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Title:
The atmospheric motion of the Beta Cephei star - 12 Lacertae
Authors:
Mathias, P.; Gillet, D.; Crowe, R.
Affiliation:
AA(Haute-Provence, Observatoire, Saint-Michel-l'Observatoire, France), AB(Haute-Provence, Observatoire, Saint-Michel-l'Observatoire, France), AC(Hawaii Univ., Hilo)
Publication:
Astronomy and Astrophysics (ISSN 0004-6361), vol. 257, no. 2, p. 681-692. (A&A Homepage)
Publication Date:
04/1992
Category:
Astrophysics
Origin:
STI
NASA/STI Keywords:
STELLAR ATMOSPHERES, STELLAR OSCILLATIONS, STELLAR SPECTRA, VARIABLE STARS, H ALPHA LINE, RADIAL VELOCITY, SILICON, STELLAR MODELS, TEMPORAL RESOLUTION
Bibliographic Code:
1992A&A...257..681M

Abstract

The Beta Cephei star 12 Lacertae has been studied at high spectral (R = lambda/delta-lambda between 15,000 and 70,000) and time resolution (around 7 min), with a high SNR (around 200), using the 152-cm telescope of the Observatoire de Haute-Provence and its spectrograph AURELIE. Two spectral ranges were considered: one around the H-alpha line and the second around the Si III 4553 A line. The velocity curves obtained were all different from one another, sometimes showing a stillstand, with various 2 K amplitudes and gamma velocities. It is suggested that these latter changes are not the result of an interaction with a hypothetical companion, but rather due to interactions between several pulsation modes of both radial and nonradial origin. The main interference produces a beat period around 8.9 d. Except for this last phenomenon, the overall atmospheric motion of 12 Lacertae seems similar to that occurring in BW Vulpeculae and Sigma Scorpii. In particular, the occurrence of two shock waves per pulsation period is supported by the observations. We suggest that the appearance of numerous iron lines, producing an opacity increase, is at the origin of the stronger shock, while the smaller one could be due to the CNO kappa mechanism.

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