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Author name code: shchukina
ADS astronomy entries on 2022-09-14
author:"Shchukina, Natalya G."
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Title: Results of observations of wave motions in the Solar facula
Authors: Shchukina, N. G.; Kostyk, R. I.
2022KFNT...38...71S Altcode:
No abstract at ADS
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Title: Velocity Field Diagnostics of the Quiet Sun Using the
Lambda-Meter Method: Si I 1082.7 nm Line
Authors: Shchukina, N. G.; Kostyk, R. I.
2020KPCB...36....1S Altcode:
The validity of the lambda-meter method for determining the quiet
Sun velocity field using the Si I 1082.7 nm line is investigated. To
this end, the intensity profiles of this line were calculated for the
solar disk center by means of NLTE simulations in a three-dimensional
model atmosphere describing the small-scale magnetic activity in
the quiet solar photosphere. The velocity field recovered using
the lambda-meter method from theoretical NLTE profiles of the Si I
1082.7 nm line was compared with the velocity field from the model
atmosphere. The influence of atmospheric and instrumental effects on
the results is considered. These effects are atmospheric turbulence
and light diffraction by telescope aperture, such as VTT, GREGOR,
and EST/DKIST. It is shown that, in the case of observations of
the Si I 1082.7 nm line on large-diameter telescopes like GREGOR and
EST/DKIST with a spatial resolution substantially better than 0.27″,
the lambda-meter method provides reliable values of the velocity field
for the lower and upper solar photosphere. For the middle photosphere,
the correlation between the inferred and the real velocities is
worse, particularly when using the smaller diameter telescopes like
VTT. Under a poor spatial resolution exceeding 2″, information about
the velocity field can be obtained only for the uppermost photospheric
layers. For this case, the lambda-meter velocities turn out to be
noticeably smaller than the real values.
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Title: Long-term monitoring of spectral line variations with the
11-year cycle. Quiet Sun.
Authors: Osipov, S. N.; Shchukina, N. G.; Kostyk, R. I.; Stodilka,
M. I.
2020A&AT...31..465O Altcode:
The monitoring program of long-term variation of selected solar
spectral lines is described. The aim of the program is to study
how the physical parameters of the quiet solar atmosphere change
over the last solar cycle 24. The research is based on high spectral
resolution observations of the quiet Sun using the Ernest Gurtovenko
horizontal solar telescope of the Main Astronomical Observatory of the
National Academy of Sciences of Ukraine. Since 2012 the observations
are performed daily, when the weather conditions allow. We found that
the line core depths and full widths at half maximum of the Fe I solar
spectral lines correlate with the cycle modulation of the total unsigned
magnetic field and the Wolf numbers of the Sun. The behaviour of these
line parameters can be explained by variations of the temperature of
the quiet photosphere during the 11-year cycle.
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Title: Diagnostics of the velocity field of the quiet Sun using the
lambda-meter method: The Si I 1082.7 nm line
Authors: Shchukina, N. G.; Kostyk, R. I.
2020KFNT...36a...3S Altcode: 2020KFNT...36....3S
No abstract at ADS
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Title: The diagnostic potential of the weak field approximation for
investigating the quiet Sun magnetism: the Si I 10 827 Å line
Authors: Shchukina, N. G.; Trujillo Bueno, J.
2019A&A...628A..47S Altcode:
<BR /> Aims: We aim to investigate the validity of the weak field
approximation (WFA) for determining magnetic fields in quiet regions
of the solar photosphere using the polarization caused by the Zeeman
effect in the Si I 10 827 Å line. <BR /> Methods: We solved the NLTE
line formation problem by means of multilevel radiative transfer
calculations in a three-dimensional (3D) snapshot model taken from
a state-of-the-art magneto-convection simulation of the small-scale
magnetic activity in the quiet solar photosphere. The 3D model
used is characterized by a surface mean magnetic field strength of
about 170 G. The calculated Stokes profiles were degraded because
of the atmospheric turbulence of Earth and light diffraction by the
telescope aperture. We apply the WFA to the Stokes I, Q, U, V profiles
calculated for different seeing conditions and for the apertures of
the VTT, GREGOR, EST and DKIST telescopes. We compare the inferred
longitudinal and transverse components of the magnetic field with
the original vertical and horizontal fields of the 3D model. <BR />
Results: We find that with a spatial resolution significantly better
than 0.5″ the surface maps of the magnetic field inferred from
the Stokes profiles of the Si I 10 827 Å line applying the WFA are
close to the magnetic field of the model on the corrugated surface,
corresponding to line optical depth unity at Δλ ≈ 0.1 Å for a
disk-center line of sight. The correlation between them is relatively
high, except that the inferred longitudinal and transverse components
of the magnetic field turn out to be lower than in the 3D model. <BR />
Conclusions: The use of the WFA for interpreting high-spatial-resolution
spectropolarimetric observations of the Si I 10 827 Å line obtained
with telescopes like GREGOR, EST, and DKIST allows the longitudinal
and transverse components of the magnetic field to be retrieved with
reasonable precision over the whole quiet solar photosphere, the result
being worse for telescopes of lower aperture.
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Title: Robust method for determination of magnetic field strength
in solar photosphere
Authors: Prysiazhnyi, A. I.; Stodilka, M. I.; Shchukina, N. G.
2018KFNT...34f...3P Altcode:
No abstract at ADS
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Title: Robust Method for Determination of Magnetic Field Strength
in the Solar Photosphere
Authors: Prysiazhnyi, A. I.; Stodilka, M. I.; Shchukina, N. G.
2018KPCB...34..277P Altcode:
The classical method for determining the magnetic field strength from
the distance between the peaks of blue and red wings of the Stokes
V profile of a magnetically sensitive spectral line is modified. To
reduce the influence of noise and to more accurately measure the
distance between these peaks, the observed Stokes V profile was
approximated by a modified wavelet-function. The parameters of the
best fitted approximation function were determined by multidimensional
optimization. Following such an approach, the magnetic field strength
can be found analytically using such an approximation. We investigate
the modified method by means of calculations of the Fe I λ 1564.8
nm Stokes V and I profiles in a three-dimensional snapshot model
atmosphere. Magneto-convection snapshot model with small-scale dynamo
action performed by Rempel was used. It was found that the method
proposed is less sensitive to noise and the shape of the observed
V-signal of the line. This makes it possible to conclude that the
approach of determining of the magnetic field strength from the observed
splitting of the Fe I λ 1564.8 nm Stokes V profile is more reliable
in comparison with the classical one.
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Title: A Novel Investigation of the Small-scale Magnetic Activity
of the Quiet Sun via the Hanle Effect in the Sr I 4607 Å Line
Authors: del Pino Alemán, T.; Trujillo Bueno, J.; Štěpán, J.;
Shchukina, N.
2018ApJ...863..164D Altcode: 2018arXiv180607293D
One of the key research problems in stellar physics is to decipher the
small-scale magnetic activity of the quiet solar atmosphere. Recent
magneto-convection simulations that account for small-scale dynamo
action have provided three-dimensional (3D) models of the solar
photosphere characterized by a high degree of small-scale magnetic
activity, similar to that found through theoretical interpretation of
the scattering polarization observed in the Sr I 4607 Å line. Here
we present the results of a novel investigation of the Hanle effect
in this resonance line based on 3D radiative transfer calculations
in a high-resolution magneto-convection model having most of
the convection zone magnetized close to the equipartition and a
surface mean field strength < B> ≈ 170 G. The Hanle effect
produced by the model’s magnetic field depolarizes the zero-field
scattering polarization signals significantly, to the extent that the
center-to-limb variation (CLV) of the calculated spatially averaged
polarization amplitudes is compatible with the observations. The
standard deviation of the horizontal fluctuations of the calculated
scattering polarization signals is very sensitive to the model’s
magnetic field, and we find that the predicted spatial variations
are sufficiently sizable so as to be able to detect them, especially
with the next generation of solar telescopes. We find that at all
on-disk positions, the theoretical scattering polarization signals are
anticorrelated with the continuum intensity. To facilitate reaching
new observational breakthroughs, we show how the theoretically
predicted polarization signals and spatial variations are modified
when deteriorating the signal-to-noise ratio and the spectral and
spatial resolutions of the simulated observations.
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Title: A Si I atomic model for NLTE spectropolarimetric diagnostics
of the 10 827 Å line
Authors: Shchukina, N. G.; Sukhorukov, A. V.; Trujillo Bueno, J.
2017A&A...603A..98S Altcode:
<BR /> Aims: The Si I 10 827 Å line is commonly used for
spectropolarimetric diagnostics of the solar atmosphere. First, we aim
at quantifying the sensitivity of the Stokes profiles of this line to
non-local thermodynamic equilibrium (NLTE) effects. Second, we aim at
facilitating NLTE diagnostics of the Si I 10 827 Å line. To this end,
we propose the use of a relatively simple silicon model atom, which
allows a fast and accurate computation of Stokes profiles. The NLTE
Stokes profiles calculated using this simple model atom are very similar
to those obtained via the use of a very comprehensive silicon model
atom. <BR /> Methods: We investigate the impact of the NLTE effects
on the Si I 10 827 Å line by means of multilevel radiative transfer
calculations in a three-dimensional (3D) model atmosphere taken from a
state-of-the-art magneto-convection simulation with small-scale dynamo
action. We calculate the emergent Stokes profiles for this line at the
solar disk center and for every vertical column of the 3D snapshot
model, neglecting the effects of horizontal radiative transfer. <BR
/> Results: We find significant departures from LTE in the Si I 10
827 Å line, not only in the intensity but also in the linearly and
circularly polarized profiles. At wavelengths around 0.1 Å, where
most of the Stokes Q, U, and V peaks of the Si I 10 827 Å line occur,
the differences between the NLTE and LTE profiles are comparable with
the Stokes amplitudes themselves. The deviations from LTE increase
with increasing Stokes Q, U, and V signals. Concerning the Stokes V
profiles, the NLTE effects correlate with the magnetic field strength
in the layers where such circular polarization signals are formed. <BR
/> Conclusions: The NLTE effects should be taken into account when
diagnosing the emergent Stokes I profiles as well as the Stokes Q, U,
and V profiles of the Si I 10 827 Å line. The sixteen-level silicon
model atom proposed here, with six radiative bound-bound transitions,
is suitable to account for the physics of formation of the Si I 10
827 Å line and for modeling and inverting its Stokes profiles without
assuming LTE.
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Title: Center-to-limb variation of the continuum intensity and linear
polarization of stars with transiting exoplanets
Authors: Shchukina, N. G.; Trujillo, B.; Vasilyeva, I. E.; Frantseva,
K. V.
2017KFNT...33d..29S Altcode:
No abstract at ADS
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Title: Center-to-limb variation of the continuum intensity and linear
polarization of stars with transiting exoplanets
Authors: Shchukina, N. G.; Trujillo Bueno, J.; Vasilyeva, I. E.;
Frantseva, K. V.
