Author name code: thomas-dick ADS astronomy entries on 2022-09-14 author:("Thomas, Richard N." OR ="Thomas, Richard") NOT =author:"Thomas, R." year:1940-1995 ------------------------------------------------------------------------ Title: Cataclysmic variables and related objects Authors: Hack, Margherita; Ladous, Constanze; Jordan, Stuart D.; Thomas, Richard N.; Goldberg, Leo; Pecker, Jean-Claude Bibcode: 1993NASSP.507.....H Altcode: 1993cvro.nasa.....H; 1993QB835.H27...... No abstract at ADS Title: Solar-stellar chromospheres and coronae Authors: Thomas, Richard N. Bibcode: 1992MmSAI..63..731T Altcode: Empirical solar eclipse investigations have delineated chromospheric-coronal structure as fixed by interaction between mass and dissipative nonradiative energy fluxes. Current O-star data appear to agree with historical solar data in delineating the interaction of these two fluxes as the origin of a universally structured chromosphere-corona. Title: Modeling Utility of Rapid Variability Diagnostics of OB Stars Authors: Doazan, V.; Thomas, R. N. Bibcode: 1991ESOC...36..287D Altcode: 1991rvos.conf..287D No abstract at ADS Title: Sun-Hot Star Contrast in Chromospheric/Coronal Te(r). Nonradiative Heating vs. Outflow Enhanced Opacity Authors: Doazan, V.; Thomas, R. N. Bibcode: 1991mcch.conf..319D Altcode: No abstract at ADS Title: Implications on stellar structure/evolution of the observed association between energy/mass fluxes and multi-regional atmospheric structure Authors: Doazan, V.; Thomas, R. N. Bibcode: 1990ESASP.310..297D Altcode: 1990eaia.conf..297D No abstract at ADS Title: The first decade of envelope formation of 59 Cygni in the far UV and optical regions. II. Authors: Doazan, V.; Barylak, M.; Rusconi, L.; Sedmak, G.; Thomas, R. N.; Bourdonneau, B. Bibcode: 1989A&A...210..249D Altcode: Coordinated far-UV and optical observations of 59 Cygni are presented which, together with earlier results, describe the behavior of the entire atmosphere of the star during the first decade of formation and evolution of a new cool H-alpha emitting envelope. The data delineate an entire episode composed of a series of organized changes in the size of the mass outflow from the star, the mass content of the cool H-alpha emitting envelope, and the kinematic behavior of the cool envelope. A net increase in both the mass outflow from the star and the envelope's mass content occurs between the beginning and the end of this episode in a sequence of cyclic changes of the mass outflow from the star, the envelope's velocity distribution, and the envelope mass content. The modeling implications of these patterns are discussed. Title: FGK stars and T Tauri stars Authors: Cram, Lawrence E.; Kuhi, Leonard V.; Jordan, Stuart; Thomas, Richard; Goldberg, Leo; Pecker, Jean-Claude Bibcode: 1989NASSP.502.....C Altcode: 1989QB843.C6C73....; 1989fstt.book.....C The purpose of this book, FGK Stars and T Tauri Stars, like all other volumes of this series, is to exhibit and describe the best space data and ground based data currently available, and also to describe and critically evaluate the status of current theoretical models and physical mechanisms that have been proposed to interpret these data. The method for obtaining this book was to collect manuscripts from competent volunteer authors, and then to collate and edit these contributions to form a well structured book, which will be distributed to an international community of research astronomers by NASA and by the French CNRS. Title: The vanishing shell phase of PLEIONE in the far UV in 1988. Authors: Doazan, V.; Thomas, R. N.; Bourdonneau, B. Bibcode: 1988A&A...205L..11D Altcode: Far UV observations made with the IUE in 1988, when the shell spectrum of Pleione was vanishing in the visible region, are compared with previous IUE observations made when the shell was strong (1979) and when it began to weaken (1985). Between the epochs of strong shell and vanishing shell: (1) the apparent continuum level increases in all the observed far UV spectral range, the largest increase occurring at shortest wavelengths; (2) the CIV and SiIV resonance lines, which were not detectable during the epoch of strong shell, are identified without ambiguity in this B8Ve star when the shell spectrum vanishes; and (3) when the shell spectrum is strong, the MgII resonance lines exhibit a strong, broad absorption. When the shell spectrum vanishes, this absorption is much weaker and the MgII doublet shows double emission peaks with deep absorption cores, as is often observed in Be/shell spectra. Title: A ten-year `active' episode of mass outflow from the Be-star 59 Cyg: facts and implications Authors: Doazan, Vera; Thomas, Richard N. Bibcode: 1988ESASP.281b.121D Altcode: 1988IUE88...2..121D; 1988uvai....2..121D A study of the activity surrounding a 10 yr episode of increased mass-outflow for the Be star 59 Cyg identifies long-term patterns of coordinated variability, found in the visual and far UV. In the context of century-long visual studies of the similar long-term variability patterns of 59 Cyg and gamma Cas, two alternative interpretations of such observations as to the significance of Be stars for general stellar structure and evolution are possible: the variability suggests a nonthermal structure for the stellar interior, so that neither mass-loss or luminosity are time-constant; or Be stars do not exist in a long-lasting evolutionary stage, but represent a transition-phase between two such long-term evolutionary stages. The alternatives are not mutually exclusive. Title: O stars and Wolf-Rayet stars Authors: Conti, Peter S.; Underhill, Anne B.; Jordan, Stuart; Thomas, Richard N.; Goldberg, Leo; Pecker, Jean-Claude; Baade, D.; Divan, L.; Garmany, C. D.; Henrichs, H. F.; Kudritzki, R. P.; Pauldrach, A.; Prévot-Burnichon, M. -L.; Puls, J. Bibcode: 1988NASSP.497.....C Altcode: 1988oswr.book.....C Basic information is given about O and Wolf-Rayet stars indicating how these stars are defined and what their chief observable properties are. Part 2 of the volume discussed four related themes pertaining to the hottest and most luminous stars. Presented are: an observational overview of the spectroscopic classification and extrinsic properties of O and Wolf-Rayet stars; the intrinsic parameters of luminosity, effective temperature, mass, and composition of the stars, and a discussion of their viability; stellar wind properties; and the related issues concerning the efforts of stellar radiation and wind on the immediate interstellar environment are presented.

Contents: Perspective (R. N. Thomas).Part I. Introduction (L. Divan, M.-L. Prévot-Burnichon).1. Introducing the O and Wolf-Rayet stars.Part II. One perspective on O, Of, and Wolf-Rayet stars emphasizing winds and mass loss, with remarks on environment and evolution:2. Overview of O, Of, and Wolf-Rayet populations (P. S. Conti). 3. Intrinsic stellar parameters (P. S. Conti, D. Baade). 4. Stellar winds: (a) Introduction (P. S. Conti). (b) Mass loss from O stars (C. D. Garmany). (c) Mass loss in Wolf-Rayetstars (P. S. Conti). (d) Radiation-driven winds of hot luminous stars (R. P. Kudritzki, A. Pauldrach, J. Puls). (e) Intrinsic variability in ultraviolet spectra of early-type stars: the discrete absorption lines (H. Henrichs). 5. Environments and evolution (P. S. Conti).Part III. Another perspective on O, Of, and Wolf-Rayet stars, emphasizing model atmospheres and possibilities for atmospheric heating (A. B. Underhill): 6. Understanding the O and Wolf-Rayet stars. 7. Model Atmospheres and the theory of spectra for O and Wolf-Rayet stars. 8. The physics of the mantles of hot stars. 9. Summary of processes influencing the spectra of O and Wolf-Rayet stars. Title: BE Shell of Pleione Authors: Thomas, Richard Bibcode: 1988iue..prop.3261T Altcode: No abstract at ADS Title: Implications of Variable Mass-Outelow on Modeling. Authors: Doazan, V.; Thomas, R. N. Bibcode: 1988ASSL..142..205D Altcode: 1988mosg.proc..205D Observational evidence for variability in mass outflow from Be stars is summarized, and theoretical models which account for this variability are discussed. Sample data are presented graphically, and it is pointed out that the entire profiles of highly excited resonance lines in Be stars exhibit strong strength, velocity, and shape variations, including organized large-amplitude variability patterns in the FUV. In the context of the radiation-driven wind model of mass outflow, particular attention is given to variations in the mass-outflow velocity in individual stars, stellar-atmospheric structures, the mathematical treatment of variable chromosphere-corona opacity, cooling terms to account for the temperature of the H-alpha-emitting envelope (10,000-20,000 K), and self-interactions of a variable mass outflow. Title: O stars and Wolf-Rayet stars. Authors: Baade, D.; Conti, P. S.; Divan, L.; Garmany, C. D.; Henrichs, H. F.; Kudritzki, R. P.; Pauldrach, A.; Prévot-Burnichon, M. -L.; Puls, J.; Underhill, A. B.; Thomas, R. N. Bibcode: 1988NASSP.497.....B Altcode: Contents: Perspective (R. N. Thomas).Part I. Introduction (L. Divan, M.-L. Prévot-Burnichon).1. Introducing the O and Wolf-Rayet stars.Part II. One perspective on O, Of, and Wolf-Rayet stars emphasizing winds and mass loss, with remarks on environment and evolution:2. Overview of O, Of, and Wolf-Rayet populations (P. S. Conti). 3. Intrinsic stellar parameters (P. S. Conti, D. Baade). 4. Stellar winds: (a) Introduction (P. S. Conti). (b) Mass loss from O stars (C. D. Garmany). (c) Mass loss in Wolf-Rayetstars (P. S. Conti). (d) Radiation-driven winds of hot luminous stars (R. P. Kudritzki, A. Pauldrach, J. Puls). (e) Intrinsic variability in ultraviolet spectra of early-type stars: the discrete absorption lines (H. Henrichs). 5. Environments and evolution (P. S. Conti).Part III. Another perspective on O, Of, and Wolf-Rayet stars, emphasizing model atmospheres and possibilities for atmospheric heating (A. B. Underhill): 6. Understanding the O and Wolf-Rayet stars. 7. Model Atmospheres and the theoryof spectra for O and Wolf-Rayet stars. 8. The physics of the mantles of hot stars. 9. Summary of processes influencing the spectra of O andWolf-Rayet stars. Title: Long-term variability of the far-UV high velocity components in gammaCas (1978-1986). Authors: Doazan, V.; Rusconi, L.; Sedmak, G.; Thomas, R. N.; Bourdonneau, B. Bibcode: 1987A&A...182L..25D Altcode: A synthesis of the authors' long term observations of γ Cas in the visual and in the far UV, combined with IUE archived spectra, shows that: (1) The occurrence of the high velocity components observed in the Si IV, C IV, and N V resonance lines exhibits a long term variability pattern, which is associated with the cyclic V/R variations of the Balmer emission-lines: they are frequently observed when V/R > 1, while they are absent/rarely present when V/R < 1. (2) During the present V/R > 1 half-cycle, the observed components do not fit the column density vs. velocity correlation derived by Henrichs et al. (1983). γ Cas is one more example of a Be star which exhibits associated far UV and visual long term variability patterns. Title: Far-UV variability of theta CrB in 1985-86 : a progression toward higher velocities. Authors: Doazan, V.; Rusconi, L.; Sedmak, G.; Thomas, R. N. Bibcode: 1987A&A...173L...8D Altcode: New far UV observations of θ CrB obtained with the IUE in 1985 - 1986 are presented. They show that the far UV spectrum of that star has usually continued to exhibit the apparently low excitation state observed from mid-84 to mid-85. However, the C IV resonance lines are occasionally conspicuous and exhibit an even higher outflow velocity than during the preceding epochs of variation, when the C IV resonance lines were strong and frequently present. Such a long term progression toward higher expansion velocities has not yet been observed in any other Be star. Title: Empirical-theoretical modeling of Be variable mass-loss via variable: Photospheric mass-outflow; Coronal opacity; Radiation-amplified wind-piston, driving pulsating cool-envelope Authors: Doazan, Vera; Thomas, Richard N. Bibcode: 1987LNP...274...96D Altcode: 1987stpu.conf...96D No abstract at ADS Title: Far UV variability of theta CrB in 1980-1985. II. Evidence for variability patterns and ionization dependence. Authors: Doazan, V.; Morossi, C.; Stalio, R.; Thomas, R. N. Bibcode: 1986A&A...170...77D Altcode: Far UV observations of Theta CrB obtained in 1980-1985 with the IUE are presented which provide evidence for long-term variability patterns associating the shape, velocity and strength of the Si IV, Al III, and Fe III lines. A differential variable behavior between lines arising from different ionization levels is also noted. The present results are in contradiction with the findings of Underhill (1985), and it is suggested that her results are biased by the averaging of velocities, which lowered the amplitude of the velocity variations, and by the higher weight given to the period of time when the expansion velocities were constant. Title: The CIV resonance lines in Be stars: their variability, their `disappearances' and their association with Balmer emission-line variability Authors: Doazan, V.; Thomas, R. N. Bibcode: 1986ESASP.263..381D Altcode: 1986niia.conf..381D; 1986NIA86......381D More than eight years of IUE observations of Be stars were analyzed. Results show that variability is an outstanding property of the far UV spectrum of Be stars. This variability is best seen in the C IV resonance lines which show: remarkable changes in profile and velocity, as well as in the presence, location, and strength of narrow absorption components; large variations in strength going from strong to undetectable lines; and variability patterns associated with those exhibited by the Balmer emission lines. Title: Ultraviolet and visual variability of theta CrB during a normal B-phase following a shell phase (1980-1985). Authors: Doazan, V.; Marlborough, J. M.; Morossi, C.; Peters, G. J.; Rusconi, L.; Sedmak, G.; Stalio, R.; Thomas, R. N.; Willis, A. Bibcode: 1986A&A...158....1D Altcode: Based on far-UV and visual observations made between 1980 and 1985, the phenomena characterizing the end of a shell phase of Theta-CrB, and the normal B-phase following it, are described as part of a long-term study of Be stars. The strength, shape, and velocity of the C IV, Si IV, and Al III resonance lines, and the Fe III lines of low excitation, show associated variability patterns over the whole range of ionization observable in the IUE and visual spectra. The observed variability pattern consists of a one-year narrow-line stage where the lines show narrow absorption cores close to rest wavelength, a two-year series of abrupt changes between a weak and a strong line, and a damping out of these variations leaving the observed spectrum in a lower ionization state. The existence of a phase-lag between similar phenomena occurring in the superionized and subionized/normally ionized regions, is noted. Title: Luminosity and colour variations of 88 HER through phase changes fromthe far UV to the visual spectral regions. II. Empirical