Reflection effect in close binaries: effects of reflection on spectral lines

Reflection effect phenomenon is studied on the formation of spectral lines in a close binary system when primary component has an extended atmosphere and the secondary component is a point source. Irradiation effect is calculated using one dimensional rod model and self radiation is calculated using continuum radiative transfer equation in spherically symmetric atmosphere. The total radiation is the sum of the radiation of the individual components and the mutually reflected light. Line profiles are also computed along the line of sight observer at infinity for irradiation, self radiation and total radiation and compared in order to study the reflection effect on spectral lines. It is found that the radiation field varies on the primary component when angle of incidence changes from the secondary component. The contour maps show that the radiative interaction makes the outer surface of the primary star warm when its companion illuminates the radiation. The effect of reflection on spectral lines is studied and noticed that the flux in the lines increases at all frequency points and the cores of the lines received more flux than the wings and equivalent width changes accordingly.     

Reflection effect in close binaries. III. Distribution of radiation incident from an extended source

We have studied the effects of irradiation from an extended surface of the secondary component on the atmosphere of the primary. We have considered an isothermal and purely scattering medium. The resultant radiation field due to irradiation from an extended surface and self-radiation is different from that due to irradiation from a point source and self-radiation. In the case of the point source the middle layers of the exposed part of the atmosphere show maximum reflection while in the former case the reflection gradually decreases from the centre of the component towards the surface of the outermost layers of the atmosphere. The reflection effect appears to be strongly dependent on the density distribution of the electrons.     

Detection of the first thermonuclear X-ray burst from AX J1754.2-2754

When analyzing the archival data of the INTEGRAL observatory, we detected an intense X-ray burst recorded on April 16, 2005, by the JEM-X and IBIS/ISGRI telescopes from the weak and poorly studied source AX J1754.2-2754. Analysis of its time profiles and spectra allows this event to be attributed to type I X-ray bursts associated with thermonuclear explosions on the surfaces of neutron stars and the source itself to X-ray bursters. Peculiarities of the X-ray emission observed at the initial evolutionary phase of the burst point to a dramatic expansion and a corresponding cooling of the neutron star photosphere that took place at this time under the action of radiation pressure. Assuming the luminosity of the source at this phase to be the Eddington one, we have estimated the distance to the burst to be d = 6.6 ± 0.3 kpc (for a hydrogen atmosphere of the neutron star) and d = 9.2 ± 0.4 kpc (for a helium atmosphere).     

Radiative transfer effects in rotationally distorted stars

A general expression for the gravity darkening of the tidally and non-uniformly rotating Roche components of close binary systems is used to calculate the uniform rotational effects on line profiles in an expanding atmosphere. We consider a non-local thermodynamic equilibrium (non-LTE) two-level atom approximation in an extended atmosphere, and use Von Zeipel's theorem for the incident radiation at the maximum optical depth  (τ=τ_max)  in the atmosphere. These calculations are performed with uniform rotational velocities of 1, 4 and 8 mtu (mean thermal units). It is found that rotation dilutes the radiation field which is similar to the expansion velocity.
We also study rotational aspects, which make the outer layers of the star distorted. The equation of line transfer is solved in the comoving frame of the expanding atmosphere of the primary using complete redistribution in the line. We use a linear law for the velocity of expansion such that the density varies as r ⁻³, where r is the radius of the star, satisfying the law of conservation of mass. It is found that rotation broadens the line profile, and P-Cygni-type line profiles are obtained.     

The X-ray burst detected in 1991 from the transient source SAX J1747.0-2853

We present the observations of an intense X-ray burst from the recurrent transient source SAXJ1747.0-2853 located near the Galactic center. The burst was detected by the ART-P telescope onboard the Granat observatory on October 20, 1991. The burst time profile exhibits features that clearly point to an increase in the photospheric radius of the neutron star at the burst onset. This increase is attributable to an expansion of its outer hydrogen-rich atmospheric envelope under radiation pressure. After hydrogen-envelope outflow and photospheric contraction, the radiation flux emerging from deep within the star continued to rise, which several seconds later led to a recurrent, weaker photospheric expansion attributable to the outflow of the outer helium-envelope layers. Based on the described picture, we determined the distance to the source, d=7.9±0.4 kpc. No radiation was detected by the ART-P telescope from the source in quiescence. Actually, the source itself was discovered only seven years later by the BeppoSAX satellite during its X-ray activity.     