2017KPCB...33..166S Altcode:
The limb darkening and center-to-limb variation of the continuum
polarization is calculated for a grid of one-dimensional stellar
model atmospheres and for a wavelength range between 300 and 950
nm. Model parameters match those of the transiting stars taken from
the NASA exoplanet archive. The limb darkening of the continuum
radiation for these stars is shown to decrease with the rise in
their effective temperature. For the λ = 370 nm wavelength, which
corresponds to the maximum of the Johnson-Cousins UX filter, the
limb darkening values of the planet transiting stars lie in a range
between 0.03 and 0.3. The continuum linear polarization depends
not only on the effective temperature of the star but also on its
gravity and metallicity. Its value decreases for increasing values of
these parameters. In the UX band, the maximum linear polarization of
stars with transiting planets amounts to 4%, while the minimum value
is approximately 0.3%. The continuum limb darkening and the linear
polarization decrease rapidly with wavelength. At the R band maximum
(λ = 700 nm), the linear polarization close to the limb is in fact two
orders of magnitude smaller than in the UX band. The center- to-limb
variation of the continuum intensity and the linear polarization of
the stars with transiting planets can be approximated, respectively,
by polynomials of the fourth and the sixth degree. The coefficients
of the polynomials, as well as the IDL procedures for reading them,
are available in electronic form. It is shown that there are two
classes of stars with high linear polarization at the limb. The first
one consists of cold dwarfs. Their typical representatives are HATS-6,
Kepler-45, as well as all the stars with similar parameters. The second
class of stars includes hotter giants and subgiants. Among them we have
CoRoT-28, Kepler-91, and the group of stars with effective temperatures
and gravities of approximately 5000 K and 3.5, respectively.
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Title: Monitoring program of selected Fraunhofer lines over the
11-year cycle of solar activity
Authors: Osipov, S.; Kostik, R.; Shchukina, N.
2017psio.confE.109O Altcode:
No abstract at ADS
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Title: Impact of surface dynamo magnetic fields on the solar abundance
of the CNO elements
Authors: Shchukina, N.; Sukhorukov, A.; Trujillo Bueno, J.
2016A&A...586A.145S Altcode:
Most studies of the solar metallicity, based on abundance determinations
of the CNO elements, ignore the fact that the quiet solar photosphere
is significantly magnetized by a small-scale magnetic field with a
mean field strength of ~100 G. Here we quantify how this significant
magnetization affects determinations of the abundances of these chemical
elements. To this end, we used two three-dimensional models of the solar
photosphere taken from a magneto-convection simulation with small-scale
dynamo action, one virtually unmagnetized, and the other characterized
by a mean field strength of 160 G in the low photosphere. We performed
local thermodynamic equilibrium spectral synthesis for a large set of C
I, N I, and O I lines to derive abundance corrections. We included the
magnetic broadening of the lines (direct effect) and the magnetically
induced changes of the photospheric temperature stratification (indirect
effect). We find that these small-scale dynamo magnetic fields only
negligibly affect the determination of the solar abundances of carbon,
nitrogen, and oxygen.
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Title: Evershed flow observed in neutral and singly ionized iron lines
Authors: Khomenko, E.; Collados, M.; Shchukina, N.; Díaz, A.
2015A&A...584A..66K Altcode: 2015arXiv151000334K
The amplitudes of the Evershed flow are measured using pairs of
carefully selected Fe i and Fe ii spectral lines that are close in
wavelength and registered simultaneously. A sunspot belonging to the
NOAA 11582 group was scanned using the spectrograph of the German Vacuum
Tower Telescope (Observatorio del Teide, Tenerife). Velocities were
extracted from intensity profiles using the λ-meter technique. The
formation heights of the observed spectral lines were calculated using
semi-empirical models of a bright and dark penumbral filament taking
into account the sunspot location at the limb. Our objective is to
compare azimuthally averaged amplitudes of the Evershed flow extracted
from neutral and ion lines. We find measurable differences in the radial
component of the flow. All five pairs of lines show the same tendency;
the flow measured from the Fe i lines has an amplitude that is a few
hundred ms<SUP>-1</SUP> larger than that of the Fe ii lines. This
tendency is preserved at all photospheric heights and radial distances
in the penumbra. We discuss the possible origin of this effect.
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Title: The impact of surface dynamo magnetic fields on the solar
iron abundance
Authors: Shchukina, N.; Trujillo Bueno, J.
2015A&A...579A.112S Altcode:
Most chemical abundance determinations ignore that the solar photosphere
is significantly magnetized by the ubiquitous presence of a small-scale
magnetic field. A recent investigation has suggested that there
should be a significant impact on the derived iron abundance, owing
to the magnetically induced changes on the photospheric temperature
and density structure (indirect effect). The three-dimensional (3D)
photospheric models used in that investigation have non-zero net
magnetic flux values and stem from magneto-convection simulations
without small-scale dynamo action. Here we address the same problem
by instead using 3D models of the quiet solar photosphere that result
from a state-of-the-art magneto-convection simulation with small-scale
dynamo action, where the net magnetic flux is zero. One of these 3D
models has negligible magnetization, while the other is characterized
by a mean field strength of 160 Gauss in the low photosphere. With
such 3D models we carried out spectral synthesis for a large set of Fe
i lines to derive abundance corrections, taking the above-mentioned
indirect effect and the Zeeman broadening of the intensity profiles
(direct effect) into account. We conclude that if the magnetism of the
quiet solar photosphere is mainly produced by a small-scale dynamo,
then its impact on the determination of the solar iron abundance
is negligible. <P />Table 1 is available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201425569/olm">http://www.aanda.org</A>
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Title: Continuum polarization of stars as a result of occupation by
transiting exoplanets
Authors: Shchukina, N.; Frantseva, K.; Trujillo Bueno, J.
2014ysc..conf...12S Altcode:
No abstract at ADS
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Title: Influence of the small-scale photospheric magnetic field on
the solar abundances of CNO-elements
Authors: Sukhorukov, A.; Shchukina, N.; Vasilyeva, I.
2014ysc..conf...35S Altcode:
No abstract at ADS
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Title: Periodic variations of the H α profile width in the
chromosphere of coronal holes as a possible indicator of Alfvén waves
Authors: Zubkova, A. V.; Kobanov, N. I.; Sklyar, A. A.; Kostyk, R. I.;
Shchukina, N. G.
2014AstL...40..222Z Altcode:
We analyze the oscillations of the H α profile width based on our
observations of the chromosphere at the base of solar coronal holes. The
maximum oscillation amplitude averaged over ten time series is 64 m 0
A. Direct calculations show that this value cannot be reached through
temperature oscillations, because the periodic intensity fluctuations
observed during our experiment did not exceed 5%, corresponding to H α
profile broadening only by 1.5-2 m Å. We hypothesize that the observed
variations can result from the propagation of torsional Alfvén waves
in the chromosphere of coronal holes.
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Title: Influence of magnetic field on propagation of five-minute
oscillations in the sun's atmosphere: Phase shifts
Authors: Kostik, R. I.; Shchukina, N. G.; Kobanov, N. I.; Pulyaev,
V. A.
2014KPCB...30...40K Altcode:
No abstract at ADS
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Title: Oscillator strengths for selected Fe II lines in the range
λλ 300-400 nm
Authors: Shchukina, N. G.; Vasil'eva, I. E.
2013KPCB...29...53S Altcode:
No abstract at ADS
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Title: NLTE formation of the solar spectrum of silicon: Abundance
of silicon in a three-dimensional model of the solar atmosphere
Authors: Shchukina, N. G.; Sukhorukov, A. V.
2013KPCB...29...17S Altcode:
No abstract at ADS
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Title: Non-LTE Determination of the Silicon Abundance Using a
Three-dimensional Hydrodynamical Model of the Solar Photosphere
Authors: Shchukina, N.; Sukhorukov, A.; Trujillo Bueno, J.
2012ApJ...755..176S Altcode:
Confrontations of spectroscopic observations with local thermodynamic
equilibrium (LTE) spectral syntheses in a three-dimensional (3D)
hydrodynamical model of the solar photosphere led to a downward
revision of the photospheric and meteoritic silicon abundances. Here we
derive the photospheric silicon abundance taking into account non-LTE
(NLTE) effects in the same 3D model. We show that the above-mentioned
downward revision of the silicon abundance is caused by using the LTE
approximation in the context of 3D modeling, an experimental scale of
oscillator strengths, and a small number of Si I lines. We demonstrate
that no revision of the solar silicon abundance is required if NLTE
effects are taken into account and one uses a "solar" oscillator
strength scale and an extended list of Si I lines. The NLTE abundance
value we find by fitting the equivalent widths of 65 Si I lines is
A <SUP>NLTE</SUP> <SUB>Si</SUB> = 7.549 ± 0.016. This value agrees
well with the silicon abundance that had been recommended earlier by
Grevesse & Sauval and Lodders for the solar photosphere and CI
chondrite meteorites.
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Title: NLTE formation of the solar silicon spectrum: Silicon abundance
in one-dimensional models of the solar atmosphere
Authors: Sukhorukov, A. V.; Shchukina, N. G.
2012KPCB...28..169S Altcode:
No abstract at ADS
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Title: “Solar” oscillator strength scale and determination of the
LTE silicon abundance in the solar atmosphere
Authors: Shchukina, N. G.; Sukhorukov, A. V.
2012KPCB...28...49S Altcode:
No abstract at ADS
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Title: Solar spectrum of silicon and diagnostics of the solar
atmosphere
Authors: Sukhorukov, A. V.; Shchukina, N. G.
2012KPCB...28...27S Altcode:
No abstract at ADS
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Title: Acoustic waves in the solar atmosphere at high spatial
resolution. II. Measurement in the Fe I 5434 Å line
Authors: Bello González, N.; Flores Soriano, M.; Kneer, F.; Okunev,
O.; Shchukina, N.
2010A&A...522A..31B Altcode:
<BR /> Aims: We investigate the energy supply of the solar chromosphere
by acoustic waves. <BR /> Methods: A time sequence with high spatial
and temporal resolution from the quiet Sun disc centre in Fe i
5434 Å (Landé factor g = 0) is analysed. We used models from a
numerical simulation of granular convection and apply NLTE spectral
line transfer to determine the height of formation. For estimates of
acoustic energy flux, we adopted wave propagation with inclinations
of the wave vector with respect to the vertical of 0°, 30°, and
45°. For a granular and an intergranular model, the transmissions of
the atmosphere to high-frequency waves were determined for the three
inclination angles. Wavelet and Fourier analyses were performed
and the resulting power spectra were corrected for atmospheric
transmission. <BR /> Results: We find waves with periods down to ~40
s. They occur intermittently in space and time. The velocity signal
is formed at a height of 500 km in the granular model and at 620 km
in the intergranule. At periods shorter than the acoustic cutoff
(~190 s), ~40% of the waves occur above granules and ~60% above
intergranules. By adopting vertical propagation, we estimate total
fluxes above granules of 2750-3360 W m<SUP>-2</SUP>, and of 910-1 000
W m<SUP>-2</SUP> above intergranules. The weighted average is 1730-2
060 W m<SUP>-2</SUP>. The estimates of the total fluxes increase by 15%
when inclined wave propagation of 45° is assumed.
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Title: Fe I line pairs with different magnetic sensitivity
Authors: Vasilyeva, I. E.; Shchukina, N. G.
