Asteroseismology of the visual binary 70 Ophiuchi

Context. Convection in stars excites resonant acoustic waves. The frequencies of these oscillations depend on the sound speed inside the star, which in turn depends on density, temperature, gas motion, and other properties of the stellar interior. Therefore, analysis of the oscillations provides an unrivaled method to probe the internal structure of a star. Aims. Solar-like oscillations in the primary of the visual binary 70 Ophiuchi are investigated. Methods. 70 Ophiuchi A was observed with the Harps spectrograph mounted on the 3.6-m telescope at the ESO La Silla Observatory ( Chile) during 6 nights in July 2004 allowing us to collect 1758 radial velocity measurements with a standard deviation of about 1.39 m s(-1). Results. The power spectrum of the high precision velocity time series clearly presents several identifiable peaks between 3 and 6 mHz showing regularity with a large spacing of Delta v = 161.7 +/- 0.3 mu Hz. Fourteen individual modes were identified with amplitudes in the range 11 to 14 cm s(-1).