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Investigating Protostellar Accretion (IPA) is a JWST Cycle 1 GO program that uses NIRSpec integral field units and MIRI Medium Resolution Spectrograph to obtain 2.9–28 μ m spectral cubes of young, deeply embedded protostars with luminosities of 0.2–10,000 L _⊙ and central masses of 0.15–12 M _⊙ . In this Letter, we report the discovery of a highly collimated atomic jet from the Class 0 protostar IRAS 16253−2429, the lowest-luminosity source ( L _bol = 0.2 L _⊙ ) in the IPA program. The collimated jet is detected in multiple [Fe ii ] lines and [Ne ii ], [Ni ii ], and H i lines but not in molecular emission. The atomic jet has a velocity of about 169 ± 15 km s ^−1 , after correcting for inclination. The width of the jet increases with distance from the central protostar from 23 to 60 au, corresponding to an opening angle of 2.°6 ± 0.°5. By comparing the measured flux ratios of various fine-structure lines to those predicted by simple shock models, we derive a shock speed of 54 km s ^−1 and a preshock density of 2.0 × 10 ^3 cm ^−3 at the base of the jet. From these quantities and using a suite of jet models and extinction laws, we compute a mass-loss rate between 0.4 and 1.1 ×10 ^−10 M _⊙ yr ^−1 . The low mass-loss rate is consistent with simultaneous measurements of low mass accretion rate (2.4 ± 0.8 × 10 ^−9 M _⊙ yr ^−1 ) for IRAS 16253−2429 from JWST observations, indicating that the protostar is in a quiescent accretion phase. Our results demonstrate that very low-mass protostars can drive highly collimated, atomic jets, even during the quiescent phase.

We investigate the bright CO fundamental emission in the central regions of five protostars in their primary mass assembly phase using new observations from JWST’s Near-Infrared Spectrograph and Mid-Infrared Instrument. CO line emission images and fluxes are extracted for a forest of ∼150 rovibrational transitions from two vibrational bands, v = 1−0 and v = 2−1. However, ^13 CO is undetected, indicating that ^12 CO emission is optically thin. We use H _2 emission lines to correct fluxes for extinction and then construct rotation diagrams for the CO lines with the highest spectral resolution and sensitivity to estimate rotational temperatures and numbers of CO molecules. Two distinct rotational temperature components are required for v = 1 (∼600 to 1000 K and 2000 to ∼10 ^4 K), while one hotter component is required for v = 2 (≳3500 K). ^13 CO is depleted compared to the abundances found in the interstellar medium, indicating selective UV photodissociation of ^13 CO; therefore, UV radiative pumping may explain the higher rotational temperatures in v = 2. The average vibrational temperature is ∼1000 K for our sources and is similar to the lowest rotational temperature components. Using the measured rotational and vibrational temperatures to infer a total number of CO molecules, we find that the total gas masses range from lower limits of ∼10 ^22 g for the lowest mass protostars to ∼10 ^26 g for the highest mass protostars. Our gas mass lower limits are compatible with those in more evolved systems, which suggest the lowest rotational temperature component comes from the inner disk, scattered into our line of sight, but we also cannot exclude the contribution to the CO emission from disk winds for higher mass targets.

Investigating Protostellar Accretion is a Cycle 1 JWST program using the NIRSpec+MIRI integral field units to obtain 2.9–28 μ m spectral cubes of five young protostars with luminosities of 0.2–10,000 L _⊙ in their primary accretion phase. This paper introduces the NIRSpec 2.9–5.3 μ m data of the inner 840–9000 au with spatial resolutions from 28 to 300 au. The spectra show rising continuum emission; deep ice absorption; emission from H _2 , H i , and [Fe ii ]; and the CO fundamental series in emission and absorption. Maps of the continuum emission show scattered light cavities for all five protostars. In the cavities, collimated jets are detected in [Fe ii ] for the four

The effects of metallicity on the evolution of protoplanetary disks may be studied in the outer Galaxy where the metallicity is lower than in the solar neighborhood. We present the VLT/KMOS integral field spectroscopy in the near-infrared of ∼120 candidate young stellar objects (YSOs) in the CMa- ℓ 224 star-forming region located at a Galactocentric distance of 9.1 kpc. We characterize the YSO accretion luminosities and accretion rates using the hydrogen Br γ emission and find a median accretion luminosity of $\mathrm{log}({L}_{\mathrm{acc}})=-{0.82}_{-0.82}^{+0.80}{L}_{\odot }$ . Based on the measured accretion luminosities, we investigate the hypothesis of star formation history in the CMa- ℓ 224. Their median values suggest that Cluster C, where most of YSO candidates have been identified, might be the most evolved part of the region. The accretion luminosities are similar to those observed toward low-mass YSOs in the Perseus and Orion molecular clouds, and they do not reveal the impact of lower metallicity. Similar studies in other outer Galaxy clouds covering a wide range of metallicities are critical to gain a complete picture of star formation in the Galaxy.