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Introduction
Additional affiliations
August 2021 - December 2022
December 2016 - June 2021
November 2011 - November 2016
Education
April 2014 - November 2016
October 2012 - March 2014
October 2009 - September 2012
Publications
Publications (65)
With the steady improvement of the observing capabilities and numerical simulations, an efficient data management of large data volumes has become mandatory. The Institute for Solar Physics (KIS) has developed the Science Data Centre (SDC), a data infrastructure to store, curate, and disseminate science-ready data from the German solar-observing fa...
o he Observatory for Solar and Environmental Research (KSO; Austria) provide regular full-disk observations of the Sun in the core of the chromospheric Halpha absorption line. In this paper, we present a deep learning method that provides reliable extractions of solar filaments from Halpha filtergrams. First, we trained the object detection algorit...
We compare a method for inferring the photospheric vector magnetic field using only spectroscopy to a conventional method based on polarimetry. The magnetic field strength B and inclination angle can be inferred from the Zeeman splitting using only Stokes I . We applied this method to a sunspot observed with the Vacuum Tower Telescope and compared...
Context. Our understanding of the solar magnetic coronal structure is tightly linked to the shape of open field regions, specifically coronal holes. A dynamically evolving coronal hole coincides with the local restructuring of open to closed magnetic field, which leads to changes in the interplanetary solar wind structure.
Aims. By investigating th...
The European Solar Telescope (EST) is a project aimed at studying the magnetic connectivity of the solar atmosphere, from the deep photosphere to the upper chromosphere. Its design combines the knowledge and expertise gathered by the European solar physics community during the construction and operation of state-of-the-art solar telescopes operatin...
The strong chromospheric absorption lines Ca H & K are tightly connected to stellar surface magnetic fields. Only for the Sun, spectral activity indices can be related to evolving magnetic features on the solar disk. The Solar Disk-Integrated (SDI) telescope feeds the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) of the Large Bi...
The strong chromospheric absorption lines Ca ii H & K are tightly connected to stellar surface magnetic fields. Only for the Sun, spectral activity indices can be related to evolving magnetic features on the solar disk. The Solar Disk‐Integrated (SDI) telescope feeds the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) of the Large...
Context. The chromospheric H α spectral line is a strong line in the spectrum of the Sun and other stars. In the stellar regime, this spectral line is already used as a powerful tracer of stellar activity. For the Sun, other tracers, such as Ca II K, are typically used to monitor solar activity. Nonetheless, the Sun is observed constantly in H α wi...
The chromospheric H-alpha spectral line is a strong line in the spectrum of the Sun and other stars. In the stellar regime, this spectral line is already used as a powerful tracer of stellar activity. For the Sun, other tracers (i.e, CaII K) are typically used to monitor solar activity. We used observations of full-disk H-alpha filtergrams of the C...
Aims. In this work, we explore the spectral window containing Fraunhofer lines formed in the solar photosphere, around the magnetically sensitive Cr I lines at 5780.9, 5781.1, 5781.7, 5783.0, and 5783.8 Å, with Landé g -factors between 1.6 and 2.5. The goal is to simultaneously analyze 15 spectral lines, comprising Cr I , Cu I , Fe I , Mn I , and S...
Filaments are omnipresent features in the solar chromosphere, one of the atmospheric layers of the Sun, which is located above the photosphere, the visible surface of the Sun. They are clouds of plasma reaching from the photosphere to the chromosphere, and even to the outer-most atmospheric layer, the corona. They are stabalized by the magnetic fie...
The spectral window, containing Fraunhofer lines formed in the solar photosphere, around the magnetically sensitive Cr I lines at 5780.9, 5781.1, 5781.7, 5783.0, and 5783.8 \r{A}, with Land\'e g-factors between 1.6 and 2.5, is explored. The goal is to analyze simultaneously 15 spectral lines, which comprise Cr I, Cu I, Fe I, Mn I, and Si I lines, w...
