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HOPS 87 is a Class 0 protostellar core known to harbor an extremely young bipolar outflow and a hot corino. We report the discovery of localized, chemically rich regions near the bases of the two-lobe bipolar molecular outflow in HOPS 87 containing molecules such as H _2 CO, ^13 CS, H _2 S, OCS, and CH _3 OH, the simplest complex organic molecule (COM). The locations and kinematics suggest that these localized features are due to jet-driven shocks rather than being part of the hot-corino region encasing the protostar. The COM compositions of the molecular gas in these jet-localized regions are relatively simpler than those in the hot-corino zone. We speculate that this simplicity is due to either the liberation of ice with a less complex chemical history or the effects of shock chemistry. Our study highlights the dynamic interplay between the protostellar bipolar outflow, disk, inner-core environment, and the surrounding medium, contributing to our understanding of molecular complexity in solar-like young stellar objects.

We conducted a Ka -band (26.1–35 GHz) line survey toward Orion KL using the TianMa 65 m Radio Telescope (TMRT). It is the first blind line survey in the Ka band and achieves a sensitivity at the mK level (1–3 mK at a spectral resolution of ∼1 km s ^−1 ). In total, 592 Gaussian features are extracted. Among them, 257 radio recombination lines (RRLs) are identified. The maximum Δ n of RRLs of H, He, and C are 20, 15, and 5, respectively. Through stacking, we have detected the β lines of ion RRLs (RRLs of C ^+ with the possible contribution of other ions like O ^+ ) for the first time, and a tentative signal of the γ lines of ion RRLs can also be seen on the stacked spectrum. Besides this, 318 other line features were assigned to 37 molecular species, and 10 of these species were not detected in the Q -band survey of TMRT. The vibrationally excited states of nine species were also detected. The emission of most species can be modeled under LTE. A number of transitions of E-CH3OH ( J _2 − J _1 ) display maser effects, which are confirmed by our modeling, and besides the bumping peak at J ∼ 6, there is another peak at J ∼ 13. Methylcyanoacetylene (CH _3 C _3 N) is detected in Orion KL for the first time. This work emphasizes that the Ka band, which was long ignored for spectral line surveys, is very useful for surveying RRLs and molecular lines simultaneously.

Protostellar outflows and jets are almost ubiquitous characteristics during the mass accretion phase and encode the history of stellar accretion, complex organic molecule (COM) formation, and planet formation. Episodic jets are likely connected to episodic accretion through the disk. Despite the importance, studies on episodic accretion and ejection links have not been done yet in a systematic fashion using high-sensitivity and high-resolution observations. To explore episodic accretion mechanisms and the chronologies of episodic events, we investigated 39 fields containing protostars with Atacama Large Millimeter/submillimeter Array observations of CO, SiO, and 1.3 mm continuum emission. We detected SiO emission in 19 fields, where 17 sources are driving molecular jets. Jet velocities, mass-loss rates, mass accretion rates, and periods of accretion events appear to have some dependence on the driving forces of the jet (e.g., bolometric luminosity, envelope mass). Next, velocities and mass-loss rates appear to be somewhat correlated with the surrounding envelope mass, suggesting that the presence of high mass around protostars increases the ejection–accretion activity. We determine mean periods of ejection events of 20–175 yr for our sample, which could be associated with perturbation zones of ∼2−25 au extent around the protostars. In addition, mean ejection periods show an apparent anticorrelation with the envelope mass, where high accretion rates may trigger more frequent ejection events. The observed periods of outburst/ejection are much shorter than the freezeout timescale of the simplest COMs like CH _3 OH, suggesting that episodic events could affect the ice–gas balance inside and around the snowline.

The internal structure of the prestellar core G208.68-19.02-N2 (G208-N2) in the Orion Molecular Cloud 3 (OMC-3) region has been studied with the Atacama Large Millimeter/submillimeter Array. The dust continuum emission revealed a filamentary structure with a length of ∼5000 au and an average H _2 volume density of ∼6 × 10 ^7 cm ^−3 . At the tip of this filamentary structure, there is a compact object, which we call a nucleus , with a radius of ∼150–200 au and a mass of ∼0.1 M _⊙ . The nucleus has a central density of ∼2 × 10 ^9 cm ^−3 with a radial density profile of r ^−1.87±0.11 . The density scaling of the nucleus is ∼3.7 times higher than that of the singular isothermal sphere (SIS). This as well as the very low virial parameter of 0.39 suggests that the gravity is dominant over the pressure everywhere in the nucleus. However, there is no sign of CO outflow localized to this nucleus. The filamentary structure is traced by the N _2 D ^+ 3–2 emission, but not by the C ^18 O 2–1 emission, implying the significant CO depletion due to high density and cold temperature. Toward the nucleus, the N _2 D ^+ also shows the signature of depletion. This could imply either the depletion of the parent molecule, N _2 , or the presence of the embedded very-low luminosity central source that could sublimate the CO in the very small area. The nucleus in G208-N2 is considered to be a prestellar core on the verge of first hydrostatic core (FHSC) formation or a candidate for the FHSC.