Five new hot-Jupiter transits investigated with Swift-UVOT

TL;DR

This study uses Swift-UVOT to observe five hot Jupiters, detecting one clear and one marginal transit, and explores atmospheric features and mass-loss effects through UV measurements, revealing potential cloud formation influences.

Contribution

First UV transit observations of five hot Jupiters with Swift-UVOT, analyzing atmospheric properties and potential cloud effects in the UV spectrum.

Findings

Detected one clear and one marginal transit among five hot Jupiters.

Planetary radii in NUV are 50-100% larger than optical measurements.

No correlation between mass-loss rate and NUV/optical radius ratio.

Abstract

Short wavelength exoplanet transit measurements have been used to probe mass-loss in exoplanet atmospheres. We present the Swift-UVOT transit light curves for five hot Jupiters orbiting UV-bright F-type stars: XO-3, KELT-3, WASP-3, WASP-62, and HAT-P-6. We report one positive transit detection of XO-3b and one marginal detection of KELT-3b. We place upper limits on the remaining three transit depths. The planetary radii derived from the NUV transit depths of both potential detections are 50-100% larger than their optical radius measurements. We examine the ratio $R_{\rm NUV}/R_{\rm opt}$ for trends as a function of estimated mass-loss rate, which we derive from X-ray luminosity obtained from the Swift-XRT, or XMM-Newton in the case of WASP-62. We find no correlation between the energy-limited photoevaporative mass-loss rate and the $R_{\rm NUV}/R_{\rm opt}$ ratio. We also search for trends based on the equilibrium temperature of the hot Jupiters. We find a possible indication of a transition in the $R_{\rm NUV}/R_{\rm opt}$ ratio around $T_{\rm eq} = 1700~{\rm K}$, analogous to the trends found for NIR water features in transmission spectra. This might be explained by the formation of extended cloud decks with silicate particles $\leq 1~\mu{\rm m}$. We demonstrate that the Swift-UVOT filters could be sensitive to absorption from aerosols in exoplanet atmospheres.