Revealing Short-period Exoplanets and Brown Dwarfs in the Galactic Bulge using the Microlensing Xallarap Effect with the \textit{Nancy Grace Roman Space Telescope}

TL;DR

The paper explores the Roman Space Telescope's ability to detect short-period exoplanets and brown dwarfs in the Galactic bulge through the xallarap effect in microlensing light curves, enabling new insights into these populations.

Contribution

It analytically estimates the detection capabilities of Roman for short-period planets and brown dwarfs using the xallarap effect, a novel application for this survey.

Findings

Roman can detect Jupiters down to 0.5 M_Jup with 30-day periods

Approximately 10 hot/warm Jupiters and 30 close-in BDs will be detected

Detections will include measurements of masses and orbital parameters

Abstract

The \textit{Nancy Grace Roman Space Telescope} (\textit{ Roman}) will provide an enormous number of microlensing light curves with much better photometric precisions than ongoing ground-based observations. Such light curves will enable us to observe high-order microlensing effects which have been previously difficult to detect. In this paper, we investigate \textit{Roman}'s potential to detect and characterize short-period planets and brown dwarfs (BDs) in source systems using the orbital motion of source stars, the so-called xallarap effect. We analytically estimate the measurement uncertainties of xallarap parameters using the Fisher matrix analysis. We show that the \textit{Roman} Galactic Exoplanet Survey (RGES) can detect warm Jupiters with masses down to 0.5 $M_{\rm Jup}$ and orbital period of 30 days via the xallarap effect. Assuming a planetary frequency function from \citet{Cumming+2008}, we find \textit{Roman} will detect $\sim10$ hot and warm Jupiters and $\sim30$ close-in BDs around microlensed source stars during the microlensing survey. These detections are likely to be accompanied by the measurements of the companion's masses and orbital elements, which will aid in the study of the physical properties for close-in planet and BD populations in the Galactic bulge.