OGLE-2015-BLG-1609Lb: Sub-jovian planet orbiting a low-mass stellar or brown dwarf host

TL;DR

This paper analyzes a microlensing event OGLE-2015-BLG-1609, detecting a sub-Jovian planet orbiting a low-mass star or brown dwarf, using comprehensive modeling and Bayesian analysis to determine the host's nature.

Contribution

It introduces a detailed modeling approach incorporating Galactic priors to better constrain microlensing parameters and determine the host object of the planet.

Findings

Detected a planetary anomaly with survey data from OGLE and MOA.

Identified the host as a brown dwarf with 34% probability or an M-dwarf with 66% probability.

Improved methods for modeling microlensing events with Bayesian priors.

Abstract

We present a comprehensive analysis of a planetary microlensing event OGLE-2015-BLG-1609. The planetary anomaly was detected by two survey telescopes, OGLE and MOA. Each of these surveys collected enough data over the planetary anomaly to allow for an unambiguous planet detection. Such survey detections of planetary anomalies are needed to build a robust sample of planets that could improve studies on the microlensing planetary occurrence rate by reducing biases and statistical uncertainties. In this work, we examined different methods for modeling microlensing events using individual datasets, particularly we incorporated a Galactic model prior to better constrain poorly defined microlensing parallax. Ultimately, we fitted a comprehensive model to all available data, identifying three potential typologies, with two showing comparably high Bayesian evidence. Our analysis indicates that the host of the planet is a brown dwarf with a probability of 34%, or a low-mass stellar object (M-dwarf) with the probability of 66%.