Influence of the evolving stellar X-ray luminosity distribution on exoplanetary mass loss

¹ INAF – Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy e-mail: [tpenz;giusi]@astropa.inaf.it
² Space Research Institute, Austrian Academy of Sciences, Schmiedlstr. 6, 8042 Graz, Austria e-mail: helmut.lammer@oeaw.ac.at

Received: 27 July 2007
Accepted: 28 September 2007

Abstract

Aims.We investigate the influence of high-energy stellar radiation at close-in orbits on atmospheric mass loss during the stellar evolution of a G-type star.

Methods.High-energy stellar luminosity varies over a wide range for G field stars. The X-ray luminosity distributions from the Pleiades, the Hyades, and the field are used to derive a scaling law for the evolution of the stellar X-ray luminosity distribution. A modified energy-limited escape approach is taken for calculating atmospheric mass loss for a broad range of planetary parameters.

Results.We show that the evolution of close-in exoplanets strongly depends on the detailed X-ray luminosity history of their host stars, which varies over several orders-of-magnitude for G stars. Stars located in the high-energy tail of the luminosity distribution can evaporate most of its planets within 0.5 AU, while a significant fraction of planets can survive if exposed to a moderate X-ray luminosity. We show the change on an initial planetary mass distribution caused by atmospheric escape.