Discovery of $δ$ Scuti pulsation in the Herbig Ae star VV Ser

Abstract

A new observational study of the Herbig Ae star VV Ser has been performed in order to detect and accurately measure pulsation frequencies in the $δ$ Scuti range. As it belongs to the continuous field of view of the asteroseismological satellite COROT, this study also aims at characterizing the properties of VV Ser as a potential ``COROT additional program'' candidate. CCD time series photometry in the Johnson V filter has been obtained during three consecutive years. The resulting light curves have been subject to detailed frequency analysis and the derived frequencies have been compared to model predictions. Seven pulsation frequencies have been measured on the basis of the best dataset obtained in 2004, ranging from $\sim$ 31 to $\sim$ 118 $μHz$, with an accuracy of the order of 0.5 $μHz$. The comparison with an extensive set of asteroseismological models shows that all the observed periodicities can be reproduced if the stellar mass is close to $4 M_{\odot}$. Conversely, the measured frequencies can be associated to $p$ modes only if the effective temperature is significantly lower than that obtained from the spectral type conversion. The present results seem to suggest that more accurate spectral type determination is necessary in order to discriminate the best fit model solution. In any case, the stellar mass of VV Ser is close to the upper mass limit ($\sim 4 M_{\odot}$) for this class of pulsators.