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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
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Title: Cataclysmic variables and related objects
Authors: Hack, Margherita; Ladous, Constanze; Jordan, Stuart D.;
Thomas, Richard N.; Goldberg, Leo; Pecker, Jean-Claude
1993NASSP.507.....H Altcode: 1993cvro.nasa.....H; 1993QB835.H27......
No abstract at ADS
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Title: Solar-stellar chromospheres and coronae
Authors: Thomas, Richard N.
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.
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Title: Modeling Utility of Rapid Variability Diagnostics of OB Stars
Authors: Doazan, V.; Thomas, R. N.
1991ESOC...36..287D Altcode: 1991rvos.conf..287D
No abstract at ADS
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Title: Sun-Hot Star Contrast in Chromospheric/Coronal
Te(r). Nonradiative Heating vs. Outflow Enhanced Opacity
Authors: Doazan, V.; Thomas, R. N.
1991mcch.conf..319D Altcode:
No abstract at ADS
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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.
1990ESASP.310..297D Altcode: 1990eaia.conf..297D
No abstract at ADS
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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.
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.
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Title: FGK stars and T Tauri stars
Authors: Cram, Lawrence E.; Kuhi, Leonard V.; Jordan, Stuart; Thomas,
Richard; Goldberg, Leo; Pecker, Jean-Claude
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.
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Title: The vanishing shell phase of PLEIONE in the far UV in 1988.
Authors: Doazan, V.; Thomas, R. N.; Bourdonneau, B.
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.
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Title: A ten-year `active' episode of mass outflow from the Be-star
59 Cyg: facts and implications
Authors: Doazan, Vera; Thomas, Richard N.
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.
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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.
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. <P
/>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.
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Title: BE Shell of Pleione
Authors: Thomas, Richard
1988iue..prop.3261T Altcode:
No abstract at ADS
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Title: Implications of Variable Mass-Outelow on Modeling.
Authors: Doazan, V.; Thomas, R. N.
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.
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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.
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.
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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.
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.
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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.
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.
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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.
1987LNP...274...96D Altcode: 1987stpu.conf...96D
No abstract at ADS
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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.
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.
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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.
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.
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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.
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.
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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.
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.
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Title: Book-Review - Effect of Variable Mass Loss on the Local
Stellar Environment - Trieste Workshop 1983
Authors: Stalio, R.; Thomas, R. N.; Tschape, R.
1986AN....307..148S Altcode:
No abstract at ADS
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Title: The M-type stars
Authors: Johnson, Hollis Ralph; Querci, Francois R.; Jordan, Stuart;
Thomas, Richard; Goldberg, Leo; Pecker, Jean-Claude
1986NASSP.492.....J Altcode: 1986mts..book.....J; 1986QB843.M16M89...
No abstract at ADS
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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.
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.
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Title: Book-Review - Stellar Atmospheric Structural Patterns
Authors: Thomas, R. N.; Gussmann, E. A.
1985AN....306..341T Altcode:
No abstract at ADS
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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.
1985rbcc.conf..321B Altcode:
No abstract at ADS
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Title: Summary of working group on chromospheric heating and energy
balance.
Authors: Thomas, R. N.
1985cdm..proc...15T Altcode:
No abstract at ADS
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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.
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.
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Title: Book-Review - Stellar Atmospheric Structural Patterns
Authors: Thomas, R. N.; Mihalas, D.
1984Obs...104..275T Altcode:
No abstract at ADS
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Title: Book-Review - Stellar Atmospheric Structural Patterns
Authors: Thomas, R. N.
1984S&T....68Q.327T Altcode:
No abstract at ADS
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Title: Book-Review - Stellar Atmospheric Structural Patterns
Authors: Thomas, R. N.
1984Sci...225R.503T Altcode:
No abstract at ADS
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Title: Possible identifying characteristics of Be stars.
Authors: Doazan, V.; Thomas, R. N.
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.
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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.
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.
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Title: Be-Stars
Authors: Baade, D.; Doazan, V.; Marlborough, M.; Polidan, R.; Peters,
G.; Smith, M.; Thomas, R. N.; Willson, L. A.
1984rcch.conf..321B Altcode:
No abstract at ADS
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Title: Book-Review - Stellar Atmospheric Structural Patterns -
Monograph Series on Nonthermal Phenomena in Stellar Atmospheres
Authors: Thomas, R. N.
1984Natur.310..805T Altcode:
No abstract at ADS
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Title: Empirical-Theoretical Structural Patterns for Stellar
Atmospheres and Their Local Environment Relative to Variable Mass Loss
Authors: Thomas, R. N.
1984evml.conf....3T Altcode:
No abstract at ADS
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Title: Effects of variable mass loss on the local stellar environment
Authors: Stalio, Roberto; Thomas, Richard N.
1984evml.conf.....S Altcode: 1984QB809.E34......; 1984evml.book.....S
No abstract at ADS
---------------------------------------------------------
Title: Pas de deux
Authors: Thomas, R. N.
1983Obs...103..172T Altcode:
No abstract at ADS
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Title: Stellar atmospheric structural patterns
Authors: Thomas, R. N.
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.
