Washington Photometry of the Multiple Stellar Populations in the Globular Cluster NGC 1851

The detailed analysis of multiple populations (MPs) in globular clusters (GCs), both spectroscopically and photometrically, has become an exciting area in astronomy. Multiple red giant branches (RGBs), subgiant branches (SGBs), and even main sequences are being observed in many GCs while broad abundance distributions of certain elements are being detected in most, if not all, GCs. UV photometry has been crucial in exhibiting these MPs, but the Johnson U and the Stromgren and Sloan u filters that have previously been used are inefficient and sensitive to reddening and atmospheric extinction. Our analysis of NGC 1851 with the broader and slightly redder Washington C filter shows to be very effective at detecting the previously observed double RGB and SGB, but with using relatively little telescope time. Remarkably, we have also detected a previously unobserved double main sequence (MS).