA..15.9981S Altcode: We present a model which attributes the variability of the stellar radiative energy flux to the imbalance between the contributions from dark starspots and bright faculae. The stellar radiative energy flux variations are modeled from the individual component's spectra, by weighting them with corresponding filling factors. The filling factors are deduced by extrapolating the sunspot and facular filling factors dependencies on solar CaII S-index to stars with different levels of the chromospheric activity. Our approach allows us to model the stellar photometric variability vs. activity dependency and reproduce the transition from spot-dominated to facula-dominated regimes of variability. We show how the effect of inclination (arising due to the random position of the Earth-bound observer relative to the directions of stellar rotational axis) can affect these dependencies and present the modeling of the individual stellar photometric light curves. Title: VizieR Online Data Catalog: Sun chromospheric CaII-HK emission (Shapiro+, 2013) Authors: Shapiro, A. I.; Schmutz, W.; Cessateur, G.; Rozanov, E. Bibcode: 2013yCat..35520114S Altcode: 2013yCat..35529114S Monitoring of the photometric and chromospheric HK emission data series of stars similar to the Sun in age and average activity level showed that there is an empirical correlation between the average stellar chromospheric activity level and the photometric variability. In general, more active stars show larger photometric variability. Interestingly, the measurements and reconstructions of the solar irradiance show that the Sun is significantly less variable than indicated by the empirical relationship.

We aim to identify possible reasons for the Sun to be currently outside of this relationship.

We employed different scenarios of solar HK emission and irradiance variability and compared them with available time series of Sun-like stars.

(6 data files). Title: What can we learn about the Sun with PREMOS/PICARD? Authors: Cessateur, Gaël; Shapiro, Alexander; Schmutz, Werner; Krivova, Natalie; Solanki, Sami K.; Yeo, Kok Leng; Thuillier, Gérard Bibcode: 2013EGUGA..1511720C Altcode: Total and Spectral Solar Irradiance are key input parameters to atmospheric/oceanic and space weather models. We present here spectral solar irradiance data from the radiometer PREMOS onboard the PICARD satellite. This instrument convers the solar spectrum from the Ultraviolet to near-infrared, and provides valuable information and nourishes theoretical models. Based on redundancy strategies, instrumental degradation has been mostly corrected, revealing surprising behavior from the visible and near-infrared filters. We compare these data with those from the VIRGO/SOHO and SOLSTIC/SORCE experiments. Finally we use COSI to model the variability of the irradiance, assuming that the latter is determined by the evolution of the solar surface magnetic field as seen with SDO/HMI data. A direct comparison shows a very good correlation for most of channels from PREMOS. Title: Recent variability of the solar spectral irradiance and its impact on climate modelling Authors: Ermolli, I.; Matthes, K.; Dudok de Wit, T.; Krivova, N. A.; Tourpali, K.; Weber, M.; Unruh, Y. C.; Gray, L.; Langematz, U.; Pilewskie, P.; Rozanov, E.; Schmutz, W.; Shapiro, A.; Solanki, S. K.; Woods, T. N. Bibcode: 2013ACP....13.3945E Altcode: 2012ACPD...1224557E; 2013arXiv1303.5577E The lack of long and reliable time series of solar spectral irradiance (SSI) measurements makes an accurate quantification of solar contributions to recent climate change difficult. Whereas earlier SSI observations and models provided a qualitatively consistent picture of the SSI variability, recent measurements by the SORCE (SOlar Radiation and Climate Experiment) satellite suggest a significantly stronger variability in the ultraviolet (UV) spectral range and changes in the visible and near-infrared (NIR) bands in anti-phase with the solar cycle. A number of recent chemistry-climate model (CCM) simulations have shown that this might have significant implications on the Earth's atmosphere. Motivated by these results, we summarize here our current knowledge of SSI variability and its impact on Earth's climate.

We present a detailed overview of existing SSI measurements and provide thorough comparison of models available to date. SSI changes influence the Earth's atmosphere, both directly, through changes in shortwave (SW) heating and therefore, temperature and ozone distributions in the stratosphere, and indirectly, through dynamical feedbacks. We investigate these direct and indirect effects using several state-of-the art CCM simulations forced with measured and modelled SSI changes. A unique asset of this study is the use of a common comprehensive approach for an issue that is usually addressed separately by different communities.

We show that the SORCE measurements are difficult to reconcile with earlier observations and with SSI models. Of the five SSI models discussed here, specifically NRLSSI (Naval Research Laboratory Solar Spectral Irradiance), SATIRE-S (Spectral And Total Irradiance REconstructions for the Satellite era), COSI (COde for Solar Irradiance), SRPM (Solar Radiation Physical Modelling), and OAR (Osservatorio Astronomico di Roma), only one shows a behaviour of the UV and visible irradiance qualitatively resembling that of the recent SORCE measurements. However, the integral of the SSI computed with this model over the entire spectral range does not reproduce the measured cyclical changes of the total solar irradiance, which is an essential requisite for realistic evaluations of solar effects on the Earth's climate in CCMs.

We show that within the range provided by the recent SSI observations and semi-empirical models discussed here, the NRLSSI model and SORCE observations represent the lower and upper limits in the magnitude of the SSI solar cycle variation.

The results of the CCM simulations, forced with the SSI solar cycle variations estimated from the NRLSSI model and from SORCE measurements, show that the direct solar response in the stratosphere is larger for the SORCE than for the NRLSSI data. Correspondingly, larger UV forcing also leads to a larger surface response.

Finally, we discuss the reliability of the available data and we propose additional coordinated work, first to build composite SSI data sets out of scattered observations and to refine current SSI models, and second, to run coordinated CCM experiments. Title: The place of the Sun among the Sun-like stars Authors: Shapiro, A. I.; Schmutz, W.; Cessateur, G.; Rozanov, E. Bibcode: 2013A&A...552A.114S Altcode: 2013arXiv1303.2245S Context. Monitoring of the photometric and chromospheric HK emission data series of stars similar to the Sun in age and average activity level showed that there is an empirical correlation between the average stellar chromospheric activity level and the photometric variability. In general, more active stars show larger photometric variability. Interestingly, the measurements and reconstructions of the solar irradiance show that the Sun is significantly less variable than indicated by the empirical relationship.
Aims: We aim to identify possible reasons for the Sun to be currently outside of this relationship.
Methods: We employed different scenarios of solar HK emission and irradiance variability and compared them with available time series of Sun-like stars.
Results: We show that the position of the Sun on the diagram of photometric variability versus chromospheric activity changes with time. The present solar position is different from its temporal mean position as the satellite era of continuous solar irradiance measurements has accidentally coincided with a period of unusually high and stable solar activity. Our analysis suggests that although present solar variability is significantly smaller than indicated by the stellar data, the temporal mean solar variability might be in agreement with the stellar data. We propose that the continuation of the photometric program and its expansion to a larger stellar sample will ultimately allow us to constrain the historical solar variability.

Appendices A and B are available in electronic form at http://www.aanda.orgAll time series are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/552/A114 Title: Modeling the detailed Lyman-α line profile Authors: Schoell, Micha; Haberreiter, Margit; Schmutz, Werner; Shapiro, Alexander Bibcode: 2013EGUGA..1512813S Altcode: The variability of the solar spectral irradiance is an important driver in global circulation models. The Lyman-α spectral line is of particular interest as it exhibits a high variability and has strong impact on the ozone concentration and temperature in the Earth's atmosphere. For a complete understanding of the variation of the Lyman-α line it is important to be able to model its detailed line profile. We present recent work on the improvement of the modeling efforts of this important spectral line. We employ an updated version of the COde for Solar Irradiance (COSI) along with existing model atmospheres with an improved implementation of the temperature and turbulent velocity in the chromosphere and transition region. With the latest modifications we are able to reproduce high resolution observations taken with the SUMER instrument onboard of SOHO. This is an important step towards the reliable reconstruction of the irradiance in the Lyman-α spectral line. Title: The Sun among the Sun-like stars Authors: Cessateur, Gaël; Shapiro, Alexander; Schmutz, Werner; Rozanov, Eugene Bibcode: 2013EGUGA..15.8980C Altcode: Monitoring of the photometric and chromospheric HK emission data series of stars similar to the Sun in average activity level and age showed that there is a correlation between the stellar average chromospheric activity level and photometric variability. We aim to understand whether the Sun obeys the empirical relationship prompted by the stellar data and to identify possible reasons for the Sun to be currently outside of this relationship. Title: Quasi-Periodic Pulsations during the onset of solar flares: multi-instrumental comparison Authors: West, M. J.; Dolla, L.; Marque, C.; Seaton, D. B.; Van Doorsselaere, T.; Dominique, M.; Berghmans, D.; Cabanas, C.; De Groof, A.; Schmutz, W.; Verdini, A.; Zender, J.; Zhukov, A. N. Bibcode: 2013enss.confE..82W Altcode: Quasi-periodic pulsations have been observed in the rising phase of solar flares for many years. Observations have been made over a wide spectral range, extending from X-rays to radio wavelengths. The current generation of spacebourne instruments, especially SDO, EVE and ESP, have exceptionally high sampling rates and allow us to make more detailed observations of this phenomena. In this work, we compare short-period oscillations (around 10 s) observed in flare events by multiple instruments: the radiometer channels of SDO/EVE-ESP (soft X-ray, coronal and chromospheric passbands), the EUV channels of the radiometer PROBA2/LYRA, the RHESSI passbands and short-wavelength radio observations. Title: The EUI instrument on board the Solar Orbiter mission: from breadboard and prototypes to instrument model validation Authors: Halain, J. -P.; Rochus, P.; Renotte, E.; Appourchaux, T.; Berghmans, D.; Harra, L.; Schühle, U.; Schmutz, W.; Auchère, F.; Zhukov, A.; Dumesnil, C.; Delmotte, F.; Kennedy, T.; Mercier, R.; Pfiffner, D.; Rossi, L.; Tandy, J.; BenMoussa, A.; Smith, P. Bibcode: 2012SPIE.8443E..07H Altcode: The Solar Orbiter mission will explore the connection between the Sun and its heliosphere, taking advantage of an orbit approaching the Sun at 0.28 AU. As part of this mission, the Extreme Ultraviolet Imager (EUI) will provide full-sun and high-resolution image sequences of the solar atmosphere at selected spectral emission lines in the extreme and vacuum ultraviolet. To achieve the required scientific performances under the challenging constraints of the Solar Orbiter mission it was required to further develop existing technologies. As part of this development, and of its maturation of technology readiness, a set of breadboard and prototypes of critical subsystems have thus been realized to improve the overall instrument design. The EUI instrument architecture, its major components and sub-systems are described with their driving constraints and the expected performances based on the breadboard and prototype results. The instrument verification and qualification plan will also be discussed. We present the thermal and mechanical model validation, the instrument test campaign with the structural-thermal model (STM), followed by the other instrument models in advance of the flight instrument manufacturing and AIT campaign. Title: Confronting a solar irradiance reconstruction with solar and stellar data Authors: Judge, P. G.; Lockwood, G. W.; Radick, R. R.; Henry, G. W.; Shapiro, A. I.; Schmutz, W.; Lindsey, C. Bibcode: 2012A&A...544A..88J Altcode: Context. A recent paper by Shapiro and colleagues (2011, A&A, 529, A67) reconstructs spectral and total irradiance variations of the Sun during the holocene. Aims. In this note, we comment on why their methodology leads to large (0.5%) variations in the solar TSI on century-long time scales, in stark contrast to other reconstructions which have ∼ 0.1% variations. Methods. We examine the amplitude of the irradiance variations from the point of view of both solar and stellar data. Results. Shapiro et al.'s large amplitudes arise from differences between the irradiances computed from models A and C of Fontenla and colleagues, and from their explicit assumption that the radiances of the quiet Sun vary with the cosmic ray modulation potential. We suggest that the upper photosphere, as given by model A, is too cool, and discuss relative contributions of local vs. global dynamos to the magnetism and irradiance of the quiet Sun. We compare the slow (>22 yr) components of the irradiance reconstructions with secular changes in stellar photometric data that span 20 years or less, and find that the Sun, if varying with such large amplitudes, would still lie within the distribution of stellar photometric variations measured over a 10-20 year period. However, the stellar time series are individually too short to see if the reconstructed variations will remain consistent with stellar variations when observed for several decades more. Conclusions. By adopting model A, Shapiro et al. have over-estimated quiet-Sun irradiance variations by about a factor of two, based upon a re-analysis of sub-mm data from the James Clerk Maxwell telescope. But both estimates are within bounds set by current stellar data. It is therefore vital to continue accurate photometry of solar-like stars for at least another decade, to reveal secular and cyclic variations on multi-decadal time scales of direct interest to the Sun. Title: Solar Spectral Irradiance as observed by LYRA/PROBA2 and PREMOS/PICARD Authors: Cessateur, Gaël.; Kretzschmar, Matthieu; Krivova, Natalie; Schmutz, Werner; Solanki, Sami K.; Thuillier, Gerard; Shapiro, Alexander; Schoell, Micha; Shapiro, Anna; Dominique, Marie; Tagirov, Rinat; Wehrli, Christoph; Yeo, Kok Leng Bibcode: 2012cosp...39..287C Altcode: 2012cosp.meet..287C No abstract at ADS Title: Comparison of Solar Irradiance reconstructions with stellar data Authors: Schmutz, Werner; Shapiro, Alexander Bibcode: 2012cosp...39.1725S Altcode: 2012cosp.meet.1725S A recent paper by Shapiro and colleagues reconstructs spectral and total irradiance variations of the Sun during the holocene. They derive a total and spectral solar irradiance that was substantially lower during the Maunder minimum than the one observed today. The difference is remarkably larger than other estimations published in the recent literature. In this presentation we examine the spectral reconstructions in the light of stellar data. We compare the observed and predicted solar variability with that of stars as observed by Radick et al. (1998), Lockwood et al. (2007) and Hall et al. (2009) in the b and y filters for the last 10- 20 years. Title: Modeling of the atmospheric response to a strong decrease of the solar activity Authors: Rozanov, Eugene V.; Egorova, Tatiana A.; Shapiro, Alexander I.; Schmutz, Werner K. Bibcode: 2012IAUS..286..215R Altcode: We estimate the consequences of a potential strong decrease of the solar activity using the model simulations of the future driven by pure anthropogenic forcing as well as its combination with different solar activity related factors: total solar irradiance, spectral solar irradiance, energetic electron precipitation, solar protons and galactic cosmic rays. The comparison of the model simulations shows that introduced strong decrease of solar activity can lead to some delay of the ozone recovery and partially compensate greenhouse warming acting in the direction opposite to anthropogenic effects. The model results also show that all considered solar forcings are important in different atmospheric layers and geographical regions. However, in the global scale the solar irradiance variability can be considered as the most important solar forcing. The obtained results constitute probably the upper limit of the possible solar influence. Development of the better constrained set of future solar forcings is necessary to address the problem of future climate and ozone layer with more confidence. Title: New X-Ray Detections of WNL Stars Authors: Skinner, Stephen L.; Zhekov, Svetozar A.; Güdel, Manuel; Schmutz, Werner; Sokal, Kimberly R. Bibcode: 2012AJ....143..116S Altcode: 2012arXiv1203.5098S Previous studies have demonstrated that putatively single nitrogen-type Wolf-Rayet stars (WN stars) without known companions are X-ray sources. However, almost all WN star X-ray detections so far have been of earlier WN2-WN6 spectral subtypes. Later WN7-WN9 subtypes (also known as WNL stars) have proved more difficult to detect, an important exception being WR 79a (WN9ha). We present here new X-ray detections of the WNL stars WR 16 (WN8h) and WR 78 (WN7h). These new results, when combined with previous detections, demonstrate that X-ray emission is present in WN stars across the full range of spectral types, including later WNL stars. The two WN8 stars observed to date (WR 16 and WR 40) show unusually low X-ray luminosities (Lx ) compared to other WN stars, and it is noteworthy that they also have the lowest terminal wind speeds (v ∞). Existing X-ray detections of about a dozen WN stars reveal a trend of increasing Lx with wind luminosity Lwind = (1/2)Ṁv2∞, suggesting that wind kinetic energy may play a key role in establishing X-ray luminosity levels in WN stars. Title: Solar Spectral Irradiance as observed by LYRA/PROBA2 and PREMOS/PICARD Authors: Cessateur, G.; Shapiro, A. I.; Dominique, M.; Kretzschmar, M.; Krivova, N.; Shapiro, A. V.; Schmutz, W.; Schoell, M.; Solanki, S.; Tagirov, R.; Thuillier, G.; Wehrli, C.; Yeo, K. L. Bibcode: 2012EGUGA..14.8254C Altcode: Total and Spectral Solar Irradiance are key input parameters to atmospheric/oceanic and space weather models. Both vary on time-scales ranging from days to millennia, although a complete picture of the solar irradiance variability is still missing. The recent launch of two European missions PROBA-2 with LYRA radiometer onboard and PICARD with PREMOS package onboard provides therefore valuable information and nourishes theoretical models. Both instruments covers the solar spectrum from the EUV to near-infrared. Here we present spectral solar irradiance data from these two recent missions. After a proper correction of the degradation and non-solar signatures, we compare these data with those from the VIRGO/SOHO and SOLSTICE+SIM/SORCE experiments. Both LYRA and PREMOS have also observed several solar eclipses, which allows us to accurately retrieve the center-to-limb variations (CLVs) of the quiet Sun's brightness at the wavelengths of the corresponding channels. CLVs play indeed an important role in modelling of the solar irradiance variability. We show that calculations with the published COde for Solar Irradiance (COSI) yield CLVs that are in good agreement with measurements. Finally we use COSI to model the variability of the irradiance, assuming that the latter is determined by the evolution of the solar surface magnetic field as seen with SDO/HMI data. These theoretical results are compared to PREMOS and LYRA measurements. Title: Time Delays in Quasi-periodic Pulsations Observed during the X2.2 Solar Flare on 2011 February 15 Authors: Dolla, L.; Marqué, C.; Seaton, D. B.; Van Doorsselaere, T.; Dominique, M.; Berghmans, D.; Cabanas, C.; De Groof, A.; Schmutz, W.; Verdini, A.; West, M. J.; Zender, J.; Zhukov, A. N. Bibcode: 2012ApJ...749L..16D Altcode: 2012arXiv1203.6223D We report observations of quasi-periodic pulsations (QPPs) during the X2.2 flare of 2011 February 15, observed simultaneously in several wavebands. We focus on fluctuations on timescale 1-30 s and find different time lags between different wavebands. During the impulsive phase, the Reuven Ramaty High Energy Solar Spectroscopic Imager channels in the range 25-100 keV lead all the other channels. They are followed by the Nobeyama RadioPolarimeters at 9 and 17 GHz and the extreme-ultraviolet (EUV) channels of the Euv SpectroPhotometer (ESP) on board the Solar Dynamic Observatory. The zirconium and aluminum filter channels of the Large Yield Radiometer on board the Project for On-Board Autonomy satellite and the soft X-ray (SXR) channel of ESP follow. The largest lags occur in observations from the Geostationary Operational Environmental Satellite, where the channel at 1-8 Å leads the 0.5-4 Å channel by several seconds. The time lags between the first and last channels is up to ≈9 s. We identified at least two distinct time intervals during the flare impulsive phase, during which the QPPs were associated with two different sources in the Nobeyama RadioHeliograph at 17 GHz. The radio as well as the hard X-ray channels showed different lags during these two intervals. To our knowledge, this is the first time that time lags are reported between EUV and SXR fluctuations on these timescales. We discuss possible emission mechanisms and interpretations, including flare electron trapping. Title: A New Solar Spectral Irradiance Reconstruction based on MGII and Neutral Monitoring Indices for Use in Climate Modelling Authors: Thuillier, G.; Bolsée, D.; DeLand, M.; Melo, S. M. L.; Schmutz, W.; Shapiro, A. Bibcode: 2012EGUGA..14.8248T Altcode: For atmosphere and climate studies, the solar spectral irradiance may be necessary at a time where no data exist. Use of proxies is then mandatory. In order to represent the solar forcing as variable in chemistry-climate numerical models, we need consistent series of temporal solar total and spectral variability covering over the periods of interest. While measurements are available, there is currently no harmonized series with some understanding of its accuracy and precision that can be readily implemented in model simulations. In this paper we present a new method to reconstruct the solar spectrum irradiance in the Ly α-400 nm region, and its variability, based on the Mg II index and neutron monitor data. This approach has the advantage of being independent of the absolute calibration and aging of the instruments. First, the Mg II index is derived using solar spectra from Ly α (121 nm) to 410 nm measured from 1978 to 2010 by several space missions. The variability of the spectra with respect to a chosen reference spectrum as a function of time and wavelength is scaled to the derived Mg II index. Then, the set of coefficients expressing the spectral variability can be applied to a chosen reference spectrum to reconstruct the solar spectra within a given time frame or a Mg II index values. The accuracy of this method is estimated by calculating the standard deviation between the measured spectra and their reconstruction. For the second step, the relationship between the Mg II index and the neutron monitor data is searched for the 30-year of Mg II index availability. Finally, the reconstruction at a given date consists in using the neutron monitor data at that date, derive the corresponding Mg II index and use the coefficients of SSI variability to obtain the SSI at that date using a chosen reference spectrum. One major advantage is that using technology of today, we can reconstruct the solar spectral irradiance consistently from today to times when cosmogenic isotope data are available. This calibration can be re-accessed at any time, if necessary. Reconstruction for the Maunder minimum will be shown as well as variation of stratospheric components concentration inferred by solar variability. Title: Signature of the 27-day solar rotation cycle in mesospheric OH and H2O observed by the Aura Microwave Limb Sounder Authors: Shapiro, A. V.; Rozanov, E.; Shapiro, A. I.; Wang, S.; Egorova, T.; Schmutz, W.; Peter, Th. Bibcode: 2012ACP....12.3181S Altcode: 2011ACPD...1128477S The mesospheric hydroxyl radical (OH) is mainly produced by the water vapor (H2O) photolysis and could be considered as a proxy for the influence of the solar irradiance variability on the mesosphere. We analyze the tropical mean response of the mesospheric OH and H2O data as observed by the Aura Microwave Limb Sounder (MLS) to 27-day solar variability. The analysis is performed for two time periods corresponding to the different phases of the 11-yr cycle: from December 2004 to December 2005 (the period of "high activity" with a pronounced 27-day solar cycle) and from August 2008 to August 2009 ("solar minimum" period with a vague 27-day solar cycle). We demonstrate, for the first time, that in the mesosphere the daily time series of OH concentrations correlate well with the solar irradiance (correlation coefficients up to 0.79) at zero time-lag. At the same time H2O anticorrelates (correlation coefficients up to -0.74) with the solar irradiance at non-zero time-lag. We found that the response of OH and H2O to the 27-day variability of the solar irradiance is strong for the period of the high solar activity and negligible for the solar minimum conditions. It allows us to suggest that the 27-day cycle in the solar irradiance and in OH and H2O are physically connected. Title: The Solar Spectral Irradiance as a Function of the Mg II Index for Atmosphere and Climate Modelling Authors: Thuillier, G.; DeLand, M.; Shapiro, A.; Schmutz, W.; Bolsée, D.; Melo, S. M. L. Bibcode: 2012SoPh..277..245T Altcode: We present a new method to reconstruct the solar spectrum irradiance in the Ly α - 400 nm region, and its variability, based on the Mg II index and neutron-monitor measurements. Measurements of the solar spectral irradiance available in the literature have been made with different instruments at different times and different spectral ranges. However, climate studies require harmonised data sets. This new approach has the advantage of being independent of the absolute calibration and aging of the instruments. First, the Mg II index is derived using solar spectra from Ly α (121 nm) to 410 nm measured from 1978 to 2010 by several space missions. The variability of the spectra with respect to a chosen reference spectrum as a function of time and wavelength is scaled to the derived Mg II index. The set of coefficients expressing the spectral variability can be applied to the chosen reference spectrum to reconstruct the solar spectra within a given time frame or Mg II index values. The accuracy of this method is estimated using two approaches: direct comparison with particular cases where solar spectra are available from independent measurements, and calculating the standard deviation between the measured spectra and their reconstruction. From direct comparisons with measurements we obtain an accuracy of about 1 to 2%, which degrades towards Ly α. In a further step, we extend our solar spectral-irradiance reconstruction back to the Maunder Minimum introducing the relationship between the Mg II index and the neutron-monitor data. Consistent measurements of the Mg II index are not available prior to 1978. However, we remark that over the last three solar cycles, the Mg II index shows strong correlation with the modulation potential determined from the neutron-monitor data. Assuming that this correlation can be applied to the past, we reconstruct the Mg II index from the modulation potential back to the Maunder Minimum, and obtain the corresponding solar spectral-irradiance reconstruction back to that period. As there is no direct measurement of the spectral irradiance for this period we discuss this methodology in light of the other proposed approaches available in the literature. The use of the cosmogenic-isotope data provides a major advantage: it provides information about solar activity over several thousands years. Using technology of today, we can calibrate the solar irradiance against activity and thus reconstruct it for the times when cosmogenic-isotope data are available. This calibration can be re-assessed at any time, if necessary. Title: Influence of the Precipitating Energetic Particles on Atmospheric Chemistry and Climate Authors: Rozanov, E.; Calisto, M.; Egorova, T.; Peter, T.; Schmutz, W. Bibcode: 2012omee.book..151R Altcode: No abstract at ADS Title: Modeling of the Solar Spectral Irradiance as observed by LYRA/PROBA2 and PREMOS/PICARD Authors: Shapiro, A.; Cessateur, G.; Dominique, M.; Krivova, N. A.; Lachat, D.; Rozanov, E.; Schmutz, W. K.; Shapiro, A. V.; Tagirov, R. V.; Thuillier, G. O.; Wehrli, C. Bibcode: 2011AGUFMGC22A..07S Altcode: Measurements and modeling of the solar irradiance have gained an increased attention during the last few decades. Nevertheless a complete picture of the solar variability is still missing. Therefore a launch of every new space mission devoted to the measurements of the spectral solar irradiance provides a crucial piece of complementary information and nourishes the theoretical models. We present here spectral solar irradiance data from the recent European missions PROBA-2 (launched on November 2, 2009) and PICARD (launched on June 15, 2010) and their theoretical interpretation. The PREMOS package onboard PICARD comprises two experiments, one observing solar irradiance in five (two UV, one visible and two near infrared) spectral channels with filter radiometers the other measuring TSI with absolute radiometers. LYRA is a solar VUV radiometer onboard PROBA-2, which is a technologically oriented ESA micro-mission, and is observing the solar irradiance in two UV and two EUV spectral channels. The passbands of the UV channels in the both experiments were selected on the ground of relevance for the terrestrial ozone concentration. The PREMOS and LYRA measurements were carefully corrected for the degradation and cleaned for non-solar signatures. We provide a comparison with the VIRGO/SOHO and SOLSTICE+SIM/SORCE data. Both LYRA and PREMOS have observed several solar eclipses. The analysis of these observations allows us to accurately retrieve the center-to-limb variations (CLV) of the solar brightness, which play an important role in the modeling of the solar irradiance variability on the time scale of the solar rotation. We show that the calculations with the recently developed and published COde for Solar Irradiance (COSI) yield the CLV which are in a good agreement with the measurements. The irradiance in all channels shows a clear variability on time-scale of the solar rotation. The amplitude and the profile of the variability strongly depend on the wavelength. We use COSI as a tool for modeling the variability of the irradiance, assuming that the latter is determined by the evolution of the solar surface magnetic field. The theoretical results are compared with the PREMOS and LYRA measurements. Finally we show that COSI and other semi-empirical and empirical models allow to reconstruct the entire solar spectrum from the observations in a few passbands. Hence the PREMOS and LYRA measurements can be used as a proxies for the nowcasting of the solar irradiance (UV-visible-IR) with the high cadence rate and spectral resolution. Title: The Solar Spectral Irradiance Measured on Board the International Space Station and the Picard Spacecraft Authors: Thuillier, G. O.; Bolsee, D.; Schmidtke, G.; Schmutz, W. K. Bibcode: 2011AGUFMGC22A..05T Altcode: On board the International Space Station, the spectrometers SOL-ACES and SOLSPEC measure the solar spectrum irradiance from 17 to 150 nm and 170 to 2900 nm, respectively. On board PICARD launched on 15 June 2010, the PREMOS instrument consists in a radiometer and several sunphotometers operated at several fixed wavelengths. We shall present spectra at different solar activity levels as well as their quoted accuracy. Comparison with similar data from other missions presently running in space will be shown incorporating the PREMOS measurements. Some special solar events will be also presented and interpreted. Title: PREMOS Absolute Radiometer Calibration and Implications to on-orbit Measurements of the Total Solar Irradiance Authors: Fehlmann, A.; Kopp, G.; Schmutz, W. K.; Winkler, R.; Finsterle, W.; Fox, N. Bibcode: 2011AGUFMGC21C..05F Altcode: On orbit measurements starting in the late 1970's, have revealed the 11 year cycle of the Total Solar Irradiance (TSI). However, the absolute results from individual experiments differ although all instrument teams claim to measure an absolute value. Especially the data from the TIM/SORCE experiment confused the community as it measures 0.3 % lower than the other instruments, e.g. VIRGO/SOHO by PMOD/WRC, which clearly exceeds the uncertainty stated for the absolute characterization of the experiments. The PREMOS package on the PICARD platform launched in June 2010 is the latest space experiment by PMOD/WRC measuring the TSI. We have put great effort in the calibration and characterization of this instrument in order to resolve the inter-instrument differences. We performed calibrations at the National Physical Laboratory (NPL) in London and the Laboratory for Atmospheric and Space Physics (LASP) in Boulder against national SI standards for radiant power using a laser beam with a diameter being smaller than the aperture of the instrument. These measurements together with the World Radiometric Reference (WRR) calibration in Davos allowed to compare the WRR and the SI radiant power scale. We found that the WRR lies 0.18 % above the SI radiant power scale which explains a part of the VIRGO-TIM difference. The Total solar irradiance Radiometer Facility (TRF) at the LASP allows to generate a beam that over fills the apertures of our instruments, giving the presently best available representation of solar irradiance in a laboratory. These irradiance calibrations revealed a stray light contribution between 0.09 and 0.3 % to the measurements which had been underestimated in the characterization of our instruments. Using the irradiance calibrations, we found that the WRR lies 0.32 % above the TRF scale which in turn explains the full VIRGO-TIM difference. The first light PREMOS measurements in space confirmed our findings. If we use the WRR calibration, PREMOS yields a TSI value of 1365.5 ± 1.2 W/m2 (k=1) which is in excellent agreement with VIRGO (1365.4 W/m2). Else, applying the TRF calibration to PREMOS, we obtain a TSI value of 1360.9 ± 0.4 W/m2 (k=1) which is in excellent agreement with TIM (1361.3 W/m2). Title: LYRA and SWAP, the two Solar Instruments on-board PROBA2 Authors: Dominique, M.; Berghmans, D.; Schmutz, W. K.; Dammasch, I.; De Groof, A.; Halain, J.; Hochedez, J.; Kretzschmar, M.; Seaton, D. B. Bibcode: 2011AGUFMSH13B1949D Altcode: PROBA2 (http://proba2.sidc.be) is an ESA micro-satellite that was launched in November 2009. Two instruments on-board, SWAP and LYRA, are devoted to solar observations. SWAP (PI: D. Berghmans) is an EUV imager observing the corona with a bandpass centered on 174 Å at a cadence of 1-2 min. Its high contrast images, large FOV and flexible off-pointing capabilities make SWAP particularly well suited for the study of coronal eruptions. LYRA (PI: M. Dominique) is a UV-EUV radiometer observing in four spectral channels, chosen for their relevance in solar physics and aeronomy. Its very fast acquisition cadence (up to 100 Hz) allows scientists to perform detailed analysis of solar flares. We discuss the characteristics of both instruments, review their performance and evolution, and highlight their complementarity to other missions. We also present the data products that can be downloaded from the mission website and give an overview of the various investigations for which SWAP and LYRA data are currently used (CMEs, flares, solar variability, and many others). Title: Solar total irradiance in cycle 23 Authors: Krivova, N. A.; Solanki, S. K.; Schmutz, W. Bibcode: 2011A&A...529A..81K Altcode: 2011arXiv1102.3077K Context. The most recent minimum of solar activity was deeper and longer than the previous two minima as indicated by different proxies of solar activity. This is also true for the total solar irradiance (TSI) according to the PMOD composite.
Aims: The apparently unusual behaviour of the TSI has been interpreted as evidence against solar surface magnetism as the main driver of the secular change in the TSI. We test claims that the evolution of the solar surface magnetic field does not reproduce the observed TSI in cycle 23.
Methods: We use sensitive, 60-min averaged MDI magnetograms and quasi-simultaneous continuum images as an input to our SATIRE-S model and calculate the TSI variation over cycle 23, sampled roughly every two weeks. The computed TSI is then compared with the PMOD composite of TSI measurements and with the data from two individual instruments, SORCE/TIM and UARS/ACRIM II, that monitored the TSI during the declining phase of cycle 23 and over the previous minimum in 1996, respectively.
Results: Excellent agreement is found between the trends shown by the model and almost all sets of measurements. The only exception is the early, i.e. 1996 to 1998, PMOD data. Whereas the agreement between the model and the PMOD composite over the period 1999-2009 is almost perfect, the modelled TSI shows a steeper increase between 1996 and 1999 than implied by the PMOD composite. On the other hand, the steeper trend in the model agrees remarkably well with the ACRIM II data. A closer look at the VIRGO data, which are the basis of the PMOD composite after 1996, reveals that only one of the two VIRGO instruments, the PMO6V, shows the shallower trend present in the composite, whereas the DIARAD measurements indicate a steeper trend.
Conclusions: Based on these results, we conclude that (1) the sensitivity changes of the PMO6V radiometers within VIRGO during the first two years have very likely not been correctly evaluated; and that (2) the TSI variations over cycle 23 and the change in the TSI levels between the minima in 1996 and 2008 are consistent with the solar surface magnetism mechanism. Title: A new approach to the long-term reconstruction of the solar irradiance leads to large historical solar forcing Authors: Shapiro, A. I.; Schmutz, W.; Rozanov, E.; Schoell, M.; Haberreiter, M.; Shapiro, A. V.; Nyeki, S. Bibcode: 2011A&A...529A..67S Altcode: 2011arXiv1102.4763S Context. The variable Sun is the most likely candidate for the natural forcing of past climate changes on time scales of 50 to 1000 years. Evidence for this understanding is that the terrestrial climate correlates positively with the solar activity. During the past 10 000 years, the Sun has experienced the substantial variations in activity and there have been numerous attempts to reconstruct solar irradiance. While there is general agreement on how solar forcing varied during the last several hundred years - all reconstructions are proportional to the solar activity - there is scientific controversy on the magnitude of solar forcing.
Aims: We present a reconstruction of the total and spectral solar irradiance covering 130 nm-10 μm from 1610 to the present with an annual resolution and for the Holocene with a 22-year resolution.
Methods: We assume that the minimum state of the quiet Sun in time corresponds to the observed quietest area on the present Sun. Then we use available long-term proxies of the solar activity, which are 10Be isotope concentrations in ice cores and 22-year smoothed neutron monitor data, to interpolate between the present quiet Sun and the minimum state of the quiet Sun. This determines the long-term trend in the solar variability, which is then superposed with the 11-year activity cycle calculated from the sunspot number. The time-dependent solar spectral irradiance from about 7000 BC to the present is then derived using a state-of-the-art radiation code.
Results: We derive a total and spectral solar irradiance that was substantially lower during the Maunder minimum than the one observed today. The difference is remarkably larger than other estimations published in the recent literature. The magnitude of the solar UV variability, which indirectly affects the climate, is also found to exceed previous estimates.We discuss in detail the assumptions that lead us to this conclusion.

