GeminiFocus 2015 Year in Review | Page 20

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