Author name code: gadun
ADS astronomy entries on 2022-09-14
author:"Gadun, A."
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Title: Fourier analysis of Fe I lines in the spectra of the Sun,
{\alpha} Centauri A, Procyon, Arcturus, and Canopus
Authors: Sheminova, V. A.; Gadun, A. S.
Bibcode: 2010arXiv1004.3286S
Altcode:
We used spectral observations of Fe I line profiles with a 200 000
resolution to determine micro and macroturbulent velocities in the
atmospheres of the Sun as a star, {\alpha} Cen A, Procyon ({\alpha}
CMi), Arcturus ({\alpha} Boo), and Canopus ({\alpha} Car). Isotropic
microturturbulent velocities (V_mi) and radial-tangential macroturbulent
velocities (V_ma,RT) were found to be a quite suitable approximation
to the velocity field in the atmospheres of all stars studied except
Canopus. The average velocities V_mi and V_ma,RT are 0.8 +/- 0.1
and 2.6 +/- 0.3 km/s for the Sun as a star, 0.8 +/- 0.2 and 2.9 +/-
0.4 km/s for {\alpha} Cen A, 0.8 +/- 0.3 and 5.9 +/- 0.2 km/s for
Procyon, 1.0 +/- 0.2 and 4.6 +/- 0.3 km/s for Arcturus. The velocity
field in the atmosphere of Canopus can be described by an anisotropic
radial-tangential distribution of microturbulence with V_mi,RT = 2.1
km/s and anisotropic distribution of macroturbulence with V_ma,rad =
17 +/- 2 km/s and V_ma,tan = 1.3 +/- 1.0 km/s. From Fourier analysis
of broadening and shapes of three spectral lines of Fe I, we have
derived the rotation velocity V_e sini = 3.5 +/- 0.2 km/s for Canopus.
Title: Convective shifts of iron lines in the solar photosphere
Authors: Sheminova, V. A.; Gadun, A. S.
Bibcode: 2002KFNT...18...18S
Altcode: 2010arXiv1004.3438S
The influence of a convective structure of the solar photosphere
on the shifts of spectral iron lines was studied. Based on the 2-D
time-dependent HD solar model atmosphere, we synthesized the line
profiles in the visual and infrared spectral ranges. The dependence
of the lines shifts on excitation potential, wavelength, and line
strength was analyzed in combination with the depression contribution
functions. The magnitude of line shifts was found to depend on the
difference between the contributions from central parts of granules
and from intergranular lanes. Deep in the photosphere the central
areas with upflows give the main contribution in the absorption of
spatially unresolved weak and moderate lines. The contribution from
intergranular lanes is small for these lines. In the upper solar
photosphere layers the convective overshooting region is located,
and the physical conditions drastically change there. As a result, the
line depression contribution from intergranular lanes with downflows
grows significantly, while the contributions from the central areas
of granules become smaller. This is the reason why blue line shifts
decrease and become red, in particular for the strong photospheric
lines, which are completely formed in the convective overshootung
region. The convective blueshifts observed in infrared lines are smaller
than in the visual spectral range because the effective absorption
layers are located higher in the photosphere and extend further into
the convective overshooting region due to a greater opacity in the
infrared range. We also calculated the effective formation depth of
visual and infrared synthetic lines, and their dependence on main line
parameters is illustrated.
Title: A formation mechanism of magnetic elements in regions of
mixed polarity
Authors: Gadun, A. S.; Solanki, S. K.; Sheminova, V. A.; Ploner,
S. R. O.
Bibcode: 2001SoPh..203....1G
Altcode:
We present 2-D, fully compressible radiation-MHD simulations of
the solar photospheric and subphotospheric layers that run for
2 hours of solar time starting from a magnetic configuration
with mixed polarities. In the atmospheric layers the simulation
reveals a correlation between field strength and inclination, with a
nearly vertical strong-field magnetic component and a more horizontal
weak-field component, in agreement with the observations. Our simulation
also shows that magnetic flux is converted from one of these states to
the other. In particular, magnetic flux sheets can also be formed when
a new downflow lane starts due to granule fragmentation. The dynamics
of the granulation and field-line reconnection are found to play a
role in the initial stages of a magnetic element's formation. The
simulation predicts that during or shortly after their formation
magnetic elements could be associated with oppositely polarized flux
at a small spatial scale.
Title: Small-Scale Magnetic Elements in 2-D Nonstationary
Magnetogranulation
Authors: Gadun, A. S.; Solanki, S. K.
Bibcode: 2001ASSL..259..295G
Altcode: 2001dysu.conf..295G
2-D simulations of magnetogranulation provide evidence of a close
connection between the magnetic field and nonstationary thermal
convection. Fragmentation of large granules can lead to the formation
of compact nearly vertical magnetic tubes from a weaker horizontal
field. Conversely, the dissolution of granules can lead to a merging
of magnetic elements and either to field cancellation (leading to the
transformation of strong vertical field to its weaker horizontal state)
or to the formation of broader and stronger magnetic structures.
Title: The Formation of One-Lobed Stokes V Profiles in an
Inhomogeneous Atmosphere
Authors: Ploner, S. R. O.; Schussler, M.; Solanki, S. K.; Sheminova,
V. A.; Gadun, A. S.; Frutiger, C.
Bibcode: 2001ASPC..236..371P
Altcode: 2001aspt.conf..371P
We assess the diagnostic potential of the observed pathological Stokes V
profiles that differ strongly from the customary, nearly antisymmetric
two-lobed shape. In particular, we consider the formation of one-lobed
Stokes V profiles using the results of an MHD simulation. We find
that the majority of one-lobed profiles is produced in regions of
weak horizontal field with significant cancellation caused by mixed
polarity along the line of sight. A minority of one-lobed profiles
originates close to strong magnetic field concentrations with strong
gradients of velocity and magnetic field strength.
Title: An Example of Reconnection and Magnetic Flux Recycling near
the Solar Surface
Authors: Ploner, S. R. O.; Schüssler, M.; Solanki, S. K.; Gadun, A. S.
Bibcode: 2001ASPC..236..363P
Altcode: 2001aspt.conf..363P
No abstract at ADS
Title: Correlative relationships in an inhomogeneous solar atmosphere
Authors: Gadun, A. S.; Hanslmeier, A.; Kučera, A.; Rybák, J.;
Wöhl, H.
Bibcode: 2000A&A...363..289G
Altcode:
We analyse the correlative relationships between various quantities
derived from 2-D inhomogeneous and time-dependent model atmospheres
and between selected simulated line parameters to compare them with
height-dependent correlations derived from spectral observations. We
detect three photospheric regions: thermal convection, overshooting
convection and a transition layer. We also show that correlations
found for the model data and those computed within simulated spectral
observations are a good testing tool for line formation depths. As
an example, we examine two criteria, providing heights of line core
formation in LTE, and conclude that the approach which defines
this quantity as geometrical height at line center optical depth
τλ0 = 1 is likely more suitable for diagnostic purposes
than the method based on depression contribution function.