atmospheric modelling an association between photospheric. Authors: Doazan, V.; Thomas, R. N.; Barylak, M. Bibcode: 1986A&A...159...75D Altcode: In this paper, hereafter called Paper II, we analyse and interpret the observations, presented in Paper I, of the luminosity variations, from the far-UV to the visual region, of 88 Her as it changes from the quasi-normal B phase to the Be-shell phase. These observations show two remarkable facts: (i) The luminosity decreases, in all the observed wavelengths, when the star changes from the quasi-normal B phase to the beginning of the Be-shell phase; and (ii) the luminosity increases, in all the observed wavelengths, as the Be-shell spectrum develops. In Paper I, we showed that the basic assumption of traditional Be star modelling, which attributes all the observed luminosity variations to changes in the physical conditions of the exophotospheric cool envelope - while the photosphere remains invariable - did not agree with the observations. In this Paper II, we analyze the data without any preconceived assumptions on what are the atmospheric regions producing the luminosity changes; we admit that the observed luminosity variations may arise from changes of the structure and thermodynamic state of both the photosphere and the exophotospheric cool envelope. We present an iterative approach to such disguostics of the comparative roles of the photosphere and envelope: each higher- order in the iteration adds one more atmospheric region and/or one more kind of absorption/emission process in the envelope. We show that different spectral regions respond quite differently, in amplitude of change, to changes in photospheric temperature, and in absorption/emission by the cool envelope. We emphasize that the sensitivity of our diagnostic approach comes from our focus on luminosity changes which accompany phase changes, and on our analysis of such luminosity changes and their wavelength dependence over a broad wavelength range - from the far-UV to the visual region. We conclude from our analysis: 1) The major cause which produces the luminosity drop, when the star varies from the quasi-normal B phase to the beginning of the Be-shell phase, is a decrease in photospheric temperature by about 1000 K. However, in order to adequately represent the wavelength dependence of these luminosity changes, it is necessary to also take into account the effect of the envelope absorption and emission. 2) Apparently, this decrease in photospheric thermal energy is associated with that increase in mass-outflow, which produces that increase in mass-content of the envelope, which is observed as a strengthening of the shell-spectrum. 3) The strengthening of the shell-spectrum, which reflects the increase in mass-content, and presumably the size of the envelope, is associated with a monotonic increase in luminosity which, according to our diagnostics, demands either an increase in photospheric radius with little change in photo spheric temperature or a mild increase in photo spheric temperature and in envelope radius but no change in photospheric radius. The observations are inadequate for a definitive choice between the two alternatives; although we favor the latter, from considerations based on physical consistency and observations of other stars. 4) These results leave us with a choice between searching either for a direct way of converting thermal energy of the photosphere into mass-outflow, or for a subphotospheric diversion of some energy from photospheric thermal energy into nonthermal energy modes which produce and amplify mass-outflow. Title: Book-Review - Effect of Variable Mass Loss on the Local Stellar Environment - Trieste Workshop 1983 Authors: Stalio, R.; Thomas, R. N.; Tschape, R. Bibcode: 1986AN....307..148S Altcode: No abstract at ADS Title: The M-type stars Authors: Johnson, Hollis Ralph; Querci, Francois R.; Jordan, Stuart; Thomas, Richard; Goldberg, Leo; Pecker, Jean-Claude Bibcode: 1986NASSP.492.....J Altcode: 1986mts..book.....J; 1986QB843.M16M89... No abstract at ADS Title: The development of the new Be phase of 59 CYG in the visual and in the far UV in 1978-1983. Authors: Doazan, V.; Grady, C. A.; Snow, T. P.; Peters, G. J.; Marlborough, J. M.; Barker, P. K.; Bolton, C. T.; Bourdonneau, B.; Kuhi, L. V.; Lyons, R. W.; Polidan, R. S.; Stalio, R.; Thomas, R. N. Bibcode: 1985A&A...152..182D Altcode: A tentative synthesis of visual and IUE observations of 59 Cyg during 1978-1983 when the new Be phase began to develop is presented. The study reveals correlation between those spectral features originating in the cool H-alpha-emitting envelope and features originating in superionized regions exhibiting C IV and N V lines. The long-term variability patterns of the V/R ratio, the H-alpha emission, and the C IV absorption reveal striking similarities and a close correlation. The early development of the new Be phase is accompanied by remarkably large and striking C IV line-profile changes. It is also suggested that short-term V/R variations at H-alpha may be associated with short-term C IV changes. Title: Book-Review - Stellar Atmospheric Structural Patterns Authors: Thomas, R. N.; Gussmann, E. A. Bibcode: 1985AN....306..341T Altcode: No abstract at ADS Title: Trieste Workshop 1984: special session in Be stars. Authors: Baade, D.; Doazan, V.; Marlborough, M.; Polidan, R.; Peters, G.; Smith, M.; Thomas, R. N.; Willson, L. A. Bibcode: 1985rbcc.conf..321B Altcode: No abstract at ADS Title: Summary of working group on chromospheric heating and energy balance. Authors: Thomas, R. N. Bibcode: 1985cdm..proc...15T Altcode: No abstract at ADS Title: An episodic red-wing structure of Si IV, λ1394 Å, in γ Cas. Authors: Doazan, V.; Sedmak, G.; Stalio, R.; Thomas, R. N.; Willis, A. J. Bibcode: 1984NASCP2349..243D Altcode: 1984fiue.rept..243D; 1984IUE84......243D International Ultraviolet Explorer (IUE) observations of gamma Cas obtained in January 1983 show the conspicuous presence of a red-wing structure in the SiIV, 1394 A, resonance line in gamma Cas. The 1403 A, shows a much less enhanced trace of the same effect. A comparison between 1938 IUE spectra with previous ones obtained in 1980 show that in January 1983 the red absorption wing is strongly depressed relative to the 1980 profile where the red feature was absent. It is concluded that this red wing feature is in absorption rather than in emission. This same wing-structure is suggested on 1982 IUE spectra. Combining long-term variations of gamma Cas in the visual with published far-UV data, it is noted that this red feature seems to occur preferentially at epochs where the V/R ratio of the violet and red emission peaks at H-alpha is less than one. It is suggested that these two characteristics, visual and far UV, are linked to the flow-deceleration in the outer-atmosphere. Title: Book-Review - Stellar Atmospheric Structural Patterns Authors: Thomas, R. N.; Mihalas, D. Bibcode: 1984Obs...104..275T Altcode: No abstract at ADS Title: Book-Review - Stellar Atmospheric Structural Patterns Authors: Thomas, R. N. Bibcode: 1984S&T....68Q.327T Altcode: No abstract at ADS Title: Book-Review - Stellar Atmospheric Structural Patterns Authors: Thomas, R. N. Bibcode: 1984Sci...225R.503T Altcode: No abstract at ADS Title: Possible identifying characteristics of Be stars. Authors: Doazan, V.; Thomas, R. N. Bibcode: 1984ESASP.218..297D Altcode: 1984iue..conf..297D Physical parameters whose size and behavior may identify a Be star independently of the presence (or non-presence) of H alpha emission are discussed. A decelerated model for Be and similar stars and an assertion that mass outflow variability is a sufficiant condition to produce the necessary deceleration are discussed. The far UV spectral changes in the CIV and A1III resonance lines of the Be star, theta CrB, during its normal B phase, 1980 to 1984 are summarized It is suggested that the observed changes in ionization reflect changes in the nonradiative heating of the chromosphere-corona, and that such variable heating, together with variable mass-loss, are Be-star characteristics. Title: Abrupt changes in the C IV resonance lines of theta CR B. Authors: Doazan, V.; Morossi, C.; Stalio, R.; Thomas, R. N.; Willis, A. Bibcode: 1984A&A...131..210D Altcode: It is noted that the Theta CrB far-UV spectrum changes from conspicuous presence, to complete disappearance, to reappearance at a higher velocity than the previous one, have occurred with a phase lag of about 3 years after the disappearance of a weak shell phase of short duration which was observed in the visible in 1979. This sequence is interpreted in the framework of the Doazan and Thomas (1982) Be-star atmospheric model, as the dissipation and reformation of successive layers in the outer atmosphere. This dissipation proceeded from the outermost subionized layers to the innermost superionized layers. The C IV lines' reappearance at a higher velocity suggests an increase of mass flux and nonradiative energy flux. If Theta CrB's behavior resembles that of 59 Cyg, this set of circumstances could lead to the formation of a new, cool, H-alpha emitting/absorbing envelope. Title: Be-Stars Authors: Baade, D.; Doazan, V.; Marlborough, M.; Polidan, R.; Peters, G.; Smith, M.; Thomas, R. N.; Willson, L. A. Bibcode: 1984rcch.conf..321B Altcode: No abstract at ADS Title: Book-Review - Stellar Atmospheric Structural Patterns - Monograph Series on Nonthermal Phenomena in Stellar Atmospheres Authors: Thomas, R. N. Bibcode: 1984Natur.310..805T Altcode: No abstract at ADS Title: Empirical-Theoretical Structural Patterns for Stellar Atmospheres and Their Local Environment Relative to Variable Mass Loss Authors: Thomas, R. N. Bibcode: 1984evml.conf....3T Altcode: No abstract at ADS Title: Effects of variable mass loss on the local stellar environment Authors: Stalio, Roberto; Thomas, Richard N. Bibcode: 1984evml.conf.....S Altcode: 1984QB809.E34......; 1984evml.book.....S No abstract at ADS Title: Pas de deux Authors: Thomas, R. N. Bibcode: 1983Obs...103..172T Altcode: No abstract at ADS Title: Stellar atmospheric structural patterns Authors: Thomas, R. N. Bibcode: 1983NASSP.471.....T Altcode: 1983sasp.nasa.....T; 1983QB809.T46...... Contents: Part I: Thermodynamic overview of the stellar atmosphere. (1) Introductory comments on stellar atmospheric structure and its modeling. (2) Speculative-theoretical modeling of the atmosphere enveloping a hypothetical (closed, thermal) star.(3) Empirical-theoretical survey of the varieties of peculiarities and anomalies in the atmospheres enveloping actual stars. Part II: Thermodynamic and gas-dynamic background (following volume). Part III: Radial structure of atmosphere and local environment. (4) Characteristics of distinctive regions comprising stellar atmospheres. (5) Observed distinctive radial sequences of the distinctive atmospheric regions comprising stellar atmospheres. (6) Inferences on the thermodynamic characteristics of a star from the distinctive radial sequences of the distinctive atmospheric regions comprising that stellar atmosphere. Title: Empirical-theoretical approach by contrast to summary of speculative-theoretical modeling by Hearn Authors: Thomas, R. N. Bibcode: 1983obvf.proc..218T Altcode: The mechanisms of solar and stellar winds are investigated using an empirical-theoretical approach which is contrasted to the more purely theoretical closed-system thermodynamic approach of Parker (1958), as summarized by Hearn (1982). The need to use observational data on such objects as Wolf-Rayet stars and Be stars to determine the equations and boundary conditions of stellar-atmosphere models is stressed. The thermodynamically quasi-linear mass and momentum equations of Cannon and Thomas (1975, 1977) are presented and characterized, the inadequacy of the velocity fields of radiative-acceleration theory is argued, and some observational data are summarized to illustrate the point. A current empirical model involving a standard photosphere with T(eff) and g specified, and exophotosphere with monotonically increasing mass flux and nonthermal velocity, and local environments with nongravitational deceleration is briefly described. Title: Variable mass-flux in Be stars Authors: Doazan, V.; Thomas, R. N. Bibcode: 1983HvaOB...7...97D Altcode: The available observational data concerning the variability of Be stars is briefly reviewed, and some different hypotheses concerning the origin of Be variability are examined. It is shown that variability in Be stars is not restricted to short time scales. In fact, long term variations (such as 'E/C' variations of the intensity of the emission components of H I lines relative to neighboring continua) may be greater in amplitude than short term variations. It is recommended that future calculations of Be rotational velocities (v sin i) take into account the uncertainty of short-term line profile variations. Observations of variability in the ultraviolet and X-ray regions are discussed within the framework of the mass-flux model of Doazan and Thomas (1982), in which mass-flux and nonradiative energy are assumed to be independent parameters. Title: Observational basis for velocity fields in stellar atmospheres Authors: Stalio, Roberto; Thomas, Richard N. Bibcode: 1983obvf.proc.....S Altcode: 1984QB809.O27...... Solar and stellar winds and mass-loss phenomena are discussed in reviews of recent observations and current theory. Topics examined include mass loss from the sun, the O-type stars, Wolf-Rayet stars, the Parker theory, B stars, T Tauri stars, Balmer line emission from Be stars, novae, symbiotic stars, planetary nebulae, and dwarf novae. Graphs, tables, diagrams, sample spectra, and extensive discussion on each contribution are provided. For individual items see A84-39477 to A84-39487 Title: The effect on empirical atmospheric modeling of the mass-flux as an independent parameter Authors: Thomas, R. N. Bibcode: 1982ApJ...263..870T Altcode: Observational data on atmospheric structure and mass fluxes from the sun and Be stars are applied to test the adequacy of the original Parker 'hot corona' approach to predicting atmospheric structure and the size of the mass flux from only the radiative and nonradiative energy fluxes, and from gravity, and imposing the condition that thermal and escape points must coincide. Observations do not support this latter condition. It is concluded that the Parker approach is an asymptotic approximation to the very low mass flux limit in a nonvariable stellar atmosphere. Title: Empirical atmospheric velocity patterns from combined IUE and visual observations : the Be stars. Authors: Doazan, V.; Thomas, R. N. Bibcode: 1982ESASP.176..287D Altcode: 1982iue..conf..287D; 1982IUE3r......287D Observations of 59 Cyg show the strongest displacements of the far UV superionized lines at epochs of minimum H alpha emission. Phases of strongest mass flux, measured in the chromospheric coronal regions, do not coincide with phases of largest mass content in the overlying cool H alpha envelope. Velocities in the chromosphere-corona range up to 1500 km/sec; those in the H alpha and Fe II emission