The Explosion in Orion-KL as Seen by Mosaicking the Magnetic Field with ALMA

Cortés, Paulo C.; Gouellec, Valentin J. M. Le; Hull, Charles L. H.; Girart, J. M.; Louvet, F.; Fomalont, Edward B.; Kameno, Seiji; Moellenbrock, G.; Nagai, Hiroshi; Nakanishi, Koji; Villard, Eric

doi:10.3847/1538-4357/abcafb

Cited by 18 publications

(9 citation statements)

References 65 publications

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“…While this mechanism could in principle be at work for example around massive protostars where radiative pressure drives the outflow (Mignon-Risse et al 2021), its conditions seem very sensitive to the flow properties (high velocities to enhance the alignment efficiency, but not as high as to disrupt the dust grains) and quite unable to explain the large range of observations showing polarized dust emission in protostars. We also stress that no convincing observational signature of such alignment process was yet found in protostellar environments (Cortes et al 2021;Aso et al 2021).…”

Section: Significance Of Other Polarization-producing Processes In Pr...mentioning

confidence: 76%

Is the mm/submm dust polarization a robust tracer of the magnetic field topology in protostellar envelopes? A model exploration

Valdivia¹,

Maury²,

Hennebelle³

2022

Preprint

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Context. High resolution (sub-) millimeter polarization observations have opened a new era in the understanding of how magnetic fields are organized in star forming regions, unveiling an intricate interplay between the magnetic fields and the gas in protostellar cores. However, to assess the role of the magnetic field in the process of solar-type star formation, it is key to be able to understand to what extent these polarized dust emission are good tracers of the magnetic field in the youngest protostellar objects. Aims. In this paper, we present a thorough investigation of the fidelity and limitations of using dust polarized emission to map the magnetic field topologies in low-mass protostars. Methods. To assess the importance of these effects, we have performed the analysis of magnetic field properties in 27 realizations of MHD models following the evolution of physical properties in star-forming cores. Assuming a uniform population of dust grains which sizes follow the standard MRN, we analyze the synthetic polarized dust emission maps produced if these grains align with the local B-field thanks to Radiative Torques (B-RATs).Results. We find that (sub-)millimeter polarized dust emission is a robust tracer of the magnetic field topologies in inner protostellar envelopes and is successful at capturing the details of the magnetic field spatial distribution down to radii ∼ 100 au. Measurements of the line-of-sight averaged magnetic field line orientation using the polarized dust emission are precise to < 15 • (typical of the error on polarization angles obtained with observations from large mm polarimetric facilities such as ALMA) in about 75 − 95% of the independent lines of sight peering through protostellar envelopes. Large discrepancies between the integrated B-field mean orientation and the orientation reconstructed from the polarized dust emission are mostly observed in (i) lines of sight where the magnetic field is highly disorganized and (ii) lines of sight probing large column densities. Our analysis shows that high opacity of the thermal dust emission and low polarization fractions could be used to avoid utilizing the small fraction of measurements affected by large errors.

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Section: Significance Of Other Polarization-producing Processes In Pr...mentioning

confidence: 76%

Is the mm/submm dust polarization a robust tracer of the magnetic field topology in protostellar envelopes? A model exploration

Valdivia¹,

Maury²,

Hennebelle³

2022

Preprint

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“…In addition, the B-field lines seemed to be distorted at the Orion-KL position (see Fig. 1 of [23]; see also the ALMA observations of Cortes et al 2021 [8]). Thanks to the high angular resolution and sensitivity provided by NIKA2-Pol at 1.15 mm, this distortion seems to be confirmed and even looks like another hourglass, on smaller scales, centered on Orion KL, which is suggestive of local gravitational collapse at this location (see Fig.…”

