Mining the Metal-rich Stars for Planets

We examine the correlation between stellar metallicity and the presence of short-period planets. It appears that approximately 1% of dwarf stars in the solar neighborhood harbor short-period planets characterized by near-circular orbits and orbital periods P<20 days. However, among the most metal-rich stars (defined as having [Fe/H]>0.2 dex), it appears that the fraction increases to 10%. Using the Hipparcos database and the Hauck & Mermilliod compilation of Strömgren uvby photometry, we identify a sample of 206 metal-rich stars of spectral type K, G and F which have an enhanced probability of harboring short-period planets. Many of these stars would be excellent candidates for addition to radial velocity surveys. We have searched the Hipparcos epoch photometry for transiting planets within our 206 star catalog. We find that the quality of the Hipparcos data is not high enough to permit unambiguous transit detections. It is, however, possible to identify candidate transit periods. We then discuss various ramifications of the stellar metallicity-planet connection. First, we show that there is preliminary evidence for increasing metallicity with increasing stellar mass among known planet-bearing stars. This trend can be explained by a scenario in which planet-bearing stars accrete an average of 30 M_⊕ of rocky material after the gaseous protoplanetary disk phase has ended. We present dynamical calculations which suggest that a survey of metallicities of spectroscopic binary stars can be used to understand the root cause of the stellar metallicity-planet connection.