{"id":{"repo_id":"freiburg-diss","oai_identifier":"oai:freidok.uni-freiburg.de:2459"},"canonical_url":"https://search.dev.ndltd.org/etd/freiburg-diss/oai:freidok.uni-freiburg.de:2459","repository":{"repo_id":"freiburg-diss","name":"University of Freiburg","base_url":"https://freidok.uni-freiburg.de/oai/oai2.php"},"display":{"title":"High resolution spectroscopy of photospheric bright points","abstract":"Photospheric bright points are proxies for small-scale magnetic flux concentrations.
These magnetic elements are thought to be the building blocks of the solar magnetic field
and are important to understand many physical processes on the Sun, e.g. the variability of the solar irradiance.
Because of their small size (100-200 km in diameter) the observations of photospheric bright points put special requirements on the seeing conditions, instrumental setup and post-processing techniques.
The motivation of this work comes from theoretical predictions concerning flows associated with magnetic elements. Solar magneto-convection simulations indicate that the formationof these structures is accompanied with large downflows that can reach velocities of several km/s. In some cases, the downflowing gas may rebound in the deeper layers which can cause
an upward-propagating shock.
MHD simulations have usually much better resolution that observational data, so advanced observational techniques need to be applied to compare them.
Speckle reconstruction techniques are widely used to improve the quality of ground-based solar observations. To date, there have been no comprehensive analysis of photometric errors of the speckle reconstruction process and of the influence of the speckle deconvolution on spectral line profiles. In this thesis, the results of such an analysis are presented, followed by a conclusion that speckle-reconstructed spectral line profiles can be used for quantitative spectroscopy.
The data set presented in this thesis consists of speckle-reconstructed G-band images and quasi-simultaneous two-dimensional spectra in the neutral iron line at 557.6 nm. The choice of the G-band - a molecular bandhead at around 430 nm - for observations of photospheric bright points is motivated by their increased contrast with respect to the surroundings at this wavelength range.
In this analysis, spectral profiles were used to determine line-of-sight velocities at photospheric bright points locations. I found that the majority of bright points are associated with downflow regions, which is consistent with previous findings. Velocities derived from the line core (formed in higher photospheric layers)are reduced in comparison with velocities of the line wing which is formed lower in the atmosphere, in agreement with some theoretical predictions. Individual cases of photospheric bright points were studied in order to understand their interaction with surrounding granular flow. The maximum downflow usually do not coincides with the maximum G-band intensity. No downflows with velocities of few km/s as predicted by MHD simulations
have been found, but it may be due to the lack of sufficient spatial resolution.
There were only very few photospheric bright points in the analyzed data which showed upflows with respect to their immediate surroundings.","abstract_html":"Photospheric bright points are proxies for small-scale magnetic flux concentrations. <br>These magnetic elements are thought to be the building blocks of the solar magnetic field <br>and are important to understand many physical processes on the Sun, e.g. the variability of the solar irradiance. <br>Because of their small size (100-200 km in diameter) the observations of photospheric bright points put special requirements on the seeing conditions, instrumental setup and post-processing techniques. <br> <br> The motivation of this work comes from theoretical predictions concerning flows associated with magnetic elements. Solar magneto-convection simulations indicate that the formationof these structures is accompanied with large downflows that can reach velocities of several km/s. In some cases, the downflowing gas may rebound in the deeper layers which can cause <br>an upward-propagating shock. <br>MHD simulations have usually much better resolution that observational data, so advanced observational techniques need to be applied to compare them. <br> <br> Speckle reconstruction techniques are widely used to improve the quality of ground-based solar observations. To date, there have been no comprehensive analysis of photometric errors of the speckle reconstruction process and of the influence of the speckle deconvolution on spectral line profiles. In this thesis, the results of such an analysis are presented, followed by a conclusion that speckle-reconstructed spectral line profiles can be used for quantitative spectroscopy. <br> <br> The data set presented in this thesis consists of speckle-reconstructed G-band images and quasi-simultaneous two-dimensional spectra in the neutral iron line at 557.6 nm. The choice of the G-band - a molecular bandhead at around 430 nm - for observations of photospheric bright points is motivated by their increased contrast with respect to the surroundings at this wavelength range. <br> <br> In this analysis, spectral profiles were used to determine line-of-sight velocities at photospheric bright points locations. I found that the majority of bright points are associated with downflow regions, which is consistent with previous findings. Velocities derived from the line core (formed in higher photospheric layers)are reduced in comparison with velocities of the line wing which is formed lower in the atmosphere, in agreement with some theoretical predictions. Individual cases of photospheric bright points were studied in order to understand their interaction with surrounding granular flow. The maximum downflow usually do not coincides with the maximum G-band intensity. No downflows with velocities of few km/s as predicted by MHD simulations <br>have been found, but it may be due to the lack of sufficient spatial resolution. <br>There were only very few photospheric bright points in the analyzed data which showed upflows with respect to their immediate surroundings.","abstract_has_math":false,"creators":["Mikurda, Katarzyna"],"institution":null,"degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":null,"school":null,"contributors":["Lühe, Oskar von der"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":null,"date_issued":"","date_published":null,"updated_at":"2026-07-24T02:22:46Z","subjects":["Photosphäre, Photosphärische Bright Points","Sun, Photosphere, Spectroscopy, Photospheric Bright Points, Speckle Imaging"],"languages":[],"rights":[],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"https://freidok.uni-freiburg.de/data/2459","outbound_label":"Repository record","outbound_source":"source_url"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Lühe, Oskar von der"]},{"key":"dc:creator","label":"Author","values":["Mikurda, Katarzyna"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:type","label":"Dc Type","values":["DoctoralThesis"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Photosphäre, Photosphärische Bright Points","Sun, Photosphere, Spectroscopy, Photospheric Bright Points, Speckle Imaging"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["Photospheric bright points are proxies for small-scale magnetic flux concentrations.
