Multi - periodic oscillations of α Hya ⋆

We report the detection of multi-periodic oscillations of the cool evolved star α Hya (HD 81797, K3II-III). Two-hundred and forty-three high-resolution spectra (R = 48 000) of this star have been obtained in March and April 2005 with FEROS at the 2.2 m-MPG/ESO telescope in La Silla Observatory, Chile. We observed oscillations in the stellar radial velocity and the asymmetry of the spectral line profile. We detected oscillation frequencies of the stellar radial velocity in two frequency regions, ν = 2 − 30 µHz and ν = 50 − 120 µHz. The corresponding periods are P = 0.6−5.6 days and P = 2.3−5.5 hours, respectively. In addition to these oscillations we also observed a trend in the radial velocity which shows evidence for a long-term variability. Furthermore, our measurements show a correlation between the variation in the radial velocity and the asymmetry of the spectral line profile, as measured in the bisector velocity spans. The line bisectors also show oscillations in the same frequency regions as those of the radial velocity. We identified 13 oscillation frequencies in the bisector variation with equidistant separations of 8.09 ± 0.32 µHz in the lower frequency region and 7.69 ± 0.47 µHz in the higher frequency region. The source of the short-term oscillations of α Hya is obviously due to non-radial stellar pulsations. These oscillations may have a similar origin like oscillations in solar-like stars. The detection of the multi-periodic oscillations in α-Hya makes this star to be an amenable target for asteroseismology, in particular, as it is a star in the red giant branch.