V. G. Klochkova

Using Cepheids to determine the galactic abundance gradient I. The solar neighbourhood

A number of studies of abundance gradients in the galactic disk have been performed in recent years. The results obtained are rather disparate: from no detectable gradient to a rather signicant slope of about 0: 1d ex kpc 1 . The present study concerns the abundance gradient based on the spectroscopic analysis of a sample of classical Cepheids. These stars enable one to obtain reliable abundances of a variety of chemical elements. Additionally, they have well determined distances which allow an accurate determination of abundance distributions in the galactic disc. Using 236 high resolution spectra of 77 galactic Cepheids, the radial elemental distribution in the galactic disc between galactocentric distances in the range 6{11 kpc has been investigated. Gradients for 25 chemical elements (from carbon to gadolinium) are derived. The following results were obtained in this study. Almost all investigated elements show rather flat abundance distributions in the middle part of galactic disc. Typical values for iron-group elements lie within an interval from 0:02 to 0:04 dex kpc 1 (in particular, for iron we obtained d(Fe/H)/dRG = 0:029 dex kpc 1 ). Similar gradients were also obtained for O, Mg, Al, Si, and Ca. For sulphur we have found a steeper gradient ( 0:05 dex kpc 1 ). For elements from Zr to Gd we obtained (within the error bars) a near to zero gradient value. This result is reported for the rst time. Those elements whose abundance is not expected to be altered during the early stellar evolution (e.g. the iron-group elements) show at the solar galactocentric distance (El/H) values which are essentially solar. Therefore, there is no apparent reason to consider our Sun as a metal-rich star. The gradient values obtained in the present study indicate that the radial abundance distribution within 6{11 kpc is quite homogeneous, and this result favors a galactic model including a bar structure which may induce radial flows in the disc, and thus may be responsible for abundance homogenization.

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.

OPTICAL SPECTRUM OF THE IR SOURCE IRC + 10420 IN 1992-1996

To understand the evolutionary stage of the peculiar supergiant IRC+10420, we have been taking spectra for several years at the 6m telescope. The optical spectrum of IRC+10420 of the years from 1992 through 1996 points to the increase in the temperature: spectral class A5 instead of the former F8, as was pointed out by Humpreys et al., (1973). Now it resembles the spectra of late-type B[e] stars. The spectrum contains absorptions (mainly of ions) formed in the photosphere, apparently stationary with respect to the star center of mass, and emissions too, which can be formed in the fossil expanding envelope as well as partly in its compressing region. Using our spectra and spectral data obtained by Oudmaijer (1995) we estimated the atmospheric parameters Teff=8500 K, logg=1.0, Vt=12km/s and concluded that metallicity of IRC+10420 is solar: the average value [(V,Cr,Fe)/H]=-0.03. Combination of results allows us to consider IRC+10420 as a massive supergiant evolving to the WR-stage.

The peculiar variable V838 Monocerotis

Spectroscopic observations of the peculiar variable V838 Mon during the period from the second light outburst until the fast dimming are presented. We describe high resolution (R ≈ 60 000) high S /N spectra obtained a day before the second light maximum and low resolution (R ≈ 6000) spectra covering the whole period. The temporal run of intensities and radial velocities of various lines is presented. Using Na  D IS lines we determine the reddening distance of V838 Mon d > 3.1 kpc, and kinematic distance d > 4 kpc. We estimate that V838 Mon is slightly metal deficient but otherwise has a quite solar-like chemical composition except for enhanced abundances of Li, Ba and La.

