C,T1,T2: A complementary method to detect Multiple Populations with the Washington filter system

Abstract

In this research we test the ability of a three Washington filter combination, (C-T1)-(T1-T2), compared with that of the traditional C-T1 color to find multiple populations on two globular clusters: NGC 7099 and NGC 1851, types I and II Globular clusters, respectively. Our improved photometry and membership selection, now using Gaia proper motions, finds that the second population stars are more centrally concentrated than first population stars, as expected and contrary to our previous findings for NGC 7099. We find that multiple populations are more easily detected in both clusters using the new (C-T1)-(T1-T2) color, although C-T1 conserves the best width/error ratio. We also search for differences of both colors while splitting the red-RGB and the blue-RGB in NGC 1851, but no significant improvement was found.