Author name code: athay
ADS astronomy entries on 2022-09-14
author:"Athay, R. Grant"
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Title: The Solar Interior-Atmospheric System
Authors: Athay, R. G.; Low, B. C.; White, O. R.
Bibcode: 2008ASPC..383..315A
Altcode:
This article discusses an unpublished paradigm by Athay that relates
the general properties of the solar photosphere, chromosphere, and
corona to the stream of photons, kinetic energy, and magnetic fields
flowing from the solar interior. Using the Athay paradigm, we discuss
the physics of the solar atmosphere and its coupling to the solar
dynamo to clarify the connection of observed structures and variations
in the three layers to their hydromagnetic interpretation. The details
of the eleven-year cycles of solar activity are quite different, but
each cycle exhibits two invariant features. First, the chromosphere and
corona are always present above the photosphere in its turbulent state
maintained by the radiative flux escaping at the surface as the solar
luminosity. Second, the solar magnetic field is globally reversed early
in each cycle, accompanied by systematic drifts in magnetic activity
shown in the sunspot butterfly diagram of each cycle. We describe a
scenario for the corresponding systematic changes in the upper solar
atmosphere that recover the minimum-activity corona from one cycle
to the next. We discuss in some detail the mechanisms that heat the
atmosphere and process the magnetic flux continually emerging from the
interior, providing a unified view of the interior-atmospheric system.
Title: An Ionization Instability and the Base of the Corona
Authors: Athay, R. Grant
Bibcode: 2002ApJ...565..630A
Altcode:
A chromosphere of partially ionized atoms in a turbulent, magnetic,
solar-type star may be subject to a thermal instability due
to ionization, which we propose in this paper. The instability
occurs when changing magnetic fields cause ion heating so that a
proton-electron pair are heated preferentially with respect to neutral
atoms. This preferential heating, when partial ionization is present,
causes any small temperature change to be amplified. An increase in
temperature increases the ionization, which in turn increases the local
heating. Similarly, a decrease in temperature decreases the ionization,
which decreases the heating. The layer of instability occurs between two
stable layers: the chromosphere, in which the ionization is too low,
and the corona, in which the ionization is essentially complete. Such
an atmosphere tends to be bimodal; it is either fully neutral or fully
ionized. We use the models of Fontenla and coworkers to demonstrate the
instability, but any magnetic stellar model in which ions are heated
preferentially over neutral hydrogen will exhibit the same instability.
Title: Are Spicules Related to Coronal Heating?
Authors: Athay, R. G.
Bibcode: 2000SoPh..197...31A
Altcode:
We suggest that the waxing and waning of chromospheric and coronal
heating leads to a dynamic solar atmosphere which, under the right
circumstances, may produce spicules. Little is known about the heating
process. However, Anderson and Athay (1989a) concluded from their study
of chromospheric heating that the heating rate per gram of chromospheric
matter is only a small fraction of the heating rate per gram of coronal
matter. We postulate that the increased heating rate in the corona is a
consequence of heating charged particles as opposed to heating neutral
atoms. This leads to a specific degree of hydrogen ionization at which
coronal heating begins to predominate over chromospheric heating. It
also introduces the likelihood that the waxing and waning of the
heating rates will have relatively large consequences in the levels
where hydrogen ionization is becoming significant. It is demonstrated
that changes in the heating rates are capable of inducing increases
and decreases in coronal mass comparable to the mass contained in a
typical spicule.
Title: Excitation of O i Lines in the Solar Chromosphere
Authors: Athay, R. Grant; Judge, Philip G.
Bibcode: 1995ApJ...438..491A
Altcode:
Observations of O I lines in the solar spectrum are examined to
determine whether differences in behavior of lines of the quintet
and triplet term systems are consistent with collisional excitation
and/or photoexcitation of both quintets and triplets. Intensities,
IIR, in near-infrared emission lines observed above the
limb at total eclipse decrease exponentially with height h. The
inverse scale heights (d In IIR/dh) for the triplet
lines at 844.6 nm and quintet lines at 777.2 nm are found to be
in the ration of 1.45. Ultraviolet O I emission-line intensities
IUV observed on the solar disk show strong variations, and
the distributions of triplet (130.4 nm) and quintet line intensities
about the means are different. Variances in In IUV are
found to have a triplet-to-quintet ratio of 1.50, in close agreement
with the ratio of d In IIR/dh. It is shown that the simple
assumption of collisional excitation of quintets and triplets coupled
with collisional de-excitation of the quintets leads to the correct
ratios for both the UV variances and d In IIR/dh. Also,
under this assumption d In IIR/dh for the quintet lines
is predicted to have the same value as d In I/dh at the head of the
hydrogen Balmer continuum, which, in fact, it does. On the other hand,
Carlsson & Judge (1993) have shown that collision rates computed
from the Vernazza, Avrett, & Loeser (1981, hereafter VAL) model
chromosphere using current estimates of O I collision strengths are
too low to produce the observed mean intensity in O I 130.4 nm. In
a similar sense, we find that the predicted intensity of O I 130.4
nm is much too weak relative to O I 135.6 nm, and that the VAL mean
models A-F cannot reproduce the observed behavior of these lines,
even including photoexcitation by H Ly-beta. These difficulties are
removed by increasing specific electron-atom collision rates. Such
increases could reflect large errors in atomic cross sections close
to threshold and/or the inadequacy of the assumptions made by VAL for
predicting line intensities. The latter alternative a likely factor. We
conclude that the O I UV lines are very sensitive to inhomogeneities,
much more than more traditional chromospheric lines (e.g., Mg II k)
which are formed over similar regions of the chromosphere. Such lines
could therefore provide valuable diagnostics of departures of the
chromopsheric plasma from mean models and thereby place constraints
upon heating mechanisms, once accurate atomic data become available.
Title: Separation of Low First Ionization Potential Ions from High
First Ionization Potential Neutrals in the Low Chromosphere
Authors: Athay, R. Grant
Bibcode: 1994ApJ...423..516A
Altcode:
Spectroscopic data from two flights of the Naval Research Laboratory's
High Resolution Telescope and Spectrograph (HRTS) are analyzed
for evidence of variations in relative abundances in the low
chromosphere. Comparisons of sunspot, active region, and quiet-Sun
data from HRTS II reveal decreases of intensities of sunspot lines
from the first ionization stages of elements with low first ionization
potential relative to both the active region and the quiet Sun. C
I lines, however, are more intense in the sunspot than either the
active region or the quiet Sun. Within a sunspot in Spacelab II data,
the C I line at 156.1 nm is near its average intensity, whereas the
Fe II line at 156.3 is much weaker than average. Both spots suggest
a relative high value for the C I/Fe II abundance ratio. Within the
zone of the same magnetic polarity as the sunspot (leading polarity)
in the Spacelab II data, the brightest plages in C I show large C I/Fe
II intensity ratios similar to those found in the sunspot. By contrast,
the zones of following polarity on either side of the leading polarity
show several well-defined areas of unusually low C I/Fe II intensity
ratios associated with dark features in C I. The plages within these
same zones have near normal or somewhat enhanced values for the C I/Fe
II intensity ratios. It is noteworthy, also, that many of the brightest
areas in C I do not coincide spatially with the brightest regions in
Fe II. Neither do the darkest areas in C I align well with the darkest
areas in Fe II. The association of high C I/Fe II intensity ratios
with the zone of leading polarity and low-intensity ratios with zones
of following polarity suggests that the iron abundance is dependent
on the field polarity and is relatively low in the sunspot and the
brighter plages in the zone of leading polarity and relatively high
in C I dark flocculi in zones of following polarity. Failure of the
brightest and darkest features in C I to align with the brightest
and darkest features in Fe II further suggests that in the case of
these particular features the Fe II abundance may vary inversely with
the gas pressure, as well as with magnetic polarity. Other possible
interpretations are discussed but are considered as being less viable.
Title: Velocity Gradients in the Chromosphere-Corona Transition Region
Authors: Athay, R. G.; Dere, K. P.
Bibcode: 1991ApJ...381..323A
Altcode:
Velocity data obtained from Doppler shifts of EUV spectral lines
observed with the High Resolution Telescope and Spectrograph flown
on Spacelab II are analyzed to determine the properties of the mean
velocities V-bar and its spatial variance V(sigma), for chromospheric
and transition region lines. The lines studied include the ions O I,
C I, Fe II, C II, Si III, Si IV, and C IV. The constancy of V(sigma)
from center to limb together with a systematic maximum redshift in
V-bar in central disk regions is interpreted to mean that the plasma
flow is divergent from the tops of closed field lines and that the
cool plasma more or less fills the magnetic loops from which most of
the radiation originates. The same is true of the hotter plasma. It
is suggested that the crossfield component of Delta T is large and
that the alternation from cool loops to hot loops occurs on spatial
scales much less than 1 arcsec.
Title: Chromospheric and Transition Region Diagnostics Using
Emission-Line Intensities
Authors: Athay, R. G.; Dere, K. P.
Bibcode: 1991ApJ...379..776A
Altcode:
EUV emission-line intensities from the HRTS experiment on Spacelab 2 are
analyzed to determine the causes of intensity variations from point to
point on the solar surface. Chromospheric lines of O I and transition
region lines of C II, Si IV, and C IV exhibit saturation effects that
limit the line intensities in the brighter regions. No such effect
is found in lines of C I, Fe II, or Si III. The chromospheric lines
saturate because the optical thickness exceeds the thermalization depth,
whereas the transition region lines saturate because of the geometry
of the unresolved fine structure. The latter is assumed to consist
of elongated cylinder-like features oriented along magnetic lines of
force that are mainly vertical. Saturation occurs when the optical
thickness along the axis of the cylinders exceeds unity. Estimates
based on the observed saturation effects give fill factors for the fine
structure 0.005 and 0.4 at 100,000 K and 30,000 K, respectively. The
corresponding lengths of the cylinders are estimated at 1000 km and
40 km at the two temperatures.
Title: A Model of the Solar Chromosphere-Corona Transition Region
Based on Classical Thermal Conduction
Authors: Athay, R. Grant
Bibcode: 1990ApJ...362..364A
Altcode:
A hot corona cooled by inward thermal conduction very likely results
in a transition region whose isotherms follow a highly roughened
surface. Assuming a checkerboard of cool peaks and hot valleys in
surfaces of constant temperature and using the observed emission measure
at T = 60,000 K, the ratio of the mean height of the cool peaks to the
mean separation of peaks and valleys has a value of 160. By allowing
nearly all of the parallel conduction flux of 1 million ergs/sq cm
per sec at 1 million K in the hot valleys to flow across magnetic
field lines into the cool peaks, a predicted emission measure in
very good agreement with the low-temperature branch of the observed
emission measure, including the Ly-alpha region, is found. This purely
conductive model has the advantages of explaining both the observed
emission measure curve and the wide vertical extent of the transition
region at the limb without introducing ad hoc secondary heat sources.
Title: Bifurcation in the Low Chromosphere
Authors: Athay, R. Grant; Dere, K. P.
Bibcode: 1990ApJ...358..710A
Altcode:
Bright chromospheric faculae of diameter d(c) covering an area of
the solar disk f(c) smaller than 1 yield a predictable level of limb
brightening. For a resolution diameter d(r), the combination of f(c) and
d(c) leads, also, to a prediction of the fraction, phi(0), of observing
pixels (resolution areas) that are free of facular emission. Data from
the first flight of the High Resolution Telescope and Spectrograph of
the U.S. Naval Research Laboratory with d(r) about 1 arcsec are used to
measure both the level of limb brightening and phi(0) in EUV emission
lines of O I, C I, and Fe II. The results favor f(c) about 0.9 and d(c)
greater than about 2.5 arcssec. It is concluded that the chromospheric
temperature rise is present over about 90 percent of the solar surface.
Title: C iv plasma flow near active region filaments
Authors: Athay, R. Grant
Bibcode: 1990SoPh..126..135A
Altcode:
Selected CIVV0 lines (lines separating adjacent regions of
strong blue shift and strong red shift) located near the solar limb
and oriented parallel to the radius vector from disk center are shown
to be closely aligned with Hα dark filaments in active regions. The
filaments, in turn, are known to lie in the vicinity of magnetic neutral
lines. The radial orientation of the V0 lines minimizes
uncertainties in image registration and their location near the limb
ensures that the observed fluid motion has major components paralleling
V0. It follows that the filaments are located at sites of
velocity shear, and, by inference, of magnetic shear. For a case in
which a given V0 line is observed near both east and west
limbs, the gradient of Doppler velocity across the V0 line
reverses sign from one limb to the other as is expected for horizontal
steady flow. Thus, the velocity vectors remain fixed with respect to
the filament.
Title: Temperature and Center-Limb Variations of Transition Region
Velocities
Authors: Athay, R. G.; Dere, K. P.
Bibcode: 1989ApJ...346..514A
Altcode:
HRTS data from the Spacelab 2 mission are used to derive the
center-limb and temperature variations of the mean velocity and the
velocity variance in the solar chromosphere and transition zone. The
mean velocity is found to vary much more rapidly from center to limb
and with temperature than does the velocity variance. Also, the mean
velocity shows a characteristic signature at some magnetic neutral
lines in accordance with the findings of Klimchuk (1987) from Solar
Maximum Mission (SMM) data. The velocity variance does not show a
characteristic signature at the neutral lines but shows an inverse
correlation with intensity. The latter is interpreted as reduced
velocity variance in strong field regions. The results are discussed
in terms of downflow along lines of force in magnetic arcades.
Title: Model Solar Chromosphere with Prescribed Heating
Authors: Anderson, Lawrence S.; Athay, R. Grant
Bibcode: 1989ApJ...346.1010A
Altcode:
Computed model solar chromospheres for prescribed departures from
radiative equilibrium are specified in terms of the local mechanical
(nonradiative) heat input. The computations are fully non-LTE and
include millions of spectral lines. From the variety of models
considered, the requirements on the heat input for a positive
temperature gradient, dT/dh, in different layers of the chromosphere
are discussed. The derived radiative cooling function for different
models show that the cooling function is model-dependent. By comparing
the computed models with the Vernazza, Avrett, and Loeser (1981) models,
it is shown that the VAL-C model is characterized by a total heat flux
1.4 x 10 to the 7th ergs/sq cm/per sec, most of which is dissipated
near the base of the temperature plateau. Half of the radiation loss
is provided by Fe II, with Ca II, Mg II, and H playing important,
but secondary, roles. CO molecules and H(-) are of lesser importance
even near the temperature minimum, except in cases of minimal heating.
Title: Chromospheric and Coronal Heating
Authors: Anderson, Lawrence S.; Athay, R. Grant
Bibcode: 1989ApJ...336.1089A
Altcode:
From computations for a theoretical model chromosphere matched to the
empirical model of Vernazza, Avrett, and Loeser published in 1981,
it is concluded that the required magnitude and mass dependence of the
heat input are compatible with heating by sound waves whose velocity
amplitude is near the sound speed. However, the required rate of
heat input per gram increases markedly at the top of the neutral
chromosphere, and a different form of heating appears necessary in
the corona and transition region.
Title: The Relationship Between R.M.S. Doppler Velocities and
Temperature in the Solar Transition Region
Authors: Athay, R. Grant
Bibcode: 1988SoPh..116..223A
Altcode:
An attempt is made in this paper to determine the coefficient a in a
power-law relationship of the form Vσ~Tα between
the r.m.s. velocity fluctuation, Vσ for raster images with
3″ resolution and the temperature, T of line formation using SMM
solar data. For T between 8000 and 105 K, the data suggest a
best fit with 3/4 ≲ α < 1. It is argued, however, that unresolved
fine structure tends to reduce the observed value of Vσ and
that higher resolution data may yield different values for α. Skylab
data have shown that the non-thermal line broadening velocity, ξ,
is proportional to T1/2. Also, for all temperatures less
than 105 K, ξ ≫ Vσ. This latter result,
however, is again dependent on spatial resolution and may not be
true in observations made with sufficient spatial resolution. The
magnitudes of both Vσ and ξ indicate that bulk motions
play important roles in the structure of the solar atmosphere as well
as in its energy and momentum balance. It is important, therefore,
to identify the true nature of such motions with better accuracy than
is possible with currently available data.
Title: The Origin of Solar He II Radiation
Authors: Athay, R. G.
Bibcode: 1988ApJ...329..482A
Altcode:
Doppler images made cospatially and nearly cotemporally in C IV and
He II lines with the Ultraviolet Spectrometer/Polarimeter experiment
on SMM permit a direct comparison of macroscopic velocity amplitudes
observed for the two ions. Similarly, the line profiles for the two
ions permit a comparison of the total line-broadening velocities, which
are the root mean squares of the thermal and nonthermal microscopic
velocities. Assuming that the C IV ion is predominant at 100,000 K,
arguments are presented based on relative velocity amplitudes and
line intensities that indicate a most probable temperature for the
He II plasma of approximately 80,000 K. Collisional processes play a
major role in the excitation of solar He II radiation in both active
and quiet regions.
Title: The hot solar envelope.
Authors: Athay, R. Grant
Bibcode: 1988mwa..work....7A
Altcode: 1988mwa..conf....7A
Contents: 1. Introduction. 2. The solar interior. 3. Overview of the
solar atmosphere. 4. The photosphere. 5. The chromosphere. 6. The
transition region. 7. The corona.
Title: Characteristics of the Expansion Associated with Eruptive
Prominences
Authors: Athay, R. G.; Low, B. C.; Rompolt, B.
Bibcode: 1987SoPh..110..359A
Altcode:
Gradients of Hα and electron scattering intensities derived from
instantaneous radial distributions of erupting prominence material
observed at several solar radii by Illing and Athay (1986) are often
markedly smaller than those inferred by comparing the intensities
observed near several radii to average prominence intensities
observed near the limb. In this paper, we show that gradients derived
by following individual features in their outward progression with
time yield values that are consistent with limb observations and that
usually exceed the values obtained from instantaneous distributions. We
conclude from the diversity of observed gradients that the prominence
eruption cannot be described by a self-similar expansion in which the
expansion velocity is a function of radius and time only. However,
we cannot rule out possible self-similar solutions that allow the
expansion velocity to be a function of angular direction.
Title: The Magnetic and Velocity Structure Adjacent to Solar Active
Regions
Authors: Athay, R. Grant; Klimchuk, J. A.
Bibcode: 1987ApJ...318..437A
Altcode:
Results from a number of earlier papers relating velocity patterns
observed in the C IV line at 154.8 nm to photospheric magnetic-field
patterns are combined to develop a qualitative model of the
magnetic-field geometry outside of the strong field areas of active
regions. The motion is assumed to originate at the crests of magnetic
arcades and flow downward along field lines, which are assumed to
be elliptical in shape with the major axis in the photosphere. It is
found that the ratio of the major axis to the minor axis of the ellipse
must be less than two for fields under 100 G. Also, it is concluded
that the magnetic neutral surfaces defined by the loci of horizontal
field lines are often tilted at a large angle to the vertical at the
altitude of the C IV emission.
Title: Radiative Cooling in the Solar Chromosphere
Authors: Anderson, L. S.; Athay, R. G.
Bibcode: 1987BAAS...19R.930A
Altcode:
No abstract at ADS
Title: Downflows in coronal loops
Authors: Athay, R. G.
Bibcode: 1987Natur.327..685A
Altcode:
The existence of the solar wind requires a net outflow of material at
all depths in the solar atmosphere. Thus, the observation of a prevalent
downflow at temperatures near 105 K1,2 presents a
considerable challenge. Two classes of flow models have been suggested,
each involving flow along closed magnetic-field lines that extend above
the chromosphere into the hotter transition region and corona. Type-(l)
models3,4,5 assume unidirectional equilibrium flows along
field lines and rely on asymmetry in the flow and plasma properties
to produce an apparent downflow. Type-(2) models2,6, by
comparison, assume a series of episodic upflows and subsequent downflows
along each line of force and rely on asymmetry in the plasma properties
and flow durations to produce a statistically prevalent downflow. Here
I argue that observational evidence strongly suggests that both types
of flow are present but that type-(2) flow is predominant.
