Bibcode
Milone, A. P.; Stetson, P. B.; Piotto, G.; Bedin, L. R.; Anderson, J.; Cassisi, S.; Salaris, M.
Bibliographical reference
Astronomy and Astrophysics, Volume 503, Issue 3, 2009, pp.755-764
Advertised on:
9
2009
Journal
Citations
73
Refereed citations
67
Description
We have analyzed ACS/WFC and WFPC2 images from HST, as well as
ground-based data to study the radial distribution of the double
sub-giant branch (SGB) recently discovered in the Galactic globular
cluster NGC 1851. We found that the SGB split can be followed all the
way from the cluster center out to at least 8´ from the center.
Beyond this distance out to the tidal radius at ~11.7 arcmin, there are
simply too few SGB stars to identify the sequences. The number ratio of
the bright SGB to the faint SGB stars shows no significant radial trend.
Furthermore, we have found that the ratio of blue horizontal-branch (HB)
stars plus RR Lyrae to the red HB stars also remains constant from the
cluster center to the outer envelope.
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, under GO-11233.