arXiv subjects

A. Diercke

Publications and source records attributed to A. Diercke.

At least 19 recordsLinked to original sources

arXiv2025

An Unusual Velocity Field in a Sunspot Penumbra

The photospheric Evershed flow is normally oriented radially outward, yet sometimes opposite velocities are observed not only in the chromosphere but also in the photospheric layers of the penumbra. We study the velocity field in a special case of an active region with two mature sunspots, where one of them formed several days later than the main one. Between the two spots, flux emergence is still ongoing influencing the velocity pattern. We observed the active region NOAA 12146 on August 24, 2014, with the GREGOR Fabry-P\'erot Interferometer (GFPI) and the Blue Imaging Channel (BIC) of the GREGOR solar telescope at Observatorio del Teide on Tenerife. Context data from the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) complement the high-resolution data. In the penumbra of a newly formed spot, we observe opposite Doppler velocity streams of up to +-2 km/s very close to each other. These velocities extend beyond the outer penumbral boundary and cross also the polarity-inversion line. The properties of the magnetic field do not change significantly between these two streams. Although the magnetic field is almost horizontal, we do not detect large transversal velocities in horizontal flow maps obtained with the local correlation technique. The ongoing emergence of magnetic flux in an active region causes flows of opposite directions intruding the penumbra of a pre-existing sunspot.

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arXiv2022

Solar Hα excess during Solar Cycle 24 from full-disk filtergrams of the Chromospheric Telescope

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 Chromospheric Telescope (ChroTel) to extract the imaging H-alpha excess and deficit, which are related to bright features (plage regions) and dark absorption features (filaments and sunspots), respectively. The aim of this study is to introduce the imaging H-alpha excess and deficit as tracers of solar activity and compare them to other established indicators: the relative sunspot number, the F10.7cm radio flux, and the MgII index. The H-alpha excess and deficit follow the behavior of the solar activity over the course of the cycle, whereby the peak of the H-alpha deficit is shortly after the solar maximum. The H-alpha excess is closely correlated to the chromospheric MgII index. The highest correlation of the H-alpha deficit is found with the F10.7cm radio flux. The H-alpha deficit reflects the cyclic behavior of polar crown filaments and their disappearance shortly before the solar maximum. We investigated the mean intensity distribution for H-alpha excess regions for solar minimum and maximum, whereby the shape of the distributions is very similar, but with different amplitudes. Furthermore, we investigate whether the area coverage fraction or the changing H-alpha excess in the active regions dominates temporal variability in solar H-alpha observations. The area coverage fraction and the H-alpha excess are strongly correlated, whereas the weak correlation between the area coverage fraction and mean intensity leaves us pessimistic that the degeneracy between these two quantities can be broken for the modeling of unresolved stellar surfaces.

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arXiv2021

Multiple Stokes I inversions to infer magnetic fields in the spectral range around Cr I 5782 Å

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, 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, without polarimetry to infer the thermodynamic and magnetic properties in strongly magnetized plasmas using an inversion code. The study is based on a new setup at the Vacuum Tower Telescope (VTT, Tenerife) which includes fast spectroscopic scans in the wavelength range around the Cr I 5781.75 Å line. The snapshot 385 of the Enhanced Network simulation from the Bifrost code serves to synthesize all the lines, which are in turn inverted simultaneously with SIR to establish the best inversion strategy. This strategy is then applied to VTT observations of a sunspot belonging to NOAA 12723 on 2018 September 30 and the results are compared to full-disk vector-field data obtained with the Helioseismic and Magnetic Imager (HMI). The 15 simultaneously inverted intensity profiles (Stokes I) delivered accurate temperatures and Doppler velocities when compared against the simulations. The derived magnetic fields and inclinations are most accurate when the fields are oriented along the line-of-sight (LOS) and less accurate when the fields are transverse to the LOS. In general, the results appear similar to the HMI vector-field data, although some discrepancies exist. The analyzed spectral range has the potential to deliver thermal, dynamic, and magnetic information in strongly magnetized features on the Sun, such as pores and sunspots, even without polarimetry. The highest sensitivity of the lines is found in the lower photosphere, on average around $\log τ= -1$. The multiple-line inversions provide smooth results across the whole field-of-view.

