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1.
A. V. Shavrina N. S. Polosukhina J. Zverko V. Khalak V. V. Tsymbal J. Žižňovský 《Astronomy Reports》2001,45(10):784-796
The spectra of two roAp stars have been analyzed as part of a project to study lithium in magnetic Ap stars. Variability of the Li I 6708 Å resonance doublet and rare-earth lines was detected, which can be explained using an oblique rotator model with the lithium spots located at the magnetic poles. Synthetic spectra obtained at different rotational phases have yielded the first data on the atmospheric chemical compositions of these spotted stars. Using refined atomic data and the most complete line lists has enabled a detailed study of the spectra near the Li I 6708 Å line and computation of the Li I line profile taking into account the spotted distribution of the lithium over the stellar surfaces. The positions of two lithium spots and lithium abundances for each of the spots have been determined. 相似文献
2.
We investigate the HD 182255, a star earlier suspected to be helium-weak. We show it to be a SiHe-w-type CP object. Our study
revealed four regions with anomalous elemental abundances on the stellar surface near the equator of rotation. Its magnetic
field could not be measured, apparently due to the unfavorable orientation of the star. The star is seen almost (rotation)
pole on, the inclination of its rotation axis is i = 12°. The magnitude of HD 182255 varies as a result of its rotation owing to the nonuniform distribution of chemical elements
on its surface, which leads to the variable blanketing effect. The helium and silicon abundances increase with depth, i.e.,
the stratification typical of CP stars is observed. The star undergoes nonradial pulsations and nonstationary variations of
the structure of its upper atmosphere. 相似文献
3.
Yu. V. Glagolevskij G. A. Chountonov A. V. Shavrina Ya. V. Pavlenko 《Astrophysics》2010,53(1):133-146
This is a preliminary study of the star HD 35502. Its magnetic field has been measured in different phases of its period.
Preliminary values of the magnetic field parameters have been obtained based on a central quadrupole model. The effective
magnetic field Be varies over 0-5000 G, the average surface magnetic field ranges over 6300-6700 G, the field at the poles
is Bp=7000 G, and the angle between the quadrupole axis and the axis of rotation is β = 80o. As a first approximation, the
surface helium is concentrated around the (negative) pole and for τ > 1 its abundance is reduced by approximately 2-4 dex,
which confirms the hypothesis of helium diffusion under the action of gravitation and wind in a stable atmosphere. The chemical
elements Si and Cr are concentrated in four spots on the magnetic equator between the magnetic poles, or in a ring coincident
with the magnetic equator; precisely which is not clear at present. 相似文献
4.
5.
Yu. V. Glagolevskij A. V. Shavrina J. Sylvestre G. A. Chountonov Ya. V. Pavlenko V. R. Khalak 《Astrophysical Bulletin》2009,64(2):166-175
Surface helium and silicon distribution of a He-weak CP star HD21699 was examined using the spectra obtained at different phases of the star’s rotational period. The abundance of helium over the whole surface is weak, but in the magnetic polar regions it is strong, apparently due to the impact of stellar wind. Silicon accumulates in the region with a horizontal alignment of the magnetic lines, as follows from the theory. The abundance of helium and silicon increases with depth. Moreover, the boundary of the abundance variation is very sharp and its depth practically does not change with the rotational period phase. Accounting for the stratification of chemical elements considerably changes the deduced temperature distribution with depth as well as the form of the hydrogen line profile. 相似文献
6.
The temperature distribution with depth in the atmosphere of the magnetic star HD21699 is modelled for each observed rotational
phase using Hδ line profiles obtained with a signal to noise ratio S/N = 1000. The observed temperature distributions were
averaged within and outside the region of the magnetic spots. It appears that these average temperatures are equal to within
the limits of error. This shows that the magnetic field does not affect the physical condition of the matter in the star and
does not disturb its thermodynamic state. 相似文献
7.
Spectral observations of Ap-CP stars with the BTA (Special Astronomical Observatory, Russian Academy of Sciences) using the
NES echelle spectrometer have revealed several stars with an anomalous lithium abundance. The oscillating star HD 12098, which
is the first roAp star in the northern hemisphere of the sky, merits special attention. Strong, variable LiI 6708 Å line was
observed in the spectrum of this star. There are not enough observations for a reliable analysis by Doppler mapping, but there
are enough to indicate the presence of lithium spots on the surface of this star similar to the roAp stars HD 83368 and HD
60435, on whose surfaces spots with a high lithium abundance have been reliably detected. Parameters for a model of its atmosphere
have been chosen using the method of synthetic spectra based on atmospheric models including lines from the VALD list and
several additional blended REE lines calculated by the authors. The profile of the lithium LiI 6708 Å blend has been calculated
taking the magnetic field into account using the SYNTHM code. A lithium abundance has been determined for two phases of the
rotation of HD 12098 that is anomalously high compared to the solar and meteoritic abundances. The large difference in the
lithium abundance in the two phases (in two different regions on the star's surface) exceeds 0.5 dex and is very close to
that which we have found by analyzing the spectra of the roAp stars HD 83368 and HD 60435. Thus, we have discovered yet another
roAp star, HD 12098, with lithium spots on its surface.
Translated from Astrofizika, Vol. 51, No. 4, pp. 607–616 (November 2008). 相似文献
8.
A reconstruction of the line-of-sight component and modulus of the surface-magnetic-field vector is proposed, using a model with artificial point sources of the magnetic field with “virtual” magnetic charges in the body of a star. This approach for the direct calculation of the field from the superposition of the potentials of individual magnetic charges enables the reconstruction of most possible configurations of the surface magnetic field of a star. Proper choice of the axis orientations for the three coordinate systems used makes it possible to obtain a simple representation for the vector components of the surface magnetic field. In a dipole approximation, the expression for the line-of-sight component of the magnetic field averaged over the visible disk of the star reduces to the form obtained in other studies. 相似文献
9.
A. V. Yushchenko V. F. Gopka A. V. Shavrina V. A. Yushchenko S. V. Vasileva S. M. Andrievsky A. A. Raikov S. Kim P. Rittipruk Y. Jeong Y.-W. Kang 《Kinematics and Physics of Celestial Bodies》2017,33(5):199-216
The chemical composition of the PMMR23 red supergiant located in the Small Magellanic Cloud (SMC) is analyzed. The abundance of 35 chemical elements and the upper limits of abundance for Tl and U are found. The relative abundance of heavy elements is higher by 0.6–1.0 dex with respect to iron peak elements. The spectra of several SMC red supergiants PMMR27, PMMR28, and PMMR144—located in the region where the velocities of stars and interstellar gas are quite high— show the emission components in the wings of the hydrogen line. This emission is not detected for PMMR23. A possibility of interstellar gas accretion on the atmospheres of PMMR23 and other supergiants in Magellanic Clouds is discussed. The analysis is carried out using spectra measured at ESO 3.6 m telescope with the spectral resolving power R = 30000. 相似文献
10.
Principal Astronomical Observatory, Ukrainian Academy of Sciences. Translated from Astrofizika, Vol. 28, No. 3, pp. 595–598, May–June, 1988. 相似文献