Title: Excitation of Solar He II Lines
Authors: Athay, R. G.
Bibcode: 1987BAAS...19Q.930A
Altcode:
No abstract at ADS
Title: Solar physics from space
Authors: Athay, R. Grant
Bibcode: 1987sacd.proc.1169A
Altcode:
The application of the High Resolution Solar Observatory (HRSO),
an economical version of the Solar Optical Telescope, to the study
of solar and astrophysical phenomena is considered. Recent conceptual
changes in solar physics are discussed, with emphasis on the present
understanding of the interactions between the solar magnetic fields
and plasma. It is noted that the HRSO will be well suited to the
investigation of the intense activity of the upper chromosphere and
corona which is thought to result from magnetic field stresses generated
in the photosphere by turbulent plasma flow.
Title: Solar physics from space.
Authors: Athay, R. G.
Bibcode: 1987aasi.conf.1169A
Altcode:
The needs for the High Resolution Solar Observatory (HRSO) are
discussed and illustrated in terms of what we presently know about
the interactions between the solar magnetic fields and plasma.
Title: Analysis of the prominence associated with the coronal mass
ejection of August 18, 1980
Authors: Athay, R. Grant; Illing, Rainer M. E.
Bibcode: 1986JGR....9110961A
Altcode:
Coronal mass ejections detected with the Solar Maximum Mission
coronagraph/polarimeter are often accompanied by erupting prominence
material observed both in Hα and in the electron scattering
continuum. Hα emission is concentrated in bright filaments moving
radially outward. The same filaments are seen in the electron scattering
continuum as regions of enhanced brightness. In this paper we develop
a diagnostic method based on the observed Hα and continuum brightness
to derive the electron density, line of sight thickness, and degree
of ionization of hydrogen as functions of the temperature of the
prominence filaments. Our method differs from that of Poland and Munro
(1976) in the treatment of Ly α excitation. Analysis of data from
the event of August 18, 1980, illustrates that the rising prominence
material has decreased density, increased temperature, and increased
ionization of hydrogen relative to quiescent prominences in the lower
corona. Hydrogen is found to be 90-99% ionized, electron densities are
near 108 cm-3, and the temperature is
near 20,000 K. The increased ionization is due mainly to the decreased
density. Use of the results is made here and in an accompanying paper by
Illing and Hundhausen to determine the total mass ejected in the event.
Title: Radiation Loss Rates in Lyman Alpha for Solar Conditions
Authors: Athay, R. G.
Bibcode: 1986ApJ...308..975A
Altcode:
Mean radiation loss rates per unit volume in Lyman-alpha are computed
for solar conditions as a function of the optical thickness of
the radiating region. No significant corrections to the optically
thin coronal approximation are found until the Lyman-alpha optical
thickness at line center exceeds 100. At larger optical thicknesses
the corrections can be large as a result of the increased ionization
of hydrogen from absorptions in the Balmer continuum. The correction
suggested by McClymont and Canfield (1983) is found to be too large
for most solar applications.
Title: Magnetic Shear. III. Hale Region 17255
Authors: Athay, R. G.; Jones, H. P.; Zirin, H.
Bibcode: 1986ApJ...303..877A
Altcode:
Hale active region 17255, which in many respects was the most vigorous
active region observed during the first operational period of SMM,
appears to lie between two large areas of flow (observed in C IV)
converging toward the major axis of the region. In the 6-day period
from November 6-12, 1980, the major axis of the region rotates by
about 25 deg. Several segments of the magnetic neutral line show C
IV flow velocities of opposite sign on either side of the neutral
line. Those segments whose orientation is favorable for measuring
velocity components parallel to the neutral line show evidence that
such flow is present, which is interpreted as evidence for magnetic
shear. This, together with other evidence, suggests that magnetic
shear is widespread in this region, as in the two previous regions
studied. It is concluded that magnetic shear is often associated with
flaring activity but is not a sufficient condition for flaring to occur.
Title: Magnetic Shear. IV. Hale Regions 16740, 16815, and 16850
Authors: Athay, R. G.; Klimchuk, J. A.; Jones, H. P.; Zirin, H.
Bibcode: 1986ApJ...303..884A
Altcode:
Dopplergrams made in C IV 1548 A are studied for evidence of velocity
shear near H-alpha dark filaments and for large-scale flow convergent on
active regions. The three regions studied support earlier conclusions
that shear is a common property of active regions and that active
regions may be the foci of converging plasma flow. Flow patterns
near filaments show divergence or convergence as well as shear. Also
the sense of the shear can be either cyclonic or anticyclonic. No
preference is noted for convergence or divergence or for a particular
sense of shear, and there appears to be no correlation between the
sense of the shear and the sign of the velocity gradient normal to
the filament. The close association of H-alpha dark filaments with
shear lines leads to the suggestion that the filaments may arise from
a cooling instability induced by the Bernoulli effect.
Title: The Origin of EUV Radiation
Authors: Athay, R. G.
Bibcode: 1986BAAS...18..686A
Altcode:
No abstract at ADS
Title: Radiation output.
Authors: Athay, R. G.
Bibcode: 1986psun....2....1A
Altcode:
Contents: Basic concepts and definitions (formation of spectra, energy
balance, notation, escape probability and scattering depth, escape
coefficient, creation and destruction probabilities, thermalization and
degradation lengths, intra-atmosphere exchange probability, the source
function, the transfer equation). Spectral diagnostics (temperature,
density, velocity, magnetic field, and abundance diagnostics). The
role of radiation in determining atmospheric properties (photosphere,
line blanketing and cooling, the chromosphere, characteristics of
chromosphere radiation loss, temperature minimum, the first and second
temperature plateau, the transition region, the corona). Nonradial
structure (fluid motions and magnetic fields, photosphere and
temperature minimum region, chromosphere and transition region,
corona). Temporal fluctuations. Challenges for the future (radiation
diagnostics, influence of radiation on atmospheric properties,
observations).
Title: Chromospheric fine structure.
Authors: Athay, R. G.
Bibcode: 1986psun....2...51A
Altcode:
Contents: Properties of chromospheric structure (network and
supergranule cells, network coarse and fine structure, supergranule
cell structure, active region structure). Velocity and magnetic
structure. Magnetohydrodynamic structure (a new look at fine structure,
lifting forces). Major problems (energy balance, momentum balance,
the Sun as a star).
Title: The chromosphere and transition region — Current status
and future directions of models
Authors: Athay, R. G.
Bibcode: 1985SoPh..100..257A
Altcode:
This essay on the chromosphere and transition region begins with a
general discussion of mechanically heated atmospheres and goes on
to discuss both descriptive and physical models. The descriptive
models include the thermodynamic and fluid dynamic properties of
the atmosphere as deduced from observations. Particular features of
the models are identified with the properties of the radiation loss
associated with the ionization of hydrogen and with the properties of
thermal conduction. The role of spicules in chromosphere and transition
region properties is emphasized. Physical models that attempt to
predict the basic features of the descriptive models are reviewed.
Title: Fine Structure and Dynamics of the Chromosphere and Transition
Region and Future Directions of Models
Authors: Athay, R. G.
Bibcode: 1985tphr.conf..205A
Altcode:
No abstract at ADS
Title: Magnetic shear. II - Hale region 17244
Authors: Athay, R. G.; Jones, H. P.; Zirin, H.
Bibcode: 1985ApJ...291..344A
Altcode:
A B-gamma(delta) sunspot group with growing delta-spots of trailing
polarity shows evidence in H-alpha filament structure of a transition
from a state of weak magnetic shear to a state of strong shear. The
shear develops in the chromosphere and transition region to the
corona overlying the photospheric magnetic neutral line separating the
delta-spots from the leading polarity at a time when the delta-spots are
undergoing rapid growth. Several major flares occur along the sheared
portion of the neutral line following the shear development. Other
segments of the neutral line far removed from the delta-spots show
similar evidence of shear in the H-alpha filament structure and in C
IV velocity patterns as well. These 'quiescent' regions of shear are
relatively steady or decaying with time and show very little related
activity.
Title: Magnetic shear. I - Hale region 16918
Authors: Athay, R. G.; Jones, H. P.; Zirin, H.
Bibcode: 1985ApJ...288..363A
Altcode:
Material motion observed in spectral lines of C IV, C II, and Ca
II formed in the chromosphere-corona transition region and upper
chromosphere exhibits patterns that are closely identified with magnetic
field structure at photospheric levels. Assuming that the fluid flow
follows magnetic lines of force, the authors use chromospheric and
transition region Dopplergrams to infer the broad features of the
magnetic field geometry in these upper layers. For Hale region 16918
they find an area in the transition region and upper chromosphere,
centered roughly over the photospheric magnetic neutral line, in which
the lines of force show a strong tendency to parallel the photospheric
neutral line. The authors interpret this as evidence for magnetic shear,
which is pronounced in the upper layers of the atmosphere.
Title: Fine structure and dynamics of the chromosphere and transition
regionand future directions of models.
Authors: Athay, R. G.
Bibcode: 1985MPARp.212..205A
Altcode:
It is argued that solar fine structure should be studied with the intent
of answering questions whose interest extends beyond solar physics. The
fine structure of the chromosphere and transition region is discussed
from the standpoint of its role in determining the global and mesoscale
structure of the atmosphere and as an indicator of the basic energy
and momentum inputs to the atmosphere. Conversely, the radiation losses
from the global atmosphere are discussed in terms of the fine structure.
Title: An implementation plan for priorities in solar-system space
physics
Authors: Krimigis, Stamatios M.; Athay, R. Grant; Baker, Daniel; Fisk,
Lennard A.; Fredricks, Robert W.; Harvey, John W.; Jokipii, Jack R.;
Kivelson, Margaret; Mendillo, Michael; Nagy, Andrew F.
Bibcode: 1985STIN...9014154K
Altcode:
The scientific objectives and implementation plans and priorities
of the Space Science Board in areas of solar physics, heliospheric
physics, magnetospheric physics, upper atmosphere physics,
solar-terrestrial coupling, and comparative planetary studies are
discussed and recommended programs are summarized. Accomplishments
of Skylab, Solar Maximum Mission, Nimbus-7, and 11 other programs are
highlighted. Detailed mission plans in areas of solar and heliospheric
physics, plasma physics, and upper atmospheric physics are also
described.
Title: Analysis of HI Balmer-alpha Emission from an Eruptive
Prominence above 3 Solar Radii
Authors: Illing, R. M. E.; Athay, R. G.; Hundhausen, A. J.
Bibcode: 1985BAAS...17..514I
Altcode:
No abstract at ADS
Title: Dynamics of the Chromosphere and Transition Region
Authors: Athay, R. G.
Bibcode: 1985IAUTA..19..108A
Altcode: 1985IAUT...19..108A
No abstract at ADS
Title: The origin of spicules and heating of the lower transition
region
Authors: Athay, R. G.
Bibcode: 1984ApJ...287..412A
Altcode:
A model of the solar corona and transition region is proposed in which
the atmosphere is kinematic rather than static. The kinematic character
results from an assumed lack of stationarity in the energy input, which
is considered to fluctuate both spatially and temporally. Fluctuations
in the energy input lead to two types of atmospheric regions: one
that is experiencing a diminishing heating rate and another that is
experiencing an increasing heating rate. Regions of diminishing heating
are associated with decreasing temperatures and downflow, whereas
regions of increasing heating are associated with rising temperatures
and upflow. Spicules are a possible manifestation of the upflow as an
aftermath of the downflow. The heating of spicule material results in
an emission measure closely resembling that observed in the temperature
range 30,000-300,000 K.
Title: Are Extreme Ultraviolet Bursts Members of the Flare Family
Authors: Athay, R. G.
Bibcode: 1984SoPh...93..123A
Altcode:
A number of properties of EUV bursts are found to be consistent with
the conclusion that they are at the low energy extreme of the family
of events including flares. The incidence of EUV bursts exceeds that of
flares by over two orders of magnitude, which suggests the possibility
that, in total, they may be as important energetically as flares. The
faster EUV bursts have light curves resembling those observed in hard
X-rays at the times of flares.
Title: SMM / Solar Maximum Mission / UVSP Observations of the
Distribution of Transition Region Oscillations and Other Properties
in a Sunspot
Authors: Henze, W.; Tandberg-Hanssen, E.; Reichmann, E. J.; Athay,
R. G.
Bibcode: 1984SoPh...91...33H
Altcode:
Observations of a sunspot in the CIV line at 1548 Å formed in the
transition region have been analyzed to obtain the time variations
and/or mean values of the velocity, intensity, longitudinal magnetic
field, and line width. Oscillations with periods between approximately
110 and 200 s are observed only over the umbra where the transition
region magnetic field is highest and the line width is smallest. When
periodic intensity variations occur at the same frequency as the
velocity oscillations, the peak intensities occur slightly before the
maximum upward motions. No periodic variations in the transition region
magnetic field have been detected. Scatter diagrams are presented which
show possible relationships between the flow velocity, emission line
intensity, line width, and transition region magnetic field.
Title: Probabilistic equations for line source functions: accurate
and approximate.
Authors: Athay, R. G.
Bibcode: 1984mrt..book...79A
Altcode: 1984mrt..conf...79A
An exact expression for line source functions is derived in terms of
the local and non-local probabilities for gaining and losing photons
in the bandwidth of the line. Examples of exact and approximate
solutions are given for Voigt profiles, for constant and variable
Planck function, and for constant and variable Doppler width. Two
approximate second-order differential equations are derived in terms of
purely local probabilities for gaining and losing photons. Examples of
solutions using terms in first-order differentials demonstrate that
the approximate equations are quite accurate for both constant and
variable Planck functions.
Title: Probabilistic Equations for Line Source Functions - Accurate
and Approximate
Authors: Athay, R. G.
Bibcode: 1984mrt..book...29A
Altcode:
No abstract at ADS
Title: Vector Magnetic Fields in Prominences - Part Three - Hei d3
Stokes Profile Analysis for Quiescent and Eruptive Prominences
Authors: Athay, R. G.; Querfeld, C. W.; Smartt, R. N.; Landi
Degl'Innocenti, E.; Bommier, V.
Bibcode: 1983SoPh...89....3A
Altcode:
Observations of linear polarization in two resolved components of HeI
D3 are interpreted using the Hanle effect to determine vector
magnetic fields in thirteen prominences. As in all vector magnetic
field measurements, there is a two-fold ambiguity in field direction
that is symmetric to a 180° rotation about the line-of-sight. The
polar angles of the fields show a pronounced preference to be close to
90° from the local solar radius, i.e., the field direction is close
to horizontal. Azimuth angles show internal consistency from point to
point in a given prominences, but because of the rotational symmetry,
the fields may be interpreted, in most cases, as crossing the prominence
either in the same sense as the underlying photospheric fields or in
the opposite sense.
Title: Fluid motions in the solar chromosphere-corona transition
region. IV - Mass motions over sunspot umbrae
Authors: Gurman, J. B.; Athay, R. G.
Bibcode: 1983ApJ...273..374G
Altcode:
Doppler velocity measurements in the C IV resonance line λ1548.19 have
been obtained over the umbrae of eight sunspots with the Ultraviolet
Spectrometer and Polarimeter (UVSP) on the Solar Maximum Mission. The
velocity bandpass of these observations is approximately ±30 km
s-1, and their spatial resolution is 3" × 3". Although a
few individual resolution elements display flow velocities ∼ ±15
km s-1 relative to the quiet network, we measure a mean
upflow of (1.2 ± 5.6) km s-1 when averaged over all the
resolution elements. Means over individual umbrae frequently show
smaller variances, which is evidence for a real distribution of umbral
transition region velocity fields. We also examine two possible
explanations for the smaller nonthermal broadening of the sunspot C
IV line.
Title: Fluid motions in the solar chromosphere-corona transition
region. III - Active region flows from wide slit Dopplergrams
Authors: Athay, R. G.; Gurman, J. B.; Henze, W.
Bibcode: 1983ApJ...269..706A
Altcode:
Large-scale velocity patterns observed in C IV in active regions show
close correspondence with photospheric magnetic field patterns. In a
large majority of cases, magnetic neutral lines show blueshift on their
sun center side and redshift on their limbward side. The large-scale
flow is consistent with widespread loop structure having downflow in
both legs of the loops. Studies of individual bright loops, confirm
that the flow is downward in most cases. However, an important subset
of loops show flow from one end of the loop to the other.
Title: Photospheric, Chromospheric and Transition-Region Flows in
AR 2517
Authors: Athay, R. G.; Jones, H. P.; Zirin, H.
Bibcode: 1983BAAS...15Q.719A
Altcode:
No abstract at ADS
Title: Fluid motions in the solar chromosphere-corona transition
region. I - Line widths and Doppler shifts for C IV
Authors: Athay, R. G.; Gurman, J. B.; Henze, W.; Shine, R. A.
Bibcode: 1983ApJ...265..519A
Altcode:
Matrices of line profiles for C IV, λ1548, observed with a 3" aperture
and sampled in 3" intervals in active and quiet solar regions, show
a pronounced tendency for line width to increase with increasing
redshift. The correlation between increasing central intensity of the
line and increasing redshift demonstrated by some authors is clearly
present in these data but is weakened by the not infrequent occurrence
of regions of strong redshift but with low intensity. Sunspots show
both systematically narrower line profiles over umbral areas and strong
redshifts on their Sun-center side. The latter result is consistent
with a reverse Evershed effect.
Title: Responses of transition region models to magnetic field
geometry and downflow velocities
Authors: Athay, R. G.
Bibcode: 1982ApJ...263..982A
Altcode:
Models of the chromosphere-corona transition region in which energy
is supplied by thermal conduction and downflow of hot material and
lost by radiation are investigated for different magnetic field
geometries and for different dependences of downflow velocity on the
local temperature. It is shown that neither the field geometry nor
the dependence of velocity on temperature are important factors in
the comparison of empirical and theoretical emission measures. Each
of the models works well for T higher than 250,000 K but fails badly
for temperatures lower than that.
Title: Fluid motions the solar chromosphere-corona transition
region. II Active region flows in C IV from narrow slit Dopplergrams
Authors: Athay, R. G.; Gurman, J. B.; Shine, R. A.; Henze, W.
Bibcode: 1982ApJ...261..684A
Altcode:
From a study of Dopplergrams made with two narrow slits in the opposite
wings of the C IV line, N λ1548, we find widespread evidence for
steady flow patterns associated with large sunspots and, on a larger
scale, with active region magnetic field patterns. The characteristic
sunspot flow is in the reverse Evershed sense with a substantial
vertical component. Active region flows indicate oppositely directed
velocities with mainly horizontal components on either side of magnetic
neutral lines. Some neutral lines show flow toward the neutral line,
whereas others show flow away from the neutral line.
Title: The role of spicules in heating the solar atmosphere
Authors: Athay, R. G.; Holzer, T. E.
Bibcode: 1982ApJ...255..743A
Altcode:
From observations of downflowing material at transition region
temperature, together with reasonable assumptions about the fate
of spicules after they disappear from view in the visual spectrum,
it is shown that the rise and fall of spicular material can supply
the thermal energy required by radiative losses from the transition
region and upper chromosphere in the network. If sufficient heat
is added to spicules, in conjunction with their acceleration, the
spicule phenomenon may also play a major role in the production and
maintenance of much of the solar corona. Thus, the processes whereby
spicules are generated and heated may be of central importance to the
energy balance of the outer solar atmosphere. This conclusion points
to the need for developing an understanding of the acceleration and
heating of spicules and to the need for observations of spicules after
they have disappeared in the visual spectrum.
Title: Chromospheric structure in relation to radiation losses.
Authors: Athay, R. G.
