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1. The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Orion Protostars. VI. Insights from Radiative Transfer Modeling

   https://doi.org/10.3847/1538-4357/ac574d  

   Sheehan, Patrick D. ; Tobin, John J. ; Looney, Leslie W. ; Megeath, S. Thomas ( April 2022 , The Astrophysical Journal)

   Abstract We present Markov Chain Monte Carlo radiative transfer modeling of a joint ALMA 345 GHz and spectral energy distribution data set for a sample of 97 protostellar disks from the VLA and ALMA Nascent Disk and Multiplicity Survey of Orion Protostars. From this modeling, we derive disk and envelope properties for each protostar, allowing us to examine the bulk properties of a population of young protostars. We find that disks are small, with a median dust radius of 29.4 − 2.7 + 4.1 au and a median dust mass of 5.8 − 2.7 + 4.6 M ⊕ . We find no statistically significant difference between most properties of Class 0, Class I, and flat-spectrum sources with the exception of envelope dust mass and inclination. The distinction between inclination is an indication that the Class 0/I/flat-spectrum system may be difficult to tie uniquely to the evolutionary state of protostars. When comparing with Class II disk dust masses in Taurus from similar radiative transfer modeling, we further find that the trend of disk dust mass decreasing from Class 0 to Class II disks is no longer present, though it remains unclear whether such a comparison is fair owing to differences inmore »star-forming region and modeling techniques. Moreover, the disks we model are broadly gravitationally stable. Finally, we compare disk masses and radii with simulations of disk formation and find that magnetohydrodynamical effects may be important for reproducing the observed properties of disks.« less
2. Protostellar and Protoplanetary Disk Masses in the Serpens Region

   https://doi.org/10.3847/1538-4357/ac8ff0  

   Anderson, Alexa R. ; Williams, Jonathan P. ; Marel, Nienke van der ; Law, Charles J. ; Ricci, Luca ; Tobin, John J. ; Tong, Simin ( October 2022 , The Astrophysical Journal)

   We present the results from an Atacama Large Millimeter/submillimeter Array (ALMA) 1.3 mm continuum and¹²CO (J= 2 − 1) line survey spread over 10 deg²in the Serpens star-forming region of 320 young stellar objects, 302 of which are likely members of Serpens (16 Class I, 35 flat-spectrum, 235 Class II, and 16 Class III). From the continuum data, we derive disk dust masses and show that they systematically decline from Class I to flat-spectrum to Class II sources. Grouped by stellar evolutionary state, the disk mass distributions are similar to other young (<3 Myr) regions, indicating that the large-scale environment of a star-forming region does not strongly affect its overall disk dust mass properties. These comparisons between populations reinforce previous conclusions that disks in the Ophiuchus star-forming region have anomalously low masses at all evolutionary stages. Additionally, we find a single deeply embedded protostar that has not been documented elsewhere in the literature and, from the CO line data, 15 protostellar outflows, which we catalog here.
3. 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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4. Anisotropic Infall and Substructure Formation in Embedded Disks

   https://doi.org/10.3847/1538-4357/ac54a8  

   Kuznetsova, Aleksandra ; Bae, Jaehan ; Hartmann, Lee ; Low, Mordecai-Mark Mac ( March 2022 , The Astrophysical Journal)

   The filamentary nature of accretion streams found around embedded sources suggests that protostellar disks experience heterogenous infall from the star-forming environment, consistent with the accretion behavior onto star-forming cores in top-down star-cluster formation simulations. This may produce disk substructures in the form of rings, gaps, and spirals that continue to be identified by high-resolution imaging surveys in both embedded Class 0/I and later Class II sources. We present a parameter study of anisotropic infall, informed by the properties of accretion flows onto protostellar cores in numerical simulations, and varying the relative specific angular momentum of incoming flows as well as their flow geometry. Our results show that anisotropic infall perturbs the disk and readily launches the Rossby wave instability. It forms vortices at the inner and outer edges of the infall zone where material is deposited. These vortices drive spiral waves and angular momentum transport, with some models able to drive stresses corresponding to a viscosity parameter on the order ofα∼ 10⁻². The resulting azimuthal shear forms robust pressure bumps that act as barriers to radial drift of dust grains, as demonstrated by postprocessing calculations of drift-dominated dust evolution. We discuss how a self-consistent model of anisotropic infall canmore »account for the formation of millimeter rings in the outer disk as well as producing compact dust disks, consistent with observations of embedded sources.

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5. Protoplanetary disk masses in NGC 2024: Evidence for two populations

   https://doi.org/10.1051/0004-6361/201937403  

   van Terwisga, S. E. ; van Dishoeck, E. F. ; Mann, R. K. ; Di Francesco, J. ; van der Marel, N. ; Meyer, M. ; Andrews, S. M. ; Carpenter, J. ; Eisner, J. A. ; Manara, C. F. ; et al ( August 2020 , Astronomy & Astrophysics)

   Context. Protoplanetary disks in dense, massive star-forming regions are strongly affected by their environment. How this environmental impact changes over time is an important constraint on disk evolution and external photoevaporation models. Aims. We characterize the dust emission from 179 disks in the core of the young (0.5 Myr) NGC 2024 cluster. By studying how the disk mass varies within the cluster, and comparing these disks to those in other regions, we aim to determine how external photoevaporation influences disk properties over time. Methods. Using the Atacama Large Millimeter/submillimeter Array, a 2.9′× 2.9′ mosaic centered on NGC 2024 FIR 3 was observed at 225 GHz with a resolution of 0.25″, or ~100 AU. The imaged region contains 179 disks identified at IR wavelengths, seven new disk candidates, and several protostars. Results. The overall detection rate of disks is 32 ± 4%. Few of the disks are resolved, with the exception of a giant ( R = 300 AU) transition disk. Serendipitously, we observe a millimeter flare from an X-ray bright young stellar object (YSO), and resolve continuum emission from a Class 0 YSO in the FIR 3 core. Two distinct disk populations are present: a more massive one in themore »east, along the dense molecular ridge hosting the FIR 1-5 YSOs, with a detection rate of 45 ± 7%. In the western population, towards IRS 1, only 15 ± 4% of disks are detected. Conclusions. NGC 2024 hosts two distinct disk populations. Disks along the dense molecular ridge are young (0.2–0.5 Myr) and partly shielded from the far ultraviolet radiation of IRS 2b; their masses are similar to isolated 1–3 Myr old SFRs. The western population is older and at lower extinctions, and may be affected by external photoevaporation from both IRS 1 and IRS 2b. However, it is possible these disks had lower masses to begin with.« less