Chemical Abundance Verifiction of Candidate Omega Centauri Tidal Debris Stars

Skipper, Joy, Astronomy, University of Virginia
Skipper, Joy, Arts & Sciences Undergraduate-sasu, University of Virginia

The Omega Centauri star system has several peculiar features that set it apart from other Milky Way globular clusters, such as its large mass, extended size, oblate shape, internal rotation, large age and metallicity spreads, and retrograde orbit. Because of these properties it is thought that Omega Cen may instead be a heavily stripped remnant of a Milky Way-captured dwarf spheroidal galaxy , now currently orbiting (backwards) near the Galactic plane (e.g., Lee et al. 1999, Majewski et al. 2000). In an earlier study, high resolution spectroscopy was undertaken of a dozen Omega Cen candidates identified by Majewski et al. (2012) on the basis of their Omega Cen-like kinematics, and most were found by Majewski et al. to exhibit very high [Ba/Fe] abundance patterns -- a characteristic currently thought to be uniquely characteristic of Omega Cen stars with [Fe/H] approximately greater than or equal to -1.7. We expand on this previous work with an expanded subsample of stars chosen from the same parent sample. We compare derived [Ba/Fe] abundances for these suspected stripped Omega Cen stars to those stars in the Omega Cen core, other globular cluster and field stars. For these data, we have employed multiple atomic transitions to derive reliable [Ba/Fe] ratios. Of the 15 candidates observed, 12 exhibit barium abundances consistent with that of the Omega Cen system, while the remaining 3 appear to be more consistent with typical Milky Way halo stars. These newly-confirmed Omega Cen debris stars double the sample from the previous study and allows for a more complete mapping of Omega Cen tidal debris and sheds further light upon the parent object's complex chemical and dynamical evolution. This provides strong evidence that a large majority of these retrograde stars in the Omega Cen kinematical regime predicted by the model in Majewski et al. (2012) were indeed once a part of the Omega Cen system.

BS (Bachelor of Science)
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