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I.R. Seitenzahl, K. Callerame, E.M. Green (Steward Observatory, University of Arizona), G. Fontaine (Dept. de Physique, Universite de Montreal), B. White, E. Hyde, G. Milone, M. Giovanni (Steward Observatory, University of Arizona)
During the course of an ongoing CCD monitoring program to search for eclipses, reflection effects and ellipsoidal variations in subdwarf B (sdB) stars, we have serendipitously discovered a new type of multimode sdB pulsator having periods on the order of an hour, with approximate peak-to-peak amplitudes less than a few hundredths of a magnitude. We have so far identified more than a dozen of these new long period pulsators, or LPsdBV stars, all in the range 25,000 < Teff < 30,000 K and 5.4 < log g < 5.7. The LPsdBV pulsational periods are at least a factor of 10 longer than typical periods of the nonradial, multimode sdB pulsators extensively discussed in the literature during the last few years (e.g. Koen et al. 1999, MNRAS, 306, 213; Charpinet, Fontaine, & Brassard 2001, PASP, 113, 775). The previously known short period sdB pulsators oscillate in acoustic modes (p-modes), for which the envelope opacity instability mechanism is predicted and observed to be largest in the hottest sdB stars, those with temperatures > 31,000 K. The long periods we are now detecting presumably indicate pulsations due to core modes (g-modes), although the driving mechanism is currently unknown. The very different pulsational characteristics of the LPsdBV stars, and the fact that they populate a completely different region of the temperature-gravity diagram from the short period sdBV stars, strongly support their identification as a new class of pulsating sdB stars. This work was supported by NSF grants AST-9731655 and AST-0098699.
The author(s) of this abstract have provided an email address for comments about the abstract: bgreen@as.arizona.edu
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Bulletin of the American Astronomical Society, 34
© 2002. The American Astronomical Soceity.