Title: Size-dependent properties of simulated 2-D solar granulation
Authors: Gadun, A. S.; Hanslmeier, A.; Pikalov, K. N.; Ploner,
S. R. O.; Puschmann, K. G.; Solanki, S. K.
Bibcode: 2000A&AS..146..267G
Altcode:
Two time-dependent sets of two-dimensional hydrodynamic models of solar
granulation have been analyzed to obtain dependence of simulated thermal
convection on the horizontal size of the convection cells. The two
sets of models treat thermal convection either as fully non-stationary,
multiscale convection (granular convection is a surface phenomenon) or
as quasi-steady-state convection cells (they treat granular convection
as a collection of deep-formed cells). The following results were
obtained: 1) quasi-steady convection cells can be divided into 3
groups according to their properties and evolution, namely small-scale
(up to L ~ 900 km), intermediate-scale (1000-1500 km) and large-scale
(larger 1500 km) convection cells. For the first group thermal damping
due to radiative exchange of energy, mostly in the horizontal direction,
is very important. Large-scale cells build up a pressure excess, which
can lead to their total fragmentation. Similar processes also acts on
the fully non-stationary convection. 2) The largest horizontal size
of convection cells for which steady-state solutions can be obtained
is about 1500 km. This corresponds to granules, i.e. the bright
parts of the convection cells, with a diameter of about 1000 km. 3)
In addition to the zone of high convective instability associated
with the partial ionization of hydrogen, we identify another layer
harboring important dynamic processes in steady-state models. Just
below the hydrogen-ionization layer pressure fluctuations and the
acoustic flux are reduced. Steady-state models with reflecting lateral
boundaries even exhibit an inversion of pressure fluctuations there. 4)
From observational point of view the surface convection differs from
steady-state deep treatment of thermal convection in the dependence
of vertical granular velocities on their sizes for small-scale
inhomogeneous. However, they cannot be distinguished by the dependence
of temperature or emergent intensity of brightness structures. 5) Both
kinds of models demonstrate the inversion of density in subphotospheric
layers. It is more pronounced in small-scale cells and inside hot
upflows. 6) The brightness of simulated granules linearly increases
with their size for small granules and is approximately constant or
even decreases slightly for larger granules. For intergranular lanes
the simulations predict a decrease of their brightness with increasing
size. It falls very rapidly for narrow lanes and remains unchanged
for broader lanes. 7) A quantitative comparison of the brightness
properties of simulated granulation with real observations shows
that the strong size-dependence of the properties of the smallest
simulated granules is not accessible to current observations due to
their limited spatial resolution. The observed size dependences result
rather from spatial smoothing and the granule-finding algorithm. We
do not exclude, however, an influence of the limitations of the 2-D
treatment of thermal convection on the present results.
Title: Evolution of Solar Magnetic Tubes from Observations of Stokes
Parameters
Authors: Sheminova, V. A.; Gadun, A. S.
Bibcode: 2000ARep...44..701S
Altcode: 2012arXiv1210.3495S
Basic scenarios and mechanisms for the formation and decay of
small-scale magnetic elements and their manifestation in synthesized
Stokes profiles of the Fe I 15648.5 Å infrared line are considered
in the context of two-dimensional modeling of nonstationary
magnetogranulation on the Sun. The stage of convective collapse is
characterized by large redshifts in the V profiles accompanied by
complete Zeeman splitting of the I profiles. This is due to intense
downward flows of material, which facilitates the concentration
of longitudinal field with an amplitude of about several kG in the
tube. The dissipation of strong magnetic structures is characterized
by blueshifts in their profiles, which result from upward fluxes that
decrease the magnetic field in the tube. Typical signatures during
key stages in the evolution of compact magnetic elements should
be detectable via observations with sufficiently high spatial and
temporal resolution.
Title: Is solar mesogranulation a surface phenomenon?
Authors: Ploner, S. R. O.; Solanki, S. K.; Gadun, A. S.
Bibcode: 2000A&A...356.1050P
Altcode:
Convection is the main form of energy transport in the subsurface
layers of the sun and other cool stars. The imprint of cellular
convection can be directly observed on the solar surface, with
a hierarchy of four size scales. The smallest observed convection
cells, called granules, have typical horizontal sizes of 1,000-2,000
km and have been successfully reproduced by numerical simulations
\citep{spruit:97,stein:nordlund:98}. Cells at three larger scales are
also detected \citep{leighton:etal:62,november:etal:81,beck:etal:98},
but these have so far not been amenable to numerical modelling,
so that their formation scenarios remain untested. Here we present
a numerical simulation which resolves both the granular and the next
larger, mesogranular, scale. The mesogranules have horizontal extents
of 5,000-10,000 km. Our 2D simulation reproduces key properties of both
granules and mesogranules. In addition, our simulation demonstrates
that the observed mesogranulation is driven close to the solar surface
and therefore rules out the text-book explanation of mesogranulation
as cellular convection driven by superadiabaticity in the deeper
layer where neutral helium ionizes. By proxy, this result also casts
doubt on the traditional explanation of supergranulation, even larger
convection cells with diameters of 20,000-30,000 km, as being driven
by the yet deeper second ionization of helium.
Title: Fe II lines in the problem of the diagnostic of solar
photospheric shocks
Authors: Gadun, A. S.; Hanslmeier, A.
Bibcode: 2000KFNT...16..130G
Altcode:
We propose to use Fe II lines observed near the solar limb for the
detection of photospheric shocks at granule edges. Their theoretical
spectral scans synthesized with 2-D models provide a more clear
evidence for photospheric shocks as compared to spectral lines of
neutral elements.
Title: Correlative analysis of 2-D solar atmosphere
Authors: Gadun, A. S.; Hanslmeier, A.
Bibcode: 2000KFNT...16..121G
Altcode:
Correlations between various parameters of 2-D inhomogeneous
time-dependent solar atmospheres are analyzed to be directly related
to height-dependent correlations found on the basis of spectral
simulations. We detect four photospheric regions with thermal and
overshooting convection, transition zone, and fully oscillating
layears. The correlations found for the model data and those computed
within simulated spectral scans are a good testing tool for systems
of spectral line heights if these correlations are analyzed in
comparison. In particular, we examine two methods providing the heights
of line core formation in LTE and show that the approach which defines
this quantity as a geometrical height at the optical depth of line
center τλ0 = 1 is more suitable for diagnostic purpose
than the method based on depression contribution function.
Title: Two-dimensional nonstationary magnetogranulation
Authors: Gadun, A. S.
