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 ? _⊙(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.     

The evolutionary status of UX CVn

We have analyzed available spectroscopic and photometric observations of the close binary UX CVn using model atmospheres. Theoretical spectra and light curves were derived from models of a precataclysmic variable and a close binary consisting of degenerate stars. We have used the 6-m telescope of the Special Astrophysical Observatory to obtain ten moderate-resolution spectra at three orbital phases. Our analysis of the radial-velocity curve shows that the orbital period of the system has been stable over 40 yrs, and the variations of the intensities of lines of various elements at different phases and radial velocities indicates an absence of the reflection effect. As a result, we have classified UX CVn as a detached close binary consisting of a hot, low-luminosity sub-dwarf primary and a white-dwarf secondary.     

Results of the First Year of the 3BS Polar Search Program

Astronomy Letters - We present the results of the first year of searching for polar candidates within the 3BS (3-Band Survey) program using medium-band filters. Observational data for 84 selected...     

Observations of eclipses of UU Sge

We have performed spectroscopy and photometry of eclipses of the pre-cataclysmic variable UUSge using the 6-m telescope of the Special AstrophysicalObservatory and the 1.5-mRussian-Turkish telescope. Our analysis of variations of the B-V and V-R color indices during the eclipses indicates that the temperature of the secondary is T _eff,2 = 6000?6300 K. A similar value, T _eff,2 = 6200 ± 200 K, follows from our comparison of the observed spectrum of UU Sge at the total eclipse phase and theoretical spectra of late-type stars. We identify 27 absorption lines of 11 chemical elements in the secondary??s spectrum. Their abnormal intensities indicate possible high-velocity turbulent motions (up to ?? _turb = 10.0 km/s) in the atmosphere of the star and the presence of hot gas above its surface.     

Observational restrictions on sodium and aluminium abundance variations in evolution of the galaxy

In this paper we construct and analyze the uniform non-LTE distributions of the aluminium ([Al/Fe]-[Fe/H]) and sodium ([Na/Fe]-[Fe/H]) abundances in the sample of 160 stars of the disk and halo of our Galaxy with metallicities within ?4.07 ≤ [Fe/H] ≤ 0.28. The values of metallicity [Fe/H] and microturbulence velocity ξ _turb indices are determined from the equivalent widths of the Fe II and Fe I lines. We estimated the sodium and aluminium abundances using a 21-level model of the Na I atom and a 39-level model of the Al I atom. The resulting LTE distributions of [Na/Fe]-[Fe/H] and [Al/Fe]-[Fe/H] do not correspond to the theoretical predictions of their evolution, suggesting that a non-LTE approach has to be applied to determine the abundances of these elements. The account of non-LTE corrections reduces by 0.05–0.15 dex the abundances of sodium, determined from the subordinate lines in the stars of the disk with [Fe/H] ≥ ?2.0, and by 0.05–0.70 dex (with a strong dependence on metallicity) the abundances of [Na/Fe], determined by the resonance lines in the stars of the halo with [Fe/H] ≤ ?2.0. The non-LTE corrections of the aluminium abundances are strictly positive and increase from 0.0–0.1 dex for the stars of the thin disk (?0.7 ≤ [Fe/H] ≤ 0.28) to 0.03–0.3 dex for the stars of the thick disk (?1.5 ≤ [Fe/H] ≤ ?0.7) and 0.06–1.2 dex for the stars of the halo ([Fe/H] ≤ ?2.0). The resulting non-LTE abundances of [Na/Fe] reveal a scatter of individual values up to Δ[Na/Fe] = 0.4 dex for the stars of close metallicities. The observed non-LTE distribution of [Na/Fe]-[Fe/H] within 0.15 dex coincides with the theoretical distributions of Samland and Kobayashi et al. The non-LTE aluminium abundances are characterized by a weak scatter of values (up to Δ[Al/Fe] = 0.2 dex) for the stars of all metallicities. The constructed non-LTE distribution of [Al/Fe]-[Fe/H] is in a satisfactory agreement to 0.2 dex with the theoretical data of Kobayashi et al., but strongly differs (up to 0.4 dex) from the predictions of Samland.     

