Author name code: judge ADS astronomy entries on 2022-09-14 author:"Judge, Philip G." ------------------------------------------------------------------------ Title: Thermal and Non-thermal Properties of Active Region Recurrent Coronal Jets Authors: Paraschiv, Alin R.; Donea, Alina C.; Judge, Philip G. Bibcode: 2022ApJ...935..172P Altcode: 2022arXiv220712612P We present observations of recurrent active region coronal jets, and derive their thermal and non-thermal properties, by studying the physical properties of the plasma simultaneously at the base footpoint and along the outflow of jets. The sample of analyzed solar jets were observed by SDO-AIA in extreme ultraviolet and by RHESSI in the X-ray domain. The main thermal plasma physical parameters, such as temperature, density, energy flux contributions, etc., are calculated using multiple inversion techniques to obtain the differential emission measure from extreme-ultraviolet filtergrams. The underlying models are assessed, and their limitations and applicability are scrutinized. Complementarily, we perform source reconstruction and spectral analysis of higher energy X-ray observations to further assess the thermal structure and identify non-thermal plasma emission properties. We discuss a peculiar penumbral magnetic reconnection site, which we previously identified as a "Coronal Geyser." Evidence supporting cool and hot thermal emission, as well as non-thermal emission, is presented for a subset of geyser jets. These active region jets are found to be energetically stronger than their polar counterparts, but we find their potential influence on heliospheric energetics and dynamics to be limited. We scrutinize whether the geyser does fit the non-thermal erupting microflare picture, finding that our observations at peak flaring times can only be explained by a combination of thermal and non-thermal emission models. This analysis of geysers provides new information and observational constraints applicable to theoretical modeling of solar jets. Title: A Spectroscopic Survey of Infrared 1-4 μm Spectra in Regions of Prominent Solar Coronal Emission Lines of Fe XIII, Si X, and Si IX Authors: Ali, Aatiya; Paraschiv, Alin Razvan; Reardon, Kevin; Judge, Philip Bibcode: 2022ApJ...932...22A Altcode: 2022arXiv220308636A The infrared solar spectrum contains a wealth of physical data about the Sun and is being explored using modern detectors and technology with new ground-based solar telescopes. One such instrument will be the ground-based Cryogenic Near-IR Spectro-Polarimeter of the Daniel K. Inouye Solar Telescope (DKIST), which will be capable of sensitive imaging of the faint infrared solar coronal spectra with full Stokes I, Q, U, and V polarization states. Highly ionized magnetic dipole emission lines have been observed in galaxies and the solar corona. Quantifying the accuracy of spectral inversion procedures requires a precise spectroscopic calibration of observations. A careful interpretation of the spectra around prominent magnetic dipole lines is essential for deriving physical parameters and particularly for quantifying the off-limb solar coronal observations from DKIST. In this work, we aim to provide an analysis of the spectral regions around the infrared coronal emission lines of Fe XIII 1074.68 nm, Fe XIII 1079.79 nm, Si X 1430.10 nm, and Si IX 3934.34 nm, aligning with the goal of identifying solar photospheric and telluric lines that will help facilitate production of reliable inversions and data products from four sets of solar coronal observations. The outputs can be integrated in processing pipelines to produce level 2 science-ready data. Title: The mercurial Sun at the heart of our solar system Authors: Judge, Philip Gordon Bibcode: 2022arXiv220503498J Altcode: As the powerhouse of our solar system, the Sun's electromagnetic planetary influences appear contradictory. On the one hand, the Sun for aeons emitted radiation which was "just right" for life to evolve in our terrestrial Goldilocks zone, even for such complex organisms as ourselves. On the other, in the dawn of Earth's existence the Sun was far dimmer than today, and yet evidence for early liquid water is written into geology. Now in middle age, the Sun should be a benign object of little interest to society or even astronomers. However, for physical reasons yet to be fully understood, it contains a magnetic machine with a slightly arrhythmic 11 year magnetic heartbeat. Although these variations require merely 0.1% of the solar luminosity, this power floods the solar system with rapidly changing fluxes of photons and particles at energies far above the 0.5eV thermal energy characteristic of the photosphere. Ejected solar plasma carries magnetic fields into space with consequences for planets, the Earth being vulnerable to geomagnetic storms. This chapter discusses some physical reasons why the Sun suffers from such ailments, and examine consequences through time across the solar system. A Leitmotiv of the discussion is that any rotating and convecting star must inevitably generate magnetic "activity" for which the Sun represents the example par excellence. Title: Efficient and Automated Inversions of Magnetically Sensitive Forbidden Coronal Lines: CLEDB - The Coronal Line Emission DataBase Magnetic Field Inversion Algorithm Authors: Paraschiv, Alin Razvan; Judge, Philip Gordon Bibcode: 2022SoPh..297...63P Altcode: 2022arXiv220414111P We present CLEDB, a "single-point inversion" algorithm for inferring parameters using I , Q , U , and V Stokes parameters of forbidden magnetic dipole lines formed in the solar corona. We select lines of interest and construct databases of Stokes parameters for combinations of plasma thermal and magnetic configurations. The size and complexity of such databases are drastically reduced by taking advantage of symmetries. Using wavelength-integrated line profiles, each of which might be decomposed beforehand into several line-of-sight components, we search for nearest matches to observed Stokes parameters computed for the elongation corresponding to the observed region. The method is intended to be applied to two or more lines observed simultaneously. The solutions initially yield magnetic orientation, thermal properties, and the spatial position of the emitting plasma in three dimensions. Multiple possible solutions for each observation are returned, including irreducible degeneracies, where usually sets of two solutions are compatible with the two input I , Q , U , and V measurements. In solving for the scattering geometry, this method avoids an additional degeneracy pointed out by Dima and Schad (Astrophys. J.889, 109, 2020). The magnetic field strength is separately derived from the simple ratio of observed to database Stokes V data, after the thermal properties and scattering geometry solutions have been determined. Title: Study the tortoise, not just the hare Authors: Judge, P. Bibcode: 2022fysr.confE..50J Altcode: Darwin encountered enormous Galapagos tortoises in 1835 around the time that Schwabe was collecting sunspot numbers. The creatures were slow and easy to study. Of course, fauna from the Galapagos played a central role in our understanding of evolution of life; genetic records imprinted in modern animals have since given us pages in the book of life history. Skumanich's 1972 work represents the first 3 pages in the book of stellar magnetic evolution, studying (like Darwin) only what was observable at a given time. The Sun and stars continue to be studied by politically palatable 1-10 year long missions, measuring short duration phenomena -- analogous to the peculiar springtime "boxing" of the March Hare. Stellar activity measurements over multiple decades (sampling sun-like cycling) are now a part of history, just as their need from space weather, dynamo theory, exoplanet habitability seems greater than ever. The communities must support tortoise-like measurements of stellar chromospheric signatures, extending the record begun in 1965, and used by Andy in 1972. A "palatable path" might be through development of automated observatories at under-privileged colleges, I present some ideas along these lines. Title: How to Measure the Magnetic Origins of Coronal Dynamics Authors: Gilbert, Holly; Judge, Philip Bibcode: 2021AGUFMSH12C..03G Altcode: To identify the origins of coronal dynamics, we have examined how we might measure magnetic free energy and topology and their evolution above the solar surface. Given the challenges associated with extrapolations based upon magnetic field measurements in the photosphere, we identify a region in the near UV part of the spectrum as optimal for studying the development of magnetic free energy over active regions. We demonstrate that the challenges are best met through a combination of near UV lines of bright Mg II, and lines of Fe II and Fe I mostly within the 4s-4p transition array. The lines form across the entire chromosphere and into the lower transition region. Based upon the recently-reported successful suborbital space measurements of magnetic fields with the CLASP2 instrument, we argue that a modest space-borne telescope will be able to make significant advances in the attempts to predict solar eruptions. Title: CLEDB - An Algorithm for Inverting Vector Magnetic Fields in The Solar Corona Authors: Paraschiv, Alin; Judge, Philip Bibcode: 2021AGUFMSH42B..06P Altcode: We present an algorithm capable of inverting coronal vector magnetic field information from observations of polarized light. The CLEDB algorithm implements two branches that can process full Stokes IQUV spectro-polarimetric observations of one or two coronal emission lines.The 1-line branch uses analytical approximations to derive line of sight integrated magnetic field products. When posing an inversion problem, the second branch allows for more degrees of freedom enabling us to break intrinsic degeneracies. Thus, by utilizing 2-line Stokes observations, we recover the 3D magnetic fields and volumetric locations of emitting structures for single-point voxels. In practice, forward calculation in the order of 107-109 atomic plasma, magnetic, and geometric configurations are needed in order to satisfy solution resolution criteria.Forward modelling this many solutions in an iterative fashion is dreadfully time consuming, rendering such approach as unfeasible. We bypassed the limitation by building databases, that store vast sets of synthetic Stokes IQUV signals, via forward modelling of parameter combinations. Using a 2 fitting approach has proved to be significantly more robust in matching such databases with Stokes IQUV observations.Additionally, the database theoretical calculations gain intrinsic access to otherwise non-observable input parameters, e.g. atomic alignment, that can be used to break inherent degeneracies encountered when attempting analytical inversions like in the 1-line case. The dimensionality of the problem at hand can be further reduced by 1-2 orders of magnitude by using native symmetries when building and querying databases. The goal of robustly resolving vector coronal magnetometry has been hard to achieve. The need for inverting magnetic fields from solar spectro-polarimetric observations is crucial, as the next generation of coronal capable instruments like DKIST Cryo-NIRSP, DL-NIRSP, and UCOMP will become operational. Benchmarks of the CLEDB algorithm tested against synthetic data are explored, while we wait for the first ever full Stokes spectro-polarimetric observations to become available. Title: From 1973 to the 2020s, from SKYLAB to 3D vector magnetic fields in prominences Authors: Lacatus, Daniela; Judge, Philip; Gilbert, Holly; Paraschiv, Alin; Berger, Thomas Bibcode: 2021AGUFMSH42B..05L Altcode: Routine measurement of the vector magnetic fields threading prominences would mark a significant advance in our ability to determine the dynamics of the Sun's corona. Gilbert et al. (AGU abstract #849653) have identified the near-UV (250-281 nm) as a prime region for measurements of magnetic fields within the chromosphere and lower transition region. Here, we perform an in depth analysis of the near UV spectra of all prominences observed by the SKYLAB SO82B instrument during 1973, for the first time. Using over 100 spectral lines we process the photographic data from scratch, and solve for plasma properties of several prominences. Given the known complexity of the thermal and dynamical conditions within prominence plasma, we develop a model to find mean electron temperatures, densities and mass columns which capture each spectrums essential characteristics. Prominence plasmas are optically thick in the cores of many spectral lines of Fe II and Mg II present in this spectral region. The different optical depths probe different surfaces along the line-of-sight, so that near-UV spectro-polarimetry will uniquely determine vector magnetic fields within the 3D volume of prominences. Therefore, we show that this technique offers the best future method for answering critical problems related to coronal dynamics, not only above active regions as shown by Gilbert et al., but also in prominence plasmas. Title: Atomic Structure Calculations of Landé g Factors of Astrophysical Interest with Direct Applications for Solar Coronal Magnetometry Authors: Schiffmann, Sacha; Brage, Tomas; Judge, Philip Gordon; Paraschiv, Alin Razvan; Wang, Kai Bibcode: 2021ApJ...923..186S Altcode: We perform a detailed theoretical study of the atomic structure of ions with ns 2 np m ground configurations and focus on departures from LS coupling, which directly affect the Landé g factors of magnetic dipole lines between levels of the ground terms. Particular emphasis is given to astrophysically abundant ions formed in the solar corona (those with n = 2,3) with M1 transitions spanning a broad range of wavelengths. Accurate Landé g factors are needed to diagnose coronal magnetic fields using measurements from new instruments operating at visible and infrared wavelengths, such as the Daniel K. Inouye Solar Telescope. We emphasize an explanation of the dynamics of atomic structure effects for nonspecialists. Title: The enduring mystery of the solar corona Authors: Judge, Philip G. Bibcode: 2021PhyW...34...38J Altcode: Physicists have long known that the Sun's magnetic fields make its corona much hotter than the surface of the star itself. But how - and why - those fields transport and deposit their energy is still a mystery, as Philip G Judge explains. Title: Erratum: Spectral Lines for Polarization Measurements of the Coronal Magnetic Field. II. Consistent Treatment of the Stokes Vector for Magnetic-dipole Transitions (1999, ApJ, 522, 524) Authors: Casini, R.; Judge, P. G. Bibcode: 2021ApJ...917...50C Altcode: No abstract at ADS Title: Measuring the Magnetic Origins of Solar Flares, Coronal Mass Ejections, and Space Weather Authors: Judge, Philip; Rempel, Matthias; Ezzeddine, Rana; Kleint, Lucia; Egeland, Ricky; Berdyugina, Svetlana V.; Berger, Thomas; Bryans, Paul; Burkepile, Joan; Centeno, Rebecca; de Toma, Giuliana; Dikpati, Mausumi; Fan, Yuhong; Gilbert, Holly; Lacatus, Daniela A. Bibcode: 2021ApJ...917...27J Altcode: 2021arXiv210607786J We take a broad look at the problem of identifying the magnetic solar causes of space weather. With the lackluster performance of extrapolations based upon magnetic field measurements in the photosphere, we identify a region in the near-UV (NUV) part of the spectrum as optimal for studying the development of magnetic free energy over active regions. Using data from SORCE, the Hubble Space Telescope, and SKYLAB, along with 1D computations of the NUV spectrum and numerical experiments based on the MURaM radiation-magnetohydrodynamic and HanleRT radiative transfer codes, we address multiple challenges. These challenges are best met through a combination of NUV lines of bright Mg II, and lines of Fe II and Fe I (mostly within the 4s-4p transition array) which form in the chromosphere up to 2 × 104 K. Both Hanle and Zeeman effects can in principle be used to derive vector magnetic fields. However, for any given spectral line the τ = 1 surfaces are generally geometrically corrugated owing to fine structure such as fibrils and spicules. By using multiple spectral lines spanning different optical depths, magnetic fields across nearly horizontal surfaces can be inferred in regions of low plasma β, from which free energies, magnetic topology, and other quantities can be derived. Based upon the recently reported successful sub-orbital space measurements of magnetic fields with the CLASP2 instrument, we argue that a modest space-borne telescope will be able to make significant advances in the attempts to predict solar eruptions. Difficulties associated with blended lines are shown to be minor in an Appendix. Title: Magnetic Connections across the Chromosphere-Corona Transition Region Authors: Judge, Philip Bibcode: 2021ApJ...914...70J Altcode: 2021arXiv210407753J The plasma contributing to emission from the Sun between the cool chromosphere (≤104 K) and hot corona (≥106 K) has been subjected to many different interpretations. Here we look at the magnetic structure of this transition region (TR) plasma, based upon the implications of CLASP2 data of an active region recently published by Ishikawa et al., and earlier Interface Region Imaging Spectrograph (IRIS) and Solar Dynamics Observatory (SDO) data of quiet regions. Ishikawa et al. found that large areas of sunspot plages are magnetically unipolar as measured in the cores of Mg II resonance lines, formed in the lower TR under low plasma-β conditions. Here we show that IRIS images in the line cores have fibrils that are well aligned with the overlying coronal loop segments seen in the 171 Å channel of SDO. When the TR emission in active regions arises from plasma magnetically and thermally connected to the corona, then the line cores can provide the first credible magnetic boundary conditions for force-free calculations extended to the corona. We also re-examine IRIS images of dynamic TR cool loops previously reported as a major contributor to TR emission from the quiet Sun. Dynamic cool loops contribute only a small fraction of the total TR emission from the quiet Sun. Title: On Single-point Inversions of Magnetic Dipole Lines in the Corona Authors: Judge, Philip; Casini, Roberto; Paraschiv, Alin Razvan Bibcode: 2021ApJ...912...18J Altcode: 2021arXiv210303824J Prompted by a recent paper by Dima and Schad, we reconsider the problem of inferring magnetic properties of the corona using polarimetric observations of magnetic dipole (M1) lines. Dima and Schad point to a potential source of degeneracy in a formalism developed by Plowman, which under some circumstances can lead to the solution being under-determined. Here we clarify the nature of the problem. Its resolution lies in solving for the scattering geometry using the elongation of the observed region of the corona. We discuss some conceptual problems that arise when casting the problem for inversion in the observer's reference frame, and satisfactorily resolve difficulties identified by Plowman, Dima, and Schad. Title: Critical Science Plan for the Daniel K. Inouye Solar Telescope (DKIST) Authors: Rast, Mark P.; Bello González, Nazaret; Bellot Rubio, Luis; Cao, Wenda; Cauzzi, Gianna; Deluca, Edward; de Pontieu, Bart; Fletcher, Lyndsay; Gibson, Sarah E.; Judge, Philip G.; Katsukawa, Yukio; Kazachenko, Maria D.; Khomenko, Elena; Landi, Enrico; Martínez Pillet, Valentín; Petrie, Gordon J. D.; Qiu, Jiong; Rachmeler, Laurel A.; Rempel, Matthias; Schmidt, Wolfgang; Scullion, Eamon; Sun, Xudong; Welsch, Brian T.; Andretta, Vincenzo; Antolin, Patrick; Ayres, Thomas R.; Balasubramaniam, K. S.; Ballai, Istvan; Berger, Thomas E.; Bradshaw, Stephen J.; Campbell, Ryan J.; Carlsson, Mats; Casini, Roberto; Centeno, Rebecca; Cranmer, Steven R.; Criscuoli, Serena; Deforest, Craig; Deng, Yuanyong; Erdélyi, Robertus; Fedun, Viktor; Fischer, Catherine E.; González Manrique, Sergio J.; Hahn, Michael; Harra, Louise; Henriques, Vasco M. J.; Hurlburt, Neal E.; Jaeggli, Sarah; Jafarzadeh, Shahin; Jain, Rekha; Jefferies, Stuart M.; Keys, Peter H.; Kowalski, Adam F.; Kuckein, Christoph; Kuhn, Jeffrey R.; Kuridze, David; Liu, Jiajia; Liu, Wei; Longcope, Dana; Mathioudakis, Mihalis; McAteer, R. T. James; McIntosh, Scott W.; McKenzie, David E.; Miralles, Mari Paz; Morton, Richard J.; Muglach, Karin; Nelson, Chris J.; Panesar, Navdeep K.; Parenti, Susanna; Parnell, Clare E.; Poduval, Bala; Reardon, Kevin P.; Reep, Jeffrey W.; Schad, Thomas A.; Schmit, Donald; Sharma, Rahul; Socas-Navarro, Hector; Srivastava, Abhishek K.; Sterling, Alphonse C.; Suematsu, Yoshinori; Tarr, Lucas A.; Tiwari, Sanjiv; Tritschler, Alexandra; Verth, Gary; Vourlidas, Angelos; Wang, Haimin; Wang, Yi-Ming; NSO and DKIST Project; DKIST Instrument Scientists; DKIST Science Working Group; DKIST Critical Science Plan Community Bibcode: 2021SoPh..296...70R Altcode: 2020arXiv200808203R The National Science Foundation's Daniel K. Inouye Solar Telescope (DKIST) will revolutionize our ability to measure, understand, and model the basic physical processes that control the structure and dynamics of the Sun and its atmosphere. The first-light DKIST images, released publicly on 29 January 2020, only hint at the extraordinary capabilities that will accompany full commissioning of the five facility instruments. With this Critical Science Plan (CSP) we attempt to anticipate some of what those capabilities will enable, providing a snapshot of some of the scientific pursuits that the DKIST hopes to engage as start-of-operations nears. The work builds on the combined contributions of the DKIST Science Working Group (SWG) and CSP Community members, who generously shared their experiences, plans, knowledge, and dreams. Discussion is primarily focused on those issues to which DKIST will uniquely contribute. Title: Spectroscopic Inversions & Calibrations for DKIST Coronal Observations Authors: Ali, A.; Paraschiv, A.; Reardon, K.; Judge, P. G. Bibcode: 2020AGUFMSH0280014A Altcode: The Cryo-NIRSP's (Cryogenic Near-IR Spectro-Polarimeter) is one of the DKIST instruments capable of sensitive imaging of faint infrared coronal solar spectra, and its primary goal is to measure the full polarization state (Stokes I, Q, U and V) of spectral lines originating on the Sun at different wavelengths. Producing data products from off-limb solar coronal observations from the DKIST telescope is essential when trying to study its future observations. Quantifying the accuracy of spectral inversion procedures based on its spectral comparisons to absorption and telluric calibrated spectra will give insight to interpreting valid DKIST observations and its ultimate findings. Using simulated contaminated data of both pure and noisy data sets has allowed us to compare the wavelength shifts and broadening properties to help pinpoint where contamination would affect the data set as a whole, and by how much. In doing so, we developed code that will eventually be integrated in the DKIST Level-2 pipeline. Working to compare these findings to absorption and telluric readings will further help minimize the uncertainties read in through observations, and give direction on how to reduce the original coronal data in hopes to refine it. Understanding the origins and magnitude of the contamination would therefore help refine the original coronal data and make it compatible for data processing, and would assist the automation of processing the data observed by the DKIST telescope. Title: Spectropolarimetric Insight into Plasma Sheet Dynamics of a Solar Flare Authors: French, R.; Judge, P. G.; Matthews, S.; van Driel-Gesztelyi, L.; Long, D. Bibcode: 2020AGUFMSH045..03F Altcode: Magnetic reconnection is thought to lie at the heart of energy release in solar flares, but the process is not yet fully understood. We examine spectropolarimetric data from the CoMP coronagraph, acquired a few hours into the evolution of the September 10th 2017 X8.2-class flare. We find a striking and spatially coherent low polarisation structure, aligned with the hot plasma sheet observed in EUV. By elimination, we find the significant depolarisation to be a result of small-scale sub-pixel magnetic structure along the plasma sheet, consistent with theory of reconnection instabilities. This interpretation of ongoing reconnection is supported by further Hinode/EIS observations and AIA DEMs, from well beyond the impulsive phase of the flare. The plasma sheet remains visible in CoMP linear polarisation over a day into the flare's evolution, several hours after its last appearance in EUV. We conclude that polarisation measurements with new coronagraphs, such the DKIST CRYO-NIRSP instrument, will further enhance our understanding of magnetic reconnection during eruptive flares. Title: Automated Single Point Inversions of Infrared Forbidden Lines for DKIST Coronal Observations Authors: Paraschiv, A.; Judge, P. G.; Ali, A. Bibcode: 2020AGUFMSH0280013P Altcode: We present preliminary results on an inversion scheme that can be applied to polarimetric measurements of forbidden lines formed in the solar corona.

We aim to find optimal fits to synthetic CLE data, delivering information on the vector magnetic field, thermal properties and line of sight position from a single point in the corona. We calculate the azimuthal angle from the linear polarization and estimate the line-of-sight magnetic fields via the magnetograph formulation. Our method complements these calculations to achieve vector magnetic fields. We create a database of emergent Stokes profiles from a Monte Carlo exploration of the parameter space. In building the database set, we first reduce the line formation problem to an irreducible form, factoring out linear parameters such as the magnetic field strength, and using native symmetries in the line formation problem to reduce the dimensionality of the needed calculations. We "precondition" the observed data with simple linear transformations and a rotation of the Stokes profiles around the line-of-sight axis through Sun center, which affects only the linearly polarized components. We show that calculations confined to the ecliptic plane are sufficient to explore the full 3D space. After the best-fit profiles are found, the necessary transformations are applied in reverse to the matching geometric, magnetic and thermal parameters to estimate them in 3D space. We then highlight the natural degeneracies in the analysis and examine their accuracy and sensitivity to noise. Title: Inevitable consequences of ion-neutral damping of intermediate MHD waves in Sun-like stars Authors: Judge, Philip G. Bibcode: 2020MNRAS.498.2018J Altcode: 2020MNRAS.tmp.2062J; 2020arXiv200803607J In the context of the solar atmosphere, we re-examine the role of neutral and ionized species in dissipating the ordered energy of intermediate-mode MHD waves into heat. We solve conservation equations for the hydrodynamics and for hydrogen and helium ionization stages, along closed tubes of magnetic field. First, we examine the evolution of coronal plasma under conditions where coronal heating has abruptly ceased. We find that cool (<105K) structures are formed lasting for several hours. MHD waves of modest amplitude can heat the plasma through ion-neutral collisions with sufficient energy rates to support the plasma against gravity. Then we examine a calculation starting from a cooler atmosphere. The calculation shows that warm (>104) K long (> several Mm) tubes of plasma arise by the same mechanism. We speculate on the relevance of these solutions to observe properties of the Sun and similar stars whose atmospheres are permeated with emerging magnetic fields and stirred by convection. Perhaps this elementary process might help to explain the presence of 'cool loops' in the solar transition region and the production of broad components of transition region lines. The production of ionized hydrogen from such a simple and perhaps inevitable mechanism may be an important step towards finding the more complex mechanisms needed to generate coronae with temperatures in excess of 106K, independent of a star's metallicity. Title: Dynamics of Late-stage Reconnection in the 2017 September 10 Solar Flare Authors: French, Ryan J.; Matthews, Sarah A.; van Driel-Gesztelyi, Lidia; Long, David M.; Judge, Philip G. Bibcode: 2020ApJ...900..192F Altcode: 2020arXiv200713377F In this multi-instrument paper, we search for evidence of sustained magnetic reconnection far beyond the impulsive phase of the X8.2-class solar flare on 2017 September 10. Using Hinode/EIS, CoMP, SDO/AIA, K-Cor, Hinode/XRT, RHESSI, and IRIS, we study the late-stage evolution of the flare dynamics and topology, comparing signatures of reconnection with those expected from the standard solar flare model. Examining previously unpublished EIS data, we present the evolution of nonthermal velocity and temperature within the famous plasma sheet structure, for the first four hours of the flare's duration. On even longer timescales, we use differential emission measures and polarization data to study the longevity of the flare's plasma sheet and cusp structure, discovering that the plasma sheet is still visible in observations of CoMP linear polarization on 2017 September 11, long after its last appearance in EUV. We deduce that magnetic reconnection of some form is still ongoing at this time—27 hr after flare onset. Title: New Light on an Old Problem of the Cores of Solar Resonance Lines Authors: Judge, Philip G.; Kleint, Lucia; Leenaarts, Jorrit; Sukhorukov, Andrii V.; Vial, Jean-Claude Bibcode: 2020ApJ...901...32J Altcode: 2020arXiv200801250J We reexamine a 50+ yr old problem of deep central reversals predicted for strong solar spectral lines, in contrast to the smaller reversals seen in observations. We examine data and calculations for the resonance lines of H I, Mg II, and Ca II, the self-reversed cores of which form in the upper chromosphere. Based on 3D simulations, as well as data for the Mg II lines from the Interface Region Imaging Spectrograph (IRIS), we argue that the resolution lies not in velocity fields on scales in either of the micro- or macroturbulent limits. Macroturbulence is ruled out using observations of optically thin lines formed in the upper chromosphere, and by showing that it would need to have unreasonably special properties to account for critical observations of the Mg II resonance lines from the IRIS mission. The power in "turbulence" in the upper chromosphere may therefore be substantially lower than earlier analyses have inferred. Instead, in 3D calculations horizontal radiative transfer produces smoother source functions, smoothing out intensity gradients in wavelength and in space. These effects increase in stronger lines. Our work will have consequences for understanding the onset of the transition region, for understanding the energy in motions available for heating the corona, and for the interpretation of polarization data in terms of the Hanle effect applied to resonance line profiles. Title: Automated Single Point Inversions of Infrared Forbidden Lines for DKIST Coronal Observations Authors: Paraschiv, A.; Judge, P. Bibcode: 2020SPD....5120302P Altcode: We present preliminary results on an inversion scheme that can be applied to polarimetric measurements of forbidden lines formed in the solar corona. We aim to find optimal fits to synthetic CLE data, delivering information on the vector magnetic field, thermal properties and line of sight position from a single point in the corona. The azimuthal angle is derived from the linear polarization and the line-of-sight magnetic fields are derived via the magnetograph formulation. Our method complements these calculations to achieve full vector magnetic fields. We create a database of emergent Stokes profiles from a Monte Carlo exploration of the parameter space. In building the database set, we first reduce the line formation problem to an irreducible form, factoring out linear parameters such as the magnetic field strength, and using native symmetries in the line formation problem to reduce the dimensionality of the needed calculations. We "precondition" the observed data with simple linear transformations and a rotation of the Stokes profiles around the line-of-sight axis through Sun center, which affects only the linearly polarized components. We show that calculations confined to the ecliptic plane are sufficient to explore the full 3D space. After the best-fit profiles are found, the necessary transformations are applied in reverse to the matching geometric, magnetic and thermal parameters to estimate them in 3D space. We then highlight the natural degeneracies in the analysis and examine their accuracy and sensitivity to noise. Title: Spectropolarimetric Insight into Plasma Sheet Dynamics of a Solar Flare Authors: French, R.; Judge, P.; Matthews, S.; van Driel-Gesztelyi, L.; Long, D. Bibcode: 2020SPD....5121102F Altcode: Magnetic reconnection is thought to lie at the heart of energy release in solar flares, but the process is not yet fully understood. We examine spectropolarimetric data from the CoMP coronagraph, acquired a few hours into the evolution of the September 10th 2017 X8.2-class flare. We find a striking and spatially coherent low polarisation structure, aligned with the hot plasma sheet observed in EUV. By elimination, we find the significant depolarisation to be a result of small-scale sub-pixel magnetic structure along the plasma sheet, consistent with theory of reconnection instabilities. This interpretation of ongoing reconnection is supported by further Hinode/EIS observations and AIA DEMs, from well beyond the impulsive phase of the flare. The plasma sheet remains visible in CoMP linear polarisation over a day into the flare's evolution, several hours after its last appearance in EUV. We conclude that polarisation measurements with new coronagraphs, such the DKIST CRYO-NIRSP instrument, will further enhance our understanding of magnetic reconnection during eruptive flares. Title: A New Facility for Airborne Solar Astronomy: NASA's WB-57 at the 2017 Total Solar Eclipse Authors: Caspi, Amir; Seaton, Daniel B.; Tsang, Constantine C. C.; DeForest, Craig E.; Bryans, Paul; DeLuca, Edward E.; Tomczyk, Steven; Burkepile, Joan T.; Casey, Thomas "Tony"; Collier, John; Darrow, Donald "DD"; Del Rosso, Dominic; Durda, Daniel D.; Gallagher, Peter T.; Golub, Leon; Jacyna, Matthew; Johnson, David "DJ"; Judge, Philip G.; Klemm, Cary "Diddle"; Laurent, Glenn T.; Lewis, Johanna; Mallini, Charles J.; Parent, Thomas "Duster"; Propp, Timothy; Steffl, Andrew J.; Warner, Jeff; West, Matthew J.; Wiseman, John; Yates, Mallory; Zhukov, Andrei N.; NASA WB-57 2017 Eclipse Observing Team Bibcode: 2020ApJ...895..131C Altcode: 2020arXiv200409658C NASA's WB-57 High Altitude Research Program provides a deployable, mobile, and stratospheric platform for scientific research. Airborne platforms are of particular value for making coronal observations during total solar eclipses because of their ability both to follow the Moon's shadow and to get above most of the atmospheric air mass that can interfere with astronomical observations. We used the 2017 August 21 eclipse as a pathfinding mission for high-altitude airborne solar astronomy, using the existing high-speed visible-light and near/midwave infrared imaging suite mounted in the WB-57 nose cone. In this paper, we describe the aircraft, the instrument, and the 2017 mission; operations and data acquisition; and preliminary analysis of data quality from the existing instrument suite. We describe benefits and technical limitations of this platform for solar and other astronomical observations. We present a preliminary analysis of the visible-light data quality and discuss the limiting factors that must be overcome with future instrumentation. We conclude with a discussion of lessons learned from this pathfinding mission and prospects for future research at upcoming eclipses, as well as an evaluation of the capabilities of the WB-57 platform for future solar astronomy and general astronomical observation. Title: The Sun: A Very Short Introduction Authors: Judge, Philip Gordon Bibcode: 2020svsi.book.....J Altcode: The Sun, as our nearest star, is of enormous importance for life on Earth - providing the warm radiation and light which allowed complex life to evolve. The Sun plays a key role in influencing our climate, whilst solar storms and high-energy events can threaten our communication infrastructure and satellites.

This Very Short Introduction explores what we know about the Sun, its physics, its structure, origins, and future evolution. Philip Judge explains some of the remaining puzzles about the Sun that still confound us, using elementary physics, and mathematical concepts. Why does the Sun form spots? Why does it flare? As he shows, these and other nagging difficulties relate to the Sun's continually variable magnetism, which converts an otherwise dull star into a machine for flooding interplanetary space with variable radiation, high-energy particles and magnetic ejections. Throughout, Judge highlights the many reasons that the Sun is important, and why scientists engage in solar research. Title: Sun-like Stars Shed Light on Solar Climate Forcing Authors: Judge, P. G.; Egeland, R.; Henry, G. W. Bibcode: 2020ApJ...891...96J Altcode: 2020arXiv200204633J Recently published precise stellar photometry of 72 Sun-like stars obtained at the Fairborn Observatory between 1993 and 2017 is used to set limits on the solar forcing of Earth's atmosphere of ±4.5 W m-2 since 1750. This compares with the +2.2 ± 1.1 W m-2 IPCC estimate for anthropogenic forcing. Three critical assumptions are made. In decreasing order of importance they are: (a) most of the brightness variations occur within the average time series length of ≈17 yr; (b) the Sun seen from the ecliptic behaves as an ensemble of middle-aged solar-like stars; and (c) narrowband photometry in the Strömgren b and y bands are linearly proportional to the total solar irradiance. Assumption (a) can best be relaxed and tested by obtaining more photometric data of Sun-like stars, especially those already observed. Eight stars with near-solar parameters have been observed from 1999, and two since 1993. Our work reveals the importance of continuing and expanding ground-based photometry, to complement expensive solar irradiance measurements from space. Title: Some thoughts on emission-line spectroscopy Authors: Judge, Philip G. Bibcode: 2020MNRAS.491..576J Altcode: 2019MNRAS.tmp.2640J The interpretation of emission lines formed in large astrophysical plasmas such as the solar atmosphere faces many challenges. Relatively simple line-ratio estimates of physical parameters, while appealing, are heavily laden with assumptions. In practical cases, some critical assumptions are neither defensible from first principles, nor testable by experiment. Free parameters and functional forms must be defined, whose numbers of degrees of freedom exceed the number of independent data points. These issues are illustrated in the particular case of using lines of Si IV and O IV formed in the solar transition region, observed for decades, most recently using the IRIS mission. The problems highlighted are in addition to well-known problems of mathematical ill-posedness. Title: Spectropolarimetric Insight into Plasma Sheet Dynamics of a Solar Flare Authors: French, Ryan J.; Judge, Philip G.; Matthews, Sarah A.; van Driel-Gesztelyi, Lidia Bibcode: 2019ApJ...887L..34F Altcode: 2019arXiv191112666F We examine spectropolarimetric data from the Coronal Multi-channel Polarimeter (CoMP) instrument, acquired during the evolution of the 2017 September 10 X8.2 solar flare on the western solar limb. CoMP captured linearly polarized light from two emission lines of Fe XIII at 1074.7 and 1079.8 nm, from 1.03 to 1.5 solar radii. We focus here on the hot plasma sheet lying above the bright flare loops and beneath the ejected coronal mass ejection. The polarization has a striking and coherent spatial structure, with unexpectedly small polarization aligned with the plasma sheet. By elimination, we find that small-scale magnetic field structure is needed to cause such significant depolarization, and suggest that plasmoid formation during reconnection (associated with the tearing-mode instability) creates magnetic structure on scales below instrument resolution of 6 Mm. We conclude that polarization measurements with new coronagraphs, such as the upcoming Daniel K. Inouye Solar Telescope, will further enhance our understanding of magnetic reconnection and development of turbulence in the solar corona. Title: Coronal Solar Magnetism Observatory Science Objectives Authors: Gibson, S. E.; Tomczyk, S.; Burkepile, J.; Casini, R.; DeLuca, E.; de Toma, G.; de Wijn, A.; Fan, Y.; Golub, L.; Judge, P. G.; Landi, E.; McIntosh, S. W.; Reeves, K.; Seaton, D. B.; Zhang, J. Bibcode: 2019AGUFMSH11C3395G Altcode: Space-weather forecast capability is held back by our current lack of basic scientific understanding of CME magnetic evolution, and the coronal magnetism that structures and drives the solar wind. Comprehensive observations of the global magnetothermal environment of the solar atmosphere are needed for progress. When fully implemented, the COSMO suite of synoptic ground-based telescopes will provide the community with comprehensive and simultaneous measurements of magnetism, temperature, density and plasma flows and waves from the photosphere through the chromosphere and out into the corona. We will discuss how these observations will uniquely address a set of science objectives that are central to the field of solar and space physics: in particular, to understand the storage and release of magnetic energy, to understand CME dynamics and consequences for shocks, to determine the role of waves in solar atmospheric heating and solar wind acceleration, to understand how the coronal magnetic field relates to the solar dynamo, and to constrain and improve space-weather forecast models. Title: High-Altitude Instrumentation for Infrared Observations of the Solar Corona Authors: Samra, J.; Cheimets, P.; DeLuca, E.; Golub, L.; Hannigan, J. W.; Judge, P. G.; Madsen, C. A.; Marquez, V.; Tañón Reyes, N.; Tomczyk, S. Bibcode: 2019AGUFMSH43B..07S Altcode: High-altitude infrared remote sensing is a promising new method for measuring coronal plasma and magnetic fields. We present new results from a recent airborne eclipse mission and outline concepts for future airborne and balloon-based instruments for coronal spectroscopy and spectro-polarimetry.