Section: A Possible New Local Hourglass At the Orion-kl Positionmentioning

confidence: 86%

Probing the role of magnetic fields in star-forming filaments: NIKA2-Pol commissioning results toward OMC-1

et al. 2022

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Dust polarization observations are a powerful, practical tool to probe the geometry (and to some extent, the strength) of magnetic fields in starforming regions. In particular, Planck polarization data have revealed the importance of magnetic fields on large scales in molecular clouds. However, due to insufficient resolution, Planck observations are unable to constrain the B-field geometry on prestellar and protostellar scales. The high angular resolution of 11.7 arcsec provided by NIKA2-Pol 1.15 mm polarimetric imaging, corresponding to 0.02 pc at the distance of the Orion molecular cloud (OMC), makes it possible to advance our understanding of the B-field morphology in star-forming filaments and dense cores (IRAM 30m large program B-FUN). The commissioning of the NIKA2-Pol instrument has led to several challenging issues, in particular, the instrumental polarization or intensity-to-polarization “leakage” effect. In the present paper, we illustrate how this effect can be corrected for, leading to reliable exploitable data in a structured, extended source such as OMC-1. We present a statistical comparison between NIKA2-Pol and SCUBA2-Pol2 results in the OMC-1 region. We also present tentative evidence of local pinching of the B-field lines near Orion-KL, in the form of a new small-scale hourglass pattern, in addition to the larger-scale hourglass already seen by other instruments such as Pol2.

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“…The 1σ systematic uncertainty in polarization fraction for a single-pointing, onaxis linear polarization observations with ALMA is 0.03% of Stokes I (corresponding to a minimum detectable polarization fraction of 0.1%). The 1σ systematic errors increase to ∼0.5% near the FWHM of the primary beam in Band 7 observations; however, these errors are reduced by mosaicking (Hull et al 2020;Cortes et al 2021). Furthermore, the offaxis errors within the inner 1 3 of the FWHM at Band 7 are at most 0.1% (Hull et al 2020), and our small mosaic has been setup so that all of the emission from the β Pic disk falls within the inner 1 3 of one of the three pointings; the systematic errors in polarization fraction are thus approximately 2 × smaller than the statistical errors in our measurements (see Sections 3 and Table 1).…”

Section: Observations and Imagingmentioning

confidence: 94%

Polarization from Aligned Dust Grains in the β Pic Debris Disk

Hull

Yang

Cortés

et al. 2022

ApJ

Self Cite

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We present 870 μm Atacama Large Millimeter/submillimeter Array polarization observations of thermal dust emission from the iconic, edge-on debris disk β Pic. While the spatially resolved map does not exhibit detectable polarized dust emission, we detect polarization at the ∼3σ level when averaging the emission across the entire disk. The corresponding polarization fraction is P frac = 0.51% ± 0.19%. The polarization position angle χ is aligned with the minor axis of the disk, as expected from models of dust grains aligned via radiative alignment torques (RAT) with respect to a toroidal magnetic field (B-RAT) or with respect to the anisotropy in the radiation field (k-RAT). When averaging the polarized emission across the outer versus inner thirds of the disk, we find that the polarization arises primarily from the SW third. We perform synthetic observations assuming grain alignment via both k-RAT and B-RAT. Both models produce polarization fractions close to our observed value when the emission is averaged across the entire disk. When we average the models in the inner versus outer thirds of the disk, we find that k-RAT is the likely mechanism producing the polarized emission in β Pic. A comparison of timescales relevant to grain alignment also yields the same conclusion. For dust grains with realistic aspect ratios (i.e., s > 1.1), our models imply low grain-alignment efficiencies.

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The Explosion in Orion-KL as Seen by Mosaicking the Magnetic Field with ALMA

Cited by 18 publications

References 65 publications

Is the mm/submm dust polarization a robust tracer of the magnetic field topology in protostellar envelopes? A model exploration

Is the mm/submm dust polarization a robust tracer of the magnetic field topology in protostellar envelopes? A model exploration

Probing the role of magnetic fields in star-forming filaments: NIKA2-Pol commissioning results toward OMC-1

Polarization from Aligned Dust Grains in the β Pic Debris Disk

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