The Keck metal-poor planet search . On the frequency of gas giant planets in the metal-poor regime
Abstract
We present an analysis of three years of precision radial velocity measurements of 160 metal-poor stars observed with Keck/HIRES. We report on variability and long-term velocity trends for each star in our sample. We identify several long-term, low-amplitude radial-velocity variables worthy of follow-up with direct imaging techniques. We place lower limits on the detectable companion mass as a function of orbital period. None of the stars in our sample exhibits radial-velocity variations compatible with the presence of Jovian planets with periods shorter than the survey duration (3 yr). The resulting average frequency of gas giants orbiting metal-poor dwarfs with -2.0≲[Fe/H]≲ -0.6 is f_p<0.67%. By combining our dataset with the Fischer & Valenti (2005) uniform sample, we confirm that the likelihood of a star to harbor a planet more massive than Jupiter within 2 AU is a steeply rising function of the host's metallicity. However, the data for stars with -1.0≲[Fe/H]≲ 0.0 are compatible, in a statistical sense, with a constant occurrence rate f_p≃1%. Our results usefully inform theoretical studies of the process of giant planet formation across two orders of magnitude in metallicity.
- Publication:
-
Memorie della Societa Astronomica Italiana Supplementi
- Pub Date:
- 2010
- Bibcode:
- 2010MSAIS..14..173S
- Keywords:
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- planetary systems: formation;
- stars: abundances;
- stars: statistics;
- techniques: radial velocities