Author name code: sheminova
ADS astronomy entries on 2022-09-14
author:"Sheminova, Valentina A."
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Title: Convective Line Shifts in the Spectra of Solar-Type Stars
Authors: Sheminova, V. A.
Bibcode: 2022KPCB...38...83S
Altcode: 2022arXiv220400830S
The Doppler line shifts in the spectra of the Sun and stars
with effective temperatures from 4800 to 6200 K were measured and
the average connective (granulation) velocities were estimated. The
absolute scale of the line shifts for the stars was established on the
basis of the derived dependence of the shifts of solar lines on optical
depth. For FGK solar-type stars, curves of convection velocities as a
function of the height in the atmosphere in a large range of heights
from 150 to 700 km were obtained for the first time. All these curves
indicate a decrease in blue shifts with height, which means that the
granulation velocities through the photosphere slow down to zero. In
the lower chromosphere, red shifts of strong Mg I lines are observed,
which indicate a change in the direction of granulation velocities to
the opposite and confirm the effects of reversal of granulation at
heights above 600 km. In cooler K stars, granulation shifts change
with height on average from -50 to 100 m/s, while they change more
sharply in hotter FG stars from -700 to 300 m/s. The gradient of
the line shift curves increases with an increase in the effective
temperature and a decrease in gravity, metallicity, and age of the
star. The connective velocity of the star averaged over all analyzed
heights increases from -90 to -560 m/s from colder to hotter stars. It
correlates with macroturbulence, asymmetry of spectral lines, and the
rotation velocity of the star. We also obtained the radial velocities
of the stars and compared them with the SIMBAD data. Our analysis has
shown that the individual granular velocities of the stars must be
taken into account when determining the radial velocities.
Title: Convective lineshifts in the spectra of the Sun and solar-type
stars
Authors: Sheminova, V. A.
Bibcode: 2022KFNT...38...39S
Altcode:
No abstract at ADS
Title: The influence of the medium physical conditions and atomic
constants on the Stokes profiles of absorption lines in the solar
spectrum
Authors: Sheminova, V. A.
Bibcode: 2022arXiv220306867S
Altcode:
The Stokes profiles of Fe I lines in the photosphere of the Sun
are calculated within the Unno-Beckers-Landi-Dagl`Innocenti
theory. Estimates of the magnetic strengthening of the lines
were obtained. The changes in the Stokes profiles depending on
the excitation potential, wavelength, equivalent width, Lande
factor, micro-macroturbulent velocities, radial velocity, damping
constant, atmospheric model, magnetic field strength and direction
are considered. The graphically presented variations of the Stokes
profiles make it possible to determine the initial values of the
input parameters for solving the problems of magnetic field vector
reconstruction by the inversion method. The presented dependencies of
the magnetic strengthening on the line parameters will help to correctly
select magnetically sensitive lines for the investigation of sunspots,
flux tubes, plages, and other magnetic features.
Title: Macro-microturbulence in the solar photosphere
Authors: Sheminova, V. A.
Bibcode: 2022arXiv220206037S
Altcode:
The velocity distribution of the large and small-scale motion in solar
photosphere has been obtained by crossing method based on fitting the
observed and calculated equivalent widths as well as the central depths
of the spectral lines at the center of the and the limb of the solar
disk. We used about 200 Fe I lines. According to our results the motions
in photosphere are anisotropic. The radial component of microturbulent
velocity decreases from 1.0 to 0.3 km/s and the tangential one from
1.7 to 1.3 km/c at the photosphere heights from 200 to 500 km (log
tau_5 = -1.4 and -3.5). At the same heights the radial component of
the macroturbulent velocity decreases from 1.8 to 1.2 km/s and the
tangential one from 2.3 to 0.8 km/s.
Title: Effect of the anomalous dispersion in the solar atmosphere
on results of magnetic field measurements by the line-ratio method
Authors: Lozitskii, V. G.; Sheminova, V. A.
Bibcode: 2021arXiv211204346L
Altcode:
On the basis of Stokes parameter calculations for the Fe I 524.7 and
525.0 nm lines and the Holweger-Muller model atmosphere, the effect of
the anomalous dispersion on solar magnetic field measurements by the
line-ratio method is analyzed. It is shown that with the present-day
observational accuracy the anomalous dispersion should be taken into
consideration in the line-ratio method only when the following four
conditions are fulfilled simultaneously: a) the inclination of the
magnetic lines to the line of sight does not exceed 20 degrees; b) the
magnetic field strength is larger than 100 mT; c) the cross profile of
the magnetic field in subtelescopic flux tubes is rectangular; and d)
the parts of the magnetically sensitive line profiles close to the
line center (<4 pm) are used.
Title: The Gaia-ESO Survey: a new approach to chemically
characterising young open clusters. II. Abundances of the
neutron-capture elements Cu, Sr, Y, Zr, Ba, La, and Ce
Authors: Baratella, M.; D'Orazi, V.; Sheminova, V.; Spina, L.;
Carraro, G.; Gratton, R.; Magrini, L.; Randich, S.; Lugaro, M.;
Pignatari, M.; Romano, D.; Biazzo, K.; Bragaglia, A.; Casali, G.;
Desidera, S.; Frasca, A.; de Silva, G.; Melo, C.; Van der Swaelmen,
M.; Tautvaišienė, G.; Jiménez-Esteban, F. M.; Gilmore, G.; Bensby,
T.; Smiljanic, R.; Bayo, A.; Franciosini, E.; Gonneau, A.; Hourihane,
A.; Jofré, P.; Monaco, L.; Morbidelli, L.; Sacco, G.; Sbordone, L.;
Worley, C.; Zaggia, S.
Bibcode: 2021A&A...653A..67B
Altcode: 2021arXiv210712381B
Context. Young open clusters (ages of less than 200 Myr) have
been observed to exhibit several peculiarities in their chemical
compositions. These anomalies include a slightly sub-solar iron
content, super-solar abundances of some atomic species (e.g. ionised
chromium), and atypical enhancements of [Ba/Fe], with values up to
~0.7 dex. Regarding the behaviour of the other s-process elements like
yttrium, zirconium, lanthanum, and cerium, there is general disagreement
in the literature: some authors claim that they follow the same trend
as barium, while others find solar abundances at all ages.
Aims:
In this work we expand upon our previous analysis of a sample of five
young open clusters (IC 2391, IC 2602, IC 4665, NGC 2516, and NGC 2547)
and one star-forming region (NGC 2264), with the aim of determining
abundances of different neutron-capture elements, mainly Cu I, Sr I,
Sr II, Y II, Zr II, Ba II, La II, and Ce II. For NGC 2264 and NGC 2547
we present the measurements of these elements for the first time.
Methods: We analysed high-resolution, high signal-to-noise spectra
of 23 solar-type stars observed within the Gaia-ESO survey. After a
careful selection, we derived abundances of isolated and clean lines
via spectral synthesis computations and in a strictly differential way
with respect to the Sun.
Results: We find that our clusters have
solar [Cu/Fe] within the uncertainties, while we confirm that [Ba/Fe] is
super-solar, with values ranging from +0.22 to +0.64 dex. Our analysis
also points to a mild enhancement of Y, with [Y/Fe] ratios covering
values between 0 and +0.3 dex. For the other s-process elements we
find that [X/Fe] ratios are solar at all ages.
Conclusions:
It is not possible to reconcile the anomalous behaviour of Ba and
Y at young ages with standard stellar yields and Galactic chemical
evolution model predictions. We explore different possible scenarios
related to the behaviour of spectral lines, from the dependence on the
different ionisation stages and the sensitivity to the presence of
magnetic fields (through the Landé factor) to the first ionisation
potential effect. We also investigate the possibility that they may
arise from alterations of the structure of the stellar photosphere due
to the increased levels of stellar activity that affect the spectral
line formation, and consequently the derived abundances. These effects
seem to be stronger in stars at ages of less than ~ 100 Myr. However,
we are still unable to explain these enhancements, and the Ba puzzle
remains unsolved. With the present study we suggest that other elements,
for example Sr, Zr, La, and Ce, might be more reliable tracer of the
s-process at young ages, and we strongly encourage further critical
observations. Based on observations collected with the FLAMES
instrument at VLT/UT2 telescope (Paranal Observatory, ESO, Chile),
for the Gaia- ESO Large Public Spectroscopic Survey (188.B-3002,
193.B-0936).
Title: The line asymmetry in the spectra of the Sun and solar-type
stars
Authors: Sheminova, V. A.
Bibcode: 2020KFNT...36f..65S
Altcode: 2020KFNT...36...65S; 2020arXiv201213791S
We have analysed the asymmetry of lines Fe I and Fe II in spectra of
a solar flux using three FTS atlases and the HARPS atlas and also in
spectra of 13 stars using observation data on the HARPS spectrograph. To
reduce observation noise individual line bisectors of each star have
been averaged. The obtained average bisectors in the stellar spectra are
more or less similar to the shape C well known to the Sun. In stars with
rotation velocities greater than 5 km/s the shape of the bisectors is
more like /. The curvature and span of the bisectors increase with
the temperature of the star. Our results confirm the known facts
about strong influence of rotation velocity on the span and shape of
bisectors. The average convective velocity was determined based on
the span of the average bisector, which shows the largest difference
between the velocity of cold falling and hot rising convective flows
of the matter. It's equal to -420 m/s for the Sun as a star. In stars,
it grows from -150 to -700 m/s with an effective temperature of 4800
to 6200 K, respectively. For stars with greater surface gravity and
greater metallicity, the average convective velocity decreases. It also
decreases with star age and correlates with the velocity of micro and
macroturbulent movements. The results of solar flux analysis showed
that absolute wavelength scales in the atlases used coincide with an
accuracy of about -10 m/s, except for the FTS-atlas of Hinkle et al.,
whose scale is shifted and depends on the wavelength. In the range
from 450 to 650 nm, the scale shift of this atlas varies from -100 to
-330 m/s, respectively, and it equals on average of ∼240 m/s. The
resulting average star bisectors contain information about the fields
of convective velocities and may be useful for hydrodynamic modeling
of stellar atmospheres in order to study the characteristic features
of surface convection.
Title: Asymmetry of Lines in the Spectra of the Sun and Solar-Type
Stars
Authors: Sheminova, V. A.
