Detection of frequency spacings in the young O-type binary HD 46149 from CoRoT photometry

Abstract

Aims. Using the CoRoT space based photometry of the O-type binary HD 46149, stellar atmospheric effects related to rotation can be separated from pulsations, because they leave distinct signatures in the light curve. This offers the possibility of characterising and exploiting any pulsations seismologically. Methods. Combining high-quality space based photometry, multi-wavelength photometry, spectroscopy and constraints imposed by binarity and cluster membership, the detected pulsations in HD 46149 are analyzed and compared with those for a grid of stellar evolutionary models in a proof-of-concept approach.Results. We present evidence of solar-like oscillations in a massive O-type star, and show that the observed frequency range and spacings are compatible with theoretical predictions. Thus, we unlock and confirm the strong potential of this seismically unexplored region in the HR diagram.

Seismic modelling of theβ Cephei star HD 180642 (V1449 Aquilae)

“…The O9V star HD 46202 behaves in a similar way to known β Cep stars (e.g., Aerts et al 2010, for an extensive overview of all types of pulsators across the HertzsprungRussell diagram) but none of its modes is predicted to be excited by the theory that is able to explain the β Cep instability strip . Moreover, the O8.5V star HD 46149 appears to oscillate in stochastic modes fulfilling scaling laws and échelle diagrams with clear ridges for modes of equal degree but consecutive radial orders as those observed for Sun-like stars (Degroote et al 2010b). This implies that this star must have an outer convection zone of considerable size, a suggestion made for massive stars in general, independently of seismic data, from theoretical work (Cantiello et al 2009).…”

“…On the observational side, we made an extensive search for ridges in échelle diagrams constructed for the CoRoT residual light curve of HD 180642 discussed in Paper I, adopting the same method as in the case of the CoRoT data of the O8.5V pulsator HD 46149 (Degroote et al 2010b). In doing so, we considered numerous values for a large frequency spacing.…”

“…Subsequently, we computed all frequency differences for all the axisymmetric modes Belkacem et al (2009, upper panel) and in Paper I (middle panel). For comparison, we also show the échelle diagram of the O8.5V star HD 46149 reproduced from Degroote et al (2010b), where clear ridges produced by stochastically excited modes are found. The size of the symbols scales with the power of the frequency.…”

“…More recently, high-precision time-resolved space photometry has been obtained by the ongoing missions CoRoT (Baglin et al 2006;Auvergne et al 2009) and Kepler (Burocki et al 2010;Gilliland et al 2010) providing significant progress in particular subfields of asteroseismology. Notable discoveries have been made of oscillation properties unknown prior to the era of space asteroseismology for solar-like oscillations, not only in both FGK-type main-sequence stars (e.g., Michel et al 2008;Chaplin et al 2011) and red giants (e.g., De Ridder et al 2009;Beck et al 2011;Bedding et al 2011), but also in a massive O-type star (Degroote et al 2010b).…”

An asteroseismic study of the O9V star HD 46202 from CoRoT space-based photometry

“…As part of the asteroseismology programme, several O-type stars were observed by CoRoT during the second short run SRa02 pointing towards the anticentre of the Galaxy, e.g., the O-star binaries HD 46149 (Degroote et al 2010) and HD 47129 (Mahy et al 2011). In this paper, we present a study of the single O9V star HD 46202, which is a member of the young open cluster NGC 2244 in the Rosette Nebula.…”