The APOGEE-2 Survey of the Orion Star-forming Complex. II. Six-dimensional Structure

By M. Kounkel, K. Covey, Genaro Suárez, C. Rom'an-Z'uniga, Jesús Hernández, Keivan G. Stassun, Karl O. Jaehnig, Eric D. Feigelson, K. P. Ram'irez, A. Roman-Lopes and 10 more. Astronomical Journal, 2018

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We present an analysis of spectroscopic and astrometric data from APOGEE-2 and Gaia DR2 to identify structures toward the Orion Complex. By applying a hierarchical clustering algorithm to the six-dimensional stellar data, we identify 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 this method we reconstruct the older populations in the regions that are currently largely devoid of molecular gas, such as Orion C (which includes the σ Ori cluster) and Orion D (the population that traces Ori OB1a, OB1b, and Orion X). We report on the distances, kinematics, and ages of the groups within the Complex. The Orion D group is in the process of expanding. On the other hand, Orion B is still in the process of contraction. In λ Ori the proper motions are consistent with a radial expansion due to an explosion from a supernova; the traceback age from the expansion exceeds the age of the youngest stars formed near the outer edges of the region, and their formation would have been triggered when they were halfway from the cluster center to their current positions. We also present a comparison between the parallax and proper-motion solutions obtained by Gaia DR2 and those obtained toward star-forming regions by the Very Long Baseline Array.

Subfields: Astronomy and Astrophysics, Spectroscopy

View Paper: https://www.semanticscholar.org/paper/33920e3eefb3e0ea08e49fff51e8a5c1644920bd

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Citations in the corpus

Evidence for a Systematic Offset of −80 μas in the Gaia DR2 Parallaxes (2018, methodology): “Finally, an analysis by Kounkel et al. (2018) of 55 young stars with Very Large Baseline Array parallaxes finds an offset of −74±34 µas, with mild evidence for a scale error term (at 1σ confidence).”
Global hierarchical collapse in molecular clouds. Towards a comprehensive scenario (2019, background): “Then they quote Ward & Kruijssen (2018), Kuhn et al. (2019), and Kounkel et al. (2018) as examples that Gaia shows no such radial motions in Orion and other complexes, again concluding that the observations contradict the GHC scenario.”
Kinematics in Young Star Clusters and Associations with Gaia DR2 (2018, methodology): “In Appendix A we compare our distance estimate to 386±8 pc from Kounkel et al. (2018) and discuss effects of the three-dimensional structure of Orion A. • Our distance estimate for NGC 1333 of 296±5 pc is ∼25% larger than the distance from Hirota et al. (2008) of 235±18 pc.”