envelope, and absorption shell, do not exceed 1 to 200 km/sec. The density in the postcoronal regions is not fixed by a monotonically-outward accelerated flow; strong deceleration and cooling of the mass-flow within a few radii are required. The Be stars have the same atmospheric pattern as planetary nebulae but the decelerated cool regions occur within a few radii as contrasted to the 1 million or more radii for normal planetary nebulae. Title: Gross Structural Pattern for the Atmospheres of Be-Stars and Some Closely Related Stars Authors: Doazan, V.; Stalio, R.; Thomas, R. N. Bibcode: 1982IAUS...98..489D Altcode: No abstract at ADS Title: The Active Ultraviolet Phase of 59-CYGNI Authors: Doazan, V.; Grady, C.; Kuji, L. V.; Marlborough, J. M.; Snow, T. P.; Thomas, R. N. Bibcode: 1982IAUS...98..415D Altcode: No abstract at ADS Title: Rotational velocity versus mass loss in Be stars Authors: Doazan, V.; Franco, M. L.; Stalio, R.; Thomas, R. N. Bibcode: 1982IAUS...98..319D Altcode: C IV and Si IV resonance line profiles of 21 Be, B-shell and normal stars are studied with the aim of detecting evidences for mass loss. It is found that almost all sampled here are losing mass. A relation between an estimated lower limit for the rate of mass loss and the observed rotational velocity was searched for but not found. Title: B stars with and without emission lines. Monograph Series on Nonthermal Phenomena in Stellar Atmospheres. Authors: Underhill, A. B.; Doazan, V.; Lesh, J. R.; Aizenman, M. L.; Thomas, R. N. Bibcode: 1982NASSP.456.....U Altcode: No abstract at ADS Title: Empirical atmospheric velocity patterns from combined IUE and visual observations: the Be-similar stars. Authors: Doazan, V.; Stalio, R.; Thomas, R. N. Bibcode: 1982NASCP2238..584D Altcode: 1982IUE82......584D; 1982auva.nasa..584D; 1982NASCP2338..584D The velocity pattern which panspectral observations of the Be stars suggest, and an outline of its extension via similar panspectral observations of the Be similar stars are summarized. The time dependent interaction between the stellar mass flux and the local environment produced jointly by the star itself and its original environment are emphasized. Title: Opening Remarks Authors: Thomas, R. N. Bibcode: 1982obvf.confD..22T Altcode: No abstract at ADS Title: Global picture of a Be star Authors: Thomas, R. N. Bibcode: 1982NASSP.456..409T Altcode: 1982bsel.nasa..409T An attempt is made to synthesize the observational material on Be stars into a empirical pattern of atmospheric structure. The sequence of atmospheric regions is developed and empirical-numerical estimates of location and structure of the regions are described. Inferences are drawn concerning the general stellar structure required to generate the nonthermal fluxes which produce the observed atmospheric pattern. In particular the atmospheric and subatmospheric origins of mass flux are addressed. Title: Empirical - Theoretical Approach by Contrast to Summary of Speculative - Theoretical Modeling by Hearn Authors: Thomas, R. N. Bibcode: 1982obvf.conf..218T Altcode: No abstract at ADS Title: Observational Basis for Velocity Fields in Stellar Atmospheres Authors: Stalio, Roberto; Thomas, Richard N. Bibcode: 1982obvf.conf.....S Altcode: 1982obvf.book.....S No abstract at ADS Title: Short-term UV line profile variation in 59 Cyg. Authors: Grady, C. A.; Doazan, V.; Peters, G. J.; Willis, A. J.; Snow, T. P.; Aitken, D. K.; Barker, P. K.; Bolton, C. T.; Henrichs, H. F.; Kitchen, C. R.; Kuhi, L. V.; Marlborough, J. M.; Meikle, W. P. S.; Mendzies, J.; Oegerle, W.; Polidan, R. S.; Rosner, R.; Selvelli, P. L.; Stalio, R.; Thomas, R. N.; Vaiana, G.; Whitelock, P. A.; Wilson, R.; Wu, C. -C. Bibcode: 1982NASCP2238..425G Altcode: 1982NASCP2338..425G; 1982auva.nasa..425G The International ultraviolet Explorer high dispersion spectra of 59 Cyg obtained as part of the long term monitoring program have shown that noticeable variation can occur in C 5 and N 5 on timescales 3 hours t24 to 28 hours. In order to begin to resolve whether these changes occur continuously or sporadically, 48 hours were devoted to monitoring this star in January 1982. The January spectra show no short term variation, which may be consistent with sporadic rather than continuous variation. Title: Proposed three-phase modeling of Be stars from combined UV and visual observations. Authors: Doazan, V.; Stalio, R.; Thomas, R. N. Bibcode: 1981NASCP2171..149D Altcode: 1981NASCP3171..149D; 1981uviu.nasa..149D; 1980IUE80......149D Far ultraviolet observations of the behavior of wind velocity and superionization values as a function of the phase of the (Be, B shell, B normal) pattern established by visual observations for gamma Cas and 59 Cyg are translated into a crude atmospheric model for the Be phase and several kinds of mass flux variability across the three phases. Title: Stellar variability and individuality - Observations and implications Authors: Costero, R.; Doazan, V.; Stalio, R.; Thomas, R. N. Bibcode: 1981ASSL...89..131C Altcode: 1981IAUCo..59..131C; 1981emls.proc..131C Attention is given to the implications of the observed nonthermal mass fluxes on the modeling of stellar structure and evolution. Current problems concerning observations of variability in spectrum and luminosity are related to the question whether the variability is sufficiently large to require fundamental changes regarding the modeling of stellar atmospheres. Aspects of variability are evaluated, taking into account Be stars and B supergiants. Quentions regarding an apparent 'individuality' in appearance among stars of the same taxonomic class are also investigated. It is concluded that no serious consideration can be given to models and computations for mass loss and its evolutionary effects, which are expressed wholly in terms of thermal parameters. Title: Observational Results on Mass-Loss in B-Stars Authors: Doazan, V.; Thomas, R. N.; Groupe Etoiles Variables de L'Observatoire de Nice Bibcode: 1981pbs..work...85D Altcode: No abstract at ADS Title: A scheme of atmospheric regions. III - Chromospheres of emission-line stars. 1 - Formation of H alpha emission line cores in T Tauri-type stars Authors: Heidmann, N.; Thomas, R. N. Bibcode: 1980A&A....87...36H Altcode: We focus on the effects of the velocity field, and changed density distribution, accompanying our model of a mass-flux on an expanded version of our earlier, static, model of Hα emission from a low-lying chromosphere. Our aim lies on understanding the variability, between "peculiar" and normal stars, and for a given star, in Hα emission and other allied characteristics. We find that the velocity field alone, ignoring effects of changed density distribution, does not suffice to remove the contradictions earlier found on the total Hα emission and large central self-reversal of the profile. Including the effects of changed density distribution introduces a wide variety of possible models, depending upon the size of the mass-flux. A better resolution of the contradictions requires consideration of extended, not only low-lying, chromospheres-coronas-postcoronas. Title: Te - Structure of the wind in gamma Cas. Authors: Doazan, V.; Selvelli, P. L.; Stalio, R.; Thomas, R. N. Bibcode: 1980ESASP.157..145D Altcode: 1980iue..conf..145D; 1980IUE2n......145D UV observations of the wind in gamma Cas, via measure of line displacements, delineate two distinct and nonoverlapping velocity regions where absorbing ions for Si4, C4, N5 are concentrated at about 100 km/sec and 1400 km/sec. Absence of appreciable numbers of these ions absorbing at intermediate velocities suggests the presence of a corona too hot to support such ions in those atmospheric regions where such velocities occur; observed soft X-ray emission at coronal intensities from gamma Cas supports this picture. Visual studies show that the present phase of gamma Cas is moderately strong Be, and not B-shell. This Be-phase UB velocity behavior is contrasted with the present, rising from quasi B-normal, toward Be, phase behavior of 59 Cyg, where only the high velocity regime is observed in superionized species, and only the low velocity regime in photospheric Si4. Title: Variable wind-velocity in 59 Cyg. Authors: Doazan, V.; Kuhi, L. V.; Marlborough, J. M.; Snow, T. P.; Thomas, R. N. Bibcode: 1980ESASP.157..151D Altcode: 1980iue..conf..151D; 1980IUE2n......151D Combined UV and visual observations of 59 Cyg in 1972, 1975, late 1978, and at several epochs in 1979 are summarized. Visual observations suggest a similar pattern of long term variability for 59 Cyg and gamma Cas, within which are placed the UV data on 59 Cyg. During the 1978-79 epoch of small but increasing H alpha emission, the C4 and N5 lines reached maximum expansion velocities of some 750 km/sec, whereas the Si4 lines showed neither appreciable displacements nor asymmetry. Line displacements of N5 varied by a factor 2, and appeared to oscillate, but line components that correspond to violet displacements 100 km/s were not identified. This 1978-79 situation is unlike the situation of strong Be phase of 59 Cyg in 1972 and 1975, and of Gamma Cas in 1978-79, where expansion at less than 100 km/s was observed. Title: Variable mass flux in the Be star 59 Cyg. Authors: Doazan, V.; Kuhi, L. V.; Thomas, R. N. Bibcode: 1980ApJ...235L..17D Altcode: The paper reports observations of 59 Cygni (B1.5 Ve) made in 1978 December with IUE at high resolution simultaneously with visual spectral observations. The C IV and probably the N V resonance absorption lines show whole-line violet displacements of 750 km/s, exceeding the photospheric escape velocity. Si IV and lesser ions show violet displacements less than 50 km/s. The implied mass loss is strongly variable noting Marlborough's observations showing N V and O VI violet displacements of 50 km/s. Long-term study of H(alpha) behavior, combined with these far-UV data, suggests that large mass flux coincides with a phase of rapidly increasing H(alpha) emission; while a large, but quasi-stationary H(alpha) emission phase is associated with fewer superionized atoms of O VI and N V moving with very high mass-flow velocities. Title: 59 Cygni Authors: Thomas, Richard Bibcode: 1979iue..prop..378T Altcode: No abstract at ADS Title: The thermodynamic requirements on atmospheric models imposed by observed stellar nonthermal mass-fluxes and by those observed nonthermal features enhanced in Xe stars. Authors: Thomas, R. N. Bibcode: 1979IAUS...83..215T Altcode: No abstract at ADS Title: High resolution spectrometry. Proceedings of the 4th International Colloquium on Astrophysics, held in Trieste, July 3_-_7, 1978. Authors: Hack, M.; Thomas, R. N. Bibcode: 1978hrsp.book.....H Altcode: No abstract at ADS Title: Concluding Remarks Authors: Thomas, R. N. Bibcode: 1978hrs..conf..702T Altcode: No abstract at ADS Title: Forecast of future in solar physics Authors: Thomas, R. N. Bibcode: 1977MmSAI..48..579T Altcode: No abstract at ADS Title: What is a stellar atmosphere Authors: Thomas, R. N. Bibcode: 1977MmSAI..48..339T Altcode: The nonequilibrium thermodynamic basis for modeling a stellar structure, subatmosphere, and atmosphere is formulated, along with the thermodynamic characterization of a star as a concentration of matter and energy in the interstellar medium. The analytical formulation of nonequilibrium thermodynamic models is discussed in the case where the nonisothermal storage modes are kinetic modes. Title: The origin of stellar winds: subatmospheric nonthermal storage modes versus radiation pressure. Authors: Cannon, C. J.; Thomas, R. N. Bibcode: 1977ApJ...211..910C Altcode: Most current models of matter-flux in hot stars place its origin in radiation pressure, and then model the flow explicitly to produce no chromosphere-corona. Our model of the stellar atmosphere as a transition zone between stellar interior and interstellar medium places the origin of matter-flux, chromosphere-corona, and spectral 'emission classes' in subatmospheric nonthermal kinetic energy storage, equally for all stars, hot or cold. Current observations of both hot and cold stars suggest chromospheres to be a universal phenomenon, correlated with matter-fluxes, and enhanced in 'emission-class' stars. To clarify the difference between the two kinds of models above, we reformulate the wind-tunnel analogy to stellar winds, suggesting that stars satisfy an 'imperfect,' rather than 'perfect,' such model; i.e., transonic shocks occur before the throat, corresponding to an imposed outward velocity in the storage section, or subatmosphere. We then investigate the stability of an arbitrary stellar atmosphere, hot or cold, to suggest a cause for such an outward subatmospheric velocity. Title: Irreversibility, evolution, Evolution, and the process of local concentration Authors: Thomas, Richard N. Bibcode: 1977FoPh....7..137T Altcode: We suggest that some general questions of irreversibility and of quasi- Equilibrium vs. non- Equilibrium configurations (terminology is explained in the text), with respect to both biophysical and physical structures, can be clarified by generalizing results from investigations of stellar structure in relation to its environment. Such work has evolved from considerations of the stellar atmosphere as a transition zone between the quasi- Equilibrium stellar interior and the non- Equilibrium interstellar medium. As opposed to suggestions of irreversibility originating in the large (Gal-Or, e.g.), we suggest that the origin is local, in coupling between different storage modes for matter and energy. In contract to suggestions of non- Equilibrium biophysical structures arising in fluctuations from a quasi- Equilibrium state (Prigogine et al.), we suggest that they arise via condensations within a non- Equilibrium, steady-state, unstable environment. Generalization from stellar prototype studies of the process of such concentration indicates that the general process of forming structures in the Universe follows a hierarchy of such greater degree of Equilibrium concentrations formed in lower degree of Equilibrium environments. Title: Critical Summary of the Colloquium Authors: Thomas, R. N. Bibcode: 1977ebhs.coll..487T Altcode: 1977IAUCo..36..487T No abstract at ADS Title: Boundary conditions with mass-loss: general considerations. Authors: Thomas, R. N. Bibcode: 1977saif.conf..143T Altcode: No abstract at ADS Title: Radiation loss and mechanical heating in the low solar chromosphere. Authors: Praderie, F.; Thomas, R. N. Bibcode: 1976SoPh...50..333P Altcode: We discuss Ulmschneider's claim to have established that the short-period acoustic wave energy input is the only one able to balance the chromospheric radiation loss. We first review the range of uncertainty in empirical and radiative equilibrium models, on which estimates of the excess radiation coming from mechanical heating rest. We then show that Ulmschneider's estimate of this excess radiation from such models uses an over-simplified computational method. The resultant of uncertainty in models and in computational methods suggests that Ulmschneider's results on excess radiation from heating in the low chromosphere