Anchoring Magnetic Field in Turbulent Molecular Clouds

Li, Hua-bai; Dowell, C. D.; Goodman, Alyssa A.; Hildebrand, R. H.; Novak, Giles

doi:10.1088/0004-637x/704/2/891

Cited by 100 publications

(138 citation statements)

References 36 publications

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“…The magnetic fields seem to have a bimodal behavior, where the field is either parallel or perpendicular to the major axis of the cloud (Li et al 2009(Li et al , 2013Soler et al 2013;Planck Collaboration et al 2016a. This orderliness and bimodality of the magnetic fields is also observed at the 0.1-0.01 pc protostellar core scale (Koch et al 2014;Zhang et al 2014).…”

Section: Magnetic Fields At Different Spatial Scalesmentioning

confidence: 97%

ALMA Observations of Dust Polarization and Molecular Line Emission from the Class 0 Protostellar Source Serpens SMM1

Hull

Girart

Tychoniec

et al. 2017

ApJ

113

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We present high angular resolution dust polarization and molecular line observations carried out with the Atacama Large Millimeter/submillimeter Array (ALMA) toward the Class 0 protostar Serpens SMM1. By complementing these observations with new polarization observations from the Submillimeter Array (SMA) and archival data from the Combined Array for Research in Millimeter-wave Astronomy (CARMA) and the James Clerk Maxwell Telescopes (JCMT), we can compare the magnetic field orientations at different spatial scales. We find major changes in the magnetic field orientation between large (∼0.1 pc) scales-where the magnetic field is oriented E-W, perpendicular to the major axis of the dusty filament where SMM1 is embedded-and the intermediate and small scales probed by CARMA (∼1000 au resolution), the SMA (∼350 au resolution), and ALMA (∼140 au resolution). The ALMA maps reveal that the redshifted lobe of the bipolar outflow is shaping the magnetic field in SMM1 on the southeast side of the source; however, on the northwestern side and elsewhere in the source, lowvelocity shocks may be causing the observed chaotic magnetic field pattern. High-spatial-resolution continuum and spectral-line observations also reveal a tight (∼130 au) protobinary system in SMM1-b, the eastern component of which is launching an extremely high-velocity, one-sided jet visible in both =  (J CO 2 1) and =  (J SiO 5 4); however, that jet does not appear to be shaping the magnetic field. These observations show that with the sensitivity and resolution of ALMA, we can now begin to understand the role that feedback (e.g., from protostellar outflows) plays in shaping the magnetic field in very young, star-forming sources like SMM1.

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Section: Magnetic Fields At Different Spatial Scalesmentioning

confidence: 97%

ALMA Observations of Dust Polarization and Molecular Line Emission from the Class 0 Protostellar Source Serpens SMM1

Hull

Girart

Tychoniec

et al. 2017

ApJ

113

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“…Li et al (2009) used optical backgroundstarlight polarimetry to probe field morphology on cloud scales (200 pc) and sub-millimeter dust polarimetry to probe fields on much smaller core scales (a few × 0.1 pc). They showed that magnetic-field orientations are broadly consistent from cloud-to core-scales.…”

Section: Introductionmentioning

confidence: 99%

Synthetic Observations of Magnetic Fields in Protostellar Cores

Lee

Hull

Offner

2017

ApJ

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The role of magnetic fields in the early stages of star formation is not well constrained. In order to discriminate between different star formation models, we analyze 3D magnetohydrodynamic simulations of low-mass cores and explore the correlation between magnetic field orientation and outflow orientation over time. We produce synthetic observations of dust polarization at resolutions comparable to millimeter-wave dust polarization maps observed by CARMA and compare these with 2D visualizations of projected magnetic field and column density. Cumulative distribution functions of the projected angle between the magnetic field and outflow show different degrees of alignment in simulations with differing mass-to-flux ratios. The distribution function for the less magnetized core agrees with observations finding random alignment between outflow and field orientations, while the more magnetized core exhibits stronger alignment. We find that fractional polarization increases when the system is viewed such that the magnetic field is close to the plane of the sky, and the values of fractional polarization are consistent with observational measurements. The simulation outflow, which reflects the underlying angular momentum of the accreted gas, changes direction significantly over the first ∼ 0.1 Myr of evolution. This movement could lead to the observed random alignment between outflows and the magnetic fields in protostellar cores.

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“…Li et al 2009). However, as of today, no consistent scenario exists that explains how magnetic fields in Herbig Ae/Be stars are generated and how they interact with the circumstellar environment.…”

Section: Introductionmentioning

confidence: 99%

HARPS spectropolarimetry of three sharp-lined Herbig Ae stars: New insights

Järvinen

Carroll

Hubrig

et al. 2015

A&A

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Aims. Recently, several arguments have been presented that favour a scenario in which the low detection rate of magnetic fields in Herbig Ae stars can be explained by the weakness of these fields and rather large measurement uncertainties. Spectropolarimetric studies involving sharp-lined Herbig Ae stars appear to be a promising approach for the detection of such weak magnetic fields. These studies offer a clear spectrum interpretation with respect to the effects of blending, local velocity fields, and chemical abundances, and allow us to identify a proper sample of spectral lines appropriate for magnetic field determination. Methods. High-resolution spectropolarimetric observations of the three sharp-lined (v sin i < 15 km s −1 ) Herbig Ae stars HD 101412, HD 104237, and HD 190073 have been obtained in recent years with the HARPS spectrograph in polarimetric mode. We used these archival observations to investigate the behaviour of their longitudinal magnetic fields. To carry out the magnetic field measurements, we used the multi-line singular value decomposition (SVD) method for Stokes profile reconstruction. Results. We carried out a high-resolution spectropolarimetric analysis of the Herbig Ae star HD 101412 for the first time. We discovered that different line lists yield differences in both the shape of the Stokes V signatures and their field strengths. They could be interpreted in the context of the impact of the circumstellar matter and elemental abundance inhomogeneities on the measurements of the magnetic field. On the other hand, due to the small size of the Zeeman features on the first three epochs and the lack of near-IR observations, circumstellar and photospheric contributions cannot be estimated unambiguously. In the SVD Stokes V spectrum of the SB2 system HD 104237, we detect that the secondary component, which is a T Tauri star, possesses a rather strong magnetic field B z = 129 ± 12 G, while no significant field is present in the primary component. Our measurements of HD 190073 confirm the presence of a variable magnetic field and indicate that the circumstellar environment may have a significant impact on the observed polarization features.

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Anchoring Magnetic Field in Turbulent Molecular Clouds

Cited by 100 publications

References 36 publications

ALMA Observations of Dust Polarization and Molecular Line Emission from the Class 0 Protostellar Source Serpens SMM1

ALMA Observations of Dust Polarization and Molecular Line Emission from the Class 0 Protostellar Source Serpens SMM1

Synthetic Observations of Magnetic Fields in Protostellar Cores

HARPS spectropolarimetry of three sharp-lined Herbig Ae stars: New insights

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