We present an analysis of three years of precision radial velocity measurements of 160 metal-poor stars observed with HIRES on the Keck 1 telescope .
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 .
Our survey would have detected , with a 99.5 \% confidence level , over 95 \% of all companions on low-eccentricity orbits with velocity semi-amplitude K \gtrsim 100 m s ^ { -1 } , or M _ { p } \sin i \gtrsim 3.0 M _ { \mathrm { J } } ( P / \mathrm { yr } ) ^ { ( 1 / 3 ) } , for orbital periods P \lesssim 3 yr. 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 .
The resulting average frequency of gas giants orbiting metal-poor dwarfs with -2.0 \lesssim [ Fe/H ] \lesssim - 0.6 is f _ { p } < 0.67 \% ( at the 1 \sigma confidence level ) .
We examine the implications of this null result in the context of the observed correlation between the rate of occurrence of giant planets and the metallicity of their main-sequence solar-type stellar hosts .
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 \lesssim [ Fe/H ] \lesssim 0.0 are compatible , in a statistical sense , with a constant occurrence rate f _ { p } \simeq 1 \% .
Our results can usefully inform theoretical studies of the process of giant planet formation across two orders of magnitude in metallicity .