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arXiv2020

Filigree in the Surroundings of Polar Crown and High-Latitude Filaments

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$α$ 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 (ChroTel) provided full-disk context observations in H$α$, Ca II K, and He I 10830 A. The Helioseismic and Magnetic Imager (HMI) and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) provided line-of-sight magnetograms and ultraviolet (UV) 1700 A filtergrams, respectively. We study filigree in the vicinity of polar crown and high-latitude filaments and relate their locations to magnetic concentrations at the filaments' footpoints. Bright points are a well studied phenomenon in the photosphere at low latitudes, but they were not yet studied in the quiet network close to the poles. We examine size, area, and eccentricity of bright points and find that their morphology is very similar to their counterparts at lower latitudes, but their sizes and areas are larger. Bright points at the footpoints of polar crown filaments are preferentially located at stronger magnetic flux concentrations, which are related to bright regions at the border of supergranules as observed in UV filtergrams. Examining the evolution of bright points on three consecutive days reveals that their amount increases while the filament decays, which indicates they impact the equilibrium of the cool plasma contained in filaments.

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arXiv2020

High-resolution spectroscopy of an erupting minifilament and its impact on the nearby chromosphere

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$α$ acquired by the echelle spectrograph of the Vacuum Tower Telescope (VTT), Tenerife, Spain, photospheric magnetic field observations from the Helioseismic and Magnetic Imager (HMI), and UV/EUV imaging from the Atmospheric Imaging Assembly (AIA) of the Solar Dynamics Observatory (SDO). The H$α$ line profiles were noise-stripped using Principal Component Analysis (PCA) and then inverted to produce physical and cloud model parameter maps. The minifilament formed between small-scale, opposite-polarity magnetic features through a series of small reconnection events and it erupted within an hour after its appearance in H$α$. Its development and eruption exhibited similarities with large-scale erupting filaments, indicating the action of common mechanisms. Its eruption took place in two phases, namely a slow rise and a fast expansion, and it produced a coronal dimming, before the minifilament disappeared. During its eruption we detected a complicated velocity pattern, indicative of a twisted, thread-like structure. Part of its material returned to the chromosphere producing observable effects on nearby low-lying magnetic structures. Cloud model analysis showed that the minifilament was initially similar to other chromospheric fine structures, in terms of optical depth, source function and Doppler width, but it resembled a large-scale filament on its course to eruption. High spectral resolution observations of the chromosphere can provide a wealth of information regarding the dynamics and properties of minifilaments and their interactions with the surrounding atmosphere.

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arXiv2020

Magnetic Flux Emergence in a Coronal Hole

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 target. On 24~September 2017, a very extended non-polar coronal hole developed patches of flux emergence, which contributed to the decrease of the overall area of the coronal hole. These flux emergence patches erode the coronal hole and transform the area into a more quiet-Sun-like area, whereby bipolar magnetic structures play an important role. Conversely, flux cancellation leads to the reduction of opposite-polarity magnetic fields and to an increase in the area of the coronal hole. Other global coronal hole characteristics, including the evolution of the associated magnetic flux and the aforementioned area evolution in the EUV, are studied using data of the \textit{Helioseismic and Magnetic Imager} (HMI) and \textit{Atmospheric Imaging Assembly} (AIA) onboard the \textit{Solar Dynamics Observatory} (SDO). The interplanetary medium parameters of the solar wind display parameters compatible with the presence of the coronal hole. Furthermore, a particular transient is found in those parameters.

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arXiv2020

High-resolution spectroscopy of a surge in an emerging flux region

High-spectral resolution observations using the VTT echelle spectrograph in the chromospheric H$α$ line were obtained in the early growth phase of active region NOAA 12722. Noise-stripped H$α$ line profiles yield maps of line-core and bisector velocities, which were contrasted with velocities inferred from Cloud Model inversions. The SDO provided additional continuum images, line-of-sight (LOS) magnetograms, and UV/EUV images, which link the different solar atmospheric layers. The active region started as a bipolar region with continuous flux emergence when a new flux system emerged in the leading part during the VTT observations, resulting in two homologous surges. While flux cancellation at the base of the surges provided the energy for ejecting the cool plasma, strong proper motions of the leading pores changed the magnetic field topology making the region susceptible for surging. Despite the surge activity in the leading part, an arch filament system in the trailing part of the old flux remained stable. Thus, stable and violently expelled mass-loaded ascending magnetic structures can co-exist in close proximity. Investigating the height dependence of LOS velocities revealed the existence of neighboring strong up- and downflows. However, downflows occur with a time lag. The opacity of the ejected cool plasma decreases with distance from the base of the surge while the speed of the ejecta increases. The location at which the surge becomes invisible in H$α$ corresponds to the interface where the surge brightens in He II 304. Broad-shoulders and dual-lobed H$α$ profiles suggest accelerated/decelerated and highly structured LOS plasma flows. Significantly broadened H$α$ profiles imply significant heating at the base of the surges, which is also supported by bright kernels in UV/EUV images uncovered by swaying motions of dark fibrils at the base of the surges.

