A spectroscopic search for non-radial pulsations in the δ Scuti star γ Bootis

Abstract

High-resolution spectroscopic observations of the rapidly rotating δScuti star γBootis have been carried out in 2005, over six consecutive nights, in order to search for line-profile variability. Time-series, consisting of flux measurements at each wavelength bin across the TiII 4571.917 Å line profile as a function of time, have been Fourier analysed.

The results confirm the early detection reported by Kennelly et al. of a dominant periodic component at frequency 21.28 cycles d^-1 in the observer's frame, probably due to a high-azimuthal-order sectorial mode. Moreover, we found other periodicities at 5.06, 12.02cyclesd^-1, probably present but not secure, and at 11.70 and 18.09cyclesd^-1, uncertain. The latter frequency, if present, should be identifiable as another high-azimuthal-order sectorial mode and the three additional terms as low-l modes as proved by the analysis of the first three moments of the line. Owing to the short time baseline and the one-site temporal sampling we consider our results only preliminary but encouraging for a more extensive multisite campaign.

A refinement of the atmospheric physical parameters of the star has been obtained from our spectroscopic data and adopted for preliminary computations of evolutionary models of γBootis.