In this talk, I will give a brief review of the substructure studies in the nearby halo revolutionized by Gaia DR2. I will also introduce a novel clustering method, StarGO, based on Self-Organizing-Maps, and its application to member identification for streams and open clusters. The main part of this talk is about our recent work on the substructures found in LAMOST DR3 very metal-poor (VMP) star catalog (https://arxiv.org/abs/1910.07538). One of the most interesting results is that we found one VMP dominated substructure Rg5 is dynamically associated with two highly r-process-enhanced stars with [Fe/H] ∼ −3. This finding indicates that its progenitor might be an ultra-faint dwarf (UFD) galaxy that has experienced r-process enrichment from neutron star mergers. This study has taken the first steps in finding dynamical associations between disrupted dwarf galaxies and r-process-enhanced stars, which is crucial for studying their birth environments. This helps us understand the star forming activities, nucleosynthetic events, and chemical evolution in UFDs and other dwarf galaxies in the very early universe. The great advantage of studying debris in the nearby halo is that high-resolution spectroscopic observations are much more readily obtainable, so we expect this field of activity to have a rich future in the coming decades.
Zhen Yuan got her Bachelor Degree in Physics from Nanjing University in 2009, and PhD in Physics from University of Minnesota in 2015. She was a postdoc at Shanghai Jiao Tong University before she became LAMOST FELLOW at SHAO. Zhen has developed deep interests in dwarf galaxy related science, and now is focusing on studying the debris of dwarf galaxies in the Milky Way using data from Gaia with a variety of spectroscopic and photometric surveys.