The airborne infrared spectrometer (AIR-Spec) was commissioned during the 2017 total solar eclipse, when it observed five infrared coronal emission lines from the NSF Gulfstream V research jet. These magnetically sensitive emission lines of highly ionized magnesium, silicon, sulfur, and iron are promising candidates for future observations of the coronal magnetic field, and their characterization is an important first step toward developing the next generation of instrumentation for coronal magnetometry. The second AIR-Spec research flight took place during the July 2, 2019 total solar eclipse across the south Pacific. Higher sensitivity and reduced jitter enabled more precise measurements of emission line properties and plasma density, temperature, and line-of-sight velocity up to one solar radius from the solar limb. Atmospheric absorption was significant, even at altitude, and atmospheric modeling was required to extract accurate line intensities.

AIR-Spec is a slit spectrometer that measures light over a 1.55 solar radius field of view in three spectral passbands between 1.4 and 3 microns. The successful eclipse missions overcame a number of engineering challenges, centered around maintaining adequate resolution and signal-to-noise ratio in a compact and inexpensive package on a moving platform. AIR-Spec is a pathfinder for future infrared spectrometers and spectro-polarimeters, including a balloon-based coronagraph that will measure the global coronal magnetic field and an airborne spectrometer that will survey the infrared emission corona during a future eclipse. Title: Novel observations of the middle corona during the 2017 total solar eclipse Authors: Caspi, A.; Seaton, D. B.; Tsang, C.; DeForest, C.; Bryans, P.; Samra, J.; DeLuca, E.; Tomczyk, S.; Burkepile, J.; Gallagher, P.; Golub, L.; Judge, P. G.; Laurent, G. T.; West, M.; Zhukov, A. Bibcode: 2019AGUFMSH13A..10C Altcode: Total solar eclipses offer rare opportunities to study the middle corona. This intriguing region contains complex interfaces and transitions between physical regimes, but has historically been under-observed due to the challenges of observing its dim emission so close to the bright inner corona and blinding solar disk. The unique circumstances of a total solar eclipse coupled with a high-altitude observing platform provide nearly space-quality observing conditions, including for wavelengths inaccessible by ground-based observatories, but with availability of ground-quality resources, including high-speed, high-resolution, wide-field coronography typically inaccessible from space. We used the 2017 August 21 "Great American" total solar eclipse to observe the solar corona from ~1.02 to ~3 RSun in both visible (533.9 ± 4.75 nm) and medium-wave infrared (3-5 μm) light using stabilized telescopes on two of NASA's WB-57F high-altitude research aircraft. This pathfinding mission utilized existing instrumentation to evaluate the platform performance, guide instrumentation development, and explore new discovery space for future studies of the middle corona.

We present the high-speed (30 Hz), high-resolution (3 arcsec/pixel) visible and IR observations obtained during the eclipse, and analysis of these observations in the context of coronal structure and dynamics. We discuss the limitations of the prototype data and pathways forward for future instrumentation and missions optimized for the range of observable parameters in the middle corona. We also discuss the benefits of such eclipse studies to an understanding of the corona as a single, unified system, from its origins at the solar surface to its extension into the heliosphere, particularly within the context of a developing multi- and inter-disciplinary research collaboration, COHERENT (the "Corona as a Holistic Environment" Research Network). Title: Solar Eclipse Observations from the Ground and Air from 0.31 to 5.5 Microns Authors: Judge, Philip; Berkey, Ben; Boll, Alyssa; Bryans, Paul; Burkepile, Joan; Cheimets, Peter; DeLuca, Edward; de Toma, Giuliana; Gibson, Keon; Golub, Leon; Hannigan, James; Madsen, Chad; Marquez, Vanessa; Richards, Austin; Samra, Jenna; Sewell, Scott; Tomczyk, Steven; Vera, Alysha Bibcode: 2019SoPh..294..166J Altcode: We present spectra and broad-band polarized light data from a novel suite of instruments deployed during the 21st August 2017 total solar eclipse. Our goals were to survey solar spectra at thermal infrared wavelengths during eclipse, and to test new technology for measuring polarized coronal light. An infrared coronal imaging spectrometer, flown at 14.3 km altitude above Kentucky, was supported on the ground by observations from Madras, Oregon (elevation 683 m) and Camp Wyoba on Casper Mountain, Wyoming (2402 m). In Wyoming we deployed a new infrared Fourier Transform Spectrometer (FTS), three low-dispersion spectrometers loaned to us by Avantes, a novel visible-light camera PolarCam, sensitive to linear polarization, and one of two infrared cameras from FLIR Systems, the other operated at Madras. Circumstances of eclipse demanded that the observations spanned 17:19 to 18:26 UT. We analyze spectra of the limb photosphere, the chromosphere, prominences, and coronal lines from 310 nm to 5.5 μm. We calibrated data photometrically using the solar disk as a source. Between different spectrometers, the calibrations were consistent to better than 13%. But the sensitivities achieved were insufficient to detect coronal lines from the ground. The PolarCam data are in remarkable agreement with polarization data from the K-Cor synoptic instrument on Mauna Loa, and with FLIR intensity data acquired in Madras. We discuss new results, including a detection of the He I 1083 nm multiplet in emission during the whole of totality. The combination of the FTS and AIR-Spec spectra reveals for the first time the effects of the telluric extinction on the infrared coronal emission lines, to be observed with upcoming Daniel K. Inouye Solar Telescope. Title: Multiwavelength High-resolution Observations of Chromospheric Swirls in the Quiet Sun Authors: Shetye, Juie; Verwichte, Erwin; Stangalini, Marco; Judge, Philip G.; Doyle, J. G.; Arber, Tony; Scullion, Eamon; Wedemeyer, Sven Bibcode: 2019ApJ...881...83S Altcode: We report observations of small-scale swirls seen in the solar chromosphere. They are typically 2 Mm in diameter and last around 10 minutes. Using spectropolarimetric observations obtained by the CRisp Imaging Spectro-Polarimeter at the Swedish 1 m Solar Telescope, we identify and study a set of swirls in chromospheric Ca II 8542 Å and Hα lines as well as in the photospheric Fe I line. We have three main areas of focus. First, we compare the appearance, morphology, dynamics, and associated plasma parameters between the Ca II and Hα channels. Rotation and expansion of the chromospheric swirl pattern are explored using polar plots. Second, we explore the connection to underlying photospheric magnetic concentration (MC) dynamics. MCs are tracked using the SWAMIS tracking code. The swirl center and MC remain cospatial and share similar periods of rotation. Third, we elucidate the role swirls play in modifying chromospheric acoustic oscillations and found a temporary reduction in wave period during swirls. We use cross-correlation wavelets to examine the change in period and phase relations between different wavelengths. The physical picture that emerges is that a swirl is a flux tube that extends above an MC in a downdraft region in an intergranular lane. The rotational motion of the MC matches the chromospheric signatures. We could not determine whether a swirl is a gradual response to the photospheric motion or an actual propagating Alfvénic wave. Title: HAOS-DIPER: HAO Spectral Diagnostic Package For Emitted Radiation Authors: Judge, P. G. Bibcode: 2019ascl.soft05009J Altcode: HAOS-DIPER works with and manipulates data for neutral atoms and atomic ions to understand radiation emitted by some space plasmas, notably the solar atmosphere and stellar atmospheres. HAOS-DIPER works with quantum numbers for atomic levels, enabling it to perform tasks otherwise difficult or very tedious, including a variety of data checks, calculations based upon the atomic numbers, and searching and manipulating data based upon these quantum numbers. HAOS-DIPER handles conditions from LTE to coronal-like conditions, in a manner controlled by one system variable !REGIME, and has some capability for estimating data for which no accurate parameters are available and for accounting for the effects of missing atomic levels. Title: High-cadence Visible and Infrared Spectra of the Sun during Eclipse Authors: Judge, P.; Tomczyk, S.; Hannigan, J.; Sewell, S. Bibcode: 2019ApJ...877...10J Altcode: We study novel spectra from 310 nm to 5.5 μm obtained during the 2017 August 21 eclipse. Four spectrometers were deployed at Camp Wyoba (altitude 2402 m) on Casper Mountain, WY. Three low-resolution ({ \mathcal R } ≲ 1000) Avantes spectrometers obtained useful spectra from 310 nm to 2.3 μm, at cadences from 8 to 500 ms. To maximize photometric precision, these instruments were fed with optical fibers placed in the pupil planes of two small (D = 5 cm) telescopes, thereby integrating all light from the field of view. We also acquired higher-resolution ({ \mathcal R } ≈ 30000) spectra with a new infrared Fourier Transform Spectrometer, fed by a Sun-tracking heliostat, at a 2.5 s cadence. We calibrate the fluxes using counts obtained during partial eclipse, with known limb-darkened photospheric intensities. Fluxes of chromospheric lines, including Ca II H, K, and Hα, obtained near third contact, were measured every 20 ms, a sampling in height above the limb of 5.6 km. The behavior found corresponds to that found in traditional (image-plane) flash spectra. Two unknown chromospheric emission lines are noted. Based upon our measurements and earlier calculations, we propose new eclipse experiments to uncover clues to the origin and structure of spicules. Title: COSMO Science Authors: Gibson, Sarah; Tomczyk, Steven; Burkepile, Joan; Casini, Roberto; Deluca, Ed; de Toma, Giuliana; deWijn, Alfred; Fan, Yuhong; Golub, Leon; Judge, Philip; Landi, Enrico; Lin, Haosheng; McIntosh, Scott; Reeves, Kathy; Seaton, Dan; Zhang, Jie Bibcode: 2019shin.confE..32G Altcode: Space-weather forecast capability is held back by our current lack of basic scientific understanding of CME magnetic evolution, and the coronal magnetism that structures and drives the solar wind. Comprehensive observations of the global magnetothermal environment of the solar atmosphere are needed for progress. When fully implemented, the COSMO suite of synoptic ground-based telescopes will provide the community with comprehensive and simultaneous measurements of magnetism, temperature, density and plasma flows and waves from the photosphere through the chromosphere and out into the corona. We will discuss how these observations will uniquely address a set of science objectives that are central to the field of solar and space physics: in particular, to understand the storage and release of magnetic energy, to understand CME dynamics and consequences for shocks, to determine the role of waves in solar atmospheric heating and solar wind acceleration, to understand how the coronal magnetic field relates to the solar dynamo, and to constrain and improve space-weather forecast models. Title: Erratum: “Discovery of New Coronal Lines at 2.843 and 2.853 μm” (2018, ApJL, 856, L29) Authors: Samra, Jenna E.; Judge, Philip G.; DeLuca, Edward E.; Hannigan, James W. Bibcode: 2019ApJ...873L..25S Altcode: No abstract at ADS Title: Measuring solar surface magnetic fields without ambiguity Authors: Judge, Philip G. Bibcode: 2019MNRAS.482.5542J Altcode: 2018MNRAS.tmp.2891J The goal of this paper is to find a method to yield solar surface magnetic field measurements while inflicting minimal prior assumptions on the acceptable solutions. A small spacecraft placed at least 0.1 radian away from the Earth-Sun line can, with vector field observations from the Earth, offer unambiguous determinations of magnetic fields from the Sun. A telescope of between 10 and 40 cm aperture operating at ultraviolet (UV) wavelengths can, with a simple Stokes-V polarimeter, enhance observations made with the suite of large telescopes on the Earth. A 40 cm aperture can achieve the same diffraction limit at 400 nm that Daniel K. Innouye Solar Telescope (DKIST) might achieve at 4 microns. Even a 10 cm aperture offers higher signal to noise in Stokes V than DKIST can Q and U in magnetic fields outside sunspots, transverse to the line of sight, offering enormous benefits for understanding magnetic components transverse to the Earth-Sun line. We identify UV and infrared (IR) lines of Fe I that are useful for joint spacecraft-DKIST observations. Benefits of space observations also include line-of-sight fields measured in strong chromospheric lines in the UV that are free of seeing, such as Ca II H&K and Mg II h&k. A simple mission devoted to such space measurements will enhance our understanding of solar magnetism and hence, space weather and space climate, for decades to come. Title: VizieR Online Data Catalog: UV spectrum of molecular hydrogen in the Sun (Jaeggli+, 2018) Authors: Jaeggli, S. A.; Judge, P. G.; Daw, A. N. Bibcode: 2019yCat..18550134J Altcode: Ultraviolet (UV) lines of molecular hydrogen have been observed in solar spectra for almost four decades, but the behavior of the molecular spectrum and its implications for solar atmospheric structure are not fully understood. Data from the High-Resolution Telescope Spectrometer (HRTS) instrument revealed that H2 emission forms in particular regions, selectively excited by a bright UV transition region and chromospheric lines. We test the conditions under which H2 emission can originate by studying non-LTE models, sampling a broad range of temperature stratifications and radiation conditions. Stratification plays the dominant role in determining the population densities of H2, which forms in greatest abundance near the continuum photosphere. However, opacity due to the photoionization of Si and other neutrals determines the depth to which UV radiation can penetrate to excite the H2. Thus the majority of H2 emission forms in a narrow region, at about 650km in standard one-dimensional (1D) models of the quiet Sun, near the {tau}=1 opacity surface for the exciting UV radiation, generally coming from above. When irradiated from above using observed intensities of bright UV emission lines, detailed non-LTE calculations show that the spectrum of H2 seen in the quiet-Sun Solar Ultraviolet Measurement of Emitted Radiation atlas spectrum and HRTS light-bridge spectrum can be satisfactorily reproduced in 1D stratified atmospheres, without including three-dimensional or time-dependent thermal structures. A detailed comparison to observations from 1205 to 1550Å is presented, and the success of this 1D approach to modeling solar UV H2 emission is illustrated by the identification of previously unidentified lines and upper levels in HRTS spectra.

(3 data files). Title: Chapter 5 - Spectroscopy and Atomic Physics Authors: Judge, Philip G. Bibcode: 2019sgsp.book..127J Altcode: 2019sgsp.book..127. A short guide to spectroscopy is given with an emphasis on the elementary physics needed to understand and begin modeling the radiation emerging from astrophysical plasmas using the Sun as a guide, without bias toward a particular region of the Sun's atmosphere. The Sun is the astronomical body par excellence upon which our tools for exploring the universe have been most carefully developed. Observable solar plasmas span a broad range of conditions and consequently extremes of local thermodynamic equilibrium deep in the atmosphere, to extreme non-local thermodynamical equilibrium conditions in the corona and wind, including nonstatistical equilibrium conditions. For brevity, important subjects are omitted, notably non-Maxwellian electron distributions, line broadening, polarization, particle diffusion, and high-energy and collective phenomena of importance, at radio and hard x-ray wavelengths. Title: Eclipse Science from 50,000 Feet: New Coronal Results from NASA WB-57F High-Altitude Aircraft Observations of the 2017 Total Solar Eclipse Authors: Caspi, Amir; Tsang, Constantine; Seaton, Daniel B.; DeForest, Craig; Bryans, Paul; DeLuca, Edward; Tomczyk, Steven; Burkepile, Joan; Casey, Thomas Anthony; Collier, John; Darrow, Donald DD; Del Rosso, Dominic; Durda, Daniel D.; Gallagher, Peter; Gascar, Jasmine; Golub, Leon; Jacyna, Matthew; Johnson, David DJ; Judge, Philip G.; Klemm, Cary; Laurent, Glenn Thomas; Lewis, Johanna; Mallini, Charles; Parent, Thomas Duster; Propp, Timothy; Steffl, Andrew; Warner, Jeff; West, Matthew John; Wiseman, John; Yates, Mallory; Zhukov, Andrei Bibcode: 2018tess.conf31302C Altcode: Total solar eclipses present rare opportunities to study the complex solar corona, down to altitudes of just a few percent of a solar radius above the surface. Studying the corona is critical to gaining a better understanding of the dominant driver of space weather that affects human assets on Earth and elsewhere. For example, it is still poorly understood how the corona is heated to temperatures of 1-2 MK globally and up to 5-10 MK above active regions, while the underlying chromosphere is 100 times cooler. The stability of large-scale coronal structures and the extent of their reach to the middle and outer corona are also not well known, limited in large part by sensitivities and fields of view of existing observations.

Airborne observations during a total eclipse provide unique advantages. By flying in the stratosphere at altitudes of 50 kft or higher, they avoid all weather, the seeing quality is enormously improved, and additional wavelengths such as near-IR also become available due to significantly reduced water absorption. An airborne observatory can also follow the Moon's shadow, increasing the total observing time by 50% or more.

We present current results of solar coronal measurements from airborne observations of the 2017 Great American Total Solar Eclipse using two of NASA's WB-57 high-altitude research aircraft, each equipped with two 8.7-inch telescopes feeding high-sensitivity visible (green line and nearby continuum) and medium-wave IR (3-5 μm) cameras operating at high cadence (30 Hz) with ∼3 arcsec/pixel platescale and ±3 Rsun fields of view. The two aircraft flew along the eclipse path, separated by ∼110 km, to observe a total of ∼7.5 minutes of totality in both visible and MWIR. These observations enable groundbreaking studies of high-speed coherent motion - including possible Alfvén waves and nanojets - in the lower and middle corona that could shed light on coronal heating processes and the formation and stability of coronal structures. Our MWIR observations of a cool prominence and hot coronal active region plasma will be combined with spectra from the AIR-Spec instrument, flown concurrently on NCAR's HIAPER GV. We review the WB-57 eclipse mission and the current results of analysis on the visible and IR coronal measurements, along with an outlook for future analysis and missions. Title: Solar UV Molecular Hydrogen Fluorescence Authors: Daw, Adrian Nigel; Jaeggli, Sarah Amelia; Judge, Philip G.; Roueff, Evelyne; Abgrall, Hervé Bibcode: 2018tess.conf21706D Altcode: Solar observations of ultraviolet molecular hydrogen lines indicate that H2 emission forms in particular regions, selectively excited by bright UV transition region and chromospheric lines. IRIS frequently observes numerous H2 lines during flares and smaller energetic events, but the diagnostic value of these lines for probing the structure of the solar atmosphere has heretofore remained largely unexploited. We present a synthesis method for H2 emission, using 1-D non-LTE models sampling a broad range of temperature stratifications and input radiation conditions from the atmosphere above, and compare the results to observations by IRIS, SUMER and HRTS from 1205 to 1550 Å. Because opacity due to photoionization of silicon and other neutrals determines the depth to which UV radiation can penetrate to excite the H2, the majority of H2 emission forms in a narrow region near the tau=1 opacity surface for the exciting UV radiation, generally coming from above. The success of this 1-D approach to modeling solar UV H2 emission is illustrated by the identification of previously unidentified lines and upper levels. Applications of the observed emission and implications for solar atmospheric structure are discussed. Title: Discovery of New Coronal Lines at 2.843 and 2.853 μm Authors: Samra, Jenna E.; Judge, Philip G.; DeLuca, Edward E.; Hannigan, James W. Bibcode: 2018ApJ...856L..29S Altcode: Two new emission features were observed during the 2017 August 21 total solar eclipse by a novel spectrometer, the Airborne Infrared Spectrometer (AIR-Spec), flown at 14.3 km altitude aboard the NCAR Gulfstream-V aircraft. We derive wavelengths in air of 2.8427 ± 0.00009 μm and 2.8529 ± 0.00008 μm. One of these lines belongs to the 3{{{p}}}53{{d}}{}3{{{F}}}3^\circ \to 3{{{p}}}53{{d}}{}3{{{F}}}4^\circ transition in Ar-like Fe IX. This appears to be the first detection of this transition from any source. Minimization of residual wavelength differences using both measured wavelengths, together with National Institute of Standards and Technology (NIST) extreme ultraviolet wavelengths, does not clearly favor assignment to Fe IX. However, the shorter wavelength line appears more consistent with other observed features formed at similar temperatures to Fe IX. The transition occurs between two levels within the excited 3{{{p}}}53{{d}} configuration, 429,000 cm-1 above the ground level. The line is therefore absent in photo-ionized coronal-line astrophysical sources such as the Circinus Galaxy. Data from a Fourier transform interferometer (FTIR) deployed from Wyoming show that both lines are significantly attenuated by telluric H2O, even at dry sites. We have been unable to identify the longer wavelength transition. Title: Formation of the UV Spectrum of Molecular Hydrogen in the Sun Authors: Jaeggli, S. A.; Judge, P. G.; Daw, A. N. Bibcode: 2018ApJ...855..134J Altcode: 2018arXiv180203779J Ultraviolet (UV) lines of molecular hydrogen have been observed in solar spectra for almost four decades, but the behavior of the molecular spectrum and its implications for solar atmospheric structure are not fully understood. Data from the High-Resolution Telescope Spectrometer (HRTS) instrument revealed that H2 emission forms in particular regions, selectively excited by a bright UV transition region and chromospheric lines. We test the conditions under which H2 emission can originate by studying non-LTE models, sampling a broad range of temperature stratifications and radiation conditions. Stratification plays the dominant role in determining the population densities of H2, which forms in greatest abundance near the continuum photosphere. However, opacity due to the photoionization of Si and other neutrals determines the depth to which UV radiation can penetrate to excite the H2. Thus the majority of H2 emission forms in a narrow region, at about 650 km in standard one-dimensional (1D) models of the quiet Sun, near the τ = 1 opacity surface for the exciting UV radiation, generally coming from above. When irradiated from above using observed intensities of bright UV emission lines, detailed non-LTE calculations show that the spectrum of H2 seen in the quiet-Sun Solar Ultraviolet Measurement of Emitted Radiation atlas spectrum and HRTS light-bridge spectrum can be satisfactorily reproduced in 1D stratified atmospheres, without including three-dimensional or time-dependent thermal structures. A detailed comparison to observations from 1205 to 1550 Å is presented, and the success of this 1D approach to modeling solar UV H2 emission is illustrated by the identification of previously unidentified lines and upper levels in HRTS spectra. Title: Magnetic Diagnostics of the Solar Corona: Synthesizing Optical and Radio Techniques Authors: Casini, R.; White, S. M.; Judge, P. G. Bibcode: 2018smf..book..145C Altcode: No abstract at ADS Title: Chasing the Great American 2017 Total Solar Eclipse: Coronal Results from NASA's WB-57F High-Altitude Research Aircraft Authors: Caspi, A.; Tsang, C.; DeForest, C. E.; Seaton, D. B.; Bryans, P.; Burkepile, J.; Casey, T. A.; Collier, J.; Darrow, D.; DeLuca, E.; Durda, D. D.; Gallagher, P.; Golub, L.; Judge, P. G.; Laurent, G. T.; Lewis, J.; Mallini, C.; Parent, T.; Propp, T.; Steffl, A.; Tomczyk, S.; Warner, J.; West, M. J.; Wiseman, J.; Zhukov, A. Bibcode: 2017AGUFMSH24A..05C Altcode: Total solar eclipses present rare opportunities to study the complex solar corona, down to altitudes of just a few percent of a solar radius above the surface, using ground-based and airborne observatories that would otherwise be dominated by the intense solar disk and high sky brightness. Studying the corona is critical to gaining a better understanding of physical processes that occur on other stars and astrophysical objects, as well as understanding the dominant driver of space weather that affects human assets at Earth and elsewhere. For example, it is still poorly understood how the corona is heated to temperatures of 1-2 MK globally and up to 5-10 MK above active regions, while the underlying chromosphere is 100 times cooler; numerous theories abound, but are difficult to constrain due to the limited sensitivities and cadences of prior measurements. The origins and stability of coronal fans, and the extent of their reach to the middle and outer corona, are also not well known, limited in large part by sensitivities and fields of view of existing observations. Airborne observations during the eclipse provide unique advantages; by flying in the stratosphere at altitudes of 50 kft or higher, they avoid all weather, the seeing quality is enormously improved, and additional wavelengths such as near- IR also become available due to significantly reduced water absorption. For an eclipse, an airborne observatory can also follow the shadow, increasing the total observing time by 50% or more. We present results of solar coronal measurements from airborne observations of the 2017 Great American Total Solar Eclipse using two of NASA's WB-57 high-altitude research aircraft, each equipped with two 8.7" telescopes feeding high-sensitivity visible (green-line) and medium-wave IR (3-5 μm) cameras operating at high cadence (30 Hz) with 3 arcsec/pixel platescale and ±3 R_sun fields of view. The aircraft flew along the eclipse path, separated by 110 km, to observe a summed 7.5 minutes of totality in both visible and NIR, enabling groundbreaking studies of high-speed wave motions and nanojets in the lower corona, the structure and extent of coronal fans, and constraints on a potential primordial dust ring around the Sun. We review the mission, and the results of analysis on the visible and IR coronal measurements. Title: Formation of the UV Spectrum of Molecular Hydrogen in the Sun Authors: Jaeggli, S. A.; Judge, P. G.; Daw, A. N. Bibcode: 2017AGUFMSH52B..01J Altcode: UV lines of molecular hydrogen in the Sun have been observed for almost four decades, but the behavior of the spectra and their implications for solar atmospheric structure are not fully understood. Data from the HRTS instrument revealed that H2 emission forms in particular regions, selectively excited by bright UV transition region and chromospheric lines. We test the conditions under which H2 emission can originate by studying non-LTE models with increasingly complex temperature stratification. Stratification plays the dominant role in determining the population densities of H2, which can form in abundance only within about 700 km of the continuum photosphere where 3D and dynamic structure generally play secondary roles to stratification. When irradiated from above using observed intensities of bright UV emission lines, detailed non-LTE calculations show that the spectrum of H2 can be satisfactorily modeled in 1D stratified atmospheric models, with no need to invoke unusual 3D or time dependent thermal structures. Title: Multi-wavelength observations of the solar atmosphere from the August 21, 2017 total solar eclipse Authors: Tomczyk, S.; Boll, A.; Bryans, P.; Burkepile, J.; Casini, R.; DeLuca, E.; Gibson, K. L.; Judge, P. G.; McIntosh, S. W.; Samra, J.; Sewell, S. D. Bibcode: 2017AGUFMSH24A..04T Altcode: We will conduct three experiments at the August 21, 2017 total solar eclipse that we call the Rosetta Stone experiments. First, we will obtain narrow-bandpass images at infrared wavelengths of the magnetically sensitive coronal emission lines of Fe IX 2855 nm, Mg VIII 3028 nm and Si IX 3935 nm with a FLIR thermal imager. Information on the brightness of these lines is important for identifying the optimal lines for coronal magnetometry. These images will also serve as context images for the airborne AirSpec IR coronal spectroscopy experiment (Samra et al). Second, we will obtain linear polarization images of the visible emission lines of Fe X 637 nm and Fe XI 789 nm as well as the continuum polarization near 735 nm. These will be obtained with a novel detector with an integral array of linear micro-polarizers oriented at four different angles that enable polarization images without the need for liquid crystals or rotating elements. These measurements will provide information on the orientation of magnetic fields in the corona and serve to demonstrate the new detector technology. Lastly, we will obtain high cadence spectra as the moon covers and uncovers the chromosphere immediately after 2nd contact and before third contact. This so-called flash spectrum will be used to obtain information about chromospheric structure at a spatial resolution higher than is possible by other means. In this talk, we will describe the instrumentation used in these experiments and present initial results obtained with them. This work is supported by a grant from NASA, through NSF base funding of HAO/NCAR and by generous loans of equipment from our corporate partners, FLIR, 4D Technologies and Avantes. Title: Polarization Observations of the Total Solar Eclipse of August 21, 2017 Authors: Burkepile, J.; Boll, A.; Casini, R.; de Toma, G.; Elmore, D. F.; Gibson, K. L.; Judge, P. G.; Mitchell, A. M.; Penn, M.; Sewell, S. D.; Tomczyk, S.; Yanamandra-Fisher, P. A. Bibcode: 2017AGUFMSH13B2477B Altcode: A total solar eclipse offers ideal sky conditions for viewing the solar corona. Light from the corona is composed of three components: the E-corona, made up of spectral emission lines produced by ionized elements in the corona; the K-corona, produced by photospheric light that is Thomson scattered by coronal electrons; and the F-corona, produced by sunlight scattered from dust particles in the near Sun environment and in interplanetary space. Polarized white light observations of the corona provide a way of isolating the K-corona to determine its structure, brightness, and density. This work focuses on broadband white light polarization observations of the corona during the upcoming solar eclipse from three different instruments. We compare coronal polarization brightness observations of the August 21, 2017 total solar eclipse from the NCAR/High Altitude Observatory (HAO) Rosetta Stone experiment using the 4-D Technology PolarCam camera with the two Citizen PACA_CATE17Pol telescopes that will acquire linear polarization observations of the eclipse and the NCAR/HAO K-Cor white light coronagraph observations from the Mauna Loa Solar Observatory in Hawaii. This comparison includes a discussion of the cross-calibration of the different instruments and reports the results of the coronal polarization brightness and electron density of the corona. These observations will be compared with results from previous coronal measurements taken at different phases of the solar cycle. In addition, we report on the performance of the three different polarimeters. The 4-D PolarCam uses a linear polarizer array, PACA_CATE17Pol uses a nematic liquid crystal retarder in a single beam configuration and K-Cor uses a pair of ferroelectric liquid crystal retarders in a dual-beam configuration. The use of the 4-D PolarCam camera in the Rosetta Stone experiment is to demonstrate the technology for acquiring high cadence polarization measurements. The Rosetta Stone experiment is funded through the NASA award NNH16ZDA001N-ISE. The Citizen Science approach to measuring the polarized solar corona during the eclipse is funded through NASA award NNX17AH76G. The NCAR Mauna Loa Solar Observatory is funded by the National Science Foundation. Title: Surveying the IR corona during the 2017 solar eclipse Authors: Bryans, P.; Hannigan, J. W.; Sewell, S. D.; Judge, P. G. Bibcode: 2017AGUFMSH13B2479B Altcode: The spectral emission of the infrared solar corona is the most promising direct diagnostic of the coronal magnetic field, and yet remains poorly measured. During the 2017 total solar eclipse, we will perform the first spectral survey of the IR corona using the NCAR Airborne Interferometer. This Fourier Transform Infrared Spectrometer is configured to observe the coronal spectrum from 1.5 to 5.5 microns at R 10,000 from a ground-based site. The location is atop Casper Mountain, Wyoming (42.73ºN, 106.32ºW, 2400 masl), 8 km from the center-line of totality. In this presentation, we will outline the need for such measurements, describe the instrument design and adaptation for the eclipse measurement, observation scheme, and present preliminary results. We will also discuss implications for observing infrared coronal lines from the ground, for example with the upcoming DKIST facility. Title: ASPIRE - Airborne Spectro-Polarization InfraRed Experiment Authors: DeLuca, E.; Cheimets, P.; Golub, L.; Madsen, C. A.; Marquez, V.; Bryans, P.; Judge, P. G.; Lussier, L.; McIntosh, S. W.; Tomczyk, S. Bibcode: 2017AGUFMSH13B2480D Altcode: Direct measurements of coronal magnetic fields are critical for taking the next step in active region and solar wind modeling and for building the next generation of physics-based space-weather models. We are proposing a new airborne instrument to make these key observations. Building on the successful Airborne InfraRed Spectrograph (AIR-Spec) experiment for the 2017 eclipse, we will design and build a spectro-polarimeter to measure coronal magnetic field during the 2019 South Pacific eclipse. The new instrument will use the AIR-Spec optical bench and the proven pointing, tracking, and stabilization optics. A new cryogenic spectro-polarimeter will be built focusing on the strongest emission lines observed during the eclipse. The AIR-Spec IR camera, slit jaw camera and data acquisition system will all be reused. The poster will outline the optical design and the science goals for ASPIRE. Title: Efficient Radiative Transfer for Dynamically Evolving Stratified Atmospheres Authors: Judge, Philip G. Bibcode: 2017ApJ...851....5J Altcode: We present a fast multi-level and multi-atom non-local thermodynamic equilibrium radiative transfer method for dynamically evolving stratified atmospheres, such as the solar atmosphere. The preconditioning method of Rybicki & Hummer (RH92) is adopted. But, pressed for the need of speed and stability, a “second-order escape probability” scheme is implemented within the framework of the RH92 method, in which frequency- and angle-integrals are carried out analytically. While minimizing the computational work needed, this comes at the expense of numerical accuracy. The iteration scheme is local, the formal solutions for the intensities are the only non-local component. At present the methods have been coded for vertical transport, applicable to atmospheres that are highly stratified. The probabilistic method seems adequately fast, stable, and sufficiently accurate for exploring dynamical interactions between the evolving MHD atmosphere and radiation using current computer hardware. Current 2D and 3D dynamics codes do not include this interaction as consistently as the current method does. The solutions generated may ultimately serve as initial conditions for dynamical calculations including full 3D radiative transfer.

