Asteroseismology of  Centauri A^*

Evidence of rotational splitting

¹ Danish Asteroseismology Centre, Institut for Fysik og Astronomi, Aarhus Universitet, Ny Munkegade, Bygn. 1520, 8000 Aarhus C., Denmark e-mail: bazot@phys.au.dk
² Laboratoire d'Astrophysique de Toulouse-Tarbes, Observatoire Midi-Pyrénées, CNRS, UMR 5572, UPS, 14 Av. E. Belin, 31400 Toulouse, France
³ Observatoire de Haute Provence, 04870 St Michel l'Observatoire, France
⁴ Institut d'Astrophysique de Paris, 98bis Bd Arago, 75014 Paris, France

Received: 25 May 2006
Accepted: 13 March 2007

Abstract

Context.Asteroseismology provides a unique tool for studying stellar interiors. Recently p modes have been detected on the bright solar-like star α Cen A thanks to high-precision radial-velocity measurements. However, a better characterisation of these p modes is clearly needed to constrain theoretical models.

Aims.We observed α 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 high-precision radial-velocity sequences and computed the acoustic spectrum of α Cen A.

Results.We identify 34 p modes with angular degree 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 α 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 α Cen A leads to a list of now well-identified p-mode frequencies and shows the importance of taking the rotation into account in order to properly characterise the p modes even in quite short campaigns.