The Photometric Revolution – Stellar Parameters and Elemental Abundances for over 100 Million Stars… and Counting
Prof. Tim Beers
Department of Physics & Astronomy
University of Notre Dame
Galactic Archaeologists are opening a revolutionary era for the determination of stellar parameters, such as effective temperature, surface gravity, metallicity, and ages, for a substantial fraction of the stars in the Milky Way, and eventually in dwarf galaxies and other nearby galaxies of the Local Group. The most recent surveys implement a combination of narrow- and intermediate-band filters that further enable measurements of a subset of the most important elements for probing stellar populations, in addition to [Fe/H], such as [C/Fe], [N/Fe], [Mg/Fe], and [Ca/Fe]. The recently (or nearly) completed surveys, including the SkyMapper Southern Survey (SMSS) and The Stellar Abundances for Galactic Exploration Survey (SAGES) in the North, have already contributed over 50 million stars with estimates of [Fe/H]. The ongoing Javalambre Photometric Local Universe Survey (J-PLUS) and the Southern Local Universe Survey (S-PLUS) will contribute another 50 million stars with additional elemental abundances over the next two years. For those who hunger for the most chemically primitive stars, we have already identified over 1 million Very Metal-Poor stars with [Fe/H] < -2.0, and over 50,000 Extremely Metal-Poor stars with [Fe/H] < -3.0. Extension of these techniques to other large-scale surveys in the future will also be discussed.
Candidate Members of the VMP/EMP Disk System of the Milky Way from the SkyMapper and SAGES Surveys
Jihye Hong
Graduate Student, Department of Physics & Astronomy
University of Notre Dame
Recent photometric surveys are relatively free from the target-selection biases often associated with large-scale spectroscopic studies, significantly increasing the observable number of stars. Over 50 million stars from the SMSS DR2 and SAGES surveys have been used to derive the photometric-metallicity estimates with comparable accuracy to existing low- and medium- resolution (R ∼ 1,800) spectroscopic surveys (Huang et al. 2022, 2023). We then employed about 11.5 million stars from these surveys with available full-space motions based on astrometry and radial velocities available from Gaia DR3 to obtain dynamical parameters with the Action-based GAlaxy Modelling Architecture (AGAMA, Vasiliev 2019) package. After applying several quality cuts designed to produce the best available metallicity and dynamical estimates, we analyzed about 5.86 million stars in the combined SMSS/SAGE sample. We employed two techniques to identify between 876 and 1,476 VMP/EMP stars, respectively, that appear to be members of the Galactic disk system on rapid prograde orbits (rotation velocity > 150 ); 1,496 unique candidate VMP/EMP disk-like stars were identified, with the majority having orbital eccentricities ≤ 0.4. This large number of VMP/EMP stars associated with the Milky Way’s disk system strongly suggests the presence of an early-forming primordial disk.