is subject to overestimation by an order of magnitude. Title: Solar Astrophysics: Ghettosis from, or Symbiosis with, Stellar and Galactic Astrophysics? Authors: Pecker, J. -C.; Thomas, R. N. Bibcode: 1976SSRv...19..217P Altcode: The purpose of the paper is to show how the solar-stellar symbiotic approach has led to the modeling of a star as a concentration of matter and energy. By 'solar-stellar symbiosis' is meant the philosophy of investigation according to which one asks what change in our general understanding of stellar structure and of stellar spectroscopic diagnostics is required to satisfy both the sun and an unusual star when, for example, some feature of an unusual star is discovered. The evolution of stellar models is traced, from walled, thermodynamic-equilibrium models to de-isolated models featuring transition zones and nonlocal thermodynamic equilibrium. Title: Significance of asymmetric emission line profiles on mass-flux and chromosphere from T Tauri stars. Authors: Dumont, S.; Heidmann, N.; Thomas, R. N. Bibcode: 1976sgov.meet..233D Altcode: No abstract at ADS Title: Mass flux in stars. The origin of stellar winds: subatmospheric non-thermal storage modes vs radiation pressure. Authors: Cannon, C. J.; Thomas, R. N. Bibcode: 1975MSRSL...9..231C Altcode: 1975assp.conf..231C; 1975apes.conf..231C No abstract at ADS Title: Mass, energy and momentum transport in the solar atmosphere. Authors: Cram, L. E.; Thomas, R. N. Bibcode: 1975MmArc.105...11C Altcode: No abstract at ADS Title: Chairman's introduction to Cram's review paper Authors: Thomas, R. N. Bibcode: 1975cesra...5...11T Altcode: No abstract at ADS Title: Stellar atmospheres,, nonequilibrium in thermodynamics, and irreversibility. Authors: Thomas, R. N. Bibcode: 1975AdChP..32..259T Altcode: No abstract at ADS Title: A Scheme of Stellar Atmospheric Regions. II. Properties and Significance of Mass Flux Authors: Thomas, R. N. Bibcode: 1973A&A....29..297T Altcode: Summary. We show that observed mass-fluxes from stars require photo spheric systematic velocities in excess of those which would exist if mass-fluxes came only from radiative effects. Thus we infer that chromospheres and mass-fluxes of the observed sizes are always associated, and depend upon a storage in the star of non-thermal kinetic energy. A complete picture of atmospheric structure thus requires adding mass-flux to radiative flux and gravity as the parameters necessary to compute atmospheric models. Either a fourth parameter, or specification of the storage mode for non- thermal energy is necessary to specify the kind of lateral inhomogeneities which occur. We show that such a model predicts the kind of line-broadening, and the luminosity dependence, represented by the WilsonBappu and similar effects, and to first-order it has nothing to do with turbulence. We suggest a sequence of non-radial pulsations might represent one kind of sequence of non-thermal 1(inetic energy storage. Key words: mass-flux - non-thermal kinetic energy storage - chromospheres Title: A Scheme of Stellar Atmospheric Regions. I. The General Approach Authors: Pecker, J. -C.; Praderie, F.; Thomas, R. N. Bibcode: 1973A&A....29..289P Altcode: Summary. We develop the idea of the stellar atmosphere as a transition zone between the quasi-equilibrium stellar interior and the wholly non-equilibrium interstellar medium. The transition is between a primarilystorage, and a primarily-propagation, configuration for the energy associated with each of the radiation and mass-fluxes. Each phase of the transition, for the radia tive flux, gives rise to one region of the photosphere; for the mass-flux, to one region of the hylosphere. We provide a schematic outline of the phases in this paper. Key words: transition-zone - mass-flux - radiation- flux - stellar atmosphere Title: Chromospheres of T Tauri-type stars. Authors: Dumont, S.; Heidmann, N.; Kuhi, L. V.; Thomas, R. N. Bibcode: 1973A&A....29..199D Altcode: Summary. The observed total fluxes of H cc emission for some 20 T Tauri stars in the Taurus-Auriga cloud are used to test the hypothesis that the observed emission features can be produced by a chromosphere without recourse to an extended envelope. Under the assumption that the Balmer continuum emission is produced in the chromosphere and that H cc is photoionization dominated, we obtain total emission fluxes that are in good agreement with the observed values. However the predicted profiles have a necessary central reversal which is not always present in the observed ones. It is suggested that the agreement can be improved by the introduction of a velocity gradient as required by our present ideas on the existence of chromospheres. This point will be investigated in detail in a later paper Key words: T Tauri stars - chromosphere - H cc emission line Title: The Wolf-Rayet Stars - the General Problems of Extended Atmospheres and Non-Classical Atmospheric Models Authors: Thomas, Richard N. Bibcode: 1973IAUS...49....3T Altcode: No abstract at ADS Title: Theory of stellar atmospheres (Théorie des atmosphères stellaires). Authors: Thomas, R. N. Bibcode: 1973IAUTA..15..537T Altcode: No abstract at ADS Title: Suggested interpretation of the correlations in intensity fluctuations in the lines Ca ii H and K, magnesium b, and hydrogen Hβ Authors: Thomas, Richard N. Bibcode: 1972SoPh...27..303T Altcode: No abstract at ADS Title: On Estimates of the Nonradiative Energy Input to the Solar Chromosphere from the H¯ Emission. Authors: Praderie, F.; Thomas, R. N. Bibcode: 1972ApJ...172..485P Altcode: The inclusion of non-LTB effects in the computation of mechanical heating in a gray atmosphere changes previous LTE estimates by a factor of 4b11-. Title: The Temperature Control Bracket Authors: Gebbie, K. B.; Thomas, R. N. Bibcode: 1971ApJ...168..461G Altcode: The factors determining the temperature distribution in a stellar atmosphere are divided into transfer effects and population effects. As a measure of the latter, we introduce the Temperature Control Bracket [TCB], which, in radiative equilibrium, describes the control of T by the quantity and spectral distribution of the radiation field. Algebraic expressions for the [TCB] are given in terms of the microscopic rate processes for a pure hydrogen atmosphere. A caricatured computation is presented to demonstrate the influence of the various physical effects on the distribution of T5 in radiative equilibrium. Title: Solar Chromosphere and the General Structure of a Stellar Atmosphere Authors: Thomas, Richard N.; Gebbie, Katharine B. Bibcode: 1971spas.conf...84T Altcode: No abstract at ADS Title: Solar spicules and chromospheric heating. Authors: Thomas, R. N. Bibcode: 1971tmp..conf..331T Altcode: No abstract at ADS Title: Saturation in Fraunhofer lines Authors: Pecker, J. -C.; Thomas, R. N. Bibcode: 1970Obs....90..207P Altcode: No abstract at ADS Title: The Temperature Control Bracket Authors: Gebbie, K. B.; Thomas, R. N. Bibcode: 1970BAAS....2S.316G Altcode: No abstract at ADS Title: On the Dependence of T_{e} upon Quantity Versus Quality of the Radiation Field in a Stellar Atmosphere Authors: Gebbie, K. B.; Thomas, R. N. Bibcode: 1970ApJ...161..229G Altcode: We derive a simple algebraic expression for T (r) that demonstrates as a function of collisions how and where the control of T shifts from the quantity to the quality of the radiation field in a stellar atmosphere. We obtain explicit formulae for the gray case and show that mechanical heating and nongray processes can be treated algebraically as perturbations. We illustrate the size and effect of these processes by applying them to the Sun in the region tO-2> T5> 1O- . Title: Part B. Theoretical Methods for Handling Non-Lte Problems Authors: Thomas, R. N.; Hearn, A. G. Bibcode: 1970sfss.coll...85T Altcode: 1970IAUCo...2...85T No abstract at ADS Title: Definition of the Physical Problems Connected with Extended Atmospheres Authors: Thomas, R. N. Bibcode: 1970sfss.coll...38T Altcode: 1970IAUCo...2...38T No abstract at ADS Title: What Should we do to Know More about Chromospheres and Coronae of Stars? (introductory Paper) Authors: Thomas, R. N. Bibcode: 1970sfss.coll..259T Altcode: 1970IAUCo...2..259T No abstract at ADS Title: Recent Eclipse Data and the Solar Limb Authors: Gebbie, K. B.; Weart, S. R.; Thomas, R. N. Bibcode: 1969BAAS....1Q.277G Altcode: No abstract at ADS Title: Non-Lte Diagnostic Stellar Spectroscopy. I. Conceptual and Analytical Back-Ground Authors: Gebbie, K. B.; Thomas, R. N. Bibcode: 1968ApJ...154..271G Altcode: We outline an approach to the determination of the state of a stellar atmosphere and delineate those regions where thermodynamic equilibrium state parameters can be adopted either because collisional processes dominate or because the radiation field satisfies certain homogeneity conditions. It is regions satisfying these homogeneity conditions that must be used to determine the boundary values for the state parameters of the LTE interior. The observable regions of a star do not in general satisfy these conditions, and for these layers we summarize an alternative approach to specifying the state parameters and the analytical basis for determining their values. This paper then provides the background for the specific applications in succeeding papers Title: Non-Lte Diagnostic Stellar Spectroscopy. II. on the Schuster Mechanism for the Production of Emission Lines Authors: Gebbie, K. B.; Thomas, R. N. Bibcode: 1968ApJ...154..285G Altcode: We investigate the conditions under which the Schuster mechanism can produce emission lines. We consider Schuster's original formulation, together with Mime's modification and a general non-LTE formulation. We conclude that while emission lines may result in particular circumstances, it is unlikely that observations of bright lines can be interpreted by this mechanism Title: Saturation in Fraunhofer lines Authors: Pecker, J. -C.; Thomas, R. N. Bibcode: 1968Obs....88..115P Altcode: No abstract at ADS Title: Wolf-rayet stars Authors: Gebbie, Katharine B.; Thomas, Richard N. Bibcode: 1968wrs..conf.....G Altcode: No abstract at ADS Title: Opening Remarks Authors: Thomas, Richard N. Bibcode: 1968wrs..conf....1T Altcode: No abstract at ADS Title: Summary of Problems, Ideas, and Conclusions on the Physical Structure of the Wolf-Rayet Stars Authors: Thomas, Richard N. Bibcode: 1968wrs..conf..237T Altcode: No abstract at ADS Title: Symposium on Wolf-Rayet Stars: A Summary Authors: Thomas, R. N. Bibcode: 1968ApL.....2..143T Altcode: No abstract at ADS Title: Aerodynamic phenomena in stellar atmospheres, proceedings from Symposium no. 28 held at the Centre international d'astrophysique de l'observatoire de Nice, 2-14 September, 1965. Authors: Thomas, Richard Nelson Bibcode: 1967IAUS...28.....T Altcode: No abstract at ADS Title: Buchbesprechungen: Some Aspects of Non-Equilibrium Thermodynamics in the Presence of a Radiation Field. (Ref. K. H. BÖHM) Authors: Thomas, R. N. Bibcode: 1966ZA.....63..282T Altcode: No abstract at ADS Title: Some Problems of Radiation Transfer in Quiescent Stellar Atmospheres Authors: Thomas, R. N. Bibcode: 1966iart.conf...32T Altcode: No abstract at ADS Title: Computation of the Line Source Function. A Review of the Physical Problem Authors: Thomas, R. N. Bibcode: 1965SAOSR.174...71T Altcode: No abstract at ADS Title: Possible Implications of the Observed Profile of (λ 6374) Fe X. Authors: Pecker Wimel, C.; Thomas, R. N. Bibcode: 1965ApJ...141..834P Altcode: No abstract at ADS Title: Some aspects of non-equilibrium thermodynamics in the presence of a radiation field Authors: Thomas, Richard Nelson Bibcode: 1965sane.book.....T Altcode: 1965QB461.T5....... No abstract at ADS Title: Comment on the Difference Between a Non-Lte and a Pure Model for the Line-Blanketing Effect. Authors: Thomas, Richard N. Bibcode: 1965ApJ...141..333T Altcode: No abstract at ADS Title: Some Limits on the Effect of Coronal Self-Emission on the Excitation State of Coronal Ions. Authors: Pecker, Charlotte; Thomas, Richard N. Bibcode: 1963ApJ...137..967P Altcode: We continue our earlier work, which showed that isolation of the ground configuration from higher lying configurations is invalid in computing the excitation state of coronal ions, to inquire into the effect of self-emission in some of the resonance lines of these ions. We set limits on the optical thickness of the corona and upper chromosphere for ions of ionization state exceeding He ii, finding a value <= 10 for the range of ions and range of conditions from normal atmosphere to coronal condensations. With this limit on r, we show that mimicking the ionic configuration by that of a two-level atom sets an upper limit on the built-up radiation field. We approximate the atmospheric model and the solution to the transfer equation for a two-level atom with very small E, to compute the relation between this=upper limit on radiation field and r1, the optical thickness of the atmosphere. We conclude that n> 10 is to produce an observable effect on the line; and thus that the C-N-O-Si group in the undisturbed atmosphere is the most useful set of ions for more detailed investigation In coronal condensations, other ions may possibly be used Title: Comment on Empirical Inference of Doppler Widths. Authors: Thomas, Richard N. Bibcode: 1963ApJ...137...38T Altcode: The region of validity of Athay's suggested method for obtaining AXD in strong Fraunhofer lines is investigated, and the analytical background for checking its applicability to several classes of lines is presented Generally speaking, one must be cautious in the use of the proposed method Title: Excitation of the Red and Green Coronal Lines. Authors: Pecker, Charlotte; Thomas, Richard N. Bibcode: 1963IAUS...16...33P Altcode: No abstract at ADS Title: Review of Publications- Brief Notices: Aerodynamical Phenomena in Stellar Atmospheres, I.A.U. Symposium no. 12, edited Authors: Thomas, R. N. Bibcode: 1962JRASC..56..184T Altcode: 1962JRASC..56..181T No abstract at ADS Title: The Structure of Regions of Coronal-Line Emission. Authors: Jefferies, J. T.; Pecker, C. W.; Thomas, R. N. Bibcode: 1962ApJ...135..653J Altcode: No abstract at ADS Title: Excitation of the red and green coronal lines Authors: Pecker, Ch.; Thomas, R. N. Bibcode: 1962AnAp...25..100P Altcode: No abstract at ADS Title: Physics of the Solar Chromosphere (Ref. C. DE JAGER) Authors: Thomas, R. N.; Athay, R. G. Bibcode: 1962ZA.....55...66T Altcode: No abstract at ADS Title: Buchbesprechung über: Aerodynamic Phenomena in Stellar Atmospheres. (Ref. K. H. BÖHM) Authors: Thomas, R. N. Bibcode: 1962ZA.....56...68T Altcode: No abstract at ADS Title: The Source Function in a Non-Equilibrium Atmosphere. VIII. Solution for a Two Level Atom in a Finite Atmosphere. Authors: Thomas, R. N.; Zirker, J. B. Bibcode: 1961ApJ...134..733T Altcode: The solution for the variation with optical depth of the source function for a two-level atom in a finite atmosphere, with and without temperature gradient, is presented. Even for an optical thickness of the atmosphere as high as tO , the emergent intensity differs by an order of magnitude from that for the