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

Young stellar objects;envelopes;bipolar outflows;disks;Bayesian inference;visibility modeling;Grain Growth;magnetic fields;radio interferometry;Berkeley-Illinois-Maryland Association (BIMA);Combined Array for Research in Millimeter-wave Astronomy (CARMA);L1448 IRS 2;L1448 IRS 3;L1157;CI Tau;DL Tau;DO Tau;FT Tau;Haro 6-13;HL Tau

Kwon, Woojin

关键词: Young stellar objects;    envelopes;    bipolar outflows;    disks;    Bayesian inference;    visibility modeling;    Grain Growth;    magnetic fields;    radio interferometry;    Berkeley-Illinois-Maryland Association (BIMA);    Combined Array for Research in Millimeter-wave Astronomy (CARMA);    L1448 IRS 2;    L1448 IRS 3;    L1157;    CI Tau;    DL Tau;    DO Tau;    FT Tau;    Haro 6-13;    HL Tau;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/14711/Kwon_Woojin.pdf?sequence=2&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Physical properties of the three main structures in young stellar objects (YSOs), envelopes,bipolar outflows, and circumstellar disks, have been studied using radio interferometers: theBerkeley-Illinois-Maryland Association (BIMA) array and the Combined Array for Researchin Millimeter-wave Astronomy (CARMA).(1) Envelopes: Three Class 0 YSOs (L1448 IRS 2, L1448 IRS 3, and L1157) havebeen 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 grainshave significantly grown already at the earliest stage. In addition, we discussed the radialdependence of the dust opacity spectral index detected in L1448 IRS 3B and also estimated the density distribution ofthe 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 L1448IRS 3, which has three Class 0 YSOs, using BIMA. We clearly identified two interactingbipolar 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, weshowed that the “binary system” can be bound gravitationally and we estimated the specificangular momentum, which is between those of binary stars and molecular cloud cores. Inaddition, we marginally detected linear polarizations at the center of IRS 3B (implying atoroidal 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, DOTau, FT Tau, Haro 6-13, and HL Tau) in our T Tauri disk survey using CARMA. Thedata 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 andviscous 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 ofHL Tau, which is gravitationally unstable and can be fragmented. Besides, CI Tau andDL Tau appear to have a spiral pattern. Moreover, we found that more evolved diskshave a shallower density gradient and that disks with a smaller dust opacity spectral index are less massive, whichimplies “hidden” masses in the cold midplane and/or in large grains. Finally, we found thatthe 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 experienceddust settlement and has weak accretion. This implies that the accretion disk model couldbe applied to disks only in a limited age range.