MOA-2020-BLG-135Lb: A New Neptune-class Planet for the Extended MOA-II Exoplanet Microlens Statistical Analysis

Abstract

We report the light-curve analysis for the event MOA-2020-BLG-135, which leads to the discovery of a new Neptune-class planet, MOA-2020-BLG-135Lb. With a derived mass ratio of $q=1.52_{-0.31}^{+0.39}\times 10^{-4}$ and separation $s\approx 1$, the planet lies exactly at the break and likely peak of the exoplanet mass-ratio function derived by the MOA collaboration (Suzuki et al. 2016). We estimate the properties of the lens system based on a Galactic model and considering two different Bayesian priors: one assuming that all stars have an equal planet-hosting probability and the other that planets are more likely to orbit more massive stars. With a uniform host mass prior, we predict that the lens system is likely to be a planet of mass $m_{\mathrm{planet}}=11.3_{-6.9}^{+19.2}{M}_{\oplus }$ and a host star of mass $M_{\mathrm{host}}=0.23_{-0.14}^{+0.39}{M}_{\odot }$, located at a distance $D_L=7.9_{-1.0}^{+1.0}\mathrm{kpc}$. With a prior that holds that planet occurrence scales in proportion to the host star mass, the estimated lens system properties are $m_{\mathrm{planet}}=25_{-15}^{+22}{M}_{\oplus }$, $M_{\mathrm{host}}=0.53_{-0.32}^{+0.42}{M}_{\odot }$, and $D_L=8.3_{-1.0}^{+0.9}\mathrm{kpc}$. This planet qualifies for inclusion in the extended MOA-II exoplanet microlens sample.

14 pages, 6 figures, 4 tables, published in AJ