T Tauri stars

T Tauri stars

(tor -ÿ, -ee) Variable stars of spectral type G or later whose spectra are dominated by strong emission lines, usually attributed to chromospheric activity and stellar winds in these stars. They are invariably embedded in dense patches of gas and dust that may require observations in the infrared: the dust absorbs the visible light of the star and reradiates it at longer wavelengths. The prototype is T Tauri. T Tauri stars are usually found together in groups (T associations) and are the youngest optically observable stages in the life of a star of about the Sun's mass; more massive counterparts are observed as Ae and Be stars. They are frequently associated with Herbig–Haro objects.

There is much evidence that T Tauri stars are young objects, for instance they have a high abundance of lithium, an element destroyed fairly early in a star's life, and they are surrounded by gas and dust. They are thought to be young protostars that have only recently contracted out of the interstellar medium (see star formation). Lying above the main sequence in the Hertzsprung–Russell diagram, they are still contracting and losing mass (see T Tauri wind). Their spectral lines reveal that some are extremely rapid rotators, throwing off material at speeds of up to 300 km s–1. The irregular light variations are believed to arise partly from activity in the chromospheres of these young stars, and partly by the obscuring effect of the patchy dust in the cocoon as it moves in front of the star.

The original class of T Tauri stars, characterized by strong hydrogen emission lines, are often known as classical T Tauri stars (CTTS) to distinguish them from naked or weak-line T Tauri stars (WTTS); the latter have very weak hydrogen emission lines, often discovered in X-rays, and are much less active than the classical type. WTTS may represent a later phase of pre-main-sequence evolution than CTTS or a different evolutionary channel, as may be suggested by the apparently higher frequency of binaries among WTTS than among CTTS and main-sequence stars. See also FU Orionis; YY Orionis stars.

References in periodicals archive ?
He presented evidence that the T Tauri stars as a class are newly formed.
T Tauri stars are usually found in groups, embedded in dense patches of gas and dust from which they formed.
Unlike the Orion Nebula, it isn't forming massive stars but contains hosts of low-mass protostars in the process of formation: so-called T Tauri stars.
Classical T Tauri stars are often surrounded by dust and gas.
The odd thing is that it's been remarkably difficult to find spectroscopic binaries among the classical T Tauri stars.
The pair say that "naked" T Tauri stars, those that seem to have lost their disks, actually do have them; they've just turned invisible.
Sure enough, slight amounts of X-ray-excited molecular hydrogen appeared in 13 T Tauri stars that the team targeted.
T Tauri stars show outbursts of this kind, and so do FU Orionis stars, but FU Orionis spectra show absorption of light by calcium, whereas Object 50 shows emission by calcium.
The variations we see in T Tauri stars are not evolutionary changes as such, only instabilities in the disk.
Its spectrum shows anomalously intense blue emission lines of neutral iron at 4046 and 4132 angstroms, as well as other unusual features shared by many young, premain-sequence variables - which have become known as the T Tauri stars.
5-meter Isaac Newton Telescope in the Canary Islands to take high-dispersion spectra of 36 T Tauri stars.
Much slower, broader bipolar outflows are found in many well-studied protostars, particularly the famous T Tauri stars.