Does the HD 209458 planetary system pose a challenge to the stellar atmosphere models?

Free access article

Issue		A&A Volume 506, Number 3, November II 2009


Page(s)		1335 - 1340
Section		Stellar atmospheres
DOI		http://dx.doi.org/10.1051/0004-6361/200912423
Published online		03 September 2009

A&A 506, 1335-1340 (2009)
DOI: 10.1051/0004-6361/200912423

Does the HD 209458 planetary system pose a challenge to the stellar atmosphere models?

A. Claret

Instituto de Astrofísica de Andalucía, CSIC, Apartado 3004, 18080 Granada, Spain
e-mail: claret@iaa.es

Received 4 May 2009 / Accepted 8 July 2009

Abstract
Aims. There are very few comparisons between theoretical and empirical limb-darkening coefficients (LDCs). To develop this scenario, we analyse the case of the HD 209458 planetary system for which 10 passband measurements of linear and quadratic LDCs are available.
Methods. The empirical data for HD 209458 were derived from the light curves obtained with the Hubble Space Telescope (HST). Since the corresponding effective wavelengths differ from those usually adopted, we computed monochromatic calculations to gain some insight into the problem. The theoretical LDCs were computed by adopting the least-squares method (LSM) but with a larger numerical resolution (100 $\mu$ points instead of 11). The flux conservation method (FCM) was also applied. The plane-parallel stellar atmosphere model ATLAS and the spherically symmetrical PHOENIX model were adopted in the calculations.
Results. We found systematic disagreement between the theoretical and empirical LDCs for the linear case. Disagreements are also found when we compared the quadratic LDCs with observations. Even taking into account uncertainties in the metallicity, micro-turbulent velocity, and effective temperature in the calculation of the theoretical LDCs, the corresponding shifted curves cannot match the empirical data. It seems that the current atmosphere models are unable to explain the specific intensity distribution of HD 209458.

Key words: stars: atmospheres -- planetary systems

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