SIVIERO A., MUNARI U., SORDO R., DALLAPORTA S., MARRESE P.M., ZWITTER T. and MILONE E.F.
Abstract (from CDS):
The orbit and physical parameters of the previously unsolved eclipsing binary V432 Aur, discovered by Hipparcos, have been derived with errors better than 1% from extensive Echelle spectroscopy and B, V photometry. Synthetic spectral analysis of both components has been performed, yielding Teff and logg in close agreement with the orbital solution, a metallicity [Z/Z☉]=-0.6 and rotational synchronization for both components. Direct comparison on the theoretical L, Teff plane with the Padova evolutionary tracks and isochrones for the masses of the two components (1.22 and 1.08M☉) provides a perfect match and a 3.75 Gyr age. The more massive and cooler component is approaching the base of the giant branch and displays a probable pulsation activity with an amplitude of ΔV=0.075mag and Δrad.vel.=1.5km/s. With a Teff=6080K it falls to the red of the nearby instability strip populated by δ Sct and γ Dor types of pulsating variables. Orbital modeling reveals a large and bright surface spot on it. The pulsations activity and the large spot(s) suggest the presence of macro-turbulent motions in its atmosphere. They reflect in a line broadening that at cursory inspection could be taken as indication of a rotation faster than synchronization, something obviously odd for an old, expanding star.