Bibcode: 1982SAOSR.392A...3A
Altcode: 1982csss....2....3A
It is assumed that cool star chromospheres are heated by mechanical
energy dissipation that depends quasilinearly on density and cooled
by radiation loss and it is shown that the basic properties of
chromospheres are determined by the ionization of hydrogen. It is
hydrogen ionization that provides the freedom for chromospheres
to adjust their radiation losses to balance the prescribed
heat input, resulting in an extended region of low temperature
gradient. Chromospheric radiation losses in cool stars occur mainly in
the strongest spectral lines at wavelengths greater than about 2000
A and the fraction of the chromosphere is effectively thin. The most
important lines include Ca II H and K and the infrared triplet and Mg II
h and k. The strong lines of other abundant species, are less important
because their high excitation energies reduce the collisional excitation
rates. Lyman alpha losses are important because of the overwhelming
abundance of hydrogen. However, the inability of chromospheres to
adjust their Lyman alpha losses limits the geometrical thickness of
the effectively thin region in Lyman alpha and limits the total Lyman
alpha flux.
Title: Steady flows in the solar transition region observed with SMM
Authors: Gebbie, K. B.; Hill, F.; November, L. J.; Gurman, J. B.;
Shine, R. A.; Woodgate, B. E.; Athay, R. G.; Tandberg-Hanssen, E. A.;
Toomre, J.; Simon, G. W.
Bibcode: 1981ApJ...251L.115G
Altcode:
Steady flows in the quiet solar transition region have been observed
with the Ultraviolet Spectrometer and Polarimeter experiment on the
Solar Maximum Mission (SMM) satellite. The persistent vertical motions
seen at disk center have spatial rms amplitudes of 1.4 km/s in the C
II line, 3.9 km/s in Si IV, and 4.2 km/s in C IV. The amplitudes of
the more horizontal flows seen toward the limb tend to be somewhat
higher. Plots of steady vertical velocity versus intensity seen at
disk center in Si IV and C IV show two distinct branches.
Title: Stellar chromospheres and coronae
Authors: Athay, R. G.
Bibcode: 1981ApJ...250..709A
Altcode:
An attempt is made to provide an updated explanation of the essential
structure features of the solar atmosphere based, where possible,
on the constraints imposed by the physics of the solar plasma. The
chromospheric temperature plateaus are identified with plasma properties
determined by the degree of ionization of hydrogen. This is possible
because the energy loss is solely by radiation and the nature of
the radiation loss changes rather discontinuously as the degree of
ionization increases. The ionization conditions are discussed in
relation to other stars. In the case of the transition region and
the corona, the plasma is essentially fully ionized and, in addition,
the role of radiation enters somewhat indirectly.
Title: Chromosphere-corona transition region models with magnetic
field and fluid flow
Authors: Athay, R. G.
Bibcode: 1981ApJ...249..340A
Altcode:
Energy balance models of the chromosphere-corona transition region are
computed for a segment of average sun network using assumed magnetic
field geometry. The energy fluxes considered include radiation,
conduction, enthalpy, and gravitational potential energy, but do not
include mechanical heating. Two classes of models are considered:
conduction driven and flow driven. In the former class, the thermal
conductive flux vanishes at the base of the transition region, and
in the latter class the thermal conductive flux increases with depth
or remains constant. The conduction driven models require primarily
outflow, whereas the flow driven models require downflow. Flow-driven
models give best overall agreement with observations for T between
300,000 and 1,000,000 K, but neither class of models is satisfactory for
T less than 100,000 K. It is concluded however, that the flow-driven
models have ample energy supply even in the low transition region,
and there is no apparent need for additional energy sources.
Title: The chromosphere and transition region.
Authors: Athay, R. G.
Bibcode: 1981NASSP.450...85A
Altcode: 1981suas.nasa...85A
An empirical definition of the chromosphere and chromosphere-corona
transition region is presented. Various general characteristics of
the chromosphere are described and include: radiative equilibrium;
spatial and temporal fluctuations; spectral characteristics; and
thermodynamic structure.
Title: Stellar chromospheres and coronae.
Authors: Athay, R. G.
Bibcode: 1981BAAS...13..547A
Altcode:
No abstract at ADS
Title: Preliminary observations and results obtained with the
ultraviolet spectrometer and polarimeter
Authors: Tandberg-Hanssen, E.; Cheng, C. C.; Athay, R. G.; Beckers,
J. M.; Brandt, J. C.; Chapman, R. D.; Bruner, E. C.; Henze, W.; Hyder,
C. L.; Gurman, J. B.
Bibcode: 1981ApJ...244L.127T
Altcode:
New observation with the Ultraviolet Spectrometer and Polarimeter
(UVSP) of a number of manifestations of solar activity obtained
during the first three months of Solar Maximum Mission operations are
presented. Attention is given to polarimetry in sunspots, oscillations
above sunspots, density diagnostics of transition-zone plasmas in
active regions, and the eruptive prominence - coronal transient link.
Title: SMM/UVSP Observations of Oscillations and Other Properties
in a Sunspot
Authors: Henze, W.; Tandberg-Hanssen, E.; Reichmann, E. J.; Shine,
R. A.; Woodgate, B. E.; Gurman, J. B.; Athay, R. G.
Bibcode: 1981BAAS...13..858H
Altcode:
No abstract at ADS
Title: Stellar Chromospheres and Coronae
Authors: Athay, R. G.
Bibcode: 1981BAAS...13Q.545A
Altcode:
No abstract at ADS
Title: Active Region Flows in the Transition Region
Authors: Athay, R. G.; Gurman, J. B.; Henze, W.
Bibcode: 1981BAAS...13..914A
Altcode:
No abstract at ADS
Title: Solar maximum mission experiment: Ultraviolet spectroscopy
and polarimetry on the solar maximum mission
Authors: Tandberg-Hanssen, E.; Cheng, C. C.; Woodgate, B. E.; Brandt,
J. C.; Chapman, R. D.; Kenney, P. J.; Michalitsianos, A. G.; Shine,
R. A.; Athay, R. G.; Beckers, J. M.; Bruner, E. C.; Rehse, R. A.;
Schoolman, S. A.; Gurman, J. B.; Hyder, C. L.; Henze, W.
Bibcode: 1981AdSpR...1m.275T
Altcode: 1981AdSpR...1..275T
We describe the Ultraviolet Spectrometer and Polarimeter (UVSP) on the
Solar Maximum Mission (SMM) spacecraft. The instrument, which operates
in the wavelength range 1150 - 3600 Å, has a spatial resolution of 2-3
arc sec and a spectral resolution of 0.02 Å FWHM in second order. A
Gregorian telescope, focal length 1.8 m, feeds a 1 m Ebert-Fastie
spectrometer. A polarimeter comprising rotating Mg F2
waveplates can be inserted behind the spectrometer entrance slit and
allows all four Stokes parameters to be determined. The observing
modes include rasters, spectral scans, velocity measurements, and
polarimetry. Finally, we present examples of initial observations made
since launch.
Title: Observations of mass motions in ctive regions.
Authors: Athay, R. G.
Bibcode: 1981sars.work...83A
Altcode:
Results of observations from Skylab, ground-based instruments and OSO 8
indicators of mass motions in solar active regions are reviewed. The
flows detected are classified as steady, including supergranular
flow, Evershed flow and chromosphere and transition region flows;
quasi-steady, including fibril motions, spicules, coronal rain and
coronal loops; transient, including surges and sprays and EUV bursts;
oscillations; and nonthermal line widths due to unresolved fluid
motions.
Title: Solar Maximum Mission experiment: ultraviolet spectroscopy
and polarimetry on the Solar Maximum Mission.
Authors: Tandberg-Hanssen, E.; Woodgate, B. E.; Athay, R. G.; Beckers,
J. M.; Brandt, J. C.; Bruner, E. C.; Chapman, R. D.; Cheng, C. -C.;
Gurman, J. B.; Hyder, C. L.; Kenney, P. J.; Michalitsianos, A. G.;
Rehse, R. A.; Schoolman, S. A.; Shine, R. A.; Henze, W.
Bibcode: 1981hea..conf..275T
Altcode:
No abstract at ADS
Title: Steady Flows in the Solar Transition Region Observed with
the UVSP Experiment on SMM
Authors: Gebbie, K. B.; Hill, F.; Toomre, J.; November, L. J.; Simon,
G. W.; Athay, R. G.; Bruner, E. C.; Rehse, R.; Gurman, J. B.; Shine,
R. A.; Woodgate, B. E.; Tandberg-Hanssen, E. A.
Bibcode: 1980BAAS...12..907G
Altcode:
No abstract at ADS
Title: Transition Region Oscillations in Sunspots
Authors: Gurman, J. B.; Shine, R. A.; Woodgate, B. E.;
Tandberg-Hanssen, E. A.; Bruner, E. C.; Schoolman, S. A.; Athay, R. G.
Bibcode: 1980BAAS...12..906G
Altcode:
No abstract at ADS
Title: Temporal and spatial fluctuations in strengths and widths of
C IV and SI II lines observed with OSO 8
Authors: Athay, R. G.; White, O. R.
Bibcode: 1980ApJ...240..306A
Altcode:
The spatial and temporal fluctuations in widths and strengths
are examined for three EUV lines: C IV, wavelength 1548 and Si II,
wavelengths 1816.93 and 1817.45 observed with an effective aperture of
2 x 20 arcsec and with time resolution less than 30 s. Three classes
of fluctuations with substantial amplitude are identified: (1) short
term fluctuations with a characteristic fluctuation time near 5 min,
(2) intermediate term fluctuations with a characteristic time of 30
min or longer, and (3) large scale spatial fluctuations associated
with supergranule cell, network, and plage structure.
Title: Impulsive EUV bursts observed in C iv with OSO-8
Authors: Athay, R. G.; White, O. R.; Lites, B. W.; Bruner, E. C., Jr.
Bibcode: 1980SoPh...66..357A
Altcode:
Time sequences of profiles of the λ1548 line of C IV containing 51 EUV
bursts observed in or near active regions are analyzed to determine the
brightness, Doppler shift and line broadening characteristics of the
bursts. The bursts have mean lifetimes of approximately 150s, and mean
increases in brightness at burst maximum of four-fold as observed with a
field of view of 2″ × 20″. Mean burst diameters are estimated to be
3″, or smaller. All but three of the bursts show Doppler shifts with
velocities sometimes exceeding 75 km s−1; 31 are dominated
by red shifts and 17 are dominated by blue shifts. Approximately
half of the latter group have red-shifted precursors. We interpret
the bursts as prominence material, such as surges and coronal rain,
moving through the field of view of the spectrometer.
Title: The Ultraviolet Spectrometer and Polarimeter (UVSP) on the
Solar Maximum Mission and Initial Results in Polarimetry
Authors: Tandberg-Hanssen, E.; Athay, R. G.; Bruner, E. C.; Beckers,
J. M.; Brandt, J. C.; Chapman, R. D.; Cheng, C. C.; Gurman, J.;
Henze, W.; Brown, Teledyne; Hyder, C. L.; Michalitsianos, A. G.;
Shine, R. A.; Schoolman, S. A.; Woodgate, B. E.
Bibcode: 1980BAAS...12..534T
Altcode:
No abstract at ADS
Title: Temporal and Spatial Fluctuations in Widths of Solar EUV Lines
Authors: Athay, R. G.; White, O. R.
Bibcode: 1980LNP...114...53A
Altcode: 1980IAUCo..51...53A; 1980sttu.coll...53A
No abstract at ADS
Title: Chromospheric oscillations observed with OSO 8. IV. Power
and phase spectra for C IV.
Authors: Athay, R. G.; White, O. R.
Bibcode: 1979ApJ...229.1147A
Altcode:
OSO 8 time series of profiles of the C IV line at 1548 A and for the
continuum near 1900 A are analyzed to determine the properties of
solar oscillations in the lower transition region and to obtain phase
delays between the temperature-minimum region and the lower transition
region. Power-spectrum and phase-spectrum analyses of 30-min data
segments are performed. It is found that: (1) short-duration periodic
oscillations in the 3-5 mHz band occur in about 20% of the 30-min
segments; (2) these oscillations are of solar origin and have phase
delays with height characteristic of waves propagating vertically
with phase speeds close to the sound speed; (3) maximum intensity
lags maximum redshift by about 120 deg and leads maximum blueshift
by approximately 60 deg; (4) most of the solar fluctuations in the C
IV line are low-amplitude aperiodic events in which the fluctuation
in intensity is correlated with blueshift; and (5) the intensity
fluctuations are proportional to mean intensity (A) in bright solar
features but to the square root of A in quiet solar regions.
Title: Chromospheric Oscillations Observed with OSO 8. II. Average
Phase Spectra for SI II.
Authors: White, O. R.; Athay, R. Grant
Bibcode: 1979ApJS...39..347W
Altcode:
Time series of intensity and Doppler-shift fluctuations in the Si II
emission lines λ1816.93 and λ1817.45 are Fourier analyzed to determine
the frequency variation of phase differences between intensity and
velocity and between these two lines formed 300 km apart in the middle
chromosphere. Average phase spectra show that oscillations between
2 and 9 mHz in the two lines have time delays from 35 to 40s, which
is consistent with the upward propagation of sound waves at 8. 7.5
km s-1. In this same frequency band near 3 mHz, maximum
brightness leads maximum blueshift by 600. At frequencies above 11 mHz
where the power spectrum is flat, the phase differences are uncertain,
but approximately 65% of the cases indicate upward propagation. At these
higher frequencies, the phase lead between intensity and blue Doppler
shift ranges from 0° to 180° with an average value of 90°. However,
the phase estimates in this upper band are corrupted by both aliasing
and randomness inherent to the measured signals. Phase differences in
the two narrow spectral features seen at 10.5 and 27 mHz in the power
spectra are shown to be consistent with properties expected for aliases
of the wheel rotation rate of the spacecraft wheel section.
Title: Chromospheric oscillations observed with OSO 8. I. Basic
measurements and analytical methods.
Authors: White, O. R.; Athay, R. G.
Bibcode: 1979ApJS...39..317W
Altcode:
Time series of solar EUV line profiles observed with OSO 8 have
fluctuations arising from instrumental, satellite, and solar
sources. The fluctuations are partly noiselike, partly from long-term
drifts, and partly from periodic oscillations. The Sun contributes to
all three types of fluctuations. However, instrumental effects also
contribute to the noiselike fluctuations and long-term drifts, and
the satellite wheel rotation induces spurious oscillations. Analytical
procedures are discussed for applying Fourier transform techniques and
related statistical tests to isolate the different types of fluctuations
and, in particular, to study the solar oscillations. Strong solar
oscillations are identified near 3 mHz, and aliases of the wheel
rotation frequency are identified at 10.5 and 27 mHz.
Title: Solar maximum ultraviolet spectrometer and polarimeter
Authors: Tandberg-Hanssen, E.; Woodgate, B. E.; Brandt, J. C.;
Chapman, R. D.; Hyder, C. L.; Michalitsianos, A. G.; Shine, R. A.;
Athay, R. G.; Beckers, J. M.; Bruner, E. C.
Bibcode: 1979SPIE..184..264T
Altcode:
The objectives of the UVSP experiment are to study solar ultraviolet
radiations, particularly from flares and active regions, and to measure
constituents in the terrestrial atmosphere by the extinction of sunlight
at satellite dawn and dusk. The instrument is designed to observe the
Sun at a variety of spectral and spatial resolutions in the range from
1150 to 3600 A. A Gregorian telescope with effective focal length of
1.8 m is used to feed a 1 m Ebert-Fastie spectrometer. A polarimeter
containing rotatable magnesium fluoride waveplates is included behind
the spectrometer entrance slit and will allow all four Stokes parameters
to be determined. Velocities on the Sun can also be measured. The
instrument is controlled by a computer which can interact with the data
stream to modify the observing program. The observing modes, including
rasters, spectral scans, velocity measurements, and polarimetry, are
also described along with plans for mission operations, data handling,
and analysis of the observations.
Title: Chromospheric and coronal heating by sound waves.
Authors: Athay, R. G.; White, O. R.
Bibcode: 1978ApJ...226.1135A
Altcode:
An upper limit to the energy flux in sound waves in the chromosphere
is obtained from observational data, and the required heat input to
the chromosphere is examined. The height dependence of both the energy
flux in sound waves and the required heat input is analyzed. It is
found that the heat input has two maxima and that the flux in sound
waves is too low to produce the second maximum. It is concluded
that the low chromosphere may be heated by sound waves but that a
different mechanism heats the upper chromosphere, transition region,
and corona. The possibility is considered that the microturbulence
derived from line broadening is produced by Alfven waves rather than
sound waves.
Title: Spectrum synthesis of chromospheric lines of Si II and Si III.
Authors: Tripp, D. A.; Athay, R. G.; Peterson, V. L.
Bibcode: 1978ApJ...220..314T
Altcode:
Profiles of emission lines of Si II and Si III in the EUV spectrum
near the solar limb and near disk center are synthesized using a range
of temperature and microturbulence models. Reasonably good agreement
between computed and observed profiles near disk center is obtained with
the Vernazza, Avrett, and Loeser (VAL, 1973) temperature model but with
a modified microturbulence model. The adopted microturbulent velocity is
equal to the mean thermal velocity of hydrogen temperatures above 7000
K and, at lower temperatures, decreases linearly to a value of 1 km/s in
the low chromosphere. The 20,000-K temperature plateau in the VAL model
is found to be of importance in determining the central intensities
in the Si II lines at 1816, 1265, and 1533 A, and in determining the
total intensity of the Si III line at 1206 A. The VAL temperature model
with modified microturbulence does not give good agreement with the
observed profiles near the solar limb. This failure is attributed to
departures from spherical symmetry in the temperature and density model.
Title: Solar EUV emission line profiles of Si ii and Si iii and
their center to limb variations
Authors: Nicolas, K. R.; Brueckner, G. E.; Tousey, R.; Tripp, D. A.;
White, O. R.; Athay, R. G.
Bibcode: 1977SoPh...55..305N
Altcode:
Spectral line profiles of Si II and Si III are presented which were
observed both at solar center and near the quiet solar limb with the
Naval Research Laboratory EUV spectrograph of ATM/SKYLAB. Absolute
intensities and line profiles are derived from the photographic data. A
brief discussion is given of their center-to-limb variations and of
the optical thickness of the chromosphere in these lines. Nonthermal
broadening velocities are found for the optically thin lines from
their full width at half maximum intensity (FWHM).
Title: Modeling the solar photosphere and chromosphere
Authors: Athay, R. G.
Bibcode: 1977MmSAI..48..401A
Altcode:
Some aspects of modeling the solar photosphere and chromosphere with
allowance for the characteristics produced by hydrodynamic and magnetic
processes, on the basis of modern solar data are examined. The problem
of asigning heights, geometrical or optical, to specific features of
the solar atmosphere is discussed, along with the establishment of
reference points and height scales.
Title: Chromospheric motions observed by the University of Colorado
experiment on OSO-8
Authors: Athay, R. G.
Bibcode: 1977MmSAI..48..509A
Altcode:
The Harvard experiment flown on Skylab did not have a spectral
resolution sufficient to detect Doppler shifting of chromospheric and
chromosphere-corona transition lines. An experiment flown by the Naval
Research Laboratory on Skylab had sufficient spectral resolution to
study Doppler shifts, but did not have sufficient spatial and temporal
resolution for studying oscillations. The OSO-8 experiment discussed
in the present paper provided (for the first time) observations of the
EUV emission lines of the chromosphere and lower transition region
with sufficient spectral spatial, and temporal resolution to assess
the velocities associated with chromospheric oscillations and the
impulsive brightenings of the transition region lines. The associated
power spectra are given and discussed.
Title: Phase Differences Between Intensity and Doppler-Shift and
Between Two EUV Emission Lines of SI II for 300 SEC and 95 SEC
Chromospheric Oscillations.
Authors: White, O. R.; Athay, R. G.
Bibcode: 1977uxsa.coll...13W
Altcode: 1977IAUCo..43...13W
No abstract at ADS
Title: The Solar Chromosphere and Corona: Quiet Sun (Book Review)
Authors: Athay, R. G.
Bibcode: 1977ApL....19...29A
Altcode:
No abstract at ADS
Title: Power Spectrum Analysis of Time Series in Positions and
Intensities of Solar EUV Lines Observed with OSO-8.
Authors: Athay, R. G.; White, O. R.
Bibcode: 1977uxsa.coll...12A
Altcode: 1977IAUCo..43...12A
No abstract at ADS
Title: Preliminary results from the Orbiting Solar Observatory 8:
transition-zone dynamics over a sunspot.
