Gravity-Darkening Analysis of Misaligned Hot Jupiter MASCARA-4 b

TL;DR

This study analyzes the misaligned orbit of hot Jupiter MASCARA-4 b around a rapidly rotating star using gravity-darkening effects, revealing its true spin-orbit angle, orbit eccentricity, and variable stellar irradiation.

Contribution

It provides the first detailed gravity-darkening analysis of MASCARA-4 b, measuring its true spin-orbit angle and orbit eccentricity, and modeling its insolation variation due to stellar gravity-darkening.

Findings

Measured the true spin-orbit angle as approximately 104°.

Detected a secondary eclipse indicating a slightly eccentric orbit.

Found that the planet's insolation varies by 4% due to gravity-darkening.

Abstract

MASCARA-4 b is a hot Jupiter in a highly-misaligned orbit around a rapidly-rotating A3V star that was observed for 54 days by the Transiting Exoplanet Survey Satellite (\tess). We perform two analyses of MASCARA-4 b using a stellar gravity-darkened model. First, we measure MASCARA-4 b's misaligned orbital configuration by modeling its \tess~photometric light curve. We take advantage of the asymmetry in MASCARA-4 b's transit due to its host star's gravity-darkened surface to measure MASCARA-4 b's true spin-orbit angle to be $104^{\circ+7^\circ}_{-13^\circ}$. We also detect a $\sim4\sigma$ secondary eclipse at $0.491\pm0.007$ orbital phase, proving that the orbit is slightly eccentric. Second, we model MASCARA-4 b's insolation including gravity-darkening and find that the planet's received XUV flux varies by $4$\% throughout its orbit. MASCARA-4 b's short-period, polar orbit suggests that the planet likely underwent dramatic orbital evolution to end up in its present-day configuration and that it receives a varying stellar irradiance that perpetually forces the planet out of thermal equilibrium. These findings make MASCARA-4 b an excellent target for follow-up characterization to better understand orbital evolution and current-day of planets around high-mass stars.