Astrophys. J., 706, 1277-1298 (2009/December-1)
Stromgren photometry of Galactic globular clusters. II. Metallicity distribution of red giants in ω Centauri.
CALAMIDA A., BONO G., STETSON P.B., FREYHAMMER L.M., PIERSIMONI A.M., BUONANNO R., CAPUTO F., CASSISI S., CASTELLANI M., CORSI C.E., DALL'ORA M., DEGL'INNOCENTI S., FERRARO I., GRUNDAHL F., HILKER M., IANNICOLA G., MONELLI M., NONINO M., PATAT N., PIETRINFERNI A., PRADA MORONI P.G., PRIMAS F., PULONE L., RICHTLER T., ROMANIELLO M., STORM J. and WALKER A.R.
Abstract (from CDS):
We present new intermediate-band Strömgren photometry based on more than 300 u, v, b, y images of the Galactic globular cluster ω Cen. Optical data were supplemented with new multiband near-infrared (NIR) photometry (350 J, H, Ksimages). The final optical-NIR catalog covers a region of more than 20x20 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 Strömgren metallicity indices, we estimate the photometric metallicity for ~4000 RGs, the largest sample ever collected. The metallicity distributions show multiple peaks ([Fe/H]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]phot≲ -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] ~ 0). The last group includes only a small fraction of stars (∼8%±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 Strömgren metallicity indices display a robust correlation with α-elements ([Ca+Si/H]) when moving from the MI to the MR regime ([Fe/H] ≳ -1.7 dex).
globular clusters: general - globular clusters: individual: Omega Centauri - stars: abundances - stars: evolution
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<Available at CDS (J/ApJ/706/1277): table3.dat table4.dat table6.dat table7.dat table8.dat>
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