T Tauri star

T Tauri star A very young eruptive variable star, less than 10 million years old, with a mass similar to or somewhat less than that of the Sun; abbr. INT (or IT if no nebulosity is present). T Tauri stars have diameters several times the Sun's, and are still contracting. Their spectral types are F–M. On the Hertzsprung–Russell diagram they lie on Hayashi tracks above the main sequence. T Tauri stars are classified according to their spectra as either classical, weak-line, or naked. Classical T Tauri stars have strong emission lines, and are much brighter in the infrared than other stars of similar temperature. This is thought to be due to surrounding disks of warm dust, similar to the early solar nebula, which may be sites for planet formation. Weak-line objects show less evidence of surrounding material, while naked T Tauri stars show none at all. T Tauri stars exhibit irregular variability ranging from ultraviolet flares on a time-scale of minutes to optical variations on time-scales of days, months, or years. The prototype, T Tauri itself, lies within Hind's Variable Nebula and varies irregularly between 8th and 13th magnitudes. See also fu orionis star.