0 Assigned ID: 804 ----- Attempting Submission 1 (Fri Apr 11 20:55:44 GMT 2014) ----- Phase II ID is a required field. Couldn't identify "AR" as a legal selection. Observing Description is a required field. 0 We propose a study to determine the formation pathways of a new class of stars: the "sub-subgiants" (a.k.a "red stragglers"), identified in star clusters as stars that are redder than the main sequence but fainter than the giant branch in an optical color-magnitude diagram. First discovered about 15 years ago in the open cluster M67, today there are 47 sub-subgiants known in both open and globular clusters, most discovered using a combination of HST and Chandra data. Yet their origins remain a mystery. We propose a rigorous theoretical investigation into the origins of sub-subgiants, exploring all likely formation channels -- through detailed modeling of stellar and binary evolution and stellar mergers -- and specifically targeting the ability of each formation channel to explain the observed HST optical and UV magnitudes. RESOLVED STELLAR POPULATIONS Default Small false true false false true SUPPORTED