Solar-like Oscillations in the G2 Subgiant β Hydri from Dual-Site Observations

We have observed oscillations in the nearby G2 subgiant star β Hyi using high-precision velocity observations obtained over more than a week with the HARPS and UCLES spectrographs. The oscillation frequencies show a regular comb structure, as expected for solar-like oscillations, but with several l = 1 modes being strongly affected by avoided crossings. These data, combined with those we obtained five years earlier, allow us to identify 28 oscillation modes. By scaling the large-frequency separation from the Sun, we measure the mean density of β Hyi to an accuracy of 0.6%. The amplitudes of the oscillations are about 2.5 times solar and the mode lifetime is 2.3 days. A detailed comparison of the mixed l = 1 modes with theoretical models should allow a precise estimate of the age of the star.