Tuesday, February 2, 2016

From Microlensing, how Common are Snowline Region Exoplanets?

The frequency of snowline-region planets from four-years of OGLE-MOA-Wise second-generation microlensing


Shvartzvald et al


We present a statistical analysis of the first four seasons from a "second-generation" microlensing survey for extrasolar planets, consisting of near-continuous time coverage of 8 deg2 of the Galactic bulge by the OGLE, MOA, and Wise microlensing surveys. During this period, 224 microlensing events were observed by all three groups. Over 12% of the events showed a deviation from single-lens microlensing, and for ∼1/3 of those the anomaly is likely caused by a planetary companion. For each of the 224 events we have performed numerical ray-tracing simulations to calculate the detection efficiency of possible companions as a function of companion-to-host mass ratio and separation. Accounting for the detection efficiency, we find that 55+34−22% of microlensed stars host a snowline planet. Moreover, we find that Neptunes-mass planets are ∼10 times more common than Jupiter-mass planets. The companion-to-host mass ratio distribution shows a deficit at q∼10−2, separating the distribution into two companion populations, analogous to the stellar-companion and planet populations, seen in radial-velocity surveys around solar-like stars. Our survey, however, which probes mainly lower-mass stars, suggests a minimum in the distribution in the super-Jupiter mass range, and a relatively high occurrence of brown-dwarf companions.

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