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An Observational Study of Accretion Processes in T Tauri Stars
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics.
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. , p. 33
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 841
Keyword [en]
Astronomy, Star formation, T Tauri stars, Emission lines, Accretion, NLTE radiative transfer
Keyword [sv]
Astronomi
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
URN: urn:nbn:se:uu:diva-3420ISBN: 91-554-5634-0 (print)OAI: oai:DiVA.org:uu-3420DiVA, id: diva2:162741
Public defence
2003-05-26, Polhemsalen, Ångströmlaboratoriet, Uppsala, 13:15
Opponent
Supervisors
Available from: 2003-05-05 Created: 2003-05-05 Last updated: 2012-02-27Bibliographically approved
List of papers
1. Formation of Fe X-Fe XIV coronal lines in the accretion shock of T Tauri stars
Open this publication in new window or tab >>Formation of Fe X-Fe XIV coronal lines in the accretion shock of T Tauri stars
2001 (English)In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 369, no -, p. 965-970Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-90396 (URN)
Available from: 2003-05-05 Created: 2003-05-05 Last updated: 2012-02-27Bibliographically approved
2. Spectroscopy of T Tauri stars with UVES: Observations and analysis of RU Lup
Open this publication in new window or tab >>Spectroscopy of T Tauri stars with UVES: Observations and analysis of RU Lup
2002 (English)In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 391, no -, p. 595-608Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-90397 (URN)
Available from: 2003-05-05 Created: 2003-05-05 Last updated: 2012-02-27Bibliographically approved
3. The Photosphere and Veiling Spectrum of T Tauri Stars
Open this publication in new window or tab >>The Photosphere and Veiling Spectrum of T Tauri Stars
2003 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 408, no 2, p. 693-706Article in journal (Refereed) Published
Abstract [en]

Using recent high signal-to-noise and high spectral resolution ( ) observations with VLT/UVES, we have analysed the photosphere and veiling spectrum of five T Tauri stars. With a grid of 1-dimensional plane-parallel hydrostatic model atmospheres from the MARCS consortium we have determined their atmospheric properties, calculated synthetic spectra and determined the spectrum of the veiling continuum. Our analysis of the veiling spectrum supports the view that veiling can be represented by a combination of continuum sources. However, for the most strongly accreting stars we find a broad region around 5300 Å where the derived level of veiling is consistently higher than expected from continuum sources.

National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-90398 (URN)10.1051/0004-6361:20030637 (DOI)
Available from: 2003-05-05 Created: 2003-05-05 Last updated: 2017-12-14Bibliographically approved
4. NLTE Calculations of Hydrogen Emission Lines in T Tauri Stars
Open this publication in new window or tab >>NLTE Calculations of Hydrogen Emission Lines in T Tauri Stars
(English)Manuscript (Other academic)
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-90399 (URN)
Available from: 2003-05-05 Created: 2003-05-05 Last updated: 2012-02-27Bibliographically approved
5. The close T Tauri binary V 4046 Sagitarii
Open this publication in new window or tab >>The close T Tauri binary V 4046 Sagitarii
(English)Manuscript (Other academic)
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-90400 (URN)
Available from: 2003-05-05 Created: 2003-05-05 Last updated: 2012-02-27Bibliographically approved

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