Ground-based solar observations are severely affected by Earth’s turbulent atmosphere. As a consequence, observed image quality and prevailing seeing conditions are closely related. Partial correction of image degradation is nowadays provided in real time by adaptive optics (AO) systems. In this study, different metrics of image quality are compare...
High-resolution observations of polar crown and high-latitude filaments are scarce. We present a unique sample of such filaments observed in high-resolution H\(\upalpha \) narrow-band filtergrams and broad-band images, which were obtained with a new fast camera system at the Vacuum Tower Telescope (VTT), Tenerife, Spain. The Chromospheric Telescope...
The H α spectral line is a well-studied absorption line revealing properties of the highly structured and dynamic solar chromosphere. Typical features with distinct spectral signatures in H α include filaments and prominences, bright active-region plages, superpenumbrae around sunspots, surges, flares, Ellerman bombs, filigree, and mottles and rose...
High-resolution observations of polar crown and high-latitude filaments are scarce. We present a unique sample of such filaments observed in high-resolution H$\alpha$ narrow-band filtergrams and broad-band images, which were obtained with a new fast camera system at the Vacuum Tower Telescope (VTT), Tenerife, Spain. The Chromospheric Telescope (Chr...
The H{\alpha} spectral line is a well-studied absorption line revealing properties of the highly structured and dynamic solar chromosphere. Typical features with distinct spectral signatures in H{\alpha} include filaments and prominences, bright active-region plages, superpenumbrae around sunspots, surges, flares, Ellerman bombs, filigree, and mott...
Ground-based solar observations are severely affected by Earth's turbulent atmosphere. As a consequence, observed image quality and prevailing seeing conditions are closely related. Partial correction of image degradation is nowadays provided in real-time by adaptive optics (AO) systems. In this study, different metrics of image quality are compare...
We study the evolution of a minifilament eruption in a quiet region at the center of the solar disk and its impact on the ambient atmosphere. We used high spectral resolution imaging spectroscopy in H α acquired by the echelle spectrograph of the Vacuum Tower Telescope, Tenerife, Spain; photospheric magnetic field observations from the Helioseismic...
We study the evolution of a mini-filament eruption in a quiet region at the center of the solar disk and its impact on the ambient atmosphere. We used high-spectral resolution imaging spectroscopy in H$\alpha$ acquired by the echelle spectrograph of the Vacuum Tower Telescope (VTT), Tenerife, Spain, photospheric magnetic field observations from the...
A joint campaign of various space-borne and ground-based observatories, comprising the Japanese Hinode mission (HOP~338, 20\,--\,30~September 2017), the GREGOR solar telescope, and the \textit{Vacuum Tower Telescope} (VTT), investigated numerous targets such as pores, sunspots, and coronal holes. In this study, we focus on the coronal hole region t...
Aims. The regular pattern of quiet-Sun magnetic fields was disturbed by newly emerging magnetic flux, which led a day later to two homologous surges after renewed flux emergence, affecting all atmospheric layers. Hence, simultaneous observations in different atmospheric heights are needed to understand the interaction of rising flux tubes with the...
A joint campaign of various space-borne and ground-based observatories, comprising the Japanese Hinode mission (Hinode Observing Plan 338, 20 – 30 September 2017), the GREGOR solar telescope, and the Vacuum Tower Telescope (VTT), investigated numerous targets such as pores, sunspots, and coronal holes. In this study, we focus on the coronal hole re...
High-spectral resolution observations using the VTT echelle spectrograph in the chromospheric H$\alpha$ line were obtained in the early growth phase of active region NOAA 12722. Noise-stripped H$\alpha$ line profiles yield maps of line-core and bisector velocities, which were contrasted with velocities inferred from Cloud Model inversions. The SDO...
We study the dynamics of plasma along the legs of an arch filament system (AFS) from the chromosphere to the photosphere, observed with high-cadence spectroscopic data from two ground-based solar telescopes: the GREGOR telescope (Tenerife) using the GREGOR Infrared Spectrograph in the He i 10830 Å range and the Swedish Solar Telescope (La Palma) us...
