<Tr> <Td> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> </Td> </Tr> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> <P> T Tauri stars (TTS) are a class of variable stars named after their prototype--T Tauri . They are found near molecular clouds and identified by their optical variability and strong chromospheric lines . T Tauri stars are pre-main - sequence stars in the process of contracting to the main sequence along the Hayashi track, a luminosity--temperature relationship obeyed by infant stars of less than 3 solar masses (M) in the pre-main - sequence phase of stellar evolution . It ends when a star of 0.5 M develops a radiative zone, or when a larger star commences nuclear fusion on the main sequence . </P> <P> T Tauri stars are the youngest visible F, G, K, M spectral type stars (<2 M). Their surface temperatures are similar to those of main - sequence stars of the same mass, but they are significantly more luminous because their radii are larger . Their central temperatures are too low for hydrogen fusion . Instead, they are powered by gravitational energy released as the stars contract, while moving towards the main sequence, which they reach after about 100 million years . They typically rotate with a period between one and twelve days, compared to a month for the Sun, and are very active and variable . </P>

Where are t-tauri stars found on the hr diagram