A T-Tauri Star (TTS) is a Variable Star with certain specific Emission Lines (Hydrogen, Ca II, Fe I, S II, O I, Li I), judged to be very young (Pre-Main-Sequence Star) dwarfs (2.5 solar mass or less). They often have Protoplanetary Disks and are near Molecular Clouds. Their energy is from gravitation rather than Fusion, the latter not yet started. They generally have a fast rotation (period of 1-12 days).
Lick Observatory Calcium Line Survey (LkCl)
Pico Dos Dias Survey (PDS)
Pre-Main-Sequence Star (PMS)
Protoplanetary Disk (PPD)
Stellar Age Determination