These magnetic elements are thought to be the building blocks of the solar magnetic field
and are important to understand many physical processes on the Sun, e.g. the variability of the solar irradiance.
Because of their small size (100-200 km in diameter) the observations of photospheric bright points put special requirements on the seeing conditions, instrumental setup and post-processing techniques.
The motivation of this work comes from theoretical predictions concerning flows associated with magnetic elements. Solar magneto-convection simulations indicate that the formationof these structures is accompanied with large downflows that can reach velocities of several km/s. In some cases, the downflowing gas may rebound in the deeper layers which can cause
an upward-propagating shock.
MHD simulations have usually much better resolution that observational data, so advanced observational techniques need to be applied to compare them.
Speckle reconstruction techniques are widely used to improve the quality of ground-based solar observations. To date, there have been no comprehensive analysis of photometric errors of the speckle reconstruction process and of the influence of the speckle deconvolution on spectral line profiles. In this thesis, the results of such an analysis are presented, followed by a conclusion that speckle-reconstructed spectral line profiles can be used for quantitative spectroscopy.
The data set presented in this thesis consists of speckle-reconstructed G-band images and quasi-simultaneous two-dimensional spectra in the neutral iron line at 557.6 nm. The choice of the G-band - a molecular bandhead at around 430 nm - for observations of photospheric bright points is motivated by their increased contrast with respect to the surroundings at this wavelength range.
In this analysis, spectral profiles were used to determine line-of-sight velocities at photospheric bright points locations. I found that the majority of bright points are associated with downflow regions, which is consistent with previous findings. Velocities derived from the line core (formed in higher photospheric layers)are reduced in comparison with velocities of the line wing which is formed lower in the atmosphere, in agreement with some theoretical predictions. Individual cases of photospheric bright points were studied in order to understand their interaction with surrounding granular flow. The maximum downflow usually do not coincides with the maximum G-band intensity. No downflows with velocities of few km/s as predicted by MHD simulations
have been found, but it may be due to the lack of sufficient spatial resolution.
There were only very few photospheric bright points in the analyzed data which showed upflows with respect to their immediate surroundings.","Photosphärische Bright Points sind Proxies von kleinskaligen magnetischen Flusskonzentrationen.
Man glaubt das diese magnetischen Elemente Bausteine des solaren magnetischen Feldes sind, und somit als sehr wichtig für das Verständnis von vielen physikalischen Prozessen unserer Sonnen
anzusehen sind (z.B. die Variabilität der solaren Irradiation.).
Wegen der geringen Größe von photosphärischen Bright Points (100-200 km im Durchmesser) gestaltet sich ihre Beobachtung schwierig und bedarf spezieller Anforderungen an das Seeing, dem instrumentellem
Setup und an post verarbeitenden Techniken.
Die Motivation der vorliegenden Arbeit leitet sich von der theoretischen Vorhersage von flussassoziierten magnetischen Elementen ab. Simulationen der solare Magnetokonvektion indizieren, dass die Entstehung dieser Strukturen in Begleitung mit großen Downflows in der Größenordnung
von mehreren km/s auftreten. In einigen Fällen konnte gezeigt werden, dass das Downflow-Gas in tieferen Lagen zurückprallt und somit aufwärts propagierende Schockwellen anregen kann. Üblicherweise haben MHD Simulationen eine höhere Auflösung als Beobachtungsmaterial, sodass fortschrittliche Beobachtungstechniken zur Verifikation der Simulationsergebnisse notwendig sind.