Appendix is only available in electronic form at http://www.aanda.org Title: The atmospheric effects of October 2003 solar proton event simulated with the chemistry-climate model SOCOL using complete and parameterized ion chemistry Authors: Egorova, T.; Rozanov, E.; Ozolin, Y.; Shapiro, A.; Calisto, M.; Peter, Th.; Schmutz, W. Bibcode: 2011JASTP..73..356E Altcode: October 2003 solar proton events (SPE) is rather well covered by the observations; therefore its studies represent a good way for model validation and intercomparison. Here we apply chemistry-climate model (CCM) SOCOL with complete (SOCOLi) and parameterized ion chemistry to evaluate the accuracy of a commonly used ion chemistry parameterization scheme. We performed ensemble experiments with and without SPE to characterize the effect of the October 2003 SPE on the NOx, HOx, ClOx and O3 in the middle atmosphere. Preliminary comparison of the simulated effects against MIPAS observations revealed rather good general agreement for most of the species. Comparison of the results obtained with complete and parameterized ion chemistry representation showed that the model with parameterized ion chemistry underestimates the effect of SPE on chemical composition of the middle atmosphere by up to 40% for NOx and N2O, up to 70% for HOx and ClOx and up to 600% for HNO3. The parameterization is more accurate for ozone, however the model with parameterized ion chemistry underestimates ozone depletion by up to 15% during the SPE in the mesosphere and by 10% 2 weeks later in the stratosphere, which can be important for the long-term effects of SPE on the ozone layer. Title: Sensitivity of the Earth’s middle atmosphere to short-term solar variability and its dependence on the choice of solar irradiance data set Authors: Shapiro, A. V.; Rozanov, E.; Egorova, T.; Shapiro, A. I.; Peter, Th.; Schmutz, W. Bibcode: 2011JASTP..73..348S Altcode: We simulate the time evolution of the neutral and charged species in the terrestrial middle atmosphere using a 1-D radiative-convective model with interactive neutral and ion chemistry driven by four different sets of daily spectral solar irradiance (SSI) available in the literature for the year 2000. Obtained daily time series of ozone, hydroxyl and electron densities are used to calculate their sensitivity to the short-term SSI variability at 205 nm. All applied SSI data sets possess 27-day solar rotation cycle; however, its amplitude and phase as well as the correlation between considered SSI time series differ among data sets leading to the different behavior of the atmospheric response. Contrary, the ozone and hydroxyl sensitivities to the SSI changes during solar rotation cycle are almost identical for all applied SSI data sets in the stratosphere. In the mesosphere, the difference in correlation between SSI in Herzberg continuum and Lyman-α line in considered SSI data sets leads to substantial scatter of the sensitivity estimates based on 205 nm. Our results show that for the sensitivity analysis in the stratosphere based on the SSI at 205 nm any considered SSI data sets can be applied. For the mesosphere, where the sensitivity strongly varies among applied SSI data sets more robust results can be obtained using the sensitivity calculations based on the SSI in Lyman-α line. Title: The Sun-Climate Connection Through Measurements and Modeling: The Picard Investigation Authors: Thuillier, Gérard; Dewitte, Steven; Schmutz, Werner; Picard Team Bibcode: 2011sswh.book..365T Altcode: No abstract at ADS Title: The Shape of the Solar Limb: Models and Observations Authors: Thuillier, G.; Claudel, J.; Djafer, D.; Haberreiter, M.; Mein, N.; Melo, S. M. L.; Schmutz, W.; Shapiro, A.; Short, C. I.; Sofia, S. Bibcode: 2011SoPh..268..125T Altcode: 2010SoPh..tmp..202T; 2010SoPh..tmp..226T In this paper we compare observed, empirical, and modelled solar limb profiles and discuss their potential use to derive physical properties of the solar atmosphere. The PHOENIX, SolMod3D, and COSI radiative transfer codes as well as VAL-C models are used to calculate the solar limb shape under different assumptions. The main properties of each model are shown. The predicted limb shape as a function of wavelength for different features on the solar disk, such as quiet Sun, sunspots, and faculae, is investigated. These models provide overall consistent limb shapes with some discrepancies that are discussed here in terms of differences in solar atmosphere models, opacities, and the algorithms used to derive the solar limb profile. Our analysis confirms that the most common property of all models is limb shapes that are much steeper than what is observed, or predicted by the available empirical models. Furthermore, we have investigated the role of the Fraunhofer lines within the spectral domain used for the solar limb measurements. Our results show that the presence of the Fraunhofer lines significantly displaces the limb inflection point from its position estimated assuming only the photospheric continuum. The PICARD satellite, launched on 15 June 2010, will provide measurements of the limb shape at several wavelengths. This work shows that the precision of these measurements allows for discrimination among the available models. Title: New X-ray Detections Of Late Nitrogen-type (WNL) Wolf-Rayet Stars Authors: Skinner, Steve L.; Guedel, M.; Schmutz, W.; Zhekov, S. Bibcode: 2011AAS...21733819S Altcode: 2011BAAS...4333819S We present results of recent X-ray observations of nitrogen-type Wolf-Rayet (WR) stars, focusing on late WN7 - WN9 subtypes. These observations were obtained as part of a broader X-ray survey of single WN stars using XMM-Newton and Chandra aimed at determining their X-ray properties and identifying plausible emission mechanisms. None of the WN survey targets is known to be a member of a binary system. We report unambiguous detections of WR 78 (WN7h) and WR 79a (WN9ha), and a possible (faint) detection of WR 16 (WN8h). These new WNL detections, along with previous detections of WN2 - WN6 stars, demonstrate that WN stars are X-ray sources across their full range of spectral subtypes. The X-ray luminosities of WN stars span a broad range (even among stars of similar spectral subtype) with typical values log Lx = 31.5 - 33.5 (ergs/s). There is some evidence that Lx is proportional to wind kinetic energy. WN star X-ray spectra show higher absorption than expected from optical extinction, likely due to their powerful metal-rich winds. Their spectra reveal strong emission lines from ionized metals and spectral fits typically require two components consisting of cool (kT < 1 keV) and hot (kT > 2 keV) plasma. Only cool plasma is anticipated if the X-rays arise in radiative wind shocks, so the presence of hot plasma implies other as yet unidentified X-ray production mechanisms are at work. Magnetic fields may play a role, but in contrast to magnetically-active solar-like stars, WN stars do not show large-amplitude X-ray flares in observations typically spanning a half day. But, more extensive monitoring at higher time-resolution is needed. Alternatively, unseen companions at close separation could play a role in WN star X-ray emission in some cases (esp. higher Lx objects), either via their intrinsic emission or as colliding wind secondaries. Title: New SSI and TSI reconstruction suggests large value of the radiative solar forcing Authors: Shapiro, A.; Schmutz, W. K.; Thuillier, G.; Rozanov, E.; Haberreiter, M.; Schoell, M.; Shapiro, A.; Nyeki, S. Bibcode: 2010AGUFMGC21B0875S Altcode: We have developed and published the COde for Solar Irradiance (COSI) which allows us to calculate the entire solar spectrum. COSI reproduces the spectral irradiance measured by SOLSTICE (up to 320 nm) and SIM (from 320 nm onward) onboard the SORCE satellite during the 2008 solar minimum as well as SOLSPEC during the ATLAS 3 mission in 1994 with high accuracy. COSI is also used as a tool for modeling the variability of the solar irradiance. In our new reconstruction we represent the quiet Sun as a combination of two components. The first corresponds to the least active areas of the Sun as presently observed, while the second component is responsible for the magnetic activity of the quiet Sun. The time-dependent filling factors of these components are calculated based on the solar activity as derived from cosmogenic isotope concentrations in natural archieves. This allows us to obtain a time-dependent reconstructed solar spectrum from 7000 BC to the present with a temporal resolution of 22 years. From 1610 onward we have additional information from sunspot numbers, which allows the reconstruction of the spectral solar irradiance with a yearly resolution. These basic assumptions lead to a total and spectral solar irradiance that was substantially lower during the Maunder minimum than observed today. The difference is remarkably larger than other estimations published in the recent literature. Using our reconstruction as an input to a chemistry-climate model we show that the enhanced UV variability results in significant variations of stratospheric ozone and temperature. Title: The effect of flares on total solar irradiance Authors: Kretzschmar, Matthieu; de Wit, Thierry Dudok; Schmutz, Werner; Mekaoui, Sabri; Hochedez, Jean-François; Dewitte, Steven Bibcode: 2010NatPh...6..690K Altcode: 2010arXiv1003.5258K Flares are powerful bursts of energy released by relatively poorly understood processes that take place in the atmospheres of stars. However, although solar flares, from our own Sun, are the most energetic events in the solar system, in comparison to the total output of the Sun they are barely noticeable. Consequently, the total amount of radiant energy they generate is not precisely known, and their potential contribution to variations in the total solar irradiance incident on the Earth has so far been overlooked. In this work, we identify a measurable signal from relatively moderate solar flares in total solar irradiance data. We find that the total energy radiated by flares exceeds by two orders of magnitude the flare energy radiated in the soft-X-ray domain only, indicating a major contribution in the visible domain. These results have implications for our understanding of solar-flare activity and the variability of our star. Title: NLTE solar irradiance modeling with the COSI code Authors: Shapiro, A. I.; Schmutz, W.; Schoell, M.; Haberreiter, M.; Rozanov, E. Bibcode: 2010A&A...517A..48S Altcode: 2010arXiv1004.3048S Context. The solar irradiance is known to change on time scales of minutes to decades, and it is suspected that its substantial fluctuations are partially responsible for climate variations.
Aims: We are developing a solar atmosphere code that allows the physical modeling of the entire solar spectrum composed of quiet Sun and active regions. This code is a tool for modeling the variability of the solar irradiance and understanding its influence on Earth.
Methods: We exploit further development of the radiative transfer code COSI that now incorporates the calculation of molecular lines. We validated COSI under the conditions of local thermodynamic equilibrium (LTE) against the synthetic spectra calculated with the ATLAS code. The synthetic solar spectra were also calculated in non-local thermodynamic equilibrium (NLTE) and compared to the available measured spectra. In doing so we have defined the main problems of the modeling, e.g., the lack of opacity in the UV part of the spectrum and the inconsistency in the calculations of the visible continuum level, and we describe a solution to these problems.
Results: The improved version of COSI allows us to reach good agreement between the calculated and observed solar spectra as measured by SOLSTICE and SIM onboard the SORCE satellite and ATLAS 3 mission operated from the Space Shuttle. We find that NLTE effects are very important for the modeling of the solar spectrum even in the visual part of the spectrum and for its variability over the entire solar spectrum. In addition to the strong effect on the UV part of the spectrum, NLTE effects influence the concentration of the negative ion of hydrogen, which results in a significant change of the visible continuum level and the irradiance variability.

Figures 13 and 14 are only available in electronic form at http://www.aanda.org Title: Towards a New Formation Flying Solar Coronagraph Authors: Lamy, P.; Vives, S.; Curdt, W.; Dame, L.; Davila, J.; Defise, J. M.; Fineschi, S.; Heinzel, P.; Kuzin, S.; Schmutz, W.; Tsinganos, K.; Turck-Chieze, S.; Zhukov, A. Bibcode: 2010ASPC..424...15L Altcode: We briefly describe an investigation aiming at the development of a giant solar coronagraph instrument onboard of two satellites, separated by about 150 m in formation flight for the detailed observation of the solar coronal plasma. The European Space Agency (ESA) has selected this instrument as the only payload onboard the Proba 3 satellites which will be launched in 2013. The Greek team is developing the command control board of the coronagraph. Title: Chandra Detects the Rare Oxygen-type Wolf-Rayet Star WR 142 and OB Stars in Berkeley 87 Authors: Sokal, Kimberly R.; Skinner, Stephen L.; Zhekov, Svetozar A.; Güdel, Manuel; Schmutz, Werner Bibcode: 2010ApJ...715.1327S Altcode: 2010arXiv1004.0462S We present first results of a Chandra X-ray observation of the rare oxygen-type Wolf-Rayet (WR) star WR 142 (= Sand 5 = St 3) harbored in the young, heavily obscured cluster Berkeley 87. Oxygen-type WO stars are thought to be the most evolved of the WRs and progenitors of supernovae or gamma-ray bursts. As part of an X-ray survey of supposedly single WR stars, we observed WR 142 and the surrounding Berkeley 87 region with Chandra ACIS-I. We detect WR 142 as a faint yet extremely hard X-ray source. Due to weak emission, its nature as a thermal or non-thermal emitter is unclear and thus we discuss several emission mechanisms. Additionally, we report seven detections and eight non-detections by Chandra of massive OB stars in Berkeley 87, two of which are bright yet soft X-ray sources whose spectra provide a dramatic contrast to the hard emission from WR 142. Title: X-ray Emission from Nitrogen-Type Wolf-Rayet Stars Authors: Skinner, Stephen L.; Zhekov, Svetozar A.; Güdel, Manuel; Schmutz, Werner; Sokal, Kimberly R. Bibcode: 2010AJ....139..825S Altcode: 2009arXiv0912.1326S We summarize new X-ray detections of four nitrogen-type Wolf-Rayet (WR) stars obtained in a limited survey aimed at establishing the X-ray properties of WN stars across their full range of spectral subtypes. None of the detected stars is so far known to be a close binary. We report Chandra detections of WR 2 (WN2), WR 18 (WN4), and WR 134 (WN6), and an XMM-Newton detection of WR79a (WN9ha). These observations clearly demonstrate that both WNE and WNL stars are X-ray sources. We also discuss Chandra archive detections of the WN6h stars WR 20b, WR 24, and WR 136 and ROSAT non-detections of WR 16 (WN8h) and WR 78 (WN7h). The X-ray spectra of all WN detections show prominent emission lines and an admixture of cool (kT < 1 keV) and hot (kT > 2 keV) plasma. The hotter plasma is not predicted by radiative wind shock models and other as yet unidentified mechanisms are at work. Most stars show X-ray absorption in excess of that expected from visual extinction (A V), likely due to their strong winds or cold circumstellar gas. Existing data suggest a falloff in X-ray luminosity toward later WN7-9 subtypes, which have higher L bol but slower, denser winds than WN2-6 stars. This provides a clue that wind properties may be a more crucial factor in determining emergent X-ray emission levels than bolometric luminosity. Title: Effects of the solar spectral irradiance changes during the first half of 20th century on chemistry and climate Authors: Rozanov, Eugene; Dorf, Davos; Arfeuille, F.; Brünnimann, S.; Calisto, M.; Egorova, T.; Fischer, A.; Heckendorn, P.; Luo, B. -P.; Peter, T.; Rozanov, E.; Shapiro, A. V.; Schmutz, W.; Schraner, M.; Stenke, A.; Zubov, V. Bibcode: 2010cosp...38...21R Altcode: 2010cosp.meet...21R The attribution of climate and chemistry changes in the past requires understanding of the role of different natural forcing such as volcanic eruptions and solar irradiance. The first half of the 20th century is characterized by an increase in solar activity (and presumably solar irradi-ance) reaching the maximum in the year 1957. Therefore, to elucidate the contribution of the solar irradiance to the climate change we have carried out two 60-year long transient ensemble simulations with the chemistry-climate model SOCOL spanning the first half of 20th century, driven by the prescribed time evolution of the sea surface temperature, sea ice distribution, volcanic aerosols, greenhouse gases, ozone depleting substances, sources of CO and NOx, land use, and quasi-biennial oscillation. For the first run we have applied constant solar spectral irradiance, while the second run has been driven by time dependent solar spectral irradiance. The simulated time series of different atmospheric quantities have been analyzed to estimate the climate and chemistry response to the changes of solar spectral irradiance. The analyses showed statistically significant solar signal from the mesosphere down to the surface. The max-imum ozone response ( 4%) is found in the tropical middle stratosphere, while the temperature response maximizes in the tropical stratopause reaching 1.2K. The contribution of the solar spectral irradiance variability to the global mean surface temperature changes is rather small; however, the downward propagation of the solar signal leads to noticeable land surface temper-ature response over some geographical locations. Its magnitude can reach 0.6 K over Siberia, Scandinavia, Central USA and Canada. The cooling due to solar irradiance is observed over Northern Canada, China and Northern Africa. Title: Modeling the impact of the solar UV irradiance on the middle atmosphere Authors: Rozanov, Eugene; Egorova, Tatiana; Shapiro, Anna; Shapiro, Alexander; Schmutz, Werner Bibcode: 2010cosp...38.1103R Altcode: 2010cosp.meet.1103R Modeling of the middle atmosphere response to the short-term variability of the solar spec-tral irradiance (SSI) is important to understand the mechanisms responsible for the Sun-Earth connections. The analysis of the recent publications shows that there is still substantial dis-agreement between the simulated and observed responses of the middle atmosphere to the daily SSI variability. Among other problems this disagreement can be caused by not perfect quality of the available SSI data sets which are necessary to drive models and extract the response of the middle atmosphere from the observed time series. To elucidate the role of the SSI data we exploited column and full versions of the climate-chemistry-ionosphere model SOCOL, which is based on a general circulation model and includes complete representation of the chemistry of neutral and ionized species in the atmosphere from the ground up to the mesopause. We have performed a series of experiments driven by different available observed and reconstructed daily SSI data sets to estimate the middle atmosphere response to the SSI variability during the solar rotation cycle as well as to the short-time increase of the solar UV irradiance occurred in January 2004. Our results showed that the sensitivity analysis in the stratosphere gives similar results for all SSI data sets when it is based on the SSI at 205 nm, while for the mesosphere the sensitivity based on the SSI in Lyman-line is more robust. The analysis of the correlation between ozone, hydroxyl and electron densities daily time series simulated with different SSI data sets showed substantial disagreement which emphasizes the necessity of more accurate representation of SSI for the nowcasting of the middle atmosphere state. The comparison of the short-term changes in the middle atmosphere in January 2004 with the appropriate obser-vations allows the evaluation of the model performance, which will be discussed together with the perspectives of the model application for the space weather nowcasting using the solar UV irradiance data acquired by LYRA instrument onboard ESA PROBA-2 satellite and available in near-real time. Title: First results from the LYRA solar UV radiometer Authors: Hochedez, Jean-François; Dammasch, I.; Schmutz, Werner Bibcode: 2010cosp...38.1090H Altcode: 2010cosp.meet.1090H On November 2, 2009, the PROBA2 space mission of ESA was launched into a sun-synchronous polar orbit allowing quasi-permanent solar observation. Onboard PROBA2, LYRA is the first radiometer in space that benefits from diamond ultraviolet detectors. LYRA consists of four large pass band channels. Each channel observes the irradiance of the Sun behind a thin metallic foil or behind an interference filter. The detectors are either UV silicon diodes or diamond detectors, the latter having been specifically designed for LYRA. The combination of the spectral transmission of the filters and of the responsivity of the detectors makes the twelve LYRA channels sensitive to different soft X-ray and UV pass bands. Their exact choice was made in relation to scientific questions in solar physics, aeronomy, and Space Weather. `First Light' of the experiment occurred on January 6, 2010, and LYRA was subsequently commissioned successfully. After few days, it measured the first solar flares of the new solar cycle, with an unprecedented high time resolution of 0.5 s. In the spring of 2010, LYRA data will start feeding research investigations and space weather forecasts. The proposed talk presents early results obtained with the measurements of the first months in space. Title: Modeling of the current TSI and SSI and its reconstruction to the past Authors: Shapiro, Alexander; Schmutz, Werner; Thuillier, Gerard; Schoell, Micha; Haberreiter, Margit; Rozanov, Eugene Bibcode: 2010cosp...38..134S Altcode: 2010cosp.meet..134S We have developed and published the COde for Solar Irradiance (COSI) which provides physical modeling of the entire solar spectrum as a contribution from the quiet Sun and active regions. This code allows us to reach a good agreement between the calculated and observed solar spectrum as measured by SOLSTICE and SIM onboard the SORCE satellite and ATLAS 3 mission operated from the Space Shuttle. We find that NLTE effects are very important for the modeling of the solar spectrum even in the visible part of the spectrum and for its variability over the entire solar spectrum. We employ the assumption that the quiet Sun consists of two components. The first corresponds to the average quiet network and it is responsible for all magnetic activity of the quiet Sun. The second represents the Sun that is basically free from any magnetic activity. We use the reconstructed open magnetic flux data as well as the TSI and SSI observed by SORCE during this peculiar solar minimum to find the filling factors of these components. We use the sunspot numbers to reconstruct the filling factors of the solar active components. This approach allows us to obtain an annually averaged TSI and SSI back to the Maunder Minimum. These basic assumptions lead to aTSI and SSI that was substantially different during the Maunder minimum than as it is observed today. The difference is remarkably larger than other estimations published in the recent literature. Title: Total Solar Irradiance: Present status of TSI observations Authors: Schmutz, Werner; Fehlmann, Andr; Finsterle, Wolfgang; Rozanov, Eugene Bibcode: 2010cosp...38.1689S Altcode: 2010cosp.meet.1689S Total Solar Irradiance is measured by pyrheliometers. These instruments are either fully charac-terized and measure in absolute units or they are traceable to the World Radiometric Reference (WRR) at the World Radiation Center in Davos. The WRR in turn is so far only traceable to SI in power but not in irradiance. The added difficulty when discussing metrology of pyrheliome-ters in space is that the WRR is operated in air. Thus, so far, measurements of TSI in space rely on the full characterization of the instruments and a fully traceable TSI measurements has not yet been flown. This talk will give an overview over existing space observations of TSI and discusses the dif-ferences in the absolute and relative values between the various experiments. The challenge for future experiments is to get full traceability of the measurements in space. There are two upcoming experiments, PREMOS on PICARD and GLORY/TIM, which will yield TSI measurements which will be SI traceable. Title: ASPIICS / PROBA-3: a formation flying externally-occulted giant coronagraph mission Authors: Lamy, Philippe; Damé, Luc; Curdt, W.; Davila, J.; Defise, J. M.; Fineschi, S.; Heinzel, P.; Howard, R.; Kuzin, S.; Schmutz, W.; Tsinganos, K.; Turck-Chièze, S.; Zhukov, A. Bibcode: 2010cosp...38.2858L Altcode: 2010cosp.meet.2858L Classical externally-occulted coronagraphs are presently limited in their performances by the distance between the external occulter and the front objective. The diffraction fringe from the occulter and the vignetted pupil which degrades the spatial resolution prevent useful observa-tions of the white light corona inside typically 2-2.5 Rsun. Formation flying offers an elegant solution to these limitations and allows conceiving giant, externally-occulted coronagraphs us-ing a two-component space system with the external occulter on one spacecraft and the optical instrument on the other spacecraft at distances of hundred meters. Such an instrument has just been selected by ESA to fly (by the end of 2013) on its PROBA-3 mission, presently in phase B, to demonstrate formation flying. It will perform both high spatial resolution imaging of the solar corona as well as 2-dimensional spectroscopy of several emission lines (in partic-ular the forbidden line of FeXIV at 530.285 nm) from the coronal base out to 3 Rsun using a Fabry-Perot interferometer. The classical design of an externally-occulted coronagraph is adapted to the formation flying configuration allowing the detection of the very inner corona as close as 0.05 Rsun from the solar limb. By tuning the position of the occulter spacecraft, it may even be possible to try reaching the chromosphere and the upper part of the spicules. ASPIICS/PROBA-3 mission, payload and scientific objectives are detailed. Title: The Absolute Solar Irradiance Spectrum at Solar Minimum Activity Measured by the SOLSPEC and SOL-ACES Spectrometers from 17 to 3000 nm Placed on Board the International Space Station Authors: Thuillier, Gerard; Bolsee, David; Schmidtke, Gerhard; Schmutz, Werner; Shapiro, Alexander; Nikutowski, Bernd Bibcode: 2010cosp...38...17T Altcode: 2010cosp.meet...17T Two instruments placed on the COLOMBUS laboratory on the International Space Station constitute a payload named SOLAR measuring the spectral solar irradiance from 17 to 3000 nm for solar, atmospheric and climatology physics for which the sun-climate connection also re-quires the precise and absolute knowledge of the solar spectral irradiance. Given the significant improvements in atmosphere, climate and solar modelling, accurate data are needed. SOL-SPEC primary objectives are the measurement of the Sun absolute spectral irradiance and its variability from 165 to 3080 nm. SOLSPEC has been developed by LATMOS (France), Institut d'Aéronomie Spatiale (Belgique), and Landessternwarte (Germany). It has been calibrated in the absolute scale by using the blackbody of the Physikalisch-Technische Bundesanstalt (PTB), Braunschweig. SOL-ACES primary objectives are the measurements of the Sun absolute spec-tral irradiance from 17 to 140 nm. This instrument as developed by the Fraunhofer Institute (Freiburg, Germany) uses three-current ionisation chambers repeatedly filled with different gases to re-calibrate the three spectrometers, which are changing their efficiencies e.g. by the interaction with solar radiation. We present a composite solar spectrum for the July 2008 period, at a very low solar as occurred at the end of solar cycle 23. It has been built using SOLSPEC, SOL-ACES and TIMED SEE data. Comparison with data obtained during the ATLAS 3 period (November 1994), SORCE measurements and theoretical modelling using the COSI code will be presented. Differences will be commented (difference of the two activity levels, accuracy). Title: Chandra X-ray Observations of the Young Stellar Cluster Berkeley 87 and its Oxygen-type Wolf-Rayet Star WR 142 Authors: Skinner, Steve L.; Sokal, K. R.; Zhekov, S. A.; Guedel, M.; Schmutz, W. Bibcode: 2010AAS...21547811S Altcode: 2010BAAS...42Q.567S Berkeley 87 is a heavily-reddened young open cluster lying in an obscured region of Cygnus. Age estimates for cluster members are typically in the range 1 - 3 Myr. Berkeley 87 is noteworthy as an example of a galactic open cluster harboring a rare oxygen-type Wolf-Rayet star, WR 142 (= Sand 5 = St 3; spectral type WO2). WO stars are the most highly-evolved WR stars and are likely supernova or gamma-ray burst (GRB) progenitors. The wind of WR 142 has a exceptionally high terminal speed in excess of 5000 km/s and may be producing shock waves in the surrounding cluster. We present results of a Chandra ACIS-I observation of Berkeley 87 centered on WR 142. The Chandra spectrum of WR 142 is exceptionally hard for a WR star, and shows excess low-energy absorption above that expected from its visual extinction. Some of this excess absorption likely arises in its powerful metal-rich wind. We compare its spectrum with the much softer X-ray spectra of cluster OB stars. We discuss the Chandra image of Berkeley 87, which reveals a large and diverse population of X-ray emitting young stars. Title: Multi-spacecraft observation of a magnetic cloud Authors: de Lucas, Aline; Dal Lago, Alisson; Schwenn, Rainer; Clúa de Gonzalez, Alicia L.; Marsch, Eckart; Lamy, Philippe; Damé, Luc; Curdt, W.; Davila, J.; Defise, J. M.; Fineschi, S.; Heinzel, P.; Howard, R.; Kuzin, S.; Schmutz, W.; Tsinganos, K.; Turck-Chièze, S.; Zhukov, A. Bibcode: 2010cosp...38.1921D Altcode: 2010cosp.meet.1921D Classical externally-occulted coronagraphs are presently limited in their performances by the distance between the external occulter and the front objective. The diffraction fringe from the occulter and the vignetted pupil which degrades the spatial resolution prevent useful observa-tions of the white light corona inside typically 2-2.5 Rsun. Formation flying offers an elegant solution to these limitations and allows conceiving giant, externally-occulted coronagraphs us-ing a two-component space system with the external occulter on one spacecraft and the optical instrument on the other spacecraft at distances of hundred meters. Such an instrument has just been selected by ESA to fly (by the end of 2013) on its PROBA-3 mission, presently in phase B, to demonstrate formation flying. It will perform both high spatial resolution imaging of the solar corona as well as 2-dimensional spectroscopy of several emission lines (in partic-ular the forbidden line of FeXIV at 530.285 nm) from the coronal base out to 3 Rsun using a Fabry-Perot interferometer. The classical design of an externally-occulted coronagraph is adapted to the formation flying configuration allowing the detection of the very inner corona as close as 0.05 Rsun from the solar limb. By tuning the position of the occulter spacecraft, it may even be possible to try reaching the chromosphere and the upper part of the spicules. ASPIICS/PROBA-3 mission, payload and scientific objectives are presented. Title: The PICARD Mission: an investigation based on measurements dedicated to solar and climate modeling Authors: Thuillier, Gerard; Schmutz, Werner; Dewitte, Steven Bibcode: 2010cosp...38.1094T Altcode: 2010cosp.meet.1094T PICARD mission is dedicated to the study of the solar activity origin using several key solar measurements. The project also includes development of the solar convective zone and climate models to evaluate the consequences for the Earth'climate of the solar activity. The measure-ments are the total and spectral solar irradiance, solar diameter, limb shape, solar asphericity, and helioseismic waves, which are key inputs for solar physics modeling. The measurements will be carried out by two absolute radiometers, sunphotometers, and a metrological imag-ing telescope onboard a microsatellite built by the French Space Agency CNES, with launch scheduled for March 2010. The radiometers are similar to the ones flown on board SOHO. The imaging telescope contains an angular reference allowing a permanent control of the instrument geometric scale, which is referred to angular stars distances. Optical distortion and flatfield of the imaging telescope are foreseen to be regularly measured. The measurements in space will have correlative measurements from ground using an identical imaging telescope, associated to the measurement of the local turbulence and aerosols localization and concentration. The op-portunity of diameter measurements by solar eclipse method will be used and finally the Solar Disk Sextant instrument will be regularly flown as an external measurement validation. An after launch activities is scheduled for three months, which consists in several instrument checks and recording of some scientific data. Given the launch date, these preliminary measurements will be shown. Images in UV, CaII line and solar photospheric continuum will be presented with some analysis of their contains. Furthermore, preliminary information concerning the radiometric and spectrometric measurements will be given. Title: Response of the middle atmosphere to short-term solar irradiance variability during different Quasi-Biennial Oscillation phases Authors: Shapiro, Anna; Rozanov, Eugene; Shapiro, Alexander; Egorova, Tatiana; Schmutz, Werner; Peter, Thomas Bibcode: 2010cosp...38..138S Altcode: 2010cosp.meet..138S Variability of the spectral solar irradiance (SSI) is known to cause changes in the chemistry and dynamics of the middle atmosphere. Because the analysis of the observed temperature responses to the decadal scale is difficult owing to rather short time series we aim on the study of the middle atmosphere response to the short-term SSI variability associated with the Sun rotation cycle. One of the main problems here is that the response of the atmosphere usually derived using the cross-correlation analysis depends on the atmospheric state and internal variability. In particular, the distribution and variability of the temperature and gas species in the tropical middle atmosphere depends on the phase of quasi-biennial oscillation (QBO). We have applied the chemistry-climate model SOCOL and simulated the dependence of the middle atmosphere response to the short-term solar variability during different QBO phases with a series of ensemble runs. We have found that the hydroxyl sensitivities to the SSI changes during solar rotation cycle are almost identical for the different QBO phases if we forced the model by identical photolysis while the ozone sensitivities to the SSI changes are different for some layers of the stratosphere. Title: Model studies of the solar limb shape variation with wavelenght within the PICARD project. Authors: Melo, Stella M. L.; Thuillier, Gerard; Claudel, Jennyfer; Haberreiter, Margit; Mein, Nicole; Schmutz, Werner; Shapiro, Alexander; Sofia, Sabatino; Short, Christopher I. Bibcode: 2010cosp...38.1756M Altcode: 2010cosp.meet.1756M Solar images in the visible wavelength range show that the disk centre is brighter than the limb region. This phenomenon, which is both known as "centre to limb variation (CLV)", or "limb darkening function", is know to depend on wavelength. Since the CLV is determined by the density and temperature stratification, as well as the chemical composition of the so-lar photosphere, its measurement is important to validate theoretical assumption made when building numerical models of the solar atmosphere. The definition of the solar diameter is nor-mally adopted as the separation between two inflection points at opposite ends of a line passing through the center of the solar disk. Therefore, in order to understand long term variability on the solar diameter, it is important to understand what drives the dependence of the position of the inflection point on wavelength. In this paper we use different available solar atmosphere models to study this dependence. The results presented here refer to quiet Sun conditions and encompass the visible and near infra-red spectral regions, which are the regions of interest for the PICARD Satellite Mission. In a first step we utilize the solar atmosphere parameters with a radiative transfer code. This allows for the study of the impact of different factors such as opacities, electron density and temperature from different models on the results. Then, we compare results obtained using each solar atmosphere model. Our results are compared with existent ground based measurements performed by the Pic du Midi telescope, the balloon board measurements with the Solar Disk Sextant experiment, and with the measurements by the Michelson Doppler Imager on board SoHO satellite. The model simulations show that the position of the inflection point is sensitive to the different parameters and model assumptions. Furthermore, our study shows, for the first time, that the position of the inflection point changes dramatically with and outside of Fraunhofer lines. Title: Pre-flight calibration of LYRA, the solar VUV radiometer on board PROBA2 Authors: Benmoussa, A.; Dammasch, I. E.; Hochedez, J. -F.; Schühle, U.; Koller, S.; Stockman, Y.; Scholze, F.; Richter, M.; Kroth, U.; Laubis, C.; Dominique, M.; Kretzschmar, M.; Mekaoui, S.; Gissot, S.; Theissen, A.; Giordanengo, B.; Bolsee, D.; Hermans, C.; Gillotay, D.; Defise, J. -M.; Schmutz, W. Bibcode: 2009A&A...508.1085B Altcode: Aims. LYRA, the Large Yield Radiometer, is a vacuum ultraviolet (VUV) solar radiometer, planned to be launched in November 2009 on the European Space Agency PROBA2, the Project for On-Board Autonomy spacecraft.
Methods: The instrument was radiometrically calibrated in the radiometry laboratory of the Physikalisch-Technische Bundesanstalt (PTB) at the Berlin Electron Storage ring for SYnchroton radiation (BESSY II). The calibration was done using monochromatized synchrotron radiation at PTB's VUV and soft X-ray radiometry beamlines using reference detectors calibrated with the help of an electrical substitution radiometer as the primary detector standard.
Results: A total relative uncertainty of the radiometric calibration of the LYRA instrument between 1% and 11% was achieved. LYRA will provide irradiance data of the Sun in four UV passbands and with high temporal resolution down to 10 ms. The present state of the LYRA pre-flight calibration is presented as well as the expected instrument performance.
Title: Solar Surface Magnetism and Irradiance on Time Scales from Days to the 11-Year Cycle Authors: Domingo, V.; Ermolli, I.; Fox, P.; Fröhlich, C.; Haberreiter, M.; Krivova, N.; Kopp, G.; Schmutz, W.; Solanki, S. K.; Spruit, H. C.; Unruh, Y.; Vögler, A. Bibcode: 2009SSRv..145..337D Altcode: The uninterrupted measurement of the total solar irradiance during the last three solar cycles and an increasing amount of solar spectral irradiance measurements as well as solar imaging observations (magnetograms and photometric data) have stimulated the development of models attributing irradiance variations to solar surface magnetism. Here we review the current status of solar irradiance measurements and modelling efforts based on solar photospheric magnetic fields. Thereby we restrict ourselves to the study of solar variations from days to the solar cycle. Phenomenological models of the solar atmosphere in combination with imaging observations of solar electromagnetic radiation and measurements of the photospheric magnetic field have reached high enough quality to show that a large fraction (at least, about 80%) of the solar irradiance variability can be explained by the radiative effects of the magnetic activity present in the photosphere. Also, significant progress has been made with magnetohydrodynamic simulations of convection that allow us to relate the radiance of the photospheric magnetic structures to the observations. Title: Solution to the discrepancy between the seismic and photospheric solar radius Authors: Haberreiter, M.; Kosovichev, A. G.; Schmutz, W. Bibcode: 2009EGUGA..11.3961H Altcode: Two methods are usually used to observationally determine the solar radius: One is the observation of the intensity profile at the limb, the other one uses f-mode frequencies to derive a 'seismic' solar radius which is then corrected to optical depth unity. The two methods are inconsistent and lead to a difference in the solar radius of approx. 0.3 Mm. Based on radiative transfer calculations we show that this discrepancy can be explained by the difference between the height at disk center where tau500=1 and the inflection point of the intensity profile on the limb. We calculate the intensity profile of the limb for the MDI continuum and the continuum at 5000 A for two atmosphere structures and compare the position of the inflection points with the radius at optical depth unity. The calculated difference between the 'seismic' radius and the inflection point is 0.347 Mm with respect to optical depth unity and 0.333 Mm with respect to the Rossland mean opacity. We conclude that the standard solar radius in evolutionary models has to be lowered by 0.333 Mm and is 695.66 Mm. This correction reconciles inflection point measurements and the seismic radius within the uncertainty. This finding is very important for the analysis of the solar diameter measurements with the SODISM instrument on PICARD. Title: POLAR investigation of the Sun—POLARIS Authors: Appourchaux, T.; Liewer, P.; Watt, M.; Alexander, D.; Andretta, V.; Auchère, F.; D'Arrigo, P.; Ayon, J.; Corbard, T.; Fineschi, S.; Finsterle, W.; Floyd, L.; Garbe, G.; Gizon, L.; Hassler, D.; Harra, L.; Kosovichev, A.; Leibacher, J.; Leipold, M.; Murphy, N.; Maksimovic, M.; Martinez-Pillet, V.; Matthews, B. S. A.; Mewaldt, R.; Moses, D.; Newmark, J.; Régnier, S.; Schmutz, W.; Socker, D.; Spadaro, D.; Stuttard, M.; Trosseille, C.; Ulrich, R.; Velli, M.; Vourlidas, A.; Wimmer-Schweingruber, C. R.; Zurbuchen, T. Bibcode: 2009ExA....23.1079A Altcode: 2008ExA...tmp...40A; 2008arXiv0805.4389A The POLAR Investigation of the Sun (POLARIS) mission uses a combination of a gravity assist and solar sail propulsion to place a spacecraft in a 0.48 AU circular orbit around the Sun with an inclination of 75° with respect to solar equator. This challenging orbit is made possible by the challenging development of solar sail propulsion. This first extended view of the high-latitude regions of the Sun will enable crucial observations not possible from the ecliptic viewpoint or from Solar Orbiter. While Solar Orbiter would give the first glimpse of the high latitude magnetic field and flows to probe the solar dynamo, it does not have sufficient viewing of the polar regions to achieve POLARIS’s primary objective: determining the relation between the magnetism and dynamics of the Sun’s polar regions and the solar cycle. Title: The DynaMICCS perspective. A mission for a complete and continuous view of the Sun dedicated to magnetism, space weather and space climate Authors: Turck-Chièze, S.; Lamy, P.; Carr, C.; Carton, P. H.; Chevalier, A.; Dandouras, I.; Defise, J. M.; Dewitte, S.; Dudok de Wit, T.; Halain, J. P.; Hasan, S.; Hochedez, J. F.; Horbury, T.; Levacher, P.; Meissonier, M.; Murphy, N.; Rochus, P.; Ruzmaikin, A.; Schmutz, W.; Thuillier, G.; Vivès, S. Bibcode: 2009ExA....23.1017T Altcode: 2008ExA...tmp...42T The DynaMICCS mission is designed to probe and understand the dynamics of crucial regions of the Sun that determine solar variability, including the previously unexplored inner core, the radiative/convective zone interface layers, the photosphere/chromosphere layers and the low corona. The mission delivers data and knowledge that no other known mission provides for understanding space weather and space climate and for advancing stellar physics (internal dynamics) and fundamental physics (neutrino properties, atomic physics, gravitational moments...). The science objectives are achieved using Doppler and magnetic measurements of the solar surface, helioseismic and coronographic measurements, solar irradiance at different wavelengths and in-situ measurements of plasma/energetic particles/magnetic fields. The DynaMICCS payload uses an original concept studied by Thalès Alenia Space in the framework of the CNES call for formation flying missions: an external occultation of the solar light is obtained by putting an occulter spacecraft 150 m (or more) in front of a second spacecraft. The occulter spacecraft, a LEO platform of the mini sat class, e.g. PROTEUS, type carries the helioseismic and irradiance instruments and the formation flying technologies. The latter spacecraft of the same type carries a visible and infrared coronagraph for a unique observation of the solar corona and instrumentation for the study of the solar wind and imagers. This mission must guarantee long (one 11-year solar cycle) and continuous observations (duty cycle > 94%) of signals that can be very weak (the gravity mode detection supposes the measurement of velocity smaller than 1 mm/s). This assumes no interruption in observation and very stable thermal conditions. The preferred orbit therefore is the L1 orbit, which fits these requirements very well and is also an attractive environment for the spacecraft due to its low radiation and low perturbation (solar pressure) environment. This mission is secured by instrumental R and D activities during the present and coming years. Some prototypes of different instruments are already built (GOLFNG, SDM) and the performances will be checked before launch on the ground or in space through planned missions of CNES and PROBA ESA missions (PICARD, LYRA, maybe ASPIICS). Title: Wolf-Rayet Stars at the Highest Angular Resolution Authors: Millour, Florentin; Chesneau, Olivier; Driebe, Thomas; Matter, Alexis; Schmutz, Werner; Lopez, Bruno; Petrov, Romain G.; Groh, José H.; Bonneau, Daniel; Dessart, Luc; Hofmann, Karl-Heinz; Weigelt, Gerd Bibcode: 2009Msngr.135...26M Altcode: Interferometric observations of high-mass evolved stars provide new and very valuable information of their nature. With the unique capabilities of the VLTI, direct images of their closest environment where mass loss and dust formation occur, can be obtained. The breakthrough of the VLTI in terms of angular resolution as well as spectral resolution allows competing theoretical models, based on indirect constraints, to be tested. The high angular resolution made available by the VLTI shows that there is still a lot to discover about these massive stars. Title: A Survey of X-ray Emission from Wolf-Rayet Stars Authors: Skinner, Steve L.; Zhekov, S.; Guedel, M.; Schmutz, W.; Sokal, K. Bibcode: 2009AAS...21349120S Altcode: 2009BAAS...41..470S Previous X-ray studies of Wolf-Rayet (WR) stars have focused mainly on WR binary systems whose luminous high-temperature X-ray emission is thought to originate (at least partially) in colliding wind shocks between the two stars. Much less is known about the X-ray emission of putatively single WR stars, for which evidence of binarity is lacking. We present new results from an ongoing X-ray survey of single WR stars conducted with Chandra and XMM-Newton. Our objectives are to quantify the X-ray properties of single WRs and identify plausible emission mechanisms.

