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On the Nature of Stars with Planets
We consider the metallicities and kinematics of nearby stars known tohave planetary-mass companions in the general context of the overallproperties of the local Galactic disk. We have used Strömgrenphotometry to determine abundances both for the extrasolar planet hoststars and for a volume-limited sample of 486 F, G, and K stars selectedfrom the Hipparcos Catalogue. The latter data show that the Sun liesnear the modal abundance of the disk, with over 45% of local starshaving supersolar metallicities. Twenty of the local stars (4.1%) areknown to have planetary-mass companions. Using that ratio to scale datafor the complete sample of planetary host stars, we find that thefraction of stars with extrasolar planets rises sharply with increasingabundance, confirming previous results. However, the frequency remainsat the 3%-4% level for stars within +/-0.15 dex of solar abundance andfalls to ~1% only for stars with abundances less than one-half solar.Given the present observational constraints, both in velocity precisionand in the available time baseline, these numbers represent a lowerlimit to the frequency of extrasolar planetary systems. A comparisonbetween the kinematics of the planetary host stars and a representativesample of disk stars suggests that the former have an average age thatis ~60% of the latter.
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