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Circumstellar Structure Properties of Young Stellar Objects: Envelopes, Bipolar Outflows, and Disks

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Title: Circumstellar Structure Properties of Young Stellar Objects: Envelopes, Bipolar Outflows, and Disks
Author(s): Kwon, Woojin
Director of Research: Looney, Leslie W.
Doctoral Committee Chair(s): Looney, Leslie W.
Doctoral Committee Member(s): Crutcher, Richard M.; Gammie, Charles F.; McCall, Benjamin J.; Sutton, Edmund C.
Department / Program: Astronomy
Discipline: Astronomy
Degree Granting Institution: University of Illinois at Urbana-Champaign
Degree: Ph.D.
Genre: Dissertation
Subject(s): Young stellar objects envelopes bipolar outflows disks Bayesian inference visibility modeling grain growth magnetic fields radio interferometry BIMA CARMA L1448 IRS 2 L1448 IRS 3 L1157 CI Tau DL Tau DO Tau FT Tau Haro 6-13 HL Tau
Abstract: Physical properties of the three main structures in young stellar objects (YSOs), envelopes, bipolar outflows, and circumstellar disks, have been studied using radio interferometers: the Berkeley-Illinois-Maryland Association (BIMA) array and the Combined Array for Research in Millimeter-wave Astronomy (CARMA). (1) Envelopes: Three Class 0 YSOs (L1448 IRS 2, L1448 IRS 3, and L1157) have been observed by CARMA at 1.3 mm and 2.7 mm continuum. Through visibility modeling to fit the two wavelength continuum data simultaneously, we found that the dust opacity spectral index of Class 0 YSOs is around unity, which implies that dust grains have significantly grown already at the earliest stage. In addition, we discussed the radial dependence of the dust opacity spectral index detected in L1448 IRS 3B and also estimated the density distribution of the three targets. (2) Bipolar outflows: Polarimetric observations in the 1.3 mm continuum and CO, as well as spectral line observations in 13CO and C18O have been carried out toward L1448 IRS 3, which has three Class 0 YSOs, using BIMA. We clearly identified two interacting bipolar outflows from the “binary system” of IRS 3A and 3B and estimated the velocity, inclination, and opening angle of the 3B bipolar outflow, using Bayesian inference. Also, we showed that the “binary system” can be bound gravitationally and we estimated the specific angular momentum, which is between those of binary stars and molecular cloud cores. In addition, we marginally detected linear polarizations at the center of IRS 3B (implying a toroidal magnetic field) in continuum and at the bipolar outflow region in CO. (3) Circumstellar disks: We present the results of 6 objects (CI Tau, DL Tau, DO Tau, FT Tau, Haro 6-13, and HL Tau) in our T Tauri disk survey using CARMA. The data consist of 1.3 mm and 2.7 mm continuum with an angular resolution up to 0.13′′. Through visibility modeling of two disk models (power-law disk with a Gaussian edge and viscous accretion disk) to fit the two wavelength data simultaneously in Bayesian inference, we constrained disk properties. In addition, we detected a dust lane at 100 AU radius of HL Tau, which is gravitationally unstable and can be fragmented. Besides, CI Tau and DL Tau appear to have a spiral pattern. Moreover, we found that more evolved disks have a shallower density gradient and that disks with a smaller dust opacity spectral index are less massive, which implies “hidden” masses in the cold midplane and/or in large grains. Finally, we found that the accretion disk model is preferred by HL Tau, which has a strong bipolar outflow and accretion, while the power-law disk model is preferred by DL Tau, which has experienced dust settlement and has weak accretion. This implies that the accretion disk model could be applied to disks only in a limited age range.
Issue Date: 2010-01-06
URI: http://hdl.handle.net/2142/14711
Rights Information: Copyright 2009 Woojin Kwon
Date Available in IDEALS: 2012-01-07
Date Deposited: December 2
 

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