Discovery of Cephei stars in the Magellanic Clouds

As a by-product of the extensive microlensing surveys, photometric data for millions stars in the Magellanic Clouds have been obtained. In addition, the optimal image subtraction method applied to these data by the OGLE-II resulted in the discovery of about 70,000 variable candidates. Periodogram analysis of about 8000 stars from this sample lying in the upper main sequence led us to the discovery of only three Cephei-type variables in the LMC and two candidates in the SMC. These are the first extragalactic stars of this type. The variables constitute a very small fraction of all early B-type stars falling within the range of magnitudes when the Cephei stars are distributed. They are roughly two orders of magnitude less frequent in the Magellanic Clouds than in the Galaxy. The low number of Cephei stars in the Magellanic Clouds is in accordance with the strong dependence of the driving mechanism on the metallicity. The direct spectroscopic determination of the metallicities in the discovered variables will provide a good test for the theory of the pulsational stability in massive main-sequence stars.

 
Print this abstract