Bibcode: 2020KPCB...36..291S
Altcode:
We have analysed the asymmetry of lines Fe I and Fe II in spectra of
a solar flux using three FTS atlases and the HARPS atlas and also in
spectra of 13 stars using observation data on the HARPS spectrograph. To
reduce observation noise individual line bisectors of each star have
been averaged. The obtained average bisectors in the stellar spectra
are more or less similar to the shape C well known to the Sun. In stars
with rotation speeds greater than 5 km/s the shape of the bisectors
is more like /. The curvature and span of the bisectors increase with
the temperature of the star. Our results confirm the known facts
about strong influence of rotation velocity on the span and shape
of bisectors. The average convective speed was determined based on
the span of the average bisector, which shows the largest difference
between the velocity of cold falling and hot rising convective flows of
the matter. It's equal to -420 m/s for the Sun as a star. In solar-type
stars, it grows from -150 to -700 m/s with an effective temperature of
4800 to 6200 K, respectively. For stars with greater surface gravity
and greater metallicity, the average convective velocity decreases. It
also decreases with star age and correlates with the speed of micro
and macroturbulent movements. The results of solar flux analysis showed
that absolute wavelength scales in the FTS atlases used coincide with
an accuracy of about -10 m/s, except for the atlas of Hinkle, etc.,
whose scale is shifted and depends on the wavelength. In the range
from 450 to 650 nm, the scale shift of this atlas varies from -100
to -330 m/s, respectively, and it equals on average of -240 m/s. The
resulting average star bisectors contain information about the fields
of convective velocities and may be useful for hydrodynamic modeling
of stellar atmospheres in order to study the characteristic features
of surface convection.
Title: Turbulence and Rotation in Solar-Type Stars
Authors: Sheminova, V. A.
Bibcode: 2019KPCB...35..129S
Altcode: 2019arXiv190712241A
Stellar spectra with a high resolution of 115000 obtained with the HARPS
spectrograph provide an opportunity to examine turbulence velocities and
their depth distributions in the photosphere of stars. Fourier analysis
was performed for 17 iron lines in the spectra of 13 stars with an
effective temperature of 4900--6200 K and a logarithm of surface gravity
of 3.9--5.0 as well as in the spectrum of the Sun as a star. Models
of stellar atmospheres were taken from the MARCS database. The
standard concept of isotropic Gaussian microturbulence was assumed
in this study. A satisfactory fit between the synthesized profiles of
spectral lines and observational data verified the reliability of the
Fourier method. The most likely estimates of turbulence velocities, the
rotation velocity, and the iron abundance and their photospheric depth
distribution profiles were obtained as a result. Microturbulence does
not vary to any significant degree with depth, while macroturbulence
has a marked depth dependence. The macroturbulence velocity increases
with depth in the stellar atmosphere. The higher the effective
temperature of a star and the stronger the surface gravity, the
steeper the expected macroturbulence gradient. The mean macroturbulence
velocity increases for stars with higher temperatures, weaker gravity,
and faster rotation. The mean macro- and microturbulence velocities
are correlated with each other and with the rotation velocity in the
examined stars. The ratio between the macroturbulence velocity and the
rotation velocity in solar-type stars varies from 1 (the hottest stars)
to 1.7 (the coolest stars). The age dependence of the rotation velocity
is more pronounced than that of the velocity of macroturbulent motions.
Title: Fourier analysis of spectra of solar-type stars
Authors: Sheminova, V. A.
Bibcode: 2017KPCB...33..217S
Altcode:
Fourier transform techniques were used to determine the macroturbulent
velocity under the condition that mictoturbulent and stellar rotation
velocities are not known. In order to distinguish the effects of
rotation from macroturbulence effects in slowly rotating stars,
primarily the main lobe of residual Fourier transforms of the observed
lines, which were taken from the solar spectrum and the spectra of two
other stars, was used. This case of Fourier analysis of spectral lines
is the most complicated one. The end results were in a satisfactory
agreement with the data obtained using different methods. The average
values of microturbulent, macroturbulent, and rotation velocities
were 0.85, 2.22, and 1.75 km/s for the Sun as the star; 0.58, 1.73,
and 0.78 km/s for HD 10700; and 1.16, 3.56, and 6.24 km/s for HD
1835. It was found that the macroturbulent velocity decreases with
altitude in the atmosphere of the Sun and HD 1835. In the case of
HD 10700, the macroturbulent velocity did not change with altitude,
and the determined rotation velocity was two times lower than the one
obtained using other methods. It was concluded that Fourier transform
techniques are suitable for determining the velocities in atmospheres
of solar-type stars with very slow rotation.
Title: Fourier analysis of spectra of solar-type stars
Authors: Sheminova, V. A.
Bibcode: 2017KFNT...33e..27S
Altcode: 2017arXiv171106866S
We used Fourier transform techniques to determine macroturbulent
velocity. The analysis is done with mictoturbulent velocity and rotation
velocity as an unknown quantities. In order to distinguish the effects
of rotation from macroturbulence effects in slowly rotating stars,
primarily the main lobe of residual Fourier transforms of the observed
lines, which were taken from the solar spectrum and the spectra of two
other stars, was used. This case of Fourier analysis of spectral lines
is the most complicated one. The end results were in a satisfactory
agreement with the data obtained using different methods. We have
obtained the average values of microturbulent, macroturbulent, and
rotation velocities were 0.85, 2.22, and 1.75 km/s for the Sun as
the star, 0.58, 1.73, and 0.78 km/s for HD 10700, and 1.16, 3.56, and
6.24 km/s for HD 1835. It was found that the macroturbulent velocity
decreases with height in the atmosphere of the Sun and HD 1835. In
the case of HD 10700, the macroturbulent velocity did not change with
height, and the determined rotation velocity was two times lower than
the one obtained using other methods. It was concluded that Fourier
transform techniques are suitable for determining the velocities in
atmospheres of solar-type stars with very slow rotation.
Title: Iron abundance in the atmosphere of Arcturus
Authors: Sheminova, V. A.
Bibcode: 2015KPCB...31..172S
Altcode: 2015arXiv150901700S
Abundance of iron in the atmosphere of Arcturus has been determined from
the profiles or regions of the profiles of the weak lines sensitive to
iron abundance. The selected lines of Fe I and Fe II were synthesized
with the MARCS theoretical models of the atmosphere. From the observed
profiles of lines available with a high spectral resolution in the atlas
by Hinkle and Wallace (2005), the values of the iron abundance $A =
6.95 \pm 0.03$ and the radial-tangential macroturbulent velocity $5.6
\pm 0.2$ km/s were obtained for Arcturus. The same physical quantities
were found for the Sun as a star; they are $7.42 \pm 0.02$ and $3.4
\pm 0.3$ km/s, respectively. For Arcturus, the iron abundance relative
to the solar one was determined with the differential method as [Fe/H]
$=-0.48 \pm 0.02$.
Title: Formation depths of Fraunhofer lines
Authors: Gurtovenko, E. A.; Sheminova, V. A.
Bibcode: 2015arXiv150500975G
Altcode:
We have summed up our investigations performed in 1970--1993. The
main task of this paper is clearly to show processes of formation
of spectral lines as well as their distinction by validity and by
location. For 503 photospheric lines of various chemical elements
in the wavelength range 300--1000 nm we list in Table the average
formation depths of the line depression and the line emission for the
line centre and on the half-width of the line, the average formation
depths of the continuum emission as well as the effective widths of the
layer of the line depression formation. Dependence of average depths of
line depression formation on excitation potential, equivalent widths,
and central line depth are demonstrated by iron lines.
Title: Abundance sensitive points of line profiles in the stellar
spectra
Authors: Sheminova, V. A.; Cowley, C. R.
Bibcode: 2014MNRAS.443.1967S
Altcode: 2014arXiv1406.6817S
Many abundance studies are based on spectrum synthesis and χ-squared
differences between the synthesized and an observed spectrum. Much
of the spectra so compared depend only weakly on the elemental
abundances. Logarithmic plots of line depths rather than relative
flux make this more apparent. We present simulations that illustrate
a simple method for finding regions of the spectrum most sensitive
to abundance, and also some caveats for using such information. As
expected, we find that weak features are the most sensitive. Equivalent
widths of weak lines are ideal features, because of their sensitivity
to abundances, and insensitivity to factors that broaden the line
profiles. The wings of strong lines can also be useful, but it is
essential that the broadening mechanisms be accurately known. The very
weakest features, though sensitive to abundance, should be avoided or
used with great caution because of uncertainty of continuum placement
as well as numerical uncertainties associated with the subtraction of
similar numbers.
Title: Temperature stratification of the atmosphere of Arcturus
Authors: Sheminova, V. A.
Bibcode: 2013KPCB...29..176S
Altcode: 2013arXiv1309.3148S
A brief overview of the results of the investigations of the red giant
star Arcturus is given. One-dimensional LTE modeling of the atmospheres
of Arcturus and the Sun as a star is carried out on the basis of
synthesis of the extended wings of the H and K Ca II lines. It is found
that the local continuum in this spectral region is underestimated by
an average of 12% in the atlases of Arcturus. The average deficit in
UV absorption amounts to 43% for Arcturus whereas it is 9% for the
Sun. For Arcturus the correction factor to the continuum opacity at
the wavelengths of 390.0, 392.5, 395.0, 398.0, and 400.0 nm equals
2.20, 1.90, 1.70, 1.55, and 1.45. The model atmosphere of Arcturus
obtained from the best-fit of the wings of the H and K Ca II lines
corresponds to the model atmosphere with the fundamental parameters
T_eff = 4286 K, log g = 1.66, and [Fe/H]=-0.52 derived by Ramirez and
Allende Prieto (2011). The temperature stratification of Arcturus'
atmosphere is presented in tabular form. To obtain more accurate
temperature stratification in the future, we need a high spectral
resolution spectrum calibrated to absolute fluxes with high accuracy.
Title: The Wings of Ca II H and K as Photospheric Diagnostics and
the Reliability of One-Dimensional Photosphere Modeling
Authors: Sheminova, V. A.
Bibcode: 2012SoPh..280...83S
Altcode: 2012SoPh..tmp..174S; 2012arXiv1207.2020S
The extended wings of the Ca II H and K lines provide excellent
diagnostics of the temperature stratification of the photosphere
of the Sun and of other cool stars, thanks to their LTE opacities
and source functions and their large span in formation height. The
aim of this study is to calibrate the usage of the H and K wings in
a one-dimensional interpretation of spatially averaged spectra and
in deriving per-pixel stratifications from resolved spectra. I use
multi-dimensional simulations of solar convection to synthesize the
H and K wings, derive one-dimensional models from these wings as if
they were observed, and compare the resulting models to the actual
simulation input. I find that spatially averaged models constructed
from the synthesized wings generally match the simulation averages
well, except for the deepest layers of the photosphere where large
thermal inhomogeneities and Planck-function non-linearity gives
large errors. The larger the inhomogeneity, the larger the error. The
presence of strong network fields increases such inhomogeneity. For
quiet photospheric conditions the temperature excesses reach about 200
K. One-dimensional stratification fits of discrete structures such as
granulation and small-scale magnetic concentrations give satisfactory
results with errors that are primarily due to steep temperature
gradients and abrupt changes of temperature with depth. I conclude that
stratification modeling using the H and K wings is a useful technique
for the interpretation of solar high-resolution observations.
