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1.
Our high-resolution spectral observations have revealed variability of the optical spectrum of the cool star identified with the IR source IRAS 20508+2011. We measured the equivalent widths of numerous absorption lines of neutral atoms and ions at wavelengths 4300–7930 Å, along with the corresponding radial velocities. Over the four years of our observations, the radial velocity derived from photospheric absorption lines varied in the interval V r⊙ = 15–30 km/s. In the same period, the Hα profile varied from being an intense bell-shaped emission line with a small amount of core absorption to displaying two-peaked emission with a central absorption feature below the continuum level. At all but one epoch, the positions of the metallic photospheric lines were systematically shifted relative to the Hα emission: ΔV r = V r(met) ? V r(Hα, emis) ≈ ?23 km/s. The Na D doublet displayed a complex profile with broad (half-width ≈ 120 km/s) emission and photospheric absorption, as well as an interstellar component. We used model atmospheres to determine the physical parameters and chemical composition of the star’s atmosphere: T eff = 4800 K, log g = 1.5, ξt = 4.0 km/s. The metallicity of the star differs little from the solar value: [Fe/H]⊙ = ?0.36. We detected overabundances of oxygen [O/Fe]⊙ = +1.79 (with the ratio [C/O] ≈ ?0.9), and α-process elements, as well as a deficit of heavy metals. The entire set of the star’s parameters suggests that the optical component of IRAS 20508+2011 is an “O-rich” AGB star with luminosity M v ≈ ?3m that is close to its evolutionary transition to the post-AGB stage. 相似文献
2.
The chemical compositions of the atmospheres of six metal-poor stars are analyzed. Spectra with signal-to-noise ratios of no less than 100 and a resolution of R≈17 000 were obtained using the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. The abundances of Li, O, α-process elements (Mg, Si, Ca, Ti), Na, K, Sc, iron-peak elements (Cr, Mn, Fe, Ni, Cu, Zn), and s-process elements (Y, Ba) are derived. The star G251-54 ([Fe/H]=?1.55, T eff=5541 K, logg=3.58) is deficient in some elements compared to both stars with similar metallicities and the Sun. The atmosphere of G251-54 has the following elemental abundances relative to iron: [O/Fe]=+0.47, [α/Fe]≈?0.3, [Na/Fe]=?0.60, [Sc/Fe]=?0.57, [Cr, Ni, Fe]≈0, [Zn/Fe]=+0.16, [Cu/Fe]=?0.66, [Y/Fe]=?0.70, and [Ba/Fe]=?1.35. The remaining five stars have metallicities in the range ?1.6<[Fe/H]相似文献
3.
The abundances of 19 chemical elements in the atmospheres of five stars belonging to three globular clusters have been determined by applying the model-atmospheremethod to 430.0–790.0 nm spectra obtained with the échelle spectrometer of the 6-m telescope of the Special Astrophysical Observatory. The abundances of silicon, calcium, iron-peak elements, copper, zinc, and neutron-capture elements follow the abundance patterns for halo stars. The abundance of sodium in M 10 giants provides evidence that different mixing mechanisms operate in halo and cluster stars or that light elements are enriched in different ways in the pre-stellar matter from which some globular clusters and halo stars were formed. 相似文献
4.
Klochkova V. G. Panchuk V. E. Tavolzhanskaya N. S. Yushkin M. V. 《Astronomy Letters》2020,46(8):528-540
Astronomy Letters - Evidence of wind variability and velocity stratification in the extended atmosphere has been found in the spectra of the supergiant V340 Ser ( $${=}$$ IRAS 17279 $$-$$ 1119)... 相似文献
5.
We report on the development of a fast crossed-dispersion spectrograph (CRAB) mounted at the Nasmyth focus of the 6-m telescope. The spectrograph is designed for visible and near-infrared (3800–10 500 Å) CCD observations with the spectral resolution R=4000. We give the basic parameters of the optical scheme and the parameters of the echelle frame. We determined the gain involved in putting the spectrograph into observational practice and discuss the possible range of spectroscopic problems for which the instrument is optimal. 相似文献
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7.
The optical layout and performance characteristics of a device for measuring the four Stokes parameters are reported, and the principle of its operation is described. The device is designed for use in the NES echelle spectrograph mounted in the Nasmyth-2 focus of the 6-meter telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. Tests of the device operating on the telescope showed the gain in throughput to be a factor of 2.7 and 6 in the red (5000–7000 Å Å) and blue (3500–4700 Å Å) parts of the spectrum, respectively, compared to an analyzer based on Fresnel rhombi. 相似文献
8.
Valentina G. Klochkova Eugene L. Chentsov Tonu Kipper Vladimir E. Panchuk Nonna S. Tavolganskaya Maxim V. Yushkin 《Astrophysics and Space Science》2011,335(1):83-89
We present a spectral atlas of 4 B and A stars containing spectra in a poorly studied spectral range of 305–452 nm. The atlas
is based on high resolution (R=60 000) spectra obtained with the 6 meter telescope (SAO, Russia) combined with the NES-spectrograph. The procedure of spectral
lines identification and compilation of the atlas is discussed in detail. Using the spectral data we thoroughly investigated
the velocity field in expanding atmospheres and envelopes of hot evolved stars β Ori, α Cyg and supergiant KS Per with the extreme hydrogen deficiency. The complete atlas and list of the identified spectral lines
will be available via the astronomical database SIMBAD. 相似文献
9.
I. I. Romanyuk V. E. Panchuk N. E. Piskunov D. O. Kudryavtsev 《Astrophysical Bulletin》2007,62(1):26-35
The possibility of investigating the vertical structure of the magnetic field in chemically peculiar main-sequence stars is discussed. The nonuniform distribution of chemical elements over the surface complicates the problem substantially. The most efficient measurements are shown to be those of the longitudinal field components based on spectral lines with wavelengths longer and shorter than 3646 Å (shortward and longward of the Balmer jump), which form at different optical depths in the atmosphere. Various methodological problems are addressed that must be overcome in order to accomplish the task. The brightest magnetic star α 2 CVn is observed with the echelle spectrometer equipped with an Uppsala CCD chip. New observations corroborate our previous result: the longitudinal component of the magnetic field B e of the α 2 CVn star increases with depth by about 30% over the atmosphere thickness scale. 相似文献
10.
Peculiarities and variations in the optical spectrum of the post-AGB star V448 Lac = IRAS 22223+4327
Multi-epoch observations with high spectral resolution acquired in 1998–2008 are used to study the time behavior of the spectral-line profiles and velocity fields in the atmosphere and circumstellar shell of the post-AGB star V448 Lac. Asymmetry of the profiles of the strongest absorption lines with lower-level excitation potentials χ low < 1 eV and time variations of these profiles have been detected, most prominently the profiles of the resonance lines of BaII, YII, LaII, SiII. The peculiarities of these profiles can be explained using a superposition of stellar absorption line and shell emission lines. Emission in the (0; 1) 5635 Å Swan system band of the C2 molecule has been detected in the spectrum of V448 Lac for the first time. The core of the Hα line displays radial-velocity variations with an amplitude of ΔV r ≈ 8 km/s. Radial-velocity variations displayed by weak metallic lines with lower amplitudes, ΔV r ≈ 1–2 km/s, may be due to atmospheric pulsations. Differential line shifts, ΔV r = 0–8 km/s have been detected on various dates. The position of the molecular spectrum is stationary in time, indicating a constant expansion velocity of the circumstellar shell, V exp = 15.2 km/s, as derived from the C2 and NaI lines. 相似文献