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Formation of Fe X-Fe XIV coronal lines in the accretion shock of T Tauri stars
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics.
2001 (English)In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 369, no -, 965-970 p.Article in journal (Refereed) Published
Place, publisher, year, edition, pages
2001. Vol. 369, no -, 965-970 p.
URN: urn:nbn:se:uu:diva-90396OAI: oai:DiVA.org:uu-90396DiVA: diva2:162736
Available from: 2003-05-05 Created: 2003-05-05 Last updated: 2012-02-27Bibliographically approved
In thesis
1. An Observational Study of Accretion Processes in T Tauri Stars
Open this publication in new window or tab >>An Observational Study of Accretion Processes in T Tauri Stars
2003 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is a detailed observational study of the accretion processes in T Tauri stars (TTS). The interaction between the central star, the circumstellar disk and the magnetic field gives rise to a wide range of features in the spectra of TTS. The current picture of TTS is based on rather simple models assuming that accretion is a homogeneous and axisymmetric process. Although these models have been successful in explaining some observational signatures of TTS such as the shape of emission lines, the static nature of these models makes them unsuitable for describing the strong variability of the veiling spectrum and emission lines of TTS. An improved understanding of this variability is of key importance to study the dynamic processes related to the accretion flow and the winds.

This study is based on a set of high-quality spectroscopic observations with the UVES spectrograph at the 8-m VLT in 2000 and 2002. These spectra, with exposure times as short as 10-15 minutes, have high spectral resolution and high signal-to-noise ratios and cover a large part of the optical wavelength range. From this dataset we determine the basic physical parameters of several TTS and model their photospheres. These models then serve as a basis for a detailed investigation of variations of the veiling continuum and line emission. We confirm that the level of veiling correlates with some of the strongest emission lines and that coherent changes in accretion occur on a timescale of a few hours, comparable to the free-fall time from the disk to the star. From the properties of the emission lines formed close to the central star and in the stellar wind we derive restrictions on the geometry of the observed systems.

Because the intrinsic axial symmetry of a single star makes it almost impossible to disentangle rotational modulation from inhomogeneity and axial asymmetry of the accretion flow, we study a series of spectra of a close spectroscopic binary at different orbital phases and derive the 3D structure of flows between the disk and the star. Finally, we calculate the profiles of hydrogen emission lines by iteratively solving 3D NLTE radiative transfer in a state-of-the-art magnetospheric model.

Place, publisher, year, edition, pages
Uppsala: Institutionen för astronomi och rymdfysik, 2003. 33 p.
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 841
Astronomy, Star formation, T Tauri stars, Emission lines, Accretion, NLTE radiative transfer, Astronomi
National Category
Astronomy, Astrophysics and Cosmology
Research subject
urn:nbn:se:uu:diva-3420 (URN)91-554-5634-0 (ISBN)
Public defence
2003-05-26, Polhemsalen, Ångströmlaboratoriet, Uppsala, 13:15
Available from: 2003-05-05 Created: 2003-05-05 Last updated: 2012-02-27Bibliographically approved

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Stempels, H.C.
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