Pulsating B and Be stars in the Small Magellanic CloudP. Diago,1 J. Gutiérrez-Soto,1,2 J. Fabregat,1,2 & C. Martayan2,3
1
Observatorio Astronómico, Universidad de Valencia, Polígono
La Coma, 46980 Paterna, Spain
Context: The current models of stellar pulsation do not predict the presence of instability strips in the B spectral domain at very low metallicities. As the metallicity of the SMC is lower than Z=0.005, it constitutes a very suitable object to test these predictions. Aims: To investigate the existence of B-type pulsators at low metallicities, searching for short-term periodic variability in absorption-line B and Be stars in the SMC. The analysis has been performed in a sample of 313 B and Be stars with accurately determined fundamental astrophysical parameters. Methods: Photometric light curves of the MACHO project have been analyzed using standard Fourier techniques and linear and non-linear least squares fitting methods. The position of the pulsating stars in the HR diagram has been used to ascertain their nature and to map the instability regions in the SMC. Results: We have detected 9 absorption-line B stars showing short-period variability, two among them being multiperiodic. One star is a beta Cephei variable and the remaining 8 are SPB stars. The SPB instability strip in the SMC is shifted towards higher temperatures with respect to the Galaxy. In the Be star sample, 32 stars are short-period variables, 20 among them multiperiodic. 4.9% of B stars and 25.3% of Be stars are pulsating stars. Conclusions: beta Cephei and SPB stars do exist at the SMC metallicity. The fraction of SPB stars in the SMC is similar or only slightly lower than in the Galaxy. Conversely, the fraction of pulsating Be stars in the SMC is significantly lower than in the Galaxy. As in the Galaxy, the fraction of pulsating Be stars in the SMC is much higher than the fraction of pulsating absorption-line B stars.
Submitted to A&A
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Last modified: October 8, 2007
David McDavid