An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

A → T Tauri star in which → accretion from a → circumstellar disk is responsible for ultraviolet and infrared excess emission and for a moderate to strong emission line spectrum superimposed on the photospheric spectrum. Classical T Tauri stars probably evolve into → weak-line T Tauri stars when their disks are fully accreted by the stars.

→ classical; → T Tauri star.

The most famous young stellar object, the prototype of → T Tauri stars which is located in the Taurus-Auriga star forming region at a distance of about 140 pc. T Tauri is about 2.4 solar masses and about 7 million years old. Complex structures of shock heated gas indicative of outflows surround the star, both on sub-arcsecond and larger scales. The → accretion rate is estimated to be (3-6) x 10^-8 solar masses per year. T Tauri has a companion (about 0.7 arcseconds apart) which is invisible in the optical and has been observed to be strongly variable in infrared. It is an intermediate mass young star (2.5 solar masses) surrounded by a → circumstellar disk. This star is itself a → close binary, the component being a low mass star (0.6 solar masses) also surrounded by circumstellar material.

T, letter of alphabet; Tauri genitive of → Taurus.

A member of a class of young stellar objects of roughly 1 solar mass showing strong → infrared excess emission attributed to → circumstellar disks and found within or close to molecular clouds. T Tauri stars are → protostars in the final stages of formation to become a stable → main sequence star. The nuclear reactions in their core have not yet stabilised and the stars are known for the variability of their brightness. See also → classical T Tauri star, → weak-line T Tauri star.

→ T Tauri; → star.

A T Tauri star that lacks strong emission lines in its optical spectrum, and lacks both strong → stellar wind and → infrared excess. These objects are believed to be → pre-main sequence stars without obvious signs for disk → accretion. Weak-line T Tauri stars result from the evolution of → classical T Tauri stars.

→ weak; → line; → T Tauri star.