Ivanna Escala (Caltech)
"Chemical Abundances in the Outer Disk, Giant Stellar Stream, and Inner Halo of Andromeda"
Measurements of chemical abundances ([Fe/H] and [alpha/Fe]) in individual stars can probe the formation history of a galaxy. In contrast to the Milky Way, relatively little is known about [alpha/Fe] of individual red giant branch stars in Andromeda (M31). To make progress with existing telescopes, we have measured abundances from deep, low- and medium-resolution DEIMOS spectra of individual M31 RGB stars using spectral synthesis. I will present measurements of [alpha/Fe] and [Fe/H] for 91 M31 RGB stars across 5 fields spanning the inner halo, Giant Stellar Stream, and outer disk. Prior to our work, only 4 M31 halo stars had such measurements. I will discuss what the abundance distributions reveal about the progenitor(s) of M31’s halo, including the Giant Stellar Stream progenitor, and the formation of M31’s disk.