Authors: Bruner, E. C., Jr.; Chipman, E. G.; Lites, B. W.; Rottman,
G. J.; Shine, R. A.; Athay, R. G.; White, O. R.
Bibcode: 1976ApJ...210L..97B
Altcode:
No abstract at ADS
Title: Preliminary results from the Orbiting Solar Observatory 8:
velocities in the solar chromosphere observed in the Si II lambda
1816 line.
Authors: Chipman, E. G.; Bruner, E. C., Jr.; Shine, R. A.; Lites,
B. W.; Rottman, G. J.; Athay, R. G.; White, O. R.
Bibcode: 1976ApJ...210L.103C
Altcode:
No abstract at ADS
Title: Preliminary results from the Orbiting Solar Observatory 8:
observations of optically thin lines.
Authors: Shine, R. A.; Roussel-Dupre, D.; Bruner, E. C., Jr.; Chipman,
E. G.; Lites, B. W.; Rottman, G. J.; Athay, R. G.; White, O. R.
Bibcode: 1976ApJ...210L.107S
Altcode:
The University of Colorado spectrometer aboard OSO 8 has measured
the high temperature C IV resonance lines (at 1548 and 1551 A) and
the Si IV resonance lines (at 1393 and 1402 A) formed in the solar
chromosphere-corona transition region. Preliminary results include
studies of mean profiles, a comparison of cell and network profiles,
and the behavior of the lines at the extreme solar limb.
Title: Preliminary results from the Orbiting Solar Observatory 8:
persistent velocity fields in the chromosphere and transition region.
Authors: Lites, B. W.; Bruner, E. C., Jr.; Chipman, E. G.; Shine,
R. A.; Rottman, G. J.; White, O. R.; Athay, R. G.
Bibcode: 1976ApJ...210L.111L
Altcode:
No abstract at ADS
Title: Periodic Fluctuations in the Solar Transition Zone
Authors: Bruner, E. C., Jr.; Chipman, E. G.; Shine, R. A.; Lites,
B. W.; Rottman, G. J.; Orrall, F. Q.; Athay, R. G.; White, O. R.
Bibcode: 1976BAAS....8Q.313B
Altcode:
No abstract at ADS
Title: Model Calculations of Chromospheric Lines Observed by OSO-8
Authors: Shine, R. A.; Lites, B. W.; Chipman, E. G.; Rousel-Dupree,
D.; Bruner, E. C., Jr.; Rottman, G. J.; Orrall, F. Q.; Athay, R. G.;
White, O. R.
Bibcode: 1976BAAS....8..331S
Altcode:
No abstract at ADS
Title: Velocities in the Solar Chromosphere Observed in the CII
λ1336 Line
Authors: Chipman, E. G.; Bruner, E. C., Jr.; Shine, R. A.; Lites,
B. W.; Rottman, G. J.; Orrall, F. Q.; White, O. R.; Athay, R. G.
Bibcode: 1976BAAS....8..312C
Altcode:
No abstract at ADS
Title: OSO-8 Observations of Mean Vertical Motions in the Solar
Transition Region
Authors: Roussel-Dupree, D. C.; Shine, R. A.; Chipman, E. G.; Bruner,
E. C., Jr.; Lites, B. W.; Rottman, G. J.; Orrall, F. Q.; Athay, R. G.;
White, O. R.
Bibcode: 1976BAAS....8..312R
Altcode:
No abstract at ADS
Title: Short Period Chromospheric Oscillations Observed with OSO-8
Authors: Athay, R. G.; White, O. R.; Bruner, E. C., Jr.; Chipman,
E. G.; Lites, B. W.; Shine, R. A.; Orrall, F. Q.
Bibcode: 1976BAAS....8..312A
Altcode:
No abstract at ADS
Title: Supergranulation Velocity Fields Observed in the Solar
Transition Region with OSO-8
Authors: November, L. J.; Toomre, J.; Gebbie, K. B.; Simon, G. W.;
Bruner, E. C., Jr.; Chipman, E. G.; Lites, B. W.; Shine, R. A.;
Orrall, F. Q.; Athay, R. G.; White, O. R.
Bibcode: 1976BAAS....8..311N
Altcode:
No abstract at ADS
Title: Repetitive Brightenings in Active Region Transition Zone
Lines as Observed with OSO-8
Authors: Lites, B. W.; Hansen, E. R.; Shine, R. A.; Chipman, E. G.;
Bruner, E. C., Jr.; Orrall, F. Q.; Athay, R. G.; White, O. R.; Rottman,
G. J.
Bibcode: 1976BAAS....8Q.331L
Altcode:
No abstract at ADS
Title: Probabilistic radiative transfer: an integral-equation
approach.
Authors: Athay, R. G.
Bibcode: 1976ApJ...204..160A
Altcode:
The kinetic equilibrium equations of radiative transfer and
steady-state populations of energy levels are formulated in terms of
the probabilities for photon creation, destruction, and transport. This
new formulation is used to derive an approximate equation, a special
case of which has been used elsewhere. The probabilistic formulation
leads to new approaches for obtaining rapid, approximate solutions,
and, in addition, is amenable to solution by lambda iteration.
Title: The solar chromosphere and corona: Quiet sun
Authors: Athay, R. G.
Bibcode: 1976ASSL...53.....A
Altcode: 1976scco.conf.....A; 1976assl...53.....A; 1975ASSL...53.....A
This volume treats the chromosphere and corona of the quiet sun as a
unified topic, stressing their common origin in the mechanical-energy
flux generated in the hydrogen convection zone beneath the
photosphere. It is noted at the outset that the sharply different
physical regimes occurring in the corona and the chromosphere are
related to the response of the atmosphere to the mechanical-energy input
rather than to fundamentally different mechanisms of energy input. A
broad overview of the methods and objectives of chromospheric and
coronal studies is presented, and analytical methods for interpreting
spectroscopic data are described. The major questions dealt with include
structures observed in the photosphere, chromosphere, and corona;
macroscopic motions in the solar atmosphere; solar magnetic-field
phenomena; spectral characteristics of the chromosphere and corona;
analyses of IR, radio, and XUV spectral data; empirical models of
the chromosphere and corona; the chromospheric structure inferred
from spectral lines; wave generation in the sun; and heating of the
chromosphere and corona.
Title: An Archetype Hydrogen Atmosphere Problem
Authors: Athay, R. G.; Mihalas, D.; Shine, R. A.
Bibcode: 1975SoPh...45...15A
Altcode:
Populations for the first three bound states and the continuum of
hydrogen are determined for an isothermal, hydrostatic atmosphere at 20
000 K. The atmosphere is treated as being optically thin in the Balmer
and Paschen continua and illuminated by continuum radiation at these
wavelengths with prescribed radiation temperatures. The atmosphere is
optically thick in the 2-1, 3-1, 3-2 and c-1 transitions. Three stages
of approximation are treated: radiative detailed balance in the 2-1,
3-1 and 3-2 transitions,
Title: High Resolution Spectroscopy From Orbiting Solar Observatory
VIII: Transition Zone Dynamics Over a Sunspot
Authors: Bruner, E. C., Jr.; Chipman, E. G.; Lites, B. W.; Rottman,
G. J.; Shine, R. A.; Athay, R. G.; White, O. R.
Bibcode: 1975BAAS....7..522B
Altcode:
No abstract at ADS
Title: Persistent Velocity Fields in the Middle Chromosphere
Authors: Lites, B. W.; Bruner, E. C., Jr.; Chipman, E. G.; Shine,
R. A.; Rottman, G. J.; White, O. R.; Athay, R. G.
Bibcode: 1975BAAS....7..522L
Altcode:
No abstract at ADS
Title: Velocities in the Solar Chromosphere Observed in the Si II
λ1816 Line
Authors: Chipman, E. G.; Bruner, E. C., Jr.; Shine, R. A.; Lites,
B. W.; Rottman, G. J.; White, O. R.; Athay, R. G.
Bibcode: 1975BAAS....7..522C
Altcode:
No abstract at ADS
Title: OSO-8 Observations of Optically Thin Lines
Authors: Shine, R. A.; Rousell-Dupree, D.; Bruner, E. C., Jr.; Chipman,
E. G.; Lites, B. W.; Rottman, G. J.; Athay, R. G.; White, O. R.
Bibcode: 1975BAAS....7Q.552S
Altcode:
No abstract at ADS
Title: Theoretical Chromospheric Flare Spectra. I: Hydrogen
Equilibrium for the Kinematic Flare-Shock Models of Nakagawa et
al. (1973)
Authors: Canfield, Richard C.; Athay, R. Grant
Bibcode: 1974SoPh...34..193C
Altcode:
We simultaneously solve the equations of radiative transfer and
statistical equilibrium for a model hydrogen atom including Lyman-α,
Lyman-β, Balmer-α and the Lyman, Balmer and Paschen continua. The
model atmospheres we use are the results of Nakagawa et al. (1973)
for a kinematic model of the chromospheric solar flare.
Title: Radiation Pressure in Stellar Atmospheres with Application
to Solar Spicules
Authors: Athay, R. G.
Bibcode: 1974IAUS...56...23A
Altcode:
No abstract at ADS
Title: Chromospheric fine structure: proceedings from IAU Symposium
no. 56 held at Surfer's Paradise, Qld., Australia, 3-7 September 1973.
Authors: Athay, R. Grant
Bibcode: 1974IAUS...56.....A
Altcode: 1974QB528.C48......; 1974IAUS...56.....B
No abstract at ADS
Title: Problems in Coronal Physics.
Authors: Athay, R. G.
Bibcode: 1973BAAS....5..419A
Altcode:
No abstract at ADS
Title: Coronal Density and Temperature Gradients
Authors: Athay, R. Grant
Bibcode: 1973SoPh...29..357A
Altcode:
Mean density models of the solar corona show evidence for two
distinctive density regimes characterized by different density
gradients. High density gradients are identified with regions of
predominantly open magnetic lines of force and low density gradients
are identified with regions of predominantly closed magnetic lines
of force. Spectroscopic data yielding equivalent widths of forbidden
lines of Fe X and Fe XIV strongly suggest that the coronal temperature
for r > 2.5 R⊙ decreases considerably less rapidly
in equatorial regions than r−2/7, which is the decrease
predicted by conduction models with open field lines.
Title: Radiation and structure of the solar atmosphere (Radiation
et structure de l'atmosphère solaire).
Authors: Athay, R. G.; Delbouille, L.; Pierce, A. K.; Rigutti, M.
Bibcode: 1973IAUTA..15..129A
Altcode:
No abstract at ADS
Title: The Effects of Departures from LTE in Stellar Spectra
Authors: Mihalas, Dimitri; Athay, R. Grant
Bibcode: 1973ARA&A..11..187M
Altcode:
No abstract at ADS
Title: F i Ionization and Excitation Equilibrium in the Solar
Atmosphere
Authors: Athay, R. Grant; Lites, B. W.
Bibcode: 1972ApJ...176..809A
Altcode:
Computations for a 15-level model Fe I atom in the solar atmosphere
indicate that many of the Fe I spectral lines are strongly influenced
by departures from LTE. The strong lines originating from the ground
term and low-lying metastable terms have a strong chromospheric
contribution. Although for many of the lines the source functions
saturate to the Planck function near the temperature minimum
(τ_5000 ≈ 10-4) and lower, the ionization equilibrium
does not saturate to the Saha condition until τ_5000 > 3 ×
10-3. The low-lying levels in Fe I reach maximum absolute
populations near τ_5000 = 3 × 10-3, and lines originating
from these levels tend to be formed at atmospheric depths where τ_5000;
≤ 3 × 10-3. For high-excitation levels in Fe I, departures
of the line source function from the Planck function extend deeper
into the photosphere and may influence abundances derived from lines
originating from these high lying levels. From the weakness of the
principal Fe II lines in the far-ultraviolet (λ2599, in particular)
relative to lines of Si II and Mg II it is suggested that the Fe II
f-values of Corliss and Bozman are too high by a factor of the order of
10+2. Fe I photoionization from the lowest levels may be a significant
source of opacity in the region 1600-2000 Å.
Title: A Probabilistic Formulation of the Noncoherent-Scattering
Problem
Authors: Athay, R. Grant
Bibcode: 1972ApJ...176..659A
Altcode:
The noncoherent-scattering problem is formulated in terms of the
mean intensity J, averaged over the absorption profile and the mean
number of scatterings required for photon escape. This leads to major
simplifications in the resultant equations for j. In particular,
the integration over frequency is taken into account at each step,
and it is no longer necessary to integrate the final equations over
frequency. Also, use of the mean intensity eliminates the need to
integrate over angle. Thus, the usual equations in three dimensions
(optical depth, frequency, and direction angle) are replaced by a
first-order differential equation in one dimension (mean number of
scatterings). For certain idealized problems algebraic solutions are
readily obtained. The method appears to offer major simplifications
for problems dealing with multidimensional media.
Title: A First Order Analysis of Variations of the Limb Darkening
and the Shapes for Solar Fraunhofer Lilnes
Authors: Athay, R. G.; Lites, B. W.; White, O. R.; Brault, J. W.
Bibcode: 1972SoPh...24...18A
Altcode:
New center-to-limb measurements in FeI lines show changes in both
the line profiles and the limb darkening curves that appear to be
characteristic of many other solar lines. Here we seek the constraints
placed on the atmospheric model by these effects. We find that in
addition to a depth varying source function we must also allow the
ratio of the continuous absorption coefficient to the total absorption
coefficient to pass through a minimum in the mid-photosphere. Such an
effect is consistent with inward increases of the Doppler width and
damping constant in the upper photosphere and an inward increase of
the ionization for both iron and hydrogen in the low photosphere.
Title: A Probabilistic Formulation of the Non-Coherent Scattering
Problem.
Authors: Athay, R. G.
Bibcode: 1972BAAS....4R.212A
Altcode:
No abstract at ADS
Title: FeI Ionization and Excitation Equilibrium in the Solar
Atmosphere.
Authors: Lites, B. W.; Athay, R. G.
Bibcode: 1972BAAS....4..212L
Altcode:
No abstract at ADS
Title: Radiation Transport in Spectral Lines
Authors: Athay, R. Grant
Bibcode: 1972rtsl.book.....A
Altcode: 1972QB871.A84......
No abstract at ADS
Title: Thermalization Lengths and Mean Numbers of Scatterings for
Line Photons
Authors: Athay, R. G.; Skumanich, A.
Bibcode: 1972lfpm.conf..167A
Altcode:
No abstract at ADS
Title: Radiation transport in spectral lines.
Authors: Athay, R. G.
Bibcode: 1972GAM.....1.....A
Altcode:
No abstract at ADS
Title: Thermalization Lengths and Mean Numbers of Scatterings for
Line Photons
Authors: Athay, R. Grant; Skumanich, A.
Bibcode: 1971ApJ...170..605A
Altcode:
A simple algebraic method is given for the derivation of approximate
thermalization lengths, mean number of scatterings for line photons,
and scaling laws for the maximum value of the line-source function
in finite atmospheres. The method utilizes only the shape of the line
absorption coefficient.
Title: Hydrogen Ionization and n=2 Population for Model Spicules
and Prominences
Authors: Poland, A.; Skumanich, A.; Athay, R. G.; Tandberg-Hanssen, E.
Bibcode: 1971SoPh...18..391P
Altcode:
Using slab model atmospheres that are irradiated from both sides by
photospheric, chromospheric, and coronal radiation fields we have
determined the ionization and excitation equilibrium for hydrogen.
Title: Radiation and Structure of the Solar Atmosphere (Radiation
et Structure de 1'Atmosphère Solaire)
Authors: Athay, R. Grant
Bibcode: 1971IAUTB..14..110A
Altcode:
No abstract at ADS
Title: The Chromosphere-Corona Transition Region
Authors: Athay, R. G.
Bibcode: 1971ASSL...27...36A
Altcode: 1971psc..conf...36A
No abstract at ADS
Title: The Problem of Consistency in Multilevel Line-Transfer
Solutions
Authors: Athay, R. Grant
Bibcode: 1970BAAS....2T.291A
Altcode:
No abstract at ADS
Title: The Ionization Equilibrium and the N = 2 Population of Hydrogen
in Quiescent Prominences
Authors: Poland, A.; Athay, R. G.; Skumanich, A.; Tandberg-Hanssen, E.
Bibcode: 1970BAAS....2R.338P
Altcode:
No abstract at ADS
Title: The Chromospheric Abundance of Iron
Authors: Athay, R. G.
Bibcode: 1970A&A.....7..305A
Altcode:
A critical comparison is made between the methods of deriving the
chromospheric iron abundance used by Pecker and Pottasch (1969) and
by Athay (1968). It is suggested that the differences in the results
obtained by the two methods are explainable in terms of the inherent
inaccuracies in either of the methods. An alternative source of the
differences is an inconsistency between Fe I and Fe n !.values.
Title: A Non-Lte Line-Blanketed Solar Model
Authors: Athay, R. Grant
Bibcode: 1970ApJ...161..713A
Altcode:
Line-blanketing effects are evaluated for selected strong solar lines
and for representative cases from the remaining lines. A composite
blanketing curve representing the effect of all lines is constructed
from the combined blanketing curves for the selected and representative
lines. Separate composite blanketing curves are obtained for four model
atmospheres with different assumed temperature distributions, T1. The
blanketing functions are used to compute blanketed model atmospheres,
whose temperature distributions are Tb. A self-consistent model for
which Tb T1 is obtained by iteration. In the self- consistent model
the boundary temperature is 43300 K with estimated error limits
of +1500. It is shown that the tendency for a temperature rise at
small r produced by the Cayrel mechanism is strongly resisted by the
blanketing mechanism and that temperatures as high as 46000 near m =
I0- -t0- would require substantial input of mechanical energy.
Title: Theoretical Line Intensities.IX. Comment on the Effectively
Thick Approximation
Authors: Athay, R. Grant
Bibcode: 1970ApJ...161..709A
Altcode:
It is shown that, in the effectively thick approximation, emission-line
fluxes may exhibit temperature and density dependences that are very
different from those found in the optically thin case. Under certain
circumstances the line flux may even vary inversely with density.
Title: Velocity Effects on the Profiles of Hα and Two FeI Lines
Authors: Athay, R. G.
Bibcode: 1970SoPh...12..175A
Altcode:
Profiles are computed for Ha and two FeI lines for a differentially
moving atmosphere. The results show that the profiles are asymmetric
and that velocity measurements made in the Doppler cores will often
lead to erroneous results when the velocity gradient is significant
in the regions of the atmosphere where the core forms.
Title: A Line-Blanketed Solar Model
Authors: Athay, R. Grant
Bibcode: 1970BAAS....2Q.181A
Altcode:
No abstract at ADS
Title: Emission Cores in H and K Lines. V. Asymmetries in
K2 and K3
Authors: Athay, R. Grant
Bibcode: 1970SoPh...11..347A
Altcode:
Enhancement of the violet K2 emission peak results when the
atmospheric layers at heights where K3 forms are moving
downward with velocities of 10-20 km/sec or when the K2
layers and those immediately below are moving upward with velocities
of 3-7 km/sec. Evidence favoring the former alternative is cited.
Title: Bandwidth Requirements in Spectral Line Transfer Calculations
Authors: Athay, R. Grant
Bibcode: 1970sfss.coll..179A
Altcode: 1970IAUCo...2..179A
No abstract at ADS
Title: Radiation and structure of the solar atmosphere.
Authors: Athay, R. G.; Pierce, A. K.; Rigutti, M.
Bibcode: 1970IAUTA..14..111A
Altcode:
No abstract at ADS
Title: A Self-Consistent Model Atmosphere Program with Applications
to Solar OI Resonance Lines
Authors: Athay, R. Grant; Canfield, R. C.
Bibcode: 1970sfss.coll...65A
Altcode: 1970IAUCo...2...65A
No abstract at ADS
Title: Abundance Determination in the Chromosphere
Authors: Athay, R. G.