Title: The Study of Ground-Level Ozone in Kiev and its Impact on
Public Health
Authors: Shavrina, A. V.; Mikulskaya, I. A.; Kiforenko, S. I.;
Sheminova, V. A.; Veles, A. A.; Blum, O. B.
Bibcode: 2011KosNT..17a..52S
Altcode: 2012arXiv1204.1902S
Ground-level ozone in Kiev for the episode of its high contentration
in August 2000 is simulated with the model of urban air pollution
UAM-V. The study of total ozone over Kyiv and its concentration
changes with height in the troposphere is made on the basis of
ground-based observations with the infrared Fourier-spectrometer in
the Main Astronomical Observatory of National Academy of Sciences of
Ukraine as part of the ESA-NIVR-KNMI project no 2907. In 2008, the
satellite Aura-OMI data OMO3PR on profiles of the atmosphere ozone
became available. The data include the ozone content in the lower
layer of the atmosphere, beginning in 2005. They can be used for the
evaluation of the ground-level ozone concentrations in all cities of
Ukraine. Some statistical investigation of ozone air pollution in Kiev
and medical statistics data of respiratory system diseases is carried
out with the application of the «Statistica» package. The regression
analysis, prognostic regression simulation, and retrospective prognosis
of the epidemiological situation with respect to respiratory system
pathologies in Kiev during 2000-2007 are performed.
Title: The 2D MHD simulation of solar magnetogranulation: Horizontal
magnetic fields
Authors: Sheminova, V. A.
Bibcode: 2010JPhSt..14.2903S
Altcode:
The solar horizontal magnetic fields on scales less than the spatial
resolution of solar telescopes are investigated. A synthetic infrared
spectropolarimetric diagnostics based on the 2D MHD simulation of
magnetoconvection in а network region is used for this purpose. We
find that the spatial average unsigned magnetic horizontal field
strength at τ5 = 1 is 244 G and the most probable strength is equal
to 50 G. The magnetic horizontal field surpasses by the factor 1.3,
on average, the vertical field at the range of heights 0-400 km in the
photosphere. It is caused by the stronger flux density of horizontal
field and the larger area fraction occupied by them. Strong horizontal
magnetic fluxes are visible on the surface in the form of small
spots with the strength more than 500 G. The results of the Stokes
diagnostics with respect to horizontal magnetic fields are qualitatively
in agreement with that observed a board the "Hinode" satelite.
Title: Total ozone columns and vertical ozone profiles above Kiev
in 2005-2008
Authors: Shavrina, A. V.; Kroon, M.; Sheminova, V. A.; Pavlenko,
Ya. V.; Veles, A. A.; Synyavski, I. I.; Romanyuk, Ya. O.
Bibcode: 2010arXiv1007.4694S
Altcode:
The study of total ozone columns above Kiev and variations of ozone
concentrations in the troposphere at different altitudes above Kiev
was carried out using ground-based Fourier Transform InfraRed (FTIR)
spectrometric observations that are taken on a routine basis at the
Main Astronomical Observatory of the National Academy of Sciences of
Ukraine (MAO NASU). This study was performed within the framework of
the international ESA-NIVR-KNMI OMI-AO project no.2907 entitled OMI
validation by ground-based remote sensing: ozone columns and atmospheric
profiles during the time frame 2005-2008. The infrared FTIR spectral
observations of direct solar radiation in the wavelength range of 2-12
micron as transmitted through the Earth's atmosphere were performed
during the months of April-October of each year. The aim of the project
was the validation of total ozone columns and vertical ozone profiles
as obtained by the Ozone Monitoring Instrument (OMI)) onboard of the
NASA EOS-Aura scientific satellite platform. The modeling of the ozone
spectral band shape near 9.6 microns was performing with the MODTRAN
code and a molecular band model based on the HITRAN-2004 molecular
database. The a-priori information for the spectral modeling consisted
of water vapor and temperature profiles from the NASA EOS-Aqua-AIRS
satellite instrument, stratospheric ozone profiles from the NASA
EOS-Aura-MLS satellite instrument, TEMIS-KNMI climatological ozone
profiles and surface ozone concentration measurements performed at the
specific times of infrared spectra observations. The troposphere ozone
variability was analyzed for two typical episodes: the spring episode
of enhanced total ozone columns and the summer episode of enhanced
surface ozone concentrations.
Title: Two-dimensional MHD models of solar
magnetogranulation. Dynamics of magnetic elements
Authors: Sheminova, V. A.
Bibcode: 2010arXiv1007.3377S
Altcode:
We present the results of a statistical analysis of the Doppler shifts
and the asymmetry parameters of V profiles of the Fe I 630.25 nm line
produced by 2D MHD simulations of solar granulation. The realism of
the simulations tested using the magnetic ratio of Fe I 524.71 and
525.02 nm lines. The Stokes spectra were synthesized in snapshots with
a mixed polarity field having a mean magnetic flux density of 0.2 mT
and mean unsigned field strength of 35 mT. We found that downflows
with a velocity of 0.5 km/s predominate, on the average, in areas
with some network magnetic elements at the disk center. In separate
strong fluxtubes the average velocity is equal to 3 km/s and the
maximum velocity is 9 km/s. In weak diffuse magnetic fields upflows
dominate. Their average velocity is 0.5 km/s and maximal one is 3
km/s. The V-profile asymmetry depends on the spatial resolution. The V
profiles synthesized with high spatial resolution (35 km) have average
amplitude and area asymmetries -1%, 1%, respectively. The asymmetry
scatter is \pm70% for weak profiles and \pm10% for strong ones. The
profiles with low spatial resolution (700 km) have average amplitude
and area asymmetries 3%, -2\%, respectively. Low spatial resolution is a
reason why the amplitude asymmetry is always positive and greater than
the area asymmetry in V profiles observed. We found weak correlation
between the asymmetry of V profiles and velocity. Upflows cause negative
asymmetry, on the average, and downflows cause positive asymmetry. We
examined center-to-limb variations of vertical velocity in magnetic
elements. Beginning from cos theta = 0.9, the average velocity abruptly
increases from 0.5 to 2 km/s and then slightly varies closer to the
limb. We found nonlinear oscillations of vertical velocity with power
peaks in the 5-minute and 3-minute bands.
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: Horizontal magnetic fields in the solar photosphere
Authors: Sheminova, V. A.
Bibcode: 2009ARep...53..477S
Altcode: 2009arXiv0906.2711S; 2009AZh....86..518S
Two-dimensional simulations of time-dependent solar magnetogranulation
are used to analyze the horizontal magnetic fields and the response of
the synthesized Stokes profiles of the IR FeI λ1564.85 nm line to the
magnetic fields. The 1.5-h series of MHD models used for the analyses
reproduces a region of the magnetic network in the photosphere with an
unsigned magnetic flux density of 192 G at the solar surface. According
to the magnetic-field distribution obtained, the most probable absolute
strength of the horizontal magnetic field at an optical depth of τ
5 = 1( τ 5 denotes τ at λ = 500 nm) is 50 G,
while the mean value is 244 G. On average, the horizontal magnetic
fields are stronger than the vertical fields to heights of about 400 km
in the photosphere due to their higher density and the larger area they
occupy. The maximum factor by which the horizontal fields are greater
is 1.5. Strong horizontal magnetic flux tubes emerge at the surface
as spots with field strengths of more than 500 G. These are smaller
than granules in size, and have lifetimes of 3-6 min. They form in
the photosphere due to the expulsion of magnetic fields by convective
flows coming from deep subphotospheric layers. The data obtained
qualitatively agree with observations with the Hinode space observatory.
Title: Surface Ozone in Kiev
Authors: Shavrina, A. V.; Mikulskaya, I. A.; Kiforenko, S. I.; Blum,
O. B.; Sheminova, V. A.; Veles, A. A.
Bibcode: 2009OAP....22...43S
Altcode:
The study of total ozone over Kiev and its concentration changes with
height in the troposphere has been made on the base of ground-based
observations with the infrared Fourier-spectrometer in the Main
Astronomical Observatory of National Academy of Sciences of Ukraine
(MAO NASU) as part of ESA-NIVR-KNMI project no 2907 "OMI validation by
ground based remote sensing: ozone columns and atmospheric profiles
"(2005-2008) [1,2,4]. Ground-level ozone in Kiev for an episode
of its high concentrations in August 2000 was also simulated with
the model of urban air pollution UAM-V [5,6]. In 2008 the satellite
data Aura-OMI on profiles of ozone in the atmosphere OMO3PR became
available (http://disc.sci.gsfc.nasa.gov/ Aura/data-holdings/OMI/
omo3pr_v003.shtml). They include ozone content in the lower layer of
the atmosphere, beginning from 2005, which can be used to evaluate
the ground-level ozone in all cities of Ukraine. The comparison of the
data of ozone air pollution in Kiev (ozone - the pollutant of the first
class of danger) and medical statistics data of of respiratory system
(RS) diseases of the city population was carried out with the package
"Statistica". A regression analysis, prognostic regression modelling,
and retrospective prognosis of the epidemiological situation with
respect to RS pathologies in Kiev in 2000-2006 were performed.
Title: Stokes Diagnostics of 2D MHD-Simulated Solar Magnetogranulation
Authors: Sheminova, V. A.
Bibcode: 2009SoPh..254...29S
Altcode: 2008SoPh..tmp..190S; 2009arXiv0902.1125S
The properties of solar magnetic fields on scales less than the
spatial resolution of solar telescopes are studied. A synthetic
infrared spectropolarimetric diagnostic based on a 2D MHD simulation
of magnetoconvection is used for this. Analyzed are two time sequences
of snapshots that likely represent two regions of the network fields
with their immediate surroundings on the solar surface with unsigned
magnetic flux densities of 300 and 140 G. In the first region from the
probability density functions of the magnetic field strength it is
found that the most probable field strength at log τ5=0
is equal to 250 G. Weak fields (B<500 G) occupy about 70% of
the surface, whereas stronger fields (B>1000 G) occupy only 9.7%
of the surface. The magnetic flux is −28 G and its imbalance is
−0.04. In the second region, these parameters are correspondingly
equal to 150 G, 93.3%, 0.3%, −40 G, and −0.10. The distribution
of line-of-sight velocities on the surface of log τ5=−1
is estimated. The mean velocity is equal to 0.4 km s−1
in the first simulated region. The average velocity in the granules
is −1.2 km s−1 and in the intergranules it is 2.5 km
s−1. In the second region, the corresponding values of the
mean velocities are equal to 0, −1.8, and 1.5 km s−1. In
addition the asymmetry of synthetic Stokes V profiles of the Fe I
1564.8 nm line is analyzed. The mean values of the amplitude and area
asymmetry do not exceed 1%. The spatially smoothed amplitude asymmetry
is increased to 10% whereas the area asymmetry is only slightly varied.