The National Center for Atmospheric Research is sponsored by the National Science Foundation. Title: Eclipse Science Results from the Airborne Infrared Spectrometer (AIR-Spec) Authors: Samra, J.; Cheimets, P.; DeLuca, E.; Golub, L.; Judge, P. G.; Lussier, L.; Madsen, C. A.; Marquez, V.; Tomczyk, S.; Vira, A. Bibcode: 2017AGUFMSH24A..06S Altcode: We present the first science results from the commissioning flight of the Airborne Infrared Spectrometer (AIR-Spec), an innovative solar spectrometer that will observe the 2017 solar eclipse from the NSF/NCAR High-Performance Instrumented Airborne Platform for Environmental Research (HIAPER). During the eclipse, AIR-Spec will image five magnetically sensitive coronal emission lines between 1.4 and 4 microns to determine whether they may be useful probes of coronal magnetism. The instrument will measure emission line intensity, FWHM, and Doppler shift from an altitude of over 14 km, above local weather and most of the absorbing water vapor. Instrumentation includes an image stabilization system, feed telescope, grating spectrometer, infrared camera, and visible slit-jaw imager. Results from the 2017 eclipse are presented in the context of the mission's science goals. AIR-Spec will identify line strengths as a function of position in the solar corona and search for the high frequency waves that are candidates for heating and acceleration of the solar wind. The instrument will also identify large scale flows in the corona, particularly in polar coronal holes. Three of the five lines are expected to be strong in coronal hole plasmas because they are excited in part by scattered photospheric light. Line profile analysis will probe the origins of the fast and slow solar wind. Finally, the AIR-Spec measurements will complement ground based eclipse observations to provide detailed plasma diagnostics throughout the corona. AIR-Spec will measure infrared emission of ions observed in the visible from the ground, giving insight into plasma heating and acceleration at radial distances inaccessible to existing or planned spectrometers. Title: The Magnetic Future of the Sun Authors: Judge, Philip G.; Egeland, Ricky; Metcalfe, Travis S.; Guinan, Edward; Engle, Scott Bibcode: 2017ApJ...848...43J Altcode: 2017arXiv171005088J We analyze space- and ground-based data for the old (7.0 ± 0.3 Gyr) solar analogs 16 Cyg A and B. The stars were observed with the Cosmic Origins UV Spectrographs on the Hubble Space Telescope (HST) on 2015 October 23 and 2016 February 3, respectively, and with the Chandra X-ray Observatory on 2016 February 7. Time-series data in Ca II data are used to place the UV data in context. The UV spectra of 18 Sco (3.7 ± 0.5 Gyr), the Sun (4.6 ± 0.04 Gyr), and α Cen A ({5.4}-0.2+1.2 {Gyr}) appear remarkably similar, pointing to a convergence of magnetic heating rates for G2 main-sequence stars older than ≈2-4 Gyr. But the B component’s X-ray (0.3-2.5 keV) flux lies 20× below a well-known minimum level reported by Schmitt. As reported for α Cen A, the coronal temperature probably lies below that detectable in soft X-rays. No solar UV flux spectra of comparable resolution to those of stellar data exist, but they are badly needed for comparison with stellar data. Center-to-limb variations are reevaluated for lines such as Ca II through X-rays, with important consequences for observing activity cycles in such features. We also call into question work that has mixed solar intensity-intensity statistics with flux-flux relations of stars. Title: Solar Spectral Lines with Special Polarization Properties for the Calibration of Instrument Polarization Authors: Li, W.; Casini, R.; del Pino Alemán, T.; Judge, P. G. Bibcode: 2017ApJ...848...82L Altcode: We investigate atomic transitions that have previously been identified as having zero polarization from the Zeeman effect. Our goal is to identify spectral lines that can be used for the calibration of instrumental polarization of large astronomical and solar telescopes, such as the Daniel K. Inouye Solar Telescope, which is currently under construction on Haleakala. We use a numerical model that takes into account the generation of scattering polarization and its modification by the presence of a magnetic field of arbitrary strength. We adopt values for the Landé factors from spectroscopic measurements or semi-empirical results, thus relaxing the common assumption of LS-coupling previously used in the literature. The mechanisms dominating the polarization of particular transitions are identified, and we summarize groups of various spectral lines useful for the calibration of spectropolarimetric instruments, classified according to their polarization properties. Title: Atomic physics and solar polarimetry Authors: Judge, P. G. Bibcode: 2017CaJPh..95..847J Altcode: 2017arXiv170707090J Observational solar physics is entering a new era with the advent of new 1.5 m class telescopes with adaptive optics, as well as the Daniel K. Inouye 4 m telescope which will become operational in 2019. Major outstanding problems in solar physics all relate to the solar magnetic field. Spectropolarimetry offers the best, and sometimes only, method for accurate measurements of the magnetic field. In this paper we highlight how certain atomic transitions can help us provide both calibration data, as well as diagnostic information on solar magnetic fields, in the presence of residual image distortions through the atmosphere close to, but not at the diffraction limits of large and polarizing telescopes. Particularly useful are spectral lines of neutrals and singly charged ions of iron and other complex atoms. As a proof-of-concept, we explore atomic transitions that might be used to study magnetic fields without the need for an explicit calibration sequence, offering practical solutions to the difficult challenges of calibrating the next generation of solar spectropolarimetric telescopes. Suggestions for additional work on atomic theory and measurements, particularly at infrared wavelengths, are given. There is some promise for continued symbiotic advances between solar physics and atomic physics. Title: A Novel Strategy to Seek Biosignatures at Enceladus and Europa Authors: Judge, Philip Bibcode: 2017AsBio..17..852J Altcode: 2017arXiv170707230J A laboratory experiment is suggested in which conditions similar to those in the plume ejecta from Enceladus and, perhaps, Europa are established. Using infrared spectroscopy and polarimetry, the experiment might identify possible bio-markers in differential measurements of water from the open-ocean, from hydrothermal vents, and abiotic water samples. Should the experiment succeed, large telescopes could be used to acquire sensitive infrared spectra of the plumes of Enceladus and Europa, as the satellites transit the bright planetary disks. The extreme technical challenges encountered in so doing are similar to those of solar imaging spectropolarimetry. The desired signals are buried in noisy data in the presence of seeing-induced image motion and a changing natural source. Some differential measurements used for solar spectropolarimetry can achieve S/N ratios of $10^5$ even in the presence of systematic errors two orders of magnitude larger. We review the techniques and likelihood of success of such an observing campaign with some of the world's largest ground-based telescopes, as well as the long anticipated James Webb Space Telescope. We discuss the relative merits of the new 4m Daniel K. Inouye Solar Telescope, as well as the James Webb Space Telescope and larger ground-based observatories, for observing the satellites of giant planets. As seen from near Earth, transits of Europa occur regularly, but transits of Enceladus will begin again only in 2022. Title: Magnetic Diagnostics of the Solar Corona: Synthesizing Optical and Radio Techniques Authors: Casini, R.; White, S. M.; Judge, P. G. Bibcode: 2017SSRv..210..145C Altcode: 2017SSRv..tmp...91C In this contribution we review the current state-of-the-art of coronal magnetometry, in both optical and radio domains. We address the achievable objectives and the challenges of present measurement techniques and interpretation tools. In particular, we focus on the role that these observations can play for constraining and validating numerical models of the global coronal magnetic field. With regard to optical techniques, we mainly focus on the use of M1 diagnostics, further developing the theory of the formation of their polarization signatures in the magnetized corona. Title: On the Fine Structure Splitting of the 3p43d 4D5/2 and 3p43d 4D7/2 Levels of Fe X Authors: Judge, Philip; Hutton, Roger; Li, Wenxian; Brage, Tomas Bibcode: 2017arXiv170707077J Altcode: We study UV spectra obtained with the SO82-B slit spectrograph on board SKYLAB to estimate the fine structure splitting of the Cl-like 3p4 3d 4D J=5/2 and 3p4 3d 4D J=7/2 levels of Fe X. The splitting is of interest because the Zeeman effect mixes these levels, producing a "magnetically induced transition" (MIT) from 3p4 3d 4D J=7/2 to 3p5 2Po J=3/2 for modest magnetic field strengths characteristic of the active solar corona. We estimate the splitting using the Ritz combination formula applied to two lines in the UV region of the spectrum close to 1603.2 Angstrom, which decay from the level 3p4(1D)3d 2G J=7/2 to these two lower levels. The MIT and accompanying spin-forbidden transition lie near 257 Angstrom. By careful inspection of a deep exposure obtained with the S082B instrument we derive a splitting of <~ 7 +/- 3 cm-1. The upper limit arises because of a degeneracy between the effects of non-thermal line broadening and fine-structure splitting for small values of the latter parameter. Although the data were recorded on photographic film, we solved for optimal values of line width and splitting of 8.3 +/- 0.9 and 3.6 +/- 2.7 cm-1. Title: An Explanation of Remarkable Emission-line Profiles in Post-flare Coronal Rain Authors: Lacatus, Daniela A.; Judge, Philip G.; Donea, Alina Bibcode: 2017ApJ...842...15L Altcode: 2017arXiv170707069L We study broad redshifted emission in chromospheric and transition region lines that appears to correspond to a form of post-flare coronal rain. Profiles of Mg II, C II, and Si IV lines were obtained using IRIS before, during, and after the X2.1 flare of 2015 March 11 (SOL2015-03-11T16:22). We analyze the profiles of the five transitions of Mg II (the 3p-3s h and k transitions, and three lines belonging to the 3d-3p transitions). We use analytical methods to understand the unusual profiles, together with higher-resolution observational data of similar phenomena observed by Jing et al. The peculiar line ratios indicate anisotropic emission from the strands that have cross-strand line center optical depths (k line) of between 1 and 10. The lines are broadened by unresolved Alfvénic motions whose energy exceeds the radiation losses in the Mg II lines by an order of magnitude. The decay of the line widths is accompanied by a decay in the brightness, suggesting a causal connection. If the plasma is ≲99% ionized, ion-neutral collisions can account for the dissipation; otherwise, a dynamical process seems necessary. Our work implies that the motions are initiated during the impulsive phase, to be dissipated as radiation over a period of an hour, predominantly by strong chromospheric lines. The coronal “rain” we observe is far more turbulent than most earlier reports have indicated, with implications for plasma heating mechanisms. Title: Are All Flare Ribbons Simply Connected to the Corona? Authors: Judge, Philip G.; Paraschiv, Alin; Lacatus, Daniela; Donea, Alina; Lindsey, Charlie Bibcode: 2017ApJ...838..138J Altcode: 2017arXiv170707072J We consider the observational basis for the belief that flare ribbons in the chromosphere result from energy transport from the overlying corona. We study ribbons of small flares using magnetic and intensity data from the Hinode, Solar Dynamics Observatory, and IRIS missions. While most ribbons appear connected to the corona and overlie regions of significant vertical magnetic field, we examine one ribbon with no clear evidence for such connections. Evolving horizontal magnetic fields seen with Hinode suggest that reconnection with preexisting fields below the corona can explain the data. The identification of just one, albeit small, ribbon, with no apparent connection to the corona, leads us to conclude that at least two mechanisms are responsible for the heating that leads to flare ribbon emission.

The National Center for Atmospheric Research is sponsored by the National Science Foundation. Title: Vector Magnetic Field Measurements along a Cooled Stereo-imaged Coronal Loop Authors: Schad, T. A.; Penn, M. J.; Lin, H.; Judge, P. G. Bibcode: 2016ApJ...833....5S Altcode: 2016arXiv161005332S The variation of the vector magnetic field along structures in the solar corona remains unmeasured. Using a unique combination of spectropolarimetry and stereoscopy, we infer and compare the vector magnetic field structure and three-dimensional morphology of an individuated coronal loop structure undergoing a thermal instability. We analyze spectropolarimetric data of the He I λ10830 triplet (1s2s{}3{S}1-1s2p{}3{P}{2,1,0}) obtained at the Dunn Solar Telescope with the Facility Infrared Spectropolarimeter on 2011 September 19. Cool coronal loops are identified by their prominent drainage signatures in the He I data (redshifts up to 185 km s-1). Extinction of EUV background radiation along these loops is observed by both the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory and the Extreme Ultraviolet Imager on board spacecraft A of the Solar Terrestrial Relations Observatory, and is used to stereoscopically triangulate the loop geometry up to heights of 70 Mm (0.1R Sun) above the solar surface. The He I polarized spectra along this loop exhibit signatures indicative of atomic-level polarization, as well as magnetic signatures through the Hanle and Zeeman effects. Spectropolarimetric inversions indicate that the magnetic field is generally oriented along the coronal loop axis, and provide the height dependence of the magnetic field intensity. The technique we demonstrate is a powerful one that may help better understand the thermodynamics of coronal fine-structure magnetism. Title: Estimates Of Magnetic Plage Filling Factors Using The Cn Band Authors: Saar, Steven H.; Judge, Philip Bibcode: 2016csss.confE.151S Altcode: The 388nm CN band (like the better known "G band" of CH) is used in the Sun to locate strong magnetic concentrations. Magnetic network and plage are bright in these molecular bands, since the enhanced chromospheric heating there destroys the molecule, erasing its absorption and allowing the continuum to shine through. We take advantage of this to estimate the filling factor of strong fields in active dwarf stars. CN band depths in active stars can be compared with those of inactive stars of very similar temperature and metallicity, and after an adjustment for line-blanketing, used to estimate a magnetic plage filling factor. We estimate filling factors for a two stars, and compare them to direct Stokes I line-broadening measurements. Limitations, caveats, and future directions are briefly considered. Title: On the Fine Structure Splitting of the 3p43d 4D5/2 and 3p43d 4D7/2 Levels of Fe X Authors: Judge, Philip G.; Hutton, Roger; Li, Wenxian; Brage, Tomas Bibcode: 2016ApJ...833..185J Altcode: We study UV spectra obtained with the SO82-B slit spectrograph on board SKYLAB to estimate the fine structure (FS) splitting of the Cl-like 3{{{p}}}43{{d}}{}4{{{D}}}5/2 and 3{{{p}}}43{{d}}{}4{{{D}}}7/2 levels of Fe x. The splitting is of interest because the Zeeman effect mixes these levels, producing a “magnetically induced transition” (MIT) from 3{{{p}}}43{{d}}{}4{{{D}}}7/2 to 3{{{p}}}5{}2{{{P}}}3/2{{o}} for modest magnetic field strengths characteristic of the active solar corona. We estimate the splitting using the Ritz combination formula applied to two lines in the UV region of the spectrum close to 1603.2 Å, which decay from the level 3{{{p}}}4{(}1{{D}})3{{d}}{}2{{{G}}}7/2 to these two lower levels. The MIT and accompanying spin-forbidden transition lie near 257 Å. By careful inspection of a deep exposure obtained with the S082B instrument, we derive a splitting of ≲ 7+/- 3 cm-1. The upper limit arises because of a degeneracy between the effects of non-thermal line broadening and FS splitting for small values of the latter parameter. Although the data were recorded on photographic film, we solved for optimal values of line width and splitting of 8.3 ± 0.9 and 3.6 ± 2.7 cm-1. Title: An airborne infrared spectrometer for solar eclipse observations Authors: Samra, Jenna; Cheimets, Peter; DeLuca, Edward; Galeros, John; Gauron, Thomas; Golub, Leon; Guth, Giora; Hertz, Edward; Judge, Philip; Koutchmy, Serge; Marquez, Vanessa Bibcode: 2016SPIE.9908E..5US Altcode: This paper presents the design of an innovative solar spectrometer that will y on the NSF/NCAR Gulfstream V High-Performance Instrumented Airborne Platform for Environmental Research (GV HIAPER) during the 2017 solar eclipse. The airborne infrared spectrometer (AIR-Spec) is groundbreaking in two aspects: it will image infrared coronal emission lines that have never been measured, and it will bring high resolution imaging to GV HIAPER. The instrument development faces the challenges of achieving adequate resolution and signal-to-noise ratio in a compact package mounted to a noisy moving platform. To ensure that AIR-Spec meets its research goals, the instrument is undergoing pre-flight modeling and testing. The results are presented with reference to the instrument requirements. Title: An Airborne Infrared Spectrometer for Solar Eclipse Observations Authors: Samra, Jenna; DeLuca, Edward; Golub, Leon; Cheimets, Peter; Judge, Philip Bibcode: 2016shin.confE.155S Altcode: The airborne infrared spectrometer (AIR-Spec) is an innovative solar spectrometer that will observe the 2017 solar eclipse from the NSF/NCAR High-Performance Instrumented Airborne Platform for Environmental Research (HIAPER). AIR-Spec will image five infrared coronal emission lines to determine whether they may be useful probes of coronal magnetism.

The solar magnetic field provides the free energy that controls coronal heating, structure, and dynamics. Energy stored in coronal magnetic fields is released in flares and coronal mass ejections and ultimately drives space weather. Therefore, direct coronal field measurements have significant potential to enhance understanding of coronal dynamics and improve solar forecasting models. Of particular interest are observations of field lines in the transitional region between closed and open flux systems, providing important information on the origin of the slow solar wind.

While current instruments routinely observe only the photospheric and chromospheric magnetic fields, AIR-Spec will take a step toward the direct observation of coronal fields by measuring plasma emission in the infrared at high spatial and spectral resolution. During the total solar eclipse of 2017, AIR-Spec will search for five magnetically sensitive coronal emission lines between 1.4 and 4 μm from the HIAPER Gulfstream V at an altitude above 14.9 km. The instrument will measure emission line intensity, width, and Doppler shift, map the spatial distribution of infrared emitting plasma, and search for waves in the emission line velocities.

AIR-Spec consists of an optical system (feed telescope, grating spectrometer, and infrared detector) and an image stabilization system, which uses a fast steering mirror to correct the line-of-sight for platform perturbations. To ensure that the instrument meets its research goals, both systems are undergoing extensive performance modeling and testing. These results are shown with reference to the science requirements. Title: The March 11, 2015 X2.1 flare: peculiar post-flare spectral signatures Authors: Lacatus, Daniela Adriana; Donea, A.; Judge, P. G. Bibcode: 2016shin.confE.207L Altcode: The only X-class flare of 2015 observed by IRIS occurred at 16:22 UT on 11 March 2015, in AR 12297. This flare generated significant seismic transients in the photosphere at the eastern location of the flare. IRIS observations of the chromosphere and transition region help us understand the physics of the sunquake. In this work we will analyze this event using data from IRIS, SDO, and RHESSI. Unfortunately, the IRIS rasters scanned the area between the main footpoints of the solar flare. Whereas, the main X-ray emission dominates the eastern footprint. Significant enhancements in the chromospheric and TR lines intensities were measured. The forbidden line of Fe XXI 1354.1 Å is detected after the flare peak. Important plasma downflows were identified in the majority of the observed lines, consistent with magnetic field reconfiguration. An erupting filament develops at 16:12 UT and moves rapidly towards the eastern part of the active region. Title: HST/COS FUV Spectrophotometry of the Key Binary Solar Twins 16 Cyg A&B: Astrophysical Laboratories for the Future Sun and Older Solar Analogs Authors: Guinan, Edward F.; Dewarf, Laurence; Engle, Scott G.; Judge, Philip G.; Metcalfe, Travis S. Bibcode: 2016hst..prop13861G Altcode: The fortuitous location of the wide G1.5V/G2.5V binary 16 Cyg A&B as the brightest stars in the Kepler Field is a "game changer," permitting the determination of the stars' fundamental properties from asteroseismolgy analyses. Recent studies returned precise determinations of the stars' basic properties including masses and age (6.8+/-0.4 Gyr), along with the rotation periods. Thus, 16 Cyg A&B are now the oldest solar-mass analogs with reliable ages and physical properties. Only the Sun has better determined physical properties. 16 Cyg A&B now serve as old-age anchors for Rotation-Age-Activity-Irradiance relations (and Gyrochronology studies) for solar-type stars. Extensive Ca II HK spectrophotometry reveals low levels of chromospheric emission are below the lowest values for our Sun. These stars serve as critical test beds for studying solar/stellar dynamos for stars less active than the Sun. These advances have catapulted 16 Cyg A&B into a prominent place in solar/stellar astrophysics for studying the evolution, internal structure, magnetic dynamos, angular momentum loss, and FUV irradiances of old solar-mass stars. Although 16 Cyg has been observed from X-ray - IR, there are no observations in the FUV region where most of the crucial diagnostic chromospheric & transition region emissions occur. We request COS FUV medium resolution (G130M, G160M) spectra (six orbits/star). This permits the important FUV (1150-1750A) line emission strengths, profiles and Doppler shifts to be analyzed and compared with the Sun and other solar-analogs. This program is complemented by Ca II HK, high precision uvby observations, and by proposed Chandra X-ray coronal observations. Title: Airborne Infrared Spectrograph for Eclipse Observations Authors: Golub, L.; Cheimets, P.; DeLuca, E. E.; Samra, J.; Judge, P. G. Bibcode: 2015AGUFMSH51C2454G Altcode: Direct measurements of the coronal magnetic field have significant potential to enhance our understanding of coronal dynamics, and improve forecasting models. Of particular interest are observations of coronal field lines in the Transition Corona, the transitional region between closed and open flux systems, providing important information on eruptive instabilities and on the origin of the slow solar wind. While current instruments routinely observe the photospheric and chromospheric magnetic fields, the proposed airborne spectrometer will take a step toward the direct observation of coronal fields by measuring plasma emission in the infrared at high spatial and spectral resolution. The targeted lines are five forbidden magnetic dipole transitions between 1.4 and 4 um. The airborne system will consist of a telescope, grating spectrometer and pointing/stabilization system to be flown on the NSF/NCAR High-performance Instrumented Airborne Platform for Environmental Research (HIAPER) during the 21 August 2017 total solar eclipse. We will discuss the scientific objectives of the 2017 flight, describe details of the instrument design, and present the observing program for the eclipse. Title: On Helium 1083 nm Line Polarization during the Impulsive Phase of an X1 Flare Authors: Judge, Philip G.; Kleint, Lucia; Sainz Dalda, Alberto Bibcode: 2015ApJ...814..100J Altcode: 2015arXiv151009218J We analyze spectropolarimetric data of the He i 1083 nm multiplet (1s2s{}3{S}1-1s2p{}3{P}2,1,0o) during the X1 flare SOL2014-03-29T17:48, obtained with the Facility Infrared Spectrometer (FIRS) at the Dunn Solar Telescope. While scanning active region NOAA 12017, the FIRS slit crossed a flare ribbon during the impulsive phase, when the helium line intensities turned into emission at ≲twice the continuum intensity. Their linear polarization profiles are of the same sign across the multiplet including 1082.9 nm, intensity-like, at ≲5% of the continuum intensity. Weaker Zeeman-induced linear polarization is also observed. Only the strongest linear polarization coincides with hard X-ray (HXR) emission at 30-70 keV observed by RHESSI. The polarization is generally more extended and lasts longer than the HXR emission. The upper J = 0 level of the 1082.9 nm component is unpolarizable thus, lower-level polarization is the culprit. We make non-LTE radiative transfer calculations in thermal slabs optimized to fit only intensities. The linear polarizations are naturally reproduced, through a systematic change of sign with wavelength of the radiation anisotropy when slab optical depths of the 1082.9 component are ≲1. Neither are collisions with beams of particles needed, nor can they produce the same sign of polarization of the 1082.9 and 1083.0 nm components. The He i line polarization merely requires heating sufficient to produce slabs of the required thickness. Widely different polarizations of Hα, reported previously, are explained by different radiative anisotropies arising from slabs of different optical depths. Title: UV Spectra, Bombs, and the Solar Atmosphere Authors: Judge, Philip G. Bibcode: 2015ApJ...808..116J Altcode: 2015arXiv150608336J A recent analysis of UV data from the Interface Region Imaging Spectrograph (IRIS) reports plasma “bombs” with temperatures near 8 × 104 K within the solar photosphere. This is a curious result, first because most bomb plasma pressures p (the largest reported case exceeds 103 dyn cm-2) fall well below photospheric pressures (\gt 7× {10}3), and second, UV radiation cannot easily escape from the photosphere. In the present paper the IRIS data is independently analyzed. I find that the bombs arise from plasma originally at pressures between ≤ 80 and 800 dyne cm-2 before explosion, i.e., between ≥ 850 and 550 km above {τ }500=1. This places the phenomenon’s origin in the low-mid chromosphere or above. I suggest that bomb spectra are more compatible with Alfvénic turbulence than with bi-directional reconnection jets. Title: Century-long monitoring of solar irradiance and Earth's albedo using a stable scattering target in space. Authors: Judge, P. G.; Egeland, R. Bibcode: 2015MNRAS.448L..90J Altcode: 2015arXiv150101253J An inert sphere of a few metres diameter, placed in a special stable geosynchronous orbit in perpetuo, can be used for a variety of scientific experiments. Ground-based observations of such a sphere, `GeoSphere', can resolve very difficult problems in measuring the long-term solar irradiance. GeoSphere measurements will also help us understand the evolution of Earth's albedo and climate over at least the next century. Title: Photon Mean Free Paths, Scattering, and Ever-Increasing Telescope Resolution Authors: Judge, P. G.; Kleint, L.; Uitenbroek, H.; Rempel, M.; Suematsu, Y.; Tsuneta, S. Bibcode: 2015SoPh..290..979J Altcode: 2014arXiv1409.7866J; 2015SoPh..tmp....3J We revisit an old question: what are the effects of observing stratified atmospheres on scales below a photon mean free path λ? The mean free path of photons emerging from the solar photosphere and chromosphere is ≈ 102 km. Using current 1 m-class telescopes, λ is on the order of the angular resolution. But the Daniel K. Inoue Solar Telescope will have a diffraction limit of 0.020″ near the atmospheric cutoff at 310 nm, corresponding to 14 km at the solar surface. Even a small amount of scattering in the source function leads to physical smearing due to this solar "fog", with effects similar to a degradation of the telescope point spread function. We discuss a unified picture that depends simply on the nature and amount of scattering in the source function. Scalings are derived from which the scattering in the solar atmosphere can be transcribed into an effective Strehl ratio, a quantity useful to observers. Observations in both permitted (e.g., Fe I 630.2 nm) and forbidden (Fe I 525.0 nm) lines will shed light on both instrumental performance as well as on small-scale structures in the solar atmosphere. Title: On the Origin of a Sunquake during the 2014 March 29 X1 Flare Authors: Judge, Philip G.; Kleint, Lucia; Donea, Alina; Sainz Dalda, Alberto; Fletcher, Lyndsay Bibcode: 2014ApJ...796...85J Altcode: 2014arXiv1409.6268J Helioseismic data from the Helioseismic Magnetic Imager instrument have revealed a sunquake associated with the X1 flare SOL2014-03-29T17:48 in active region NOAA 12017. We try to discover if acoustic-like impulses or actions of the Lorentz force caused the sunquake. We analyze spectropolarimetric data obtained with the Facility Infrared Spectrometer (FIRS) at the Dunn Solar Telescope (DST). Fortunately, the FIRS slit crossed the flare kernel close to the acoustic source during the impulsive phase. The infrared FIRS data remain unsaturated throughout the flare. Stokes profiles of lines of Si I 1082.7 nm and He I 1083.0 nm are analyzed. At the flare footpoint, the Si I 1082.7 nm core intensity increases by a factor of several, and the IR continuum increases by 4% ± 1%. Remarkably, the Si I core resembles the classical Ca II K line's self-reversed profile. With nLTE radiative models of H, C, Si, and Fe, these properties set the penetration depth of flare heating to 100 ± 100 km (i.e., photospheric layers). Estimates of the non-magnetic energy flux are at least a factor of two less than the sunquake energy flux. Milne-Eddington inversions of the Si I line show that the local magnetic energy changes are also too small to drive the acoustic pulse. Our work raises several questions. Have we missed the signature of downward energy propagation? Is it intermittent in time and/or non-local? Does the 1-2 s photospheric radiative damping time discount compressive modes?

The National Center for Atmospheric Research is sponsored by the National Science Foundation. Title: A Flare Observed in Coronal, Transition Region, and Helium I 10830 Å Emissions Authors: Zeng, Zhicheng; Qiu, Jiong; Cao, Wenda; Judge, Philip G. Bibcode: 2014ApJ...793...87Z Altcode: 2014arXiv1408.0236Z On 2012 June 17, we observed the evolution of a C-class flare associated with the eruption of a filament near a large sunspot in the active region NOAA 11504. We obtained high spatial resolution filtergrams using the 1.6 m New Solar Telescope at the Big Bear Solar Observatory in broadband TiO at 706 nm (bandpass: 10 Å) and He I 10830 Å narrow band (bandpass: 0.5 Å, centered 0.25 Å to the blue). We analyze the spatio-temporal behavior of the He I 10830 Å data, which were obtained over a 90''×90'' field of view with a cadence of 10 s. We also analyze simultaneous data from the Atmospheric Imaging Assembly and Extreme Ultraviolet Variability Experiment instruments on board the Solar Dynamics Observatory spacecraft, and data from the Reuven Ramaty High Energy Solar Spectroscopic Imager and GOES spacecrafts. Non-thermal effects are ignored in this analysis. Several quantitative aspects of the data, as well as models derived using the "0D" enthalpy-based thermal evolution of loops model code, indicate that the triplet states of the 10830 Å multiplet are populated by photoionization of chromospheric plasma followed by radiative recombination. Surprisingly, the He II 304 Å line is reasonably well matched by standard emission measure calculations, along with the C IV emission which dominates the Atmosphere Imaging Assembly 1600 Å channel during flares. This work lends support to some of our previous work combining X-ray, EUV, and UV data of flares to build models of energy transport from corona to chromosphere. Title: Detection of Supersonic Downflows and Associated Heating Events in the Transition Region above Sunspots Authors: Kleint, L.; Antolin, P.; Tian, H.; Judge, P.; Testa, P.; De Pontieu, B.; Martínez-Sykora, J.; Reeves, K. K.; Wuelser, J. P.; McKillop, S.; Saar, S.; Carlsson, M.; Boerner, P.; Hurlburt, N.; Lemen, J.; Tarbell, T. D.; Title, A.; Golub, L.; Hansteen, V.; Jaeggli, S.; Kankelborg, C. Bibcode: 2014ApJ...789L..42K Altcode: 2014arXiv1406.6816K Interface Region Imaging Spectrograph data allow us to study the solar transition region (TR) with an unprecedented spatial resolution of 0.''33. On 2013 August 30, we observed bursts of high Doppler shifts suggesting strong supersonic downflows of up to 200 km s-1 and weaker, slightly slower upflows in the spectral lines Mg II h and k, C II 1336, Si IV 1394 Å, and 1403 Å, that are correlated with brightenings in the slitjaw images (SJIs). The bursty behavior lasts throughout the 2 hr observation, with average burst durations of about 20 s. The locations of these short-lived events appear to be the umbral and penumbral footpoints of EUV loops. Fast apparent downflows are observed along these loops in the SJIs and in the Atmospheric Imaging Assembly, suggesting that the loops are thermally unstable. We interpret the observations as cool material falling from coronal heights, and especially coronal rain produced along the thermally unstable loops, which leads to an increase of intensity at the loop footpoints, probably indicating an increase of density and temperature in the TR. The rain speeds are on the higher end of previously reported speeds for this phenomenon, and possibly higher than the free-fall velocity along the loops. On other observing days, similar bright dots are sometimes aligned into ribbons, resembling small flare ribbons. These observations provide a first insight into small-scale heating events in sunspots in the TR. Title: CLE: Coronal line synthesis Authors: Judge, Philip G.; Casini, Roberto Bibcode: 2014ascl.soft07010J Altcode: CLE, written in Fortran 77, synthesizes Stokes profiles of forbidden lines such as Fe XIII 1074.7nm, formed in magnetic dipole transitions under coronal conditions. The lines are assumed to be optically thin, excited by (anisotropic) photospheric radiation and thermal particle collisions. Title: A particular seismic event generated during the solar flare 2014 March 29 Authors: Donea, Alina C.; Judge, P.; Kleint, L.; Sainz-Dalda, Alberto Bibcode: 2014shin.confE..49D Altcode: The X1.3 solar flare of 2014 March 29 from AR 2017 was extremely well observed, from both space and the ground. Helioseismic observations from the Helioseismic Magnetic Imager (HMI) aboard the Solar Dynamics Observatory (SDO) indicate that this flare generated a weak seismic transient. All previous strong seismic transients to date have emanated from sunspot penumbrae, but the source of this transient lay outside the active-region penumbra close to a magnetic pore.

Uniquely, Kleint and Sainz Dalda captured ground based imaging and slit spectropolarimetry of this flare using the IBIS and FIRS instruments respectively, at the Dunn Solar Telescope in Sunspot, New Mexico. Here we report only on FIRS data along with space-based data, IBIS data will be reported elsewhere. The FIRS infrared data are not saturated even during the flare, which was observed through the rise and decay phases. We are still investigating the origins of peculiar, Zeeman-induced polarization in the He I 1083 nm multiplet.