Bibcode: 2000KFNT...16...99G
Altcode:
2-D simulation of nonstationary magnetogranulation is analyzed in
detail: mechanisms and scenarios leading to formation or cancellation
of small-scale magnetic elements, regimes of their stability,
size-dependent and field-dependent properties of the tubes formed,
as well as brightness properties of simulated magnetogranulation
to be compared with the corresponding modeling of non-magnetic
granulation. It is noted that magnetic field stabilizes the thermal
convection -- shearing instability decreases, simulated granules become
smaller. On the other hand, thermal convective flows directly influence
the evolution of the small-scale magnetic field. This simulation
confirms Vankatakrishnan's conclusion that the thermal mechanism
which strengthens the intrinsic magnetic field of thin tubes is highly
sensitive to their horizontal sizes. Two regimes of magnetoconvection
were found. A change of regimes is detected for the ratio β between
gas and magnetic pressure equal approximately to 2.0-2.5. Simulated
tubes with a horizontal size of about 150 km are the most frequent
contributors to the total area of magnetic tubes.
Title: The evolution of solar granules deduced from 2-D simulations
Authors: Ploner, S. R. O.; Solanki, S. K.; Gadun, A. S.
Bibcode: 1999A&A...352..679P
Altcode:
The evolution of solar granules is investigated on the basis of two
dimensional numerical solutions of the hydrodynamic equations describing
a compressible, radiatively coupled and gravitationally stratified
medium representative of the solar surface layers. The simulation covers
17 Mm on the solar surface and was run for over 5 h of solar time,
hence allowing the evolution of over 400 granules to be followed. A
statistical investigation of the temporal evolution of granules
therefore becomes feasible. Two types of granules can be distinguished
by their means of death: fragmenting and dissolving granules. Properties
and average evolutionary histories of these two types of granules
are considered. It is found that fragmenting granules are in general
large at birth and expand further with time. It is confirmed that
fragmentation into two (or more) parts is produced by buoyancy braking,
which in turn is initiated by the stronger horizontal flows in larger
granules. This last property, finally, is due to mass conservation. The
expansion, however, is due to a pressure excess relative to neighbouring
granules. The pressure excess is particularly marked if the neighbours
are dissolving granules. In contrast, dissolving granules are born
small and shrink before finally disappearing. The shrinkage is caused
by their neighbours which generally posses excess gas pressure and
larger horizontal flows. In summary, according our findings the fate
of a granule is decided by its properties at birth and the company
it keeps. Evidence is presented suggesting that the evolution of both
types of granules is driven by events near the solar surface.
Title: Two-dimensional simulation of solar granulation: description
of technique and comparison with observations
Authors: Gadun, A. S.; Solanki, S. K.; Johannesson, A.
Bibcode: 1999A&A...350.1018G
Altcode:
The physical properties of the solar granulation are analyzed on the
basis of 2-D fully compressible, radiation-hydrodynamic simulations and
the synthetic spectra they produce. The basic physical and numerical
treatment of the problem as well as tests of this treatment are
described. The simulations are compared with spatially averaged spectral
observations made near disk centre and high resolution spectra recorded
near the solar limb. The present simulations reproduce a significant
number of observed features, both at the centre of the solar disc and
near the solar limb. Reproduced observables include the magnitude of
continuum and line-core intensity fluctuations, line bisectors and
correlations between different line parameters. Spatially averaged
line shifts near disc centre, however, are not so well reproduced,
as are individual correlations between line parameters near the solar
limb. Possible causes of these discrepancies are discussed. The present
models predict the existence of two photospheric layers at which the
temperature fluctuations change sign. We point out a diagnostic of
the hitherto undetected upper sign reversal based on high spatial
resolution spectral observations of a sample of lines formed over a
wide range of heights in the photosphere.
Title: Formation of small-scale magnetic elements: surface mechanism
Authors: Gadun, A. S.; Sheminova, V. A.; Solanki, S. K.
Bibcode: 1999KFNT...15..387G
Altcode: 2012arXiv1210.3499G; 1999KFNT...15e.387G
The first results of a two-dimensional MHD simulation of solar
magnetogranulation are given. The medium was treated as compressible,
gravitationally stratified, radiatively coupled, partially ionized,
and turbulent. The evolution of magnetogranulation was simulated in
course of 2 hours of hydrodynamic (solar) time. A surface (magnetic
plume-like) mechanism which forms thin magnetic elements was found to
exist. This sort of field formation occurs due to fragmentation of
large-scale granules. Active role of such mechanism shows that the
magnetogranulation not only concentrates and intensifies the global
magnetic flux at the boundaries of convective cells but also forms
nearly vertical compact magnetic tubes by involving the weak horizontal
field of the photosphere, which in general may be of local nature.
Title: Spatial variations in the Li I λ671 nm resonance line in
two-dimensional artificial granulation.
Authors: Gadun, A. S.
Bibcode: 1999KFNT...15..153G
Altcode: 1999KNFT...15..153G
Spectral observations of the Li I 671 nm resonance line with high
spatial resolution were simulated based on time-dependent series of 2-D
solar model atmospheres and the LTE approach. They do not confirm the
conclusion of Kiselman (1997, 1998) that the LTE synthesis of this line
produces an extremely different correlation between spatial variations
of equivalent width and corresponding continuum intensity compared
with the NLTE simulation and actual observations. The cause of such
a discrepancy with Kiselman's results may be different atmospheric
stratification of fluctuations in the thermodynamic quantities in the
models used. Simpler single-scale (one-cell) simulations or the fully
unstable models with unevolved flows are shown to have a quasi-columnar
structure which extends over almost the whole model photosphere; they
also produce spectral LTE result in close agreement with Kiselman's
LTE plots.
Title: Two-dimensional model atmospheres of metal-poor halo
dwarfs. I. Analysis of the models.
Authors: Gadun, A. S.; Ploner, S. R. O.
Bibcode: 1999KFNT...15....3G
Altcode: 1999KNFT...15....3G
Two-dimensional radiative hydrodynamical simulations of the granulation
in metal-poor halo dwarfs are analysed and compared with similar
solar calculations. A decrease in metallicity was found to reveal
itself in the properties of surface layers, playing a role of thermal
boundary. As a result, the granulation temperature contrast grows in
the lower photosphere, radiative cooling of hot convective upflows
is more active in the middle photosphere, and temperature variations
increase in the upper photosphere. The amplitudes of atmospheric
oscillations become higher and the size distribution of granules is
shifted asymmetrically to the range of smaller scales. The photospheric
overshooting convection has a strong impact on the energy balance in
the lower photosphere with hot convective upflows predominating.
Title: Two-dimensional model atmospheres of metal-poor halo
dwarfs. II. Iron and lithium LTE abundances.
Authors: Gadun, A. S.; Ploner, S. R. O.
