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Measuring the solar atmosphere
Stockholm University, Faculty of Science, Department of Astronomy.
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The new CRISP filter at the Swedish 1-m Solar Telescope provides opportunities for observing the solar atmosphere with unprecedented spatial resolution and cadence. In order to benefit from the high quality of observational data from this instrument, we have developed methods for calibrating and restoring polarized Stokes images, obtained at optical and near infrared wavelengths, taking into account field-of-view variations of the filter properties.

In order to facilitate velocity measurements, a time series from a 3D hydrodynamical granulation simulation is used to compute quiet Sun spectral line profiles at different heliocentric angles. The synthetic line profiles, with their convective blueshifts, can be used as absolute references for line-of-sight velocities.

Observations of the Ca II 8542 Å line are used to study magnetic fields in chromospheric fibrils. The line wings show the granulation pattern at mid-photospheric heights whereas the overlying chromosphere is seen in the core of the line. Using full Stokes data, we have attempted to observationally verify the alignment of chromospheric fibrils with the magnetic field. Our results suggest that in most cases fibrils are aligned along the magnetic field direction, but we also find examples where this is not the case.

Detailed interpretation of Stokes data from spectral lines formed in the chromospheric data can be made using non-LTE inversion codes. For the first time, we use a realistic 3D MHD chromospheric simulation of the quiet Sun to assess how well NLTE inversions recover physical quantities from spectropolarimetric observations of Ca II 8542 Å. We demonstrate that inversions provide realistic estimates of depth-averaged quantities in the chromosphere, although high spectral resolution and high sensitivity are needed to measure quiet Sun chromospheric magnetic fields.

Place, publisher, year, edition, pages
Stockholm: Department of Astronomy, Stockholm University , 2010. , 51 p.
Keyword [en]
Sun, Chromosphere, Spectropolarimetry, Solar observations, Spectral lines, Solar magnetic fields
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
URN: urn:nbn:se:su:diva-43646ISBN: 978-91-7447-154-0 (print)OAI: oai:DiVA.org:su-43646DiVA: diva2:358793
Public defence
2010-11-26, FB42, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:15 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Submitted. Paper 2: Manuscript. Paper 3: Submitted. Paper 4: Submitted.Available from: 2010-11-03 Created: 2010-10-25 Last updated: 2010-11-03Bibliographically approved
List of papers
1. Solar velocity references from 3D HD photospheric models
Open this publication in new window or tab >>Solar velocity references from 3D HD photospheric models
(English)Article in journal (Refereed) Submitted
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:su:diva-43641 (URN)
Available from: 2010-10-25 Created: 2010-10-25 Last updated: 2010-11-02Bibliographically approved
2. Non-LTE inversions from a 3D MHD chromospheric model
Open this publication in new window or tab >>Non-LTE inversions from a 3D MHD chromospheric model
(English)Manuscript (preprint) (Other academic)
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:su:diva-43642 (URN)
Available from: 2010-10-25 Created: 2010-10-25 Last updated: 2010-11-02Bibliographically approved
3. Are solar chromospheric fibrils tracing the magnetic field?
Open this publication in new window or tab >>Are solar chromospheric fibrils tracing the magnetic field?
(English)Article in journal (Refereed) Submitted
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:su:diva-43644 (URN)
Available from: 2010-10-25 Created: 2010-10-25 Last updated: 2010-11-02Bibliographically approved
4. Stokes imaging polarimetry using image restoration at the Swedish 1-m Solar Telescope II: A calibration strategy for Fabry-Perot based instruments
Open this publication in new window or tab >>Stokes imaging polarimetry using image restoration at the Swedish 1-m Solar Telescope II: A calibration strategy for Fabry-Perot based instruments
(English)Article in journal (Refereed) Submitted
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:su:diva-43647 (URN)
Available from: 2010-10-25 Created: 2010-10-25 Last updated: 2010-11-02Bibliographically approved

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