Title: Tropospheric ozone columns and ozone profiles for Kiev in 2007
Authors: Shavrina, A. V.; Pavlenko, Ya. V.; Veles, A. A.; Sheminova,
V. A.; Synyavski, I. I.; Sosonkin, M. G.; Romanyuk, Ya. O.; Eremenko,
N. A.; Ivanov, Yu. S.; Monsar, O. A.; Kroon, M.
Bibcode: 2008KosNT..14e..85S
Altcode: 2010arXiv1003.1211S; 2008KosNT..14...85S
The ground-based FTIR observations were performed at the Main
Astronomical Observatory of NASU within the framework of the ESA
NIVR-KNMI project 2907 entitled "OMI validation by ground based remote
sensing: ozone columns and atmospheric profiles* for the purpose
of OMI data validation. FTIR observations were carried out during
August-October 2005, June-October 2006 and March-October 2007, mostly
under cloud free and clear sky conditions and in some days from early
morning to sunset covering a large range of solar zenith angles. Ozone
column and ozone profile data were obtained for the year 2005 using
spectral modeling of the ozone spectral band profile near 9.6 microns
with the MODTRAN3 band model based on the HITRAN-96 molecular absorption
database. The total ozone column values retrieved from FTIR observations
are biased low with respect to OMI-DOAS data by 8-10 DU on average,
where they have a relatively small standard error of about 2 %. FTIR
observations for the year 2006 were simulated by MODTRAN4 modeling. For
the retrieval of ozone column estimates and particularly ozone profiles
from our FTIR observations, we used the following data sources as input
files to construct the information for the model (a priori): satellite
Aqua-AIRS water vapor and temperature profiles; Aura-MLS stratospheric
ozone profiles (version 1.5), TEMIS climato-logical ozone profiles and
the simultaneously performed surface ozone measurements. Ozone total
columns obtained from our FTIR observations for year 2006 with MODTRAN4
modeling are matching rather well with OMI-TOMS and OMI-DOAS data where
standard errors are 0.68 % and 1.11 %, respectively. AURA-MLS data
of version 2.2 which became available in 2007 allow us to retrieve
tropospheric ozone profiles. For some days Aura-TES tropospheric
profiles were also available and were compared with our retrieved
profiles for validation. A preliminary analysis of troposphere ozone
variability was performed. The observations from March to October
demonstrate daily photo-chemical variability of tropospheric ozone
and reveal mixing processes during the night.
Title: The wings of Ca II H and K as solar fluxtube diagnostics
Authors: Sheminova, V. A.; Rutten, R. J.; Rouppe van der Voort,
L. H. M.
Bibcode: 2005A&A...437.1069S
Altcode:
We combine high-resolution Ca II H and K spectrograms from the
Swedish Vacuum Solar Telescope with standard fluxtube modeling to
derive photospheric temperature and velocity stratifications within
individual magnetic elements in plage near a sunspot. We find that 1D
on-axis modeling gives better consistency than spatial averaging over
flaring-fluxtube geometry. Our best-fit temperature stratifications
suggest that magnetic elements are close to radiative equilibrium
throughout their photospheres. Their brightness excess throughout the
H and K wings compared with the quiet photosphere is primarily due to
low density, not to mechanical heating. We conclude that the extended
H and K wings provide excellent fine-structure diagnostics for both
high-resolution observations and simulations of the solar photosphere.
Title: The temperature gradient in and around solar magnetic fluxtubes
Authors: Sheminova, V. A.; Rutten, R. J.; Rouppe van der Voort,
L. H. M.
Bibcode: 2005KFNTS...5..110S
Altcode:
We use spectra covering the outer part of the extended wing of the solar
Ca II K line observed at high angular resolution with the Swedish Vacuum
Solar Telescope to test standard solar fluxtube models. The wings of the
Ca II resonance lines are formed in LTE both with regard to excitation
(source function) and to ionization (opacity) and, therefore, sample
temperature stratifications in relatively straightforward fashion. We
obtain best fits by combining steeper temperature gradients than
those in the standard models for both the tube inside and the tube
environment. Similarly steep gradients are also determined from a
numerical magnetoconvection simulation by the late A. S. Gadun. It
is found that the energy balance in the individual magnetic elements
appears to be close to radiative equilibrium throughout the photosphere.
Title: On the origin of the extremely asymmetric Stokes V profiles
in an inhomogeneous atmosphere
Authors: Sheminova, V. A.
Bibcode: 2005KFNT...21..172S
Altcode: 2009arXiv0902.2940S
We investigated the formation of the Stokes V profiles with
unusual shape using results of 2-D MHD simulation of solar
magnetogranulation. The synthetic unusual profiles have properties in
common with those observed with the spatial resolution <1'' in active
regions outside sunspots and in the network and internetwork. Like
observed profiles they mostly appear in clusters in regions of weak
magnetic fields with mixed polarity along the polarity inversion
lines. As a rule, they are located at the edges of granules and lanes
and sometimes close to strong magnetic field concentrations with strong
gradients of velocity and magnetic field strength. It is found that
they appear as clusters in the regions of large granuls fragmentation,
where begins formation of new magnetic fluxtubes. The synthetic unusual
profiles can have from one to six lobes. The origin of singlelobed
and manylobed profiles are the same. The major processes causing
extremely asymmetry are characterized by one or multiple polarity
reversals along the line of sight as well as by gradients of velocity
and magnetic field strength. The more lobes in a profile, the more
probability of sign change of magnetic field gradient. It follows
that location regions of extremely asymmetric profiles should have a
very complicated structure of magnetic fields on small scales. This is
confirmed by straightforward results achieved in granulation simulations
which demonstrate that velocity shear at the downdraft edges creates
vortices and turbulence. This adds complexity to structure magnetic
fields mixing their polarities, in particular at the edges of granules.
Title: 2-D MHD model of solar magnetogranulation. Dynamics of
magnetic elements
Authors: Sheminova, V. A.
Bibcode: 2004KFNT...20....3S
Altcode:
Dynamic characteristics of small-scale magnetic elements in the quiet
Sun are investigated using a statistical analysis of Doppler shifts
and asymmetry of V profiles of the Fe I 630.25 nm line calculated
with nonstationary magnetohydrodynamic models. Distribution of
vertical velocities was obtained and their correlation with the
main characteristics of magnetic field was found. On the average,
the downflows predominate with an average velocity of 0.5 km/s within
magnetic elements. In strong magnetic tubes the average velocities are
equal to 3 km/s and the maximum velocities are as high as 8--9 km/s. In
weak diffuse magnetic fields upflows predominate with an average
velocity of 0.5 km/s and a maximum velocity of 3 km/s. The profiles
calculated with high spatial resolution (35 km) have an average value
of amplitude and area asymmetries close to zero (-1%). For weaker V
amplitudes the scatter of asymmetry is ±70%, and for stronger ones
it is ±10%. It was found that the spatial averaging of profiles
influences the amplitude asymmetry more than the area asymmetry. This
is a reason of the observed effect of excess of amplitude asymmetry
over area asymmetry. A weak correlation between the asymmetry of V
profiles and the velocity is found. Upflows cause, on the average,
a negative asymmetry and downflows a positive one. Center-to-limb
variations of velocities were found in magnetic elements. The average
velocity increases sharply up to 2 km/s, beginning from cosθ = 0.9,
and then it varies weakly, approaching the limb. Velocity oscillations
are investigated, and their power peaks in 5 and 3 minute bands are
found. The non-linear character of velocity oscillations are caused
by field strength fluctuations. The Doppler shifts and asymmetry
parameters obtained for spatially averaged V profiles are consistent
with the results of FTS-observations as well as with other observations
made with high spatial resolution.
Title: The line Fe I elambda 1564.8 nm and distribution of solar
magnetic fields
Authors: Sheminova, V. A.
Bibcode: 2003KFNT...19..107S
Altcode: 2012arXiv1209.6225S
We obtained the distribution of the strength of magnetic fields at
various levels of the quiet Sun's photosphere on the basis of the
2-D MHD simulation of magnetogranulation and from the synthesis
of |V| profiles maxima of the line Fe I λ 1564.8 nm. The shape
of the distribution and its maximum position vary essentially with
depth. The distribution maximum is, on the average, about 25 mT. The
distribution maximum is close to 35 mT if the spatial average of
profiles (about 0.5'') is taken into account. A difference between
obtained distributions is caused by errors of the determination of
the strength of a field from splitting of V profiles. Our analysis
of the method errors shows that the use of the line λ 1564.8 nm
in this method provides the most effective and reliable way for
measuring fields above 50 mT when the line is in the strong splitting
regime. In the weak splitting regime (lower than 17 mT) measured
field strengths are equal to about 20 mT, and in an intermediate
regime they are overestimated by 2--4 mT. Distribution found with the
help of line λ 1564.8 nm can be used as a standard for the testing
of other approaches and lines in the region of fields with B >
50 mT. The results of the analysis of synthesized profiles of the
iron line λ 630.2 nm confirm that this line is less suitable for the
study of the field strength distribution because of its weak magnetic
sensitivity to fields below 120 mT. Besides, the inclination of the
vector of a magnetic field influences strongly the separation of σ
components of this line. The effect of additional separation of V
peaks with increasing the inclination angle leads to an essential
(about 20--30 mT) overestimation of the strength of weak inclined
fields determined by the methods which do not take into account the
Q, U profiles. Our distributions of magnetic fields as well as the
distribution of asymmetry parameters and V profiles zero-crossing,
firstly, agree satisfactorily with infrared observations. Secondly,
they confirm convincingly an assumption on a continuous spectrum
of structures and values of strength of magnetic photospheric field
with mixed polarity down to the scales considerably smaller than a
resolution threshold. Thirdly, our distributions indicate that the
structure and the scales of magnetic fields are closely connected to
the granulation structure.
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: 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: 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 the FIP effect present inside solar photospheric magnetic
flux tubes?
Authors: Sheminova, V. A.; Solanki, S. K.
