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

Abstract

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 deg 2 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.

OGLE-2016-BLG-1190Lb: The First Spitzer Bulge Planet Lies Near the Planet/Brown-dwarf Boundary

“…63 The minimum in this distribution can then be regarded as the location of the mean boundary between two formation mechanisms averaged over the microlensing host-mass distribution. Shvartzvald et al (2016) found that this minimum was near q∼0.01, which corresponds to M comp ∼5 M Jup for characteristic microlensing hosts, which are typically in the M dwarf regime. This tends to indicate that this boundary scales as a function of the host mass.…”

“…This then sets the stage for whether its parallax is "adequately measured" according to the Zhu et al (2017b) criteria, or rather whether the corresponding 63 As a result, in microlensing statistical studies, the planet/brown-dwarf boundary is often defined by q. For example, Suzuki et al (2016;following Bond et al 2004) and Shvartzvald et al (2016) use q=0.03 and q=0.04, respectively, which would correspond to the conventional 13 M jup limit for stars of mass M;0.4 M e and M;0.3 M e , respectively. point-lens event would have satisfied them.…”

Ogle-2012-BLG-0724lb: A Saturn-Mass Planet Around an M Dwarf

“…Clanton & Gaudi (2014) found that the planet abundances estimated by microlensing are consistent with those found by radial velocity. Recently, Shvartzvald et al (2015) estimated planet abundance and mass function based on nine events and found that 55% of stars host a planet beyond the snow line and Neptune-mass planets are ∼10 times more common than Jupiter-mass planets. Suzuki et al (2016) found a break and possible peak in the exoplanet mass ratio function at~-q 10 4 and found 0.75 planets per star at >´-q 5 10 5 and 1.12 planets per star for > q 0.…”

The First Simultaneous Microlensing Observations by Two Space Telescopes: Spitzer and Swift Reveal a Brown Dwarf in Event Ogle-2015-BLG-1319

“…This is in contrast to estimates through other techniques, such as radial velocity and transit, which find that BDs are rare (<1%, Grether & Lineweaver 2006) at closer separations. A possible explanation for this difference besides the different separations, as suggested by Shvartzvald et al (2016), is that different host stars are mostly probed by each technique-FGK stars by radial velocity and transits versus M stars by microlensing.…”