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1. Deciphering the 3D Orion Nebula-IV: The HH 269 Flow Emerges from the Orion-S Embedded Molecular Cloud

   https://doi.org/10.3847/1538-4357/abe1b0  

   O’Dell, C. R.; Abel, N. P.; Ferland, G. J. (March 2021, The Astrophysical Journal)

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2. Stellar Proper Motions in the Orion Nebula Cluster

   https://doi.org/10.3847/1538-3881/aafb09  

   Kim, Dongwon; Lu, Jessica R.; Konopacky, Quinn; Chu, Laurie; Toller, Elizabeth; Anderson, Jay; Theissen, Christopher A.; Morris, Mark R. (March 2019, The Astronomical Journal)
3. Structure of the Source I Disk in Orion-KL

   https://doi.org/10.3847/1538-4357/ac391b  

   Wright, Melvyn; Bally, John; Hirota, Tomoya; Miller, Kyle; Harding, Tyler; Colleluori, Keira; Ginsburg, Adam; Goddi, Ciriaco; McGuire, Brett (January 2022, The Astrophysical Journal)

   Abstract This paper analyses images from 43 to 340 GHz to trace the structure of the Source I (SrcI) disk in Orion-KL with ∼12 au resolution. The data reveal an almost edge-on disk with an outside diameter ∼100 au, which is heated from the inside. The high opacity at 220–340 GHz hides the internal structure and presents a surface temperature ∼500 K. Images at 43, 86 and 99 GHz reveal structure within the disk. At 43 GHz there is bright compact emission with brightness temperature ∼1300 K. Another feature, most prominent at 99 GHz, is a warped ridge of emission. The data can be explained by a simple model with a hot inner structure, seen through cooler material. A wide-angle outflow mapped in SiO emission ablates material from the interior of the disk, and extends in a bipolar outflow over 1000 au along the rotation axis of the disk. SiO v = 0, J = 5–4 emission appears to have a localized footprint in the warped ridge. These observations suggest that the ridge is the working surface of the disk, and heated by accretion and the outflow. The disk structure may be evolving, with multiple accretion and outflow events. We discuss two sources of variability: (1) variable accretion onto the disk as SrcI travels through the filamentary debris from the Becklin–Neugebauer Object-SrcI encounter ∼550 yr ago; and (2) episodic accretion from the disk onto the protostar, which may trigger multiple outflows. The warped inner-disk structure is direct evidence that SrcI could be a binary experiencing episodic accretion. 

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4. The Radcliffe wave as the gas spine of the Orion arm

   https://doi.org/10.1051/0004-6361/202243761  

   Swiggum, C.; Alves, J.; D’Onghia, E.; Benjamin, R. A.; Thulasidharan, L.; Zucker, C.; Poggio, E.; Drimmel, R.; Gallagher III, J. S.; Goodman, A. (August 2022, Astronomy & Astrophysics)

   The Radcliffe wave is a ∼3 kpc long coherent gas structure containing most of the star-forming complexes near the Sun. In this Letter we aim to find a Galactic context for the Radcliffe wave by looking into a possible relationship between the gas structure and the Orion (local) arm. We use catalogs of massive stars and young open clusters based on Gaia Early Data Release 3 (EDR3) astrometry, in conjunction with kiloparsec-scale 3D dust maps, to investigate the Galactic XY spatial distributions of gas and young stars. We find a quasi-parallel offset between the luminous blue stars and the Radcliffe wave, in that massive stars and clusters are found essentially inside and downstream from the Radcliffe wave. We examine this offset in the context of color gradients observed in the spiral arms of external galaxies, where the interplay between density wave theory, spiral shocks, and triggered star formation has been used to interpret this particular arrangement of gas and dust as well as OB stars, and outline other potential explanations as well. We hypothesize that the Radcliffe wave constitutes the gas reservoir of the Orion (local) arm, and that it presents itself as a prime laboratory to study the interface between Galactic structure, the formation of molecular clouds in the Milky Way, and star formation. 

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5. CARMA-NRO Orion Survey: Unbiased Survey of Dense Cores and Core Mass Functions in Orion A

   https://doi.org/10.3847/1538-4365/aca4d4  

   Takemura, Hideaki; Nakamura, Fumitaka; Arce, Héctor G.; Schneider, Nicola; Ossenkopf-Okada, Volker; Kong, Shuo; Ishii, Shun; Dobashi, Kazuhito; Shimoikura, Tomomi; Sanhueza, Patricio; et al (January 2023, The Astrophysical Journal Supplement Series)

   Abstract The mass distribution of dense cores is a potential key to understanding the process of star formation. Applying dendrogram analysis to the CARMA-NRO Orion C 18 O ( J = 1–0) data, we identify 2342 dense cores, about 22% of which have virial ratios smaller than 2 and can be classified as gravitationally bound cores. The derived core mass function (CMF) for bound starless cores that are not associate with protostars has a slope similar to Salpeter’s initial mass function (IMF) for the mass range above 1 M ⊙ , with a peak at ∼0.1 M ⊙ . We divide the cloud into four parts based on decl., OMC-1/2/3, OMC-4/5, L1641N/V380 Ori, and L1641C, and derive the CMFs in these regions. We find that starless cores with masses greater than 10 M ⊙ exist only in OMC-1/2/3, whereas the CMFs in OMC-4/5, L1641N, and L1641C are truncated at around 5–10 M ⊙ . From the number ratio of bound starless cores and Class II objects in each subregion, the lifetime of bound starless cores is estimated to be 5–30 freefall times, consistent with previous studies for other regions. In addition, we discuss core growth by mass accretion from the surrounding cloud material to explain the coincidence of peak masses between IMFs and CMFs. The mass accretion rate required for doubling the core mass within a core lifetime is larger than that of Bondi–Hoyle accretion by a factor of order 2. This implies that more dynamical accretion processes are required to grow cores. 

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