Orion OB1
Orion OB1 (Ori OB1) is a contingent group of several dozen hot giant stars of spectral types O and B in Orion. Associated are thousands of lower-mass stars, and a (smaller but significant) number of protostars. It is part of the larger Orion Molecular Cloud Complex. Owing to its relative closeness and complexity it is the most closely studied OB association. The Orion OB1 consists of the following subgroups: Signatures of stellar debris disk evolution have been detected in the 1a and 1b subgroups.