Bibcode: 1999A&A...351..701S
Altcode:
The first determination of the elemental composition in the photospheric
layers of solar magnetic flux tubes is described. Stokes I and V
profiles of 13 elements observed in solar active region plage and in
the network are analysed. The abundances are obtained for elements
with high (C, O) and low (Al, Ca, Cr, Na, Ni, Sc, Si, Ti, Y, Zn) first
ionization potential (FIP) in order to investigate to what extent the
abundance anomalies observed in the upper solar atmosphere (FIP-effect)
are already present in the photospheric layers of flux tubes, which
are the source of much of the gas in the upper atmosphere. Various
sources of error are considered and the uncertainties introduced by
them are estimated. There are hints of a weak FIP-effect in the flux
tubes, corresponding to an overabundance of a factor of 1.1-1.2 of
the low-FIP elements relative to high-FIP elements, as compared to
the quiet photosphere. However, our data set a firm upper limit of
1.3-1.6 on this factor, which is well below the enhancement seen in
many parts of the upper solar atmosphere.
Title: Two-dimensional MHD models of solar magnetogranulation. Testing
of models and methods of Stokes diagnostics
Authors: Sheminova, V. A.
Bibcode: 1999KFNT...15..398S
Altcode: 1999KFNT...15e.398S; 2012arXiv1210.6499S
We carried out the Stokes diagnostic of new two-dimensional
magnetohydrodynamical models (MHDM) with continuum evolution of the
magnetogranulation in course of 2 hours of hydrodynamical (solar)
time. The results show a satisfactory agreement with the results
of Stokes diagnostics of solar-small magnetic flux tubes observed
in quiet network elements and active plages. The straightforward
methods which are often used in Stokes diagnostics of solar
magnetic elements were tested by means by means of MHDM. The
most reliable methods are determination of magnetic field
strength from the separation of the peaks of Stokes V profiles
of the Fe I λ 1564.8 nm infrared line and determination of the
magnetic inclination angle from the ratio of tg2γ ≈
{(Q2+U2)}1/2/V2. The lower
limits of such determinations are about 20 mT and 10° respectively.
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: 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 MHD models of solar magnetogranulation. Testing
of models and methods of Stokes diagnostics.
Authors: Sheminova, V. A.
Bibcode: 1999KPCB...15..298S
Altcode:
The author carried out the Stokes diagnostics of new two-dimensional
magnetohydrodynamic models with a continuous evolution of
magnetogranulation in the course of two hours of the hydrodynamic
(solar) time. The results agree satisfactorily with the Stokes
diagnostics of the solar small-scale flux tubes observed in quiet
network elements and active plages. The author concludes that the most
reliable methods are the determination of magnetic field strength
from the separation of the peaks in the Stokes V profiles of the
infrared Fe I line λ1564.8 nm and the determination of the magnetic
inclination angle.
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: Sensitivity indicators of Fraunhofer lines
Authors: Sheminova, V. A.
Bibcode: 1998A&A...329..721S
Altcode:
To estimate the sensitivity of absorption lines to the physical
conditions in the solar atmosphere, we propose indicators computed using
the depression response functions in the LTE approximation. For 604
Fe I and 58 Fe II, lines the sensitivity indicators of temperature,
pressure, and microturbulent velocity, as well as the average
geometrical height of formation of the line depression response to
changes of temperature are given in graphic and tabular forms. The
sensitivity indicators can be used not only for a choice of the
specific line, but for the photosphere diagnostics as well. The latter
application is possible only for investigations of the temperature
when the temperature fluctuations are no more than 8%. Only approximate
estimates of the pressure and microturbulent velocity are possible. Tables 1 and 2 are only available in electronic form at the CDS
via anonymous ftp to cdsarc.u-strasburg.fr (130.79.128.5) or via
http://cdsweb.u-strasbg.fr/Abstract.html
Title: Diagnostics of small-scale magnetic fields in the solar
atmosphere: main methods, results, and problems.
Authors: Tsap, T. T.; Lozitskij, V. G.; Leiko, U. M.; Sheminova,
V. A.; Gladushina, N. A.
Bibcode: 1998BCrAO..94..126T
Altcode:
When investigating extremely small-scale magnetic fields it is necessary
to use not direct but special indirect observation methods. One of the
best known methods of such a kind is the line ratio method. Another
attractive approach is related to the use of lines of the infrared
region of the spectrum.
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: 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: VizieR Online Data Catalog: Sensitivity indicators of
Fraunhofer lines (Shenimova 1998)
Authors: Sheminova, V. A.
Bibcode: 1997yCat..33290721S
Altcode:
The results of calculations of the sensitivity indicators to the
temperature, as well as the average geometrical heights of localization
of the effective response to the temperature variations are presented
for the central line depths, for the line depths on half-width, and
for the equivalent widths of the 604 Fe I and 58 Fe II absorption
lines. This list of unblended solar lines in the range of the
wavelengths 401.0-901.0nm contains the maximum of lines suitable for
the analysis of the fine structure of the line profiles and primarily
for study of the line asymmetries. (2 data files).
Title: Formation depth of Fraunhofer lines
Authors: Gurtovenko, E. A.; Sheminova, V. A.
Bibcode: 1997MAO.....1P...3G
Altcode:
We have summed up our investigations performed in 1970-1993 which
were devoted to the problem of the effective depths of spectral
absorption line formation. The main purpose of this paper is to show
the difference in the effectiveness of the various physical processes
responsible for the line absorption formation as well as to present
Tables of line formation depths. The 503 photospheric lines of various
chemical elements in the wavelength range 300-1000 nm were used for
our calculations. We list in the Tables the formation depths of both
depression and emission in line center and line half-width as well
as the average formation depths of the continuum emission for the
corresponding wavelengths. Additionally in the Tables, we give the
effective widths of the formation region of each absorption line. The
change of the average formation depths of iron lines in dependence on
excitation potential, equivalent widths, and central line intensity
are demonstrated on Figures.
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: Spectral effects simulation on the basis of two-dimensional
magnetohydrodynamic models of the solar photosphere
Authors: Atroshchenko, I. N.; Sheminova, V. A.
Bibcode: 1996KFNT...12e..32A
Altcode: 1996KFNT...12...32A
To study the structure of spatially unresolved magnetic features on the
Sun, Stokes profiles of seven photospheric iron lines are calculated
using two-dimensional (2-D) non-stationary MHD models of solar
granulation for various values of the magnetic flux. We investigate
variations of calculated absolute wavelength shifts and bisectors of I
profiles, zero-crossing wavelength shifts and parameters of asymmetry of
amplitudes and areas of V profiles as functions of the magnetic field
strength and time. The center-to-limb variations of Stokes profiles
are analyzed. The iron abundance (7.57) has been obtained taking
into account the unhomogeneities of the photosphere. It is shown that
although most of simulating spectral effects resulting from 2-D models
are basically in a satisfactory agreement with observational data, the
2-D approximation can not always give the quantitative fit. Calculated
absolute wavelength shifts of Fe II lines are sufficiently smaller
than observational ones.
Title: Numerical simulation of the interaction between solar granules
and small-scale magnetic fields
Authors: Atroshchenko, I. N.; Sheminova, V. A.
Bibcode: 1996KFNT...12d..32A
Altcode:
We investigate the interaction between solar granules and small-scale
magnetic fields n photospheric regions with different magnetic
fluxes using numerical simulation based on the full system of
radiation magnetohydrodynamics equations. Four sequences of 2D
time-dependent models were computed for photospheric regions with
average vertical magnetic fluxes of 0, 10, 20, and 30 mT. We have
not found substantial variations in the temperature structure with
average field strength while the density and gas pressure profiles in
2D models vary considerably. The solar granulation brightness field
varies substantially with the magnetic flux. The contribution of the
small-scale component to the intensity power spectrum increases with
average field strength whereas that of the large-scale component (of
about a granule size) decreases at approximately the same values of
total r.m.s. intensity fluctuations. Thus, the observed decrease in
r.m.s. intensity fluctuations with increase in the average magnetic
flux may be interpreted as smoothing of the small-scale component of
the power spectrum by the modulation transfer function of the telescope.
Title: Numerical simulation of the interaction between solar granules
and small-scale magnetic fields.
Authors: Atroshchenko, I. N.; Sheminova, V. A.
Bibcode: 1996KPCB...12d..21A
Altcode: 1996KPCB...12...21A; 2010arXiv1011.1778A
Numerical simulation based on the equations of radiation
magnetohydrodynamics is used to study the interaction of solar granules
and small-scale magnetic fields in photospheric regions with various
magnetic fluxes. Four sequences of 2-D time-dependent models were
calculated for photospheric regions with average vertical magnetic
fluxes of 0, 10, 20, and 30 mT. The models exhibit no substantial
variations in their temperature structure with varying average
field strength, while the density and gas pressure profiles display
gross changes. The solar granulation brightness field also varies
substantially with magnetic flux. The contribution of the small-scale
component to the intensity power spectrum increases with average
field strength, whereas the large-scale component (of about a granule
size) contributes less, the total rms intensity fluctuations being
approximately the same. Thus the observed decrease in rms intensity
fluctuations with growing average magnetic flux can be interpreted as
smoothing of the small-scale component in the power spectrum by the
modulation transfer function of the telescope.
Title: Simulation of spectral effects with the use of two-dimensional
magnetohydrodynamic models of the solar photosphere.
Authors: Atroshchenko, I. N.; Sheminova, V. A.
Bibcode: 1996KPCB...12e..24A
Altcode: 1996KPCB...12...24A; 2012arXiv1211.2791A
To study the structure of spatially unresolved features on the Sun, the
authors calculated the Stokes profiles of seven photospheric iron lines
using two-dimensional nonstationary MHD models of solar granulation for
various amounts of magnetic flux. The authors investigate variations
in the calculated absolute wavelength shifts and I-profile bisectors,
zero-crossing wavelength shifts, amplitude asymmetry parameters, and
V-profile areas as functions of magnetic field strength and time. The
center-to-limb variations of the Stokes profiles are analyzed. The iron
abundance is found to be 7.57, with the photosphere inhomogeneities
taken into account. Although most of the spectral effects simulated
within the scope of two-dimensional models are in satisfactory agreement
with observational data, the two-dimensional approximation cannot always
give a quantitative agreement. The absolute wavelength shifts calculated
for Fe II lines are substantially smaller than the observed ones.
Title: Influence of the height and surface magnetic field
inhomogeneity on the Stokes parameters of the magnetically sensitive
Fe I line λ525.02 nm
Authors: Lozitskij, V. G.; Sheminova, V. A.
Bibcode: 1995KFNT...11d..60L
Altcode:
On the basis of the Stokes parameters calculations for the
Holweger-Muller model atmosphere, the Fe I λ 525.02 nm line sensitivity
to some types of the height and surface magnetic field inhomogeneity
has been investigated. It has been shown that for the height gradient
of 0.4 mT/km, which is characteristic of some theoretical flux tube
models the noticeable V-parameter peak asymmetry appears, which is the
most considerable when a pure longitudinal magnetic field and a low
macroturbulent velocity are the case. There is the analogous effect
in Q-profiles for non-longitudinal fields. The Fe I λ 525.02 nm
line is sensitive to the subtelescopic fields of the mixed polarity
like those discovered by Stenflo (1993) from observations in IR
lines. The assumption is argued that due to the Wilson depression in
the small-scale flux tubes, the strong field areas with heliocentric
angles larger than 60-65° are not visible because of their screening
by surroundings with weaker magnetic fields.
