Astrophys. J., 722, 1373-1410 (2010/October-3)
Chemical abundances for 855 giants in the globular cluster omega Centauri (NGC 5139).
JOHNSON C.I. and PILACHOWSKI C.A.
Abstract (from CDS):
We present elemental abundances for 855 red giant branch (RGB) stars in the globular cluster Omega Centauri (ω Cen) from spectra obtained with the Blanco 4 m telescope and Hydra multifiber spectrograph. The sample includes nearly all RGB stars brighter than V = 13.5 and spans ω Cen's full metallicity range. The heavy α elements (Si, Ca, and Ti) are generally enhanced by ~+0.3 dex and exhibit a metallicity-dependent morphology that may be attributed to mass and metallicity-dependent Type II supernova (SN) yields. The heavy α and Fe-peak abundances suggest minimal contributions from Type Ia SNe. The light elements (O, Na, and Al) exhibit >0.5 dex abundance dispersions at all metallicities, and a majority of stars with [Fe/H]> - 1.6 have [O/Fe], [Na/Fe], and [Al/Fe] abundances similar to those in monometallic globular clusters, as well as O-Na, O-Al anticorrelations and the Na-Al correlation in all but the most metal-rich stars. A combination of pollution from intermediate-mass asymptotic giant branch stars and in situ mixing may explain the light element abundance patterns. A large fraction (27%) of ω Cen stars are O-poor ([O/Fe] < 0) and are preferentially located within 5'-10' of the cluster center. The O-poor giants are spatially similar, located in the same metallicity range, and are present in nearly equal proportions to blue main-sequence stars. This suggests that the O-poor giants and blue main-sequence stars may share a common origin. [La/Fe] increases sharply at [Fe/H] ≳ -1.6, and the [La/Eu] ratios indicate that the increase is due to almost pure s-process production.
globular clusters: general - globular clusters: individual: Omega Centauri - stars: abundances - stars: Population II
VizieR on-line data:
<Available at CDS (J/ApJ/722/1373): table2.dat table3.dat table3b.dat table4.dat table4b.dat table5.dat table6.dat table6b.dat ion.dat>
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