Testing the limb-darkening coefficients measured from eclipsing binaries

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 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 up to 10 times the solar abundance, with log values between 0.0 and 5.0, effective temperatures between 2000K and 50000K, and microturbulent velocities from 0 kmsto 8 kms.Results. The new theoretical LDCs provide better fits to the calculated specific intensities than those derived by adopting the -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 -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. © 2008 ESO.