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.
Related category• NEBULAE AND STAR CLUSTERS
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