First Observations of the Magnetic Field Geometry in Prestellar Cores

By D. Ward-Thompson, J. Kirk, R. Crutcher, J. Greaves, W. Holland, P. University, Uk, U. Illinois, Jac, Hawaii and 2 more. 2000

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We present the first published maps of magnetic fields in prestellar cores to test theoretical ideas about the way in which the magnetic field geometry affects the star formation process. The observations are JCMT-SCUBA maps of λ850 μm thermal emission from dust. Linear polarizations at typically 10 or more independent positions in each of three objects, L1544, L183, and L43, were measured, and the geometries of the magnetic fields in the plane of the sky were mapped from the polarization directions. The observed polarizations in all three objects appear smooth and fairly uniform. In L1544 and L183 the mean magnetic fields are at an angle of ~30° to the minor axes of the cores. The L43 B-field appears to have been influenced in its southern half such that it is parallel to the wall of a cavity produced by a CO outflow from a nearby T Tauri star, while in the northern half the field appears less disturbed and has an angle 44° to the core minor axis. We briefly compare our results with published models of magnetized cloud cores and conclude that no current model can explain these observations simultaneously with previous ISOCAM data.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/0d3d99a5843dd281c749025e8f5b73b6a6b2a901

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THE LEGACY OF SCUPOL: 850 μm IMAGING POLARIMETRY FROM 1997 TO 2005 (2009, unknown): “…(1987); Kenyon et al. (1994) CB 26 BG 21 0.140 Launhardt & N Henning et al. (2001); Sargent (2001) Wolf et al. (2004) L1544 SC/PC 22 0.140 ± 0.010 Kenyon et al. (1994) N Ward-Thompson et al. (2000); Crutcher et al. (2004); Nutter et al. (2004); Crutcher (2004) RNO 43 YSO 23 0.4 Zinnecker et al.…”
Cold Dark Clouds: The Initial Conditions for Star Formation (2007, background): “For cores L1544, L183, and L43, Ward-Thompson et al. (2000) and Crutcher et al. (2004) have found polarization vectors that are fairly uniform but not aligned with the minor axis of the cores by about 30◦, as it would have been expected by ambipolar diffusion models (but see Basu 2000 for an…”
The initial conditions of isolated star formation — VI. SCUBA mapping of pre-stellar cores (2005, background): “…these same models can only produce the observed core radial density profiles described above (see also Bacmann et al., 2000) if they are in the regime where the magnetic field dominates over the turbulence, in apparent contradiction with the polarisation results (Ward-Thompson et al., 2000).”
Planck intermediate results: XXXV. Probing the role of the magnetic field in the formation of structure in molecular clouds (2015, unknown): “On the scale of prestellar cores and cloud segments, these observations reveal both signiﬁcant levels of polarized emission and coherent ﬁeld morphologies (Ward-Thompson et al. 2000; Dotson et al. 2000; Matthews et al. 2009).”
An Empirical Model for Protostellar Collapse (2000, background): “SCUBA polarimetry observations of L1544 (Ward-Thompson et al. 2000) showed a magnetic field that does not align with the short axis of the core.”
The Stellar Initial Mass Function from Turbulent Fragmentation (2000, background): “This may considerably complicate the interpretation of dust polarization measurements (Ward-Thompson et al. 2000) and should be taken into account.”
Radiative torque alignment: essential physical processes (2007, background): “The pre-stellar cores studied in Ward-Thompson et al. (2000) correspond to AV = 50 − 60; the shielding column, assuming uniformity, is approximately half of these values.”
NON-IDEAL MHD EFFECTS AND MAGNETIC BRAKING CATASTROPHE IN PROTOSTELLAR DISK FORMATION (2011, background): “Well ordered magnetic fields are also inferred from polarization maps of dust continuum emission, both on the core scale (Ward-Thompson et al. 2000) and smaller (e.g., Girart et al. 2006).”
Planck intermediate results. XIX. An overview of the polarized thermal emission from Galactic dust (2014, background): “…of the polarization fraction toward large column densities on small (∼a few 0.1 pc) scales was reported previously in ground-based measurements of polarization both in emission (Ward-Thompson et al. 2000; Matthews & Wilson 2000) and extinction (e.g., Gerakines & Whittet 1995; Whittet et al. 2008).”
Magnetic Fields in Dark Cloud Cores: Arecibo OH Zeeman Observations (2008, background): “For example, Ward-Thompson et al. (2000) mapped linear polarization in L1544 (also included in this project), L183, and L43 at 1400 spatial resolution.”
SCUBA Polarization Measurements of the Magnetic Field Strengths in the L183, L1544, and L43 Prestellar Cores (2003, methodology): “The prestellar core we are interested in is not isolated; there is a second core at the western edge of the SCUBA field of view (Ward-Thompson et al. 2000) in which a classical T Tauri star, RNO 91 (Cohen 1980), is embedded.”
Collapse of Magnetized Singular Isothermal Toroids. II. Rotation and Magnetic Braking (2003, background): “Third, observations of millimeter-wave and far infrared polarization patterns do not indicate substantive toroidal fields in the noncollapsing portions of molecular and dark clouds (see, e.g., Ward-Thompson et al. 2000 for the case of starless core L1544).”
Tracing Magnetic Fields with Aligned Grains (2007, result): “However, the data obtained for pre-stellar cores in Ward-Thompson et al. (2000) seem to be at odds with the LGM97 predictions.”
The Efficiency of Grain Alignment in Dense Interstellar Clouds: a Reassessment of Constraints from Near-Infrared Polarization (2007, background): “!) polarization amplitudes toward the centers of isolated globules and starless cores1 (Hildebrand et al. 1999; Ward-Thompson et al. 2000; Wolf et al. 2003).”