semi-infinite case. For the case of non-symmetric temperature gradient, the asymmetry in source function is very considerably less than for B (T ). The use of a model consisting of a finite slab isolated in space is a better approximation for such high-excitation ions as He ii, in a low-excitation atmosphere such as the sun, than is the model of a semi-infinite atmosphere. Title: Departure from the Saha Equation for Ionized Helium. II. Atmospheric Thicknesses too Small to Satisfy Detailed Balance in the Resonance Lines. Authors: Thomas, R. N.; Zirker, J. B. Bibcode: 1961ApJ...134..740T Altcode: The results of the preceding paper for the variation of the source function in a finite atmosphere are applied to the case of He ii. A two-level atom is shown to be adequate for the treatment of the ionization equilibrium. Some comment is made on the observed values of Ly-a, Ly-fi, and 4686. Title: A Comment of the NRL Solar Lyman-Alpha Results. Authors: Jefferies, J. T.; Thomas, R. N. Bibcode: 1961ApJ...133..606J Altcode: Supplementary comments are made on the Morton-Widing analysis of the NRL Ly-a observations; they serve to bring into sharper focus its relation to current attempts at analysis of self-reversed emission cores of collison-dominated lines for gradients of T , for chromospheric structure, and for differential structure between quiet sun and plage, sunspot and flare regions. Title: Departures from the Saha Equation for Ionized Helium. I. Condition of Detailed Balance in the Resonance Lines. Authors: Thomas, Richard N.; Zirker, J. B. Bibcode: 1961ApJ...133..588T Altcode: Conditions for the validity of the assumption of detailed balance in the Lyman lines of He ii are investigated. An opacity of 106 in Lyman-a is required, which implies high opacity in the subordinate lines and resonance continuum. The are computed, including the transfer problem in the subordinate lines and resonance continuum. Title: Effect of Departures from Local Thermodynamic Equilibrium on Inferences of Stellar Atmospheric Temperatures Authors: Thomas, Richard N. Bibcode: 1961osmt.conf...14T Altcode: No abstract at ADS Title: Physics of the solar chromosphere Authors: Athay, R. Grant; Thomas, Richard N. Bibcode: 1961psc..book.....A Altcode: 1961QB528.T45...... No abstract at ADS Title: On the Extension of the Low-Chromosphere Model to the Region of Origin of the UV Solar Spectrum Authors: Thomas, Richard N. Bibcode: 1961LIACo..10..309T Altcode: 1961LIACo..10..305T; 1961MSRSL...4..309T No abstract at ADS Title: The Excitation of Ionized Helium Authors: Thomas, R. N.; Zirker, J. B. Bibcode: 1961LIACo..10..562T Altcode: 1961MSRSL...4..561T; 1961LIACo..10..561T No abstract at ADS Title: Thermodynamic Structure of the Outer Solar Atmosphere.VI. Effect of Departures from the Saha Equation on Inferred Properties of the Low Chromosphere. Authors: Pottasch, S. R.; Thomas, R. N. Bibcode: 1960ApJ...132..195P Altcode: We apply the methodology of our preceding treatment of the Saha equation under conditions of high Lyman continuous opacity to a reanalysis of the continuous emission from the lowest chromosphere. The result is a greatly steepened Trgradient, relative to the results of an earlier analysis based on the neglect of non-LTE effects. Title: The Source Function in a Non-Equilibrium Atmosphere. V. Character of the Selfreversed Emission FO CA^{+} H and K. Authors: Jefferies, J. T.; Thomas, R. N. Bibcode: 1960ApJ...131..695J Altcode: The methodology of Paper III is applied to delineate the principal parameters affecting the characteristics of the self-reversed emission cores of Ca+ H and K, in order to clarify whether current discussions in terms only of are adequate. We find two additional factors to be significant-c and the Te gradient. The factor E provides an effect in the correct direction to interpret the Wilson-Bappu effect, but of too small a size, subject to a more complete treatment of the region outside the Doppler core. The effect of the T6 gradient seems more significant, particularly as a basis for interpreting the observed solar variations. Title: The Source Function in a Non-Equilibrium Atmosphere.IV. Evaluation and Applications of the Net Radiative Bracket. Authors: Thomas, Richard N. Bibcode: 1960ApJ...131..429T Altcode: The net rate of a radiative transition between two atomic energy leve]s depends upon the local radiation field through a factor which we define as the Net Radiative Bracket (NRB). The results of previous papers in this series are applied to show that NRB depends only upon the ratio of radiation absorbed in the line to the local value of the source function in the line and to evaluate this ratio as a function of optical depth in the line. These results may also be applied to the question of the local energy balance in a chromosphere-type atmosphere and to the problem of radiative stability Title: Comment on the use of net rate processes and the equivalent 2-level atom in non-LTE computations Authors: Thomas, R. N. Bibcode: 1960AnAp...23..871T Altcode: No abstract at ADS Title: Questions of general background and methodology relating to aerodynamic phenomena in stellar atmospheres - Summary-introduction Authors: Pecker, J. -C.; Thomas, R. N. Bibcode: 1960IAUS...12....1P Altcode: 1960IAUS...12Q...1. No abstract at ADS Title: Aerodynamic phenomena in stellar atmospheres: proceedings of the International Astronomical Union Symposium no. 12 on Cosmical Gas Dynamics. Authors: Thomas, Richard Nelson Bibcode: 1960IAUS...12.....T Altcode: No abstract at ADS Title: Aerodynamic phenomena in stellar atmospheres : proceedings Authors: Thomas, Richard Nelson Bibcode: 1960akiv.book.....T Altcode: 1960akiv.book.....S No abstract at ADS Title: Summaries - R. N. Thomas Authors: Thomas, R. N. Bibcode: 1960IAUS...12..494T Altcode: No abstract at ADS Title: Departures from the Saha Equation Under Varying Conditions of Lyman Continuous Opacity. Authors: Pottasch, S. R.; Thomas, R. N. Bibcode: 1959ApJ...130..941P Altcode: A general method for determining the departure from the Saha equation in a hydrogen atmosphere is presented. The usually stated, vague condition of "high opacity in the Lyman continuum" is not sufficient to insure LTE; departures from LTE may amount to several orders of magnitude even under this condition (Fig. 2). For illustration, application of the method is made to an atmosphere of constant T and n (Fig. 1) and to an approximate chromospheric model (Fig. 3). Title: Source Function in a Non-Equilibrium Atmosphere. III. The Influence of a Chromosphere. Authors: Jefferies, John T.; Thomas, Richard N. Bibcode: 1959ApJ...129..401J Altcode: We apply the methods developed in the preceding two papers to investigate the depth dependence of the source function for resonance lines in an atmosphere having a chromospheric distribution of T, superposed upon a photospheric one. The derived behavior of SL( ) for the neutral and ionized metals differs and mimics the observed behavior of such lines. The hydrogen Balmer lines should behave like the neutral metals, and the predicted behavior agrees with our earlier empirical results. Title: Buchbesprechung über: Proceedings of the Third Symposium on Cosmical Gas Dynamics (Cambridge) Mass. 24. __29. 6. 1957. (Ref. A. UNSÖLD) Authors: Burgers, J. M.; Thomas, R. N. Bibcode: 1959ZA.....48..158B Altcode: No abstract at ADS Title: Preface Authors: Burgers, J. M.; Thomas, R. N. Bibcode: 1958RvMP...30..908B Altcode: 1958IAUS....8..908B No abstract at ADS Title: The Source Function in a Non-Equilibrium Atmosphere. II. The Depth Dependence of the Source Function for Resonance and Strong Subordinate Lines. Authors: Jefferies, John T.; Thomas, Richard N. Bibcode: 1958ApJ...127..667J Altcode: We obtain an algebraic solution for the depth variation of the source function 8L (r) for resonance and strong subordinate lines by using the Eddington approximation plus the method of discrete ordinates. We show that if an observed line profile, produced in an atmosphere with the above SL (r), is analyzed under the assumption of local thermodynamic equilibrium, an underestimate of T.(r) in the outer atmospheric layer results. The derived SL(r) agrees in qualitative behavior with the source function found empirically by Athay and Thomas for the early Balmer lines of hydrogen. Title: On the Use of the Early Balmer Lines to Extend the Photospheric Model. Authors: Athay, R. G.; Thomas, R. N. Bibcode: 1958ApJ...127...96A Altcode: The early Balmer lines in the solar Fraunhofer spectrum provide information relative to the structure of the solar atmosphere. Our analysis of these lines in the disk spectrum indicates that the lines are not formed in local thermodynamic equilibrium, so that the source function is not given by B (T ). Our combined empirical and theoretical results lead us to conclude that the source function for the Balmer lines is determined to the first order by the radiation field in Ha and to the second order by the changes in electron temperature. The central intensities of the early Balmer lines show limb darkening out to cos o > 0.1. Just beyond the limb, HP, HT, and H show limb brightening, whereas Ha shows constant brightness and the lines H10 and above show further limb darkening. The limb brightening in HP, H , and H may be attributed to decreasing opacity in the early Lyman lines without necessarily changing the electron temperature. The absence of limb brightening in Ha may be attributed to high opacity in the spicules, and the absence of limb brightening in the lines H10 and above may be attributed to lower opacity in these lines than in the earlier lines. Title: Cosmical Gas Dynamics, proceedings from IAU Symposium no. 8. Authors: Burgers, Johannes Martinus; Thomas, Richard Nelson Bibcode: 1958IAUS....8.....B Altcode: No abstract at ADS Title: On Trad for the early Balmer lines. Authors: Thomas, Richard N. Bibcode: 1957AJ.....62..147T Altcode: An earlier-reported inquiry into the relation between Tex and Te for the early Balmer lines is continued. Two observational results must be interpreted: (I) the fact that limb-darkening measures of individual lines and combined results from line-profiles at the center of the disk give a monotonic Trad vs. N2 relation with scatter small relative to total change in Trad (de Jager 1952; Bo~hm-Vitense 1954); (2) the indication of small but systematic differences between various lines in the relation of (I) (Athay and Thomas 1957). The framework for the interpretation is: (a) Trad may be taken to equal Tex over at least the central regions of the lines; (b)the assumption Tex = Te gives a result inconsistent with the general photospheric model. It is shown that the overall Trad vs. N2 curve measures the non-equilibrium factor b2 for the second quantum level; while any systematic fluctuations measure the remaining bk. A discussion is entered on the effect of using B (Tex) rather than B (Te) as the source-function S for line formation. In the upper photosphere-lower chromosphere, B~ (Tex) varies considerably, while By(Te) varies only slightly; thus results from analyses of line profile and integrated intensity, based on Se = Bp (Te), must be reexamined. Athay, R. G. and Thomas, R. N. 1957, A. J. 62, 3. Bo~hm-Vitense, E. 1954, Zs. Astroph. 34, 209. de Jager, C. 1952, Rech. Astr. Obs. Utrecht 13, Part I. Harvard College Observatory, Cambridge, Mass., and Boulder Laboratories, National Bureau of Standards, Boulder, Colo. Title: The Numbers and Motions of Solar Spicules. Authors: Athay, R. G.; Thomas, R. N. Bibcode: 1957ApJ...125..804A Altcode: In this paper we interpret spicule motions in terms of two spicule models, one with constant velocity and one decelerating in the solar gravitational field. The available statistics slightly favor the gravitational model but do not indicate clearly which model is preferred. We estimate the total number of spicules on the sun by fitting the two spicule models to the observed distribution of spicules with height. This leads to total spicule numbers of 1.4 X 10 to 1.3 X 1O for the two models. Title: The Chromosphere Near Active Regions. Authors: Athay, R. G.; Thomas, R. N. Bibcode: 1957ApJ...125..788A Altcode: Eclipse data show abnormal chromospheric and coronal emission above active sunspot regions. In this paper we analyze data for such regions on 1952,1936, and 1932 eclipse spectrograms and attempt to show how the chromospheric structure differs from normal chromospheric regions. If we assume that the chromosphere has two components of different temperature and density at a given height, we find that the principal difference between the active regions and the normal regions is a larger proportion of the hotter component in the active region. We also find that the temperatures in the two components are relatively unchanged over ihe active regions, which is consistent with the assumption of thermal stability for the chromospheric radiation field (Athay and Thomas 1956). Title: Some comments on photospheric models. Authors: Athay, R. G.; Thomas, R. N. Bibcode: 1957AJ.....62....3A Altcode: Models for the upper photospheric layers are usually derived by assuming that the excitation temperature, Tex, in the cores of the early Balmer lines is the same as the kinetic temperature, Te. From the observed center-to-limb variations in the line intensities, one then obtains a photo- spheric model with P0 decreasing monotonically with height. From eclipse data, however, we find that the central parts of these early Balmer lines are formed at heights of 2000 to 4000 km above the base of the chromosphere, and, in addition, that P0 is either constant or increasing with height. In this paper we attempt to integrate eclipse observations with disk observations in order to join the photospheric model to the low chromospheric model. The data indicate that Pox for Ha decreases across the disk, then remains constant for the first 4000 km in the chromosphere before it decreases further. For H~, H~ and H~, however, the drop in Pox across the disk is followed by a sharp rise in Pox at the limb, which, in turn, is followed by a rather rapid decrease in Pox with height. We interpret this behavior in terms of the differences in the optical depths in the lines and in terms of the non-uniformities arising from spicule structure. In all cases P0 obtained from other chromospheric data exceeds Pox in the early Balmer lines. In order to check the validity of identifying Pex with P0, we use the line profiles on the disk to obtain an empirical relation between Pex and the Doppler widths of the lines. If we ignore mass motions, the profiles show clearly that Te > Pex If the observed effects are attributed to mass motions, random velocity fields of the order of 13 km/sec are required. Such velocity fields could, conceivably, arise from spicule motions, but it seems unlikely. Furthermore, we find that the individual curves of Tex versus height for the early Balmer lines do not join smoothly, again indicating that Te # Tex. Thus, we conclude that Tex in the early Balmer lines does not serve as a sound basis for deriving photospheric models. This work was supported by the Office of