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1. Disks and Outflows in the Intermediate-mass Star-forming Region NGC 2071 IR

   https://doi.org/10.3847/1538-4357/ac7464  

   Cheng, Yu ; Tobin, John J. ; Yang, Yao-Lun ; van ’t Hoff, Merel L. R. ; Sadavoy, Sarah I. ; Osorio, Mayra ; Díaz-Rodríguez, Ana Karla ; Anglada, Guillem ; Karnath, Nicole ; Sheehan, Patrick D. ; et al ( July 2022 , The Astrophysical Journal)

   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, watermore »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.

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2. Digging into the Interior of Hot Cores with ALMA (DIHCA). II. Exploring the Inner Binary (Multiple) System Embedded in G335 MM1 ALMA1

   https://doi.org/10.3847/1538-4357/ac5bd8  

   Olguin, Fernando A. ; Sanhueza, Patricio ; Ginsburg, Adam ; Chen, Huei-Ru Vivien ; Zhang, Qizhou ; Li, Shanghuo ; Lu, Xing ; Sakai, Takeshi ( April 2022 , The Astrophysical Journal)

   Abstract We observed the high-mass protostellar core G335.579–0.272 ALMA1 at ∼200 au (0.″05) resolution with the Atacama Large Millimeter/submillimeter Array (ALMA) at 226 GHz (with a mass sensitivity of 5 σ = 0.2 M ⊙ at 10 K). We discovered that at least a binary system is forming inside this region, with an additional nearby bow-like structure (≲1000 au) that could add an additional member to the stellar system. These three sources are located at the center of the gravitational potential well of the ALMA1 region and the larger MM1 cluster. The emission from CH 3 OH (and many other tracers) is extended (>1000 au), revealing a common envelope toward the binary system. We use CH 2 CHCN line emission to estimate an inclination angle of the rotation axis of 26° with respect to the line of sight based on geometric assumptions and derive a kinematic mass of the primary source (protostar+disk) of 3.0 M ⊙ within a radius of 230 au. Using SiO emission, we find that the primary source drives the large-scale outflow revealed by previous observations. Precession of the binary system likely produces a change in orientation between the outflow at small scales observed here and largemore »scales observed in previous works. The bow structure may have originated from the entrainment of matter into the envelope due to the widening or precession of the outflow, or, alternatively, an accretion streamer dominated by the gravity of the central sources. An additional third source, forming due to instabilities in the streamer, cannot be ruled out as a temperature gradient is needed to produce the observed absorption spectra.« less
3. Dust Hot Spots at 10 au Scales around the Class 0 Binary IRAS 16293–2422 A: A Departure from the Passive Irradiation Model

   https://doi.org/10.3847/2041-8213/aca53a  

   Maureira, María José ; Gong, Munan ; Pineda, Jaime E. ; Liu, Hauyu Baobab ; Silsbee, Kedron ; Caselli, Paola ; Zamponi, Joaquin ; Segura-Cox, Dominique M. ; Schmiedeke, Anika ( December 2022 , The Astrophysical Journal Letters)

   Characterizing the physical conditions at disk scales in class 0 sources is crucial for constraining the protostellar accretion process and the initial conditions for planet formation. We use ALMA 1.3 and 3 mm observations to investigate the physical conditions of the dust around the class 0 binary IRAS 16293–2422 A down to ∼10 au scales. The circumbinary material’s spectral index,α, has a median of 3.1 and a dispersion of ∼0.2, providing no firm evidence of millimeter-sized grains therein. Continuum substructures with brightness temperature peaks ofT_b∼ 60–80 K at 1.3 mm are observed near the disks at both wavelengths. These peaks do not overlap with strong variations ofα, indicating that they trace high-temperature spots instead of regions with significant optical depth variations. The lower limits to the inferred dust temperature in the hot spots are 122, 87, and 49 K. Depending on the assumed dust opacity index, these values can be several times higher. They overlap with high gas temperatures and enhanced complex organic molecular emission. This newly resolved dust temperature distribution is in better agreement with the expectations from mechanical instead of the most commonly assumed radiative heating. In particular, we find that the temperatures agree with shock heatingmore »predictions. This evidence and recent studies highlighting accretion heating in class 0 disks suggest that mechanical heating (shocks, dissipation powered by accretion, etc.) is important during the early stages and should be considered when modeling and measuring properties of deeply embedded protostars and disks.

