Chemical enrichment mechanisms in Omega Centauri

clues from neutron-capture elements

V. D'Orazi*, R. Gratton, E. Pancino, A. Bragaglia, E. Carretta, S. Lucatello, C. Sneden

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingConference proceeding contribution


In the complex picture of multiple stellar populations in globular clusters (GCs), a special role is played by NGC 5139 (omega Centauri). At variance with the majority of GCs, omega Cen exhibits significant star-to-star variations in metallicity and in relative neutron-capture element abundance ratios with respect to Fe, along with split evolutionary sequences as revealed from colour-magnitude diagrams. Combining information from photometry and spectroscopy, several studies suggested that an age spread of several Gyr has to be invoked to explain (at least partially) some of the observed features. However, a comprehensive understanding of the formation, evolution and chemical enrichment processes is still not at hand. Relatively metal-rich a Cen stars display neutron-capture abundance distributions dominated by contributions from the s-process, but it is not clear what roles have been played by the so-called main and weak s-process components in generating these abundances. To gain better insight into this question we derived lead (Pb) abundances for several omega Cen cluster members, because this element can only be produced by the mains-process. We analysed high-resolution UVES@VLT spectra of a sample of twelve red-giant branch stars, deriving abundances of Pb and also of Y, Zr, La, Ce, Eu, and the C+N+O sum. Spectral synthesis was applied to all features, taking into account isotopic shifts and/or hyperfine structure as needed. We measured for the first time the Pb content in w Cen, discovering a clear hint for a Pb production occurring at [Fe/H]> -1.7 dex. Our data suggest that the role of the weak component in the production of s-process elements is negligible. Moreover, evidence gathered from the abundances of other elements indicates that the main component occurring in this GC is peculiar and shifted towards higher mass polluters than the standard one.

Original languageEnglish
Title of host publicationGalactic archaeology
Subtitle of host publicationnear-field cosmology and the formation of the milky way
EditorsWako Aoki, Miho Ishigaki, Takuma Suda, Takuji Tsujimoto, Nobou Arimoto
Place of PublicationSan Francisco
Number of pages2
ISBN (Electronic)9781583817995
ISBN (Print)9781583817988
Publication statusPublished - 2012
EventConference on the Galactic Archaeology - Near-Field Cosmology and the Formation of the Milky Way - Shuzenji, Japan
Duration: 1 Nov 20114 Nov 2011

Publication series

NameAstronomical Society of the Pacific Conference Series


ConferenceConference on the Galactic Archaeology - Near-Field Cosmology and the Formation of the Milky Way

Cite this

D'Orazi, V., Gratton, R., Pancino, E., Bragaglia, A., Carretta, E., Lucatello, S., & Sneden, C. (2012). Chemical enrichment mechanisms in Omega Centauri: clues from neutron-capture elements. In W. Aoki, M. Ishigaki, T. Suda, T. Tsujimoto, & N. Arimoto (Eds.), Galactic archaeology: near-field cosmology and the formation of the milky way (Vol. 458, pp. 217-218). (Astronomical Society of the Pacific Conference Series; Vol. 458). San Francisco: ASTRONOMICAL SOC PACIFIC.