Bibcode: 1969cctr.conf..243A
Altcode:
No abstract at ADS
Title: Boundary Conditions on Model Solar Chromospheres
Authors: Athay, R. Grant
Bibcode: 1969SoPh....9...51A
Altcode:
It is shown that the gas pressure in the corona provides a rather
stringent boundary condition on model chromospheres and limits the
thickness of those regions of the chromosphere in which the temperature
is less than 10 000 K to less than or about 2000 km.
Title: Theoretical Line Intensities. VIII. Comment on the Effectively
Thin Approximation
Authors: Athay, R. Grant
Bibcode: 1969ApJ...157..281A
Altcode:
The effectively thin approximation for the formation of spectral lines
is discussed from the standpoints of photon-degradation processes and
the random walk of scattered photons. It is shown that for some lines
the optical thickness of the effectively thin layer is fixed by atomic
rate coefficients and is independ- ent of the model atmosphere
Title: Computed Profiles for Solar Mg b and Na D Lines
Authors: Athay, R. Grant; Canfield, Richard C.
Bibcode: 1969BAAS....1..272A
Altcode:
No abstract at ADS
Title: Computed Profiles for Solar MG b- and NA D-Lines
Authors: Athay, R. Grant; Canfield, Richard C.
Bibcode: 1969ApJ...156..695A
Altcode:
Profiles are computed for the Doppler cores of solar Mg b- and
Na D-lines for multilevel model atoms and for selected ranges of
chromospheric parameters. Comparison of computed and observed profiles
from center to limb on the solar disk yields the depth variation
of the horizontal and vertical components of microturbulence. The
two components are found to be of unequal amplitude for r~> 1O~
and pass through minima near r~ = 1O~. The profiles also suggest that
fle(Tc) at Tc = 104_106 obtained from eclipse data is more reasonable
than that of the Bilderberg model
Title: Theoretical Line Intensities. VII. Wavelength and Depth
Dependence of Line-Blanketing Effects for Pure Absorption and
Non-Coherent Scattering
Authors: Athay, R. Grant; Skumanich, A.
Bibcode: 1969ApJ...155..273A
Altcode:
The processes involved in line blanketing are investigated in detail
for a two-level atom whose spectral line is formed partially in pure
absorption and partially in non-coherent scattering (non-LTE). Line and
continuum interactions are included through absorption of line photons
by continuum processes, and vice versa. Interactions with the thermal
energy of particles are included through collisional excitations
and de-excitations. Calculations of the "local" blanketing effect,
designated by e, are made for lines of different equivalent widths, in
different spectral regions, and for different absorption profiles. We
consider an atmosphere in which B(r) is linear. In general, such an
atmosphere is not in radiative equilibrium and requires mechanical
energy to maintain the assumed temperature profile even if no lines
are present in the spectrum. If lines are added to the spectrum without
distorting B(r), the local energy requirements are changed by an amount
e and the total energy (per unit area) is changed by an amount E =
J'edr. For a Milne-Eddington (M-E) atmosphere in pure absorption (LTE)
and linear B(r), E is shown to be positive (mechanical energy must be
added to the atmosphere) and equal to the flux "blocked" out by the
equivalent widths of the lines, »=W~H~c. In the corresponding case for
a Schuster-Schwarzschild (S-S) atmosphere, just the reverse is true,
E = - ~ and energy must be removed from the atmos- phere to preserve
the linear B(r). In the limiting case of an isothermal atmosphere
in LTE, E -p 0 for the M-E atmosphere. When scattering (non-LTE) is
present for a M-E atmosphere, E is the same as for LTE for saturated
lines in all spectral regions, while it is approximately the same for
iøisaturated lines in the violet and visual spectral regions. In
the case of the S-S atmosphere, the LTE result for the integrated
blanketing remains unchanged. However, in both cases the local LTE and
non-LTE blanketing effects as given by e differ appreciably, mainly in
the degree of thermal cooling at the boundary. Equations derived to
express the self-consistent (radiative equilibrium) problem provide,
we believe, more accurate and numerically more tractable calculations
of the blanketed temperature profile
Title: Calculations of Solar Hydrogen Lines: Comparative Solutions
for a Standard Line Transfer Problem
Authors: Athay, R. G.; Avrett, E. H.; Beebe, H. A.; Johnson, H. R.;
Poland, A. I.; Cuny, Y.
Bibcode: 1968rla..conf..169A
Altcode:
No abstract at ADS
Title: Degradation Lengths and Emergent Fluxes for Lyman-α and
Lyman-β
Authors: Athay, R. G.
Bibcode: 1968rla..conf..241A
Altcode:
No abstract at ADS
Title: Computed Profiles of Mg b and Na D Lines
Authors: Athay, R. G.; Canfield, R. C.
Bibcode: 1968rla..conf..363A
Altcode:
No abstract at ADS
Title: Emission Cores in H and K Lines. IV: Center-to-Limb Variation
Authors: Athay, R. Grant; Skumanich, A.
Bibcode: 1968SoPh....4..176A
Altcode:
Calculations are made for the center-limb variations of the
K2 and K3 components of the solar Ca II K line
using an optically thick model of the chromosphere. The center-limb
variations are shown to require an increase of Doppler width with
height in the chromosphere and to depend critically upon the location
of the point where ΔλD has increased by a factor e. Good
agreement with observations is found when, and only when, the increase
in ΔλD occurs nearly simultaneously with the increase in
chromospheric temperature.
Title: Theoretical Line Intensities.VI. Milne-Eddington Curves of
Growth for Non-Coherent Scattering
Authors: Athay, R. Grant; Skumanich, A.
Bibcode: 1968ApJ...152..211A
Altcode:
Curves of growth are derived for different mixtures of non-coherent
scattering and pure absorption and compared with similar curves computed
by Wrubel for mixtures of coherent scattering and pure absorption. The
curves induding fractional non-coherent scattering tend to mimic the
pure coherent scattering curves on the linear portion of the curve
of growth but tend to bridge over to the pure absorp- tion curves for
very strong line
Title: Emission Cores in h- and K-Lines III. The Wilson-Bappu Effect
Authors: Athay, R. Grant; Skumanich, A.
Bibcode: 1968ApJ...152..141A
Altcode:
Widths of the emission components, W2, of the H- and K-lines of Ca
ii are investigated, assuming that the lines are formed in optically
thick chromospheres with temperature increasing outward. The line
source function S is computed from an equation relating S to the
Planck function and the divergence of the line flux W2 is found to be
particularly sensitive to chromospheric opacity both in the line and
in the continuum, to the damping parameter a, and to the chromospheric
Doppler width We interpret the results to mean that the Wilson-Bappu
effect arises primarily from changes in Doppler width, and, fur- ther,
that there is a tendency among the chromospheres of late-type stars
to have approximately the same line and continuum opacities and to
have a < 3 X 1O~. To a first approximation, the intensity of the
emission component is found to be uncorrelated with W
Title: Wavelength and Depth Dependence of Line Blanketing Effects
for Pure Absorption and Noncoherent Scattering.
Authors: Athay, R. Grant; Skumanich, A.
Bibcode: 1968AJS....73Q...3A
Altcode:
The processes involved in line blanketing are investigated in detail
for a two-level atom whose spectral line is formed partially in pure
absorption and partia~lly in non coherent scattering. Line and continuum
interactions (back-warming) as well as interactions with the thermal
energy of particles (local-cooling) are included. Calculations of the
"local" blanketing effect are made for Milne-Eddington and Schuster-
Schwarzschild atmospheres for lines of different equivalent widths, in
different spectral regions and for different absorption profiles. Both
back-warming and local-cooling are present to some degree at all
depths. Generally, however, back-warming predominates near r c 1
and local- cooling in the higher, line-forming layers. We consider
an atmosphere in which B (T) is linear. Such an atmosphere requires
mechanical energy to maintain the assumed B (T). The presence of
lines changes the local energy requirements by an amount e and the
total energy (per unit area) by an amount E= f e dr. For the case
of pure absorption (LTE) in an AI-E atmosphere, E is shown to be
positive (the atmosphere is cooled by the lines and energy must be
added). The back-warming and local-cooling effects are each wavelength
and depth dependent, sometimes reinforcing and sometimes counteract~ng
each other. They combine to give E = ~ W, the equivalent width of the
lines, in all cases, however. When scattering (non-LTE) is present in
the ~tE case the back-warming effect remains relatively unchanged in
the violet and visual regions of the spectrum but decreases markedly
in the red. The local-cooling effectdecreasesmarkedly in all spectral
regions. The nel effect leaves e very nearly the same for lines in the
violet and visual, except in the surface layers, and diminishes e at
all depths in the red. We still find E~~W in the violet and visual
spectral regions. In the extreme case of an isothermal atmosphere,
however, we find E = -~W, i.e., the atmosphere is now heated by the
lines and requires an energy sink equal to the equivalent widths. The
S-S atmosphere gives E = -~W for lines of any strength, at any
wavelength and irrespective of whether pure absorption or scattering
dominates. The detailed behavior of e (r) depends upon all of these
parameter, however. A full treatment of line blanketing must include
a proper classification of lines according to wavelength, equivalent
width, the relative role of pure absorption versus scattering and
the depth variation of the absorption coefficient, the latter being
particularly important. Equations derived to express the self-consistent
(radiative equilibrium) problem provide, we believe, more accurate and,
numerically, more tractable calculations of the blanketed temperature
profile.
Title: Relative Abundances of O, Mg, Cr, Mn, Fe and Ni in the Solar
Chromosphere
Authors: Athay, R. G.
Bibcode: 1968ApL.....1...71A
Altcode:
No abstract at ADS
Title: Emission Cores in H and K Lines. I: The Optically Thick
Chromosphere
Authors: Athay, R. Grant; Skumanich, A.
Bibcode: 1968SoPh....3..181A
Altcode:
Profiles of the H and K lines of MgII and the K line of Ca II are
computed using a two-level atom for five model atmospheres distinguished
from each other mainly by the location of the temperature minimum. In
the five models the temperature minimum and the chromospheric
temperature are adjusted to give best agreement between computed and
observed profiles. The parameters ɛ and r0 are prescribed
as functions of τ from a density model of the atmosphere. By comparing
computed and observed profiles of the K3, K2
and inner K1 components of the lines we determine both
the approximate depth variation of ΔλD and the best of
the temperature models. We find that the Doppler width increases
rapidly with height in the chromosphere beginning from a value of
1.6 km/sec at τ0 ≈ 10−2. This latter
value corresponds closely to the thermal velocity of Mg atoms in
the upper photosphere. The preferred temperature model is one for
which the temperature minimum occurs near τ0(λ 2800) ≈
10−4-10−5 with a value Tmin≲
4200 ° and which has a temperatu near 7000 ° at τ0 =
10−6 where K2 is formed. The intensity in
K3 is determined largely by dΔλD/dτ in the
K2 and K3 regions.
Title: Frequency-Dependent Line Source Functions.
Authors: Athay, R. G.; Skumanich, A.
Bibcode: 1968AJS....73S...2A
Altcode:
By the use of a previously described differential equation method
for solving resonance line transfer (Skumanich, Astron. J. 71,
871,1966) the frequency dependence of the line source function has
been studied with the view of explaining the discrepancy between the
derived solar minimum temperature of 42000K based on Ca II K analysis
(Athay, R. G., and Skumanich, A., Solar Phys. 2, to be published)
and the minimum temperature of 46000K derived from other observations
(Bilderberg Conference, Solar Phys., to be published). Several cases
were calculated for atmospheres with and without a chromospheric
temperature rise. These include (1) noncoherent scattering, (2)
coherent scattering, and (3) partially coherent scattenug in the
atoms rest frame (for lines with a finite dispersion width). These
calculations differ from others in that the exact scattering functions
were used. A comparison of line profiles for the non coherent case
with that for complete redistribution (frequency-independent source
function) shows, in agreement with earlier results based on iterative
solutions, that complete redistribution (or uncorrelated scattering)
is a good approximation for this case with intensity differences
amounting to only 5 to 7% of the continuum. Furthermore, our results
for isothermal atmospheres corroborates, in general, the earlier (three
frequency point) calculations of Jefferies and White (Astrophys. J. 132,
767,1960). In the chromospheric case we find that essentially complete
coherency is required to depress the source function by the necessary
factor of 2 outside the Doppler core and thus allow the "radiation"
temperature to fall below the kinetic temperature in comparison with
the complete redistribution calculations.
Title: Reply: on the Relative Abundances in the Solar Corona as
Determined from the Ultraviolet Spectrum
Authors: Athay, R. Grant
Bibcode: 1967ApJ...150..365A
Altcode:
No abstract at ADS
Title: Broadening of H and K Emission Cores and the Wilson-Bappu
Effect.
Authors: Athay, R. Grant; Skumanich, A.
Bibcode: 1967AJ.....72..784A
Altcode:
Widths of K2 components W ofIl and K lines are investigated, assuming
that they are formed in optically thick chromospheres with temperature
increasing outward. The source * function S is computed from an equation
relating S to the Planck function B and the divergence of the line
flux. At very large optical depths in the line S~B. Hence 8(r) mimics
the minimum in B (r) then rises with B (r) in the chromosphere until
the flux divergence forces S(r) to decrease to S(ro)~~B (ro). The
K2 maximum results from the maximum in 8(T) and, for the sun, lies
near the edge of the Doppler core. W is investigated as a function of
the following chromospheric parameters: line opacity TO*, continuum
opacity Tc*, electron density ne*, temperature T*, Doppler width AND*,
and damping parameter a*. W is particularly sensitive to TO*, Tc*,
a*, and AND*, but relatively insensitive to T* and fle*. Changes in
W resulting from TO*, Tc*, and a* arise from the displacement of K2
between the Doppler core and line wings and are associated with major
changes in the character of the profile. On the other hand, changes
in AND* change W through a rather uniform scaling of the K2 and K3
profile without seriously affecting the location of K2 relative to the
Doppler core. We interpret these results to mean that the Wilson-Bappu
effect arises primarily from changes in AND*, and, further, that there
is a tendency among the chromospheres of all late-type stars to have
approximately the same values of Tc*, TO*, and a*. Increases in the
K2 intensity 12 result from increases in T* and/or increases in ne*,
which leaves 12 uncorrelated with W. To a first approximation, 12 ne*B*
at T5OOO 10-~.
Title: On the Origin of Spicules in the Chromosphere-Corona Transition
Region
Authors: Kuperus, Max; Athay, R. Grant
Bibcode: 1967SoPh....1..361K
Altcode:
Qualitative arguments are presented to show that in the
chromosphere-corona transition region the energy which is transported
downwards by heat conduction cannot be disposed of by radiative losses
only. The region therefore is unstable and forced to be in motion,
which may give rise to spicule-like phenomena.
Title: An integral equation for the line source function and its
numerical solution
Authors: Athay, R. G.; Skumanich, A.
Bibcode: 1967AnAp...30..669A
Altcode:
No abstract at ADS
Title: Radiative Energy Loss from the Solar Chromosphere and Corona
Authors: Athay, R. Grant
Bibcode: 1966ApJ...146..223A
Altcode:
Quantitative estimates of the rate of energy loss from the solar
chromosphere and corona by radiative processes are considered in the
hope that these estimates will aid in identifying the mechanical energy
input mechanism. Estimated rates of energy loss are derived partially
from observational data and partially from a model atmosphere. A new
theoretical basis for estimating the energy loss is derived. It is shown
that Osterbrock's estimate is probably too high by about an order of
magnitude. The rate of energy loss per cubic centimeter is found to
decrease with height, whereas the rate per gram first increases with
height and then remains constant and the rate per gram of positive
ions is essentially constant at all heights. If it is assumed that the
available mechanical energy can be represented by the kinetic energy
of photospheric macroscopic motions whose rms velocity is 1 km/sec,
a characteristic time for the conversion of mechanical energy to
radiant energy is about 600 sec.
Title: Theoretical Line Intensities. V. Solar UV Emission Lines of
Heavy Elements
Authors: Athay, R. Grant
Bibcode: 1966ApJ...145..784A
Altcode:
Analysis of the solar ultraviolet emission lines for eleven elements
heavier than helium yields values for relative abundances and a
relationship between T and dT dk in the chromosphere-corona transition
region. The derived abundances, with the single exception of oxygen,
are within 30 per cent of the photo- spheric abundances found by
Goldberg, Mtiller, and Aller. Oxygen is found to have a relative
abundance about one-half as large as the photospheric value. In the
chromosphere-corona transition T '12dT /dh is constant with height,
corresponding to a constant flux of coiiducted energy.
Title: Theoretical Line Intensities.IV. Source Functions and
Equivalent Widths
Authors: Athay, R. Grant
Bibcode: 1966ApJ...144.1159A
Altcode:
A frequency-independent source function S8j is defined for spectral
lines and a method of evaluating Ski simultaneously with the evaluation
of the equivalent width of the line is discussed. The form of the
resulting equations illustrates clearly the role of microscopic rate
processes in determining equivalent widths.
Title: Theoretical Line Intensities. I. Strong Emission Lines.
Authors: Athay, R. Grant
Bibcode: 1965ApJ...142..724A
Altcode:
A new method is derived for computing the contribution to the total
intensities of emission lines formed out of thermodynamic equilibrium
in the outer regions of stellar atmospheres. The method is much simpler
and more easily applied than existing methods. The simplicity and ease
of application are achieved by sacrificing information regarding the
shape of the line and, consequently, by limiting the amount of detailed
information that can be derived concerning the atmosphere producing
the radiation. The method is very useful, nevertheless.
Title: Theoretical Line-Intensities II Excitation of Chromospheric
he II and Hydrogen.
Authors: Athay, R. Grant
Bibcode: 1965ApJ...142..732A
Altcode:
Values of bj for He ii and hydrogen are computed for a range of n, and
Te appropriate to the upper chromosphere. The observed solar-radiation
field is used to compute radiative-transition rates in subordinate
transitions. Solutions are obtained for varying degrees of departure
from radiative detailed balance in the resonance series of He ii
and hydrogen. The calculations are made in order to establish the
explicit dependence of bj on hypothetical departures from radiative
detailed balance in the various transitions in the resonance series. The
results are of immediate value for computing the expected intensities
of the resonance series lines for hydrogen and He ii which is done
in a following paper. No attempt is made in this paper to establish
internal consistency between the assumed fle, Te, and departures from
radiative detailed balance.
Title: Theoretical Line Intensities. III. Solar UV Lines and Continua
of h, he i, and he II and the Chromospheric Model
Authors: Athay, R. Grant
Bibcode: 1965ApJ...142..755A
Altcode:
Energy fluxes escaping the solar atmosphere are computed for the
2-1 and 3-I lines of H, He I, and He ii and for certain subordinate
transitions for He I and He ii, using a new technique recently developed
by Athay (1965a). Good agreement with observed fluxes is obtained with
a relatively simple model chromosphere consistent with the fluxes
observed in He I singlets and triplets observed at eclipse and with
radio data. It is shown that local density increases in spicules and
plages will produce increased brightness in the 2-1 lines and in the
subordinate lines of He I and He ii. The 3-1 lines tend to be formed
higher in the atmosphere than the 2-1 lines, particularly for He ii,
and they show smaller increases in brightness associated with local
increases in density than do the 2-1 lines. Local changes in temperature
result in relatively weak change in the intensities of H and He I lines.
Title: Total Fluxes in Strong Emission Lines
Authors: Athay, R. G.
Bibcode: 1965SAOSR.174..411A
Altcode:
No abstract at ADS
Title: The Chromospheric Spectrum at Eclipse
Authors: Athay, R. Grant
Bibcode: 1965ASSL....1..151A
Altcode: 1965sosp.conf..151A
No abstract at ADS
Title: Source-Function Equality in Multiplets.
Authors: Athay, R. Grant
Bibcode: 1964ApJ...140.1579A
Altcode:
Necessary and sufficient conditions are derived for equality of
source functions for different lines within multiplets at a given
location in a stellar atmosphere. The approach involves an algebraic
treatment of the statistical equilibrium equations together with a
parametric representation of the solutions to the coupled transfer
equations. Waddell's criterion for source-function equality within
multiplets is shown to be sufficient but not necessary
Title: Doppler Shifts and Line Broadening in Spicules.
