New seismological results on the G 0 IV η Bootis ⋆

Several attempts have been made to detect solar-like oscillations in the G0 IV star η Boo. We present here new observations on this star simultaneously conducted with two spectrographs: Coralie mounted on the 1.2-m Swiss telescope at the ESO La Silla Observatory (Chile) and Elodie based on the 1.93-m telescope at the Observatoire de Haute Provence (France). In total, 1239 spectra were collected over 13 nights. The power spectrum of the high precision velocity time series clearly presents several identifiable peaks between 0.4 and 1.0 mHz showing regularity with a large and small separations of ∆ν=39.9μHz and δν02 =3.95 μHz respectively. Twenty-two individual frequencies have been identified. Detailed models based on these measurements and non– asteroseismic observables were computed using the Geneva evolution code including shellular rotation and atomic diffusion. By combining these seismological data with non–asteroseismic observations, we determine the following global parameters for η Boo: a mass of 1.57 ± 0.07M⊙, an age t = 2.67 ± 0.10Gyr and an initial metallicity (Z/X)i = 0.0391 ± 0.0070. We also show that the mass of η Boo is very sensitive to the choice of the observed metallicity, while the age of η Boo depends on the input physics used. Indeed, a higher metallicity favours a higher mass, while non–rotating models without overshooting predict a smaller age.