The planetary host stars

The overwhelming majority of planetary systems have been discovered through radial velocity surveys, with a handful of recent additions from transit surveys and microlensing programs. Radial velocity surveys focus on solar-like stars, for obvious reasons, so it is not surprising that most of the ESP hosts are late-F to early-K dwarfs; moreover, almost all lie within 50 parsecs of the Sun (Figure 2).

Approximately 90% of the solar-type stars within 25 parsecs of the Sun are included in either the UC or Geneva surveys, although only the UC survey has published a catalog of non-detections (Nidever et al. 2001). Building on the local completeness of these surveys, Figure 3 shows the distribution of semi-major axes/projected separation as a function of mass for all known companions of solar-type stars within 25 parsecs of the Sun; the distribution clearly shows the brown dwarf desert, and provides the most effective demonstration that extrasolar planets are not simply a low-mass tail to the stellar/brown dwarf companion mass function.

3.1. Stars and planetary properties Given the correlation between planetary frequency and metallicity, one might expect a bias towards higher mass planets in metal-rich stars; the current data, however, do not support that contention. This suggests that high metallicity acts as a trigger for planet formation, rather than playing a key role in the formation mechanism itself. Metal-rich systems ([m/H] > 0.1) do include a higher proportion of short-period, hot Jupiters, perhaps reflecting higher viscous drag in the protoplanetary disk (Sozzetti 2004; Boss, this conference).

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