Stellar Photospheric Abundances as a Probe of Disks and Planets

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).