Episodic accretion: the interplay of infall and disc instabilities

Using zoom-simulations carried out with the adaptive mesh-refinement code RAMSES with a dynamic range of up to 2(27) approximate to 1.34 x 10(8) we investigate the accretion profiles around six stars embedded in different environments inside a (40 pc) 3 giant molecular cloud, the role of mass infall and disc instabilities on the accretion profile, and thus on the luminosity of the forming protostar. Our results show that the environment in which the protostar is embedded determines the overall accretion profile of the protostar. Infall on to the circumstellar disc may trigger gravitational disc instabilities in the disc at distances of around similar to 10 to similar to 50 au leading to rapid transport of angular momentum and strong accretion bursts. These bursts typically last for about similar to 10 to a similar to 100 yr, consistent with typical orbital times at the location of the instability, and enhance the luminosity of the protostar. Calculations with the stellar evolution code MESA show that the accretion bursts induce significant changes in the protostellar properties, such as the stellar temperature and radius. We apply the obtained protostellar properties to produce synthetic observables with RADMC3D and predict that accretion bursts lead to observable enhancements around 20 to 200 mu m in the spectral energy distribution of Class 0 type young stellar objects.