An Etymological Dictionary of Astronomy and Astrophysics
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A → stellar association containing a number of → reflection nebulae. The stars are of low or intermediate mass and young, less than a million years old. They are still surrounded by patches of dust that reflect and absorb light from the interstellar cloud in which they formed. This type of association was first suggested by Sidney van den Bergh (1966, AJ 71, 900).

R, from → reflection; → association.

1) A large, loose grouping of 10 to 1000 stars that are of similar spectral type and share a common origin. The members move together through space, but have become gravitationally → unbound. Stellar associations are primarily identified by their common movement vectors and ages. → OB association; → T association; → R association.
2) An → unbound stellar agglomeration for which the age of the stars is smaller than the → crossing time (Giels & Portegies Zwart, 2010, MNRAS Letters, astro-ph/1010.1720). See also → star cluster.

The concept of stellar association was first introduced by Viktor A. Ambartsumian (1908-1996), Armenian astrophysicist (1947, Stellar Evolution and Astrophysics, Armenian Acad. of Sci.; German translation, Abhandl. Sowjetischen Astron. Ser. 1. 33, 1951). → stellar; → association.