2009KPCB...25..319V Altcode:
No abstract at ADS
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Title: The solar Ba{II} 4554 Å line as a Doppler diagnostic: NLTE
analysis in 3D hydrodynamical model
Authors: Shchukina, N. G.; Olshevsky, V. L.; Khomenko, E. V.
2009A&A...506.1393S Altcode: 2009arXiv0905.0985S
Aims: The aim of this paper is to analyse the validity of the
Dopplergram and λ-meter techniques for the Doppler diagnostics
of solar photospheric velocities using the Ba II 4554 Å line. <BR
/>Methods: Both techniques are evaluated by means of NLTE radiative
transfer calculations of the Ba II 4554 Å line in a three-dimensional
hydrodynamical model of solar convection. We consider the cases of
spatially unsmeared profiles and the profiles smeared to the resolution
of ground-based observations. <BR />Results: We find that: (i)
speckle-reconstructed Dopplergram velocities reproduce the “true”
velocities well at heights around 300 km, except for intergranular lanes
with strong downflows where the velocity can be overestimated; (ii)
the λ-meter velocities give a good representation of the “true”
velocities through the whole photosphere, both under the original and
reduced spatial resolutions. The velocities derived from the inner wing
of smeared Ba II 4554 Å line profiles are more reliable than those for
the outer wing. Only under high spatial resolution does the inner wing
velocities calculated in intergranular regions give an underestimate
(or even a sign reversal) compared with the model velocities; (iii)
NLTE effects should be taken into account in modelling the Ba II 4554
Å line profiles. Such effects are more pronounced in intergranular
regions. <BR />Conclusions: Our analysis supports the opinion that the
Dopplergram technique applied to the Ba II 4554 Å line is a valuable
tool for the Doppler diagnostics of the middle photosphere around
300 km. The λ-meter technique applied to this line gives us a good
opportunity to “trace” the non-thermal motions along the whole
photosphere up to the temperature minimum and lower chromosphere. <P
/>Appendix is only available in electronic form at http://www.aanda.org
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Title: Solar granulation from photosphere to low chromosphere observed
in Ba II 4554 Å line
Authors: Kostik, R.; Khomenko, E.; Shchukina, N.
2009A&A...506.1405K Altcode: 2009arXiv0909.1210K
Aims: The purpose of this paper is to characterize the statistical
properties of solar granulation in the photosphere and low chromosphere
up to 650 km. <BR />Methods: We use velocity and intensity variations
obtained at different atmospheric heights from observations in Ba II
4554 Å. The observations were done during good seeing conditions at
the VTT at the Observatorio del Teide on Tenerife. The line core forms
rather high in the atmosphere and allows granulation properties to
be studied at heights that have been not accessed before in similar
studies. In addition, we analyze the synthetic profiles of the Ba II
4554 Å line by the same method computed taking NLTE effects into
account in the 3D hydrodynamical model atmosphere. <BR />Results:
We suggest a 16-column model of solar granulation depending on the
direction of motion and on the intensity contrast measured in the
continuum and in the uppermost layer. We calculate the heights of
intensity contrast sign reversal and velocity sign reversal. We show
that both parameters depend strongly on the granulation velocity and
intensity at the bottom photosphere. The larger the two parameters,
the higher the reversal takes place in the atmosphere. On average, this
happens at about 200-300 km. We suggest that this number also depends
on the line depth of the spectral line used in observations. Despite
the intensity and velocity reversal, about 40% of the column structure
of granulation is preserved up to heights around 650 km.
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Title: Three-dimensional Radiative Transfer Modeling of the Second
Solar Spectrum of Titanium
Authors: Shchukina, N. G.; Trujillo Bueno, J. T.
2009ASPC..405..275S Altcode:
Here we present multilevel radiative transfer calculations of the
scattering polarization of neutral titanium lines in a three-dimensional
model of the solar photosphere, which we have obtained from realistic
hydrodynamical simulations of solar surface convection. We consider
the particularly interesting case of the Ti I multiplet a{^5}F -
y{^5}F<SUP>o</SUP>, which is well suited for investigating the Sun's
hidden magnetism via the differential Hanle effect. After considering
the unmagnetized reference case, we show that the depolarization
produced by a volume-filling microturbulent field with a strength such
that it produces saturation of the upper-level Hanle effect leads to
a much better fit to Gandorfer's (2002) observations.
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Title: NLTE formation of the resonance Ba II line λ 455.4 nm in
the solar atmosphere
Authors: Ol'shevskii, V. L.; Shchukina, N. G.; Vasil'eva, I. E.
2008KPCB...24..145O Altcode:
No abstract at ADS
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Title: The Ba II [lambda]4554 resonance line and solar granulation
Authors: Olshevsky, V. L.; Shchukina, N. G.
2007msfa.conf..307O Altcode:
We present the results of an investigation of the impact of NLTE effects
and of granulation inhomogeneities on the solar Ba II [lambda]4554 Å
line. Our analysis is based on both the classical one-dimensional (1D)
solar atmosphere models and on the new generation of three-dimensional
(3D) hydrodynamical models. We show that NLTE and 3D effects have to
be taken into account for reliable diagnostics of the solar atmosphere
using this line. We analyse the influence of different parameters on the
line shape. It turns out to be most sensitive to collisional broadening
and barium abundance. Uncertainties in the oscillator strength, micro-
and macroturbulence (in 1D-case) have a secondary importance. We have
derived the barium abundance assuming NLTE. We find ABa = 2.16 in good
agreement with the recent result of Asplund et al. (2005).
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Title: The Hanle Effect in Atomic and Molecular Lines: A New Look
at the Sun's Hidden Magnetism
Authors: Trujillo Bueno, J.; Asensio Ramos, A.; Shchukina, N.
2006ASPC..358..269T Altcode: 2006astro.ph.12678T
This paper reviews some of the most recent advances in the application
of the Hanle effect to solar physics, and how these developments are
allowing us to explore the magnetism of the photospheric regions that
look “empty” in solar magnetograms--that is, the Sun's “hidden”
magnetism. In particular, we show how a joint analysis of the Hanle
effect in atomic and molecular lines indicates that there is a vast
amount of hidden magnetic energy and unsigned magnetic flux localized in
the (intergranular) downflowing regions of the quiet solar photosphere,
carried mainly by tangled fields at sub-resolution scales with strengths
between the equipartition field values and ∼1 kG. <P />This article
combines in one contribution Trujillo Bueno's invited keynote paper
and the contributed papers by Asensio Ramos & Trujillo Bueno and
by Shchukina & Trujillo Bueno.
---------------------------------------------------------
Title: Non-LTE Formation of Ba II Resonance Lines
Authors: Olshevsky, V. L.; Shchukina, N. G.
2006IAUJD...3E..16O Altcode:
We investigate the formation of the resonance lines of ionized Barium
in the Solar atmosphere. We have constructed atomic model of Ba II,
which includes 40 energy levels, 99 bound-bound and 39 bound-free
transitions. Using the numerical solution of radiative transfer equation
together with the statistical equilibrium equations we calculate
emergent profiles of the Ba II 4554 A resonance line under different
conditions. Line profiles are calculated in both standard 1D and 3D
atmospheric models in LTE and non-LTE approximations. We found that
non-LTE effects are very important for this line. Main NLTE mechanisms
are the resonance line scattering and photon losses. In 1D the line
shape is most sensitive to the following parameters: Barium abundance,
collisional strengths and macroturbulent velocity. Sensitivity to the
uncertainties in oscillator strengths is not so high. Taking precise
theoretical values of collisional strengths by Barklem & O'Mara
(1998) we found the best agreement with observations for the abundance
close to the "classical" value of 2.13. In 3D calculated profiles
are in a good agreement with the observations. In 1D the agreement
is worse. Thus it is critical for the modelling of Ba II lines to use
the 3D non-LTE radiative transfer.
---------------------------------------------------------
Title: Fine structure of wave motions in the solar photosphere:
Observations and theory
Authors: Kostyk, R. I.; Shchukina, N. G.; Khomenko, E. V.
2006ARep...50..588K Altcode:
Spectral observations of the 639.361-nm FeI line at the center of
the quiet solar disk with high spatial (0.4″) and temporal (10
s) resolution are used to investigate the behavior of local 5-min
oscillations over granules and intergranular lanes. The power of the
5-min oscillations in the upper photosphere (at heights of H ≈ 490 km)
is higher the faster the convective motions in the lower photosphere
(H ≈ 10 km). This suggests that turbulent convection is responsible
for the excitation of local solar oscillations. A statistical analysis
of the oscillations shows that, on average, both the intensity and
velocity of the oscillation amplitudes are greater over intergranular
lanes. This difference in amplitudes is present throughout the studied
heights in the photosphere (H = 0-490 km). The period at which the
power spectrum of velocity oscillations reaches its maximum is longer
over intergranules than over granules. Simulations of the propagation
of acoustic-gravity waves in an atmosphere taking into account the
convection pattern give a satisfactory explanation for the above
observed effects. It is concluded that the atmospheric modulation
of the 5-min oscillations is an additional or alternative mechanism
responsible for differences between these oscillations over granules
and intergranules.
---------------------------------------------------------
Title: Oxygen in Metal-Rich Stars: Abundances from [O I] 6300,
OI 7771 5 and Near-UV OH
Authors: Ecuvillon, A.; Israelian, G.; Santos, N. C.; Shchukina, N.;
Mayor, M.; Rebolo, R.
2006cams.book...50E Altcode:
Oxygen abundances of a large number of metal-rich stars, with and
without known planets, were derived from the forbidden line [O I]
6300 Å, the OI 7771-5 Å triplet and from near-UV OH lines. Non-LTE
corrections were calculated and applied to the LTE abundance results
derived from the OI 7771-5 Å triplet. Spectral synthesis was performed
for several OH lines. Results from different indicators are compared. We
study abundance trends in planet host and comparison sample stars. We
find for all the indicators that, on average, [O/Fe] clearly decreases
with [Fe/H], with significantly negative slopes in all the linear fits.
---------------------------------------------------------
Title: Oxygen abundances in planet-harbouring stars. Comparison of
different abundance indicators
Authors: Ecuvillon, A.; Israelian, G.; Santos, N. C.; Shchukina,
N. G.; Mayor, M.; Rebolo, R.
2006A&A...445..633E Altcode: 2005astro.ph..9326E
We present a detailed and uniform study of oxygen abundances in 155
solar type stars, 96 of which are planet hosts and 59 of which form
part of a volume-limited comparison sample with no known planets. EW
measurements were carried out for the [O I] 6300 Å line and the O I
triplet, and spectral synthesis was performed for several OH lines. NLTE
corrections were calculated and applied to the LTE abundance results
derived from the O I 7771-5 Å triplet. Abundances from [O I], the
O I triplet and near-UV OH were obtained in 103, 87 and 77 dwarfs,
respectively. We present the first detailed and uniform comparison
of these three oxygen indicators in a large sample of solar-type
stars. There is good agreement between the [O/H] ratios from forbidden
and OH lines, while the NLTE triplet shows a systematically lower
abundance. We found that discrepancies between OH, [O I] and the O I
triplet do not exceed 0.2 dex in most cases. We have studied abundance
trends in planet host and comparison sample stars, and no obvious
anomalies related to the presence of planets have been detected. All
three indicators show that, on average, [O/Fe] decreases with [Fe/H]
in the metallicity range -0.8< [Fe/H] < 0.5. The planet host
stars present an average oxygen overabundance of 0.1-0.2 dex with
respect to the comparison sample.
