New absolute magnitude calibrations for W Ursa Majoris type binaries

Abstract

Parallaxes of W UMa stars in the Hipparcos catalogue have been analyzed. 31 W UMa stars. which have the most accurate parallaxes (sigma(pi)/pi < 0.15) which are neither associated with a photometric tertiary nor with evidence of a Visual companion, were selected for re-calibrating the Period-Luminosity-Color (PLC) relation of W UMa stars. Using the Lutz-Kelker (LK) bias corrected (most probable) parallaxes. periods (0.26 < P < 0.87, P in days), and colors (0.04 < (B - V)(0) < 1.28) of the 31 selected W UMa, the PLC relation have been revised and re-calibrated. The difference between the old (revised but no( bias corrected) and the new (LK bias corrected) relations are almost negligible in predicting the distances of W UMa stars Up to about 100 pc. But, it increases and may become intolerable as distances of stars increase. Additionally, using (J - H)(0) and (H -K(s))(0) colors from 2MASS (Two Micron All Sky Survey) data, a PLC relation working with infrared data was derived. It can be used with infrared colors in the range -0.01 < (J-H)(0) < 0.58, and -0.10 < (H - K(s))(0) < 0.18. Despite of the fact that the 2MASS data refer to single epoch observations which are not guaranteed to be taken at maximum brightness of the W UMa stars. the established relation has been found surprisingly consistent and reliable in predicting LK corrected distances of W UMa stars. (C) 2009 WILEY-VCH Verlag GmbH & Co, KGaA, Weinheim