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Title:Observations of disks around the youngest protostars: characterizing frequency, dust properties, and magnetic fields at the earliest times
Author(s):Segura-Cox, Dominique M
Director of Research:Looney, Leslie
Doctoral Committee Chair(s):Looney, Leslie
Doctoral Committee Member(s):Gammie, Charles; Kemball, Athol; Wong, Tony
Department / Program:Astronomy
Degree Granting Institution:University of Illinois at Urbana-Champaign
Class 0
Class I
magnetic fields
star formation
high resolution
Abstract:Circumstellar disks are fundamental for accretion and angular momentum distribution during the early phases of star formation. Class 0 objects are the youngest protostars and most embedded in their natal envelopes, and circumstellar disks can form even at this earliest stage of star formation. Less-embedded Class I protostars have cleared part of their surrounding envelope, yet the envelopes enshrouding Class 0 and Class I protostars have made detection of young protostellar disks difficult; before this work, only ∼15 total Class 0 and 10 Class I disks were known. While work has begun with Class 0 disks, due to their deeply enshrouded nature, there is still much left to examine regarding disk frequency, disk radii, dust populations, disk evolution, disk structure, and presence of planetesimals in the youngest protostellar disks. Through observational work with the CARMA, VLA, and ALMA telescope arrays towards some of the youngest protostars, this dissertation addresses a variety of important and outstanding questions regarding the frequency, dust properties, and role of magnetic fields at the earliest times. How is the presence of a young protostellar disk influenced by the magnetic fields of the system? We examine subarcsecond (∼0.35′′) resolved CARMA polarization observations of the 1.3 mm dust polarization from the disk around the Class 0 protostar L1527 to understand the inferred magnetic field morphology of the system on 50 AU size scales. L1527 is the first Class 0 protostar with direct detection of linearly polarized dust emission from the circumstellar disk, indicating magnetic fields are aligned perpendicular to the rotation axis of the disk, consistent with disk-wrapped toroidal field lines. By studying disk-scale fields, we can explore if misaligned magnetic fields and rotation axis can allow enough angular momentum to remain in the system at early times to support a disk. What is the frequency of large Class 0 and I protostellar disks, and what are their properties? We analyze dust continuum emission data toward all young protostellar disk candidates around Class 0 and I sources in the Perseus molecular cloud from the 8 mm VLA Nascent Disk and Multiplicity (VANDAM) survey with ∼0.05′′ or 12 AU resolution, revealing 19 new candidate disks in the Class 0 and I phases. The survey of young protostars is the most sensitive and complete survey to-date, allowing us to understand how common large young disks are. Because we lack kinematic data on small scales to confirm any resolved, elongated structures as rotationally supported disks, we fit the deprojected, averaged, and binned data in the u,v-plane to a disk-shaped profile to determine which sources are disk candidates and model disk properties. How early can disk dust substructures, possible signs of early planet formation, be found in young disks? We study the 1.3 mm ALMA dust continuum of the disk around the Class I source IRS 63 with 7 AU resolution to search for rings and gaps in a young protostellar disk. We found a series of concentric rings and gaps in the disk, centered around the protostar. Gaps are usually attributed to planet-disk interactions, although other phenomena such as volatile snowlines, dead zones, and gravitational instabilities can produce structures in protostellar disks. Previous studies of disk substructure have revealed gaps in only the disks of more evolved Class II sources such as HL Tau. Since rings and gaps are observed in IRS 63, then planet formation or other associated disk sculpting must have started early in the Class I phase or before.
Issue Date:2017-09-01
Rights Information:Copyright 2017 by Dominique M. Segura-Cox. All rights reserved.
Date Available in IDEALS:2018-03-13
Date Deposited:2017-12

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