The Discovery of a Planetary Companion to 16 Cygni B

High precision radial velocity observations of the solar-type star 16 Cygni Btaken at McDonald Observatory and at Lick Observatory, have each independentlydiscovered periodic radial-velocity variations indicating the presence of aJovian-mass companion to this star. The orbital fit to the combined data givesa period of 800.8 days, a velocity amplitude of 43.9 m/s, and an eccentricityof 0.63. This is the largest eccentricity of any planetary system discovered sofar. Assuming that 16 Cygni B has a mass of 1.0 Msun, this implies a mass forthe companion of 1.5 sin i Jupiter masses. While the mass of this object iswell within the range expected for planets, the large orbital eccentricitycannot be explained simply by the standard model of growth of planets in aprotostellar disk. It is possible that this object was formed in the normalmanner with a low eccentricity orbit, and has undergone post-formationalorbital evolution, either through the same process which formed the ``massiveeccentric'' planets around 70 Virginis and HD114762, or by gravitationalinteractions with the companion star 16 Cygni A. It is also possible that theobject is an extremely low mass brown dwarf, formed through fragmentation ofthe collapsing protostar. We explore a possible connection between stellarphotospheric Li depletion, pre-main sequence stellar rotation, the presence ofa massive proto-planetary disk, and the formation of a planetary companion.Comment: 18 pages, 3 PostScript figures, Latex, uses aaspp4 macros, submitted to Astrophysical Journa