Asteroseismology of α Centauri A -: Evidence of rotational splitting

Context. Asteroseismology provides a unique tool for studying stellar interiors. Recently p modes have been detected on the bright solar-like star alpha Cen A thanks to highprecision radialvelocity measurements. However, a better characterisation of these p modes is clearly needed to constrain theoretical models. Aims. We observed a Cen A during five nights using the HARPS spectrograph in order to improve our knowledge of the seismic properties of this star. Methods. We performed highprecision radialvelocity sequences and computed the acoustic spectrum of a Cen A. Results. We identify 34 p modes with angular degree l = 03 in the frequency range 1.8 2.9 mHz and amplitude range 13-48 cm s(-1), in agreement with previous seismic studies. We find an enhancement of the frequency scatter with the angular degree l that indicates, considering the high inclination axis of a Cen A, rotational splitting and explains the low values of previously suggested mode lifetimes. We also derive new values for the small separations that take the effect of rotational splitting into account. Conclusions. Our seismic study of a Cen A leads to a list of now wellidentified pmode frequencies and shows the importance of taking the rotation into account in order to properly characterise the p modes even in quite short campaigns.