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We present an analysis of three years of precision radial velocitymeasurements of 160 metal-poor stars observed with HIRES on the Keck 1telescope. We report on variability and long-term velocity trends for each starin our sample. We identify several long-term, low-amplitude radial-velocityvariables worthy of follow-up with direct imaging techniques. We place lowerlimits on the detectable companion mass as a function of orbital period. Oursurvey would have detected, with a 99.5% confidence level, over 95% of allcompanions on low-eccentricity orbits with velocity semi-amplitude K > 100 m/s,or M_p*sin(i) > 3.0 M_JUP*(P/yr)^(1/3), for orbital periods P< 3 yr. None ofthe stars in our sample exhibits radial-velocity variations compatible with thepresence of Jovian planets with periods shorter than the survey duration. Theresulting average frequency of gas giants orbiting metal-poor dwarfs with -2.0< [Fe/H] < -0.6 is f_p<0.67% (at the 1-sigma confidence level). We examine theimplications of this null result in the context of the observed correlationbetween the rate of occurrence of giant planets and the metallicity of theirmain-sequence solar-type stellar hosts. By combining our dataset with theFischer & Valenti (2005) uniform sample, we confirm that the likelihood of astar to harbor a planet more massive than Jupiter within 2 AU is a steeplyrising 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 constantoccurrence rate f_p~1%. Our results can usefully inform theoretical studies ofthe process of giant planet formation across two orders of magnitude inmetallicity.

A Keck HIRES Doppler Search for Planets Orbiting Metal-Poor Dwarfs. II. On the Frequency of Giant Planets in the Metal-Poor Regime