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physical object > natural object > celestial body > collection of stars > association

association
subject			fact

association	has most luminous member
	has definition A sparsely populated grouping (mass range 102-103 Msun) of very young, massive stars lying along a spiral arm of the Milky Way, whose spectral types or motions in the sky indicate a common origin. The star density is insufficient for gravitation to hold the group together against shear by differential galactic rotation, but the stars have not yet had time to disperse completely. OB associations are composed of stars of spectral types O-B2; T associations have many young T Tauri stars. The internationally approved designation for associations is the name of the constellation followed by an arabic numeral - e.g., Perseus OB2.
	is a kind of collection of stars
collection of stars	has number of stars
	has catalog catalog about star systems
celestial body	has spectra
physical object	has location or center of gravity
	has angular momentum
	has mass
	has velocity
	has momentum
	has temperature
	has volume
	has extent
	has material

Kinds of association :

• OB association (4 kinds, 20 facts) - A loose gathering of O and B stars that typically stretches over hundreds of light-years and contains a few dozen OB stars.
• Sco-Cen association (4 facts) - An association of very young stars. The most luminous member is a B star of M_v = - 4.9.
• T association (2 facts) - Association containing many T Tauri stars. About 20 are known.