Satellites in discs: regulating the accretion luminosity

We demonstrate, using a simple analytic model, that the presence of a massivesatellite can globally modify the structure and emission properties of anaccretion disc to which it is tidally coupled. We show, using two levels ofnumerical approximation, that the analytic model gives reasonable results. Theresults are applicable to two astrophysical situations. In the case of anactive galactic nucleus, we consider the case of a $\sim 10^3\Msun$ compactcompanion to the central black-hole and show that it could modulate the emittedspectrum on a timescale of $\sim10^5$ years. In the case of a T Tauri accretiondisc, a satellite such as a sub-dwarf or giant planet could modify the discspectral energy distribution over a substantial fraction of the T Tauri starlifetime.