---------------------------------------------------------
Title: The iron and oxygen abundances in the metal-poor star HD
140283 and in the Sun
Authors: Shchukina, N. G.; Vasiljeva, I. E.; Trujillo Bueno, J.
2005KFNTS...5...95S Altcode:
We present the results of a theoretical investigation of the impact
of NLTE effects and of granulation inhomogeneities on the iron and
oxygen abundances in the metal-poor star HD 140283 and in the Sun. Our
analysis is based on both the classical one-dimensional (1D) stellar
atmosphere models and on a new generation of three-dimensional (3D)
hydrodynamical models. We consider the Sun as a reference star. The
solar iron and oxygen abundances are redefined.
---------------------------------------------------------
Title: Ba II 4554A Resonance Line Formation in the Solar Atmosphere
Authors: Olshevsky, V.; Shchukina, N.
2005ysc..conf...71O Altcode: 2005yosc.conf...71O
We investigate non-LTE radiative transfer in the the Ba II 4554 A
line in the Solar atmosphere. This line is particularly suited to
measure non thermal motions in the solar photosphere. It is also used
in Stokes vector spectropolarimetry. NLTE spectral formation modeling
is a necessary step in the formulation of reliable quantitative data
interpretation through numerical inversion. The first phase of the work
includes creation of a reliable model of the Ba II atom. It includes:
energy levels, oscillator strengths for the selected bb-transitions and
bf-transitions probabilities. We also take into account the hyper fine
structure and isotopic splitting. Next step is to calculate departure
coefficients for Ba II through numerical solution of the radiative
transfer equations. When these coefficients are derived it is possible
to apply inversion techniques to spectral observations in this line.
---------------------------------------------------------
Title: CNO, S, Zn and Cu abundances in planet-harbouring stars
Authors: Ecuvillon, A.; Israelian, G.; Santos, N. C.; Shchukina, N.;
Mayor, M.; Rebolo, R.
2005ESASP.560..527E Altcode: 2005csss...13..527E
No abstract at ADS
---------------------------------------------------------
Title: Metal-rich end of galactic chemical evolution: oxygen
abundances from [OI] 6300, OI 7771 5 and near-UV OH.
Authors: Ecuvillon, A.; Israelian, G.; Santos, N. C.; Shchukina,
N. G.; Mayor, M.; Rebolo, R.
2005IAUS..228..253E Altcode:
We present a detailed and uniform study of oxygen abundances in a
large set of 155 metal-rich dwarfs. EW measurements were carried
out for the [OI] 6300 Å line and the OI triplet, while spectral
synthesis was performed for several OH lines. NLTE corrections were
calculated and applied to the LTE abundance results derived from the
triplet. Abundances from [OI], the OI triplet and near-UV OH were
obtained in 103, 87 and 77 dwarfs, respectively. A good agreement
between [O/H] ratios from forbidden and OH lines is found, while the
NLTE triplet shows a systematically lower abundance. Nevertheless, the
consistency with other indicators improves if we consider LTE triplet
results. In any case, discrepancies between OH, [OI] and the OI triplet
hardly exceed 0.2dex. All three indicators show that, on average, [O/Fe]
decreases with [Fe/H] in the metallicity range -0.8<[Fe/H]<0.5.
---------------------------------------------------------
Title: The Impact of Non-LTE Effects and Granulation Inhomogeneities
on the Derived Iron and Oxygen Abundances in Metal-Poor Halo Stars
Authors: Shchukina, N. G.; Trujillo Bueno, J.; Asplund, M.
2005ApJ...618..939S Altcode: 2004astro.ph.10475S
This paper presents the results of a detailed theoretical investigation
of the impact of non-LTE (NLTE) effects and of granulation
inhomogeneities on the derived iron and oxygen abundances in the
metal-poor halo subgiant HD 140283. Our analysis is based on both the
“classical” one-dimensional stellar atmosphere models and on the
new generation of three-dimensional hydrodynamic models. The NLTE
calculations presented here have been carried out without inelastic
collisions with neutral hydrogen atoms. We find that if NLTE effects
are taken into account when synthesizing the Fe I spectrum in both
types of atmospheric models, then the derived iron abundance turns out
to be very similar in both cases. The emergent spectral line profiles
in both models are very much weaker in NLTE than in LTE because the
UV overionization mechanism produces a very strong underpopulation
of the Fe I levels, in particular in the granular regions of the
three-dimensional model. As a result, the NLTE effects on the derived
iron abundance are very important, amounting to ~0.9 and to ~0.6 dex in
the three- and one-dimensional cases, respectively. On the other hand,
we find that NLTE and three-dimensional effects have to be taken into
account for a reliable determination of the iron abundance from weak Fe
II lines, because the significant overexcitation of their upper levels
in the granular regions tend to produce emission features. As a result,
such Fe II lines are weaker than in LTE and the abundance correction
amounts to ~0.4 dex for the three-dimensional case. We also derive
the oxygen-to-iron abundance ratio in the metal-poor star HD 140283
by using the O I triplet at 7772-7775 Å and the forbidden [O I] line
at 6300 Å. Our results for the oxygen abundance confirm the values
reported in some recent investigations. While the oxygen abundance
derived from the O I IR triplet is not very sensitive to the presence
of granulation inhomogeneities, such three-dimensional effects amount to
~-0.2 dex for the [O I] line. The NLTE abundance correction for the O I
IR triplet turns out to be -0.2 dex, approximately. Interestingly, when
both NLTE and three-dimensional effects are taken into account there
still remain significant discrepancies in the iron abundances derived
from Fe I and Fe II lines, as well as in the oxygen abundances inferred
from the O I and [O I] lines. We conclude that the discrepancies could
be due to uncertainties in the stellar parameters of this metal-poor
star. We argue that adopting T<SUB>eff</SUB>~5600 K (instead of
T<SUB>eff</SUB>~5700 K) and [Fe/H]~-2.0 (instead of [Fe/H]~-2.5)
substantially reduces the discrepancies in the abundances of iron and
oxygen inferred from several spectral lines. Under such circumstances,
we find [O/Fe]~0.5 at [Fe/H]=-2. Obviously, our tentative conclusion
that the metallicity of this type of metal-poor star is significantly
larger than previously thought may have far-reaching implications in
stellar astrophysics.
---------------------------------------------------------
Title: Fine Structure of Convective Motions in the Solar Photosphere:
Observations and Theory
Authors: Kostyk, R. I.; Shchukina, N. G.
2004ARep...48..769K Altcode:
The granulation brightnesses and convective velocities in the solar
photosphere between the levels of formation of the continuum radiation
and the temperature minimum are examined. Spectral images of the
granulation observed in lines of neutral and ionized iron with high
spatial (0.5″) and temporal (9 s) resolutions were obtained using the
German Vacuum Tower Telescope in Izana (Tenerife, Spain). A correlation
analysis shows that the granules and intergranules change their
relative brightness at a height near 250 km, and a general reversal
of the velocity occurs near a height of 490 km, where the material
above granules begins to predominantly descend, and the material above
intergranules, to ascend. The maximum correlation coefficient between
the velocity and the line brightnesdoesnot exceed 0.75. The properties
of the brightness and velocity are analyzed in a sixteen-column
model. Four sorts of motions are most typical and efficient. In the
first two, only the sign of the relative contrast of the material
changes (an efficiency of 46%). This occurs, on average, at a height
of 270 km. In the last two motions, both the sign of the contrast
and the direction of the motion are reversed near a height of 350 km
(an efficiency of 28%). All the observed dependences are compared with
theoretical relations obtained in a three-dimensional hydrodynamical
model, with deviations from local thermodynamic equilibrium included
in the calculation of the spectral-line profiles. This model can
satisfactorily reproduce all the basic features of the convective
velocities and intensities. It is concluded that the convective motions
maintain their column structure throughout the photosphere, right to
the level of the temperature minimum. This makes a separation of the
photosphere into two regions with different granulation brightnesses
and convective motions unjustified.
---------------------------------------------------------
Title: A substantial amount of hidden magnetic energy in the quiet Sun
Authors: Trujillo Bueno, J.; Shchukina, N.; Asensio Ramos, A.
2004Natur.430..326T Altcode: 2004astro.ph..9004T; 2004astro.ph..9004B
Deciphering and understanding the small-scale magnetic activity of the
quiet solar photosphere should help to solve many of the key problems
of solar and stellar physics, such as the magnetic coupling to the
outer atmosphere and the coronal heating. At present, we can see only
~1 per cent of the complex magnetism of the quiet Sun, which highlights
the need to develop a reliable way to investigate the remaining 99 per
cent. Here we report three-dimensional radiative transfer modelling of
scattering polarization in atomic and molecular lines that indicates
the presence of hidden, mixed-polarity fields on subresolution
scales. Combining this modelling with recent observational data, we
find a ubiquitous tangled magnetic field with an average strength of
~130G, which is much stronger in the intergranular regions of solar
surface convection than in the granular regions. So the average magnetic
energy density in the quiet solar photosphere is at least two orders
of magnitude greater than that derived from simplistic one-dimensional
investigations, and sufficient to balance radiative energy losses from
the solar chromosphere.
---------------------------------------------------------
Title: Oxygen and magnesium abundance in the ultra-metal-poor giants
CS 22949-037 and CS 29498-043: Challenges in models of atmospheres
Authors: Israelian, G.; Shchukina, N.; Rebolo, R.; Basri, G.; González
Hernández, J. I.; Kajino, T.
2004A&A...419.1095I Altcode: 2004astro.ph..3033I
We report the results of a non-LTE Fe, O and Mg abundance analysis of
the carbon-nitrogen-rich ultra-metal-poor giants CS 29498-043 and CS
22949-037. The abundance of oxygen has been derived from measurements
of the oxygen triplet at 7771-5 Å in high resolution spectra obtained
with KeckI/HIRES and the forbidden line [O I] 6300 Å detected in
the TNG/SARG spectra of CS 29498-043. Detailed non-LTE analysis of
Fe lines has provided reliable stellar parameters which, however,
do not resolve the oxygen abundance conflict as derived from the O I
7771-5 Å triplet and the [O I] 6300 Å forbidden lines. We obtained
the following oxygen abundance: for CS 22949-037 [O/Fe] = 3.13, 1.95;
and for CS 29498-043; [O/Fe] = 3.02, 2.49, based on the O I 7771-5
Å triplet and the [O I] 6300 Å forbidden line, respectively. A
similar conflict appears to exist between the forbidden resonance
line Mg C I 4571 Å and several subordinate lines, such as Mg I
5172 and 5183 Å. Our analysis demonstrates the failure of standard
plane-parallel atmosphere models to describe the physical conditions
in the line-forming regions of these ultra-metal-poor giants.
