Solar-like oscillations with low amplitude in the CoRoT target HD 181906^*

¹ Laboratoire AIM, CEA/DSM-CNRS-Université Paris Diderot; CEA, IRFU, SAp, centre de Saclay, 91191 Gif-sur-Yvette, France e-mail: Rafael.Garcia@cea.fr
² Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
³ Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
⁴ LESIA, UMR8109, Université Pierre et Marie Curie, Université Denis Diderot, Obs. de Paris, 92195 Meudon Cedex, France
⁵ Laboratoire d'Astrophysique de Toulouse-Tarbes, Université de Toulouse, CNRS, 14 Av. Edouard Belin, 31400 Toulouse, France
⁶ Institut d'Astrophysique Spatiale, UMR8617, Université Paris XI, Bâtiment 121, 91405 Orsay Cedex, France
⁷ School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
⁸ Indian Institute of Astrophysics, Koramangala, Bangalore 560034, India
⁹ Astronomy Unit, Queen Mary, University of London Mile End Road, London E1 4NS, UK5
¹⁰ Sydney Institute for Astronomy, School of Physics, The University of Sydney, NSW 2006, Australia

Received: 20 February 2009
Accepted: 2 June 2009

Abstract

Context. The F8 star HD 181906 (effective temperature  K) was observed for 156 days by the CoRoT satellite during the first long run in the direction of the galactic centre. Analysis of the data reveals a spectrum of solar-like acoustic oscillations. However, the faintness of the target (m_v = 7.65) means the signal-to-noise (S/N) in the acoustic modes is quite low, and this low S/N leads to complications in the analysis.

Aims. We extract global variables of the star, as well as key parameters of the p modes observed in the power spectrum of the lightcurve.

Methods. The power spectrum of the lightcurve, a wavelet transform and spot fitting were used to obtain the average rotation rate of the star and its inclination angle. Then, the autocorrelation of the power spectrum and the power spectrum of the power spectrum were used to properly determine the large separation. Finally, estimations of the mode parameters were done by maximizing the likelihood of a global fit, where several modes were fit simultaneously.

Results. We have been able to infer the mean surface rotation rate of the star (~4 μHz) with indications of the presence of surface differential rotation, the large separation of the p modes (~87 μHz), hence also the “ridges” corresponding to overtones of the acoustic modes.