A SEARCH FOR JUPITER-MASS COMPANIONS TO NEARBY STARS

We have carefully monitored the radial velocities of 21 bright, solar- type stars for 12 years. None has shown any reflex motion due to a sub stellar companion to an upper limit of between 1 and 3 Jupiter masses (x sin i) for orbital periods less than 15 years. We can also rule out companions of more than 3 to 10 Jupiter masses (x sin i) at much long er periods based on long-term trends in the radial velocities, limits imposed by astrometry and zones of orbital stability in wide binaries. When our negative result is combined with other searches, one can say that, so far, no planets of the order of a Jupiter-mass or greater (g reater than or equal to 0.001 M(.)) have been detected in short-period , circular orbits around some 45 nearby, solar-type stars. This absenc e presents an interesting challenge to theories of planet formation. ( C) 1995 Academic Press, Inc.