Use this URL to cite or link to this record in EThOS: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.795232
Title: Resolving the gas distribution and kinematics in the inner regions of protoplanetary disks
Author: Hone, E.
ISNI:       0000 0004 8502 6794
Awarding Body: University of Exeter
Current Institution: University of Exeter
Date of Award: 2020
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Abstract:
Star formation can be characterised by the presence of accretion disks and outflows that originate from the inner regions of these disks. Despite playing a crucial role in the star formation process, the mechanism by which jets are formed is unknown. The jets appear to originate from the very inner regions of protoplanetary disks, making it difficult to observe thejet-launchingregionbyconventionalmeans. Inordertoachievethehigh-angularresolutionrequiredtoobservetheinnerdiskitisnecessarytoobservewithopticalinterferometry. In this thesis I aim to answer the question of how astrophysical jets and winds are launched from the inner regions of circumstellar disks by observing with spectrally dispersed interferometry in the near-infrared wavelength regime. In this thesis I present near-infrared, K-band VLTI/AMBER and VLT/CRIRES observations of the Herbig B[e] star MWC297. I interpret velocity-resolved images across the Brγ line, aswellas thederivedtwo-dimensionalphotocentredisplacementvectors, andfitkinematic models to our visibility and phase data in order to constrain the gas velocity field on sub-AUscales. Thevelocity-resolvedchannelmapsandmomentmapsrevealthemotionof the Brγ-emitting gas in six velocity channels, marking the first time that kinematic effects in the sub-AU inner regions of a protoplanetary disk could be directly imaged. The Brγ photocentre shifts trace a rotation-dominated velocity field, where the blue- and red-shifted emissions are displaced along a position angle of 24◦±3◦ and the approaching part of the disk is offset west of the star. The visibility drop in the line as well as the strong non-zero phase signals are modeled using a disk-wind model with a poloidal velocity of∼20kms−1. Simulations show that adding a poloidal velocity component causes the perceived system axis to shift, offeringapowerful newdiagnostic for thedetectionof non-Keplerianvelocity fields. In addition to the K-band data, I present analysis of AMBER spectro-interferometric data for MWC297 in the H-band, spectrally and spatially resolving multiple different Brackett series lines. I use the differential phase data to construct photocentre displacement vectors for each of the Brackett series lines, which show that all the lines in the H-band trace a similar velocity field. I construct a global kinematic model for the whole H-band, with the results showing that the H-band Brackett series lines originate from a compact disk wind region, with a poloidal velocity of∼220kms−1. I also present AMBER and CHARA interferometry data along with CRIRES spectroscopy data (R = 100000) of the Herbig Be star MWC147. The continuum emission is fitted with aninclinedGaussianandaringwitharadiusof0.60mas(0.39au),whichiswellwithinthe expected dust sublimation radius of 1.52 au. No significant change is detected in the measured visibilities across the Brγ line, indicating that the line-emitting gas is located in the same region as the continuum-emitting disk. The differential phase data is used to construct photocentre displacement vectors across the Brγ line, revealing a velocity profile consistent with a rotating disk. The AMBER spectro-interferometry data is fitted with a kinematic model of a disk in Keplerian rotation, where both the line-emitting and continuum-emitting components of the disk originate from the same compact region close to the central star. The presence of line-emitting gas in the same region as the K-band continuum supports the interpretation that the K-band continuum traces an optically thick gas disk. I present spectro-interferometric observations of the Brγ emission from the the T Tauri star CW Tau. I construct photocentre shifts from the GRAVITY differential phase data, which indicate motion along a PA of 120.5◦ which is close to the previously observed jet axis for this object. This suggests that the velocity field traced by the Brγ emission of CW Tau traces a high-velocity outflow close to the radius where the disk is truncated by the stellar magnetic field. Each of the individual studies in this work introduces a new insight into the jet-launching region of young stellar objects. I use observations with high-spatial and high-spectral resolution to place strong physical constraints on the morphology and velocity fields of the jet-launching regions in young stars. The technical achievements presented in this thesis demonstrate the effectiveness of spectro-interferometry as a tool for studying the dynamic physical processes associated with star formation.
Supervisor: Stefan, K. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.795232  DOI: Not available
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