Neutron-capture Element Abundances in Milky Way Dwarf Satellite Galaxies with DEIMOS

Neutron-capture elements are versatile tools. They probe the sites of exotic nucleosynthesis and can provide star formation histories of ancient galaxies with relatively fine time resolution. Dwarf spheroidal galaxies are excellent systems for making use of neutron-capture elements due to their simple structure and old stellar populations. Using neutron-capture abundances to study nucleosynthesis and dwarf galaxy star formation histories requires a large set of such measurements, which can be hard to obtain with high-resolution measurements alone. By leveraging the capabilities of the DEIMOS spectrograph, we are using medium-resolution spectra to assemble one of the largest sets of neutron-capture element abundances (including Sr, Y, Ba, La, and Eu) in dwarf spheroidal galaxies around the Milky Way to date. The large sample size allows us to probe a wide range of metallicities and see structures in the abundance pattern that would not otherwise be clear. For example, in Sculptor we find a decrease in [Ba/Eu] near the middle of the galaxy’s metallicity range, which is not easily explained by current nucleosynthesis models. This feature might be evidence for an early population of fast-rotating massive stars. We also measure [Eu/Mg], which can be used to study the potential sites of the rapid neutron-capture process. Our results suggest that the Eu production timescale at early times in the galaxy’s history is consistent with that of Mg production in supernovae. Looking forward, this work will greatly benefit from the upcoming DEIMOS Throughput Upgrade. The upgrade will especially improve the throughput in the blue wavelength range of DEIMOS, where many of the best neutron-capture element lines are found.