Title: Investigation of the magnetic and temperature sensitivity
for the Stokes parameters of absorption lines in the solar photosphere
Authors: Sheminova, V. A.
Bibcode: 1995KFNT...11b..25S
Altcode:
The response functions to perturbations in the temperature, pressure,
microturbulent velocity, and magnetic field strength have been obtained
for the Stokes parameters profiles of Fe I λλ525.06, 525.02, and Fe
II 614.92 nm lines. We use the Grossmann-Doerth, Larsson, and Solanki
(1988) technique for the numerical solution of the Unno-Rachkovskij
transfer equations. An analysis of these functions confirms that
they can be used for the quantitative estimation of the response of
Stokes profiles and for the determination of the photospheric depth
where the changes in physical conditions influence the radiative and
absorption processes in the continuum and in the line. The sensitivity
of the magnetoactive lines has been analyzed by the sensitivity
indicators calculated as the integral of the response function all
over photospheric layers. The anomalous temperature sensitivity of the
V Stokes profiles has been found for lines with high excitation and
ionization potentials, such as O I, C I, Fe II lines. The depression of
these lines increases with the temperature. The magnetic sensitivity of
the Stokes profiles is determined in the first place by the magnetic
field regime. The greatest response takes place in the weak-field and
intermediate-field regime for photospheric lines with large values
of the Lande factor, wavelength, and equivalent width. The results
of calculations of sensitivity indicators and indices of the magnetic
and temperature strengthening for magnetoactive lines are presented.
Title: Influence of the vertical and horizontal magnetic field
inhomogeneity on the Stokes parameters of the magnetically sensitive
Fe I line λ525.02 nm.
Authors: Lozitskij, V. G.; Sheminova, V. A.
Bibcode: 1995KPCB...11d..49L
Altcode: 1995KPCB...11...49L; 2021arXiv211212192L
Based on calculations of the Stokes parameters for the Holweger-Müller
model atmosphere, the authors study the sensitivity of the Fe I
λ525.02 nm line to some kinds of vertical and horizontal magnetic
field inhomogeneity. A noticeable asymmetry is shown to appear
in the V-parameter peaks when the vertical gradient is 0.4 mT/km,
which is typical of some theoretical flux tube models. The asymmetry
is most pronounced in a pure longitudinal magnetic field and at a
low macroturbulent velocity. A similar effect is observed for the Q
parameter in nonlongitudinal fields as well. The Fe I λ525.02 nm
line is sensitive also to subtelescopic fields of mixed polarity
like those observed by Stenflo in IR lines. The authors argue that
the Wilson depression in small-scale flux tubes renders strong-field
areas invisible at heliocentric angles greater than 60 - 65°, since
they are screened by surroundings with weaker magnetic fields.
Title: Investigation of the magnetic and temperature sensitivity of
the Stokes parameters of absorption lines in the solar photosphere.
Authors: Sheminova, V. A.
Bibcode: 1995KPCB...11b..19S
Altcode: 2012arXiv1211.2599S; 1995KPCB...11...19S
Response functions to perturbations in the temperature, pressure,
microturbulent velocity, and magnetic intensity were calculated for
the Stokes parameter profiles of the lines Fe I λλ525.06, 525.02 and
Fe II λ614.92. The procedure proposed by Grossmann-Doerth, Larsson,
and Solanki (1988) was used. The author shows that the depression
response functions may be used not only to determine the depths at
which changes in the physical conditions affect most effectively the
absorption and emission in the continuum and in lines, but to estimate
the response of Stokes profiles as well. The response was estimated
using sensitivity indicators calculated as an integral of the response
function over all photospheric layers. An anomalous temperature
sensitivity was found for the Stokes V profiles in lines with high
excitation and ionization potentials such as the lines of O I, C I,
Fe II. The depression of such lines increases rather than decreases
with growing temperature. The magnetic sensitivity of Stokes profiles
depends primarily on the magnetic field conditions. The response of V
profiles is the greatest under the weak-field and intermediate-field
conditions for photospheric lines with large values of the Lande
factor, wavelength, and equivalent width. The results of calculations
of sensitivity indicators are presented for magnetic lines together
with the indices of magnetic and temperature enhancement.
Title: The parameters of sensitivity of Fraunhofer lines to the
temperature gas pressure and microturbulent velocity
Authors: Sheminova, V. A.
Bibcode: 1993KFNT....9...27S
Altcode: 2012arXiv1210.5375S
The parameters are proposed for measuring the sensitivity of Fraunhofer
lines to the physical conditions in the solar atmosphere. The
parameters are calculated using depression response functions,
in LTE approximation. The line sensitivity to the temperature, gas
pressure and microturbulent velocity depending on the line parameters
and atomic parameters is investigated. The most relatively sensitive
to the temperature are weak lines and the most absolutely sensitive
are moderate lines of abundant heavy atoms with low ionization and
excitation potentials. The potential and the line strength are the
main factors of the line temperature sensitivity. The most sensitive to
the gas pressure are the medium-strong lines of light atoms with very
high excitation potentials (larger than 6 eV) and the most sensitive
to the microturbulent velocity are strong photospheric lines (8 pm <
W < 14 pm) of heavy atoms. The parameters of sensitivity are useful
also for physical diagnostics of the photosphere if fluctuations of
the temperature, gas pressure and of microturbulent velocity do not
exceed 8%, 50%, and 100 % respectively.
Title: Parameters of sensitivity of Fraunhofer lines to changes in
the temperature, gas pressure, and microturbulent velocity in the
solar photosphere.
Authors: Sheminova, V. A.
Bibcode: 1993KPCB....9e..21S
Altcode: 1993KPCB....9...21S
Parameters are proposed for measuring the sensitivity of Fraunhofer
lines to the physical conditions in the solar atmosphere. The
parameters are calculated based on depression response functions in
the LTE approximation. The sensitivity of lines to the temperature,
gas pressure, and microturbulent velocity depending on the line
and atomic parameters is investigated. The greatest relative
temperature sensitivity is shown by weak lines, while the gratest
absolute sensitivity is displayed by medium-strong lines of abundant
heavy atoms with low ionization and excitation potentials. The
excitation potential and line strength are the crucial factors
for the temperature sensitivity. The highest pressure sensitivity
is observed for medium-strong lines of light atoms with very high
excitation potentials (exceeding 6 eV), and strong photospheric lines
(8 pm < W < 14 pm) of heavy atoms are the most responsive to
the microturbulent velocity. The sensitivity parameters can also be
used to advantage for physical diagnostics of the photosphere when
the temperature, pressure, and micriturbulent velocity fluctuations
are no more than 8%, 50%, and 100%, repectively.
Title: The depth of formation of absorption lines in the solar
atmosphere.
Authors: Sheminova, V. A.
Bibcode: 1992KFNT....8...44S
Altcode: 1992KNFT....8...44S; 2012arXiv1210.4023S
The characteristics of the depression contribution functions are
studied for the Stokes profiles of the Fraunhofer lines formed in a
magnetic field. The form of the depression functions depends mainly on
the strength of splitting and the Zeeman component intensity, and is
of a complicated character with a distinctly pronounced asymmetry. The
depths of formation of magnetically sensitive lines are found by means
of these contribution functions. The calculation revealed that, in a
strong longitudinal magnetic field, the steep part of the line profile
is formed higher than the centre of the line profile. The Stokes
profiles that describe the polarization characteristics are formed
only several kilometres higher than the Stokes profile that specifies
the general depression of the unpolarized and polarized radiation. The
averaged depth of formation of the whole line profile is practically
independent of the magnetic field strength. The depths of formation of
17 photospheric lines usually used in magnetospectroscopic observations
are calculated for the models of the quiet photosphere, a flux tube,
and the sunspot umbra.
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 effect of the anomalous dispersion in the solar atmosphere
on results of magnetic field measurements using the line-ratio method.
Authors: Lozitskii, V. G.; Sheminova, V. A.
Bibcode: 1992KFNT....8...12L
Altcode: 1992KNFT....8...12L
On the basis of calculations of the Stokes parameters for the Fe I
λλ524.7 and 525.0 nm lines and the Holveger-Müller model atmosphere,
the effect of the anomalous dispersion on the line-ratio method results
is analysed. It is shown that with present-day accuracy of observational
data, the anomalous dispersion should be taken into account only when
the following conditions are simultaneously fulfilled: a) the magnetic
field slope angle exceeds 20°; b) the magnetic field strength is
larger than 100 mT; c) the fluxtube magnetic profile is rectangular;
and d) the parts of the spectral line profile close to the line centre
(Δλ < 4 pm) are used.
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: Depths of formation of magnetically sensitive absorption
lines in the solar atmosphere.
Authors: Sheminova, V. A.
Bibcode: 1992KPCB....8c..40S
Altcode: 1992KPCB....8...40S
Characteristics of the depression contribution functions are studied
for the Stokes line profiles formed in a magnetic field. The form of
the depression functions depends mainly on the strength of splitting and
the Zeeman component intensity, and is of a complicated character with a
distinctly pronounced asymmetry. The depths of formation of magnetically
sensitive lines are found by means of these contribution functions. The
calculations reveal that the steep section of the line profile is
formed higher than the profile center when a strong longitudinal
magnetic field is present. The Stokes profiles that describe the
polarization characteristics are formed only several kilometers higher
than the Stokes profile that specifies the general depression of the
unpolarized and polarized radiation. The averaged depth of formation of
the whole line profile is practically independent of the magnetic field
strength. The depths of formation of 17 photospheric lines usually used
in magnetospectroscopic observations are calculated for the models of
the quiet photosphere, a flux tube, and the sunspot umbra.
Title: Effect of the anomalous dispersion in the solar atmosphere
on results of magnetic field measurements by the "line-ratio" method.
Authors: Lozitskij, V. G.; Sheminova, V. A.
Bibcode: 1992KPCB....8a..10L
Altcode: 1992KPCB....8...10L
On the basis of Stokes parameter calculations for the Fe I λλ524.7
and 525.0 nm lines and the Holweger-Muller model atmosphere, the effect
of the anomalous dispersion on solar magnetic field measurements by the
"line-ratio" method is analyzed. It is shown that with the present-day
observational accuracy the anomalous dispersion should be taken into
consideration in the "line-ratio" method only when the following
four conditions are fulfilled simultaneously: a) the inclination of
the magnetic lines to the line of sight does not exceed 20°; b) the
magnetic field strength is larger than 100 mT; c) the cross profile of
the magnetic field in subtelescopic flux tubes is rectangular, and d)
the parts of the magnetically sensitive line profiles close to the
line center (Δλ ≤ 4 pm) are used.