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arXiv2020

Tracking downflows from the chromosphere to the photosphere in a solar arch filament system

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 Å range and the Swedish Solar Telescope (La Palma) using the CRisp Imaging Spectro-Polarimeter to observe the Ca II 8542 Å and Fe I 6173 Å spectral lines. The temporal evolution of the draining of the plasma was followed along the legs of a single arch filament from the chromosphere to the photosphere. The average Doppler velocities inferred at the upper chromosphere from the He I 10830 Å triplet reach velocities up to 20-24~km~s$^{-1}$, in the lower chromosphere and upper photosphere the Doppler velocities reach up to 11~km~s$^{-1}$ and 1.5~km~s$^{-1}$ in the case of the Ca II 8542 Å and Si I 10827 Å spectral lines, respectively. The evolution of the Doppler velocities at different layers of the solar atmosphere (chromosphere and upper photosphere) shows that they follow the same LOS velocity pattern, which confirm the observational evidence that the plasma drains towards the photosphere as proposed in models of AFSs. The Doppler velocity maps inferred from the lower photospheric Ca I 10839 Å or Fe I 6173 Å spectral lines do not show the same LOS velocity pattern. Thus, there is no evidence that the plasma reaches the lower photosphere. The observations and the nonlinear force-free field extrapolations demonstrate that the magnetic field loops of the AFS rise with time. We found flow asymmetries at different footpoints of the AFS. The NLFFF values of the magnetic field strength give us a clue to explain these flow asymmetries.

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arXiv2018

Photospheric Magnetic Fields of the Trailing Sunspots in Active Region NOAA 12396

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 observed three days later with the 1.5-meter GREGOR solar telescope on 2015 August 6. High-resolution spectropolarimetric data from the GREGOR Infrared Spectrograph (GRIS) are obtained in the photospheric Si I $λ$ 1082.7 nm and Ca I $λ$1083.9 nm lines, together with the chromospheric He I $λ$1083.0 nm triplet. These near-infrared spectropolarimetric observations were complemented by synoptic line-of-sight magnetograms and continuum images of the Helioseismic and Magnetic Imager (HMI) and EUV images of the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO).

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arXiv2018

Temporal evolution of arch filaments as seen in He I 10830 Å

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 Å spectral range. The He I triplet profiles were fitted with analytic functions to infer line-of-sight (LOS) velocities to follow plasma motions within the AFS. We tracked the temporal evolution of an individual arch filament over its entire lifetime, as seen in the He I 10830 Å triplet. The arch filament expanded in height and extended in length from 13" to 21". The lifetime of this arch filament is about 30 min. About 11 min after the arch filament is seen in He I, the loop top starts to rise with an average Doppler velocity of 6 km/s. Only two minutes later, plasma drains down with supersonic velocities towards the footpoints reaching a peak velocity of up to 40 km/s in the chromosphere. The temporal evolution of He I 10830 Å profiles near the leading pore showed almost ubiquitous dual red components of the He I triplet, indicating strong downflows, along with material nearly at rest within the same resolution element during the whole observing time. We followed the arch filament as it carried plasma during its rise from the photosphere to the corona. The material then drained toward the photosphere, reaching supersonic velocities, along the legs of the arch filament. Our observational results support theoretical AFS models and aids in improving future models.