Specifically, we would like to know if single WR stars emit predominantly soft X-rays (kT < 1 keV), as occurs in some O-type stars and is predicted for radiative wind shocks formed by the line-driven instability (LDI) mechanism. Observations to date have failed to detect any X-ray emission from single carbon-rich WC stars. In contrast, some nitrogen-rich WN stars have been detected.

Recent Chandra observations of both WR 2 (WN2) and WR 134 (WN6) reveal luminous X-ray emission (log Lx 32. erg/s) comparable

to that of some WR + OB binaries, including a hot plasma component (kT >> 1 keV). The presence of high-temperature plasma is not in agreement with the cool plasma expected for radiative wind shocks. Either these X-ray luminous WN stars harbor unseen companions or an alternative to the conventional LDI radiative wind shock model will be needed.

This research was supported by NASA grants GO8-9008X (SAO) and NNG05GA10G (GSFC). Title: NLTE model calculations for the solar atmosphere with an iterative treatment of opacity distribution functions Authors: Haberreiter, M.; Schmutz, W.; Hubeny, I. Bibcode: 2008A&A...492..833H Altcode: 2008arXiv0810.3471H Context: Modeling the variability of the solar spectral irradiance is a key factor in understanding the Sun's influence on the climate of the Earth.
Aims: As a first step toward calculating the solar spectral irradiance variations, we reproduce the solar spectrum for the quiet Sun over a broad wavelength range with an emphasis on the UV.
Methods: We introduce the radiative transfer code COSI, which calculates solar synthetic spectra under conditions of non-local thermodynamic equilibrium (NLTE). A self-consistent simultaneous solution of the radiative transfer and the statistical equation for the level populations guarantees that the correct physics is considered for wavelength regions where the assumption of local thermodynamic equilibrium (LTE) breaks down. The new concept of iterated opacity distribution functions (NLTE-ODFs) is presented, through which all line opacities are included in the NLTE radiative transfer calculation.
Results: We show that it is essential to include the line opacities in the radiative transfer to reproduce the solar spectrum in the UV.
Conclusions: Through the implemented scheme of NLTE-ODFs, the COSI code is successful in reproducing the spectral energy distribution of the quiet Sun.

Table 2 is only available in electronic form at http://www.aanda.org Title: P-mode leakage and Lyman-α intensity Authors: Finsterle, W.; Haberreiter, M.; Kosovichev, S.; Schmutz, W. Bibcode: 2008IAUS..247...74F Altcode: 2007IAUS..247...74F We present an observational test of the hypothesis that leaking p modes heat the solar chromosphere. The amplitude of the leaking p modes in magneto-acoustic portals is determined using MOTH and MDI data. We simulate the propagation of these modes into the chromosphere to determine the height where the wave energy is dissipated by shock waves. A statistical approach is then used to check if this heating process could account for the observed variability of the intensity in the Lyman-α emission. Title: Solving the Discrepancy between the Seismic and Photospheric Solar Radius Authors: Haberreiter, M.; Schmutz, W.; Kosovichev, A. G. Bibcode: 2008ApJ...675L..53H Altcode: Two methods are used to observationally determine the solar radius: One is the observation of the intensity profile at the limb; the other one uses f-mode frequencies to derive a "seismic" solar radius which is then corrected to optical depth unity. The two methods are inconsistent and lead to a difference in the solar radius of ~0.3 Mm. Because of the geometrical extension of the solar photosphere and the increased path lengths of tangential rays the Sun appears to be larger to an observer who measures the extent of the solar disk. Based on radiative transfer calculations we show that this discrepancy can be explained by the difference between the height at disk center where τ5000 = 1 (τRoss = 2/3) and the inflection point of the intensity profile on the limb. We calculate the intensity profile of the limb for the MDI continuum and the continuum at 5000 Å for two atmosphere structures and compare the position of the inflection points with the radius at τ5000 = 1 (τRoss = 2/3). The calculated difference between the seismic radius and the inflection point is 0.347 +/- 0.006 Mm with respect to τ5000 = 1, and 0.333 +/- 0.008 Mm with respect to τRoss = 2/3. We conclude that the standard solar radius in evolutionary models has to be lowered by 0.333 +/- 0.008 Mm and is 695.66 Mm. Furthermore, this correction reconciles inflection point measurements and the seismic radii within the uncertainties. Title: XMM-Newton X-ray observations of the Wolf-Rayet binary system WR 147 Authors: Skinner, S. L.; Zhekov, S. A.; Güdel, M.; Schmutz, W. Bibcode: 2007MNRAS.378.1491S Altcode: 2007MNRAS.tmp..491S; 2007arXiv0704.3235S We present results of an ~20-ks X-ray observation of the Wolf-Rayet (WR) binary system WR 147 obtained with XMM-Newton. Previous studies have shown that this system consists of a nitrogen-type WN8 star plus an OB companion whose winds are interacting to produce a colliding wind shock. X-ray spectra from the pn and MOS detectors confirm the high extinction reported from infrared studies and reveal hot plasma including the first detection of the Fe Kα line complex at 6.67 keV. Spectral fits with a constant-temperature plane-parallel shock model give a shock temperature kTshock = 2.7 keV (Tshock ~ 31 MK), close to but slightly hotter than the maximum temperature predicted for a colliding wind shock. Optically thin plasma models suggest even higher temperatures, which are not yet ruled out. The X-ray spectra are harder than can be accounted for using 2D numerical colliding wind shock models based on nominal mass-loss parameters. Possible explanations include: (i) underestimates of the terminal wind speeds or wind abundances, (ii) overly simplistic colliding wind models or (iii) the presence of other X-ray emission mechanisms besides colliding wind shocks. Further improvement of the numerical models to include potentially important physics such as non-equilibrium ionization will be needed to rigorously test the colliding wind interpretation. Title: XMM-Newton Studies of the Wolf-Rayet Colliding-Wind Binaries WR 25 (WN6h+O4f) and WR 11 (WC8+O7.5III) Authors: van der Hucht, K. A.; Raassen, A. J. J.; Mewe, R.; Antokhin, I. I.; Rauw, G.; Vreux, J. -M.; Schild, H.; Schmutz, W. Bibcode: 2007ASPC..367..159V Altcode: We report the analysis of high- and medium-resolution X-ray spectra of the Wolf-Rayet (WR) objects WR25 (HD93162, WN6h+O4f) and WR11 (γ2 Velorum, WC8+O7.5III, P =78.53 d), obtained with the reflection grating spectrometers (rgs) and the european photon imaging cameras (epicmos and <small>PN</small>) <small>CCD</small> spectrometers on board the XMM-Newton satellite. Title: Long-term reconstruction of the total solar irradiance based on neutron monitor and sunspot data Authors: Schöll, M.; Steinhilber, F.; Beer, J.; Haberreiter, M.; Schmutz, W. Bibcode: 2007AdSpR..40..996S Altcode: A new approach for the reconstruction of the past total solar irradiance (TSI) based on neutron monitor (NM) data and sunspot number (SSN) is presented. Our assumption is that the long-term trend of the TSI can be reconstructed by using radionuclide data while the reconstruction of the short-term trend can be achieved by using SSN. The reconstructed TSI correlates well, r2 = 0.84, with space-based TSI measurements. This work will serve as the basis for the reconstruction of the TSI back to the Maunder minimum and beyond by replacing NM with radionuclide data, for which longer time series exist. Title: LYRA - a solar UV radiometer using diamond detectors Authors: Theissen, A.; Benmoussa, A.; Schühle, U.; Hochedez, J. -F.; Schmutz, W. Bibcode: 2007msfa.conf...27T Altcode: LYRA, the Lyman-α radiometer, is a highcadence (100 Hz) solar VUV radiometer which will measure diskintegrated irradiances in 4 wavelength channels. Special emphasis is given on novel detectors based on diamond which will be tested for the first time in space. Two kinds of detectors are employed: MSM and PiNtype detectors. Their particular advantage compared to silicon detectors lies in their solar blindness with a UV/visible reduction ratio of at least four orders of magnitude, which simplifies the design of UV instruments. Title: Simulation of the stratospheric ozone and temperature response to the solar irradiance variability during sun rotation cycle Authors: Rozanov, E.; Egorova, T.; Schmutz, W.; Peter, Th. Bibcode: 2006JASTP..68.2203R Altcode: 2006JATP...68.2203R Despite substantial progress in atmospheric modeling, the agreement of the simulated atmospheric response to decadal scale solar variability with the solar signal in different atmospheric quantities obtained from the statistical analysis of the observations cannot be qualified as successful. An alternative way to validate the simulated solar signal is to compare the sensitivity of the model to the solar irradiance variability on shorter time scales. To study atmospheric response to the 28-day solar rotation cycle, we used the chemistry climate model SOCOL that represents the main physical chemical processes in the atmosphere from the ground up to the mesopause. An ensemble simulation has been carried out, which is comprised of nine 1-year long runs, driven by the spectral solar irradiance prescribed on a daily basis using UARS SUSIM measurements for the year 1992. The correlation of zonal mean hydroxyl, ozone and temperature averaged over the tropics with solar irradiance time series have been analyzed. The hydroxyl has robust correlations with solar irradiance in the upper stratosphere and mesosphere, because the hydroxyl concentration is defined mostly by the photolysis. The simulated sensitivity of the hydroxyl to the solar irradiance changes is in good agreement with previous estimations. The ozone and temperature correlations are more complicated because their behavior depends on non-linear dynamics and transport in the atmosphere. The model simulates marginally significant ozone response to the solar irradiance variability during the Sun rotation cycle, but the simulated temperature response is not robust. The physical nature of this is not clear yet. It seems likely that the temperature (and partly the ozone) daily fields possess their own internal variability, which is not stable and can differ from year to year reflecting different dynamical states of the system. Title: The DynaMICS perspective Authors: Turck-Chièze, S.; Schmutz, W.; Thuillier, G.; Jefferies, S.; Pallé; Dewitt, S.; Ballot, J.; Berthomieu, G.; Bonanno, A.; Brun, A. S.; Christensen-Dalsgaard, J.; Corbard, T.; Couvidat, S.; Darwich, A. M.; Dintrans, B.; Domingo, V.; Finsterle, W.; Fossat, E.; Garcia, R. A.; Gelly, B.; Gough, D.; Guzik, J.; Jiménez, A. J.; Jiménez-Reyes, S.; Kosovichev, A.; Lambert, P.; Lefebvre, S.; Lopes, I.; Martic, M.; Mathis, S.; Mathur, S.; Nghiem, P. A. P.; Piau, L.; Provost, J.; Rieutord, M.; Robillot, J. M.; Rogers, T.; Roudier, T.; Roxburgh, I.; Rozelot, J. P.; Straka, C.; Talon, S.; Théado, S.; Thompson, M.; Vauclair, S.; Zahn, J. P. Bibcode: 2006ESASP.624E..24T Altcode: 2006soho...18E..24T No abstract at ADS Title: X-ray Observations of Binary and Single Wolf-Rayet Stars with XMM-Newton and Chandra Authors: Skinner, Stephen; Güdel, Manuel; Schmutz, Werner; Zhekov, Svetozar Bibcode: 2006Ap&SS.304...97S Altcode: 2005astro.ph.11137S; 2006Ap&SS.tmp...73S We present an overview of recent X-ray observations of Wolf-Rayet (WR) stars with XMM-Newton and Chandra. These observations are aimed at determining the differences in X-ray properties between massive WR + OB binary systems and putatively single WR stars. A new XMM spectrum of the nearby WN8 + OB binary WR 147 shows hard absorbed X-ray emission (including the Fe Kα line complex), characteristic of colliding wind shock sources. In contrast, sensitive observations of four of the closest known single WC (carbon-rich) WR stars have yielded only non-detections. These results tentatively suggest that single WC stars are X-ray quiet. The presence of a companion may thus be an essential factor in elevating the X-ray emission of WC + OB stars to detectable levels. Title: Scientific Objectives of the Novel Formation Flying Mission Aspiics Authors: Turck-Chièze, S.; Schmutz, W.; Thuillier, G.; Jefferies, S.; Pallé; Dewitt, S.; Ballot, J.; Berthomieu, G.; Bonanno, A.; Brun, A. S.; Christensen-Dalsgaard, J.; Corbard, T.; Couvidat, S.; Darwich, A. M.; Dintrans, B.; Domingo, V.; Finsterle, W.; Fossat, E.; Garcia, R. A.; Gelly, B.; Gough, D.; Guzik, J.; Jiménez, A. J.; Jiménez-Reyes, S.; Kosovichev, A.; Lambert, P.; Lefebvre, S.; Lopes, I.; Martic, M.; Mathis, S.; Mathur, S.; Nghiem, P. A. P.; Piau, L.; Provost, J.; Rieutord, M.; Robillot, J. M.; Rogers, T.; Roudier, T.; Roxburgh, I.; Rozelot, J. P.; Straka, C.; Talon, S.; Théado, S.; Thompson, M.; Vauclair, S.; Zahn, J. P. Bibcode: 2006ESASP.617E.164L Altcode: 2006soho...17E.164L No abstract at ADS Title: Development of an SI Traceable Absolute Radiometer for Space and Ground-Based Use Authors: Schlifkowitz, U.; Finsterle, W.; Schmutz, W. Bibcode: 2006ESASP.617E.159S Altcode: 2006soho...17E.159S No abstract at ADS Title: The EUV Variability Experiment (EVE) on the Solar Dynamics Observatory (SDO): Science Plan and Instrument Overview Authors: Turck-Chièze, S.; Schmutz, W.; Thuillier, G.; Jefferies, S.; Pallé; Dewitt, S.; Ballot, J.; Berthomieu, G.; Bonanno, A.; Brun, A. S.; Christensen-Dalsgaard, J.; Corbard, T.; Couvidat, S.; Darwich, A. M.; Dintrans, B.; Domingo, V.; Finsterle, W.; Fossat, E.; Garcia, R. A.; Gelly, B.; Gough, D.; Guzik, J.; Jiménez, A. J.; Jiménez-Reyes, S.; Kosovichev, A.; Lambert, P.; Lefebvre, S.; Lopes, I.; Martic, M.; Mathis, S.; Mathur, S.; Nghiem, P. A. P.; Piau, L.; Provost, J.; Rieutord, M.; Robillot, J. M.; Rogers, T.; Roudier, T.; Roxburgh, I.; Rozelot, J. P.; Straka, C.; Talon, S.; Théado, S.; Thompson, M.; Vauclair, S.; Zahn, J. P. Bibcode: 2006ESASP.617E.165W Altcode: 2006soho...17E.165W No abstract at ADS Title: The Dynamics Project Authors: Turck-Chièze, S.; Schmutz, W.; Thuillier, G.; Jefferies, S.; Pallé; Dewitt, S.; Ballot, J.; Berthomieu, G.; Bonanno, A.; Brun, A. S.; Christensen-Dalsgaard, J.; Corbard, T.; Couvidat, S.; Darwich, A. M.; Dintrans, B.; Domingo, V.; Finsterle, W.; Fossat, E.; Garcia, R. A.; Gelly, B.; Gough, D.; Guzik, J.; Jiménez, A. J.; Jiménez-Reyes, S.; Kosovichev, A.; Lambert, P.; Lefebvre, S.; Lopes, I.; Martic, M.; Mathis, S.; Mathur, S.; Nghiem, P. A. P.; Piau, L.; Provost, J.; Rieutord, M.; Robillot, J. M.; Rogers, T.; Roudier, T.; Roxburgh, I.; Rozelot, J. P.; Straka, C.; Talon, S.; Théado, S.; Thompson, M.; Vauclair, S.; Zahn, J. P. Bibcode: 2006ESASP.617E.162T Altcode: 2006soho...17E.162T No abstract at ADS Title: VizieR Online Data Catalog: Wolf-Rayet population in M83 (Hadfield+, 2005) Authors: Hadfield, L. J.; Crowther, P. A.; Schild, H.; Schmutz, W. Bibcode: 2006yCat..34390265H Altcode: We have observed M83 with the ESO Very Large Telescope UT4 (Yepun) and Focal Reduced/Low Dispersion Spectrograph #2 (FORS2). The detector consists of a mosaic of two 2048x1024 MIT/LL CCDs which in conjunction with the standard collimator provides a field-of-view 6.8'x6.8' and an image scale of 0.126"/pixel. Photometric observations of M83 were made between May-June 2002 with follow-up spectroscopic data being acquired during April-June 2003.

FORS2 was used on 2 June 2002 to obtain narrow-band images with central wavelengths 4684{AA}, 4781{AA} and band widths of 66{AA} and 68{AA} respectively. These were obtained consecutively for each Field in seeing conditions between 0.6-0.8" with individual exposures of 1800s. The {lambda}4684 filter is coincident with the strong WR emission features which incorporates the N III ({lambda}4640{AA}), C III ({lambda}4650{AA}) and He II ({lambda}4686{AA}) emission lines, whereas the latter samples a wavelength region relatively free from emission, providing a measure of the continuum level.

