The Observational Signatures of Convectively Excited Internal Gravity Modes in Main Sequence Stars

TL;DR

This paper predicts observable flux and velocity signals from convectively excited gravity modes in main sequence stars, highlighting their detectability with space telescopes like Kepler and CoRoT, especially in massive stars.

Contribution

It provides detailed predictions of g-mode signatures in main sequence stars, emphasizing the conditions for their detectability and their evolution during the stellar lifecycle.

Findings

Detectable flux variations (~10 microMag) in stars > 2-3 solar masses.

Surface velocity perturbations < 0.3 mm/s for solar g-modes.

Flux perturbations increase up to ~100 microMag at the end of the main sequence.

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.