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Atmospheres of cool stars (Record no. 14471)

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fixed length control field 04599nam a2200229Ia 4500
003 - CONTROL NUMBER IDENTIFIER
control field IN-BaIIA
005 - DATE AND TIME OF LATEST TRANSACTION
control field 20211110142841.0
008 - FIXED-LENGTH DATA ELEMENTS--GENERAL INFORMATION
fixed length control field 211028s9999 xx 000 0 eng d
040 ## - CATALOGING SOURCE
Transcribing agency IIA Library
080 ## - UNIVERSAL DECIMAL CLASSIFICATION NUMBER
Universal Decimal Classification number 043:52
Item number SIN
100 ## - MAIN ENTRY--PERSONAL NAME
Personal name Singh, P
9 (RLIN) 25712
Relator term Author
245 #0 - TITLE STATEMENT
Title Atmospheres of cool stars
Remainder of title a thesis submitted for the degree of Doctor of Philosophy in the faculty of science, Bangalore University, Bangalore
Statement of responsibility, etc. P. Singh
Medium [Ph.D Thesis]
260 ## - PUBLICATION, DISTRIBUTION, ETC.
Place of publication, distribution, etc. Bangalore
Name of publisher, distributor, etc. Indian Institute of Astrophysics
Date of publication, distribution, etc. 1995
300 ## - PHYSICAL DESCRIPTION
Extent 90p.
500 ## - GENERAL NOTE
General note Thesis Supervisor A. Peraiah
502 ## - DISSERTATION NOTE
Degree type Doctor of Philosophy
Name of granting institution Indian Institute of Astrophysics, Bangalore
Year degree granted 1995
520 ## - SUMMARY, ETC.
Summary, etc. In this study I use partial frequency redistribution (PRD) functions to examine their effects on spectral line formation in spherically symmetric and expanding atmospheres of cool giant and supergiant stars. Primary aim of this investigation is to bring out the differences between the emergent spectral line profiles resulting from PRD and complete redistribution (CRD) under the influence of various physical parameters characterizing the atmospheres of cool giants and supergiants. The appreciation of this aspect will be important for quantitative analysis of stellar spectra and for computing model atmospheres of such stars.<br/>In a scattering process, both the direction and the frequency of a photon may change. These changes are described by partial frequency redistribution functions. There a.re following four categories of redistribution functions: Case I, zero line width, denoted by RI. It does not apply to any real line; demonstrates the effects of Doppler redistribution alone to an observer in the laboratory frame. Case ll, radiation, damping in the upper state and coherence in the atom's rest frame, denoted by RII. It applies to resonance lines in low density media. Case III, complete redistribution in the atom's frame, denoted by R lll. Case IV, subordinate line redistribution between two broadened states, denoted by Rv. It applies to non-coherent subordinate line scattering. Complete redistribution is a limiting approximation which implies that there is a complete reshuffling of atoms in their excited state in such a way that there is no correlation between the frequencies of the incoming and the scattered photons. <br/>The assumption of CRD has been widely used in earlier works on line transfer because it not only simplifies the numerical. solution of the transfer equation but also provides a good approximation to reality in those media which are dense enough to support high collision rates. However, in the extended and tenuous atmospheres of cool giants and supergiants where low densities (and hence low collision rates) prevail, CRD is not expected to yield accurate emergent spectral line profiles. Moreover, in the wings of strong resonance lines, the scattering is nearly coherent. This leads to a deviation of the line profiles from those calculated in accordance with the assumption of CRD. Therefore, a natural recourse to the application of partial frequency redistribution can lead to more accurate line profiles. <br/>Over the last two decades, considerable progress has been made in using partial frequency redistribution functions to study the spectral line formation in idealized stellar atmospheres. Most of these studies are limited to the assumption of plane-parallel geometry and/or the absence of velocity fields. These assumptions a.re unrealistic because the real atmospheres of cool giants and supergiants expand and are geometrically extended. There are only few papers in literature which have taken into account both the spherical geometry and the expansion effects to study PRD effects on emergent line profiles in idealized atmospheres. These studies employ either RI or R II. R III has usually been represented by CRD. Some studies have been done to model the spectral lines formed in the expanding chromospheres of red giants using R II. So far, the combined effects of sphericity and velocity fields on the differences between the solutions resulting from Rv and the CRD have not been explored. As an important feature of the present work I make a detailed comparative study of the PRD effects of R II, R III and Rv on the spectral line formation in the atmospheres of cool giants and supergiants taking into account both the sphericity and the expansion effects.
650 ## - SUBJECT ADDED ENTRY--TOPICAL TERM
Topical term or geographic name entry element Cool stars
9 (RLIN) 5425
700 ## - ADDED ENTRY--PERSONAL NAME
Personal name A. Peraiah
Relator term Supervisor
9 (RLIN) 48850
856 ## - ELECTRONIC LOCATION AND ACCESS
Uniform Resource Identifier <a href="http://prints.iiap.res.in/handle/2248/151">http://prints.iiap.res.in/handle/2248/151</a>
Link text Click Here to Access eThesis
942 ## - ADDED ENTRY ELEMENTS (KOHA)
Koha item type Thesis & Dissertations
Source of classification or shelving scheme Universal Decimal Classification
Holdings
Withdrawn status Lost status Source of classification or shelving scheme Damaged status Not for loan Home library Current library Shelving location Date acquired Full call number Barcode Date last seen Price effective from Koha item type
    Universal Decimal Classification     IIA Library-Bangalore IIA Library-Bangalore General Stacks 13/02/2002 043:52/ SIN 15393 05/11/2021 13/02/2002 Thesis & Dissertations

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