Fe and Al Abundances for 180 Red Giants in the Globular Cluster Omega Centauri (NGC 5139)

Abstract

We present radial velocities, Fe, and Al abundances for 180 red giant branch (RGB) stars in the Galactic globular cluster Omega Centauri ($\omega$ Cen). The majority of our data lie in the range 11.0$<$V$<$13.5, which covers the RGB from about 1 mag. above the horizontal branch to the RGB tip. The selection procedures are biased towards preferentially observing the more metal--poor and luminous stars of $\omega$ Cen. Abundances were determined using equivalent width measurements and spectrum synthesis analyses of moderate resolution spectra (R$\approx$13,000) obtained with the Blanco 4m telescope and Hydra multifiber spectrograph. Our results are in agreement with previous studies as we find at least four different metallicity populations with [Fe/H]=--1.75, --1.45, --1.05, and --0.75, with a full range of --2.20$\la$[Fe/H]$\la$--0.70. [Al/Fe] ratios exhibit large star--to--star scatter for all populations, with the more than 1.0 dex range of [Al/Fe] decreasing for stars more metal--rich than [Fe/H]$\sim$--1.4. The minimum [Al/Fe] abundance observed for all metallicity populations is [Al/Fe]$\sim$+0.15. The maximum abundance of log $\epsilon$(Al) is reached for stars with [Fe/H]$\sim$--1.4 and does not increase further with stellar metallicity. We interpret these results as evidence for type II SNe providing the minimum [Al/Fe] ratio and a mass spectrum of intermediate mass asymptotic giant branch stars causing the majority of the [Al/Fe] scatter. These results seem to fit in the adopted scheme that star formation occurred in $\omega$ Cen over $>$1 Gyr.

Accepted for publication in ApJ, 77 pages, 17 figures, 7 Tables

References in corpus (9)

• Thermohaline mixing: A physical mechanism governing the photospheric composition of low-mass giants
• Stellar Models and Yields of Asymptotic Giant Branch Stars
• A model for the Globular Cluster extreme anomalies
• The Rotation of Sub-Populations in omega Centauri
• The self-enrichment scenario in intermediate metallicity globular clusters
• A spectral atlas of post-main-sequence stars in omega Centauri: kinematics, evolution, enrichment and interstellar medium
• Modeling the chemical evolution of Omega Centauri using three-dimensional hydrodynamical simulations
• Medium resolution spectroscopy in Omega Centauri: abundances of 400 subgiant and turn-off region
• Abundances on the Main Sequence of Omega Centauri

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