PN G068.1+11.0: A young pre-cataclysmic variable with an extremely hot primary

An analysis of spectroscopic and photometric data for the young pre-cataclysmic variable (PCV) PN G068.1+11.0, which passed through its common-envelope stage relatively recently, is presented. The spectroscopic and photometric data were obtained with the 6-m telescope and Zeiss-1000 telescope of the Special Astrophysical Observatory. The light curves show sinusoidal brightness variations with the orbital-period time scale and brightness-variation amplitudes of Δm = 1_.^m41, 1_.^m62, and 1_.^m57 in the B, V, and R bands, respectively. The system’s spectrum exhibits weak HI (Hβ–Hδ) andHeII λλ4541, 4686, 5411 Å absorption lines during the phases of minimum brightness, as well as HI, HeII, CIII, CIV, NIII, and OII emission lines whose intensity variations are synchronized with variations of the integrated brightness of the system. The emission-line formation in the spectra can be fully explained by the effects of fluorescence of the ultraviolet light from the primary at the surface of the cool star. All the characteristics of the optical light of PN G068.1+11.0 confirm that it is a young PCV containing sdO subdwarf. The radial velocities were measured from a blend of lines of moderately light elements, CIII+NIII λ4640 Å, which is formed at the surface of the secondary due to reflection effects. The ephemeris of the system has been improved through a joint analysis of the radial-velocity curves and light curves of pre-cataclysmic variable, using modelling of the reflection effects. The fundamental parameters of PN G068.1+11.0 have been determined using two evolutionary tracks for planetary-nebula nuclei of different masses (0.7 M_⊙and 0.78M_⊙). The model spectra for the system and a comparison with the observations demonstrate the possibility of refining the components’ effective temperatures if the quality of the spectra used is improved.     

Spectroscopic study of the optical counterpart to the fast X-ray transient IGR J17544-2619 based on observations at the 1.5-m RTT-150 telescope

We present the results of our long-term photometric and spectroscopic observations at the Russian–Turkish RTT-150 telescope for the optical counterpart to one of the best-known sources, representatives of the class of fast X-ray transients, IGR J17544-2619. Based on our optical data, we have determined for the first time the orbital and physical parameters of the binary system by the methods of Doppler spectroscopy.We have calculated theoretical spectra of the optical counterpart by applying non- LTE corrections for selected lines and obtained the parameters of the stellar atmosphere (T _eff = 33 000 K, log g = 3.85, R = 9.5 R _⊙, and M = 23 M _⊙). The latter suggest that the optical star is not a supergiant as has been thought previously.     

Spectral and photometric studies of polar CRTS CSS 130604 J 215427+155714

We present the results of spectroscopic and photometric studies of a new polar CRTS CSS130604 J 215427+155714, conducted at the telescopes of the SAO RAS. Analysis of the photometric series of observations allowed to clarify the orbital period of the system, P _o = 0_. ^d 0672879 (±0.0000003). We build radial velocity curves and trace the intensity variations in the Hβ and H_γ hydrogen lines and He II λ 4686 ?A ionized heliumline. Based on the Hβ and He II lines we build Doppler maps. It is shown that the line formation region is localized near the Lagrange point. The following parameter estimates of the system are obtained:M ₁ = 0.83 ± 0.10M _⊙, M ₂ = 0.15 ± 0.01M _⊙, q = M ₂/M ₁ = 0.18 ± 0.03, i = 53? ± 5?. Based on the results of spectral, photometric and previously published polarimetric observations the possible geometric model of the system is discussed.     

Observations of Candidates for Eclipsing Cataclysmic Variables with the RTT-150 Telescope

Astronomy Letters - We present the results of our photometric and spectroscopic observations. We have studied four cataclysmic variable stars: 2XMM J183251.4-100106, MLS1809017 J224712+461815,...     

On the formation of TW Crv optical radiation

We present the analysis of the optical radiation of the young pre-cataclysmic variable TW Crv. Spectroscopic and photometric observations were obtained at the SAO RAS 6-m BTA telescope and at the Russian-Turkish RTT-150 telescope. The light curves of the system posses nearly sinusoidal shapes with the amplitudes of Δ_m > 0.^m7, what is typical for young pre-cataclysmic variables with sdO-subdwarfs and orbit inclinations of less than 45?. The optical spectrum contains dominant radiation of the hot subdwarf with the HI and He II absorption lines and strong emission lines, which are formed in the atmosphere of the secondary owing to the reflection effects. Radial velocities of the cool star were measured by analyzing the λλ 4630–4650 Å Bowen blend, which for the first time allowed to determine the component masses. A numerical simulation of the light curves and spectra of TW Crv, obtaining a complete set of systems fundamental parameters was carried out. The hot star parameters prompt its belonging to the sdOsubdwarf class at the stage of transition to the cooling white dwarf sequence. The absence of its observable planetary nebula is caused by a long-lasting evolution of the system after the common envelope state. The secondary component has a luminosity excess, which is typical for other young sdO-subdwarf precataclysmic variables. Its position on the “age??luminosity excess” diagram points at the accuracy of the obtained set of TW Crv fundamental parameters and at the similarity of its evolutionary and physical conditions with that of other BE UMa-type objects.