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