Star formation : circumstellar environment around Young Stellar Objects

Abstract

In this thesis we have undertaken a detailed study of the evolution of young circumstellar disks from the early pre-main sequence phase to the main sequence phase. We have used several observational diagnostics of the disks such as emission-lines, infrared excess and polarization, and have followed their evolution in time. From our study, we show that the accretion activity in intermediate mass young stars declines rapidly and is terminated in about 3-5 Myr. The inner disk is found to dissipate on similar timescale. Further, we show that the optical depth of the circumstellar dust disks decreases steadily with increasing stellar age from the early pre-main sequence phase to the late main sequence phase