AAS 201st Meeting, January, 2003
Session 117. Delta Scuti and Pulsating Friends
Poster, Thursday, January 9, 2003, 9:20am-4:00pm, Exhibit Hall AB

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[117.12] A New Class of Pulsating Stars: Gravity-mode Pulsators among Subdwarf B Stars

E.M. Green (Steward Obervatory, University of Arizona), G. Fontaine (Dept. de Physique, Universite de Montreal)

During the course of an ongoing CCD monitoring program to investigate low-level light variations in subdwarf B (sdB) stars, we serendipitously discovered a new class of multimode pulsators with periods of the order of an hour. These periods are a factor of ten longer than those of previously known multimode sdB pulsators (EC 14026 stars), implying the new pulsations are due to gravity modes rather than pressure modes. The iron opacity instability that drives the short period EC14026 stars is effective in hot sdB's. The new long period pulsators are found only among cooler sdB stars, where they are surprisingly common. The mechanism responsible for exciting the deeper g-modes in cool sdB's is currently unknown, but the temperature and gravity range in which these stars occur must be an important clue. We present an update of the observational results for this new class of pulsating sdB stars, discuss some possible implications, and describe a planned multisite photometric and spectroscopic monitoring campaign for one particularly outstanding target.

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