The coronal evolution of pre-main-sequence stars

TL;DR

This paper investigates the evolution of X-ray emission in pre-main-sequence stars, revealing that stars on Henyey tracks exhibit lower X-ray luminosity ratios due to the decay of coronal activity as they develop radiative cores, especially in intermediate-mass stars.

Contribution

It provides new insights into how X-ray luminosity declines during PMS evolution, particularly highlighting differences between stars on Hayashi and Henyey tracks and the impact of radiative core development.

Findings

Stars on Henyey tracks have lower $ ext{log}(L_X/L_*)$ than those on Hayashi tracks.

X-ray luminosity decays faster with age in intermediate-mass PMS stars.

Main sequence A-type stars generally lack detectable X-ray emission, indicating corona loss during PMS evolution.

Abstract

The bulk of X-ray emission from pre-main-sequence (PMS) stars is coronal in origin. We demonstrate herein that stars on Henyey tracks in the Hertzsprung-Russell diagram have lower $\log(L_X/L_\ast)$, on average, than stars on Hayashi tracks. This effect is driven by the decay of $L_X$ once stars develop radiative cores. $L_X$ decays faster with age for intermediate mass PMS stars, the progenitors of main sequence A-type stars, compared to those of lower mass. As almost all main sequence A-type stars show no detectable X-ray emission, we may already be observing the loss of their coronae during their PMS evolution. Although there is no direct link between the size or mass of the radiative core and $L_X$, the longer stars have spent with partially convective interiors, the weaker their X-ray emission becomes. This conference paper is a synopsis of Gregory, Adams and Davies (2016).