Investigating variable accretion in T Tauri stars using FUV spectroscopy with UVIT

T Tauri stars (TTSs) are low-mass pre-main-sequence (PMS) stars, surrounded by protoplanetary disks. Accreting TTS are called Classical TTS (CTTS) and are characterized by strong line emission in UV (C IV, Si IV, He II) and optical (Hα). Non-accreting, disk-less weak-line TTS (WTTS) shows weak emission lines due to chromospheric activity and lack of H2 emission from disks. Variability in line luminosities is one of the defining characteristics of CTTSs. The main source of variability is thought to be the change in accretion rate. While optical spectroscopic and photometric surveys commonly search for variability, a few T Tauri stars have repeated observations in the UV. The evolution of the UV spectrum is moreover unknown, despite the importance of UV in heating the disk gas, influencing gas chemistry, and driving photo evaporative winds. Recently, a monitoring program in UV spectroscopy has been initiated using the Hubble Space Telescope (HST), named Ultra-violet Legacy Library of Young Stars as Essential Standards (ULLYSES). Being members of the ULLYSES program, we have developed follow-up FUV spectroscopic observations using UVIT on AstroSat.  30 ks was allotted in the current observational cycle as a part of a pilot study to observe a TTS (HD202917) and the observation is completed. We also obtained simultaneous ground-based optical spectra using CHIRON at the SMARTS telescope.  I will present the results from this UVIT program and discuss how UVIT can be used to make a complementary program to the ULLYSES.