Interaction of the X-ray source radiation with the atmosphere of the normal star in close binary systems

The structure of the stellar atmosphere irradiated by an X-ray source is calculated. On the basis of these numerical calculations an approximate theory of the X-ray reprocessing is formulated. The interaction of X-rays with the stellar atmosphere induces a considerable stellar wind. However, the main part of the X-ray energy is reemitted.The optical appearances of the close binary system including an X-ray source are discussed. The light curve of such a system is obtained. The mass-loss rate of a star with the size close to that of its Roche lobe is evaluated in the isothermal approximation. Most likely, the accretion of matter on to a neutron star, or a black hole, is the cause of the X-ray luminosity. The accreting matter is supplied with the mass outflow from the normal component induced by X-rays. The X-ray luminosity is shown to have an upper limit stipulated by the outflow saturation.The model of HZ Her=Her X1 system is constructed which accounts for the observed light curve. The optical appearances of the system are due to the X-ray heating of the face of the X-ray source area of the normal star. The radiation of this hot area is partly reflected by the surface of the disc around the X-ray source. The thin disc is formed by the accretion of matter by the X-ray source. The effective reflection of hard X-rays (hv15–30 keV) by the stellar surface is considered. This phenomenon makes it possible to detect those X-ray pulsars whose beam does not intercept the Earth.The model of Sco X1 as a black hole in a close binary system is discussed.     

X-ray emission associated with gamma-ray bursts

The energy spectra of gamma-ray bursts differ from those of black-body radiation and are similar to the thermal bremsstrahlung spectra of optically thin plasma. This could be realized if the source is located in the outer atmosphere of a neutron star. In this case, almost one half of the emitted photons hit the surface of the star. The surface of the star is heated to a temperature of the order 10⁷ K, and a dominant flux of X-rays with a black-body spectrum would be expected. The X-rays produced by this mechanism are detectable in the energy range from a few keV to 10 keV. This model is discussed in relation to the recent observations in the X-ray region at the time of gamma-ray bursts, and modifications of this model are also presented. The observation in this energy range will bring us valuable information on the nature of gamma-ray burst sources.     

On the formation of pulsar radiation diagrmas

A model of pulsars is discussed in which formation of a polar diagram of the radiation is influenced by the motion of the source around a neutron star with a velocity close to that of light. For a power-law frequency-spectrum of the radiation and isotropy of the diagram in a system of coordinates rotating with the source, the width of the observed pulse is shown to be independent of frequency.The proposed explanation of the second period characteristics of type CP 1919 pulsars is based on the effect of relativistic motion of the radiation source. The positions are established (relative to the axis of rotation of the star) of the local sources of radiation in the optical and in the radio ranges for the pulsar NP 0532. It is shown how the polarization characteristics of the optical radiation of this pulsar may be connected with the effects of relativistic orbiting of the source of radiation about the star.     

Diffraction of electromagnetic waves in Schwarzschild's space-time

In order to study the gravitational lens effect in detail this paper investigates the electromagnetic radiation generated by an electric dipole oscillating with high frequency in the Schwarzschild metric outside the horizon. Expressions for the Newman-Penrose tetrad components characterizing the radiation field are derived in a suitable approximation. The Poynting vector is discussed in the region behind the deflecting mass (black hole, neutron star) in the fully coherent case for large distances of source and observer from the centre of the lens. Intensity and gain in the focal region coincide with the corresponding values applying to scalar radiation. An observer sees double images of the source outside the focal region. The results (positions of the images, relative intensities) are compared with those occurring in the case of an incident plane wave (recently treated by Herlt and Stephani) and with the properties of the images in the (geometrical optics) limit of incoherent radiation.     

