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Velocity variations of semiregular variables in the infrared
T. Lebzelter *
Received 10 July 1999 / Accepted 1 September 1999
We obtained time series of high resolution spectra around 1.6 µm for 15 short period semiregular variables to study the velocity variations in their atmospheres with the help of second overtone vibration-rotational lines of CO. All objects of our sample clearly show velocity variations of a few km s-1. The amplitude of the `blue' SRVs (according to Kerschbaum & Hron 1992) is on the average a factor of two smaller than that of the `red' SRVs. Periodicity of the variations differs from star to star. Some SRVs vary with the period listed in the General Catalogue of Variable Stars (GCVS4), others with a considerable longer period. But for all SRVs the measured velocities at 1.6 µm are over a large part of the cycle smaller than the velocities found in the literature. Different explanations of this feature are discussed. We think that the observed difference in mean velocity might be caused by a blueshift due to large convective cells on the stellar surface.
Key words: stars: variables: general stars: AGB and post-AGB stars: atmospheres
* Visiting Astronomer, Kitt Peak National Observatory, National Optical Astronomy Observatories, which is operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation.
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Online publication: November 3, 1999