A spectroscopic search for non-radial pulsations in the delta Scuti star gamma Bootis

TL;DR

This study used high-resolution spectroscopy over six nights to detect and analyze non-radial pulsations in the delta Scuti star gamma Bootis, confirming previous findings and identifying multiple periodicities.

Contribution

First spectroscopic detection of multiple non-radial pulsation modes in gamma Bootis, expanding understanding of its oscillation spectrum.

Findings

Confirmed dominant pulsation at 21.28 c/d

Detected additional periodicities at 5.06, 12.09, 11.70, and 18.09 c/d

Identified modes as high azimuthal order sectorial and low-l modes

Abstract

High-resolution spectroscopic observations of the rapidly rotating delta Scuti star gamma Bootis have been carried out on 2005, over 6 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 A line profile as a function of time, have been Fourier analyzed. The results confirm the early detection reported by Kennelly et al. (1992) of a dominant periodic component at frequency 21.28 c/d in the observer's frame, probably due to a high azimuthal order sectorial mode. Moreover, we found other periodicities at 5.06 c/d, 12.09 c/d, probably present but not secure, and at 11.70 c/d and 18.09 c/d, uncertain. The latter frequency, if present, should be identifiable as another high azimuthal order sectorial mode and three additional terms, probably due to 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 gamma Bootis.