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Spectroscopic studies of hot, luminous stars

Siebert, Kaj Wik; (1999) Spectroscopic studies of hot, luminous stars. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

Results of detailed spectroscopic analyses of selected early-type stars are presented. Atmospheric parameters are derived for 23 O-type stars by comparing high-resolution echelle observations with hydrogen/helium non-LTE model spectra. Effective temperatures. Surface gravities and helium abundances are derived for each star. And the effects of micro-turbulence on the adopted parameters are investigated. The derived helium abundances are considered in an evolutionary context, concentrating on trying to understand the chemically divergent OC/ON stars. A clear relation between carbon/nitrogen abundance anomalies and derived helium number fractions is found. Other possible explanations for the observed abundance anomalies are considered. There has also been proposed (and appears to be) a relation between the line broadening in early-type stars and their surface chemical composition. Two possible sources for line broadening, stellar rotational and macroturbulence, are considered and the 'best-fir' broadening type is found by careful fitting of stellar absorption lines. Both macroturbulent and rotational velocities are derived for the ()-star sample. A statistical analysis of the line-broadening properties of early-type stars is also undertaken. By cross-correlating International Ultraviolet Explorer spectra of B stars against several stellar template spectra, the effects of line-broadening on the cross-correlation functions (CCDs) are investigated, and calibrations between CCF full-width half-maximum and rotational velocity are derived. These calibrations are used to find rotational velocities for over 700 stars.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Spectroscopic studies of hot, luminous stars
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest.
Keywords: Pure sciences; Early-type stars
URI: https://discovery.ucl.ac.uk/id/eprint/10097661
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