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Author name code: dappen
ADS astronomy entries on 2022-09-14
author:"Dappen, Werner"
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Title: Ionization of heavy elements and the adiabatic exponent in
the solar plasma
Authors: Baturin, V. A.; Oreshina, A. V.; Däppen, W.; Ayukov, S. V.;
Gorshkov, A. B.; Gryaznov, V. K.; Iosilevskiy, I. L.
2022A&A...660A.125B Altcode: 2022arXiv220209331B
Context. The adiabatic exponent Γ<SUB>1</SUB> is studied as a
thermodynamic quantity in the partially ionized plasma of the solar
convection zone. <BR /> Aims: The aim of this study is to understand the
impact of heavy elements on the Γ<SUB>1</SUB> profile. We calculated
Γ<SUB>1</SUB> with the SAHA-S equation of state for different
chemical compositions of plasma, and we analyzed contributions of
individual elements to Γ<SUB>1</SUB>. We attempted to determine
the mass fractions of the heavy elements using our analysis of the
Γ<SUB>1</SUB> profile. <BR /> Methods: We studied the decrease in
Γ<SUB>1</SUB> due to the ionization of heavy elements in comparison
with the value obtained for a pure hydrogen-helium plasma. These types
of differences are denoted as "Z contributions", and we analyzed them
for eight elements (C, N, O, Ne, Mg, S, Si, and Fe) as well as for a
mixture of elements corresponding to the solar chemical composition. The
contributions of the heavy elements are studied on an adiabat in the
lower part of the convection zone, where the influence of hydrogen and
helium to the Z contribution is minimal. The Z-contribution profiles
are unique for each chemical element. We compared linear combinations
of individual Z contributions with the exact Z contribution. Applying a
least-squares technique to the decomposition of the full Z contribution
to a basis of individual-element contributions, we obtained the mass
fractions of the heavy elements. <BR /> Results: The Z contribution
of heavy elements can be described by a linear combination of
individual-element Z contributions with a high level of accuracy of 5 ×
10<SUP>−6</SUP>. The inverse problem of estimating the mass fractions
of heavy elements from a given Γ<SUB>1</SUB> profile was considered
for the example of solar-type mixtures. In ideal numerical simulations,
the mass fractions of the most abundant elements could be determined
with a relative accuracy better than a few tenths of a percent. In the
presence of random or systematic errors in the Γ<SUB>1</SUB> profile,
abundance estimations become remarkably less accurate, especially
due to unknown features of the equations of state. If the amplitude
of the errors does not exceed 10<SUP>−4</SUP>, we can expect a
determination of at least the oxygen abundance with a relative error of
about 10%. Otherwise, the results of the method would not be reliable.
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Title: Better Physics for Modelling Stars and their Oscillations
Authors: Trampedach, R.; Houdek, G.; Däppen, W.
2020svos.conf..317T Altcode:
Our interpretation of stellar observations can only be as good
as our stellar models and the strong constraints provided by
asteroseismology demand very good models indeed. We have approached
modelling improvements from three angles: Including effects of
realistic 3D convection on the structure of stellar surface layers,
including non-adiabatic effects of that convection on oscillations,
and finally improving and modernising the equation of state for stellar
plasmas. We present a review of our progress on all three fronts.
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Title: Interpolation of equation-of-state data
Authors: Baturin, V. A.; Däppen, W.; Oreshina, A. V.; Ayukov, S. V.;
Gorshkov, A. B.
2019A&A...626A.108B Altcode: 2019arXiv190508303B
<BR /> Aims: We use Hermite splines to interpolate pressure and
its derivatives simultaneously, thereby preserving mathematical
relations between the derivatives. The method therefore guarantees
that thermodynamic identities are obeyed even between mesh points. In
addition, our method enables an estimation of the precision of the
interpolation by comparing the Hermite-spline results with those
of frequent cubic (B-) spline interpolation. <BR /> Methods: We
have interpolated pressure as a function of temperature and density
with quintic Hermite 2D-splines. The Hermite interpolation requires
knowledge of pressure and its first and second derivatives at every
mesh point. To obtain the partial derivatives at the mesh points, we
used tabulated values if given or else thermodynamic equalities, or,
if not available, values obtained by differentiating B-splines. <BR
/> Results: The results were obtained with the grid of the SAHA-S
equation-of-state (EOS) tables. The maximum lgP difference lies in
the range from 10<SUP>-9</SUP> to 10<SUP>-4</SUP>, and Γ<SUB>1</SUB>
difference varies from 10<SUP>-9</SUP> to 10<SUP>-3</SUP>. Specifically,
for the points of a solar model, the maximum differences are one
order of magnitude smaller than the aforementioned values. The poorest
precision is found in the dissociation and ionization regions, occurring
at T ∼ 1.5 × 10<SUP>3</SUP>-10<SUP>5</SUP> K. The best precision is
achieved at higher temperatures, T > 10<SUP>5</SUP> K. To discuss
the significance of the interpolation errors we compare them with
the corresponding difference between two different equation-of-state
formalisms, SAHA-S and OPAL 2005. We find that the interpolation errors
of the pressure are a few orders of magnitude less than the differences
from between the physical formalisms, which is particularly true for
the solar-model points.
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Title: Equation of state SAHA-S meets stellar evolution code CESAM2k
Authors: Baturin, V. A.; Däppen, W.; Morel, P.; Oreshina, A. V.;
Thévenin, F.; Gryaznov, V. K.; Iosilevskiy, I. L.; Starostin, A. N.;
Fortov, V. E.
2017A&A...606A.129B Altcode: 2017arXiv170804937B
Context. We present an example of an interpolation code of the SAHA-S
equation of state that has been adapted for use in the stellar evolution
code CESAM2k. <BR /> Aims: The aim is to provide the necessary data
and numerical procedures for its implementation in a stellar code. A
technical problem is the discrepancy between the sets of thermodynamic
quantities provided by the SAHA-S equation of state and those necessary
in the CESAM2k computations. Moreover, the independent variables
in a practical equation of state (like SAHA-S) are temperature and
density, whereas for modelling calculations the variables temperature
and pressure are preferable. Specifically for the CESAM2k code, some
additional quantities and their derivatives must be provided. <BR />
Methods: To provide the bridge between the equation of state and
stellar modelling, we prepare auxiliary tables of the quantities
that are demanded in CESAM2k. Then we use cubic spline interpolation
to provide both smoothness and a good approximation of the necessary
derivatives. Using the B-form of spline representation provides us with
an efficient algorithm for three-dimensional interpolation. <BR />
Results: The table of B-spline coefficients provided can be directly
used during stellar model calculations together with the module of
cubic spline interpolation. This implementation of the SAHA-S equation
of state in the CESAM2k stellar structure and evolution code has been
tested on a solar model evolved to the present. A comparison with other
equations of state is briefly discussed. <BR /> Conclusions: The choice
of a regular net of mesh points for specific primary quantities in the
SAHA-S equation of state, together with accurate and consistently smooth
tabulated values, provides an effective algorithm of interpolation in
modelling calculations. The proposed module of interpolation procedures
can be easily adopted in other evolution codes.
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Title: Dynamic Screening in Solar and Stellar Nuclear Reactions
Authors: Däppen, W.; Mussack, K.
2012CoPP...52..149D Altcode:
No abstract at ADS
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Title: Microphysics of Stellar Interiors
Authors: Däppen, Werner
2011iasa.confE...5D Altcode:
No abstract at ADS
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Title: High-Precision Equation-of-State Formalisms for Solar and
Stellar Modeling
Authors: Däppen, Werner
2011CoPP...51..328D Altcode:
No abstract at ADS
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Title: Dynamic Screening Correction for Solar p-p Reaction Rates
Authors: Mussack, Katie; Däppen, Werner
2011ApJ...729...96M Altcode: 2011arXiv1102.5073M
The solar abundance controversy inspires renewed investigations of
the basic physics used to develop solar models. Here we examine
the correction to the proton-proton reaction rate due to dynamic
screening effects. Starting with the dynamic screening energy from the
molecular-dynamic simulations of Mao et al., we compute a reaction-rate
correction for dynamic screening. We find that, contrary to static
screening theory, this dynamic screening does not significantly change
the reaction rate from that of the bare Coulomb potential.
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Title: Dynamic screening in solar and stellar nuclear reactions
Authors: Mussack, Katie; Däppen, Werner
2010Ap&SS.328..153M Altcode: 2010Ap&SS.tmp....8M; 2009arXiv0909.2646M
In the hot, dense plasma of solar and stellar interiors, the Coulomb
interaction is screened by the surrounding plasma. Although the
standard Salpeter approximation for static screening is widely
accepted and used in stellar modeling, the question of dynamic
screening has been revisited. In particular, Shaviv and Shaviv
apply the techniques of molecular dynamics to the conditions in the
solar core in order to numerically determine the dynamic screening
effect. By directly calculating the motion of ions and electrons due to
Coulomb interactions, they compute the effect of screening without the
mean-field assumption inherent in the Salpeter approximation. Here we
reproduce their numerical analysis of the screening energy in the plasma
of the solar core and conclude that the effects of dynamic screening
are relevant and should be included in the treatment of the plasma,
especially in the computation of stellar nuclear reaction rates.
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Title: Emulating the OPAL equation of state
Authors: Lin, Hsiao-Hsuan; Däppen, Werner
2010Ap&SS.328..175L Altcode: 2010Ap&SS.tmp...27L
The equation of state for the structure of the Sun and stars has to
be precise to allow comparisons with observations, i.e., helioseismic
inversions of thermodynamic quantities. Among the two of the most
popular formalisms are (1) the OPAL equation of state developed
at Livermore and (2) the Mihalas-Hummer-Däppen (MHD) equation of
state. While OPAL has a solid theoretical foundation, and matches the
observational data better, the MHD formalism is more intuitive, easy to
realize, and has the possibility of adjustable parameters. Furthermore,
it an open-source product in contrast to the proprietary OPAL. Recently
a version of MHD has been obtained by including the so-called
“Plank-Larkin partition function” and by adding scattering-state
terms. The resulting formalism matches OPAL rather well. Here, we report
on the next logical step, the implementation of this MHD upgrade into
the simple and popular CEFF equation of state. Such an implementation
will make it a flexible and convenient tool, allowing an approximative
on-line implementation of OPAL in solar and stellar models.
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Title: Accurate and versatile equations of state for the Sun and
Sun-like stars
Authors: Däppen, Werner
2010Ap&SS.328..139D Altcode: 2010Ap&SS.tmp...37D
For models of the Sun and Sun-like stars, a high-quality equation
of state is crucial. In addition, helioseismic and asteroseismic
observations also put constraints on the physical formalisms. Thus,
they effectively turn the Sun and the stars into laboratories
for dense plasmas. Currently, the main astrophysical beneficiary
of a good equation of state is the determination of the chemical
composition. Here, seismic data have supplemented spectroscopic
information. Recently, there has been theoretical progress in the
equation of state, thanks to renewed rigorous and phenomenological
approaches.
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Title: The solar-interior equation of state with the path-integral
formalism. I. Domain of validity
Authors: Perez, A.; Mussack, K.; Däppen, W.; Mao, D.
2009A&A...505..735P Altcode:
Aims: This is the first paper in a series that deals with solar-physics
applications of the equation-of-state formalism based on the formulation
of the so-called “Feynman-Kac (FK) representation”. Here, the FK
equation of state is presented and adapted for solar applications. Its
domain of validity is assessed. The practical application to the Sun
will be dealt with in Paper II. Paper III will extend the current
FK formalism to a higher order. <BR />Methods: A recent rigorous
quantum-statistical formalism for Coulomb systems is used to compute
the thermodynamical quantities for solar modeling, taking into account
the necessary requirements on smoothness and accuracy. The FK formalism
being a virial expansion, it suffers from the well-known deficiency
that it is limited to nearly full ionization. This point is elaborated
in detail, and the quantitative criterion for the domain of validity
of the FK equation of state is established. <BR />Results: Use of the
FK equation of state is limited to physical conditions for which more
than 90% of helium is ionized. This includes the inner region of the
Sun out to about .98 of the solar radius. Despite this limitation,
in the parts of the Sun where it is applicable, the FK equation of
state has the power to be more accurate than the equations of state
currently used in solar modeling. The FK approach is especially suited
to study physical effects such as Coulomb screening, bound states,
the onset of recombination of fully ionized species, as well as
diffraction and exchange effects. <BR />Conclusions: Despite technical
difficulties in its application, there are unique features in the FK
approach that promise to turn it into the most exact of the available
formalisms, provided FK is restricted to the deeper layers of the
Sun where more than 90% of helium is ionized. The localizing power
of helioseismology allows a test of the FK equation of state. Such a
test will be beneficial both for better solar models and for tighter
solar constraints of the equation of state.
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Title: Dynamic Screening in Solar Plasma
Authors: Mao, Dan; Mussack, Katie; Däppen, Werner
2009ApJ...701.1204M Altcode: 2009arXiv0906.3406M
In the hot, dense plasma of solar and stellar interiors, Coulomb
potentials are screened, resulting in increased nuclear reaction
rates. Although Salpeter's approximation for static screening
is widely accepted and used in stellar modeling, the question of
screening in nuclear reactions has been revisited. In particular,
the issue of dynamic effects has been raised by Shaviv and Shaviv
who apply the techniques of molecular dynamics to the conditions
in the Sun's core in order to numerically determine the effect of
screening. By directly calculating the motion of ions and electrons
due to Coulomb interactions, the simulations are used to compute the
effect of screening without the mean field assumption inherent in
Salpeter's approximation. In this paper, we reproduce their numerical
analysis of the screening energy in the plasma of the solar core and
conclude that the effects of dynamic screening are relevant and should
be included when stellar nuclear reaction rates are computed.
