Seismic modelling of the β Cephei star HD 180642 (V1449 Aquilae)

¹ Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
e-mail: conny@ster.kuleuven.be
² Department of Astrophysics, IMAPP, Radboud University Nijmegen, PO Box 9010, 6500 GL Nijmegen, The Netherlands
³ LESIA, Observatoire de Paris, CNRS, UPMC, Université Paris-Diderot, 92195 Meudon, France
⁴ Institut d’Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août 17, 4000 Liège, Belgium
⁵ Royal Observatory of Belgium, Ringlaan 3, 1180 Brussels, Belgium

Received: 5 July 2011
Accepted: 19 August 2011

Abstract

Context. We present modelling of the β Cep star HD 180642 based on its observational properties deduced from CoRoT and ground-based photometry as well as from time-resolved spectroscopy.

Aims. We investigate whether present-day state-of-the-art models are able to explain the full seismic behaviour of this star, which has extended observational constraints for this type of pulsator.

Methods. We constructed a dedicated database of stellar models and their oscillation modes tuned to fit the dominant radial mode frequency of HD 180642, by means of varying the hydrogen content, metallicity, mass, age, and core overshooting parameter. We compared the seismic properties of these models with those observed.

Results. We find models that are able to explain the numerous observed oscillation properties of the star, for a narrow range in mass of 11.4–11.8 M_⊙ and no or very mild overshooting (with up to 0.05 local pressure scale heights), except for an excitation problem of the ℓ = 3, p₁ mode. We deduce a rotation period of about 13 d, which is fully compatible with recent magnetic field measurements. The seismic models do not support the earlier claim of solar-like oscillations in the star. We instead ascribe the power excess at high frequency to non-linear resonant mode coupling between the high-amplitude radial fundamental mode and several of the low-order pressure modes. We report a discrepancy between the seismic and spectroscopic gravity at the 2.5σ level.