Bibcode: 1999KFNT...15...17G
Altcode: 1999KFNT...15a..17G; 1999KNFT...15...17G
The effect of atmospheric inhomogeneities on the iron and lithium LTE
abundances is estimated at 0.2 - 0.3 dex based on two-dimensional model
atmospheres of metal-poor halo stars ([M/H] = -2) with Teff
and log g close to the solar values. Spectral observations of Fe I
and Li I lines in stellar spectra were used. The absolute value of the
lithium LTE abundance found with 2D-models ranges from 2.0 to 2.4 in
the hydrogen scale.
Title: Formation of small-scale magnetic elements: surface mechanism.
Authors: Gadun, A. S.; Sheminova, V. A.; Solanki, S. K.
Bibcode: 1999KPCB...15..291G
Altcode:
The authors present results of a two-dimensional MHD simulation of the
solar magnetogranulation. The medium was assumed to be compressible,
gravitationally stratified, radiatively coupled, partially ionized,
and turbulent. The simulated magnetogranulation evolved over the
course of two hours of hydrodynamic (solar) time. A surface (magnetic
plume-like) mechanism which forms thin magnetic elements was found to
operate during the process of granule fragmentation. The activity of
such a mechanism suggests that the magnetogranulation can concentrate
and intensify the global magnetic flux at the boundaries of convective
cells and can also form nearly vertical compact magnetic flux tubes
by involving the weak horizontal photospheric field, which may be,
in general, of local (turbulent) nature.
Title: Two-dimensional model atmospheres of metal-poor halo
dwarfs. II. Iron and lithium LTE abundances.
Authors: Gadun, A. S.; Ploner, S. R. O.
Bibcode: 1999KPCB...15...10G
Altcode:
The effect of atmospheric inhomogeneities on the iron and lithium LTE
abundances is estimated at 0.2 - 0.3 dex based on two-dimensional
time-dependent model atmospheres of metal-poor halo stars ([M/H] =
-2) with Teff and log g close to the solar values. Spectral
observations of Fe I and Li I lines in stellar spectra were used. The
absolute value of the lithium LTE abundance found with the 2-D models
ranges from 2.0 to 2.4 on the hydrogen scale.
Title: Granulation Near the Solar Limb: Observations and 2-D Modeling
Authors: Gadun, A. S.; Solanki, S. K.; Johannesson, A.
Bibcode: 1999ASSL..239..201G
Altcode: 1999msa..proc..201G
Based on high spatial resolution spectra and using 2-D fully
compressible, HD simulations of granules we analyze the correlations
between spectral line parameters: their CLV, height-dependence and
sensitivity to spatial resolution. We also point out some discrepancies
between the model results and observations.
Title: Two-dimensional model atmospheres of metal-poor halo
dwarfs. I. Analysis of the models.
Authors: Gadun, A. S.; Ploner, S. R. O.
Bibcode: 1999KPCB...15....1G
Altcode:
Two-dimensional radiative hydrodynamical simulations of granulation
in metal-poor halo dwarfs are analyzed and compared with similar
calculations for the Sun. A decrease in metallicity was found to
make itself evident in the properties of surface layers, which
fulfil the rôle of a thermal boundary. As a consequence, the
granulation temperature contrast grows in the lower photosphere,
the radiative cooling of hot convective upflows is more active in
the middle photosphere, and temperature variations increase in the
upper photosphere. The amplitudes of atmospheric oscillations become
higher, and the size distribution of granules is asymmetrically shifted
toward smaller scales. The photospheric overshooting convection has
a strong impact on the energy balance in the lower photosphere, with
hot convective upflows being dominant in it.
Title: Spatial variations in the Li I λ671 nm resonance line in
two-dimensional simulated granulation.
Authors: Gadun, A. S.
Bibcode: 1999KPCB...15..115G
Altcode:
Spectral observations of the Li λ671 nm resonance line with high
spatial resolution were simulated in the context of the LTE approach
with the use of time series of 2-D solar model atmospheres. The
simulation results do not confirm the conclusion of Kiselman (1997,
1998) that the LTE synthesis of this line produces an extremely
different correlation between spatial variations of equivalent width and
the corresponding continuum intensity compared with the NLTE simulation
and actual observations. The disagreement with Kiselman's results may
be caused by different atmospheric stratification of fluctuations in
the thermodynamic quantities in the models used. Simpler single-scale
(one-cell) simulations or fully unstable models with unevolved flows
are shown to have a quasi-columnar structure which extends almost over
the whole model photosphere; they also produce spectral LTE results
in close agreement with Kiselman's LTE plots.
Title: Two-dimensional model atmospheres of the Sun: influence of
lateral boundary conditions.
Authors: Gadun, A. S.
Bibcode: 1998KFNT...14..245G
Altcode: 1998KNFT...14..245G
Influence of two kinds of lateral boundary conditions is studied in
context of two-dimensional numerical modeling of solar granulation. The
models with periodical conditions on lateral boundaries with respect
to the similar models with reflecting sides demonstrate a) more
essential contribution of large-scale inhomogeneous structures;
b) larger amplitude of vertical oscillations near and above region
of traditional temperature minimum. Parameters of primary mode of
model oscillations do not depend on kind of lateral boundaries,
however. Spectral calculations of 14 Fe I and 12 Fe II lines were
additionally made as a test.
Title: Temporal Evolution of Artificial Solar Granules
Authors: Ploner, S. R. O.; Solanki, S. K.; Gadun, A. S.; Hanslmeier, A.
Bibcode: 1998SSRv...85..261P
Altcode:
We study the evolution of artificial granulation on the basis of 2-D
hydrodynamical simulations. These clearly show that granules die in
two different ways. One route to death is the well known bifurcation
or fragmentation of a large granule into 2 smaller ones (exploding
granules). The other pathway to death is characterized by merging
intergranular lanes and the accompanying dissolution of the granule
located between them. It is found that the lifetime and maximum
brightness is independent of the way in which granules evolve and
die. They clearly differ in size, however, with exploding granules
being in general significantly larger.
Title: Temporal Evolution of Artificial Solar Granules
Authors: Ploner, S. R. O.; Solanki, S. K.; Gadun, A. S.; Hanslmeier, A.
Bibcode: 1998sce..conf..261P
Altcode:
No abstract at ADS
Title: Fourier analysis of Fe I lines in spectra of the Sun, α
Centauri A, Procyon, Arcturus and Canopus.
Authors: Sheminova, V. A.; Gadun, A. S.
Bibcode: 1998KFNT...14..219S
Altcode: 1998KNFT...14..219S; 1998KFNT...14c.219S
Spectral observations with resolution 200000 have been used to study
turbulent velocities in the atmospheres of the Sun, α Centauri A,
Procyon, Arcturus, Canopus, and to estimate the rotation velocity
(Vesin i) of Canopus. It was found that the isotropic
microturbulent velocities and radial-tangential macroturbulent
velocities are quite suitable approximations to describe velocity
field in the atmospheres of all stars studied except Canopus.
Title: Fourier analysis of Fe I lines in the spectra of the Sun,
α Centauri A, Procyon, Arcturus, and Canopus.
