Astrometric Membership Tests for the Zinn-Newell-Gibson "UV-Bright"
  Stars in Galactic Globular Clusters
  In 1972, Zinn, Newell, & Gibson (ZNG) published a list of 156 candidate
"UV-bright" stars they had found in 27 Galactic globular clusters (GCs), based
on photographs in the U and V bands. UV-bright stars lie above the horizontal
branch (HB) and blueward of the asymptotic-giant branch (AGB) and red-giant
branch in the clusters' color-magnitude diagrams. They are in rapid
evolutionary phases--if they are members and not unrelated bright foreground
stars. The ZNG list has inspired numerous follow-up studies, aimed at
understanding late stages of stellar evolution. However, the ZNG candidates
were presented only in finding charts, and celestial coordinates were not
given. Using my own collection of CCD frames in u and V, I have identified all
of the ZNG objects, and have assembled their coordinates, parallaxes, and
proper motions from the recent Gaia Early Data Release 3 (EDR3). Based on the
Gaia astrometry, I have determined which objects are probable cluster members
(45% of the sample). For the members, using photometry from EDR3, I have
assigned the stars to various evolutionary stages, including luminous post-AGB
stars, and stars above the HB. I point out several ZNG stars of special
interest that have still, to my knowledge, never been studied in detail. This
study is an adjunct to a forthcoming survey of the Galactic GCs in the uBVI
photometric system, designed for detection of low-gravity stars with large
Balmer discontinuities.
