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Session 70 - Planetary Systems Near & Far.
Display session, Friday, January 09
Exhibit Hall,
World-wide Doppler monitoring of 300 FGK main sequence stars has revealed eight stars that exhibit Keplerian velocity variations indicative of planetary companions. The masses (M\sin i) range from 0.5 - 7 M_JUP and the semimajor axes range from 0.04 - 2.1 AU. The distribution of companion masses exhibits a peak at the lowest masses, from 0 -- 10 M_JUP, relative to the those at higher masses (per mass bin) from 10 -- 70 M_JUP (the ``brown dwarfs''). The peak at the lowest masses suggests the discovery of a new class of astronomical objects having masses mostly below \sim5 M_JUP, and most easily identified with ``giant planets''. Ongoing Doppler planet searches of 500 stars will improve the statistics of their occurrence and orbital characteristics.
Selection effects favor the detection of companions with small orbital semimajor axes. Nonetheless, these jupiters within 2 AU imply that they formed either in situ or beyond several AU but suffered inward orbital migration. Indeed, inward migration looms as an inexorable aspect of planet formation, either by tidal coupling to the T Tauri disk or by the viscous drainage of material inward in the accretion disk. The migration time for giant planets at 5 AU appears to be less than a million years, both theoretically and observationally. Thus, jupiters may commonly migrate inward during the T Tauri phase, while other giant planets continue to form farther out.
