25 Orionis group
goruh-e 25-Šekârgar, ~ 25-Oryon
Fr.: groupe de 25 Orionis
A group of nearly 200 low-mass → pre-main-sequence stars, concentrated within ~ 1 of the early → B star → 25 Orionis, in the component a of the → Orion OB1 Association. The group also harbors the → Herbig Ae/Be star V346 Ori and a dozen other early-type stars. The velocity distribution for the low-mass stars shows a narrow peak at 19.7 km s-1, offset ~ 10 km s-1 from the velocity characterizing the younger stars of the Ori OB1b subassociation, and 4 km s-1 from the velocity of widely spread young stars of the Ori OB1a population. This indicates that the 25 Ori group is a distinct kinematic entity. The low-mass members follow a well-defined band in the → color-magnitude diagram, consistent with an age of ~ 7-10 Myr (Briceno et al., 2007, ApJ 661, 1119).