Wave Heating and F-type Stars

I sometimes have research ideas that I think are cool, but that don’t make sense for me to pursue. I generally just make a note of them and move on. This is the eighteenth post in a series describing some of the ideas I’ve accumulated.

Wave Heating and F-type Stars

What’s the idea?

Convection zones emit internal gravity waves at their boundaries. There is some uncertainty as to exactly how much power escapes in these waves, but estimates are of order $L_{\rm conv}\mathcal{M}$, where $L_{\rm conv}$ is the heat carried by convection and $\mathcal{M}$ is the convective Mach number.

In F-type stars $\mathcal{M}$ approaches unity in the subsurface convection zone, and $L_{\rm conv}$ approaches the total luminosity of the star. That means that internal gravity waves carry comparable luminosity to the entire star, which seems like an important effect to consider.

Why is this important?

Waves are emitted downward, into the star, and then damp, producing heat. The net result should be a significant rearrangement of the thermal structure of the near-surface layers. This should be readily observable in surface properties like $T_{\rm eff}$ and possibly also in asteroseismic measurements. If this can be predicted and observed it would be a dramatic confirmation of an oft-neglected effect (wave emission by convection).

How can I get started?

I’d start by looking through this Atlas to figure out which stars have the highest ratio $L_{\rm conv}\mathcal{M}/L$, where $L$ is the total luminosity of the star. Then I’d work out where the waves damp in the star, using methods like these. I’d then build MESA models that remove the wave luminosity from the convection zone (as a cooling term) and inject it lower down where the waves are expected to damp. I’d compare those with models that neglect wave heating and see what differences arise.

If the differences are significant, I’d go looking for ways to test my models with observations.This should be doable with archival data given how many F-type stars have been observed and characterized.