Naval Research and the Geophysics Research Directorate, Air Force Cambridge Research Center. High Altitude Observatory, Boulder, Cob., and Harvard College Observatory, Cambridge, Mass. Title: The Source Function in a Non-Equilibrium Atmosphere. I. The Resonance Lines. Authors: Thomas, Richard N. Bibcode: 1957ApJ...125..260T Altcode: The source function for the central core of resonance lines is investigated under the assumption that the core is formed in the chromosphere. The conclusions reached are as follows: (1) The absorption coefficient is Doppler over a core some three Doppler widths in extent. (2) The frequency dependence of the emission coefficient follows closely that of the absorption coefficient, the difference amounting to about a factor of 4 over the Doppler core, a region where the absorption coefficient varies by about 1O thus the mechanism of line formation is essentially formally equivalent to that of pure absorption or of completely non-coherent scattering, the formal distinction between the two fading (3) Completely generally, the source function lies intermediate between a value fixed by collisional excitation with radiative de-excitation and a value fixed by photoelectric ionixations with recapture. For the ydrogen and non-metal group and for the neutral metals, the collisional term dominates only for Te> 75OO looooe; for singly ionixed metals, the collisional term dominates for Te > 35OO . Discussions of eclipse data make it probable that the cores of the strong resonance lines have chromospheric origin, so the collisional component of the source function may predominate In this case, a rough knowledge of ne(re) permits an inference of Te( e) from the line profile in the region of the core. Title: On the uniformity of the lower chromosphere Authors: Thomas, Richard N.; Athay, R. G. Bibcode: 1957IAUS....4..279T Altcode: No abstract at ADS Title: LYMAN-α and the Structure of the Solar Chromosphere. Authors: Athay, R. G.; Thomas, R. N. Bibcode: 1956ApJ...124..586A Altcode: We investigate the range of chromospheric models compatible with present rocket observations of Lyman-a and conclude that it is considerable. We would require detailed observations of the line profile, with resolution better than one Doppler half-width, to be more specific on the actual model. We find a considerable difference between T and a radiation temperature defined by the line intensity, in conformity with earlier discussions of the non-equilibrium chromosphere by ourselves and by Giovanelli. A discussion of the relation of these results to the limb flare and SID correlations found by C. Warwick suggests a more extended investigation of the non-spherically symmetric model and its relation to the ch romospheric opacity in Lyman-a. Title: Features of the Solar Spectrum as Imposed by the Physics of the Sun Authors: Thomas, Richard N. Bibcode: 1956SciMo..83..135T Altcode: No abstract at ADS Title: Some Characteristics of a Chromospheric Model. Authors: Athay, R. G.; Thomas, R. N. Bibcode: 1956ApJ...123..309A Altcode: Some general conditions that must be satisfied by a chromospheric model are discussed: (1) The available data on variations in chromospheric structure over the solar activity cycle indicate the highest emission gradients at sunspot maximum. (2) The evidence bearing on the choice of an energy or momentum perturbation as the chief characteristic of the low chromosphere is discussed, and a conclusion favoring the energy perturbation is reached. The maximum in the nonradiative energy input appears to lie near 500 km. (3) Some considerations on the effect of departures from spherical symmetry in the chromosphere are discussed in terms of hot versus cold spicules and of the thermodynamics of the resulting configurations. We conclude, both from an a priori thermodynamic standpoint and from existing data, that the spicules must be cold. Title: Temperature Gradients in the Chromosphere. Authors: Athay, R. G.; Thomas, R. N. Bibcode: 1956ApJ...123..299A Altcode: Our earlier determinations of electron temperature, Te, in the chromosphere by analysis of eclipse data are supplemented in this paper by considerations of the energy balance. We assume that Te may have only those values for which there is thermal stability. If an increase in Te, at a given height, results in an increase in the energy radiated, the model is stable. However, if an increase in Te causes a decrease in the energy radiated, there is no stable value of Te. Two regions of stability surmounted by regions of instability are recognized: (1) in the low chromosphere neutral hydrogen emission is stable and is the principal source of emission; (2) neutral hydrogen emission becomes unstable at a height where hydrogen becomes sufficiently ionized. At this height, Te increases abruptly until stable emission from He Ir balances the energy input; (3) He Ir emission also becomes unstable at sufficient ionization, and Te increases abruptly to a coronal value where either free-free emission or emission from multiply ionized metals predominates. Models of the chromosphere derived from 1952 eclipse data show good agreement with the conclusions based on thermal stability considerations. Title: Aerodynamic Problems in Stellar Atmospheres Authors: Thomas, Richard N. Bibcode: 1956SCoA....1..123T Altcode: No abstract at ADS Title: Astroballistics Authors: Thomas, Richard N. Bibcode: 1956SCoA....1...49T Altcode: No abstract at ADS Title: Temperature Gradients in the Chromosphere Authors: Athay, R. G.; Thomas, R. N. Bibcode: 1955PASP...67..339A Altcode: No abstract at ADS Title: The Thermodynamic State of the Outer Solar ATMOSPHERE.IV.SELF-ABSORPTION and the Population of the Second Quantum Level. Authors: Athay, R. G.; Thomas, R. N. Bibcode: 1955ApJS....1..491A Altcode: The quantitative dependence of the observed logarithmic emission gradient, fl , of the Balmer lines upon quantum number provides a direct substantiation of the influence of self-absorption on the higher lines (n greater than about 10). An analysis assuming that the ( , n) dependence arises only from seifabsorption permits a direct determination of the population of the second quantum level, n , as a function of height, leading to a scale height of 2000 kin for n2 by contrast with 500 km for the highest quantum levels. The scale height for the non-Boltzmann term, b2, is thus 600 kin. The derived self- absorption is so large that at H1 1 only some 7 per cent of the (slitless spectrograph) emission at h = 1000 kin escapes from the chromosphere. The analysis is seif-consistent, provided that T, is sufficiently low that b10 is less than about 2; a discrepancy arises because the line emission is relatively too great for that of the continuum, leading to excessive empirical b . The question of a nonuniform chromosphere arises and is deferred, together with a general model, pending the analysis of the continuum. Title: The Thermodynamic State of the Outer Solar Atmosphere. III, IV, and V. Authors: Athay, S.; Matsushima, R. G.; Athay, R. N.; Thomas, R. G.; Menzel, D. H.; Pecker, J. -C.; Thomas, R. N. Bibcode: 1955ApJ...121..775A Altcode: No abstract at ADS Title: The Thermodynamic State of the Outer Solar ATMOSPHERE.V.A.MODEL of the Chromosphere from the Continuum Emission. Authors: Athay, R. G.; Menzel, D. H.; Pecker, J. -C.; Thomas, R. N. Bibcode: 1955ApJS....1..505A Altcode: Four semi-independent analyses of 1952 eclipse data contribute to a determination of n and T in the solar chromosphere in the height range from -120 km to 6000 km: (1) The intensity of the continuous emission at X 4700 indicates that T, increases with height from about 4800 at - 65 km. (2) The emission, per cubic centimeter, in the Balmer continuum attains a maximum near 500 km, which indicates that here the free electrons begin to come mainly from H rather than from metals, and thus places the limits: 5000 < T < 7000 , 4 X 1011 <n < S X 1011 at this height. (3) The intensities of the continuum at X 4700 and X 3640 require values of T as follows: 5000 at 500 km, 6100 at 1000 km, and 6700 at 3000 kin. In the interval 1()()( 3000 kin the ionization of H increases from about 3 to about 80 per cent. (4) Above 3000 kin no data on the Balmer free-bound continuum exist, and an extension of the results of 3 to greater heights requires the use of the height gradient of the Balmer lines to replace that of the continuum. Such a technique fixes T only within certain limits, which, at 6000 km, are: 2 X 10 < T < 1.2 X 10 . The chief uncertainty of the analysis lies in the use of the assumption of a continuous distribution of material in the atmosphere. The results of the analysis suggest the validity of such assumption below about 2500 kin, and its breakdown above about 3000 km. An estimate of optical depth in the continuum, from the present analysis, at a height of 500 km produces a value agreeing well with an estimate based on the analysis of the lines. Title: "Turbulence", kinetic temperature, and electron temperature in stellar atmospheres Authors: Bhatnagar, P. L.; Krook, M.; Menzel, D. H.; Thomas, R. N. Bibcode: 1955VA......1..296B Altcode: The phenomenological use of the term "astronomical turbulence" is reviewed and earlier conclusions that the physical nature of the phenomenon is more likely anisotropic mass-motion, or jet-prominences, than the customary aerodynamic turbulence are restated. The primary problem under such conditions is the relative importance of mechanical energy-transport and momentum transport in perturbing the structure of the atmosphere. The problem of the difference between kinetic temperatures of the atoms and electrons is treated, and it is concluded that the difference is negligible in those parts of the stellar atmosphere which are in a statistically-steady state. Title: Comments on the Structure of the Chromosphere Authors: Thomas, R. N. Bibcode: 1955stat.conf...29T Altcode: 1954stat.conf...29T No abstract at ADS Title: A model of the chromosphere from 1952 eclipse data. Authors: Athay, R. G.; Pecker, J. C.; Thomas, R. N.; Menzel, D. H. Bibcode: 1954AJ.....59..314A Altcode: An analysis of the Balmer free-bound emission at X3640 and the continuum intensities at ~4700 was carried out using data from the slitless spectrograms obtained by the High Altitude Observatory at Khartoum, Sudan. The data gave intensities at X3640 and ~4700 at intervals of approximately 100 km between 0 and 2400 km above the limb and intensities at X4700 at many additional heights between 2400 and 48,000 km. The Balmer line data, which extended from 100 to 6400 km, was used to supplement the free- bound data for heights between 2400 and 6000 km. Values of electron density, Ne, and kinetic temperature, Te, were determined at heights between 0 and 6000 km. The analysis was based on the assumption of a homogeneous chromosphere, with Ne and Te depending upon height only. The continuum at X4700 was assumed to come from H- emission and electron scattering of photospheric light. The results of the analysis of the continuum data gave a chromospheric model that could be divided into three distinct regions with the following properties: Region I (o to 500 km). In this region Te increases from 50000K at the photospheric limb (tangential optical depth I, radial optical depth 0.005) to 600&K at 500 km. Hydrogen begins to ionize near the top of this region with NpHNe. This result is consistent with a marked increase with height of the quantity NeNpTJ in the region near 500 km, which was inferred from the Balmer free-bound and line emission. Thus it appears that the "boundary temperature," T,nin~42000K, occurs below a radial optical depth of 0.005. Region 2 (1000 to 3500 km). The ionization of hydrogen increases from 5 per cent at the base to 99 per cent at the top of this region. Te increases slowly from 60000K to > 70000 K. The low gradient of Te suggests that the external energy supply suffices only for the ionization. Region 3 (~3500 km up). Further ionization of hydrogen is negligible and a large rise in Te occurs. The free-bound emission is too weak to measure in this region and an accurate evaluation of Te is difficult. An extrapolation of the free- bound intensities to 6000 km based on the ob- served intensities of the Balmer lines between 2400 and 6400 km gives Te 7 X io40K. The analysis allowed an accurate determination of Te in the region ~1500 km, and the probable errors in the data plus the errors introduced in the analytical procedures were not likely to cause errors of more than ~3000 in Te. However, in higher regions the values of Te were quite sensitive to the analytical procedures at~d errors of a factor 2 in Te are possible. The eclipse spectrograms at heights above 5500 km show Ha, and all other strong chromospheric lines that persist to these heights, as irregular beaded structures. This irregular structure is presumably due to spicule activity at these heights and requires the consideration of a non-uniform chromospheric model, at least in the upper levels of the chromosphere. A study of the Fe xi line at X7892 on the eclipse spectrograms showed that there was strong emission in this line at heights well below 10,000 km and suggested that the emission started in the regions where the chromospheric lines break up into a spicule structure. The work reported in this paper was supported by the Office of Naval Research and carried out in close cooperation with the Naval Research Laboratory. High A ititude Observatory, Boulder, Colo. and Harvard College Observatory, Cambridge, Mass. Title: The Physical Theory of Meteors.IV. Inquiry Into the Radiation Problem-A Laboratory Model. Authors: Thomas, Richard N.; White, William C. Bibcode: 1953ApJ...118..555T Altcode: The similarity in atomic spectrum between meteor and artificial meteor (ultra-speed pellet) is discussed. The meteor is equivalent to a mono-energetic atomic beam; the pellet, to a high-temperature furnace in a highly transient and probably nonequilibrium state. The excitation mechanism is probably atom-atom inelastic collision in both cases. A consideration of the pellet molecular spectrum strengthens these conclusions. The pellet molecular spectrum appears to provide information on diffusion processes in the wake. Present spectrophotometric data on both meteor and pellet are very incomplete. Title: Analysis of the Balmer continuum from the 1952 eclipse. Authors: Dimock, D. L.; Billings, D. E.; Athay, R. G.; Thomas, R. N. Bibcode: 1953AJ.....58Q.213D Altcode: The continuum intensities mentioned in the preceding paper were analyzed to determine the electron temperature and density in the chromosphere.' Two equations relating these two quantities were obtained by taking the ratio of the intensity at X3647 to the intensity at X3700 and by taking the difference between these two intensities after the intensity at X3700 was corrected empirically to X3647. The quantity obtained by subtracting the two intensities represented the free-bound emission in the Balmer continuum. The quantity represented by the ratio of the two intensities included the contributions from electron scattering, free-free emission, and free-bound