THE DISCOVERY OF A PLANETARY COMPANION TO 16-CYGNI-B

High-precision radial-velocity observations of the solar-type star 16 Cygni B (HR 7504, HD 186427), taken at McDonald Observatory and at Lic k Observatory, have each independently discovered periodic radial-velo city variations indicating the presence of a Jovian-mass companion to this star. The orbital fit to the combined McDonald and Lick data give s a period of 800.8 days, a velocity amplitude (K) of 43.9 m s(-1), an d an eccentricity of 0.63. This is the largest eccentricity of any pla netary system discovered so far. Assuming that 16 Cygni B has a mass o f 1.0 M., the mass function then implies a mass for the companion of 1 .5/sin i Jupiter masses. While the mass of this object is well within the range expected for planets, the large orbital eccentricity cannot be explained simply by the standard model of growth of planets in a pr otostellar disk. It is possible that this object was formed in the nor mal manner with a low-eccentricity orbit and has undergone postformati onal orbital evolution either through the same process that has been p roposed to have formed the ''massive eccentric'' planets around 70 Vir ginis and HD 114762, or by gravitational interactions with the compani on star 16 Cygni A. It is also possible that the object is an extremel y low mass brown dwarf formed through fragmentation of the collapsing protostar. We explore a possible connection between stellar photospher ic Li depletion, pre-main-sequence stellar rotation, the presence of a massive protoplanetary disk, and the formation of a planetary compani on.