Revealing Short-period Exoplanets and Brown Dwarfs in the Galactic Bulge Using the Microlensing Xallarap Effect with the Nancy Grace Roman Space Telescope

The Nancy Grace Roman Space Telescope (Roman) will provide an enormous number of microlensing light curves with much better photometric precision 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 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 Fisher matrix analysis. We show that the Roman Galactic Exoplanet Survey can detect warm Jupiters with masses down to 0.5 M-Jup and orbital periods of 30 days via the xallarap effect. Assuming a planetary frequency function from Cumming et al., we find Roman will detect similar to 10 hot and warm Jupiters and similar to 30 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.

Automated summary

The Nancy Grace Roman Space Telescope is expected to detect and characterize short-period planets and brown dwarfs in source systems using the xallarap effect, with potential to detect warm Jupiters down to 0.5 M-Jup and orbital periods of 30 days. Based on estimates, Roman will likely detect around 10 hot and warm Jupiters, as well as 30 close-in BDs during the microlensing survey, providing valuable insights into the physical properties of these celestial bodies in the Galactic bulge.