Authors: Sheminova, V. A.; Gadun, A. S.
Bibcode: 1998KPCB...14..169S
Altcode:
Spectral observations of Fe I lines with a 200000 resolution
were used to determine turbulent velocities in the atmospheres
of the Sun, α Cen A, Procyon (α CMi), Arcturus (α Boo),
and Canopus (α Car) and estimate the rotation velocity
(Vesin i) of Canopus. Isotropic microturbulent velocities
(Vmi) and radial-tangential macroturbulent velocities
(VmaRT) were found to be a quite suitable
approximation to the velocity field in the atmospheres of all stars
studied except Canopus. The average velocities Vmi
and VmaRT are 0.8±0.1 and 2.6±0.3 km/s
for the Sun as a star, 0.8±0.2 and 2.9±0.4 km/s for α Cen A,
0.8±0.3 and 5.9±0.2 km/s for Procyon, 1.0±0.2 and 4.6±0.3
km/s for Arcturus. The velocity field in the atmosphere of Canopus
can be described by an anisotropic radial-tangential distribution
of microturbulence (VmiRT = 2.1 km/s) and
anisotropic macroturbulent velocities with greatly different radial
and tangential components (Vmarad = 17±2 km/s
and Vmatan = 1.3±1.0 km/s); Vesin
i for Canopus is 3.5±0.2 km/s.
Title: Two-dimensional solar model atmospheres: influence of lateral
boundary conditions.
Authors: Gadun, A. S.
Bibcode: 1998KPCB...14..187G
Altcode:
The authors study two kinds of lateral boundary conditions
in the context of a two-dimensional numerical modeling of solar
granulation. The models with periodic conditions on lateral boundaries
are found to differ from the similar models with reflecting sides in
that the large-scale inhomogeneous structures are more important in
them and the amplitude of vertical oscillations near and above the
traditional temperature minimum region is larger. Parameters of the
principal mode of model oscillations turn out to be independent of
the kind of lateral boundaries. Test calculations for 14 Fe I lines
and 12 Fe II lines reveal that the iron abundance determined to fit
the equivalent widths of the lines found from observations is also
insensitive to changes in lateral boundary conditions.
Title: Absolute shifts of Fe I and Fe II solar spectral lines in
active areas (solar disk centre)
Authors: Brandt, P. N.; Gadun, A. S.; Sheminova, V. A.
Bibcode: 1997KFNT...13e..75B
Altcode:
Absolute shifts of Fe I and Fe II lines have been estimated based on the
spectral observations obtained with Fourier spectrometer. The weak Fe I
lines and all Fe II lines demonstrate a red shift tendency in comparison
with their positions in quiet areas; the strong Fe I lines, the cores of
which are formed higher than 425 km, have more bluer shifts increasing
with decreasing lower excitation potential. To interpret these results,
the two-dimensional MHD models are used, which reproduce relative red
shifts of lines formed in deep photospheric layers. However, the blue
shifts of lines formed in higher levels could not confirmed within
the framework of these models.
Title: 1-D and 2-D model atmospheres: iron and lithium LTE abundances
in the Sun.
Authors: Gadun, A. S.; Pavlenko, Ya. V.
Bibcode: 1997A&A...324..281G
Altcode:
We discuss LTE abundance determinations of iron and lithium in the solar
atmosphere using a grid of one-dimensional (1-D) and two-dimensional
(2-D) model atmospheres. These models differ mainly in the convection
treatment. We found that the influence of atmospheric inhomogeneities
on the iron abundance comprises ~0.1dex for weak Fe I lines with low
excitation potentials, and does not exceed ~0.05dex for weak Fe II
lines. 2-D models show lower iron abundances for Fe I lines. On the
other hand, lithium abundances obtained for 1-D homogeneous and 2-D
inhomogeneous model atmospheres differ up to 0.1-0.2dex. 2-D model
atmospheres result in lower lithium abundances, in contradiction with
the recent suggestion of Kurucz (1995, Prepr. of Harvard-Smith. Cent. of
Astrophys., no. 4054, 1).
Title: Asymmetry and line-parameter variations in
granular-intergranular regions in 2D artificial granulation
Authors: Gadun, A. S.; Hanslmeier, A.
Bibcode: 1997KFNT...13c..24G
Altcode:
Two sets of 2D models of solar granulation are used to interpret
published observations of the spectral lines of Fe I 491.154, 491.178,
and 649.499 nm obtained with high spectral and spatial resolution
over selected granular-intergranular regions. We study variations of
continuum intensity, residual intensity in the line cores, Doppler
velocities, and line asymmetries over granular-intergranular areas
in the center of the solar disk, and compare the correlation between
these parameters obtained from models with observational ones. It
is found that 2D models of the solar granulation that describe the
convective motions as quasi-stationary, cellular, and laminar with the
system of quasi-column vertical photospheric velocities show the high
correlation values between the line-parameter variations and cannot
explain the observational behavior of spectral line characterstics
over single granular-intergranular areas. A good reproduction of
observational results can be found only by applying 2D models that
treat the solar thermal convection as a fully nonstationary system
with interacting flows.
Title: Bisectors and line-parameter variations over granular and
intergranular regions in 2-D artificial granulation.
Authors: Gadun, A. S.; Hanslmeier, A.; Pikalov, K. N.
Bibcode: 1997A&A...320.1001G
Altcode:
Two sets of two-dimensional models of the solar granulation have
been used to interpret the published observations of spectral lines
of Fe I 4911.54, 4911.78, and 6494.99Å obtained with high spectral
and spatial resolution over selected granular and intergranular
regions. The models differ by the horizontal size of the modeling
region and treatment of thermal convection. We study the variations
of continuum intensity, residual intensity in the line cores, Doppler
velocities, line asymmetries over granular and intergranular areas
in the center of the solar disk and compare the correlation between
these parameters obtained from models with observational ones. A
good reproduction of the observational results can be found only by
applying d models that treat the solar thermal convection as a fully
non-stationary system with interacting flows. Such models also take
into account the important role of secondary motions that influence
the middle and upper photosphere. As essential perturbing factors
there appear photospheric flows with supersonic velocities which
can change the photometric profiles of granules, create regions with
inversion of temperature distribution and impact onto the velocity
field. Variations of line parameters strongly depend on limitations
in spatial resolution (spatial smearing). This was simulated in the
models by applying different Gaussian smearing functions. Seeing was
found to affect variations of equivalent widths, full widths at half
maxima, and bisectors of the lines most strongly.
Title: Variations of line parameters and bisectors over
granular-intergranular regions in the 2-D artificial solar
granulation.
Authors: Gadun, A. S.; Hanslmeier, A.