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arXiv2018

High-Cadence Imaging and Imaging Spectroscopy at the GREGOR Solar Telescope - A Collaborative Research Environment for High-Resolution Solar Physics

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 atmospheric seeing, thus enabling post-facto image restoration. Consequently, large-format and high-cadence detectors are nowadays used in solar observations to facilitate image restoration. Based on our experience during the "early science" phase with the 1.5-meter GREGOR solar telescope (2014-2015) and the subsequent transition to routine observations in 2016, we describe data collection and data management tailored towards image restoration and imaging spectroscopy. We outline our approaches regarding data processing, analysis, and archiving for two of GREGOR's post-focus instruments (see http://gregor.aip.de), i.e., the GREGOR Fabry-Perot Interferometer (GFPI) and the newly installed High-Resolution Fast Imager (HiFI). The heterogeneous and complex nature of multi-dimensional data arising from high-resolution solar observations provides an intriguing but also a challenging example for "big data" in astronomy. The big data challenge has two aspects: (1) establishing a workflow for publishing the data for the whole community and beyond and (2) creating a Collaborative Research Environment (CRE), where computationally intense data and post-processing tools are co-located and collaborative work is enabled for scientists of multiple institutes. This requires either collaboration with a data center or frameworks and databases capable of dealing with huge data sets based on Virtual Observatory (VO) and other community standards and procedures.

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arXiv2018

Image Quality in High-resolution and High-cadence Solar Imaging

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 correction provided by an adaptive optics (AO) system. This study presents high-cadence (160 Hz) G-band and blue continuum image sequences obtained with the High-resolution Fast Imager (HiFI) at the 1.5-meter GREGOR solar telescope, where the speckle masking technique is used to restore images with nearly diffraction-limited resolution. HiFI employs two synchronized large-format and high-cadence sCMOS detectors. The Median Filter Gradient Similarity (MFGS) image quality metric is applied, among others, to AO-corrected image sequences of a pore and a small sunspot observed on 2017 June 4 and 5. A small region-of-interest, which was selected for fast imaging performance, covered these contrast-rich features and their neighborhood, which were part of active region NOAA 12661. Modifications of the MFGS algorithm uncover the field- and structure-dependency of this image quality metric. However, MFGS still remains a good choice for determining image quality without a priori knowledge, which is an important characteristic when classifying the huge number of high-resolution images contained in data archives. In addition, this investigation demonstrates that a fast cadence and millisecond exposure times are still insufficient to reach the coherence time of daytime seeing. Nonetheless, the analysis shows that data acquisition rates exceeding 50 Hz are required to capture a substantial fraction of the best seeing moments, significantly boosting the performance of post-facto image restoration.

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arXiv2018

High-resolution imaging and near-infrared spectroscopy of penumbral decay

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 as imaging spectroscopy and near-infrared (NIR) spectropolarimetry. Horizontal proper motions were estimated with LCT, whereas LOS velocities were computed with spectral line fitting methods. The magnetic field properties were inferred with the SIR code for the Si I and Ca I NIR lines. At the time of the GREGOR observations, the leading sunspot had two light-bridges indicating the onset of its decay. One of the light-bridges disappeared, and an elongated, dark umbral core at its edge appeared in a decaying penumbral sector facing the newly emerging flux. The flow and magnetic field properties of this penumbral sector exhibited weak Evershed flow, moat flow, and horizontal magnetic field. The penumbral gap adjacent to the elongated umbral core and the penumbra in that penumbral sector displayed LOS velocities similar to granulation. The separating polarities of a new flux system interacted with the leading and central part of the already established active region. As a consequence, the leading spot rotated 55-degree in clockwise direction over 12 hours. In the high-resolution observations of a decaying sunspot, the penumbral filaments facing flux emergence site contained a darkened area resembling an umbral core filled with umbral dots. This umbral core had velocity and magnetic field properties similar to the sunspot umbra. This implies that the horizontal magnetic fields in the decaying penumbra became vertical as observed in flare-induced rapid penumbral decay, but on a very different time-scale.

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arXiv2018

Counter-streaming flows in a giant quiet-Sun filament observed in the extreme ultraviolet

