[en] When a phase transition occurs from a thermally stable state at temperature Tapprox. =(5--10) x 10⁴⁰K to another stable state at Tapprox. =(1.5--2) x 10⁴⁰K in a medium heated by x rays whose spectrum contains no soft photons with E<200 eV, the volume emission coefficients of optical spectral lines should undergo nonmonotonic changes. These will take the form of abrupt flares rising above the steady level by a factor of 5--20 within an interval of (1--2) x 10¹²/n/sub H/ sec, where n/sub H/ is the number density of H atoms. This effect could prove decisive for explaining the rapid variability of the spectral lines observed in Seyfert-galaxy nuclei and quasars

[en] X-ray spectra are calculated in the ionization-equilibrium approximation model for gas bubbles in the shell evolutionary phase, blown in the interstellar medium by a stellar wind. Tabulated values cover the 83-4000 eV photon energy range at Delta-E/E = 0.1 resolution, and indicate the effect of interstellar absorption on the bubble spectrum. The energy-integrated flux is tabulated against the column density N(H) of the intervening medium and the central temperature T(0) of the decelerated-wind zone. A bubble spectrum can be distinguished from that of isothermal gas (corrected for absorption): it will be significantly softer, and in particular will fall off more gradually toward low E. Both T(0) and N(H) will be underestimated if an isothermal model is used, and the bubble's X-ray luminosity will be seriously understated (by at least an order of magnitude) for the Cygnus Superbubble. 23 references

[en] Soft X-ray emission from the ring nebula NGC6888, formed by the stellar wind of the central Wolf-Rayet star HD192163, has been found after thorough processing of Einstein observation data. A new class of X-ray sources, predicted some 20 years ago, has thus been discovered. The spectral shape agrees completely with theoretical predictions, but the emission flux is more than an order of magnitude less than the predictions. (author)

[en] Phase transfer from thermally stable state with temperature T approximately -) K to another stable state with T approximately (1.5/2)x10⁴ K in a medium heated by X-rays with spectrum without soft quanta with energy less than 200 eV must be accompanied by nonmonotonous variations of emission volume coefficients of optical spectral lines. These variations look like short bursts exceeding stationary state by a factor of 5-20 during time intervals approximately (1/2)x10sup(12)/nsub(n) s, where nsub(h) is hidrogen atom density. This effect may be important for interpretation of fast spectral line variability of Seyfert gal.axies nuclei and quasars

[en] The variable linear polarization of the intrinsic radiation emitted by an oblique, precessing accretion disk is calculated for the case of pure electron scattering in an optically thick disk atmosphere. The contribution of the intrinsic disk radiation to the variable linear polarization observed in the peculiar object SS 433 is discussed

[en] An analysis of the observational data on the local interstellar medium (LISM) shows that the Sun is located in a warm, low-density H I region with low ionization, at the edge of the local H I cloud with the size of several tens of parsecs, and shaped as a horseshow encompassing the Sun. The shape of the local cloud is presumably due to the cloud compression by the shock wave at the edge of the local cavern blown by the stellar wind and supernovae explosions in the Scorpio - Centaurus association. In the interaction region, the brightest spots of soft X radiation, observed at high galactic latitudes, are formed. The local cavern, surrounded by an H I supeshell, has a shape close to spherical with the distance from the center to the edge changing from 140-150 pc to 200-230 pc in the Sun direction, where the cavern is propagating into a corridor almost free of interstellar medium. The ionization equilibrium in low-brightness H II regions of LISM is maintained mainly by the radiation of the stars of the Sco - Cen association, and the energetics of the local cavern and of the supershell - mainly by the supernovae explosions. The local cavern seems to be in a stage of slow (2-3 km/s) expansion between the phases of a faster expansion under the impact of powerful stellar wind and of supernovae explosions of the medium-mass stars

[en] The expected x-ray emission of the cavities formed by stellar wind is calculated within the framework of the model of Weaver et al. Calculated results are presented for eight ring nebulae around WR and O/sub f/ stars. Observations of them in the x-ray range will permit a test of whether a layer of hot wind exists in the cavities or whether the wind leaks out rapidly through irregularities in the structure of the shell. It is shown that observations of the ring nebulae NGC 6888 and Sh 119 are the most promising; their expected emission spectra in the 0.1--4 keV range are presented

[en] Detailed analysis of soft (0.1-4keV) X-ray emission from the 1 deg x 1 deg field centered on the star HD 192163 in the nebula NGC 6888 has revealed, besides the nebula, 3 uresolved faint X-ray sources. Two among them are the nearby G-star HD 192020 and HD 192182 with X-ray fluxes=(3-4)x10^-13 and 1x10^-13 ergxcm^-2xs^-1 respectively; the temperature of HD 192020 is 0.17-0.35 keV. A source with the coordinates (1950.0)RA=20^h10^m52^s, DEC=38 deg 01', 0 is not identified. It has the flux F_X=(1.5-3)x10^-13ergxcm^-2xs^-1 and a hard spectrum. Upper limit of flux F_X ∼ 5x10^-14ergxcm^-2xs^-1 is found for a number of 7-9^m stars

[en] In the equilibrium-ionization approximation, X-ray spectra are computed and tabulated of the emission of gas bubbles, formed by interaction of a stellar wind with the interstellar medium, at the shell stage of evolution of bubbles. The data are presented on the bubble spectra, undistorted and distorted by interstellar absorption, in the photon energy range 83-4000 eV with the energy resolution ΔE/E=0.1. Also are presented the data on their emission fluxes, inegrated over the range 83<=E<=4000 eV, in function of the hydrogen surface density Nsub(H) and temperature T₀ of the central parts of the region of the deselerated stellar wind. The main difference of the bubble spectrum from the emission of isothermal gas (depleted by interstellar absorption), which allows to distinguish between these two cases, is in a more sloping low-frequency cut-off of the bubble emission. The spectrum of the bubble as a whole proves to be considerably softer than the one of isothermal gas. The approximation of the bubble emission by the isothermal gas model leads to an underestimate of the values of T⁰ and Nsub(H) and to strong underestimate of the bubble X-ray luminosity. For the Cygnus superenvelope, this underestimate may exceed a factor of 10

[en] When interpreting observations of variable polarization of the emission of binary stars and other objects the problem arises of comparing the observed and calculated polarization curves. A description of the shape of the polarization phase curve in the (Q x U) plane independent of the choice of the zero-point of the polarization position angle is proposed for periodically variable, linearly polarized radiation on the basis of the expansion of the Stokes parameters Q and U in Fourier series. In the (Q x U) plane each Fourier component of the Stokes parameters Q and U consists of an ellipse characterized by four geometrical parameters. Several examples of the description of calculated curves of polarization of the optical emission of binary x-ray systems are given for cases when the scattering takes place in optically thick media: for scattering of the light of a tidally deformed star in its atmosphere and of the light of a star of an accretion disk, both for one lying in the orbital plane and an inclined and precessing disk. Certain properties of the polarization phase curves in the (Q x U) plane resulting from the symmetry properties of rotating systems are pointed out