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This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. ; Observed changes in protostellar brightness can be complicated to interpret. In our James Clerk Maxwell Telescope (JCMT) Transient Monitoring Survey, we discovered that a young binary protostar, HOPS 373, is undergoing a modest 30% brightness increase at 850 μm, caused by a factor of 1.8–3.3 enhancement in the accretion rate. The initial burst occurred over a few months, with a sharp rise and then a shallower decay. A second rise occurred soon after the decay, and the source is still bright one year later. The mid-IR emission, the small-scale CO outflow mapped with ALMA, and the location of variable maser emission indicate that the variability is associated with the SW component. The near-IR and NEOWISE W1 and W2 emission is located along the blueshifted CO outflow, spatially offset by ∼3 to 4'' from the SW component. The K-band emission imaged by UKIRT shows a compact H2 emission source at the edge of the outflow, with a tail tracing the outflow back to the source. The W1 emission, likely dominated by scattered light, brightens by 0.7 mag, consistent with expectations based on the submillimeter light curve. The signal of continuum variability in K band and W2 is masked by stable H2 emission, as seen in our Gemini/GNIRS spectrum, and perhaps by CO emission. These differences in emission sources complicate IR searches for variability of the youngest protostars. © 2022. The Author(s). Published by the American Astronomical Society. ; S.Y.Y. and J.E.L. are supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT; grant number 2021R1A2C1011718). G.J.H. is supported by general grants 12173003 and 11773002 awarded by the National Science Foundation of China. D.J. is supported by NRC Canada and by an ...

Prestellar cores are self-gravitating dense and cold structures within molecular clouds where future stars are born. They are expected, at the stage of transitioning to the protostellar phase, to harbor centrally concentrated dense (sub)structures that will seed the formation of a new star or the binary/multiple stellar systems. Characterizing this critical stage of evolution is key to our understanding of star formation. In this work, we report the detection of high-density (sub)structures on the thousand-astronomical-unit (au) scale in a sample of dense prestellar cores. Through our recent ALMA observations toward the Orion Planck Galactic Cold Clumps, we have found five extremely dense prestellar cores, which have centrally concentrated regions of similar to 2000 au in size, and several 10(7) cm(-3) in average density. Masses of these centrally dense regions are in the range of 0.30 to 6.89 M. For the first time, our higher resolution observations (0.8 '' similar to 320 au) further reveal that one of the cores shows clear signatures of fragmentation; such individual substructures/fragments have sizes of 800-1700 au, masses of 0.08 to 0.84 M, densities of 2 - 8 x 10(7) cm(-3), and separations of similar to 1200 au. The substructures are massive enough (greater than or similar to 0.1 M) to form young stellar objects and are likely examples of the earliest stage of stellar embryos that can lead to widely (similar to 1200 au) separated multiple systems. ; Ministry of Science and Technology, China 108-2112-M-001-048- 108-2112-M-001-052- international partnership program of the Chinese Academy of Sciences 114231KYSB20200009 National Natural Science Foundation of China (NSFC) 12073061 Shanghai Pujiang Program 20PJ1415500 ANID AFB 170002 AFB-170002 National Natural Science Foundation of China (NSFC) U1631237 NRC Canada Natural Sciences and Engineering Research Council of Canada (NSERC) Spanish Government AYA2017-88754-P State Agency for Research of the Spanish Ministry of Science and Innovation through the "Unit of Excellence Maria de Maeztu 2020-2023" award CEX2019-000918-M Basic Science Research Program through the National Research Foundation of Korea (NRF) - Ministry of Education, Science and Technology NRF-2019R1A2C1010851 National Science Foundation (NSF) AST-1715876 National Natural Science Foundation of China (NSFC) 11911530226 11725313 11873086 Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT) Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research (KAKENHI) 20H05645 Yunnan Province of China 2017HC018 Chinese Academy of Sciences MoST 108-2112-M-001-017 MoST 109-2112-M-001-023 ; Versión publicada - versión final del editor