A Candidate High-Velocity Exoplanet System in the Galactic Bulge

TL;DR

This paper confirms a high-velocity exoplanet system in the galactic bulge with a low-mass host star, using adaptive optics imaging and Gaia data, demonstrating the potential of future surveys like Roman for similar discoveries.

Contribution

It provides the first confirmed measurement of a high-velocity exoplanet system with a low-mass host star in the galactic bulge, utilizing AO imaging and Gaia data.

Findings

Confirmed the lens system as a high-velocity exoplanet with a low-mass host star.

Measured host star mass of approximately 0.19 solar masses.

Determined the exoplanet mass to be about 29 Earth masses.

Abstract

We present an analysis of adaptive optics (AO) images from the Keck-I telescope of the microlensing event MOA-2011-BLG-262. The original discovery paper by Bennett et al. 2014 reports two distinct possibilities for the lens system; a nearby gas giant lens with an exomoon companion or a very low mass star with a planetary companion in the galactic bulge. The $\sim$10 year baseline between the microlensing event and the Keck follow-up observations allows us to detect the faint candidate lens host (star) at $K = 22.3$ mag and confirm the distant lens system interpretation. The combination of the host star brightness and light curve parameters yields host star and planet masses of $M_{\rm host} = 0.19 \pm 0.03M_{\odot}$ and $m_p = 28.92 \pm 4.75M_{\oplus}$ at a distance of $D_L = 7.49 \pm 0.91\,$kpc. We perform a multi-epoch cross reference to \textit{Gaia} DR3 and measure a transverse velocity for the candidate lens system of $v_L = 541.31 \pm 65.75$ km s$^{-1}$. We conclude this event consists of the highest velocity exoplanet system detected to date, and also the lowest mass microlensing host star with a confirmed mass measurement. The high-velocity nature of the lens system can be definitively confirmed with an additional epoch of high-resolution imaging at any time now. The methods outlined in this work demonstrate that the \textit{Roman} Galactic Exoplanet Survey (RGES) will be able to securely measure low-mass host stars in the bulge.