The Southern Flanking Fields of the 25 Orionis Group

Abstract

The stellar group surrounding the Be (B1Vpe) star 25 Orionis was discovered to be a pre-main-sequence population by the Centro de Investigaciones de Astronomia (CIDA) Orion Variability Survey and subsequent spectroscopy. We analyze Sloan Digital Sky Survey multi-epoch photometry to map the southern extent of the 25 Ori group and to characterize its pre-main-sequence population. We compare this group to the neighboring Orion OB1a and OB1b subassociations and to active star formation sites (NGC 2068/NGC 2071) within the Lynds 1630 dark cloud. We find that the 25 Ori group has a radius of 1.4 degrees, corresponding to 8-11 pc at the distances of Orion OB1a and OB1b. Given that the characteristic sizes of young open clusters are a few pc or less this suggests that 25 Ori is an unbound association rather than an open cluster. Due to its PMS population having a low Classical T Tauri fraction (~10%) we conclude that the 25 Ori group is of comparable age to the 11 Myr Orion OB1a subassociation.

arXiv comment37 pages, 13 figures, 2 tables (1 large); accepted for publication in AJ

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Cited by in corpus (7)

• 25 Orionis: A Kinematically Distinct 10 Myr Old Group in Orion OB1a
• The Palomar Transient Factory Orion Project: Eclipsing Binaries and Young Stellar Objects
• Search for flares and associated CMEs on late-type main-sequence stars in optical SDSS spectra
• Young stars and brown dwarfs surrounding Alnilam (eps Ori) and Mintaka (del Ori)
• The low mass star and sub-stellar populations of the 25 Orionis group
• System IMF of the 25 Ori Group from Planetary-Mass Objects to Intermediate/High-Mass Stars
• Open Clusters ASCC21 as a Probable Birthplace of the Neutron Star Geminga