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  1. Abstract

    We present Very Large Array observations toward the Class 0 protostar L1157 MMS at 6.8 and 9 mm with a resolution of ∼0.″04 (14 au). We detect two sources within L1157 MMS and interpret these sources as a binary protostar with a separation of ∼16 au. The material directly surrounding the binary system within the inner 50 au radius of the system has an estimated mass of 0.11M, calculated from the observed dust emission. We interpret the observed binary system in the context of previous observations of its flattened envelope structure, low rates of envelope rotation from 5000 to 200 au scales, and an ordered, poloidal magnetic field aligned with the outflow. Thus, L1157 MMS is a prototype system for magnetically regulated collapse, and the presence of a compact binary within L1157 MMS demonstrates that multiple star formation can still occur within envelopes that likely have dynamically important magnetic fields.

  2. Abstract We present H -band (1.65 μ m) and SOFIA HAWC+ 154 μ m polarization observations of the low-mass core L483. Our H -band observations reveal a magnetic field that is overwhelmingly in the E–W direction, which is approximately parallel to the bipolar outflow that is observed in scattered IR light and in single-dish 12 CO observations. From our 154 μ m data, we infer a ∼45° twist in the magnetic field within the inner 5″ (1000 au) of L483. We compare these new observations with published single-dish 350 μ m polarimetry and find that the 10,000 au scale H -band data match the smaller-scale 350 μ m data, indicating that the collapse of L483 is magnetically regulated on these larger scales. We also present high-resolution 1.3 mm Atacama Large Millimeter/submillimeter Array data of L483 that reveals it is a close binary star with a separation of 34 au. The plane of the binary of L483 is observed to be approximately parallel to the twisted field in the inner 1000 au. Comparing this result to the ∼1000 au protostellar envelope, we find that the envelope is roughly perpendicular to the 1000 au HAWC+ field. Using the data presented, we speculatemore »that L483 initially formed as a wide binary and the companion star migrated to its current position, causing an extreme shift in angular momentum thereby producing the twisted magnetic field morphology observed. More observations are needed to further test this scenario.« less
    Free, publicly-accessible full text available June 1, 2023
  3. 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,more »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.« less