Journal
ASTROPHYSICAL JOURNAL
Volume 669, Issue 2, Pages 1298-1315Publisher
UNIV CHICAGO PRESS
DOI: 10.1086/521702
Keywords
binaries : close; celestial mechanics; methods : statistical; planetary systems
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At least two arguments suggest that the orbits of a large fraction of binary stars and extrasolar planets shrank by 1-2 orders of magnitude after formation: ( 1) the physical radius of a star shrinks by a large factor from birth to the main sequence, yet many main-sequence stars have companions orbiting only a few stellar radii away, and ( 2) in current theories of planet formation, the regionwithin similar to 0.1 AU of a protostar is too hot and rarefied for a Jupiter-mass planet to form, yet many hot Jupiters'' are observed at such distances. We investigate orbital shrinkage by the combined effects of secular perturbations from a distant companion star (Kozai oscillations) and tidal friction. We integrate the relevant equations of motion to predict the distribution of orbital elements produced by this process. Binary stars with orbital periods of 0.1-10 days, with a median of similar to 2 days, are produced from binaries with much longer periods ( 10 to similar to 10(5) days), consistent with observations indicating that most or all short-period binaries have distant companions ( tertiaries). We also make two new testable predictions: ( 1) For periods between 3 and 10 days, the distribution of the mutual inclination between the inner binary and the tertiary orbit should peak strongly near 40 degrees and 140 degrees. ( 2) Extra-solar planets whose host stars have a distant binary companion may also undergo this process, in which case the orbit of the resulting hot Jupiter will typically be misaligned with the equator of its host star.
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