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1. The transition of polarized dust thermal emission from the protostellar envelope to the disc scale

   https://doi.org/10.1093/mnras/stab2105  

   Lam, Ka Ho; Chen, Che-Yu; Li, Zhi-Yun; Yang, Haifeng; Cox, Erin G; Looney, Leslie W; Stephens, Ian (August 2021, Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT Polarized dust continuum emission has been observed with Atacama Large Millimeter/submillimeter Array in an increasing number of deeply embedded protostellar systems. It generally shows a sharp transition going from the protostellar envelope to the disc scale, with the polarization fraction typically dropping from $${\sim } 5{{\ \rm per\ cent}}$$ to $${\sim } 1{{\ \rm per\ cent}}$$ and the inferred magnetic field orientations becoming more aligned with the major axis of the system. We quantitatively investigate these observational trends using a sample of protostars in the Perseus molecular cloud and compare these features with a non-ideal magnetohydrodynamic disc formation simulation. We find that the gas density increases faster than the magnetic field strength in the transition from the envelope to the disc scale, which makes it more difficult to magnetically align the grains on the disc scale. Specifically, to produce the observed $${\sim } 1{{\ \rm per\ cent}}$$ polarization at $${\sim } 100\, \mathrm{au}$$ scale via grains aligned with the B-field, even relatively small grains of $$1\, \mathrm{\mu m}$$ in size need to have their magnetic susceptibilities significantly enhanced (by a factor of ∼20) over the standard value, potentially through superparamagnetic inclusions. This requirement is more stringent for larger grains, with the enhancement factor increasing linearly with the grain size, reaching ∼2 × 104 for millimetre-sized grains. Even if the required enhancement can be achieved, the resulting inferred magnetic field orientation in the simulation does not show a preference for the major axis, which is inconsistent with the observed pattern. We thus conclude that the observed trends are best described by the model where the polarization on the envelope scale is dominated by magnetically aligned grains and that on the disc scale by scattering. 

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2. An early transition to magnetic supercriticality in star formation

   https://doi.org/10.1038/s41586-021-04159-x  

   Ching, T.-C.; Li, D.; Heiles, C.; Li, Z.-Y.; Qian, L.; Yue, Y. L.; Tang, J.; Jiao, S. H. (January 2022, Nature)

   Abstract Magnetic fields have an important role in the evolution of interstellar medium and star formation 1,2 . As the only direct probe of interstellar field strength, credible Zeeman measurements remain sparse owing to the lack of suitable Zeeman probes, particularly for cold, molecular gas 3 . Here we report the detection of a magnetic field of +3.8 ± 0.3 microgauss through the H  I narrow self-absorption (HINSA) 4,5 towards L1544 6,7 —a well-studied prototypical prestellar core in an early transition between starless and protostellar phases 8–10 characterized by a high central number density 11 and a low central temperature 12 . A combined analysis of the Zeeman measurements of quasar H  I absorption, H  I emission, OH emission and HINSA reveals a coherent magnetic field from the atomic cold neutral medium (CNM) to the molecular envelope. The molecular envelope traced by the HINSA is found to be magnetically supercritical, with a field strength comparable to that of the surrounding diffuse, magnetically subcritical CNM despite a large increase in density. The reduction of the magnetic flux relative to the mass, which is necessary for star formation, thus seems to have already happened during the transition from the diffuse CNM to the molecular gas traced by the HINSA. This is earlier than envisioned in the classical picture where magnetically supercritical cores capable of collapsing into stars form out of magnetically subcritical envelopes 13,14 . 

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3. Radio Continuum and Water Maser Observations of the High-mass Protostar IRAS 19035+0641 A

   https://doi.org/10.3847/1538-4357/ad182f  

   Rodríguez, Tatiana M; Momjian, Emmanuel; Hofner, Peter; Sarma, Anuj P; Araya, Esteban D (February 2024, The Astrophysical Journal)

   We present Very Large Array 1.3 cm continuum and 22.2 GHz H2O maser observations of the high-mass protostellar object IRAS 19035+0641 A. Our observations unveil an elongated bipolar 1.3 cm continuum structure at scales ≲500 au, which, together with a rising in-band spectral index, strongly suggests that the radio emission toward IRAS 19035+0641 A arises from an ionized jet. In addition, eight individual water maser spots well aligned with the jet axis were identified. The Stokes V spectrum of the brightest H2O maser line (∼100 Jy) shows a possible Zeeman splitting and is well represented by the derivatives of two Gaussian components fitted to the Stokes I profile. The measured B_los are 123 (±27) and 156 (±8) mG, translating to a preshock magnetic field of ≈7 mG. Subsequent observations to confirm the Zeeman splitting showed intense variability in all the water maser spots, with the brightest maser completely disappearing. The observed variability in a 1 yr timescale could be the result of an accretion event. These findings strengthen our interpretation of IRAS 19035+0641 A as a high-mass protostar in an early accretion/outflow evolutionary phase. 

