EDP Sciences
Free access
Issue
A&A
Volume 419, Number 2, May IV 2004
Page(s) L13 - L16
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20040129


A&A 419, L13-L16 (2004)
DOI: 10.1051/0004-6361:20040129

Letter

The effect of evaporation on the evolution of close-in giant planets

I. Baraffe1, F. Selsis2, G. Chabrier1, T. S. Barman3, F. Allard1, P. H. Hauschildt4 and H. Lammer5

1  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: selsis@obs.u-bordeaux1.fr
3  Department of Physics, Wichita State University, Wichita, KS 67260-0032, USA
    e-mail: travis.barman@wichita.edu
4  Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
    e-mail: yeti@hs.uni-hamburg.de
5  Space Research Institute, Austrian Academy of Sciences, Schmieldstrasse 6, 8042 Graz, Austria
    e-mail: helmut.lammer@oeaw.ac.at

(Received 16 January 2004 / Accepted 4 April 2004)

Abstract
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. 2003). Our analysis leads to the existence of a critical mass for a given orbital distance  $m_{\rm crit}(a)$ below which the evaporation timescale becomes shorter than the thermal timescale of the planet. For planets with initial masses below  $m_{\rm crit}$, 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  $m_{\rm crit}(a)$ should be present at an orbital distance  a of a star. For planets with initial masses above  $m_{\rm crit}$, evaporation does not affect the evolution of the radius with time.


Key words: planetary systems -- stars: individual: HD 209458, OGLE-TR-56

Offprint request: I. Baraffe, ibaraffe@ens-lyon.fr

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