Testing the limb-darkening coefficients measured from eclipsing binaries

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

Received: 9 January 2008
Accepted: 5 February 2008

Abstract

Aims. The numerical methods used to compute limb-darkening coefficients (LDCs) are still a matter of discussion. To improve this scenario, we have revised our earlier calculations and compare the new LDCs with previous theoretical ones, as well as with empirical values measured from eclipsing binaries.

Methods. We present new LDCs, based on the least-squares method but computed with higher numerical resolution (100 μ points instead of 11). The LDCs are computed for the following photometric bands: Johnson-Cousins, Strömgren, Geneva, and Walraven systems. Bolometric and monochromatic calculations are also available on request. The computations are presented for 19 metallicities ranging from 10^-5 up to 10⁺¹ times the solar abundance, with log g values between 0.0 and 5.0, effective temperatures between 2000 K and 50 000 K, and microturbulent velocities from 0  km s^-1 to 8  km s^-1.

Results. The new theoretical LDCs provide better fits to the calculated specific intensities than those derived by adopting the r-integration. The improvement is approximately one order of magnitude. When compared with empirical linear LDCs measured for nine eclipsing binaries, it was not possible to distinguish our results from those provided by the r-integration method. However, this comparison also reveals that the theoretical atmosphere models are unable to give a satisfactory fit to the observations. This result is supported by a recent investigation of transiting extrasolar planets. These discrepancies may also be related to problems with the empirical LDC values themselves.