Stellar kinematics in Orion Complex with Gaia

We identify the groups with the unsupervised clustering algorithm, Shared Nearest Neighbor (SNN), which previously identified 12 new stellar substructures in the Orion Complex. For each of the two groups, we derive the 3D space motions of individual stars using Gaia-EDR3 proper motions supplemented by radial velocities from Gaia-DR2, APOGEE-2, and GALAH DR3.

We present evidence for radial expansion of the two groups from a common center. Unlike previous work, our study suggests that evidence of stellar group expansion is confined only to OBP-near and Briceno-1, whereas the rest of the groups in the complex show more complicated motions. Interestingly, the stars in the two groups lie at the center of a dust shell, as revealed via an extant 3D dust map.