Non-radial pulsations in the γ Doradus star HD 195068

¹ Observatoire de la Côte d'Azur, Dpt. Gemini, UMR 6203, BP 4229, 06304 Nice Cedex 04, France e-mail: Slobodan.Jankov@obs-azur.fr
² Laboratoire Univ. d'Astroph. de Nice (LUAN), UMR 6525, Parc Valrose, 06108 Nice Cedex 02, France
³ Astronomical Observatory, MSEP of Serbia 146007, Volgina 7, 11 050 Belgrade, Serbia and Montenegro

Received: 22 March 2005
Accepted: 31 January 2006

Abstract

We present high resolution spectroscopic observations of the γ Doradus star HD 195068. About 230 spectra were collected over 2 years. Time series analysis performed on radial velocity data shows a main peak at 1.61 d^-1 , a frequency not yet detected in photometry. The Hipparcos photometric 1.25 d^-1 frequency is easily recovered as is 1.30 d^-1 while the third photometric frequency, 0.97 d^-1 , is only marginally present. The good quality of our data, which includes 196 spectra collected over seven consecutive nights, shows that both the 1.61 d^-1 and intermediate 1.27 d^-1 (mixture of 1.25 and 1.30 d^-1 ) frequencies are present in the line profile variations. Using the Fourier-Doppler Imaging (FDI) method, the variability associated with 1.61 d^-1 can be successfully modeled by a non-radial pulsation mode , . For the intermediate frequency 1.27 d^-1 we deduce , . Evidence that the star is not pulsating in the radial mode () rules out a previous classification as an RR Lyrae type star. We investigate the time variability of FDI power spectra concluding that the observed temporal variability of modes can be explained by a beating phenomenon between closely spaced frequencies of two non-radial modes. The distribution of the oscillation power within the line profile indicates that there is a significant tangential velocity component of oscillations characteristic of high radial order gravity modes which are predicted to be observed in γ Doradus type stars.