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 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 micromagnitudes at frequencies ~ 10 microHz (0.8 1/d) near the solar metallicity zero-age main sequence. The flux variations are largest for stars with M > 5 solar masses, but are potentially detectable down to M ~ 2 - 3 solar masses. 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 micromagnitudes at the terminal-age main sequence. Using the same convective excitation model, we confirm previous predictions that solar g-modes produce surface velocity perturbations of < 0.3 mm/s. This implies that stochastically excited g-modes are more easily detectable in the photometry of massive main sequence stars than in the Sun.