The atmospheric motion of the beta Cephei star: 12 Lacertae
P. Mathias
- D. Gillet
- R. Crowe
Received August 27; accepted September 20, 1991
Abstract:
The beta Cephei star 12 Lacertae has been studied at high spectral (R between
15000 and 70000) and time resolution (around 7 min), with a high
signal-to-noise ratio (around 200), using the 152-cm telescope of the
Observatoire de Haute-Provence (OHP) and its spectrograph AURELIE. Two spectral
ranges were considered: one around the Halpha line and the second around the
Si III 4553 Å line.
The velocity curves obtained were all different from one
to another, sometimes showing a stillstand, with various 2K-amplitude 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 non radial origin. The main
interference produces a beat period around 8.9d. Except for this last
phenomenon, the overall atmospheric motion of 12 Lacertae seems similar to that
occuring in BW Vulpeculae and sigma Scorpii. In particular, the occurence 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.
Keywords:
lines: profiles -- shock waves -- stars: variables: other --
stars: 12 Lac
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