Using spectropolarimetric data of Si I and He I lines from FIRS, we investigate the evolution of both photosphere and chromosphere above and around the seismic source. Together with data from AIA and from RHESSI, these data offer unique new insight into how the flare energy is channeled into and through the photosphere into the Sun's interior as a seismic transient. We present acoustic properties of the seismic event and their relationship to photospheric and chromospheric plasma and magnetic fields from FIRS, and to the evolving plasmas seen from space from UV to X-ray wavelengths. Title: Insights on the solar dynamo from stellar observations Authors: Egeland, Ricky; Martens, Petrus C.; Judge, Philip G. Bibcode: 2014AAS...22421105E Altcode: A successful dynamo model should not only explain the broad characteristics of the magnetic field cycle for the Sun (22-year sunspot cycle with polarity reversals, migration of active latitudes toward the poles throughout the cycle, and Joy’s law), but should also be able to explain the cycling behavior observed in Solar-analog stars, which are very close to the Sun in essential characteristics. Our aim is to develop a set of constraints on dynamo models from the observed behavior of solar-analog stars obtained from a number of long-running synoptic surveys of cycling activity (Mount Wilson Observatory HK survey, Lowel Observatory Solar-Stellar Spectrograph, and the Fairborn Observatory Automatic Photoelectric Telescope survey), in conjuncture with stellar rotation and differential rotation data obtained by the Kepler Mission and other sources. By carefully piecing together the best data available today, we will provide an improved understanding of the parameter space in which Solar-like dynamos operate. Title: A FLARE OBSERVED IN CORONAL, TRANSITION REGION AND HELIUM I 10830 Å EMISSIONS Authors: Zeng, Zhicheng; Qiu, Jiong; Cao, Wenda; Judge, Philip G. Bibcode: 2014AAS...22412309Z Altcode: On June 17, 2012, we observed the evolution of a C-class flare associated with the eruption of a filament near a large sunspot in the active region NOAA 11504. We obtained high spatial resolution filtergrams using the 1.6 m New Solar Telescope at the Big Bear Solar Observatory in TiO broad-band (bandpass: 10 Å)and He I 10830 Å narrow-band (bandpass: 0.5 Å, centered 0.25 Å to the blue). We analyze the spatio-temporal behavior of the He I 10830 Å data, which were obtained over a 90×90 arcsends field of view with a cadence of 10 sec. We also analyze simultaneous data from the Atmospheric Imaging Assembly and Extreme Ultraviolet Variability Experiment instruments on board the Solar Dynamics Observatoryspacecraft, and data from Reuven Ramaty High Energy Solar Spectroscopic Imager and GOES spacecrafts. Several quantitative aspects of the data, as well as models derived using the “0D” Enthalpy-Based Thermal Evolution of Loops model (EBTEL: Klimchuk et al. 2008) code, indicate that the 10830 Å multiplet is formed primarily by photoionization of chromospheric plasma followed by radiative recombination. Surprisingly, the He II 304 Å line is reasonably well matched by standard emission measure calculations, along with the C IV emission which dominates the AIA 1600 Å channel during flares. This work lends support to some of our previous work combining X-ray, EUV and UV data of flares to buildmodels of energy transport from corona to chromosphere. Title: Single-point Inversion of the Coronal Magnetic Field Authors: Plowman, Joseph; Casini, Roberto; Judge, Philip G.; Tomczyk, Steven Bibcode: 2014AAS...22432324P Altcode: The Fe XIII 10747 and 10798 Å lines observed in the solar corona are sensitive to the coronal magnetic field in such a way that, in principle, the full vector field at a point on the line of sight can be inferred from their combined polarization signals. This paper presents analytical inversion formulae for the field parameters and analyzes the uncertainty of magnetic field measurements made from such observations, assuming emission dominated by a single region along the line-of-sight. We consider the case of the current CoMP instrument as well as the future COSMO and ATST instruments. Uncertainties are estimated with a direct analytic inverse and with an MCMC algorithm. We find that (in effect) two components of the vector field can be recovered with CoMP, and well-recovered with COSMO or ATST, but that the third component can only be recovered when the solar magnetic field is strong and optimally oriented. Title: Spectropolarimetric Observations of a Small Active Region with IBIS Authors: Tarr, Lucas; Judge, Philip G. Bibcode: 2014AAS...22442204T Altcode: We have used the Interferometric BI--dimensional Spectrograph (IBIS) instrument at the Dunn Solar Telescope to measure the polarimetric Stokes IQUV signals for the small active region, NOAA 11304. We used three lines generally corresponding to three atmospheric heights ranging from the photosphere to low corona: Fe I 6302Å, NaI 5896Å, and CaII 8542Å. Each set of profiles has been inverted using the NICOLE code to determine the vector magnetic field at the three heights throughout the field of view, or the line--of--sight field, as allowed by the level of polarization signal. Comparisons are made between the magnetic and thermal structures with the goal of constraining chromospheric models with the information obtained at multiple heights. Title: FORWARD: Forward modeling of coronal observables Authors: Gibson, Sarah E.; Kucera, Therese A.; Casini, Roberto; Dove, James; Forland, Blake; Judge, Philip; Rachmeler, Laurel Bibcode: 2014ascl.soft05007G Altcode: 2014ascl.soft05007F FORWARD forward models various coronal observables and can access and compare existing data. Given a coronal model, it can produce many different synthetic observables (including Stokes polarimetry), as well as plots of model plasma properties (density, magnetic field, etc.). It uses the CHIANTI database (ascl:9911.004) and CLE polarimetry synthesis code, works with numerical model datacubes, interfaces with the PFSS module of SolarSoft (ascl:1208.013), includes several analytic models, and connects to the Virtual Solar Observatory for downloading data in a format directly comparable to model predictions. Title: The Solar Chromosphere Observed at 1 Hz and 0.''2 Resolution Authors: Lipartito, Isabel; Judge, Philip G.; Reardon, Kevin; Cauzzi, Gianna Bibcode: 2014ApJ...785..109L Altcode: 2014arXiv1401.4474L We recently reported extremely rapid changes in chromospheric fine structure observed using the IBIS instrument in the red wing of Hα. Here, we examine data obtained during the same observing run (2010 August 7), of a mature active region NOAA 11094. We analyze more IBIS data including wavelength scans and data from the Solar Dynamics Observatory, all from within a 30 minute interval. Using a slab radiative transfer model, we investigate the physical nature of fibrils in terms of tube-like versus sheet-like structures. Principal Component Analysis shows that the very rapid Hα variations in the line wings depend mostly on changes of line width and line shift, but for Ca II 854.2 the variations are dominated by changes in column densities. The tube model must be rejected for a small but significant class of fibrils undergoing very rapid changes. If our wing data arise from the same structures leading to "type II spicules," our analysis calls into question much recent work. Instead, the data do not reject the hypothesis that some fibrils are optical superpositions of plasma collected into sheets. We review how Parker's theory of tangential discontinuities naturally leads to plasma collecting into sheets, and show that the sheet picture is falsifiable. Chromospheric fine structures seem to be populated by both tubes and sheets. We assess the merits of spectral imaging versus slit spectroscopy for future studies. Title: From Forbidden Coronal Lines to Meaningful Coronal Magnetic Fields Authors: Judge, P. G.; Habbal, S.; Landi, E. Bibcode: 2013SoPh..288..467J Altcode: 2013arXiv1304.3863J We review methods to measure magnetic fields within the corona using the polarized light in magnetic-dipole (M1) lines. We are particularly interested in both the global magnetic-field evolution over a solar cycle, and the local storage of magnetic free energy within coronal plasmas. We address commonly held skepticisms concerning angular ambiguities and line-of-sight confusion. We argue that ambiguities are, in principle, no worse than more familiar remotely sensed photospheric vector fields, and that the diagnosis of M1 line data would benefit from simultaneous observations of EUV lines. Based on calculations and data from eclipses, we discuss the most promising lines and different approaches that might be used. We point to the S-like [Fe XI] line (J=2 to J=1) at 789.2 nm as a prime target line (for the Advanced Technology Solar Telescope (ATST) for example) to augment the hotter 1074.7 and 1079.8 nm Si-like lines of [Fe XIII] currently observed by the Coronal Multi-channel Polarimeter (CoMP). Significant breakthroughs will be made possible with the new generation of coronagraphs, in three distinct ways: i) through single-point inversions (which encompasses also the analysis of MHD wave modes), ii) using direct comparisons of synthetic MHD or force-free models with polarization data, and iii) using tomographic techniques. Title: Using large telescopes to answer: why must the Sun have a chromosphere and corona? Authors: Judge, P.; Casini, R. Bibcode: 2012IAUSS...6E.106J Altcode: I will discuss the potential for ground-based telescopes such as the ATST to make breakthrough discoveries about the long standing mysteries of the solar chromosphere and corona. The biggest advances will hinge upon the ability to diagnose magnetic fields through high s/n spectropolarimetry. Title: Removal of Spectro-polarimetric Fringes by Two-dimensional Pattern Recognition Authors: Casini, R.; Judge, P. G.; Schad, T. A. Bibcode: 2012ApJ...756..194C Altcode: 2012arXiv1208.5104C We present a pattern-recognition-based approach to the problem of the removal of polarized fringes from spectro-polarimetric data. We demonstrate that two-dimensional principal component analysis can be trained on a given spectro-polarimetric map in order to identify and isolate fringe structures from the spectra. This allows us, in principle, to reconstruct the data without the fringe component, providing an effective and clean solution to the problem. The results presented in this paper point in the direction of revising the way that science and calibration data should be planned for a typical spectro-polarimetric observing run. Title: Analysis of Seeing-induced Polarization Cross-talk and Modulation Scheme Performance Authors: Casini, R.; de Wijn, A. G.; Judge, P. G. Bibcode: 2012ApJ...757...45C Altcode: 2011arXiv1107.0367C We analyze the generation of polarization cross-talk in Stokes polarimeters by atmospheric seeing, and its effects on the noise statistics of spectropolarimetric measurements for both single-beam and dual-beam instruments. We investigate the time evolution of seeing-induced correlations between different states of one modulation cycle and compare the response to these correlations of two popular polarization modulation schemes in a dual-beam system. Extension of the formalism to encompass an arbitrary number of modulation cycles enables us to compare our results with earlier work. Even though we discuss examples pertinent to solar physics, the general treatment of the subject and its fundamental results might be useful to a wider community. 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: Evidence for Sheet-like Elementary Structures in the Sun's Atmosphere? Authors: Judge, Philip G.; Reardon, Kevin; Cauzzi, Gianna Bibcode: 2012ApJ...755L..11J Altcode: Narrow, thread-like structures in the Sun's chromosphere are currently understood to be plasma guided along narrow tubes of magnetic flux. We report on 1 s cadence imaging spectroscopic measurements of the Hα line with the IBIS Fabry-Pérot instrument at the Dunn Solar Telescope, obtained +0.11 nm from line center. Rapid changes grossly exceeding the Alfvén speed are commonly seen along the full extent of many chromospheric threads. We argue that only an optical superposition effect can reasonably explain the data, analogous to striations of curtains blowing in the wind. Other explanations appear to require significant contrivances to avoid contradicting various aspects of the data. We infer that the absorbing plasma exists in two-dimensional sheet-like structures within the three-dimensional magnetofluid, related perhaps to magnetic tangential discontinuities. This interpretation demands a re-evaluation of basic assumptions about low-β solar plasmas, as advocated by Parker, with broader implications in astrophysics and plasma physics. Diverse, high-cadence observations are needed to further define the relationship between magnetic field and thermal fine structure. Title: Solar and stellar activity: diagnostics and indices Authors: Judge, Philip G.; Thompson, Michael J. Bibcode: 2012IAUS..286...15J Altcode: 2012arXiv1201.4625J We summarize the fifty-year concerted effort to place the ``activity'' of the Sun in the context of the stars. As a working definition of solar activity in the context of stars, we adopt those globally-observable variations on time scales below thermal time scales, of ~105 yr for the convection zone. So defined, activity is dominated by magnetic-field evolution, including the 22-year Hale cycle, the typical time it takes for the quasi-periodic reversal in which the global magnetic-field takes place. This is accompanied by sunspot variations with 11 year periods, known since the time of Schwabe, as well as faster variations due to rotation of active regions and flaring. ``Diagnostics and indices'' are terms given to the indirect signatures of varying magnetic-fields, including the photometric (broad-band) variations associated with the sunspot cycle, and variations of the accompanying heated plasma in higher layers of stellar atmospheres seen at special optical wavelengths, and UV and X-ray wavelengths. Our attention is also focussed on the theme of the Symposium by examining evidence for deep and extended minima of stars, and placing the 70-year long solar Maunder Minimum into a stellar context. Title: Spectropolarimetry of a Limb Active Region and its Cool Coronal Structures Authors: Judge, Philip G.; Kleint, L.; Casini, R.; Schad, T. Bibcode: 2012AAS...22052119J Altcode: During the SDO mission we have regularly used the IBIS and FIRS spectropolarimeters at the Dunn Solar Telescope to measure magnetic fields and plasma parameters from photosphere up to the coronal base. Here we analyze data of a region at and above the east limb (later named NOAA 11302) obtained on September 22nd 2011. The measurements show an erupting prominence, remarkably uniform cool plumes and some material seemingly draining into the active region along post-flare loops. The imaging Fabry-Perot instrument IBIS obtained 30 scans of intensity spectra (30s cadence) and 40 scans of Stokes parameters (90s cadence) in lines of Fe I 630 nm, Na I 596 nm, Ca II 852 nm and H-alpha 656 nm, with an angular resolution near 0.2", over a 40"x80" field of view. The FIRS slit was scanned across the solar image to obtain Stokes profiles including lines of Si I 1028.7 nm and He I 1083 nm. We obtained 3 FIRS scans covering a 90"x75" area with cadences of between half an hour and an hour simultaneously with IBIS, at a lower angular resolution. Simultaneous broad band Ca II K and G-band data were obtained with a cadence of 5s. We discuss the vector magnetic fields and plasma properties of NOAA 11302, with emphasis on cool

plasma structures extending many Mm into the corona. Title: Radiating Current Sheets in the Solar Chromosphere Authors: Goodman, Michael L.; Judge, Philip G. Bibcode: 2012ApJ...751...75G Altcode: 2014arXiv1406.1211G An MHD model of a hydrogen plasma with flow, an energy equation, NLTE ionization and radiative cooling, and an Ohm's law with anisotropic electrical conduction and thermoelectric effects is used to self-consistently generate atmospheric layers over a 50 km height range. A subset of these solutions contains current sheets and has properties similar to those of the lower and middle chromosphere. The magnetic field profiles are found to be close to Harris sheet profiles, with maximum field strengths ~25-150 G. The radiative flux FR emitted by individual sheets is ~4.9 × 105-4.5 × 106 erg cm-2 s-1, to be compared with the observed chromospheric emission rate of ~107 erg cm-2 s-1. Essentially all emission is from regions with thicknesses ~0.5-13 km containing the neutral sheet. About half of FR comes from sub-regions with thicknesses 10 times smaller. A resolution <~ 5-130 m is needed to resolve the properties of the sheets. The sheets have total H densities ~1013-1015 cm-3. The ionization fraction in the sheets is ~2-20 times larger, and the temperature is ~2000-3000 K higher than in the surrounding plasma. The Joule heating flux FJ exceeds FR by ~4%-34%, the difference being balanced in the energy equation mainly by a negative compressive heating flux. Proton Pedersen current dissipation generates ~62%-77% of the positive contribution to FJ . The remainder of this contribution is due to electron current dissipation near the neutral sheet where the plasma is weakly magnetized. Title: Radiating Current Sheets in the Solar Chromosphere Authors: Goodman, Michael L.; Judge, P. G. Bibcode: 2012AAS...22052116G Altcode: An MHD model of a Hydrogen plasma with flow, an energy equation, NLTE ionization and radiative cooling, and an Ohm's law with anisotropic electrical conduction and thermoelectric effects is used to self-consistently generate atmospheric layers over a 50 km height range. A subset of these solutions contain current sheets, and have properties similar to those of the lower and middle chromosphere. The magnetic field profiles are found to be close to Harris sheet profiles, with maximum field strengths 25-150 G. The radiative flux F_R emitted by individual sheets is 4.9 x 10^5 - 4.5 x 10^6 ergs-cm^{-2}-s^{-1}, to be compared with the observed chromospheric emission rate of 10^7 ergs-cm^{-2}-s^{-1}. Essentially all emission is from regions with thicknesses 0.5 - 13 km containing the neutral sheet. About half of F_R comes from sub-regions with thicknesses 10 times smaller. A resolution < 5-130 m is needed to resolve the properties of the sheets. The sheets have total H densities 10^{13}-10^{15} cm^{-3}. The ionization fraction in the sheets is 2-20 times larger, and the temperature is 2000-3000 K higher than in the surrounding plasma. The Joule heating flux F_J exceeds F_R by 4-34 %, the difference being balanced in the energy equation mainly by a negative compressive heating flux. Proton Pedersen current dissipation generates 62-77 % of the positive contribution to F_J. The remainder of this contribution is due to electron current dissipation near the neutral sheet where the plasma is weakly magnetized. These solutions represent the first, first principles theoretical proof of the existence of radiating current sheets under chromospheric conditions. The existence of these solutions suggests the existence of sub-resolution, horizontal current sheets in the chromosphere that are sites of strong Joule heating driven radiative emission. Title: Key- or tomb- stones in the bridge from photosphere to corona? Authors: Judge, Philip G. Bibcode: 2012decs.confE..28J Altcode: The Sun's atmosphere must get from photospheric pressures of 10(5) dyn cm(-2) , where gas pressures and Reynolds stresses dominate, to coronal pressures of 10(-1) dyne cm(-2) , where magnetic stresses become dominant, within a mere 2000km. Outside of sunspots, the photospheric boundary layer exhibits hydrodynamic turbulent structure. The low pressure chromosphere- corona transition, while poorly understood, is clearly ordered by magnetic fields. Across the intervening scale heights, the richness of coupled magneto- hydrodynamics in a partially ionized atmosphere out of LTE, within which ions become magnetized, somehow leads to what we observe as the "magnetic chromosphere". We understand only the overall thermal structure of the chromosphere, it behaves as a thermostat: in response to heating energy is stored in latent heat of ionization and lost to radiation. But in terms of the magnetic structure, we must deal with: interaction with the plasma including multi-fluid effects, especially ion-neutral damping; effects of stratification on coupling wave modes; the existence of weak, discontinuous solutions to the MHD equations (current sheets). To generate discussion, I will argue that we have little idea what the chromosphere does to the incoming flux of EM energy from beneath, and that current generations of MHD models are far from providing this understanding. We must not let apparent "successes" of, e.g., potential field models on large scales seduce us into thinking we understand how the Sun makes the photosphere-corona transition. Title: The Connection of Type II Spicules to the Corona Authors: Judge, Philip G.; de Pontieu, Bart; McIntosh, Scott W.; Olluri, Kosovare Bibcode: 2012ApJ...746..158J Altcode: 2011arXiv1112.6174D; 2011arXiv1112.6174J We examine the hypothesis that plasma associated with "Type II" spicules is heated to coronal temperatures, and that the upward moving hot plasma constitutes a significant mass supply to the solar corona. One-dimensional hydrodynamical models including time-dependent ionization are brought to bear on the problem. These calculations indicate that heating of field-aligned spicule flows should produce significant differential Doppler shifts between emission lines formed in the chromosphere, transition region, and corona. At present, observational evidence for the computed 60-90 km s-1 differential shifts is weak, but the data are limited by difficulties in comparing the proper motion of Type II spicules with spectral and kinematic properties of an associated transition region and coronal emission lines. Future observations with the upcoming infrared interferometer spectrometer instrument should clarify if Doppler shifts are consistent with the dynamics modeled here. Title: Spectropolarimetry Of The Footpoints Of A C-class Flare In The Chromosphere Authors: Kleint, Lucia; Judge, P. Bibcode: 2011SPD....42.0308K Altcode: 2011BAAS..43S.0308K Flares are well-known solar phenomena but have rarely been imaged in high resolution polarimetry and even less often in the chromosphere. We observed the declining phase of a C-class flare in NOAA 10940 on January 29, 2007 with the IBIS instrument (0.17"/px), taking quasi-simultaneous spectropolarimetric images in the chromosphere (8542 [[Unable to Display Character: &#506]]) and in the photosphere (6302 [[Unable to Display Character: &#506]]).

Only the inner wings and core of the chromospheric line are seen to brighten in IBIS, the underlying photosphere remaining undisturbed. TRACE images reveal the connectivity of the chromospheric flaring plasma to the overlying corona: IBIS fortuitously captured the chromospheric flares associated with both footpoints of a loop systems seen in TRACE.