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Title: A smooth equation of state for solar and stellar abundance
determinations
Authors: Däppen, Werner; Mao, Dan
2009JPhA...42u4006D Altcode:
The modulation of the equation of state by the chemical composition
leads to a natural method to determine the helium and heavy-element
abundance in the sun and stars. For solar helium this has indeed become
the only reliable method. However, one has to keep in mind that the
result is only as good as the quality of the equation of state. So far,
there are only theoretical formalisms, but no experiments, for the
relevant physical conditions. It is obvious that sharp theoretical
tools in the form of smooth thermodynamic (and opacity) quantities
are crucial for the interpretation of the astrophysical data, both for
abundance determinations and improvements of the theory. An emulator of
the OPAL equation of state was developed, by which the OPAL equation
of state can be applied directly in stellar models, without recourse
to pre-computed tables.
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Title: Rigorous and Phenomenological Equations of State
Authors: Däppen, Werner; Mao, Dan
2008IAUS..252...27D Altcode:
For solar and stellar modeling, a high-quality equation of state
is crucial. But the inverse is also true: the astrophysical data
(helioseismic today, asteroseismic tomorrow) put constraints on
the physical formalisms, making the Sun and the stars laboratories
for plasma physics. One of the main astrophysical benefits from a
good equation of state is an improved abundance determination. Recent
theoretical progress in the equation of state has involved both rigorous
and phenomenological approaches, giving the user a considerable choice.
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Title: Seismic Abundance Determination in the Sun and in Stars
Authors: Däppen, Werner
2007AIPC..948..179D Altcode:
The modulation of the equation of state by the chemical composition
leads to a natural helio- and asteroseismic method to determine the
helium and heavy-element abundance. The idea was first proposed by
Douglas Gough, who suggested to exploit the thermodynamic signature of
each element. For solar helium this became indeed the only reliable
method. Its result (0.24-0.25 in mass fraction) turned out to be
substantial lower than the calibrated values for age-zero solar
models (0.27-0.28), a discrepancy which drew renewed attention to
the importance of the effect of gravitational settling of helium
and heavier elements. One has to keep in mind that the result is
only as good as the quality of the equation of state, and so far,
there are only theoretical formalisms, but no experiments, for
the relevant physical conditions. Astrophysical constraints on the
quality of the equation of state, however, might come from the solar
heavy-element abundance determination. For the heavy elements there
are spectroscopic measurements (recently somewhat clouded in doubt
though). These measurements can be used to constrain the equation of
state. As a consequence, the seismic element determinations become
part of a larger project, making the Sun and stars laboratories to
study thermodynamic properties of Coulomb systems under conditions not
(yet) achieved on Earth. In this enterprise, asteroseismology will
play an important parallel role, where the lack of solar-quality data
will be more than compensated by the possibility to study stars of
significantly different element abundances.
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Title: Evaluation of Molecular-Dynamics Simulations for the Study
of Hot Dense Coulomb Systems
Authors: Mussack, Katie; Mao, Dan; Däppen, Werner
2007AIPC..948..207M Altcode:
In the plasma of solar and stellar interiors, Coulomb potentials
are screened, resulting in increased nuclear reaction rates. Though
Salpeter's approximation for static screening is widely accepted
and used in stellar modelling, the question of screening in nuclear
reactions has recently been revisited. In particular the issue of
dynamic effects has been raised by Shaviv and Shaviv who apply the
techniques of molecular dynamics to the conditions in the Sun's
core in order to numerically determine the effect of screening. By
directly calculating the motion of ions and electrons due to Coulomb
interactions, they are able to compute the effect of screening without
the mean field assumption inherent in Salpeter's approximation. However,
Shaviv and Shaviv's work includes a variety of assumptions that
must be evaluated before their results can be accepted. We carried
out a pilot study of a small system under conditions similar to the
solar core in order to examine the assumptions and approximations in
Shaviv and Shaviv's numerical simulations. Our work confirms Shaviv and
Shaviv's conclusion that instead of relying on the static approximation,
dynamic effects must also be considered.
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Title: The Solar-Interior Equation of State with the Path-Integral
Formalism I. Domain of Validity
Authors: Perez, Asher; Mussack, Katie; Dappen, Werner; Mao, Dan
2007arXiv0705.0547P Altcode:
This is the first paper in a series that deals with solar-physics
applications of the equation-of-state formalism based on the formulation
of the so-called "Feynman-Kac (FK) representation". Here, the FK
equation of state is presented and adapted for solar applications. Its
domain of validity is assessed. The practical application to the Sun
will be dealt with in Paper II. Paper III will extend the current
FK formalism to a higher order. Use of the FK equation of state is
limited to physical conditions for which more than 90% of helium is
ionized. This incudes the inner region of the Sun out to about .98
of the solar radius. Despite this limitation, in the parts of the
Sun where it is applicable, the FK equation of state has the power to
be more accurate than the equations of state currently used in solar
modeling. The FK approach is especially suited to study physical effects
such as Coulomb screening, bound states, the onset of recombination of
fully ionized species, as well as diffraction and exchange effects. The
localizing power of helioseismology allows a test of the FK equation
of state. Such a test will be beneficial both for better solar models
and for tighter solar constraints of the equation of state.
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Title: Helioseismology and Plasma Physics
Authors: Däppen, W.
2007ASPC..370....3D Altcode:
Helioseismology has become a very successful diagnosis of the equation
of state. Although the gas in the solar interior is only weakly
coupled and weakly degenerate, the great observational accuracy of
the helioseismological measurements puts strong constraints on the
nonideal part of the equation of state. For solar and stellar modeling,
a high-quality equation of state is crucial. But the inverse is also
true: the observational data put constraints on the physical formalisms,
thus making the Sun and the stars laboratories for plasma physics. The
main diagnostic methods are discussed.
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Title: Molecular-dynamics simulations of hot dense Coulomb systems
Authors: Mussack, K.; Mao, D.; Däppen, W.
2006ESASP.624E..20M Altcode: 2006soho...18E..20M
No abstract at ADS
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Title: A Synoptic Comparison of the Mihalas-Hummer-Däppen and OPAL
Equations of State
Authors: Trampedach, R.; Däppen, W.; Baturin, V. A.
2006ApJ...646..560T Altcode: 2006astro.ph..4352T
A detailed comparison is carried out between two popular equations of
state (EOSs), the Mihalas-Hummer-Däppen (MHD) and OPAL equations of
state, which have found widespread use in solar and stellar modeling
during the past two decades. They are parts of two independent efforts
to recalculate stellar opacities: the international Opacity Project (OP)
and the Livermore-based OPAL project. We examine the difference between
the two EOSs in a broad sense, over the whole applicable ϱ-T range,
and for three different chemical mixtures. Such a global comparison
highlights both their differences and their similarities. We find that
omitting a questionable hard-sphere correction, τ, to the Coulomb
interaction in the MHD formulation, greatly improves the agreement
between the MHD and OPAL EOSs. We also find signs of differences
that could stem from quantum effects not yet included in the MHD EOS,
and differences in the ionization zones that are probably caused by
differences in the mechanisms for pressure ionization. Our analysis
not only gives a clearer perception of the limitations of each EOS for
astrophysical applications, but also serves as guidance for future work
on the physical issues behind the differences. The outcome should be
an improvement of both EOSs.
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Title: The equation of state for the solar interior
Authors: Däppen, Werner
2006JPhA...39.4441D Altcode:
Helioseismology has become a very successful diagnosis of the equation
of state. Although the gas in the solar interior is only weakly
coupled and weakly degenerate, the great observational accuracy of the
helioseismological measurements puts strong constraints on the nonideal
part of the equation of state. For solar and stellar modelling, a
high-quality equation of state is crucial. But the inverse is also true:
the astrophysical data (helioseismic today, asteroseismic tomorrow)
can put constraints on the physical formalisms, thus making the Sun
and the stars laboratories for plasma physics.
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Title: The Chemical Composition and Equation of State of the Sun
Inferred from Seismic Models through an Inversion Procedure
Authors: Lin, Chia-Hsien; Däppen, Werner
2005ApJ...623..556L Altcode:
The remarkable quality of present helioseismic data provides the
possibility to investigate the microscopic physics of the solar
interior. An inversion procedure to reveal the equation of state
and chemical composition in the Sun has been developed. The
method is based on using the discrepancy in the adiabatic
gradient γ<SUB>1</SUB>≡(∂lnP/∂lnρ)<SUB>s</SUB> (s being
the specific entropy) to infer the discrepancies in the equation
of state and in the chemical composition between the Sun and solar
models. Adequate accuracy and stability of the procedure have been
demonstrated. Our inverted δγ<SUB>1</SUB>/γ<SUB>1</SUB> between
the Sun and model S of Christensen-Dalsgaard et al. is consistent
with the earlier result obtained by Basu et al. We also found that
the inverted δγ<SUB>1</SUB>/γ<SUB>1</SUB> between the Sun and an
envelope model implemented with the so-called CEFF equation of state
(Christensen-Dalsgaard & Däppen) basically shows two dips. The
dips are located at 0.975 and 0.988 R<SUB>solar</SUB>. Both dips
cannot be eliminated merely by tuning the helium abundance over a
reasonable range; hence, it appears that the dips are a manifestation
of inappropriate approximations used in the equation of state of the
underlying models.
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Title: Equation-of-State and Phase-Transition in Models of Ordinary
Astrophysical Matter
Authors: Celebonovic, Vladan; Gough, Douglas; Däppen, Werner
2004AIPC..731.....C Altcode:
No abstract at ADS
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Title: Development of Molecular-Dynamics Tools to Study Hot Dense
Coulomb Systems
Authors: Mao, D.; Mussack, K.; Däppen, W.
2004ESASP.559..560M Altcode: 2004soho...14..560M
No abstract at ADS
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Title: The chemical composition and equation of state of the Sun
inferred from seismic models through an inversion procedure
Authors: Lin, Chia-Hsien; Däppen, Werner
2004AIPC..731..230L Altcode:
The present helioseismic data, with their remarkable precision,
provide the possibility to investigate the microscopic physics of
the solar interior. In this study, we are specifically interested in
the chemical composition and equation of state (EOS). Since these
properties are not directly measurable, we chose the adiabatic
gradient, γ1 ≡ ∂lnP/∂lnρ|s, as the probe to examine these
properties. Specifically, we infer the discrepancies in the chemical
composition and EOS by the discrepancy in γ1, i.e., δγ1/γ1,
between two solar structures. <P />Even though the heavy elements
only constitute less than 2% of the solar material, our inversion
results showed that the variation in the relative abundances among
heavy elements would result in discernible features in δγ1/γ1.
---------------------------------------------------------
Title: The Chemical Composition and Equation of State of the Sun
Inferred from Seismic Models Through AN Inversion Procedure
Authors: Däppen, W.; Lin, C. -H.
2004ESASP.559..400D Altcode: 2004soho...14..400D
No abstract at ADS
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Title: Phenomenological and Rigorous Equations of State for Solar
and Stellar Modeling
Authors: Dappen, W.
2004ESASP.559..261D Altcode: 2004soho...14..261D
No abstract at ADS
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Title: Equations of state for solar and stellar modeling
Authors: Däppen, Werner
2004AIPC..731....3D Altcode:
Helioseismology has become the most successful diagnosis of the equation
of state for the plasma of stellar interiors. Although in the solar
interior the plasma is only weakly coupled and weakly degenerate, the
great observational accuracy of the helioseismological observations puts
nevertheless strong constraints on the nonideal part of the equation
of state. For solar and stellar modeling, a high-quality equation
of state is crucial. But the inverse is also true: the astrophysical
data put constraints on the physical formalisms, making the Sun and
the stars novel laboratories for plasma physics.
---------------------------------------------------------
Title: Isolating the effects of chemical composition in the equation
of state
Authors: Lin, Chia-Hsien; Däppen, Werner
2004AIPC..731..219L Altcode:
The effects of different chemical compositions and of different
equation-of-state formalisms on a solar structure are often mixed. The
reason being that the chemical composition in modern, sophisticated
equations of state cannot be easily adjusted. Therefore, most of related
studies simply consider the combined effect of the two, rather than
individual effect. The actual error in the formalism of the equation
of state is thus inevitably obscured. <P />The aim of this paper is
to examine and isolate the effects of varying chemical compositions,
in hope to help to extract the effects purely from the formalism
of equation of state. <P />We present a strategy and the results of
examining the effects of the ionization of individual element.
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Title: Emulating the Opal Equation of State
Authors: Liang, A.; Däppen, W.
2004ESASP.559..548L Altcode: 2004soho...14..548L
No abstract at ADS
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Title: Equation of State for the Internal Structure of Solar-Type
Stars
Authors: Baturin, V. A.; Däppen, W.
2003ARep...47..685B Altcode:
The physical basis for thermodynamical modeling of plasma under the
conditions typical of moderate-mass stars is considered. We apply
the method of thermodynamic potentials to introduce chemical and
physical plasma models that represent basic, modern descriptions
of a nondegenerate, weakly nonideal plasma. Ionization of an
ideal multicomponent plasma at low temperatures is used as a basic
approximation for the solar convection zone and in the corresponding
chemical picture. The effects of Coulomb free-free and bound-free
electron interactions are classified according to their appearance
in the solar interior. Modeling internal stellar structure requires a
formalism with nonideal ionization at high densities (frequently called
pressure ionization). Perspectives for describing such ionization are
considered in the framework of several models.
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Title: Helioseismic constraints on the chemical composition and the
equation of state
Authors: Lin, Chia-Hsien; Däppen, Werner
2003ESASP.517..337L Altcode: 2003soho...12..337L
The intrinsic γ<SUB>1</SUB> difference is defined as the discrepancy in
the adiabatic exponent γ<SUB>1</SUB>, resulting from the discrepancies
in the equation of state and the chemical composition. The other
part of the γ<SUB>1</SUB> difference, "induced" by the discrepancy
in the internal structure (i.e., pressure, density or temperature) is
excluded. Our examination of solar models revealed that the discrepancy
in the heavy-element composition and the discrepancy in the equation of
state result in different and independent features in the functional
form of the intrinsic γ<SUB>1</SUB> difference. Therefore, the two
discrepancies can be distinguished by looking for the features that
do not change when only either the equation of state or the chemcical
composition is being varied. The possibility of such a strategy was
already discussed in an earlier study (Gong, Däppen and Nayfonov
2001), although only theoretically. Our inversion tests demonstrate
the potential of its realization. In this paper, we present our initial
inversion results between the Sun and various solar models and discuss
the strengths and limits of our inversion code.