We study the dynamics of plasma along the legs of an arch filament system (AFS) from the chromosphere to the photosphere, observed with high-cadence spectroscopic data from two ground-based solar telescopes: the GREGOR telescope (Tenerife) using the GREGOR Infrarred Spectrograph (GRIS) in the He I 10830 \r{A} range and the Swedish Solar Telescope (...
Polar crown filaments form above the polarity inversion line between the old magnetic flux of the previous cycle and the new magnetic flux of the current cycle. Studying their appearance and their properties can lead to a better understanding of the solar cycle. We use full-disk data of the Chromospheric Telescope (ChroTel) at the Observatorio del...
Polar crown filaments form above the polarity inversion line between the old magnetic flux of the previous cycle and the new magnetic flux of the current cycle. Studying their appearance and their properties can lead to a better understanding of the solar cycle. We use full-disk data of the Chromospheric Telescope (ChroTel) at the Observatorio del...
Aims. In this study, we analyzed a filament system, which expanded between moving magnetic features (MMFs) of a decaying sunspot and opposite flux outside of the active region from the nearby quiet-Sun network. This configuration deviated from a classical arch filament system (AFS), which typically connects two pores in an emerging flux region. Thu...
In this study, we analyzed a filament system, which expanded between moving magnetic features (MMFs) of a decaying sunspot and opposite flux outside of the active region from the nearby quiet-Sun network. This configuration deviated from a classical arch filament system (AFS), which typically connects two pores in an emerging flux region. Thus, we...
The Sun is our dynamic host star due to its magnetic fields causing plentiful of activity in its atmosphere. From high energetic flares and coronal mass ejections (CMEs) to lower energetic phenomena such as jets and fibrils. Thus, it is of crucial importance to learn about formation and evolution of solar magnetic fields. These fields cover a wide...
The Chromospheric Telescope (ChroTel) is a small 10‐cm robotic telescope at Observatorio del Teide on Tenerife (Spain), which observes the entire sun in Hα, Ca ii K, and He i 10 830 Å. We present a new calibration method that includes limb‐darkening correction, removal of nonuniform filter transmission, and determination of He i Doppler velocities....
The Chromospheric Telescope (ChroTel) is a small 10-cm robotic telescope at Observatorio del Teide on Tenerife (Spain), which observes the entire Sun in H$\alpha$, CaII K, and HeI 10830\AA. We present a new calibration method that includes limb-darkening correction, removal of non-uniform filter transmission, and determination of HeI Doppler veloci...
he Chromospheric Telescope (ChroTel) observes the entire solar disk since 2011 in three different chromospheric wavelengths: Hα, Ca ii K, and He i . The instrument records full-disk images of the Sun every three minutes in these different spectral ranges. The ChroTel observations cover the rising and decaying phase of solar cycle 24. We started ana...
Aims . We study the evolution of an arch filament system (AFS) and of its individual arch filaments to learn about the processes occurring in them.
Methods . We observed the AFS at the GREGOR solar telescope on Tenerife at high cadence with the very fast spectroscopic mode of the GREGOR Infrared Spectrograph (GRIS) in the He I 10 830 Å spectral ran...
We study the evolution of an arch filament system (AFS) and of its individual arch filaments to learn about the processes occurring in them. We observed the AFS at the GREGOR solar telescope on Tenerife at high cadence with the very fast spectroscopic mode of the GREGOR Infrared Spectrograph (GRIS) in the He I 10830 \AA\ spectral range. The He I tr...
The solar magnetic field is responsible for all aspects of solar activity. Sunspots are the main manifestation of the ensuing solar activity. Combining high-resolution and synoptic observations has the ambition to provide a comprehensive description of the sunspot growth and decay processes. Active region NOAA 12396 emerged on 2015 August 3 and was...
