Asiago eclipsing binaries program

I. V432 Aurigae

¹ Dipartimento di Astronomia dell'Università di Padova, Osservatorio Astrofisico, 36012 Asiago (VI), Italy
² Osservatorio Astronomico di Padova, Sede di Asiago, 36012 Asiago (VI), Italy
³ CISAS, Centro Interdipartimentale Studi ed Attività Spaziali dell'Università di Padova
⁴ Via Filzi 9, 38034 Cembra (TN), Italy
⁵ University of Ljubljana, Department of Physics, Jadranska 19, 1000 Ljubljana, Slovenia
⁶ Physics and Astronomy Department, University of Calgary, Calgary T2N 1N4, Canada

Corresponding author: U. Munari, munari@pd.astro.it

Received: 25 September 2003
Accepted: 7 January 2004

Abstract

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 T_eff and  in close agreement with the orbital solution, a metallicity [ ]  = -0.6 and rotational synchronization for both components. Direct comparison on the theoretical  plane with the Padova evolutionary tracks and isochrones for the masses of the two components (1.22 and 1.08 ) 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  = 0.075 mag and Δrad.vel. = 1.5 km s^-1. With a T_eff = 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.