Optical Identifications of Five INTEGRAL Hard X-ray Sources in the Galactic Plane Region

The results of optical identifications of five hard X-ray sources in the Galactic plane region from the INTEGRAL all-sky survey are presented. The X-ray data on one source (IGRJ20216+4359) are published for the first time. The optical observations were performed with 1.5-m RTT-150 telescope (TUBITAK National Observatory, Antalya, Turkey) and 6-m BTA telescope (Special Astrophysical Observatory, Nizhny Arkhyz, Russia). A blazar, three Seyfert galaxies, and a high-mass X-ray binary are among the identified sources.Comment: 7 pages, 10 figures, Astronomy Letters, v. 34, p. 65

1RXS J180834.7+101041 is a new cataclysmic variable with non-uniform disc

Results of photometric and spectroscopic investigations of the recently discovered disc cataclysmic variable star 1RXS J180834.7+101041 are presented. Emission spectra of the system show broad double peaked hydrogen and helium emission lines. Doppler maps for the hydrogen lines demonstrate strongly non-uniform emissivity distribution in the disc, similar to that found in IP Peg. It means that the system is a new cataclysmic variable with a spiral density wave in the disc. Masses of the components (M_WD = 0.8 +/- 0.22 M_sun and M_RD = 0.14 +/- 0.02 M_sun), and the orbit inclination (i = 78 +/- 1.5 deg) were estimated using the various well-known relations for cataclysmic variables.Comment: 4 pages, 3 figures, conference "European White Dwarf Workshop, 2010", Tuebingen, German

On the reconstruction of the surface structure of the spotted stars

We have developed and tested a light-curve inversion technique for photometric mapping of spotted stars. The surface of a spotted star is partitioned into small area elements, over which a search is carried out for the intensity distribution providing the best agreement between the observed and model light curves within a specified uncertainty. We have tested mapping techniques based on the use of both a single light curve and several light curves obtained in different photometric bands. Surface reconstruction artifacts due to the ill-posed nature of the problem have been identified. © 2013 Pleiades Publishing, Ltd

Multipassband photometric mapping of three fast rotating stars: HII 1883, AP 86 and AP 226

© 2014 COSPAR. The analysis of multipassband photometry was carried out for three rapidly rotating stars: HII 1883, AP 86 and AP 226. Two different approaches were used for starspot mapping. In the first approach the stellar spottedness is approximated by set of circular spots. Spot parameters (coordinates of the spot center, radius and temperature) are searched by fitting of observed light curves. The idea of the second approach is consisted in partition of the stellar surface into small areas. Searching of the temperature distribution is carried out by the fitting of the observed light curves. Stellar atmosphere theory was used for modeling of the theoretical light curves in both techniques

The new pre-cataclysmic binary PG 2200+085

We present the results of spectroscopic-- and orbit--sampled photometric observations of the faint UV-excess object PG 2200+085. The optical CCD photometry observations of this object were performed by the Russian-Turkish 1.5-meter telescope RTT150 at the TUBITAK National Observatory (Turkey). The long-slit optical spectroscopy observations with 2.6 A resolution were carried out by 6-meter telescope BTA at the Special Astrophysical Observatory (Russia). The photometric variations over two nights are almost sinusoidal with an amplitude \Delta m_V = 0.04 m and a period of P = 0.3186 d. Such a light curve is typical of a detached close binary with an illumination effect or the ellipsoidal deformation of a secondary star. The observed spectrum clearly displays a featureless blue continuum of a hot component and a rich absorption--line and molecular band K--star spectrum. The CaII line profiles with strong emission cores are remarkably similar to those of V471 Tau. We tentatively classify PG 2200+085 as a pre-cataclysmic binary of the V471 Tau type.Comment: 8 pages, 5 figures, accepted for publication in A&

The nature of the unique precataclysmic variable V664 Cas with two-peaked balmer lines in its spectrum

We analyze photometric and spectroscopic observations of the close binary system V664 Gas. All the characteristics of its radiation are consistent with the star being a cataclysmic variable with powerful reflection effects. The orbital period is refined (P = 0.5816475 d) and the ephemerides of the system determined. The U, B, V, R light curves of V664 Gas display sinusoidal variations with similar amplitudes near Δm = 1.1m. This suggests that a hot spot on the surface of the secondary always dominates the optical radiation of the system. The spectra contain emission lines, two-peaked hydrogen lines, and narrow lines of helium and heavy elements in high ionization states, whose intensities vary synchronously with the brightness. The Hell λ4686 Å line has broad absorption wings that form in the atmosphere of the O subdwarf. The mass function, f(m) = 0.007M⊙, is the lowest among all precataclysmic variables: the mass of the secondary exceeds the mass of the primary by more than a factor of 1.6. A full set of fundamental parameters for V664 Gas is determined based on modeling of the spectra and light curves, taking into account reflection effects in the system. Most of the emission lines are formed under conditions of appreciable deviations from local thermodynamic equilibrium. The possibility of carrying out correct modeling of the Balmer-line profiles assuming the stellar radiation is absorbed in a planetary nebula is demonstrated. © 2004 MAIK "Nauka/ Interperiodica"

Supersoft X-ray sources. Parameters of stellar atmospheres

ROSAT spectra of 11 supersoft X-ray sources are approximated with theoretical spectra obtained in LTE models for the atmospheres of hot white dwarfs with line blanketing. The confidence intervals of parameters derived from these approximations-Teff, log, g, NH, and R2/d2 - are determined. The results are compared with predictions for a model with stable/recurrent thermonuclear burning on the white-dwarf surface. © 2003 MAIK "Nauka/Interperiodica"