J. Cummings Poster

Washington Photometry of the Multiple Populations of the Globular Cluster NGC 1851
J. Cummings (Universidad de Concepcion), D. Geisler, and S. Villanova

The detailed analysis of multiple populations in globular clusters (GCs), both spectroscopically and photometrically, has become an exciting area in astronomy. Multiple red giant branches (RGBs), subgiant branches (SGBs), or main sequences are being observed in many GCs while broad distributions of elemental abundances are being detected in most, if not all, GCs. UV photometry has been crucial in exhibiting these multiple populations, but the Johnson U and the Stromgren and Sloan u filters that have previously been used are inefficient.  Our analysis of NGC 1851 shows that using the more efficient Washington C filter is effective at detecting the double RGB and SGB previously observed but with relatively little telescope time at the SWOPE 1-meter telescope.  Remarkably, we have also detected two main sequences and two sequences in the red horizontal branch, both previously unobserved. Matching this photometry to NGC 1851's well studied RGB abundances also show that the two branches generally exhibit different abundances in a variety of elements (e.g., Ba, Na, O, Ca).  Simultaneously considering both Ba and O abundances or Ba and Na abundances, we have been able to more cleanly separate the two RGBs into defined abundance groups.  The less populated red RGB primarily consists of only Ba-rich and O-poor (Na-rich) stars, while the more populated blue RGB primarily consists of all Ba-poor stars and Ba-rich and O-rich (Na-poor) stars.  With the effective and efficient C filter, observing multiple populations even in the Magellanic Clouds may now be possible.