摘要：Tycho-Gaia Astrometric Solution (TGAS) parallax data are used to determine absolute magnitudes M V for 318 W UMa-type (EW) contact binary stars. A very steep (slope −9), single-parameter (), linear calibration can be used to predict M V to about 0.1–0.3 mag over the whole range of accessible orbital period, days. A similar calibration for the most common systems with days predicts M V values to about 0.06–0.16 mag. For orbital period values both shorter and longer than the central range, the period dependence is respectively steeper and shallower, i.e., the binaries are fainter in M V than predicted by the whole-range linear law. The steepness of the relation for short-period systems implies important consequences for the detectability of the faintest binaries, defining the short-period cut-off of the period distribution. Although the scatter around the linear -fit is fairly large (0.2–0.4 mag), the current data do not support the inclusion of a color term in the calibration.
