V. E. Panchuk

The high-resolution spectrograph of the 6-m Large Azimuthal Telescope (BTA)

This paper presents the main parameters and design features of a cross-dispersed quartz diffraction spectrograph permanently mounted on one of the two Nasmyth-focus platforms of the 6-m Large Azimuthal Telescope (BTA). The Nasmyth Echelle Spectrograph is intended for the study of stars with high spectral resolution, R=60000. The spectrograph is equipped with various pre-slit devices (polarization analyzers, an iodine cell, etc.), and image slicers. An active-optics system that stabilizes the position of a stars image on the entrance slit of the spectrograph to within about 0.1″ is mounted in the pre-slit part of the spectrograph. The optical layout of the Nasmyth Echelle Spectrograph is designed to obtain spectra without substantially reducing the spectral resolution in a wide wavelength range λ=300-1000nm. A unique mosaic composed of two echelle gratings is used as the main dispersive element of the spectrograph.

Analysis of atmospheric abundances in classical barium stars

We present our analysis of elemental abundances in the atmospheres of 16 classical barium stars derived from high-resolution spectra and model atmospheres. Comparison of the results with analogous data for moderate barium stars and normal red giants shows that the abundance patterns for elements before the iron peak are the same for all three groups of red giants, testifying to a similar origin. For binary systems, we confirm the influence of the orbital period and, hence, the component separation, on the overabundance of s-process elements. The amount of enrichment in s-process elements is also influenced by mass, metallicity, and evolutionary phase. Any of these parameters can be important in individual objects.

High-resolution fiber-fed spectrographs

We analyze the properties of high-resolution spectrographs fed from the telescope through optical fiber links. We report the results of tests performed with the fiber-fed spectrograph that we developed for 1–2 m telescopes.

Radial velocity measurements with stellar spectrographs of the 6-m telescope

Solutions are considered that allow the accuracy of stellar radial velocity measurements with the spectroscopic instruments of the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences to be improved. The factors that limit the accuracy of spectroscopic Vr measurements are analyzed both in general and for the particular design of the telescope and its housing.

V2324 Cyg—an F-type star with fast wind

High-resolution optical spectroscopy of the V2324 Cyg variable star associated with the IR source IRAS 20572+4919 is performed for the first time. More than 200 absorption features (mostly Fe II, Ti II, Cr II, Y II, Ba II, and Y II) are identified in the wavelength interval from 4549 to 7880 Å. The spectral type and rotation velocity of the star are found to be F0 III and V sin i = 69 km/s, respectively. Neutral-hydrogen and NaI D lines have complex P Cyg-type profiles. Neither systematic trend of radial velocity Vr with line depth Ro nor temporal variability of Vr have been found. We found that the value for the average heliocentric radial velocity is Vr = −16.8 ± 0.6 km/s. The radial velocities inferred from the cores of the absorption components of the Hβ and NaI wind lines vary from −140 to −225 km/s (and the expansion velocities of the corresponding layers, from about 120 to 210 km/s). The maximum expansion velocity is found for the blue component of the split Hα absorption: 450 km/s for December 12, 1995. The method of model atmospheres is used to determine the following parameters of the star: effective temperature Teff = 7500 K, surface gravity log g = 2.0, microturbulence velocity ξt = 6.0 km/s, and metallicity, which is equal to the solar value. The main peculiarity of the chemical composition of the star is the overabundance of lithium and sodium. The results cast some doubt on the classification of V2324 Cyg as a post-AGB star.

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 χlow < 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 ΔVr ≈ 8 km/s. Radial-velocity variations displayed by weak metallic lines with lower amplitudes, ΔVr ≈ 1–2 km/s, may be due to atmospheric pulsations. Differential line shifts, ΔVr = 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, Vexp = 15.2 km/s, as derived from the C2 and NaI lines.Repeated observations with high spectral resolution acquired in 1998–2008 are used to study the temporal behavior of the spectral line profiles and velocity field in the atmosphere and circumstellar envelope of the post-AGB star V448 Lac. Asymmetry of the profiles of the strongest absorption lines with low-level excitation potentials f χlow < 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 peculiarity 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 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 ∆Vr≈8 km/s. Radial velocity variations displayed by weak metallic lines with lower amplitudes, ∆Vr≈1–2 km/s, may be due to atmospheric pulsations. Differential line shifts, ∆Vr=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, Vexp =15.2 km/s, as derived from the C2 and NaI lines.

