Piotto, G.; Milone, A. P.; Bedin, L. R.; Anderson, J.; King, I. R.; Marino, A. F.; Nardiello, D.; Aparicio, A.; Barbuy, B.; Bellini, A.; Brown, T. M.; Cassisi, S.; Cool, A. M.; Cunial, A.; Dalessandro, E.; D’Antona, F.; Ferraro, F. R.; Hidalgo, S.; Lanzoni, B.; Monelli, M.; Ortolani, S.; Renzini, A.; Salaris, M.; Sarajedini, A.; van der Marel, R. P.; Vesperini, E.; Zoccali, M.
Bibliographical reference
The Astronomical Journal, Volume 149, Issue 3, article id. 91, 28 pp. (2015).
Description
In this paper we describe a new UV-initiative Hubble Space Telescope
project (GO-13297) that will complement the existing F606W and F814W
database of the Advanced Camera for Surveys Globular Cluster (GC)
Treasury by imaging most of its clusters through UV/blue WFC3/UVIS
filters F275W, F336W, and F438W. This “magic trio” of
filters has shown an uncanny ability to disentangle and characterize
multiple population (MP) patterns in GCs in a way that is exquisitely
sensitive to C, N, and O abundance variations. Combination of these
passbands with those in the optical also gives the best leverage for
measuring helium enrichment. The dozen clusters that had previously been
observed in these bands exhibit a bewildering variety of MP patterns,
and the new survey will map the full variance of the phenomenon. The
ubiquity of multiple stellar generations in GCs has made the formation
of these cornerstone objects more intriguing than ever; GC formation and
the origin of their MPs have now become one and the same problem. In
this paper we will describe the database and our data reduction
strategy, as well as the uses we intend to make of the final photometry,
astrometry, and PMs. We will also present preliminary
color–magnitude diagrams from the data so far collected. These
diagrams also draw on data from GO-12605 and GO-12311, which served as a
pilot project for the present GO-13297.
Based on observations with the NASA/ESA Hubble Space Telescope, obtained
at the Space Telescope Science Institute, which is operated by AURA,
Inc., under NASA contract NAS 5-26555.
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