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Atomspheres of the components of close binary stars a thesis submitted to for the degree of doctor of philosophy in the faculty of Science, Bangalore University, Bangalore

Rao, M. S

Atomspheres of the components of close binary stars a thesis submitted to for the degree of doctor of philosophy in the faculty of Science, Bangalore University, Bangalore [Ph.D Thesis] M. S. Rao - Bangalore Indian Institute of Astrophysics 2001 - x, 178p.

Thesis Supervisor Prof. A. Peraiah

For theoretical modeling of binary systems one has to consider realistic
models which takes into account the radiative transfer, hydrodynamics.
reflection effect etc. Since the problem is complex, we study in the thesis
some of idealized models which will help us in understanding the important
physical processes in close binaries. Intially we have computed the
theoretical lines in the expanding and extended distorted atmospheres of
the components of close binary system. I have considered the necessary
geometrical formalism for illumination of a stellar atmospheres from a
source. We describe the method to calculate the radiation field from the
irradiated surface of the component in a binary system.
Chapter 1
Discrete Space theory of Radiative transfer: In this chapter a
concise description of the lnethod of obtaining the solution of radiative
transfer equation which can be applied to different geometrical and physical
systellls is given. This method was developed by Grant and Peraiah
(1972), and Peraiah and Grant(1973). This chapter deals with (1) interaction
principle (2) star product (3) calculation of radiation field at
internal points (4) integration of monochromatic radiative transfer equation
and derivation of rand t operators of the" cell". (5) flux conservation
and (6) line formation in expanding media.
The radiative transfer equation in spherical symmetry is used for calculating
the self radiation of the primary star in a binary system.
Chapter 2
Reflection effect in close binaries : The aim of this section is to
estimate the radiation field along the spherical surface of a primary component
irradiated by an external point source of radiation. This can be
applied to very widely separated systems. The transfer of radiation incident
on the atmosphere of the component from the companion cannot be
studied by using any symmetric solution of the equation of transfer. This
needs a special treatment. We adopt angle-free one dimensional model
(see Sobolev 1963).
Chapter 3
Incident radiation from an extended source: The effects of irradiation
from an extended source of the secondary cOInponent on the
atmospheres of the primary are studied.
Chapter 4
(1) Effects of reflection on spectral line forlllation: Effects of
reflection on formation of spectral lines in a purely scattering atmosphere
and studied how the equivalent widths change when irradiation from the
secondary is taken into account. However, these calculations were done
in static atnlospheres. So in the next step we have included the expanding
(2) Effects of irradiation on the line formation in the expanding
atmospheres of the components of a close binary system : We
studied the formation of lines in the irradiated expanding atmospheres
of the component of close binary system. We considered two-level atom
approximation in non-LTE situation with complete l'<.'clistribution. We
assumed that the dust scatters isotropically in the atmosphere. The line
profiles of the dusty atmosphere are compared with those formed in dust
free atmosphere. The profiles are presented for different velocities of
expansion, proximity of secondary component to the primary, and dust
optical depths.
The line profiles for a dust free atmosphere with and without reflection
effects are computed and compared.
Chapter 5
Distorted surface due to self rotation and tidal forces: In this
chapter a general expression for gravity darkening of the tidally uniformly
rotating roche components of close binary system is derived. This theory
is used to calculate the line profiles taking into account rotation and
expansion velocities.
Chnpter 6
Effect of gravity darkening on spectral line forlnation : We studied
the transfer of line radiation in the atmospheres of close binary components
whose atmospheres are distorted by the self radiation and tidal
forces due to the presence of the secondary component. The distortion
is measured in terms of the ratio of angular velocities at the equator and
pole, mass ratio of the two components, the ratio of centrifugal force to
that of gravity at the equator and the ratio of the equatorial radius to the
distance between the centers of gravity. We obtain the equation of the
distorted surface by solving a seventh degree equation which contains the
above parameters. Transfer of line radiation is studied in such asymmetric
atmosphere assuming complete redistribution and a two-level atom
approximation. The atmosphere is assumed to be expanding radially.
Various black body temperatures are being used to describe the total
luminosity of the components for the purpose of irradiation.
Chapter 7
Conclusions: We present important results obtained from this study
of research from each chapter.

binary stars


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