Title: What is the difference between `emission' and `depression'
contribution functions?
Authors: Gurtovenko, E. A.; Sheminova, V. A.; Sarychev, A. P.
Bibcode: 1991SoPh..136..239G
Altcode:
The right approach to the problem of the depth of Fraunhofer line
formation enables us to distinguish the main processes involved in
the formation of a Fraunhofer line and to locate the depths for these
processes in the photosphere.
Title: The influence of the medium physical conditions and atomic
constants on the Stokes profiles of absorption lines in the solar
spectrum
Authors: Sheminova, V. A.
Bibcode: 1991ITF....87P...3S
Altcode:
In the frame of Unno-Beckers-Landy degl'Innocenti theory the estimations
of the magnetic strengthening of the FeI lines are obtained and
their behavior depending on the excitation potential, the wavelength,
the equivalent width, the Lande factor, the microturbulent velocity,
the bulk velocity, the damping constant, the atmospheric model, the
strength and direction of the magnetic field is studied. Variations of
the Stokes profiles presented in the graphic form allow the initial
values of input parameters to be obtained when deriving the magnetic
field vector by the inversion code. The obtained dependences of magnetic
strengthening allow the correct choice of magnetic sensitive lines to
be realized when simulation of the structure inhomogeneity.
Title: Vychislenie profilej Stoks-parametrov magnitochuvstvitelnyh
linij pogloshchenija v zvezdnyh atmosferah Title: Vychislenie
profilej Stoks-parametrov magnitochuvstvitelnyh linij pogloshchenija
v zvezdnyh atmosferah Title: Calculating Stokes parameter profiles
of magnetically sensitive absorption lines in stellar atmospheres.
Authors: Sheminova, Valentina
Bibcode: 1990vpsp.book.....S
Altcode:
The calculation algorithms of Stokes parameter profiles of magnetically
sensitive absorption lines for SPANSATM program are presented. This
program is a new modification of the SPANSAT program. It is the program
for LTE-calculation of absorption line formed in the presence of a
magnetic field in stellar atmospheres. The program can be applied to
the Sun or to stars of the solar type.
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: On the possibility to improve the homogeneous photospheric
model of the Sun.
Authors: Gurtovenko, E. A.; Sheminova, V. A.
Bibcode: 1988KFNT....4...18G
Altcode:
Modelling of differences of solar oscillator strengths derived from
equivalent widths and central intensities with variations of nominal
temperature of the photospheric model and characteristics of the
photospheric velocity field has been made. The accuracy of determining
chemical element abundances is evaluated by applying the specific
uncertainties of the distribution of temperature and velocity field
amplitude in the solar photosphere. The investigations of temperature
and luminosity variations of the Sun from precise observations of
Fraunhofer lines may bring fruitful results. The line symmetry of light
elements with high excitation potential may serve as a "sensitive"
indicator of physical inhomogeneity of solar and stellar atmospheres.
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: Crossing Method for Studying the Turbulence in Solar and
Stellar Atmospheres - Part One - Application to the Sun
Authors: Gurtovenko, E. A.; Sheminova, V. A.
Bibcode: 1986SoPh..106..237G
Altcode:
A new `crossing' method for the study of turbulent velocities
in solar and stellar photospheres is considered. The method does
not need knowledge of the abundance and oscillator strengths for
determining the microturbulent velocity, if the macroturbulent
velocity is adopted; or it allows investigation of the micro- and
macro-velocities simultaneously, if the abundance and oscillator
strengths are known. Using the crossing method for 200 lines of neutral
iron we obtain microturbulent velocities for a large range of depths in
the solar photosphere. The distribution of macroturbulent velocities
with depth is also investigated. The total velocity field calculated
from the obtained micro- and macro-velocities agrees with previous
results from independent methods. This demonstrates the reliability
of using the crossing method for separate determination of the micro-
and macroturbulent velocities in solar and stellar atmospheres.
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: On the difference in the depths of formation of the centers
of weak Fraunhofer lines and the far wings of strong ones
Authors: Gurtovenko, E. A.; Sheminova, V. A.
Bibcode: 1985AZh....62..988G
Altcode:
The Voigt function H(a,v) influences the absorption coefficient of the
centre and of the wing of a Fraunhofer line differently. The absorption
coefficient of the line centre is K(0) ≡ N/ΔλD, and
the one of the far wings is K(v) ≡ Nγ. Here N is the concentration
of absorbing atoms, ΔλD is the Doppler width, γ is the
damping-broadening constant, sharply increasing downward into the
photosphere. Due to this, the effective depths of formation of far
wings of strong lines are larger than those of weak lines having the
same atomic parameters.
Title: On the difference in the depths of formation of the centers
of weak Fraunhofer lines and the far wings of strong ones
Authors: Gurtovenko, É. A.; Sheminova, V. A.
Bibcode: 1985SvA....29..578G
Altcode:
No abstract at ADS
Title: On the Difference in the Depths of Formation of the Centers
of Weak Fraunhofer Lines and the Far Wings of Strong Ones
Authors: Gurtovenko, E. A.; Sheminova, V. A.
Bibcode: 1985SvA....29..572G
Altcode:
No abstract at ADS
Title: Macro-microturbulence in the solar photosphere.
Authors: Sheminova, V. A.
Bibcode: 1985KFNT....1...50S
Altcode:
Comparing the equivalent widths and the central depths of about 200
Fe I lines with calculated values the distribution of the large-scale
motion velocities in the photosphere has been obtained. The motions are
anisotropic. At the heights from 200 to 500 km the radial component
of Vmac decreases from 2.0 to 1.3 km s-1, and
the tangential one decreases from 2.3 to 1.0 km s-1.
Title: Velocity Field in the Region of the Temperature Minimum of
the Solar Atmosphere - Preliminary Results of a Determination of
the Amplitude of the General Velocity Field
Authors: Gurtovenko, E. A.; Sheminova, V. A.; Rutten, R. J.
Bibcode: 1985SvA....29...72G
Altcode:
No abstract at ADS
Title: Velocity field in the region of the temperature minimum of
the solar atmosphere - Preliminary results of a determination of
the amplitude of the general velocity field
Authors: Gurtovenko, E. A.; Sheminova, V. A.; Rutten, R. J.
Bibcode: 1985AZh....62..124G
Altcode:
The weak Fraunhofer lines in the near wings of H, K Ca II lines have
been analysed to study the velocity amplitude of the general velocity
field in the middle and outer photospheric layers. The results
confirm the basic well-known data on the velocity amplitude in the
middle photospheric layers. Besides, it is shown that the radial and
tangential components of the velocity amplitude continue to decrease
with height also in the outer photosphere.
Title: On the difference of effective depths in formation of moderate
and faint Fraunhofer lines.
Authors: Gurtovenko, Eh. A.; Sheminova, V. A.
Bibcode: 1985BSolD1985...70G
Altcode:
It is shown that the tables by the authors (1978) of effective depths
of faint Fraunhofer lines are correct for lines having central depths
dc < 0.1. A conclusion is made on the expediency of
calculation of the depths of formation of moderate and strong Fraunhofer
lines in the solar spectrum.
Title: Turbulence in the Photosphere of the Sun as a Star - Part Two
Authors: Sheminova, V. A.
Bibcode: 1984BSolD...4...75S
Altcode:
No abstract at ADS
Title: Turbulence in the Photosphere of the Sun as a Star - Part One
Authors: Sheminova, V. A.
Bibcode: 1984BSolD...3...75S
Altcode:
No abstract at ADS
Title: "Turbulence" in the photosphere of the sun as a star. I. A
method of calculation of precise line profiles for the solar flux.
Authors: Sheminova, V. A.
Bibcode: 1984BSolD1984Q..75S
Altcode:
A method is described for the calculation of precise line profiles of
the integral spectrum of the entire solar disc taking into account
the solar rotation and macroturbulence. The influence of the errors
of the photospheric parameters and some other initial parameters on
the accuracy of the calculated integral line profile is studied.
Title: Determination of microturbulent and macroturbulent velocity
and an improved evaluation of the damping constant from Fraunhofer
line profiles
Authors: Sheminova, V. A.
Bibcode: 1984AAfz...51...42S
Altcode:
When comparing theoretical profiles of moderate lines of Fe I, their
equivalent widths and central intensities with the observed lines the
following values were obtained: damping constant (2.5γ6),
microturbulent velocity (Vrad = 0.8 km s-1
at the optical depth τ5 = 0.08, Vtg = 1.4
km s-1 at the optical depth τ5 = 0.03),
macroturbulent velocity (Vrad = 1.6 km s-1
at the optical depth τ5 = 0.04, Vtg = 2.3 km
s-1 at the optical depth τ5 = 0.01). Two models
of the solar atmosphere (HOLMU and VAL) were used in the calculations.
Title: Turbulence in the photosphere of the sun as a
star. III. Micro-macroturbulence.
Authors: Sheminova, V. A.
Bibcode: 1984BSolD1984...70S
Altcode:
Equalizing computed and observed equivalent widths of Fe I lines in
the solar emission flux isotropic microturbulence of the sun as a star
was found. Macroturbulence has been calculated from central intensities.
Title: Microturbulent velocity distribution in the solar photosphere
Authors: Sheminova, V. A.
Bibcode: 1984AAfz...53...15S
Altcode:
A method of simultaneous calculation of the widths and central depths of
Fe I lines in the solar photosphere has permitted a determination of the
velocity distribution of the moving small-size elements in altitudes of
150-550 km. It is found that amplitude of the microturbulent velocity
decreases with altitude from 1.4 km/s to 0.5 km/s between 150 and 350
km and increases from 350 to 550 km. The results are compared with
parameterizations of the phenomena found in other theoretical models.
Title: The effect of deviations from LTE on weak lines of Fe I
Authors: Sheminova, V. A.; Matveev, Y. B.
Bibcode: 1984AAfz...53...19S
Altcode:
It is shown that when deviations from local thermodynamic equilibrium
(LTE) are taken into account in calculations of the line profiles of Fe
I in the solar photosphere, the equivalent widths and central depths
of the line with low excitation potentials can decrease by an average
of 10 percent. The iron abundance value derived from the equivalent
widths of weak Fe I increases by 0.07 dex and is finally equal to 7.65
(+ or - 0.03).
Title: "Turbulence " in the photosphere of the sun as a star. II. The
general velocity field.
Authors: Sheminova, V. A.
