A. Peraiah
Articles written in Journal of Astrophysics and Astronomy
Volume 1 Issue 1 September 1980 pp 3-16
Comoving frame calculations have been used to compute the spectral lines formed in rapidly expanding spherical media. We have employed the angle-averaged partial frequency redistribution function
Volume 1 Issue 1 September 1980 pp 17-23
Lines formed in rotating and expanding atmospheres
Spectral lines formed in a rotating and expanding atmosphere have been computed in the frame of the observer at infinity. Two kinds of velocity laws are employed: (i) a uniform radial velocity of the gas and (ii) velocity increasing with radius (
Generally, the lines are broadened when rotation is introduced. However, when radial motion is also present, broadening becomes asymmetric and the red emission and blue absorption are enhanced.
Volume 1 Issue 2 December 1980 pp 101-111
A direct iteration has been performed to obtain a simultaneous solution of the equations of line transfer in an expanding spherically symmetric atmosphere in the comoving frame with statistical equilibrium for a non-LTE, two-level atom. The solution converges in three or four iterations to an accuracy of 1 per cent of the ratio of the population densities of the two levels. As initial values, the upper level population was set equal to zero or to the LTE densities. The final solution on convergence indicates enhanced population of these levels over the initial values assumed, Large velocity gradients enhance this effect whereas large geometrical sizes of the atmospheres tend to reduce it.
Volume 1 Issue 2 December 1980 pp 113-117
Effects of high velocities on photoionization lines
We have treated formation of spectral lines in a commoving frame where photoionization is predominant over collisional processes. We have assumed that the radiation field for causing photoionization is a function of Planck function. We have also considered the situation in which the continuum contributes to the radiation in the line. In all the models the quantity
Volume 2 Issue 1 March 1981 pp 81-86
Photon escape probabilities in expanding atmospheres
A. Peraiah K. E. Rangarajan D. Mohan Rao
A comparison of mean number of scatterings and escape probabilities has been made in isotropic scattering and dipole scattering by using the angle-averaged partial frequency redistribution function
We find that the partial frequency redistribution gives a larger mean number of scatterings compared to that given by complete redistribution. Velocities tend to reduce the mean number of scatterings and in crease the mean escape probabilities.
Volume 2 Issue 3 September 1981 pp 245-252
Effects of redistribution with dipole scattering on line source functions
The partial frequency redistribution function for zero natural line width with dipole scattering (R_{I}) has been considered in obtaining the simultaneous solution of the statistical equilibrium and line transfer equations in the comoving frame of the expanding gas. We have considered a non-LTE two level atom in an expanding spherical medium whose outer radii are 3, 10 and 20 times the stellar radius with a total optical depth
Volume 2 Issue 3 September 1981 pp 277-284
A. Peraiah G. Raghunath K. N. Nagendra
We have investigated the effects of increasing optical depths on spectral lines formed in a rotating and expanding spherical shell. We have assumed a shell whose outer radius is 3 times the inner radius, with the radial optical depths equal to 10, 50, 100, 500. We have employed a constant velocity with no velocity gradients in the shell. The shell is assumed to be rotating with velocities varying as 1/_{ρ}, where_{ρ} is the perpendicular distance from the axis of rotation, implying the conservation of angular momentum. Two expansion (radial) velocities are treated: (1)
Volume 3 Issue 3 September 1982 pp 297-302
On the Balmer progression in the expanding shell of Pleione
An attempt has been made to explain the Balmer progression in velocities seen in Pleione and other shell stars. Equations of conservation of mass and momentum are simultaneously solved with assumptions which simplify the calculations of the solution. We have considered the radiation pressure due to lines and continuum. It is found that the high-excitation lines are formed where the velocity gradients are high.
Volume 3 Issue 4 December 1982 pp 485-497
Reflection effect in close binaries. I. Distribution of radiation from a point source
The radiation field along an irradiated surface of a component in a binary system is calculated. The source of irradiation is assumed to be a point source. This is done primarily to understand easily how the incident radiation will get changed after it is being scattered by the atmosphere. It is noticed that the maximum radiation comes from intermediate points of the atmosphere, the reason being that here we have the combined radiation due to the star and incident radiation from the point source outside the star although both are diluted.
Volume 4 Issue 1 March 1983 pp 11-17
We have calculated the effects of irradiation from a point source observed at infinity. Plane-parallel approximation and spherically-symmetric approximations are employed in calculating the self-radiation field for the sake of comparison. It is found that there are considerable changes in the radiation received at infinity between the approximation of plane-parallel stratification and spherical symmetry.
Volume 4 Issue 2 June 1983 pp 151-159
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.
Volume 4 Issue 3 September 1983 pp 175-182
The law of limb darkening has been calculated when the atmosphere of the primary component is illuminated by the extended surface of the secondary component in a binary system. The specific intensities calculated at infinity show marked changes when the plane-parallel approximation is replaced by the assumption of spherical symmetry. The middle portions of the illuminated surface reflect maximum radiation while the innermost and outermost layers show lesser amount of reflected radiation.
Volume 4 Issue 3 September 1983 pp 183-189
Reflection effect in close binaries. V. Effects of reflection on spectral line formation
The effects of reflection on the formation of spectral lines is investigated. We have assumed a purely scattering atmosphere and studied how the equivalent widths change due to irradiation from the secondary. Generally, the flux in the lines is increased at all frequency points, the cores of the lines receiving more flux than the wings. Moreover, the proximity of the secondary component changes the equivalent widths considerably. The further away the secondary is from the primary the higher are the equivalent widths.
Volume 5 Issue 2 June 1984 pp 169-180
Effects of partial frequency redistribution functions R_{II}, R_{III} and R_{V} on source functions
D. Mohan Rao K. E. Rangarajan A. Peraiah
The effects of partial frequency redistribution on the formation of spectral lines have been studied. We considered the angle-averaged R_{II}, R_{III} and
Volume 11 Issue 2 June 1990 pp 193-208
Radiative transfer with Compton scattering in plane parallel geometry
We have solved the equation of radiative transfer with Compton scattering. The specific intensity has been expanded by Taylor series with respect to wavelength and the first three terms have been retained in solving the transfer equation. It is noted that in a medium stratified in plane parallel layers, the multiple Compton scattering redistributes the initial energy over a range of 3 to 5 Compton wavelengths. A good fraction of the incident radiation is transferred across the layer with redistribution in wavelength, the actual value depending on the optical thickness of the medium
Volume 11 Issue 2 June 1990 pp 209-219
Equivalent widths of hydrogen Lyman alpha line in an expanding spherical atmosphere
We have calculated the profiles of hydrogen Lyman a line in an expanding spherical atmosphere containing dust and gas. We have investigated the variation of equivalent widths with velocities of expansion of the atmosphere, together with the amount of dust present in the medium. We have drawn curves of growth for different velocities and dust optical depths
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