(3 data files). Title: LYRA, a solar UV radiometer on Proba2 Authors: Hochedez, J. -F.; Schmutz, W.; Stockman, Y.; Schühle, U.; Benmoussa, A.; Koller, S.; Haenen, K.; Berghmans, D.; Defise, J. -M.; Halain, J. -P.; Theissen, A.; Delouille, V.; Slemzin, V.; Gillotay, D.; Fussen, D.; Dominique, M.; Vanhellemont, F.; McMullin, D.; Kretzschmar, M.; Mitrofanov, A.; Nicula, B.; Wauters, L.; Roth, H.; Rozanov, E.; Rüedi, I.; Wehrli, C.; Soltani, A.; Amano, H.; van der Linden, R.; Zhukov, A.; Clette, F.; Koizumi, S.; Mortet, V.; Remes, Z.; Petersen, R.; Nesládek, M.; D'Olieslaeger, M.; Roggen, J.; Rochus, P. Bibcode: 2006AdSpR..37..303H Altcode: LYRA is the solar UV radiometer that will embark in 2006 onboard Proba2, a technologically oriented ESA micro-mission. LYRA is designed and manufactured by a Belgian Swiss German consortium (ROB, PMOD/WRC, IMOMEC, CSL, MPS and BISA) with additional international collaborations. It will monitor the solar irradiance in four UV passbands. They have been chosen for their relevance to Solar Physics, Aeronomy and Space Weather: (1) the 115 125 nm Lyman-α channel, (2) the 200 220 nm Herzberg continuum range, (3) the Aluminium filter channel (17 70 nm) including He II at 30.4 nm and (4) the Zirconium filter channel (1 20 nm). The radiometric calibration will be traceable to synchrotron source standards (PTB and NIST). The stability will be monitored by onboard calibration sources (LEDs), which allow to distinguish between potential degradations of the detectors and filters. Additionally, a redundancy strategy maximizes the accuracy and the stability of the measurements. LYRA will benefit from wide bandgap detectors based on diamond: it will be the first space assessment of a pioneering UV detectors program. Diamond sensors make the instruments radiation-hard and solar-blind: their high bandgap energy makes them insensitive to visible light and, therefore, make dispensable visible light blocking filters, which seriously attenuate the desired ultraviolet signal. Their elimination augments the effective area and hence the signal-to-noise, therefore increasing the precision and the cadence. The SWAP EUV imaging telescope will operate next to LYRA on Proba2. Together, they will establish a high performance solar monitor for operational space weather nowcasting and research. LYRA demonstrates technologies important for future missions such as the ESA Solar Orbiter. Title: Simultaneous measurement of the total solar irradiance and solar diameter by the PICARD mission Authors: Thuillier, Gérard; Dewitte, Steven; Schmutz, Werner; Picard Team Bibcode: 2006AdSpR..38.1792T Altcode: A mission dedicated to simultaneous measurements of the solar diameter, spectral, and total solar irradiance is presently in development for launch end of the year 2008 on board of a microsatellite under the responsibility of Centre National d'Etudes Spatiales. The payload will consist of an imaging telescope, three filter radiometers with in total twelve channels, and two independent absolute radiometers. The scientific aims are presented as well as the concepts and properties of the instrumentation. This mission is named PICARD after the pioneering work of Jean Picard (1620-1682) who precisely determined the solar diameter during the Maunder minimum. Title: The PICARD mission: scientific objectives and status of development Authors: Thuillier, G.; Dewitte, S.; Schmutz, W. Bibcode: 2006cosp...36..170T Altcode: 2006cosp.meet..170T Jean Picard a French astronomer measured the solar diameter during the Maunder minimum and his observations opened an important question about the diameter variation with solar activity The solar diameter solar activity relationship remains unclear till this time however it is an important relation for solar physics The PICARD mission will carry out several key measurements such as total and spectral solar irradiance solar diameter limb shape solar asphericity and helioseismologic observations These measurements represent key inputs to validate solar models and to understand the origin of the solar activity These measurements will be carried out by three metrological instruments under the responsibility of Belgium France and Switzerland which will provide absolute radiometers sunphotometers and an imaging telescope The platform is a microsatellite built by the French Space Agency CNES The launch is foreseen by October 2008 This date will allow to have PICARD and Solar Dynamics Observatory NASA in space at the same period for complementary simultaneous measurements Given the specific observations by each mission a strong synergy exists between these two programs Past and present solar diameter measurements reveal discrepancies among results with solar activity consisting either correlation anticorrelation or no variation To understand the role of the atmosphere ground based instruments will be also run during the mission allowing PICARD to extent its domain of interest toward the atmosphere physics by comparing ground and space simultaneous Title: Space Weather with ESA's PROBA2 Mission Authors: Lawrence, G.; Berghmans, D.; Hochedez, J. -F.; Ben-Moussa, A.; Defise, J. -M.; Delouille, V.; Dominique, M.; Katsitannis, A.; Lecat, J. -H.; Nicula, B.; Schmutz, W.; Slemzin, V.; Theissen, A. Bibcode: 2005ESASP.592..685L Altcode: 2005ESASP.592E.137L; 2005soho...16E.137L No abstract at ADS Title: Development of a phase-sensitive absolute radiometer for space and ground-based use Authors: Schlifkowitz, Uwe; Finsterle, Wolfgang; Schmutz, Werner Bibcode: 2005ESASP.590..467S Altcode: 2005erbp.conf..467S Absolute radiometers with a phase-sensitive signal analysis are already being used in space successfully (Lawrence et al. (2000)). These instruments are operated with relatively long shutter periods of several minutes. Unfortunately, they have a large thermal capacity and are rather large and heavy and are therefore unsuitable for use on space missions where there is only a limited amount of load capacity available. The aim of our project is to develop a radiometer with a relatively small cavity and thermal capacity, which is based on phase-sensitive signal analysis as well, and which will have a much better accuracy than traditional instruments. With the help of the phase-sensitive analysis, many thermal sources of irritation, such as the so-called non-equivalence of the electric and radiative heating, can be eliminated. We hope to be able to run a radiometer experiment on both Solar Orbiter and Solar Dynamic Observatory (SDO) spacecraft, where the main advantage of reduced weight comes in. As a side effect, radiometers with small shutter periods are suitable for ground-based use as well, as they can handle fast changes in irradiance, i.e. altitude of the sun. Title: SWAP: an EUV imager for solar monitoring on board of PROBA2 Authors: Katsiyannis, Athanassios C.; Berghmans, David; Hochedez, Jean-Francois; Nicula, Bogdan; Lawrence, Gareth; Defise, Jean-Marc; Ben-Moussa, Ali; Delouille, Veronique; Dominique, Marie; Lecat, Jean-Herve; Schmutz, W.; Theissen, Armin; Slemzin, Vladimir Bibcode: 2005SPIE.5901..236K Altcode: PROBA2 is an ESA technology demonstration mission to be launched in early 2007. The two primary scientific instruments on board of PROBA2 are SWAP (Sun Watcher using Active Pixel System detector and Image Processing) and the LYRA VUV radiometer. SWAP provides a full disk solar imaging capability with a bandpass filter centred at 17.5 nm (FeIX-XI) and a fast cadence of ≈1 min. The telescope is based on an off-axis Ritchey Chretien design while an extreme ultraviolet (EUV) enhanced APS CMOS will be used as a detector. As the prime goal of the SWAP is solar monitoring and advance warning of Coronal Mass Ejections (CME), on-board intellige nce will be implemented. Image recognition software using experimental algorithms will be used to detect CMEs during the first phase of eruption so the event can be tracked by the spacecraft without huma n intervention. LYRA will monitor solar irradiance in four different VUV passbands with a cadence of up to 100 Hz. The four channels were chosen for their relevance to solar physics, aeronomy and space weather: 115-125 nm (Lyman-α), 200-220 nm Herzberg continuum, the 17-70 nm Aluminium filter channel (that includes the HeII line at 30.4 nm) and the 1-20 nm Zirconium filter channel. On-board calibration sources will monitor the stability of the detectors and the filters throughout the duration of the mission. Title: A spectroscopic search for the non-nuclear Wolf-Rayet population of the metal-rich spiral galaxy M 83 Authors: Hadfield, L. J.; Crowther, P. A.; Schild, H.; Schmutz, W. Bibcode: 2005A&A...439..265H Altcode: 2005astro.ph..6343H We present a catalogue of non-nuclear regions containing Wolf-Rayet stars in the metal-rich spiral galaxy M 83 (NGC 5236). From a total of 283 candidate regions identified using He ii λ4686 imaging with VLT-FORS2, Multi Object Spectroscopy of 198 regions was carried out, confirming 132 WR sources. From this sub-sample, an exceptional content of ~1035 ± 300 WR stars is inferred, with N(WC)/N(WN) ~ 1.2, continuing the trend to larger values at higher metallicity amongst Local Group galaxies, and greatly exceeding current evolutionary predictions at high metallicity. Late-type stars dominate the WC population of M 83, with N(WC8-9)/N(WC4-7) = 9 and WO subtypes absent, consistent with metallicity dependent WC winds. Equal numbers of late to early WN stars are observed, again in contrast to current evolutionary predictions. Several sources contain large numbers of WR stars. In particular, #74 (alias region 35 from de Vaucouleurs et al.) contains ~230 WR stars, and is identified as a Super Star Cluster from inspection of archival HST/ACS images. Omitting this starburst cluster would result in revised statistics of N(WC)/N(WN) ~ 1 and N(WC8-9)/N(WC4-7) ~ 6 for the "quiescent" disk population. Including recent results for the nucleus and accounting for incompleteness in our spectroscopic sample, we suspect the total WR population of M 83 may exceed 3000 stars. Title: The Disk Wolf-Rayet Population of the Nuclear Starburst Galaxy M83 Authors: Crowther, Paul A.; Hadfield, Lucy J.; Schild, Hans; Schmutz, Werner Bibcode: 2005ASSL..329...21C Altcode: 2005sdlb.proc...21C No abstract at ADS Title: Reconstruction of the solar UV irradiance back to 1974 Authors: Haberreiter, M.; Krivova, N. A.; Schmutz, W.; Wenzler, T. Bibcode: 2005AdSpR..35..365H Altcode: The variability of the solar UV irradiance has strong effects on the terrestrial atmosphere. In order to study the solar influence for times when no UV observations are available, it is necessary to reconstruct the variation of the UV irradiance with time on the basis of proxies. We present reconstructions of the solar UV irradiance based on the analysis of space-based and ground-based magnetograms of the solar disk going back to 1974. With COde for Solar Irradiance (COSI) we calculate solar intensity spectra for the quiet Sun and different active regions and combine them according to their fractional area on the solar disk, whereby their time-dependent contributions over the solar cycle lead to a variability in radiation. COSI calculates the continuum and line formation under conditions which are out of local thermodynamic equilibrium (non-LTE). The applied temperature and density structures include the chromosphere and transition region, which is particularly important for the UV. The reconstructions are compared with observations. Title: Modeling of the Joule heating influence on the circulation and ozone concentration in the middle atmosphere Authors: Zubov, V.; Rozanov, E.; Shirochkov, A.; Makarova, L.; Egorova, T.; Kiselev, A.; Ozolin, Yu.; Karol, I.; Schmutz, W. Bibcode: 2005JASTP..67..155Z Altcode: 2005JATP...67..155Z A chemistry climate model is used to evaluate of the possible influence of Joule heating induced by the solar wind and interplanetary magnetic field (IMF) elements on the ozone concentration and dynamics of the Earth atmosphere. The Joule heating rates in the stratosphere are parameterized on the base of the time series of the solar wind and IMF parameters taken from the NASA database (Interplanetary Medium Data Book, NASA, USA, 1999) for 1996. The results of the 10-year-long model run with the additional Joule source of heat are compared with the output of the unperturbed (control) 20-year-long model run. Both simulations are performed in equilibrium mode with prescribed boundary conditions and for the minimum of the 11-year solar cycle. The comparison of the model outputs shows that the simulated atmosphere is rather sensitive to the introduced Joule heating. The most significant changes were found in the lower stratosphere of the northern hemisphere (NH). The NH lower-stratospheric temperature increases by 1 3 K almost throughout the whole year with the significance level at 95% or higher. In boreal summer, the changes of the ozone concentration are anti-correlated with the temperature as expected from the gas phase photochemical theory. In boreal autumn and spring, the variations of the ozone mixing ratio can be affected not only by the local temperature changes but also by the redistribution of the meridional circulation in the stratosphere. In the southern hemisphere (SH), the additional Joule heating leads to a significant increase of the stratospheric temperature for the austral winter (∼2K). The most substantial SH ozone changes (∼10%) are found in the lower stratosphere during the austral spring. Title: Influence of solar 11-year variability on chemical composition of the stratosphere and mesosphere simulated with a chemistry-climate model Authors: Egorova, T.; Rozanov, E.; Zubov, V.; Schmutz, W.; Peter, Th. Bibcode: 2005AdSpR..35..451E Altcode: An understanding of observed global chemistry and climate changes caused by solar activity changes is a high priority in modern geosciences. Here, we discuss the influence of the ultraviolet spectral irradiance variability during solar cycle on chemical composition of the stratosphere and mesosphere with chemistry-climate model that fully describes the interactions between chemical and thermo-dynamical processes. We have performed several 20-year long steady-state runs and found a significant influence of solar irradiation on the chemical composition in the stratosphere and mesosphere. An enhanced photolysis during solar maximum results in destruction of methane, nitrous oxide and CFCs providing an increase in the chemical activity of the atmosphere with more pronounced effects in the mesosphere. In the mesosphere, an increase of HO x caused by more intensive water vapor photolysis results in significant ozone depletion there. More intensive methane oxidation gives statistically significant rise to the stratospheric humidity. The influence of dynamical perturbations has been identified over high latitude areas. The response of OH is found to be in a good agreement with observation data. The response of the other species is hard to validate, because of the lack of theoretical and observational studies. Title: Preface (The Sun, solar analogs and the climate) Authors: Rüedi, Isabelle; Güdel, Manuel; Schmutz, Werner Bibcode: 2005ssac.confD...5R Altcode: 2005SAAS...34D...5R No abstract at ADS Title: Solar signal in atmospheric ozone, temperature and dynamics simulated with CCM SOCOL in transient mode Authors: Rozanov, E.; Schraner, M.; Egorova, T.; Ohmura, A.; Wild, M.; Schmutz, W.; Peter, T. Bibcode: 2005MmSAI..76..876R Altcode: We have carried out a set of transient runs of the Chemistry-Climate Model SOCOL covering 1975-2000 driven by time evolving sea surface temperature and sea ice distributions, sulfate aerosol loading, spectral solar irradiance, greenhouse gases and ozone destroying substances. We present the solar signal in the atmosphere extracted from these transient runs. For the estimation of the atmospheric response to the solar irradiance variability we use multiple regression analysis to define the contribution of the imposed solar radiance changes to the time evolution of the simulated quantities and to estimate their sensitivity to the solar irradiance changes from the solar maximum to minimum cases. The solar signal extracted from the transient runs has been compared to the solar signal obtained from the steady-state simulations with the same model. In general, the ozone response obtained from the transient simulation is closer to the observation data analysis than the results obtained from the steady-state experiment. The ozone response in the lower mesosphere and upper stratosphere to the solar irradiance changes is mostly positive (≈ 1-2%). Above 30 km the ozone response is well pronounced (< 5%) and occurs at 40 km over the middle latitudes. The ozone response is smaller (< 2%) in the tropical middle stratosphere, while two additional maximums appear in the UTLS over the northern high and southern middle latitudes. The solar signal in the temperature extracted from the transient runs resembles the results of the steady-state run by the location and magnitude of the warming spots. The differences appear to be substantial only in the UTLS region over the middle latitudes. They comprise in the additional warming with magnitude exceeding 0.6 K. These elevated temperatures presumably reflect an intensification of the polar vortices. The solar signal obtained for several other simulated quantities is also analyzed. Title: The Sun, Solar Analogs and the Climate Authors: Haigh, Joanna D.; Lockwood, Michael; Giampapa, Mark S.; Rüedi, Isabelle; Güdel, Manuel; Schmutz, Werner Bibcode: 2005ssac.conf.....H Altcode: 2005SAAS...34.....H This book presents the lecture notes of the 34th Saas-Fee Advanced Course "The Sun, Solar Analogs and the Climate" given by leading scientists in the field. Emphasis is on the observed variability of the Sun and the present understanding of the variability's origin as well as its impact on the Earth's climate. The solar variability is then studied in the broader context of solar-type stars, allowing for better understanding of the solar-activity cycle and the magnetic activity in general. This book provides an accessible and up-to-date introduction to the field for graduate students and serves as a modern source of reference for active researchers in this field. Title: Assessment of the ozone and temperature variability during 1979 1993 with the chemistry-climate model SOCOL Authors: Rozanov, E.; Schraner, M.; Schnadt, C.; Egorova, T.; Wild, M.; Ohmura, A.; Zubov, V.; Schmutz, W.; Peter, Th. Bibcode: 2005AdSpR..35.1375R Altcode: The chemistry-climate model SOCOL has been applied for the study of ozone and temperature anomalies during 1979-1993. Temperature and ozone anomalies have been obtained for a set of model runs forced by all major stratospheric forcing mechanisms. Forcings have been prescribed separately and together to assess their individual influence on stratospheric ozone and temperature. The results of these simulations have been compared to available satellite data. The model captures well ozone depletion and cooling in the upper stratosphere due to increases in the abundance of greenhouse gases and ozone depleting substances in the atmosphere. In the lower stratosphere, the model reproduces the warming over tropical and middle latitudes caused by the El-Chichon and Pinatubo eruptions. However, the simulated ozone response is overestimated in comparison with SAGE data. The best agreement with observations has been obtained for the run with all forcings included. This emphasizes the importance of the volcanic and solar forcings for the correct reproduction of observed trends. Comparison of near-global total ozone anomalies confirms an overestimation of ozone depletion just after volcanic eruptions, while the overall agreement with the model is fairly good. Title: The Wolf-Rayet Population in Region B of NGC 5253 Authors: Sidoli, F.; Smith, L. J.; Crowther, P. A.; Vacca, W. D.; Schmutz, W. Bibcode: 2004ASPC..322..217S Altcode: We present Keck+HIRES data of Region B in NGC 5253 and compare for the first time the observed WR line profiles of this cluster to new evolutionary synthesis models which can synthesize WR features. Using this technique we determine the massive star population for the cluster. Title: Parameterization of the heating in the middle stratosphere due to solar wind-induced electric currents Authors: Makarova, L. N.; Shirochkov, A. V.; Nagurny, A. P.; Rozanov, E.; Schmutz, W. Bibcode: 2004JASTP..66.1173M Altcode: 2004JATP...66.1173M A new mechanism of thermal heating in the middle stratosphere by the solar wind-induced electric currents is proposed. This process occurs mostly at 20-30km altitude where a permanent layer of heavy ion-clusters is produced by the galactic cosmic rays and by some other sporadically occurring sources. The currents in this layer control the electric fields in the stratosphere. Numerical estimation of the possible atmospheric heating rate due to this process shows that such heating could reach 1-2K/day that is comparable to the heating due to the absorption of the solar UV radiation. Thus, the electric fields and currents induced by the solar wind energy are candidates for producing relevant additional heating in the middle stratosphere (altitudes 20-30km). This process may alter the thermal structure of the polar stratosphere and the structure of the polar stratospheric vortex, and as a result, the global climate/weather system. In this paper, we describe the parameterization of this heating suitable for the application in climate and general circulation models. Title: Wind clumping and the wind-wind collision zone in the Wolf-Rayet binary γ2 Velorum observations at high and low state. XMM-Newton observations at high and low state Authors: Schild, H.; Güdel, M.; Mewe, R.; Schmutz, W.; Raassen, A. J. J.; Audard, M.; Dumm, T.; van der Hucht, K. A.; Leutenegger, M. A.; Skinner, S. L. Bibcode: 2004A&A...422..177S Altcode: 2004astro.ph..4610S We present XMM-Newton observations of γ2 Velorum (WR 11, WC8+O7.5III, P = 78.53 d), a nearby Wolf-Rayet binary system, at its X-ray high and low states. At high state, emission from a hot collisional plasma dominates from about 1 to 8 keV. At low state, photons between 1 and 4 keV are absorbed. The hot plasma is identified with the shock zone between the winds of the primary Wolf-Rayet star and the secondary O giant. The absorption at low state is interpreted as photoelectric absorption in the Wolf-Rayet wind. This absorption allows us to measure the absorbing column density and to derive a mass loss rate .M = 8 × 10-6 M⊙ yr-1 for the WC8 star. This mass loss rate, in conjunction with a previous Wolf-Rayet wind model, provides evidence for a clumped WR wind. A clumping factor of 16 is required. The X-ray spectra below 1 keV (12 Å) show no absorption and are essentially similar in both states. There is a rather clear separation in that emission from a plasma hotter than 5 MK is heavily absorbed in low state while the cooler plasma is not. This cool plasma must come from a much more extended region than the hot material. The Neon abundance in the X-ray emitting material is 2.5 times the solar value. The unexpected detection of C V (25.3 Å) and C VI (31.6 Å) radiative recombination continua at both phases indicates the presence of a cool (∼40 000 K) recombination region located far out in the binary system.

Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and the USA (NASA). Title: XMM-Newton X-ray observations of γ2 Velorum (WC8 + O7.5III) Authors: Raassen, A. J. J.; Mewe, R.; van der Hucht, K. A.; Schmutz, W.; Schild, H.; Dumm, T.; Güdel, M.; Audard, M.; Leutenegger, M. A.; Skinner, S. L. Bibcode: 2004NuPhS.132..697R Altcode: The spectrum of the binary system γ2 Velorum (WC8 + O7.5III) has been observed with RGS and EPIC-MOS aboard XMM-Newton. The system shows a 'high state' when the O-star is between the Wolf-Rayet star and the observer (near periastron) and a 'low state' when most of the spectrum is absorbed by the dense stellar wind of the Wolf-Rayet star (near apastron). The spectrum has been model-led by a 4-T plasma, using SPEX. The absorption affects the hot temperature component (kT = 1.5 keV) that is formed by the collision of the Wolf-Rayet wind and the O-star wind, and the second hot component (kT = 0.65 keV) for which the origin is still unclear. Part of the spectrum is not sensitive to the absorption by the stellar wind. This concerns a low-temperature component (kT = 0.23 keV) and features that are produced by plasma that has been photoionized by X-ray radiation from the hot component. In the RGS spectrum features of Radiative Recombination Continua (RRC) of C VI and C V of this photoionized plasma are detected. Title: An exceptional population of late-type WC stars in the metal-rich spiral galaxy M 83 Authors: Crowther, P. A.; Hadfield, L. J.; Schild, H.; Schmutz, W. Bibcode: 2004A&A...419L..17C Altcode: 2004astro.ph..3636C We have surveyed the metal-rich spiral galaxy M 83 (NGC 5236) for its Wolf-Rayet population using VLT-FORS2 narrow-band imaging and follow-up spectroscopy. From a total of 280 candidates identified using He II λ4686 imaging, Multi Object Spectroscopy of 198 sources was carried out, revealing 132 objects containing bona-fide Wolf-Rayet features. From this sample, an exceptional W-R content of ∼1030 is inferred, with N(WC)/N(WN) ∼ 1.3, continuing the trend to larger values at higher metallicity amongst Local Group galaxies. More dramatic is the dominance of late-type WC stars in M 83 with N(WC8-9)/N(WC4-7) = 9 which we attribute to the sensitivity of the classification line C III λ5696 to mass-loss, providing the strength of WC winds scale with metallicity. One young massive compact cluster, #74 in our catalogue, hosts 20% of the entire galactic population, namely ∼180 late WC stars and ∼50 late WN stars.

Based on observations made with ESO Telescopes at the Paranal Observatory under programme ID 69.B-0125. Title: Chemical and dynamical response to the 11-year variability of the solar irradiance simulated with a chemistry-climate model Authors: Egorova, T.; Rozanov, E.; Manzini, E.; Haberreiter, M.; Schmutz, W.; Zubov, V.; Peter, T. Bibcode: 2004GeoRL..31.6119E Altcode: 2004GeoRL..3106119E Atmospheric effects of the solar irradiance variations during 11-year solar cycle are investigated using a chemistry-climate model. The model is enhanced by a more detailed parameterization of the oxygen and ozone UV heating rates. The simulated ozone response to the imposed solar forcing shows a positive correlation in the tropical stratosphere and a negative correlation in the tropical mesosphere, in agreement with theoretical expectation. The model suggests an acceleration of the polar night jets in both hemispheres and a dipole structure in the temperature changes at high latitudes. The model results also show an alteration of the tropospheric circulation air resulting in a statistically significant warming of 1 K in the annual mean surface air temperature over North America and Siberia. This supports the idea of a solar-climate connection. Title: Evaluation of UV and Visible radiation influence on dynamics and chemistry of the atmosphere with CCM SOCOL. Authors: Egorova, T.; Rozanov, E.; Zubov, V.; Manzini, E.; Haberreiter, M.; Schmutz, W.; Peter, T. Bibcode: 2004cosp...35..718E Altcode: 2004cosp.meet..718E To separate the influence of UV and visible radiation on the global atmosphere and to investigate the effects of solar variability during 11-year solar cycle we have carried out four 20-year long steady state simulations with observed spectral solar fluxes: (1) Solar minimum; (2) Solar maximum; (3) Solar maximum for UV radiation only; and (4) Solar maximum for Visible radiation only. As a modeling tool we have used the chemistry-climate model SOCOL. The obtained results for experiment runs have been compared with the solar minimum case. The simulated ozone response is positively correlated with solar irradiance in the tropical stratosphere and negatively correlated in the mesosphere, which is in an agreement with theoretical expectation. For the experiment 2 the model suggests a weak acceleration of the polar night jets resulting in a dipole structure in the temperature response over the high latitudes of both hemispheres. These dynamical changes lead to an alternation of the tropospheric circulation, which in turn, influences the surface air temperature resulting in a statistically significant warming of 1 K in the annual mean surface air temperature over North America and Siberia. The pattern in surface temperature changes resembles the signal of positive AO phases, which implies downward propagation of the solar signal via intensification of the polar night jets. For the simulation where only the visible radiation was enhanced we have also obtained a stratospheric response. This response appears only over the high latitudes and is caused by upward propagating dynamical perturbations. Our analysis of the surface air temperature response shows that the visible and UV radiation dominates in different geographical regions providing a substantial combined effect. Title: Reconstruction of solar UV irradiance back to 1974 Authors: Haberreiter, M.; Krivova, N. A.; Schmutz, W.; Wenzler, T. Bibcode: 2004cosp...35.2707H Altcode: 2004cosp.meet.2707H The variability of the solar UV irradiance has strong effects on the terrestrial atmosphere. In order to study the solar influence for times when no UV observations are available, it is necessary to reconstruct the variation of the UV irradiance with time on the basis of proxies. We present reconstructions of the solar UV irradiance based on the analysis of space-based and ground-based magnetograms of the solar disk going back to 1974. With COSI (COde for Solar Irradiance) we calculate solar intensity spectra for the quiet Sun and different active regions and combine them according to their fractional area on the solar disk, whereby their time-dependent contributions over the solar cycle lead to a variability in radiation. COSI calculates the continuum and line formation in non-local thermodynamic equilibrium (non-LTE). The applied temperature and density structures include the chromosphere and transition region, which is particularly important for the UV. The reconstructions are compared with observations. Title: Assessment of the Ozone and Temperature Trends for 1975-2000 with a transient Chemistry-Climate Model Authors: Rozanov, E.; Schraner, M.; Wild, M.; Egorova, T.; Zubov, V.; Manzini, E.; Austin, J.; Ohmura, A.; Schmutz, W.; Peter, T. Bibcode: 2004cosp...35.2640R Altcode: 2004cosp.meet.2640R We have simulated the changes of the atmospheric state during the last 25 years of the 20th century with the Chemistry-Climate Model SOCOL extending form the ground up to 80 km. We have carried out four 25-year long transient runs forced by the observed sea surface temperature/sea ice (SST/SI) distributions. For the first simulation only the time evolving SST/SI are prescribed. For the second and third simulations we have added the time evolution of the Greenhouse Gases (GHG) and Ozone Destructing Substances (ODS). In the forth simulation we consider the forcing due to the both GHG and ODS. The obtained trends in the ozone and temperature are compared with available observation data. The obtained time evolution of the temperature and ozone fields for the forth run are closer to the observation data than the results of all other runs. The model captures the formation of the ozone ``hole'' over the southern high-latitudes, cooling and ozone depletion in the upper stratosphere and warming in the troposphere. However, a substantial total ozone depletion observed in 1992-1993 is not captured by the model, because of the lack of volcanic aerosols after the Pinatubo eruption in our experiments. We expect that this feature will be correctly reproduced in the ongoing experiment where the volcanic aerosol is taken into account. The model simulates an increase of the stratospheric water vapor mixing ratio by of about 7%/decade which is most likely connected to the tropospheric warming and subsequent increase of the water vapor in the upper troposphere. Title: Solar-Blind Diamond Detectors for Lyra, the Solar VUV Radiometer on Board Proba II Authors: Benmoussa, A.; Hochedez, J. -F.; Schmutz, W. K.; Schühle, U.; Nesládek, M.; Stockman, Y.; Kroth, U.; Richter, M.; Theissen, A.; Remes, Z.; Haenen, K.; Mortet, V.; Koller, S.; Halain, J. P.; Petersen, R.; Dominique, M.; D'Olieslaeger, M. Bibcode: 2003ExA....16..141B Altcode: Fabrication, packaging and experimental results on the calibration of metal-semiconductor-metal (MSM) photodetectors made on diamond are reported. LYRA (Lyman-α RAdiometer onboard PROBA-2) will use diamond detectors for the first time in space for a solar physics instrument. A set of measurement campaigns was designed to obtain the XUV-to-VIS responsivity of the devices and other characterizations. The measurements of responsivity in EUV and VUV spectral ranges (40 240 nm) have been carried out by the Physkalisch-Technische Bundesanstalt (PTB) in Germany at the electron storage ring BESSY II. The longer wavelength range from 210 to 1127 nm was measured with monochromatic light by using a Xe-lamp at IMO-IMOMEC. The diamond detectors exhibit a photoresponse which lie in the 35 65 mA/W range at 200 nm (corresponding to an external quantum efficiency of 20 40%) and indicate a visible rejection ratio (200 500 nm) higher than four orders of magnitude. Title: Traceable radiometry underpinning terrestrial- and helio-studies (TRUTHS) Authors: Fox, N.; Aiken, J.; Barnett, J. J.; Briottet, X.; Carvell, R.; Frohlich, C.; Groom, S. B.; Hagolle, O.; Haigh, J. D.; Kieffer, H. H.; Lean, J.; Pollock, D. B.; Quinn, T.; Sandford, M. C. W.; Schaepman, M.; Shine, K. P.; Schmutz, W. K.; Teillet, P. M.; Thome, K. J.; Verstraete, M. M.; Zalewski, E. Bibcode: 2003AdSpR..32.2253F Altcode: The Traceable Radiometry Underpinning Terrestrial- and Helio- Studies (TRUTHS) mission offers a novel approach to the provision of key scientific data with unprecedented radiometric accuracy for Earth Observation (EO) and solar studies, which will also establish well-calibrated reference targets/standards to support other EO missions. This paper presents the TRUTHS mission and its objectives. TRUTHS will be the first satellite mission to calibrate its EO instrumentation directly to Sl in orbit, overcoming the usual uncertainties associated with drifts of sensor gain and spectral shape by using an electrical rather than an optical standard as the basis of its calibration. The range of instruments flown as part of the payload will also provide accurate input data to improve atmospheric radiative transfer codes by anchoring boundary conditions, through simultaneous measurements of aerosols, particulates and radiances at various heights. Therefore, TRUTHS will significantly improve the performance and accuracy of EO missions with broad global or operational aims, as well as more dedicated missions. The provision of reference standards will also improve synergy between missions by reducing errors due to different calibration biases and offer cost reductions for future missions by reducing the demands for on-board calibration systems. Such improvements are important for the future success of strategies such as Global Monitoring for Environment and Security (GMES) and the implementation and monitoring of international treaties such as the Kyoto Protocol. TRUTHS will achieve these aims by measuring the geophysical variables of solar and lunar irradiance, together with both polarised and unpolarised spectral radiance of the Moon, Earth and its atmosphere. Published by Elsevier Ltd on behalf of COSPAR. Title: The PICARD mission Authors: Thuillier, Gérard; Joukoff, Alexandre; Schmutz, Werner Bibcode: 2003ESASP.535..251T Altcode: 2003iscs.symp..251T PICARD is an investigation dedicated to the Sun-climate connection. The mission objectives are the study of the solar forcing on the Earth's climate, and the physics of the Sun. It consists of simultaneous measurements of the absolute total and spectral solar irradiance, the diameter and solar shape, and to carry out helioseismologic observations to probe the Sun's interior. These measurements obtained all along the mission will allow to study their variations as a function of the solar activity. The observations will be carried out by three instruments placed on board a microsatellite built by Centre National d'Etudes Spatiales (France). Ground-based observations will complement the space observations. Title: Modelling the solar UV radiation Authors: Haberreiter, M.; Schmutz, W. Bibcode: 2003ESASP.535..289H Altcode: 2003iscs.symp..289H We model the solar spectrum with emphasis on the UV range with the spherical non-LTE atmosphere code COSI (COde for Solar Irradiance). Presently, we explicitly treat 31 levels in non-LTE and apply to 17 levels of neutral metals the latest theoretical photoionization cross sections. The atmosphere models are based on the observed temperature and density structures by Fontenla et al. (1999), which include the chromosphere and transition region. We compare synthetic spectra from 2000 to 7500 Å in local thermodynamic equilibrium (LTE) with calculations from a Kurucz model, as well as theoretical Balmer line profiles computed in non-LTE with observations. Title: XMM-Newton high-resolution x-ray spectroscopy of the Wolf-Rayet object WR25 (WN6HA+04F) Authors: Raassen, A. J. J.; van der Hucht, K. A.; Mewe, R.; Antokhin, I.; Rauw, G.; Vreux, J. -M.; Schmutz, W.; Güdel, M. Bibcode: 2003AdSpR..32.1161R Altcode: We report the analysis of the X-ray spectrum of the Wolf-Rayet star WR 25, observed by RGS and EPIC-MOS on board XMM-Newton. Temperatures up to 40 MK have been determined. Strong absorption, exceeding the value due to the Inter Stellar Medium (ISM) has been detected and assigned to the dense stellar wind. Title: XMM-Newton high-resolution X-ray spectroscopy of the Wolf-Rayet object WR 25 in the Carina OB1 association Authors: Raassen, A. J. J.; van der Hucht, K. A.; Mewe, R.; Antokhin, I. I.; Rauw, G.; Vreux, J. -M.; Schmutz, W.; Güdel, M. Bibcode: 2003A&A...402..653R Altcode: We report the analysis of the first high-resolution X-ray spectra of the Wolf-Rayet (WR) object WR 25 (HD 93162, WN6ha+O4f) obtained with the Reflection Grating Spectrometers (RGS) and the European Photon Imaging Cameras (EPIC-MOS and PN) CCD spectrometers on board the XMM-Newton satellite. The spectrum exhibits bright emission lines of the H- and He-like ions of Ne, Mg, Si and S, as well as Fe XVII i to Fe XX and Fe XXV lines. Line fluxes have been measured. The RGS and EPIC spectra have been simultaneously fitted to obtain self-consistent temperatures, emission measures, and elemental abundances. Strong absorption by the dense WR stellar wind and the interstellar medium (ISM) is observed equivalent to NH = 7 x 1021 cm-2. Multi-temperature (DEM) fitting yields two dominant components around temperatures of 7.0 and 32 MK, respectively. The XMM intrinsic (i.e. unabsorbed, corrected for the stellar wind absorption and the absorption of ISM) X-ray luminosity of WR 25 is Lx(0.5-10 keV) = 1.3 x 1034 erg s-1, and Lx(0.5-10 keV) = 0.85 x 1034 erg s-1, (when correcting for the ISM only) assuming d=3.24 kpc. The obtained chemical abundances are subsolar, except for S. This may be real, but could equally well be due to a weak coupling to the continuum, which is strongly influenced by the absorption column density and the subtracted background. The expected high N-abundance, as observed in the optical wavelength region, could not be confirmed due to the strong wind absorption, blocking out its spectral signature. The presence of the Fe XXV emission-line complex at ~ 6.7 keV is argued as being indicative for colliding winds inside a WR+O binary system.

Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and the USA (NASA). Title: A large Wolf-Rayet population in NGC 300 uncovered by VLT-FORS2 Authors: Schild, H.; Crowther, P. A.; Abbott, J. B.; Schmutz, W. Bibcode: 2003A&A...397..859S Altcode: 2002astro.ph..9259S We have detected 58 Wolf-Rayet candidates in the central region of the nearby spiral galaxy NGC 300, based on deep VLT-FORS2 narrow-band imaging. Our survey is close to complete except for heavily reddened WR stars. Of the objects in our list, 16 stars were already spectroscopically confirmed as WR stars by Schild & Testor and Breysacher et al., to which 4 stars are added using low resolution FORS2 datasets. The WR population of NGC 300 now totals 60, a threefold increase over previous surveys, with WC/WN>=1/3, in reasonable agreement with Local Group galaxies for a moderately sub-solar metallicity. We also discuss the WR surface density in the central region of NGC 300. Finally, analyses are presented for two apparently single WC stars - #29 (alias WR3, WC5) and #48 (alias WR13, WC4) located close to the nucleus, and at a deprojected radius of 2.5 kpc, respectively. These are among the first models of WR stars in galaxies beyond the Local Group, and are compared with early WC stars in our Galaxy and LMC.

