Abstract
Astron.Astrophys.467:1215-1226,2007 We present the most precise light curve ever obtained of a detached eclipsing
binary star and use it investigate the inclusion of non-linear limb darkening
laws in eclipsing binary light curve models. This light curve, of the bright
system beta Aurigae, was obtained using the star tracker aboard the WIRE
satellite and contains 30000 datapoints with a scatter of 0.3 mmag. We analyse
it using a version of the EBOP code modified to include non-linear limb
darkening and to directly incorporate observed times of minimum light and
spectroscopic light ratios into the solution as individual observations. We
also analyse the dataset with the WD code to ensure that the two models give
consistent results. EBOP provides an excellent fit to the WIRE data. Whilst the
fractional radii are only defined to a precision of 5%, including an accurate
published spectroscopic light ratio improves this dramatically to 0.5%. Using
non-linear limb darkening improves the quality of the fit significantly and
causes the measured radii to increase by 0.4%. It is possible to derive all of
the limb darkening coefficients from the light curve, although they are
strongly correlated with each other, and they agree with theoretical
predictions. The radii and masses of the components of beta Aur are R_A = 2.762
+/- 0.017 Rsun, R_B = 2.568 +/- 0.017 Rsun, M_A = 2.376 +/- 0.027 Msun and M_B
= 2.291 +/- 0.027 Msun. Theoretical stellar models can match these parameters
for a solar metal abundance and an age of 450-500 Myr. The Hipparcos
trigonometric parallax and an interferometrically-derived orbital parallax give
distances to beta Aur which are in excellent agreement with each other and with
distances derived using surface brightness relations and several sets of
empirical and theoretical bolometric corrections (abridged).