HEATING OF A STAR BY DISK ACCRETION

We examine various ways in which disk accretion can heat an accreting star. These include (1) radiation emitted from the disk surface that i s intercepted by the stellar surface, (2) radiative flux directly acro ss the disk-star interface, and (3) advection of thermal energy from t he disk into the star. For each of these, the physics of the boundary layer between the disk and the star is crucial for determining the amo unt of stellar heating that occurs. We assess the importance of the me thods listed above for heating the star in accreting pre-main-sequence stars and cataclysmic variables, using recent models of boundary laye rs in these systems. We find that intercepted radiation tends to be th e most important source of stellar heating in thin disk systems such a s T Tauri stars and high-M over dot cataclysmic variables. We argue th at direct radiation across the disk-star interface will be unimportant in steady state systems. However, it may be important in outbursting systems, where the disk temperature rises and falls rapidly. Advection of thermal energy into the star becomes the dominant source of stella r heating in thick disk systems such as FU Orionis objects.