Authors: Athay, R. Grant; Bessey, R. J.
Bibcode: 1964ApJ...140.1174A
Altcode:
Doppler shifts measured for solar spicuies in Ha, D3, and H (Ca ii)
suggest that the anomalously broad lines of Ca ii (Athay 1961) are due,
in part, to inadequate spatial resolution as suggested by Zirker (1962),
but that this is not the primary cause of the anomalous broadening. Ha
and H and K spicules are found to have predominantly wide profiles at
low and intermediate heights, but at great heights the profile widths
for most of the few remaining features are only about one-third as
wide as at lower heights. It appears that this results mainly, however,
from the fact that the features with narrow profiles are intrinsically
brighter at great heights than are the features with wide profiles
It does not appear to result from strong systematic decrease of line
width with height for individual spicules. Only a small percentage of
the features with wide profiles resolves into clusters of spicules
with narrow profiles at great heights. Doppler velocities are found
to be less than 12 km/sec for about two-thirds of equatorial spicules
with the remaining one-third showing Doppler velocities up to about 30
km/sec. Almost all polar spicules have Doppler velocities less than 12
km/sec. No other significant differences between polar and equatorial
spicules were found.
Title: The Challenge of Chromospheric Physics
Authors: Athay, R. Grant
Bibcode: 1964Sci...143.1129A
Altcode:
No abstract at ADS
Title: Depth of Formation of MG i Lines in the Solar Atmosphere.
Authors: Athay, R. Grant
Bibcode: 1963ApJ...138..680A
Altcode:
Estimates of optical depths in Mg 1 lines are obtained from their
shapes and intensities in the Fraunhofer spectrum, their chromospheric
intensities, and by computation using a model atmosphere. Curves
are derived showing the relationship between the surfaces r = 1 and
geometrical depth in the solar atmosphere as a function of wavelength
displacement from line center.
Title: Depth of Formation of MgI Lines in the Solar Spectrum.
Authors: Athay, R. Grant
Bibcode: 1963AJ.....68..272A
Altcode:
Estimates of optical depths in Mg' lines are made from their shapes and
intensities in the Fraunhofer spectrum, their chromospheric intensities,
and by computation using a model atmosphere. Curves are derived showing
the relationship between the surfaces T = 1 and geometrical depth in
the solar atmosphere as a function of wavelength from line center.
Title: Excitation of Chromospheric he I.
Authors: Athay, R. Grant
Bibcode: 1963ApJ...137..931A
Altcode:
New calculations are carried out for bj for the singlet and
triplet states of He 1, using corrected transition rates from
our earlier analysis (Athay and Johnson 1960). The new results
differ considerably from our earlier calculations and lead to a new
chromospheric model, whose major changes are in the geometry of the
helium regions. Chromospheric emission observed at the limb at heights
above 1000 km is largely confined to spicules with electron densities,
,i , of the order of . Helium regions are identified as hot shells,
having electron temperatures, T 5 X 10 , incasing colder spicule
cores. Interspicule regions must have n <= 3 X 1010 and T >=
3 X 10 . This new model is consistent with radio data at millimeter
wavelengths and is similar to that proposed by Moriyama (1961).
Title: Excitation of Chromospheric MG I.
Authors: Athay, R. Grant; House, L. L.
Bibcode: 1963ApJ...137..601A
Altcode:
Our earlier analysis of chromospheric Mg I data is extended to
discussions of both empirical and theoretical departures from radiative
detailed balance in the strong singlet and triplet lines. At 500 km,
general agreement between the empirical and theoretical values is
obtained for all lines, assuming an isothermal, spherically symmetric
atmosphere. At heights of 1000 and 1500 km, however, further evidence
is found for strong departures from spherical symmetry.
Title: Coronal Ionization by Two-Step Collision Processes.
Authors: Athay, R. Grant; Hyder, Charles L.
Bibcode: 1963ApJ...137...21A
Altcode:
We suggest that ionization by electron impact for some coronal ions
may take place via the double process of collisional excitation to
metastable levels, thence collisional ionization from these excited
levels rather than by direct ionization from the ground state. The
relative efficiency of this double-collision process depends primarily
on the mean decay lifetimes for the excited levels. A specific
computation based on estimated upper limits to the mean lifetimes of
excited levels in the Fe x-Fe xv sequence shows a flatter spectrum
of ion densities and a somewhat lower ionization temperature than is
obtained from direct collisional ionization from the ground state,
assuming that the abundance of Fe x equals that of Fe xiv. The two-step
collision mechanism permits the possibility of a density dependence
in the ionization equilibrium.
Title: Astronautical Investigations of the Sun
Authors: Athay, R. Grant
Bibcode: 1963ASST....5....1A
Altcode:
No abstract at ADS
Title: Ionization and Excitation Equilibrium of CA II in the Solar
Atmosphere.
Authors: Athay, R. Grant; Zirker, J. B.
Bibcode: 1962ApJ...136..242A
Altcode:
Ionization and excitation configurations for Ca ii are computed for
conditions appropriate to the solar chromosphere. The populations
of energy levels are found to depart sharply from the LTE values at
corresponding values of T . The dominant ionization process of Ca ii is
shown to be via collisions from the 3D level and to exhibit fundamental
differences from H, He, and Mg I, as well as some similarities. For
electron densities and temperatures such as are expected in most of
the solar chromosphere and corona, the ratio Ca u/Ca iii is shown to
be essentially independent of electron density rather than directly
proportional, as predicted by the Saha equation. Computations of
opacities and occupation numbers indicate that the Ca ii H and K lines
in the Fraunhofer spectrum are formed near the top of the hydrogen
temperature plateau, where T 150OO , and that the Ca ii emission from
spicules arises from regions where T0 15000 rather than the much higher
temperature derived from profiles of hydrogen and helium lines
Title: Ionization and Excitation Equilibrium of Call in the Solar
Atmosphere.
Authors: Athay, R. Grant; Zirker, J. B.
Bibcode: 1962AJ.....67S.110A
Altcode:
The ionization and excitation equilibrium of Caii is computed for
conditions appropriate to the outer solar atmosphere. Populations of
energy levels are found to depart sharply from the LTE populations at
corresponding values of Te. The dominant ionization process of Caii is
shown to be via collisions from the 3D level and to exhibit fundamental
differences from H, He, and Mgi. For electron densities and temperatures
such as are expected in most of the chromosphere and corona, the ratio
Caii/Caiii is shown to be inversely proportional to electron density,
rather than directly proportional as predicted by the Saha equation. The
50% ionization stage of Caii is reached for Te =10000~140000, depending
upon the degree of radiative detailed balance attained in the H and
K lines. Computations of opacities and occupation numbers indicate
that the Caii H and K lines in the Fraunhofer spectrum are formed near
the top of the hydrogen temperature plateau where Te~l3 0000 and that
Te 15 0000 in the regions within spicules and prominences where the
Caii emission arises. % ionization stage of Caii is reached for Te
=10000~140000, depending upon the degree of radiative detailed balance
attained in the H and K lines. Computations of opacities and occupation
numbers indicate that the Caii H and K lines in the Fraunhofer spectrum
are formed near the top of the hydrogen temperature plateau where Te~l3
0000 and that Te 15 0000 in the regions within spicules and prominences
where the Caii emission arises. % ionization stage of Caii is reached
for Te =10000~140000, depending upon the degree of radiative detailed
balance attained in the H and K lines. Computations of opacities
and occupation numbers indicate that the Caii H and K lines in the
Fraunhofer spectrum are formed near the top of the hydrogen temperature
plateau where Te~l3 0000 and that Te 15 0000 in the regions within
spicules and prominences where the Caii emission arises.
Title: Departures from Thermodynamic Equilibrium in Chromospheric
MG i, CA i, and O I.
Authors: Athay, R. Grant; House, Lewis L.
Bibcode: 1962ApJ...135..500A
Altcode:
Comparisons of intensities of Mg I and 0 I emission lines in the
flash-spectrum of the low chromosphere reveal evidence of marked
departures from a Boltzmann distribution of populations of energy
levels. These departures are in the same sense as those found earlier
for He I, viz , an overpopulation of the levels connected to the
ground state through optically forbidden transitions relative to the
levels with permitted transitions. A search for a similar effect in
the populations of the excited singlets and triplets of Ca I has not
indicated a significant departure from a Boltzmann distribution for the
levels studied. However, evidence is found that the ratio Ca i/Ca ii is
much greater than would be expected in thermodynamic equilibrium. In
the case of Mg I, the optical thickness of the chromosphere in the
triplet lines is obtained directly from the observed intensity of the
forbidden intercombination line X 4571 (33P-31S). Computed populations
of energy levels for a model Mg I atom under a range of temperature
and density show satisfactory agreement with observational data for
choices of chromospheric temperatures and densities consistent with
a model departing from spherical symmetry given by Thomas and Athay
(1961, chap. 7).
Title: Physics of the Solar Chromosphere (Ref. C. DE JAGER)
Authors: Thomas, R. N.; Athay, R. G.
Bibcode: 1962ZA.....55...66T
Altcode:
No abstract at ADS
Title: The Doppler Cores of Strong Fraunhofer Lines.
Authors: Athay, R. Grant
Bibcode: 1961ApJ...134..765A
Altcode:
A simple method for obtaining approximate values for AXD in strong
Fraunhofer lines is applied to some of the solar lines and compared
with results obtained by the more exact method of comparing profiles
within multiplets of known relative theoretical strengths. Even though
the method is crude, it gives results within about 20 per cent of the
more accurate values. The essential agreement between results obtained
by the two methods leads to the important conclusion that, for the
multiplets studied, the source functions do not change appreciably
for the different lines within the multiplet at a fixed depth in the
atmosphere. It is further concluded that the core of the Ha line is
thermally broadened.
Title: Line Broadening in Chromospheric Spicules.
Authors: Athay, R. Grant
Bibcode: 1961ApJ...134..756A
Altcode:
Profiles of the H, K, X 8498 and X 8542 lines of Ca ii, H of hydrogen
and 7772 and 7774 lines of O i for chromospheric spicules are used
in conjunction with earlier observations of hydrogen, helium, and Ca
IL line profiles to investigate the line-broadening mechanisms. The
analysis tends to confirm an earlier suggestion that the Ca ii lines
are broadened, in part, by a macroscopic motion of the ions not shared
by the neutral atoms and that this additional velocity may arise from
an interaction between the systematic spicule motion and magnetic
lines of force. The analysis suggests that in optically thin lines the
halfwidth increases slowly with height in spicules, which is borne out
by earlier observations of the D3 line. In the H and K lines and in Ha,
which are broadened, in part, by self-absorption, the half-widths are
observed to decrease with height. At a mean height of about 5000 km,
the kinetic temperature in spicules is found to be of the order of
50000 from Hp, H , and D3 profiles. The presence of Ca ii emission in
the spicules suggests the possibility of regions of lower temperature
resulting from temperature gradients perpendicular to the spicule axes.
Title: Further Evidence of Broadening of Call Line Profiles in
Chromospheric Spicules by Magnetic Fields.
Authors: Athay, R. Grant
Bibcode: 1961AJ.....66..278A
Altcode:
X8498, and X8542 lines of Caii, HE of hydrogen and X7772 and X7774
lines of Oi for chromospheric spicules are used in conjunction
with earlier observations of hydrogen, helium, and Caii profiles to
investigate the line- broadening mechanisms. The Caii profiles are all
markedly non-Gaussian, and, with the instrumental resolution used, are
indistinguishable from rectangular profiles. The total linewidths at the
half-intensity points are 0.86 A for the H and K lines, 1.28A for ~8542,
and 0.90A for X8498. All profiles studied other than those of Caii and
H~ are Gaussian in shape and consistent with a kinetic temperature of
the order of 40-50 0000 and a macroscopic broadening velocity of about
8 km7sec. The width of N8498 corresponds to a broadening velocity of 16
km~sec. Self-absorption is shown to be negligible in this line. Hence,
the Caii lines are apparently broadened by a macroscopic motion not
shared by the neutral atoms. This additional m-~otion of the ions
may arise from an interaction between the systematic spicule velocity
and magnetic lines of force. Both the shapes and widths of the X8498
profile can be explained by assuming that the Caii ions either spiral
about, or follow sinusoidal perturbations in the lines of force, such
as may be induced by hydromagnetic waves. At the densities occurring in
spicules, the neutral atoms would not necessarily mimic such motions
of the ions. The H, K, and N8542 lines of Caii show an additional
broadening over that in X8498 that is reasonably consistent with
self-absorption arising from the probable opacities in these lines.
Title: Impulsive Phenomena of the Solar Atmosphere. I. Some Optical
Events Associated with Flares Showing Explosive Phase.
Authors: Athay, R. Grant; Moreton, G. E.
Bibcode: 1961ApJ...133..935A
Altcode:
A new class of optical phenomena of the solar atmosphere associated
with flares is described. These phenomena are characterized by higher
velocities ( 1500 km/sec) and shorter time scales than has been
indicated by previous observations. An explanation of some of the
observed phenomena is offered in terms of corpuscular streams ejected
from flares at the time of an "explosive phase" occurring during the
rise to maximum brightness.
Title: The Balmer: Paschen Ratio in the Chromosphere and the
Equilibrium Populations of Hydrogen Angular-Momentum States.
Authors: House, Lewis L.; Athay, R. Grant; Zirin, Harold
Bibcode: 1961ApJ...133..608H
Altcode:
The work reported in this paper is a test of the hypothesis that the
angular-momentum states of hydrogen are not populated according to
their statistical weights. The anomalous ratio of the hydrogen Balmer to
Paschen lines observed at the 1952 eclipse is investigated in relation
to both observations and theoretical calculations. The Paschen decrement
is used to test for a reduced population of states of higher angular
momentum; such a depopulation of states was previously suggested as
accounting for the anomalous ratio. The decrement does not confirm the
suggestion. A statistical equilibrium analysis of the angular-momentum
states is used to determine departures in the populations from their
LTE values. The results indicate that departures are too small to
give the observed Balmer: Paschen ratio. An calculation shows that it
is reasonable to average together the substates of different angular
momentum in hydrogen chromospheric calculations.
Title: Sources of Solar Ultraviolet Radiation
Authors: Athay, R. Grant
Bibcode: 1961JGR....66..385A
Altcode:
Recent work related to the interpretation of the observed solar
ultraviolet radiation is summarized from two standpoints: (1) the
source of energy giving rise to the radiation, and (2) the physical
conditions in the solar atmosphere where the radiation originates. Data
on the ultraviolet spectrum are of great astrophysical importance
for determining the energy balance and thermodynamic structure of the
upper solar chromosphere and lower corona, but the lack of adequate
atomic cross sections seriously limits the practical astrophysical
usefulness of such data.
Title: Physics of the solar chromosphere
Authors: Athay, R. Grant; Thomas, Richard N.
Bibcode: 1961psc..book.....A
Altcode: 1961QB528.T45......
No abstract at ADS
Title: The Cosmic Ray Flares of July 1959 and November 1960 and Some
Comments on Physical Properties and Characteristics of Flares
Authors: Athay, R. G.
Bibcode: 1961spre.conf..837A
Altcode:
No abstract at ADS
Title: Departures from Thermodynamic Equilibrium in Chromospheric MgI,
CaI, and OI.
Authors: House, Lewis L.; Athay, R. Grant
Bibcode: 1961AJ.....66U.286H
Altcode:
Line intensities from the chromospheric flash spectrum observed at
the 1952 total eclipse clearly indicate marked departures from LTE in
Mgi and Oi. The same is suggested for Cai, but not unambiguously. The
following remarks relate only to Mgi. The stronger triplets X5184 and
X3838 are influenced by self-absorption for heights below about 2500
km. The forbidden line X4571 is observed, and is shown to be free from
self-absorption. Its intensity leads directly to the opacities in the X5
184 and X3838 triplets. At 500 km the radial opacities at line center
are T5i94 3 and T3539 7, establishing that the centers of these lines
in the Fraunhofer spectrum are chromospheric in origin. The singlet
line X5528 is observed to fall off much more rapidly with height than
the triplets even in the absence of self-absorption. The singlet to
triplet ratios give unambiguous evidence of departures from LTE. At
1000 km, the intensity of X4571 is enhanced relative to X5528 by
factors of 20 to 200 for assumed values of Te of 60000 and 10 0000,
respectively. Solutions to the statistical equilibrium equations yield
populations of energy levels in good agreement with the empirical
values for opacities consistent with those in the chromosphere. The
departures from LTE in 3'S and 33P are shown to be the same and
essentially independent of height. Typical computed values are b3'5~25
at 60000 and 200 at 80000. The departures from LTE in the higher triplet
levels are also relatively independent of height. Typical values are
b435~1.4 at 60000 and 3.3 at 80000. For the upper level of N5528, 4'd,
the departure from LTE depends strongly on height thereby accounting
for the steep gradient in the X5528 emission.
Title: The Equilibria and Ultraviolet Spectra of h, he i, and he II
in the Solar Atmosphere.
Authors: Athay, R. Grant
Bibcode: 1960ApJ...131..705A
Altcode:
The ionization equilibrium equations and source functions for the
ions H, He I, and He ii are considered under conditions appropriate
to the solar chromosphere. The equations are formulated in terms
of both occupation numbers and bk parameters, in order to clarify
their relationship to earlier work for H and He I. In the case of
the ionization equations for H, somewhat more approximate forms are
adopted from those appearing in earlier works, in order to illustrate
more clearly the dominant transitions in the equilibrium The three
ions considered here exhibit fundamental differences as well as
many similarities in both the ionization equations and the source
functions. A consideration of the ultraviolet spectra indicates that
the central intensities in the Lyman-p lines are influenced mainly
by the "local" value of Te near the region r = 1, whereas the central
intensities of the Lyman-a lines are influenced by the distribution of
T throughout a large range in r and cannot be described solely in terms
of the "local' value of Te near r = 1. For this reason, observations
of the Lyman-p profiles and fluxes by means of rockets and satellites
become a much more valuable supplement to Lyman-a observations than
had previously been supposed.
Title: The Excitation of he i in the Spectrum.
Authors: Athay, R. Grant; Johnson, Hollis R.
Bibcode: 1960ApJ...131..413A
Altcode:
The excitation and ionixation of He I in the solar atmosphere is
computed for a range of values of n and T# and the radiation field in
the resonance lines Good agreement is found between the observed and
computed parameters for T and n 1011. The criterion for the X 10830
and x 5876 lines to show as emission lines against the solar disk is
found to be fle > 1012 almost independently of Te.
Title: Hβ, Hγ and K profiles in chromospheric spicules
Authors: Athay, R. G.
Bibcode: 1960AnAp...23..250A
Altcode:
No abstract at ADS
Title: Anomalous broadening of the CaII K line in spicules.
Authors: Athay, R. Grant
Bibcode: 1959AJ.....64..323A
Altcode:
Caii K lzne ~ spicules. Observations of the profiles of the H~, Hp,
H~, D3 and K lines for polar spicules suggest a spicule model in which
the hydrogen, Hei and Caii atoms producing the observed lines are
well-mixed, but in which the Caii ions have a non-thermal component
of velocity not shared by hydrogen and Hei. An alternative model in
which the hydrogen and Caii atoms producing the Balmer lines and the K
line are physically separated by temperature stratification from the
Hei atoms producing the D3 line satisfies some aspects of the data
and allows hydrogen and Caii to share the same non-thermal velocity
field. However, this alternative model is not compatible with the
relative intensities of the Ho~ and D3 lines, nor with the absence
of the strong lines of such ions as Srii and T~ii. The Hfl, H~ and D3
profiles are gaussian, and for the majority of spicules the half-widths
for a given line are the same to within the probable errors in the
observations. The profiles of these lines indicate a kinetic temperature
of 50,0000 and a non-thermal velocity component of about 7 km~sec. The
Ha profile is apparently broadened to some extent by self-absorption,
which is consistent with the above model. The K line, however, appears
to be broadened by a non-thermal velocity component of about 30 km/sec,
which corresponds to the mean spicule velocity. It is suggested that
the broadening of the K line is due either to the spiralling of the
Caii ions about magnetic lines of force oriented at some angle to
the spicule motion, or to the forced oscillations of the Caii ions by
perturbations in a magnetic field lying in the direction of the spicule
motion. High Altitude Observatory University of Colorado Boulder, Colo.
