Discovery and analysis of Gamma Doradus type pulsations in the Cloud and the effect of metallicity on pulsation

Abstract

We present multi-site photometric observations of the F0 IV star HR 2740=QW Pup which reveal it to be a Gamma Dor type variable pulsating with four frequencies: 1.0434, 0.9951, 1.1088, 0.9019 c\d. These data were obtained at the European Southern Observatory and South African Astronomical Observatory over a time baseline spanning from 1997 January 14 to 1997 February 11. The 1.0434 c\d term dominates in amplitude (10 mmag) over the other three (each less than 5 mmag); the light curve comprising these four frequencies seems to be very stable and no residual power is left in the power spectrum. During the analysis particular attention was paid to methodological aspects, which cannot be neglected considering the proximity of the frequencies to 1 c\d. Physical parameters were also derived for all the well-known Gamma Dor stars, confirming that this class is very homogenous. In the framework of the campaign, two Ap stars (OU Pup=HR 2746 and PR Pup=HR 2761) were also observed. The photometric differences between these rotating variables and HR 2740 are emphasized, corroborating the pulsational nature of the Gamma Dor stars. It is further demonstrated that the rotational splitting cannot be a suitable explanation of the observed frequency content of HR 2740.