Bibcode: 1997KPCB...13c..17G
Altcode: 1997KPCB...13Q..17G
Variations in the Fe I lines λλ 491.154, 491.178, and 649.499
nm in the solar spectrum observed with high spectral and spatial
resolution in selected granular-intergranular regions are interpreted
with the use of two sets of solar granulation models which differ
by the horizontal size of the region modeled and by treatment of
thermal convection. The authors analyze variations of the continuum
intensity, residual intensity in the line cores, Doppler velocities,
equivalent widths, half-widths, and asymmetries of synthesized lines
in the center of the solar disk, as well as correlations between the
parameter variations. The authors compare also these correlations
with those between the observed line parameters. It is found that the
models which describe the solar thermal convection as quasi-stationary,
cellular, and laminar motions show strong correlation between line
parameter variations and cannot reproduce the behavior of spectral
line characteristics observed in individual granular-intergranular
areas. Observational results are well reproduced by the models where
the thermal convection is treated as a completely nonstationary system
with active secondary motions in the middle and upper photosphere.
Title: Absolute shifts of Fe I and Fe II lines in solar active regions
(disk center).
Authors: Brandt, P. N.; Gadun, A. S.; Sheminova, V. A.
Bibcode: 1997KPCB...13e..65B
Altcode: 2010arXiv1005.2064B; 1997KPCB...13...65B
Absolute shifts of Fe I and Fe II lines in solar active regions were
estimated from Fourier-transform spectra. Weak Fe I lines and all Fe
II lines tend to be red-shifted as compared to their positions in quiet
areas, while strong Fe I lines, whose cores are formed above the level
log τ5 ≍ -3 (about 425 km), are relatively blue-shifted,
the shift growing with decreasing lower excitation potential. The
authors interpret the results through two-dimensional MHD models,
which adequately reproduce red shifts of the lines formed deep in the
photosphere. Blue shifts of the lines formed in higher layer do not
gain substance from the models.
Title: Characteristics of simulated granules in two-dimensional
numerical hydrodynamical modeling of solar granulation
Authors: Gadun, A. S.; Vorob'ev, Yu. Yu.
Bibcode: 1996ARep...40..569G
Altcode:
No abstract at ADS
Title: Two-dimensional hydrodynamical modeling of solar granules:
The power spectrum of simulated granules
Authors: Gadun, A. S.; Pikalov, K. N.
Bibcode: 1996ARep...40..578G
Altcode:
No abstract at ADS
Title: Power Spectra of Artificial Granulation
Authors: Gadun, A. S.; Pikalov, K. N.
Bibcode: 1996SoPh..166...43G
Altcode:
Two-dimensional, non-stationary hydrodynamic models of solar granulation
with gray and non-gray atmospheres have been used to obtain spatial,
temporal, and spatio-temporal power spectra. The temperature, density of
kinetic energy, monochromatic intensity, integrated flux, and vertical
velocity spectra have been studied for a comparison with the Kolmogorov
power law as well as for a qualitative understanding of oscillations,
which are reproduced as a result of modelling.
Title: Iron abundance derived from two-dimensional inhomogeneous
solar model atmospheres. Fe I and Fe II lines (center of the disk).
Authors: Gadun, A. S.
Bibcode: 1996KPCB...12d..13G
Altcode: 1996KPCB...12...13G
Two-dimensional hydrodynamic solar model atmospheres are used to
determine the iron abundance in the solar photosphere by fitting
calculated equivalent widths and central depths of Fe I and Fe II
lines to observed ones. The effect of atmospheric inhomogeneities is
found to give rise to uncertainties in the iron abundance of about 0.1
dex for weak Fe I lines with low excitation potentials and 0.05 dex
for weak Fe II lines. A self-consistent velocity field in 2-D models
with a statistically wide spectrum of inhomogeneities would suffice
to reproduce observed line profiles.
Title: Artificial Granules in 2-D Solar Models
Authors: Gadun, A. S.; Vorob'yov, Yu. Yu.
Bibcode: 1995SoPh..159...45G
Altcode:
Two-dimensional, hydrodynamic, time-dependent models of solar
granulation have been used to determine characteristics of
artificial granules. It is found that the evolution of granules
which subsequently fragment, respectively disappear, is fundamentally
different. Dissolution of artificial granules is the basic process
(48%-58%) in 2-D models. The number of small-scale and short-lived
granules increases continuously toward the smaller scales. The main
contributor to the total area are the granules with sizes about
∼900-1000 km. The mean lifetime of artificial granules is estimated
to be 6-11 min.
Title: Changes in the Fe II line parameters depending on magnetic flux
(solar disk center).
Authors: Brandt, P. N.; Gadun, A. S.
Bibcode: 1995KPCB...11d..36B
Altcode: 1995KPCB...11...36B
Analyzes the fine structure of 30 Fe II lines in three areas near the
center of the solar disk. Changes in the line bisectors depending
on magnetic flux are given. The central depths of lines are shown
to decrease with growing filling factor; the equivalent widths of
weak lines decrease also, while the equivalent widths of medium and
medium-strong lines remain unchanged or increase. The dependence of
these variations on excitation potential, line strength, and depth
of line formation is analyzed. Self-consistent two-dimensional MHD
models of solar granulation have been computed for the interpretation
of observational data. The authors present some parameters of the
models together with the results of calculations made with 2D MHD and
nonmagnetic hydrodynamic models for two Fe I and Fe II lines insensitive
to magnetic fields. The calculations confirm qualitatively the observed
behavior of line asymmetries.
Title: Three-dimensional hydrodynamic models of solar granulation
and their application to a spectral analysis problem.
Authors: Atroshchenko, I. N.; Gadun, A. S.
Bibcode: 1994A&A...291..635A
Altcode:
The results of three-dimensional hydrodynamic simulations of
solar granulation, obtained using two different algorithms are
presented. Sequences of 3-D hydrodynamic, time-dependent models have
been used to determine iron abundance in the solar photosphere. The
results of iron abundance determination from the equivalent widths
and central depths of 42 FeI and 32 FeII lines are presented. The iron
abundance has also been estimated from the line asymmetries and their
absolute shifts. The conclusion was made that FeII lines are the most
suitable for iron abundance determination in the LTE approximation,
since they are not very sensitive to the temperature structure of models
and to NLTE effects. To clear up the influence of the inhomogeneous
structure of 3-D models on spectral line calculations, computations on
the basis of 1-D models were carried out. The results of hydrodynamic
simulations of granulation on Procyon, using the numerical technique
developed for modelling solar granulation, are presented in comparison
with the ones obtained for the Sun. The inhomogeneous models of the
photosphere of Procyon permitted us to reproduce line asymmetries,
observed in the spectrum of Procyon, and to estimate the rotation
velocity of this star as 3.5 km/s. The temperature structure of the
3-D models of Sun and Procyon was also approximated by the mixing
length theory with variable A (i.e. it was supposed that mixing length
parameter A is varied with depth).
Title: Iron abundance and microturbulence in Arcturus, Canopus,
alpha CEN A and Sun from FeI and FeII lines.