---------------------------------------------------------
Title: Oxygen Abundances in Ultra-metal-poor Giants CS29498-043
and CS22949-037
Authors: Israelian, G.; Shchukina, N.; Rebolo, R.; Basri, G.; González
Hernández, J. I.
2004oee..sympE..27I Altcode:
Abundances of oxygen in two ultra-metal-poor giants have been derived
from measurements of the oxygen triplet at 7771-5Å in the near-IR
performed in high-resolution and high S/N ratio spectra obtained with
KeckI/HIRES. A detailed non-LTE analysis of Fe lines has been carried
out for our targets providing more reliable stellar parameters and
metallicities.
---------------------------------------------------------
Title: Stellar granulation and the NLTE formation Žf the Fe I lines:
The metal-poor halo star HD 140283
Authors: Shchukina, N. G.; Trujillo Bueno, J.; Vasil'va, I.
2003KFNT...19..441S Altcode: 2003KFNT...19e.441S
The NLTE Fe I line formation problem in a three-dimensional granulation
model of the metal-poor halo star HD 140283 is considered. The
self-consistent solutions of the kinetic and radiative transfer
equations were obtained with a realistic atomic model Fe I + Fe II. The
effects of horizontal radiative transfer are neglected. The near-UV
overionisation effect is found to lead to sizeable Fe I opacity deficits
in the granular atmospheric regions. This NLTE effect tends to produce
weaker emergent spectral lines than in LTE because they are formed
deeper in the stellar granules where the source functions are close
to the Planck function. The NLTE effects in the integranule spectra
are small. If NLTE effects are shown to be fully taken into account
both in the three-dimensional and one-dimensional models of the star
HD 140283 the iron abundance is in close agreement for both cases.
---------------------------------------------------------
Title: Towards a Reliable Diagnostics of `Turbulent' Magnetic Fields
Via the Hanle Effect in the Sr I λ4607 Å Line
Authors: Shchukina, N.; Trujillo Bueno, J.
2003ASPC..307..336S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Non-LTE Determination of Iron and Oxygen Abundances Using 3D
Hydrodynamical Models: the Metal-Poor Star HD140283
Authors: Shchukina, N. G.; Vasiljeva, I. E.; Trujillo Bueno, J.;
Asplund, M.
2003IAUS..210P.B10S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Oxygen abundances derived from UV OH and O I IR lines in very
metal-poor stars
Authors: García López, Ramón J.; Israelian, Garik; Rebolo, Rafael;
Bonifacio, Piercarlo; Molaro, Paolo; Basri, Gibor; Shchukina, Natalya
2002HiA....12..413G Altcode:
Oxygen abundances have been derived in a sample of very metal-poor
stars using the O I triplet at λλ7771-5 Å and OH lines in the near
UV. A detailed NLTE analysis of iron lines has been carried out for
one of the observed stars, BD +23°3130, providing consistent values
of effective temperature and surface gravity that are in very good
agreement with independent estimates from the infrared flux method and
Hipparcos parallaxes, respectively. These parameters, especially the
higher gravity obtained with respect to previous analyses, reduce the
discrepancies claimed between the oxygen abundances determined from OH,
O I triplet and [O I] λ6300 Å lines, and give consistent abundances
to within 0.16 dex for BD +23°3130 ([Fe/H]<SUB>NLTE</SUB> = -2.43). The
oxygen abundances derived for this new sample confirm previous findings
for a progressive linear increase in the oxygen-to-iron ratio with a
slope -0.33±0.02 (including NLTE corrections to the iron abundances
for all the stars considered) from solar metallicity to [Fe/H]~ -3, and
[O/Fe] values as high as ~1.1 for stars with [Fe/H]<~ -2.5. These
results can be interpreted as evidence for oxygen overproduction in
the very early epoch of the formation of the Galactic halo, possibly
associated with supernova events with very massive progenitor stars.
---------------------------------------------------------
Title: Oxygen abundances derived in unevolved very metal-poor stars
Authors: García López, R. J.; Israelian, G.; Rebolo, R.; Bonifacio,
P.; Molaro, P.; Basri, G.; Shchukina, N.
2001NewAR..45..519G Altcode:
Oxygen abundances have been derived in a sample of very metal-poor
stars from observations of the O I triplet at λλ 7771-5 Å and OH
lines in the near UV. Iron abundances derived in LTE were corrected
for NLTE effects following Thévenin and Idiart [ApJ 521 (1999)
753]. Furthermore, a detailed NLTE analysis of iron lines has been
carried out for one of the observed stars, BD +23° 3130 ([Fe/H]
<SUB>NLTE</SUB>=-2.43), providing consistent values of effective
temperature, surface gravity and metallicity, that are in good agreement
with independent estimates from the infrared flux method, Hipparcos
parallaxes and recent NLTE work in the literature, respectively. These
parameters, especially the higher gravity obtained with respect to
previous analyses, reduce the discrepancies claimed by Fulbright and
Kraft [AJ 118 (1999) 527] between the oxygen abundances determined
from OH and [O I] λ 6300 Å lines, and give a similar abundance from
the O I triplet for BD+23° 3130. A mean value of the oxygen-to-iron
ratio [O/Fe]=0.78±0.16 for this star is fully consistent with the
abundances derived from the three sets of features. This consistency,
which is found using 1D hydrostatic model atmospheres, strongly
constrains the effects predicted by 3D hydrodynamical models on
these three indicators. The oxygen abundances derived for this new
sample confirm previous findings for a progressive linear increase
in the oxygen-to-iron ratio with a slope -0.33±0.02 (including NLTE
corrections to the iron abundances for all the stars considered)
from solar metallicity to [Fe/H]∼-3, and [O/Fe] values as high as
∼1.1 for stars with [Fe/H]<-2.5. These results can be interpreted
as evidence for oxygen overproduction in the very early epoch of the
formation of the Galactic halo, possibly associated with supernova
events with very massive progenitor stars.
---------------------------------------------------------
Title: Five-minute oscillations above granules and intergranular lanes
Authors: Khomenko, E. V.; Kostik, R. I.; Shchukina, N. G.
2001A&A...369..660K Altcode:
We discuss the links between the photospheric 5-min oscillations and
the granulation pattern using a 30-min time series of CCD spectrograms
of solar granulation recorded with high spatial (0{<SUP>”</SUP>}5) and
temporal (9.3 s) resolution. The observed images contain the Fe \sc{i
5324 Å spectral line with good height coverage from the low photosphere
up to the temperature minimum region. Amplitudes, phases and periods
of the 5-min oscillations are found to be different above granules
and intergranular lanes. Strong oscillations occur well separated
temporally and spatially. Many features of this different behaviour
can be described in the frame of a relatively simple model of wave
propagation in the solar atmosphere. To that aim, we have introduced
oscillations into a 3D snapshot of a theoretical time dependent solar
model atmosphere. NLTE synthesis of the time series of the Fe \sc{i
5324 Å line profiles was performed taking into account granular and
oscillatory components of the velocity field. Both, observations and
theoretical modeling, lead to similar results: (i) oscillations above
granules and intergranular lanes occur with different periods; (ii)
the most energetic intensity oscillations occur above intergranular
lanes; the most energetic velocity oscillations occur above granules
and lanes with maximum contrast, {i.e.} above the regions with maximum
convective velocities; (iii) velocity oscillations at the lower layers
of the atmosphere lead oscillations at the upper layers in intergranular
lanes. In granules the phase shift is nearly zero. We conclude that
differences in oscillations above granules and lanes are caused mainly
by variations of the physical conditions in these structures.
---------------------------------------------------------
Title: Fe I Lines in the Spectra of Solar-like Stars: NLTE Effects,
Temperature Diagnostics and the Iron Abundance (CD-ROM Directory:
contribs/shchukin)
Authors: Shchukina, N. G.; Trujillo Bueno, J.
2001ASPC..223..868S Altcode: 2001csss...11..868S
No abstract at ADS
---------------------------------------------------------
Title: Oxygen abundances in very metal-poor stars
Authors: García López, R. J.; Israelian, G.; Rebolo, R.; Bonifacio,
P.; Molaro, P.; Basri, G.; Shchukina, N.
2001hsa..conf..221G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Simulation of Temporal Variations of the Solar Line Fe
I 532. 4185 nm by the 5-min Oscillations (CD-ROM Directory:
contribs/khomenko)
Authors: Khomenko, E. V.; Shchukina, N. G.
2001ASPC..223..680K Altcode: 2001csss...11..680K
No abstract at ADS
---------------------------------------------------------
Title: Granulation and five-minute oscillations
Authors: Khomenko, E. V.; Kostik, R. I.; Shchukina, N. G.
2000KFNTS...3..431K Altcode:
We discuss the links between the photospheric 5-min oscillations and
granulation patterns using a 30-min time series of CCD spectral images
of solar granulation recorded with high spatial (0.5”) and temporal
(9.3 s) resolution. The observed images contain Fe I 5324 Å line. Our
observations and theoretical modeling lead to the similar results:
(i) period of oscillations varies above granules and lanes; (ii)
amplitudes of the velocity oscillations grow with the contrast of
granulation. Amplitudes of the intensity oscillations are larger in
intergranular lanes than in granules. Our simple model describes the
basic features of the oscillations above granules and intergranular
lanes. We conclude that differences in these oscillations are caused
mainly by variations of the physical conditions in these structures.
---------------------------------------------------------
Title: Interaction of Granulation with the 5-min Photospheric
Oscillations
Authors: Kostik, R. I.; Shchukina, N. G.; Khomenko, E. V.
1999ESASP.448..319K Altcode: 1999ESPM....9..319K; 1999mfsp.conf..319K
No abstract at ADS
---------------------------------------------------------
Title: Fe I lines in the spectra of cool stars: NLTE corrections of
iron abundance in the Sun.
Authors: Shchukina, N. G.
1999KFNT...15..523S Altcode: 1999KNFT...15..523S
A self-consistent solution of the kinetic and radiative transfer
equations is carried out for two types of solar-like model atmospheres
using a very realistic iron atomic model. The results were used to
investigate the NLTE effects in the solar photospheric iron abundance
determined from Fe I lines. The author shows that the errors in the
solar photospheric abundance due to these effects can be statistically
described by functions depending on line formation height and excitation
potential of the lower level.
---------------------------------------------------------
Title: Local 5-min oscillations above solar granules and intergranular
space
Authors: Kostyk, R. I.; Shchukina, N. G.
1999AstL...25..678K Altcode:
A time series of granulation spectral images with high spatial (less
than 0.5 arcsec) and temporal (9.3 s) resolutions has been obtained with
the German vacuum tower telescope (VTT) on the Canary Islands in an
effort to study the local 5-min solar oscillations. Observations were
carried out with a CCD array in the FeI lambda 532.4185-nm line.The
5-min intensity and velocity fluctuations near the temperature minimum,
where this line originates, are shown to respond differently to the fine
photospheric structure. The most energetic velocity fluctuations occur
above the regions where the convective velocities are at a maximum;
the main power of the velocity fluctuations above granules concentrates
at lower frequencies than that in integranular space. The amplitude
of the intensity fluctuations in the lambda 532.4185-nm emission above
granules is, on the average, approximately a factor of 2 smaller.
