Astrophysical Institute Potsdam Research Articles

16th Potsdam Thinkshop: The rotation periods of cool stars: Measurements, uses, connections and prospects

This topical issue of Astronomische Nachrichten/Astronomical Notes contains a cross section of the articles that were presented at the 16th Potsdam Thinkshop, which was organized by the Leibniz Institute for Astrophysics Potsdam (AIP) and held on its campus in Babelsberg in September 2019. The title of the Thinkshop was “The rotation periods of cool stars: Measurements, uses, connections and prospects.” The motivations for organizing this Thinkshop were manifold. Rotation periods are rapidly becoming available for large numbers of cool stars, both from ground-based efforts and from space missions such as Kepler, Gaia, TESS, and—before long—PLATO. These rotation periods offer independent and complementary information about stars in comparison to prior techniques. For instance, they are often used to derive ages for cool stars via a procedure known as gyrochronology. Rotation also helps to interpret and illuminate various magnetic and activity behaviors of stars, and rotation in turn is likely itself affected by various internal and external factors. Related topics include open clusters, membership verification, metallicity dependence, binary stars, effects of close companions, and various others, which might be relevant to the aims of well-reasoned measurement, usage, and interpretation of rotation periods and to the future prospects of gyrochronology. The workshop enabled researchers to present their results in a more intimate setting than often possible, and significant time was reserved for discussions and interaction. The Scientific Organizing Committee consisted of Sydney Barnes (AIP, chair), Constantine Deliyannis (Indiana University, United States), Elisa Distefano (INAF, Catania, Italy), Jose D. do Nascimento (DFTE-UFRN, Brazil & CfA-SAO, United States), Thomas Granzer (AIP), Silva Järvinen (AIP), Elisabeth Newton (Dartmouth College, United States), Steven Saar (CfA, United States), and Klaus Strassmeier (AIP). A total of 54 participants from a number of different continents attended the Thinkshop. Further information is available on the Internet at: https://thinkshop.aip.de/16/cms/. All of the relevant topics listed above were mentioned in some form or the other during the Thinkshop, and many were discussed extensively. We are pleased to include a selection of the presented articles in this Special Issue. All contributions to this issue were reviewed by expert referees. We would like to express our gratitude to the Leibniz Institute for Astrophysics Potsdam for hosting this conference and to the AIP administrative staff for their competent administrative support.

Commentary: Making my way in physics

Commentary: Making my way in physics

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

AbstractA 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.

Two Observatories in Istanbul: from the Late Ottoman Empire to the Young Turkish Republic

From the 17 century onward, the Ottoman Empire entered a phase of weakening, as a consequence of many factors including the dissolution of political stability, the loss of territory and decreasing revenue. In the second half of the 19 century, as an attempt to reinforce power of the central authority, the Ottomans undertook major reforms called Tanzimat. During this period, individuals started to establish professional and learned associations similar to those in the West which eventually led to the creation of a Faculty of Science and to the Ottoman University (Darulfunun, 1900). In this context of reform and opening to the West, the Imperial Observatory (Rasathane-i Amire) was founded in 1868 with the support of France. Its primary aim was to exchange data between European and Ottoman meteorological stations. The Imperial Observatory occupied several locations before reaching its final setting in Kandilli (1911), on the Asian side of the Bosphorus where other activities were developed such as sismology, astronomy, meteorology and magnetic studies. Following the spirit of the newly founded Republic in 1923, a serious reform of the academic programmes and a purging of the staff of the Ottoman University led to the establishment of the Istanbul University in the historical quarter of Beyazit (1933). The Istanbul astronomical Observatory was founded in the same year and its construction started in 1935. The university reform was largely influenced by the presence of German and other European scholars, many of them Jewish, escaping from Nazi persecution. In particular, Erwin Finlay-Freundlich from Potsdam Observatory became the first director of Istanbul Observatory. Kandilli and Istanbul University observatories are briefly presented here, stressing the main steps of their creation and their astronomical heritage.

Potsdam Library of Astronomical Photographic Plates

We present the Potsdam photographic plate library at the Leibniz Institute for Astrophysics Potsdam. It includes plate archives, data from plate index catalogues and extracts from astronomical logbooks, as well as digitized plate images and interfaces for accessing all the available information. The plate index catalogues and the digitized images of the Potsdam astronomical photographic plates are prepared according to the standards of the Wide-Field Plate Database and German Astrophysical Virtual Observatory. The high-resolution digitization of the plates (in standardized FITS file format), the low-resolution plate previews (in TIFF and JPEG file format), as well as suitable digitization of the catalogues, logbooks, and relevant scientific research papers (in JPEG and TIFF) are made using commercial flatbed scanners.

