AAS 199th meeting, Washington, DC, January 2002
Session 109. Galactic Center and Milky Way Formation
Oral, Wednesday, January 9, 2002, 10:00-11:30am, Jefferson East

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[109.05] Galactic Archaeology: The Chemical Composition of a Fossil Stellar Stream

I. I. Ivans (Univ. of Texas at Austin)

Mounting evidence suggests that the Milky Way may have formed by an ``assembly'' process. Star formation and chemical enrichment possibly took place in proto-galactic fragments (subsystems possibly resembling small irregular galaxies) prior to and during their assembly into the Galaxy. Clear evidence of an ancient galactic merger has been uncovered in the local solar neighbourhood (in a statistically significant clumping of stars in angular momentum phase space, along with an additional trail of stars).

These stars, possibly the debris originating from the accretion of a dwarf galaxy system, could have experienced an entirely different chemical history from those born within the Milky Way. Equally interesting is the prospect of discovering that the smaller and less massive dwarf galaxy or proto-galactic fragment could have produced abundance patterns indistinguishable from those of ``normal'' halo field stars. I have employed high resolution stellar spectra to analyze the abundances of important elements which are required (i) to help unravel the nucleosynthetic history of these stars and (ii) that could set further constraints on the evolution of low-mass dwarf galaxies as they existed at the time of the merger. At this meeting, I will report initial chemical composition results which were derived in order to infer the mass function and star formation history of the merger object, as well as to test the ``universality'' of the heavy element r-process production mechanism.

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