AAS 207th Meeting, 8-12 January 2006
Session 191 Extrasolar Planets
Oral, Thursday, 10:00-11:30am, January 12, 2006, Virginia

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[191.06] A Model of Planets Orbiting Giant Stars for the Long Secondary Periods and the Fraction of Stars with Planets

A. Retter (Penn State University)

A major problem in the field of asteroseismology is the unexpected presence of a sequence of long periods of about 1-4 years in the period-luminosity diagram of variable red giant stars. We propose that these periodicities are a result of the presence of Jupiter-like planets in orbits in the outer envelopes or accretion disks of these stars. We suggest that the variations are formed by a combination of eclipses, ellipsoidal variations and accretion of stellar material by the planets, whose masses might have increased into the brown dwarfs range. The planets scenario seems like the simplest explanation for the existence of periods of the order of years in the light curves of giant stars. These stars may have swallowed their inner planets during the secular expansion to large radii in the recent past, in line with the model recently proposed for the peculiar nova-like outburst of V838 Mon and similar objects. Our work may have a significant impact on the formation theories of planets, the evolution of stars and the fraction of stars that harbor planets. It further suggests that planets have already been observed several decades ago. According to our model, about 25-50% of variable red giant stars possess Jupiter-like planets with separations of a few astronomical units. From the observed orbital distribution of periods in stars with planets, we conclude that nearly all variable red giant stars have massive Jupiter-like planets. Therefore, it seems likely that most stars have planets. Possible selection effects may, however, influence this estimate.

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