Based on observations made with ESO Telescopes at the Paranal Observatory under programme ID 65.H-0705(A). Title: Wolf-Rayet stars at 1 - 2 Mpc Authors: Crowther, Paul A.; Abbott, Jay B.; Drissen, Laurent; Schild, Hansrüdi; Schmutz, Werner; Royer, Pierre; Smartt, Stephen J. Bibcode: 2003IAUS..212..547C Altcode: We present new narrow-band imaging and optical spectroscopy of Wolf-Rayet stars in the Local Group dwarf galaxy IC 10 (Gemini-N- GMOS) and Sculptor group spiral galaxy NGC 300 (VLT FORS 2}). Title: Representation of Opacity Data in Solar Model Atmosphere Calculations Authors: Haberreiter, M.; Rozanov, E.; Rüedi, I.; Schmutz, W. Bibcode: 2003ASPC..288..165H Altcode: 2003sam..conf..165H Rozanov et al. (2002) have determined that the influence of the solar irradiance variability on the chemical composition in the stratosphere is dominated by two narrow bands in the UV centered around 215 nm and 265 nm. We have evaluated the dominant opacity sources at these wavelengths and find it necessary to include the complex continuum absorption cross sections from the lower levels of neutral metals. We present our straightforward solution how to describe these opacities. There is the obvious need to treat the line blanketing which mainly depends on the completeness of the line list. We base our calculations on a combination of the spherically symmetric non-LTE `Kiel-code' and the spectral synthesis by the SYNSPEC code. In order to evaluate the quality of our computations we compare our predictions with the UV spectrum observed by SUSIM. Title: XMM-Newton and Very Large Array Observations of the Variable Wolf-Rayet Star EZ Canis Majoris: Evidence for a Close Companion? Authors: Skinner, Stephen L.; Zhekov, Svetozar A.; Güdel, Manuel; Schmutz, Werner Bibcode: 2002ApJ...579..764S Altcode: 2002astro.ph..7171S We present new X-ray and radio observations of the Wolf-Rayet star EZ CMa (HD 50896) obtained with XMM-Newton and the Very Large Array (VLA). This WN4 star exhibits optical and UV variability at a period of 3.765 days whose cause is unknown. Binarity may be responsible, but the existence of a companion has not been proven. The radio spectral energy distribution of EZ CMa determined from VLA observations at five frequencies is in excellent agreement with predictions for free-free wind emission, and the ionized mass-loss rate allowing for distance uncertainties is M=3.8(+/-2.6)×10-5 Msolar yr-1. The CCD X-ray spectra show prominent Si XIII and S XV emission lines and can be acceptably modeled as an absorbed multitemperature optically thin plasma, confirming earlier ASCA results. Nonsolar abundances are inferred with Fe notably deficient. The X-ray emission is dominated by cooler plasma at a temperature kTcool~0.6 keV, but a harder component is also detected, and the derived temperature is kThot~3.0-4.2 keV if the emission is thermal. This is too high to be explained by radiative wind shock models, and the X-ray luminosity of the hard component is 3 orders of magnitude lower than expected for accretion onto a neutron star companion. We show that the hard emission could be produced by the Wolf-Rayet wind shocking onto a normal (nondegenerate) stellar companion at close separation. Finally, using comparable data sets we demonstrate that the X-ray and radio properties of EZ CMa are strikingly similar to those of the WN5-6 star WR 110. This similarity points to common X-ray and radio emission processes in WN stars and discredits the idea that EZ CMa is anomalous within its class. Title: Towards a spherical code for the evaluation of solar UV-bands that influence the chemical composition in the stratosphere Authors: Haberreiter, M.; Hubeny, I.; Rozanov, E.; Rüedi, I.; Schmutz, W.; Wenzler, T. Bibcode: 2002ESASP.508..209H Altcode: 2002soho...11..209H We present our analysis of data taken by SUSIM onboard UARS. We reconstruct the variability of the UV irradiance and compare it to available data. Up to now we model the solar irradiance according to the 3-component model by Unruh et al. (1999) based on LTE synthetic spectra modeled with Kurucz' ATLAS9 code. Our new approach will be that with COSI (COde for Solar Irradiance) we model solar continuum and line formation in spherical symmetry and in non-local thermodynamic equilibrium (non-LTE). We present our first synthetic solar spectra (calculated in LTE) and validate them against spectra computed with Kurucz' ATLAS9 code. Title: XMM-Newton Detection of Hard X-Ray Emission in the Nitrogen-Type Wolf-Rayet Star WR 110 Authors: Skinner, Stephen L.; Zhekov, Svetozar A.; Güdel, Manuel; Schmutz, Werner Bibcode: 2002ApJ...572..477S Altcode: 2002astro.ph..3270S We have used the excellent sensitivity of XMM-Newton to obtain the first high-quality X-ray spectrum of a Wolf-Rayet (W-R) star that is not known to be a member of a binary system. Our target, the nitrogen-type star WR 110 (HD 165688), was also observed and detected with the Very Large Array at four different frequencies. The radio flux density increases with frequency according to a power law Sν~ν+0.64+/-0.10, in very good agreement with the behavior expected for free-free wind emission. The radio data give an ionized mass-loss rate M=4.9×10-5 Msolar yr-1 for an assumed spherical constant-velocity wind. The undispersed CCD X-ray spectra reveal strong emission lines from He-like ions of Mg, Si, and S. The emission measure distribution shows a dominant contribution from cool plasma with a characteristic temperature kTcool~0.5 keV (~6 MK). Little or no excess absorption of this cool component above the value expected from the visual extinction is present. We conclude that the bulk of the cool plasma detected by XMM-Newton lies at hundreds of stellar radii or more if the wind is approximately spherical and homogeneous, but it could lie closer to the star if the wind is clumped. If the cool plasma is due to instability-driven wind shocks, then typical shock velocities are vs~340-550 km s-1 and the average filling factor of X-ray-emitting gas in the wind is no larger than f~10-6. A surprising result is the unambiguous detection of a hard X-ray component that is clearly seen in the hard-band images and the spectra. This hard component accounts for about half of the observed flux and can be acceptably fitted by a hot, optically thin thermal plasma or a power-law model. If the emission is thermal, then a temperature kThot>=3 keV is derived. Such high temperatures are not predicted by current instability-driven wind shock models, and a different mechanism is thus required to explain the hard X-rays. We examine several possible mechanisms and show that the hard emission could be accounted for by the W-R wind shocking onto a close stellar companion that has so far escaped detection. However, until persuasive evidence for binarity is found, we are left with the intriguing possibility that the hard X-ray emission is produced entirely by the Wolf-Rayet star. Title: Estimation of the ozone and temperature sensitivity to the variation of spectral solar flux Authors: Rozanov, E.; Egorova, T.; Fröhlich, C.; Haberreiter, M.; Peter, T.; Schmutz, W. Bibcode: 2002ESASP.508..181R Altcode: 2002soho...11..181R We have applied a 1-D steady-state radiative-convective model with interactive photochemistry to estimate the sensitivity of temperature and ozone mixing ratio to the observed variability of the extraterrestrial spectral solar irradiance. We have carried out several runs using the spectral solar flux for minimum and maximum solar activity conditions. The results show that the ozone and temperature in the stratosphere are mostly sensitive to the solar flux variations in the spectral area between 200 and 220 nm, where they positively correlate with solar flux intensity. In the upper stratosphere and mesosphere the effects of the solar flux variability in the Lyman-α line and Schumann-Runge band are found to be very important. The obtained results have an implication for the optimal choice of wavelength to be measured from a satellite and for the understanding of what kind of radiation code should be used in a GCM aimed to study solar-climate connections. Title: Solar Irradiance Variations over Solar Cycles 21 to 23 Authors: Pap, J. M.; Kuhn, J.; Jones, H.; Turmon, M.; Arge, N.; Schmutz, W.; Floyd, L. Bibcode: 2002AAS...200.2803P Altcode: 2002BAAS...34..679P In this paper we describe the science requirements and a new measurement strategy to better understand solar variability and its potential effect on climate. We study the relation between the variations in solar total and UV irradiances and solar magnetic fields as observed within the last three decades. The results of our analysis raise important questions: (1) is there a significant non-magnetic component in the observed irradiance variations?; (2) may polar magnetic fields play a role in irradiance changes?; (3) is there a strict linear relationship between solar variability and irradiance variations as the current irradiance models used in climate studies assume? The results presented in this paper underscore the need to further develop new measurement and analysis techniques to study and predict the climate impact of solar variability. Title: XMM-newton high-resolution x-ray - spectroscopy of wr 25 Authors: Raassen, A.; van der Hucht, K.; Mewe, R.; Antokhin, I.; Guedel, M.; Schmutz, W. Bibcode: 2002cosp...34E1592R Altcode: 2002cosp.meetE1592R We report the analysis of the first high-resolution X-ray spectra of the WN6ha star WR 25 (HD 93162) obtained with the reflection grating spectrometers (rgs) and the european photon imaging cameras (epic- mos and -pn) ccd spectrometers on board XMM-Newton. The spec- trum exhibits bright emission lines of the H- and He-like ions of Ne, Mg, Si and S, as well as lines of Fe xvii to Fe xx and Fe xxv. Line fluxes have been determined. The rgs and epic spectra have been simultane- ously fitted to obtain self-consistent temperatures, emission measures, and elemental abundances. Multi-temperature fitting yields two dom- inant components around temperatures of 7 and 30 MK, respectively. An interstellar absorption value, related to the optically thick wind of the WR star is obtaines as NH in the range 3-6 1021 cm-2 . The pres- ence of the Fe xxv emission-line complex at6.7 keV is argued as being indicative for colliding winds inside the WR+O binary system. Title: Long-term solar irradiance variations: results and perspectives Authors: Pap, J.; Fleck, B.; Frohlich, C.; Jones, H.; Kuhn, J.; Schmutz, W. Bibcode: 2002cosp...34E.553P Altcode: 2002cosp.meetE.553P In this paper we show the recent result on irradiance variations and their relation to solar magnetic activity over solar cycles 21 to 23. Comparison of the multi-decade long irradiance and magnetic field measurements indicates that the shape and magnitude of irradiance variations are different from that of magnetic indices. Specifically, while magnetic indices show that solar cycle 23 is weaker than the two previous cycles, the long-term variation of total solar irradiance over solar cycles 21 to 23 is rather symmetrical, showing that its maximum and minimum levels were about the same within their measuring uncertainties. These results raise questions like: (1) is there a strict linear relationship between solar variability and irradiance variations as the current irradiance models used in climate studies assume?; (2) what is the role of polar magnetic fields in irradiance changes?; (3) is there a significant non-magnetic component in the observed irradiance variations? The results presented in this paper underscore the need to further develop new measurement and analysis techniques to study and predict the climate impact of solar variability. Title: Model Assessment Of The Short And Long-Terms Solar UV Variability Effects On The Climate And Global Ozone. Authors: Rozanov, E.; Egorova, T.; Haberreiter, M.; Schmutz, W. Bibcode: 2002cosp...34E.802R Altcode: 2002cosp.meetE.802R A search for the mechanisms responsible for the detected solar-climate connections is under way. One potential candidate is he variability of the Solar UV radiationt because it can influence the temperature and dynamics in the entire atmosphere throughout the perturbation of the ozone and radiative heating in the middle atmosphere. We have applied a 3-D GCM with interactive chemistry to evaluate the sensitivity of the ozone, temperature and dynamics in the stratosphere and mesosphere to the changes of the Solar irradiance along 11-year Solar activity and 28-day Sun rotation cycles. The simulated changes of the global ozone, temp erature and zonal wind are extensively compared to the available observation data obtained from different satellite instruments. We also compare the simulated responses to those obtained from the experiment with the non-interactive chemical-transport model to emphasize the role of climate-chemistry interaction. Title: JOSO national report 2000-2001 - Switzerland Authors: Schmutz, W. Bibcode: 2002joso.book..116S Altcode: This report reviews the advances in solar physics in Switzerland in 2000-2001. The solar physics is carried out at: 1) Institute of Astronomy, ETH Zurich, 2) Physikalisch-Meteorologisches Observatorium Davos, World Radiation Centre (PMOD/WRC) Davos. Title: COSI - a new spherical NLTE COde for the calculation of Solar Irradiance Authors: Haberreiter, M.; Rozanov, E.; Schmutz, W. Bibcode: 2002cosp...34E.789H Altcode: 2002cosp.meetE.789H The influence of the solar irradiance variability on the chemical composition in the stratosphere and mesosphere is dominated by Lyand two wavelength bands from 200 to 220 nm and 260 to 280 nm (Rozanov et al., 2002). We model the variablity in these wavelengths using the approach from Unruh et al. (1999). However, as nonLTE continuum and line formation is important for wavelengths below 200 nm, we reconstruct the solar UV spectra with COSI - a combination of the spherical 'Kielcode' (Hamann &Schmutz, 1987) and the spectrum synthesis program SYNSPEC (Hubeny, 1988). With COSI we also account for the center to limb variations of the solar irradiance. We present our results and compare them to our analysis of SUSIM data. Title: Stellar and circumstellar variability of the Be star mu Cen IV Authors: Rivinius, Th.; Stefl, S.; Stahl, O.; Wolf, B.; Kaufer, A.; Baade, D.; Dumm, Th.; Gäng, Th.; Gracia, J.; Gummersbach, C.; Jankovics, Kaper L.; Kovacs, J.; Lehmann, H.; Mandel, H.; Peitz, J.; Schafer, D.; Schweickhardt, J.; Schmutz, W.; Szeifert, Th.; Tubbesing, S. Bibcode: 2001JAD.....7....5R Altcode: For the bright southern Be star mu Cen, we publish all spectra that have been used in the previous papers of this series. An overview of the data is given and the published results obtained with these data are summarized. All data have been obtained from La Silla. In detail, these are 28 spectra taken with Flash at the ESO 50-cm (400 nm to 670 nm), 426 blue and 443 red spectra taken with Heros using the ESO 50-cm and the ESO 1.52-m (350 nm to 860 nm), 47 spectra taken with Feros at the ESO 1.5-m (370 nm to 920 nm), 2 x 348 spectra taken with the Boller and Chivens at the ESO 1.52-m (345 nm to 510 nm), and 310 spectra of He I 6678 and 27 spectra of Si III 4553 taken with the CAT/CES. mu Cen was found to be a multiperiodic non-radially pulsating star, with indications for a coupling between the multiperiodic beating and the star-to-disk mass transfer. Title: 2 Micron Narrowband Adaptive Optics Imaging in the Arches Cluster Authors: Blum, R. D.; Schaerer, D.; Pasquali, A.; Heydari-Malayeri, M.; Conti, P. S.; Schmutz, W. Bibcode: 2001AJ....122.1875B Altcode: 2001astro.ph..6496B Canada-France-Hawaii-Telescope adaptive optics bonnette images through narrowband filters in the K band are presented for the Arches cluster. Continuum fluxes, line fluxes, and equivalent widths are derived from high angular resolution images, some nearly diffraction limited, for the well-known massive stars in the Arches cluster. Images were obtained in the lines He I 2.06 μm, H I Brγ (2.17 μm), and He II 2.19 μm, as well as continuum positions at 2.03, 2.14, and 2.26 μm. In addition, fluxes are presented for H I Pα (1.87 μm) and a nearby continuum position (1.90 μm) from Hubble Space Telescope archival data.2 The 2 μm and Pα data reveal two new emission-line stars and three fainter candidate emission-line objects. Indications for a spectral change of one object between earlier observations in 1992-1993 and our data from 1999 are found. The ratio of He II 2.19 μm to Brγ emission exhibits a narrow distribution among the stars, suggesting a narrow evolutionary spread centered predominantly on spectral types O4 If or Wolf-Rayet stars of the WN7 subtype. From the approximate spectral types of the identified emission-line stars and comparisons with evolutionary models we infer a cluster age between ~2 and 4.5 Myr. Title: SIM3D: Solar Irradiance Monitor-3D-view Authors: Schmutz, W.; Fröhlich, C.; Rüedi, I.; Roth, H.; Wehrli, Ch.; Wyss, J. Bibcode: 2001ESASP.493..447S Altcode: 2001sefs.work..447S No abstract at ADS Title: Chandra Detection of a Close X-Ray Companion and Rich Emission-Line Spectrum in the Wolf-Rayet Binary γ Velorum Authors: Skinner, Stephen L.; Güdel, Manuel; Schmutz, Werner; Stevens, Ian R. Bibcode: 2001ApJ...558L.113S Altcode: We present first results of a high-resolution X-ray observation of the nearby Wolf-Rayet binary system γ2 Velorum (WC8 + O7.5) using the Chandra High-Energy Transmission Grating (HETG). Emission lines from Mg, Si, S, Ne, and Fe dominate the spectrum and imply a range of plasma temperatures from ~4 MK up to at least ~25 MK. The strongest lines are broadened, but no Doppler shifts are detected. He-like triplets show strong forbidden lines with no significant weakening from collisional effects or photoexcitation, contrasting sharply with the diluted forbidden lines of single O-type supergiants such as ζ Puppis. These results imply that some lines such as the Ne IX triplet are formed in cooler plasma at tens of stellar radii or more from the O star, well outside of the central wind interaction region located near the O star surface. Lastly, we report the discovery of a new X-ray source lying only 4.8" north of γ2 Vel that is very likely a low-mass pre-main-sequence star. Title: Long-term spectroscopic monitoring of the Luminous Blue Variable AG Carinae Authors: Stahl, O.; Jankovics, I.; Kovács, J.; Wolf, B.; Schmutz, W.; Kaufer, A.; Rivinius, Th.; Szeifert, Th. Bibcode: 2001A&A...375...54S Altcode: We have extensively monitored the Luminous Blue Variable AG Car (HD 94910) spectroscopically. Our data cover the years 1989 to 1999. In this period, the star underwent almost a full S Dor cycle from visual minimum to maximum and back. Over several seasons, up to four months of almost daily spectra are available. Our data cover most of the visual spectral range with a high spectral resolution (lambda /Delta lambda ~ 20 000). This allows us to investigate the variability in many lines on time scales from days to years. The strongest variability occurs on a time scale of years. Qualitatively, the variations can be understood as changes of the effective temperature and radius, which are in phase with the optical light curve. Quantitatively, there are several interesting deviations from this behaviour, however. The Balmer lines show P Cygni profiles and have their maximum strength (both in equivalent width and line flux) after the peak of the optical light curve, at the descending branch of the light curve. The line-width during maximum phase is smaller than during minimum, but it has a local maximum close to the peak of the visual light curve. We derive mass-loss rates over the cycle from the Hα line and find the highest mass loss rates (log dot {M}/({M}_sun yr-1) ~ -3.8, about a factor of five higher than in the minimum, where we find log dot {M}/({M}_sun yr-1) ~ -4.5) after the visual maximum. Line-splitting is very commonly observed, especially on the rise to maximum and on the descending branch from maximum. The components are very long-lived (years) and are probably unrelated to similar-looking line-splitting events in normal supergiants. Small apparent accelerations of the components are observed. The change in radial velocity could be due to successive narrowing of the components, with the absorption disappearing at small expansion velocities first. In general, the line-splitting is more likely the result of missing absorption at intermediate velocities than of excess absorption at the velocities of the components. The HeI lines and other lines which form deep in the atmosphere show the most peculiar variations. The HeI lines show a central absorption with variable blue- and red-shifted emission components. Due to the variations of the emission components, the HeI lines can change their line profile from a normal P Cyg profile to an inverse P Cyg-profile or double-peak emission. In addition, very broad (+/-1500 km s-1) emission wings are seen at the strongest HeI lines of AG Car. At some phases, a blue-shifted absorption is also present. The central absorption of the HeI lines is blue-shifted before and red-shifted after maximum. Possibly, we directly see the expansion and contraction of the photosphere. If this explanation is correct, the velocity of the continuum-forming layer is not dominated by expansion but is only slightly oscillating around the systemic velocity. Based on observations collected at the European Southern Observatory at La Silla, Chile. Title: High resolution spectroscopy of symbiotic stars. VI. Orbital and stellar parameters for AR Pavonis Authors: Schild, H.; Dumm, T.; Mürset, U.; Nussbaumer, H.; Schmid, H. M.; Schmutz, W. Bibcode: 2001A&A...366..972S Altcode: 2000astro.ph.11562S We present new dynamical parameters of the AR Pav binary system. Our observations consist of a series of high resolution optical/NIR spectra from which we derive the radial velocity curve of the red giant as well as its rotation velocity. Assuming co-rotation, we determine the stellar radius (130 Rsun) of the red giant. Based on this we derive the red giant's luminosity and mass (2.0 Msun) as well as the distance of the system (4.9 kpc). The binary mass function finally yields the companion's mass (0.75 Msun) and the binary separation (1.95 AU). We find that the red giant does not fill its Roche lobe. We review the radial velocity data of Thackeray & Hutchings (\cite{Thacker74}), and compare it with our red giant's orbit. We find that their RV curves of the blue absorption system and the permitted emission lines are in anti-phase with the red giant, and that the forbidden emission lines are shifted by a quarter of a period. The blue absorptions and the permitted emission lines are associated with the hot companion but not in a straightforward way. The blue absorption system only tracks the hot component's orbital motion whilst it is in front of he red giant, whereas at other phases line blanketing by interbinary material leads to perturbations. We finally present UV light curves based on IUE archive spectra. We clearly detect eclipses in the continuum at all wavelengths. The eclipse light curves are unusual in that they show a slow and gradual decline prior to eclipse which is followed by a sharp increase after eclipse. Based on observations obtained at the European Southern Observatory, La Silla, Chile; the observations were granted for the ESO programs 47.7-081, 48.7-083, 49.7-041, 50.7-129, 51.7-093, 52.7-068, 53.7-083, 54.E-061, 55.E-446, 56.E-526. Title: The γ Velorum binary system. II. WR stellar parameters and the photon loss mechanism Authors: De Marco, O.; Schmutz, W.; Crowther, P. A.; Hillier, D. J.; Dessart, L.; de Koter, A.; Schweickhardt, J. Bibcode: 2000A&A...358..187D Altcode: 2000astro.ph..4081D In this paper we derive stellar parameters for the Wolf-Rayet star in the gamma Velorum binary system (WR11), from a detailed non-LTE model of its optical and infrared spectra. Compared to the study of Schaerer et al., the parameters of the WC8 star are revised to a hotter effective temperature (T_eff ~ 57 kK), a higher luminosity (log (L/Lsun) = 5.00), and a lower mass-loss rate (log(dot {M} / Msun/yr) = -5.0, using a 10% clumping filling factor). These changes lead to a significant decrease in wind efficiency number, from 144 to 7, so that the driving mechanism of the wind of this WR star may be simply radiation pressure on lines. The derived spectroscopic luminosity is found to be 40% lower than that derived by De Marco & Schmutz through the mass-luminosity relationship for WR stars (log (L/Lsun) = 5.2). The paper furthermore presents a comparison of the independently-developed modelling programs, cmfgen and isa-wind. Overall, there seems to be very reasonable agreement between the derived parameters for WR11, except for the carbon content, which is 2 times higher for cmfgen (C/He=0.15 vs. 0.06, by number). The comparison also confirms a disparity in the predicted flux at $lambda mbda$<400 Ä, found by Crowther et al., which will have effects on several nebular line strengths. The paper also presents the first independent check of the photon loss mechanism proposed by Schmutz. We conclude that, not only is it important to include very many lines to realistically model line blanketing, but in particular those ones that critically interact with strong resonance lines (e.g. He ii\ lambda 303.78). The inclusion of these latter lines may significantly alter the wind ionization structure. Based on observations collected at the European Southern Observatory at La Silla, Chile. ESO proposals Nrs. 56.D-327, 57.D-517 and 56.D-0700} Title: A wind accretion wake in RW Hydrae? Authors: Dumm, T.; Folini, D.; Nussbaumer, H.; Schild, H.; Schmutz, W.; Walder, R. Bibcode: 2000A&A...354.1014D Altcode: RW Hydrae is an eclipsing detached binary star system, consisting of a mass losing M-giant and a hot white dwarf on circular orbits. We analyze UV observations of RW Hydrae. Approximately at phi = 0.78, clearly unrelated to the primary eclipse, we detect in the UV light curve an event with significantly reduced UV flux. The spectral characteristics of this event indicate Rayleigh scattering due to a high column density of neutral hydrogen in the line of sight to the hot white dwarf. We model this observation in the framework of an accretion wake trailing the white dwarf. This interpretation is analogous to comparable models for zeta Aur systems and X-ray binaries. We find qualitative agreement between our 3D hydrodynamical accretion simulation and the observed UV light curve of RW Hya. Based on observations with the International Ultraviolet Explorer and observations 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 No. NAS5-26555. Title: WR Stars in Star Forming Regions Authors: Schmutz, Werner; Vacca, Wiliam D. Bibcode: 2000fepc.conf..307S Altcode: WR galaxies are characterized by broad emission features at 4686 A and occasionally at 4640 A and 5805 A. The features are attributed to stellar emission from a large population of WR stars. The presence of WR stars allows a determination of the age of the starburst. In a few WR galaxies the 4640 emission line has been measured to be as large or larger than the He II 4686 line. We demonstrate that a 4640/4686 ratio larger than unity cannot be produced by any known population of WR stars and discuss the implications for the interpretation of the star formation histories in WR galaxies. Title: High resolution spectroscopy of symbiotic stars. V. Orbital and stellar parameters for FG Ser (AS 296) Authors: Mürset, U.; Dumm, T.; Isenegger, S.; Nussbaumer, H.; Schild, H.; Schmid, H. M.; Schmutz, W. Bibcode: 2000A&A...353..952M Altcode: For the eclipsing symbiotic binary FG Ser (AS 296) we have obtained a series of high resolution optical spectra. Combining the measured radial velocity variations for the red giant with published eclipse photometry gives a binary period of 650 days. We derive the radial velocity curve of the red giant, yielding the orbital parameters of the system and a mass function of mtief f=0.039 Msun. We further determine the rotation velocity of the red giant, and assuming corotation derive its photospheric radius. Together with the spectral type surface temperature this yields the position of the red giant in the HR-diagram and a mass estimate of Mtief c=1.7 Msun. Combining this value with mtief f results in a mass of Mtief h=0.60 Msun for the hot star. With a binary separation of 1.95 AU and a radius of the red giant of 105 Rsun we find that FG Ser is a detached binary with the red giant well inside the Roche lobe. Based on observations obtained at the European Southern Observatory, La Silla, Chile; the observations were granted for the ESO programs 47.7-081, 48.7-083, 49.7-041, 50.7-129, 51.7-093, 52.7-068, 53.7-083, 54.E-061, 55.E-446, 56.E-526 } Title: PICARD: Solar Diameter, Irradiance and Climate Authors: Damé, L.; Cugnet, David; Herse, Michel; Crommelynck, Dominique; Dewitte, Stevens; Joukoff, Alexandre; Ruedi, Isabelle; Schmutz, Werner; Wehrli, Christoph; Delmas, Christian; Laclare, Francis; Rozelot, Jean-Pierre Bibcode: 2000ESASP.463..223D Altcode: 2000sctc.proc..223D No abstract at ADS Title: Wolf-Rayet nebulae as tracers of stellar ionizing fluxes. I. M1-67 Authors: Crowther, Paul A.; Pasquali, A.; De Marco, Orsola; Schmutz, W.; Hillier, D. J.; de Koter, A. Bibcode: 1999A&A...350.1007C Altcode: 1999astro.ph..8200C We use WR124 (WN8h) and its associated nebula M1-67, to test theoretical non-LTE models for Wolf-Rayet (WR) stars. Lyman continuum ionizing flux distributions derived from a stellar analysis of WR124, are compared with nebular properties via photo-ionization modelling. Our study demonstrates the significant role that line blanketing plays in affecting the Lyman ionizing energy distribution of WR stars, of particular relevance to the study of H ii regions containing young stellar populations. We confirm previous results that non-line blanketed WR energy distributions fail to explain the observed nebular properties of M1-67, such that the predicted ionizing spectrum is too hard. A line blanketed analysis of WR124 is carried out using the method of Hillier & Miller (1998), with stellar properties in accord with previous results, except that the inclusion of clumping in the stellar wind reduces its wind performance factor to only ~ 2. The ionizing spectrum of the line blanketed model is much softer than for a comparable temperature unblanketed case, such that negligible flux is emitted with energy above the He i lambda 504 edge. Photo-ionization modelling, incorporating the observed radial density distribution for M1-67 reveals excellent agreement with the observed nebular electron temperature, ionization balance and line strengths. An alternative stellar model of WR124 is calculated, following the technique of de Koter et al. (1997), augmented to include line blanketing following Schmutz et al. (1991). Good consistency is reached regarding the stellar properties of WR124, but agreement with the nebular properties of M1-67 is somewhat poorer than for the Hillier & Miller code. Title: Circumstellar matter around M-giants in symbiotic binaries: SY MUSCAE and RW Hydrae Authors: Dumm, T.; Schmutz, W.; Schild, H.; Nussbaumer, H. Bibcode: 1999A&A...349..169D Altcode: For the eclipsing symbiotic binary system SY Mus we present evidence for an asymmetric density distribution around the M-giant. We obtain this result from an improved orbital solution. We determine a revised orbital period of P=625.0+/- 0.5 d from UV eclipse observations and a re-analysis of the visual light curve. Based on new radial velocity observations, we measure the epoch of mid-eclipse accurately to within +/- 6 days, or 1/100 of the period. At ingress the eclipse curve is steeper and closer to mid-eclipse than at egress. From measured column densities of neutral hydrogen during egress we conclude that the mass loss rate of the M-giant is of the order of dot {M} ~5*10(-7) Msun/yr. The eclipse of the UV light in SY Mus and RW Hya can be partially explained by Rayleigh scattering but there is also an additional source of opacity. HST high resolution UV observations of RW Hya during egress reveal that this additional flux attenuation is due to blanketing by numerous absorption lines, predominantly Fe ii. Line blanketing is an important effect that has to be taken into account to explain the eclipse of SY Mus and of other symbiotic binaries. Based on observations made with IUE, HST and at the European Southern Observatory at La Silla (Chile). ESO observations were granted for the proposals 47.7-081, 48.7-083, 49.7-041, 50.7-129, 51.7-093, 52.7-068, 53.7-083, 54.E-061, 55.E-446, 56.E-526 57.D-684, 58.D-248, 59.D-700, 60.D-714. The visual brightness estimates were done by the RASNZ. Title: ORFEUS spectroscopy of the O BT VI lines in symbiotic stars and the Raman scattering process Authors: Schmid, H. M.; Krautter, J.; Appenzeller, I.; Barnstedt, J.; Dumm, T.; Fromm, A.; Gölz, M.; Grewing, M.; Gringel, W.; Haas, C.; Hopfensitz, W.; Kappelmann, N.; Krämer, G.; Lindenberger, A.; Mandel, H.; Mürset, U.; Schild, H.; Schmutz, W.; Widmann, H. Bibcode: 1999A&A...348..950S Altcode: We present orfeus spectra of the O vi lambda lambda 1032,1038 emission lines in the symbiotic stars AG Dra, V1016 Cyg, RR Tel, CD-43(deg) 14304, AG Peg and Z And. The O vi emission lines can convert into broad and highly polarized emission lines at lambda 6825 and lambda 7082 in a Raman scattering process by neutral hydrogen. From a comparison of direct and Raman scattered radiation we extract new information on the scattering geometry in symbiotic systems. The nebular O vi emission lines are in all objects redshifted by about +40 km s(-1) . This can be explained as a radiative line transfer effect in a slowly expanding emission region. A comparable redshift is measured in the Raman scattered O vi lines. In AG Peg the O vi emissions show beside a narrow nebular line a broad component from a fast stellar wind outflow. Many interstellar absorption lines of molecular hydrogen are detected, particularly near the O vi lambda 1038 component. With model calculations we investigate their impact on the O vi lines. From the dereddened line fluxes of the direct and Raman scattered O vi lines we derive the scattering efficiency, which is defined as photon flux ratio N_Raman/N_O VI. The efficiencies derived for RR Tel, V1016 Cyg and Z And indicate that about 30% of the released O vi lambda 1032 photons interact with the neutral scattering region. The efficiencies for AG Dra and CD-43(deg14304) are much higher, which may suggest that the O vi nebulosity is embedded in a H(0) -region. The D-type system RR Tel shows strong line profile differences between the direct O vi emission, which is single-peaked, and the Raman scattered emission, which is double-peaked. This indicates that the neutral scattering region in RR Tel ``sees'' different O vi line profiles, implying that the O vi nebulosity is far from spherically symmetric. In a tentative model we suggest for RR Tel an O vi flow pattern where material streams from the cool giant towards the hot component, which further accelerates the gas radially. For the S-type systems AG Dra, CD-43(deg14304) and Z And the line profile differences between the direct and the Raman scattered O vi emissions are less pronounced. This may suggest that the O vi profiles depend less on the emission direction than in the D-type system RR Tel. For AG Peg we detect for the first time the Raman scattered emission at lambda 6825. The Raman line shows a narrow, nebular component as the O vi line, but no equivalent emission to the broad O vi wind component. The higher conversion efficiency for the narrow component indicates that the nebular O vi emission is significantly closer to the cool giant than the hot, mass losing component, and strongly supports previous colliding wind models for this object. Based on observations taken during the orfeus-spas i and orfeus-spas ii space shuttle missions, and ground based data collected at the ESO 2.2m and 3.6m telescopes at La Silla, Chile, and the 4.2m William Herschel Telescope at La Palma, Canary Islands. ESO observations were granted for the programs 52.7-040 and 58.D-0866. Title: Revised mass determination of the super massive Wolf-Rayet star WR 22 Authors: Schweickhardt, J.; Schmutz, W.; Stahl, O.; Szeifert, Th.; Wolf, B. Bibcode: 1999A&A...347..127S Altcode: We analyze the orbital motion of the WN 7+abs + O binary WR 22 based on 88 high resolution optical spectra obtained in 1996. We determine a period of P=80.336 +/- 0.0013 d and a radial velocity semi-amplitude K_WR = 70.6 +/- 0.8 km s^{-1} for the Wolf-Rayet star. By averaging six He i lines it is possible to detect the weak absorptions of the O companion. The spectral class of the O star is O 9 III (O 8-O 9.5) but the luminosity class is uncertain and brightness arguments indicate a luminosity class V. For the orbit of the O companion we derive K_O = 190 +/- 10 km s^{-1}. This leads to a mass ratio q = M_WR/M_O = 2.69 +/- 0.14. We obtain masses of 55.3 +/- 7.3: M_{\odot} and 20.6 +/- 1.7: M_{\odot} for the WR and for the O star, respectively. Our mass determination revises down considerably the last published value for the mass of the Wolf-Rayet component but even with the new mass WR 22 remains ``the most massive Wolf-Rayet star ever weighed''. Based on observations collected at the European Southern Observatory at La Silla, Chile. ESO proposals Nr. 56.D-327 and 57.D-517. Title: On the 4640 Angstrom feature in Wolf-Rayet galaxies Authors: Schmutz, W.; Vacca, W. D. Bibcode: 1999NewA....4..197S Altcode: Several Wolf-Rayet galaxies exhibit broad emission features around 4640 Å in their optical spectra. These features are usually identified as N III and C III/C IV emission lines from WR stars. In a few WR galaxies the flux in this feature has been measured to be as large or larger than that in the corresponding He IIλ4686 stellar emission line. We demonstrate that a 4640/4686 flux ratio larger than unity cannot be produced by any known population of WR stars. In particular, we show that the enhanced ratio cannot be explained by the presence of carbon lines from WC stars. We examine the possible origins of the broad λ4640 feature and offer several possible explanations for the enhanced strength in this emission feature. The most plausible explanations involve the presence of large numbers of Of stars in the starburst regions and/or the contamination of the stellar lines by nebular emission features. We discuss the implications that both possibilities have for the interpretation of the star formation histories in WR galaxies, as derived from their massive star content. We find that the instantaneous burst scenario cannot be correct for any metal-rich region whose optical spectrum exhibits both an enhanced 4640/4686 flux ratio and C IV 5808 emission from WC stars. These regions must have experienced a "multiple-burst" star-formation event, composed of several instantaneous bursts separated by short time intervals (a few Myr). Title: The γ Velorum binary system. I. O star parameters and light ratio Authors: De Marco, Orsola; Schmutz, W. Bibcode: 1999A&A...345..163D Altcode: In this paper we demonstrate how previous determinations of the light ratio between the O and Wolf-Rayet stellar components of the gamma Vel system are affected by large uncertainties. This is due, amongst other things, to the difficulty of measuring the equivalent widths of emission and absorption lines. We then present a new technique to de-blend and measure spectral lines, in which we compensate for the observed absorption features with synthetic profiles. From the new values of the diagnostic line strengths we determine a hotter spectral type for the O star companion (O7.5) than previously published. The light ratio is then determined, together with the stellar parameters, via a spectroscopic analysis. We obtain Delta M_V=1.47+/-0.13 mag. From the light ratio and the system's luminosity we find M_V(O) = -5.14 mag and M_V(WR) = -3.67 mag. Simultaneously we determine ifmmode T_eff else T_efffi(O) = 35 000 K, L(O) = 2.1x10(5) Lsun and cal M(O) = 30 Msun. An age of 3.59x10(6) yr is derived from these parameters and evolutionary tracks. We find that the H/He abundance ratio is solar. From a hydro-dynamical calculation of the radiation-driven wind we obtain dot{M}(O) = 1.8x10(-7) Msun yr(-1) and vinfty(O) = 2500 km s(-1) . From the O star mass derived here and the mass ratio from the literature we derive the mass of the Wolf-Rayet star, cal M(WR) = 9 Msun. The mass-luminosity relation for Wolf-Rayet stars then leads to L(WR) = 1.5x10(5) Lsun. We finally present the gamma Vel Wolf-Rayet spectrum de-convolved from the O star in the range 3800-6700 Angstroms. Title: ISO observations of CH Cyg Authors: Schild, H.; Dumm, T.; Folini, D.; Nussbaumer, H.; Schmutz, W. Bibcode: 1999ESASP.427..397S Altcode: 1999usis.conf..397S The symbiotic red giant CH Cyg is a bright IR source and we discuss the salient spectral features of its SWS and LWS spectrum. We find strong OH and weak H2O emission between 60 and 130 μm. This is qualitatively different from W Hya, a single semiregular M8-M9 giant, where OH emission is absent and the dominant cooling species in the molecular envelope is water. Apart from the well known photospheric absorptions of CO, OH and SiO we also suspect traces of HCl. We find relatively weak PAH features which indicate that apart from the oxygen rich material from the red giant, there may be carbon rich material ejected from the companion star. Much of the ISO wavelength range is dominated by the emission of silicate dust. A good model fit can be obtained with standard dust properties. We present a procedure by which radii of symbiotic red giants can be determined if the J and K magnitudes and the distance is known. The radius of the red giant in CH Cyg is R=280+/-65 Rodot. Title: Long term spectroscopy of Wolf-Rayet binaries Authors: Schweickhardt, J.; Schmutz, W.; Kaufer, A.; Stahl, O.; Wolf, B. Bibcode: 1999IAUS..193...98S Altcode: No abstract at ADS Title: Spectroscopic analyses of the Wolf-Rayet stars in NGC 3603. Authors: Schmutz, W.; Drissen, L. Bibcode: 1999RMxAC...8...41S Altcode: The authors report the measurements of the He I λ 10830 Å line strengths with HST/NICMOS for the three WR stars HD 97950-A1, B, C in NGC 3603. They combine these new observations with H I/He II line strengths from published HST/FOS spectra to derive the stellar parameters of the WR stars. Compared to previous results our analyses yield similar parameters for HD 97950-A1 and C but a considerably hotter temperature and higher luminosity for HD 97950-B. The authors confirm that all three WR stars contain a large amount of hydrogen, possibly close to a solar H/He ratio, which implies that these WR stars are still in an early phase of their evolution. It appears that the three WR stars in NGC 3603 are the most massive stars that were formed in the cluster. Title: Why should we compare Wolf-Rayet codes? Authors: De Marco, O.; Schmutz, W.; Koesterke, L.; Hamann, W. -R.; de Koter, A. Bibcode: 1999IAUS..193..231D Altcode: No abstract at ADS Title: Revised stellar parameters of Wolf-Rayet stars Authors: Schmutz, W.; De Marco, O. Bibcode: 1999IAUS..193..147S Altcode: No abstract at ADS Title: On WR Stars as Age Indicators in Star Forming Regions Authors: Schmutz, W.; Vacca, W. D. Bibcode: 1999ASPC..192...73S Altcode: 1999sdsg.conf...73S No abstract at ADS Title: Analyses of Wolf-Rayet Stars in Local Group Galaxies Authors: Schmutz, W.; De Marco, O.; Schild, H.; Crowther, P.; Howarth, I. Bibcode: 1999IAUS..192..277S Altcode: No abstract at ADS Title: On the perspectives of using XMM to study fundamental parameters of early-type stars Authors: Rauw, G.; van der Hucht, K. A.; Mewe, R.; Güdel, M.; Vreux, J. -M.; Gosset, E.; Schmutz, W.; Stevens, I. R. Bibcode: 1999IAUS..193...90R Altcode: No abstract at ADS Title: The stellar parameters of the SMC Wolf-Rayet binary HD 5980 Authors: Schweickhardt, J.; Schmutz, W. Bibcode: 1999IAUS..193..101S Altcode: No abstract at ADS Title: Ejected nebulae as probe of Wolf-Rayet Lyman continua Authors: Pasquali, A.; Crowther, P. A.; Schmutz, W.; Hillier, D. J. Bibcode: 1999IAUS..193..380P Altcode: No abstract at ADS Title: γ2 Velorum, photon loss and the velocity field Authors: De Marco, O.; Schmutz, W.; de Koter, A. Bibcode: 1999IAUS..193..229D Altcode: No abstract at ADS Title: γ2 Velorum revisited Authors: De Marco, O.; Schmutz, W.; Koesterke, L.; Hamann, W. -R. Bibcode: 1999IAUS..193..227D Altcode: No abstract at ADS Title: High resolution spectroscopy of symbiotic stars. IV. BX Monocerotis: orbital and stellar parameters Authors: Dumm, T.; Muerset, U.; Nussbaumer, H.; Schild, H.; Schmid, H. M.; Schmutz, W.; Shore, S. N. Bibcode: 1998A&A...336..637D Altcode: We investigate the orbit and the components of the symbiotic BX Mon system with new high resolution spectroscopy, IUE spectra, published photographic magnitudes, and brightness estimates from the RASNZ. We review the available photometry and deduce a new binary period of 1401 days. We also find evidence in the IUE data that BX Mon is an eclipsing system. With our high resolution spectroscopy we determine the radial velocity curve of the M giant from photospheric absorption features. BX Mon is unusual for a symbiotic star in that its hot component is also observable in the optical wavelength region. From corresponding absorption features we are able to measure the hot component's radial velocity. We determine semi-amplitudes for the cool and the hot components of 4.3 km s(-1) and 29 km s(-1) , respectively. The mass ratio is thus ~ 7 which is among the highest yet found for symbiotic systems. The orbit of BX Mon is eccentric with an ellipticity of e=0.49. The binary mass function is 0.0076 M_sun. We determine the mass of the red giant as M_r=3.7 Msun and the mass of the hot component as M_h=0.55 M_sun. This low M_h suggests that even relatively high mass symbiotics are unlikely to be supernova Type I progenitors. The distance to BX Mon of 3 kpc is determined with the Na I lambda lambda5890 ,5896 interstellar absorption lines and the interstellar extinction feature at 2200 Angstroms. For the luminosity of the cool component we find L_r=3400 Lsun and a stellar radius R_r=160 Rsun. The red giant's radius remains within the inner Lagrangian point, even at periastron. The hot component is unlikely to be a main sequence star. Based on observations obtained at the European Southern Observatory, La Silla (Chile), visual brightness data from the RASNZ, and UV spectra from the IUE archive. ESO observations were granted for the programs 47.7-081, 48.7-083, 49.7-041, 50.7-129, 51.7-093, 52.7-068, 53.7-083, 54.E-061, 55.E-446, 56.E-526 Title: HST NICMOS Observations of Circumstellar Matter Around CYG X-3 Authors: Schmutz, W.; Vacca, W. D.; Close, L.; Rayner, J.; Geballe, T. R.; Schild, H.; Walder, R. Bibcode: 1998ESOC...55..123S Altcode: 1998nvlt.proc..123S Models of the evolution of massive binaries predict that only a few such objects should survive the common envelope phase and result in systems containing a compact object plus a Wolf-Rayet star (c+WR). According to these models, a vast amount of stellar material is lost during the common envelope phase prior to the c+WR phase. We are attempting to test these models by searching for the presence of such circumbinary material around the only known c+WR object: Cyg X-3. Since the large reddening towards Cyg X-3 prevents any investigation in the optical, deep infrared exposures of Cyg X-3 with the NICMOS NIC-2 camera aboard HST and the Pa$\alpha$ narrow band filter have been used to image the system at high spatial resolution. The HST images have only recently been acquired and their analysis is currently underway. Here we report the possible detection of emission at a distance of about 0".3. This result is preliminary and needs confirmation by NIC-1 observations with its better sampling of the stellar profile. Title: Mass-Loss Rate and He/H Abundance of the Erupting Component in the Small Magellanic Cloud System HD 5980 Authors: Koenigsberger, G.; Peña, M.; Schmutz, W.; Ayala, S. Bibcode: 1998ApJ...499..889K Altcode: The binary Wolf-Rayet system HD 5980 in the Small Magellanic Cloud underwent a major luminous blue variable-type eruptive event in 1994. It is the first such recorded event in which the apparent precursor transits from WNE to WNL spectral types prior to the eruption. In this paper we analyze the spectrum of the system obtained when the outburst was declining (1994 December), but the dominant spectrum was that of the eruptor. From non-LTE analysis we obtain Ṁ=10-3 M⊙ yr-1, N[He]/N[H] = 0.43 (by number; Y = 0.63 by mass), v∞ = 600 km s-1, T* = 35,500 K, and Leruptor = 3 × 106L⊙. A comparison of the He/H abundance derived here and an estimate obtained from published data of 20 yr ago leads us to conclude that the member of the binary system that underwent the eruption is the star formerly classified as an O7 supergiant. The considerable amount of He in this star indicates that it is in transition to becoming an H-poor W-R. By comparing the stellar parameters with single-star evolutionary tracks, we derive that the progenitor was more massive than 120 M⊙, and that its current mass is close to 80 M⊙. Title: Wind accretion in the symbiotic binary system RW Hya Authors: Dumm, T.; Folini, D.; Muerset, U.; Nussbaumer, H.; Schild, H.; Schmutz, W.; Walder, R. Bibcode: 1998AGAb...14...34D Altcode: 1998AGM....14..C18D RW Hya is a detached eclipsing symbiotic binary system with known stellar and orbital parameters, consisting of a mass-loosing M2 giant and a white dwarf. HST spectra indicate the absence of a fast wind from the white dwarf, consequently we expect the companion to accrete material from the wind of the M giant. We have done a three-dimensional wind accretion simulation which we compare with observations. IUE and HST UV observations show that out of eclipse, for a short period of \Delta \phi=0.04 there is a reduction of the white dwarf continuum by Rayleigh and dust scattering. We interpret this effect as the signature of the accretion shock cone. Accretion models predict a shock cone with enhanced density. In this cone, we expect the formation of neutral hydrogen and dust. When the white dwarf is then viewed through this structure its radiation gets obscured. We numerically solve the 3D Euler equations with a polytropical index \gamma=1, yielding the circumstellar velocity and density structure in RW Hya. The momentum of the M giant wind which is a free parameter in the simulation, is set by the observed orbital orientation of the shock cone. Based on the theoretical circumstellar structure, we can calculate nebular emission line profiles for different viewing angles. We present a time series of observed optically thin emission lines. In these observations, we aim at separating the observed line profile into two components, one originating in the accretion shock cone, the other formed in the ionized red giant wind. In RW Hya we then get the chance to compare observations of the wind accretion region with numerical simulations. Title: ORFEUS Spectroscopy of the OVI Lines in Symbiotic Stars and the Raman Scattering Process Authors: Schmid, H. M.; Appenzeller, I.; Krautter, J.; Mandel, H.; Dumm, T.; Mürset, U.; Schild, H.; Schmutz, W.; Barnstedt, J.; Gölz, M.; Grewing, M.; Gringel, W.; Haas, C.; Hopfensitz, W.; Kappelmann, N.; Krämer, G. Bibcode: 1998ESASP.413..357S Altcode: 1998uabi.conf..357S No abstract at ADS Title: Non-LTE Model Atmospheres with Line Blanketing and Photon Loss Authors: Schmutz, W. Bibcode: 1998ASPC..131..119S Altcode: 1998phls.conf..119S No abstract at ADS Title: High resolution spectroscopy of symbiotic stars. III. Radial velocity curve for CD--43(deg) 14304 Authors: Schmid, H. M.; Dumm, T.; Murset, U.; Nussbaumer, H.; Schild, H.; Schmutz, W. Bibcode: 1998A&A...329..986S Altcode: We have obtained a series of high resolution optical spectra of the symbiotic system CD-43(deg14304) . We derive the radial velocity curve of the cool component and determine an orbital period of about 1448 days and a mass function of m_f=0.013M_sun for this binary. We present line profiles of Hα and the Raman scattered line at lambda 6825 for various orbital phases. The Hα line shows very strong variations in flux and spectroscopic structure which are locked to the orbital phase. Much less variability is seen in the Raman scattered line. Based on observations obtained at the European Southern Observatory, La Silla, Chile Title: X-Ray Spectroscopy with XMM: A New Powerful Tool to Determine Fundamental Parameters of Early-type Stars Authors: Mewe, R.; Rauw, G.; van der Hucht, K. A.; Vreux, J. -M.; Gosset, E.; Guedel, M.; Schmutz, W.; Stevens, I. R.; Kahn, S. Bibcode: 1998sxmm.confE..69M Altcode: No abstract at ADS Title: The orbital motion of gamma^2 Velorum Authors: Schmutz, W.; Schweickhardt, J.; Stahl, O.; Wolf, B.; Dumm, T.; Gang, Th.; Jankovics, I.; Kaufer, A.; Lehmann, H.; Mandel, H.; Peitz, J.; Rivinius, Th. Bibcode: 1997A&A...328..219S Altcode: We analyze the orbital motion of gamma (2) Velorum based on high resolution optical spectra obtained in 1995 and 1996. By combining our data with values from the literature we find a period P=78.53+/- 0.01 d. We determine radial velocity semi-amplitudes K_WR= 122+/- 2 \ifmmode kms^{-1} \else kms(-1) \fi and K_O= 38.4+/- 2 \ifmmode kms^{-1} \else kms(-1) \fi for the Wolf-Rayet star and the O star, respectively. The given errors are the standard deviations of the results from individual lines. The inclination of the system is i=65(deg) . This result is obtained by combining M_Osin(3) i from the orbital analysis with the mass M_O= 29 \ifmmode M_{\odot} \else Msun\fi , obtained from its luminosity and stellar evolution tracks. The mass of the Wolf-Rayet component is M_WR=9 \ifmmode M_{\odot} \else Msun\fi . Our O star velocity curve disagrees by 15 sigma from a previously published result. We have identified the reason for the disagreement in the failure to correct for the WR emission that affects the measurements of the absorption line centers. The correction could have introduced systematic errors that may be larger than the given precision of the amplitudes. However, we can set an upper limit of K_O<50 \ifmmode kms^{-1} \else kms(-1) \fi from uncorrected measurements. This yields an upper limit for the Wolf-Rayet mass of M_WR<12 \ifmmode M_{\odot} \else Msun\fi . We find systematic phase-shifts between the velocity curves of some emission lines. We also observe that some (but not all) emission lines deviate significantly in the 1995 data set from the line's orbital solution defined by the 1996 observations. These phenomena may indicate that the radial velocities of the emission lines could be subject to systematic distortions and that the errors of the orbital motion are larger than the internal precision given here. Title: A spectral analysis of HDE 269445 from optical and infrared observations. Authors: Pasquali, A.; Schmutz, W.; Nota, A.; Origlia, L. Bibcode: 1997A&A...327..265P Altcode: We present new, near-IR spectroscopic observations of HDE 269445, which we combine with published HST and IUE ultraviolet data and optical high resolution spectra. We discuss the spectral morphology of the star from UV to near-IR wavelengths, concentrating on profile variations in the UV and optical H and He lines. From a spectroscopic analysis with non-LTE model atmospheres, we derive for HDE 269445: T_*_=34000K, R_*_=43Rsun_, log˙(M)(Msun_/yr)=-4.5 and He/H=0.4/0.6 by number. These parameters are in good agreement with those previously derived by Pasquali et al. (1997ApJ...478..340P) who used only ultraviolet and optical lines. Therefore, our analysis confirms that a combination of optical and infrared lines can be fruitfully used to determine stellar and wind properties when ultraviolet data are not available. Our model calculations only fit the broad component underneath a strong core emission. We interpret the discrepancy between the observed and the model line profiles as the effect of a non-spherical wind which has a hot, fast polar component and a cold, slow equatorial component. The time-variability detected in some H and He lines indicates that the wind geometry may be variable and the star has undergone changes in T_eff_ and ˙(M). These properties are similar to those observed for the galactic LBV AG Carinae by Leitherer et al. (1994ApJ...428..292L) and we may suspect that HDE 269445 is also a Luminous Blue Variable. This could explain why HDE 269445 has defied easy spectral classification, and, although originally classified as a Ofpe/WN9, it has always represented a peculiarity for this spectral type. Title: Fundamental Stellar Parameters of γ2 Velorum from HIPPARCOS Data Authors: Schaerer, Daniel; Schmutz, Werner; Grenon, Michel Bibcode: 1997ApJ...484L.153S Altcode: 1997astro.ph..3061S We report parallax measurements by the HIPPARCOS satellite of γ2 Velorum and a few related objects. The distance of γ2 Vel is d = 258+41-31 pc, significantly smaller than the commonly adopted value to Vela OB2. For ζ Puppis d = 429+120-77 pc is in agreement with the canonical distance.