Authors: Gadun, A. S.
Bibcode: 1994AN....315..413G
Altcode:
The iron abundance and microturbulent velocities in Arcturus, Canopus,
and alpha Cen A have been determined from FeI and FeII lines relative
to the Sun. Alpha Cen A is found to have an enhanced iron abundance,
while Canopus and Arcturus are found to have a deficiency of iron. The
behavior of the determined microturbulent velocities is discussed.
Title: The application of three-dimensional models of the solar
photosphere for spectral analysis problems. Fe I and Fe II lines
(solar disk centre).
Authors: Gadun, A. S.
Bibcode: 1994KFNT...10...33G
Altcode: 1994KNFT...10...33G
The LTE determination of iron abundance using 42 Fe I and 32 Fe
II lines was carried out for two sequences of three-dimensional
models: a cool one with the "gray" atmosphere and a hot one with the
"non-gray" atmosphere. The results indicate that abundance of chemical
elements may be estimated from line asymmetry and absolute wavelength
shifts. However, specific structure of 3D-models leads to abundance
differences between 3D-models and 1D-hydrostatic ones. The assumptions
and limitations of 3D-models application for spectral analysis problems
are discussed.
Title: Changes of the Fe I spectral line parameters as a functin of
the magnetic flux (solar disk centre).
Authors: Brandt, P. N.; Gadun, A. S.
Bibcode: 1993KFNT....9....8B
Altcode: 1993KNFT....9....8B
The parameter variations of the 281 Fe I lines (asymmetry, depth,
equivalent width, halfwidth) are analysed in three regions near the
solar disk centre, having different magnetic fluxes. The analysis
shows that the line parameter variations depend on the line strength,
the lower excitation potential and the line sensitivity to the magnetic
field. A qualitative interpretation of the results is given.
Title: Changes in the parameters of Fe I spectral lines as a function
of the magnetic flux (solar disc center).
Authors: Brandt, P. N.; Gadun, A. S.
Bibcode: 1993KPCB....9c...5B
Altcode: 1993KPCB....9....5B
Parameters of 281 Fe I lines (asymmetry, depth, equivalent width,
halfwidth) are analyzed in three regions near the solar disk center
which have different magnetic fluxes. The parameters are shown to vary
with the line intensiy, lower excitation potential, and line sensitivity
to the magnetic field. The results are interpreted qualitatively.
Title: The "Fraunhofer Solar Spectrum" data bank.
Authors: Gadun, A. S.; Sosonkina, M. M.; Sheminova, V. A.
Bibcode: 1992KFNT....8...80G
Altcode: 1992KNFT....8...80G
A relational data base model has been developed for the IBM PC
XT/AT-type computers managed by MS-DOS/PC-DOS of the versions 3.0 and
later. The data base includes the following characteristics of the
solar spectrum Fraunhofer lines: the wavelength, chemical element
symbol and its ionization state, atomic transition, Lande factors,
excitation potential of the lower level, central depth, equivalent
width, oscillator strengths, height of formation. The program of
data manipulation provides a user with ample opportunities in sampling
lines. At present the data bank contains information about 662 unblended
lines in the solar spectrum belonging to Fe I, Fe II, Ni I, Sc I,
Sc II, Ti I, Ti II, V I, V II, Cr I, Cr II, Y I, Y II, Zr I, Zr II.
Title: The "Fraunhofer solar spectrum" data bank.
Authors: Gadun, A. S.; Sosonkina, M. M.; Sheminova, V. A.
Bibcode: 1992KPCB....8b..71G
Altcode: 1992KPCB....8...71G
A relational data base model has been developed for the IBM PC XT/AT
computers managed by the MS-DOS/PC-DOS version 3.0 and later. The
data base includes the following characteristics of the Fraunhofer
lines in the solar spectrum: the wavelength, chemical element's
symbol and its ionization state, atomic transition, Lande factors,
excitation potential of the lower level, central depth, equivalent
width, oscillator strength, height of formation. The data manipulation
program provides a user with ample opportunities in sampling lines. At
present, the data bank contains information about 662 unblended lines
in the solar spectrum belonging to Fe I, Fe II, Ni I, Sc I, Sc II,
Ti I, Ti II, V I, V II, Cr I, Cr II, Y I, Y II, Zr I, Zr II.
Title: Fine structure of the Fraunhofer lines - Observation results
and their interpretation
Authors: Atroshchenko, I. N.; Gadun, A. S.; Kostyk, R. I.
Bibcode: 1990KFNT....6R...3A
Altcode:
Observation results on line asymmetry and absolute line shift in the
spectra of the solar photosphere are presented and their theoretical
interpretation is discussed. Empirical data are presented on the
line asymmetry and line shifts for the center of the solar disk,
for center-to-limb transition, for the spectrum of the sun as a star,
and for active regions. Data are also presented concerning variations
of line asymmetry as a function of the phase of the solar cycle. The
semiempirical approach to the interpretation of Fraunhofer line
asymmetry and absolute line shifts is also discussed. The results of
a multidimensional numerical simulation of convective motions in the
superadiabatic region and in the solar photosphere are presented.
Title: Fine structure of the Fraunhofer lines: observation results
and their interpretation.
Authors: Atroshchenko, I. N.; Gadun, A. S.; Kostyk, R. I.
Bibcode: 1990KNFT....6R...3A
Altcode:
The review embraces results of the spectral line observations and
their theoretical interpretation. The empirical data on the line
asymmetry and absolute wavelength shifts are presented for the solar
centre, for different positions on the solar limb and for the Sun as a
star. Their dependence on the phase of the solar activity cycle is also
reviewed. Interpretation of these data on the basis of semiempirical
models is discussed. The multidimensional numerical simulation results
of convective motions in the superadiabatic region and in the solar
photosphere are presented.
Title: Analysis of Absorption Line Profiles in the Spectra of the
Sun and Procyon - Velocity Field and Size of Inhomogeneities
Authors: Gadun, A. S.; Kostyk, R. I.
Bibcode: 1990SvA....34..260G
Altcode:
No abstract at ADS
Title: Analysis of absorption line profiles in the solar and Procyon
spectra : velocity field and sizes of turbulent eddies.
Authors: Gadun, A. S.; Kostyk, R. I.
Bibcode: 1990AZh....67..520G
Altcode:
It is shown that the turbulent velocity and the sizes of turbulent
eddies in the Procyon atmosphere are 1.5-2.5 times larger than in
the solar atmosphere. A comparative analysis of the variation of
these parameters with height revealed substantial differences between
convection processes on the sun and Procyon.
Title: Determination of the rotation parameters of the solar
atmosphere from asymmetries of Fraunhofer lines.
Authors: Gadun, A. S.; Pikalov, K. N.
