Solar-like oscillations in the metal-poor subgiant ν Indi II. Acoustic spectrum and mode lifetime.

Context. Convection in stars excites resonant acoustic waves which depend on the sound speed inside the star, which in turn depends on properties of the stellar interior. Therefore, asteroseismology is an unrivaled method to probe the internal structure of a star. Aims. We made a seismic study of the metal-poor subgiant star ν Indi with the goal of constraining its interior structure. Methods. Our study is based on a time series of 1201 radial velocity measurements spread over 14 nights obtained from two sites, Siding Spring Observatory in Australia and ESO La Silla Observatory in Chile. Results. The power spectrum of the high precision velocity time series clearly presents several identifiable peaks between 200 and 500 µHz showing regularity with a large and small spacing of ∆ν = 25.14 ± 0.09 µHz and δν02 = 2.96 ± 0.22 µHz at 330 µHz. Thirteen individual modes have been identified with amplitudes in the range 53 to 173 cm s −1 . The mode damping time is estimated to be about 16 days (1-σ range between 9 and 50 days), substantially longer than in other stars like the Sun, the α Cen system or the giant ξ Hya.