Faig A. Musaev

Thorium-rich halo star HD 221170: Further evidence against the universality of the r-process ,

We report the abundance determination in the atmosphere of the bright halo star HD 221170. The spectra were taken with the Terskol Observatorys 2.0-m telescope with a resolution R = 45 000 and signal-to-noise ratio up to 250 in the wavelength region 3638-10 275 A. The adopted atmospheric parameters correspond to an effective temperature Teff = 4475 K, a surface gravity log g = 1.0, a microturbulent velocity vmicro = 1.7 km s −1 , and a macroturbulent velocity vmacro = 4k m s −1 . The abundances of 43 chemical elements were determined with the method of spectrum synthesis. The large overabundances (by 1 dex relative to iron) of elements with Z > 38 are shown to follow the same pattern as the solar r-abundances. The present HD 221170 analysis confirms the non-universality of the r-process, or more exactly the observation that the astrophysical sites hosting the r-process do not always lead to a unique relative abundance distribution for the bulk Ba to Hg elements, the Pb-peak elements, and the actinides.

The evolutionary status of the UX Orionis star RZ Piscium

The star RZ Psc is one of the most enigmatic members of the UX Ori star family. It shows all properties that are typical for these stars (the light variability, high linear polarization in deep minima, the blueing effect) except for one: it lacks any signatures of youth. With the lithium line 6708 u as a rough estimate for the stellar age, we show that the ”lithium” age of RZ Psc lies between the age of stars in the Pleiades (∼70 Myr) and the Orion (∼10 Myr) clusters. We also roughly estimated the age of RZ Psc based on the proper motion of the star using the Tycho-2 catalog. We found that the star has escaped from its assumed birthplace near to the Galactic plane about 30-40 Myr ago. We conclude that RZ Psc is a post-UXOr star, and its sporadic eclipses are caused by material from the debris disk.

Chemical composition of 15 photometric analogues of the Sun

The results of a spectroscopic analysis of 15 stars that are photometric analogues of the Sun are reported. The effective temperatures and surface gravities in the stellar atmospheres are derived from published photometric indices and the HIPPARCOS parallaxes. The abundances of 33 elements ranging from lithium to europium are analyzed based on high-dispersion spectra taken with the new Coudé echelle spectrometer of the Terskol Observatory in the northern Caucasus. The main parameters of most of the stars agree with the data of an [Fe/H] catalog published in 2001. Our study of the chemical compositions of the sample stars indicates that photometric analogues of the Sun can be divided into three groups according to their elemental abundances: six stars have solar chemical composition, four have abundance excesses, and five have some abundance deficiencies. The sample contains two metal-deficient subgiants (HD 133002 and HD 225239). Our results demonstrate that photometric similarity is not a sufficient criterion to consider a star as solar analogue. When several criteria, including chemical composition, are simultaneously taken into account, only four stars from the sample can be considered true solar analogues: HD 10307, HD 34411, HD 146233 (18 Sco), and HD 186427 (16 Cyg B). These results confirm the previously published suggestion that 18 Sco is the most probable twin of the Sun: essentially all the parameters of the two stars coincide within the errors.

CHEMICAL ABUNDANCE PATTERNS FOR SHARP-LINED STARS

In order to increase the completeness of the investigations of stellar abundances, we can use spectrum synthesis method, new atomic data and observation of stellar spectra with resolution comparable to solar spectral atlases. We made a brief review of main problems of these three ways. We present new results of abundance determinations in the atmospheres of four stars. The first is the implementation of new atomic data to well known Przybylski`s star. We show that the number of spectral lines, which can be identificated in the spectrum of this star, can be significantly higher. The second example is the investigation of Cyg. We found the abundances of 51 elements in the atmosphere of this mild barium star. The third example is halo star HD221170. Our preliminary abundance pattern consists of 42 elements. The heaviest elements in this pattern are U and Th. The last star is the spectroscopic binary HD153720. The number of elements investigated in the spectra of components of this star is not large, but the results show that the components are Am-stars.

Observational constraints on potassium synthesis during the formation of stars of the Galactic disk

The non-LTE potassium abundances in the atmospheres of 33 Galactic-disk stars are derived and the parameters of the atmospheres of 23 of the stars are determined. Neglecting departures from LTE results in a systematic overestimation of the potassium abundances and an increase in their dispersion, even for differential analyses relative to the Sun. The non-LTE corrections are significant ((−0.2)–(−0.6) dex) and depend on the surface gravities and effective temperatures of the stars. The mean potassium abundance for a sample of ten stars with [Fe/H]∼0.0 is in agreement with the solar and meteoritic abundances (log ɛ⊙(K)=5.12). As the stellar metallicity increases from [Fe/H]=(−1.0) to (0.2) dex, the [K/Fe] ratio decreases systematically from 0.3 dex to −0.1 dex. The derived dependence [K/Fe]-[Fe/H] is in agreement with the results of published model calculations of the chemical evolution of the Galaxy. This indicates the dominance of explosive oxygen burning in massive type II supernovae during the synthesis of potassium in the Galactic disk.

