Figure 4.
Magnitude-color
diagram for all stars
detected in the RCW 41
cluster. Stars marked
with a blue polygon or a
red square are the YSOs.
The pre-main sequence
models used to estimate
the cluster’s age are
shown with the solid
color lines.
SofI (Son of Isaac) on the New Technology
Telescope, and the new GeMS/GSAOI images in H-band. The region shown here is the
cluster’s center, where the stellar density is
the highest. GeMS/GSAOI not only resolves
many more stars, but by concentrating the
light over smaller areas it also enhances the
sensitivity and limiting magnitude in this
crowded region. Determining the stellar
content of young clusters (by resolving their
individual members and gaining access to
their faintest ones) is a key in understanding
the process of their star formation.
Young Stellar Objects:
Identification and Cluster Age
Determination
Based on the photometry derived from
GeMS/GSAOI, complemented by images
taken by NASA’s infrared Spitzer Space
Telescope, we have identified a total of 80
Young Stellar Object (YSO) candidates based
on their unusual red colors. Indeed, these
recently-formed stars are still embedded in
native material, and circumstellar emission
from each star’s disk and envelope dominate
the spectral energy distribution.
The signature of their youth, however, reveals itself at longer wavelengths, where
their spectrum significantly deviates from a
pure photospheric emission. Constructing
color-color diagrams, we find that YSOs tend
to cluster in a specific region, making them
easy to identify.
Once identified, these candidate YSOs can
then be used to estimate the age of the cluster. Indeed, in the absence of proper motion studies, or spectrosco pic information,
the distinction of true low-mass members
from the contaminating field stars projected
along the line of sight is difficult. We therefore used these YSO sources, which are more
likely associated with the cluster, to derive
an approximate age of the region.
Age determination was done through the
color-magnitude diagram shown in Figure
4. For each YSO, we track its position with
respect to pre-main sequence models. The
different models assume different colors for
different YSO age. This allows us to basically
assign an age for each object. Of course uncertainties are large. However, this exercise
allowed us to find evidence for the cohabitation of two potentially distinct populations
of YSOs.
More specifically, we found that two-thirds
of the YSOs were young, with a mean age
lower than 3 million years (Myr), while onethird had a mean age of about 5 Myr. This
might be the sign of an evolutionary star
formation sequence (progression) at work in
this region.
18
GeminiFocus
2015 Year in Review
January 2016