---------------------------------------------------------
Title: Five-minute oscillations and fine structure of the solar
photosphere. II.
Authors: Kostyk, R. I.; Shchukina, N. G.
1999KFNT...15..135K Altcode: 1999KNFT...15..135K
The evolution of spectra of the solar Fe I λ 532.4185 nm line averaged
statistically over granules and intergranules of different brightness
are studied. The observations were carried out with the Vacuum Tower
Telescope at the Observatorio del Teide, Tenerife. The response to
the fine structure of the lower photosphere turns out to be clearly
different for the five minute oscillations of the velocity and the
intensity observed in such spectra. The amplitudes of line intensity
oscillations above intergranular lanes are nearly two times larger
than over granules. The power spectrum of intensity oscillations
is dominated by high-frequency oscillations, while the velocity
oscillations gain power in the low-frequency band. The amplitudes of
the velocity oscillations over granules and intergranules of the same
brightness contrast are virtually equal. The most energetic velocity
oscillations are shown to occur over areas where the largest convective
velocities are observed.
---------------------------------------------------------
Title: Five-minute oscillations and the fine structure of the solar
photosphere. I.
Authors: Kostyk, R. I.; Shchukina, N. G.
1999KFNT...15...25K Altcode: 1999KNFT...15...25K
The authors analyse the spatial relationship between the solar
granulation and the local five-minute oscillations of velocity and
intensity observed in the Fe I λ532.4185 nm line. The time series of
CCD spectral images of solar granulation taken at the Germany Vacuum
Tower Telescope (VTT) were recorded with high spatial (<0.5 arcsec)
and temporal (9.3 s) resolution. In the temperature minimum region,
where the line is formed, the most energetic intensity oscillations
are shown to occur mainly over dark intergranular lanes, while strong
velocity oscillations are observed over granules and intergranules. The
amplitude of the latter oscillations increases with the granulation
brightness contrast. The spatially averaged power of intensity
oscillations is concentrated at higher frequencies compared to the
power of velocity oscillations.
---------------------------------------------------------
Title: Five-minute oscillations and the fine structure of the solar
photosphere. II.
Authors: Kostyk, R. I.; Shchukina, N. G.
1999KPCB...15..102K Altcode:
The authors examine the evolution of the solar Fe I λ 532.4185 nm line
spectrum averaged over granules and intergranular lanes of different
brightness. The five-minute velocity and intensity oscillations
observed in this spectrum are shown to occur differently over various
fine-structure features in the photosphere. The amplitudes of line
intensity oscillations above intergranular lanes are nearly twice as
large as above granules. The bulk of the power of these oscillations
fall on high frequencies, while the velocity oscillations gain their
power in the low-frequency band. The velocity oscillation amplitudes
are virtually equal over granules and dark lanes of the same brightness
contrast. The most energetic velocity oscillations are observed over
the areas with the highest convection velocities,.
---------------------------------------------------------
Title: Five-minute oscillations and the fine structure of the solar
photosphere. I.
Authors: Kostyk, R. I.; Shchukina, N. G.
1999KPCB...15...16K Altcode:
The authors analyze the spatial relationship between the solar
granulation and the local five-minute velocity and intensity
oscillations observed in the Fe I λ532.4185 nm line. The spectral
granulation images were recorded with high spatial and temporal
resolution (<0.5 arcsec and 9.3 s) at the German Vacuum Tower
Telescope. In the temperature minimum region, where the line is
formed, the most energetic intensity oscillations occur mainly over
dark intergranular lanes. Strong velocity oscillations are observed
over granules and intergranules, their amplitude increasing with
the granulation brightness contrast. The space-averaged intensity
oscillation power is concentrated at higher frequencies compared to
the power of velocity oscillations.
---------------------------------------------------------
Title: Fe I lines in spectra of cool stars: temperature diagnostic
of the solar-like atmosphere.
Authors: Shchukina, N. G.
1998KFNT...14..415S Altcode: 1998KNFT...14..415S
NLTE modelling of Fe I lines is employed with a comprehensive atomic
models and for a few models of solar-like atmosphere. Errors that arise
in LTE inversion of these lines to recover temperature of the atmosphere
are estimated. The temperature uncertainties due to the neglect of
NLTE effects in the Fe I lines depend on the line formation height and
on the excitation potential of the lower level EPL as a parameter. The
errors might reach a few hundred degrees for the photospheric lines and
thousand degrees for the chromospheric ones. LTE inversion techniques
generally lead to structures with temperature monotonically decreasing
outside while there are appreciable differences between structures
recovered using various EPL classes of the Fe I lines. Among all these
lines three subclasses are selected for whom the LTE assumption masks
the NLTE effects in the same structure. The latter turns out to be a
HOLMUL-like if the "real Sun" is close to the MACKKL model.
---------------------------------------------------------
Title: Fe I lines in spectra of cool stars: NLTE effects in solar-like
atmosphere.
Authors: Shchukina, N. G.; Trujillo Bueno, J.
1998KFNT...14..315S Altcode: 1998KNFT...14..315S
A detailed NLTE investigation of Fe I lines is carried out for the
MACKKL quiet solar atmospheric model using a very realistic iron atomic
model. This improved atomic model consists of about 250 multiplets and
nearly 500 UV, optical and IR bound-bound and bound-free transitions
including the regime near the Fe I continuum. The authors find and
discuss some interesting statistical regularities with respect to
the errors found for the heights of formation, source functions,
equivalent widths and the central depths of the Fe I lines when the
LTE approximation is adopted.
---------------------------------------------------------
Title: Fe I lines in the spectra of cool stars: NLTE effects in
solar-like atmospheres.
Authors: Shchukina, N. G.; Trujillo Bueno, J.
1998KPCB...14..242S Altcode:
A detailed NLTE investigation of Fe I lines is carried out within
the framework of the MACKKL model of the quiet solar atmosphere. The
authors used a realistic iron atom model which allows for the fine
term structure and has about 250 levels; it involves nearly 500 UV,
optical, and IR bound-bound and bound-free transitions and includes the
conditions near the Fe I continuum. Errors that arise in the heights
of formation, source functions, equivalent widths, and central depths
of the Fe I lines within the LTE approximation are statistically
studied. The authors demonstrate that the behavior of the errors can
be described by a parametric set of curves depending on height of
line formation, the parameter being the excitation potential of the
lower level.
---------------------------------------------------------
Title: Fe I lines in the spectra of cool stars: temperature
diagnostics of solar-like atmospheres.
Authors: Shchukina, N. G.
1998KPCB...14..317S Altcode:
The NLTE modeling of Fe I lines was carried out with a realistic
iron atom model for several solar-like model atmospheres. The author
found that the LTE inversion used to reconstruct the atmospheric
temperature from these lines gave rise to temperature errors which
depend on the height in the atmosphere and the excitation potential
of the lower level. The errors may be as large as several hundred
degrees for the photospheric lines and several thousand degrees for
the chromospheric lines. The lines in different EPL classes are shown
to reconstruct various structures with temperatures monotonically
decreasing outward. The author selected three subclasses of Fe I lines
for which the LTE approximation masks the NLTE effects by a unique
temperature-height relationship. This relationship closely matches the
temperature distribution in the HOLMUL model provided that the actual
solar atmosphere is close to the MACKKL model.
---------------------------------------------------------
Title: NLTE effects in iron spectrum of sunspots.
Authors: Shchukina, N. G.; Trujillo Bueno, J.
1998IBUAA..12R..32S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Problem of iron abundance in the solar photosphere.
Authors: Kostyk, R. I.; Shchukina, N. G.; Rutten, R. J.
1998BCrAO..94..118K Altcode:
The authors analyze the causes of the discrepancies.
---------------------------------------------------------
Title: High spatial resolution observations of the solar spectral
lines.
Authors: Kostyk, R. I.; Shchukina, N. G.; Briand, C.
1998IBUAA..12...39K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Are NLTE effects important for the inversion of iron lines?
Authors: Socas-Navarro, H.; Trujillo Bueno, J.; Ruiz Cobo, B.;
Shchukina, N. G.
1997joso.proc...86S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Is LTE a Suitable Approximation for Fe I - based Diagnostics
of the Thermal Structure of Sunspots?
Authors: Shchukina, N. G.; Trujillo Bueno, J.
1997ASPC..118..207S Altcode: 1997fasp.conf..207S
NLTE effects in iron lines are carefully investigated for the
sunspot umbral model of Maltby et. al. (1986). Our model atom is
realistic: it has hundreds of levels including many high-excited
ones among which infrared transitions take place. The self-consistent
solution of the kinetic and radiative transfer equations is obtained
using recently-developed multilevel transfer methods suitable for
efficiently handling hundreds of radiative transitions in detail
from the ultraviolet to the infrared. These NLTE multilevel transfer
calculations allow us to investigate whether the currently-used LTE
approximation is suitable for diagnosing the temperature structure of
sunspots via Fe I lines.
---------------------------------------------------------
Title: The Instrumentation of the Main Astronomical Observatory of
the National Academy of Sciences of Ukraine
Authors: Kostik, R. I.; Shchukina, N. G.
1997ASPC..118..372K Altcode: 1997fasp.conf..372K
The instrumentation and observational programs of the Solar Physics
Department of the Main Astronomical Observatory are described. The
observatory has two solar horizontal telescopes. The first one is the
44 cm telescope located near Kyiv. This telescope has a spectrograph
with a double pass system. It was designed for low scattered light
and high spectral resolution. The second one is installed at Terskol
High-Altitude Station in the Central Caucasus, at an altitude of 3100
m. This 65 cm telescope with its spectrograph is used for simultaneous
photoelectric and photographic measurements of five solar spectral
regions in the range from 3000 Angstroms to 12000 Angstroms. One of the
scientific programs consists in the observation of solar irradiance
fluctuations with the DIFOS photometer aboard the Ukraine-Russian
satellite CORONAS-I, which was launched on March 2, 1994. These space
observations will be continued during the new mission CORONAS-F.
---------------------------------------------------------
Title: The solar iron abundance: not the last word.
Authors: Kostik, R. I.; Shchukina, N. G.; Rutten, R. J.
1996A&A...305..325K Altcode:
Determinations of the solar iron abundance have converged to the
meteoritic value with the FeII studies of Holweger et al. (1990),
Biemont et al. (1991) and Hannaford et al. (1992) and the FeI results
of Holweger et al. (1991). However, the latter authors pointed out
that Blackwell et al. (1984) obtained a discordant result from similar
oscillator strengths. A recent debate on this lingering discrepancy
by the Oxford and Kiel contenders themselves has not clarified
the issue. We do so here by showing that it stems from systematic
differences between equivalent widths and oscillator strengths which
masquerade as difference in fitted damping enhancement factors. We first
discuss the various error sources in classical abundance determination
and then emulate both sides of the debate with abundance fits of our
own. Our emulation of the Oxford side shows that the abundance anomaly
claimed by Blackwell et al. (1984) for solar FeI 2.2eV lines vanishes
when equivalent width measurements from other authors are combined
with better evaluation of the collisional damping parameter. On the
Kiel side, we find that the oscillator strengths of Bard et al. (1991)
used by Holweger et al. (1991) produce a suspicious trend when used
to fit solar FeI lines, whereas comparable application of oscillator
strengths from Oxford does not. The trend is mainly set by categories
of FeI lines not measured at Oxford; for lines of overlap the two sets
agree and deliver the iron abundance value A_Fe_=7.62+/-0.04 which
exceeds the meteorite value. The dissimilar lines may suffer from
solar line-formation effects. We conclude that the issue of the solar
iron abundance remains open. Definitive oscillator strengths are still
needed, as well as verification of classical abundance determination
by more realistic representations of the solar photosphere and of
photospheric line formation.
