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A. P. Boss (Carnegie Institution)
Giant planets have been detected in two wide (640 - 1100 AU) hierarchical triple systems (16 Cygni, HD 178911) and in two closer (~100 AU) binaries (Tau Boo, HD 114762). Recently a giant planet has been claimed in a binary system with a semi-major axis of only ~ 20 AU (Gamma Cephei). While the triple systems are wide enough for planet formation to proceed in more or less the same way as it does around single stars, the formation of the planets in these binary systems is likely to have been affected in some way by the presence of the second star. Here we show that in the context of the disk instability mechanism for the rapid formation of giant planets, the presence of a binary companion may be able to trigger the formation of self-gravitating gas clumps in a marginally gravitationally stable disk, through the tidal forces exerted near periastron. 3D gravitational, radiative hydrodynamical calculations of the evolution of a marginally gravitationally stable disk (outer disk T = 70 K, minimum Toomre Q = 1.8) of radius 20 AU and mass 0.09 solar masses, orbiting a solar-mass protostar, have been carried out, subject to the tidal forces of a solar-mass secondary on an orbit with e = 0.5. The 3D models show that following repeated periastrons of the a = 50 AU binary, the maximum density in the midplane is significantly enhanced over that encountered without a secondary, triggering clump formation. The disks cool by a combination of internal vertical convection and radiative losses from their surfaces, permitting a disk instability to proceed to clump formation in spite of tidal compressional heating.
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.