Speckle-Rekonstruktionsverfahren werden weitestgehend zur Qualitätsverbesserung von erdgebundenen solaren Beobachtungen verwendet. Bis jetzt gab es keine umfangreichen Analysen der photometrischen
Fehler von Speckle-Rekonstruktionsprozessen und deren Einflüsse auf die Speckle-Dekonvolution von spektralen Linienprofilen. In dieser Arbeit werden Ergebnisse solcher Analysen präsentiert mit der Schlussfolgerung, dass Speckle-rekonstruierte spektrale Linienprofile zur quantitativen Spektroskopie verwendet werden können.
In dieser Arbeit haben wir einen Datensatz bestehend aus speckle rekonstruierten G-Band Bildern und quasi simultanen 2-dimensionalen Spektren der neutralen Eisenlinie bei 577.6 nm verwendet.
Die Wahl des G-Band, das ein Molekül-Bandhead bei ungefähr 430 nm darstellt, für die Beobachtung von photosphärischen Bright Points zu verwenden ist über den ansteigenden Umgebungskontrast in diesem Wellenlängenbereich motiviert.
In der Analyse wurden Spektralprofile verwendet um die Line-of-Sight Geschwindigkeiten an den Lokationen von Bright Points zu bestimmen.
Im Zuge der Arbeit haben wir herausgefunden, dass ein Großteil der Bright Points mit Downflow Regionen assoziiert sind. Somit konnten vorherige Ergebnisse bestätigt werden. Die Geschwindigkeiten in den Linienkernen, welche in höheren photosphärischen Lagen entstehen, sind geringer im Vergleich zu den Geschwindigkeiten in den Linienflügeln, welche ihren Ursprung tiefer in der Atmosphäre haben. Diese Beobachtung steht in Einklang mit theoretischen Vorhersagen.
Einzelne Fälle von photosphärischen Bright Points wurden untersucht um die Interaktion mit der umliegenden Granulation besser zu verstehen.
Der maximale Downflow stimmt im Allgemeinen nicht mit der maximalen G-Band Intensität überein.
Heutige MHD Simulation sagen Downflows in der Größenordnung von einigen km/s voraus. Diese Vorhersagen konnten durch unsere Ergebnisse nicht bestätigt werden. Es besteht allerdings durchaus die Möglichkeit, dass unsere Ergebnisse auf eine eingeschränkte räumliche Auflösung zurückzuführen sind.
Es gab nur wenige photosphärische Bright Points in den Beobachtungsdaten, die Upflows im Zusammenhang mit deren unmittelbaren Umgebungen zeigten."]},{"key":"dc:format.medium","label":"Dc Format Medium","values":["application/pdf"]},{"key":"dc:title","label":"Title","values":["High resolution spectroscopy of photospheric bright points","Hochauflösende Spektroskopie von photosphärischen Bright Points"]}]}],"canonical_facts":{"dc:contributor":["Lühe, Oskar von der"],"dc:creator":["Mikurda, Katarzyna"],"dc:description.abstract":["Photospheric bright points are proxies for small-scale magnetic flux concentrations.
These magnetic elements are thought to be the building blocks of the solar magnetic field
and are important to understand many physical processes on the Sun, e.g. the variability of the solar irradiance.
Because of their small size (100-200 km in diameter) the observations of photospheric bright points put special requirements on the seeing conditions, instrumental setup and post-processing techniques.
The motivation of this work comes from theoretical predictions concerning flows associated with magnetic elements. Solar magneto-convection simulations indicate that the formationof these structures is accompanied with large downflows that can reach velocities of several km/s. In some cases, the downflowing gas may rebound in the deeper layers which can cause
an upward-propagating shock.
MHD simulations have usually much better resolution that observational data, so advanced observational techniques need to be applied to compare them.
Speckle reconstruction techniques are widely used to improve the quality of ground-based solar observations. To date, there have been no comprehensive analysis of photometric errors of the speckle reconstruction process and of the influence of the speckle deconvolution on spectral line profiles. In this thesis, the results of such an analysis are presented, followed by a conclusion that speckle-reconstructed spectral line profiles can be used for quantitative spectroscopy.
The data set presented in this thesis consists of speckle-reconstructed G-band images and quasi-simultaneous two-dimensional spectra in the neutral iron line at 557.6 nm. The choice of the G-band - a molecular bandhead at around 430 nm - for observations of photospheric bright points is motivated by their increased contrast with respect to the surroundings at this wavelength range.
In this analysis, spectral profiles were used to determine line-of-sight velocities at photospheric bright points locations. I found that the majority of bright points are associated with downflow regions, which is consistent with previous findings. Velocities derived from the line core (formed in higher photospheric layers)are reduced in comparison with velocities of the line wing which is formed lower in the atmosphere, in agreement with some theoretical predictions. Individual cases of photospheric bright points were studied in order to understand their interaction with surrounding granular flow. The maximum downflow usually do not coincides with the maximum G-band intensity. No downflows with velocities of few km/s as predicted by MHD simulations
have been found, but it may be due to the lack of sufficient spatial resolution.