---------------------------------------------------------
Title: Solar oscillator strengths for neutral calcium lines of the
singlet system.
Authors: Shchukina, N. G.; Perekhod, A. V.
1996KPCB...12b..45S Altcode: 1996KPCB...12...45S
The oscillator strengths of twelve neutral calcium lines of the singlet
system were determined by fitting the theoretical equivalent widths and
central depths of the lines to those observed in the solar spectrum
at the disk center. The neglect of departure from LTE was found to
produce uncertainties of about 0.2 dex on the average in the oscillator
strengths derived from equivalent widths. The oscillator strengths
deduced from central depths turn out to be much mote sensitive to
NLTE effects. Uncertainties increase with line depth and are as high
as 1.5 dex for the strongest lines.
---------------------------------------------------------
Title: Is the problem of solar iron abundance solved?
Authors: Kostik, R. I.; Shchukina, N. G.
1995AdSpR..15g..69K Altcode: 1995AdSpR..15...69K
We revise the solar photospheric abundance of iron from Fe I lines
based on two scales of oscillator strengths gf (Oxford [1-6] and Kiel
[7]). In order to answer the question of Holweger et al. [8] why the
gf of both scales agree but abundances deviate, we analyse different
sources of errors in the solar iron abundance determinations. The
most important reason of the abundance discrepancy is connected with
the damping enhancement factor, E. However, the results obtained do
not allow to infer a final value of the solar iron abundance. The
“high” abundance derived from the Oxford scale of gf [2] seems to be
more preferable in view of a smaller root mean square error epsilon in
the iron abundance determination and a more pronounced minimum of the
function epsilon(E) in comparison with the “low” abundance case [8].
---------------------------------------------------------
Title: The Determination of the Solar Iron Abundance from Fe I Lines
Authors: Kostik, R. I.; Shchukina, N. G.; Rutten, R. J.
1995ASPC...78..399K Altcode: 1995aapn.conf..399K
No abstract at ADS
---------------------------------------------------------
Title: Solar oscillator strengths for neutral calcium lines of the
triplet system.
Authors: Shchukina, N. G.; Perekhod, A. V.
1994KFNT...10...32S Altcode: 1994KNFT...10...32S
No abstract at ADS
---------------------------------------------------------
Title: Does the iron abundance anomaly obtained from the 2.2 eV Fe
I lines really exist in the solar atmosphere?
Authors: Kostyk, R. I.; Shchukina, N. G.
1994KFNT...10...51K Altcode: 1994KNFT...10...51K
No abstract at ADS
---------------------------------------------------------
Title: The non-LTE formation of Li I lines in cool stars
Authors: Carlsson, M.; Rutten, R. J.; Bruls, J. H. M. J.; Shchukina,
N. G.
1994A&A...288..860C Altcode:
We study the non-LTE (non local thermodynamic equilibrium)
formation of Li I lines in the spectra of cool stars for a grid of
radiative-equilibrium model atmospheres with variation in effective
temperature, gravity, metallicity and lithium abundance. We analyze
the mechanisms by which departures from LTE (local thermodynamic
equilibrium) arise for Li I lines, first for the young sun (prior to
its lithium depletion) and then across the cool-star grid. There are
various mechanisms which compete in their effects on emergent Li I
line strengths. Their neglect produces errors in lithium abundance
determinations that vary in sign as well as size, both across the
stellar grid and between different Li I lines (Figs). The errors are
appreciable for all cooler stars and largest for cool lithium-rich
metal-poor giants. They reverse sign between lithium-rich stars and
lithium-poor stars for the λ=670.8nm resonance line, but not for the
λ=610.4nm subordinate line. The non-LTE corrections are large enough
that they should be taken into account in ongoing debates on lithium
synthesis and depletion. We provide convenient numerical approximations
of our results (Table 1) to this purpose. We end the paper with some
examples in which non-LTE corrections change the slope of published
relationships.
---------------------------------------------------------
Title: Is the problem of solar iron abundance solved?
Authors: Kostyk, R. I.; Shchukina, N. G.
1994KFNT...10...54K Altcode: 1994KNFT...10...54K
The authors revised the solar iron abundance from photospheric Fe
I lines using two scales of oscillator strengths gf. The first one
is Oxford high-precision laboratory measurements of Fe I transition
probabilities. The second scale recently obtained in a hollow-cathode
experiment by Bard et al. differs from the former by 0.03 dex in the
absolute scale. The abundance values A = 7.64±0.04 and A = 7.50±0.07
respectively were determined. In order to explain the puzzle why gf
of both scales agree but abundances deviate the authors have analysed
the possible sources of errors in determinations of solar abundance.
---------------------------------------------------------
Title: The Non-LTE Formation of Li I Lines from Cool Stars
Authors: Carlsson, M.; Rutten, R. J.; Bruls, J. H. M. J.; Shchukina,
N. G.
1994ASPC...64..270C Altcode: 1994csss....8..270C
No abstract at ADS
---------------------------------------------------------
Title: The formation of helioseismology lines. I. NLTE effects in
alkali spectra.
Authors: Bruls, J. H. M. J.; Rutten, R. J.; Shchukina, N. G.
1992A&A...265..237B Altcode:
The authors study the NLTE formation of the solar K I and Na I resonance
lines employed in helioseismology. They combine standard modeling of
the solar atmosphere with comprehensive alkali model atoms, complete
up to the Rydberg regime near the continuum, to study various NLTE
mechanisms which interact to make the alkali population balances more
complex than is the case for other minority species. In particular,
they discuss a "photon suction" process which produces overpopulation
of the neutral stage by driving a population flow from the reservoir in
the singly ionized stage. They isolate this and other mechanisms with
specifically tailored model atoms and provide a choice of simplified
model atoms, trading precision against size, which are appropriate
for future use in numerical simulations of the solar atmosphere.
---------------------------------------------------------
Title: The formation of the MG I emission features near 12 microns
Authors: Carlsson, M.; Rutten, R. J.; Shchukina, N. G.
1992A&A...253..567C Altcode:
The formation of two Mg I 12-micron emission features in the
solar spectrum, the existence of which was reported by Murcray et
al. (1981), is explained using plane-parallel nonlocal thermodynamic
equilibrium modeling with a radiative-equilibrium model atmosphere
without chromosphere. It is shown that these emissions are a natural
consequence of population depletion by line photon losses followed by
population replenishment from the ionic reservoir in the highly excited
levels. The results confirm the suggestion by Lemke and Holweger (1987)
that the 12-micron lines are formed in the photosphere and disprove
the claim by Zirin and Popp (1989) that the temperature minimum occurs
much deeper than in standard models of the solar atmosphere.
---------------------------------------------------------
Title: Formation of the MG 112 TTM Lines
Authors: Carlsson, M.; Rutten, R. J.; Shchukina, N. G.
1992ASPC...26..518C Altcode: 1992csss....7..518C
No abstract at ADS
---------------------------------------------------------
Title: The formation mechanism of the lines of the C I solar infrared
multiplet λ1069,5 nm.
Authors: Shchukina, N. G.
1991KFNT....7...38S Altcode: 1991KNFT....7...38S
The formation mechanisms of the C I infrared multiplet lines for
the solar atmosphere are discussed. The NLTE level population of the
multiplet is caused by two circumstances: the pumping of the lower
level by ultraviolet photons of the C I lines λλ165.72 and 258.29 nm
in the upper photosphere and lower chromosphere; overrecombination and
followed cascade, transitions throughout the atmosphere due to deficit
of photons in the infrared bound-free continua and high-excitation
lines. The latter increases the multiplet levels population
compensating the depopulation through pumped near-ultraviolet lines
that connect the lower level of the multiplet to levels close to the
continuum. Ultraviolet 2.4 - 3.8 eV photons do not affect essentially
the resulting distribution of departure coefficients.
---------------------------------------------------------
Title: The formation mechanism of the lines of the C I infrared
multiplet at λ1069.5 nm in the spectrum of the Sun.
Authors: Shchukina, N. G.
1991KPCB....7d..30S Altcode: 1991KPCB....7...30S
Mechanisms of formation of the lines of the C I infrared multiplet at
λ1069.5 nm in the solar atmosphere are discussed. It is shown that
the principal causes of departure from LTE of its level populations
are "pumping" of the lower level in the upper photosphere and lower
chromosphere by the UV radiation field in the lines λλ165.75 and
258.29 nm and recombination-cascade processes due to an IR-photon
deficit in subordinate bound-free continua and highly excited lines of
C I. These latter processes not only compensate the drainage of atoms
from muliplet levels on absorption of photons of highly excited lines
in the visible region of the spectrum, but also result in additional
population of these levels. Photons of the near UV continuum with
energies of 2.4 - 3.8 eV are incapable of significantly disturbing
the established distribution of the LTE departure coefficients.
---------------------------------------------------------
Title: The effects of departure from the local thermodynamical
equilibrium in the solar Fraunhofer spectrum. Infrared multiplet C
I λ1069.5 nm.
Authors: Shchukina, N. G.; Shcherbina, T. G.
1990KFNT....6...44S Altcode: 1990KNFT....6...44S
The non-LTE formation of the infrared multiplet λ1069.5 nm of neutral
carbon observed in the spectrum of quiet regions on the solar disk is
considered. Departure coefficients of multiplet's levels for a model
atom with twenty levels are obtained. The non-LTE centre-to-limb
profiles and equivalent widths of the lines are evaluated and
compared with the LTE case and observations of de Jager and Neven. The
influence on some profile parameters of uncertainties in the abundance,
damping constant, oscillator strengths, macroturbulent velocities,
local continuum choice, temperature structure of the atmosphere and
the value of departure coefficients is analysed. The lower limit of
solar carbon abundance found from the multiplet is 8.55 dex. The best
agreement with observations is reached for lg A(C) = 8.63.
---------------------------------------------------------
Title: Temperature Diagnostics of the Upper Photosphere
Authors: Shchukina, N. G.; Shcherbina, T. G.; Rutten, R. J.
1990IAUS..138...29S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Formation of the Mg I 12-Micron Emission Lines
Authors: Carlsson, M.; Rutten, R. J.; Shchukina, N. G.
1990PDHO....7..260C Altcode: 1990dysu.conf..260C; 1990ESPM....6..260C
Contents: The Mg I 12 μm line, LTE or NLTE, chromospheric formation,
photospheric formation, collisional NLTE; departure diffusion.