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4. Joint Analysis of H I Absorption Zeeman Measurements and the Morphology of Filamentary H I Emission

   https://doi.org/10.3847/1538-4357/adff52  

   Nowotka, Marta; Clark, Susan E; Burkhart, Blakesley; Fissel, Laura; Ching, Tao-Chung; Robishaw, Timothy; Heiles, Carl (October 2025, The Astrophysical Journal)

   Abstract We present a joint analysis of HIabsorption Zeeman measurements and the morphology of filamentary HIemission to investigate the 3D structure of the magnetic field in the diffuse neutral interstellar medium. Our analysis is based on the Arecibo Millennium Survey and new data from the Five-hundred-meter Aperture Spherical radio Telescope toward radio sources 3C 75, 3C 207, and 3C 409. Toward 3C 409, we make a 4σZeeman detection and inferB_LOS = 9.1 ± 1.9μG, in agreement with Arecibo results. We quantify the dispersion of HIfilaments at the locations and velocities of Zeeman components using GALFA-HInarrow-channel emission maps. Focusing on a subsample of 42 spectrally distinct components, we find a weak but statistically significant positive correlation (Spearmanρ= 0.3,p= 0.01) between ∣B_LOS∣ and the circular variance of HIfilament orientation angles. To examine its origin, we characterize the environments probed by HIabsorption using dust emission, 3D dust maps, OH absorption, and CO emission. We find evidence that existing HIabsorption Zeeman measurements trace magnetic fields that are coherent on parsec scales, probe primarily local gas (100–500 pc, often at distances consistent with the Local Bubble wall), and exhibit systematic differences in the magnitude ofB_LOS. We attribute the correlation between Zeeman measurements and filamentary HImorphology to large-scale variations in magnetic field strength and/or inclination angle across different Galactic environments, which could arise due to the Local Bubble geometry or enhanced total field strength in denser regions. 

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5. Early Planet Formation in Embedded Disks (eDisk). VIII. A Small Protostellar Disk around the Extremely Low Mass and Young Class 0 Protostar IRAS 15398–3359

   https://doi.org/10.3847/1538-4357/ad003a  

   Thieme, Travis J; Lai, Shih-Ping; Ohashi, Nagayoshi; Tobin, John J; Jørgensen, Jes K; Insa_Choi, Jinshi Sai; Aso, Yusuke; Williams, Jonathan P; Yamato, Yoshihide; Aikawa, Yuri; et al (November 2023, The Astrophysical Journal)

   Abstract Protostellar disks are an ubiquitous part of the star formation process and the future sites of planet formation. As part of the Early Planet Formation in Embedded Disks large program, we present high angular resolution dust continuum (∼40 mas) and molecular line (∼150 mas) observations of the Class 0 protostar IRAS 15398–3359. The dust continuum is small, compact, and centrally peaked, while more extended dust structures are found in the outflow directions. We perform a 2D Gaussian fitting and find the deconvolved size and 2σradius of the dust disk to be 4.5 × 2.8 au and 3.8 au, respectively. We estimate the gas+dust disk mass assuming optically thin continuum emission to be 0.6M_J–1.8M_J, indicating a very low mass disk. The CO isotopologues trace components of the outflows and inner envelope, while SO traces a compact, rotating disk-like component. Using several rotation curve fittings on the position–velocity diagram of the SO emission, the lower limits of the protostellar mass and gas disk radius are 0.022M_⊙and 31.2 au, respectively, from our Modified 2 single power-law fitting. A conservative upper limit of the protostellar mass is inferred to be 0.1M_⊙. The protostellar mass accretion rate and the specific angular momentum at the protostellar disk edge are found to be in the range of (1.3–6.1) × 10⁻⁶M_⊙yr⁻¹and (1.2–3.8) × 10⁻⁴km s⁻¹pc, respectively, with an age estimated between 0.4 × 10⁴yr and 7.5 × 10⁴yr. At this young age with no clear substructures in the disk, planet formation would likely not yet have started. This study highlights the importance of high-resolution observations and systematic fitting procedures when deriving dynamical properties of deeply embedded Class 0 protostars. 

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