Our hour-long image sequence shows the evolution and weakening of the chromospheric flare, and reveals unresolved opposite magnetic field components with large velocities with respect to the average Sun. In the chromosphere, we find redshifted components but in the photosphere we see observe blueshifts. We will present high resolution movies of the flaring plasma seen in both footpoints of the loop system. We will discuss the implications of these measurements for models of the storage and release of energy for this class of small flare, and possible connections to the formation of the penumbra that appears later at this location. Title: A Ring of Polarized Light: Evidence for Twisted Coronal Magnetism in Cavities Authors: Dove, J. B.; Gibson, S. E.; Rachmeler, L. A.; Tomczyk, S.; Judge, P. Bibcode: 2011ApJ...731L...1D Altcode: Coronal prominence cavities may be manifestations of twisted or sheared magnetic fields capable of storing the energy required to drive solar eruptions. The Coronal Multi-Channel Polarimeter (CoMP), recently installed at Mauna Loa Solar Observatory, can measure polarimetric signatures of current-carrying magnetohydrodynamic (MHD) systems. For the first time, this instrument offers the capability of daily full-Sun observations of the forbidden lines of Fe XIII with high enough spatial resolution and throughput to measure polarimetric signatures of current-carrying MHD systems. By forward-calculating CoMP observables from analytic MHD models of spheromak-type magnetic flux ropes, we show that a predicted observable for such flux ropes oriented along the line of sight is a bright ring of linear polarization surrounding a region where the linear polarization strength is relatively depleted. We present CoMP observations of a coronal cavity possessing such a polarization ring. Title: Thermal Fine Structure and Magnetic Fields in the Solar Atmosphere: Spicules and Fibrils Authors: Judge, Philip G.; Tritschler, Alexandra; Chye Low, Boon Bibcode: 2011ApJ...730L...4J Altcode: 2011arXiv1102.1517J The relationship between observed structures in the solar atmosphere and the magnetic fields threading them is known only for the solar photosphere, even then imprecisely. We suggest that some of the fine structures in the more tenuous chromosphere and corona—specifically some populations of spicules and fibrils—correspond to warps in two-dimensional sheet-like structures, as an alternative to conventional interpretations in terms of tube-like structures. The sheets are perhaps related to magnetic tangential discontinuities, which Parker has argued arise naturally in low-β conditions. Some consequences of this suggestion, if it can be confirmed, are discussed. Title: A ring of polarized light: evidence for twisted coronal magnetism in cavities (Invited) Authors: Dove, J.; Rachmeler, L.; Gibson, S. E.; Judge, P. G.; Tomczyk, S. Bibcode: 2010AGUFMSH54A..01D Altcode: Determining coronal magnetic fields is crucial to modeling the processes that power and trigger solar flares and coronal mass ejections. Coronal prominence cavities have been modeled as magnetic flux ropes, and have been observed to erupt bodily as coronal mass ejections. One promising technique for establishing the magnetic morphology of cavities is to use spectropolarimetry of the infrared (IR) forbidden lines of Fe XIII (at 1074.7 nm and 1079.8 nm). The Coronal Multi-Channel Polarimeter is currently situated at the Mauna Loa Solar Observatory (MLSO), and has begun taking daily full-Sun observations of line-of-sight integrated Stokes parameters for these lines. For a variety of analytic coronal magnetohydrodynamic models, we have determined forward-calculations of CoMP observables using the formalism of Judge and Casini (2001). We show that different MHD models and orientations do yield distinguishing observational characteristics. In particular, a common characteristic for spheroidal flux ropes oriented along the observational line of sight is a ring of linear polarization surrounding a region where the linear polarization strength is relatively depleted (the heart of darkness). Such a polarization ring has been found in an observation of a coronal cavity taken by CoMP in April 2005 from Sacramento Peak. Cavities are ubiquitous features, particularly at this time of the solar cycle. The daily observations to be taken by CoMP at MLSO will allow us to further probe these structures, constraining models of coronal magnetism and providing a testbed for future capabilities of the proposed Coronal Solar Magnetism Observatory (COSMO). Title: Magnetic Field Measurements at the Photosphere and Coronal Base Authors: Judge, P. G.; Centeno, R.; Tritschler, A.; Uitenbroek, H.; Jaeggli, S.; Lin, H. Bibcode: 2010AGUFMSH31A1783J Altcode: We have obtained vector polarimetric measurements in lines of Fe I (630nm), Ca II (854nm) and He I (1083nm) of several active regions during 3-14 June 2010. The measurements were made at the Dunn Solar Telescope at Sacramento Peak Observatory, using the FIRS and IBIS instruments simultaneously. We discuss these and SDO data for NOAA 11076. The seeing was very good or excellent and the adaptive optics system functioned well. In this preliminary analysis we compare extrapolations of photospheric fields with the constraints available from Stokes polarimetry, including the morphology and kinematic properties of fibrils. Connections to the corona will also be discussed. The implications for field extrapolations from photospheric measurements will be discussed. We will make the reduced data freely available on the web for interested researchers. Title: Discovery of a 1.6 Year Magnetic Activity Cycle in the Exoplanet Host Star ι Horologii Authors: Metcalfe, T. S.; Basu, S.; Henry, T. J.; Soderblom, D. R.; Judge, P. G.; Knölker, M.; Mathur, S.; Rempel, M. Bibcode: 2010ApJ...723L.213M Altcode: 2010arXiv1009.5399M The Mount Wilson Ca HK survey revealed magnetic activity variations in a large sample of solar-type stars with timescales ranging from 2.5 to 25 years. This broad range of cycle periods is thought to reflect differences in the rotational properties and the depths of the surface convection zones for stars with various masses and ages. In 2007, we initiated a long-term monitoring campaign of Ca II H and K emission for a sample of 57 southern solar-type stars to measure their magnetic activity cycles and their rotational properties when possible. We report the discovery of a 1.6 year magnetic activity cycle in the exoplanet host star ι Horologii and obtain an estimate of the rotation period that is consistent with Hyades membership. This is the shortest activity cycle so far measured for a solar-type star and may be related to the short-timescale magnetic variations recently identified in the Sun and HD 49933 from helioseismic and asteroseismic measurements. Future asteroseismic observations of ι Hor can be compared to those obtained near the magnetic minimum in 2006 to search for cycle-induced shifts in the oscillation frequencies. If such short activity cycles are common in F stars, then NASA's Kepler mission should observe their effects in many of its long-term asteroseismic targets. Title: A Chromospheric Conundrum? Authors: Judge, Philip; Knölker, Michael; Schmidt, Wolfgang; Steiner, Oskar Bibcode: 2010ApJ...720..776J Altcode: 2010arXiv1007.1203J We examine spectra of the Ca II H line, obtained under good seeing conditions with the VTT Echelle Spectrograph in 2007 June, and higher resolution data of the Ca II λ8542 line from Fabry-Pérot instruments. The VTT targets were areas near disk center which included quiet Sun and some dispersed plage. The infrared data included quiet Sun and plage associated with small pores. Bright chromospheric network emission patches expand little with wavelength from line wing to line center, i.e., with increasing line opacity and height. We argue that this simple observation has implications for the force and energy balance of the chromosphere, since bright chromospheric network emission is traditionally associated with enhanced local mechanical heating which increases temperatures and pressures. Simple physical considerations then suggest that the network chromosphere may not be able to reach horizontal force balance with its surroundings, yet the network is a long-lived structure. We speculate on possible reasons for the observed behavior. By drawing attention to a potential conundrum, we hope to contribute to a better understanding of a long-standing unsolved problem: the heating of the chromospheric network. Title: On the Solar Chromosphere Observed at the LIMB with Hinode Authors: Judge, Philip G.; Carlsson, Mats Bibcode: 2010ApJ...719..469J Altcode: 2010arXiv1004.1398J Broadband images in the Ca II H line, from the Broadband Filter Imager (BFI) instrument on the Hinode spacecraft, show emission from spicules emerging from and visible right down to the observed limb. Surprisingly, little absorption of spicule light is seen along their lengths. We present formal solutions to the transfer equation for given (ad hoc) source functions, including a stratified chromosphere from which spicules emanate. The model parameters are broadly compatible with earlier studies of spicules. The visibility of Ca II spicules down to the limb in Hinode data seems to require that spicule emission be Doppler shifted relative to the stratified atmosphere, either by supersonic turbulent or organized spicular motion. The non-spicule component of the chromosphere is almost invisible in the broadband BFI data, but we predict that it will be clearly visible in high spectral resolution data. Broadband Ca II H limb images give the false impression that the chromosphere is dominated by spicules. Our analysis serves as a reminder that the absence of a signature can be as significant as its presence. Title: Magnetic field measurements at the photosphere and coronal base Authors: Judge, Philip; Centeno, R.; Tritschler, A.; Uitenbroek, H.; Jaeggli, S.; Lin, H. Bibcode: 2010shin.confE..56J Altcode: We have obtained vector polarimetric measurements in lines of Fe I (630nm), Ca II (854nm) and He I (1083) of several active regions during 3-14 June 2010. The measurements were made at the Dunn Solar Telescope at Sacramento Peak Observatory, using the FIRS and IBIS instruments simultaneously. We discuss data for NOAA 11076 observed on 4 June 2010. The seeing was very good or excellent and the adaptive optics system functioned well. In this preliminary analysis we compare linear extrapolations of photospheric fields with the constraints available from Stokes polarimetry, including the morphology and kinematic properties of fibrils. The implications for field extrapolations from photospheric measurements will be discussed. We will make the reduced data freely available on the web for interested researchers. Title: Forward modeling of spectropolarimetric data to interpret coronal magnetic features Authors: Rachmeler, Laurel A.; Gibson, S. E.; Dove, J.; Judge, P. G. Bibcode: 2010shin.confE..53R Altcode: We present a forward model that creates various forms of coronal observational data from simulated systems. Along with plane of sky parameter slices and integrated emission images, this model calculates the full Stokes vectors from forbidden infrared lines. It is clear that photospheric magnetograph data is not sufficient to ascertain coronal magnetic fields. The coronal Stokes vectors provide additional information about the magnetic morphology above the solar limb, specifically the relative strength of the integrated plane of sky and line of sight field. Our forward model helps to determine which physical features can be identified in the observations as a specific component of a theoretical model, without requiring a full 3D inversion of the Stokes profiles. We have found that flux ropes are theoretically identifiable in the simulated data, and we use this technique to explore the disambiguation of pre-CME filament structure. Title: Historical Eclipses and the Recent Solar Minimum Corona Authors: Judge, P. G.; Burkepile, J.; de Toma, G.; Druckmüller, M. Bibcode: 2010ASPC..428..171J Altcode: 2010arXiv1001.5278J We have studied the corona as seen at the eclipses of 1878, 1900, 1901, and others. These eclipses occurred during extended sunspot minimum conditions. We compare these data with those of the recent solar minimum corona, using data from the eclipses of July 22, 2009 and August 1, 2008. An attempt to characterize the global solar magnetic fields is made. We speculate on the origin of the non-dipolar structure seen in the 2008 and 2009 eclipse images. Title: Fabry-Pérot Versus Slit Spectropolarimetry of Pores and Active Network: Analysis of IBIS and Hinode Data Authors: Judge, Philip G.; Tritschler, Alexandra; Uitenbroek, Han; Reardon, Kevin; Cauzzi, Gianna; de Wijn, Alfred Bibcode: 2010ApJ...710.1486J Altcode: 2010arXiv1001.0561J We discuss spectropolarimetric measurements of photospheric (Fe I 630.25 nm) and chromospheric (Ca II 854.21 nm) spectral lines in and around small magnetic flux concentrations, including a pore. Our long-term goal is to diagnose properties of the magnetic field near the base of the corona. We compare ground-based two-dimensional spectropolarimetric measurements with (almost) simultaneous space-based slit spectropolarimetry. We address the question of noise and crosstalk in the measurements and attempt to determine the suitability of Ca II measurements with imaging spectropolarimeters for the determination of chromospheric magnetic fields. The ground-based observations were obtained 2008 May 20, with the Interferometric Bidimensional Spectrometer (IBIS) in spectropolarimetric mode operated at the Dunn Solar Telescope at Sunspot, NM. The space observations were obtained with the Spectro-Polarimeter of the Solar Optical Telescope aboard the Japanese Hinode satellite. The agreement between the near-simultaneous co-spatial IBIS and Hinode Stokes-V profiles at 630.25 nm is excellent, with V/I amplitudes compatible to within 1%. The IBIS QU measurements are affected by residual crosstalk from V, arising from calibration inaccuracies, not from any inherent limitation of imaging spectroscopy. We use a Principal Component Analysis to quantify the detected crosstalk. QU profiles with V crosstalk subtracted are in good agreement with the Hinode measurements, but are noisier owing to fewer collected photons. Chromospheric magnetic fields are notoriously difficult to constrain by polarization of Ca II lines alone. However, we demonstrate that high cadence, high angular resolution monochromatic images of fibrils in Ca II and Hα, seen clearly in IBIS observations, can be used to improve the magnetic field constraints, under conditions of high electrical conductivity. Such work is possible only with time series data sets from two-dimensional spectroscopic instruments such as IBIS, under conditions of good seeing. Title: Coronal Emission Lines as Thermometers Authors: Judge, Philip G. Bibcode: 2010ApJ...708.1238J Altcode: 2009arXiv0911.4085J Coronal emission-line intensities are commonly used to measure electron temperatures using emission measure and/or line ratio methods. In the presence of systematic errors in atomic excitation calculations and data noise, the information on underlying temperature distributions is fundamentally limited. Increasing the number of emission lines used does not necessarily improve the ability to discriminate between different kinds of temperature distributions. Title: The chromosphere: gateway to the corona? ...Or the purgatory of solar physics? Authors: Judge, P. G. Bibcode: 2010MmSAI..81..543J Altcode: I argue that one should attempt to understand the solar chromosphere not only for its own sake, but also if one is interested in the physics of: the corona; astrophysical dynamos; space weather; partially ionized plasmas; heliospheric UV radiation; the transition region. I outline curious observations which I personally find puzzling and deserving of attention. Title: Activity Cycles of Southern Asteroseismic Targets Authors: Metcalfe, Travis S.; Judge, P. G.; Basu, S.; Henry, T. J.; Soderblom, D. R.; Knoelker, M.; Rempel, M. Bibcode: 2010AAS...21542416M Altcode: 2010BAAS...42..333M The Mount Wilson Ca HK survey revealed magnetic activity variations in a large sample of solar-type stars with timescales ranging from 2.5 to 25 years. This broad range of cycle periods is thought to reflect differences in the rotational properties and the depths of the surface convection zones for stars with various masses and ages. Asteroseismic data will soon provide direct measurements of these quantities for individual stars, but many of the most promising targets are in the southern sky (e.g., alpha Cen A & B, beta Hyi, mu Ara, tau Cet, nu Ind), while long-term magnetic activity cycle surveys are largely confined to the north. In 2007 we began using the SMARTS 1.5-m telescope to conduct a long-term monitoring campaign of Ca II H & K emission for a sample of 57 southern solar-type stars to measure their magnetic activity cycles and their rotational properties when possible. This sample includes the most likely southern asteroseismic targets to be observed by the Stellar Oscillations Network Group (SONG), currently scheduled to begin operations in 2012. We present selected results from the first two years of the survey, and from the longer time baseline sampled by a single-epoch survey conducted in 1992. Title: New Perspectives on the Photosphere/Corona Interface (Keynote) Authors: Judge, P. G. Bibcode: 2009ASPC..415....7J Altcode: I review the role of the chromosphere as the lower boundary for the corona. I highlight the need for measurements of the chromospheric magnetic field as the plasma regimes change from β >1 to <1, using a striking observational example. I also review some physical processes which can alter the magnetic free energy as it traverses the chromosphere. Multi-fluid effects appear to be important in determining the supply of mass, momentum and energy into the overlying corona. Such effects have been only partly studied in the literature. I re-iterate the obvious conclusion, often ignored, that one must understand specific chromospheric processes if one is to have hope of addressing the nature of the supply of mass, momentum, and energy into the corona. Title: Activity Cycles of Southern Asteroseismic Targets Authors: Metcalfe, T. S.; Judge, P. G.; Basu, S.; Henry, T. J.; Soderblom, D. R.; Knoelker, M.; Rempel, M. Bibcode: 2009arXiv0909.5464M Altcode: The Mount Wilson Ca HK survey revealed magnetic activity variations in a large sample of solar-type stars with timescales ranging from 2.5 to 25 years. This broad range of cycle periods is thought to reflect differences in the rotational properties and the depths of the surface convection zones for stars with various masses and ages. Asteroseismic data will soon provide direct measurements of these quantities for individual stars, but many of the most promising targets are in the southern sky (e.g., alpha Cen A & B, beta Hyi, mu Ara, tau Cet, nu Ind), while long-term magnetic activity cycle surveys are largely confined to the north. In 2007 we began using the SMARTS 1.5-m telescope to conduct a long-term monitoring campaign of Ca II H & K emission for a sample of 57 southern solar-type stars to measure their magnetic activity cycles and their rotational properties when possible. This sample includes the most likely southern asteroseismic targets to be observed by the Stellar Oscillations Network Group (SONG), currently scheduled to begin operations in 2012. We present selected results from the first two years of the survey, and from the longer time baseline sampled by a single-epoch survey conducted in 1992. Title: Mining a Massive Brightpoint Database for Science Authors: McIntosh, Scott W.; Sitongia, L.; Markel, R.; Judge, P. G.; Davey, A. R. Bibcode: 2009SPD....40.1525M Altcode: We update the analysis of McIntosh & Gurman [2005, Sol. Phys., 228, 285] to incorporate changes to the automatic EUV Bright Point (BP) detection algorithm of data from the Extreme-ultraviolet Imaging Telescope (EIT) on the Solar and Heliospheric Observatory (SOHO). We discuss the implementation of the BP catalog as a searchable database for the community and some of the basic manipulations on that database. We present the multi-wavelength differential rotation rates for the previous solar cycle and make an initial foray into the connection of this most ubiquitous coronal structure and the larger scale magnetic dynamo. Title: On magnetic field ``reconstruction'' Authors: Judge, P. G. Bibcode: 2009A&A...493.1121J Altcode: Context: Solanki and colleagues have presented intriguing 3D “reconstructions” of magnetic fields from the vector polarimetry of the He I 1083 nm multiplet.
Aims: In this Research Note I re-examine the reconstruction technique used.
Methods: Using a simple dipole field, I examine the reconstruction technique as applied to the theoretical fields. I assume that the He line forms in two locations, (1) along the magnetic loops and (2) in a horizontal plane.
Results: The planar interpretation can account for all aspects of the data, but the loop interpretation has geometrical and physical problems.
Conclusions: The data by themselves are not sufficient to determine which picture is more applicable. Nevertheless I argue that the planar interpretation makes more physical sense and that the early reconstructions lead to spurious results. I suggest additional tests that might help constrain the problem further. Title: The Solar Chromosphere: Old Challenges, New Frontiers Authors: Ayres, T.; Uitenbroek, H.; Cauzzi, G.; Reardon, K.; Berger, T.; Schrijver, C.; de Pontieu, B.; Judge, P.; McIntosh, S.; White, S.; Solanki, S. Bibcode: 2009astro2010S...9A Altcode: No abstract at ADS Title: Physics of the chromosphere and the lower coronal boundary conditions Authors: Judge, P. Bibcode: 2008AGUFMSH51C..03J Altcode: I will review observations and theoretical work concerning the role of the chromosphere as the lower boundary for the corona. I will highlight the need for measurements of the chromospheric magnetic field as the plasma regimes change from beta > 1 to < 1, using a striking observational example. I will review some of the important physical processes occurring within the partially ionized chromosphere which can greatly alter the conditions at the coronal base from those expected based only upon photospheric measurements. I will re-iterate the obvious conclusion, but one often ignored, that one must understand specific chromospheric processes if one is to have hope of addressing the nature of the supply of mass, momentum and energy into the corona. Title: On the Magnetic Structure of the Solar Transition Region Authors: Judge, Philip; Centeno, Rebecca Bibcode: 2008ApJ...687.1388J Altcode: 2008arXiv0805.1436J We examine the hypothesis that cool loops dominate emission from solar transition region plasma below temperatures of 2 × 105 K. We compare published VAULT images of H Lyα, a lower transition region line, with nearly contemporaneous magnetograms from Kitt Peak, obtained during the second flight (VAULT-2) on 2002 June 14. The measured surface fields and potential extrapolations suggest that there are too few short loops and that Lyα emission is associated with the base regions of longer, coronal loops. VAULT-2 data of network boundaries have an asymmetry on scales larger than supergranules, also indicating an association with long loops. We complement the Kitt Peak data with very sensitive vector polarimetric data from the spectropolarimeter on board Hinode to determine the influence of very small magnetic concentrations on our analysis. From these data, two classes of behavior are found. Within the cores of strong magnetic flux concentrations (>5 × 1018 Mx) associated with active network and plage, small-scale mixed fields are absent, and any short loops can connect just the peripheries of the flux to cell interiors. Core fields return to the surface via longer, most likely coronal, loops. In weaker concentrations, short loops can connect concentrations and produce mixed fields within network boundaries, as suggested by Dowdy and colleagues. The VAULT-2 data that we examined are associated with strong concentrations. We conclude that the cool-loop model applies only to a small fraction of the VAULT-2 emission, but we cannot discount a significant role for cool loops in quieter regions. We suggest a physical picture for how network Lyα emission may occur through the cross-field diffusion of neutral atoms from chromospheric into coronal plasma. Title: An Explanation of the Solar Transition Region Authors: Judge, Philip Bibcode: 2008ApJ...683L..87J Altcode: 2008arXiv0807.1706J Prompted by high-resolution observations, I propose an explanation for the 40+ year old problem of structure and energy balance in the solar transition region. The ingredients are simply cross-field diffusion of neutral atoms from cool threads extending into the corona, and the subsequent excitation, radiation, and ionization of these atoms via electron impact. The processes occur whenever chromospheric plasma is adjacent to coronal plasma, and are efficient even when ion gyrofrequencies exceed collision frequencies. Cool threads—fibrils and spicules perhaps—grow slowly in thickness as a neutral, ionizing front expands across the magnetic field into coronal plasma. Radiative intensities estimated for H Lyα are within an order of magnitude of those observed, with no ad hoc parameters; only thermal parameters and geometric considerations are needed. I speculate that the subsequent dynamics of the diffused material might also explain observed properties of trace elements. Title: The Fainting of α Centauri A, Resolved Authors: Ayres, Thomas R.; Judge, Philip G.; Saar, Steven H.; Schmitt, Jürgen H. M. M. Bibcode: 2008ApJ...678L.121A Altcode: Beginning in 2003, XMM-Newton snapshot monitoring of α Centauri (HD 128620, 128621: G2 V, K1 V) documented a steady fading of the primary's X-ray corona, which had all but disappeared by early 2005. The steep decline in LX was at odds with the previous two decades of high-energy measurements, which showed only modest variability of the Sun-like star. A Chandra LETGS spectrum in 2007 June, however, fully resolved the source of the curious X-ray darkening: a depletion of plasma above ~2 MK had substantially depressed the line spectrum where the XMM-Newton response peaks (λ lesssim 30 Å), even though the overall coronal luminosity, dominated by longer wavelength emissions, had declined only slightly. This is reminiscent of the Sun's magnetic activity cycle, where the 2-3 MK active regions of sunspot maximum give way to the spatially pervasive, but cycle-independent, 1 MK "quiet corona" at minimum. This emphasizes that any discussion of cyclic coronal variability in low-activity stars will depend crucially on the energy coverage of the measurements. Title: An Instrument to Measure Coronal Emission Line Polarization Authors: Tomczyk, S.; Card, G. L.; Darnell, T.; Elmore, D. F.; Lull, R.; Nelson, P. G.; Streander, K. V.; Burkepile, J.; Casini, R.; Judge, P. G. Bibcode: 2008SoPh..247..411T Altcode: 2008SoPh..tmp....3T We have constructed an instrument to measure the polarization of light emitted by the solar corona in order to constrain the strength and orientation of coronal magnetic fields. We call this instrument the Coronal Multichannel Polarimeter (CoMP). The CoMP is integrated into the Coronal One Shot coronagraph at Sacramento Peak Observatory and employs a combination birefringent filter and polarimeter to form images in two wavelengths simultaneously over a 2.8R field of view. The CoMP measures the complete polarization state at the 1074.7 and 1079.8 Fe XIII coronal emission lines, and the 1083.0 nm He I chromospheric line. In this paper we present design drivers for the instrument, provide a detailed description of the instrument, describe the calibration methodology, and present some sample data along with estimates of the uncertainty of the measured magnetic field. Title: Instruments: HRC Authors: Kraft, Ralph; Kenter, Almus; Ayres, Thomas R.; Judge, Philip G.; Saar, Steven H.; Schmitt, Jurgen H. M. M.; Anderson, Gemma; Gaensler, Bryan; Chicago Team Bibcode: 2008ChNew..15...13K Altcode: No abstract at ADS Title: The COronal Solar Magnetism Observatory Authors: Burkepile, J.; Tomczyk, S.; Lin, H.; Zurbuchen, T.; Judge, P.; Casini, R. Bibcode: 2007AGUFMSH53A1070B Altcode: Measurements of coronal and chromospheric magnetic fields are arguably the most important observables required for advances in our understanding of the emergence of magnetic flux into the solar atmosphere and the processes responsible for the production of solar activity, coronal heating and coronal dynamics. The COronal Solar Magnetism Observatory (COSMO) is a proposed ground-based suite of instruments designed for routine study of coronal and chromospheric magnetic fields and their environment. The facility consists of 3 instruments: 1) a meter-class aperture coronal magnetometer devoted to obtaining the highest quality polarimetric data of forbidden lines of Fe XIII 1074.7 and 1079.8 nm.; 2) a chromosphere and prominence magnetometer devoted primarily to measurements of lines of helium (D3, 1083 nm) and perhaps Halpha, that will provide full disk vector magnetic field observations; 3) a white-light polarized-brightness (pB) coronagraph that will observe down to 1.05 solar radii at very high time cadence (15 seconds) at high signal-to-noise. This new facility will be operated by the High Altitude Observatory of the National Center for Atmospheric Research (HAO/NCAR) in collaboration with the University of Hawaii and the University of Michigan. COSMO will enhance the value of existing and new observatories on the ground (SOLIS, ATST, and FASR) and in space (SOHO, TRACE, GOES, SOLAR-B, STEREO, SDO) by providing unique and crucial observations of the global coronal and chromospheric magnetic field and its evolution. Title: Alfven Waves in the Solar Corona Authors: Tomczyk, S.; McIntosh, S. W.; Keil, S. L.; Judge, P. G.; Schad, T.; Seeley, D. H.; Edmondson, J. Bibcode: 2007AGUFMSH21A0289T Altcode: We present observations of the coronal intensity, line-of-sight velocity, and linear polarization obtained in the FeXIII 1074.7 nm coronal emission line with the Coronal Multi-channel Polarimeter (CoMP) instrument. Analysis of these observations reveal ubiquitous upward propagating waves with phase speeds of 1-4 Mm/s and trajectories consistent with the direction of the magnetic field inferred from the linear polarization measurements. We can definitively identify these as Alfvén waves. An estimate of the energy carried by the waves that we spatially resolve indicates that they are unable to heat the solar corona, however, unresolved waves may carry sufficient energy. Title: Alfvén Waves in the Solar Corona Authors: Tomczyk, S.; McIntosh, S. W.; Keil, S. L.; Judge, P. G.; Schad, T.; Seeley, D. H.; Edmondson, J. Bibcode: 2007Sci...317.1192T Altcode: Alfvén waves, transverse incompressible magnetic oscillations, have been proposed as a possible mechanism to heat the Sun’s corona to millions of degrees by transporting convective energy from the photosphere into the diffuse corona. We report the detection of Alfvén waves in intensity, line-of-sight velocity, and linear polarization images of the solar corona taken using the FeXIII 1074.7-nanometer coronal emission line with the Coronal Multi-Channel Polarimeter (CoMP) instrument at the National Solar Observatory, New Mexico. Ubiquitous upward propagating waves were seen, with phase speeds of 1 to 4 megameters per second and trajectories consistent with the direction of the magnetic field inferred from the linear polarization measurements. An estimate of the energy carried by the waves that we spatially resolved indicates that they are too weak to heat the solar corona; however, unresolved Alfvén waves may carry sufficient energy. Title: Asteroseismic signatures of stellar magnetic activity cycles Authors: Metcalfe, T. S.; Dziembowski, W. A.; Judge, P. G.; Snow, M. Bibcode: 2007MNRAS.379L..16M Altcode: 2007MNRAS.tmpL..50M; 2007arXiv0704.1606M Observations of stellar activity cycles provide an opportunity to study magnetic dynamos under many different physical conditions. Space-based asteroseismology missions will soon yield useful constraints on the interior conditions that nurture such magnetic cycles, and will be sensitive enough to detect shifts in the oscillation frequencies due to the magnetic variations. We derive a method for predicting these shifts from changes in the MgII activity index by scaling from solar data. We demonstrate this technique on the solar-type subgiant β Hyi, using archival International Ultraviolet Explorer spectra and two epochs of ground-based asteroseismic observations. We find qualitative evidence of the expected frequency shifts and predict the optimal timing for future asteroseismic observations of this star. Title: The Outer Solar Atmosphere during the Maunder Minimum: A Stellar Perspective Authors: Judge, Philip G.; Saar, Steven H. Bibcode: 2007ApJ...663..643J Altcode: By comparing solar data with data of ``flat activity'' stars at UV and soft X-ray wavelengths, we estimate solar chromospheric, transition region, and coronal emission as it might have existed during the Maunder minimum (1645-1715), the most recent of several episodes of persistently weak sunspot activity. Several flat activity stars from the Mount Wilson S-index survey have been observed with the Hubble Space Telescope and ROSAT. Drawing on published data, we reassess the criteria by which a star may be considered as a Maunder minimum candidate. Of our targets, HD 10700 and HD 143761 are the most likely such candidates. Solar UV spectra from the SOHO and UARS spacecraft, and soft X-ray data from the SNOE spacecraft are compared with the stellar UV and X-ray data. The comparison suggests that the radiative output of the Maunder minimum chromosphere, transition region, and corona were similar to (or at least not much less than) those observed under conditions close to current solar minima. In turn, this suggests that the emitting structures (which on the Sun at sunspot minimum are small scale, <<Rsolar), including the magnetic network, were also similar. These results have implications for the nature of the surface magnetic fields and irradiance during the Maunder and other magnetic minima, and for the solar dynamo. Title: Spectral Lines for Polarization Measurements of the Coronal Magnetic Field. V. Information Content of Magnetic Dipole Lines Authors: Judge, P. G. Bibcode: 2007ApJ...662..677J Altcode: Stokes profiles of typical magnetic dipole coronal emission lines contain information on the embedded magnetic fields, but the interpretation of the lines is subject to ambiguities. The present study illuminates the information content of coronal emission line measurements that include all four Stokes parameters. The simplest case of localized emission along the line of sight, such as that from a single bright loop, is scrutinized. Knowledge of the ``atomic alignment'' is central to the diagnosis of magnetic fields beyond determining the field's azimuth projected on the plane of the sky. For localized emission, a method to determine the atomic alignment is presented, combining Stokes I, Q, and U observations and statistical equilibrium calculations, related to work by Querfeld. The method yields the sign of the alignment under conditions that might exist 25% of the time, thereby reducing the Van Vleck ambiguity from one of 90° to 180°. Even then, the magnitude of the alignment is sometimes ambiguous. With measurements of Stokes V, unambiguous knowledge of the alignment also yields the vector field B with just an ambiguity of 180° in the plane of the sky. In other, more general cases, neither the sign nor the magnitude of the atomic alignment can be uniquely determined. Suggestions are made as to how these more serious ambiguities might be ameliorated by assuming continuity of magnetic fields underlying the polarization maps, an idea first expressed by House in 1972. Some conclusions are offered concerning the relative merits of formal inversions, diagnosis of magnetic properties from a localized region, tomography using solar rotation, and forward modeling. Title: Observations of the Solar Chromosphere Authors: Judge, P. Bibcode: 2006ASPC..354..259J Altcode: I summarize observational properties of the solar chromosphere with emphasis on some of Bob Stein's continuing interests, with an historical slant. Bob's interests always concern basic physical processes, so I try to identify some basic facts about the chromosphere from the myriads of observations from radio to UV wavelengths. The observations suggest a simple demarcation between the ``low'' chromosphere and ``high'' chromosphere which depends on the local plasma-β. Relatively simple properties are exhibited in high-β regions (hydrostatic equilibrium, three-minute compressive oscillations), and obviously complex thermal properties of the ``fine structure'' observed for many decades, arise in low-β chromospheric regions. The latter appears to share properties more in common with the intermingled lower corona, where the energetically dominant magnetic structure is arguably simpler than the high-β regions. But like the coronal heating problem, the thermal structure of the upper chromosphere is far more complex and is manifested as fine structure. Title: The Coronal Solar Magnetic Observatory (COSMO) Authors: Tomczyk, S.; Zurbuchen, T.; Kuhn, J.; Lin, H.; Judge, P.; Burkepile, J.; Casini, R. Bibcode: 2006AGUFMSM12A..03T Altcode: Measurement of magnetic fields in the corona is arguably the most important observable required for advances in our understanding of the emergence of magnetic flux into the solar atmosphere and the processes responsible for the production of solar activity, coronal heating and coronal dynamics. We discuss plans for the COronal Solar Magnetic Observatory (COSMO), which is a proposed ground-based suite of instruments designed to routinely study coronal magnetic fields and their environment. The core of the facility includes a meter-class coronagraph with instrumentation dedicated to measuring the coronal magnetic field using the polarization of forbidden emission lines in the infrared. Supporting instruments focus on prominence magnetometry and the dynamics of the electron-scattered corona (K-corona) and chromosphere. In addition to acquiring routine synoptic observations of coronal magnetic fields, the COSMO project will include the establishment of a community-based user advisory panel to accept observational campaigns submitted by members of the scientific community at-large. COSMO will enhance the value of existing and new observatories on the ground (SOLIS, ATST, FASR) and in space (SOHO, TRACE, GOES, Solar-B, STEREO and SDO) by providing unique and crucial observations of the global coronal magnetic field and its evolution and dynamics. Title: Spectral Lines for Polarization Measurements of the Coronal Magnetic Field. IV. Stokes Signals in Current-carrying Fields Authors: Judge, P. G.; Low, B. C.; Casini, R. Bibcode: 2006ApJ...651.1229J Altcode: We present the first theoretical, forward calculations of the Stokes profiles of several magnetic dipole (``M1'') coronal emission lines produced in current-carrying magnetic structures. An idealized coronal model of Low, Fong, and Fan is used, which describes a spherically symmetric, hydrostatic background atmosphere, isothermal at a coronal temperature of 1.6×106 K. Embedded is a global, axisymmetric magnetic field that is everywhere potential except at a quiescent prominence, consisting of an infinitesimally thin, equatorial current sheet whose weight is supported by the outward discrete Lorentz force in the sheet. This model contains a physically nontrivial, localized magnetic structure, although the atmospheric plasma is thermally of the simplest stratification possible. The calculated M1 coronal lines show clear and distinct signatures of the presence and magnitude of this localized magnetic structure, in both linear and circular polarizations, even though the thermal structure is almost homogeneous. The morphology of maps of linear polarization is particularly sensitive to the existence and strength of the current sheets, as field lines wrap around them according to the Biot-Savart law, and the linear polarization responds to different projections of field line directions onto local radius vectors. Of the M1 lines studied, those of Fe XIII (1074.7 nm) and Si X (1430.1 nm) are especially promising because of their relatively strong linear polarization. These forward calculations provide a basis for optimism that emission-line measurements may reveal the presence and nature of current systems in the corona, and provide motivation for developing instruments capable of routinely measuring polarized light in forbidden coronal lines. Title: Observational aspects of sunspot oscillations Authors: Bogdan, T. J.; Judge, P. G. Bibcode: 2006RSPTA.364..313B Altcode: No abstract at ADS Title: Wavelet Phase Coherence Analysis: Application to a Quiet-Sun Magnetic Element Authors: Bloomfield, D. Shaun; McAteer, R. T. James; Lites, Bruce W.; Judge, Philip G.; Mathioudakis, Mihalis; Keenan, Francis P. Bibcode: 2004ApJ...617..623B Altcode: A new application of wavelet analysis is presented that utilizes the inherent phase information residing within the complex Morlet transform. The technique is applied to a weak solar magnetic network region, and the temporal variation of phase difference between TRACE 1700 Å and SOHO/SUMER C II 1037 Å intensities is shown. We present, for the first time in an astrophysical setting, the application of wavelet phase coherence, including a comparison between two methods of testing real wavelet phase coherence against that of noise. The example highlights the advantage of wavelet analysis over more classical techniques, such as Fourier analysis, and the effectiveness of the former to identify wave packets of similar frequencies but with differing phase relations is emphasized. Using cotemporal, ground-based Advanced Stokes Polarimeter measurements, changes in the observed phase differences are shown to result from alterations in the magnetic topology. Title: Evaluation of Seeing-Induced Cross Talk in Tip-Tilt-Corrected Solar Polarimetry Authors: Judge, Philip G.; Elmore, David F.; Lites, Bruce W.; Keller, Christoph U.; Rimmele, Thomas Bibcode: 2004ApOpt..43.3817J Altcode: We reanalyze the effects of atmosphere-induced image motions on the measurement of solar polarized light using a formalism developed by Lites. Our reanalysis is prompted by the advent of adaptive optics (AO) systems that reduce image motion and higher-order aberrations, by the availability of liquid crystals as modulation devices, and by the need to understand how best to design polarimeters for future telescopes such as the Advanced Technology Solar Telescope. In this first attempt to understand the major issues, we analyze the influence of residual image motion (tip-tilt) corrections of operational AO systems on the cross talk between Stokes parameters and present results for several polarization analysis schemes. Higher-order wave-front corrections are left for future research. We also restrict our discussion to the solar photosphere, which limits several important parameters of interest, using some recent magnetoconvection simulations. Title: A Comparison of the Outer Atmosphere of the ``Flat Activity'' Star τ Ceti (G8 V) with the Sun (G2 V) and α Centauri A (G2 V) Authors: Judge, Philip G.; Saar, Steven H.; Carlsson, Mats; Ayres, Thomas R. Bibcode: 2004ApJ...609..392J Altcode: Driven by the desire to understand the roles of acoustic and magnetic mechanisms in heating the outer atmospheres of Sun-like stars, we compare solar UV spectra with archival STIS spectra from the Hubble Space Telescope of α Cen A (G2 V) and new STIS spectra of the extremely inactive dwarf star τ Cet (G8 V, V=3.5). The activity of τ Cet shows occasional rotational modulations but no long-term cyclic variation. It may be in a phase analogous to the solar Maunder minimum. Solar disk center intensities from both the HRTS instrument and the SUMER instrument on SOHO were converted to Sun-as-a-star fluxes by using center-to-limb data from Dammasch and colleagues. The derived solar flux spectrum represents conditions near the minimum of the solar magnetic activity cycle. We find that the τ Cet line profiles differ systematically from those of the Sun and α Cen A. While lines formed in the middle chromospheres appear similar, the entire emission from the upper chromosphere to the middle transition region of τ Cet has lower flux densities by factors of ~2, the line widths are significantly narrower, and, uniquely, the transition region lines are not significantly redshifted. The soft X-ray surface flux of τ Cet, measured between 0.1 and 2.4 keV, is ~9×103 ergs cm-2 s-1, several times smaller than the median solar value. We also find that the UV spectrum of α Cen serves as a proxy for a Sun-as-a-star spectrum when the Sun is in an intermediate phase of its activity cycle but that its coronal emission may be somewhat smaller. We discuss the implications of these results for magnetic fields and heating mechanisms in the stars and speculate that τ Cet's UV spectrum might represent the solar spectrum during a grand minimum phase. Title: Background-Induced Measurement Errors of the Coronal Intensity, Density, Velocity, and Magnetic Field Authors: Penn, M. J.; Lin, H.; Tomczyk, S.; Elmore, D.; Judge, P. Bibcode: 2004SoPh..222...61P Altcode: The effect of a background signal on the signal-to-noise ratio is discussed, with particular application to ground-based observations of emission lines in the solar corona with the proposed Advanced Technology Solar Telescope. The concepts of effective coronal aperture and effective coronal integration time are introduced. Specific expressions are developed for the 1σ measurement errors for coronal intensity, coronal electron density, coronal velocity, and coronal magnetic field measurements using emission lines and including a background. Title: On the Formation of Extreme-Ultraviolet Helium Lines in the Sun: Analysis of SOHO Data Authors: Judge, Philip G.; Pietarila, Anna Bibcode: 2004ApJ...606.1258J Altcode: The resonance lines of helium in the Sun are several times stronger than expected, relative to lines of other ions. To explore the origins of this ``helium enhancement,'' we have studied data from the SUMER, CDS, MDI, and EIT instruments on the Solar and Heliospheric Observatory (SOHO). Time series data obtained in a quiet region and a coronal hole indicate that the spatio-temporal properties of the He I 584 Å, and He II 304 and 1084 Å lines are qualitatively unlike other chromospheric and transition region lines. Helium line intensities vary slowly compared to chromospheric oscillations and to transient transition region brightenings seen in other lines, yet they vary rapidly (both spatially and temporally) compared to the coronal radiation. This suggests that photoionization/recombination plays a minor excitation role in these lines. The Doppler shift of the 584 Å line shows a remarkably clear 4-8 mHz oscillation, with no accompanying line intensity oscillation. Transient brightenings are used to show that nonradial photon scattering might explain the previously found diffuse appearance of the network but cannot account for the reduced network/internetwork intensity contrast in the 584 Å line. We propose a new enhancement mechanism, based on arguments in a companion paper, in which predominantly neutral species such as helium diffuse across magnetic field lines into regions of hot coronal plasma, but charged ions do not. The enhanced internetwork helium emission may arise from the diffusion of helium atoms across the chromospheric canopy; the enhanced network emission may have contributions from diffusion from spicules. This mechanism may naturally explain why the 584 Å line shows Doppler shift, but not intensity, oscillations. Finally, if a mechanism such as ``velocity redistribution'' dominates helium emission, spectroheliograms of helium lines will be bright in regions of large temperature gradients parallel to the magnetic field. Differences between helium and other spectroheliograms may then reveal the relative contributions of ``classical'' and ``cool loop'' models to the observed emission. Title: Solar Physics at Evergreen Authors: Zita, E. J.; Bogdan, T. J.; Carlsson, M.; Judge, P.; Heller, N.; Johnson, M.; Petty, S. Bibcode: 2004APS..NWS.C1005Z Altcode: We have recently established a solar physics research program at The Evergreen State College. Famed for its cloudy skies, the Pacific Northwest is an ideal location for solar physics research activities that do not require local observations. Collaborators from the High Altitude Observatory (HAO) at the National Center for Atmospheric Research have shared solar data from satellite-borne instruments such as TRACE and SUMER. HAO colleagues also share data from computer simulations of magneto-hydrodynamics (MHD) in the chromosphere, generated by the Institute for Theoretical Astrophysics (ITA) at the University of Oslo. Evergreen students and faculty learned to analyze data from satellites and simulations, in Boulder and Oslo, and established an infrastructure for continuing our analyses in Olympia. We are investigating the role of magnetic waves in heating the solar atmosphere. Comparing data from satellites and simulations shows that acoustic oscillations from the photosphere cannot effectively propagate into the chromosphere, but that magnetic waves can carry energy up toward the hot, thin corona. We find that acoustic waves can change into magnetic waves, especially near the magnetic "canopy," a region where the sound speed is comparable to magnetic wave speeds. Understanding MHD wave transformations and their role in energy transport can help answer outstanding questions about the anomalous heating of the solar atmosphere. Ref: Waves in the magnetized solar atmosphere II: Waves from localized sources in magnetic flux concentrations. Bogdan et al., 2003, ApJ 597 Title: On the Formation of the Resonance Lines of Helium in the Sun Authors: Pietarila, Anna; Judge, Philip G. Bibcode: 2004ApJ...606.1239P Altcode: To investigate the cause of anomalously bright resonance lines of helium in the Sun, we have studied the magnitude of the enhancements and some proposals made to explain them. Calculations in new semiempirical solar models indicate that the resonance lines of helium are enhanced by factors of 2-5 for He I and between 2 and 9 for He II, depending on the elemental abundances assumed. These enhancements are substantially less than earlier work has suggested, with the differences arising from radiative transfer not only in helium lines but also in lines of less abundant elements. Photon scattering, even with small line center optical depths (of order unity or less) throughout the transition region, is shown to significantly modify line intensities and their center-to-limb variation. This effect has important consequences both for our analysis and also for the analysis of solar EUV lines in general, including emission measure analyses. We have re-examined some proposals to explain the enhancements based on the ``ionizing plasma'' picture. The proposals include explicit heating (the ``burst'' picture) and heating via advection (diffusive and/or flowing models and the ``velocity redistribution'' [VR] proposal). We argue that the original VR mechanism must be modified to include kinetic effects for helium atoms, which reduce the effects of VR. The VR mechanism also naturally predicts helium lines that are blue-shifted relative to lines less sensitive to VR, which contradicts observations for the He I 584 Å line. Ionizing plasma models also potentially lead to enhancement of Δn>=1 transitions (n is the principal quantum number) in other atoms and ions. Existing observational evidence for enhanced Δn>=1 transitions in other ions is weak. We conclude that the ionizing plasma scenarios are not the sole cause of the helium enhancement. Instead, in a companion paper, we propose that the thermodynamic properties of noble gases in the upper chromosphere will lead to enhancement of their spectral lines if cross-field diffusion into coronal plasma is important. Finally, we show that, surprisingly, multifluid flows of the kind computed by Fontenla and colleagues can reproduce observed intensities of several lines of C and Si and may contain a resolution to the helium enhancement problem. Title: Initial Magnetic Field Measurements from The Coronal Multi-Channel Polarimeter Authors: Tomczyk, S.; Card, G. L.; Darnell, T.; Elmore, D. F.; Casini, R.; Judge, P. G.; Burkepile, J. Bibcode: 2004AAS...204.2002T Altcode: 2004BAAS...36..686T We have constrcted a filter-based polarimeter optimized for the measurement of magnetic fileds in the solar corona. The instrument will observe the coronal emission lines of FeXIII at 1074.7 and 1079.8 nm as well as the chromospheric HeI emission line at 1083 nm. The instrument consists of a polarimeter allowing complete Stokes I,Q,U,V measurement followed by a Lyot birefringent filter with dual passbands of 0.14 nm width. Both the polarimeter and filter employ liquid crystals for rapid electro-optical tuning. This instrument was deployed to the 20-cm One Shot coronagraph at NSO's Sacramento Peak Observatory in January of 2004.

Measurement of the longitudinal Zeeman effect provides information on the strength of the line-of-sight component of the magnetic field while the observation of resonance scattering will constrain the plane-of-sky field direction. Precise measurement of plasma velocity is also possible. Such measurements are critical for addressing many outstanding problems in coronal physics.

The operation and performance of the instrument will be described. We will also describe the methodology for the coronal magnetic field measurement. Initial measurements taken with the instrument will be presented. This research was supported by the NSF. Title: Chromospher-corona transition region line emissions Authors: Fontenla, J.; Judge, P. Bibcode: 2004cosp...35..668F Altcode: 2004cosp.meet..668F We study the effects of diffusion and flows on the transition region trace-species emission lines and the radiative losses produced by them and compare them with observations. We find that mass flows can have dramatic effects on the line emissions through the effect on non-local ionization and in this way completely alter the radiative losses and the structure of the transition regions. Also, in static cases thermal diffusion can have a very significant effect on the elemental abundance variation that in turn affects the line emissions and radiative losses leading to reduced abundances of trace species at temperatures around 10^5 K, and the details this effect is dependent on the first-ionization-potential. This is due to the combination of large temperature gradient and increased mean free path and is expected to occur for all species. However, the mass flows would reduce this effect and especially in the case of downflows the thermal diffusion can have complex results. Also, species diffusion flows can arise from specific boundary conditions and may not be directly related to a simultaneous mass flow. We discuss several scenarios that may arise in typical dynamic cases that have been observed. We show that the transition region emissions have the large fluctuations in space and time, much more than the chromospheric emissions, and that the radiated energy can be easily explained in terms of the downward energy flow from the corona coupled with enthalpy and ionization energy carried by the up and down mass flows often observed. Title: Oscillatory Signatures above Quiet Sun Magnetic Elements Authors: Bloomfield, D. S.; McAteer, R. T. J.; Lites, B. W.; Judge, P. G.; Mathioudakis, M.; Keenan, F. P. Bibcode: 2004ESASP.547...51B Altcode: 2004soho...13...51B A new application of wavelet analysis is presented. The data used are part of Joint Observing Proposal 72 between SoHO and TRACE, obtained on 1998 May 16 with accompanying groundbased data taken with the Dunn Solar Telescope at Sacramento Peak, New Mexico. A weak magnetic network region is studied and the temporal variation of phase difference between TRACE 1700 Å and SoHO/SUMER C II intensities is shown. The example clearly highlights the advantages of wavelet analysis over more classical techniques such as Fourier analysis, where the effectiveness of the technique to identify wavepackets with differing phase difference relations is emphasised. Title: A Coronal Multi Channel Polarimeter For Magnetic Field Measurements Authors: Darnell, T.; Tomczyk, S.; Card, G.; Judge, P. G.; Casini, R.; Burkepile, J. Bibcode: 2003AGUFMSH42B0505D Altcode: The Coronal Multi-channel Polarimeter (CoMP) is a filter-based polarimeter designed to provide quantitative measurements of magnetic fields in the solar corona. It will measure the Stokes parameters at the 1074.7 and 1079.8 FeXIII coronal emission lines (1.67 x 106 degrees K), and the 1083.0 nm HeI chromospheric line. The CoMP is based on a four stage birefringent filter and is designed such that the corona is imaged in two wavelengths simultaneously. The strength of the line-of-sight component of the coronal magnetic field is inferred from the measured amplitude of the Stokes V profile and an estimate of the plane-of-sky direction is made from the Stokes U/Q ratio. Further, inference of line-of-sight velocities can be made from Stokes I (red and blue wing) amplitudes. Finally, it may be possible to obtain a coronal density diagnostic capability from the ratio of the 1074.7/1079.8 amplitudes. This poster will present the latest test results as well as any preliminary data that have been obtained. Title: On the Origin of the Basal Emission from Stellar Atmospheres: Analysis of Solar C II Lines Authors: Judge, Philip G.; Carlsson, Mats; Stein, Robert F. Bibcode: 2003ApJ...597.1158J Altcode: Combining a variety of data with radiation hydrodynamic simulations, we examine the heating of the Sun's internetwork chromosphere and the hypothesis that the chromospheric ``basal'' emission arises because of acoustic wave dissipation. We focus on the 2s2p22D-2s22p2Po multiplet of C II near 1335 Å, whose basal level of chromospheric emission has been reliably determined for stars and the Sun by Schrijver and colleagues. By accounting for center-to-limb variations and the different spectral bandpasses of the instruments used, we find that Schrijver's C II solar basal intensity substantially exceeds stellar values, and that it can be identified with intensities seen in typical internetwork regions with the SUMER instrument on the SOHO spacecraft. Some time-series data sets of internetwork regions are then examined and compared with simulations made specifically for a typical observational data set, with vertical velocities at the lower boundaries fixed from observations with the MDI instrument on SOHO. The simulations can qualitatively account for the observed internetwork UV continuum fluctuations seen with SUMER, formed 0.6-0.85 Mm above the photosphere. However, they fail to capture almost any property of the observed internetwork C II multiplet, which is formed substantially higher. The time-averaged simulations can account for between 1/7 and 1/4 of the C II basal intensities; they predict oscillatory power between 5 and 10 mHz, whereas internetwork observations are dominated by low-frequency (<2 mHz) power of solar origin. The average simulated C II intensities, which have a large contribution from the transition region heated by conduction down from a coronal upper boundary, fall short even of the smaller stellar basal intensities by a factor of >=2. Together with known properties of weak, internetwork photospheric magnetic fields, we conclude that the internetwork upper chromosphere is probably dominated by magnetic heating. Thus, the solar basal (and internetwork) intensities of the C II 1335 Å multiplet originate from magnetic, and not acoustic, mechanisms, in contradiction to the commonly accepted picture Title: The Sun As A Guide To The Stars Authors: Judge, P. Bibcode: 2003csss...12..158J Altcode: I review the ``Sun as a guide to the stars'' with emphasis on solar magnetism: its origins and effects. I do not present an in-depth review but instead try to highlight the current status of relevant solar physics. The first half of the discussion focuses on what we have learned about dynamo process on both large (ℓ ≈ Rsun) and small (ℓ ≪ Rsun) scales. The second half focuses on the observed effects of the emerging magnetic fields, especially the problem of atmospheric heating. I make no attempt to be complete in referencing, but instead try to point to some key references (mostly reviews) as appropriate. Some WWW resources are listed. Title: An Estimate of the Sun's ROSAT-PSPC X-Ray Luminosities Using SNOE-SXP Measurements Authors: Judge, Philip G.; Solomon, Stanley C.; Ayres, Thomas R. Bibcode: 2003ApJ...593..534J Altcode: Using solar soft X-ray irradiance measurements from the SXP instrument on the SNOE satellite, we relate the solar surface flux densities and their variability to those of stars as measured with the PSPC instrument on ROSAT. We translate SNOE-SXP measurements into equivalent ROSAT-PSPC counts using model spectra calculated from the CHIANTI package. Using the SNOE-SXP measurements has significant advantages over earlier studies: the absolute calibration is known to +/-25%, SNOE measures the Sun as if it were an unresolved star, it has operated over a significant fraction of the solar cycle, and its three wavelength channels overlap substantially with that of the ROSAT-PSPC instrument. The predicted solar X-ray luminosities and surface flux densities are compared with measurements from the ROSAT database. We find that we can estimate the luminosity of the Sun as seen in the 0.1-2.4 keV (``RASS'') passband of ROSAT-PSPC to within +/-50%, not counting sources of systematic uncertainty mentioned in an appendix: the result lies between 1027.1 and 1027.75 ergs s-1 (measured in the existing data set, only partially covering a full solar cycle) and between 1026.8 and 1027.9 ergs s-1 (extrapolated to the full activity range of a typical solar cycle). The solar luminosities lie close to the median behavior found for a volume-limited (d<13 pc) sample of G stars studied in 1997 by Schmitt, revealing the Sun to be a normal or slightly inactive G dwarf. A factor of 1.5 peak-to-peak variation in the RASS passband is predicted due simply to rotational modulations (i.e., those filtered to include periods P<81 days). The ratio of maximum/minimum RASS luminosities from the magnetic activity cycle (filtered to include periods P>81 days) are estimated to be 0.7-0.8 in log10LRASS, a ratio of 5 or 6. These variations are much smaller than both recent estimates of solar X-ray variability and the range of X-ray luminosities seen within Schmitt's sample. It is suggested that the reported absence of ``solar-like'' cyclic emission in stellar X-rays might partly arise because the Sun is less variable than assumed in some earlier work. Repeated ROSAT observations of α Cen A during 1995-1998 show X-ray behavior reminiscent of the Sun during activity minimum conditions. Title: Investigating the role of plasma topography on chromospheric oscillations observed by TRACE Authors: McIntosh, S. W.; Fleck, B.; Judge, P. G. Bibcode: 2003A&A...405..769M Altcode: We present the results of an investigation into the interaction of the topographic structure of the solar chromospheric plasma with the wave modes manifesting themselves in the UV continua formed there. We show that there is a distinct correlation between the inferred plasma topography, the phase-differences between and suppression of oscillations in different levels of the solar atmosphere. We interpret these factors as evidence of interaction between the oscillations and the extended magnetic ``canopy''. This work is based on the analysis of joint observations made by the Solar and Heliospheric Observatory (SOHO) spacecraft and the Transition Region and Coronal Explorer (TRACE). Title: Towards the Measurement of Coronal Magnetic Fields Authors: Judge, P. G. Bibcode: 2003ASPC..307..437J Altcode: No abstract at ADS Title: Determination of Hyperfine-Induced Transition Rates from Observations of a Planetary Nebula Authors: Brage, Tomas; Judge, Philip G.; Proffitt, Charles R. Bibcode: 2002PhRvL..89B1101B Altcode: 2002PhRvL..89.1101B Observations of the planetary nebula NGC3918 made with the STIS instrument on the Hubble Space Telescope reveal the first unambiguous detection of a hyperfine-induced transition 2s2p

