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Title:
The Spectra of Mira Variable Stars.
Authors:
Crowe, Richard Alan
Affiliation:
AA(UNIVERSITY OF TORONTO (CANADA).)
Publication:
Thesis (PH.D.)--UNIVERSITY OF TORONTO (CANADA), 1984.Source: Dissertation Abstracts International, Volume: 45-09, Section: B, page: 2955.
Publication Date:
00/1984
Category:
Physics: Astronomy and Astrophysics
Origin:
UMI
Bibliographic Code:
1984PhDT........65C

Abstract

The catalog of Keenan, Garrison and Deutsch (1974) has been extended by the addition of 483 blue spectrograms of 72 Southern Hemisphere Mira variables. About 190 direct and image-tube plates at a dispersion of 120 (ANGSTROM)/mm were obtained in Chile between 1977 and 1982. Spectral types, emission-line ratios for H(delta) 4101/H(gamma) 4340/H(beta) 4861 and eye-estimated intensities of the absorption lines Ca I (lamda)4226, Cr I (lamda)4254 and Sr II (lamda)4077 have been tabulated. Spectral montages for six stars are used to illustrate changes in the visual spectra of Mira variables through their respective cycles. Radial velocities of absorption and emission line systems have been determined for 22 Northern Hemisphere Mira variables. These were measured from approximately 65 spectra obtained on baked IIa-O plates at a dispersion of 12 (ANGSTROM)/mm with the DDO 1.88-m telescope. Most of these Northern Hemisphere stars were observed close to maximum light, and so only in a few cases (for example, R Trianguli) is there any useful phase information available. It can be shown from this data that the irregular behaviour of absorption features in Mira variables is the consequence of a second shock front which is higher up in the atmosphere than the one producing Balmer emission, as has been proposed by Hill and Willson, 1979b). We present evidence that strong emission is associated with weak-line cycles (when overlying TiO absorption is also weaker) and that the velocity gradient is directly responsible for the weakening by the escape enhancement process (Mihalas, 1978). Since the shock strength varies from cycle to cycle, we do not expect the affected lines to maintain the same equivalent width at the same phase in different cycles. There is, however, a great deal of internal scatter from star to star which confuses the interpretation. The separation of Mira variables into two groups (namely, those with spectral types earlier and later than M5e at maximum light) helps to clarify the overall perspective of these enigmatic stars.
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