  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).