---------------------------------------------------------
Title: Modifications of the equation of state to achieve desired
changes in thermodynamic quantities
Authors: Liang, Aihua; Däppen, Werner
2003ESASP.517..333L Altcode: 2003soho...12..333L
Various helioseismological applications are subject to the uncertainty
in the equation of state. A typical example is the helioseismic
determination of the helium abundance in the convection zone. Only
confidence in the quality of the equation of state will lead to a
reliable result. There are several methods to improve the quality,
depending on the type of the equation of state. Some equations of
state are rather fundamental, but become very complicated for realistic
astrophysical matter. An example is the OPAL equation of state developed
at Livermore. Other equations of state are more intuitive and less
rigorous, but easier in their practical realization. An example is
the Mihalas-Hummer-Däppen (MHD) equation of state. It makes sense
therefore to try to modify the physical parameters in MHD, such that
it can emulate OPAL. The result will be a flexible tool for stellar
modelers. We report on preliminary work in this direction, based on
a systematic study of the response of the thermodynamic quantities to
several classes of modifications of the occupation probabilities, as
well as different truncations of the internal partition functions. We
have also re-visited the issue of the so-called Planck-Larkin partition
function (PLPF).
---------------------------------------------------------
Title: Investigating inversion uncertainties resulting from mode
selections
Authors: Lin, Chia-Hsien; Däppen, Werner
2003ESASP.517..341L Altcode: 2003soho...12..341L
The quality of an inversion depends on many factors. In addition to
the well known ones, such as the target function, the surface term
and the suppression parameters, different inversion codes utilizing
different matrix inversion algorithms could also bring in an additional
uncertainty. Therefore, it is important to assess the uncertainty
and the stability of an inversion code prior using it to obtain any
reliable result. The examination of our inversion code suggested the
following: low-degree low-order modes are essential for an accurate
inversion; when the quantity being inverted contains narrow features
near the surface, the inversions using different mode sets would be
inconsistent. In this paper, we show some representative results,
in order to invite stimulating discussions and insightful suggestions.
---------------------------------------------------------
Title: Solar constraints on the equation of state
Authors: Däppen, Werner
2003safd.book..179D Altcode:
Helioseismology has become a very successful diagnosis of the equation
of state of the plasma of the solar interior. Although the gas in the
solar interior is only weakly coupled and weakly degenerate, the great
observational accuracy of the helioseismological measurements puts
strong constraints on the nonideal part of the equation of state. The
helioseismic verification of major nonideal effects in the equation
of state of solar matter has become well established. The dominant
contribution is the Coulomb pressure, conventionally described in the
Debye-Hückel approximation. However, in the last years, the increased
precision of the helioseismic diagnosis has brought significant
observational progress beyond the Debye-Hückel approximation. The
helioseismic detection of a signature of relativistic electrons was
a striking example. Very recently, effects of the excited states of
the atoms and ions of heavy elements were discovered, which have a
promising potential both for statistical mechanics and solar physics,
in particular, the helioseismic determination of the heavy-elemental
abundance.
---------------------------------------------------------
Title: The plasma-solid transition: Some implications in astrophysics
Authors: Celebonovic, V.; Dappen, W.
2002SerAJ.165...23C Altcode: 2002astro.ph..6009C
Using a criterion proposed by Salpeter and standard solid-state physics,
we have determined the Debye temperature of a solid in equilibrium
with the electron gas surrounding it. The results obtained can have
astrophysical applications in the determination of parameters of
interstellar and interplanetary clouds.
---------------------------------------------------------
Title: Effects of Heavy Elements and Excited States in the Equation
of State of the Solar Interior
Authors: Gong, Zhigang; Däppen, Werner; Nayfonov, Alan
2001ApJ...563..419G Altcode: 2001astro.ph..8307G
Although 98% of the solar material consists of hydrogen and helium,
the remaining chemical elements contribute in a discernible way to
the thermodynamic quantities. An adequate treatment of the heavy
elements and their excited states is important for solar models that
are subject to the stringent requirements of helioseismology. The
contribution of various heavy elements in a set of thermodynamic
quantities has been examined. Characteristic features that
can trace individual heavy elements in the adiabatic exponent
γ<SUB>1</SUB>=(∂lnp/∂lnϱ)<SUB>s</SUB> (s being specific entropy),
and hence in the adiabatic sound speed, were searched. It has emerged
that prominent signatures of individual elements exist and that these
effects are greatest in the ionization zones, typically located near
the bottom of the convection zone. The main result is that part of
the features found here depend strongly on both the given species
(atom or ion) and its detailed internal partition function, whereas
other features only depend on the presence of the species itself, not
on details such as the internal partition function. The latter features
are obviously well suited for a helioseismic abundance determination,
while the former features present a unique opportunity to use
the Sun as a laboratory to test the validity of physical theories
of partial ionization in a relatively dense and hot plasma. This
domain of plasma physics has so far no competition from terrestrial
laboratories. Another, quite general, finding of this work is that the
inclusion of a relatively large number of heavy elements has a tendency
to smear out individual features. This affects both the features that
determine the abundance of elements and the ones that identify physical
effects. This property alleviates the task of solar modelers because it
helps to construct a good working equation of state that is relatively
free of the uncertainties from basic physics. By the same token, it
makes more difficult the reverse task, which is constraining physical
theories with the help of solar data.
---------------------------------------------------------
Title: Changes in convective properties over the solar cycle: effect
on p-mode damping rates
Authors: Houdek, G.; Chaplin, W. J.; Appourchaux, T.;
Christensen-Dalsgaard, J.; Däppen, W.; Elsworth, Y.; Gough, D. O.;
Isaak, G. R.; New, R.; Rabello-Soares, M. C.
2001MNRAS.327..483H Altcode:
Measurements of both solar irradiance and p-mode oscillation
frequencies indicate that the structure of the Sun changes with
the solar cycle. Balmforth, Gough & Merryfield investigated the
effect of symmetrical thermal disturbances on the solar structure
and the resulting pulsation frequency changes. They concluded that
thermal perturbations alone cannot account for the variations in both
irradiance and p-mode frequencies, and that the presence of a magnetic
field affecting acoustical propagation is the most likely explanation
of the frequency change, in the manner suggested earlier by Gough &
Thompson and by Goldreich et al. Numerical simulations of Boussinesq
convection in a magnetic field have shown that at high Rayleigh number
the magnetic field can modify the preferred horizontal length scale
of the convective flow. Here, we investigate the effect of changing
the horizontal length scale of convective eddies on the linewidths
of the acoustic resonant mode peaks observed in helioseismic power
spectra. The turbulent fluxes in these model computations are obtained
from a time-dependent, non-local generalization of the mixing-length
formalism. The modelled variations are compared with p-mode linewidth
changes revealed by the analysis of helioseismic data collected by
the Birmingham Solar-Oscillations Network (BiSON); these low-degree
(low-l) observations cover the complete falling phase of solar activity
cycle 22. The results are also discussed in the light of observations
of solar-cycle variations of the horizontal size of granules and with
results from 2D simulations by Steffen of convective granules.
---------------------------------------------------------
Title: Generalized Fermi-Dirac functions and derivatives: properties
and evaluation
Authors: Gong, Z.; Zejda, L.; Däppen, W.; Aparicio, J. M.
2001CoPhC.136..294G Altcode: 2001astro.ph..2329G
The generalized Fermi-Dirac functions and their derivatives are
important in evaluating the thermodynamic quantities of partially
degenerate electrons in hot dense stellar plasmas. New recursion
relations of the generalized Fermi-Dirac functions have been found. An
effective numerical method to evaluate the derivatives of the
generalized Fermi-Dirac functions up to third order with respect to
both degeneracy and temperature is then proposed, following Aparicio
[Ap.J.S.S. 117 (1998) 627]. A Fortran program based on this method,
together with a sample test case, is provided. Accuracy and domain
of reliability of some other, popularly used analytic approximations
of the generalized Fermi-Dirac functions for extreme conditions are
investigated and compared with our results.
---------------------------------------------------------
Title: The plasma-solid transition
Authors: Celebonovic, V.; Dappen, W.
2001astro.ph..2284C Altcode:
Using a criterion proposed by Salpeter and standard solid-state
physics,we have determined conditions for the occurence of the
plasma-solid transition.Possible astrophysical applications are
discussed.
---------------------------------------------------------
Title: Inversion for the adiabatic gradient γ<SUB>1</SUB> to examine
equation-of-state effects
Authors: Lin, Chia-Hsien; Däppen, Werner
2001ESASP.464..527L Altcode: 2001soho...10..527L
The inversion method SOLA (subtractive optimally localized averages)
has been successfully applied to study various properties of the
solar interior. The focus of the present work is on the microscopic
properties of solar matter. The following topics are prime targets of
our investigation: (I) ionization of helium and heavy-elements in the
deeper parts of the convection zone; (II) the discrepancy in the results
of the helioseismic helium abundance determination from different
inversion procedures; (III) the possibility of a remainder of not fully
ionized helium in the solar core. For the diagnosis of the equation
of state, an inversion for the adiabatic gradient γ<SUB>1</SUB> =
(∂ln p/∂ln ρ)<SUB>s</SUB> (s being specific entropy), and not sound
speed, is the most appropriate. This is because the adiabatic gradient
is mainly a function of the microscopic physics (ionization reaction;
Coulomb pressure correction; pressure ionization; etc.) rather than
the macroscopic structure of the model. We are adopting the inversion
technique of Basu, Däppen & Nayfonov (1999) and modify it for
our purposes. Preliminary results are presented in this paper.
---------------------------------------------------------
Title: MHD Equation of State with Relativistic Electrons
Authors: Gong, Zhigang; Däppen, Werner; Zejda, Ladislav
2001ApJ...546.1178G Altcode:
The Mihalas-Däppen-Hummer (MHD) equation of state does not include
the effect of relativistic partially degenerate electrons, although
nonrelativistic partial degeneracy is taken into account. The discovery
of a relativistic correction in helioseismology forces us to perform
an appropriate upgrade of the MHD equation of state. We have adopted
the method of J. M. Aparicio to evaluate the relativistic Fermi-Dirac
functions. Our calculations confirm the validity of the approximation
used, which works well for the weakly relativistic electrons under
solar-center conditions. However, our results will also provide reliable
thermodynamic quantities in the stronger relativistic regime as found
in more massive stars. Since a particular feature of the original MHD
papers was an explicit list of the adopted free energy and its first-
and second-order analytical derivatives, we give the corresponding
relativistic quantities in the Appendix.
---------------------------------------------------------
Title: Extracting the excitation function on solar oscillations by
means of deconvolution
Authors: Lin, Chia-Hsien; Däppen, Werner
2001ESASP.464..649L Altcode: 2001soho...10..649L
Acoustic oscillations normally are excited by continuous convective
motion. Because of the turbulent nature of convection, the low-degree
modes generated by convection should be uncorrelated. However, in
earlier studies (e.g., Baudin, Gabriel, Gibert, Palle & Regulo
(1996), Foglizzo (1998)), a possible correlation between different
modes was noticed in the IPHIR data. It was suspected that there
might have been occasional solar activities as excitation sources
during this period of time. However, the existence of this kind of
excitation mechanism was not directly shown. The goal of this study
is to reconstruct the forcing function that causes the excitation. In
typical observations of solar oscillations, the sampling time (around
1 minute) is insufficient to resolve the excitation resulting from
continuous convection. Thus, only infrequent excitation caused by
irregular events can be revealed. Therefore, this method can become a
tool to investigate infrequent solar events. The testing results from
artificial signals have been reported in our previous paper (Lin &
Däppen, 2000). Here, we present our current status of the application
to four sets of real signals: SOI/MDI, VIRGO, GOLF and IPHIR.
---------------------------------------------------------
Title: Solar Interior: Equation of State and Opacity
Authors: Däppen, W.
2000eaa..bookE2002D Altcode:
In stellar models, the equation of state and opacity are, together
with nuclear reaction rates, the fundamental material properties. The
structure of a star is a result of (i) a balance of forces, (ii)
a balance between the energy loss at the stellar surface and energy
generation in the core and (iii) stationary energy transport between
the core and the surface (see SOLAR INTERIOR: STANDARD MODEL...
---------------------------------------------------------
Title: Stellar Interiors: Thermodynamics
Authors: Däppen, W.
2000eaa..bookE2122D Altcode:
Material properties and stellar models...
---------------------------------------------------------
Title: Seismology of the solar envelope: sound-speed gradient in
the convection zone and its diagnosis of the equation of state
Authors: Baturin, V. A.; Däppen, W.; Gough, D. O.; Vorontsov, S. V.
2000MNRAS.316...71B Altcode:
We report the results of an asymptotic inversion of solar oscillation
data for the gradient of the sound speed in the convection zone. This
gradient reveals details of the non-ideal Coulomb interactions between
particles, including pressure ionization. A simplified physical model
is used to track down the effect of various physical assumptions in
the sound-speed derivative. The model contains a calibration for the
size of the H and He atoms and the He<SUP>+</SUP> ion. We find that,
for the pressure-ionization regions of hydrogen and helium, such a
model matches the data better than any of the currently available
parameter-free theories.
---------------------------------------------------------
Title: The plasma-solid transition:two simple examples
Authors: Celebonovic, V.; Dappen, W.
2000astro.ph..7337C Altcode:
Using a simple criterion proposed by Kirzhnitz,we have discussed the
plasma-solid transition in two simple model cases: the Fermi-Dirac and
Bose Einstein gas.Some possibilities of astrophysical applications of
our results are also indicated.
