Luminosity function of contact binaries based on the ASAS survey

Abstract

The luminosity function for contact binary stars of the W~UMa-type is evaluated on the basis of the ASAS photometric project covering all stars south of delta= +28 within a magnitude range 8<V<13. Lack of colour indices enforced a limitation to 3373 systems with P<0.562 days (i.e. 73% of all systems with P<1 day) where a simplified Mv(log P) calibration could be used. The spatial density relative to the main sequence FGK stars of 0.2%, as established previously from the Hipparcos sample to V=7.5, is confirmed. While the numbers of contact binaries in the ASAS survey are large and thus the statistical uncertainties small, derivation of the luminosity function required a correction for missed systems with small amplitudes and with orbital periods longer than 0.562 days; the correction, by a factor of 3 times, carries an uncertainty of about 30%.