  Protoplanetary disks, debris disks, and disrupted or evaporating planets can
all feed accretion onto stars. The photospheric abundances of such stars may
then reveal the composition of the accreted material. This is especially likely
in B to mid-F type stars, which have radiative envelopes and hence less
bulk--photosphere mixing. We present a theoretical framework (\texttt{CAM})
considering diffusion, rotation, and other stellar mixing mechanisms, to
describe how the accreted material interacts with the bulk of the star. This
allows the abundance pattern of the circumstellar material to be calculated
from measured stellar abundances and parameters ($v_{\rm rot}$, $T_{\rm eff}$).
We discuss the \lboo\ phenomenon and the application of \texttt{CAM} on stars
hosting protoplanetary disks (HD~100546, HD~163296), debris disks (HD~141569,
HD~21997), and evaporating planets (HD~195689/KELT-9).
