- Friday, October 19, 2018 from 4:00pm to 5:00pm
- Barnard Hall, 103 - view map
APOGEE Chemical Abundances of the Sagittarius Dwarf Galaxy
The Department of Physics & Astronomy
The University of Utah
The Apache Point Observatory Galactic Evolution Experiment (APOGEE) provides the opportunity of measuring elemental abundances for C, N, O, Na, Mg, Al, Si, P, K, Ca, V, Cr, Mn, Fe, Co, and Ni in vast numbers of stars. We analyze the chemical-abundance patterns of these elements for 158 red giant stars belonging to the Sagittarius dwarf galaxy (Sgr). This is the largest sample of Sgr stars with detailed chemical abundances, and it is the first time that C, N, P, K, V, Cr, Co, and Ni have been studied at high resolution in this galaxy. We find that the Sgr stars with [Fe/H] ≳ -0.8 are deficient in all elemental abundance ratios (expressed as [X/Fe]) relative to the Milky Way, suggesting that the Sgr stars observed today were formed from gas that was less enriched by Type II SNe than stars formed in the Milky Way. By examining the relative deficiencies of the hydrostatic (O, Na, Mg, and Al) and explosive (Si, P, K, and Mn) elements, our analysis supports the argument that previous generations of Sgr stars were formed with a top-light initial mass function, one lacking the most massive stars that would normally pollute the interstellar medium with the hydrostatic elements. We then exploit the unique chemical abundance patterns of Sgr to conduct a chemical tagging exercise on the APOGEE data to identify Sgr stream stars in the Milky Way. We find that our chemical tagging method is able to return ~90% Sgr-like members, with half of these stars likely Sgr stream stars, and the other half belonging to the recently characterized "accreted halo" population. We use the chemical abundance patterns of these stars to draw conclusions about the star formation history of Sgr and of the progenitor of the "accreted halo" population.
- Department of Physics