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Abstract The vertical settling of dust grains in a circumstellar disk, characterized by their scale height, is a pivotal process in the formation of planets. This study offers in-depth analysis and modeling of the radial scale height profile of dust grains in the HL Tau system, leveraging high-resolution polarization observations. We resolve the inner disk’s polarization, revealing a significant nearside–farside asymmetry, with the nearside being markedly brighter than the farside in polarized intensity. This asymmetry is attributed to a geometrically thick inner dust disk, suggesting a large aspect ratio ofH/R≥ 0.15, whereHis the dust scale height andRis the radius. The first ring at 20 au exhibits an azimuthal contrast, with polarization enhanced along the minor axis, indicating a moderately thick dust ring withH/R ≈ 0.1. The absence of the nearside–farside asymmetry at larger scales implies a thin dust layer, withH/R < 0.05. Taken together, these findings depict a disk with a turbulent inner region and a settled outer disk, requiring a variable turbulence model withαincreasing from 10⁻⁵at 100 au to 10^−2.5at 20 au. This research sheds light on dust settling and turbulence levels within protoplanetary disks, providing valuable insights into the mechanisms of planet formation. 

Abstract Due to dust grain alignment with magnetic fields, dust polarization observations of far-infrared emission from cold molecular clouds are often used to trace magnetic fields, allowing a probe of the effects of magnetic fields on the star formation process. We present inferred magnetic field maps of the Pillars of Creation region within the larger M16 emission nebula, derived from dust polarization data in the 89 and 154μm continuum using the Stratospheric Observatory For Infrared Astronomy/High-resolution Airborne Wideband Camera. We derive magnetic field strength estimates using the Davis–Chandrasekhar–Fermi method. We compare the polarization and magnetic field strengths to column densities and dust continuum intensities across the region to build a coherent picture of the relationship between star-forming activity and magnetic fields in the region. The projected magnetic field strengths derived are in the range of ∼50–130μG, which is typical for clouds of similarn(H₂), i.e., molecular hydrogen volume density on the order of 10⁴–10⁵cm⁻³. We conclude that star formation occurs in the finger tips when the magnetic fields are too weak to prevent radial collapse due to gravity but strong enough to oppose OB stellar radiation pressure, while in the base of the fingers the magnetic fields hinder mass accretion and consequently star formation. We also support an initial weak-field model (<50μG) with subsequent strengthening through realignment and compression, resulting in a dynamically important magnetic field. 

Abstract Circumstellar disk dust polarization in the (sub)millimeter is, for the most part, not from dust grain alignment with magnetic fields but rather indicative of a combination of dust self-scattering with a yet unknown alignment mechanism that is consistent with mechanical alignment. While the observational evidence for scattering has been well established, that for mechanical alignment is less so. Circum-multiple dust structures in protostellar systems provide a unique environment to probe different polarization alignment mechanisms. We present ALMA Band 4 and Band 7 polarization observations toward the multiple young system L1448 IRS3B. The polarization in the two bands are consistent with each other, presenting multiple polarization morphologies. On the size scale of the inner envelope surrounding the circum-multiple disk, the polarization is consistent with magnetic field dust grain alignment. On the very small scale of compact circumstellar regions, we see polarization that is consistent with scattering around sourceaandc, which are likely the most optically thick components. Finally, we see polarization that is consistent with mechanical alignment of dust grains along the spiral dust structures, which would suggest that the dust is tracing the relative gas flow along the spiral arms. If the gas-flow dust grain alignment mechanism is dominant in these cases, disk dust polarization may provide a direct probe of the small-scale kinematics of the gas flow relative to the dust grains. 

Abstract We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the Class 0 protostar IRAS 04166+2706, obtained as part of the ALMA Large Program Early Planet Formation in Embedded Disks. These observations were made in the 1.3 mm dust continuum and molecular lines at angular resolutions of $\sim 0\stackrel{″}{.}05$(∼8 au) and $\sim 0\stackrel{″}{.}16$(∼25 au), respectively. The continuum emission shows a disklike structure with a radius of ∼22 au. Kinematical analysis of¹³CO (2–1), C¹⁸O (2–1), H₂CO (3_0,3–2_0,2), CH₃OH (4₂–3₁) emission demonstrates that these molecular lines trace the infalling-rotating envelope and possibly a Keplerian disk, enabling us to estimate the protostar mass to be 0.15M_⊙ < M_⋆ < 0.39M_⊙. The dusty disk is found to exhibit a brightness asymmetry along its minor axis in the continuum emission, probably caused by a flared distribution of the dust and the high optical depth of the dust emission. In addition, the¹²CO (2–1) and SiO (5–4) emissions show knotty and wiggling motions in the jets. Our high-angular-resolution observations revealed the most recent mass ejection events, which have occurred within the last ∼25 yr. 

ABSTRACT Recent (sub)millimetre polarization observations of protoplanetary discs reveal toroidally aligned, effectively prolate dust grains large enough (at least $$\sim 100$$\mu$$m) to efficiently scatter millimetre light. The alignment mechanism for these grains remains unclear. We explore the possibility that gas drag aligns grains through gas–dust relative motion when the grain’s centre of mass is offset from its geometric centre, analogous to a badminton birdie’s alignment in flight. A simple grain model of two non-identical spheres illustrates how a grain undergoes damped oscillations from flow-induced restoring torques which align its geometric centre in the flow direction relative to its centre of mass. Assuming specular reflection and subsonic flow, we derive an analytical equation of motion for spheroids where the centre of mass can be shifted away from the spheroid’s geometric centre. We show that a prolate or an oblate grain can be aligned with the long axis parallel to the gas flow when the centre of mass is shifted along that axis. Both scenarios can explain the required effectively prolate grains inferred from observations. Application to a simple disc model shows that the alignment time-scales are shorter than or comparable to the orbital time. The grain alignment direction in a disc depends on the disc (sub-)structure and grain Stokes number (St) with azimuthal alignment for large St grains in sub-Keplerian smooth gas discs and for small St grains near the gas pressure extrema, such as rings and gaps. 

Abstract The HH 111 protostellar disk has recently been found to host a pair of spiral arms. Here we report the dust polarization results in the disk as well as the inner envelope around it, obtained with the Atacama Large Millimeter/submillimeter Array in continuum atλ∼ 870μm and ∼0.″05 resolution. In the inner envelope, polarization is detected with a polarization degree of ∼6% and an orientation almost everywhere parallel to the minor axis of the disk and thus likely to be due to the dust grains magnetically aligned mainly by toroidal fields. In the disk, the polarization orientation is roughly azimuthal on the far side and becomes parallel to the minor axis on the near side, with a polarization gap in between on the far side near the central protostar. The disk polarization degree is ∼2%. The polarized intensity is higher on the near side than the far side, showing a near–far side asymmetry. More importantly, the polarized intensity and thus polarization degree are lower in the spiral arms but higher in between the arms, showing an anticorrelation of the polarized intensity with the spiral arms. Our modeling results indicate that this anticorrelation is useful for constraining the polarization mechanism and is consistent with the dust self-scattering by the grains that have grown to a size of ∼150μm. The interarms are sandwiched and illuminated by two brighter spiral arms and thus have higher polarized intensity. Our dust self-scattering model can also reproduce the observed polarization orientation parallel to the minor axis on the near side and the observed azimuthal polarization orientation at the two disk edges in the major axis. Further modeling work is needed to study how to reproduce the observed near–far side asymmetry in the polarized intensity and the observed azimuthal polarization orientation on the far side.