---------------------------------------------------------
Title: Symposium No.138 of the International Astronomical Union
"Solar photosphere: structure, convection and magnetic fields",
held in Kiev, USSR, 15 - 20 May, 1989.
Authors: Shchukina, N. G.
1989KFNT....5...89S Altcode: 1989KNFT....5...89S
No abstract at ADS
---------------------------------------------------------
Title: Book Review: The galaxy and the solar system. / U Arizona
Press, 1986.
Authors: Kotov, V. A.; Kostik, R.; Shchukina, N.; Švestka, Zdeněk;
Kotov, V. A.
1988SoPh..115..203K Altcode: 1988SoPh..115..203S
No abstract at ADS
---------------------------------------------------------
Title: The effects of departure from the local thermodynamical
equilibrium in the solar Fraunhofer spectrum. Oxygen.
Authors: Shchukina, N. G.
1987KFNT....3...36S Altcode:
The non-LTE formation of the O I lines λλ 130.2 - 130.6, 135.6 -
135.9, 777.2 - 777.5, 844.6 nm observable in the spectrum of quiet
regions on the solar disk is discussed. The departure coefficients for
twelve levels of O I and O II are obtained. The non-LTE center-to-limb
profiles and equivalent widths of the lines are evaluated and
compared with LTE-case and with observations. The influence of
radiative and collisional processes, hydrogen radiation of Lyman-β
and Lyman-continuum is analysed. The non-LTE effects for lines of O I
are higher than the errors of precise solar observations and must be
taken into account.
---------------------------------------------------------
Title: The effects of deviation from local thermodynamical equilibrium
in the solar Fraunhofer lines. K I resonance line λ769.9 nm.
Authors: Shchukina, N. G.
1987KFNT....3...40S Altcode:
The non-LTE formation of the K I resonance line λ769.9 nm observed in
the spectrum of quiet regions on the solar disk is discussed. Deviation
from LTE coefficients for six levels of K I are obtained. Non-LTE
effects in the line source function and centre-to-limb profiles
are evaluated. The influence of some parameters on the solution
is analysed. The centre-to-limb variations of theoretical residual
central intensity and profile of λ769.9 nm are in close agreement
with observations. The conclusion is made that LTE-assumption is not
valid for the K I resonance line. The improved abundance of potassium
is lg A(K) = 5.08±0.1.
---------------------------------------------------------
Title: Excitation and ionization rates of neutral carbon by electrons.
Authors: Shchukina, N. G.; Shcherbina, T. G.
1986KFNT....2...31S Altcode:
A unified simple algorithm (as a function a parameter Θ) is suggested
for calculation of excitation and ionization rates of the C I atom by
electron impact according to approximation functions most frequently
used in stellar spectroscopy. The parameter Θ is tabulated for some
collisional transitions of the C I atom in the temperature range T =
2000 - 50,000K. The algorithm is of particular interest for the non-LTE
synthesis problem.
---------------------------------------------------------
Title: All-Union conference on "Radiation and composition of the sun",
held in Pulkovo, 9 - 11 October 1985.
Authors: Gurtovenko, Eh. A.; Shchukina, N. G.
1986KFNT....2...95G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The effect of radiation on the population of oxygen levels
in the solar atmosphere. III. The radiation field of O I bound-free
continua.
Authors: Shchukina, N. G.
1986KFNT....2...14S Altcode:
The effect of solar radiation in the bound-free continuum of neutral
oxygen on the population of high-excited O I levels and lower O
II levels is studied. The Lyman continuum radiation field in the
upper chromosphere is shown to rise the pumping of high-excited
levels of neutral oxygen. Peculiarities of departure of the oxygen
ionization equilibrium from LTE are caused by deviation of the mean
bound-free intensity from the Planck function. In the absence of the
chromosphere oxygen over-ionization occurs in the upper layers of the
solar atmosphere.
---------------------------------------------------------
Title: On the role of the collisional processes in the formation of
the O I solar resonance doublet 1355-8 Å.
Authors: Shchukina, N. G.
1986BSolD1985...49S Altcode:
The importance of collisional excitation of the
<SUP>5</SUP>S<SUP>0</SUP>-level and collisional coupling between higher
triplet-quintets levels for formation of solar oxygen doublet 1355-8
Å is considered. The collisional coupling of these levels causes a
considerable dependence of doublet intensity on Lyman pumping of the
<SUP>3</SUP>D<SUP>0</SUP>-level O I.
---------------------------------------------------------
Title: The influence of radiation on the population of oxygen levels
in the solar atmosphere. II. The radiation field of O I lines with
account ofinterlocking and subordinate photoionization processes.
Authors: Shchukina, N. G.
1985KFNT....1...56S Altcode:
Radiative interlocking of neutral oxygen lines is shown to increase the
non-LTE effects in those solar atmosphere layers where O I levels are
underpopulated. The occupation numbers of <SUP>5</SUP>S<SUP>0</SUP>
atoms of O I are found to be dependent considerably on the radiation
field of the quintet lines 926.6,777.2-.5 nm in the chromosphere and the
temperature minimum region. The departure coefficients of neutral oxygen
levels are sensitive to chromospheric temperature inversion. The effects
of a radiative field of the solar hydrogen L<SUB>&</SUB>beta; line
is considered for its effect on the occupation number of neutral oxygen.
---------------------------------------------------------
Title: The influence of radiative processes on the population of
atomic oxygen levels in the solar atmosphere. I. The radiation field
of the Lymancontinuum and O I lines without interlocking.
Authors: Shchukina, N. G.
1985KFNT....1...29S Altcode:
Radiative transfer in lines of neutral oxygen, its bound-free ground and
singlet continua are analyzed for their effect of the population of the
O I singlet, triplet, quintet states and the first states of O II. The
Lyman continuum radiation field does not affect the LTE departure
coefficients of highly-excited O I levels, if interlocking effects are
neglected. The departure coefficients of these levels are controlled by
the radiation field of neutral oxygen lines. The departure from LTE for
O II is due mainly to photoionization processes (for the chromosphere)
and radiative processes in the O I lines (for the photosphere).
---------------------------------------------------------
Title: Temperature effects when interpreting the dependence of oxygen
red triplet strengths on the luminosity of a star.
Authors: Shchukina, N. G.
1985KFNT....1...26S Altcode:
Some temperature effects are considered which should be taken into
account under the non-LTE consideration of dependence of the strengths
of the neutral oxygen red triplet 777.2 - 777.5 nm on the luminosity
of the star. The non-LTE equivalent widths of these lines are shown
to be of higher sensitivity (as compared with the LTE-case) to the
temperature distribution in the region of their formation.
---------------------------------------------------------
Title: The influence of the formation of CO molecules on solar
oxygen lines.
Authors: Shchukina, N. G.
1985BSolD1985...50S Altcode:
The formation of CO molecules in the upper photosphere is shown to be
of no great importance for non-LTE profiles of neutral oxygen lines:
1355-8, 7772-5, 8446 Å. The central intensities of these lines are
increased by no more than 1%.
---------------------------------------------------------
Title: On measurements of the solar spectral energy transmitted
through narrow-band filters.
Authors: Gurtovenko, Eh. A.; Troyan, V. I.; Shchukina, N. G.
1985ppic.conf...47G Altcode:
The calculations have been carried out and practical recommendations
were given to construct a photometric model of solar radiation in
absolute energy units for the wavelength range of 0.32 - 1.2 μm.
---------------------------------------------------------
Title: On the Role of Recombination Cascade Processes for the
Formation of the Solar Resonance Doublet I355-OA-OI
Authors: Shchukina, N. G.
1985BSolD...7...78S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Influence of Formation of Co/ Molecule on the Solar
Oxygen Lines
Authors: Shchukina, N. G.
1985BSolD...8...50S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the role of recombination-cascade processes for the
formation of the solar resonance doublet 1355-8 Å O I.
Authors: Shchukina, N. G.
1985BSolD1985...78S Altcode:
The contribution of radiative terms in the line source function of
the solar resonance doublet 1355-8 Å is discussed. The lines of this
doublet are shown to be collision-dominated provided radiative processes
in 9266 and 7772-5 Å O I are compensated by that of 1355-8 Å. The
negligibility of the interlocking of 9266, 7772-5 Å with 1355-8 Å
in non-LTE approach weakens the intensity of the doublet nearly by a
factor of 5.
---------------------------------------------------------
Title: On the Role of Collisional Processes in the Formation of the
Solar Resonance Doublet 1355-8A OI
Authors: Shchukina, N. G.
1985BSolD..12...49S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the importance of some parameters of the solar
spectrum synthesis of neutral potassium under non-LTE
conditions. III. Temperature.
Authors: Shchukina, N. G.
1985BSolD1985...84S Altcode:
The temperature effects on the profile of the resonance line λ7699
are discussed. The increase of temperature by 300K in the temperature
minimum region is shown to change the central residual intensity of
this line by 12%.
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Title: The Importance of Some Parameters in Non-Lte Solar Spectrum
Synthesis of Neutral Potassium KI - Part Two
Authors: Shchukina, N. G.
1983BSolD...1...71S Altcode:
No abstract at ADS
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Title: On the importance of some parameters of the solar
spectrum synthesis of neutral potassium under non-LTE
conditions. II. Photoionization.
Authors: Shchukina, N. G.
1983BSolD1983...71S Altcode:
The significance of the methods of mean intensity calculations in
the photoionization continuum is considered for non-LTE spectrum
synthesis. It is found that photoionization mean intensity
uncertainties, arising from the choice of these methods, produce
markedly stronger changes in departure coefficients and profile of the
resonance line λ 7699 than photoionization cross-section uncertainties.
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Title: On the importance of some parameters of the solar
spectrum synthesis of neutral potassium under non-LTE
conditions. I. Multi-level structure.
Authors: Shchukina, N. G.; Alexsandrova, I. I.
1982BSolD1982..100S Altcode:
The multilevel effects on departure coefficients, source functions and
profile of the resonance line λ 7699 K I are discussed. The four-level
and seven-level atom models of neutral potassium are compared. Both
atom models give a rather better agreement in the λ 7699 K I source
function and departure coefficients. The additional higher energy
levels do not influence the centre to limb profile synthesis of λ 7699.
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Title: Deviation from local thermodynamic equilibrium in the solar
atmosphere - Results of investigations
Authors: Shchukina, N. G.
1981AAfz...44...24S Altcode:
Results of studies on the effect of deviation from LTE on the solar
Fraunhofer spectrum are summarized. Deviation from LTE is expected to
occur in lines of all strengths formed at depths above tau<SUB>c</SUB>
equal to unity (where tau<SUB>c</SUB> is the continuum optical
depth). Forbidden lines of the Fraunhofer spectrum probably have
LTE source functions. In the continuum the deviation from LTE exists
in the UV (2500-912 A and the Lyman continuum), while the visible,
IR, millimeter, and centimeter continua are evidently formed in LTE
conditions.
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Title: Analysis of the solar spectrum of neutral potassium, with
allowance for deviation from LTE. I - Initial estimates of level
populations
Authors: Shchukina, N. G.
1981AAfz...45...13S Altcode:
No abstract at ADS
