The Lick Observatory Planet Search

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Abstract
We have constructed a precision Doppler technique with which we have detected 6 extrasolar planets to date. Doppler precision is achieved by inserting an iodine absorption cell in the telescope, providing a fiducial wavelength scale against which to measure Doppler shifts. Our current precision is 3 m s−1, which corresponds to one part in one hundred million in wavelength, or 1/1000 th of a pixel on the CCD detector. As of 1996 August, our survey of 120 stars has revealed six stars that show velocity variations consistent with Jupiter-mass companions in Keplerian orbits. These objects span a greater range of orbital radii and eccentricity than the planets in our own solar system. Three of these objects are «51 Peg-type» planets with circular orbits having radii 0.15 AU or less. The other three objects have masses between 1.7 and 6.5 MJUP, eccentricities between 0.01 and 0.6, and semi-major axes between 0.4 and 2.1 AU. We have not found any objects having masses between 10 and 80 MJUP, the domain usually associated with brown dwarfs. These six new companions represent a new population of objects having extremely low masses, similar to that of Jupiter. We have begun a survey of an additional 400 stars using the Keck 10-m telescope, which will allow the detection of Neptune-mass planets.

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