3
Po0→2s2
1
S0 in the berylliumlike emission line spectrum of N IV at 1487.89Å. A nebular model allows us to confirm a transition rate of 4×10-4 sec(-1±33% for this line. The measurement represents the first independent confirmation of the transition rate of hyperfine-induced lines in low ionization stages, and it provides support for the techniques used to compute these transitions for the determination of very low densities and isotope ratios. Title: Observational and Interpretational Challenges Authors: Judge, P. Bibcode: 2002ASPC..277...45J Altcode: 2002sccx.conf...45J No abstract at ADS Title: Spectroscopic Detection of the 3.934 Micron Line of Si IX in the Solar Corona Authors: Judge, P. G.; Tomczyk, S.; Livingston, W. C.; Keller, C. U.; Penn, M. J. Bibcode: 2002ApJ...576L.157J Altcode: We report the detection of the 2s22p23P1-->0 line of Si IX using the McMath-Pierce telescope on Kitt Peak. Observations were made of the solar disk and at various heights above the limb between 2002 May 13 and 17, under nonideal sky conditions, using the 13.5 m vertical spectrograph and an InSb single-diode detector. We report a new rest wavelength for the line and discuss its potential use as a diagnostic of coronal magnetic fields using ground-based telescopes. Our observations give λrest=3.93434+/-0.00007 μm, consistent with earlier less accurate values, but it places the blue wing of the line under a strong telluric N2O line. In the active regions observed, the line's intensity is comparable to or larger than predicted in earlier work for the quiet Sun. Title: Challenges of Measuring Coronal Magnetic Fields Authors: Judge, P. Bibcode: 2002AAS...200.3406J Altcode: 2002BAAS...34..691J Measurements of components of the vector magnetic field in the solar corona can potentially yield information critical to our understanding of coronal structure, dynamics and heating. I will review techniques for making such measurements, in particular those that can be applied outside of active regions. Forbidden coronal emission lines appear to have the highest potential to address outstanding problems in coronal physics, especially those related to the storage and release of magnetic free energy. Measurements of the full Stokes vector of M1 lines of magnetic dipole (M1) character can constrain both the line-of-sight field strength, B&|slash, through the longitudinal Zeeman effect seen in Stokes V profiles, and the direction of the vector field projected onto the plane-of-the-sky, through the analysis of resonance scattering-induced linear polarization seen in Stokes Q and U, in the so-called ``strong field'' regime of the Hanle effect. Coupled with additional data and models, accurate polarimetry can reveal information on coronal magnetic fields, including current systems, unobtainable by other means available now or in the near future. I will discuss the current challenges presented by such measurements for both for the ATST project and in more general terms. Title: Physical consequences of the inclusion of anomalous resistivity in the dynamics of 2D magnetic reconnection Authors: Roussev, I.; Galsgaard, K.; Judge, P. G. Bibcode: 2002A&A...382..639R Altcode: The aim of the present paper is to explore the role of anomalous resistivity on the dynamics of magnetic reconnection in a 2D environment of relevance to the solar transition region. We adopt an ad hoc but explicit form of the anomalous resistivity, motivated by a streaming instability, in which the resistivity jumps suddenly as the electron drift velocity exceeds some fraction of the mean electron thermal speed. Experiments have been conducted to investigate the impact of various critical speeds and arbitrary scaling constants of the resistivity level on the time-dependent evolution of the magnetic reconnection process. The specific threshold value is found to influence the dynamics of the reconnection, with higher values providing a localised on-off effect of patchy diffusion. For a given normalised value of the anomalous resistivity, the amount of Joule heating released scales inversely with the threshold value. The total energy release is found to be above the lower limit of ``quiet'' Sun nano-flares required to maintain a hot corona. The reconnection events discussed here may be important to the energy balance of the solar transition region and overlying corona, as already suggested in earlier work based on SUMER observations. Title: On the Nature of Magnetic Shadows in the Solar Chromosphere Authors: McIntosh, S. W.; Judge, P. G. Bibcode: 2001ApJ...561..420M Altcode: Recent multi-instrument spacecraft studies of the solar photosphere and chromosphere have uncovered a feature-a ``magnetic shadow''-not previously discussed in the literature. A region of the midchromosphere neighboring, but not within, a network magnetic element exhibits a suppression of both the mean UV line/continuum intensity and the characteristic 3 minute oscillation that is clearly observed elsewhere in apparently similar internetwork regions. The clearest cases appear to occur rarely, and their properties stand in obvious contrast to the well-known ``aureoles'' of enhanced variability seen surrounding some plage regions. It is imperative to understand more clearly the nature of the shadow region, not least because the suppressed atmospheric heating within it has implications for heating processes elsewhere in the chromosphere that are dependent on, or at least related to, the 3 minute oscillation. Based on the measured photospheric magnetic field, its upward extrapolation, and the appearance of spectral features formed above the midchromosphere, we suggest that a shadow occurs when magnetic structures, in a relatively weak background field, ``close'' locally within the chromosphere, suppressing the upward propagation of magnetoatmospheric waves into the chromosphere. Title: A Study of Chromospheric Oscillations Using the SOHO and TRACE Spacecraft Authors: Judge, Philip G.; Tarbell, Theodore D.; Wilhelm, Klaus Bibcode: 2001ApJ...554..424J Altcode: We analyze line and continuum time-series data of the solar atmosphere, with between 10 and 60 s cadence, using the MDI and SUMER instruments on the SOHO spacecraft and the UV bandpasses on the TRACE satellite. The co-aligned data sets sample spectral features formed from photosphere to the middle transition region, spanning five decades in pressure, under quiet-Sun and plage conditions. We discuss power, phase difference, and coherence spectra, and examine data in the time domain. The observed photospheric and chromospheric oscillations are strongly coupled for frequencies between 2 and 8 mHz. Phase coherences decrease with increasing height, with only occasional periods and locations of observable coherence up to heights where transition region emission lines are formed. The middle chromosphere (in the SUMER continua) oscillates in several megameter (Mm) diameter coherent patches with power predominantly in the 5-7 mHz range. The TRACE data, formed in the upper photosphere, show smaller patterns superimposed on these large-scale oscillations, resulting (at least in part) from granulation. At the observed spatial scales, all the observed properties point to p-modes, especially the ``pseudomodes'' just above the acoustic cutoff frequency, as the dominant mode of the chromospheric dynamics. Smaller scale ``acoustic event'' drivers, associated with granular dynamics, appear to be less important. The predominant internetwork chromospheric oscillations arise from regions much larger horizontally than vertically. If propagating largely vertically, this can naturally explain why the one-dimensional simulations of Carlsson & Stein might be more successful than expected. The chromospheric response to the p-mode driving is, however, intermittent in space and time. Some of the intermittency appears to result from the interaction of the upward-propagating waves with magnetic fields. Evidence for this includes suppressed intensities and oscillations near quiet-Sun network elements (which we dub ``magnetic shadows''), absence of oscillations in internetwork regions neighboring plage magnetic fields, and a change in character of the quiet-Sun internetwork oscillations between the 119 and 104 nm continua formed at 1 and 1.2 Mm. The latter might be caused by canopy fields that form between these heights under typical quiet-Sun conditions. A SUMER-only data set reported by Wikstøl et al. has a factor of 3 more oscillatory power in the 104 nm continuum than the data analyzed here, with stronger coherences extending into the solar transition region. Together, these data support the general picture that the chromosphere oscillates primarily in response to forcing by the p-modes, they are therefore large-scale (several Mm across) waves, and they are often strongly influenced by magnetic effects (internetwork fields, or the overlying canopy), before the oscillations even reach the transition region. Title: An Observational Manifestation of Magnetoatmospheric Waves in Internetwork Regions of the Chromosphere and Transition Region Authors: McIntosh, S. W.; Bogdan, T. J.; Cally, P. S.; Carlsson, M.; Hansteen, V. H.; Judge, P. G.; Lites, B. W.; Peter, H.; Rosenthal, C. S.; Tarbell, T. D. Bibcode: 2001ApJ...548L.237M Altcode: We discuss an observational signature of magnetoatmospheric waves in the chromosphere and transition region away from network magnetic fields. We demonstrate that when the observed quantity, line or continuum emission, is formed under high-β conditions, where β is the ratio of the plasma and magnetic pressures, we see fluctuations in intensity and line-of-sight (LOS) Doppler velocity consistent with the passage of the magnetoatmospheric waves. Conversely, if the observations form under low-β conditions, the intensity fluctuation is suppressed, but we retain the LOS Doppler velocity fluctuations. We speculate that mode conversion in the β~1 region is responsible for this change in the observational manifestation of the magnetoatmospheric waves. Title: Towards a Global Picture: Observable Effects Induced by or Related to Magnetic Fields Authors: Judge, P. G.; Charbonneau, P. Bibcode: 2001ASPC..248..659J Altcode: 2001mfah.conf..659J No abstract at ADS Title: Coronal Magnetometry: A Feasibility Study Authors: Judge, P. G.; Casini, R.; Tomczyk, S.; Edwards, D. P.; Francis, E. Bibcode: 2001STIN...0227999J Altcode: Measurements of components of the vector magnetic field in the solar corona can potentially yield information critical to our understanding of coronal structure, dynamics and heating. In this report we re-examine various techniques for such measurements, in particular those that can be applied outside of active regions, to investigate issues critical to the development of a new 'coronal magnetometer,' and to lay down some foundations upon which a suitable instrument may be developed for synoptic observations. The well-known forbidden coronal emission lines of magnetic dipole (M1) character appear to have the highest potential to address outstanding problems in coronal physics, especially those related to the storage and release of magnetic free energy. Measurements of the full Stokes vector of M1 lines can constrain both the line-of-sight (LOS) field strength, through the longitudinal Zeeman effect seen in Stokes V profiles, and the direction of the vector field projected onto the plane-of-the-sky (POS), through the analysis of resonance scattering-induced linear polarization seen in Stokes Q and U, in the so-called 'strong field' regime of the Hanl effect. Title: A Synthesis Code for Forbidden Coronal Lines Authors: Judge, P. G.; Casini, R. Bibcode: 2001ASPC..236..503J Altcode: 2001aspt.conf..503J No abstract at ADS Title: Spectral Lines for Polarization Measurements of the Coronal Magnetic Field. III. Atomic Data for Si IX Authors: Brage, Tomas; Judge, Philip G.; Jönsson, Per; Edwards, D. P. Bibcode: 2000ApJ...540.1114B Altcode: We report on large-scale ab initio multiconfiguration Dirac-Fock (MCDF) calculations for spectral lines of Si IX, with emphasis on the forbidden transitions 2p2 3PJ-->J'. The J=0-->J'=1 transition at 3.9346 μm holds promise as a diagnostic of coronal magnetic fields if and when future coronagraphic instruments can measure the polarized light at this wavelength. Title: Erratum: Spectral Lines for Polarization Measurements of the Coronal Magnetic Field. II. Consistent Treatment of the Stokes Vector for Magnetic-Dipole Transitions Authors: Casini, R.; Judge, P. G. Bibcode: 2000ApJ...533..574C Altcode: In the paper ``Spectral Lines for Polarization Measurements of the Coronal Magnetic Field. II. Consistent Treatment of the Stokes Vector for Magnetic-Dipole Transitions,'' by R. Casini and P. G. Judge (ApJ, 522, 524 [1999]), several typographical errors were introduced during the production process. The corrections are as follows: 1. In the second entry of the fourth panel of Table 1, sqrt(3)/2 cosϑ should read sqrt(3/2) cosϑ 2. The left-hand sides of equations (23a) and (23b) should be as in the left-hand sides of equations (22a) and (22b). 3. In equations (24c) and (24e), ρK'0(αJ) should read ρK'0K''J') 4. In equations (24e) and (24f), JK''0α'J,αJ') should read JK''0α'J',αJ) 5. The very first sentence in the legend of Figure 5 should be deleted. The Press sincerely apologizes for these errors. A last typographical error, which instead is the complete responsibility of the authors, is the absence of a minus sign in front of the right-hand sides of equations (43a) and (43b). Title: Chromospheric and Transition Region Internetwork Oscillations: A Signature of Upward-propagating Waves Authors: Wikstøl, Ø.; Hansteen, V. H.; Carlsson, M.; Judge, P. G. Bibcode: 2000ApJ...531.1150W Altcode: We analyze spectral time series obtained on 1997 April 25 with the SUMER instrument on SOHO. Line and continuum data near 1037 Å were acquired at a cadence of 16 s. This spectral region was chosen because it contains strong emission lines of C II, formed in the upper chromosphere/lower transition region; O VI, formed in the upper transition region; and neighboring continuum emission formed in the middle chromosphere. The time series reveal oscillatory behavior. Subsonic (3-5 km s-1 amplitude) Doppler velocity oscillations in the C II and O VI lines, with periods between 120 and 200 s, are prominent. They are seen as large-scale coherent oscillations, typically of 3-7 Mm length scale, occasionally approaching 15 Mm, visible most clearly in internetwork regions. The Doppler velocity oscillations are related to oscillations seen in the continuum intensity, which precede upward velocity in C II by 40-60 s. The C II Doppler shift precedes the O VI Doppler shift by 3-10 s. Oscillations are also present in the line intensities, but the intensity amplitudes associated with the oscillations are small. The continuum intensity precedes the C II intensity by 30-50 s. Phase difference analysis shows that there is a preponderance of upward-propagating waves in the upper chromosphere that drive an oscillation in the transition region plasma, thus extending the evidence for upward-propagating waves from the photosphere up to the base of the corona. Title: On Spectroscopic Filling Factors and the Solar Transition Region Authors: Judge, P. G. Bibcode: 2000ApJ...531..585J Altcode: The concept of spectroscopic filling factors is examined by assuming that observable astrophysical plasmas are inhomogeneous and must therefore be described using functions ζ(n), the emission measure differential in electron density n. Using a formal definition for the spectroscopic filling factor (fs) and simple distribution functions, it is shown that (1) fs differs from the geometric filling factor f unless the plasma is truly homogeneous [ζ(n)=ζ0δ(n-n0)], (2) fs depends on the choice of line pairs for the same ζ(n), (3) fs systematically underestimates f, and (4) fs departs more from f the broader the distribution ζ(n). Implications for the particular case of the unresolved solar transition region are discussed. A dynamic ``classical'' transition region model appears to satisfy observed properties, including tiny filling factors (10-5-10-2) as well as filamentary models. This work highlights the nonunique interpretation of spectral data in terms of unresolved plasma structure. Title: Non-Uniqueness of Atmospheric Modeling Authors: Judge, Philip G.; McIntosh, Scott W. Bibcode: 1999SoPh..190..331J Altcode: We focus on the deceptively simple question: how can we use the emitted photons to extract meaningful information on the transition region and corona? Using examples, we conclude that the only safe way to proceed is through forward models. In this way, inherent non-uniqueness is handled by adding information through explicit physical assumptions and restrictions made in the modeling procedure. The alternative, `inverse' approaches, including (as a restricted subset) many standard '`spectral diagnostic techniques', rely on more subjective choices that have, as yet, no clear theoretical support. Emphasis is on the solar transition region, but necessarily discussing the corona, and with implications for more general problems concerning the use of photons to diagnose plasma conditions. Title: Transition Region Oscillations Authors: Hansteen, V. H.; Wisktol, O.; Carlsson, M.; Judge, P. G. Bibcode: 1999ESASP.446..351H Altcode: 1999soho....8..351H We analyze time series data obtained April 25th 1997 with the SUMER instrument on SOHO. Line and continuum data near 1037 were acquired at a cadence of 16s. This spectral region was chosen because it contains strong emission lines of C II, formed in the upper chromosphere/lower transition region, O VI, formed in the upper transition region, as well as neighboring continuum emission formed in the middle chromosphere. The dataset reveals oscillatory behavior containing valuable information on the physical structure of the chromosphere and transition region. Prominent in the data are subsonic (3-5 km/s amplitude) velocity oscillations with periods between 120 and 200 sec. They are seen as large scale coherent oscillations, typically of 3--7 Mm length scale but sometimes approaching 15Mm, visible most clearly in internetwork regions. The oscillations are present in C II and O VI velocities, as well as in the continuum intensity. The continuum intensity precedes upward velocity in the C II line by 40-60s and the C III velocity precedes the O VI velocity by 3-10s. The oscillations are also present in the intensities of the two lines, but the intensity amplitudes associated with the oscillations are small. We find that the continuum intensity precedes the C II intensity by 30-50s. These phase shifts indicate that there are upward propagating waves in the upper chromosphere that drive an oscillation in the transition region plasma. The oscillations seem to be present in most internetwork areas at any time, thus they are the dominant resolvable dynamical feature of the internetwork chromosphere and transition region. Title: On the Doppler Shifts of Solar Ultraviolet Emission Lines Authors: Peter, H.; Judge, P. G. Bibcode: 1999ApJ...522.1148P Altcode: We examine emission-line profiles observed with the Solar Ultraviolet Measurement of Emitted Radiation (SUMER) instrument during the roll of the SOHO spacecraft on 1997 March 20. SUMER data were acquired in selected wavelength bands including lines from the low chromosphere to the corona. Our main aim is to determine the center-to-limb behavior of emission lines formed in the chromosphere, transition region, and corona, especially of the observed Doppler shifts, to try to form a consistent picture of the basic kinematic properties of the emitting plasmas. To achieve this we combine the roll data with data from the full disk discussed elsewhere and fitted Gaussian profiles to the cores of the line profiles. The Doppler-shift data at large spatial scales (>50") clearly reveal center-to-limb redshift behavior consistent with a cosϑ variation in all transition region lines. The three ``coronal'' lines in the data set (of Ne VIII and Mg X) reveal center-to-limb behavior consistent with disk-center blueshifts, in contradiction to some previous work. The redshift to blueshift transition occurs at electron temperatures of about 5×105 K. Furthermore, we present evidence for an outflow of the fast solar wind from the coronal holes throughout the whole transition region. These results confirm and extend earlier work and point toward a (re-) measurement of rest wavelengths of lines formed at coronal temperatures in the laboratory. Together these results provide a firmer observational foundation for the development of classes of models to account for the well-known redshifts and point to the need to develop models that can also account for the coronal-line blueshifts. Title: Spectral Lines for Polarization Measurements of the Coronal Magnetic Field. II. Consistent Treatment of the Stokes Vector forMagnetic-Dipole Transitions Authors: Casini, R.; Judge, P. G. Bibcode: 1999ApJ...522..524C Altcode: We present a compact, self-consistent formulation for the description of polarized radiation from magnetic-dipole transitions occurring in the magnetized solar corona. This work differs from earlier treatments by Sahal-Bréchot and House in the 1970s, in that the radiative emission coefficients for the four Stokes parameters, I, Q, U, and V, are treated to first order in a Taylor expansion of the line profile in terms of the Larmor frequency of the coronal magnetic field. In so doing, the influence on the scattered radiation of both atomic polarization, induced through anisotropic irradiation, and the Zeeman effect is accounted for in a consistent way. It is found that the well-known magnetograph formula, relating the V profile to the frequency derivative of the I profile, must be corrected in the presence of atomic alignment produced by anisotropic irradiation. This correction is smallest for lines where collisions and cascades dominate over excitation by anisotropic radiation, but it systematically increases with height above the solar limb (up to a theoretical maximum of 100%, in the collisionless regime and in the limit of vanishing longitudinal magnetic field). Although the correction to the magnetograph formula must be calculated separately for each line as a function of heliocentric distance, it is likely to be small for some lines of practical interest, along lines of sight close to the solar limb. Title: Probable Detection of a Bright Infrared Coronal Emission Line of Si IX near 3.93 Microns Authors: Kuhn, J. R.; MacQueen, R. M.; Streete, J.; Tansey, G.; Mann, I.; Hillebrand, P.; Coulter, R.; Lin, H.; Edmunds, D.; Judge, P. Bibcode: 1999ApJ...521..478K Altcode: We report here the probable detection of an emission line of Si IX that was observed from an open C130 aircraft over the Pacific Ocean during the 1998 total solar eclipse. Although the IR data themselves are inconclusive because of the uncertainty in the precise central wavelengths of the narrowband filters during the eclipse, the consistency of the measured IR limb excess with simultaneous EUV emission measured by SOHO/Coronal Diagnostic Spectrometer and the EUV Imager Telescope support our detection claim. This line appears to be the brightest IR coronal line yet observed, and its existence may significantly improve future prospects for obtaining optical coronal magnetic field measurements. Title: TRACE Images of the Solar Chromosphere, Transition Region, and Low Corona at High Cadence and High Spatial Resolution Authors: Tarbell, T. D.; Handy, B. N.; Judge, P. G. Bibcode: 1999AAS...194.7801T Altcode: 1999BAAS...31..960T We present TRACE images and movies showing C IV emission (transition region at 80,000 degrees) and UV continuum (temperature minimum region) of quiet and active regions. TRACE images using the 1550, 1600, and 1700 Angstroms filters can be combined to estimate the total emission in the C IV 1548 and 1550 lines and the UV continuum. These are supplemented in different observations with MDI magnetograms, TRACE 171 Angstroms images (Fe IX/X and perhaps O VI), and SUMER spectra of chromospheric and transition region lines from SOHO JOP 72. In quiet sun, bright C IV transients are seen in the vicinity of flux emergence, flux cancellation, and less dramatic interactions of small magnetic structures. Some of these are accompanied by high-velocity explosive events seen in SUMER spectra. The C IV emission can be well-separated from the photospheric magnetic footpoints, suggesting that it takes place on current sheets higher in the atmosphere separating different flux systems. In active regions, both bright and dark fibrils or loops are seen in C IV. Many nano/micro/sub flares are seen, some but not all of which are associated with emerging flux. The C IV emission of "moss" regions, footpoints of hot coronal loops, is contrasted with that of similar plage which does not have hot loops above it. This work was supported by the NASA contracts and grants for TRACE, MDI, and SOHO. Title: Lines of OIV and SIV in the Goddard High-Resolution Spectrograph spectrum of RR Tel: constraints on atomic data Authors: Harper, G. M.; Jordan, C.; Judge, P. G.; Robinson, R. D.; Carpenter, K. G.; Brage, T. Bibcode: 1999MNRAS.303L..41H Altcode: High signal-to-noise ratio spectra of RR Tel obtained at medium resolution with the Goddard High-Resolution Spectrograph (GHRS) on the Hubble Space Telescope (HST) are used to test available atomic data for the OIV 2s^22p ^2P-2s2p^2 ^4P multiplet (UV 0.01). The fine-structure intervals of the 2s2p^2 ^4P term given by Moore (1983) appear to need revision. The flux ratios of lines within multiplet UV (0.01), which have a common upper level, depend only on transition probabilities. The observed flux ratio of lines from the ^4P_3/2 level differs from that predicted by theory, but this difference cannot be attributed to a blend with a line of SIV]. At the electron densities in the RR Tel nebula, other flux ratios give information on the relative electron excitation rates between the ^2P and ^4P fine-structure levels. Using the collision strengths calculated by Zhang, Graziani & Pradhan, the rate to the ^4P_5/2 level, relative to the rates to the other J states, appears to be underestimated by ~ 10 per cent, which is within the expected uncertainty of 20 per cent. We also discuss the SIV 3s^23p ^2P-3s3p^2 ^4P multiplet. Title: Spectral decomposition by genetic forward modelling Authors: McIntosh, S. W.; Diver, D. A.; Judge, P. G.; Charbonneau, P.; Ireland, J.; Brown, J. C. Bibcode: 1998A&AS..132..145M Altcode: We discuss the analysis of real and simulated line spectra using a genetic forward modelling technique. We show that this Genetic Algorithm (GA) based technique experiences none of the user bias or systematic problems that arise when faced with poorly sampled or noisy data. An important feature of this technique is the ease with which rigid a priori constraints can be applied to the data. These constraints make the GA decomposition much more accurate and stable, especially at the limit of instrumental resolution, than decomposition algorithms commonly in use. Title: Evidence in Support of the ``Nanoflare'' Picture of Coronal Heating from SUMER Data Authors: Judge, P. G.; Hansteen, V.; Wikstøl, Ø.; Wilhelm, K.; Schühle, U.; Moran, T. Bibcode: 1998ApJ...502..981J Altcode: We study high signal-to-noise profiles of O IV emission lines obtained using the SUMER instrument on SOHO. Data for the quiet Sun obtained close to the disk center and at the solar limb were acquired. After careful data processing in which disk data were analyzed differentially against limb data, we find a systematic correlation between a density-sensitive emission-line ratio and Doppler shift across the same emission-line profiles. While unidentified blended lines cannot be completely discounted, the data suggest that the effects of such blends are small. Based on theoretical results in an earlier paper, we argue that if wave motions are responsible for the observed behavior, then the data reveal evidence for compressive waves propagating downward from the corona to the chromosphere. This analysis naturally lends support to the dominance of the ``nanoflare'' mechanism for coronal heating over other theories that invoke upward wave propagation, but other mechanisms capable of generating downward-propagating waves cannot be discounted. If, instead, steady flows are the cause of the observed behavior, such as return flows from spicules, then they must be such that the density is higher in the downflowing plasma. While these particular data do not allow us to discriminate between waves or steady flows, additional data from SOHO should be able to address this problem. This work required and achieved very accurate wavelength calibrations (better than 1/5 of a pixel on the detectors), taking SUMER close to its observational capabilities. We therefore present the elements of the analysis and calibration of SUMER data that may be of interest to other users. Title: On Inferring the Properties of Dynamic Plasmas from Their Emitted Spectra: The Case of the Solar Transition Region Authors: Wikstøl, Øivind; Judge, P. G.; Hansteen, Viggo Bibcode: 1998ApJ...501..895W Altcode: We reexamine the issue of inferring physical properties of solar plasmas using EUV and UV observations. We focus on the question of whether one can determine if typical structures seen as bright in typical ``transition-region'' lines are formed in the thermal interface between the coronal and chromospheric plasmas. Since 1983, Feldman and colleagues have proposed, based upon Skylab and other data, that much of the transition-region emission is formed in so-called unresolved fine structures (UFS) that are magnetically and thermally disconnected from the corona. This has led others to consider theoretical models of the transition region that differ from classical models. We examine the evidence cited in support of the UFS picture, specifically by relaxing the implicit assumption of a static atmospheric structure. Noting that observational data alone do not contain the information necessary to infer essential properties of the emitting plasmas, we argue that additional information must be added through forward calculations using physical models. MHD models of coronal flux tubes are then examined with explicit assumptions and boundary conditions, not as an attempt to ``fit'' observed data, but in order to study the formation of emission lines in dynamically evolving plasmas that are unresolved in space and time. We show that incorrect conclusions can be drawn by applying reasonable and traditional diagnostic methods to spectral data when unresolved dynamic evolution of the emitting plasma is important but not accounted for. In the particular case of the transition region, we show that the UFS interpretation is not unique, and is likely to be incorrect in the presence of unresolved dynamics. Most or all of the evidence for UFS is amenable to a different, equally reasonable interpretation, in which the transition-region emission is at all times formed in the time-varying thermal interface between the corona and the chromosphere. This work is likely to be important for a wider range of astrophysical plasmas than simply in the solar transition region. At stake is our basic ability to correctly diagnose physical conditions of plasmas for which heating mechanisms are not yet understood, but which are likely to be time dependent. Title: Hyperfine Induced Transitions as Diagnostics of Isotopic Composition and Densities of Low-Density Plasmas Authors: Brage, Tomas; Judge, Philip G.; Aboussaïd, Abdellatif; Godefroid, Michel R.; Jönsson, Per; Ynnerman, Anders; Froese Fischer, Charlotte; Leckrone, David S. Bibcode: 1998ApJ...500..507B Altcode: The J = 0 --> J' = 0 radiative transitions, usually viewed as allowed through two-photon decay, may also be induced by the hyperfine (HPF) interaction in atoms or ions having a nonzero nuclear spin. We compute new and review existing decay rates for the nsnp 3PoJ --> ns2 1SJ'=0 transitions in ions of the Be (n = 2) and Mg (n = 3) isoelectronic sequences. The HPF induced decay rates for the J = 0 --> J' = 0 transitions are many orders of magnitude larger than those for the competing two-photon processes, and when present are typically 1 or 2 orders of magnitude smaller than the decay rates of the magnetic quadrupole (J = 2 --> J' = 0) transitions for these ions. Several HPF induced transitions are potentially of astrophysical interest in ions of C, N, Na, Mg, Al, Si, K, Cr, Fe, and Ni. We highlight those cases that may be of particular diagnostic value for determining isotopic abundance ratios and/or electron densities from UV or EUV emission-line data. We present our atomic data in the form of scaling laws so that, given the isotopic nuclear spin and magnetic moment, a simple expression yields estimates for HPF induced decay rates. We examine some UV and EUV solar and nebular data in light of these new results and suggest possible applications for future study. We could not find evidence for the existence of HPF induced lines in the spectra we examined, but we demonstrate that existing data have come close to providing interesting upper limits. For the planetary nebula SMC N2, we derive an upper limit of 0.1 for 13C/12C from Goddard High-Resolution Spectrograph data obtained by Clegg. It is likely that more stringent limits could be obtained using newer data with higher sensitivities in a variety of objects. Title: Spectral Lines for Polarization Measurements of the Coronal Magnetic Field. I. Theoretical Intensities Authors: Judge, P. G. Bibcode: 1998ApJ...500.1009J Altcode: Infrared emission lines are potentially sensitive probes of components of the coronal vector magnetic field, through the Zeeman effect, and on its direction projected onto the plane of the sky, through fluorescent polarization of scattered photospheric light. Prompted by the advent of sensitive infrared array detectors, existing atomic data were reexamined to compile a complete list of coronal lines that may yield a detectable Zeeman effect, through careful differential measurements of Stokes profiles, at typical coronal field strengths of order 10 G. ``Average'' intensities were computed for a subset of promising forbidden coronal lines. A representative coronal density structure was used. The distribution of plasma with temperature was, at all heights in the corona, assumed to be that described by a standard differential emission measure from extreme-ultraviolet observations of the solar disk. Effects of excitation by photospheric radiation were included, as well as cascades from collisionally excited higher levels having the same principal quantum number as the ground levels. The largest source of error in the computed intensities lies in the form assumed for the emission measure distribution. The assumed density and temperature structure is too simple for detailed comparisons with observations of a particular coronal structure. Nevertheless, existing observed intensities are consistent with the calculations, which suggests that the theoretical intensities of (as yet) unobserved lines can be used as a basis for further study. The strongest predicted lines arise from magnetic dipole transitions within the ground terms of the 2sm2pn and 3sm3pn, m = 1, 2, n = 1, ..., 5, configurations. The most promising lines lie between 1 and 10 μm, the lower limit being set by the need to detect small field strengths. The upper limit is set by the small Einstein A-coefficients and the smaller intensities of the exciting photospheric light, both of which lead to smaller forbidden line intensities. The most promising lines include [Fe XIII] 1.0747, 1.0798 μm [Si X] 1.43 μm [Si IX] 2.58, 3.93 μm [Mg VIII] 3.03 μm and [Mg VII] 5.50, 9.03 μm. An aircraft experiment is being prepared to obtain targeted portions of the coronal spectrum between 1 and 10 μm during the 1998 February 26 eclipse, with the goal of detecting some of these promising lines. This work will help toward the planning and development of efficient magnetographs, perhaps space-borne, for the routine measurement of coronal magnetic fields in the quiet and active Sun. Title: The relation between line ratio and emission measure analyses Authors: McIntosh, S. W.; Brown, J. C.; Judge, P. G. Bibcode: 1998A&A...333..333M Altcode: Spectroscopic diagnosis of the temperature and density structure of hot optically thin plasmas from emission line intensities is usually described in two ways. The simplest approach, the `line ratio' method, uses an observed ratio of emission line intensities to determine a `spectroscopic mean' value of electron temperature < T_e > or electron density < ne>. The mean value is chosen to be the theoretical value of T_e or ne which matches the observed value. The line ratio method is stable, leading to well defined values of < T_e > or < n_e > for each line pair but, in the realistic case of inhomogeneous plasmas, these are hard to interpret since each line pair yields different mean parameter values. The more general `differential emission measure' (DEM) method recognizes that observed plasmas are better described by distributions of temperature or density along the line of sight, and poses the problem in inverse form. It is well known that the DEM function is the solution to the inverse problem, which is a function of T_e, n_e, or both. Derivation of DEM functions, while more generally applicable, is unstable to noise and errors in spectral and atomic data. The mathematical relation between these two approaches has never been precisely defined. In this paper we demonstrate the formal equivalence of the approaches, and discuss some potentially important applications of methods based upon combining the line ratio and DEM approaches. Title: The Structure of the Chromosphere Properties Pertaining to Element Fractionation Authors: Judge, P. G.; Peter, H. Bibcode: 1998SSRv...85..187J Altcode: We review the structure and dynamics of the solar chromosphere with emphasis on the quiet Sun and properties that are relevant to element fractionation mechanisms. Attention is given to the chromospheric magnetic field, its connections to the photosphere, and to the dynamical evolution of the chromosphere. While some profound advances have been made in the “unmagnetized” chromosphere, our knowledge of the magnetically controlled chromosphere, more relevant for the discussion of element fractionation, is limited. Given the dynamic nature of the chromosphere and the poorly understood magnetic linkage to the corona, it is unlikely that we will soon know the detailed processes leading to FIP fractionation. Title: On Chromospheric Heating Mechanisms of ``Basal Flux'' Stars Authors: Judge, P. G.; Carpenter, K. G. Bibcode: 1998ApJ...494..828J Altcode: Several pieces of evidence have been pieced together over recent years to support the notion that the chromospheric emission measured from stars with convection zones results in part from the upward propagation and dissipation of acoustic waves. One argument, based on a statistical analysis of available UV data of such stars across the H-R diagram, suggests the presence of an omnipresent ``basal'' level of chromospheric heating, which has been postulated as resulting from nonlinear acoustic wave heating.

