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Abstract We present velocity-resolved Stratospheric Observatory for Infrared Astronomy (SOFIA)/upgrade German REceiver for Astronomy at Terahertz Frequencies observations of [O i ] and [C ii ] lines toward a Class I protostar, L1551 IRS 5, and its outflows. The SOFIA observations detect [O i ] emission toward only the protostar and [C ii ] emission toward the protostar and the redshifted outflow. The [O i ] emission has a width of ∼100 km s −1 only in the blueshifted velocity, suggesting an origin in shocked gas. The [C ii ] lines are narrow, consistent with an origin in a photodissociation region. Differential dust extinction from the envelope due to the inclination of the outflows is the most likely cause of the missing redshifted [O i ] emission. Fitting the [O i ] line profile with two Gaussian components, we find one component at the source velocity with a width of ∼20 km s −1 and another extremely broad component at −30 km s −1 with a width of 87.5 km s −1 , the latter of which has not been seen in L1551 IRS 5. The kinematics of these two components resemble cavity shocks in molecular outflows and spot shocks in jets. Radiative transfer calculations of the [O i ], high- J CO, and H 2 O lines in the cavity shocks indicate that [O i ] dominates the oxygen budget, making up more than 70% of the total gaseous oxygen abundance and suggesting [O]/[H] of ∼1.5 × 10 −4 . Attributing the extremely broad [O i ] component to atomic winds, we estimate an intrinsic mass-loss rate of (1.3 ± 0.8) × 10 −6 M ⊙ yr −1 . The intrinsic mass-loss rates derived from low- J CO, [O i ], and H i are similar, supporting the model of momentum-conserving outflows, where the atomic wind carries most momentum and drives the molecular outflows. 

We present ∼10–40μm SOFIA-FORCAST images of 11isolatedprotostars as part of the SOFIA Massive (SOMA) Star Formation Survey, with this morphological classification based on 37μm imaging. We develop an automated method to define source aperture size using the gradient of its background-subtracted enclosed flux and apply this to build spectral energy distributions (SEDs). We fit the SEDs with radiative transfer models, developed within the framework of turbulent core accretion (TCA) theory, to estimate key protostellar properties. Here, we release the sedcreator python package that carries out these methods. The SEDs are generally well fitted by the TCA models, from which we infer initial core massesM_cranging from 20–430M_⊙, clump mass surface densities Σ_cl∼ 0.3–1.7 g cm⁻², and current protostellar massesm_*∼ 3–50M_⊙. From a uniform analysis of the 40 sources in the full SOMA survey to date, we find that massive protostars form across a wide range of clump mass surface density environments, placing constraints on theories that predict a minimum threshold Σ_clfor massive star formation. However, the upper end of them_*−Σ_cldistribution follows trends predicted by models of internal protostellar feedback that find greater star formation efficiency in higher Σ_clconditions. We also investigate protostellar far-IR variability by comparison with IRAS data, finding no significant variation over an ∼40 yr baseline.

 

We present Atacama Large Millimeter Array band 6/7 (1.3 mm/0.87 mm) and Very Large Array Ka-band (9 mm) observations toward NGC 2071 IR, an intermediate-mass star-forming region. We characterize the continuum and associated molecular line emission toward the most luminous protostars, i.e., IRS1 and IRS3, on ∼100 au (0.″2) scales. IRS1 is partly resolved in the millimeter and centimeter continuum, which shows a potential disk. IRS3 has a well-resolved disk appearance in the millimeter continuum and is further resolved into a close binary system separated by ∼40 au at 9 mm. Both sources exhibit clear velocity gradients across their disk major axes in multiple spectral lines including C¹⁸O, H₂CO, SO, SO₂, and complex organic molecules like CH₃OH,¹³CH₃OH, and CH₃OCHO. We use an analytic method to fit the Keplerian rotation of the disks and give constraints on physical parameters with a Markov Chain Monte Carlo routine. The IRS3 binary system is estimated to have a total mass of 1.4–1.5M_⊙. IRS1 has a central mass of 3–5M_⊙based on both kinematic modeling and its spectral energy distribution, assuming that it is dominated by a single protostar. For both IRS1 and IRS3, the inferred ejection directions from different tracers, including radio jet, water maser, molecular outflow, and H₂emission, are not always consistent, and for IRS1 these can be misaligned by ∼50°. IRS3 is better explained by a single precessing jet. A similar mechanism may be present in IRS1 as well but an unresolved multiple system in IRS1 is also possible.