AAS 197, January 2001
Session 46. Variable Stars

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[46.02] Resolving pulsations across the surface of a pulsating subdwarf B star.

M.D. Reed, S.D. Kawaler (Iowa State University), Whole Earth Telescope (Xcov 17) Collaboration

Studies of pulsating subdwarf B (sdBV or EC14026) stars have blossomed since their discovery just a few years ago (Kilkenny et al. 1997, MNRAS, 285, 640). Yet despite the incredible member discovery rate, we know very little about the pulsations themselves. Only a few EC14026 stars have had the advantage of multi-site data, and only one of these has yielded reasonably secure mode identifications (Kawaler, 1999,A.S.P. Conf. Ser. Vol 169, 158); a necessary step to combine theory and observations.

PG~1336-018 was discovered to be a pulsating sdB star by Kilkenny et al. (1998, MNRAS, 296, 329), with the added bonus that it is also an eclipsing binary. The companion is a late-type ~M5 dwarf, so the stellar radii are comparable, yet the companion contributes little to the integrated flux. With an orbital period of 2.4 hours, PG~1336 should be tidally locked, so we know where to look for rotationally split modes (which can be used to discern non-radial from radial pulsations). At an inclination of 86o, the companion covers about half of the pulsator during primary eclipse. Since pulsations manifest themselves as a geometric effect (alternating hot and cool regions on the star's surface), as the visible surface area changes (during eclipse), so might the observed pulsation amplitudes. PG~1336 was the target of a Whole Earth Telescope run in April, 1999 (Reed et al. 2000, BaltA, 9, 183). Though the run was not optimized to search for pulsations during eclipse, we have nonetheless used the data as a test of the viability of identifying pulsation modes from the eclipse data. Here we report on our first attempt to identify modes using the unique properties of this eclipsing pulsating star.

We gratefully acknowledge support from the NASA Astrophysics Theory Program through award NAG~5-8352

The author(s) of this abstract have provided an email address for comments about the abstract: mreed@iastate.edu

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