The observational signatures of convectively excited gravity modes in main-sequence stars

Abstract

We predict the flux and surface velocity perturbations produced by convectively excited gravity modes (g-modes) in main-sequence stars. Core convection in massive stars can excite g-modes to sufficient amplitudes to be detectable with high-precision photometry by Kepler and Convection, Rotation and planetary Transits (CoRoT), if the thickness of the convective overshoot region is ≲30 per cent of a pressure scale height. The g-modes manifest as excess photometric variability, with amplitudes of ~10 μmag at frequencies ≲10 μHz (0.8 d-1) near the solar metallicity zero-age main sequence. The flux variations are largest for stars with M ≳ 5M⊙, but are potentially detectable down to M ~ 2-3M⊙. During the main-sequence evolution, radiative damping decreases such that ever lower frequency modes reach the stellar surface and flux perturbations reach up to ~100 μmag at the terminal-age main sequence. Using the same convective excitation model, we confirm previous predictions that solar gmodes produce surface velocity perturbations of≲0.3mm s-1. This implies that stochastically excited g-modes are more easily detectable in the photometry of massive main-sequence stars than in the Sun. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.