STROeMGREN PHOTOMETRY OF GALACTIC GLOBULAR CLUSTERS. II. METALLICITY DISTRIBUTION OF RED GIANTS IN omega CENTAURI
- European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching (Germany)
- Universita di Roma Tor Vergata, Via della Ricerca Scientifica 1, 00133 Rome (Italy)
We present new intermediate-band Stroemgren photometry based on more than 300 u, v, b, y images of the Galactic globular cluster omega Cen. Optical data were supplemented with new multiband near-infrared (NIR) photometry (350 J, H, K{sub s} images). The final optical-NIR catalog covers a region of more than 20 x 20 arcmin squared across the cluster center. We use different optical-NIR color-color planes together with proper-motion data available in the literature to identify candidate cluster red-giant (RG) stars. By adopting different Stroemgren metallicity indices, we estimate the photometric metallicity for approx4000 RGs, the largest sample ever collected. The metallicity distributions show multiple peaks ([Fe/H]{sub phot} = -1.73 +- 0.08, -1.29 +- 0.03, -1.05 +- 0.02, -0.80 +- 0.04, -0.42 +- 0.12, and -0.07 +- 0.08 dex) and a sharp cutoff in the metal-poor (MP) tail ([Fe/H]{sub phot} approx< -2 dex) that agree quite well with spectroscopic measurements. We identify four distinct subpopulations, namely, MP ([Fe/H] <= -1.49), metal-intermediate (MI; -1.49 < [Fe/H] <= -0.93), metal-rich (MR; -0.95 < [Fe/H] <= -0.15), and solar metallicity ([Fe/H] approx 0). The last group includes only a small fraction of stars (approx8% +- 5%) and should be confirmed spectroscopically. Moreover, using the difference in metallicity based on different photometric indices, we find that the 19% +- 1% of RGs are candidate CN-strong stars. This fraction agrees quite well with recent spectroscopic estimates and could imply a large fraction of binary stars. The Stroemgren metallicity indices display a robust correlation with alpha-elements ([Ca+Si/H]) when moving from the MI to the MR regime ([Fe/H] approx> -1.7 dex).
- OSTI ID:
- 21378101
- Journal Information:
- Astrophysical Journal, Vol. 706, Issue 2; Other Information: DOI: 10.1088/0004-637X/706/2/1277; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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