Bibcode: 1990KFNT....6...43G
Altcode: 1990KNFT....6...43G
The solar rotation velocity has been found from comparison of central
depths and asymmetries of Fraunhofer lines in the spectrum of the Sun
as a star with central depths and asymmetries of the same lines at
different distances from the solar centre. The effect of rotation on
line asymmetries and line central depths was studied. The conclusion
is made that the new method may be used for the determination of
the rotation rate of slow rotating stars from the comparison of line
asymmetries at different distances from the stellar disk centre (using
multidimensional convective models).
Title: Comparative Analysis of Physical Conditions in the Solar and
Procyon Atmospheres
Authors: Atroshchenko, I. N.; Gadun, A. S.; Kostik, R. I.; Pikalov,
K. N.
Bibcode: 1990IAUS..138..421A
Altcode:
No abstract at ADS
Title: Modeling of convective motions in the envelope of
procyon. II. Asymmetry of the spectral lines
Authors: Atroshchenko, I. N.; Gadun, A. S.; Kostyk, R. I.
Bibcode: 1989Ap.....31..765A
Altcode: 1990Ap.....31..765A
No abstract at ADS
Title: Modeling of convective motions in the envelope of
procyon. I. ideology and analysis of three-dimensional models
Authors: Atroshchenko, I. N.; Gadun, A. S.; Kostyk, R. I.
Bibcode: 1989Ap.....31..580A
Altcode: 1990Ap.....31..580A
No abstract at ADS
Title: Three-Dimensional Simulation of Convective Motions in the
Procyon Envelope
Authors: Atroshchenko, I. N.; Gadun, A. S.; Kostik, R. I.
Bibcode: 1989ASIC..263..521A
Altcode: 1989ssg..conf..521A
No abstract at ADS
Title: Asymmetry of Absorption Lines in the Solar and Procyon Spectra
Authors: Atroshchenko, I. N.; Gadun, A. S.; Kostik, R. I.
Bibcode: 1989ASIC..263..135A
Altcode: 1989ssg..conf..135A
No abstract at ADS
Title: The Simulation of the Convective Motions in the Procyon
Envelope - Part Two - Spectral Line Asymmetries
Authors: Atroschenko, F. N.; Gadun, A. S.; Kostyk, R. I.
Bibcode: 1989Afz....31..589A
Altcode:
No abstract at ADS
Title: The simulation of the convective motions in the Procyon
envelope. I. Ideology and analysis of the three-dimensional
inhomogeneous models.
Authors: Atroshchenko, I. N.; Gadun, A. S.; Kostyk, R. I.
Bibcode: 1989Afz....31..281A
Altcode:
No abstract at ADS
Title: SPANSAT: the Program for LTE Calculations of Absorption Line
Profiles in Stellar Atmospheres
Authors: Gadun, A. S.; Sheminova, V. A.
Bibcode: 1988ITF....87P...3G
Altcode:
The calculation algorithms and controlling macrolanguage for basic
modification of SPANSAT program are presented. It is the program for
LTE-calculation of absorption line profiles in stellar atmospheres. The
program can be applied to the Sun or to Stars of the solar type.
Title: Rotation of the Solar Atmosphere at Different Altitudes
Authors: Gadun, A. S.; Kostyk, R. I.; Sheminova, V. A.
Bibcode: 1987SvA....31..557G
Altcode:
No abstract at ADS
Title: The rotation of the solar atmosphere at different altitudes
Authors: Gadun, A. S.; Kostyk, R. I.; Sheminova, V. A.
Bibcode: 1987AZh....64.1066G
Altcode:
A new method for determining the solar rotation velocity is proposed. A
comparison was made between the observed central depths of Fraunhofer
lines in the spectrum of the sun as a star and calculations based on
center-limb observations. For altitudes in the range of 100-1100 km
above the level of the continuous spectrum, the solar rotation velocity
hardly changes.
Title: Approximative models of the solar convective zone in an
approach of mixing length theory modifications.
Authors: Atroshchenko, I. N.; Gadun, A. S.
Bibcode: 1986KFNT....2...21A
Altcode:
The models of the solar convective zone consistent with HOLMU and VAL
80 semi-empirical models of the solar atmosphere at the outer boundary
and with the Abraham-Eben (1971) model of the internal solar structure
at the inner boundary were constructed in the approximation of mixing
length theory modifications. Limitations are put on the velocities of
rising convective elements in agreement with observations.
Title: Rotation of the solar photosphere from observations of central
depthsof Fraunhofer lines.
Authors: Gadun, A. S.; Kostyk, R. I.; Sheminova, V. A.
Bibcode: 1985KFNT....1R..53G
Altcode:
The solar rotation velocity for different heliographic latitudes has
been found from comparison of the central depths of Fraunhofer lines
in the spectrum of the sun as a star with the central depths of the
same lines at different distances from the solar centre.
Title: The fine structure of Fraunhofer lines in the spectrum of
the sun as a star.
Authors: Gadun, A. S.; Kostyk, R. I.
Bibcode: 1985KFNT....1...24G
Altcode: 1985KFNT....1R..24G
The Fraunhofer lines in the spectrum of integrated sunlight are shown
to have asymmetries similar to the asymmetry of the spectrum of the
solar disk centre. It is found that the asymmetry varies with line
strength and does not practically depend on the lower level excitation
potential, ionization degree and atomic weight.
Title: Models of the solar convective zone.
Authors: Gadun, A. S.
Bibcode: 1985KFNT....1...66G
Altcode:
Models of the solar convective zone consistent with Abraham's and
Eben's model of the internal solar structure on the inner boundary,
and HSRA, HOLMU, VAL 80 semi-empirical models and Nelson's (1978)
theoretical two-dimensional model on the outer boundary were obtained
on the basis of the mixing length theory. Calculated velocities of
rising convective elements were compared with the observed ones.
Title: Application of the integral method to plotting of the light
curve and for determining the mean radius of XZ Cyg.
Authors: Gadun, A. S.; Zaikova, L. P.; Romanov, Iu. S.
Bibcode: 1982AAfz...46...23G
Altcode:
The light curves of XZ Cyg are calculated for two phases of the
Blazhko effect (at minimum and maximum light-variation amplitudes)
from variations of radius and temperature, with allowance for the
content of heavy elements in the stellar atmosphere. Mean radii of
3.83 x 10 to the 11th cm and 3.90 x 10 to the 11th cm were obtained
for minimum and maximum light-variation amplitudes, respectively,
on the basis of a comparison of calculated and observed light curves.
Title: Visual observations of DY Peg.
Authors: Atroshchenko, I. N.; Gadun, A. S.; Kudlinkov, S. V.; Melnikov,
S. N.; Chausovskiy, A. M.
Bibcode: 1981ATsir1158....6A
Altcode: 1981ATsir1158....1A
No abstract at ADS
Title: On the period of NW Lyrae.
Authors: Gadun, A. S.
Bibcode: 1977ATsir.958....8G
Altcode:
No abstract at ADS