Universität zu Köln

Wojtczak, Jan Alexander (2024). Accretion-ejection mechanisms in the inner disk of T Tauri stars - A study with VLTI GRAVITY. PhD thesis, Universität zu Köln.

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Abstract

The fundamental aim of the project described in this thesis was to explore how well spatially resolved observations of the inner regions of T Tauri stars would line up with the theoretical predictions of the magnetospheric accretion paradigm. To this end, interferometric data obtained for a sample of 7 T Tauri stars with VLTI GRAVITY was analysed. This data contains the K-band continuum emission originating from the hot dust of the inner disk, as well as the Bracket-Gamma hydrogen recombination line. The line spectra, interferometric visibilities and interferometric differential phases were used to spatially constrain the emission region, using GRAVITY’s high resolution (R=4000) mode to derive spectrally dispersed characteristic sizes in 13 different spectral channels across the line profile. These sizes were compared against the co- rotation radii of stars, which served as proxies for the actual magnetospheric truncation radius. Additionally, the relative photocenter offsets of the Brγ emission region were deprojected from the differential phase data for the same spectral channels, creating photocenter shift profiles of the line. In order to gain a better understanding of the expected signatures across the line for these observables, I made use of radiative transfer simulations of an axisymmetric magnetospheric accretion model. From the simulated image, synthetic interferometric observables were computed and compared against the observational trends. I found again that the magnetospheric accretion scenario was only able to match the two weakest accretors in the sample well, whereas the behaviour of the observables at high red- and blushifted velocities did not align with the model predictions. In the final part of the project, I extended the radiative transfer simulations to include not only a larger parameter grid, as well as non-axisymmetric magnetospheric configurations, but most importantly an analytical, parametric disk wind model.

Item Type:	Thesis (PhD thesis)
Translated title:	Title Language UNSPECIFIED German
Creators:	Creators Email ORCID ORCID Put Code Wojtczak, Jan Alexander wojtczak@ph1.uni-koeln.de UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-734798
Date:	2024
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Physics > Institute of Physics I
Subjects:	Physics
Uncontrolled Keywords:	Keywords Language Astronomy, Astrophysics, YSOs, Star formation, VLTI, GRAVITY, T Tauri stars, circumstellar disk English
Date of oral exam:	28 May 2024
Referee:	Name Academic Title Labadie, Lucas Prof. Dr. Walch-Gassner, Stefanie Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/73479