T association

A T association is a grouping of T Tauri stars, up to several thousand strong, typically embedded in and partly obscured by the nebula from which it formed. It is one of the main types of stellar association. Examples include the Taurus-Auriga T Association, the nearby TW Hydrae Association, and Vela T1 and T2. Additionally, many T Tauri stars are found in other groupings not named as T associations; for example, at least 2,000 T Tauris are believed to exist in the Scorpius-Centaurus OB Association and a handful in the young open cluster Collinder 197. T associations gradually break up after 10 million years or so as the component stars go their separate ways. The recently-found and nearby Horologium Association, lying about 200 light-years away and believed to be about 10 million years old, contains at least 10 young stars of which half a dozen are characterized as post-T Tauri.