Discovery of δ Scuti pulsation in the Herbig Ae star VV Serpentis

V. Ripepi, S. Bernabei, M. Marconi, A. Ruoppo, F. Palla, M. J. P. F. G. Monteiro, J. P. Marques, P. Ferrara, S. Marinoni, L. Terranegra

Abstract
Context. The study of pulsation in pre-main-sequence intermediate mass stars represents an important tool for deriving information on the stellar parameters and structure, as well as for testing the validity of current theoretical models. The interest in this class of variable stars has significantly increased during the last decade and about 30 members are presently known in the literature. Aims. A new observational study of the Herbig Ae star VV Ser has been performed to detect and accurately measure pulsation frequencies in the δ Scuti range, thus enlarging the sample of known pulsators and contributing to the empirical definition of the pre-main-sequence instability strip. 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.
Methods. CCD time series photometry in the Johnson V filter has been obtained for three consecutive years. The resulting light curves have been subject to detailed frequency analysis and the derived frequencies have been compared to model predictions.
Results. Seven pulsation frequencies have been measured on the basis of the best data set obtained in 2004, ranging from ∼31 to ∼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_o. Conversely, the measured frequencies can be associated with p modes only if the effective temperature is significantly lower than that obtained from the spectral type conversion.
Conclusions. The present results seem to suggest that more accurate spectral type determination is necessary to discriminate the best-fit model solution. In any case, the stellar mass of VV Ser is close to the upper mass limit (∼4 M_o) for this class of pulsators.

Astronomy and Astrophysics
Volume 462, Page 1023
January 2007

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