Location: online at https://uu-se.zoom.us/j/62091586806
Abstract:
Gaia DR2 has shown the Milky Way to have several previously unknown stellar populations; most notably the Gaia-Sausage-Enceladus (GSE) population. These could only be detected thanks to Gaia’s exquisite astrometry. However, the nature of these kinematic structures and their origin needs a deeper characterization of their stars than possible with Gaia DR2 data alone. We examine the kinematic properties, metallicity distribution functions, and population ages of stars possibly belonging to the GSE and Sequoia populations using SkyMapper and APOGEE elemental abundance information. GSE has a mean [Fe/H] of -1.2 and is most apparent at high JR. We show that the selection of GSE stars is quickly contaminated by disk stars below JR of 900 km/s. Using a population age analysis, we estimate both GSE and Sequoia to be old, peaking between 10 and 14 Gyr. We also find both GSE and Sequoia have characteristically low [Al/Fe].