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

TL;DR

This study measures the high-energy X-ray emission from the host star CoRoT-7, providing insights into the atmospheric erosion of its super-earth planets, especially CoRoT-7b, due to stellar irradiation.

Contribution

First detection of X-ray emission from CoRoT-7 and estimation of its impact on planetary mass loss in the super-earth regime.

Findings

CoRoT-7 emits X-rays with a luminosity of 3×10^28 erg/s.

The XUV irradiation on CoRoT-7b is approximately 37000 erg/cm^2/s.

CoRoT-7b has likely lost 4-10 Earth masses due to evaporation.

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 (3.5 sigma) X-ray detection of CoRoT-7. We determine a coronal temperature of ca. 3 MK and an X-ray luminosity of 3*10^28 erg/s. The level of XUV irradiation on CoRoT-7b amounts to ca. 37000 erg/cm^2/s. 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*10^11 g/s and has lost ca. 4-10 earth masses in total.