X-ray irradiation and mass-loss of the hot Jupiter WASP-43b

Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
e-mail: stefan.czesla@hs.uni-hamburg.de

Received: 12 July 2013
Accepted: 29 October 2013

Abstract

We report the X-ray detection of the low-mass K7V star WASP-43, which is orbited by a hot Jupiter in one of the closest exoplanet orbits known to date. The high mean density of the planet implies a massive core with ≈130 M_⊕, yielding a heavy-element mass-fraction of 20%. From an 18 ks long XMM-Newton observation, we derive an X-ray luminosity of 6.7^+3.5_-3.3 × 10²⁷ ergss^-1, which puts WASP-43 among the active K-stars, which is compatible with its relatively young age derived in previous studies. The X-ray luminosity translates into a soft X-ray flux of (10.2 ± 5.4) × 10³ erg cm^-2  s^-1 at the substellar point. According to our modeling, the combined X-ray and extreme ultraviolet flux may trigger mass-loss at a rate of up to ≈10¹² gs^-1 via energy-limited atmospheric escape. We infer that it is unlikely that the planet has lost more than 2.5% of its current mass through that channel and that activity-induced mass-loss has not substantially altered its evolution.