<P> T Tauri stars (TTS) are a class of variable stars associated with youth . They are less than about ten million years old . This class is named after the prototype, T Tauri, a young star in the Taurus star - forming region . 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> While T Tauri itself was discovered in 1852, the T Tauri class of stars were initially defined by Alfred Harrison Joy in 1945 . </P> <P> T Tauri stars comprise the youngest visible F, G, K and 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> <P> There is evidence of large areas of starspot coverage, and they have intense and variable X-ray and radio emissions (approximately 1000 times that of the Sun). Many have extremely powerful stellar winds; some eject gas in high - velocity bipolar jets . Another source of brightness variability are clumps (protoplanets and planetesimals) in the disk surrounding T Tauri stars . </P>

What is the temperature of a t tauri star
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