Title: The continuous spectrum of the low chromosphere
Authors: Athay, R. G.
Bibcode: 1959Obs....79...12A
Altcode:
No abstract at ADS
Title: The Number of Spicules in the Middle Chromosphere.
Authors: Athay, R. G.
Bibcode: 1959ApJ...129..164A
Altcode:
Statistics are given for the number of Ha spicules observed at the
solar limb for heights of 3000 km and above. The observed numbers are
analyzed to obtain the spatial distribution of spicules. It is found
that at a height of 3000 km there are about 9.3 x 10 spicules on the sun
and that these spicules cover about 0.6 per cent of the solar surface.
Title: The excitation of chromospheric HeI lines.
Authors: Johnson, Hollis R.; Athay, R. Grant
Bibcode: 1959AJ.....64R.335J
Altcode:
Relative intensities of singlet and triplet lines of Hei in the solar
chromosphere allow a determination of bn exp E~n/Te~, where ~,` is
the ionization energy of the level n and bn is a non- thermodynamic
equilibrium factor. We have computed bn'5 for values of Te ranging
from 10,0000 to 50,0000 for an idealized helium atom consisting of a
continuum and IS level and the levels 25, 2P, and n = 3, 4 and 5 in the
excited singlets and triplets. Computed and observed values of b exp
E~n/Te~ for the triplets agree for all Te even though b varies with
Te. The relative populations of the triplets are determined almost
entirely by the radiative transitions, which, because of the low
chromospheric opacity in the triplets, are independ~nt of the ambient
Te. For the singlets, however, the occupation numbers of the excited
levels depend critically upon R~, the net radiative transition rates to
the ground state, which are functions of TO, the chromospheric opacity
in the first resonance line. Thus, both Te and TO are parameters
of the calculations, with TO, in turn, being a function of Te and
ne. The electron density, ne, may be estimated from the absolute
line intensities. In order to relate Re to TO, we use the source-
function computations of Jefferies and Thomas (1959). Computed values
of be exp E~n/Te~ and TO for the singlets agree satisfactorily with
the empirical be exp E~.~/Te~ for Te 4o,ooo0~5o 0000 Uncertainties
in atomic constants and Rn may permit a Te as low as 30,0000, but
certainly not as low as 25,0000. At chromospheric densities, helium
becomes predominantly Heii at Te 20,000, and predominantly Heiii at
Te 55,ooo0. Chromospheric helium is, there- fore, predominantly Heii
as suggested earlier by Athay and Menzel (1956). REFERENCES Athay,
R. G. and Meuzel, D. H. 1956, Ap. J. 123, 285. Jefferies, J. T. and
Thomas, R. N. 1959, Ap. J. 129, 401. National Bureau of Standards and
High A ltitude Observatory Boulder, Colorado
Title: A model of the chromosphere from radio and optical data
Authors: Athay, R. G.
Bibcode: 1959IAUS....9...98A
Altcode:
No abstract at ADS
Title: The Solar Ultraviolet Spectrum of He II.
Authors: Athay, R. Grant
Bibcode: 1958ApJ...128..447A
Altcode:
No abstract at ADS
Title: On the Use of the Early Balmer Lines to Extend the Photospheric
Model.
Authors: Athay, R. G.; Thomas, R. N.
Bibcode: 1958ApJ...127...96A
Altcode:
The early Balmer lines in the solar Fraunhofer spectrum provide
information relative to the structure of the solar atmosphere. Our
analysis of these lines in the disk spectrum indicates that the lines
are not formed in local thermodynamic equilibrium, so that the source
function is not given by B (T ). Our combined empirical and theoretical
results lead us to conclude that the source function for the Balmer
lines is determined to the first order by the radiation field in Ha and
to the second order by the changes in electron temperature. The central
intensities of the early Balmer lines show limb darkening out to cos
o > 0.1. Just beyond the limb, HP, HT, and H show limb brightening,
whereas Ha shows constant brightness and the lines H10 and above show
further limb darkening. The limb brightening in HP, H , and H may be
attributed to decreasing opacity in the early Lyman lines without
necessarily changing the electron temperature. The absence of limb
brightening in Ha may be attributed to high opacity in the spicules,
and the absence of limb brightening in the lines H10 and above may be
attributed to lower opacity in these lines than in the earlier lines.
Title: Hα and D3 profiles in chromospheric spicules
Authors: Athay, R. G.
Bibcode: 1958AnAp...21...98A
Altcode:
No abstract at ADS
Title: On the relative intensities of chromospheric Balnier and
Paschen lines.
Authors: Athay, R. G.; Zirin, Harold
Bibcode: 1957AJ.....62..137A
Altcode:
The flash spectrum of the solar chromosphere includes hydrogen Balmer
and Paschen lines originating in common upper levels. We denote the
intensity of the Balmer line arising from the transition n to 2 by B
and the intensity of the Paschen line arising from the transition n
to 3 by Pn. If all terms of the same n are populated in proportion to
their statistical weights and if self-absorption is small, Bn/Pn 3.3
for n > 9. Self-absorption will tend to reduce the observed ratio of
Bn$Pn. From spectrograms obtained at the 1952 eclipse, we find Bn/Pn 8
for n > 14. The discrepancy between observed and predicted ratios of
Bn/Pn is too large to be accounted for by photometric errors. This may
be illustrated by comparing continuum intensities in the ultraviolet
and infrared and by comparing intensities of the H and K lines with
the intensities of the infrared Caii triplet. The relative continuum
intensities for the corona, derived from the same spectrograms,
follow the photospheric curve. Furthermore, the Caii lines have very
nearly the predicted relative intensities. If we discount photometric
errors, then the observed ratio of Bn/Pn implies that some of the
multiplets normally present in the Paschen lines are suppressed. In
fact, it seems necessary to assume that only the s, and d terms are
populated. In this case, the predicted ratio of Bn/Pn 6, which is in
satisfactory agreement with the observations. The above assumption can
be justified if it can be shown that most of the electrons in the upper
term arrive via excitations from the IS, 25 and 2 terms. Quantitative
estimates of rates of excitations from these low- lying terms and rates
of three-body recombinations from the continuum using the Thompson
collision cross-section indicate that three-body recombinations form
the primary source of electrons for the upper levels. This would
imply that all of the multiplets are populated and Bn7Pn should be
3.3. Thus, the Thompson collision cross-section leads to a contradiction
between predicted and observed ratios of Bn/Pn. Observations of the
Paschen-Balmer ratio in prominences are now in progress at Climax. This
work was carried out under the sponsorship of the Office of Naval
Research and the Geophysics Research Directorate, Air Force Cambridge
Research Center. High Altitude Observatory, Boulder, Colo.
Title: Physical Conditions in the Solar Limb Prominence Observed at
the 1952 Eclipse.
Authors: Athay, R. G.; Orrall, Frank Q.
Bibcode: 1957ApJ...126..167A
Altcode:
At the time of the 1952 eclipse a small, rather faint, prominence
was located near the equator on the west solar limb. Redman and
Zanstra (1952) have previously discussed the continuous spectrum of
this prominence, and in this paper we discuss the line spectrum. By
combining the line data with the continuum data, we arrive at the
following conclusions: (1) the optical thickness of the central part
of the prominence in the center of Ha is less than or near unity,
and none of the observed hydrogen- and heliumline intensities are
seriously affected by self-absorption; (2) the hydrogen energy levels
and the helium triplet energy levels are overpopulated relative to the
thermodynamic equilibrium populations at T4 (3) helium is predominantly
singly ionized; (4) T is near 20000 and fle >- 1011; and (5) the
prominence is in a steady state, with its radiated energy balanced by
an external energy supply.
Title: The Numbers and Motions of Solar Spicules.
Authors: Athay, R. G.; Thomas, R. N.
Bibcode: 1957ApJ...125..804A
Altcode:
In this paper we interpret spicule motions in terms of two spicule
models, one with constant velocity and one decelerating in the
solar gravitational field. The available statistics slightly favor
the gravitational model but do not indicate clearly which model is
preferred. We estimate the total number of spicules on the sun by
fitting the two spicule models to the observed distribution of spicules
with height. This leads to total spicule numbers of 1.4 X 10 to 1.3
X 1O for the two models.
Title: The Chromosphere Near Active Regions.
Authors: Athay, R. G.; Thomas, R. N.
Bibcode: 1957ApJ...125..788A
Altcode:
Eclipse data show abnormal chromospheric and coronal emission above
active sunspot regions. In this paper we analyze data for such regions
on 1952,1936, and 1932 eclipse spectrograms and attempt to show how the
chromospheric structure differs from normal chromospheric regions. If we
assume that the chromosphere has two components of different temperature
and density at a given height, we find that the principal difference
between the active regions and the normal regions is a larger proportion
of the hotter component in the active region. We also find that the
temperatures in the two components are relatively unchanged over ihe
active regions, which is consistent with the assumption of thermal
stability for the chromospheric radiation field (Athay and Thomas 1956).
Title: Some comments on photospheric models.
Authors: Athay, R. G.; Thomas, R. N.
Bibcode: 1957AJ.....62....3A
Altcode:
Models for the upper photospheric layers are usually derived by assuming
that the excitation temperature, Tex, in the cores of the early Balmer
lines is the same as the kinetic temperature, Te. From the observed
center-to-limb variations in the line intensities, one then obtains a
photo- spheric model with P0 decreasing monotonically with height. From
eclipse data, however, we find that the central parts of these early
Balmer lines are formed at heights of 2000 to 4000 km above the base
of the chromosphere, and, in addition, that P0 is either constant or
increasing with height. In this paper we attempt to integrate eclipse
observations with disk observations in order to join the photospheric
model to the low chromospheric model. The data indicate that Pox for
Ha decreases across the disk, then remains constant for the first 4000
km in the chromosphere before it decreases further. For H~, H~ and H~,
however, the drop in Pox across the disk is followed by a sharp rise
in Pox at the limb, which, in turn, is followed by a rather rapid
decrease in Pox with height. We interpret this behavior in terms of
the differences in the optical depths in the lines and in terms of
the non-uniformities arising from spicule structure. In all cases P0
obtained from other chromospheric data exceeds Pox in the early Balmer
lines. In order to check the validity of identifying Pex with P0, we use
the line profiles on the disk to obtain an empirical relation between
Pex and the Doppler widths of the lines. If we ignore mass motions,
the profiles show clearly that Te > Pex If the observed effects
are attributed to mass motions, random velocity fields of the order
of 13 km/sec are required. Such velocity fields could, conceivably,
arise from spicule motions, but it seems unlikely. Furthermore, we find
that the individual curves of Tex versus height for the early Balmer
lines do not join smoothly, again indicating that Te # Tex. Thus, we
conclude that Tex in the early Balmer lines does not serve as a sound
basis for deriving photospheric models. This work was supported by the
Office of Naval Research and the Geophysics Research Directorate, Air
Force Cambridge Research Center. High Altitude Observatory, Boulder,
Cob., and Harvard College Observatory, Cambridge, Mass.
Title: Variations in the Thermodynamic State of the Chromosphere
over the Sunspot Cycle
Authors: Athay, R. G.; Menzel, D. H.; Orrall, F. Q.
Bibcode: 1957SCoA....2...35A
Altcode:
No abstract at ADS
Title: Physical conditions in solar prominences.
Authors: Orrall, F. Q.; Athay, R. G.
Bibcode: 1957AJ.....62R..28O
Altcode:
Spectra of four solar limb-prominences, obtained with slitless
spectrographs at eclipse, are analyzed to determine electron density,
Ne, and kinetic temperature, Te For three of the prominences, the
data consist of the continuous emission XX65oo-35oo. Data for the
fourth prominence include the continuous emission X~4Ioo- 3600 and
line emission in several hydrogen, helium and metal lines. We assume
that Te and Ne are constant throughout each prominence. From the ratio
of the Balmer free-bound em ission to the remaining components of the
continuous emission at X3647, we limit P0 in the four prominences to
the range 5200 to 2.5 X i~~. We reduce the upper limit on Te to 2 X
i~~ for the three prominences for which we have extensive continuum
data. At Te = 5500; Ne = 1010 and at Te = 2 >c i&, N0 = 2.7
X 1011. Analysis of the hydrogen and helium line data for the fourth
prominence yields the following conclusions: (i) the optical thickness
of the central part of the prominence in the center of Ha is less
than or near unity and none of the observed hydrogen and helium line
intensities are seriously affected by self-absorption; (2) the hydrogen
energy levels and the helium triplet energy levels are over-populated
relative to the thermodynamic equilibrium populations at Te; (3) helium
is predominantly singly ionized if the hydrogen: helium ratio is near
10: I; (4) P0 is near the upper limit of 2.5 X i~~ and Ne > 10"; (5)
the prominence is in a steady-state with the energy radiated balanced
by an external energy supply. This work was supported by the Geophysics
Research Directorate, Air Force Cambridge Research Center. Sacramento
Peak Observatory, N. M., and High Altitude Observatory, Boulder, Colo.
Title: On the uniformity of the lower chromosphere
Authors: Thomas, Richard N.; Athay, R. G.
Bibcode: 1957IAUS....4..279T
Altcode:
No abstract at ADS
Title: Chromospheric profiles of the early Balmer lines.
Authors: Athay, R. G.; Smith, Elske V. P.
Bibcode: 1957AJ.....62S...2A
Altcode:
This constitutes a preliminary report on work being done at the
Sacramento Peak Observatory in studying the chromospheric Balmer lines
with the high-dispersion coronagraph-spectrograph. These spectra were
obtained by occulting the solar disk and placing the slit tangential to
the limb. The limb spectrum was obtained by means of a radial slit. This
spectrum must be subtracted from the chromospheric spectrum to obtain
the true emission profile. The corrected profiles can be reproduced
satisfactorily by curves computed by introducing an appropriate optical
depth. We find that the optical depths and the widths of the 107e
points for the respective Balmer lines are as follows: Hn: To = 10 =
1.82 TO = 6 = 1.11 TO =3 ($) =0.83 To = I = 0.70 These data are fairly
consistent in view of the fact that they may not all refer to the same
height in the chromosphere. Under the assumption that the lines are
broadened only by the optical-depth effect and thermal Doppler broad-
* Of papers presented a the Joint Meeting of the American Astronomical
Society and the Astronomical Society of the Pacific, Berkeley, Calif.,
August 24-28, 1956. ening we find a kinetic temperature of approximately
30,0000. Variation of the profile with height in the chromosphere has
thus far only been studied for Ha. Here it is clearly seen that the
profile decreases in half-width and indicates diminishing optical
depth with increasing height. Structure within the emission lines
becomes more pronounced with increasing height in the chromosphere. The
emission features are presumably spicules or groups of spicules. Some
of the spicules exhibit marked radial velocities and some have large
wings to the blue or the red. The profiles of different spicules at
a given cross-section differ somewhat, but this does not necessarily
imply that conditions differ in various spicules. Spicule profiles
are, however, decidedly wider than prominence lines. This work was
supported by contract with the Geophysics Research Directorate,
Air Force Cambridge Research Center. High A ititude Observatory,
Sacramento Peak Observatory, Harvard College Observatory.
Title: LYMAN-α and the Structure of the Solar Chromosphere.
Authors: Athay, R. G.; Thomas, R. N.
Bibcode: 1956ApJ...124..586A
Altcode:
We investigate the range of chromospheric models compatible with present
rocket observations of Lyman-a and conclude that it is considerable. We
would require detailed observations of the line profile, with resolution
better than one Doppler half-width, to be more specific on the actual
model. We find a considerable difference between T and a radiation
temperature defined by the line intensity, in conformity with earlier
discussions of the non-equilibrium chromosphere by ourselves and by
Giovanelli. A discussion of the relation of these results to the limb
flare and SID correlations found by C. Warwick suggests a more extended
investigation of the non-spherically symmetric model and its relation
to the ch romospheric opacity in Lyman-a.
Title: Some Characteristics of a Chromospheric Model.
Authors: Athay, R. G.; Thomas, R. N.
Bibcode: 1956ApJ...123..309A
Altcode:
Some general conditions that must be satisfied by a chromospheric model
are discussed: (1) The available data on variations in chromospheric
structure over the solar activity cycle indicate the highest emission
gradients at sunspot maximum. (2) The evidence bearing on the choice
of an energy or momentum perturbation as the chief characteristic of
the low chromosphere is discussed, and a conclusion favoring the energy
perturbation is reached. The maximum in the nonradiative energy input
appears to lie near 500 km. (3) Some considerations on the effect of
departures from spherical symmetry in the chromosphere are discussed
in terms of hot versus cold spicules and of the thermodynamics of
the resulting configurations. We conclude, both from an a priori
thermodynamic standpoint and from existing data, that the spicules
must be cold.
Title: A Model of the Chromosphere from the Helium and Continuum
Emissions.
Authors: Athay, R. G.; Menzel, D. H.
Bibcode: 1956ApJ...123..285A
Altcode:
Helium4ine emission observed in the flash spectrum at the Khartoum
eclipse is interpreted in terms of a chromospheric model. The He I
triplets have excitation temperatures of 6000 , and the singlets have
excitation temperatures of 20000 . It is demonstrated that ultraviolet
emission from the corona cannot account for the observed excitation of
helium. A model of the chromosphere is derived from the helium data
combined with the continuum data at X 3640 and X 4700. A two-column
model, with Te and fle varying from column to column along a horizontal
surface, is needed to satisfy the data. The model gives T.(h) and
fle(h) in both types of columns. The cooler columns are identified
with the spicules on the basis of the observed spicule structure on
the spectrograms.
Title: Temperature Gradients in the Chromosphere.
Authors: Athay, R. G.; Thomas, R. N.
Bibcode: 1956ApJ...123..299A
Altcode:
Our earlier determinations of electron temperature, Te, in the
chromosphere by analysis of eclipse data are supplemented in this paper
by considerations of the energy balance. We assume that Te may have only
those values for which there is thermal stability. If an increase in
Te, at a given height, results in an increase in the energy radiated,
the model is stable. However, if an increase in Te causes a decrease
in the energy radiated, there is no stable value of Te. Two regions
of stability surmounted by regions of instability are recognized: (1)
in the low chromosphere neutral hydrogen emission is stable and is the
principal source of emission; (2) neutral hydrogen emission becomes
unstable at a height where hydrogen becomes sufficiently ionized. At
this height, Te increases abruptly until stable emission from He Ir
balances the energy input; (3) He Ir emission also becomes unstable at
sufficient ionization, and Te increases abruptly to a coronal value
where either free-free emission or emission from multiply ionized
metals predominates. Models of the chromosphere derived from 1952
eclipse data show good agreement with the conclusions based on thermal
stability considerations.
Title: Temperature Gradients in the Chromosphere
Authors: Athay, R. G.; Thomas, R. N.
Bibcode: 1955PASP...67..339A
Altcode:
No abstract at ADS
Title: The helium chromosphere.
Authors: Athay, R. G.
