Detection of small-amplitude oscillations in the G-giant HD 76294 (ζ hydrae)

We made a precise radial-velocity measurement of the G-giant zeta Hya with an iodine cell technique, and found small-amplitude oscillations. The time scale of the oscillations was 6-10 hours, in which a wavy motion was clearly seen. Their power spectrum shows a maximum peak frequency of 38.3 mu Hz. A further period analysis with a pre-whitening procedure reveals that the four peaks, including 38.3 mu Hz, are significant. The peak frequency of the power envelope of the oscillations is about 35 mu Hz, which is quite low compared with a value (about 60 mu Hz) predicted by the scaling law. We also point out that the power excess is confined to a very narrow bandwidth (40 mu Hz) compared with previously observed G giants, zeta Hya and epsilon Oph.