  High precision radial velocity observations of the solar-type star 16 Cygni B
taken at McDonald Observatory and at Lick Observatory, have each independently
discovered periodic radial-velocity variations indicating the presence of a
Jovian-mass companion to this star. The orbital fit to the combined data gives
a period of 800.8 days, a velocity amplitude of 43.9 m/s, and an eccentricity
of 0.63. This is the largest eccentricity of any planetary system discovered so
far. Assuming that 16 Cygni B has a mass of 1.0 Msun, this 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
protostellar disk. It is possible that this object was formed in the normal
manner with a low eccentricity orbit, and has undergone post-formational
orbital evolution, either through the same process which formed the ``massive
eccentric'' planets around 70 Virginis and HD114762, or by gravitational
interactions with the companion star 16 Cygni A. It is also possible that the
object is an extremely low mass brown dwarf, formed through fragmentation of
the collapsing protostar. We explore a possible connection between stellar
photospheric Li depletion, pre-main sequence stellar rotation, the presence of
a massive proto-planetary disk, and the formation of a planetary companion.

Astrophysics