Volume 419, Number 2, May IV 2004
|Page(s)||L13 - L16|
|Published online||03 May 2004|
Letter to the Editor
The effect of evaporation on the evolution of close-in giant planets
CRAL (UMR 5574 CNRS), École Normale Supérieure, 69364 Lyon Cedex 07, France e-mail: [ibaraffe; chabrier; fallard]@ens-lyon.fr
2 Centro de Astrobiología (INTA-CSIC), Ctra. de Ajalvir km 4, 28850 Torrejón de Ardoz, Madrid, Spain e-mail: firstname.lastname@example.org
3 Department of Physics, Wichita State University, Wichita, KS 67260-0032, USA e-mail: email@example.com
4 Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany e-mail: firstname.lastname@example.org
5 Space Research Institute, Austrian Academy of Sciences, Schmieldstrasse 6, 8042 Graz, Austria e-mail: email@example.com
Corresponding author: I. Baraffe, firstname.lastname@example.org
Accepted: 4 April 2004
We include the effect of evaporation in our evolutionary calculations of close-in giant planets, based on a recent model for thermal evaporation taking into account the XUV flux of the parent star (Lammer et al. [CITE]). Our analysis leads to the existence of a critical mass for a given orbital distance below which the evaporation timescale becomes shorter than the thermal timescale of the planet. For planets with initial masses below mcrit, evaporation leads to a rapid expansion of the outer layers and of the total planetary radius, speeding up the evaporation process. Consequently, the planet does not survive as long as estimated by a simple application of mass loss rates without following consistently its evolution. We find out that the transit planet HD 209458b might be in such a dramatic phase, although with an extremely small probability. As a consequence, we predict that, after a certain time, only planets above a value should be present at an orbital distance a of a star. For planets with initial masses above mcrit, evaporation does not affect the evolution of the radius with time.
Key words: planetary systems / stars: individual: HD 209458, OGLE-TR-56
© ESO, 2004
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