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Title:Probing planetary disks: from birth to protoplanets
Author(s):Cox, Erin Guilfoil
Director of Research:Looney, Leslie
Doctoral Committee Chair(s):Looney, Leslie
Doctoral Committee Member(s):Gammie, Charles; Liu, Xin; Wong, Tony
Department / Program:Astronomy
Discipline:Astronomy
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:Ph.D.
Genre:Dissertation
Subject(s):star formation
polarization
Abstract:Protoplanetary disks set the physical and chemical conditions for the planets that will eventually form inside of them. While the exact details of the process remain a large area of research, it is the gas and dust in these disks that will grow into planets. By the Class II phase of a protostar’s evolution, large disks are common (so there is a large mass reservoir available) and it is commonly assumed that most of the planet formation process occurs at this time. However, with the advent of high-sensitivity interferometers, such as the VLA or ALMA, we are finding that large disks can grow even at the earliest times of a protostars life (Class 0 phase). These young objects are heavily obscured in their dusty natal envelope and often carry information from the cloud with them (i.e., the local magnetic field). In fact, theoretical studies have shown that these fields can directly influence whether a disk can grow in Class 0 sources. Through observational studies of both evolved and young protostars, the research presented in this dissertation concentrates on observing planet formation via grain growth inferred by disk substructure, examining the role magnetic fields have in the youngest sources, and probing the way magnetic fields are traditionally inferred. I first present an unbiased survey of the evolved disks in the ρ Ophiuchus cloud using ALMA. I measured the flux and radius from ∼ 50 pre-main-sequence stellar systems. I found that binary systems are both dimmer and have smaller disks than their isolated components. I used these results to test if these disks were smaller due to tidal truncation, and found that the disks surrounding binaries in this cloud are too small to have been affected by truncation. This survey also revealed six transition and gapped disks, indicating active planet formation in these sources. I then present work examining the magnetic fields of the Class 0 protostar, IRAS 4A, to infer disk growth at young stages. This is the first result of the VANDAM survey and uses dust continuum polarization to infer the projected magnetic field morphology at disk-scales. I show that the inferred field has an azimuthal pattern, which appears to be from the field lines being dragged down to a rotating disk. Since this source is very well studied, I use previous sub-/millimeter flux data to show that large (∼ cm size) dust grains have grown in the 10kyr age of IRAS 4A. Then I show the results from an ALMA polarization study of ten protostars. Here we looked at dust continuum polarization observations of 3 sources that are candidate disks from 8 mm data, 2 sources that are likely fragmenting disks, 1 close binary and 4 sources that do not have discernible disks down to ∼ 12 au. I found that all sources show ordered polarization, as well as a low polarization fraction, in the inner ∼ 150 au and that outside of that radius, the polarization becomes higher and more disordered. The disk candidates all show a polarization morphology that is akin to self-scattering in the disk region. However, this morphology can also be attributed to a tightly wrapped toroidal field in an inclined disk. Lastly, since these observations probe the interface of an infalling envelope down to disk-scales, we see, possibly for the first time, that the polarization mechanism likely changes as the density increases. Finally, I present the full polarization results from the VANDAM survey. This survey observed all known protostars (Class 0 and Class I sources) in the Perseus Molecular Cloud using both A- and B-configuration (∼ 12 au and ∼ 50 au resolution, respectively) at Ka-band (8 mm and 1 cm) and using the A-configuration at C-band (4 cm and 6 cm). The main goals of VANDAM were to characterize the multiplicity of these young sources, and so the integration time was ∼ 30 minutes on each source. With these observations, I present the upper limits of polarization at ∼ 50 au. I find that most of the upper limits are ⪆ 30% peak polarization.
Issue Date:2018-07-11
Type:Thesis
URI:http://hdl.handle.net/2142/101701
Rights Information:Copyright 2018 Erin Guilfoil Cox
Date Available in IDEALS:2018-09-27
Date Deposited:2018-08


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