Identifying Active Young Stars from the LAMOST MRS and TESS Survey

Active young stars (aYSs) serve as a crucial laboratory for studying early stellar magnetic activity, angular momentum evolution, and planet formation environments. Building upon the methodology established in our previous work (Paper I), we apply and refine a data-driven scheme to identify aYSs in the extensive Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) Medium-Resolution Spectroscopic survey (MRS), complemented by the Transiting Exoplanet Survey Satellite (TESS) photometric survey. By simultaneously measuring the H α 6563 Å emission line as an activity proxy and lithium i 6708 Å absorption line as a youthfulness indicator in 397,811 spectra of 191,007 stars with T eff ≤ 7000 K and log g ≥ 3.5 , we have diagnosed 17,961 spectra of 9783 aYS candidates. For 1973 candidates with the TESS light curves, we have performed variability classification, revealing a diverse population including 514 rotational variables, 35 eclipsing binaries, 2 transiting exoplanetary system candidates, 108 pulsating stars, 25 T Tauri stars, 88 flaring stars, and 27 irregular variables. Despite a scarcity of low-mass candidates, the sample robustly confirms the established lithium–age and H α –Rossby number relations. This work provides a wide-field catalog of aYSs and demonstrates the feasibility of detecting aYSs at high Galactic latitudes, serving as a valuable precursor for deep wide-field surveys such as the planned Chinese Space Station Survey Telescope (CSST).