The total mass of γ2 Vel derived from its parallax, the angular size of the semimajor axis as measured with intensity interferometry, and the period are M(W-R + O) = 29.5 +/- 15.9 Msolar. This result favors the orbital solution of Pike et al. over that of Moffat et al. The stellar parameters for the O star companion derived from line-blanketed non-LTE atmosphere models are Teff = 34,000 +/- 1500 K, log L/Lsolar = 5.3 +/- 0.15, from which an evolutionary mass of M = 29 +/- 4 Msolar and an age of 4.0+0.8-0.5 Myr is obtained from single-star evolutionary models. With non-LTE model calculations including He and C, we derive a luminosity log L/Lsolar ~ 4.7 +/- 0.2 for the W-R star. The mass-luminosity relation of hydrogen-free W-R stars implies a mass of MW-R ~ 5 +/- 1.5 Msolar.

From our data we favor an age of about 10 Myr for the bulk of the Vela OB2 stars. Evolutionary scenarios for ζ Pup and γ2 Vel are discussed in the light of our results.

Based on data from the ESA HIPPARCOS astrometry satellite. Title: Search for ionized material around Cyg X-3 Authors: Schmutz, Werner Bibcode: 1997hst..prop.7838S Altcode: 1997hst..prop.4164S Models of the evolution of massive binaries predict that a few such objects should survive the common envelope phase and result in systems containing a compact object plus a Wolf-Rayet star {c+WR}. According to these models, a vast amount of stellar material is lost during the common envelope phase prior to the c+WR phase. We propose to test these models by searching for the presence of this circumbinary material around the only known c+WR object: Cyg X-3. Since the large reddening towards Cyg X-3 prevents any investigation in the optical, deep exposures with NIC-2 and the PaAlpha narrow band filter centered on Cyg X-3 will be used to image the system at high spatial resolution. By exposing NIC-1 and NIC-3 in parallel, we will simultaneously cover spatial scales up to 100" . {Although NIC-3 will be out of focus its PaAlpha images will still be superior to ground-based images.} We have already attempted to image Cyg X-3 from the ground using adaptive optics techniques on a 4m telescope. Our exposure yielded a marginal detection of extended nebular emission. While further ground based observations will not significantly inprove upon these images, observations with NICMOS will yield much deeper images. Our goal is to obtain a clear detection of the nebular PaAlpha emission, the strength of which can be used to estimate the initial mass of the WR star; its morphology can be used to constrain models of the mass loss during the common envelope phase. Title: Photon loss from the helium Lyα line - the key to the acceleration of Wolf-Rayet winds. Authors: Schmutz, W. Bibcode: 1997A&A...321..268S Altcode: It is demonstrated that the ionization equilibrium of helium in non-LTE atmospheres for Wolf-Rayet stars is very sensitive to photon loss from the Heii Lyα line. A removal of 0.001% of the photons is sufficient to initiate an abruptly recombining ionization equilibrium. The assumption of photon loss allows to address the wind momentum problem of Wolf-Rayet stars. It is possible for the first time to construct a line blanketed non-LTE model of a Wolf-Rayet star that reproduces the observed spectrum and simultaneously, provides the radiation force to drive its outer velocity structure. A method is developed to determine the free model parameters L, R_phot_, ˙(M), vinfinity_, v_phot_, C (clumping factor), and f (photon loss factor), by an analysis of an observed Wolf-Rayet spectrum. The method is applied to the spectrum of the WN5 star HD 50896 resulting in good fits in shape and strength to the observed helium emission lines. In particular the profile of the Hei λ10830 line, which is a tracer of the outer velocity structure, is reproduced remarkably well. The hydrodynamically calculated velocity law differs significantly from the commonly adopted β-law with β=1. The outer part can be approximated by a β-law with β=3 if the core radius of the atmosphere model is used, or by β=8, if the velocity law is calculated referring to the hydrostatic radius of a stellar evolution model in the Wolf-Rayet phase. Close to the photosphere the velocity structure is flat with an expansion velocity of v_phot_ =~1100 km/s. The resulting luminosity L= 5.5x10^5^ Lsun_ and terminal wind velocity vinfinity_=2060 km/s are found to be considerably larger than the values from previous determinations. On the other hand, the mass loss rate is lower ˙(M)=3.2x10^-5^ Msun_yr^-1^ due to an inhomogeneous wind with a clumping factor C=~4. There is evidence for a decrease of the clumping factor with distance from the star. The photon loss factor is determined empirically to have a value of f=~10^-4^. It is proposed that a Bowen resonance-fluorescence mechanism removes a small fraction of photons from the radiation field of the helium Lyα resonance line. Photon loss calculated theoretically from the interaction of metal lines close in wavelength to the Heii Lyα line yields a depth dependent factor in the range 10^-4^...10^-3^. In the recombination zone, where the photon loss influences the ionization structure, its value is f^*^=~10^-4^ in excellent agreement with the empirically determined value. The lines CaV λ303.74, FeVI λλ303.70,303.80, 303.83, and OIII λ303.80 are roughly of equal importance. The wind momentum calculated by the present model exceeds the single scattering limit by a factor of 6 in contrast to previous estimates that yielded factors 50-100. With a momentum ratio of 6 the Wolf-Rayet winds are no longer distinct from other radiation driven winds but they fit as more extreme versions to the winds of O stars. Title: Irradiated red giant atmospheres in S-type symbiotic stars. Authors: Schwank, M.; Schmutz, W.; Nussbaumer, H. Bibcode: 1997A&A...319..166S Altcode: We present non-LTE calculations for an expanding red giant's atmosphere ionized from the outside by the radiation of a nearby hot radiation source. We show that the hydrogen emission lines emerge from a narrow transition zone where hydrogen changes from ionized to neutral. In this region the Balmer lines are optically thick, and their profiles crucially depend on the magnitude of optical thickness which in turn, depends on the velocity gradient within that region. Balmer decrements of the model calculations depend on the densities in the recombination zone of the radiatively ionized wind. We find a large variety of complex line profiles, that in some cases could be mistaken for accretion disk profiles. The profiles depend on the velocity law in the formation zone at sub-sonic velocities, but contrary to expectation, the profiles do not reflect the terminal velocity of the wind. The central part of our model profiles compare well with the observed profile of the eclipsing binary SY Mus at maximum light. Title: O Stars in Transition. II. Fundamental Properties and Evolutionary Status of Ofpe/WN9 Stars from HST Ultraviolet Observations Authors: Pasquali, Anna; Langer, Norbert; Schmutz, Werner; Leitherer, Claus; Nota, Antonella; Hubeny, Ivan; Moffat, Anthony F. J. Bibcode: 1997ApJ...478..340P Altcode: We present new HST/FOS ultraviolet spectroscopic observations of seven LMC Ofpe/WN9 stars. We find that Ofpe/WN9 stars have slow winds with terminal velocities of about 400 km s-1 and high mass-loss rates of the order of 2-5 × 10-5 M⊙ yr-1. Ofpe/WN9 stellar temperatures and radii are in the range 30,000-39,000 K, and 19-39 R⊙, respectively. Stellar luminosities are between log (L/L⊙) = 5.6 and 6.3.

We study the Ofpe/WN9 stars winds and examine their evolutionary status. We find that Ofpe/WN9 stars are intermediate between O and W-R stars in terms of the wind momentum flux. We also find that the stellar properties and wind momentum of the Ofpe/WN9 sample place them in the evolutionary sequence: O --> Of --> H-rich WNL --> Ofpe/WN9, for initial stellar masses less than ~100 M⊙.

In view of persisting discrepancies of standard massive star models with observations, we compute massive main-sequence models according to three different evolutionary scenarios. We find that both higher mass-loss rate and enhanced mixing between core and envelope are required in order to yield models compatible with the derived stellar and wind properties of Ofpe/WN9 stars. The emerging picture may be consistent with earlier evidence of Ofpe/WN9 stars being quiescent luminous blue variables (LBVs). This idea is further strengthened by the highly reduced surface H mass fractions of the Ofpe/WN9 stars. We derive Xs = 0.5 to 0.3, which still excludes Ofpe/WN9 stars from being core He-burning objects, but is almost identical to the Xs values recently measured in LBVs.

Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA for NASA under contract NAS5-26555. Title: Summary of the General Discussion Authors: Schmutz, W. Bibcode: 1997ASPC..120..115S Altcode: 1997lbv..conf..115S No abstract at ADS Title: Radiation Pressure in LBV Winds Authors: Schmutz, W. Bibcode: 1997ASPC..120..143S Altcode: 1997lbv..conf..143S No abstract at ADS Title: HST Observations of RW Hydrae Authors: Schmutz, W.; Dumm, T.; Folini, D.; Mürset, U.; Nussbaumer, H.; Schild, H.; Schmid, H. M.; Walder, R.; Shore, S. Bibcode: 1997ppsb.conf..195S Altcode: No abstract at ADS Title: Orbital and Stellar Parameters of BX Mon Authors: Dumm, T.; Folini, D.; Mürset, U.; Nussbaumer, H.; Schild, H.; Schmid, H. M.; Schmutz, W.; Walder, R. Bibcode: 1997ppsb.conf..199D Altcode: No abstract at ADS Title: Irradiated Red Giant Atmospheres in S-type Symbiotic Stars Authors: Schmutz, W.; Nussbaumer, H. Bibcode: 1997ppsb.conf..167S Altcode: No abstract at ADS Title: A Database for Galaxy Evolution Modeling Authors: Leitherer, Claus; Alloin, Danielle; Fritze-v. Alvensleben, Uta; Gallagher, John S.; Huchra, John P.; Matteucci, Francesca; O'Connell, Robert W.; Beckman, John E.; Bertelli, Gianpaolo; Bica, Eduardo; Boisson, Catherine; Bonatto, Charles; Bothun, Gregory D.; Bressan, Alessandro; Brodie, Jean P.; Bruzual, Gustavo; Burstein, David; Buser, Roland; Caldwell, Nelson; Casuso, Emilio; Cerviño, Miguel; Charlot, Stephane; Chavez, Miguel; Chiosi, Cesare; Christian, Carol A.; Cuisinier, Francois; Dallier, Richard; de Koter, Alex; Delisle, Sonya; Diaz, Angeles I.; Dopita, Michael A.; Dorman, Ben; Fagotto, Franco; Fanelli, Michael N.; Fioc, Michel; Garcia-Vargas, Maria Luisa; Girardi, Leo; Goldader, Jeffrey D.; Hardy, Eduardo; Heckman, Timothy M.; Iglesias, Jorge; Jablonka, Pascale; Joly, Monique; Jones, Lewis; Kurth, Oliver; Lancon, Ariane; Lejeune, Thibault; Loxen, Johannes; Maeder, Andre; Malagnini, Maria Lucia; Marigo, Paola; Mas-Hesse, J. Miguel; Meynet, Georges; Moller, Claudia S.; Molla, Mercedes L.; Morossi, Carlo; Nasi, Emma; Nichols, Joy S.; Odegaard, Knut J. R.; Parker, Joel Wm.; Pastoriza, Miriani G.; Peletier, Reynier; Robert, Carmelle; Rocca-Volmerange, Brigitte; Schaerer, Daniel; Schmidt, Alex; Schmitt, Henrique R.; Schommer, Robert A.; Schmutz, Werner; Roos, Margarida Serote; Silva, Laura; Stasińska, Grazyna; Sutherland, Ralph S.; Tantalo, Rosaria; Traat, Peeter; Vallenari, Antonella; Vazdekis, Alexandre; Walborn, Nolan R.; Worthey, Guy; Wu, Chi-Chao Bibcode: 1996PASP..108..996L Altcode: This paper represents a collective effort to provide an extensive electronic database useful for the interpretation of the spectra and evolution of galaxies. A broad variety of empirical and theoretical data are discussed here, and the data are made fully available in the AAS CD-ROM Series, Vo. 7. Several empirical stellar libraries are part of this database. They cover the ultraviolet spectral range observed with IUE, optical data from different ground-based telescopes, and ground-based infrared data. Spectral type coverage depends on the wavelength, but it is mostly complete for types O and M and luminosity classes V to I. A large metallicity range is covered as well. Theoretical libraries of selected spectral indices of cool stars and of stellar continuum fluxes in the temperature range 2000 K to 50,000 K, as well as Wolf-Rayet energy distributions are presented. Several libraries of star clusters and early-type galaxies have been selected for this database. We discuss an extensive set of empirical spectra templates covering the wavelength region from 1200 - 9800 A, as well as narrow-band line indices in a large number of passbands. Bench-mark spectra of nearby galaxies for model tests are included as well. We compiled numerous evolutionary models and isochrones for stars of all mass ranges of interest, wide metallicity range, and for all evolutionary phases, including the pre-main-sequence phase. The majority of the models have been computed by the Geneva and Padova groups. Evolutionary synthesis models computed by several independent groups are made available. They can be applied to old and young systems, and are optimized with respect to different aspects of input physics. The model predictions include stellar (colors, magnitudes, absorption features) and nebular (emission-line fluxes) properties. Finally, we present models of ionized gas to be used for the interpretation of active galactic nuclei and young star-forming galaxies. The community is encouraged to make use of this electronic database and to perform a critical comparison between the individual datasets. (SECTION: Galaxies) Title: Extragalactic symbiotic systems. IV. The supersoft X-ray source SMC 3. Authors: Jordan, S.; Schmutz, W.; Wolff, B.; Werner, K.; Muerset, U. Bibcode: 1996A&A...312..897J Altcode: 1996astro.ph..4076J We present a consistent model for the UV and supersoft X-ray emission from the symbiotic nova SMC3 (=RX J0048.4-7332). Following the present picture of symbiotic stars, the model consists of radiation from a hot star and an emission nebula excited by that star. The observations were compared to theoretical models in which the hot star's emission is calculated with the help of hydrostatic and Wolf-Rayet-type non-LTE model atmospheres. Our analysis clearly shows evidence for mass loss rates of several 10^-6^Msun_/yr. The minimum effective temperature compatible with both the observed UV and X-ray flux is about 260000K, which is higher than in any other star analyzed with sophisticated NLTE model atmospheres. Since the hydrostatic surface is hidden by the stellar wind no upper limit for the temperature can be determined. However, we were able to determine the total luminosity of a symbiotic nova with reasonable accuracy (L_SMC3_=10^4.05+/-0.05^Lsun_). This value is well below the Eddington limit (=~50000Lsun_). In order to reproduce the observed energy distribution a carbon-to-helium ratio >2.10^-4^ -- leading to an absorption edge at 0.39keV -- is necessary. Title: Combined stellar structure and atmosphere models for massive stars. II. Spectral evolution on the main sequence. Authors: Schaerer, D.; de Koter, A.; Schmutz, W.; Maeder, A. Bibcode: 1996A&A...312..475S Altcode: 1995astro.ph..8137S In Schaerer et al. (1995, Paper I) we have presented the first ``combined stellar structure and atmosphere models'' (CoStar) for massive stars, which consistently treat the entire mass loosing star from the center out to the outer region of the stellar wind. The models use up-to-date input physics and state-of-the-art techniques to model both the stellar interior and the spherically expanding non-LTE atmosphere. The atmosphere models include line blanketing for all elements from hydrogen to zinc. The present publication covers the spectral evolution corresponding to the main sequence interior evolution discussed in Paper I. The CoStar results presented in this paper comprise: (a) flux distributions, from the EUV to the far IR, and the ionizing fluxes in the hydrogen and helium continua, (b) absolute optical and infrared UBVRIJHKLMN photometric magnitudes and UV colors, (c) detailed line blanketed UV spectra, and (d) non-LTE hydrogen and helium line spectra in the optical and IR, including theoretical K band spectra. These results may, e.g., be used for population synthesis models intended to study the massive star content in young starforming regions. We compare our results with other predictions from LTE and non-LTE plane parallel models and point out the improvements and the importance of using adequate atmosphere models including stellar winds for massive stars. Particular emphasis is given to comparisons of the UV spectral evolution with observations, including continuum indices and several metal line signatures of P-Cygni lines and broad absorption features. Good agreement is found for most UV features. In particular, we are able to reproduce the strong observed Fe III 1920A feature in late O and early B giants and supergiants. This feature is found to depend sensitively on temperature and may be used to derive effective temperatures for these stars. We also derive a simple formula to determine mass loss rates from the equivalent width of hydrogen recombination lines (Hα, Pα and Bα) for OB stars showing net emission in one or more of these lines. Title: Understanding the Simplest Symbiotic System(s) II. The 1996 Eclipse of RW Hydrae Authors: Schmutz, Werner Bibcode: 1996hst..prop.6550S Altcode: 1996hst..prop.2961S We propose to observe the symbiotic system RW Hya duringeclipse. The observations will be compared to approved cycle 5HST observations at quadrature. The comparison will yield astringent test of our model for S-type symbiotic systems. Theproposed target, RW Hya, is a typical S-type system andcarefully selected for its characteristics: eclipsing, lineprofile variations that repeat with orbital phase, absence ofoutbursts, and UV bright. We postulate three differentemission regions: wind lines from the hot star, nebularemission from the wind of the red giant facing the hot star,and most interesting, features emerging from the wind-windinteraction zone. We predict a different eclipse behavior foreach of these regions. The GHRS observations are focused onweak low density intercombination lines that are suspected tobe formed in a shock zone between the two stars and on broadline wings and P Cygni features emergent from the stellar windof the hot object. These features are too weak to beaccessible by IUE. If our model is confirmed qualitatively bythe proposed test we will apply in a later HST cycle to covera full orbit. Doppler tomography of optically thinintercombination lines will allow to map the interaction zonein the binary system. The results will be used for aquantitative comparison with sophisticated hydrodynamiccalculations. Observational constraints are desperately neededto validate our understanding of the hydrodynamics. Title: Combined stellar structure and atmosphere models for massive stars. I. Interior evolution and wind properties on the main sequence. Authors: Schaerer, D.; de Koter, A.; Schmutz, W.; Maeder, A. Bibcode: 1996A&A...310..837S Altcode: 1995astro.ph..8134S We present the first "combined stellar structure and atmosphere models" (CoStar) for massive stars, which consistently treat the entire mass loosing star from the center out to the asymptotic wind velocity. The models use up-to-date input physics and state-of-the-art techniques to model both the stellar interior and the spherically expanding non-LTE atmosphere including line blanketing. Our models thus yield consistent predictions regarding not only the basic stellar parameters, including abundances, but also theoretical spectra along evolutionary tracks. On the same ground they allow us to study the influence of stellar winds on evolutionary models. In this first paper, we present our method and investigate the wind properties and the interior evolution on the main sequence (MS) at solar metallicity. The wind momentum and energy deposition associated with the MS evolution is given and the adopted wind properties are discussed. From our atmosphere calculations, which include the effect of multiple scattering and line overlap, we also derive theoretical estimates of mass loss driven by radiation pressure. These values are compared with the predictions from recent wind models of the Munich group (Pauldrach et al. 1990, 1994, Puls et al. 1995). While we find an overall agreement with most of their results, our estimates for the mass loss rates are larger for supergiants. Our rates are in better agreement with the observed values than those of Puls et al. (1995). A comparison between boundary conditions given by the conventional plane parallel and the new spherically expanding atmosphere approach is made. For the MS evolution the evolutionary tracks and the interior evolution are found to be basically unchanged by the new treatment of the outer layers. However, for stars close to the Eddington limit, a small uncertainty in the behaviour of the deep atmosphere is found which might marginally affect the evolution. Given the small spherical extension of the continuum forming layers in the considered evolutionary phases, the predicted stellar parameters differ negligibly from those obtained using plane parallel atmospheres. Title: High resolution spectroscopy of symbiotic stars. II. RW Hydrae: orbit, eclipses, and stellar parameters. Authors: Schild, H.; Muerset, U.; Schmutz, W. Bibcode: 1996A&A...306..477S Altcode: With IUE spectra and published optical photometry, we show that the symbiotic star RW Hya is an eclipsing binary. We use a series of high resolution optical spectra to determine the orbital elements and basic parameters of the stellar components in the system. We measure the orbital velocity amplitude of the red star and determine the binary mass function of RW Hya. Absorption line fitting yields the rotation velocity of the cool star, and, assuming co-rotation, its radius and luminosity which are found to be R_r=60_Rsun_ and L_r=600_Lsun_, respectively. The masses of the red giant and the hot companion turn out to be M_r=1.6_Msun_ and M_h=0.5_Msun_, respectively. The red giant only fills a small fraction of its Roche lobe and the presence of an accretion disk around the hot companion is highly unlikely. We present a series of Hα line profiles obtained at various orbital phases. Their variation and the eclipse light curve in the Stroemgren u and v filters indicate, that the symbiotic nebulosity is a small compact region located close to the red giant's surface. A broad pedestal Hα emission disappears at times when the hot companion passes behind the red giant. This may be an indication that a fast stellar wind streams off the hot star. The Hα profiles also indicate that at least in RW Hya, the for symbiotic stars typical double-peak structure is due to self-absorption. The fact that the symbiotic nebula has only dimensions of the order of ~0.5AU has important consequences in relation to Zanstra techniques designed to measure the luminosity and temperature of the hot companion star. Title: Variability of luminous blue variables. II. Parameter study of the typical LBV variations. Authors: de Koter, A.; Lamers, H. J. G. L. M.; Schmutz, W. Bibcode: 1996A&A...306..501D Altcode: We present predicted photometric and spectroscopic variations for Luminous Blue Variables (LBVs) based on a computed grid of Non-LTE extended and expanding atmosphere models. The effects of (i) mass loss, (ii) terminal flow velocity, (iii) rate of acceleration of the flow, (iv) minimum wind temperature, (v) effective gravity, and (vi) underlying stellar radius are investigated. We show that the characteristic variations in visual magnitude for LBVs of {DELTA}V =~ 1 to 2 mag, which occur at constant luminosity and are therefore associated with a change in photospheric radius and temperature, cannot be due to the formation of a `pseudo' photosphere in the wind induced by a dramatic increase in mass loss rate. This implies that the origin of the mechanism responsible for the variations is located below the atmosphere. The change in photospheric radius that can be achieved by changing the wind parameters (i) to (iv), using observed mass loss rates, is ~40 %. However, a change of a factor of 4 to 12, depending on luminosity, is needed to reach the observed minimum effective temperature of LBVs of T_eff_=~8000 K. We conclude that the observed increase in photospheric radius is due to the combined effect of an increase in the underlying stellar radius (vi) and a reduced effective gravity (v). Our calculations further show that mass loss and velocity structure variations may in principle cause visual magnitude changes of {DELTA}V<~0.2mag , however only if the optical depth of the wind is at the outset of the order of unity. To estimate the optical depth of the wind, we provide a simple formula. We also show the sensitivity of the profiles of several H and He i lines to changes in the photospheric and wind parameters and explain the behaviour of Hα in simple physical terms. Title: On Stars in Transition. I. Optical Spectroscopy of Ofpe/WN9 and Related Stars Authors: Nota, Antonella; Pasquali, Anna; Drissen, Laurent; Leitherer, Claus; Robert, Carmelle; Moffat, Anthony F. J.; Schmutz, Werner Bibcode: 1996ApJS..102..383N Altcode: Ofpe/WN9 stars have become one of the keys for understanding the physics of very strong stellar winds and their consequences for the evolution of massive stars. This paper is the first part of a comprehensive effort to understand the role of Ofpe/WN9 stars in the uppermost part of the Hertzsprung-Russell diagram. First, we report the results of a complete literature search on aspects most relevant to the goal of our study. This provides a database which will be used for the interpretation of our observational and theoretical results. Second, we present a complete dataset of new ground-based data. We present here high S/N, high spectral resolution echelle observations of seven Ofpe/WN9 stars and six closely related stars, with the objective to establish similarities and differences between individual objects and stellar groups, in an attempt to shed light on the true nature of Of e/ WN9 stars.