emission for the Balmer, Paschen, and higher hydrogen series. The solutions of the equations involved two additional parameters. There was a non-trivial contribution to the continuum intensities from the portion of the corona extending beyond the moqn's limb on the third contact side of the sun. The integration over the atmosphere involved an additional unknown represented by the ratio of the free-bound emission gradient to the electron density gradient. Both of these quantities were carried as parameters and solutions carried out for a range of values representing the possible extremes. The values of the latter parameter placed a condition upon the solutions, and only the solutions which were compatible with these conditions were accepted. It was found that the extreme ranges of the acceptable solutions gave quite similar results. The results show conclusively that the temperature increases rapidly with height from about 90000K at 530 km to about 25,0000K at 2400 km. The electron densities are about 6 X 1011 at 530 km and 2 X IO'~ at 2400 km. The solutions will be extended to give more specific results and to extend the range of heights to both lower and higher values. i. A. J. 58, 210, 1953. Johns Hopkins University, Baltimore, Md., High Altitude Observatory, Boulder, Cob., and Harvard College Observatory, Cambridge, Mass. Title: Comment on the progressive wave in Cepheid atmospheres. Authors: Whitney, Charles A.; Thomas, Richard N. Bibcode: 1953AJ.....58Q.235W Altcode: The "standing-"1 and "running-wave"2 models of Cepheid variables discussed in the literature are based on three implicit assumptions, i.e., the reversing layer and photosphere are (a) geometrically thin while (b) optically thick, and (c) the time average of the observed expansion velocity is zero. Only the character of the phase relation between density and velocity in a compression wave has been utilized in the "running-wave" model. There has been no attempt at a self-consistent picture from a gas-dynamic standpoint. Thomas has earlier suggested that a consideration of the propagation of the wave, and its energy transfer to the atmosphere, in atmospheres of varying gravity and effective temperature may well illuminate such observed Cepheid features as the hump on the light curve and the anomalous extent of the atmosphere.3 While a detailed investigation, under way at the Harvard Observatory, is necessary, some physical insight results from considering a third extreme model. We assume that the Cepheid disturbance is a compression wave which is geometrically thin relative to the atmosphere. The disturbance is represented by a hump on the normal temperature-optical depth curve. The variation of luminosity arises from a combination of the disturbed region's movement into less optically deep layers and a change of disturbance amplitude. The extent and character of the atmosphere determine whether the wave develops into a shock front, its change in thickness, and whether a second peak develops, corresponding to the well-known N-wave character of a mature shock. Evidently the model permits a qualitative reproduction of the observed character of the Cepheid variation, of the occurrence of emission lines, and the phase lag features. On this model the hydrogen emission lines are the first spectral lines to be observed during the new pulsation phase, not the absorption lines. Color observations should provide some of the characteristics of the model applied to a particular star. Such color observations on Cepheids have shown the variation of apparent color temperature to be greater than compatible with variations of effective temperature inferred from conventional integrations of the velocity curve.4 In an analysis of Stebbins' six-color observations of ~ Cephei, Canavaggia and Pecker have utilized monochromatic fluxes computed by Pecker for classical yellow-giant atmospheres.5 With an assumed temperature at one phase they have derived the effective temperature for ~ Cephei as a function of phase. From these temperatures, the monochromatic light curves, freed from changes of radius, were drawn and compared with the observed curves to obtain the changes of radius. A comparison with the change of radius computed from the radial velocity curve in the conventional manner, using an absolute magnitude on the revised scale, led Canavaggia and Pecker to suggest the need for a reconsideration of the pulsation hypothesis. Eggen had earlier reached a similar conclusion from different considerations.4 Using the phase of zero expansion velocity as parameter, we find that by choosing this phase to agree with the phase o.6o of maximum radius as required by the observations, we obtain excellent agreement between the variation of radius computed from color and computed from radial velocity. The phase change requires a change in systemic velocity of +10 km/sec. This new integration of the velocity curve also eliminates the observed phase lag of red vs. violet light curves.6 This interpretation of the velocity curve implies that the disturbance suffers a net displacement outwards during the time of observation. This suggests that the disturbance is geometrically thin relative to the atmosphere. The fact that the light variations can be explained in terms of fluxes computed for a single normal atmosphere indicates that the out-running wave is optically thick. The picture of an optically thick disturbance is in accord with the absence of observed hydrogen emission lines in the spectrum of a Cephei. Multi-color observations on Cepheids which do show hydrogen emission lines would be invaluable in further examining this model. I.Rosseland, Pulsation Theory of Variable Stars, 1949. 2.Schwarzschild, Circ. Harv. Coll. Obs. Nos. 429, 431, 1928. 3.A. J. 52, 158, 1947. 4.0. J. Eggen, Ap. J. "3, 367, 1951. 5.Comptes Rendus 234, 1739, 1952. 6.J. Stebbins, Ap. J. IoI, 47, 1945. Harvard College Observatory, Cambridge, Mass. Title: Kinetic temperature, electron temperature and turbulence in stellar atmospheres. Authors: Bhatnagar, P. L.; Krook, M.; Thomas, R. N. Bibcode: 1953AJ.....58Q..35B Altcode: Three assumptions characterize the normal stellar atmosphere model: hydrostatic equilibrium, radiative equilibrium, local thermodynamic equilibrium. Ignoring spectral excitation features, the chromosphere-corona atmosphere is characterized by two gross features inconsistent with the normal model: (a)The large extent of the chromospherecorona: the low density gradient. (b)High values of TE and Tk somewhere in the chromosphere-corona. The existence of (a) is inferred from an observed emission gradient, but the precise density gradient can be determined only when (b) is resolved. it seems generally agreed that, to resolve (a) and (b), the normal model must be modified by introducing some kind of field of mechanical motion. Two extreme models for such modification have been proposed to explain (a): (a. I) Models involving some type of purely macroscopic motions, loosely termed turbulence. No quantitative theory has been presented for the generation of such macroscopic motions, nor for the coupling with thermal motion. Even though the turbulence velocities are superthermic, it is implicitly assumed that any coupling with thermal motion shall not appreciably affect the atmospheric kinetic temperature. Solar eclipse observations restrict the tangential component of any macroscopic velocities to less than about 2 km$sec, but the above models have generally assumed the turbulence isotropic. (a.2) Models involving a high Tk in the atmosphere. The basic hypothesis states that any field of superthermic macroscopic motions sufficient to alter non-trivially the atmospheric density gradient implies a non-trivial rise in atmospheric Tk. The range of such models depends upon the relative significance of the energy and of the momentum supplied by the macroscopic field. Radio observers state TE must be lower than the Tk needed for such a model in the sun. All models assume TE = Tk. The self-consistency of either models (a. I) or (a.2) thus seems questionable. Three alternatives appear to span the range of resolution of the difficulty: (I)Turbulence must be replaced by radial turbulence a system of jets, or prominences, whose main function is to match (a) without heating the atmosphere significantly at the lower heights. (2)The interpretation of the radio observations which provide the low values of TE must be shown invalid; e.g., by departures from the Maxwellian velocity distribution. (3)A high Tk must be reconciled with a low TE. Various reports in the literature,1 especially concerning discharge-tube phenomena, state the possibility of configurations with TE significantly different from Tk. We have investigated the problem, theoretically, and conclude TE cannot differ significantly from Tk for TE I0 0K. We discard (3) above, then, and question the validity of such reports as that cited. I.E.g., H. Alfven, Cosmical Electrodynamics, pp. 44-46, 1950. The treatment in this reference violates the conservation of energy. Harvard College Observatory, Cambridge, Mass., and University of Utah, Salt Lake City, Utah. Title: Four Possible Meteorite Craters in Utah Authors: Thomas, Richard N. Bibcode: 1952S&T....11..300T Altcode: No abstract at ADS Title: The Physical Theory of Meteors. III. Conditions at the Meteor Surface. Authors: Thomas, Richard N. Bibcode: 1952ApJ...116..203T Altcode: The conditions at the meteor surface are investigated. It is concluded that the conventional linearized heat-transfer equation cannot be applied to determine the surface temperature of meteors. On the basis of the reaction-rate approach, it is concluded either that the meteor surface vaporizes in all cases or that, if melting occurs, the droplets are so small as to require energies equal to some 50 per cent of the vaporization energy to separate them from the meteor surface. Title: Superthermic Phenomena in Stellar Atmospheres. VIII. Comment on the Chromospheric Model. Authors: Thomas, Richard N. Bibcode: 1952ApJ...115..550T Altcode: The analytic structure for a model solar chromosphere in a statistically steady state is summarized. The dependence of the structure upon chromospheric eclipse observations is exhibited, and several checks upon the internal consistency of the model are discussed. Title: Chromospheric kinetic temperature from radio measures. Authors: Thomas, Richard N. Bibcode: 1952AJ.....57...27T Altcode: A major anomaly in the interpretation of the solar chromosphere at the present time is the apparent disagreement between temperatures inferred from optical observations and temperatures inferred from radio measures. In each case the relevant temperature is only a kinetic temperature. In the interpretation of several of the optical observations the departure from thermodynamic equilibrium of the solar chromosphere has appeared to influence appreciably the observations. The radio measures are, currently, interpreted as coming from free-free transitions in the field of the hydrogen ion. Heretofore, the influence of a departure from Maxwellian distribution of the electrons about the kinetic temperature of the chromosphere has been ignored. It appears however that an average relative departure between the high energy and the low energy ends of the velocity spectrum amounting to one part in one hundred thousand will suffice to cause an error of a factor 2 in the inferred value of the temperature. University of Utah, Salt Lake City, Utah. Title: The Physical Theory of Meteors. II. Astroballistic Heat Transfer. Authors: Thomas, Richard N.; Whipple, Fred L. Bibcode: 1951ApJ...114..448T Altcode: Previous difficulty in formulating a quantitative physical theory of meteors has in large part originated from the wide gap between terrestrial experiments and meteor observations. The physical theory of meteors falls into three aspects: air resistance, heat transfer, and radiation. This paper summarizes an attempt to analyze the heat-transfer aspect from the standpoint of the available meteor data and of some recent laboratory experiments. The section that relates to the laboratory experiments represents the first published attempt to measure heat transfer to bodies in free flight when the velocity is so high that ablation occurs-thus defining the astroballistic region. The free-flight heat transfer in the astroballistic region appears from these experiments to vary with velocity and air density according to the meteor formula rather than according to the conventional aerodynamic formulae established at lower velocities. The heat- transfer efficiency, expressed in terms of that to a Newtonian putty ball, is about 1 per cent in the region near 1-2 km/sec. The meteor results show considerable scatter in values of the heat-transfer efficiency, with no obvious dependence upon velocity or air density and with a favored estimate lying near 5 per cent. A possible interpretation of the scatter of meteor values lies in the fragmenting and flaring of meteors; and the great importance of further study on this point is emphasized. Some considerations on the manmum-sized meteorite capable of surviving intact lead to an independent gross estimate of the heattransfer efficiency. An attempt is made to interpret the deep pitting observed in some meteorites in terms of enhanced ablation on an initially irregular surface, in accordance with some additional free-ffight experiments. Title: The Physical Theory of Meteors. I. a Reaction-Rate Approach to the Rate of Mass Loss in Meteors. Authors: Cook, M. A.; Eyring, H.; Thomas, R. N. Bibcode: 1951ApJ...113..475C Altcode: The generalized reaction-rate theory is applied to the rate of mass loss in meteors. Temperatures around 3100 K are found for meteor surfaces near the point of maximum luminosity. An additional resistance term arises owing to this mass loss, with a V3 dependence, which doubles the resistance computed from the usual expression at velocities about 60 km/sec. Some comment on the mechanism of flaring is offered. Title: Astroballistic heat transfer. Authors: Thomas, Richard N.; Whipple, Fred L. Bibcode: 1951AJ.....56...49T Altcode: The astroballistic region is defined as that region where heat transfer to a solid body moving through a resisting medium is sufficiently rapid that appreciable mass-loss from the body occurs, through either melting or evaporation. Current aerodynamic theory, presumably applicable to sea-level air-densities and ballistic velocities, gives the heat transfer proportional to the temperature difference between solid body and immediately adjacent air, with proportionality factor varying as the square root of the air density; current meteor theory assumes the heat transfer at the high-velocity, low air-density meteor conditions proportional to air density and cube of the velocity. No experiments have earlier been perfor~ed to investigate the physical basis of the empirical meteor theory. We have carried out experiments in the controlled-pressure free-flight range of the Naval Ordnance Laboratory at velocities 6000 ft/sec. and less, and over an air density range one-tenth to ten times the sea-level