A Transparent Window into Early-Type Stellar Variability

TL;DR

This paper reveals that subsurface convection zones in early-type stars are less common than previously thought, especially at sub-solar metallicities, creating stability windows that impact stellar variability.

Contribution

It demonstrates the absence of convection zones in certain mass ranges of early-type stars at various metallicities, challenging prior models and identifying new observational targets.

Findings

Convection zones are absent in some stars where models predicted instability.

Stability windows vary with metallicity, notably at sub-solar levels.

These windows are promising for studying stellar variability sources.

Abstract

Subsurface convection zones are ubiquitous in early-type stars. Driven by narrow opacity peaks, these thin convective regions transport little heat but play an important role in setting the magnetic properties and surface variability of stars. Here we demonstrate that these convection zones are \emph{not} present in as wide a range of stars as previously believed. In particular, there are regions which 1D stellar evolution models report to be convectively unstable but which fall below the critical Rayleigh number for onset of convection. For sub-solar metallicity this opens up a \emph{stability window} in which there are no subsurface convection zones. For LMC metallicity this surface stability region extends roughly between $8M_\odot$ and $16M_\odot$, increasing to $8M_\odot$ -- $35M_\odot$ for SMC metallicity. Such windows are then an excellent target for probing the relative influence of subsurface convection and other sources of photometric variability in massive stars.