The Hubble Space Telescope UV Legacy Survey of Galactic Globular
  Clusters. VIII. Preliminary Public Catalog Release
  The Hubble Space Telescope (HST) UV Legacy Survey of Galactic Globular
Clusters (GO-13297) has been specifically designed to complement the existing
F606W and F814W observations of the Advanced Camera for Surveys (ACS) Globular
Cluster Survey (GO-10775) by observing the most accessible 47 of the previous
survey's 65 clusters in three WFC3/UVIS filters F275W, F336W, and F438W. The
new survey also adds super-solar metallicity open cluster NGC 6791 to increase
the metallicity diversity. The combined survey provides a homogeneous 5-band
data set that can be used to pursue a broad range of scientific investigations.
In particular, the chosen UV filters allow the identification of multiple
stellar populations by targeting the regions of the spectrum that are sensitive
to abundance variations in C, N, and O. In order to provide the community with
uniform preliminary catalogs, we have devised an automated procedure that
performs high-quality photometry on the new UV observations (along with similar
observations of seven other programs in the archive). This procedure finds and
measures the potential sources on each individual exposure using library
point-spread functions and cross-correlates these observations with the
original ACS-Survey catalog. The catalog of 57 clusters we publish here will be
useful to identify stars in the different stellar populations, in particular
for spectroscopic follow-up. Eventually, we will construct a more sophisticated
catalog and artificial-star tests based on an optimal reduction of the UV
survey data, but the catalogs presented here give the community the chance to
make early use of this HST Treasury survey.
