Schedule Oct 03, 2008
Phase Space Clumps as Probes of Milky Way Mergers: Chemical Compositions of Newly Discovered Low-Alpha Stars
Claire Lackner (Princeton)

Claire N. Lackner, 1,2
Inese I. Ivans, 1,2
Christine Allen 3
1) Carnegie Observatories
2) Princeton University
3) Instituto de Astronomia, Universidad Nacional Autonoma de Mexico

Thought to represent a population with different nucleosynthetic histories than the bulk of the Milky Way halo, stars with low alpha element abundances are rare. Until now, most low-alpha stars have been found serendipitously. We present chemical compositions for a set of halo stars selected as members of moving groups by the similarity of their galactic orbital parameters and metallicities. These stars are kinematically associated with known low-alpha stars, possible relics of past mergers, and may share their nucleosynthetic histories. Using high resolution spectra gathered at Las Campanas Observatory, W.M. Keck Observatory, and McDonald Observatory, we derive abundances for alpha-, iron peak, neutron-capture elements: Na, Mg, Si, Ca, Sc, Ti, Mn, Co, Ni, Zn, Ba, for six stars, with metallicities ranging from -1.4 to -2.9. This group contains two stars that are known to have low alpha element abundances, HD134439/HD134440. In addition, preliminary results indicate that half of the remaining stars also have low alpha element abundances, with average values for [Mg/Fe], [Si/Fe], and [Ca/Fe] of 0.1, 0.3, and 0.2 respectively. Encouraged by these results, analysis of other kinematically selected groups is currently underway.

View poster as pdf.

Author entry (protected)