Modelling a high-mass red giant observed by CoRoT^⋆

¹ Institut d’Astrophysique Spatiale, UMR8617, CNRS, Université Paris XI, Bâtiment 121, 91405 Orsay Cedex, France
e-mail: frederic.baudin@ias.u-psud.fr
² LESIA, UMR8109, CNRS, Université P. et M. Curie, Université D. Diderot, Observatoire de Paris, 92195 Meudon Cedex, France
³ GEPI, UMR8111, CNRS, Université D. Diderot, Observatoire de Paris, 92195 Meudon Cedex, France
⁴ Institut d’Astrophysique et de Géophysique, Université de Liège, Allée du 6 Aout, 4000 Liège, Belgium
⁵ Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200 B, 3001 Hervelee, Belgium
⁶ Thüringer Landessternwarte, 07778 Tautenburg, Germany
⁷ School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
⁸ Astronomical Institute “Anton Pannekoek”, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands

Received: 28 March 2011
Accepted: 23 November 2011

Abstract

Context. The advent of space-borne photometers such as CoRoT and Kepler has opened up new fields in asteroseismology. This is especially true for red giants as only a few of these stars were known to oscillate with small amplitude, solar-like oscillations before the launch of CoRoT.

Aims. The G6 giant HR 2582 (HD 50890) was observed by CoRoT for approximately 55 days. We present here the analysis of its light curve and the characterisation of the star using different observables, such as its location in the Hertzsprung-Russell diagram and seismic observables.

Methods. Mode frequencies are extracted from the observed Fourier spectrum of the light curve. Numerical stellar models are then computed to determine the characteristics of the star (mass, age, etc.) from the comparison with observational constraints.

Results. We provide evidence for the presence of solar-like oscillations at low frequency, between 10 and 20 μHz, with a regular spacing of (1.7 ± 0.1)   μHz between consecutive radial orders. Only radial modes are clearly visible. From the models compatible with the observational constraints used here, We find that HR 2582 (HD 50890) is a massive star with a mass in the range (3–5 M_⊙), clearly above the red clump. It oscillates with rather low radial order (n = 5–12) modes. Its evolutionary stage cannot be determined with precision: the star could be on the ascending red giant branch (hydrogen shell burning) with an age of approximately 155 Myr or in a later phase (helium burning). In order to obtain a reasonable helium amount, the metallicity of the star must be quite subsolar. Our best models are obtained with a mixing length significantly smaller than that obtained for the Sun with the same physical description (except overshoot). The amount of core overshoot during the main-sequence phase is found to be mild, of the order of 0.1 H_p.

Conclusions. HR 2582 (HD 50890) is an interesting case as only a few massive stars can be observed due to their rapid evolution compared to less massive red giants. HR 2582 (HD 50890) is also one of the few cases that can be used to validate the scaling relations for massive red giants stars and its sensitivity to the physics of the star.