In high-resolution solar physics, the volume and complexity of photometric, spectroscopic, and polarimetric ground-based data significantly increased in the last decade reaching data acquisition rates of terabytes per hour. This is driven by the desire to capture fast processes on the Sun and by the necessity for short exposure times "freezing" the...
In high-resolution solar physics, the volume and complexity of photometric, spectroscopic, and polarimetric ground-based data significantly increased in the last decade reaching data acquisition rates of terabytes per hour. This is driven by the desire to capture fast processes on the Sun and by the necessity for short exposure times "freezing" the...
Broad-band imaging and even imaging with a moderate bandpass (about 1 nm) provides a "photon-rich" environment, where frame selection ("lucky imaging") becomes a helpful tool in image restoration allowing us to perform a cost-benefit analysis on how to design observing sequences for high-spatial resolution imaging in combination with real-time corr...
Broad-band imaging and even imaging with a moderate bandpass (about 1 nm) provides a "photon-rich" environment, where frame selection ("lucky imaging") becomes a helpful tool in image restoration allowing us to perform a cost-benefit analysis on how to design observing sequences for high-spatial resolution imaging in combination with real-time corr...
Aims. Combining high-resolution spectropolarimetric and imaging data is key to understanding the decay process of sunspots as it allows us to scrutinize the velocity and magnetic fields of sunspots and their surroundings.
Methods. Active region NOAA 12597 was observed on 2016 September 24 with the 1.5-meter GREGOR solar telescope using high-spatial...
Combining high-resolution spectropolarimetric and imaging data is key to understanding the decay process of sunspots as it allows us scrutinizing the velocity and magnetic fields of sunspots and their surroundings. Active region NOAA 12597 was observed on 24/09/2016 with the 1.5-m GREGOR solar telescope using high-spatial resolution imaging as well...
A giant solar filament was visible on the solar surface from 2011 Nov. 8-23. The filament stretched over more than half a solar diameter. Multiwavelength data from the SDO instrument AIA (171, 193, 304, and 211\AA) were used to examine counter-streaming flows within the spine of the filament. H$\alpha$ images from the Kanzelh\"ohe Solar Observatory...
Aim. The giant solar filament was visible on the solar surface from 2011 November 8–23. Multiwavelength data from the Solar Dynamics Observatory (SDO) were used to examine counter-streaming flows within the spine of the filament.
Methods. We use data from two SDO instruments, the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic...
We study small-scale brightenings in Ca II 8542 \AA\ line-core images to determine their nature and effect on localized heating and mass transfer in active regions. High-resolution 2D spectroscopic observations of an active region in the Ca II 8542 \AA\ line were acquired with the GFPI attached to the 1.5-meter GREGOR telescope. Inversions of the s...
We study small-scale brightenings in Ca II 8542 \AA\ line-core images to determine their nature and effect on localized heating and mass transfer in active regions. High-resolution 2D spectroscopic observations of an active region in the Ca II 8542 \AA\ line were acquired with the GFPI attached to the 1.5-meter GREGOR telescope. Inversions of the s...
A new generation of solar instruments provides improved spectral, spatial, and temporal resolution, thus facilitating a better understanding of dynamic processes on the Sun. High-resolution observations often reveal multiple-component spectral line profiles, e.g., in the near-infrared He I 10830 \AA\ triplet, which provides information about the ch...
A new generation of solar instruments provides improved spectral, spatial, and temporal resolution, thus facilitating a better understanding of dynamic processes on the Sun. High-resolution observations often reveal multiple-component spectral line profiles, e.g., in the near-infrared He I 10830 \AA\ triplet, which provides information about the ch...
A huge amount of data has been acquired with the GREGOR Fabry-P\'erot Interferometer (GFPI), large-format facility cameras, and since 2016 with the High-resolution Fast Imager (HiFI). These data are processed in standardized procedures with the aim of providing science-ready data for the solar physics community. For this purpose, we have developed...
A huge amount of data has been acquired with the GREGOR Fabry-P\'erot Interferometer (GFPI), large-format facility cameras, and since 2016 with the High-resolution Fast Imager (HiFI). These data are processed in standardized procedures with the aim of providing science-ready data for the solar physics community. For this purpose, we have developed...
