High-eccentricity planets from the Anglo-Australian planet search

Abstract

We report Doppler measurements of the stars HD 187085 and HD 20782 which indi- cate two high eccentricity low-mass companions to the stars. We find HD 187085 has a Jupiter-mass companion with a 1000 d orbit. Our formal ‘best fit’ solution suggests an eccentricity of 0.47, however, it does not sample the periastron passage of the com- panion and we find that orbital solutions with eccentricities between 0.1 and 0.8 give only slightly poorer fits (based on RMS and 2 ) and are thus plausible. Observations made during periastron passage in 2007 June should allow for the reliable determi- nation of the orbital eccentricity for the companion to HD 187085. Our dataset for HD 20782 does sample periastron and so the orbit for its companion can be more reli- ably determined. We find the companion to HD 20782 has M sin i = 1.77±0.22 MJup, an orbital period of 595.86±0.03 d and an orbit with an eccentricity of 0.92±0.03. The detection of such high-eccentricity (and relatively low velocity amplitude) exoplanets appears to be facilitated by the long-term precision of the Anglo-Australian Planet Search. Looking at exoplanet detections as a whole, we find that those with higher eccentricity seem to have relatively higher velocity amplitudes indicating higher mass planets and/or an observational bias against the detection of high eccentricity systems.