Specific Star Forming Regions -- Poster Presentation
The Spatial Distribution of Low-Mass Members of the Sigma Ori
Cluster
William Sherry, NOAO
Frederick Walter (Stony Brook), Scott Wolk (CfA)
The sigma Ori cluster is a cluster low-mass stars within the
Orion OB1b group. At a age of about 3 Myrs, Orion OB1b is a fossil star
forming region. Star formation is complete and the natal gas/dust has
been cleared away. We use broad band photometry to statistically identify
the low-mass pre-main sequence population of the Sigma Ori cluster. We
find about 140 cluster members with masses between 0.2 and 1.0 Msun. We
use likely members of the cluster to estimate a radius of 3 to 5 pc and
a total mass of about 225 Msun. Photometric observations of low-mass
cluster members (V>15) are very difficult in the inner 30" of
the cluster because the 5 stars of the Sigma Ori multiple system are
very bright (V=3.8 to V=6.7). We coadded a series of roughly half second
V and I band exposures to create high dynamic range images that we could
use to search for faint cluster members close to the central O star of
the cluster. We report one new likely cluster member in the central
15" of the cluster.