However, with few exceptions, no studies have been made that test more directly the intrinsically dynamic nature of this shock-heating mechanism. Therefore, in order to search for more direct signatures of such upward-propagating shock waves in lines of C II, we examined Goddard High-Resolution Spectrograph spectra of several evolved stars that have ``basal'' levels of activity. No evidence is found to support the presence of such waves as a dominant component of the heating mechanism. Instead, behavior reminiscent of the solar transition region is seen, suggesting a magnetic heating mechanism for these stars.

We conclude that upward-propagating shock waves do not dominate the observed radiative losses from chromospheres of stars exhibiting typical ``basal'' behavior, and we suggest that the nonmagnetic origin of the basal components of all convective stars must be called into question. New solar data from the SUMER instrument on SOHO also suggest problems with the acoustic-wave interpretation, although further work is warranted.

In the course of this work, we also found a simple explanation for previously noted discrepancies between calculated and observed ratios of C II lines in the spectrum of α Ori.

Based on observations with the NASA/ESA Hubble Space Telescope, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. Title: The Structure of the Chromosphere Authors: Judge, P. G.; Peter, H. Bibcode: 1998sce..conf..187J Altcode: No abstract at ADS Title: SUMER Observations of the Quiet Solar Atmosphere: The Network Chromosphere and Lower Transition Region Authors: Judge, Philip; Carlsson, Mats; Wilhelm, Klaus Bibcode: 1997ApJ...490L.195J Altcode: We examine spectral properties of the network chromosphere and lower transition region from the SUMER instrument on the SOHO spacecraft, using time-series data sets discussed in an accompanying Letter by Carlsson, Judge, & Wilhelm. The data were obtained early in the mission with no tracking of solar features and so cannot generally be used to examine intrinsic variations in features on timescales in excess of 383 s. Upon examination of the temporal variations and some preliminary power spectrum analysis, we find the following: (1) Transition region lines show more redshift in network regions than in internetwork regions and also a correlation between line intensity brightenings and increased redshift. (2) The internetwork ``Ca II grain'' phenomenon is not seen in He I λ584 or in lines of Si III and C III. (3) Very rapid changes are seen in the network for transition region lines with no obvious correspondence with the underlying chromosphere. (4) He I λ584 line profiles show very slow time variations. (5) Small-amplitude (2-5 km s-1) coherent oscillations of 5"-10" scale length and ~130 s period are seen in Doppler shifts of Si III between regions of bright network elements. (6) Essentially all blueshifts or redshifts are substantially less than line widths. We conclude that upward-propagating acoustic shock waves do not contribute significantly to the heating of the lower transition region, and that ionization equilibrium is likely to fail for the interpretation of certain emission lines. The spatial coherency of the Si III velocity oscillations indicates that the quiet Sun's magnetic field topology is more uniform than emission-line intensity data alone might suggest. Title: Differential Emission Measures-Can we do more?? Authors: McIntosh, S. W.; Brown, J. C.; Judge, P. G. Bibcode: 1997BAAS...29.1120M Altcode: No abstract at ADS Title: SUMER Observations Confirm the Dynamic Nature of the Quiet Solar Outer Atmosphere: The Internetwork Chromosphere Authors: Carlsson, Mats; Judge, P. G.; Wilhelm, K. Bibcode: 1997ApJ...486L..63C Altcode: 1997astro.ph..6226C On 1996 March 12, during the commissioning phase of the SOHO mission, we obtained observations of the quiet-Sun with the SUMER instrument. The observations were sequences of 15-20 s exposures of ultraviolet emission-line profiles and of the neighboring continua. These data contain signatures of the dynamics of the solar chromosphere that are uniquely useful because of wavelength coverage, moderate signal-to-noise ratios, and image stability.

We focus on data for the internetwork chromosphere. The dominant observed phenomenon is an oscillatory behavior that is analogous to the 3 minute oscillations seen in CaII lines. The oscillations appear to be coherent over 3"-8" diameter areas. At any time they occur over about 50% of the area studied, and they appear as large perturbations in the intensities of lines and continua. The oscillations are most clearly seen in intensity variations in the ultraviolet (λ > 912 Å) continua, and they are also seen in the intensities and velocities of chromospheric lines of CI, NI, and OI. Intensity brightenings are accompanied by blueshifts of typically 5 km s-1. Phase differences between continuum and line intensities also indicate the presence of upward propagating waves. The detailed behavior is different between different lines, sometimes showing phase lags. The 3 minute intensity oscillations are occasionally seen in second spectra (CII λ1335) but never in third spectra (CIII and SiIII). Third spectra and HeI λ584 show oscillations in velocity that are not simply related to the 3 minute oscillations. The continuum intensity variations are consistent with recent simulations of chromospheric dynamics (Carlsson and Stein), while the line observations indicate that important ingredients are missing at higher layers in the simulations.

The data show that time variations are crucial for our understanding of the chromosphere itself and for the spectral features formed there--the quiet-Sun's chromosphere is very dynamic and not ``quiet.'' The implications of these data should be considered when planning chromospheric work with instruments such as those on SOHO. Title: Signatures of Acoustic and Magnetic Waves in Solar and Stellar Coronae Authors: Wikstøl, Øivind; Judge, Philip G.; Hansteen, Viggo H. Bibcode: 1997ApJ...483..972W Altcode: Time-dependent dynamical calculations of the radiating gas in solar coronal flux tubes are used to identify features of UV spectral-line profiles that can reveal the direction in which wave energy flows through the solar transition region. The profile features survive spatial and temporal averaging through nonlinear dependencies of line emission coefficients on thermal properties of the plasma that are correlated with fluid velocities. This approach can be applied to stellar and other unresolved sources, as well as the solar atmosphere. It can be regarded as a new angle of attack on the long-standing problem of determining coronal heating mechanisms. The approach requires low noise data of high spectral resolution. Therefore, it can take advantage of some unique properties of the SUMER instrument on SOHO. We make specific predictions for SUMER data that, in principle, can test whether energy propagates upward or downward in coronal flux tubes, thus allowing one to discriminate between competing theories of coronal heating. We are acquiring SUMER data in an attempt to do this. Title: Evidence in Support of the ``Nanoflare Picture'' of Coronal Heating from SUMER Data Authors: Judge, P.; Wikstol, O.; Hansteen, V. Bibcode: 1997SPD....28.0505J Altcode: 1997BAAS...29..909J We study high signal\--to\--noise profiles of O 4 emission lines obtained using the SUMER instrument on SoHO. Data for the quiet Sun obtained close to disk center and at the solar limb were acquired. After careful data processing in which disk data were analyzed differentially against limb data, we find a systematic correlation between a density sensitive emission line ratio and Doppler shift across the same emission line profiles. Based upon theoretical results in an earlier paper, we argue that if wave motions are responsible for the observed behavior, then the data reveal evidence for compressive waves propagating downwards from the corona to the chromosphere. This analysis therefore lends support to the dominance of the ``nanoflare'' mechanism for coronal heating (\cite{Parker1988}) over other theories that invoke upward wave propagation. If instead steady flows are the cause of the observed behavior, such as return flows from spicules, then they must be such that the density is higher in the downflowing plasma. We present time series data of other transition region lines from SoHO that suggest that episodic heating such as may occur through nanoflares is a more reasonable picture of heating mechanisms than models based upon steady flows. Title: Working Group 1: Non-Stationary Processes Authors: Judge, P. G. Bibcode: 1997ESASP.404..125J Altcode: 1997cswn.conf..125J No abstract at ADS Title: SUMER Observations Detecting Downward Propagating Waves in the Solar Transition Region Authors: Wiskstøl, Ø.; Judge, P. G.; Hansteen, V.; Wilhelm, K.; Schühle, U.; Moran, T. Bibcode: 1997ESASP.404..731W Altcode: 1997cswn.conf..731W No abstract at ADS Title: Observational signatures of nanoflare heated solar stellar coronae Authors: Wikstøl, Ø.; Judge, P. G.; Hansteen, V. H. Bibcode: 1997AdSpR..20.2289W Altcode: Using time-dependent dynamical models of the radiating gas in coronal flux tubes, we identify features in UV spectral line profiles that can reveal the direction in which energy flows through the solar transition region, in observations without temporal or spatial resolution. The profile features survive spatial and temporal averaging through non-linear dependencies of the line emission coefficients on thermal properties of the plasma that are correlated with the material velocity. This approach requires only low noise data of high spectral resolution and could naturally be applied to stars as well as the solar corona. We make predictions for the SUMER instrument that can in principle test whether energy propagates upwards or downwards in coronal flux tubes, suggesting a new angle of attack on the long standing problem of determining coronal heating mechanisms. Title: Fundamental Limitations of Emission-Line Spectra as Diagnostics of Plasma Temperature and Density Structure Authors: Judge, P. G.; Hubeny, Veronika; Brown, John C. Bibcode: 1997ApJ...475..275J Altcode: We discuss the problem of determining plasma structure from optically thin emission lines whose emission coefficients and frequency-integrated intensities are dependent on temperature T and electron density n. We cast the problem into the inverse form discussed by Hubeny & Judge (1995).

Three properties of the kernels in the integral equations lead to fundamental limitations in trying to determine the source term μ(T, n), the ``emission measure differential in temperature and density,'' from a set of emission-line intensities. First, the kernels are rather weakly dependent on n. Second, they have asymptotically identical dependencies on n. The inverse problem is therefore very poorly conditioned in the density dimension. Third, the kernels cannot (and may never) be calculated with an accuracy better than +/-10%. These properties set limits on the accuracy of all solutions, independent of the accuracy of observed line intensities. This concurs with earlier but less general work by Brown et al. (1991).

We try to determine solutions for μ(T, n), using specific target sources and numerical algorithms. Using realistic uncertainties, calculations indicate that meaningful inverse solutions for μ(T, n) cannot be obtained owing to the severe propagation of kernel errors, irrespective of the quality of observational data. Solutions for the ``emission measure differential in temperature'' ξ(T) = \smallint μ(T, n)dn are more robust against instabilities driven by poor conditioning.

Since traditional ``emission-line diagnostic ratios'' can only be defined through μ(T, n) (or some generalization thereof), our analysis casts doubt on the meaning of plasma properties derived from such line ratios, and illustrates the severe nonuniqueness of any equivalent ``inverse'' solution. This work may be important for studying a wide variety of atomic and ionic emission-line spectra, including work with instruments on SOHO and the Hubble Space Telescope. Title: The Ultraviolet Spectrum of a 3B Class Flare Observed with SOLSTICE Authors: Brekke, P.; Rottman, G. J.; Fontenla, J.; Judge, P. G. Bibcode: 1996ApJ...468..418B Altcode: An observation of the ultraviolet spectrum (1200-1800 Å) during the impulsive phase of a very extended 3B-X3 class solar flare on 1992 February 27 was obtained with the Solar-Stellar Irradiance Comparison Experiment (SOLSTICE). This observation is combined with ground-based Hα, magnetogram, and microwave data as well as hard X-ray measurements from the Ulysses spacecraft. This flare shows a dramatic enhancement of lines formed in the solar transition region. The irradiance (emitted flux density from the entire solar disk) of the resonance lines of C iv and Si iv increased by a factor of 12-13 during the impulsive phase of the flare. These irradiance enhancements are comparable with those measured during stellar flares. By taking into account the emitting flare area we infer that the radiance (specific intensity) of the flaring plasma was at least a factor of 15,000 brighter than the average solar disk radiance just prior to the event. Assuming the flare site's initial radiance was that of a typical active region, it then must have brightened by a factor of at least 3400. Such enhancement far exceeds previous published values (e.g., OSO 8, Skylab, and SMM) and indicates that many observations were affected by limited dynamic range. Thus, the SOLSTICE observation may be the first measurement of the true UV enhancement during the impulsive phase of very bright solar flares.

The Si III multiplet near 1295 Å also shows remarkable enhancement, but other allowed lines of C II, Si III (1206 Å), N V, and He II show more moderate enhancements, the weakest being H I Lyα, the irradiance of which increases only 6%. Some of the differences between the various enhancements are certainly caused by the timing of the observations since the scanning spectrometer observed different spectral features over periods of 4 minutes. Other differences due to line formation processes are being investigated but are consistent with density effects in the line emission coefficients. The inferred Lyα radiance enhancement is consistent with current post-impulsive phase flare models. However, the formation of the C IV and Si IV lines, formed during the impulsive phase of the flare, remains unknown. During the impulsive phase of the flare the strong transition region lines are systematically redshifted by 50 km s-1. Title: Intercombinations and Allowed Transitions in O IV Authors: Brage, Tomas; Judge, P. G.; Brekke, P. Bibcode: 1996ApJ...464.1030B Altcode: We report on large-scale ab initio multiconfiguration Hartree-Fock calculations for important multiplets including the UV 0.01 multiplet, 2s22p2PJ-2s2p2 4Pj', in O IV. The resulting transition probabilities should be accurate to ±5%-10% for intersystem lines and 1% or better for permitted lines.

We present new calculations of line emission coefficients using these transition probabilities and collisional rate coefficients published by Zhang, Graziani, & Pradhan in 1994. We readdress the use of these lines as diagnostics of electron densities, paying particular attention to uncertainties in density determinations. We find (1) the absolute uncertainties in derived densities are difficult to assess, but are at least ±40% controlled by uncertainties in collision strengths; (2) our new calculations bring observed and computed line ratios into better agreement (earlier papers yielding systematically different densities make the agreement worse); (3) there is additional evidence for strong blends in the 1404.8 emission feature, as argued by other authors, and/or evidence for inaccurate laboratory wavelengths; and (4) the computed branching ratios are in good agreement with observed ratios to within observational uncertainties of ±7%.