Bibcode: 1955AJ.....60..150A
Altcode:
The flash-spectrograms obtained by the High Altitude Observatory
expedition to the 1952 eclipse in Khartoum contain several helium
lines that are suitable for photometric reduction. Some of these
lines have not been studied quantitatively at previous eclipses,
and our spectrograms were taken with much greater height resolution
than had been previously attempted. These features make a study of
the helium data from the 1952 eclipse of special interest. The Hei
data include the first four lines of the 23P - n3D series, the first
three lines of the 2~P - n3S series, the first line of the 2'P -
n'D series and the first three and fifth lines of the 2'? - n'S
series. The Heii data are for X4686, 32D - 42F0. The data show maxima
in the surface brightness of the chromosphere at the limb at heights
of I 100 km for HeI emission and 1500 km for Heii emission. Both the
hydrogen and helium data show that if the chromosphere is assumed
to be uniform the radial optical depth at X5oo is 200 at the height
where the maximum Hei emission occurs. These large optical depths
exclude the possibility of excitation of chromospheric helium by
ultraviolet coronal radiation if the chromosphere is uniform. Kinetic
temperatures obtained from an analysis of the continuum data under the
assumption of a uniform chromosphere are too low to produce the observed
excitation of helium. Thus the assumption of a uniform chromosphere
appears to be invalid for the helium data, and we assume a two-region
model with all of the helium emission coming from one region. The
triplet series of Hei have excitation temperatures of 50000, and the
singlet series have excitation temperatures of 15,0000. If we assume
approximate thermodynamic equilibrium for HeiT and the singlet series
of Hei and use a relative abundance of hydrogen to helium of 7: 1,
the observed line intensities for both Hei and Heii require kinetic
temperatures of 19,000 in the regions above 1500 km that emit the
helium radiation. If we vary b1 within the limits < b1 <
i~~ the kinetic temperature in the helium region varies between
14,5000 < Te < 26,0000. The maximum in the Heii emission at
1500 km leads to Te 20,0000, in agreement with the values obtained
by other methods. Continuum data show that the electron temperatures
and densities below 4000 km in the regions that do not emit helium
radiation are essentially unchanged from the results obtained on the
assumption of a uniform chromosphere (Athay et al. 1955). Above 4000 km
the nonuniform model leads to higher temperatures in these regions. The
eclipse spectrograms show conclusively that above 5000 km the helium
radiation is in the spicules. This work was supported by the Office of
Naval Research and carried out in cooperation with the Naval Research
Laboratory. Athay, R. G., Meozel, D. H. Pecker, J-C., and Thomas,
R. N. 1955, Ap. J. Supplement 12, 505. H~gh Altitude Observatory,
Boulder, Colo.
Title: The Thermodynamic State of the Outer Solar
ATMOSPHERE.IV.SELF-ABSORPTION and the Population of the Second
Quantum Level.
Authors: Athay, R. G.; Thomas, R. N.
Bibcode: 1955ApJS....1..491A
Altcode:
The quantitative dependence of the observed logarithmic emission
gradient, fl , of the Balmer lines upon quantum number provides
a direct substantiation of the influence of self-absorption on the
higher lines (n greater than about 10). An analysis assuming that the
( , n) dependence arises only from seifabsorption permits a direct
determination of the population of the second quantum level, n ,
as a function of height, leading to a scale height of 2000 kin for
n2 by contrast with 500 km for the highest quantum levels. The scale
height for the non-Boltzmann term, b2, is thus 600 kin. The derived
self- absorption is so large that at H1 1 only some 7 per cent of
the (slitless spectrograph) emission at h = 1000 kin escapes from
the chromosphere. The analysis is seif-consistent, provided that T,
is sufficiently low that b10 is less than about 2; a discrepancy
arises because the line emission is relatively too great for that
of the continuum, leading to excessive empirical b . The question
of a nonuniform chromosphere arises and is deferred, together with a
general model, pending the analysis of the continuum.
Title: The Thermodynamic State of the Outer Solar ATMOSPHERE.V.A.MODEL
of the Chromosphere from the Continuum Emission.
Authors: Athay, R. G.; Menzel, D. H.; Pecker, J. -C.; Thomas, R. N.
Bibcode: 1955ApJS....1..505A
Altcode:
Four semi-independent analyses of 1952 eclipse data contribute to a
determination of n and T in the solar chromosphere in the height range
from -120 km to 6000 km: (1) The intensity of the continuous emission
at X 4700 indicates that T, increases with height from about 4800 at -
65 km. (2) The emission, per cubic centimeter, in the Balmer continuum
attains a maximum near 500 km, which indicates that here the free
electrons begin to come mainly from H rather than from metals, and thus
places the limits: 5000 < T < 7000 , 4 X 1011 <n < S X 1011
at this height. (3) The intensities of the continuum at X 4700 and X
3640 require values of T as follows: 5000 at 500 km, 6100 at 1000 km,
and 6700 at 3000 kin. In the interval 1()()( 3000 kin the ionization
of H increases from about 3 to about 80 per cent. (4) Above 3000 kin
no data on the Balmer free-bound continuum exist, and an extension
of the results of 3 to greater heights requires the use of the height
gradient of the Balmer lines to replace that of the continuum. Such a
technique fixes T only within certain limits, which, at 6000 km, are:
2 X 10 < T < 1.2 X 10 . The chief uncertainty of the analysis
lies in the use of the assumption of a continuous distribution of
material in the atmosphere. The results of the analysis suggest the
validity of such assumption below about 2500 kin, and its breakdown
above about 3000 km. An estimate of optical depth in the continuum,
from the present analysis, at a height of 500 km produces a value
agreeing well with an estimate based on the analysis of the lines.
Title: CN Bands in the Chromosphere.
Authors: Pecker, J. -C.; Athay, R. G.
Bibcode: 1955ApJ...121..391P
Altcode:
CN bands are observed in emission in the chromosphere between the
photospheric limb and a height of 750 km. Spectrograms obtained by
the High Altitude Observatory at the Khartoum eclipse in 1952 showed a
scale height of 210 km for the intensity of the emission in the 2 2 (0,
0) band at X 3883. The emission spectrum at 100 km gives a rotation
temperature of 4500 , and the photospheric absorption spectrum in
the Utrecht Atlas gives a rotation temperature of 4000 . At eclipse
heights other than 100 km, the data were used to determine the
temperature gradient. The rotation temperature was found to increase
with height. Photospheric and chromospheric models were used to predict
the absolute intensity of the CN emission in this band. The predicted
intensity was less than the observed intensity by a tactor of 20. The
discrepancy was accounted for by uncertainties in the absorption
coefficient, which was obtained from a study of the absorption profile
in the Utrecht Atlas.
Title: Coronal Line Intensities at the Khartoum Eclipse.
Authors: Athay, R. G.; Roberts, W. O.
Bibcode: 1955ApJ...121..231A
Altcode:
Coronal line and continuum intensities were measured at several
position angles on the limb and as a function of height above the limb
on the slitless spectrograms obtained at Khartoum by the High Altitude
Observatory. The lines XX 5303, 6374, and 7892 and the continuum were
measured at fifteen points around the limb. The relative line and
continuum intensities around the limb showed large variations. In one
active region where the emission in some lines was intense, the yellow
coronal line X 5694 was observed. In this same region the lines X 6702
and X 7060 were intense enough to measure, and it was found that lines
of high ionization potential were at maxima in intensities, whereas
lines of low ionization potential were at minima. The yellow line
was at maximum in this region, confirming that it is a high4oniza-
tion-potentia] line. The correlation between line and continuum
intensities was found to increase markedly as the ionization
potential increased for the three lines studied. The correlation
between line intensities was found to increase as the difference in
ionization potential decreased. Intensities of X 5303, X 7892, and the
continuum were measured as a function of height above the limb in four
regions. Two of these regions were active centers, one of which showed
the yellow line, and two were more nearly average regions. The change
of X 7892 intensities with height in the latter two regions showed
that the maximum intensity occurred below 10,000 km. Changes in the
relative intensities of the two lines with height showed that in the
yellow-line region the temperature decreased with height, but in the
other regions the temperature increased with height. A comparison of
the changes in line intensities to the changes in continuum intensities
showed that the average temperature in the active regions was above the
value at which the line X 5303 had a maximum intensity, but in the two
more normal regions the temperature was between the limits where the
lines X 5303 and X 7892 have maxima. The active regions were found to
be regions of high density.
Title: A model of the chromosphere from 1952 eclipse data.
Authors: Athay, R. G.; Pecker, J. C.; Thomas, R. N.; Menzel, D. H.
Bibcode: 1954AJ.....59..314A
Altcode:
An analysis of the Balmer free-bound emission at X3640 and the continuum
intensities at ~4700 was carried out using data from the slitless
spectrograms obtained by the High Altitude Observatory at Khartoum,
Sudan. The data gave intensities at X3640 and ~4700 at intervals
of approximately 100 km between 0 and 2400 km above the limb and
intensities at X4700 at many additional heights between 2400 and 48,000
km. The Balmer line data, which extended from 100 to 6400 km, was used
to supplement the free- bound data for heights between 2400 and 6000
km. Values of electron density, Ne, and kinetic temperature, Te, were
determined at heights between 0 and 6000 km. The analysis was based on
the assumption of a homogeneous chromosphere, with Ne and Te depending
upon height only. The continuum at X4700 was assumed to come from H-
emission and electron scattering of photospheric light. The results of
the analysis of the continuum data gave a chromospheric model that could
be divided into three distinct regions with the following properties:
Region I (o to 500 km). In this region Te increases from 50000K at the
photospheric limb (tangential optical depth I, radial optical depth
0.005) to 600&K at 500 km. Hydrogen begins to ionize near the top
of this region with NpHNe. This result is consistent with a marked
increase with height of the quantity NeNpTJ in the region near 500 km,
which was inferred from the Balmer free-bound and line emission. Thus
it appears that the "boundary temperature," T,nin~42000K, occurs below
a radial optical depth of 0.005. Region 2 (1000 to 3500 km). The
ionization of hydrogen increases from 5 per cent at the base to 99
per cent at the top of this region. Te increases slowly from 60000K
to > 70000 K. The low gradient of Te suggests that the external
energy supply suffices only for the ionization. Region 3 (~3500 km
up). Further ionization of hydrogen is negligible and a large rise in Te
occurs. The free-bound emission is too weak to measure in this region
and an accurate evaluation of Te is difficult. An extrapolation of the
free- bound intensities to 6000 km based on the ob- served intensities
of the Balmer lines between 2400 and 6400 km gives Te 7 X io40K. The
analysis allowed an accurate determination of Te in the region ~1500
km, and the probable errors in the data plus the errors introduced in
the analytical procedures were not likely to cause errors of more than
~3000 in Te. However, in higher regions the values of Te were quite
sensitive to the analytical procedures at~d errors of a factor 2 in Te
are possible. The eclipse spectrograms at heights above 5500 km show Ha,
and all other strong chromospheric lines that persist to these heights,
as irregular beaded structures. This irregular structure is presumably
due to spicule activity at these heights and requires the consideration
of a non-uniform chromospheric model, at least in the upper levels of
the chromosphere. A study of the Fe xi line at X7892 on the eclipse
spectrograms showed that there was strong emission in this line at
heights well below 10,000 km and suggested that the emission started
in the regions where the chromospheric lines break up into a spicule
structure. The work reported in this paper was supported by the Office
of Naval Research and carried out in close cooperation with the Naval
Research Laboratory. High A ititude Observatory, Boulder, Colo. and
Harvard College Observatory, Cambridge, Mass.
Title: Emission in Hydrogen Balmer Lines and Continuum in Flash
Spectrum of 1952 Total Solar Eclipse at Khartoum, Sudan.
Authors: Athay, R. Grant; Billings, Donald E.; Evans, John W.; Roberts,
Walter O.
Bibcode: 1954ApJ...120...94A
Altcode:
Analysis of the spectrograms of the chromospheric flash obtained
at the 1952 solar eclipse in Khartoum, Sudan, presented serious
photometric problems. Standardixing exposures made at Khartoum were
not successful because of a posteclipse failure of the film-advance
mechanism. Characteristic curves obtained from standard lamp exposures
made in Boulder after completion of the expedition could not be
trusted to represent the photometric properties of the eclipse films
and were principally useful as a first approximation to the curves
representing the eclipse spectrograms. Methods were developed that,
in spite of these problems, allowed entirely reliable determinations of
the characteristic curves of the eclipse films. A thorough, independent
check on the consistency and accuracy of the final curves was possible,
and its result was entirely satisfactory. Change with wave length of
fiim sensitivity, atmospheric absorption, and optical constants of
the spectrographs were evaluated and included in the photometry. The
integrated intensities of the hydrogen Baimer lines from H8 to H31
and at four wave lengths in the Balmer continuum were measured at two
points on the east limb on seventeen ultraviolet spectrograms; and
the intensities of Hp, H , and H were measured at one of these points
on nineteen visible spectrograms. The observations extend from 100 to
6300 km, with a height resolution of 108 1cm throughout most of the
low chromosphere. Preliminary interpretation of the line intensities
revealed that the effects of self-absorption were pronounced and
also demonstrated that there were large departures from thermodynamic
equilibrium, in the sense that the b ' s were greater than 1 at 1000 km
and increased with height. A preliminary mterpretation of the continuum
data gave a chromospheric model characterized by a large increase
of temperature with height and a relatively low electron-density
gradient. A more detailed analysis of the data is in progress.
Title: The active region on the west solar limb during the eclipse
of 25 February 1952.
Authors: Athay, R. G.; Evans, J. W.; Roberts, W. O.
Bibcode: 1954AJ.....59..182A
Altcode:
At the Khartoum eclipse there was an active region at io0S latitude
on the west limb. This region was first observed as a small sunspot
group and plage area near the east limb on 12 February. One flare was
reported in this region on 13 February, one on i6 February, two on 24
February and two on 25 February."2 The west limb spectrograms of the
chromospheric flash obtained by the High Altitude Observatory showed
a small region of enhanced emission and immediately adjacent to it
a small region of greatly reduced emission. Moon profile pictures
taken at Khartoum showed that the observed effects could not be
attributed to irregularities in the moon's profile. A few degrees
away from these regions there was a bright prominence that appeared
to be of a surge type. The region of reduced emission showed mainly
in the chromospheric lines. There was also an apparent decrease in
the coronal line intensities in the lowest levels of the corona, but
there was no marked decrease in the continuum intensity. The decrease
in the line intensities apparently resulted from either a cloud of
absorbing matter or an actual decrease in chromospheric emission. The
region of enhanced emission showed a maximum in the continuum and all
chromospheric and coronal line intensities. The greatest increase in
chromospheric lines was in He+, X4686. The yellow coronal line, X5694,
showed in this region on our spectrograms. It did not show at any
other positions, and to our knowledge has not been observed at previous
eclipses. Lyot and Doilfus have also reported this coronal line and four
new coronal lines from observations at Khartoum.3 All of these lines
were found in this region of enhanced emission. The intensities of all
of the chromospheric lines decreased much more slowly with height in
this region than in an east limb region previously analyzed,4 which
seemed to represent the undisturbed chromosphere. It was suggested
that the region of enhanced emission was caused by a limb flare. A
preliminary interpretation of the data from this region showed that
both the electron density and kinetic temperature were greater than in
the east limb region, and that the temperature increased less rapidly
with height. A more detailed analysis of this region will be published
elsewhere. This work was supported by the Office of Naval Research
and carried out in cooperation with the Naval Research Laboratory.
Title: Astronomy and Mathematics. (Book Reviews: Dialogue on
the Great World Systems; Dialogue concerning the Two Chief World
Systems--Ptolemaic & Copernican)
Authors: Kuhn, Thomas S.; Nelson, E. C.; Kron, Gerald E.; Athay,
R. Grant; Roberts, Walter Orr; Miller, Frederic H.
Bibcode: 1954Sci...119..546K
Altcode: 1954Sci...119..546G
No abstract at ADS
Title: Emission in the Hydrogen Balmer Lines and Continuum in the
Flash Spectrum of the 1952 Total Solar Eclipse at Khartoum, Sudan.
Authors: Athay, Russell G.
Bibcode: 1954PhDT.........2A
Altcode:
No abstract at ADS
Title: The active region on the west solar limb during the eclipse
of 1952 25 February
Authors: Athay, R. G.; Evans, J. W.; Roberts, W. O.
Bibcode: 1953Obs....73..244A
Altcode:
No abstract at ADS
Title: Preliminary intensities of Balmer lines from the flash spectrum
of the 1952 solar eclipse.
Authors: Athay, R. G.; Billings, D. E.; Evans, J. W.; Roberts, W. O.
Bibcode: 1953AJ.....58R..33A
Altcode:
Spectrographic observations of the flash spectrum at the February 25,
1952 solar eclipse at Khartoum, Sudan, were made by the High Altitude
Observatory of Harvard University and University of Colorado. A primary
purpose of the expedition was to obtain information about the hydrogen
Balmer and Paschen series. This information, in turn, will be used to
determine the electron temperature and electron density as a function
of height in the chromosphere. The observations employed three slitless
spectrographs covering the spectral range X88oo to X340o. *Of papers
presented at the Eighty-eighth Meeting of the American Astronomical
Society, Amherst, Mass., Dec. 28-31, 1952. We obtained 29 pairs of
visible and 17 pairs of ultraviolet spectrograms from X6400 to X3400,
which are of satisfactory quality. The 16 infrared spectrograms X88oo
to X6100 are underexposed. Imaged on the film during each exposure
were two simultaneous spectra, the pair having an intensity ratio
approximately 30:1. Each exposure also contained a data panel. The data
panel included clocks for determining the beginning and end of each
exposure and a photographic step-wedge for checking the characteristic
curve. Standard exposures from a tungsten ribbon-filament lamp taken
on the same roll of film as the eclipse spectrograms, but separately
processed, provide data for a first approximation to the characteristic
curve at any desired wave length. Corrections carried out by comparing
densities in the corresponding light and dark spectral images will then
give us reliable characteristic curves. The distribution of densities
in the coronal continuum gives further information for improving
the accuracy of the characteristic curve. More direct determination
of the characteristic curves is not possible because a part of the
standardizing program failed at the time of the eclipse. Using the
approximate characteristic curve obtained from the standard exposures,
we made preliminary measures of the intensities of the Balmer lines
near the series limit on 12 spectrograms at second contact. For this
we worked from positive prints of the original spectra. The heights at
which measurements were made extend from 700 km to 1930 km above the
base of the chromosphere, with observations every 108 km. We found
that the intensity of H31 is measurable to a height of 2150 km and
the intensity of H23 is measurable to 2700 km. In some spectrograms
a tentative identification shows H34, H35, and H36 to be resolved. We
are now initiating a more complete and more accurate reduction of the
data, working from the original films. The eclipse program of the High
Altitude Observatory is supported by the Naval Research Laboratory,
Office of Naval Research, and has been conducted in close collaboration
with the Laboratory. Three of the four authors are connected with the
High Altitude Observatory, J. W. Evans with the Upper Air Research
Observatory. High A ititude Observatory, Boulder, Cob., and Upper Air
Research Observatory, Sacramento Peak, Clouderoft, N. Mex.
Title: Analysis of the Balmer continuum from the 1952 eclipse.
Authors: Dimock, D. L.; Billings, D. E.; Athay, R. G.; Thomas, R. N.
Bibcode: 1953AJ.....58Q.213D
Altcode:
The continuum intensities mentioned in the preceding paper were
analyzed to determine the electron temperature and density in
the chromosphere.' Two equations relating these two quantities were
obtained by taking the ratio of the intensity at X3647 to the intensity
at X3700 and by taking the difference between these two intensities
after the intensity at X3700 was corrected empirically to X3647. The
quantity obtained by subtracting the two intensities represented the
free-bound emission in the Balmer continuum. The quantity represented
by the ratio of the two intensities included the contributions from
electron scattering, free-free emission, and free-bound emission for
the Balmer, Paschen, and higher hydrogen series. The solutions of the
equations involved two additional parameters. There was a non-trivial
contribution to the continuum intensities from the portion of the
corona extending beyond the moqn's limb on the third contact side of
the sun. The integration over the atmosphere involved an additional
unknown represented by the ratio of the free-bound emission gradient
to the electron density gradient. Both of these quantities were
carried as parameters and solutions carried out for a range of values
representing the possible extremes. The values of the latter parameter
placed a condition upon the solutions, and only the solutions which
were compatible with these conditions were accepted. It was found
that the extreme ranges of the acceptable solutions gave quite similar
results. The results show conclusively that the temperature increases
rapidly with height from about 90000K at 530 km to about 25,0000K at
2400 km. The electron densities are about 6 X 1011 at 530 km and 2 X
IO'~ at 2400 km. The solutions will be extended to give more specific
results and to extend the range of heights to both lower and higher
values. i. A. J. 58, 210, 1953. Johns Hopkins University, Baltimore,
Md., High Altitude Observatory, Boulder, Cob., and Harvard College
Observatory, Cambridge, Mass.