Stellar association

An association is primarily identified by commonalities in its member stars' movement vectors, ages, and chemical compositions.

Victor Ambartsumian first categorized stellar associations into two groups, OB and T, based on the properties of their stars.

[3] A third category, R, was later suggested by Sidney van den Bergh for associations that illuminate reflection nebulae.

The Hipparcos satellite provided measurements that located a dozen OB associations within 650 parsecs of the Sun.

[10] Young stellar groups can contain a number of infant T Tauri stars that are still in the process of entering the main sequence.

To summarize the characteristics of Moving groups members: they have the same age and origin, the same chemical composition and they have the same amplitude and direction in their vector of velocity.

[5] These young stellar groupings contain main sequence stars that are not sufficiently massive to disperse the interstellar clouds in which they formed.