The spatio-temporal evolution of sunspot activity, the so-called Maunder butterfly diagram, has been continously available since 1874 using data from the Royal Greenwich Observatory, extended by SOON network data after 1976. Here we present a new extended butterfly diagram of sunspot group occurrence since 1826, using the recently digitized data fr...
Improved measurements of the photospheric and chromospheric three-dimensional magnetic and flow fields are crucial for a precise determination of the origin and evolution of active regions. We present an illustrative sample of multiinstrument data acquired during a two-week coordinated observing campaign in August 2015 involving, among others, the...
The solar observatory Einstein Tower (Einsteinturm) at the Telegrafenberg in Potsdam is both a landmark of modern architecture and an important place for solar physics. Originally built for high-resolution spectroscopy and measuring the gravitational redshift, research shifted over the years to understanding the active Sun and its magnetic field. N...
Aims. Combining high-resolution and synoptic observations aims to provide a comprehensive description of flux emergence at photospheric level and of the growth process that eventually leads to a mature active region. Methods. Small active region NOAA 12118 was observed on 2014 July 18 with the 1.5-meter GREGOR solar telescope on 2014 July 18. High-...
Aims. Combining high-resolution and synoptic observations aims to provide a comprehensive description of flux emergence at photospheric level and of the growth process that eventually leads to a mature active region. Methods. Small active region NOAA 12118 was observed on 2014 July 18 with the 1.5-meter GREGOR solar telescope on 2014 July 18. High-...
Sunspot positions from various historical sets of solar drawings are analysed with respect to the tilt angles of bipolar sunspot groups. Data by Scheiner, Hevelius, Staudacher, Zucconi, Schwabe, and Spoerer deliver a series of average tilt angles spanning a period of 270 years, additional to previously found values for 20th-century data obtained by...
Accurate measurements of magnetic and velocity fields in and around solar active regions are key to unlocking the mysteries of the formation and the decay of sunspots. High spatial resolution image and spectral sequences with a high cadence obtained with the GREGOR solar telescope give us an opportunity to scrutinize 3-D flow fields with local corr...
The new generation of solar instruments provides better spectral, spatial, and temporal resolution for a better understanding of the physical processes that take place on the Sun. Multiple-component profiles are more commonly observed with these instruments. Particularly, the He I 10830 \r{A} triplet presents such peculiar spectral profiles, which...
The new generation of solar instruments provides better spectral, spatial, and temporal resolution for a better understanding of the physical processes that take place on the Sun. Multiple-component profiles are more commonly observed with these instruments. Particularly, the He I 10830 \r{A} triplet presents such peculiar spectral profiles, which...
Sunspot positions from various historical sets of solar drawings are analysed with respect to the tilt angles of bipolar sunspot groups. Data by Scheiner, Hevelius, Staudacher, Zucconi, Schwabe, and Spörer deliver a series of average tilt angles spanning a period of 270 years, additional to previously found values for -century data obtained by othe...
An accurate forecast of flare and coronal mass ejection (CME) initiation requires precise measurements of the magnetic energy buildup and release in the active regions of the solar atmosphere. We designed a new space weather mission that performs such measurements using new optical instruments based on the Hanle and Zeeman effects. The mission cons...
Most of our knowledge about the Sun's activity cycle arises from sunspot
observations over the last centuries since telescopes have been used for
astronomy. The German astronomer Gustav Sp\"orer observed almost daily the Sun
from 1861 until the beginning of 1894 and assembled a 33-year collection of
sunspot data covering a total of 445 solar rotati...
Much of our knowledge about the solar dynamo is based on sunspot
observations. It is thus desirable to extend the set of positional and
morphological data of sunspots into the past. Gustav Sp\"orer observed in
Germany from Anklam (1861-1873) and Potsdam (1874-1894). He left detailed
prints of sunspot groups, which we digitized and processed to miti...