GeminiFocus April 2018 - Page 7

For instance, fitting model isochrones in the color-magnitude space allowed us to establish the age and metallicity of the underlying stellar population; it also isolated those stars giving us an opportunity to perform a structural analysis of each object by obtaining half-light radius and ellipticity. From this we could fit the radial profile to un- derstand how the stars are distributed. We further obtained a stellar luminosi- ty function, which helped us to explore the possibilities of mass segregation. DES 1 and Eri III: A Comparative Review The sketch in Figure 4 shows the workflow from image to data products. For the cases of DES 1 and Eri III, this process worked excep- tionally well revealing that the fundamental properties of the two stellar populations are remarkably similar. They have essentially the same metallicity ([Fe/H] DES 1 = -2.38 vs. [Fe/H] = -2.40 dex) and mean alpha abundance Eri III ([α/Fe] ≈ +0.2 dex for both), along with com- parable ages (11.2 billion years (Gyr) vs. 12.5 Gyr). Structurally, DES 1 and Eri III also share simi- lar properties: ellipticity (0.41 DES 1 vs. 0.44 Eri III ); position angle (112° DES 1 vs. 109° Eri III ); and Eri III is about 1.5 times larger than DES 1 and slightly more luminous (M V, DES 1 = -2.07 vs. M V, = -1.42). Er iIII When it comes to their location in the Milky Way halo, they are projected onto the trailing filaments of neutral hydrogen gas from the Figure 3. Color-magnitude diagrams for DES 1, Eri III, and Tuc V (from left to right, respectively). The rectangular outline within each frame shows the window of the discovery photometry. The data are based on GMOS-S photometry, which trace the stellar populations in these ultra-faint dwarf candidates 3-4 magnitudes deeper than before. Figure 4. Sample work flow, from image to data products, for Eri III. April 2018 GeminiFocus 5