Ground-based observations of the β Cephei CoRoT main target HD 180 642: abundance analysis and mode identification^*,**

¹ Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200 D, 3001 Leuven, Belgium e-mail: maryline@ster.kuleuven.be
² INAF – Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate, Italy
³ Instituto de Astrofísica de Canarias, Calle via Láctea s/n, 38205 La Laguna, TF, Spain
⁴ Institut d'Astrophysique et de Géophysique de l'Université de Liège, Allée du 6 Août 17, 4000 Liège, Belgium
⁵ Department of Astrophysics, University of Nijmegen, IMAPP, PO Box 9010, 6500 GL Nijmegen, The Netherlands
⁶ Koninklijke Sterrenwacht van België, Ringlaan 3, 1180 Brussel, Belgium
⁷ UMR 6525 H. Fizeau, UNS, CNRS, OCA, Campus Valrose, 06108 Nice Cedex 2, France
⁸ BIRA-IASB, Ringlaan 3, 1180 Brussel, Belgium
⁹ Instituto de Astrofísica de Andalucía (CSIC), Apdo. 3004, 18080 Granada, Spain
¹⁰ Konkoly Observatory, PO Box 67, 1525 Budapest, Hungary
¹¹ GEPI, Observatoire de Paris, CNRS, Université Paris Diderot, place Jules Janssen, 92195 Meudon Cedex, France
¹² Instytut Astronomiczny Wroclawski, Kopernika 11, 51–622 Wroclaw, Poland
¹³ Laboratoire d'Astrophysique de Toulouse-Tarbes, Université de Toulouse, CNRS, 31400 Toulouse, France
¹⁴ Universidade de Vigo, Departamento de Física Aplicada, Campus Lagoas-Marcosende, 36310 Vigo, Spain

Received: 10 March 2009
Accepted: 17 May 2009

Abstract

The known β Cephei star HD 180 642 was observed by the CoRoT satellite in 2007. From the very high-precision light curve, its pulsation frequency spectrum could be derived for the first time (Degroote and collaborators). In this paper, we obtain additional constraints for forthcoming asteroseismic modeling of the target. Our results are based on both extensive ground-based multicolour photometry and high-resolution spectroscopy. We determine  K and  dex from spectroscopy. The derived chemical abundances are consistent with those for B stars in the solar neighbourhood, except for a mild nitrogen excess. A metallicity is obtained. Three modes are detected in photometry. The degree  is unambiguously identified for two of them: and for the frequencies 5.48694 d^-1 and 0.30818 d^-1, respectively. The radial mode is non-linear and highly dominant with an amplitude in the U-filter about 15 times larger than the strongest of the other modes. For the third frequency of 7.36673 d^-1 found in photometry, two possibilities remain: or 3. In the radial velocities, the dominant radial mode presents a so-called stillstand but no clear evidence of the existence of shocks is observed. Four low-amplitude modes are found in spectroscopy and one of them, with frequency 8.4079 d^-1, is identified as . Based on this mode identification, we finally deduce an equatorial rotational velocity of  km s^-1.