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 211Å) were used to examine counter-streaming flows within the spine of the filament. H$α$ images from the Kanzelhöhe Solar Observatory provided context information. We apply local correlation tracking (LCT) to a two-hour time series on 2011 Nov. 16 of the AIA images to derive horizontal flow velocities of the filament. To enhance the contrast of the AIA images, noise adaptive fuzzy equalization is employed, which allows us to identify and quantify counter-streaming flows in the filament. We detect counter-streaming flows in the filament, which are visible in the time-lapse movies in all examined AIA wavelength bands. In the time-lapse movies we see that these persistent flows lasted for at least two hours. Furthermore, by applying LCT to the images we clearly determine counter-streaming flows in time series of 171 and 193Å images. In the 304Å wavelength band, we only see minor indications for counter-streaming flows with LCT, while in the 211Å wavelength band the counter-streaming flows are not detectable. The average horizontal flows reach mean flow speeds of 0.5 km/s. The highest horizontal flow speeds are identified in the 171Å band with flow speeds of up to 2.5 km/s. The results are averaged over a time series of 90 min. Because the LCT sampling window has finite width, a spatial degradation cannot be avoided leading to lower estimates of the flow velocities as compared to feature tracking or Doppler measurements. The counter-streaming flows cover about 15-20% of the whole area of the EUV filament channel and are located in the central part of the spine. In conclusion, we confirm the omnipresence of counter-streaming flows also in giant quiet-Sun filaments.

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arXiv2017

Ca II 8542 Å brightenings induced by a solar microflare

We study small-scale brightenings in Ca II 8542 Å 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 Å line were acquired with the GFPI attached to the 1.5-meter GREGOR telescope. Inversions of the spectra were carried out using NICOLE. We identified three brightenings of sizes up to 2"x2". We found evidence that the brightenings belonged to the footpoints of a microflare (MF). The properties of the observed brightenings disqualified the scenarios of Ellerman bombs or IRIS bombs. However, this MF shared some common properties with flaring active-region fibrils or flaring arch filaments (FAFs): (1) FAFs and MFs are both apparent in chromospheric and coronal layers according to the AIA channels, and (2) both show flaring arches with lifetimes of about 3.0-3.5 min and lengths of about 20". The inversions revealed heating by 600 K at the footpoint location in the ambient chromosphere during the impulsive phase. Connecting the footpoints, a dark filamentary structure appeared in the Ca II line-core images. Before the start of the MF, the spectra of this structure already indicated average blueshifts, meaning upward motions of the plasma along the LOS. During the impulsive phase, these velocities increased up to -2.2 km/s. Downflows dominated at the footpoints. However, in the upper photosphere, slight upflows occurred during the impulsive phase. Hence, bidirectional flows are present in the footpoints of the MF. Conclusions: We detected Ca II brightenings that coincided with the footpoint location of an MF. The MF event led to a rise of plasma in the upper photosphere, both before and during the impulsive phase. Excess mass, previously raised to at most chromospheric layers, slowly drained downward along arches toward the footpoints of the MF.

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arXiv2017

Flows along arch filaments observed in the GRIS 'very fast spectroscopic mode'

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 Å triplet, which provides information about the chromospheric velocity and magnetic fine structure. We observed an emerging flux region, including two small pores and an arch filament system, on 2015 April 17 with the 'very fast spectroscopic mode' of the GREGOR Infrared Spectrograph (GRIS) situated at the 1.5-meter GREGOR solar telescope at Observatorio del Teide, Tenerife, Spain. We discuss this method of obtaining fast (one per minute) spectral scans of the solar surface and its potential to follow dynamic processes on the Sun. We demonstrate the performance of the 'very fast spectroscopic mode' by tracking chromospheric high-velocity features in the arch filament system.

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arXiv2017

sTools - a data reduction pipeline for the GREGOR Fabry-Pérot Interferometer and the High-resolution Fast Imager at the GREGOR solar telescope

A huge amount of data has been acquired with the GREGOR Fabry-Pérot 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 user-friendly data reduction pipeline called "sTools" based on the Interactive Data Language (IDL) and licensed under creative commons license. The pipeline delivers reduced and image-reconstructed data with a minimum of user interaction. Furthermore, quick-look data are generated as well as a webpage with an overview of the observations and their statistics. All the processed data are stored online at the GREGOR GFPI and HiFI data archive of the Leibniz Institute for Astrophysics Potsdam (AIP). The principles of the pipeline are presented together with selected high-resolution spectral scans and images processed with sTools.

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arXiv2016

Solar Physics at the Einstein Tower

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. Nowadays, telescope and spectrographs are used for research and development, i.e., testing instruments and in particular polarization optics for advanced instrumentation deployed at major European and international astronomical and solar telescopes. In addition, the Einstein Tower is used for educating and training of the next generation astrophysicists as well as for education and public outreach activities directed at the general public. This article comments on the observatory's unique architecture and the challenges of maintaining and conserving the building. It describes in detail the characteristics of telescope, spectrographs, and imagers; it portrays some of the research and development activities.

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