Distance and temperature from absolute light curves of three eclipsing binaries

Although solutions of arbitrarily scaled eclipsing binary (EB) light curves yield the temperature of only one component (given the other temperature), absolute light curves in two or more bands can directly give temperatures of both stars if combined with radial velocity data and matched to an absolute flux model. Accurate band-to-band flux calibration ratios are keys to temperature accuracy. Distance is correlated with temperature, so improved temperature accuracy leads to improved distance accuracy. Our aim is to explore reliability and robustness of the Direct Distance Estimation (DDE) algorithm in the case of negligible interstellar extinction before moving on to remote targets where extinction is a problem. Simultaneous analyses of two-component RV curves and absolute physical flux curves are carried out here for V1143 Cyg, ɛ CrA and ER Vul, with satisfactory distance checks against Hipparcos parallaxes. Checks against temperatures from spectral types are reasonably close on average for the three EBs, although DDE finds one component of ɛ CrA 470 K cooler than an averaged spectral temperature and 122 K cooler than its lowest spectral temperature. The disagreement may be related to a third star in the ɛ CrA system. An interesting sidelight is an estimate of V1143 Cygni's apsidal motion from whole curve analysis. The result differs from (previous) apsidal motion estimates via eclipse timings at the 4σ level if use is made of the Rossiter-McLaughlin rotational disturbance, but otherwise agrees. The DDE algorithm is in the 2010 public version of the Wilson-Devinney EB modelling and analysis computer program.