SPECTRAL-LINE BROADENING FUNCTIONS OF W UMA-TYPE BINARIES .2. AH VIR

Twenty-four 10 angstrom/mm spectra of the W UMa binary AH Vir have been analyzed for radial velocities and for geometrical parameters of the system components by the method of spectral-line broadening functions. It is shown that the broadening functions determined through the linear restoration process are much better defined than cross-correlation functions, even in the presence of broad spectral features. A new spectroscopic orbit for AH Vir has been determined on the basis of radial velocity information contained in the broadening functions. A combination of this orbit with a parallel solution for the geometric elements gave a new set of absolute elements of the system: a=2.80R., M1=1.36M., M2=0.41M., R1=1.40R., and R2=0.83R.. The absolute bolometric magnitude of the system was found to be 4.m07 and the distance about 94 pc. AH Vir belongs to the 00 Aql subclass of contact binaries which is characterized by the unusually low effective temperature for the observed large dimensions. The radius of the primary (more massive component) is close to what would be expected if it obeyed the Main-Sequence mass-radius relation, but the luminosity of the system (most likely produced solely by the primary component) is lower than that for the Zero-Age Main Sequence. The underluminosity of the system is due to the abnormally low effective temperature which remains significantly low after the energy transfer between components is taken into account. We speculate that the unusual properties of AH Vir result from lack of thermal equilibrium related to the mass transfer between components.