The solar-like CoRoT target HD 170987: spectroscopic and seismic observations^*

¹ Laboratoire AIM, CEA/DSM – CNRS, Université Paris Diderot – IRFU/SAp, 91191 Gif-sur-Yvette Cedex, France e-mail: savita.mathur@gmail.com
² High Altitude Observatory, NCAR, PO Box 3000, Boulder, CO 80307, USA

³ LESIA, UMR8109, Université Pierre et Marie Curie, Université Denis Diderot, Obs. de Paris, 92195 Meudon Cedex, France
⁴ Institut d'Astrophysique Spatiale, UMR 8617, Université Paris XI, Bâtiment 121, 91405 Orsay Cedex, France
⁵ Laboratoire d'Astrophysique de Toulouse-Tarbes, Université de Toulouse, CNRS, 31400 Toulouse, France
⁶ Universidad de La Laguna, Dpto de Astrofísica, 38206, Tenerife, Spain
⁷ Instituto de Astrofísica de Canarias, 38205, La Laguna, Tenerife, Spain
⁸ School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
⁹ Sydney Institute for Astronomy, School of Physics, University of Sydney, NSW 2006, Australia

¹⁰ Astronomy Unit, Queen Mary University of London, Mile End Road, London E1 4NS, UK

Received: 19 January 2010
Accepted: 28 April 2010

Abstract

Context. The CoRoT mission is in its third year of observation and the data from the second long run in the galactic centre direction are being analysed. The solar-like oscillating stars that have been observed up to now have given some interesting results, specially concerning the amplitudes that are lower than predicted. We present here the results from the analysis of the star HD 170987.

Aims. The goal of this research work is to characterise the global parameters of HD 170987. We look for global seismic parameters such as the mean large separation, maximum amplitude of the modes, and surface rotation because the signal-to-noise ratio in the observations does not allow us to measure individual modes. We also aim to retrieve the parameters of the star and its chemical composition.

Methods. We studied the chemical composition of the star through ground-based observations performed with the NARVAL spectrograph. We used several methods to calculate the global parameters from the acoustic oscillations based on CoRoT data. The light curve of the star has been interpolated with inpainting algorithms to reduce the effect of data gaps.

Results. We found the power excess related to p modes in the range [400–1200] μHz with a mean large separation of 55.2 ± 0.8 μHz with a probability above 95 % that increases to 55.9 ± 0.2 μHz in a higher frequency range [500–1250]  μHz and a rejection level of 1%. A hint of the variation of this quantity with frequency was also found. The rotation period of the star is estimated to be around 4.3 days with an inclination axis of i = 50°  . We measured a bolometric amplitude per radial mode in a range [2.4–2.9] ppm around 1000 μHz. Finally we estimate the stellar mass with a grid of models, M = 1.43 ± 0.05 , the radius, R = 1.96 ± 0.046 , and the age ~2.4 Gyr.