There were only very few photospheric bright points in the analyzed data which showed upflows with respect to their immediate surroundings.","Photosphärische Bright Points sind Proxies von kleinskaligen magnetischen Flusskonzentrationen.
Man glaubt das diese magnetischen Elemente Bausteine des solaren magnetischen Feldes sind, und somit als sehr wichtig für das Verständnis von vielen physikalischen Prozessen unserer Sonnen
anzusehen sind (z.B. die Variabilität der solaren Irradiation.).
Wegen der geringen Größe von photosphärischen Bright Points (100-200 km im Durchmesser) gestaltet sich ihre Beobachtung schwierig und bedarf spezieller Anforderungen an das Seeing, dem instrumentellem
Setup und an post verarbeitenden Techniken.
Die Motivation der vorliegenden Arbeit leitet sich von der theoretischen Vorhersage von flussassoziierten magnetischen Elementen ab. Simulationen der solare Magnetokonvektion indizieren, dass die Entstehung dieser Strukturen in Begleitung mit großen Downflows in der Größenordnung
von mehreren km/s auftreten. In einigen Fällen konnte gezeigt werden, dass das Downflow-Gas in tieferen Lagen zurückprallt und somit aufwärts propagierende Schockwellen anregen kann. Üblicherweise haben MHD Simulationen eine höhere Auflösung als Beobachtungsmaterial, sodass fortschrittliche Beobachtungstechniken zur Verifikation der Simulationsergebnisse notwendig sind.
Speckle-Rekonstruktionsverfahren werden weitestgehend zur Qualitätsverbesserung von erdgebundenen solaren Beobachtungen verwendet. Bis jetzt gab es keine umfangreichen Analysen der photometrischen
Fehler von Speckle-Rekonstruktionsprozessen und deren Einflüsse auf die Speckle-Dekonvolution von spektralen Linienprofilen. In dieser Arbeit werden Ergebnisse solcher Analysen präsentiert mit der Schlussfolgerung, dass Speckle-rekonstruierte spektrale Linienprofile zur quantitativen Spektroskopie verwendet werden können.
In dieser Arbeit haben wir einen Datensatz bestehend aus speckle rekonstruierten G-Band Bildern und quasi simultanen 2-dimensionalen Spektren der neutralen Eisenlinie bei 577.6 nm verwendet.
Die Wahl des G-Band, das ein Molekül-Bandhead bei ungefähr 430 nm darstellt, für die Beobachtung von photosphärischen Bright Points zu verwenden ist über den ansteigenden Umgebungskontrast in diesem Wellenlängenbereich motiviert.
In der Analyse wurden Spektralprofile verwendet um die Line-of-Sight Geschwindigkeiten an den Lokationen von Bright Points zu bestimmen.
Im Zuge der Arbeit haben wir herausgefunden, dass ein Großteil der Bright Points mit Downflow Regionen assoziiert sind. Somit konnten vorherige Ergebnisse bestätigt werden. Die Geschwindigkeiten in den Linienkernen, welche in höheren photosphärischen Lagen entstehen, sind geringer im Vergleich zu den Geschwindigkeiten in den Linienflügeln, welche ihren Ursprung tiefer in der Atmosphäre haben. Diese Beobachtung steht in Einklang mit theoretischen Vorhersagen.
Einzelne Fälle von photosphärischen Bright Points wurden untersucht um die Interaktion mit der umliegenden Granulation besser zu verstehen.
Der maximale Downflow stimmt im Allgemeinen nicht mit der maximalen G-Band Intensität überein.
Heutige MHD Simulation sagen Downflows in der Größenordnung von einigen km/s voraus. Diese Vorhersagen konnten durch unsere Ergebnisse nicht bestätigt werden. Es besteht allerdings durchaus die Möglichkeit, dass unsere Ergebnisse auf eine eingeschränkte räumliche Auflösung zurückzuführen sind.
Es gab nur wenige photosphärische Bright Points in den Beobachtungsdaten, die Upflows im Zusammenhang mit deren unmittelbaren Umgebungen zeigten."],"dc:format.medium":["application/pdf"],"dc:subject":["Photosphäre, Photosphärische Bright Points","Sun, Photosphere, Spectroscopy, Photospheric Bright Points, Speckle Imaging"],"dc:title":["High resolution spectroscopy of photospheric bright points","Hochauflösende Spektroskopie von photosphärischen Bright Points"],"dc:type":["DoctoralThesis"]},"updated_at":"2026-07-24T02:22:46Z"}