Summary and conclusions

More than 130 stars are now known to harbor planetary systems. The correlation between planetary frequency and metallicity is now well established, and probably reflects nature rather than nurture. We have analyzed the statistical properties of the current sample of ESP hosts, looking for other possible trends and biases. With the possible exception of a higher mean velocity perpendicular to the Plane, the planetary hosts appear to be unremarkable members of the Galactic Disk.

Several ESP host stars show enhanced a-element abundances and high velocities relative to the Sun, strongly suggesting that they are members of the thick disk. If so, this indicates that planet formation has been a constant presence in the Galactic Disk.

We briefly considered the radial abundance gradient and age-metallicity distribution of disk stars. Recent results suggest that the gradient is flatter in the vicinity of the Sun than the canonical value, but probably steepens at larger radii; there is relatively little reliable data for the inner disk, R < 6 kpc. The age-metallicity distribution of the Berkeley/ Carnegie RV sample shows substantial dispersion at all ages. While the uncertainties in these parameters limit our ability to model the full Galaxy, we can use local statistics to estimate the planetary population in the vicinity of the Sun. We estimate that there are over 3.5 x 107 'RV-detectable' planetary systems with Galactocentric radii in the range 6 to 10 kpc.

Thanks to Jeff Valenti for early access to computer-readable tables listing the results of the spectroscopic analysis of the Berkeley/Carnegie radial velocity sample.

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