Evolutionary changes in the optical spectrum of the peculiar supergiant IRC+10420

We present new spectroscopic observations of the peculiar supergiant IRC+10420. In 1997–2000, we obtained three high signal-to-noise ratio spectra of the object at 4300–8000 Å with a spectral resolution of 15 000 (20 km/ s) using the 6-m telescope of the Special Astrophysical Observatory. From our 2000 spectrum, we estimate the spectral type of IRC+10420 to be A2, corresponding to a temperature of ∼9200 K. Many emission lines were detected, identified with lines of Fe I; Fe II, Ti II, Cr II, and Sc II ions; and [O I], [Fe II], and [Ca II] forbidden lines. The radial velocity derived from absorption lines without obvious emission components (He I λ5876, O I, N I, Si II) and from absorption components of the Balmer lines is 93±1 km/s. The redshift of photospheric lines relative to the star’s center-of-mass velocity is interpreted as a consequence of scattering in the expanding, optically thick dust envelope. Both emission and absorption lines show a correlation between radial velocity and oscillator strength. We found variability in the relative intensities of the Hα and Hβ emission components. We conclude that IRC+10420 is rapidly evolving towards a Wolf-Rayet stage; the current rate of the photospheric temperature increase is ∼120 K per year. Based on the intensity of the O I (λ7773) triplet, we estimate the star’s luminosity to be Mbol=−9.5m. In all 1997–2000 spectra of IRC+10420, the He I λ5876 line has a significant equivalent width of at least 200 mÅ; this may be possible in the presence of such a low temperature due to the star’s high luminosity and the enhanced helium abundance in the supergiant’s atmosphere.

A new phase of activity of the Herbig Be star HD 200775 in 2001: Evidence for binarity

The results of high-resolution spectroscopy of the Herbig Be star HD 200775 obtained within the framework of a cooperative observing programme in 2000–2002 are presented. A new high-activity phase of the object’s Ha line occurred in the middle of 2001 in full agreement with a 3.68-year periodicity predicted by Miroshnichenko et al. (1998). A complicated picture of the Ha line profile variability near the activity maximum phase turned out to be very similar to that observed during the previous one in 1997. Variations of the radial velocity with the activity phase are detected in He I, Si II, and S II photospheric lines. The observed phenomena are interpreted in the framework of a model in which the star, together with its gaseous envelope, is a component of an eccentric binary system. A preliminary orbital solution is derived, and the system’s parameters are estimated from the radial velocity curves of the Ha emission line. We find that the orbital eccentricity is e ~ 0.3, the mean companion separation is ~1000 R?, and the secondary companion is most likely to be a ~3.5 M, pre-main sequence object. We emphasize the importance of coordinated spectroscopic and interferometric observations at different phases of the object’s activity for further understanding the properties of the system.

HD 331319: A Post-AGB F Supergiant with He I Lines

AbstractBased on CCD spectra taken with an echelle spectrometer attached to the 6-m telescope, we have determined for the first time the fundamental parameters and detailed chemical composition of HD 331319, an optical counterpart of the infrared source IRAS 19475+3119, by the model-atmosphere method. Helium lines were detected in the spectrum of this luminous (Mυ<−8m object with the effective temperature Teff=7200 K. This detection can be interpreted as a significant helium overabundance in the observed atmospheric layers and may be considered as a manifestation of helium synthesis during the preceding evolution. Nitrogen and oxygen were found to be overabundant, [N/Fe]⊙=+1.30 dex and [O/Fe]⊙=+0.64 dex, with the carbon overabundance being modest. The metallicity of the stellar atmosphere, [Fe/H]⊙=+0.25, differs only slightly from its solar value. The s-process metals are not overabundant but most likely underabundant relative to iron: [X/Fe]⊙=−0.68 for Y and Zr. Barium is also underabundant relative to iron: [Ba/Fe]⊙=−0.47. The heavier elements La, Ce, Nd, and Eu are slightly enhanced relative to iron: the mean [X/Fe]⊙=−0.16 for them. In general, the elemental abundances confirm that IRAS 19475+3119 is a post-AGB object. The metallicity in combination with the radial velocity Vr=−3.4 km s−1 and Galactic latitude

Properties of Galactic B[e] supergiants. I. CI Camelopardalis

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