---------------------------------------------------------
Title: Investigating the excitation of acoustic modes using
homomorphic deconvolution
Authors: Lin, Chia-Hsien; Däppen, Werner
2000SoPh..193..357L Altcode:
Properties of the convection zone are encrypted in the behavior of
acoustic modes (p modes) and also in the excitation mechanism. The goal
of this study is to reconstruct the pattern of the excitation (e.g.,
the rate and strength of the excitation) from an observed signal. The
method, homomorphic deconvolution, has been tested on several sets
of artificial signals. The preliminary results presented here are
promising. Further rigorous tests and the eventual application to a
real signal will be carried out in the near future.
---------------------------------------------------------
Title: The Sun as an Equation-of-State Laboratory
Authors: Däppen, Werner; Nayfonov, Alan
2000ApJS..127..287D Altcode:
Thanks to helioseismology, the equation of state of the plasma
of the solar interior can be diagnosed. Although the gas in the
solar interior is only weakly coupled and weakly degenerate, the
great observational accuracy of the helioseismic measurements puts
strong constraints on the nonideal part of the equation of state. The
helioseismic verification of major nonideal effects in the equation
of state of solar matter has become well established. The dominant
contribution is the Coulomb pressure, conventionally described in the
Debye-Hückel approximation. However, recently the increased precision
of the helioseismic diagnosis has brought significant observational
progress beyond the Debye-Hückel approximation. This is illustrated
with the subtle effect of excited states in bound systems, in particular
hydrogen.
---------------------------------------------------------
Title: Astrophysical Equation of State and Opacity
Authors: Däppen, W.; Guzik, J. A.
2000ASIC..544..177D Altcode: 2000vsea.conf..177D
No abstract at ADS
---------------------------------------------------------
Title: Atoms and Molecules
Authors: Däppen, Werner
2000asqu.book...27D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: An Introduction to Helioseismology
Authors: Christensen-Dalsgaard, J.; Däppen, W.; Dziembowski, W. A.;
Guzik, J. A.
2000ASIC..544...59C Altcode: 2000vsea.conf...59C
No abstract at ADS
---------------------------------------------------------
Title: Upgrading the MHD Equation of State to Include Relativistic
Electrons
Authors: Gong, Z.; Däppen, W.
2000ASPC..203..388G Altcode: 2000ilss.conf..388G; 2000IAUCo.176..388G
So far, the effect of relativistic electrons has not been included
in the Mihalas-Däppen-Hummer (Hummer & Mihalas 1988; Mihalas,
Däppen, & Hummer 1988; Däppen et al. 1988; hereinafter MHD)
equation of state, although degeneracy was taken into account. Following
the findings about the detectability of the relativistic effect in
helioseismological data of the solar center (Elliot & Kosovichev
1998; hereinafter EK98), we have upgraded the MHD equation of state to
include relativistic degenerate electrons. Our numerical calculation
confirms the result of EK98.
---------------------------------------------------------
Title: The MHD Equation of State with Post-Holtsmark Microfield
Distributions
Authors: Nayfonov, Alan; Däppen, Werner; Hummer, David G.; Mihalas,
Dimitri
1999ApJ...526..451N Altcode: 1999astro.ph..1360N
The Mihalas-Hummer-Däppen (MHD) equation of state is a part of the
Opacity Project (OP), where it mainly provides ionization equilibria
and level populations of a large number of astrophysically relevant
species. Its basic concept is the idea of perturbed atomic and ionic
states. At high densities, when many-body effects become dominant,
the concept of perturbed atoms loses its sense. For that reason,
the MHD equation of state was originally restricted to the plasma of
stellar envelopes, that is, to relatively moderate densities, which
should not exceed ρ<10<SUP>-2</SUP> g cm<SUP>-3</SUP>. However,
helioseismological analysis has demonstrated that this restriction is
much too conservative. The principal feature of the original Hummer
& Mihalas paper is an expression for the destruction probability of
a bound state (ground state or excited) of a species (atomic or ionic),
linked to the mean electric microfield of the plasma. Hummer &
Mihalas assumed, for convenience, a simplified form of the Holtsmark
microfield for randomly distributed ions. An improved MHD equation
of state (Q-MHD) is introduced. It is based on a more realistic
microfield distribution that includes plasma correlations. Comparison
with an alternative post-Holtsmark formalism (APEX) is made, and good
agreement is shown. There is a clear signature of the choice of the
microfield distribution in the adiabatic index γ<SUB>1</SUB>, which
makes it accessible to present-day helioseismological analysis. However,
since these thermodynamic effects of the microfield distribution are
quite small, it also follows that the approximations chosen in the
original MHD equation of state were reasonable. A particular feature
of the original MHD papers was an explicit list of the adopted free
energy and its first- and second-order analytical derivatives. The
corresponding Q-MHD quantities are given in the Appendix.
---------------------------------------------------------
Title: Helioseismic Analysis of the Hydrogen Partition Function in
the Solar Interior
Authors: Basu, Sarbani; Däppen, Werner; Nayfonov, Alan
1999ApJ...518..985B Altcode: 1998astro.ph.10132B
The difference in the adiabatic gradient γ<SUB>1</SUB> between
inverted solar data and solar models is analyzed. To obtain deeper
insight into the issues of plasma physics, the so-called intrinsic
difference in γ<SUB>1</SUB> is extracted, that is, the difference due
to the change in the equation of state alone. Our method uses reference
models based on two equations of state currently used in solar modeling,
the Mihalas-Hummer-Däppen (MHD) equation of state and the OPAL equation
of state (developed at Livermore). Solar oscillation frequencies from
the SOI/MDI instrument on board the SOHO spacecraft during its first
144 days in operation are used. Our results confirm the existence of
a subtle effect of the excited states in hydrogen that was previously
studied only theoretically (Nayfonov & Däppen). The effect stems
from an internal partition function of hydrogen, as is used in the MHD
equation of state. Although it is a pure hydrogen effect, it takes
place in somewhat deeper layers of the Sun, where more than 90% of
hydrogen is ionized, and where the second ionization zone of helium is
located. Therefore, the effect will have to be taken into account in
reliable helioseismic determinations of the astrophysically relevant
helium abundance of the solar convection zone.
---------------------------------------------------------
Title: A Comment on “On Density-dependent and Temperature-dependent
Ground-State and Continuum Effects in the Equation of State for
Stellar Interiors”
Authors: Kraeft, Wolf-Dietrich; Arndt, Stefan; Däppen, Werner;
Nayfonov, Alan
1999ApJ...516..369K Altcode:
Misunderstandings have occurred regarding the conclusions of the paper
“On Density-dependent and Temperature-dependent Ground-State and
Continuum Effects in the Equation of State for Stellar Interiors”
by S. Arndt, W. Däppen, & A. Nayfonov (1998, ApJ, 498, 349). On
occasion, its results have been interpreted as if it showed basic
flaws in the general theory of dynamical screening. The aim of this
comment is to emphasize the context in which the conclusions of the
paper must be understood in order to avoid misinterpretations.
---------------------------------------------------------
Title: Grids of stellar models. VIII. From 0.4 to 1.0
{M<SUB>sun</SUB>} at Z=0.020 and Z=0.001, with the MHD equation
of state
Authors: Charbonnel, C.; Däppen, W.; Schaerer, D.; Bernasconi, P. A.;
Maeder, A.; Meynet, G.; Mowlavi, N.
1999A&AS..135..405C Altcode: 1998astro.ph.10416C
We present stellar evolutionary models covering the mass range from 0.4
to 1 M<SUB>sun</SUB> calculated for metallicities Z=0.020 and 0.001
with the MHD equation of state \cite[(Hummer & Mihalas 1988;]
\cite[Mihalas et al. 1988;] \cite[Däppen et al. 1988).] A parallel
calculation using the OPAL \cite[(Rogers et al. 1996)] equation of
state has been made to demonstrate the adequacy of the MHD equation of
state in the range of 1.0 to 0.8 M<SUB>sun</SUB> (the lower end of the
OPAL tables). Below, down to 0.4 M<SUB>sun</SUB>, we have justified
the use of the MHD equation of state by theoretical arguments and the
findings of \cite[Chabrier & Baraffe (1997).] We use the radiative
opacities by \cite[Iglesias & Rogers (1996),] completed with the
atomic and molecular opacities by \cite[Alexander & Fergusson
(1994).] We follow the evolution from the Hayashi fully convective
configuration up to the red giant tip for the most massive stars,
and up to an age of 20 Gyr for the less massive ones. We compare our
solar-metallicity models with recent models computed by other groups and
with observations. The present stellar models complete the set of grids
computed with the same up-to-date input physics by the Geneva group
(Z=0.020 and 0.001, \cite[Schaller et al. 1992;] \cite[Bernasconi 1996,]
and \cite[Charbonnel et al. 1996;] Z=0.008, \cite[Schaerer et al. 1992;]
Z=0.004, \cite[Charbonnel et al. 1993;] Z=0.040, \cite[Schaerer et
al. 1993;] Z=0.10, \cite[Mowlavi et al. 1998;] enhanced mass loss
rate evolutionary tracks, \cite[Meynet et al. 1994).] Data available
at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)
or via http://cdsweb.u-strasbg.fr/Abstract.html
---------------------------------------------------------
Title: Investigate the Noise of Low-l P Modes
Authors: Lin, Chia-Hsien; Däppen, Werner
1999soho....9E..70L Altcode:
Turbulence and granulation in the convective region of the Sun are
believed to be responsible for the excitation of the oscillation signal
(i.e., the p modes); however, they are also the source of unwanted noise
and the cause of a non-stationary signal. In other words, the noise in
the solar data is entangled with the oscillation signal. To reduce the
noise, it may be that the usual noise reduction methods for additive
or multiplicative noise are not effective. The object of this study
is first, to investigate the specific properties of the noise and its
entanglement, and second, to separate the noise from the oscillation.
---------------------------------------------------------
Title: Research on the solar model and oscillation in 1990s (II):
progress in research on the solar oscillations.
Authors: Gong, Zhigang; Yuan, Yongquan; Li, Yan; Däppen, W.; Peng,
Meixian
1998PABei..16..305G Altcode:
Helioseismology has become a new tool for the study of the solar
interior as well as one of the most important devices to determine
the quality of the input physics that enters the solar models. The
discrepancy between theoretical and observational frequencies has
drastically decreased in the 1990s due to modified input physics and
improved stellar oscillation theory. However, the discrepancy is still
bigger than the observational error. From frequency inversion studies
the authors know more about the solar convection zone, the surface
helium abundance and rotational velocity distribution as a function of
depth and latitude. The stochastic excitation mechanism by turbulence
and the location of the excitation sources are well studied, but not
completely understood.
---------------------------------------------------------
Title: Research on the solar model and oscillation in 1990s (I):
progress in solar models.
Authors: Gong, Zhigang; Yuan, Yongquan; Däppen, W.; Li, Yan; Peng,
Meixian
1998PABei..16..287G Altcode:
The study of solar models is the most important way to understand the
global structure and properties of the Sun. Developments in solar
modelling in the 1990s are reviewed. The use of the MHD and OPAL
equations of states and of the OPAL opacity has moved the theoretical
solar oscillation frequencies much closer to the observed values. The
introduction of turbulent spectrum in the local convection theory
and the 3D hydrodynamic simulation convection models have increased
the knowledge of convective energy transportation, as well as its
influence on the global Sun. The difference of surface helium abundance
between models and inversion results has been filled by diffusion
effects. Surface lithium may be depleted by turbulent diffusion
or big mass loss. An astrophysical solution for the solar neutrino
fluxes looks unlikely. A higher probability exists for a solution from
particle physics.
---------------------------------------------------------
Title: VizieR Online Data Catalog: Grids of stellar
models. VIII. (Charbonnel+ 1999)
Authors: Charbonnel, C.; Dappen, W.; Schaerer, D.; Bernasconi, P. A.;
Maeder, A.; Meynet, G.; Mowlavi, N.
1998yCat..41350405C Altcode:
We present stellar evolutionary models covering the mass range
from 0.4 to 1M<SUB>⊙</SUB> calculated for metallicities Z=0.020
and 0.001 with the MHD equation of state (Hummer & Mihalas,
1988ApJ...331..794H, Mihalas et al., 1988ApJ...331..815M, Daeppen
et al., 1988ApJ...332..261D). A parallel calculation using the OPAL
(Rogers et al., 1996ApJ...456..902R) equation of state has been made to
demonstrate the adequacy of the MHD equation of state in the range of
1.0 to 0.8M<SUB>⊙</SUB> (the lower end of the OPAL tables). Below,
down to 0.4M<SUB>⊙</SUB>, we have justified the use of the MHD
equation of state by theoretical arguments and the findings of
Chabrier & Baraffe (1997A&A...327.1039C). We use the radiative
opacities by Iglesias & Rogers (1996ApJ...464..943I), completed
with the atomic and molecular opacities by Alexander & Fergusson
(1994ApJ...437..879A). We follow the evolution from the Hayashi fully
convective configuration up to the redgiant tip for the most massive
stars, and up to an age of 20Gyr for the less massive ones. We compare
our solar-metallicity models with recent models computed by other
groups and with observations. <P />(21 data files).
---------------------------------------------------------
Title: On Density-dependent and Temperature-dependent Ground-State
and Continuum Effects in the Equation of State for Stellar Interiors
Authors: Arndt, Stefan; Däppen, Werner; Nayfonov, Alan
1998ApJ...498..349A Altcode: 1999astro.ph..1169K
We examine the consequence of shifts in bound-state energies, as well
as the position of the continuum for thermodynamic quantities. Two
independent methods from different branches of physics are brought
together. A simple free-energy model is used to examine the
thermodynamic consequences of the results of quantum statistical
calculations of two-particle properties in a plasma using the Green's
function technique. A comparison with data inferred from helioseismology
shows that our interdisciplinary procedure works very well for lower
level approximations, such as the static screening in the effective
two-particle wave equation. However, in the case of dynamic screening
in the wave equation, the resulting thermodynamic quantities are
inconsistent with observations. This could result from the inability
of our method to compute the thermodynamic quantities or from the
inappropriate treatment of the ion contribution to the electronic
self-energy corresponding to the dielectric function used in random
phase approximation. In any case, the results superbly demonstrate
the power of helioseismology to test models of basic plasma physics.