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Title: Empirical-theoretical approach by contrast to summary of
speculative-theoretical modeling by Hearn
Authors: Thomas, R. N.
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.
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Title: Variable mass-flux in Be stars
Authors: Doazan, V.; Thomas, R. N.
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.
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.
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.
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.
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.
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.
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.
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.
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.
1982obvf.confD..22T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Global picture of a Be star
Authors: Thomas, R. N.
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.
1982obvf.conf..218T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observational Basis for Velocity Fields in Stellar Atmospheres
Authors: Stalio, Roberto; Thomas, Richard N.
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.
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.
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.
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
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.
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.
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.
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.
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
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.
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.
1978hrsp.book.....H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Concluding Remarks
Authors: Thomas, R. N.
1978hrs..conf..702T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Forecast of future in solar physics
Authors: Thomas, R. N.
1977MmSAI..48..579T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: What is a stellar atmosphere
Authors: Thomas, R. N.
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.
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.
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.
1977ebhs.coll..487T Altcode: 1977IAUCo..36..487T
No abstract at ADS
---------------------------------------------------------
Title: Boundary conditions with mass-loss: general considerations.
Authors: Thomas, R. N.
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.
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.
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.
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.
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.
1975MmArc.105...11C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Chairman's introduction to Cram's review paper
Authors: Thomas, R. N.
1975cesra...5...11T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Stellar atmospheres,, nonequilibrium in thermodynamics,
and irreversibility.
Authors: Thomas, R. N.
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.
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.
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.
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.
1973IAUS...49....3T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Theory of stellar atmospheres (Théorie des atmosphères
stellaires).
Authors: Thomas, R. N.
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.
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.
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.
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.
1971spas.conf...84T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar spicules and chromospheric heating.
Authors: Thomas, R. N.
1971tmp..conf..331T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Saturation in Fraunhofer lines
Authors: Pecker, J. -C.; Thomas, R. N.
1970Obs....90..207P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Temperature Control Bracket
Authors: Gebbie, K. B.; Thomas, R. N.
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.
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.
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.
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.
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.
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.
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.
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.
1968Obs....88..115P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Wolf-rayet stars
Authors: Gebbie, Katharine B.; Thomas, Richard N.
1968wrs..conf.....G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Opening Remarks
Authors: Thomas, Richard N.
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.
1968wrs..conf..237T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Symposium on Wolf-Rayet Stars: A Summary
Authors: Thomas, R. N.
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
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.
1966ZA.....63..282T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Some Problems of Radiation Transfer in Quiescent Stellar
Atmospheres
Authors: Thomas, R. N.
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.
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.
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
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.
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.
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.
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.
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.
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.
1962ApJ...135..653J Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Excitation of the red and green coronal lines
Authors: Pecker, Ch.; Thomas, R. N.
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.
1962ZA.....55...66T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Buchbesprechung über: Aerodynamic Phenomena in Stellar
Atmospheres. (Ref. K. H. BÖHM)
Authors: Thomas, R. N.
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.
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.
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.
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.
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.
1961osmt.conf...14T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Physics of the solar chromosphere
Authors: Athay, R. Grant; Thomas, Richard N.
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.
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.
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.
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.
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.
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.
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.
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
1960IAUS...12.....T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Aerodynamic phenomena in stellar atmospheres : proceedings
Authors: Thomas, Richard Nelson
1960akiv.book.....T Altcode: 1960akiv.book.....S
No abstract at ADS
---------------------------------------------------------
Title: Summaries - R. N. Thomas
Authors: Thomas, R. N.
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.
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.
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.
1959ZA.....48..158B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Preface
Authors: Burgers, J. M.; Thomas, R. N.
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.
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.
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
1958IAUS....8.....B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On Trad for the early Balmer lines.
Authors: Thomas, Richard N.
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.
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.
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.
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.
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.
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.
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.
1956SciMo..83..135T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Some Characteristics of a Chromospheric Model.
Authors: Athay, R. G.; Thomas, R. N.
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.
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.
1956SCoA....1..123T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Astroballistics
Authors: Thomas, Richard N.
1956SCoA....1...49T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Temperature Gradients in the Chromosphere
Authors: Athay, R. G.; Thomas, R. N.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
1948AJ.....53..188T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Superthermic Phenomena in Stellar Atmospheres.
Authors: Thomas, Richard N.
1948PhDT.........1T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Meteorics and Ballistics
Authors: Thomas, R. N.
1947PA.....55..517T Altcode: 1947HarRe.299....1T
No abstract at ADS
---------------------------------------------------------
Title: Comment on the Wolf-Rayet Atmosphere.
Authors: Thomas, Richard N.
1947ApJ...106..482T Altcode: 1947HarRe.301....1T
No abstract at ADS
---------------------------------------------------------
Title: Comment on the Wolf-Rayet atmosphere.
Authors: Thomas, Richard Nelson
1947cwra.book.....T Altcode: 1947QB883.T48......
No abstract at ADS
---------------------------------------------------------
Title: The 1922 approach to Jupiter of periodic comet Whipple
Authors: Thomas, Richard N.
1946PAAS...10..262T Altcode:
No abstract at ADS