ART-P/GRANAT observations of the X-ray source KS 1731-260

The results of observations of the transient X-ray burster KS 1731-260 with the ART-P telescope onboard the GRANAT observatory are presented. The observations were performed in 1990–1991 at the initial stage of the source’s 12-yr activity period when no studies were conducted by other X-ray observatories. The flux from KS 1731-260 is shown to have systematically decreased, forming a separate initial “minioutburst” of the source with a duration of ～2.5 yr. The decrease in flux was accompanied by an increase in the spectral hardness of KS 1731-260 and an enhancement of its burst activity; two X-ray bursts were detected in the last observing sessions when the flux decreased by 40–60%. Their analysis showed that they occurred in a medium with an appreciable hydrogen abundance; i.e., the enrichment efficiency of the material in the lower atmospheric layers of the neutron star during quasi-steady hydrogen burning was low. The BDLE model that was suggested by Grebenev et al. (2006) to describe the radiation spectra of weakly magnetized accreting neutron stars has been used for the first time to analyze the continuum radiation spectrum of the source. This model incorporates two spectral components associated with the radiation from the boundary layer formed at the place of contact between the accretion disk and the neutron star surface and with the radiation from the accretion disk proper. The model satisfactorily fits the observed radiation spectra of the source and allow such parameters of the binary system as the accretion disk inclination, the bolometric luminosity (accretion rate), and the temperature of the outer boundary layer to be estimated. The boundary layer radiation for KS 1731-260 is shown to have originated in an exponential atmosphere of moderate optical depth for Thomson scattering under conditions where comptonization had no time to form the Wien spectrum, but only modified the thermal plasma radiation spectrum.     

The effects of mass on the radiation of a relativistically rotating neutron star

We investigate the effect of mass on the radiation of a relativistically rotating neutron star. The method of Haxton and Ruffini is used to find the radiation flux from a relativistically rotating neutron star. By extending the idea of a point charge orbiting a black hole, a pulsar is modeled by simulating a relativistically rotating magnetic dipole embedded within a neutron star. The resulting equations retain the mass of the neutron star, thereby introducing effects of general relativity on the radiation from the dipole. We present exact solutions to the modeling equation as well as plots of energy spectra at different rotational velocities and inclination angles. We also present plots of total energy versus mass and two tables containing a comparison of energy ratios. These demonstrate that, for realistic neutron star masses, the high speed enhancement of the radiation is always more than compensated by the frame dragging effect, leading to a net reduction of radiation from the star. It is found that the inclusion of mass not only reduced the special relativistic enhancement, but negates it entirely as the mass of the neutron star approaches the mass limit.     

Curvature effects in extended stellar atmospheres — Pure absorption

The effects of curvature in an atmosphere with pure absorption are investigated. Numerical solution of the transfer equation has been obtained in the framework of the Discrete Space Theory of Radiative Transfer. Two cases have been considered: (a) the atmosphere is irradiated at the bottom and there is no incident radiation at the top of the atmosphere; and (b) no radiation is incident on either side of the atmosphere. It is found that the thermal sources inside the atmosphere dominantly influence the emergent radiation and this is very much so, in the spherical case and for large optical thickness. The emergent luminosities increase with the geometrical thickness although the emergent specific intensities are reduced and the former seems to be because of the larger surface area and later seems to be because of the effects of curvature.     

Dynamical and pressure structures in winds with multiple embedded evaporating clumps – I. Two-dimensional numerical simulations

Because of its key role in feedback in star formation and galaxy formation, we examine the nature of the interaction of a flow with discrete sources of mass injection. We show the results of two-dimensional numerical simulations in which we explore a range of configurations for the mass sources and study the effects of their proximity on the downstream flow. The mass sources act effectively as a single source of mass injection if they are so close together that the ratio of their combined mass injection rate is comparable to or exceeds the mass flux of the incident flow into the volume that they occupy. The simulations are relevant to many diffuse sources, such as planetary nebulae and starburst superwinds, in which a global flow interacts with material evaporating or being ablated from the surface of globules of cool, dense gas.     

Atmospheric Disturbances and Radiation Impulses Caused by Large-Meteoroid Impacts on the Surface of Mars. II. Radiation Impulse Characteristics and Parameters of the Warm Layer

This paper presents the results of the calculation of spectral and angular characteristics of radiation emitted by the disturbed region after the vertical impacts on the Martian surface of stony meteoroids with radii R ₀ from 1 to 100 m at speeds of 11–20 km/s. The time dependences are given for the density of the radiation flux incident on horizontal surface areas located at different distances from the impact point. For small impactors (R ₀= 1 m), the heating of the surface and surrounding gas by the radiation impulse from the hot region formed after the impact is insignificant even at the crater edge. However, the radiation impulse that heats up the surface is also emitted during the meteoroid flight through the atmosphere. Although this heating is insufficient to initiate evaporation, heat transfer by turbulent diffusion leads to the formation of a layer with temperatures that substantially exceed the initial temperature of the atmosphere. For large impactors (R ₀ = 100 m), the total specific impulse of the plume radiation gives rise to the emergence of the heated layer with a thickness on the order of several meters within several kilometers of the impact point. The formation of this warm layer may lead to the formation of a high-speed jet moving along the Martian surface as well as eddies at the front of the precursor with a subsequent intense rise of dust.     