---------------------------------------------------------
Title: Microphysics: Equation of State
Authors: Däppen, Werner
1998SSRv...85...49D Altcode:
The equation of state is one of the three fundamental ingredients
used to construct stellar models. The plasma of the interiors of stars
such as the Sun is only slightly non-ideal. However, the extraordinary
accuracy of the helioseismological data requires refined equations of
state. It turned out to be necessary to include a Coulomb correction,
commonly evaluated in the Debye-Hückel approximation. Higher-order
non-ideal effects have implications as well, both for plasma physics
and for solar physics. As a typical example, the recently studied
thermodynamic consequence of excited states in compound particles is
discussed. This effect is of considerable relevance in the helioseismic
determination of the helium abundance in the solar convection zone.
---------------------------------------------------------
Title: The Signature of the Internal Partition Function in
Thermodynamical Quantities of the Solar Interior
Authors: Nayfonov, Alan; Däppen, Werner
1998ApJ...499..489N Altcode:
The extraordinary accuracy of available helioseismological data
presents an opportunity to study nonideal plasma effects of the
solar interior beyond the leading-order Coulomb correction term. The
effect of different internal partition functions on a complete set of
thermodynamical quantities is examined, and it is found that there is
a clear signature of the excited states well within reach of present
helioseismic inversion techniques.
---------------------------------------------------------
Title: Helioseismic Signature of the Presence of Excited States in
the Adiabatic Exponent
Authors: Basu, Sarbani; Däppen, Werner; Nayfonov, Alan
1998ESASP.418..435B Altcode: 1998soho....6..435B
Recently, Nayfonov & Däppen (1998) have examined the signature of
the internal partition function in the equation of state. That study has
revealed interesting features about excited states and their treatment
in the equation of state. The MHD equation of state with its specific,
density-dependent occupation probabilities is causing a characteristic
“wiggle” in the thermodynamic quantities. The wiggle is absent
both in ground-state-only equations of state and in the OPAL equation
of state, which is based on the temperature-dependent Planck-Larkin
partition function. It seems that this effect of excited states has
already been observed in the Sun. Very recently, solar oscillation
frequencies were inverted for the adiabatic gradient γ<SUB>1</SUB>
in the 20% uppermost layers. The results have revealed that above
0.98 solar radii, MHD seems to give a more accurate description of
the Sun than OPAL. The quantitative reason appears to be the presence
of the excited-states wiggle in the solar data. Below the wiggle
region, the study confirmed older findings, which give preference
to the OPAL equation of state. Although the wiggle is located in the
He II ionization zone, it is a pure hydrogen effect. If confirmed it
would have a significant bearing on the helioseismic helium-abundance
determination in the solar convection zone. Specifically, it could make
the value based on the MHD equation of state (Y = 0.246) more likely
than the currently preferred one (Y = 0.249), which is based on OPAL
(Basu & Antia, 1995).
---------------------------------------------------------
Title: Solar p-mode Frequencies With Updated Atomic Opacities
Authors: Gong, Z.; Dappen, W.; Li, Y.
1998ASPC..135..266G Altcode: 1998hcsp.conf..266G
Significant differences in solar models have been found recently,
by using OPAL and OP opacity, respectively. In this work we'll study
its effect on solar oscillation frequencies, so as to figure out which
set of opacity can fit the present sun more reasonably.
---------------------------------------------------------
Title: Solar p-Mode Frequencies with OPAL and OP Opacities
Authors: Gong, Zhigang; Dappen, Werner; Li, Yan
1998ASPC..154..761G Altcode: 1998csss...10..761G
The effect of the OPAL-92 and OP opacity on the frequencies of solar
p-modes are studied. It is found that although no one can fit the
observational data, the difference of OPAL model and observation
frequencies have almost the same slope for different modes, which
is more likely to come from the non-adiabatic effect in the outer
envelope of the Sun, while the OP results have various slopes for
different modes, which is difficult to analyze. Thus, the OPAL opacity
is favored in solar model. The difference between a grey atmosphere
and the Harvard-Smithsonian solar atmosphere model is small.
---------------------------------------------------------
Title: The Influence of Low-Temperature Opacity on Solar Models and
p-Mode Frequencies
Authors: Gong, Z. G.; Däppen, W.
1998ESASP.418..465G Altcode: 1998soho....6..465G
The opacity is one of the leading input physics quantities that may
influence the structure and p-mode frequencies of the sun. Although
the most important opacity contribution on a solar model is the
atomic and ionic contribution in the interior, the influence of the
outside low-temperature opacity is also relevant. Presently, the
low-temperature opacity has a somewhat higher uncertainty than the
one of the interior, and this difference may influence more on high
order p-modes, which spend most of their life traveling through the
low-temperature opacity region. In this work we test the sensitivity
of solar structure and frequencies with some up-to-date, well accepted
low-temperature opacities.
---------------------------------------------------------
Title: Microphysics: Equation of State
Authors: Däppen, W.
1998sce..conf...49D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Application of the Filter Diagonal Spectral Estimator in
Helioseismology
Authors: Jones, Andrew R.; Belkic, Dzevad; Däppen, Werner; Lin,
Chia-Hsien; Taylor, Howard
1998ESASP.418..249J Altcode: 1998soho....6..249J
Filter Diagonalization (FD) is a non-Fourier spectral estimator that has
several possible applications in helioseismology. We show an example of
the analysis of synthetic data to demonstrate the enhancement gained
with the FD technique over a conventional Fourier Transform (FT). We
also show how FD can be used to reduce spectral noise. A preliminary
application of FD to helioseismic (LOI) data is presented, and the
possible application of FD to ring analysis is explored.
---------------------------------------------------------
Title: Helioseismic Probing of Fine Effects in the Equation of State
Authors: Däppen, Werner
1998ESASP.418..445D Altcode: 1998soho....6..445D
Although the gas in the solar interior is only weakly coupled
and weakly degenerate, the great observational accuracy of the
helioseismic measurements puts strong constraints on the nonideal
part of the equation of state. The helioseismic verification of
major nonideal effects in the equation of state of solar matter
has become well established. The dominant contribution is the
Coulomb pressure, conventionally described in the Debye-Huckel
approximation. However, the increased precision of the helioseismic
diagnosis has brought significant observational progress beyond the
Debye-Huckel approximation. Recent studies have addressed specific
nonideal effects beyond the Debye-Huckel term. A first case is the
consequence of shifts in bound-state energies and of the position
of the continuum for thermodynamic quantities. A second case is the
subtle effect of excited states in bound systems, in particular hydrogen
(Nayfonov & Däppen 1998). The effect has become apparent in recent
helioseismic inversions (Basu, Däppen, & Nayfonov 1998).
---------------------------------------------------------
Title: Structure and Rotation of the Solar Interior: Initial Results
from the MDI Medium-L Program
Authors: Kosovichev, A. G.; Schou, J.; Scherrer, P. H.; Bogart, R. S.;
Bush, R. I.; Hoeksema, J. T.; Aloise, J.; Bacon, L.; Burnette, A.; de
Forest, C.; Giles, P. M.; Leibrand, K.; Nigam, R.; Rubin, M.; Scott,
K.; Williams, S. D.; Basu, Sarbani; Christensen-Dalsgaard, J.; Dappen,
W.; Rhodes, E. J., Jr.; Duvall, T. L., Jr.; Howe, R.; Thompson, M. J.;
Gough, D. O.; Sekii, T.; Toomre, J.; Tarbell, T. D.; Title, A. M.;
Mathur, D.; Morrison, M.; Saba, J. L. R.; Wolfson, C. J.; Zayer, I.;
Milford, P. N.
1997SoPh..170...43K Altcode:
The medium-l program of the Michelson Doppler Imager instrument on board
SOHO provides continuous observations of oscillation modes of angular
degree, l, from 0 to ∽ 300. The data for the program are partly
processed on board because only about 3% of MDI observations can be
transmitted continuously to the ground. The on-board data processing,
the main component of which is Gaussian-weighted binning, has been
optimized to reduce the negative influence of spatial aliasing of the
high-degree oscillation modes. The data processing is completed in a
data analysis pipeline at the SOI Stanford Support Center to determine
the mean multiplet frequencies and splitting coefficients. The initial
results show that the noise in the medium-l oscillation power spectrum
is substantially lower than in ground-based measurements. This enables
us to detect lower amplitude modes and, thus, to extend the range of
measured mode frequencies. This is important for inferring the Sun's
internal structure and rotation. The MDI observations also reveal the
asymmetry of oscillation spectral lines. The line asymmetries agree
with the theory of mode excitation by acoustic sources localized in the
upper convective boundary layer. The sound-speed profile inferred from
the mean frequencies gives evidence for a sharp variation at the edge
of the energy-generating core. The results also confirm the previous
finding by the GONG (Gough et al., 1996) that, in a thin layer just
beneath the convection zone, helium appears to be less abundant than
predicted by theory. Inverting the multiplet frequency splittings from
MDI, we detect significant rotational shear in this thin layer. This
layer is likely to be the place where the solar dynamo operates. In
order to understand how the Sun works, it is extremely important to
observe the evolution of this transition layer throughout the 11-year
activity cycle.
---------------------------------------------------------
Title: Internal structure and rotation of the Sun: First results
from MDI data
Authors: Kosovichev, A. G.; Schou, J.; Scherrer, P. H.; Bogart, R. S.;
Bush, R. I.; Hoeksema, J. T.; Aloise, J.; Bacon, L.; Burnette, A.;
De Forest, C.; Giles, P. M.; Leibrand, K.; Nigam, R.; Rubin, M.;
Scott, K.; Williams, S. D.; Basu, Sarbani; Christensen-Dalsgaard,
J.; Däppen, W.; Rhodes, E. J., Jr.; Duvall, T. L., Jr.; Howe, R.;
Thompson, M. J.; Gough, D. O.; Sekii, T.; Toomre, J.; Tarbell, T. D.;
Title, A. M.; Mathur, D.; Morrison, M.; Saba, J. L. R.; Wolfson,
C. J.; Zayer, I.; Milford, P. N.
1997IAUS..181..203K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Helioseismic diagnosis of the equation of state
Authors: Däppen, Werner
1996BASI...24..151D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Current State of Solar Modeling
Authors: Christensen-Dalsgaard, J.; Dappen, W.; Ajukov, S. V.;
Anderson, E. R.; Antia, H. M.; Basu, S.; Baturin, V. A.; Berthomieu,
G.; Chaboyer, B.; Chitre, S. M.; Cox, A. N.; Demarque, P.; Donatowicz,
J.; Dziembowski, W. A.; Gabriel, M.; Gough, D. O.; Guenther, D. B.;
Guzik, J. A.; Harvey, J. W.; Hill, F.; Houdek, G.; Iglesias, C. A.;
Kosovichev, A. G.; Leibacher, J. W.; Morel, P.; Proffitt, C. R.;
Provost, J.; Reiter, J.; Rhodes, E. J., Jr.; Rogers, F. J.; Roxburgh,
I. W.; Thompson, M. J.; Ulrich, R. K.
1996Sci...272.1286C Altcode:
Data from the Global Oscillation Network Group (GONG) project and
other helioseismic experiments provide a test for models of stellar
interiors and for the thermodynamic and radiative properties, on which
the models depend, of matter under the extreme conditions found in the
sun. Current models are in agreement with the helioseismic inferences,
which suggests, for example, that the disagreement between the predicted
and observed fluxes of neutrinos from the sun is not caused by errors in
the models. However, the GONG data reveal subtle errors in the models,
such as an excess in sound speed just beneath the convection zone. These
discrepancies indicate effects that have so far not been correctly
accounted for; for example, it is plausible that the sound-speed
differences reflect weak mixing in stellar interiors, of potential
importance to the overall evolution of stars and ultimately to estimates
of the age of the galaxy based on stellar evolution calculations.
---------------------------------------------------------
Title: Testing Solar Models with the GONG Data
Authors: Christensen-Dalsgaard, J.; Dappen, W.; Demarque, P.; GONG
Models Team
1996AAS...188.5302C Altcode: 1996BAAS...28..903C
The wealth of very precise data from the GONG network and other
helioseismic experiments provide a unique opportunity for testing the
modeling of stellar interiors. Stellar modeling forms the basis for
much of astrophysics. Furthermore, the application and calibration of
solar models to the helioseismic data provides a test of the physics
on which the models depend; thus we can investigate the thermodynamic
and radiative properties of matter under the extreme conditions
found in the Sun. Current models are in remarkable agreement with
the helioseismic inferences within the errors in the input data; this
suggests, for example, that the disagreement between the predicted and
observed fluxes of neutrinos from the Sun is unlikely to be caused
by errors in the standard solar model. However, careful analysis
of the GONG data reveals subtle discrepancies that we attribute to
uncertainties in some of the model input physics and the neglect of
other subtle physical processes. The role of mixing inside the Sun,
due for example to rotationally induced instabilities during its past
evolution, the precise form of the hydrogen depletion profile near the
center, the efficiency of helium and heavier element diffusion below
the convection zone, and the structure of the highly superadiabatic
layer just below the photosphere, are among the significant details in
solar models, which the high-quality GONG data will greatly help to
resolve. Comparisons between theoretical predictions of solar p-mode
frequencies, previous p-mode observations and the first GONG data are
used to illustrate these points.
