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

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

Atmospheres and spectra of X-ray illuminated stars: A nongray model

We continue to study illuminated stellar atmospheres with radiative transfer. A method for computing X-ray irradiated blanketed model atmospheres is described. The heating function of such atmospheres has been found to be complicated and to have a minimum at the depth of continuum formation. We have established that the normalized heating function does not depend on the intensity of the incident radiation and atmospheric parameters. The heating of only deep layers is shown to decrease sharply with increasing angle of incidence of the irradiative flux. The effect of the soft and hard X-ray emission components on the formation of the heating function is explored. A sharp decrease in the heating of chromospheric layers when allowing for line blanketing has been ascertained. The gray model is shown to be valid, to a good approximation, for describing illuminated atmospheres. The cooling function is computed over the ranges Teff = 3000-200 000 K and log Pg from -2.0 to 8.0, and the possible existence of temperature instabilities in the chromospheres of irradiated atmospheres has been revealed

The atmospheres and spectra of X-ray illuminated stars: Line formation

The formation of lines in X-ray illuminated atmospheres and in close binary systems with X-ray sources is studied. It is shown that there are three groups of lines: "cool" (absorption lines), "normal" (absorption lines with emission cores), and "hot" (emission lines). The effect of the parameters of the irradiative X-ray flux and the observing conditions on the formation of lines of different groups is analyzed. The method of gray approximation has been found to be applicable to the synthesis of the profiles of cool and normal lines. The method of constructing synthetic spectra for close binary systems has been developed, and the possibility of determining the parameters of the systems from an analysis of lines of different groups is shown

Atmospheres and spectra of X-ray illuminated stars: A gray model

A gray model is used to explore the effect of heating of stellar atmospheres by an external X-ray flux. This flux is shown to produce additional heating functions in the surface and inner layers. The opacity sources in the X-ray region are determined. A technique for calculating the reflection effect in the gray approximation is presented. The illuminated and normal atmospheres and their spectra are shown to differ considerably

Non-LTE effects in Mg I lines for various types of stars

We have performed a detailed statistical-equilibrium analysis based on a 49-level model of the magnesium atom for the atmospheres of stars of various spectral types: Teff = 4500-12000 K, logg = 0.0 - 4.5, and [M/H] = 0 to -3. In the atmospheres of stars with Teff > 5500 K, deviations from LTE for Mg I are due to photoionization by ultraviolet radiation from the 3p level; i.e., neutral magnesium is in a state of "superionization." When Teff < 5500 K, the populations of the Mg I levels differ from their LTE values due to radiative processes in bound - bound transitions. We analyzed Mg I lines in the solar spectrum in order to empirically refine certain atomic parameters (the van der Waals broadening constant C6 and cross sections for photoionization and collisional interactions with hydrogen atoms) and the magnesium abundance in the solar atmosphere. We studied non-LTE effects for five Mg I lines for a wide range of stellar parameters. In the case of dwarfs and subdwarfs, the magnitude of non-LTE corrections to magnesium abundances does not exceed 0.1 dex for the λλ 4571, 4703, 5528, and 5711 Å lines but can be as large as ±0.2 dex for the λλ 3829-3838, 5172, and 5183 Å lines. The non-LTE corrections for giants and supergiants do not exceed 0.15 dex for the λλ 4571 and 5711 Å lines but can reach ±0.20 dex and even more for the λλ 4703, 5528, 3829-3838, 5172, and 5183 Å lines. © 2000 MAIK "Nauka/Interperiodica"

A non-LTE analysis of Mg I lines in the atmospheres of late-type stars

The formation of Mg I lines in the atmospheres of stars with Teff = 5500-7000 K, log g = 2.0-4.5, and [A] = 0, -2 is analyzed. It is shown that the Mg I level population is a nonequilibrium one, and that overionization takes place. This is the chief cause of departures from LTE in the equivalent widths of strong lines; for weak lines, the shift in the depth of their formation in the stellar atmosphere also plays a major role. Quantitatively, overionization is more pronounced in metal-poor stars. Departures from LTE grow with increasing stellar luminosity, peaking at Teff = 6500 K in main-sequence stars and growing with decreasing Teff in giants. Non-LTE magnesium-abundance corrections are calculated. They are at their peak for the λ4571, 3829-3838, 5172, and 5183 lines and reach 0.30 dex at Teff = 5500 K, log g = 2.0, and [A] = -2. For the λ4057, 4167, 4702, 4730, 5528, and 5711 lines, the non-LTE corrections do not exceed +0.15 dex for the entire range of physical parameters studied. The sensitivity of the results to variations in the input data (model atom, cross sections for the processes, etc.) is analyzed

Distribution of polarization and intensity of radiation across the stellar disk and numberical values of atmospheric characteristics governing this distribution

Computations of polarization and intensity of radiation from a unit stellar surface area are presented, as well as a study of the numerical characteristics of atmospheres - single-scattering albedo Ωλ and the initial source functionλ(δλ), which define the polarization behaviour of atmospheres. The radiatively stable models of stellar atmospheres presented by Kurucz et al. (1974) and Kurucz (1979) have been used for calculations. Since the Ωλ versus optical depth τλ dependence is rather weak, it has been assumed that Ωλ(τλ=cost. With a fixed effective temperature Teff maximum values of Ω are characteristic of stars featuring the lowest surface gravity acceleration g. Among stars with radiatively stable atmospheres, maximum values of Ω (λ=5000 Å) ≈ 0.4-0.6 are exhibited by supergiants with Teff=8000-20 000 K. The plot of Ω(λ) is characterized by discontinuities at the boundaries of spectral series for hydrogen and, sometimes, for helium. Maximum Ωλ are attained in the Lyman region of λ=912-1200 Å, where Ωλ can reach the value 0.7-0.9 for supergiants, this value being ≳ 0.3 for Main-Sequence stars. For stars with Teff ≳ 35 000 K, high values of Ωλ also are attained for λ<912 Å. Within the infrared region, Ωλ is always small because of bremsstrahlung absorption. A rapid growth of the source function Bλ with <λ typical for ultraviolet range (within the Wien part of spectrum), together with high values of Ωλ results in the strong polarization of emission from a unit stellar surface element, sometimes exceeding the values for the case of a pure electron scattering. For longer wavelengths, where the limb-darkening coefficient is smaller, the plane of polarization abruptly turns 90° in the central parts of the visible stellar disk. © 1985 D. Reidel Publishing Company