Main stellar spectrograph of the 6-meter telescope. Analysis, reconstruction, and operation

The Main Stellar Spectrograph (MSS) of the 6-m telescope of the Special Astrophysical Observatory was developed in the early 1970s and has been in permanent operation since 1975. This instrument has been successfully kept operational for a long time by equipping it with modern detectors and significantly upgrading its optical layout. In this paper we present the main parameters of the optomechanical layout of the MSS, the design features of auxiliary devices, operational experience and statistics of the use of the instrument with various detectors, and the characteristics of the corresponding observational techniques.

New spectroscopic observations of the post-AGB star V354 Lac = IRAS 22272+5435

The strongest absorption features with the lower-level excitation potentials χlow < 1 eV are found to be split in the high-resolution optical spectra of the post-AGB star V354 Lac taken in 2007–2008 with the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. Main parameters, Teff=5650 K, log g=0.2, ξt=5.0 km/s, and the abundances of 22 chemical elements in the star’s atmosphere are found. The overabundance of the s-process chemical elements (Ba, La, Ce, Nd) in the star’s atmosphere is partly due to the splitting of strong lines of the ions of thesemetals. The peculiarities of the spectrum in the wavelength interval containing the LiI λ 6707 Å line can be naturally explained only by taking the overabundances of the CeII and SmII heavy-metal ions into account. The best agreement with the synthetic spectrum is achieved assuming ɛ(LiI)=2.0, ɛ(CeII)=3.2, and ɛ(SmII)=2.7. The velocity field both in the atmosphere and in the circumstellar envelope of V354 Lac remained stationary throughout the last 15 years of our observations.

Peculiarities of the atmosphere and envelope of a post-AGB star, the optical counterpart of IRAS 23304+6347

Based on our high-spectral-resolution observations performed with the echelle spectrograph of the 6-m telescope, we have studied the peculiarities of the spectrum and the velocity field in the atmosphere and envelope of the optical counterpart of the infrared source IRAS 23304+6347. We have reached the conclusion about the absence of significant variations in the radial velocity Vr inferred from atmospheric absorptions and about its coincidence with the systemic velocity deduced from radio data. The envelope expansion velocity Vexp = 15.5 km s−1 has been determined from the positions of rotational lines of the C2 Swan (0; 0) band. A complex emission-absorption profile of the Swan (0; 1) 5635 Å band has been recorded. Our analysis of the multicomponent Na I D doublet line profile has revealed interstellar components with velocities V (IS) = −61.6 and −13.2 km s−1 as well as a circumstellar component with V (CS) = −41.0 km s−1 whose position corresponds to the velocity inferred from C2 features. The presence of the interstellar component with Vr = −61.6 km s−1 in the spectrum allows d = 2.5 kpc to be considered as a lower limit for the distance to the star. A splitting of the profiles for strong absorptions of ionized metals (Y II, Ba II, La II, Si II) attributable to the presence of a short-wavelength component originating in the circumstellar envelope has been detected in the optical spectrum of IRAS 23304+6347 for the first time.

Spectroscopy of 13 high-mass stars in the Cyg OB2 association

The NES echelle spectrograph of the 6-m telescope of the Special Astrophysical Observatory has been used to obtain high-resolution spectra for 13 hot O3-B4 stars in the Cyg OB2 association, making it possible to study weak spectral features of stellar and interstellar origin. Velocity fields in the atmospheres and interstellar medium, characteristics of optical spectra and line profiles are investigated. The cascade star-formation scheme for the association is confirmed. Evidence is presented suggesting that the hypergiant Cyg OB2 No. 12 is an LBV object and that its anomalous reddening has a circumstellar nature.