摘要：We present an analysis of spectroscopic and astrometric data from APOGEE-2 and Gaia DR2 to identify structurestoward the Orion Complex. By applying a hierarchical clustering algorithm to the six-dimensional stellar data, weidentify spatially and/or kinematically distinct groups of young stellar objects with ages ranging from 1 to 12 Myr.We also investigate the star-forming history within the Orion Complex and identify peculiar subclusters. With thismethod we reconstruct the older populations in the regions that are currently largely devoid of molecular gas, suchas Orion C (which includes the σ Ori cluster) and Orion D (the population that traces Ori OB1a, OB1b, and OrionX). We report on the distances, kinematics, and ages of the groups within the Complex. The Orion D group is inthe process of expanding. On the other hand, Orion B is still in the process of contraction. In λ Ori the propermotions are consistent with a radial expansion due to an explosion from a supernova; the traceback age from theexpansion exceeds the age of the youngest stars formed near the outer edges of the region, and their formationwould have been triggered when they were halfway from the cluster center to their current positions. We alsopresent a comparison between the parallax and proper-motion solutions obtained by Gaia DR2 and those obtainedtoward star-forming regions by the Very Long Baseline Array.
关键词：open clusters and associations: individual (Orion Complex);stars: kinematics and dynamics;stars: pre-main sequence
