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

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

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

Formation of Balmer lines in the spectra of X-ray Novae

The profiles and equivalent widths of the absorption and emission components of Balmer lines and the continuum optical spectra of X-ray novae during outbursts are calculated. A stationary self-illuminated accretion a disk around a Schwarzschild black hole is used as an instantaneous model for the X-ray nova. Each annulus of the disk is assumed to emit as a stellar atmosphere that is illuminated by the same X-ray flux. The irradiated stellar model atmospheres are calculated in the LTE approximation. The equivalent widths of the emission components of the Balmer lines are shown to depend on the X-ray flux that is intercepted by the disk (i.e., on the geometric sizes of the disk), on the optical depth of the chromospheric-like layer along the line of sight (i.e., on the inclination of the disk to the line of sight), and on the relative fraction of the soft component with E ∼ 0.1 keV in the X-ray spectrum (because it is this component that heats the upper atmosphere of the disk). A comparison of the theoretical spectra with the observed spectra of the X-ray nova V518 Per (GRO J0422+32) reveals an additional emission in the observed spectrum, which is most probably the bremsstrahlung of an optically thin, hot (T ∼ 106 K) shell

MT Ser, a binary blue subdwarf

We have classified and determined the parameters of the evolved close binary MT Ser. Our moderate-resolution spectra covering various phases of the orbital period were taken with the 6-m telescope of the Special Astrophysical Observatory. The spectra of MT Ser freed from the contribution of the surrounding nebula Abell 41 contained no emission lines due to the reflection effect. The radial velocities measured from lines of different elements showed them to be constant on a time scale corresponding to the orbital period. At the same time, we find effects of broadening for the HeII absorption lines, due to the orbital motion of two hot stars of similar types. As a result, we classify MT Ser as a system with two blue subdwarfs after the common-envelope stage. We estimate the component masses and the distance to the object from the Doppler broadening of the HeII lines. We demonstrate that the age of the ambient nebula, Abell 41, is about 35 000 years. © 2008 Pleiades Publishing, Ltd

Analysis of reflection effects in HS 2333+3927

The results of photometric and spectroscopic observations of the pre-cataclysmic variable HS 2333+3927, which is a HW Vir binary system, are analyzed. The parameters of the sdB subdwarf companion (T eff = 37 500 ± 500 K, log g = 5.7 ± 0.05) and the chemical composition of its atmosphere are refined using a spectrum of the binary system obtained at minimum brightness. Reflection effects can fully explain the observed brightness variations of HS 2333+3927, changes in the HI and HeI line profiles, and distortions of the radial-velocity curve of the primary star. A new method for determining the component-mass ratios in HW Vir binaries, based on their radial-velocity curves and models of irradiated atmospheres, is proposed. The set of parameters obtained for the binary components corresponds to models of horizontal-branch sdB subdwarfs and main-sequence stars. © 2012 Pleiades Publishing, Ltd

Element-abundance inhomogeneity of interstellar matter as it follows from the chemical composition of the O-type supergiants HDE 226868 (Cyg X-1) and α Cam

By means of synthetic spectrum modeling with non-LTE effects, we determined element abundances in the atmospheres of two O supergiants with similar physical characteristics: HDE 226868 (the optical component of Cyg X-1) and α Cam. These objects are situated at the distance about 2.5 kpc from each other. HDE 226868 has higher abundances compared to α Cam. The differences of Al, S, Zn, and averaged CNO abundances are within 0.15-0.30 dex. This is in a good qualitative agreement with the inhomogeneity of the heavy-element distribution over the Galactic disk derived by Luck et al. (2006) from Cepheids. This finding confirms the inhomogeneity of chemical-element distribution on the scale of 2 kpc and is in agreement with the concept of interstellar-matter superclouds preserving their intrinsic particularities on a time scale in excess of 1 Gyr. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Analysis of optical spectra of V1357 Cyg≡Cyg X-1

Optical spectra and light curves of the massive X-ray binary V1357 Cyg are analyzed. The calculations were based on models of irradiated plane-parallel stellar atmospheres, taking into account reflection of the X-ray radiation, asphericity of the stellar surface, and deviations from LTE for several ions. Comparison of observed spectra obtained in 2004-2005 at the Bohyunsan Observatory (South Korea) revealed variations of the depths of HI lines by up to 18% and of HeI and heavy elements lines by up to 10%. These variations are not related to the orbital motion of the star, and are probably due to variations of the stellar wind intensity. Perturbations of the thermal structure of the atmosphere due to irradiation in various states of Cyg X-1 (including outburst) do not lead to the formation of a hot photosphere with an electron temperature exceeding the effective temperature. As a result, variations of the profiles of optical lines of HI, HeI, and heavy elements due to the orbital motion of the star and variations of the irradiating X-ray flux do not exceed 1% of the residual intensities. Allowing for deviations from LTE enhances the HI and HeI lines by factors of two to three and the MgII lines by a factor of nine, and is therefore required for a fully adequate analysis of the observational data. Analysis of the HI, HeI, and HeII lines profiles yielded the following set of parameters for theOstar at the observing epoch: T eff = 30 500±500 K, log g = 3. 31±0. 05, [He/H] = 0. 42 ± 0. 05. The observed HeI line profiles have emission components that are formed in the stellar wind and increase with the line intensity. The abundances of 11 elements in the atmospheres of V1357 Cyg and α Cam, which has a similar spectral type and luminosity class, are derived. The chemical composition of V1357 Cyg is characterized by a strong excess of helium, nitrogen, neon, and silicon, which is related to the binarity of the system. © 2012 Pleiades Publishing, Ltd

Investigation of the new cataclysmic variable 1RXS J180834.7+101041

We present the results of our photometric and spectroscopic studies of the new eclipsing cataclysmic variable star 1RXS J180834. 7+101041. Its spectrum exhibits double-peaked hydrogen and helium emission lines. The Doppler maps constructed from hydrogen lines show a nonuniform distribution of emission in the disk similar to that observed in IP Peg. This suggests that the object can be a cataclysmic variable with tidal density waves in the disk. We have determined the component masses (M WD = 0.8 ± 0.22M ⊙ and M RD = 0.14 ± 0.02M ⊙) and the binary inclination (i = 78° ± 1.5°) based on well-known relations between parameters for cataclysmic variable stars. We have modeled the binary light curves and showed that the model of a disk with two spots is capable of explaining the main observed features of the light curves. © 2011 Pleiades Publishing, Ltd

Investigation of the new cataclysmic variable 1RXS J180834.7+101041

We present the results of our photometric and spectroscopic studies of the new eclipsing cataclysmic variable star 1RXS J180834.7+101041. Its spectrum exhibits double-peaked hydrogen and helium emission lines. The Doppler maps constructed from hydrogen lines show a nonuniform distribution of emission in the disk similar to that observed in IP Peg. This suggests that the object can be a cataclysmic variable with tidal density waves in the disk. We have determined the component masses (M_WD =0.8 \pm 0.22 M_sun and M_RD =0.14 \pm 0.02 M_sun) and the binary inclination (i =78 \pm 1.5 deg) based on well-known relations between parameters for cataclysmic variable stars. We have modeled the binary light curves and showed that the model of a disk with two spots is capable of explaining the main observed features of the light curves.Comment: 22 pages, 9 figures, 2 tables, published in Astronomy Letters, 2011, 37, 845-85