Dynamically Tagged Groups of Metal-poor Stars. II. The Radial Velocity Experiment Data Release 6

Abstract

Orbital characteristics based on Gaia Early Data Release 3 astrometric parameters are analyzed for ∼8000 metal-poor stars ([Fe/H] ≤ −0.8) compiled from the Radial Velocity Experiment (RAVE) Data Release 6. Selected as metal-poor candidates based on broadband photometry, RAVE collected moderate-resolution (R ∼ 7500) spectra in the region of the Ca triplet for these stars. About 20% of the stars in this sample also have medium-resolution (1200 ≲ R ≲ 2000) validation spectra obtained over a 4 yr campaign from 2014 to 2017 with a variety of telescopes. We match the candidate stars to photometric metallicity determinations from the Huang et al. recalibration of the SkyMapper Southern Survey Data Release 2. We obtain dynamical clusters of these stars from the orbital energy and cylindrical actions using the HDBSCAN unsupervised learning algorithm. We identify 179 dynamically tagged groups (DTGs) with between 5 and 35 members; 67 DTGs have at least 10 member stars. Milky Way (MW) substructures such as Gaia–Sausage–Enceladus, the Metal-weak Thick Disk, the Splashed Disk, Thamnos, the Helmi Stream, and LMS-1 (Wukong) are identified. Associations with MW globular clusters are determined for 10 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. We identify chemically peculiar stars as members of several DTGs; we find 22 DTGs that are associated with r-process-enhanced stars. Carbon-enhanced metal-poor (CEMP) stars are identified among the targets with available spectroscopy, and we assign these to morphological groups following the approach given by Yoon et al.