Photometric detection of internal gravity waves in upper main-sequence stars

I. Methodology and application to CoRoT targets

¹ Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
e-mail: dominic.bowman@kuleuven.be
² Department of Astrophysics, IMAPP, Radboud University Nijmegen, 6500 GL Nijmegen, The Netherlands
³ School of Mathematics, Statistics and Physics, Newcastle University, Newcastle-upon-Tyne NE1 7RU, UK
⁴ Planetary Science Institute, Tucson, AZ 85721, USA
⁵ Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain
⁶ Departamento de Astrofísica, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain
⁷ Sydney Institute for Astronomy (SIfA), School of Physics, The University of Sydney, NSW 2006, Australia
⁸ Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark
⁹ LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, Univ. Paris Diderot, Sorbonne Paris Cité, 5 Place Jules Janssen, 92195 Meudon, France
¹⁰ Royal Observatory of Belgium, Ringlaan 3, 1180 Brussels, Belgium

Received: 17 June 2018
Accepted: 16 November 2018

Abstract

Context. Main sequence stars with a convective core are predicted to stochastically excite internal gravity waves (IGWs), which effectively transport angular momentum throughout the stellar interior and explain the observed near-uniform interior rotation rates of intermediate-mass stars. However, there are few detections of IGWs, and fewer still made using photometry, with more detections needed to constrain numerical simulations.

Aims. We aim to formalise the detection and characterisation of IGWs in photometric observations of stars born with convective cores (M ≳ 1.5 M_⊙) and parameterise the low-frequency power excess caused by IGWs.

Methods. Using the most recent CoRoT light curves for a sample of O, B, A and F stars, we parameterised the morphology of the flux contribution of IGWs in Fourier space using an MCMC numerical scheme within a Bayesian framework. We compared this to predictions from IGW numerical simulations and investigated how the observed morphology changes as a function of stellar parameters.

Results. We demonstrate that a common morphology for the low-frequency power excess is observed in early-type stars observed by CoRoT. Our study shows that a background frequency-dependent source of astrophysical signal is common, which we interpret as IGWs. We provide constraints on the amplitudes of IGWs and the shape of their detected frequency spectrum across a range of mass, which is the first ensemble study of stochastic variability in such a diverse sample of stars.

Conclusions. The evidence of a low-frequency power excess across a wide mass range supports the interpretation of IGWs in photometry of O, B, A and F stars. We also discuss the prospects of observing hundreds of massive stars with the Transiting Exoplanet Survey Satellite (TESS) in the near future.