t-tauri stars are found near molecular clouds on the hr diagram.
t-tauri stars are found near molecular clouds on the hr diagram.
where are t-tauri stars found on the hr diagram?
near molecular clouds
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 () in the pre-main-sequence phase of stellar evolution. it ends when a star of develops a radiative zone, or when a larger star commences nuclear fusion on the main sequence.
t tauri star
at the next stage, the envelope completely disappears, having been gathered up by the disk, and the protostar becomes a classical t tauri star. the latter have accretion disks and continue to accrete hot gas, which manifests itself by strong emission lines in their spectrum. the former do not possess accretion disks. classical t tauri stars evolve into weakly lined t tauri stars. this happens after about 1 million years. the mass of the disk around a classical t tauri star is about 1–3% of the stellar mass, and it is accreted at a rate of 10 to per year. a pair of bipolar jets is usually present as well. the accretion explains all peculiar properties of classical t tauri stars: strong flux in the emission lines (up to 100% of the intrinsic luminosity of the star), magnetic activity, photometric variability and jets. the emission lines actually form as the accreted gas hits the "surface" of the star, which happens around its magnetic poles. the jets are byproducts of accretion: they carry away excessive angular momentum. the classical t tauri stage lasts about 10 million years. the disk eventually disappears due to accretion onto the central star, planet formation, ejection by jets, and photoevaporation by ultraviolet radiation from the central star and nearby stars. as a result, the young star becomes a weakly lined t tauri star, which, over hundreds of millions of years, evolves into an ordinary sun-like star, dependent on its initial mass.
accretion (astrophysics)