---------------------------------------------------------
Title: VIRGO: Experiment for Helioseismology and Solar Irradiance
Monitoring
Authors: Fröhlich, Claus; Romero, José; Roth, Hansjörg; Wehrli,
Christoph; Andersen, Bo N.; Appourchaux, Thierry; Domingo, Vicente;
Telljohann, Udo; Berthomieu, Gabrielle; Delache, Philippe; Provost,
Janine; Toutain, Thierry; Crommelynck, Dominique A.; Chevalier,
André; Fichot, Alain; Däppen, Werner; Gough, Douglas; Hoeksema,
Todd; Jiménez, Antonio; Gómez, Maria F.; Herreros, José M.; Cortés,
Teodoro Roca; Jones, Andrew R.; Pap, Judit M.; Willson, Richard C.
1995SoPh..162..101F Altcode:
The scientific objective of the VIRGO experiment (Variability of solar
IRradiance and Gravity Oscillations) is to determine the characteristics
of pressure and internal gravity oscillations by observing irradiance
and radiance variations, to measure the solar total and spectral
irradiance and to quantify their variability over periods of days to
the duration of the mission. With these data helioseismological methods
can be used to probe the solar interior. Certain characteristics of
convection and its interaction with magnetic fields, related to, for
example, activity, will be studied from the results of the irradiance
monitoring and from the comparison of amplitudes and phases of the
oscillations as manifest in brightness from VIRGO, in velocity from
GOLF, and in both velocity and continuum intensity from SOI/MDI. The
VIRGO experiment contains two different active-cavity radiometers for
monitoring the solar `constant', two three-channel sunphotometers (SPM)
for the measurement of the spectral irradiance at 402, 500 and 862 nm,
and a low-resolution imager (LOI) with 12 pixels, for the measurement
of the radiance distribution over the solar disk at 500 um. In this
paper the scientific objectives of VIRGO are presented, the instruments
and the data acquisition and control system are described in detail,
and their measured performance is given.
---------------------------------------------------------
Title: Rigorous Constraints on the Ionization of Elements in the
Solar Center
Authors: Perez, A.; Däppen, W.
1995ESASP.376b..15P Altcode: 1995help.confP..15P; 1995soho....2...15P
Results from a rigorous quantum-statistical formalism for Coulomb
systems are used to study the transition to full ionization of
astrophysically relevant elements. The authors find that, although
the formalism is in principle a low-density development, the relevant
parameters are such that it can be applied to the physical conditions
of the solar center. However, the conditions of the solar center do
not admit an isolated-atom picture. Special care has therefore to be
taken to define what is a bound state.
---------------------------------------------------------
Title: Some Aspects of Model Entropy Calculations for Stellar Plasmas
Authors: Däppen, W.; Nayfonov, A.
1995ESASP.376b..19D Altcode: 1995help.confP..19D; 1995soho....2...19D
The helioseismic determination of specific entropy inside the Sun
could provide an interesting constraint on solar models. Unlike with
more intuitive thermodynamic quantities, a greater effort has to be
made to define entropy. In models of plasmas, the arbitrary additive
constant of entropy can be normalized by applying the third law of
thermodynamics. This presents difficulties, however, because although
quantum statistical models of Coulomb systems might satisfy the third
law, their concrete (approximate) realizations of these models, such
as those used in stellar calculations, might not. The authors examine
a popular representative stellar equation of state in view of their
suitability for entropy calculations.
---------------------------------------------------------
Title: GONG '94: Helio- and Astero-Seismology from the Earth and Space
Authors: Ulrich, R. K.; Rhodes, E. J., Jr.; Dappen, W.
1995ASPC...76.....U Altcode: 1995gong.conf.....U; 1995QB539.O83G67...
No abstract at ADS
---------------------------------------------------------
Title: Solar Models and Oscillation Theory
Authors: Däppen, W.
1995ESASP.376a..19D Altcode: 1995heli.conf...19D; 1995soho....1...19D
The most important techniques used to analyze helioseismic data are
reviewed. Emphasis is on the spherically symmetric aspects of solar
structure. This is the framework of "conventional" stellar evolution
models and their oscillations. The importance of understanding stellar
physics to the prediction of helioseismic data is stressed. By doing
this the author shows that progress can be made on the inverse path:
constraining stellar physics by helioseismology, in other words,
using the Sun as a laboratory. Examples of physics issues addressed
by helioseismology are, in the spirit of the simplified spherical
models, opacity, equation of state, nuclear reaction rates, and
neutrino physics.
---------------------------------------------------------
Title: Nonideal Effects in the Solar Equation of State
Authors: Baturin, V. A.; Däppen, W.; Wang, X.; Yang, F.
1995LIACo..32...33B Altcode: 1995sews.book...33B
No abstract at ADS
---------------------------------------------------------
Title: HELIO- AND ASTEROSEISMOLOGY: Introduction
Authors: Däppen, W.
1995HiA....10..319D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Applications of Massively-Parallel Computing in Solar Modeling
Authors: Reiter, J.; Rhodes, E. J., Jr.; Dappen, W.; Korzennik, S. G.
1995ASPC...76..140R Altcode: 1995gong.conf..140R
No abstract at ADS
---------------------------------------------------------
Title: Asteroseismologie: muziek van de sterren.
Authors: Dappen, W.
1994Zenit..21..346D Altcode: 1994Zenit...21.346D
No abstract at ADS
---------------------------------------------------------
Title: Towards a helioseismic calibration of the equation of state
in the solar convective envelope
Authors: Vorontsov, S. V.; Baturin, V. A.; Dappen, W.; Gough, D. O.
1994esa..conf..545V Altcode: 1994IAUCo.147..545V
No abstract at ADS
---------------------------------------------------------
Title: Helioseismology: the Sun as a strongly-constrained,
weakly-coupled plasma
Authors: Dappen, W.
1994esa..conf..368D Altcode: 1994IAUCo.147..368D
No abstract at ADS
---------------------------------------------------------
Title: The solar interior
Authors: Turck-Chièze, S.; Däppen, W.; Fossat, E.; Provost, J.;
Schatzman, E.; Vignaud, D.
1993PhR...230...57T Altcode:
This report confronts the different aspects of the solar interior from
the experimental and theoretical points of view, discussing photospheric
abundances, neutrinos and acoustic mode measurements. The theoretical
approach mainly concerns the classical framework of stellar evolution,
nevertheless, particle interpretation of the data and astrophysical
solutions invoked in the last 10 years are coherently examined.
---------------------------------------------------------
Title: On the Influence of Treatment of Heavy Elements in the Equation
of State on the Resulting Values of the Adiabatic Exponent
Authors: Däppen, W.; Gough, D. O.; Kosovichev, A. G.; Rhodes,
E. J., Jr.
1993ASPC...40..304D Altcode: 1993ist..proc..304D
No abstract at ADS
---------------------------------------------------------
Title: Theory of Delta-Scuti Stars
Authors: Dappen, W.
1993ASPC...42..317D Altcode: 1993gong.conf..317D
No abstract at ADS
---------------------------------------------------------
Title: The equation of state.
Authors: Daeppen, Werner
1993ASPC...40..208D Altcode: 1993ist..proc..208D; 1993IAUCo.137..208D
There are two basic approaches to the equation of state for stellar
envelopes and interiors. The traditional method chooses the so-called
"chemical picture", in which the notion of atoms is maintained despite
the plasma environment. A mixture of atoms, molecules, ions, electrons
and nuclei is considered, and the occurring ionization and dissociation
reactions (thus the name chemical picture) are treated according to the
entropy-maximum (or free-energy-minimum) principle. The alternative
method is based on the so-called "physical picture", where only
fundamental particles (electrons, nuclei) explicitly enter. Through
the means of activity expansions, the problems of plasma physics and
statistical mechanics are treated simultaneously and on the same
footing. For helio- and asteroseismology, an accurate and precise
equation of state is essential. Progress towards a better equation of
state can be made in several ways: purely theoretical efforts, checks
with experiments, including astrophysical data, and comparisons between
different theoretical formalisms. Comparisons are useful to assess the
domain of temperature and density where the theoretical complications
matter, and to determine the diagnostic potential of astrophysical
observables for equation of state issues.
---------------------------------------------------------
Title: Plans for MT.WILSON - Crimean Observatory High-Degree
Helioseismology Network
Authors: Rhodes, E. J., Jr.; Cacciani, A.; Dappen, W.; Didkovsky,
L. V.; Hill, F.; Korzennik, S. G.; Kosovichev, A. G.; Kotov, V. A.;
Scherrer, P. H.
1993ASPC...42..477R Altcode: 1993gong.conf..477R
No abstract at ADS
---------------------------------------------------------
Title: Sources of uncertainty in direct seismological measurements
of the solar helium abundance
Authors: Kosovichev, A. G.; Christensen-Dalsgaard, J.; Daeppen, W.;
Dziembowski, W. A.; Gough, D. O.; Thompson, M. J.
1992MNRAS.259..536K Altcode:
The methods by which Dappen et al. (1988, 1990, 1991) and Dziembowski
et al. (1990, 1991, 1992) recently obtained discrepant estimates of
the helium abundance in the solar convection zone are compared. The
aim of the investigation reported in this paper is to identify the
main source of the discrepancy. Using as proxy data eigenfrequencies
of a set of modes of a theoretical solar model, computed with the
same physics as were the frequencies of a reference model with which
these data are compared, the two methods yield similar results. Thus
we ascertain that the principal source of the discrepancy is not in
the inversions themselves, which yield essentially a measure of the
variation of the adiabatic exponent gamma of the material in the He II
ionization zone. Instead it is in the approximations adopted in the
treatment of heavy elements in the equation of state used to relate
the variation of gamma to chemical composition. We obtain acceptably
consistent results when inverting solar data by two methods using the
same equation of state. We attempt to identify the likely residual
sources of uncertainty.
---------------------------------------------------------
Title: The Equation of State for Stellar Envelopes: Comparison of
Theoretical Results
Authors: Dappen, W.
1992RMxAA..23..141D Altcode:
A previous comparison of thermodynamical quantities, computed in the
chemical and physical pictures, revealed a remarkable agreement in the
H and He ionization zones of the Sun, despite the radically different
treatment of bound states in the two formalisms. This agreement
was due to an unexpectedly dominating (classical) Coulomb pressure
term. New comparisons, for higher temperatures and densities, and
for a representative solar mixture (H, He and 0), have demonstrated
substantial differences in the 0-ionization fractions. Also, the
thermodynamic quantities reflect these differences to a degree that
is within reach of helioseismology. Key words: EQUATION OF STATE -
STARS: INTERIOR
---------------------------------------------------------
Title: Solar oscillations and the equation of state
Authors: Christensen-Dalsgaard, Jorgen; Daeppen, Werner
1992A&ARv...4..267C Altcode:
Accurate measurements of observed frequencies of solar oscillations are
providing a wealth of data on the properties of the solar interior. The
frequencies depend on solar structure, and on the properties of the
plasma in the Sun. Here we consider in particular the dependence
on the thermodynamic state. From an analysis of the equations of
stellar structure, and the relevant aspects of the properties of the
oscillations, we argue that in the convection zone one can isolate
information about the equation of state which is relatively unaffected
by other uncertainties in the physics of the solar interior. We
review the different treatments that have been used to describe the
thermodynamics of stellar plasmas. Through application of several of
these to the computation of models of the solar envelope we demonstrate
that the sensitivity of the observed frequencies is in fact sufficient
to distinguish even quite subtle features of the physics of solar
matter. This opens up the possibility of using the Sun as a laboratory
for statistical mechanics, under conditions that are out of reach in
a terrestrial laboratory.
---------------------------------------------------------
Title: Observations of the phase differences between irradiances
and velocity for low-degree solar acoustic modes
Authors: Schrijver, C. J.; Dappen, W.; Jimenez, A.
1991A&A...251..655S Altcode:
Irradiance measurements from the IPHIR instrument flown on the
Phobos 2 mission to Mars are used to derive phase differences and
gains between broadband relative irradiance signals and full-disk
velocity variations for l = 0, 1, and 2 mode with order ranging from
12 to 32. These data are compared with contemporaneous measurements of
photospheric velocities obtained during four intervals within the 155 d
observation period of Phobos 2. It is found that the phase difference
between irradiance at 500 nm and velocity is roughly constant with an
average value of -119 +/- 3 deg from 2.5 mHz up to about 4.3 mHz with a
slight increase suggested by data up to 4.6 mHz. The phase differences
between the green and red channels do not differ significantly from zero
below 2.8 mHz, while a small difference of about 13 +/- 5 deg exists
at higher frequencies, with the red signal ahead of the green. This
jump appears to coincide with a jump in the separation between the l =
0 and l = 2 eigenfrequencies.
---------------------------------------------------------
Title: A calibration of solar envelope models using the frequencies
of intermediate-degree solar acoustic oscillations
Authors: Pamiatnykh, A. A.; Vorontsov, S. V.; Dappen, W.
1991A&A...248..263P Altcode:
The frequency dependence of the phase shift, which arises from the
reflection of internal acoustic waves (p-modes) at the outer solar
layers, can be determined from the accurately measured frequencies
of intermediate-degree p-modes. This dependence is sensitive to the
complicated structure of the outer solar layers, down to the depth
of the second ionization zone of helium. It can be used to calibrate
solar envelope models. The results of the direct tests of a variety
of solar envelope models using the phase shift inferred from the solar
oscillation frequencies are reported.
---------------------------------------------------------
Title: A theorical interpretation of the Delta Scuti-like pulsation
of the star 63 Herculis.
Authors: Mangeney, A.; Daeppen, W.; Praderie, F.; Belmonte, J. A.
1991A&A...244..351M Altcode:
Theoretical pulsation frequencies derived from a typical model
computation are used to identify the periods during which the Delta
Scuti star 63 Herculis oscillates. The frequencies are computed in
the adiabatic and linear approximations and consideration is given to
p and g modes. The possibility of rotational splitting is considered.
---------------------------------------------------------
Title: Probing the solar interior
Authors: Dappen, W.
