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Three-dimensional temperature mapping of solar photospheric fine structure using Ca II H filtergrams
Stockholm University, Faculty of Science, Department of Astronomy.
2012 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 548, A114- p.Article in journal (Refereed) Published
Abstract [en]

Context. The wings of the Ca II H and K lines provide excellent photospheric temperature diagnostics. At the Swedish 1-m Solar Telescope (SST), the blue wing of Ca II H is scanned with a narrowband interference filter mounted on a rotation stage. This provides up to 0 ''.10 spatial resolution filtergrams at high cadence that are concurrent with other diagnostics at longer wavelengths. Aims. The aim is to develop observational techniques that provide photospheric temperature stratification at the highest spatial resolution possible and use them to compare simulations and observations at different heights. Methods. We use filtergrams in the Ca II H blue wing that were obtained with a tiltable interference filter at the SST. Synthetic observations are produced from three-dimensional (3D) hydro and magneto-hydrodynamic numerical simulations and degraded to match the observations. The temperature structure obtained from applying the method to the synthetic data is compared with the known structure in the simulated atmospheres and with observations of an active region. Cross-correlation techniques using restored non-simultaneous continuum images are used to reduce high-altitude, small-scale seeing signal introduced from the non-simultaneity of the frames when differentiating data. Results. Temperature extraction using high-resolution filtergrams in the Ca II H blue wing works reasonably well when tested with simulated 3D atmospheres. The cross-correlation technique successfully compensates for the problem of small-scale seeing differences and provides a measure of the spurious signal from this source in differentiated data. Synthesized data from the simulated atmospheres (including pores) match well the observations morphologically at different observed heights and in vertical temperature gradients.

Place, publisher, year, edition, pages
2012. Vol. 548, A114- p.
Keyword [en]
techniques: image processing, Sun: faculae, plages, Sun: granulation, Sun: photosphere, Sun: magnetic topology, techniques: high angular resolution
National Category
Astronomy, Astrophysics and Cosmology
URN: urn:nbn:se:su:diva-86487DOI: 10.1051/0004-6361/201220344ISI: 000311901200114OAI: diva2:587222


Available from: 2013-01-14 Created: 2013-01-14 Last updated: 2013-01-21Bibliographically approved
In thesis
1. Three-dimensional mapping of fine structure in the solar atmosphere
Open this publication in new window or tab >>Three-dimensional mapping of fine structure in the solar atmosphere
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The effects on image formation through a tilted interference filter in a converging beam are investigated and an adequate compensation procedure is established. A method that compensates for small-scale seeing distortions is also developed with the aim of co-aligning non-simultaneous solar images from different passbands. These techniques are applied to data acquired with a narrow tiltable filter at the Swedish 1-meter Solar Telescope. Tilting provides a way to scan the wing of the Ca II H line. The resulting images are used to map the temperature stratification and vertical temperature gradients in a solar active region containing a sunspot at a resolution approaching 0''10. The data are compared with hydro-dynamical quiet sun models and magneto-hydrodynamic models of plage. The comparison gives credence to the observational techniques, the analysis methods, and the simulations. Vertical temperature gradients are lower in magnetic structures than in non-magnetic.

Line-of-sight velocities and magnetic field properties in the penumbra of the same sunspot are estimated using the CRISP imaging spectropolarimeter and straylight compensation adequate for the data. These reveal a pattern of upflows and downflows throughout the entire penumbra including the interior penumbra. A correlation with intensity positively identifies these flows as convective in origin. The vertical convective signatures are observed everywhere, but the horizontal Evershed flow is observed to be confined to areas of nearly horizontal magnetic field. 

The relation between temperature gradient and total circular polarization in magnetically sensitive lines is investigated in different structures of the penumbra. Penumbral dark cores are prominent in total circular polarization and temperature gradient maps. These become longer and more contiguous with increasing height. Dark fibril structures over bright regions are observed in the Ca II H line core, above both the umbra and penumbra.

Place, publisher, year, edition, pages
Stockholm: Department of Astronomy, Stockholm University, 2013. 41 p.
Sun, sunspots, Swedish 1-meter Solar Telescope, active regions, image processing, sunspot penumbra
National Category
Astronomy, Astrophysics and Cosmology
Research subject
urn:nbn:se:su:diva-86798 (URN)978-91-7447-634-7 (ISBN)
Public defence
2013-02-15, sal FB52, Albanova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 3: Manuscript.

Available from: 2013-01-24 Created: 2013-01-18 Last updated: 2013-01-24Bibliographically approved

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Henriques, Vasco M. J.
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