The high-energy environment in the super-Earth system CoRoT-7

¹ Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
e-mail: katja.poppenhaeger@hs.uni-hamburg.de
² Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA

Received: 23 November 2011
Accepted: 28 February 2012

Abstract

High-energy irradiation of exoplanets has been identified to be a key influence on the stability of these planets’ atmospheres. So far, irradiation-driven mass-loss has been observed only in two Hot Jupiters, and the observational data remain even more sparse in the super-Earth regime. We present an investigation of the high-energy emission in the CoRoT-7 system, which hosts the first known transiting super-Earth. To characterize the high-energy XUV radiation field into which the rocky planets CoRoT-7b and CoRoT-7c are immersed, we analyzed a 25 ks XMM-Newton observation of the host star. Our analysis yields the first clear (3.5σ) X-ray detection of CoRoT-7. We determine a coronal temperature of  ≈ 3 MK and an X-ray luminosity of 3 × 10²⁸ erg   s^-1. The level of XUV irradiation on CoRoT-7b amounts to  ≈37 000 erg   cm^-2 s^-1. Current theories for planetary evaporation can only provide an order-of-magnitude estimate for the planetary mass loss; assuming that CoRoT-7b has formed as a rocky planet, we estimate that CoRoT-7b evaporates at a rate of about 1.3 × 10¹¹ g   s^-1 and has lost  ≈4−10 earth masses in total.