We derive dynamical parameters for a large sample of 446 r-process-enhanced (RPE) metal-poor stars in the halo and disk systems of the Milky Way, based on data releases from the R-Process Alliance, supplemented by additional literature samples. This sample represents more than a 10-fold increase in size relative to that previously considered by Roederer et al. and, by design, covers a larger range of r-process-element enrichment levels. We test a number of clustering analysis methods on the derived orbital energies and other dynamical parameters for this sample, ultimately deciding on application of the HDBSCAN algorithm, which obtains 30 individual chemodynamically tagged groups (CDTGs); 21 contain between 3 and 5 stars, and 9 contain between 6 and 12 stars. Even though the clustering was performed solely on the basis of their dynamical properties, the stars in these CDTGs exhibit statistically significant similarities in their metallicity ([Fe/H]), carbonicity ([C/Fe]), and neutron-capture element ratios ([Sr/Fe], [Ba/Fe], and [Eu/Fe]). These results demonstrate that the RPE stars in these CDTGs have likely experienced common chemical-evolution histories, presumably in their parent satellite galaxies or globular clusters, prior to being disrupted into the Milky Way’s halo. We also confirm the previous claim that the orbits of the RPE stars preferentially exhibit pericentric distances that are substantially lower than the present distances of surviving ultrafaint dwarf and canonical dwarf spheroidal galaxies, consistent with the disruption hypothesis. The derived dynamical parameters for several of our CDTGs indicate their association with previously known substructures, dynamically tagged groups, and RPE groups.

Orbital characteristics based on Gaia Early Data Release 3 astrometric parameters are analyzed for ∼4000 metal-poor stars ([Fe/H] ≤ −0.8) compiled from the Best and Brightest survey. Selected as metal-poor candidates based on broadband near- and far-IR photometry, 43% of these stars had medium-resolution (1200 ≲ R ≲ 2000) validation spectra obtained over a 7 yr campaign from 2014 to 2020 with a variety of telescopes. The remaining stars were chosen based on photometric metallicity determinations from the Huang et al. recalibration of the Sky Mapper Southern Survey. Dynamical clusters of these stars are obtained from the orbital energy and cylindrical actions using the HDBSCAN unsupervised learning algorithm. We identify 52 dynamically tagged groups (DTGs) with between five and 21 members; 18 DTGs have at least 10 member stars. Milky Way (MW) substructures such as Gaia-Sausage-Enceladus, the Metal-Weak Thick-Disk, Thamnos, the Splashed Disk, and the Helmi Stream are identified. Associations with MW globular clusters are determined for eight DTGs; no recognized MW dwarf galaxies were associated with any of our DTGs. Previously identified dynamical groups are also associated with our DTGs, with emphasis placed on their structural determination and possible new identifications. Chemically peculiar stars are identified as members of several DTGs, with six DTGs that are associated with r-process-enhanced stars. We demonstrate that the mean carbon and α-element abundances of our DTGs are correlated with their mean metallicity in an understandable manner. Similarly, we find that the mean metallicity, carbon, and α-element abundances are separable into different regions of the mean rotational-velocity space.

Accurate determinations of stellar parameters and distances for large complete samples of stars are keys for conducting detailed studies of the formation and evolution of our Galaxy. Here we present stellar atmospheric parameters (effective temperature, luminosity classifications, and metallicity) estimates for some 24 million stars determined from the stellar colors of SMSS DR2 and Gaia EDR3, based on training data sets with available spectroscopic measurements from previous high/medium/low-resolution spectroscopic surveys. The number of stars with photometric-metallicity estimates is 4–5 times larger than that collected by the current largest spectroscopic survey to date—LAMOST—over the course of the past decade. External checks indicate that the precision of the photometric-metallicity estimates are quite high, comparable to or slightly better than that derived from spectroscopy, with typical values around 0.05–0.15 dex for both dwarf and giant stars with [Fe/H] > −2.01.0, 0.10–0.20 dex for giant stars with −2.0 < [Fe/H] ≤ −1.0, and 0.20–0.25 dex for giant stars with [Fe/H] ≤ −2.0, and include estimates for stars as metal-poor as [Fe/H] ∼ −3.5, substantially lower than previous photometric techniques. Photometric-metallicity estimates are obtained for an unprecedented number of metal-poor stars, including a total of over three million metal-poor (MP; [Fe/H] ≤ −1.0) stars, over half a million very metal-poor (VMP; [Fe/H] ≤ −2.0) stars, and over 25,000 extremely metal-poor (EMP; [Fe/H] ≤ −3.0) stars. Moreover, distances are determined for over 20 million stars in our sample. For the over 18 million sample stars with accurate Gaia parallaxes, stellar ages are estimated by comparing with theoretical isochrones. Astrometric information is provided for the stars in our catalog, along with radial velocities for ∼10% of our sample stars, taken from completed/ongoing large-scale spectroscopic surveys.