Bibcode
Iannicola, G.; Monelli, M.; Bono, G.; Stetson, P. B.; Buonanno, R.; Calamida, A.; Zoccali, M.; Caputo, F.; Castellani, M.; Corsi, C. E.; Dall'Ora, M.; Cecco, A. Di; Degl'Innocenti, S.; Ferraro, I.; Nonino, M.; Pietrinferni, A.; Pulone, L.; Moroni, P. G. Prada; Romaniello, M.; Sanna, N.; Walker, A. R.
Referencia bibliográfica
The Astrophysical Journal Letters, Volume 696, Issue 2, pp. L120-L124 (2009).
Fecha de publicación:
5
2009
Número de citas
21
Número de citas referidas
19
Descripción
We present accurate new ultraviolet and optical BVI photometry for the
Galactic globular cluster NGC 2808 based on both ground-based and
archival Hubble Space telescope imagery. From this we have selected a
sample of ~2000 Horizontal Branch (HB) stars; given the extensive
wavelength range considered and the combination of both high angular
resolution and wide-field photometric coverage, our sample should be
minimally biased. We divide the HB stars into three radial bins and find
that the relative fractions of cool, hot, and extreme HB stars do not
change radically when moving from the center to the outskirts of the
cluster: the difference is typically smaller than ~2σ. These
results argue against the presence of strong radial differentiation
among any stellar subpopulations having distinctly different helium
abundances. The ratio between HB and red giant (RG) stars brighter than
the ZAHB steadily increases when moving from the innermost to the
outermost cluster regions. The difference is larger than ~4σ and
indicates a deficiency of bright RGs in the outskirts of the cluster.
Based on observations collected with the ACS, WFPC2 and STIS onboard the
Hubble Space Telescope.
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