The Stellar “Snake”. III. Coevolution of Stars and Molecular Clouds Unveiled by Gaia, MWISP, and LAMOST

Abstract By combining multiband data from Gaia DR3, MWISP CO, and LAMOST DR11 low-resolution spectra/medium-resolution spectra (LRS/MRS), we investigate the coevolution of stars and their parent molecular cloud in a snakelike stellar structure, named Snake III. Based on 5D phase-space selection, we identified 5683 member stars (median age 7.6 Myr) across approximately 300 × 500 × 175 pc 3 volume, along with 12 embedded open clusters. Then we use background-eliminated extinction-parallax distances combined with 12 CO velocities to clearly identify the molecular clouds associated with the stellar complex in spatial and kinematics. The molecular cloud density increases with Galactic longitude, with older open clusters forming in cavities near higher-density regions (except ASCC 125), while young field stars currently form preferentially in present-day high-density environments, indicating that cloud density regulates the star-formation sequence. 12 CO excitation temperature, centroid velocity, velocity dispersion, and H α emission reveal that early feedback first compresses cloud edges to trigger new stars, then sweeps and disperses the parent clouds. The extremely young cluster (ASCC 125, 4.4 Myr) that lies near the densest region yet is surrounded by a shell with bidirectional density-velocity perturbations, consistent with a delayed-triggering scenario under the combined influence of UBC 178 stellar-wind feedback and a suspected supernova blast. Our results naturally demonstrate that snakelike stellar structures are filamentary relics of hierarchical star formation within giant molecular clouds. They provide direct observational evidence that cloud density and early feedback jointly modulate the progression of star formation, offering a clear and young laboratory for studying star–cloud coevolution.