Magnetospheric plasma sputtering of Io's atmosphere

The existence of an atmosphere at Io is presumed and used as a starting point to generate neutral coronae produced by magnetospheric ion sputtering from the exobase and to calculate injection of neutrals and ions into the plasma torus. Several different exobase heights, temperatures, and compositions are used to characterize the neutral and ion ejection processes associated with possible atmospheres. Collision ejection from the sputter-produced corona is shown to be an important supply of neutrals for all atmospheres considered. The net injection rates are compared with estimates of the rates required to populate the plasma torus. We show that by including the sputtered atmospheric corona produced by assuming an unattenuated incident ion flux, the supply rate to the torus can be satisfied with an exobase very close to the surface. An exobase close to the surface would imply that the atmosphere at Io is not robust enough to support a fully photodissociated corona and that a significant fraction of the incident plasma ions can penetrate to the surface, providing a sputter source of atmospheric gas. Conversely, a high exobase could only be consistent with the estimated supply rates if the incident plasma flux is attenuated or deflected. The results presented scale approximately with the magnitude of the incident ion flux and, therefore, can be used as knowledge of both the plasma flow and atmospheric composition improve.     

Red and blue shifts near compact objects

We show that radiation emitted from material falling toward a black hole or neutron star can be blue-shifted as well as red-shifted. Although the red shift can be arbitrarily large near a black hole, there is an upper limit for the blue shift of 1/2. Material incident toward the poles of a magnetic neutron star can simultaneously radiate red and blue-shifted lines. Near an oblique magnetic rotator, the red and blue shifts will show a sinusoidal variation. Such spectral variations are associated with SS 433.     

Gravitational radiation of a differentially rotating superfluid neutron star

The gravitational radiation of a neutron star with a weakly coupled superfluid component is considered. It is assumed that regions can exist in the star's core which rotate at substantially higher angular velocities than the observed angular velocities of pulsars. A star of this sort has a quadrupole moment on the order of the maximum value for the neutron star configurations that have been discussed, so it could be a powerful source of gravitational radiation for the planned Advanced LIGO detector. Translated from Astrofizika, Vol. 51, No. 4, pp. 647–652 (November 2008).     

Seasonal north-south asymmetry in solar radiation incident on jupiter's atmosphere

Although the orbital eccentricity and axial tilt are small, the near-temporal coincidence of perihelion and the northernmost excursion of the subsolar point produce asymmetries in the solar radiation incident on Jupiter's atmosphere. Calculations of the incident radiation and the latitudinal gradient of the insolation are presented. North-south asymmetries in the zonal wind and morphology of the large-scale cloud systems observed by Voyagers 1 and 2 are cited. In the absence of an identified internal mechanism capable of generating the observed asymmetries, seasonal forcing of this magnitude should be considered.     

The solar radiation incident at the top of the atmospheres of Uranus and Neptune

The latitudinal and seasonal variation of the direct solar radiation incident at the top of the atmosphere of Uranus and Neptune has been recalculated by use of updated values for the period of axial rotation and the oblateness. Values for the solar radiation are given in Watt per square meter instead of the unit used in earlier papers (calories per square centimeter per planetary day). The solar radiation averaged over a season and a year as a function of planetocentric latitude has also been reviewed. In addition, attention is made to the ratio of the solar radiation incident on an oblate planet to that incident on a spherical planet.     

A model for the temperature inversion within the atmosphere of Saturn

A model for the temperature inversion within the atmosphere of Saturn is proposed and is shown to be consistent with photometric data in the 17- to 25-μm region. The proposed model incorporates solar heating by some “aerosol,” with the aerosol heating per unit mass of the atmosphere being uniformly distributed throughout that portion of the atmosphere overlying the upper cloud deck. For a methane-to-hydrogen mixing ratio of 7 × 10^?4, the model results suggest that 20% of the incident solar radiation is absorbed by the aerosol, while this is reduced to 16% for an enhanced methane mixing ratio of 2.1 × 10^?3.