We present 350 µm polarization observations of four low-mass cores containing Class 0 protostars: L483, L1157, L1448-IRS2, and Serp-FIR1. This is the second paper in a larger survey aimed at testing magnetically regulated models for core-collapse. One key prediction of these models is that the mean magnetic field in a core should be aligned with the symmetry axis (minor axis) of the flattened YSO inner envelope (aka pseudodisk). Furthermore, the field should exhibit a pinched or hour-glass shaped morphology as gravity drags the field inward towards the central protostar. We combine our results for the four cores with results for three similar cores that were published in the first paper from our survey. An analysis of the 350 µm polarization data for the seven cores yields evidence of a positive correlation between mean field direction and pseudodisk symmetry axis. Our rough estimate for the probability of obtaining by pure chance a correlation as strong as the one we found is about 5%. In addition, we combine together data for multiple cores to create a source-averaged magnetic field map having improved signal-to-noise ratio, and this map shows good agreement between mean field direction and pseudodisk axis (they are within 15 • ). We also see hints of a magnetic pinch in the source-averaged map. We conclude that core-scale magnetic fields appear to be strong enough to guide gas infall, as predicted by the magnetically regulated models. Finally, we find evidence of a positive correlation between core magnetic field direction and bipolar outflow axis.

No abstract

We use extensive 350 um polarimetry and continuum maps obtained with Hertz and SHARC II along with HCN and HCO+ spectroscopic data to trace the orientation of the magnetic field in the Orion A star-forming region. Using the polarimetry data, we find that the direction of the projection of the magnetic field in the plane of the sky relative to the orientation of the integral-shaped filament varies considerably as one moves from north to south. While in IRAS 05327-0457 and OMC-3 MMS 1-6 the projection of the field is primarily perpendicular to the filament it becomes better aligned with it at OMC-3 MMS 8-9 and well aligned with it at OMC-2 FIR 6. The OMC-2 FIR 4 cloud, located between the last two, is a peculiar object where we find almost no polarization. The projected angle of the field is more complicated in OMC-1 where it exhibits smooth variations in its orientation across the face of this massive complex. By combining the polarimetry and spectroscopic data we were able to measure a set of average values for the inclination angle of the magnetic field relative to the line of sight. We find that the field is oriented quite close to the plane of the sky in most places. More precisely, the inclination of the magnetic field is ~73 deg. around OMC-3 MMS 6, ~74 deg. at OMC-3 MMS 8-9, ~80 deg. at OMC-2 FIR 4, ~65 deg. in the northeastern part of OMC-1, and ~49 deg. in the Bar. We also present polarimetry data for the OMC-4 region located some 13 arcminutes south of OMC-1.Comment: Accepted for publication in the ApJ, 49 pages, 10 figures, 5 table

Prestellar cores are unique laboratories for studying the chemical and physical conditions preceding star formation. We observed the prestellar core L1544 in the fundamental transition of ortho-H 2 D + (1 1,0 -1 1,1 ) at different positions over 100 00 and found a strong correlation between its abundance and the CO depletion factor. We also present a tentative detection of the fundamental transition of para-D 2 H + (1 1,0 -1 0,1 ) at the dust emission peak. Maps in N 2 H + , N 2 D + , HCO + , and DCO + are used and interpreted with the aid of a spherically symmetric chemical model that predicts the column densities and abundances of these species as a function of radius. The correlation between the observed deuterium fractionation of H þ 3 , N 2 H + , and HCO + and the observed integrated CO depletion factor across the core can be reproduced by this chemical model. In addition, a simpler model is used to study the H 2 D + ortho-to-para ratio. We conclude that, in order to reproduce the observed ortho-H 2 D + observations, the grain radius should be larger than 0.3 m.

No abstract