Long-term multicolour photometry and high-resolution spectroscopy of the two $\gamma\,$Doradus stars HD 12901 and HD 48501

Abstract

We gathered long-term multicolour Geneva UB1BB2V1VG photometric and high-resolution (R = 40 000) spectro- scopic data of the two γ Doradus stars HD 12901 and HD 48501. The photometry reveals three frequencies for each of the two stars: f1 = 1.21563 c d −1 , f2 = 1.39594 c d −1 and f3 = 2.18636 c d −1 for HD 12901 and f1 = 1.09408 c d −1 , f2 = 1.29054 c d −1 and f3 = 1.19924 c d −1 for HD 48501. The photometric amplitude is each time largest in the Geneva B1 filter and the variations in all the different filters are perfectly in phase within the measurement errors. Mode identification points out that the six modes are all � = 1 modes and that the non-adiabatic temperature variations are extremely small, in contradiction to current theo- retical predictions. Our spectra show that all the observed frequencies are intrinsic to the stars and cannot be due to binarity. We detect clear line-profile variations at low amplitude (< 1k m s −1 ) due to the oscillations of both targets. The estimated v sin i from the spectra are ∼53 km s −1 for HD 12901 and ∼29 km s −1 for HD 48501. It is at present unclear if the triplet-like structure for HD 48501 is the consequence of rotational splitting or of the large separation expected for high-order gravity modes in the asymptotic regime.