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Abstract We present 870μm polarimetric observations toward 61 protostars in the Orion molecular clouds with ∼400 au (1″) resolution using the Atacama Large Millimeter/submillimeter Array. We successfully detect dust polarization and outflow emission in 56 protostars; in 16 of them the polarization is likely produced by self-scattering. Self-scattering signatures are seen in several Class 0 sources, suggesting that grain growth appears to be significant in disks at earlier protostellar phases. For the rest of the protostars, the dust polarization traces the magnetic field, whose morphology can be approximately classified into three categories: standard-hourglass, rotated-hourglass (with its axis perpendicular to outflow), and spiral-like morphology. A total of 40.0% (±3.0%) of the protostars exhibit a mean magnetic field direction approximately perpendicular to the outflow on several × 102–103au scales. However, in the remaining sample, this relative orientation appears to be random, probably due to the complex set of morphologies observed. Furthermore, we classify the protostars into three types based on the C17O (3–2) velocity envelope’s gradient: perpendicular to outflow, nonperpendicular to outflow, and unresolved gradient (≲1.0 km s−1arcsec−1). In protostars with a velocity gradient perpendicular to outflow, the magnetic field lines are preferentially perpendicular to outflow, with most of them exhibiting a rotated hourglass morphology, suggesting that the magnetic field has been overwhelmed by gravity and angular momentum. Spiral-like magnetic fields are associated with envelopes having large velocity gradients, indicating that the rotation motions are strong enough to twist the field lines. All of the protostars with a standard-hourglass field morphology show no significant velocity gradient due to the strong magnetic braking.
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This content will become publicly available on April 22, 2026
Characterizing Magnetic Properties of Young Protostars in Orion
Abstract TheB-field Orion Protostellar Survey (BOPS) recently obtained polarimetric observations at 870μm toward 61 protostars in the Orion molecular clouds with ∼1″ spatial resolution using the Atacama Large Millimeter/submillimeter Array. From the BOPS sample, we selected the 26 protostars with extended polarized emission within a radius of ∼6″ (2400 au) around the protostar. This allows us to have sufficient statistical polarization data to infer the magnetic field strength. The magnetic field strength is derived using the Davis–Chandrasekhar–Fermi method. The underlying magnetic field strengths are approximately 2.0 mG for protostars with a standard hourglass magnetic field morphology, which is higher than the values derived for protostars with rotated hourglass, spiral, and complex magnetic field configurations (≲1.0 mG). This suggests that the magnetic field plays a more significant role in envelopes exhibiting a standard hourglass field morphology, and a value of ≳2.0 mG would be required to maintain such a structure at these scales. Furthermore, most protostars in the sample are slightly supercritical, with mass-to-flux ratios ≲3.0. In particular, the mass-to-flux ratios for all protostars with a standard hourglass magnetic field morphology are lower than 3.0. However, these ratios do not account for the contribution of the protostellar mass, which means they are likely significantly underestimated.
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- PAR ID:
- 10609005
- Publisher / Repository:
- American Astronomical Society
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 984
- Issue:
- 1
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 29
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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