Atmospheric chemical composition of the halo star HD 221170 from a synthetic-spectrum analysis

The atmospheric abundances of 30 chemical elements in the halo star HD 221170 are analyzed by fitting synthetic spectra to observed spectra (i) with a resolution of 60 000 and signal-to-noise ratios of about 200 taken with the 1.93-m telescope of the Observatoire de Haute Provence and (ii) with a resolution of 35 000 and signal-to-noise ratios of more than 100 taken with the 2-m telescope of the Terskol Peak Observatory. The derived parameters of the stellar atmosphere are Teff=4475 K, log g=1.0, [Fe/H]=−2.03, Vmicro=1.7 km/s, and Vmacro=4 km/s. The parameters Teff, log g, [Fe/H], and Vmicro can be determined by analyzing the variations of the rms error of the mean iron abundance derived using different model atmospheres. The chemical composition of the star’s atmosphere is analyzed. The abundances of a total of 35 elements in HD 221170 have been derived in this paper and in previous studies. Overall, the abundances of elements lighter than praseodymium are consistent with the elemental abundances in the atmospheres of stars with similar metal deficits. Copper and manganese are underabundant by −2.9 and −2.6 dex, respectively, relative to the Sun (when the analysis includes the effects of hyperfine structure). Heavy r-process elements (starting from praseodymium) are overabundant compared to iron-group elements. This can be explained by an enrichment in r-process elements of the material from which the star was formed.

The atmospheric lithium abundances of solar analogues

We have analyzed the lithium abundance in the atmospheres of 20 stars that are solar analogues based on high-resolution echelle spectra using model atmospheres in a non-LTE approach. In terms of their lithium abundances, the stars (which are located in a narrow range of temperatures of 5650–5900 K) can be divided into two groups: one with low lithium abundances, as in the solar atmosphere, and one with lithium abundances that are higher than the solar value by about 1 dex (with the accuracy of the lithium abundances being 0.15 dex).

Spectroscopic monitoring of V1357 Cyg = Cyg X-1 in 2002–2004

We discuss the results of optical spectroscopic monitoring of Cyg X-1 = HDE 226868/V1357 Cyg in 2002–2004. Our spectroscopy was carried out at the Terskol Observatory (Kabarda-Balkaria, Russia; the resolving power was R = 45 000 and 13 000) and at the Bohyunsan Optical Astronomy Observatory (BOAO, Korea, R = 30 000 and 44 000). Each spectrum covers most of the optical range. We obtained a total of 75 echelle spectra on 33 nights, during both “soft” and “hard” X-ray states of Cyg X-1. We study the influence of the X-rays on spectral-line profiles using RXTE/ASM X-ray data. We find that the X-ray flare of June 13, 2003 resulted in strong variations of the emission profiles of the Hα and Hellλ4686 Å lines within a night. This behavior is due to variations of the ionization state of the gas in the system. We also analyzed line-profile variations with orbital phase. A spectral atlas of Cyg X-1 was created, and the lines it contains identified. A total of 172 stellar lines and blends belonging to 12 chemical elements (H, He, C, N, O, Ne, Mg, Al, Si, S, Fe, Zn) were identified. The spectral classification of HDE 226868 as an ON star is confirmed.

Experimental Study of an Advanced Concept of Moderate-resolution Holographic Spectrographs

We present the results of an experimental study of an advanced moderate-resolution spectrograph based on a cascade of narrow-band holographic gratings. The main goal of the project is to achieve a moderately high spectral resolutionwith R up to 5000 simultaneously in the 4300-6800 A visible spectral range on a single standard CCD, together with an increased throughput. The experimental study consisted of (1) resolution and image quality tests performed using the solar spectrum; and (2) a total throughput test performed for a number of wavelengths using a calibrated lab monochromator. The measured spectral resolving power reaches values over R>4000 while the experimental throughput is as high as 55%, which is in good agreement with the modeling results. Comparing the obtained characteristics of the spectrograph under consideration with the best existing spectrographs, we conclude that the used concept can be considered a very competitive and cheap alternative to the existing spectrographs of the given class. We propose several astrophysical applications for the instrument and discuss the prospect of creating its full-scale version.

Spectroscopic Analysis of Single-Lined Spectroscopic Binaries with Unseen Companions

Detailed abundance analyses have been carried out for 20 single-lined binaries with barium-star-like orbital elements using high-dispersion échelle spectra and the model atmosphere method. No substantial differences in the atmospheric abundances of 15 program stars relative to standard stars were found. Therefore, as a group, the single-lined spectroscopic binaries show atmospheric abundances similar to single stars, and the unseen companions did not have an influence on the atmospheric abundances of the primary stars studied.