1991AdSpR..11d...5D Altcode: 1991AdSpR..11....5D
Solar oscillation frequencies have become an important tool to obtain
detailed information about the solar interior. The physical nature
of the oscillations is well understood: the modes observed so far are
standing acoustic waves (or p modes). Thus identified, they allow an
immediate diagnosis of the physical conditions in the solar interior,
through the relation of the oscillation frequencies with the local
sound speed. Besides giving an introduction to current techniques,
I describe the observational situation. The connection between solar
oscillations and the equation of state is discussed in some detail. A
separate section contains a short general review of recent progress.
---------------------------------------------------------
Title: Summary of the Institute of Theoretical Physics (ITP) program
on helioseismology (Santa Barbara, January-June 1990)
Authors: Däppen, Werner; Rhodes, Ed
1991AdSpR..11d..15D Altcode: 1991AdSpR..11...15D
The authors presented their view as participants of the ITP programme
on helioseismology, which was coordinated by D.O. Gough and J. Toomre
(Santa Barbara, Jan 1990 - June 1990). Detailed proceedings can be found
in “Challenges to theories of the structure of moderate-mass stars”
(eds. D.O. Gough and J. Toomre, Springer, Heidelberg, 1991).
---------------------------------------------------------
Title: A New Inversion for the Hydrostatic Stratification of the Sun
Authors: Däppen, W.; Gough, D. O.; Kosovichev, A. G.; Thompson, M. J.
1991LNP...388..111D Altcode: 1991ctsm.conf..111D
Inversions for the spherically symmetric component of the hydrostatic
stratification of the Sun are presented. These employ the Backus-Gilbert
optimally localized averaging procedure applied to oscillation multiplet
frequencies in the range 1.5 - 3 mHz of modes with 4 l 140 determined
by Libbrecht et al. (1990) from observations carried out in 1986. We
also obtain an estimate of the helium abundance in the solar convective
envelope.
---------------------------------------------------------
Title: Equation of state and opacity.
Authors: Daeppen, Werner; Keady, John; Rogers, Forrest
1991sia..book..112D Altcode:
The three most important physical ingredients of stellar models are
the nuclear-energy generation rates, the equation of state and the
opacity. The authors begin this chapter with a discussion of the
equation of state, not only because the equation of state plays
an important role in stellar structure, but also because it is by
itself a fundamental part of any opacity calculation. Furthermore, the
computation of the equation of state is the simpler problem. There are
two reasons for this. First, already at lower densities, where atoms
exist (i.e. where many-body effects can be neglected), it suffices for
the equation of state to know the energy levels of atoms (and their
occupation). Second, at higher densities, where many-body effects become
important (and where one cannot speak of atoms), there are at least
roads to a correct treatment of the equation of state (the authors
will show some of them in this chapter). Extending these techniques
to opacity calculations faces the difficulty that again more detailed
information about the quantum-mechanical many-body states is required.
---------------------------------------------------------
Title: The Equation of State of the Solar Interior - a Comparison
of Results from Two Competing Formalisms
Authors: Daeppen, Werner; Lebreton, Yveline; Rogers, Forrest
1990SoPh..128...35D Altcode: 1990IAUCo.121P..35D
A recently developed treatment of partition functions in the equation
of state (Mihalas, Hummer, Däppen, MH&D) has led to a substantial
improvement in the agreement between observed and theoretically
predicted solar p-mode oscillation frequencies. The MH&D equation
of state is a realization of the free-energyminimization method,
based on the so-called `chemical picture', in which ionization and
dissociation reactions are assumed to be those that maximize entropy,
or equivalently, minimize the free energy. An alternative equation of
state has recently been developed at Livermore. It realizes a virial
expansion of pressure, and is based on the `physical picture', in
which explicitly only fundamental species (i.e., electrons and nuclei)
appear. Results of a first comparison between thermodynamic quantities
of the MH&D and Livermore equations of state are presented. For
simplicity, a mixture with only hydrogen and helium (90% H and 10% He
by number) is chosen. The comparison is made for a low-density and a
high-density case. In the first case, the conditions are those of the
hydrogen and helium ionization zones of the Sun, in the second case
those of the solar centre. In both cases, the MH&D and Livermore
results agree strikingly, despite the very different formalisms they
are based on.
---------------------------------------------------------
Title: The Equation of State for Stellar Envelopes. IV. Thermodynamic
Quantities and Selected Ionization Fractions for Six Elemental Mixes
Authors: Mihalas, Dimitri; Hummer, D. G.; Mihalas, Barbara Weibel;
Daeppen, Werner
1990ApJ...350..300M Altcode:
The free-energy minimization technique in the form developed in the
preceding papers in this series is employed to evaluate thermodynamic
quantities and ionization fractions on a fine temperature and density
grid for six astrophysical mixtures of 15 elements. The mixtures
range from that appropriate to super-metal-rich stars, through solar
abundance, to that for extreme Population II objects. In this paper,
the results for solar abundances are summarized in a form that is
illustrative and which facilitates comparison with the results from
other equation of state calculations.
---------------------------------------------------------
Title: The Internal Rotation of the Sun
Authors: Däppen, Werner
1990LNP...366...69D Altcode: 1990rmsi.conf...69D
An introduction to current techniques to infer the Sun's internal
rotation from observed acoustic oscillation modes is given, and some
representative results are shown.
---------------------------------------------------------
Title: Stellar Seismology
Authors: Däppen, Werner
1990ASSL..159..357D Altcode: 1990IAUCo.121..357D; 1990insu.conf..357D
No abstract at ADS
---------------------------------------------------------
Title: Progress Towards a Unified Equation of State
Authors: Däppen, Werner
1990LNP...367...33D Altcode: 1990psss.conf...33D
A recent comparison of thermodynamical quantities, computed in the
chemical and physical picture, has revealed a remarkable agreement in
the hydrogen and helium ionization zones (on an isochore of log p =
-5.5, with p in g cm-3). This agreement is due to an unexpectedly
dominating (classical) Coulomb pressure term. The analogous comparison
at a somewhat higher density (log p = -3.5) shows still striking
similarities, despite the different treatment of bound states in
the two formalisms. The results suggest use of a relatively simple
parametrized equation of state for solar purposes.
---------------------------------------------------------
Title: Effects of Magnetic Fibrils on Solar Oscillation Frequencies:
Mean Field Theory
Authors: Zweibel, Ellen G.; Daeppen, Werner
1989ApJ...343..994Z Altcode:
It is quite likely that the solar interior magnetic field retains
the fibril structure observed at photospheric levels down to some
significant depth in the convection zone. Furthermore, previous work
has shown that the effect of magnetic fibrils on p-mode oscillation
frequencies is enhanced by 1/f, the reciprocal of the fibril
filling factor, over the effect of an equal amount of flux in diffuse
form. Previous calculations have used multiple scattering methods which
effectively preclude the inclusion of stratification or consideration
of realistic geometries. In this paper an alternative simpler method
of treating fibrils is developed on the basis of mean-field theory
originally developed by Parker (1982).
---------------------------------------------------------
Title: Modeling Epsilon Eridani and Its Oscillations
Authors: Soderblom, David R.; Dappen, Werner
1989ApJ...342..945S Altcode:
Models of the structure of the K2 V star Epsilon Eridani which
are based on star luminosity, temperature, composition, age, and
mixing-length parameter (alpha) are discussed. Comparisons are made
with models proposed by Guenther and Demarque (1986) and Guenther
(1987). Predicted oscillation frequencies are presented.
---------------------------------------------------------
Title: Structure interne: le diagnostic astérosismologique.
Authors: Däppen, W.
1989JAF....34Q...6D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Stellar structure: the asteroseismological diagnostic.
Authors: Däppen, W.
1989musi.work...11D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Rapid photometry of the δ Scuti variable 63 Her.
Authors: Mangeney, A.; Chevreton, M.; Belmonte, Juan A.; Daeppen,
W.; Saint-Pe, O.; Praderie, F.; Roca Cortés, Teodoro; Fuensalida,
J.; Alvarez, M.
1988ESASP.286..551M Altcode: 1988ssls.rept..551M
The δ Scuti variable 63 Her has been observed during 21 nights
at two observatories (Observatorio del Teide, Tenerife Island,
Spain and Observatorio Astronomico Nacional de San Pedro Martir in
Baja California, Mexico). Six frequencies of pulsation have been
unambiguously detected, among which the fundamental radial mode, two
non radial pressure-like modes and probably three gravity like modes.
---------------------------------------------------------
Title: Solar oscillation frequencies and the equation of state
Authors: Christensen-Dalsgaard, J.; Dappen, W.; Lebreton, Y.
1988Natur.336..634C Altcode:
Observed oscillation frequencies of the Sun can be used to investigate
the properties of matter under conditions that cannot be achieved on
Earth. In particular the frequencies are sensitive to the equation of
state. A recently developed treatment of the partition functions leads
to a substantial improvement in the agreement between the observed
and the computed frequencies.
---------------------------------------------------------
Title: The influence of the equation of state on the zero-age main
sequence and the Sun.
Authors: Lebreton, Y.; Daeppen, W.
1988ESASP.286..661L Altcode: 1988ssls.rept..661L
In the light of the present uncertainty in the equation of state of
stellar interiors, the authors have calculated stellar and solar models
using three different formalisms for the equation of state. They
have considered (1) a mixture of ideal gases using an artificial
pressure-ionization device, (2) an equation of state where pressure
ionization is achieved by the confined-atom model, and (3) an equation
of state containing a large number of atomic and ionic species, with
detailed internal partition functions, containing weighted occupation
probabilities. The authors have examined the effect of these equations
of state on the position of a star in the H-R diagram: the result is
either a displacement of the star on the zero-age main sequence (ZAMS)
or, for masses lower than 0.7 M<SUB><SUB>sun</SUB></SUB> a change in
the slope of the ZAMS. Furthermore they have carried out the usual
calibration procedure in order to obtain the initial He abundance Y
of the solar model.
---------------------------------------------------------
Title: Epsilon Eridani revisited.
Authors: Daeppen, W.; Soderblom, D.
1988ESASP.286..653D Altcode: 1988ssls.rept..653D
In the light of the unsatisfactory theoretical explanation of the
observed p-mode frequency separation of ɛ Eri of 172 μHz, and of the
fact that the seismological observation has not yet been confirmed,
the authors have computed a new series of models. They have taken
into account only the observational input available prior to the
seismological determination. They have obtained predictions for the
p-mode frequency separation that lie between 198 and 244 μHz.
---------------------------------------------------------
Title: High mass loss in the young Sun!
Authors: Turck-Chieze, S.; Daeppen, W.; Casse, M.
1988ESASP.286..629T Altcode: 1988ssls.rept..629T
The consequences of a possible mass loss in the early main sequence
stage of solar type stars are investigated. Special attention is
given to the Sun, the constraints from surface abundances and p-mode
observations are taken into account. Only a total mass loss smaller
than 0.2 M<SUB><SUB>sun</SUB></SUB> seems to be consistent with the
observations. Though the ensuing modifications of the internal structure
and the cosmological consequences are very small, the <SUP>3</SUP>He,
<SUP>7</SUP>Li, <SUP>9</SUP>Be surface abundances are significantly
modified.
---------------------------------------------------------
Title: Further progress on the helium abundance determination.
Authors: Daeppen, W.; Gough, Douglas O.; Thompson, M. J.
1988ESASP.286..505D Altcode: 1988ssls.rept..505D
The authors report on further progress in attempting to determine the
helium abundance in the solar convection zone by analysing the position
and shape of the "helium hump" in a thermodynamic quantity Θ which
can be inferred from the sound speed in the vicinity of the He II
ionization zone. At present they are estimating the sound speed from
frequencies of high-degree oscillations by a differential asymptotic
technique. The helium abundance Y is then determined by fitting the hump
inferred to one obtained by interpolation in a grid of theoretical model
envelopes. They have tested the procedure by carrying out a double-blind
experiment on artificial data, and have found that accurate knowledge
of the equation of state is essential for a useful determination. The
authors have also carried out the procedure on real solar data, but
they judge that the frequencies are at present too poorly determined
to enable us to obtain a reliable estimate of Y in the sun.
---------------------------------------------------------
Title: Current options for the equation of state of the solar
interior.
Authors: Daeppen, W.
1988ESASP.286..451D Altcode: 1988ssls.rept..451D
The principal open problem of the equation of state is the number
of excited states of hydrogen and helium in the zones of partial
ionization. The number of excited states is affected in two ways:
first by destruction of the levels due to the (neutral and charged)
surrounding species, and second by statistical mechanics which
governs the population of the available levels. The author discusses
recent progress in this field and explains the two principal current
"philosophies". One is the chemist's view, in which bound systems
are interpreted as autonomous species with reactions between each
other, the other is the physicist's view, in which a virial expansion
of pressure is obtained starting out from fundamental species only
(i.e. electrons and nuclei), and in which the so-called Planck-Larkin
partition function appears.
---------------------------------------------------------
Title: Modelling the variation of solar p-mode frequencies.
Authors: Daeppen, W.; Gough, Douglas O.; Turck-Chieze, S.
1988ESASP.286..511D Altcode: 1988ssls.rept..511D
The authors present a Green's function technique to study long-term
variations of the Sun (with characteristic time scales from one month
to millions of years). The method is the combination of two previous
analyses carried out independently by Gough and by Däppen. Their study
has been motivated by the recent observational progress on solar p-mode
frequency variations.
---------------------------------------------------------
Title: The Equation of State for Stellar Envelopes. III. Thermodynamic
Quantities
Authors: Daeppen, Werner; Mihalas, Dimitri; Hummer, D. G.; Mihalas,
Barbara Weibel
1988ApJ...332..261D Altcode:
The authors derive general formulae for the computation of the
thermodynamic properties of a partially ionized (and/or dissociated)
multicomponent gas in terms of second derivatives of the free energy
with respect to temperature, volume, and occupation numbers. For the
free energy used in previous work the authors give explicit analytical
expressions for all derivatives required to construct the thermodynamic
quantities. Representative results for several different thermodynamic
properties of a hydrogen-helium plasma with N(He)/N(H) = 0.10 are
presented as color plots.
