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Session 34 - Invited Talk.
Invited session, Tuesday, January 14
Frontenac Ballroom,
Highly precise Doppler measurements (errors less than \sim15 m\/s) of \sim260 Solar-type stars have revealed 7 companions that have low masses: M\sin i = 0.45 -- 7 M_JUP. These precise measurements have revealed no companions that have M\sin i in the range 10 - 80 M_JUP, normally associated with ``brown dwarfs''. Thus, the 7 companions represent a new population of extremely low--mass objects that occupy the mass range associated with giant planets. There are also possible planets detected by astrometry around one other star, and a high--mass planetary companion detected by modest--precision Doppler work.
Among the 8 planets detected by Doppler measurements, three preliminary ``classes'' are emerging. The ``51 Peg'' class contains 4 representatives, having small semimajor axes, a < 0.15 AU and circular orbits, with circularity probably primodial rather than tidally induced. A second class of ``eccentric'' planets contains 3 representatives, all having e > 0.35 and all having M\sin i > 1 M_JUP. Finally one planet (around 47 UMa) has a circular orbit, a = 2.1 AU, and M\sin i = 2.4 M_JUP, not qualitatively different from Jupiter in our Solar System.
Modifications to standard planet--formation theory are emerging to account for the 3 classes of planets. The close orbits may stem from viscous loss of orbital angular momentum in the protoplanetary disk. The high eccentricities can result from gravitational interactions of multiple planets or from resonances in the disk that feedback gravitationally on the protoplanet. The occurrence rate of true analogs of our Solar System remains unknown. New techniques, such as Keck Doppler measurements, astrometry, and ground-based interferometry, will detect Saturn and Neptune--like planets. Balloon-borne, super--smooth telescopes may augment these efforts cheaply and quickly, to make direct detections of planets.