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4. The Disk Population in a Distant Massive Protocluster

   https://doi.org/10.3847/1538-4357/ac9b54  

   Cheng, Yu ; Tan, Jonathan C. ; Tobin, John J. ; Fedriani, Rubén ; Andersen, Morten ; Wang, Junfeng ( November 2022 , The Astrophysical Journal)

   The unprecedented angular resolution and sensitivity of the Atacama Large Millimeter/submillimeter Array make it possible to unveil disk populations in distant (>2 kpc), embedded young cluster environments. We have conducted an observation toward the central region of the massive protocluster G286.21+0.16 at 1.3 mm. With a spatial resolution of 23 mas and a sensitivity of 15μJy beam⁻¹, we detect a total of 38 protostellar disks. These disks have dust masses ranging from about 53 to 1825M_⊕, assuming a dust temperature of 20 K. This sample is not closely associated with previously identified dense cores, as would be expected for disks around Class 0 protostars. Thus, we expect our sample, being flux-limited, to be mainly composed of Class I/flat-spectrum source disks, since these are typically more massive than Class II disks. Furthermore, we find that the distributions of disk masses and radii are statistically indistinguishable from those of the Class I/flat-spectrum objects in the Orion molecular cloud, indicating that similar processes are operating in G286.21+0.16 to regulate disk formation and evolution. The cluster center appears to host a massive protostellar system composed of three sources within 1200 au, including a potential binary with 600 au projected separation. Relative to thismore »center, there is no evidence for widespread mass segregation in the disk population. We do find a tentative trend of increasing disk radius versus distance from the cluster center, which may point to the influence of dynamical interactions being stronger in the central regions.

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5. Clustered Formation of Massive Stars within an Ionized Rotating Disk

   https://doi.org/10.3847/2041-8213/aca9cb  

   Galván-Madrid, Roberto ; Zhang, Qizhou ; Izquierdo, Andrés ; Law, Charles J. ; Peters, Thomas ; Keto, Eric ; Liu, Hauyu Baobab ; Ho, Paul T. P. ; Ginsburg, Adam ; Carrasco-González, Carlos ( December 2022 , The Astrophysical Journal Letters)

   We present Atacama Large Millimeter/submillimeter Array observations with a 800 au resolution and radiative-transfer modeling of the inner part (r≈ 6000 au) of the ionized accretion flow around a compact star cluster in formation at the center of the luminous ultracompact Hiiregion G10.6-0.4. We modeled the flow with an ionized Keplerian disk with and without radial motions in its outer part, or with an external Ulrich envelope. The Markov Chain Monte Carlo fits to the data give total stellar massesM_⋆from 120 to 200M_⊙, with much smaller ionized-gas massesM_ion-gas= 0.2–0.25M_⊙. The stellar mass is distributed within the gravitational radiusR_g≈ 1000 to 1500 au, where the ionized gas is bound. The viewing inclination angle from the face-on orientation isi= 49°–56°. Radial motions at radiir>R_gconverge tov_r,0≈ 8.7 km s⁻¹, or about the speed of sound of ionized gas, indicating that this gas is marginally unbound at most. From additional constraints on the ionizing-photon rate and far-IR luminosity of the region, we conclude that the stellar cluster consists of a few massive stars withM_star= 32–60M_⊙, or one star in this range of masses accompanied by a population of lower-mass stars. Any active accretion of ionized gas onto the massive (proto)stars is residual. Themore »inferred cluster density is very large, comparable to that reported at similar scales in the Galactic center. Stellar interactions are likely to occur within the next million years.

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