Multiwavelength Spectro-Photometric Monitoring of Episodically Accreting Young Low-Mass Stars

Abstract

Episodic accretion in young stellar objects (YSOs) are sudden enhance ment of the accretion rate from the circumstellar disc onto the central pre main sequence (PMS) star. During such episodes of enhanced accretion, it has been observed that the sources can brighten upto 6 magnitudes in V band which is commonly termed as “outburst” stage. The timescales of this phe nomena is very small compared to the millions of years spent in the formation stage, thereby, making these events extremely rare. Till date only about 30 YSOs have been found to undergo such outbursts. Nevertheless, episodic accretion phenomena has significant implications in the final evolution of the PMS star as one epsisode of accretion event is capable of delivering signifi cant amount of mass from the disc to the central PMS star. Feedback from this event has implications on the final evolution of the protoplanetary disc hence planet formation. The physical processes that trigger such outbursts are still poorly understood. This thesis therefore, aims to explore the episodic accretion phenomenon in detail using multiwavelength datasets. We have carried out near simultaneous optical and near-infrared (NIR) photometric and spectroscopic observations to understand the evolution of innermost re gions of the circumstellar disc which are traced out in these wavelengths. We have supplemented our observations archival photometric datasets spanning optical to mid-infrared (MIR) for better understanding of the phenomena of episodic accretion. The main highlight of this thesis is constraining the physical mechanism for the observed outburst in Gaia 20aea and for the post outburst evolution of V2493 Cyg. In addition to this, as a part of the team involved in commissioning of two NIR instruments on 3.6m Devasthal Op tical Telescope (DOT), I have carried out the calibration tests which is also presented in the present thesis.