The XUV environments of exoplanets from Jupiter-size to super-Earth

TL;DR

This study characterizes the XUV radiation environments of close-in exoplanets using XMM-Newton data, revealing how stellar irradiation impacts planetary mass loss, especially for smaller planets, and introduces new relations to estimate EUV emission.

Contribution

The paper presents new relations derived from Solar data to reconstruct EUV emission from X-ray observations, applied to characterize exoplanet irradiation levels and potential mass loss.

Findings

WASP-80b and HD149026b experience high irradiation levels.

Smaller planets likely lose more mass over time.

Detected near-UV transit of WASP-80b.

Abstract

Planets that reside close-in to their host star are subject to intense high-energy irradiation. Extreme-ultraviolet (EUV) and X-ray radiation (together, XUV) is thought to drive mass loss from planets with volatile envelopes. We present $\textit{XMM-Newton}$ observations of six nearby stars hosting transiting planets in tight orbits (with orbital period, $P_\text{orb} < 10\,$d), wherein we characterise the XUV emission from the stars and subsequent irradiation levels at the planets. In order to reconstruct the unobservable EUV emission, we derive a new set of relations from Solar $\textit{TIMED/SEE}$ data that are applicable to the standard bands of the current generation of X-ray instruments. From our sample, WASP-80b and HD$\,$149026b experience the highest irradiation level, but HAT-P-11b is probably the best candidate for Ly$\,\alpha$ evaporation investigations because of the system's proximity to the Solar System. The four smallest planets have likely lost a greater percentage of their mass over their lives than their larger counterparts. We also detect the transit of WASP-80b in the near ultraviolet with the Optical Monitor on $\textit{XMM-Newton}$.