Dissertation/Thesis Abstract

From Cores to Envelopes to Disks: A Multi-scale View of Magnetized Star Formation
by Hull, Charles Lindsay Hopkins, Ph.D., University of California, Berkeley, 2014, 152; 3720307
Abstract (Summary)

Observations of polarization in star forming regions have been made across many wavelengths, many size scales, and many stages of stellar evolution. One of the overarching goals of these observations has been to determine the importance of magnetic fields—which are the cause of the polarization—in the star formation process. We begin by describing the commissioning and the calibration of the 1.3 mm dual-polarization receiver system we built for CARMA (the Combined Array for Research in Millimeter-wave Astronomy), a radio telescope in the eastern Sierra region of California. One of the primary science drivers behind the polarization system is to observe polarized thermal emission from dust grains in the dense clumps of dust and gas where the youngest, Class 0 protostars are forming. We go on to describe the CARMA TADPOL survey—the largest high-resolution (∼1000 AU scale) survey to date of dust polarization in low-mass protostellar cores—and discuss our main findings: (1) Magnetic fields (B-fields) on scales of ∼1000 AU are not tightly aligned with protostellar outflows. Rather, the data are consistent both with scenarios where outflows and magnetic fields are preferentially misaligned (perpendicular) and where they are randomly aligned. (2) Sources with high CARMA polarization fractions have consistent B-field orientations on large scales (∼20'', measured using single-dish submillimeter telescopes) and small scales (∼2.5'', measured by CARMA). We interpret this to mean that in at least some cases B-fields play a role in regulating the infall of material all the way down to the ∼1000 AU scales of protostellar envelopes. Finally, (3) While on the whole outflows appear to be randomly aligned with B-fields, in sources with low polarization fractions there is a hint that outflows are preferentially perpendicular to small-scale B-fields, which suggests that in these sources the fields have been wrapped up by envelope rotation. This work shows that the ∼1000 AU protostellar envelope may be a turning point: at larger scales B-fields may still retain the memory of the global B-field drawn in from the ambient medium; but at smaller scales the B-fields may be affected by the dynamics of both envelope and disk rotation. This sets the stage for ALMA (the Atacama Large Millimeter/submillimeter Array), which will soon reveal the morphology of B-fields in circumstellar disks themselves.

Indexing (document details)
Advisor: Plambeck, Richard
Commitee: Heiles, Carl, Lee, Adrian, McKee, Christopher
School: University of California, Berkeley
Department: Astrophysics
School Location: United States -- California
Source: DAI-B 77/01(E), Dissertation Abstracts International
Source Type: DISSERTATION
Subjects: Astrophysics, Astronomy
Keywords: Instrumentation: interferometers, Instrumentation: polarimeters, Magnetic fields, Polarization, Stars: formation, Stars: protostars
Publication Number: 3720307
ISBN: 9781339012506
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