We determine electron densities in a variety of solar features from HRTS data from the first and second flights of this instrument. The derived electron densities vary remarkably little between quiet Sun network and active regions, but resonance line intensities vary dramatically, and we discuss reasons for this. Finally, we discuss how new high-quality data from the SUMER instrument to be flown on Solar and Heliosphereic Observatory (SO HO) could be used to address outstanding problems concerning blends and heating of the solar transition region. Title: Hyperfine induced transitions as diagnostics of low density plasmas and isotopic abundance ratios. Authors: Brage, T.; Judge, P. G.; Aboussaid, A.; Godefroid, M. R.; Jönsson, P.; Leckrone, D. S. Bibcode: 1996BAAS...28..832B Altcode: No abstract at ADS Title: Hyperfine Induced Transitions as Diagnostics of Low Density Plasmas and Isotopic Abundance ratios. Authors: Brage, T.; Judge, P. G.; Aboussaid, A.; Godefroid, M. R.; Jonsson, P.; Leckrone, D. S. Bibcode: 1996AAS...188.0705B Altcode: 1996BAAS...28V.832B We propose a new diagnostics of isotope abundance ratios and electron densities for low density plasmas, in the form of J = 0 -> J(') = 0 radiative transitions. These are usually viewed as being allowed only through two-photon decay, but they may also be induced by the hyperfine (HPF) interaction in atomic ions. This predicts a companion line to the E1] and M2 lines in the UV0.01 multiplet of ions isoelectronic to beryllium (e.g. C III, N IV, O V and Fe XXII) or magnesium (e.g. Si II, Ca IX, Fe XV and Ni XVII). As an example the companion line to the well known lambda lambda 1906.7,1908.7 lines in C III will be at 1909.597 Angstroms, but only present in the (13) C isotope (which has nuclear spin different from zero). We present new and accurate decay rates for the nsnp (3P^oJ) -> ns(2) (1S_{J('}=0)) transitions in ions of the Be (n=2) and Mg (n=3) isoelectronic sequences. We show that the HPF induced decay rates for the J = 0 -> J(') = 0 transitions are many orders of magnitude larger than those for the competing two-photon processes and, when present, are typically one or two orders of magnitude smaller than the decay rates of the magnetic quadrupole ( J = 2-> J(') = 0) transitions for these ions. We show that several of these HPF-induced transitions are of potential astrophysical interest, in ions of C, N, Na, Mg, Al, Si, K, Cr, Fe and Ni. We highlight those cases that may be of particular diagnostic value for determining isotopic abundance ratios and/or electron densities from UV or EUV emission line data. We present our atomic data in the form of scaling laws so that, given the isotopic nuclear spin and magnetic moment, a simple expression yields estimates for HPF induced decay rates. We examine some UV solar and nebular data in the light of these new results and suggest possible cases for future study. We could not find evidence for the existence of HPF induced lines in the spectra we examined, but we demonstrate that existing data have come close to providing interesting upper limits. For the planetary nebula SMC N2 we derive an upper limit of (13) C/(12) C of 0.1 from GHRS data obtained by Clegg. It is likely that more stringent limits could be obtained with newer data with higher sensitivities in a variety of objects. Title: Ultraviolet (1200 to 1800 Angstroms) Emission during the Impulsive Phase of a Class 3B-X3 Solar Flare Observed with SOLSTICE Authors: Brekke, P.; Rottman, C. J.; Fontenla, J.; Judge, P. G. Bibcode: 1996mpsa.conf..213B Altcode: 1996IAUCo.153..213B No abstract at ADS Title: The UV "sun as a star" flare spectrum observed with SOLSTICE Authors: Brekke, P.; Rottman, G. J.; Fontenla, J.; Judge, P. G. Bibcode: 1996ASPC..109..111B Altcode: 1996csss....9..111B No abstract at ADS Title: Atomic calculations inspired by the Hubble Space Telescope: intercombination and forbidden lines. Authors: Fleming, J.; Brage, T.; Harper, G.; Bell, K. L.; Hibbert, A.; Judge, P. G.; Leckrone, D. S. Bibcode: 1996BAAS...28.1203F Altcode: No abstract at ADS Title: On the Failure of Standard Emission Measure Analysis for Solar Extreme-Ultraviolet and Ultraviolet Irradiance Spectra Authors: Judge, P. G.; Woods, T. N.; Brekke, P.; Rottman, G. J. Bibcode: 1995ApJ...455L..85J Altcode: We perform emission measure analysis of new and accurate UV ( lambda > 1200 A) and extreme-ultraviolet (EUV) ( lambda <= 1200 A) irradiance ("Sun-as-a-star") emission-line spectra of the Sun. Our data consist of (1) daily averaged UV irradiances from the SOLSTICE on the UARS spacecraft and (2) EUV irradiances obtained on the same date from a \frac {1}{4} m spectrograph flown on a sounding rocket. Both instruments have a spectral resolution of roughly 1 A. The absolute uncertainties in these data are at most +/-15% (+/-2 sigma ), one of the highest photometric accuracies yet achieved. We find large, highly significant and systematic discrepancies in the emission measure analysis of transition region lines which can only be accounted for by a breakdown of one or more standard assumptions. All strong lines above 1000 A, which are from the Li and Na isoelectronic sequences, are too strong by factors of between 2.5 and 7 compared with their counterparts in the EUV region. Previous studies were tantalizingly close to finding these discrepancies, but those data lacked the wavelength coverage and relative photometric precision necessary for definitive conclusions. We argue that either dynamical effects, inaccurate treatments of atomic processes, and/or Lyman continuum absorption are the culprits. However, we favor the former explanation. In any event, this study should have implications for models of the solar transition region, for observing programs with the CDS and SUMER instruments on SOHO, and for analysis of UV spectra for stars across the cool half of the H-R diagram. Finally, the discrepancy is not seen for the "coronal" Li-like ions. Title: Solution to the Bivariate Integral Inversion Problem: The Determination of Emission Measures Differential in Temperature and Density Authors: Hubeny, Veronika; Judge, Philip G. Bibcode: 1995ApJ...448L..61H Altcode: We present a general solution to the inversion problem of determining the "source function" f(t, n) from integral equations of the form gi = \int \limits \int \limits Ki(t,n)f(t,n)dt dn. The function f(t, n) represents the most information that can be extracted from a set of observables {gi} for a source for which the kernel functions Ki(t, n), depending on the two independent variables t and n, can be calculated a priori. Our specific application is to the inversion of the equations for a set of optically thin emission line intensities gi with kernel functions Ki(t, n) which depend on both the electron density n and the temperature t, a problem defined by Jefferies and colleagues in the early 1970s. We determine "regularized" solutions [those for which derivatives of f(t, n) are minimized to constrain the allowed solutions] for f(t, n) from which the usual emission measure differential in temperature xi (t) = ∫f(t, n) dn can be obtained. Unlike some recent work, our solution is fully two-dimensional and is not restricted to cases where functional dependences are assumed to exist between t and n in f(t, n). We compare our solutions for the source terms (derived from inversions of calculated intensities from input source functions) with input source functions, for typical extreme-ultraviolet and UV lines formed in the solar transition region. Details, refinements, and applications are left to a later paper. This work is likely to be relevant to other areas of astrophysics, and can aid in planning observations with spacecraft such as the Hubble Space Telescope and the upcoming SOHO mission. Title: GHRS Observations of Cool, Low-Gravity Stars. II. Flow and Turbulent Velocities in the Outer Atmosphere of gamma Crucis (M3.4 III) Authors: Carpenter, Kenneth G.; Robinson, Richard D.; Judge, Philip G. Bibcode: 1995ApJ...444..424C Altcode: The Goddard High Resoulution Spectrograph (GHRS) on the Hubble Space Telescope (HST) has been used to obtain medium (R = 20,000) and high (R = 85,000) resoultion UV spectra of chromosphere emission features for the M3.4 III star gamma Cru. Small Science Aperture (SSA) G270M and Echelle-B spectra of selected regions in the 2300-2850 A range were obtained to determine the kinematics of the chromosphere using lines of C2), Fe2, Co2, Si1/2), Ni2, Mn2, and Mg2. Profiles of C2) (UV 0.01) lines and fluorescently excited lines of low optical depth indicate average turbulent velocities (Doppler FWHM) of 30.2 +/- 1.3 and 28.8 +/- 1.3 km/s, respectively. The fluorescent emission lines (mean RV = 21.3 +/- 0.9 km/s) and the wings of the emission components of Fe2 lines (mean RV = 22.8 +/- 0.4 km/s) are approximately at rest relative to the radial velocity of the star (21 km/s), while the C2) lines show a modest inflow (mean RV = 23.1 +/- 0.9 km/s). The more opaque lines of Fe2 and Mg2 exhibit complex profiles resulting from line formation in an optically thick, extended expanding atmosphere. The emission wings of these lines are broadened by multiple scattering, and they are centered near the photospheric radial velocity. Closer to line center, these strong lines show a strong blueshifted self-absorption feature (already seen in IUE data), indicative of formation in an expanding chromosphere, and a previously unseen dip in the profiles on the red side of line center. The absorption components, when extracted using simple Gaussian fits, show strong correlations with the relative optical depths of the lines. The derived absorption flow velocities converge to the photospheric velocity as one examines spectra features formed deeper in the atmosphere. The blueward abosrption velocity increases in magnitude from about 7 to 14 km/s with increasing line optical depth - the strong absorptions directly map the acceleration of the outflowing stellar wind, while the interpretation of the weaker redshifted absorptions is more ambiguous, indicating either an inflow of material or formation in an extended, spherically expanding outflow. The Mg2 and Fe2 profiles, taken together, imply that the wind speed decreases between the atmospheric layers where the Mg2 and Fe2 self-absorption components are formed. Interstellar absorptions are seen in the resonance lines of Mg2 (UV 1) and Fe2 (UV1) with zero-volt lower levels, at about -3 km/s, consistent with models of the interstellar medium in the direction of gamma Cru. Finally, we have detected the Mg2 'satellite lines' seen in solar spectra obtained above the limb. In gamma Cru these lines are probably fluorescently excited by H Ly beta. Title: Transition Probabilities for the UV0.01 Multiplet in N III Authors: Brage, Tomas; Fischer, Charlotte Froese; Judge, Philip G. Bibcode: 1995ApJ...445..457B Altcode: We report on large-scale ab initio multiconfiguration Hartree-Fock calculations for the UV0.01 multiplet, 2s22p2PJ - 2s2p2 4PJ prime, in N III. The resulting transition probabilities agree very well with recent semiempirical calculations, and the lifetimes for two of the three upper levels agree with experiments. The deviation for the third level is discussed. Comparisons made with the highest quality IUE echelle spectra available -- those of RR Tel and V1016 Cyg (both photoionized sources with electron densities below 108/cu cm) -- show that computed branching ratios of lines sharing a common upper level are in agreement with observations to within uncertainties of +/- 10%. High-quality solar limb data or stellar data from the Hubble Space Telescope (HST) could, in principle, be used to determine whether the theoretical or measured lifetimes for the discrepant level are in error. Unfortunately, stellar data for high-density plasmas (Ne greater than 1011/cu cm are needed) do not yet exist, and existing solar data lack the photometric precision to address this problem. Title: The Transition Regions of Capella Authors: Linsky, Jeffrey L.; Wood, Brian E.; Judge, Philip; Brown, Alexander; Andrulis, Catherine; Ayres, Thomas R. Bibcode: 1995ApJ...442..381L Altcode: We have used the Goddard High Resolution Spectrometer (GHRS) to observe the spectoscopic binary system Capella (G8 III + G1 III). Exposures with the G140L, G140M, G160M, G200M, and echelle gratings provide emission line profiles with unprecedented signal-to-noise and spectral resolving power (lambda/Delta-lambda) up to 92,000. Multi-Gaussin fits to the line profiles show that the hotter star contributes 60%-70% of the total flux in the chromospheric O I and Mg II resonance lines, but about 90% of the flux in the Si III, Si IV, and C IV lines formed in the transition region at T less than or = 105 K. We find clear evidence that the emission lines from the hotter star are systemtically redshifted relative to the photosphere with Doppler shifts of 5 +/- 1 km/s for the +9 +/- 3 km/s in the chromospheric Mg II and O I lines, respectively, increasing to +24 +/- 5 km/s for the transition region Si IV 1393.8A line. The multi-Gaussian fits to permitted transition region lines of SI III, Si IV, C IV, and N V indicate the presence of three components: moderately broad lines formed in the transition region of the hotter star (component H), narrow lines formed in the transition region of the cooler star (component C), and very broad lines that we think are formed in microflares on the hotter star (component B). The He II 1640.4 A feature has an broad profile, which indicates that it is formed by collisional excitation primarily from the hotter star, and a weak narrow component that we interpret as due to radiative recombination on the cooler star. We observed spin-forbidden emission lines of C III), O III), Si III), O IV), O V), and S IV) that are sensitive to electron density. Fainter members of the O IV) multiplet and all of the S IV) lines have never before been seen in any star than the Sun. We determine electron densities in the transition regions of the Capella stars using lines ratios of O IV) lines and emission measure analysis. The emission measures are self-consistent only when the fluxes from each emitting component are considered separately. In particular, the transition region abundance distributions appear to be different on the two stars, and the spin-forbidden lines were not detected in the B component. The emission measures for component H (the G1 star) are consistent with a constant electron pressure (or hydrostatic equilibrium) transition region with Pe = 1015 + 0.1/cu cm K and possibly solar 'coronal' abundances. Title: Excitation of O i Lines in the Solar Chromosphere Authors: Athay, R. Grant; Judge, Philip G. Bibcode: 1995ApJ...438..491A Altcode: Observations of O I lines in the solar spectrum are examined to determine whether differences in behavior of lines of the quintet and triplet term systems are consistent with collisional excitation and/or photoexcitation of both quintets and triplets. Intensities, IIR, in near-infrared emission lines observed above the limb at total eclipse decrease exponentially with height h. The inverse scale heights (d In IIR/dh) for the triplet lines at 844.6 nm and quintet lines at 777.2 nm are found to be in the ration of 1.45. Ultraviolet O I emission-line intensities IUV observed on the solar disk show strong variations, and the distributions of triplet (130.4 nm) and quintet line intensities about the means are different. Variances in In IUV are found to have a triplet-to-quintet ratio of 1.50, in close agreement with the ratio of d In IIR/dh. It is shown that the simple assumption of collisional excitation of quintets and triplets coupled with collisional de-excitation of the quintets leads to the correct ratios for both the UV variances and d In IIR/dh. Also, under this assumption d In IIR/dh for the quintet lines is predicted to have the same value as d In I/dh at the head of the hydrogen Balmer continuum, which, in fact, it does. On the other hand, Carlsson & Judge (1993) have shown that collision rates computed from the Vernazza, Avrett, & Loeser (1981, hereafter VAL) model chromosphere using current estimates of O I collision strengths are too low to produce the observed mean intensity in O I 130.4 nm. In a similar sense, we find that the predicted intensity of O I 130.4 nm is much too weak relative to O I 135.6 nm, and that the VAL mean models A-F cannot reproduce the observed behavior of these lines, even including photoexcitation by H Ly-beta. These difficulties are removed by increasing specific electron-atom collision rates. Such increases could reflect large errors in atomic cross sections close to threshold and/or the inadequacy of the assumptions made by VAL for predicting line intensities. The latter alternative a likely factor. We conclude that the O I UV lines are very sensitive to inhomogeneities, much more than more traditional chromospheric lines (e.g., Mg II k) which are formed over similar regions of the chromosphere. Such lines could therefore provide valuable diagnostics of departures of the chromopsheric plasma from mean models and thereby place constraints upon heating mechanisms, once accurate atomic data become available. Title: Consolidation and Verification of EUVE's Lunar Observing Program Authors: Judge, Philip G. Bibcode: 1995euve.prop...32J Altcode: EUVE has been providing valuable spectrometer data of the moon for the duration of the EUVE mission. Our primary goal has been to provide solar irradiance variability data at a time when such data are extremely scarce. This proposal asks for additional measurements to consolidate, calibrate and verify our program to date. The proposal differs from previous years in that an EUV spectrograph built by co-I Woods will fly on the METEOR satellite (launch October 1995) that will monitor the solar EUV irradiance on a daily basis. We therefore ask for 1 observation a day for 14 days around full moon to accurately define the phase function, and for 1 observation a month for 1 year to provide needed overlap (and redundancy, in the case of failure) with the METEOR experiment. Very short exposures are required (< 30 min each) for a total of roughly 40 Ksec. Title: GHRS Spectra of alpha Tau Authors: Carpenter, K.; Robinson, R.; Judge, P. Bibcode: 1994AAS...185.4509C Altcode: 1994BAAS...26.1380C Goddard High Resolution Spectrograph (GHRS) observations of the K5 giant alpha Tau were obtained on 8 April 1994. Spectra of approximately 40 Angstroms-wide regions centered near 1300, 1550, 1660, 1995, 2340, 2760, and 2800 Angstroms were obtained through the Small Science Aperture (SSA) with medium resolution (R=20,000) gratings. These data provide high-precision profiles of a variety of lines formed in the stellar chromosphere and transition region, including O I, Fe II, C I, C II], Si II], Mg II, and C IV. Self-reversed emission from O I, Fe II, and Mg II provide information on the wind flow velocities, with all three ions showing both red and blue-shifted absorption components, as seen previously in the Fe II emission from the later-type giants gamma Cru and mu Gem. The first evidence for hot plasma in the outer atmosphere of alpha Tau is seen in the G160M spectrum centered near 1550 Angstroms@. This spectrum shows very broad, but distinct features due to the C IV (UV 1) doublet, as well as a myriad of much narrower emissions formed at cooler temperatures, such as (fluorescent) Fe II and perhaps Ni II and C I. C I (UV 2) is seen in emission and a comparison of its flux with that in C I (UV 32) will allow an estimation of the C I chromospheric column density. Multiple observations of the C II] (UV 0.01) intercombination multiplet were obtained to search for evidence of shocks and/or propagating waves. Results of that search will be presented. Finally, very high-resolution (R=85,000) echelle spectra were obtained of the Mg II resonance doublet near 2800 Angstroms@. These emission features show strong interstellar, stellar, and circumstellar absorption components at, above, and below the stellar rest velocity. Title: The `HAO spectral diagnostics package' (HAOS-Diaper) Authors: Judge, P. G.; Meisner, R. W. Bibcode: 1994ESASP.373...67J Altcode: 1994soho....3...67J No abstract at ADS Title: The ``Monochromatic Density Diagnostic'' Technique: First Detection of Multiple Density Components in the Chromosphere of alpha Tauri Authors: Judge, P. G. Bibcode: 1994ApJ...430..351J Altcode: Emission line profiles of the red giant alpha Tau, obtained by Carpenter et al. (1991) using the echelle and medium dispersion gratings of the Goddard High Resolution Spectrograph are re-examined. Ratios of monochromatic flux densities of lines of the C II) 2s2 2p(2)P0 goes to 2s2p2 (4)P multiple near 2325 A, well-known diagnostics of electron densities in the chromospheres of cool evolved stars, change systematically with relative wavelength across the line profiles. With the justifiable assumption that these lines are optically thin, this implies that the electron density varies sytematically across the lines profiles. This is the first time that traditional electron density diagostic line ratios have been successfully applied to monochromatic line flux densities in cool stars. this work clearly demonstrates the power of very high signal-to-noise, high-resolution spectra in the UV. The monochromatic density diagonstic technique holds promise as a powerful tool for studying flows in a variety of astrophysical objects, including the Sun. The paper concludes with a compliation of ions from the boron and aluminum sequences for which this technique can be expected to produce valuable results using astronomical data from the GHRS and solar data from instruments on the Solar and Heliospheric Observatory (SOHO). Title: The Transition Regions of Capella Authors: Linsky, J. L.; Wood, B. E.; Brown, A.; Andrulis, C.; Judge, P.; Ayres, T. R. Bibcode: 1994ASPC...64...62L Altcode: 1994csss....8...62L No abstract at ADS Title: GHRS Observations and Analysis of the 0 I and C I Resonance Lines in the UV Spectrum of alpha ORI (M2 Iab) Authors: Carpenter, Kenneth G.; Robinson, Richard D.; Judge, Philip G.; Ebbets, Dennis C.; Brandt, John C. Bibcode: 1994ASPC...64...56C Altcode: 1994csss....8...56C No abstract at ADS Title: Structures in Transition Region Plasma of Active Regions Authors: Judge, Philip G.; Brekke, Paal Bibcode: 1994ASPC...68..321J Altcode: 1994sare.conf..321J No abstract at ADS Title: Solar Variability, Lunar Spectroscopy , and Earth's Upper Atmosphere Authors: Judge, Philip G. Bibcode: 1994euve.prop...55J Altcode: Solar EUV radiation and its variability is of central importance to the earths upper atmosphere. Variability of the earths upper atmosphere is a major concern to NASAs satellite missions. This proposal asks for continued measurments of solar EUV variability using EUVE to observe solar light scattered from the moon. Analysis of EUVE lunar data shows unambiguous evidence that we have detected and can quantify solar variability. We can therefore enhance our understanding of the physics of the upper atmosphere at a time when solar EUV measurements are scarce. Our aims include: (i) to understand phase and polarization dependences of solar light scattered from the moon, (ii) to better quantify variations in solar EUV irradiance, (iii) to re-calibrate these data with a rocket--launched EUV payload (already successfully achieved, but a re-observation is desirable), and (iv) to use these data with simultaneous UV measurements from UARS as inputs to upper atmospheric models. Very short exposures (< 30min.) are required. We request observations twice a lunar month, and some other observations to permit us to take the necessary steps towards converting lunar intensity data to absolute solar irradiances. The total requested time is roughly 60 Ksec. Title: On the Weakness of C I and O I Resonance Line Emission from the Chromosphere of alpha Ori. Authors: Carpenter, K.; Robinson, R.; Judge, P.; Ebbets, D.; Brandt, J. Bibcode: 1993AAS...183.1504C Altcode: 1993BAAS...25Q1313C The resonance lines from multiplets UV 2 of both O I and C I are typically quite strong in emission in the far-UV spectrum of cool stars. However, in the prototypical M-supergiant alpha Ori, these lines are remarkably weak, although other transitions from the same upper energy levels, O I (UV 146) and C I (UV 32), are observed in strong emission despite their much weaker intrinsic strengths. Due to the presence of many lines from other species in the regions around the UV 2 multiplets of O I and C I near 1302 Angstroms and 1655 Angstroms, the lines of interest suffer severe blending and progress in understanding this flux deficiency is difficult based on low resolution IUE and GHRS data. We have therefore obtained medium resolution (R=10,000) GHRS spectra of alpha Ori of these complex spectral regions, as well as the regions around the O I (UV 146) and C I (UV 32) lines near 1640 Angstroms and 1993 Angstroms, respectively, to resolve the various contributors and allow detailed study of this phenomenon. In this paper, we present the spectra and discuss the formation of the O I, C I, Fe II, and S I lines which they clearly resolve. Semi-empirical modeling of the outer atmosphere of alpha Ori and detailed radiative transfer calculations are used to study the creation and destruction of O I and C I photons. Title: Chromospheric Heating by Acoustic Shocks: A Confrontation of GHRS Observations of alpha Tauri (K5 III) with AB Initio Calculations Authors: Judge, P. G.; Cuntz, M. Bibcode: 1993ApJ...409..776J Altcode: We compare ab initio calculations of semiforbidden C II line profiles near 2325 A with recently published observations of the inactive red giant Alpha Tau (K5 III) obtained using the GHRS on board the Hubble Space Telescope. Our one-dimensional, time-dependent calculations assume that the chromosphere is heated by stochastic acoustic shocks generated by photospheric convection. We calculate various models using results from traditional (mixing length) convection zone calculations as input to hydrodynamical models. The semiforbidden C II line profiles and ratios provide sensitive diagnostics of chromospheric velocity fields, electron densities, and temperatures. We identify major differences between observed and computed line profiles which are related to basic gas dynamics and which are probably not due to technical modeling restrictions. If the GHRS observations are representative of chromospheric conditions at all epochs, then one (or more) of our model assumptions must be incorrect. Several possibilities are examined. We predict time variability of semiforbidden C II lines for comparison with observations. Based upon data from the IUE archives, we argue that photospheric motions associated with supergranulation or global pulsation modes are unimportant in heating the chromosphere of Alpha Tau. Title: Solar EUV Variability Measurements From Lunar Observations With EUVE Authors: Judge, P.; et al. Bibcode: 1993AAS...182.4129J Altcode: 1993BAAS...25..865J No abstract at ADS Title: Line Profile Variations in M Giants: Clues to Mass-Loss and Chromospheric Heating Mechanisms Authors: Judge, P. G.; Luttermoser, D. G.; Neff, D. H.; Cuntz, M.; Stencel, R. E. Bibcode: 1993AJ....105.1973J Altcode: Analysis is presented of time-series, high dispersion spectra of the Mg II, k, Ca II H, and K lines of the semiregular giants Rho Per (M4 II-III, periodicity of about 50 days), R Lyr (M5 III, period of about 46 days), and g Her (M6 III, period of about 90 days). The fine error sensor on the IUE satellite and ground based UBV photometry was used to relate line profile variations to photospheric variations. The above mentioned stars were selected to study the relative importance of convective motions and global stellar pulsations in determining the structure of the outer atmospheres. Small amplitude changes, but substantial changes in the profiles of Mg II and Ca II lines were detected. It is contended that the observed variability is due to changes in chromospheric conditions and not variations within the circumstellar shell. The picture of a steady state chromosphere, which is modulated on long time scales, is corroborated by these observations. Localized heating is found in g Her. Title: On i Lines in the Sun and Stars. I. Understanding the Resonance Lines Authors: Carlsson, M.; Judge, P. G. Bibcode: 1993ApJ...402..344C Altcode: The use of O I lines as spectral diagnostics of conditions in the chromospheres of the sun and cool stars is addressed, focusing on the resonance lines. The important processes influencing these lines are identified and an attempt it made to understand the detailed line transfer calculations in terms of simpler analytical models. How the lines respond to changes in uncertain atomic parameters is illustrated, and it is shown how the O I line flux densities depend simply and sensitively on the radiative transfer solution for hydrogen. Approximate analytical formulas are derived for the O I line flux densities in terms of the hydrogen number densities. Title: Solar Variability, Lunar Spectroscopy and Earth's Upper Atmosphere Authors: Judge, Philip G. Bibcode: 1993euve.prop...31J Altcode: Solar EUV radiation and its variability is of central importance to the earths upper atmosphere. Variability of the earths upper atmosphere is a major concern to NASAs satellite missions. This LARGE PROJECT (2 year) proposal asks for continued measurments of solar EUV variability using EUVE to observe solar light scattered from the moon. Existing EUVE data prove that we can enhance ourunderstanding of the physics of the upper atmosphere at a time when solar EUV measurements are scarce. Our aims include: (i) to understand the phase and polarization dependence of solar light scattered from the moon, (ii) to quantify variations in solar EUV irradiance, (iii) to calibrate these data with a rocket--launched EUV payload, and (iv) to use these data with simultaneous UV measurements from UARS as inputs to upper atmospheric models. Very short exposures (<30 min) are required. We request TYPE 2 observations twice a lunar month, and a variety of TYPE 1 observations to permit us to take the necessary steps towards converting lunar intensity data to absolute solar irradiances. Title: The Search for Acoustically-Driven Mass-Loss in Evolved Stars Authors: Stencel, R. E.; Brown, A.; Carpenter, K. G.; Cuntz, M.; Judge, P. Bibcode: 1992AAS...181.3603S Altcode: 1992BAAS...24.1175S Recent ab-initio calculations of stochastic stellar wind models by Cuntz (1992 in Cool Stars VII, ASP Conf. Ser. 26, p.383) have proven remarkably robust in predicting observed chromospheric flow patterns including possible variabilities with time in selected cool, evolved stars. The calculations solve the equations of hydrodynamics using the method of characteristics and assume: (i) saw-tooth shock wave profiles, and (ii) wave periods were changed stochastically while keeping the wave amplitudes constant (see Cuntz 1990 Ap.J. 349, p.141). Among the results of fitting chromospheric flow velocities is the implication that the permitted range of acoustic wave periods for a given star is constrained. We made use of the IUE satellite during August and September 1992 to repeatedly observe two stars, the yellow giant Aldebaran (K5 III) and the red supergiant, Betelgeuse (M2 Iab), in order to sample variations in their atmospheres on timescales of ~ 10(4) to ~ 10(6) seconds, which bracket the predicted mean acoustic wave periods for these objects. In particular, we obtained deep exposures in order to measure density-sensitive line ratios within the C II] intercombination features near 2325A (cf. Lennon et al. 1985 Ap.J. 294, p.200) to test the hypothesis that density fluctuations could be measured as a consequence of these acoustic waves. The results of these observations will be presented and discussed in terms of the number and amplitude of acoustic waves contributing to chromospheric heating and mass loss from these stars, as well as the wave origins in the evolving oscillatory structure of these stellar interiors. We are pleased to acknowledge IUE--NASA grant NAG5-2103 for partial support of this effort. Title: Fe II Emission Lines. II. Excitation Mechanisms in Cool Stars Authors: Judge, P. G.; Jordan, C.; Feldman, U. Bibcode: 1992ApJ...384..613J Altcode: Excitation mechanisms are discussed for the 'resonance' transitions (between the 3d(6)4s, 3d7, and 3d(6)4p configurations) of Fe II observed in emission in the near-UV spectra of cool stars. The analysis is based upon: (1) emission measure analysis of previously measured lines in IUE spectra of cool giants; (2) discussion of the behavior of Fe II lines observed above the solar limb from Skylab spectra; (3) approximate radiative-transfer calculations in a 59 level Fe-II model atom using mean escape probabilities and a parameterization of optical radiation fields; and (4) accurate radiative transfer calculations in a smaller atomic model. The solar spectra show unambiguous evidence that electron collisions are responsible for most of the Fe-II emission observed above the white-light limb. The terms leading to UV multiplets 3-6, 34-36, and 61-64 are excited by electron excitation of metastable quartet terms below about 4 eV, followed by photoexcitation in lines at optical wavelengths by photospheric radiation. A 'cool-star' diagnostic diagram is constructed showing the regimes in which electron collisions and continuum photoexcitation are important in the chromospheres of cool stars. Title: The Unusual Ultraviolet Chromospheric Spectrum of the R Coronae Borealis Star, V854 Centauri (NSV 6708), at Minimum Light Authors: Clayton, Geoffrey C.; Whitney, Barbara A.; Stanford, S. A.; Drilling, John S.; Judge, P. G. Bibcode: 1992ApJ...384L..19C Altcode: Results are presented of IUE observations of a decline of the recently discovered R CrB star, V854 Cen. These observations are of particular interest because they include spectra taken at 7 mag below maximum light. The 'chromospheric' emission spectra show striking differences from UV spectra of other R CrB stars in decline. Strong emission appears in several lines not normally seen in R CrB emission-line spectra, in particular at semiforbidden C II 2326, Mg I 2852, and C I 2965, 2967. Spectral evolution similar to that seen in visible spectra of R CrB stars is clearly seen in the UV. It is argued that the differences between V854 Cen and other R CrB stars are related to known abundance differences or to different temperature and density conditions in the emission-line regions of the various R CrB stars. The emission may also be significantly affected by the presence of dust in or near the emitting region. Title: SI II emission line diagnostics. Authors: Judge, P. G.; Carpenter, K. G.; Harper, G. M. Bibcode: 1991MNRAS.253..123J Altcode: The present study compares ratios of Si II UV emission lines in a variety of objects with computations based on recently published collisional data of Dufton and Kingston (1991). A high-quality spectrum of Alpha Tau (K5 III) obtained by Carpenter et al. (1991) is analyzed using the G270M mode of the GHRS on the HST, in addition to high-dispersion data from Skylab and IUE. Agreement between observation and theory is satisfactory for most lines. A blend with a line of Ni II accounts partially for the discrepancies and solves a problem with semiforbidden S II emission measures. Disagreement exists between certain observed flux ratios and computed values using recent atomic data for the intersystem lines. The discrepancy is most significant for Alpha Tau. The computed atomic collision strengths within the intersystem multiplet itself are argued as a possible cause of the discrepancy. Title: Coordinated IUE/HST Observations of the Flare Star AU mic: Results from IUE Authors: Carpenter, K. G.; Maran, S. P.; Brown, A.; Linsky, J. L.; Robinson, R. D.; Byrne, P. B.; Judge, P. G. Bibcode: 1991BAAS...23.1383C Altcode: No abstract at ADS Title: Fe II Emission Lines. I. Chromospheric Spectra of Red Giants Authors: Judge, P. G.; Jordan, C. Bibcode: 1991ApJS...77...75J Altcode: A 'difference filtering' algorithm developed by Ayers (1979) is used to construct high-quality high-dispersion long-wavelength IUE spectra of three giant stars. Measurements of all the emission lines seen between 2230 and 3100 A are tabulated. The emission spectrum of Fe II is discussed in comparison with other lines whose formation mechanisms are well understood. Systematic changes in the Fe II spectrum are related to the different physical conditions in the three stars, and examples are given of line profiles and ratios which can be used to determine conditions in the outer atomspheres of giants. It is concluded that most of the Fe II emission results from collisional excitation and/or absorption of photospheric photons at optical wavelengths, but some lines are formed by fluorescence, being photoexcited by other strong chromospheric lines. Between 10 and 20 percent of the radiative losses of Fe II arise from 10 eV levels radiatively excited by the strong chromospheric H Ly-alpha line. Title: Evolution of the Chromospheres and Winds of Low- and Intermediate-Mass Giant Stars Authors: Judge, P. G.; Stencel, R. E. Bibcode: 1991ApJ...371..357J Altcode: Results are presented of an empirical analysis of the global thermodynamical requirements of the winds in the outer atmospheres of a representative sample of red giant stars of low- and intermediate-mass range. Results indicate that the mass-loss rates in these stars are not strongly dependent on the actual physical processes driving the winds. It is suggested that nonlinear processes act to regulate wind energy fluxes. Possible mechanisms responsible for the chromospheric heating and the mass loss in the low- and intermediate-mass giant stars are discussed. Title: Radio Continuum Observations of a Variety of Cool Stars Authors: Drake, S. A.; Linsky, J. L.; Judge, P. G.; Elitzur, M. Bibcode: 1991AJ....101..230D Altcode: Radio-continuum observations at 2 and 6 cm are presented for 26 cool stars (F0 and later), including 10 F-K main-sequence stars and 16 F-M giant and supergiant stars. The detection of two M giants, g Her and R Lyr, is reported for the first time; a redetection of the unusual infrared carbon star IRC + 10216 is also reported. Some general conclusions are made concerning the radio-emission properties of the various types of cool stars observed. For both the detected and nondetected stars, constraints are obtained on the ionized component of their mass-loss rates. Title: The Mira/Semi-Regular Connection Authors: Judge, Philip G. Bibcode: 1991iue..prop.3983J Altcode: Substantial mass-loss for stars on the asymptotic giant branch has been inferred for Mira stars for some time. Mass-loss mechanisms involving the coupled action of stellar pulsations and dust formation have been shown to account or the observed mass-loss rates by Bowen and colleagues. Mechanisms for stars with substantial massloss, but which are not regular pulsators, are not yet identified or understood. An important goal of this proposal is to obtain the data needed to identify the mass-loss mechanism for the semi-regular stars. The Mg II line fluxes are sensitive indicators of non-radiative processes occuring in layers of evolved giants where energy and momentum is imparted to the wind. We propose to monitor the Mg II line fluxes with the LWP camera at low dispersion, for a sample of semi-regular giant stars, This sample differs from previously studied stars because the stars have far infrared excesses similar to those of Miras. Simultaneous ground based photometry will be obtained to help identify the phase of tile variation of the Mg II lines. We will compare our findings with our earlier similar studies of Miras and with our study of high dispersion Mg II line profiles of "non-dusty" semi-regulars obtained during the present (twelfth) round of IUE observations. Using the IRAS database and other constraints, we will study the relations between Mira-like behavior and the semi-regulars, both SRa and SRb types. From this study we will learn about the nature of the mass-loss process from cool giants, and obtain strong constraints on models of the evolution of the circumstellar envelopes, and hence of stellar evolution on the AGB. Title: Feii Emission Line Diagnostics of the Sun and Stars Authors: Judge, P. Bibcode: 1991ASIC..341..291J Altcode: 1991sabc.conf..291J No abstract at ADS Title: The Mira/Semi-Regular Connection II Authors: Judge, Philip G. Bibcode: 1991iue..prop.3984J Altcode: We propose to extend the present 1 year program LGMPJ, "the Mira/Semi-Regular Connection" for an extra year. The purpose is to obtain a better understanding of mass-loss mechanisms by studying the behavior of the Mg II h and k line fluxes in a more complete sample of pulsating stars. In program LGMPJ, the allotted observing time was insufficient to permit more than a preliminary study of 3 stars. Important classes of stars of various infrared and variability properties have therefore remained unstudied. The Mg II line fluxes are sensitive indicators of non-radiative processes occuring in layers of giants where energy and momentum is imparted to the wind. We will compare our findings with our earlier IUE studies of Miras and "non-dusty" semi-regulars. Using the IRAS database and other constraints, we will learn about the nature of the mass-loss process from cool giants, and obtain strong constraints on models of the evolution of the circumstellar envelopes, and hence of stellar evolution on the AGB. Title: Stringent Limits on the Ionized Mass Loss from A and F Dwarfs Authors: Brown, Alexander; Veale, Anthony; Judge, Philip; Bookbinder, Jay A.; Hubeny, Ivan Bibcode: 1990ApJ...361..220B Altcode: Following the suggestion of Willson et al. (1987) that A- and F-type main-sequence stars might undergo significant mass loss due to pulsationally driven winds, upper limits to the ionized mass loss from A and F dwarfs have been obtained using VLA observations. These stringent upper limits show that the level of ionized mass loss would have at most only a small effect on stellar evolution. Radiative-equilibrium atmospheric and wind models for early A dwarfs indicate that it is highly likely that a wind flowing from such stars would be significantly ionized. In addition, late A and early F dwarfs exhibit chromospheric emission indicative of significant nonradiative heating. The present mass-loss limits are thus representative of the total mass-loss rates for these stars. It is concluded that A and F dwarfs are not losing sufficient mass to cause A dwarfs to evolve into G dwarfs. Title: On the disappearance of OI in some high-luminosity cool stars Authors: Carpenter, K. G.; Norman, D.; Robinson, R.; Fernandez-Villacanas, J. L.; Jordan, C.; Judge, P. Bibcode: 1990ESASP.310..307C Altcode: 1990eaia.conf..307C No abstract at ADS Title: Fe II Emission Lines: Chromospheric Spectra of Red Giants Authors: Judge, P. G.; Jordan, C. Bibcode: 1990BAAS...22..848J Altcode: No abstract at ADS Title: On the Interpretation of Chromospheric Emission Lines Authors: Judge, P. G. Bibcode: 1990ApJ...348..279J Altcode: This paper reexamines the formation of ultraviolet emission lines in stellar chromospheres, using detailed radiative transfer calculations and relatively simple methods based on approximate line cooling rates, including escape probabilities. Approximations for the cooling integrals are demonstrated to work well for 'effectively thin' chromospheric lines. Two cases are identified, whose behavior can be understood using Ayres's (1979) chromospheric scaling laws relating the chromospheric structure to stellar properties: those of inactive stars, like cool giants, and more active stars like the sun. Title: Radiative Cooling Functions Below 2X10/4K Authors: Judge, P. G.; Neff, D. H. Bibcode: 1990ASPC....9...57J Altcode: 1990csss....6...57J No abstract at ADS Title: Toward Mapping the Ultraviolet Circumstellar Shells of Late-Type Stars Authors: Stencel, Robert E.; Judge, Philip G.; Carpenter, Kenneth G. Bibcode: 1990ASPC....9..467S Altcode: 1990csss....6..467S Detection of spatially resolved circumstellar matter surrounding selected cool stars, using off-source observations made with the International Ultraviolet Explorer satellite, is reported. The data demonstrate that: (1) the instrumental scattered light profile of IUE appears to depend on the ultraviolet color temperature of the star observed, and (2) certain red stars show signal in excess of the instrumental levels, at spatial offsets of 10 to 20 arc-seconds from the star. Title: The Evolution of Chromospheres and Winds of Low and Intermediate Mass Giant Stars Authors: Judge, P. G.; Stencel, R. E. Bibcode: 1990ASPC....9..411J Altcode: 1990csss....6..411J No abstract at ADS Title: Mass Loss Upper Limits for a and F Dwarfs Authors: Brown, A.; Veale, A.; Judge, P.; Bookbinder, J.; Hubeny, I. Bibcode: 1990ASPC....9..183B Altcode: 1990csss....6..183B The upper limits of the ionized mass losses of A- and F-type main sequence stars are obtained with the VLA to investigate the theory that pulsationally driven winds contribute to substantial mass loss in the stars. The upper limits are found to be at least one order of magnitude lower than the mass-loss loci proposed by Willson et al. (1987). Because any wind flowing from the stars should be detectable, the notion that A dwarfs are evolving into G dwarfs cannot be supported by the amount of mass that A and F dwarfs are shown to be losing. Title: How Consistent are Ab-Initio Models of Giant Star Chromospheres with Observations Authors: Cuntz, M.; Judge, P. G. Bibcode: 1990ASPC....9...61C Altcode: 1990csss....6...61C No abstract at ADS Title: Radiative Transfer in ab-initio Chromospheric Models Authors: Cuntz, M.; Judge, P. G. Bibcode: 1989BAAS...21Q1101C Altcode: 1989BAAS...21.1101C No abstract at ADS Title: Chromospheres of Chemically Peculiar Giant Stars (invited Paper) Authors: Judge, P. G. Bibcode: 1989eprg.proc..303J Altcode: 1989IAUCo.106..303J The chromospheres of evolved stars with peculiar chemical abundances are reviewed, emphasizing the dependence of chromospheric properties on the evolutionary status of the stars. A sample of intermediate mass stars observed in the radio, IR and UV wavelength regions is compiled. The chromospheres of MS, S, and C stars are compared with one another. The sample is used to study the relationship between stellar parameters and chromospheric heating. The results are used to construct a scenario for AGB evolution. Title: Cycle-Dependent Studies of Semi-Regular Giant Stars Authors: Judge, Philip G. Bibcode: 1989iue..prop.3423J Altcode: We propose to monitor the chromospheres and winds of the semi-regular giants Rho Per (M4 II-III, P ~ 50 days) and g Her (M6 III, P ~ 90 days) as a function of their cyclic photospheric variability using LWP observations coordinated with ground based spectroscopy and photometry. We have recently studied a sample of 42 stars covering various phases of evolution on the redand asymptoticgiant branches. We have discovered that as a star evolves from a photometrically "constant" early M stax to a semi-regular (SRb) stax near spectral type M5 III, important changes in the response of the outer atmosphere to the photospheric mechanical energy generation occur. The energy fluxes are dominated in the early phases by chromospheric heating and radiative losses, and by mass loss in the later phases. "Non-variable" and semi-regular K and M stars lose mass by a currently unidentified process. The present proposal aims to follow the response of the chromosphere and wind, via the emission and absorption components in the Mg II and Ca II resonance lines, to the underlying photospheric variability in SRb-type M stars. In this way we can test whether global photospheric variability on a long timescale (>= weeks, i.e. > acoustic cutoff period) is responsible for the enhanced massloss and dust formation in non-Mira stars later than M5 and whether the energy generated by these pulsations is related to the (observationally-inferred) chromospheric heating. Previous monitoring studies with IUE of SRb stars reveal variability but they have neither adequate phase coverage nor the ground-based support required for our study. Our study will help to provide a link between the outer atmospheres of the "non-variable" and Mira phases of stellar evolution: current theory indicates that the Miras (P > 150 days, DeltaV > 2.5 mag.) lose substantial mass because of the propagation and decay of global acoustic shocks, accompanied by dust formation, generated by the regular photospheric pulsations. Our recent study and theoretical work suggest that similar processes may be occuring in the shorterperiod, smaller amplitude SRb stars. The proposed IUE observations will help to clarify the relation of stellar winds and chromospheres to the variability properties of stars evolving up the giant branches. Title: Direct UV observations of the circumstellar envelope of alpha Orionis. Authors: Stencel, R. E.; Carpenter, K. G.; Pesce, J. E.; Skinner, S.; Brown, A.; Judge, P. Bibcode: 1988ESASP.281a.249S Altcode: 1988uvai....1..249S; 1988IUE88...1..249S Observations were made in the IUE LWP camera, low dispersion mode, with alpha Ori being offset various distances from the center of the Long Wavelength Large Aperture along its major axis. Signal was acquired at all offset positions and is comprised of unequal components of background/dark counts, telescope-scattered light, and scattered light emanating from the extended circumstellar shell. The star is known from optical and infrared observations to possess an extended, arc-minute sized, shell of cool material. Attempts to observe this shell with the IUE are described, although the deconvolution of the stellar signal from the telescope scattered light requires further calibration effort. Title: The excitation of SI emission lines in chromospheres of late-type giant stars. Authors: Judge, P. G. Bibcode: 1988MNRAS.231..419J Altcode: Constraints on the structure of the chromospheres of Alpha Boo, Alpha Tau, and Beta Gru derived from high-resolution IUE spectra are used to investigate the excitation mechanisms of emission lines of neutral sulfur, which are prominent in IUE spectra of late-type giant and supergiant stars. Observational data for the S I lines from other studies are collected and discussed together with data for the prototype M supergiant Alpha Ori. The physical conditions under which the emission lines are excited are summarized, and the atomic processes and models required to interpret the line fluxes are addressed. The processes leading to emission in Alpha Tau, Alpha Boo, and Beta Gru are identified. The requirements for more accurate atomic and spectroscopic data are discussed, and the potential diagnostic value of the various emission lines is assessed. Title: Spectroscopy of Cool Stars from IUE Data Authors: Judge, P. G. Bibcode: 1988IAUS..132..163J Altcode: IUE has revolutionized our knowledge of the outer atmospheres of cool stars, largely through the study of spectral lines, and now we possess a quite detailed knowledge of stellar chromospheres, transition regions, coronae and winds in the cool half of the HR-diagram. The aim of the present review is to highlight advances in this field using IUE data with high signal-to-noise ratios. Title: A Very Deep SWP Echellogram of Aldebaran Authors: Judge, Philip G. Bibcode: 1988iue..prop.3335J Altcode: No abstract at ADS Title: Understanding the ultraviolet spectra of cool stars. Authors: Jordan, C.; Judge, P. G. Bibcode: 1988CoAMP..21...97J Altcode: No abstract at ADS Title: Modelling the outer atmospheres and winds of K giant stars. Authors: Judge, P. G. Bibcode: 1987IAUS..122..323J Altcode: It is shown how empirically derived constraints affect models of the outer atmospheres and winds of K giants, taking α Boo (K2 III) as an example. The importance of empirical approaches prior to making semi-empirical models is stressed. The reliability of recent wind models is assessed. Title: Delta Andromedae (K3III) : an IRAS source with an unusual ultraviolet spectrum. Authors: Judge, P. G.; Jordan, C.; Rowan-Robinson, M. Bibcode: 1987MNRAS.224...93J Altcode: The IRAS survey has revealed anomalous cool infrared emission from a number of otherwise apparently normal K stars. IUE spectra of the brightest of these stars, Delta And, which is a spectroscopic binary and optical standard K3 III star, is obtained. The IUE spectra show the unexpected presence of C IV in emission, implying hot material (about 100,000 K), and evidence for a strong, high-velocity wind. It is argued that the unusual ultraviolet spectrum arises solely from the primary star and that it is another example of a 'hybrid' K star. The infrared excess appears to be caused by a primordial dust shell extending from about 1 to 30 arcsec from the primary. One of the companions of Delta And lies close to the inner edge of the shell and another one (possibly two) lies close to the outer edge, so that interesting dynamical interactions between the companions and the dust shell may be expected. The dust shell may be analogous to the Oort cometary cloud in the Solar System or to a scaled-up version of Saturn's rings. Title: δ Andromedae (K3 III): a hybrid giant in an extended dust shell. Authors: Jordan, C.; Judge, P. G.; Rowan-Robinson, M. Bibcode: 1987IAUS..122..321J Altcode: Spectra of δ And have been obtained with the International Ultraviolet Explorer in both the long and short wavelength regions. These spectra show several features unusual in a K giant as cool as δ And, in particular. The IRAS observations are interpreted in terms of a cool (≡100 K) dust cloud surrounding δ And - a spectroscopic binary system - and a third component at 1200 A.U. Title: Re-examining the "Corona-Wind Dividing Line" Diagnostics of "Non-Coronal" Atmospheres (Invited review) Authors: Judge, P. G. Bibcode: 1987LNP...291..294J Altcode: 1987csss....5..294J; 1987LNP87.291..294J A review of observations and analyses of the outer atmospheres of "non-coronnl" stars is given, with an emphasis on spectroscopic diagnostics. These stars, lying to the right of the "corona-wind division" in the HR diagram, have no detectable material above temperatures of ∼ 2×104 K, and instead of solar-like transition regions and coronae, they possess relatively massive winds and expanding "basal-flux" chromospheres. The discussion is restricted to "normal", single, red giants, i.e. oxygen-rich stars which have not evolved as far as the asymptotic giant branch, and which have not yet developed massive, dusty molecular outflows. The methods described can in principle be applied to cool star chromospheres in general. Title: High-Dispersion Observations of Alpha Bootis (K1 III) with the International Ultraviolet Explorer Authors: Ayres, T. R.; Judge, P.; Jordan, C.; Brown, A.; Linsky, J. L. Bibcode: 1986ApJ...311..947A Altcode: The authors have obtained very deeply exposed IUE echelle spectrograms of the bright, early-K giant Arcturus. They did not detect significant flux in the most prominent high-excitation species of a solar-like transition zone, C IV λ1548.2. The presence of a weak feature of Si III] λ1892.0, and possibly also Si IV λ1393.8, indicates the existence of a small amount of plasma at temperatures as hot as 6×104K. Measurements of C II] multiplet UV0.01 near 2325 Å provide a lower limit of about 5×109cm-3 for the electron density in the chromospheric layers. C II UV1 (1335 Å) emission is very weak. These results confirm that the "coronal" activity of the old red giants is considerably diminished from that of even the "quietest" of their main-sequence predecessors, stars like the Sun. Title: Constraints on the outer atmospheric structure of late-type giants stars with IUE : application to alpha Tau (K5III) and beta Gru (M5III). Authors: Judge, P. G. Bibcode: 1986MNRAS.223..239J Altcode: Empirical constaints on the outer atmospheric structures of α Tau and β Gru are derived using high resolution spectra from the International Ultraviolet Explorer (IUE) satellite, with methods which have been described and applied to α Boo (K2III) in an earlier paper. These stars have IUE spectra which are typical of giant stars later than ∼K0 which lie on the 'wind' side of the 'corona/wind division' in the H-R diagram. The methods are based on the interpretation of emission-line fluxes and profiles, combining emission measures, column density measurements from opacity-sensitive line ratios and electron-density measurements from C II] line ratios. Many of the conclusions derived earlier for α Boo are confirmed for the later type stars considered here: radiative processes are vitally important in determining the observed spectra because of the low particle densities in red giants. A consistent set of constraints is derived only when such processes are taken into account. There is no evidence from IUE that the emission regions are significantly extended in the sense suggested by previous workers. For α Tau the constraints are used to examine the reliability of an earlier chromospheric model of Kelch et al. Finally the general implications of this work on the outer atmospheres of late-type giant stars are discussed. Title: Formation of Emission Lines in the Outer Atmosphere of Arcturus (Alpha Boo K2 III) Authors: Judge, P. G.; Avrett, E. H.; Loeser, R. Bibcode: 1986BAAS...18..982J Altcode: No abstract at ADS Title: The outer atmospheres of late-type giant stars. Authors: Judge, P. G. Bibcode: 1986ESASP.263..189J Altcode: 1986niia.conf..189J; 1986NIA86......189J Results of recent work with IUE on the structure of the outer atmospheres of late-type giant stars are summarized, based on empirical constraints derived from emission lines in α Boo (K2 III), α Tau (K5 III) and β Gru (M5 III), observed with deep exposures in the high resolution mode of IUE. These stars have IUE spectra typical of giant stars on the "wind" side of the "corona-wind division" in the HR diagram. Particular attention is paid to the structure of the emitting regions, including densities, temperatures, inhomogeneities, geometric extents and velocity fields. Comparisons are made with earlier chromospheric models and with other spectroscopic work, and trends with stellar parameters are examined. Finally, the implications of this work for modelling the winds of red giants are discussed. Title: Constraints on the outer atmospheric structure of late-type giant stars with IUE : methods and application to Arcturus (alpha Boo K2III). Authors: Judge, P. G. Bibcode: 1986MNRAS.221..119J Altcode: Methods for empirically analyzing the emission lines formed in the outer atmospheres of late-type low-gravity stars are described and applied to the K2III star Alpha Boo. The methods are based on electron-density measurements, emission-measure analysis, and determination of the optical depths of emission lines. The reduction and measurement of IUE data of Alpha Boo is described. The important atomic and radiative processes which determine the emission-line fluxes of the 'diagnostic' emission lines in late-type giant stars are identified, and the effects of the scattering of radiation in optically thick lines are examined using results from probabilistic radiative transfer theory, and models for line excitation are obtained. Empirical constraints on the outer atmospheric structure of Alpha Boo are derived using the observed line fluxes and widths and the previously described models. Title: Empirical Constraints on the Outer Atmospheres of Late-Type Giant Stars with IUE Authors: Judge, P. G. Bibcode: 1986IrAJ...17..300J Altcode: Useful constraints on the outer atmospheric structure of late-type giant stars can be obtained using emission lines observed with the IUE satellite if all important processes in the atomic excitation calculations are included. Carpenter et al. (1985) did not include such effects, and therefore overestimated the geometric extent of the emission regions. The Ayres and Linsky (1975) model for Alpha Boo satisfies most of the constraints derived below 8000 K, but the model has electron densities and linewidths that are a factor of about 2 smaller than those observed. Title: Ultraviolet Observations of Young Stars in the Chameleon 1 Association Authors: Brown, A.; Linsky, J. L.; Walter, F.; Jordan, C.; Judge, P.; Gahm, G.; Feigelson, E. D. Bibcode: 1985BAAS...17R.837B Altcode: 1985BAAS...17..837B No abstract at ADS Title: Emission Line Variability of RY Tau, DR Tau and SU Aur Authors: Brown, A.; Walter, F. M.; Carpenter, K. G.; Jordan, C.; Judge, P. Bibcode: 1985BAAS...17..556B Altcode: No abstract at ADS Title: Ultraviolet spectroscopy of late-type giant and supergiant stars Authors: Judge, Philip Gordon Bibcode: 1985PhDT........44J Altcode: No abstract at ADS Title: A progress report on the analysis of long exposure SWP high resolution spectra of cool stars. Authors: Linsky, J. L.; Ayres, T. R.; Brown, A.; Carpenter, K.; Jordan, C.; Judge, P.; Gustafsson, B.; Eriksson, K.; Saxner, M.; Engvold, O.; Jensen, E.; Moe, O. K.; Simon, T. Bibcode: 1984NASCP2349..445L Altcode: 1984fiue.rept..445L; 1984IUE84......445L The IUE is the first experiment with sufficient sensitivity to obtain high resolution spectra (lambda/delta lambda is approximately 10,000) of many cool stars in the vitally important 1200 to 2000 A spectral region. These data provide qualitatively new information with which to understand the properties of and structures in the outer atmospheres of these stars. Also, these cool star spectra will be extremely useful in planning for the Space Telescope High Resolution Spectrograph, which will be 1000 times more sensitive than IUE but will be hampered by limited observing time and limited spectral bandwidth in each exposure. Very long exposure, high disperson SWP spectra of many stars located throughout the cool half of the HR diagram were obtained. These 12 to 21 hour exposures were obtained by combining NASA and Vilspa shifts so as to obtain the longest possible exposures at times of low background. Included are dwarf stars of spectral type G0 V to M2 V, G9.5 III to M5 II giants, G2 Ib to M2 Iab supergiants, a number of RS CVn-type systems, and Barium stars. Title: Precise measurements of radial velocities of emission lines in the far-ultraviolet spectra of late-type stars. Authors: Ayres, T. R.; Engvold, O.; Moe, D. K.; Simon, T.; Jordan, C.; Judge, P.; Brown, A.; Linsky, J. L. Bibcode: 1984NASCP2349..468A Altcode: 1984fiue.rept..468A; 1984IUE84......468A The radial velocities of emission lines in deep short wave prime camera echelle exposures of several late-type dwarf and giant stars were measured. The goal was to search for absolute and differential Doppler shifts of emission lines formed at different temperatures in the stellar outer atmospheres analogous to the redshifts of C IV lambda 1548 (10 to the 5th power K) which occur in the solar transition zone. Existing images, taken without the precise radial velocity precautions, of five dwarf stars, four giant stars, and three supergiants are reanalyzed. Title: Ultraviolet Spectroscopy of Cool Stars from IUE (invited Paper) Authors: Jordan, C.; Judge, P.; Johansson, S. Bibcode: 1984uxsa.coll...51J Altcode: 1984IAUCo..86...51J; 1984uxsa.conf...51J No abstract at ADS Title: Radiative processes in cool star chromospheres. Authors: Jordan, C.; Judge, P. Bibcode: 1984PhST....8...43J Altcode: 1984PhyS....8...43J Observations made with the IUE satellite between 1200 Å and 3000 Å have shown that the spectra of giant and supergiant stars later than about K0 are dominated by emission from neutral atoms and singly charged ions. The cool star spectra show many examples of photo-excitation, line-leaking and fluorescent processes, some of which are discussed here. There is evidence that the H Ly α and H Ly β lines play an important role in the production of emission from O I, S I and Fe II. Some lines which remain without satisfactory explanations in both the stellar and solar spectra are discussed.