ON THE RADIAL DISTRIBUTION OF HORIZONTAL BRANCH STARS IN NGC 2808

Journal Article · Sun May 10 00:00:00 EDT 2009 · Astrophysical Journal (Online)

DOI:https://doi.org/10.1088/0004-637X/696/2/L120; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA)· OSTI ID:21300725

Iannicola, G; Bono, G; Caputo, F; Castellani, M; Corsi, C E; Di Cecco, A; Ferraro, I; Pulone, L; Sanna, N ^[1]; Monelli, M ^[2]; Stetson, P B ^[3]; Buonanno, R ^[4]; Calamida, A ^[5]; Zoccali, M; Romaniello, M ^[6]; Dall'Ora, M ^[7]; Degl'Innocenti, S; Moroni, P G. Prada ^[8]; Nonino, M ^[9]

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1. INAF-OAR, via Frascati 33, Monte Porzio Catone, Rome (Italy)
2. IAC, Calle Via Lactea, E38200 La Laguna, Tenerife (Spain)
3. DAO-HIA, NRC, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada)
4. UniToV, Dipartimento di Fisica, via della Ricerca Scientifica 1, 00133 Rome (Italy)
5. ESO, Karl-Schwarzschild-Str. 2, 85748 Garching bei Munchen (Germany)
6. PUC, Departamento de Astronoma y Astrofisica, Casilla 306, Santiago 22 (Chile)
7. INAF-OACN, via Moiariello 16, 80131 Napoli (Italy)
8. Univ. Pisa, Dipartimento di Fisica, Largo B. Pontecorvo 2, 56127 Pisa (Italy)
9. INAF-OAT, via G.B. Tiepolo 11, 40131 Trieste (Italy)

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 {approx}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 {approx}2{sigma}. 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 {approx}4{sigma} and indicates a deficiency of bright RGs in the outskirts of the cluster.

• OSTI ID: 21300725
• Journal Information: Astrophysical Journal (Online), Journal Name: Astrophysical Journal (Online) Journal Issue: 2 Vol. 696; ISSN 1538-4357
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
99 GENERAL AND MISCELLANEOUS
ABUNDANCE
HELIUM
PHOTOMETRY
SPATIAL DISTRIBUTION
STARS
TELESCOPES
ULTRAVIOLET RADIATION