Bibcode: 1984BSolD1984R..75S
Altcode:
A model of the general velocity field is applied to unresolvable
(integral) weak line profiles over the solar disc. The profiles of
weak lines are calculated in the emission flux of the sun as a star
using the general velocity field (without discriminating micro- and
macroturbulence). It is found that the amplitude of the general velocity
field as large as 3 km sec-1 deduced from the profiles of
weak lines has been essentially overestimated. It is shown that the
calculation of profiles for strong as well as for moderate lines in the
integral solar spectrum requires a separation of turbulent velocities
into micro- and macrovelocities.
Title: Turbulence in the Photosphere of the Sun as a Star - Part
Three - Micro-Macroturbulence
Authors: Sheminova, V. A.
Bibcode: 1984BSolD...8...70S
Altcode:
No abstract at ADS
Title: Depth of formation of Fraunhofer lines
Authors: Gurtovenko, É. A.; Sheminova, V. A.
Bibcode: 1983AZh....60..982G
Altcode:
A straightforward physical discussion of the processes of formation of
the emergent photospheric radiation and the line depression observed
on the continuum background has been made.
Title: Depth of Formation of Fraunhofer Lines
Authors: Gurtovenko, E. A.; Sheminova, V. A.
Bibcode: 1983SvA....27..568G
Altcode:
No abstract at ADS
Title: Iron abundance in the sun
Authors: Sheminova, V. A.
Bibcode: 1983AAfz...50...17S
Altcode:
The abundance is determined through the equivalent widths of 107 FeI
lines. Use is made of the new system of oscillator strengths proposed by
Gurtovenko and Kostyk (1980, 1982). In logarithmic units, the abundance
is determined to be 7.58 + or - 0.03 (HRSA model; Gingerich et al.,
1971), 7.63 + or -0.03 (VAL model; Varnazza et al., 1976, 1980), and
7.64 + or - 0.03 (HOLMU model; Holweger and Muller, 1974). The value
obtained with the HOLMU model is considered the most probable, since
this model is superior in satisfying the requirements of describing
the Fraunhofer lines.
Title: A determination of microturbulent velocity on the basis of
Fe I Fraunhofer lines
Authors: Sheminova, V. A.
Bibcode: 1982AAfz...47...42S
Altcode:
The methods in current use for determining microturbulent velocities
in the solar photosphere are surveyed. These include the method of
growth curves, the method of equivalent widths, the method of central
depths, and the method of spectral line profiles. A new method is then
proposed that relies on the different reactions of the equivalent
widths and central depths of the Fraunhofer lines to changes in the
microturbulent velocities. With this method, a velocity of 0.8 km/s
is obtained for the center of the disk given an optical depth of 0.1
and an iron abundance of 7.62; when cos theta = 0.28, the velocity is
1.9 km/s for an optical depth of 0.03 and an abundance of 7.71.
Title: The abundance of titanium in the solar photosphere
Authors: Gurtovenko, E. A.; Fedorchenko, G. L.; Sheminova, V. A.
Bibcode: 1981AAfz...43...59G
Altcode:
The abundance of titanium in the solar photosphere is determined from
equivalent widths of 38 weak Fraunhofer lines of TiI. The oscillator
strengths scale of Kurucz and Peytremann (1975) is used to obtain
log(NTi/NH), + 12 = 4.95 + or - 0.05. The results are compared to other
recent investigations, from which it is concluded that the oscillator
strength system of Kurucz and Peytremann presents significant systematic
errors, and must therefore be studied in detail, using a large number
of lines for a wide range of equivalent widths.
Title: Complex investigation of the 'microturbulent' velocity and
attenuation constant in the solar photosphere. II - Determination
of the abundance of iron from weak Fraunhofer lines of Fe I
Authors: Gurtovenko, E. A.; Fedorchenko, G. L.; Sheminova, V. A.
Bibcode: 1979AAfz...37...22G
Altcode:
In the present study, the abundance of iron in the photosphere is
determined by comparing the observed and calculated equivalent line
widths of 93 weak lines of Fe I. The HSRA photospheric model and the
semiempirical gf values, tabulated by Kurucz and Peytremann (1975)
are used in the calculations. A mean value of 7.82 plus or minus 0.05
is obtained for the abundance of iron.
Title: Combined study of the 'microturbulent' velocity and
damping parameter in the solar photosphere. III - Determination of
'microturbulent' velocity from equivalent widths of Fe I lines
Authors: Sheminova, V. A.; Gurtovenko, E. A.
Bibcode: 1979AAfz...38...29S
Altcode:
No abstract at ADS
Title: Comparison of Effective Depths of Fraunhofer Line Formation
Calculated by Various Methods
Authors: Gurtovenko, E. A.; Ratnikova-Sheminova, V. A.
Bibcode: 1978SoPh...58..241G
Altcode:
The effective depths of formation of some typical Fraunhofer lines,
calculated by the methods suggested by Gurtovenko et al. (1974),
Beckers and Milkey (1975), and Makita (1977) are compared.
Title: The effective depths of formation of weak Fraunhofer lines. I.
Authors: Sheminova, V. A.; Gurtovenko, E. A.
Bibcode: 1978AAfz...36...21S
Altcode:
Previous work on the determination of effective formation depths of weak
Fraunhofer lines is reviewed. It is shown that the effective depths
of weak lines computed from the Unsoeld-Pecker contribution function
correspond to the depths at which fluctuations in the parameters
that determine the line absorption factor have the greatest effect
on variations in the observed profile of an absorption line. Formulas
are given for calculating the effective formation depths of weak lines
of various atoms and ions in the solar photosphere. Numerical results
are presented for C I, N I, O I, Mg I and II, Si I and II, S I, Ca I
and II, Sc I and II, Ti I and II, V I, Cr I and II, Fe I and II, Co I,
Ni I, and Zn I and II.
Title: Results of a calculation of the effective depths of formation
of weak Fraunhofer lines. II.
Authors: Sheminova, V. A.; Gurtovenko, Eh. A.
Bibcode: 1978AAfz...36...32S
Altcode:
No abstract at ADS
Title: Quantitative estimates of the damping constant effect on
equivalent widths of weak Fraunhofer lines.
Authors: Sheminova, V. A.
Bibcode: 1977BSolD1977...80S
Altcode:
No abstract at ADS
Title: Comparison of the profiles of weak Fraunhofer lines with the
profile of the absorption coefficient.
Authors: Gurtovenko, E. A.; Ratnikova, V. A.
Bibcode: 1977AAfz...32....3G
Altcode:
Optical and geometric depths relative to 5000 A are calculated for three
Fe I lines with the same excitation potential and different intensities:
6097 A (central intensity of 2.9%), 6392 A (central intensity of 18.8%),
and 6240 A (central intensity of 50.4%). The results show that the
depths at which the absorption-coefficient profile is close to the
line profile are not greater than the limits of the layer determining
the main region of absorption-line formation for lines with central
depressions of less than 25% to 30%.
Title: Study of microturbulence from equivalent widths of moderate
and moderately strong Fe I lines.
Authors: Gurtovenko, E. A.; Ratnikova, V. A.
Bibcode: 1976AAfz...30...14G
Altcode:
Equivalent widths of 25 weak and moderately strong Fe I Fraunhofer
lines are analyzed using data from center-limb observations of the
solar disk. An iron abundance with a logarithm of 7.04 is derived from
the weak lines. Microturbulent velocity fields are investigated by
employing the abundance values derived from moderately strong lines. A
model of quasi-isotropic microturbulent velocity smoothly increasing
with height from 0.6 km/s to 1.5 km/s (mean value, 1.1 km/s) over
the depth range between 100 and 600 km is obtained for a specified
photospheric model. It is concluded that microturbulent velocity can
be determined only by analyzing absolute values of equivalent line
widths and that the microturbulent-velocity model can be improved by
analyzing lines formed at different depths.
Title: Supplementary Remarks to `On the Average Depth of Formation of
Weak Fraunhofer Lines' by E. Gurtovenko, V. Ratnikova, and C. de Jager
Authors: Gurtovenko, E.; Ratnikova, V.; de Jager, C.
Bibcode: 1975SoPh...42...43G
Altcode:
No abstract at ADS
Title: Dependence of the formation depth of the weak Fraunhofer
lines on atomic parameters
Authors: Gurtovenko, E. A.; Ratnikova, V. A.
Bibcode: 1975SvA....18..609G
Altcode:
Using an electronic digital computer, the average depth of the formation
of weak Fraunhofer lines is calculated. A dependence of these depths
on the lower-level excitation potential is evident. The average optical
depth of the formation of weak absorption lines is determined mainly by
the excitation potential of the lower level. The larger the excitation
potential, the deeper is the formation of the absorption band. The
average depths depend also on such factors as the ionization potentials
of the neutral atom and iron, and on the partition functions. The joint
effect of these parameters can be different for lines of various atoms
and ions. A graph for some atoms and ions showing the dependences of
the average optical depth on the excitation potentials is included.
Title: Dependence of the formation depth of the weak Fraunhofer
lines on atomic parameters
Authors: Gurtovenko, E. A.; Ratnikova, V. A.
Bibcode: 1974AZh....51.1032G
Altcode:
Using an electronic digital computer, the average depth of the formation
of weak Fraunhofer lines is calculated. A dependence of these depths
on the lower-level excitation potential is evident. The average optical
depth of the formation of weak absorption lines is determined mainly by
the excitation potential of the lower level. The larger the excitation
potential, the deeper is the formation of the absorption band. The
average depths depend also on such factors as the ionization potentials
of the neutral atom and iron, and on the partition functions. The joint
effect of these parameters can be different for lines of various atoms
and ions. A graph for some atoms and ions showing the dependences of
the average optical depth on the excitation potentials is included.
Title: On the Average Optical Depth of Formation of Weak Fraunhofer
Lines
Authors: Gurtovenko, E.; Ratnikova, V.; De Jager, C.
Bibcode: 1974SoPh...37...43G
Altcode:
Methods for the determination of the average optical depth of formation
of weak Fraunhofer lines are compared, and their relative merits are
discussed. Distinction should be made between the region of origin
of the emergent radiation, and of the line depression. For weak or
fairly weak lines the average optical depth of formation of the line
depression is the relevant quantity; it should be determined by using
a computational scheme based on the classical weighting functions
of line formation; other methods give physically unsignificant or
conflicting results.
Title: Effect of Macroturbulence on Fraunhofer Line Profiles.
Authors: Gurtovenko, É. A.; Ratnikova, V. A.
Bibcode: 1971SvA....14..845G
Altcode:
No abstract at ADS
Title: Effect of Macroturbulence on Fraunhofer Line Profiles.
Authors: Gurtovenko, É. A.; Ratnikova, V. A.
Bibcode: 1970AZh....47.1053G
Altcode:
No abstract at ADS