values. We find: (I) the air-density dependence of the heat transfer shows the meteor expression to be preferable to the aerodynamic even at these low velocities; (2) the efficiency of the heat transfer is about one per cent for the velocities around 5000 ft/sec. and about 10 per cent at some kind of a mean over the meteor velocity range of 10 to 100 km/sec. We have further investigated the temperature at the surface of the meteor by a reaction-rate approach5 and find a temperature of about 30000K for meteors at maximum luminosity. An investigation of the maximum meteor size capable of reaching the earth without disintegration is now in progress by Whipple. This result when compared with observed meteor finds will yield additional information on the heat-transfer efficiency. I.Cook, Eyring, Thomas, Ap. J., in press. University of Utah, Salt Lake City, Utah, and Harvard College Observatory, Cambridge, Mass. Title: A surface mechanism analogy between meteors and explosives. Authors: Cook, Melvin A.; Thomas, Richard N. Bibcode: 1950AJ.....55R.167C Altcode: The initial process in the current picture of both the meteor and explosive reactions consists of ~ vaporization of the surface layer before appreciable heat reaches the interior of the body by conduction. The current meteor theory calculates the vaporization rate in terms of the energy supplied the surface, while the explosive theory considers the vaporization rate to be fixed by the reaction rate of the phase change from solid to gas. This last process depends upon a quasi-equilibrium state between surface layer and surrounding gas bath. If the reaction rate method could be applied to the meteor case, it would permit the determination of the efficiency of heat transfer to the meteor surface. The problem involves the fixing of a surface temperature of the meteor. One possibility gives the surface temperature to be the vaporization temperature in which case a lower limit may be set for the product pv' at which the reaction rate process reaches full efficiency. This gives an interpretation fpr the point of maximum light along the meteor trail that differs from the one currently used in meteor work. A set of experiments, projected for the near future, should determine the worth of the reaction rate method as applied to meteors. University of Utah, Salt Lake City, Utah. Title: The Thermodynamic Structure of the Outer Solar Atmosphere. II. Comment on Empirical Determinations of b_{n} and T_{e} Authors: Thomas, Richard N. Bibcode: 1950ApJ...112..337T Altcode: An apparent discrepancy between several empirical determinations of b and T is investigated. The former is resolved, while the latter is only partially so. It appears that scattered "photospheric" radiation contributes nonnegligibly to the chromospheric eclipse Balmer continuum and that there is consequently a slight polarization to be expected throughout the chromosphere. Title: Superthermic Phenomena in Stellar Atmospheres.VI. Comment on Regions of Emission Fluctuation in the Solar Atmosphere. Authors: Thomas, Richard N. Bibcode: 1950ApJ...112..343T Altcode: Regions of fluctuating.emission in the solar atmosphere must involve density fluctuations, independently of whether there is a simultaneous change in excitation. Such density fluctuation must be discussed in terms of a nonstatic model. One such model may be a supersonic jet, and a quantitative description of such a jet is provided by an extension, to the case including a gravitational field, of an early theory by Prandtl. The theory is applied to the Menzel-Cilli "hot-spot" region observed at the 1932 eclipse. Title: On the reduction of eclipse observations of the Balmer decrement. Authors: Thomas, Richard N. Bibcode: 1950AJ.....55...81T Altcode: At a previous meeting of the Society a method of using the observed Balmer decrement in the hydrogen flash-spectrum to determine the gradient of kinetic temperature and electron density was presented. A knowledge of the kinetic temperature was required from some other kind of observation. The method has been extended so that the kinetic temperature also may be obtained from the flash-spectrum observations of the Balmer decrement. The 1932 eclipse gives a value for the kinetic temperature at about the 1000 km level of some 2.5.I0~ 0K. The value obtained by Redman from the line profiles was some 3.5. I0~. Since the present data indicate an uncertainty in the above determination of some 25 per cent, the agreement with Redman s measures seems satisfactory. The method of interpretation of the flash-spectrum to obtain the thermodynamic structure of the chromosphere would then seem to be finally understood. One notes three methods that have been used: a comparison of the heights of disappearance of the hydrogen lines; a consideration of the apparent change in luminosity of a given line with height; and the present method of investigation of the self-absorption effects. Heretofore it has been assumed that either of the former two methods might be used, with equivalent results. It now seems that the three methods should be expected to yield different results; and the direction of the expected difference is in accord with the observations. The present extension of the last method depends upon a combination of the last two methods, after introducing a correction for self-absorption into the second method. The effect of departures from thermodynamic equilibrium upon the results is then shown to be vec~ small. University of Utah, Salt Lake City, Utah. Title: The Thermodynamic Structure of the Outer Solar Atmosphere. I. The General Method of Analysis and Preliminary Results. Authors: Thomas, Richard N. Bibcode: 1950ApJ...111..165T Altcode: The anomalous Balmer decrement in the solar flash spectrum is shown to result from self-absorption. The effect is analyzed numerically to obtain the population of the Baimer ground state as a function of height and thence an estimate of the kinetic temperature gradient. These results are combincd with the Balmer emission decrement to obtain an estimate of the kinetic temperature, its gradient, and the electron . Title: Hydrogen self-absorption in the solar chromosphere. Authors: Thomas, Richard N. Bibcode: 1949AJ.....54..196T Altcode: Previous attempts to calculate hydrogen self- absorption in the solar flash-spectrum have used the earlier members of the Balmer series and essentially constructed emission curves-of- growth. Work on the Balmer decrement has been directed toward a solution for the b values, ignoring effects of self-absorption. It now seems that, for at least the higher series members, the Balmer decrement depends very little on the ba and essentially entirely upon the differential self- absorption. On this basis the self-absorption has been evaluated; and the number of hydrogen atoms, along a one square centimeter column in the line of sight, in the second level obtained. The value is 1.2 1016 atoms/cm1 at the eclipse height 670 km. The change of Balmer decrement with height gives the gradient of the population in this level. Combined with the equation of hydrostatic equilibrium, this gradient permits a rough estimate of the electron temperature gradient. The temperature gradient seems to be between I and 5 X I0-~ degrees/cm at the height 1000 km. Institute for Advanced Study, Princeton, N. J. Title: Superthermic Phenomena in Stellar Atmospheres. V. on Emission Lines at High Kinetic Temperature. Authors: Thomas, Richard N. Bibcode: 1949ApJ...110...12T Altcode: The treatment of the radiation field of a high-kinetic-temperature chromosphere is continued. The conditions for emission lines to be formed and for an effective photosphere to be found in the chromo- sphere are investigated from a purely formal standpoint. For a quantitative investigation of the behavior of the Balmer series, particularly with regard to the transient appearance of emission lines,a detailed investigation of inelastic collision cross-sections seems required Title: Superthermic Phenomena in Stellar Atmospheres. III. The Chromospheric Radiation Field. Authors: Thomas, Richard N. Bibcode: 1949ApJ...109..480T Altcode: 1949HarRe.322....1T The solution for the chromospheric b~ values of Paper II is extended to the case in which the chromo- spheric radiation and absorption is included in the radiation field. That variety of the solution which takes into account absorption in the chromospheric Balmer lines predicts a Balmer decrement in the flash spectrum which agrees well with the observations. Earlier work on the theoretical Balmer decrement has neglected radiative excitation in the Balmer lines, and the assumption's physical usefulness is here questioned. The most likely N~ value and the relation between density and emission gradients are dis- cussed Title: Superthermic Phenomena in Stellar Atmospheres.IV. The Wolf-Rayet Atmosphere. Authors: Thomas, Richard N. Bibcode: 1949ApJ...109..500T Altcode: The structure of the Woif-Rayet atmosphere is considered from the standpoint of stratification and support. Itis concluded that the neglectof deviations from the Boltzmann-Saha relations in earlieranalysis obscured an ambiguity in the interpretation of the observations and that a homogeneous atmosphere with Te> Tr is as acceptable as a stratified atmosphere with Te increasing downward. Analysis of the density gradient in V 444 Cygni leads to the conclusion that nonisotropic macroscopic motions of velocity equal to that inferred from the emission-band width suffice for support of the atmosphere. Comparison of the (ionization, band-width) correlation with the velocities required for support suggests that the ionization increases outward in at least the lower atmosphere Title: On emission lines at high kinetic temperature. Authors: Thomas, R. N. Bibcode: 1949AJ.....54..137T Altcode: If one admits the existence of a general outer stellar atmosphere whose kinetic temperature exceeds the radiation temperature of the star, some other mode of energy transfer than radiation is implied. There exists thus the possibility of increasing the emission in certain spectral regions without requiring a diminution in others. The conditions for a net chromospheric emission under conditions of high kinetic temperature and non-thermodynamic equilibrium are presented, with results in general considerably different from the earlier conclusions of Menzel. The most pressing refinement needed for the general case over the type calculations already made for the solar chromosphere, where Lyman emission and Balmer absorption were found, lies in the consideration of collisional excitation from the n = 2 level. The inclusion of such a term may force the earlier Balmer members into emission under conditions of sufficiently large electron density and kinetic temperature. It is suggested that the phenomenon may find application in the transitory bright line spectrum observed by Struve in RR Lyrae. Institute of Advanced Study, Princeton University, Princeton, N. J. Title: Superthermic Phenomena in Stellar Atmospheres. II. Departure from Thermo-Dynamic Equilibrium in an Idealized Chromosphere. Authors: Thomas, Richard N. Bibcode: 1948ApJ...108..142T Altcode: The steady-state condition of a hydrogen chromosphere, characterized by a kinetic temperature of 35,000° and illuminated by a radiation field of temperature 6000°, is determined. The hydrogen is found to be 99 per cent ionized. On the basis of these results, the He i, He ii chromospheric observations cease to be anomalous. The net energy supply needed to maintain this chromosphere falls within the range that present observations of the spicule system indicate may be expected to come from a mechanical-energy supply. Transfer problems arising from the chromospheric emission are explicitly neglected Title: Superthermic Phenomena in Stellar Atmospheres. I. Spicules and the Solar Chromosphere. Authors: Thomas, Richard N. Bibcode: 1948ApJ...108..130T Altcode: 1948HarRe.311....1T An interpretation of the chromospheric spicules as a system of superthermic jets is presented. It is suggested that the spicules may thus be the source of the energy needed to give the observed high chi~omospheric kinetic temperature. The possible configuration of the spicules, discussed on a hydrody- namic basis, is interpreted to obtain an estimate of the energy put into the chromosphere Title: Stellar atmospheric "turbulence" and stellar kinematics. Authors: Thomas, R. N. Bibcode: 1948AJ.....53..206T Altcode: Earlier, the likelihood of stellar atmospheric kinetic temperatures that exceed the radiation temperature has been suggested by the author. Here, the situation in regard to the cause and consequences of such high kinetic temperatures in the solar chromosphere is considered first, as an illustration. The observed chromospheric kinetic temperature of 35,0000, from the work of Wildt and Redman, is adopted. Considering mechanical energy transport as the immediate cause of the kinetic temperature, as earlier suggested, the spicule system found by Roberts is discussed as a possible mechanism in which the velocities are superthermic. Next, the consequences of such a kinetic temperature are considered and found to require appreciable deviation from thermodynamic equilibrium, with 99 per cent of the hydrogen ionized. The heretofore anomalous observations of the behavior of chromospheric helium no longer seem anomalous on this basis. The results of these investigations indicate a pseudo-kinematic effect in radial velocity measures for stars in which the effect is more pronounced than in the sun, if the jet system be the cause, and an anomalous spectroscopic behavior. Attention is called to just such anomalies in the Wolf-Rayet stars, and their harmonious interpretation on the basis of the suggested model. In particular, the simultaneous presence of many stages of ionization for the same element may be laid to departure from thermodynamic equilibrium rather than to stratification. A kinetic temperature of 106 0K is indicated by these spectroscopic results. An independent confirmation of this temperature value is found from an analysis of the density gradient in the WolfRayet star V444 Cygni, presented by Mrs. Shapley and Kopal, for kinetic temperature. Harvard College Observatory, Cambridge, Mass. Title: Study of a close approach of comet Whipple 1933f to Jupiter in 1922 Authors: Thomas, Richard N. Bibcode: 1948AJ.....53..188T Altcode: No abstract at ADS Title: Superthermic Phenomena in Stellar Atmospheres. Authors: Thomas, Richard N. Bibcode: 1948PhDT.........1T Altcode: No abstract at ADS Title: Meteorics and Ballistics Authors: Thomas, R. N. Bibcode: 1947PA.....55..517T Altcode: 1947HarRe.299....1T No abstract at ADS Title: Comment on the Wolf-Rayet Atmosphere. Authors: Thomas, Richard N. Bibcode: 1947ApJ...106..482T Altcode: 1947HarRe.301....1T No abstract at ADS Title: Comment on the Wolf-Rayet atmosphere. Authors: Thomas, Richard Nelson Bibcode: 1947cwra.book.....T Altcode: 1947QB883.T48...... No abstract at ADS Title: The 1922 approach to Jupiter of periodic comet Whipple Authors: Thomas, Richard N. Bibcode: 1946PAAS...10..262T Altcode: No abstract at ADS