Our findings show that the Ofpe/WN9 stars form a homogeneous group, in terms of spectral distribution and wind properties, with characteristics somewhere in between the Of stars on one hand (with the weakest winds) and the B[e] stars on the other. We also find that, at least for the Of-Ofpe I WN9 stars, this progression corresponds to an evolutionary sequence. In fact, in two of the observed Of stars in our sample (HDE 313846 and HD 152408) the appearance of P Cygni profiles and strengthened emission components in both H and He I lines seems to suggest they are in a transition phase between Of and Ofpe/WN9.

We also find that five of the Ofpe I WN9 star spectra show the presence of nebular emission lines, indicating a surrounding nebulosity. We examine all the cases individually and conclude that only for S119 and BE 381 is there a clear case for an expanding shell associated with the star. This would strengthen the connection between Ofpe/WN9 stars and luminous blue variables, which also are often surrounded by circumstellar nebulae generated during one or more "violent outbursts" in their recent evolution history. Title: What we really know, what we don't know Authors: Schmutz, W. Bibcode: 1996LIACo..33..553S Altcode: 1996wrsf.book..553S No abstract at ADS Title: Spectroscopic Analysis of the Wind Lines of the Symbiotic Nova AG Peg Authors: Schmutz, W. Bibcode: 1996swhs.conf..366S Altcode: No abstract at ADS Title: Wind Structure of Red Giants in Symbiotic Systems Authors: Schmutz, W. Bibcode: 1996iue..prop.5133S Altcode: No abstract at ADS Title: Fundamental Properties of Ofpe/WN9 Stars from Ultraviolet HST Spectra1 Authors: Pasquali, A.; Schmutz, W.; Leitherer, C.; Nota, A.; Hubeny, I.; Langer, N.; Drissen, L.; Robert, C. Bibcode: 1996swhs.conf..386P Altcode: No abstract at ADS Title: Observational Constraints on the Ionization Structure and Velocity Low in Vel Authors: Schmutz, W. Bibcode: 1996iue..prop.5137S Altcode: No abstract at ADS Title: Cyg X-3: evidence for a black hole. Authors: Schmutz, W.; Geballe, T. R.; Schild, H. Bibcode: 1996A&A...311L..25S Altcode: The authors have observed time-variations in the profiles of several infrared emission lines from the X-ray binary, Cyg X-3, which is believed to consist of a Wolf-Rayet star and a compact object. It is concluded that the variations are due to the orbital motion of the Wolf-Rayet star and derive a mass function for Cyg X-3 of 2.3 Msun. Assuming reasonable values for the mass of the Wolf-Rayet star and the inclination of the system, the authors obtain a range of masses 7-40 Msun for the compact object, with a most likely value of 17 Msun. This strongly suggests that the compact component of Cyg X-3 is a black hole. Title: Theoretical Continuum Energy Distribution of Wolf-Rayet Stars Authors: Schmutz, W. Bibcode: 1996ASPC...98...92S Altcode: 1996fstg.conf...92S No abstract at ADS Title: Understanding the Simplest Symbiotic System(s) Authors: Schmutz, Werner Bibcode: 1995hst..prop.6081S Altcode: 1995hst..prop.2554S We intend to optain pilot observations of the symbiotic system RW Hya. If the expected features are found we will propose to cover a full orbital cycle of RW Hya. RW Hya is an eclipsing system that is characterized by line profile variations that repeat with orbital phase, in the absence of outbursts, and its brightness in the UV. The GHRS observations of a few selected lines will focus on weak low density intercombination lines that are suspected to be formed in a shock zone between the two stars, on broad line wings, and on P Cygni features thought to be due to a stellar wind from the hot object. These features are too weak to be accessible by IUE. Doppler tomography of the optically thin intercombination lines and eclipse observations of the wind features will allow to locate the formation region in the binary system. The results will be used for a quantitative comparison with sophisticated hydrodynamic calculations. Preliminary results of such calculations suggest that there are 3 emitting regions: the red giant's wind ionized by the hot object, a stellar wind from the hot object, and a wind-wind shock zone located between the stars. Observational constraints are desperately needed to validate our understanding of the hydrodynamics. Title: Circumstellar Nebulae around OfPe/WN9 Stars Authors: Nota, A.; Pasquali, A.; Drissen, L.; Leitherer, C.; Robert, C.; Schmutz, W. Bibcode: 1995Ap&SS.224..261N Altcode: New high resolution echelle observations of Ofpe/WN9 stars in the Large Magellanic Cloud have been obtained in the wavelength region 4000 - 8000 Å. We find that five Ofpe/WN9 stars display in their spectra nebular emission lines [NII], [SII] and also [OIII], previously unreported for BE381 and S119. At least in these two cases we can conclude that the stars are surrounded by an associated nebula, thus strengthening the relationship between Ofpe/WN9 stars and LBVs. Title: The distance to the Wolf-Rayet star HD 50896. Authors: Howarth, Ian D.; Schmutz, Werner Bibcode: 1995A&A...294..529H Altcode: We present high-resolution observations (R=~10^5^) of the interstellar Na I D lines in the spectra of 23 stars which are close to HD 50896 on the plane of the sky, plus HD 50896 itself. The results are parameterized by using simple cloud models. We confirm that HD 50896 lies beyond the cluster Cr 121 (which is in the same line of sight), and estimate D=~1.8kpc. Title: Complete Stellar Models Interior and Spectral Evolution of Massive Stars Authors: Schaerer, D.; Schmutz, W.; de Koter, A. Bibcode: 1995IAUS..164..363S Altcode: No abstract at ADS Title: Complete stellar models for massive stars Authors: Schaerer, D.; de Koter, A.; Schmutz, W. Bibcode: 1995IAUS..163..300S Altcode: No abstract at ADS Title: Combined Stellar Structure and Atmosphere Models: Exploratory Results for Wolf-Rayet Stars Authors: Schaerer, D.; de Koter, A.; Schmutz, W. Bibcode: 1995ASPC...78..467S Altcode: 1995aapn.conf..467S; 1994astro.ph.10046S In this paper we present Complete Stellar models (CoStar) for massive stars, which treat the stellar interior and atmosphere, including its wind. Particular emphasis is given to Wolf-Rayet stars. We address the question of the effective temperatures of WNE and WC stars. Our first results show a satisfactory agreement between the CoStar models and the simple temperature correction method applied by Schaller et al. (1992). An analyses of the subphotospheric structure of the WR star models shows the importance of metal opacity. This may be essential for understanding the driving mechanism of Wolf-Rayet winds. Title: Proof of a fast wind in the symbiotic nova AG Pegasi. Authors: Nussbaumer, H.; Schmutz, W.; Vogel, M. Bibcode: 1995A&A...293L..13N Altcode: Hubble Space Telescope observations of the symbiotic nova AG Peg reveal a P Cygni profile in N V λl240. This proves that the hot compact object in the binary system loses material through a fast wind. High resolution spectra allow to discern three different emission regions: the wind from the hot compact star, a nebular emission region of relatively high density located in the extended atmosphere of the red giant, and a region of lower density most probably associated with the location where the fast wind from the hot star collides with the wind from the red giant. Title: Fundamental parameters of Wolf-Rayet stars. III. The evolutionary status of WNL stars. Authors: Crowther, P. A.; Smith, L. J.; Hillier, D. J.; Schmutz, W. Bibcode: 1995A&A...293..427C Altcode: New high S/N optical observations of 9 Galactic WNL (WN7-8) stars are presented. The spectra have been analysed using tailored non-LTE model atmospheres by Crowther et al. (1994c). Here we use the derived stellar parameters and abundances for a thorough investigation of the evolutionary status and mass-loss properties of WNL stars. We have identified two distinct groups of WNL stars from their observed properties. The WNL+abs and WN7 stars have high luminosities (log L/Lsun_~5.9) and form a continuity in morphology and physical parameters from the Of stars. They appear to be intimately related to these stars, confirming the suspicion of Walborn (1973) and are descended from extremely massive progenitors (M_initial_>60Msun_) through the sequence O->Of->WNL+abs->WN7(->WNE)->WC->SN. In contrast, the evolutionary sequence for WN8 stars is identified as O->LBV or RSG->WN8->WNE->WC->SN. These stars, with lower luminosities (log L/Lsun_~5.5), are descended from less massive stars, and have either red supergiant (RSG, 25Msun_<M_initial_<40Msun_) or Luminous Blue Variable (LBV, 40Msun_<M_initial_<60Msun_) progenitors. Indeed, we identify many properties that WN8 stars have in common with LBVs, e.g. spatial distribution, association with ejecta nebulae, low binary frequency, large photometric variability. We also find that those stars with the highest terminal velocities (WN7+abs stars) have the lowest variability while the WN8 stars and LBVs (low wind velocities) are the most variable. The smooth progression of mass loss properties from O supergiants to WNL stars found by Lamers & Leitherer (1993) is confirmed with the WNL+abs stars lying intermediately between the WN8 stars and O stars. The spectroscopic differences between Ofpe and WNL+abs stars appear to be attributable principally to a difference in wind density. This naturally explains the often ambiguous Of-WN spectral classification of some Of and WNL stars (Conti & Bohannan 1989). Finally, interstellar reddenings are determined using two independent methods based on the model atmosphere continuum distributions and the observed ubv colours. We find that the UV reddening towards WR25 (WN7+abs) is highly anomalous (R=4.6), confiming the findings of Tapia et al. (1988) for stars in Tr 16 in the Carina nebula. Title: Hydrodynamnic line-blanketed atmospheres of Wolf-Rayet stars (Invited) Authors: Schmutz, W. Bibcode: 1995IAUS..163..127S Altcode: No abstract at ADS Title: High resolution spectroscopy of symbiotic stars I. SY Muscae: orbital elements, M giant radius, distance Authors: Schmutz, W.; Schild, H.; Muerset, U.; Schmid, H. M. Bibcode: 1994A&A...288..819S Altcode: We have obtained a series of high resolution optical spectra of the eclipsing symbiotic system SY Mus. We measured the radial velocity curve of the M star component, and determined its rotation velocity. Assuming co-rotation we obtain for its radius 86Rsun_. We determine M4.5 for the spectral type, i.e. its temperature is 3500K. The resulting luminosity is 1000Lsun_. The cool component is thus a giant star with a luminosity slightly larger than average. Comparison with evolutionary tracks yield an actual mass of 1.30Msun_. From the binary mass function we obtain 0.43Msun_ for the hot companion. The separation of the stellar components is 1.72AU and the distance from the center of the red giant to the inner Lagrange point L_1_ is 1.05AU. The red giant extends to less than 40% of the distance to L_1_ and therefore, the SY Mus binary system is well detached. We present line profiles of Hα and the Raman scattered line at λ6825 at various orbital phases. The Hα profile is often double-peaked and shows rapid intensity variations near quadrature. This indicates that the bulk of the Hα emission is produced in a small high density region close to the red star's surface facing the hot companion. The non-variability of the Raman scattered line at λ6825 indicates that the Raman scattering zone is large compared to the size of the red giant. We do not observe any change in the absorption spectrum of the red giant as a function of phase, i.e. there is no observable irradiation effect. Title: Hydrodynamic atmosphere models for hot luminous stars. Authors: Schaerer, D.; Schmutz, W. Bibcode: 1994A&A...288..231S Altcode: We present the first line blanketed hydrodynamic models of spherically expanding atmospheres of hot stars. The models are characterised by a simultaneous solution of the equation of motion, the non-LTE populations of hydrogen and helium, and radiation transfer in a line blanketed atmosphere. The entire domain from the optically thick photosphere out to the terminal velocity of the wind is treated. The radiative forces are evaluated consistently with the depth-dependent radiation field, taking into account multiple scattering by metal lines and line overlap. This allows us to determine mass loss rates and the velocity field resp. density structure, as well as to predict the line blanketed energy distribution, the photospheric absorption lines, and the emission features emerging from the wind. The major improvements over unified non-LTE model atmospheres advocated by the Munich group (Gabler et al. 1989) are twofold: 1) The effects of line blanketing for the radiation transfer and statistical equilibrium of hydrogen and helium are included in the atmosphere calculations. 2) The radiative force (resp. line force parameters k, α) is evaluated using the depth-dependent radiation field of the model atmosphere We present a detailed discussion of the influence of the photosphere-wind transition zone on line profiles and the effects of line blanketing on a hydrodynamic non-LTE model atmosphere. Two important results are obtained from our study: (1) We quantify the influence of line blanketing on the atmospheric structure and on the predicted spectrum. In particular, we qualitatively confirm the results obtained with core-halo models and find that the corrections of Abbott & Hummer (1985) and Bohannan et al. (1986, 1990) are also quantitatively correct. (2) We show that even "purely" photospheric lines, on which spectroscopic determinations of basic stellar parameters rely, are strongly affected by the velocity field in the transition zone between the photosphere and the wind, and not only by the mass loss rate. Thus, for the more luminous OB stars spectroscopic analyses not only depend on three parameters (g, T_eff_, H/He abundance), but also on the atmospheric structure of the wind (i.e. ˙(M), v(r)). Therefore, we add new evidence to the previously stated finding that for precise determinations of stellar parameters and abundances of hot luminous stars, the use of plane parallel models may lead to systematic errors. This implies that the recent finding of discrepancies of spectroscopic masses and helium abundances compared to predictions of standard evolutionary models could be due to the inappropriateness of photospheric models for the analysis of luminous stars. The stellar parameters of our models are those thought to be representative for the O4 I(n)f star ζ Puppis. A comparison of the synthetic spectra with the observations shows that our model fits are not satisfactory. We find good agreement only for the key lines of a spectroscopic analysis, i.e. Hγ, HeI λ4471, and HeII λ 4542. However, for all lines that show wind features our predictions are clearly not correct. Since a spectroscopic analysis is a multi-dimensional problem it is impossible to single out one stellar parameter that is responsible for the failure of the model. We tentatively interpret our result as an indication that the calculated wind structure is not correct. The reason is not obvious, but it could be simply that the commonly adopted distance to the star is wrong. In any case, the spectrum of ζ Puppis should be carefully reanalysed with hydrodynamic model atmospheres. Title: Geometry and Physical Conditions in the Stellar Wind of AG Carinae Authors: Leitherer, Claus; Allen, Richard; Altner, Bruce; Damineli, Augusto; Drissen, Laurent; Idiart, Thais; Lupie, Olivia; Nota, Antonella; Robert, Carmelle; Schmutz, Werner; Shore, Steven N. Bibcode: 1994ApJ...428..292L Altcode: AG Carinae is one of the prototypes of the class of Luminous Blue Variables (LBVs). Since 1990 the star has continuously brightened in its visual continuum. We report on a multi-instrument and -wavelength observing campaign to monitor the current activity phase of AG Car. Ground-based photometry, polarimetry, spectroscopy, and space-ultraviolet spectroscopy and spectropolarimetry have been obtained. From the variability of the polarization at ultraviolet and optical wavelengths we detect significant intrinsic polarization. Pint greater than or equal to 0.5% is a large value for a hot, luminous star, suggesting departure from spherical symmetry in the wind of AG Car. The intrinsic polarization is variable on a timescale of 2 months or less. The measured ultraviolet polarization (intrinsic + interstellar) dropped to 0.5% in 1992 May and returned to 1% in 1992 July. The results are interpreted in terms of a variable outflow with a density enhancement in the equatorial plane. A similar model was suggested for the related object R127 in the Large Magellanic Cloud (LMC). This geometry is reminiscent of the large-scale morphology of the gas nebula and dust 'jet' surrounding AG Car. It is therefore likely that physical conditions close to the stellar surface are responsible for the geometry of the spatially resolved circumstellar material around AG Car. Despite the drastic change of the photospheric conditions, the mass-loss rate did not increase. We find no evidence for a positive correlation between wind density and stellar radius. This makes models that explain the radius increase by opacity effects in the outflow unlikely. The mechanism responsible for the temperature and radius variations is still unknown but most likely has its origin in subphotospheric regions. Title: High Resolution Echelle Observations of Nebulae around Ofpe/WN9 stars Authors: Nota, A.; Leitherer, C.; Pasquali, A.; Drissen, L.; Robert, C.; Schmutz, W. Bibcode: 1994AAS...184.3113N Altcode: 1994BAAS...26..910N New high resolution echelle observations are reported of R84, R99, HDE269927c and BE381 in LMC, which were first classified as Ofpe/WN9 stars by Bohannan and Walborn (1989). Spectra in the wavelength region 4000-8000 Angstroms have been obtained with EMMI on the ESO/NTT, and display nebular [NII], [OIII] emission lines for the four LMC stars, previously unreported for HDE269927c and BE381. In the case of R99, HDE269927c and BE381 the nebular lines Hα, Hβ and [OIII] are spatially extended, suggesting the presence of a circumstellar nebula few arcsecs in size. These findings further support the evidence that a link exists between Ofpe/WN9 stars and the Luminous Blue Variables, as we had advocated in the case of the Ofpe/WN9 star S119 in the LMC. The nebulae appear to be asymmetric in the echelle spectra. Further investigation will be necessary to establish if their morphology is similar to more well known LBVS such as AG Carinae and R127. Title: GHRS observations and theoretical modeling of early type stars in R136a Authors: de Koter, A.; Heap, S.; Hubeny, I.; Lanz, T.; Hutchings, J.; Lamers, H. J. G. L. M.; Maran, S.; Schmutz, W. Bibcode: 1994AAS...184.3106D Altcode: 1994BAAS...26..909D We present the first spectroscopic observations of individual stars in R136a, the most dense part of the starburst cluster 30 Doradus in the LMC. Spectra of two stars are scheduled to be obtained with the GHRS on board the HST: R136a5, the brightest of the complex and R136a2, a Wolf-Rayet star of type WN. The 30 Doradus cluster is the only starburst region in which individual stars can be studied. Therefore, quantitative knowledge of the basic stellar parameters will yield valuable insight into the formation of massive stars in starbursts and into their subsequent evolution. Detailed modeling of the structure of the atmosphere and wind of these stars will also lead to a better understanding of the mechanism(s) that govern their dynamics. We present the first results of our detailed quantitative spectral analysis using state-of-the-art non-LTE model atmospheres for stars with extended and expanding atmospheres. The models are computed using the Improved-Sobolev Approximation wind code (ISA-WIND) of de Koter, Schmutz & Lamers (1993, A&A 277, 561), which has been extended to include C, N and Si. Our model computations are not based on the core-halo approximation, but use a unified treatment of the photosphere and wind. This approach is essential for Wolf-Rayet stars. Our synthetic spectra, dominated by the P Cygni profiles of the UV resonance lines, also account for the numerous weak metal lines of photospheric origin. Title: Hydrodynamic atmosphere models for hot luminous stars. II. Method and improvements over unified models. Authors: Schaerer, D.; Schmutz, W. Bibcode: 1994ems..conf..173S Altcode: In a paper submitted to A&A the authors present the first line blanketed hydrodynamic models of spherically expanding atmospheres of hot stars. This paper is complementary to the submitted paper. Here, the authors emphasize the advantages and the weak points of their approach and they present additional technical aspects. The models are characterised by a simultaneous solution of the equation of motion, the non-LTE populations of H and He, and radiation transfer in a line blanketed atmosphere. The entire domain from the optically thick photosphere out to the terminal velocity of the wind is treated. The radiative forces are evaluated consistently with the depth-dependent radiation field, taking into account multiple scattering by metal lines and line overlap. Title: First combined stellar structure and atmosphere models: interior and spectral evolution of massive stars Authors: Schaerer, D.; de Koter, A.; Schmutz, W.; Maeder, A. Bibcode: 1994IAUGA..22..257S Altcode: No abstract at ADS Title: First complete stellar models: interior and spectral evolution of massive stars Authors: Schaerer, D.; Schmutz, W.; de Koter, A.; Maeder, A. Bibcode: 1994IAUGA..22...40S Altcode: No abstract at ADS Title: A fast non-LTE code for expanding atmospheres : a test of the validity of the Sobolev approximation. Authors: de Koter, A.; Schmutz, W.; Lamers, J. G. L. M. Bibcode: 1993A&A...277..561D Altcode: We present a new non-LTE atmosphere code to calculate the continuum energy distribution and line profiles from stellar atmospheres with extended outfiowing envelopes. The code is fast, which makes it suited for empirical modelling. The statistical equilibrium equations and the radiative transfer in the continuum are solved with an efficient approximate lambda iteration method. The line transfer is treated using the Sobolev approximation, including the effects of the diffuse radiation field, and the continuous opacity inside the line resonance zone.

We investigate the validity of the Sobolev approximation by comparing our code with one that solves the line transfer using the co-moving frame method. We find good agreement in the calculated emission lines for Wolf-Rayet stars, O-type stars and for Luminous Blue Variables (LBVs). The modelling of photospheric hydrogen lines of O-stars with our method is less reliable. For the LBVs, we conclude that the continuum spectrum and the relatively strong wind tines, computed using the Sobolev method, agree with those computed using the comoving frame method. The mass-loss rate of the latter stars, derived by fitting individual emission lines, yields a maximum difference of 30% between the two codes. Title: The LBV AG CAR in its Current Active Phase Authors: Lupie, O. L.; Leitherer, C.; Neto, A. Damineli; Drissen, L.; Idiart, T.; Robert, C.; Nota, A.; Altner, B.; Schmutz, W.; Shore, S. Bibcode: 1993AAS...182.6306L Altcode: 1993BAAS...25..908L With an emphasis on our polarization monitoring program, we present our observations to date of AG CARINAE, the prototype Luminous Blue Variable (LBV). The star is experiencing an active phase, increasing in brightness since 1990. The variability, which is semi-periodic on time scales 10-15 years, may culminate in an eruptive episode. Although AG Car is a well-studied LBV, the geometry and physics of its environment are extremely complex. To obtain a better description of AG Car, the team has been collecting many observations during the last year: UBVRI photo-polarimetry and visual spectroscopy (Brazilian National Observatory), UV spectropolarimetry with the Hubble Space Telescope Faint Object Spectrograph, UBV photometry (Port Alegre Observatory), IUE and H-alpha spectroscopy (LaSilla). UV polarization observations were selected as part of the campaign in order to probe for asymmetric structures ejected from the star in the innermost unresolved region (within 100 stellar radii). The ground based photo-polarization monitoring program enables us to track the polarimetric variability of the entire complex and to assist in the difficult task of separating the interstellar and intrinsic polarization components. We have found that the UV and optical polarization and position angle are strongly variable in time and structure is evident across the UV resonance scattering lines. The UV and optical spectroscopy show that the Teff is decreasing, the bolometric luminosity is remaining constant, and the structure and ionization state of the wind is evolving. We will discuss how these data support models which incorporate circumstellar disks, jets, and/or plumes to explain the mass loss characteristics. Title: The Asymmetric Wind of R127 Authors: Schulte-Ladbeck, R. E.; Leitherer, C.; Clayton, G. C.; Robert, C.; Meade, M. R.; Drissen, L.; Nota, A.; Schmutz, W. Bibcode: 1993ApJ...407..723S Altcode: We present optical, linear polarimetry in broad-band UBVRI filters plus narrow-band filters centered on the emission lines of Hα and the red [N II] and spectropolarimetry in the wavelength range from 4120 A to 6770 A of the luminous blue variable R127 in the Large Magellanic Cloud. Both observations display a decrease of the percentage polarization across the Hα emission line with respect to the continuum. We assume that Hα is recombination-line dominated and thus intrinsically unpolarized, and we use the continuum-subtracted line polarization to estimate the interstellar foreground polarization. The resulting amount of intrinsic continuum polarization of R127 is very large, of order 1%-1.5%, implying both the presence of copious free electrons and a considerable asphericity in their distribution. The two data sets, taken 2 months apart, display significant variations in the continuum polarization, which confirms that the stellar-wind properties of R127 are time-dependent in the maximum state. We discuss several possible wind geometries and present arguments favoring a clumpy, axisymmetric outflow. Title: Hydrodynamic atmosphere models for hot luminous stars II. Method and improvements over unified models Authors: Schaerer, D.; Schmutz, W. Bibcode: 1993SSRv...66..173S Altcode: In a paper submitted to A&A we present the first line blanketed hydrodynamic models of spherically expanding atmospheres of hot stars. This paper is complementary to the submitted paper. Here, we emphasize the advantages and the weak points of our approach and we present additional technical aspects. The models are characterised by a simultaneous solution of the equation of motion, the non-LTE populations of H and He, and radiation transfer in a line blanketed atmosphere. The entire domain from the optically thick photosphere out to the terminal velocity of the wind is treated. The radiative forces are evaluated consistently with the depth-dependent radiation field, taking into account multiple scattering by metal lines and line overlap. Title: Line-blanketed non-LTE atmosphere models for Wolr-Rayet stars Authors: Schmutz, Werner Bibcode: 1993SSRv...66..253S Altcode: A standard non-LTE Wolf-Rayet star atmosphere model is compared with an identical model but including line-blanketing. The structures of the two models are presented in detail and the implications of blanketed models for spectroscopic analyses are discussed. Title: Unified NLTE photosphere-wind models with line blanketing for hot stars: first results for ζ puppis Authors: Schaerer, D.; Schmutz, W. Bibcode: 1993fces.conf...59S Altcode: No abstract at ADS Title: Direction of Circumstellar Line Blanketing in the Spectra of the Symbiotic Nova PU Vulpeculae Authors: Schmutz, Werner; Pereira, Claudio; Mueller, David Bibcode: 1993AnIPS..10..311S Altcode: No abstract at ADS Title: Analysis of the IR Spectrum of Cygnus X-3 Authors: Schmutz, W. Bibcode: 1993AnIPS..10..259S Altcode: No abstract at ADS Title: Theoretical Continuum Energy Distributions for Wolf-Rayet Stars Authors: Schmutz, Werner; Leitherer, Claus; Gruenwald, Ruth Bibcode: 1992PASP..104.1164S Altcode: We discuss the problem of assigning an effective temperature to models of stellar evolution in the Wolf-Rayet stage. We conclude that it is best to use models with different velocity laws depending on the stellar temperature. We follow the most simple approach and propose to use a standard law with Beta = 1 for the cooler and Beta = 2 for the hotter Wolf-Rayet stars. We present energy distributions from non-LTE model calculations with a Beta = 2 velocity law. The new calculations together with published results based on Beta = 1 allow one to synthesize realistic spectra of starburst regions. The flux tables are available in digital form from the authors. (SECTION: Stars) Title: Near-infrared spectroscopy of galactic Wolf-Rayet stars. Authors: Howarth, Ian D.; Schmutz, Werner Bibcode: 1992A&A...261..503H Altcode: We present high-quality near-IR spectra of 24 Galactic WR stars, of a broad range of subtypes, selected as having known distances. The data cover the region 0.97-1.12 micron and include the 10830-A He I triplet. Measurements of He I and He II lines, together with the absolute magnitudes, yield temperatures, luminosities, mass-loss rates, and terminal velocities for our sample. We extend that sample by including results for a further 12 stars of known distance, taken from the literature. The spectroscopic mass-loss rates are in excellent agreement with those estimated from radio data, and exceed the 'single-scattering limit' by large factors. Mass-loss rates depend only weakly on mass, but there is a statistically significant correlation between surface mass flux and temperature. Terminal velocities correlate loosely with subtype for both WR sequences. Comparison with core-helium-burning mass luminosity tracks suggests that the spectroscopic luminosities may be systematically too faint by about 0.5 dex. We suggest that the WNC stars in our sample may represent an intermediate phase between WNL and WCE subtypes. Title: The SN 1986G in Centaurus A. Authors: Cristiani, S.; Cappellaro, E.; Turatto, M.; Bergeron, J.; Bues, I.; Buson, L.; Danziger, J.; di Serego-Alighieri, S.; Duerbeck, H. W.; Heydari-Malayeri, M.; Krautter, J.; Schmutz, W.; Schulte-Ladbeck, R. E. Bibcode: 1992A&A...259...63C Altcode: We present photometric and spectroscopic observations of SN 1986 G, spanning up to one year after the explosion. The overall photometric behavior of this SN Ia results rather normal. The maximum at B = 1245+/-0.05 was reached on May 11,1986, then the decline to the inflection point was relatively fast (β_B_ = 12.0 mag/100 d), but similar to other SNe. We show that the fast, early decline rate is not due, as suspected before, to the combined effect of the strong differential absorption and peculiar spectral evolution of this SN. Also, the late time decline rate resembles that of other SN Ia (γ_V_ = 1.58 mag/100 d). The particular position of the SN in the two-color diagram may be due to some undetected spectral peculiarity in the UV-visible gap of the available observations. Although the overall spectral evolution of SN 1986 G is typical of SN Ia, some peculiarities are pointed out. The expansion velocities of the envelope at different phases, deduced from the Si II 6355 A doublet, are among the slowest ever detected. The strong broad emission at about 4100 A, usually present in the SN Ia near-maximum spectra, is missing, affecting also the kinematic evolution of the envelope as derived from the Mg II 4481 A line. High S/N ratio late time spectra are presented, showing several features identified, by comparison with published synthetic spectra, as [Fe II], (Fe III] and [Co III] lines. The broad symmetric emission line at 6560 A, may be alternatively identified with Hα, indicating then the presence of an outer shell of ionized hydrogen. Different procedures have been used for determining the reddening suffered by the SN. All agree on a total color excess E(B - v) = 1.1 mag, somewhat higher than the previous determinations. Hence, the absorption- corrected absolute magnitude results are comparable to the average values for SN Ia. Title: Radiation-driven wind theory: Not (yet?) working Authors: Schmutz, Werner; Schaerer, Daniel Bibcode: 1992LNP...401..409S Altcode: 1992aets.conf..409S Line-blanketed non-LTE models for spherically expanding atmospheres have been constructed, including multiple scattering and line overlap and without an imposed core-halo structure. They have been used to evaluate the radiation force in the winds of two Of stars, ζ Pup and R84. We find for both stars that radiation forces are not sufficient to drive the observed mass-loss rates. For S Pup the disagreement is less than a factor of two, and could in principle be explained by uncertainties in the interpretation of the observations. However, for R84 the difference is unequivocally due to a failure of the radiation-driven wind theory in its present form. Having found a case where the theory does not work we are inclined to interpret the problems for C Pup as real, and therefore we suggest that the present theory of radiation-driven winds is not sufficient for a complete understanding of the observed winds of hot stars. Title: Radiation-driven wind theory: The influence of turbulence Authors: Schaerer, Daniel; Schmutz, Werner Bibcode: 1992LNP...401..414S Altcode: 1992aets.conf..414S Line-blanketed non-LTE models for spherically expanding atmospheres without core-halo approximation, including multiple scattering and line overlap, are used to evaluate the radiation pressure in stellar winds of Of and Ofpe/WN9 stars. The enhancement of the radiative forces due to microturbulence (line-broadening is discussed. Title: Calculations of non-LTE radiative transfer in extended outflowing atmospheres using the Sobolev approximation for line transfer Authors: de Koter, A.; Schmutz, W.; Lamers, H. J. G. L. M. Bibcode: 1992LNP...401..440D Altcode: 1992aets.conf..440D The code that we are developing for the empirical modelling of LBVs using the Sobolev approximation ] for the line transfer, yields accurate results that compare well with those obtained using the co-moving frame method. By including absorption by the continuum in the resonance region in addition to escape from the resonance region we get a much more accurate result for the hydrogen ground level population. The following properties make the code extremely fast:

•

the Sobolev approximation for the line transfer Title: AG Carinae and the LBV Phenomenon (Invited Paper) Authors: Leitherer, C.; Damineli Neto, A.; Schmutz, W. Bibcode: 1992ASPC...22..366L Altcode: 1992nvos.work..366L No abstract at ADS Title: Near-Infrared Spectroscopy of Galactic Wolf-Rayet Stars Authors: Howarth, Ian D.; Schmutz, Werner Bibcode: 1992LNP...401..104H Altcode: 1992aets.conf..104H We present high-quality near-IR spectra of 24 Galactic WR stars, of a broad range of subtypes, selected as having known distances. The data cover the region 0.97μm-1.12μm and include the λ10830-Å He I triplet. Measurements of He I and He II lines, together with the absolute magnitudes, yield temperatures, luminosities, mass-loss rates, and terminal velocities for our sample. We extend that sample by including results for a further 12 stars of known distance, taken from the literature. The spectroscopic mass-loss rates are in excellent agreement with those estimated from radio data, and exceed the `single-scattering limit' by large factors. Mass-loss rates depend only weakly on mass, but there is a tight correlation between surface mass flux and temperature. Terminal velocities correlate loosely with subtype for both WR sequences. Principally because of revisions to the adopted absolute magnitudes, our luminosities average slightly fainter than found previously; that exacerbates discrepancies with the predictions of evolutionary models, but reconciles results for Galactic and LMC stars. However, comparison with core-helium-burning mass-luminosity tracks suggests that the spectroscopic luminosities may be systematically too faint by ∼0.5 dex. We suggest that the WNC stars in our sample may represent an intermediate phase between WNL and WCE subtypes. A full version of this paper is being submitted to Astronomy & Astrophysics. Title: Models for starburst regions: how warm are warmers? Authors: Leitherer, C.; Gruenwald, R.; Schmutz, W. Bibcode: 1992pngn.conf..257L Altcode: No abstract at ADS Title: Spectral analyses of Wolf-Rayet stars : hydrogen abundances in WN subtypes. Authors: Hamann, W. -R.; Duennebeil, G.; Koesterke, L.; Wessolowski, U.; Schmutz, W. Bibcode: 1991A&A...249..443H Altcode: The spectra of four WN stars are analyzed quantitatively, focusing on the hydrogen abundances. The analyses are based on multilevel non-LTE models for expanding atmospheres composed of helium and hydrogen. The resulting hydrogen fraction is found to range from 10 to 40 percent by mass, which confirms that WN atmospheres exhibit material which has undergone nuclear burning. When the hydrogen detection is correlated with the stellar temperature a clear separation between two groups can be obtained, i.e., the cool stars with stellar temperature approximately equals 35 kK exhibit hydrogen, whereas the hot stars with stellar greater than 50 kK do not. Title: Spectral analyses of 19 Wolf-Rayet (WN) stars in the LMC. Authors: Koesterke, L.; Hamann, W. R.; Schmutz, W.; Wessolowski, U. Bibcode: 1991A&A...248..166K Altcode: The helium spectra of 19 Wolf-Rayet stars in the Large Magellanic Cloud are analyzed, and their luminosities, radii, temperatures and mass-loss rates are determined. The sample covers different subtypes of the nitrogen (WN) sequence. The analyses are based on multi-level non-LTE model calculations for the spectrum formation in spherically expanding stellar atmospheres, composed of pure helium. The results are compared with a Galactic sample analyzed previously with the same methods. The stellar temperatures obtained for the LMC stars are similar to those of Galactic stars. The "late" subtypes (WNL) form a homogeneous group with T about 30 kK, while the temperatures of WNE-s stars ("early" subtypes with strong lines) range from 50 kK to 90 kK. The LMC stars tend to lower luminosities (10^4.8^ to 10^5.6^ L_sun_) than our Galactic sample, which might be a real trend irrespective of selection effects. Terminal wind velocities and mass-loss rates do not show systematic differences between LMC and Galaxy when stars of same subtypes are compared. Such differences, however, would be expected as an effect of the different metallicities if the winds were driven by radiation pressure. The mechanical momentum in the winds exceeds the single- scattering limit by a large factor (up to 50). The evolutionary status of the WR stars is discussed by comparing their positions in the HR diagram with the theoretically predicted tracks for post-red-supergiant evolution. Although recent calculations now show some general agreement, the predicted luminosities are still higher than observed, especially for the LMC stars. Title: Determinations of the interstellar reddening toward Wolf-Rayet stars of the nitrogen sequence from observed UBV color indices. Authors: Schmutz, W.; Vacca, W. D. Bibcode: 1991A&AS...89..259S Altcode: We demonstrate that continuum discontinuities, or "jumps", are present in the spectra of some Wolf-Rayet stars and that current models of Wolf-Rayet stars predict such jumps and provide good fits to the observed continua. Using a relation between the size of the He II (n = 4) jump at 3645 A and the intrinsic (b - v)_0_ color found from the model atmospheres of Wolf-Rayet stars of the nitrogen sequence, we derive a formula for calculating the color excesses, E_b-v_, of WN stars. The method assumes that helium is the major opacity source in the Wolf-Rayet atmosphere; therefore it cannot be applied to WC stars. The method requires measurements of only the u - b and b - v color indices; it is independent of any assumed values of the intrinsic colors. We investigate the differences in the various photometric and calibration systems used in the past to determine magnitudes and colors of Wolf-Rayet stars and give correction factors which we use to put all previous values onto one consistent system. Using the corrected values of the u - b and b - v colors, we then calculate color excesses for WN stars in the Galaxy and the Large and Small Magellanic Clouds from our formula. We compare our results with previous determinations of color excesses for WN stars and find generally good agreement for Galactic stars. However, there are many LMC stars for which the photometric data are not accurate enough to yield reliable reddening values. Title: Non--LTE Analysis of the Ofpe/WN9 Star HDE 269227 (R84) Authors: Schmutz, Werner; Leitherer, Claus; Hubeny, Ivan; Vogel, Manfred; Hamann, Wolf-Rainer; Wessolowski, Ulf Bibcode: 1991ApJ...372..664S Altcode: The paper presents the results of a spectral analysis of the Ofpe/WN9 star HD 269227 (R84), which assumes a spherically expanding atmosphere to find solutions for equations of radiative transfer. The spectra of hydrogen and helium were predicted with a non-LTE model. Six stellar parameters were determined for R84. The shape of the velocity law is empirically found, since it can be probed from the terminal velocity of the wind. The six stellar parameters are further employed in a hydrodynamic model where stellar wind is assumed to be directed by radiation pressure, duplicating the mass-loss rate and the terminal wind velocity. The velocity laws found by computation and analysis are found to agree, supporting the theory of radiation-driven stellar wind. R84 is surmised to be a post-red supergiant which lost half of its initial mass, possibly during the red-supergiant phase. This mass loss is also suggested by its spectroscopic similarity to S Doradus. Title: Wolf-Rayet Stars as Starting Points or as Endpoints of the Evolution of Massive Stars? Authors: Lamers, H. J. G. L. M.; Maeder, A.; Schmutz, W.; Cassinelli, J. P. Bibcode: 1991ApJ...368..538L Altcode: The paper investigates the evidence for the two interpretations of Wolf-Rayet stars suggested in the literature: (1) massive premain-sequence stars with disks and (2) massive stars which have lost most of their H-rich layers in a stellar wind is investigated. The abundance determinations which are done in two different ways and which lead to different conclusions are discussed. The composition is solar, which would suggest interpretation (1), or the CNO abundances are strongly anomalous, which would suggest interpretation (2). Results from evolutionary calculations, stellar statistics, the existence of Ofpe/WN9 transition stars and W-R stars with evolved companions show overwhelming evidence that W-R stars are not premain-sequence stars but that they are in a late stage of evolution. Moreover, the fact that W-R stars are usually in clear regions of space, whereas massive premain-sequence stars are embedded in ultracompact H II regions also shows that W-R stars are not young premain-sequence stars. Title: The Hydrogen Abundances in WN Stars Authors: Hamann, W. -R.; Duennebeil, G.; Wessolowski, U.; Schmutz, W. Bibcode: 1991IAUS..143..100H Altcode: No abstract at ADS Title: The Distance to HD 50896 (ez Cma) Authors: Schmutz, W.; Howarth, I. D. Bibcode: 1991IAUS..143..639S Altcode: No abstract at ADS Title: The Nitrogen Spectra of WN Stars: the WN6 'standard' Star HD192163 (WR136) Authors: Wessolowski, U.; Hamann, W. -R.; Schmutz, W. Bibcode: 1991IAUS..143..106W Altcode: No abstract at ADS Title: Observations Versus Atmospheric Models of WR Stars (review) Authors: Schmutz, W. Bibcode: 1991IAUS..143...39S Altcode: No abstract at ADS Title: Non-Lte Analysis of Hot Stars Including Line Blanketing Authors: Schmutz, W. Bibcode: 1991ASIC..341..191S Altcode: 1991sabc.conf..191S No abstract at ADS Title: Determination of the Interstellar Extinction Toward WN Stars from Observed UBV Color Indices Authors: Vacca, W. D.; Schmutz, W. Bibcode: 1991IAUS..143..640V Altcode: No abstract at ADS Title: Short-term activity in the gamma2 Velorum system : the O-type supergiant is a nonradially pulsating star. Authors: Baade, D.; Schmutz, W.; van Kerkwijk, M. Bibcode: 1990A&A...240..105B Altcode: The discovery of photospheric line-profile variability and associated circumstellar effects of the O star in the Gamma(2) Velorum system is reported. The subcomponents drift across the line profiles at different rates. Two pattern speeds hve been tentatively measured to be 125 and 750 km/s/day. The temporal periods are 1.94 and 0.35 day, respectively, while the two spatial periods seem to be identical to one another and are about one-sixth of the stellar circumference. A rotation period in the range of 3-6 days is inferred. Two variable emission-line components straddle the He I 667.8-nm absorption and probably show that the O star has an extended envelope. Title: Non--LTE Model Calculations for SN 1987A and the Extragalactic Distance Scale Authors: Schmutz, W.; Abbott, D. C.; Russell, R. S.; Hamann, W. -R.; Wessolowski, U. Bibcode: 1990ApJ...355..255S Altcode: We present model atmospheres for the first week of SN 1987A, based on the luminosity and density/velocity structure from hydrodynamic models of Woosley. The models account for line blanketing, expansion, sphericity, and departures from LTE in hydrogen and helium and differ from previously published efforts because our models represent ab initio calculations, i.e., they contain essentially no free parameters. The formation of the UV spectrum is dominated by the effects of line blanketing. In the absorption troughs, the Balmer line profiles were fit well by our models, but the observed emissions are significantly stronger than predicted, perhaps due to clumping. The generally good agreement between our synthetic spectra and observations provides independent support for the overall accuracy of the hydrodynamic models of Woosley. We address the question of the accuracy of the Baade-Wesselink method in a detailed discussion of its approximations. While the application of the standard method produces a distance within an uncertainty of 20% in the case of SN 1987A, systematic errors up to a factor of 2 are possible, particularly if the precursor was a red supergiant. The key parameter that determines the systematic error of the method is the density/velocity structure, which can vary for each individual supernova. The supernova- based extragalactic distance scale is not yet precise enough to be of practical interest, owing to the large possible systematic error in the Hubble constant, H_0_ ~ 60^times 2^_divided by 2_ km s^-1^ Mpc^-1^. Title: Bolometric corrections for Wolf-Rayet stars: the influence of wind-line-blanketing. Authors: Schmutz, Werner Bibcode: 1990ASPC....7..117S Altcode: 1990phls.work..117S Bolometric corrections are given resulting from pure helium model atmospheres for Wolf-Rayet stars. The accuracy of these values is discussed with regard to the major deficiencies of the models: the neglect of metal bound-free continua and line-blanketing. If metals are included, the model has to have a larger effective temperature than its pure helium counterpart. A new approach to solve the wind-line-blanketing problem is presented. The first results from this method indicate that line-blanketing makes the star appear hotter with respect to a given value of effective temperature. Thus the predicted systematic errors of the bolometric corrections from the influence of metal bound-free continua and from line-blanketing are of opposite sense. The net systematic errors of pure helium models are not yet known. Estimates of the maximum effects indicate that the current values of the bolometric corrections are unlikely to be in error by more than 1 mag. Title: The nitrogen spectra of WN stars. Authors: Wessolowski, U.; Hamann, W. -R.; Schmutz, W. Bibcode: 1990AGAb....5...10W Altcode: No abstract at ADS Title: Analyses of 19 Wolf-Rayet stars (WN) in the Large Magellanic Cloud. Authors: Koesterke, L.; Hamann, W. -R.; Wessolowski, U.; Schmutz, W. Bibcode: 1990AGAb....5...11K Altcode: No abstract at ADS Title: Analyses of Wolf-Rayet Stars. Authors: Hamann, W. -R.; Wessolowski, U.; Schmutz, W.; Schwarz, E.; Duennebeil, G.; Koesterke, L.; Baum, E.; Leuenhagen, U. Bibcode: 1990RvMA....3..174H Altcode: No abstract at ADS Title: HD193077 - a Fast Rotating Wolf-Rayet Star Authors: Schmutz, W. Bibcode: 1990ASIC..316..227S Altcode: 1990amml.conf..227S No abstract at ADS Title: High-density winds: Wolf-Rayet stars - a progress report about quantitative spectral analyses. Authors: Hamann, Wolf-Rainer; Wessolowski, Ulf; Schwarz, Eberhart; Duennebeil, Gerhard; Schmutz, Werner Bibcode: 1990ASPC....7..259H Altcode: 1990phls.work..259H Based on recent progress in non-LTE model calculations for expanding atmospheres, the authors quantitatively analyze the spectra of Wolf-Rayet stars. The obtained stellar temperatures and luminosities are surprisingly low. The authors show that the light curve of the eclipsing binary V444 Cygni can be reproduced by a model with a "cool" WR star (T* = 40 kK). This solution is not unique, but demonstrates that there is no basic contradiction between the results from the present spectral analysis and the light curve. Hydrogen abundances in WN stars are determined from a careful line fit of the H/He blends. The authors find a clear dichotomy between the "cool" (≍35 kK) stars with detectable hydrogen, and the "hot" WN stars which are hydrogen-poor. Title: The Evidence that Wolf-Rayet Stars are in a Late Stage of Evolution Authors: Lamers, H. J. G. L. M.; Maeder, A.; Schmutz, W.; Cassinelli, J. P. Bibcode: 1990ASIC..316..349L Altcode: 1990amml.conf..349L No abstract at ADS Title: Atmospheric Models for Luminous Blue Variables Authors: Leitherer, Claus; Schmutz, Werner; Abbott, David C.; Hamann, Wolf-Rainer; Wessolowski, Ulf Bibcode: 1989ApJ...346..919L Altcode: The photospheres and stellar winds of luminous blue variables are studied theoretically. Non-LTE calculations of radiation transfer in spherically extended, expanding atmospheres are combined with a hydrodynamics code for radiation-driven winds. Models are calculated which are typical for luminous blue variables in minimum and maximum states. The recombination of iron group elements from double to singly ionized stages, which occurs when the effective temperature falls below 10,000 K, can explain why the mass-loss rates increase when luminous blue variables approach their maximum states; the singly charged ions provide a much larger number of strong lines which can intercept the radiation pressure. However, the mass-loss increase by itself cannot account for the drop of the effective temperature in a self-consistent way. The corresponding increase of the wind opacity causes only a comparativley small change in the radius of continuum formation. It is concluded that the observed variability of the photospheric radius must be induced from deeper, subphotospheric regions. Title: Spectral analysis of 30 Wolf-Rayet stars. Authors: Schmutz, W.; Hamann, W. -R.; Wessolowski, U. Bibcode: 1989A&A...210..236S Altcode: The helium spectra of 30 Galactic WR stars are analyzed, and the luminosities, radii, temperatures, and mass-loss rates are determined. The analyses are based on model calculations which account for non-LTE radiation transfer in spherically expanding atmospheres. A three-dimensional grid of models is established for a wide range of stellar radii, temperatures, and mass-loss rates. The variety of resulting spectra is actually two-dimensional, as different combinations of stellar radius and mass-loss rates may yield very similar helium spectra at a given stellar temperature. Thus, the WR spectra can be described by a two-dimensional classification scheme. Individual mass-loss rates between 10 exp -3.9 and 10 exp -5.3 are found. The luminosities of WNE subtypes scatter between 10 exp 5 and 10 exp 5.5 solar luminosities while those for the late subtypes are higher. The WC stars are less luminous. Title: Spectral analysis of WN stars in the LMC. Authors: Schmutz, W.; Conti, P. S. Bibcode: 1989ASSL..157..306S Altcode: No abstract at ADS Title: NLTE Analysis of R 84 Authors: Schmutz, W.; Leitherer, C.; Torres-Dodgen, A. V.; Vogel, M.; Conti, P. S.; Hamann, W. -R.; Wessolowski, U. Bibcode: 1989ASSL..157..289S Altcode: 1989IAUCo.113..289S; 1989plbv.coll..289S No abstract at ADS Title: Changes in the Atmospheric Structure of Lbv's during Eruptions Authors: Leitherer, Claus; Abbott, David C.; Schmutz, Werner Bibcode: 1989ASSL..157..109L Altcode: 1989IAUCo.113..109L; 1989plbv.coll..109L Self-consistent radiation-hydrodynamic calculations are presented which model observations of Hubble-Sandage variables or S Doradus stars going from their minimum to maximum states. Atmospheric models are employed which use a spherically extended, dynamical NLTE atmosphere with 27 levels of H and He. The ionization state of the atmosphere and the variation of the photospheric radius are studied. Title: Atmospheric Models for Lbv's at Minimum and Maximum States Authors: Leitherer, C.; Schmutz, W.; Abbott, D. C.; Torres-Dodgen, A. V.; Hamann, W. -R.; Wessolwski, U. Bibcode: 1989ASSL..157..285L Altcode: 1989IAUCo.113..285L; 1989plbv.coll..285L No abstract at ADS Title: NLTE calculations of hydrogen line profiles for SN1987A Authors: Schmutz, W. Bibcode: 1989HiA.....8..215S Altcode: No abstract at ADS Title: NLTE Analysis of the Luminous Blue Variable R71 Authors: Leitherer, C.; Schmutz, W.; Hubeny, I. Bibcode: 1988BAAS...20.1012L Altcode: No abstract at ADS Title: Synthetic helium spectra for Wolf-Rayet stars - A grid of models Authors: Wessolowski, U.; Schmutz, W.; Hamann, W. -R. Bibcode: 1988A&A...194..160W Altcode: Theoretical profiles of the He I lines for Wolf-Rayet stars are presented, covering a large domain of stellar temperatures and radii. The present results are thus augmenting the authors' grid of synthetic He II spectra published previously. Line profiles, equivalent widths and peak intensities are given for the most prominent He I lines at 10830 Å and 5876 Å. As expected, the lines of neutral helium depend sensitively on the stellar temperature. Hence they will provide the key information for the quantitative interpretation of WR spectra. Title: Spectral analysis of the Wolf-Rayet star HD 50896. Authors: Hamann, W. -R.; Schmutz, W.; Wessolowski, U. Bibcode: 1988A&A...194..190H Altcode: The helium spectrum of the Wolf-Rayet star HD 50896 is analyzed by means of detailed non-LTE radiation transfer calculations for spherically expanding atmospheres. Satisfactory agreement between theory and observation is achieved. A systematic fit procedure yields the stellar parameters as a function of the mass-loss rate adopted. Fits are performed for the three different values log(M/(M_sun;/yr)) = -0.4, -4.4 or -4.7. The resulting luminosities are log(L/L_sun;) = 5.3, 4.9 or 4.4, respectively, while the radius of the "stellar core" becomes 4.7, 2.6 or 1.5 R_sun;. Considerations concerning the distance of HD 50896 give some preference to the first of the three quoted sets of parameters. Title: Quantitative Spectroscopy of Wolf-Rayet Stars Authors: Schmutz, W. Bibcode: 1988LNP...305..133S Altcode: 1988adse.conf..133S; 1988IAUCo.108..133S No abstract at ADS Title: NLTE Analysis of the Wolf-Rayet Star HD193077 = WN5+ABS Authors: Schmutz, W.; Hamann, W. -R.; Wessolowski, U. Bibcode: 1988LNP...305..143S Altcode: 1988adse.conf..143S; 1988IAUCo.108..143S A model atmosphere code that accounts for the special physical conditions in Wolf-Rayet atmospheres is used to analyse the spectrum of the Wolf-Rayet star HD 193077 (WN5+abs). The stellar parameters are determined such that the profiles of the helium lines He I λλ4471, 5876, He II λ5412, and the absolute visual magnitude are reproduced. Title: Spectral Analysis of the Wolf-Rayet Star HD50896 Authors: Hamann, W. -R.; Schmutz, W.; Wessolowski, U. Bibcode: 1988LNP...305..145H Altcode: 1988adse.conf..145H; 1988IAUCo.108..145H The helium spectrum of the WN5 star HD 50896 (EZ Canis Majoris, WR6) is studied. The aim is to establish a technique which allows the determination of the parameters of a Wolf-Rayet star from a systematic analysis of its spectral lines. Title: Analysis of 30 Wolf-Rayet Stars Authors: Schmutz, W.; Hamann, W. -R.; Wessolowski, U. Bibcode: 1988LNP...305..141S Altcode: 1988IAUCo.108..141S; 1988adse.conf..141S Temperatures, mass-loss rates and luminosities of 30 galactic Wolf-Rayet stars (24 WN, 6 WC) are derived by fitting the observed equivalent widths of He I λ5876 and He II λ5412 and the absolute visual magnitude. A three-dimensional grid (T*-R*-M) of model calculations provides the theoretical values. Title: Computed He II spectra for Wolf-Rayet stars - A grid of models Authors: Hamann, W. -R.; Schmutz, W. Bibcode: 1987A&A...174..173H Altcode: A grid of synthetic He II spectra for Wolf-Rayet stars is presented, covering a large range in radius and temperature. The non-LTE radiation transfer in spherically expanding atmospheres is treated in the comoving frame, and the solution is obtained by "iteration with approximate lambda operators". Results are given for the continuum flux distribution and for the profiles of the most prominent lines (He II 1640 Å and 4686 Å). The lines show the strongest emission at stellar temperatures of about 35kK, but also depend sensitively on the stellar radius. Title: NLTE Analysis of the Wolf-Rayet Star HD 193077 (WN5 + abs) Authors: Schmutz, W.; Hamann, W. -R.; Wessolowski, U. Bibcode: 1987MitAG..70..336S Altcode: No abstract at ADS Title: Analysis of 30 Wolf-Rayet Stars Authors: Schmutz, W.; Hamann, W. -R.; Wessolowski, U. Bibcode: 1987MitAG..70..338S Altcode: No abstract at ADS Title: Upper Limits for the Effective Temperature of Wolf-Rayet Stars from the Presence of Hei Authors: Schmutz, W.; Hamann, W. R.; Wessolowski, U. Bibcode: 1987IAUS..122..461S Altcode: A recently developed non-LTE code for realistic semi-empirical models of Wolf-Rayet atmospheres is used to calculate synthetic helium lines. From the resulting line strengths it can be concluded that if He I lines are present, the effective temperatures of these stars have to be less than an upper limit. This limit depends on the stellar radius and is approximately 40kK for R* = 20 R_sun; to 60kK for R* = 5 R_sun;. Title: NLTE Analysis of the Wolf-Rayet Star HD 192 163 (WN 6) Authors: Wessolowski, U.; Hamann, W. -R.; Schmutz, W. Bibcode: 1987MitAG..70..337W Altcode: No abstract at ADS Title: Spectral Analysis of the Wolf-Rayet Star HD 50896 Authors: Hamann, W. -R.; Schmutz, W.; Wessolowski, U. Bibcode: 1987MitAG..70..335H Altcode: No abstract at ADS Title: The ultraviolet variability of the symbiotic star HBV 475. III. The periodicity of HBV 475. Authors: Nussbaumer, H.; Schmutz, W.; Vogel, M. Bibcode: 1986A&A...169..154N Altcode: The symbiotic star HBV 475 (= V1329 Cyg) shows periodic variations in its spectrum, both in flux and in the wavelength positions of the emission lines. New IUE observations, extending to the October 1985 flux maximum, allow an improved period and phase determination. The periodic variation of the line profiles are interpreted as being due to illumination effects from a hot star on a stellar wind around a cool star, the hot star moving on an elliptical orbit. This model is consistent with the line flux variations observed in this object. Title: Higher mass loss rates for Wolf-Rayet stars? Authors: Schmutz, W.; Hamann, W. -R. Bibcode: 1986A&A...166L..11S Altcode: Calculations with a recently developed non-LTE code for realistic semiempirical models of Wolf-Rayet atmospheres revealed that, for effective temperatures below approximately 60 kK, the dominant ion in the radio-emitting region is not He(2+), as usually assumed, but He(+). Hence, for those Wolf-Rayet stars having effective temperatures below the quoted threshold, previous interpretations of the radio observations are not adequate. The inferred mass loss rates must be enhanced by up to a factor of 2.7, to take into account the lower free-free emissivity of He(+). Assuming all Wolf-Rayet stars to be cooler than the critical temperature, the corrected mean mass loss rate of the essentially distance-limited sample of Wolf-Rayet stars published by Abbott et al. (1986) becomes 0.00004 solar masses/yr. Title: The nitrogen abundance in Wolf-Rayet WC stars. Authors: Nussbaumer, H.; Schmutz, W. Bibcode: 1986A&A...154..100N Altcode: In order to confirm the presence of nitrogen in WC stars, the IUE spectra of the WC 8 star HD 192103 have been studied in the region 1230-1250 A. The fluxes in the spectra of HD 192103 were extracted using two different procedures: the method described by Ramella et al. (1983); and the background correction method of Schmutz (1985). It is demonstrated that there is no convincing evidence of NV 2s 2S1/2-2p 2P(0)3/2 absorption at 1238.8 A in the spectrum of WC 192103. Title: The ultraviolet variability of the symbiotic star HBV 475. II. Study of line flux variations. Authors: Mueller, B. E. A.; Nussbaumer, H.; Schmutz, W. Bibcode: 1986A&A...154..313M Altcode: The symbiotic star HBV 475 (= V1329 Cyg) is one of the few symbiotics where periodic variations in the ultraviolet line fluxes have been observed. The authors collect the IUE observations between June 1979 and December 1984. Extending the work of Nussbaumer and Schmutz (1983), who presented a detailed study of this object, the authors establish the periodicity in the ultraviolet line and continuum fluxes and in velocity shifts. There can thus be no doubt about the binary nature of this object. The line flux variations result in a period of 975 days. Title: Synthetische Helium-Spektren für Wolf-Rayet-Sterne Authors: Wessolowski, U.; Hamann, W. -R.; Schmutz, W. Bibcode: 1986MitAG..67..325W Altcode: Eine ausführliche Version dieser Arbeit (Modellgitter unter Berücksichtigung des erweiterten He-Atoms) wird demnächst bei Astronomy and Astrophysics zur Veröffentlichung eingereicht. Title: Effective Temperatures of Wolf-Rayet Stars - A Progress Report Authors: Schmutz, W.; Hamann, W. -R.; Wessolowski, U. Bibcode: 1986MitAG..67..326S Altcode: No abstract at ADS Title: Observations of Galactic Single Wn Stars Authors: Schmutz, W. Bibcode: 1986iue..prop.2602S Altcode: No abstract at ADS Title: Estimation of the true background level of SWP HI-RES images. Authors: Schmutz, W. Bibcode: 1985IUEEN..23...94S Altcode: No abstract at ADS Title: The hydrogenic 2s-1s two-photon emission Authors: Nussbaumer, H.; Schmutz, W. Bibcode: 1984A&A...138..495N Altcode: The authors give an analytical expression for the probability of the hydrogenic two-photon decay. The expression allows a very accurate description of the two-photon continuum. For the total hydrogen 2s→1s two-photon transition probability a value of A2q = 8.2249 s-1 is found. Title: The nitrogen abundance in WC stars. Authors: Schmutz, W.; Morossi, C.; Ramella, M. Bibcode: 1984ESASP.218..325S Altcode: 1984iue..conf..325S Willis (1982) identifies tentatively an absorption at 1235 Å in the IUE spectrum of the WC star HD 192103 as blue shifted P Cygni absorption of N V λ1240. The presence of nitrogen in a WC star is of interest because this observation would disagree with the predictions of theoretical stellar evolution calculations. The authors reanalysed the IUE image of this Wolf-Rayet star. On the grounds of the reprocessed spectrum and of comparisons with the same wavelength region in other Wolf-Rayet spectra, the authors conclude that most probably nitrogen is not observed in the WC star HD 192103. Title: The Neighbourhood of the Wolf-Rayet Star Ez Cma Authors: Schmutz, W. Bibcode: 1984iue..prop.1932S Altcode: No abstract at ADS Title: A model atmosphere for Wolf-Rayet stars Authors: Schmutz, W. Bibcode: 1984PhDT.........2S Altcode: The observed characteristics of the Wolf-Rayet (WR) stars are surveyed; the astrophysical interpretations proposed to explain the broad lines and the two spectral groups in WR stars are reviewed; a semiempirical spherically symmetric He model atmosphere is constructed; and the results of preliminary model computations are presented in tables and graphs and discussed. The model treats the velocity and temperature laws as free parameters, applies the Sobolev approximation to simplify radiation transfer in the lines, and calculates the continuum radiation field and the level populations alternately until convergence of the level populations is achieved. The model is found to reproduce the line strengths and continua observed in WR stars, to give luminosities as much as twice those of previous models, and to predict a strong dependance of line strengths on atmospheric structure (a possible explanation for the wide scatter of observed line strengths among stars of one subgroup). Title: On the Hydrogen Abundance in Wolf-Rayet Stars Authors: Schmutz, W. Bibcode: 1984IAUS..105..269S Altcode: With a semiempirical NLTE-model in spherical geometry the author investigates the hydrogen abundance in Wolf-Rayet stars. He finds that the flux contribution of the H-Balmer to the He-Pickering lines lies between the usually applied approximate formulae for the optically thin and optically thick case. This result can be understood with the finding that there are no optically thin helium and hydrogen lines. The influence of the temperature structure on the relative intensity of the hydrogen-helium blends to the helium lines is vanishingly small, even for peculiar temperature laws. The conclusion is that Wolf-Rayet stars are hydrogen deficient objects. Title: Ein Modell für Atmosphären von Wolf-Rayet Sternen Title: Ein Modell für Atmosphären von Wolf-Rayet Sternen Authors: Schmutz, Werner K. Bibcode: 1984PhDT.......242S Altcode: No abstract at ADS Title: Ein Modell fuer Atmosphaeren von Wolf-Rayet Sternen Authors: Schmutz, Werner Bibcode: 1984emav.book.....S Altcode: No abstract at ADS Title: The ultraviolet variability of the symbiotic star HBV 475. Authors: Nussbaumer, H.; Schmutz, W. Bibcode: 1983A&A...126...59N Altcode: Evidence is presented for the binary nature of the symbiotic star HBV 475 ( = V 1329 Cyg), based on ultraviolet observations taken with the International Ultraviolet Explorer. The fluxes in the emission lines and in the continuum observed during 1978-1982 are related. It is found that the changes in the line and continuum fluxes observed in the far ultraviolet (1200-3200 A) are consistent with the 950 d period found from the visual luminosity variations. Periodicity and amplitudes found in the wavelength shifts are shown to indicate a size of the binary system of approximately 2 x 10 to the 14th cm. The emission lines are found to originate in a radiatively ionized gas with electron density in the range of 10 to the 6th to 10 to the 7th/cu cm, and electron temperature less than 15,000 K. In addition, an indication for a hot outer envelope around the whole system is observed. Title: IUE ultra-violet spectrophotometry of 15 galactic Wolf-rayet stars. Authors: Nussbaumer, H.; Schmutz, W.; Smith, L. J.; Willis, A. J. Bibcode: 1982A&AS...47..257N Altcode: Low-resolution IUE ultraviolet spectrophotometry is presented of 15 galactic WR stars, covering most subtypes in the WN and WC sequences. The data are presented both as spectral plots and as tabulations of the observed absolute flux distributions covering the wavelength range of 1150-3090 A. The characteristics of these UV WR spectra are discussed, the equivalent widths of the most prominent emission lines having been measured. It is shown that the WR stars adhere to the normal galactic interstellar extinction law. For each star, color excesses, E(B-V), are derived by nulling the observed 2200 A features and by comparing relative intensities of optically thin HeII recombination emission lines. Title: The effective temperatures of early Wolf-Rayet stars Authors: Schmutz, W. Bibcode: 1982IAUS...99...23S Altcode: Nussbaumer et al. (1981) adopted a temperature derived from a Zanstra analysis of the He II recombination lines to account for the WR stars that exhibit deviation from the blackbody shape. According to the Nussbaumer analysis, there should be a continuum jump at 2050 A. New IUE observations of the WN 5 star HD 50896, however, did not reveal any trace of such an absorption edge. This is seen as implying that the effective temperature of this WN 5 star and probably of all WR stars with a non-black-body energy distribution is not yet known accurately. A detailed analysis is therefore undertaken with a spherically symmetric atmosphere model. Though the model is not yet in its final shape, a first result is described wherein the location of HD 50896 in the HR-diagram is to the left of the ZAMS and the Zanstra analysis is indeed not valid for this star. Title: Ultraviolet energy distribution of Wolf-rayet stars. Authors: Schmutz, W.; Smith, L. J. Bibcode: 1980ESASP.157..249S Altcode: 1980iue..conf..249S; 1980IUE2n......249S Low resolution spectra of 15 Wolf-Rayet stars (10 WN and 5 WC stars) were analyzed to investigate their UV continuum distribution. The reddening observed for Wolf-Rayet stars is found to follow the general galactic interstellar extinction law. Color excesses for each star are deduced from the observed strength of the 2200A feature. The combined de-reddened UV-visible continua are compared with black body energy distributions to deduce color temperatures. Four stars are analyzed on the basis of Cassinelli and Hartmann's theory for extended emitting regions. Title: IUE observations of galactic Wolf-Rayet stars Authors: Nussbaumer, H.; Schmutz, W.; Smith, L. J.; Willis, A. J.; Wilson, R. Bibcode: 1979IUE1.symp..259N Altcode: The paper surveys the results obtained through study of a large set of ultraviolet spectra of single WR stars obtained with IUE. Spectral features are identified and the strengths of the observed emission lines compared as a function of each subclass. In addition, a correlation is found between terminal velocity and subclass in both WN and WC sequences, and for the WC, a correlation with terminal velocity and I.P. within an individual spectrum is found, indicating considerable stratification in the WC atmospheres. A preliminary analysis of the strengths of the carbon and nitrogen emission lines observed in the spectra of HD 156385 (WC7) and HD 192163 (WN6) is given. Significant differences are found between the C/N ratios of the two stars, demonstrating the chemical separation between the WN and WC sequences. Finally, it is concluded that the WN star is at an earlier stage of evolution than the WC star.