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

Abstract

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 × 10 − 4 and separation s ≈ 1, the planet lies exactly at the break and likely peak of the exoplanet mass-ratio function derived by the Microlensing Observations in Astrophysics (MOA) Collaboration. 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 planet = 11.3 − 6.9 + 19.2 M ⊕ and a host star of mass M host = 0.23 − 0.14 + 0.39 M ⊙ , located at a distance D L = 7.9 − 1.0 + 1.0 kpc . With a prior that holds that planet occurrence scales in proportion to the host-star mass, the estimated lens system properties are m planet = 25 − 15 + 22 M ⊕ , M host = 0.53 − 0.32 + 0.42 M ⊙ , and D L = 8.3 − 1.0 + 0.9 kpc . This planet qualifies for inclusion in the extended MOA-II exoplanet microlens sample.