---------------------------------------------------------
Title: The Equation of State for Stellar Envelopes. II. Algorithm
and Selected Results
Authors: Mihalas, Dimitri; Dappen, Werner; Hummer, D. G.
1988ApJ...331..815M Altcode:
A free-energy-minimization method for computing the dissociation and
ionization equilibrium of a multicomponent gas is discussed. The adopted
free energy includes terms representing the translational free energy
of atoms, ions, and molecules; the internal free energy of particles
with excited states; the free energy of a partially degenerate
electron gas; and the configurational free energy from shielded
Coulomb interactions among charged particles. Internal partition
functions are truncated using an occupation probability formalism
that accounts for perturbations of bound states by both neutral and
charged perturbers. The entire theory is analytical and differentiable
to all orders, so it is possible to write explicit analytical formulas
for all derivatives required in a Newton-Raphson iteration; these are
presented to facilitate future work. Some representative results for
both Saha and free-energy-minimization equilibria are presented for
a hydrogen-helium plasma with N(He)/N(H) = 0.10. These illustrate
nicely the phenomena of pressure dissociation and ionization, and
also demonstrate vividly the importance of choosing a reliable cutoff
procedure for internal partition functions.
---------------------------------------------------------
Title: Asteroseismology - Results and Prospects
Authors: Dappen, W.; Dziembowski, W. A.; Sienkiewicz, R.
1988IAUS..123..233D Altcode:
The main effects of stellar mass and evolution on oscillation
frequencies are discussed with the help of simplified wave-propagation
diagrams. Frequency separations resulting from asymptotic
expressions are compared with the corresponding results from numerical
computations. The seismological issues of solar-like stars and Ap stars
are discussed in some detail, and a progress report on the equation of
state for stellar interiors is given. The review ends with a summary
of properties and important physical problems for selected classes of
variable stars.
---------------------------------------------------------
Title: Modeling the Global Oscillations of Epsilon-Eridani
Authors: Soderblom, D. R.; Dappen, W.
1988IAUS..123..281S Altcode:
The authors have reviewed the observational data for ɛ Eri to derive
the best estimates of luminosity, radius, temperature, composition, and
age, as well as the uncertainties associated with each of these. These
quantities are then used in stellar structure models to try to reproduce
the global oscillation frequencies observed by Noyes et al. The authors
can reproduce the observed frequencies and splittings at least as well
as the computations of Guenther and Demarque, yet for significantly
different stellar parameters, most notably the age.
---------------------------------------------------------
Title: Theoretical Constraints from Asteroseismological High S/n
Observations
Authors: Dappen, W.
1988IAUS..132..211D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Oscillations in Solar Models with Weakly Interacting Massive
Particles
Authors: Gilliland, Ronald L.; Dappen, Werner
1988ApJ...324.1153G Altcode:
Solar models containing concentrations as low as 10<SUP>-11</SUP> by
number of weakly interacting massive particles (WIMPs), accreted from
a galactic background population, are consistent with the observed flux
of high-energy solar neutrinos. The structural changes produced in the
solar core have also been shown to produce changes in the oscillation
frequencies of g-modes and p-modes of low angular degree and high
radial order. In this paper the authors examine the predictions for
solar oscillations over a large range of possible WIMP properties.
---------------------------------------------------------
Title: Statistical Mechanics of Partially Ionized Stellar Plasmas:
The Planck-Larkin Partition Function, Polarization Shifts, and
Simulations of Optical Spectra
Authors: Dappen, Werner; Anderson, Lawrence; Mihalas, Dimitri
1987ApJ...319..195D Altcode:
We discuss a recent controversy about the Planck-Larkin partition
function, and present optical simulations of high-quality spectra
from laboratory hydrogen plasmas (Wiese, Kelleher, and Paquette) using
several partition function formalisms. We point out that the controversy
has arisen from a misunderstanding about the use of the Planck-Larkin
partition function. A Planck-Larkin cancellation may still have its
place in equations of state that are based on quantum-statistical
many-body theory (i.e., the "physical picture"). However, experimental
evidence shows that it is inconsistent to use the Planck-Larkin
partition function as the internal partition function in simple
models of reacting gases (i.e., the "chemical picture"). Moreover,
the more sophisticated equations of state of the physical picture
will have to be subjected to the same comparison with experimental
data. We also address the question of plasma polarization shifts of
bound-state energies. We discuss the static-screened Coulomb potential
(SSCP) as an atomic potential: from theoretical considerations and
observational constraints we conclude that it should not be used. The
only useful result of the SSCP potential its prediction of the number
of excited be obtained by alternative means, e.g., by an occupation
probability formalism.
---------------------------------------------------------
Title: Hypercharge, Solar Structure, and Stellar Evolution
Authors: Gilliland, Ronald L.; Dappen, Werner
1987ApJ...313..429G Altcode:
The authors investigate the effect of proposed modifications
to the gravitational law at short range on stellar structure
and evolution. Changes to solar structure, neutrino fluxes,
and oscillation frequencies are within current observational and
theoretical uncertainties. Modifications to stellar lifetimes are
large enough that they should be considered, if the suggested changes
to gravitation prove correct.
---------------------------------------------------------
Title: Solar Oscillations and the Equation of State
Authors: Däppen, W.
1987ASIB..154..179D Altcode: 1987scpp..conf.179D
No abstract at ADS
---------------------------------------------------------
Title: Weakly interacting massive particles, solar neutrinos, and
solar oscillations
Authors: Dappen, W.; Gilliland, R. L.; Christensen-Dalsgaard, J.
1986Natur.321..229D Altcode:
Weakly interacting, massive particles (WIMPs) have
recently been proposed as a solution to the solar neutrino
problem<SUP>1-3</SUP>. Whereas standard solar models consistently
predict a detection rate of (high-energy) neutrinos 3 times higher
than that observed in the Davis experiment<SUP>4-6</SUP>, the presence
of hypothetical massive particles in the solar centre would resolve
this discrepancy. Models which incorporate a relative number of
10<SUP>-11</SUP> WIMPs with appropriate scattering cross-section would
reduce the predicted neutrino detections by <SUP>37</SUP>Cl to the
observed value, without significant changes in the solar structure
outside the central region<SUP>1-3</SUP>. We have subjected these
models to an observational test of p-mode oscillation frequencies by
computing frequency differences of low-degree, high-order oscillation
frequencies. Although standard solar models also pass this test,
WIMP models provide a better fit.
---------------------------------------------------------
Title: Progress report on helium abundance determination.
Authors: Dappen, W.; Gough, D. O.
1986ASIC..169..275D Altcode: 1986ssds.proc..275D
Intermediate results from a programme to determine the helium
abundance of the solar convection zone are presented. The method uses
the influence of helium ionization on the local sound speed, which
can be gauged from inversions of solar oscillation frequencies. The
resolution of the principal diagnostic function by the data justifies
optimism for an abundance determination in a future step.
---------------------------------------------------------
Title: Non-linear stellar oscillations - Non-radial mode interactions
Authors: Dappen, W.; Perdang, J.
1985A&A...151..174D Altcode:
A mode-coupling formalism is developed which captures an important
class of nonlinear, nonradial adiabatic stellar motions, namely
genuine oscillations about a dynamically stable equilibrium
state. Observational arguments suggesting nonlinear phenomena
among the nonradial-oscillations and indirect theoretical arguments
pointing toward hidden nonlinearities are reviewed. A scheme for
mastering the general adiabatic nonradial nonlinear stellar motion
problem by translating it into a Hamiltonian particle formalism is
shown and then refined to ecompass only 'pure' oscillations around
the radially symmetric equilibrium state, thus suppressing all
stationary circulations. The formalism is used to provide constraints
on 'pure' oscillations in an intrinsic fashion, without resorting to
Lagrange multipliers. The final Hamiltonian equations are found to
have a structure more involved than in the purely radial case. This
suggests that the nonradial nonlinear oscillations may exhibit a
broader spectrum of different clases of motion than the purely radial
stellar oscillations.
---------------------------------------------------------
Title: Nonlinear nonradial adiabatic stellar oscillations: numerical
resultsfor many-mode couplings.
Authors: Däppen, W.
1985chas.conf..273D Altcode:
The adiabatic nonlinear coupling of many linear radial modes has
been extended to nonradial modes. A variational principle for fluid
mechanics has been applied to obtain a Hamiltonian formalism. The
numerical results presented in the paper show that the nonradial modes
can cause a much more irregular motion than the radial modes. In the
case of the Sun, radial and nonradial 5-minute modes are coupled,
and they have been computed using a 'real' solar model.
---------------------------------------------------------
Title: Nonlinear nonradial adiabatic stellar oscillations - Numerical
results for many-mode couplings
Authors: Dappen, W.
1985ASIC..161..273D Altcode: 1985cia..conf..273D
The adiabatic nonlinear coupling of many linear radial modes has
been extended to nonradial modes. A variational principle for fluid
mechanics has been applied to obtain a Hamiltonian formalism. The
numerical results presented here show that the nonradial modes can
cause a much more irregular motion than the radial modes. First,
there are many near-resonant nonradial frequencies, and second,
there is a nonlinear velocity-dependent term in the Hamiltonian,
which has no radial analogue. In the case of the sun, the previous
results included coupling only for the lowest radial modes, and the
coupling coefficients were computed in a polytropic model. Here,
radial and nonradial 5-minute modes are coupled, and they have been
computed using a 'real' solar model.
---------------------------------------------------------
Title: The lithium abundance of Hyades main-sequence stars.
Authors: Cayrel, R.; Cayrel de Strobel, G.; Campbell, B.; Dappen, W.
1984ApJ...283..205C Altcode:
From high-quality Reticon spectra of Hyades G and K dwarfs, their
lithium abundance is found to decline much more rapidly with decreasing
temperature than heretofore realized. Previous observations of the 6707
Li I doublet for the cooler dwarfs have probably been contaminated by
blends. However, the new lithium-temperature relation still does not
agree with simple models of lithium burning in the convective zone,
either with or without overshooting. Models have therefore to include
other mechanisms for lithium depletion.
---------------------------------------------------------
Title: Solar oscillations - The challenge of nonlinearity
Authors: Daeppen, W.; Perdang, J.
1984MmSAI..55..299D Altcode:
Preliminary numerical and theoretical experimental results supporting
the view that the observed long period of the sun may be a nonlinear
phenomenon are presented. The nonlinear power spectrum of the surface
displacement is noted to invariably show a peak in the 2-3 hour
range. It is found that nonlinear effects set in earlier with increasing
total number of interacting modes, as can be readily understood from
the asymptotic behavior of eigenfunctions. A variant of Linstedt's
classical perturbation method indicates that the spectral peak in the
power spectrum of the surface displacement is a superposition of a
large number of nonlinear contributions.
---------------------------------------------------------
Title: An Observational Test on Stellar Interior Mixing - the Lithium
Depletion in Twelve Hyades Dwarfs
Authors: Cayrel, R.; Cayrel, G.; Campbell, B.; Dappen, W.
1984IAUS..105..537C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the Determination of the Helium Abundance of the Solar
Convection Zone
Authors: Dappen, W.; Gough, D. O.
1984LIACo..25..264D Altcode: 1984tpss.conf..264D; 1984trss.conf..264D
No abstract at ADS
---------------------------------------------------------
Title: Nonlinear Nonradial Adiabatic Stellar Oscillations : Numerical
results for Many-mode Couplings
Authors: Dappen, W.
1984LIACo..25..474D Altcode: 1984tpss.conf..474D; 1984trss.conf..474D
No abstract at ADS
---------------------------------------------------------
Title: Hydrostatic reaction of the Sun to local disturbances.
Authors: Daeppen, W.
1983A&A...124...11D Altcode:
The reaction of the solar structure to elementary perturbations is
modeled mathematically. The principal assumptions of the model of
structure and equilibrium are linearization, a mixing-length formalism,
and spherical symmetry. The resulting linearized boundary-value problem
is solved with both analytical and numerical methods, and luminosity
and radius response functions for different perturbation depths are
shown. The quantity W (= delta ln R/delta ln L) is found to be quite
frequency dependent, explaining the discrepancies among previous W
computations. It is suggested that the model presented here can be
applied to study the relationship of solar activity to luminosity,
radius, the frequency of the 5-min oscillations, or other observable
parameters.
---------------------------------------------------------
Title: An analytical version of the free-energy-minimization method
for the equation of state of stellar plasmas
Authors: Daeppen, W.
1980A&A....91..212D Altcode:
In the free energy method statistical mechanical models are used
to construct a free energy function of the plasma. The equilibrium
composition for given temperature and density is found where the
free energy is a minimum. Until now the free energy could not be
expressed analytically, because the contributions from the partially
degenerate electrons and from the inner degrees of freedom of the
bound particles had to be evaluated numerically. In the present paper
further simplifications are made to obtain an analytic expression for
the free energy. Thus the minimum is rapidly found using a second order
algorithm, whereas until now numerical first order derivatives and a
steepest- descent method had to be used. Consequently time-consuming
computations are avoided and the analytical version of the free energy
method has successfully been incorporated into the stellar evolution
programmes at Geneva Observatory. No use of thermodynamical tables
is made, either. Although some accuracy is lost by the simplified
analytical expression, the main advantages of the free energy method
over simple ideal-gas and Sacha-equation subprogrammes (as used in the
stellar programmes mentioned) are still kept. The relative errors of
the simplifications made here are estimated and they are shown not to
exceed 10% altogether. Densities up to those encountered in low-mass
main-sequence stars can be treated within the region of validity of the
method. Higher densities imply less accurate results. Nonetheless they
are consistent so that they cannot disturb the numerical integration
of the equilibrium equation in the stellar evolution model. The
input quantities of the free energy method presented here are either
temperature and density or temperature and pressure, the latter require
a rapid numerical Legendre transformation which has been developed here.
