Asiago eclipsing binaries program I. V432 Aurigae

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 log g in close agreement with the orbital solution, a metal- licity (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 1.08 M� ) 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 ∆V = 0.075 mag and ∆rad.vel. = 1.5 km s −1 . With a Teff = 6080 K 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.