Diagnostics of magnetic flux tube oscillations on the Sun based on fine-structure characteristics of the radio spectrum

The possibility of obtaining information about oscillation processes in magnetic flux tubes on the Sun by analyzing the undulating frequency drift of the zebra pattern in the dynamic spectrum of solar radio emission is discussed. It is shown that the oscillatory variation in the frequency of zebra stripes can be associated with fast magnetoacoustic (FMA) oscillations in a flux tube, which lead to oscillations in the magnetic field strength and electron number density. The October 25, 1994 event recorded by the radio spectrograph of the Astrophysical Institute Potsdam is used as an example to demonstrate the possibility of determining the parameters of FMA oscillations and the physical conditions in coronal magnetic loops from the observed zebra-pattern characteristics.

A microflare with hard X-ray-correlated gyroresonance line emission at 314 MHz

Context. Small energy release events in the solar corona can give insights into the flare process which are regularly hidden in the complex morphology of larger events. For one case we find a narrowband radio signal well correlated with the hard X-ray flare. We investigate wether these signals are probes for the flare current sheet. Aims. We aim to establish the relation between narrowband and short-duration features (<1% of the observing frequency in the spectral range 250–340 MHz, and some 5 s until 2 min, respectively) in dynamic radio spectral diagrams and simultaneously occuring HXR bursts. Methods. We use dynamic radio spectra from the Astrophysical Institute Potsdam, HXR images of RHESSI, TRACE coronal and chromospheric images, SOHO-MDI high resolution magnetogram data, and its potential field extrapolation for the analysis of one small flare event in AR10465 on September 26, 2003. We point to similar effects in e.g. the X-class flare on November 03, 2003 to demonstrate that we are not dealing with a singular phenomenon. Results. We confirm the solar origin of the extremely narrowband radio emission. From RHESSI images and the magnetic field data we identify the probable site of the radio source as well as the HXR footpoint and the SXR flare loop emission. The flare loop is included in an ongoing change of magnetic connectivity as confirmed by TRACE images of hot coronal loops. The flare energy is stored in the nonpotential magnetic field substructure around the microflare site which is relaxed to a potential one. Conclusions. We conclude that the correlated HXR footpoint/narrowband radio emission, and the transition to a second energy release in HXR without associated radio emission are direct probes of changing magnetic connectivity during the flare. We suppose that the narrowband radio emission is due to gyroresonance radiation at the second harmonic of the local electron cyclotron frequency. It follows an upper limit of the magnetic field in the radio source volume of less than 50% of the mean potential field in the same height range. This supports the idea that the narrowband radio source is situated in the immediate surroundings of the flare current sheet.

The STELLA Robotic Observatory on Tenerife

The Astrophysical Institute Potsdam (AIP) and the Instituto de Astrofísica de Canarias (IAC) inaugurated the robotic telescopes STELLA‐I and STELLA‐II (STELLar Activity) on Tenerife on May 18, 2006. The observatory is located on the Izaña ridge at an elevation of 2400 m near the German Vacuum Tower Telescope. STELLA consists of two 1.2 m alt‐az telescopes. One telescope fiber feeds a bench‐mounted high‐resolution echelle spectrograph while the other telescope feeds a wide‐field imaging photometer. Both scopes work autonomously by means of artificial intelligence. Not only that the telescopes are automated, but the entire observatory operates like a robot, and does not require any human presence on site.

The Potsdam plates of the Carte du Ciel project: I. Present inventory and plate catalogue

AbstractWe present an inventory ofthe Carte du Ciel (CdC) plates stored in the Astrophysical Institute Potsdam. The Potsdam CdC zone (+32° to +39°) was divided into 1232 areas and about 2200 plates from the first and second epochs were obtained within the framework of the CdC project. At present, only 977 plates (45% of all) are stored in AIP, the others got lost during the Second World War. The plates for the first epoch measurements had been obtained during the period 1893 May– 1900 February. The plates for the second epoch (1913 August–1924 February) can be separated into two time intervals according to the observer and the observing method used: from 1913 August till 1914 July, and from 1916 February to 1924 February. The present work aims to provide online access to the plate information, given in the plate catalogue and is the first step to online access to the plate images digitized with flatbed scanners.

A Special Radio Spectral Fine Structure Used for Plasma Diagnostics in Coronal Magnetic Traps

A specific combination of spectral fine structures in meter – decimeter dynamic spectra of solar radio burst emission is reported in observations carried out at the Astrophysical Institute Potsdam. We describe and interpret the occurrence of zebra patterns in fast drifting (type III burst-like) envelopes of absorbed continuum emission. A possible mechanism of the origin of such an involved spectral pattern is put forward, leading to a necessarily multinonequlibrium component coronal plasma. The suggested mechanism is based on the fact that during the passage of a fast electron beam through the corona the loss cone instability (which is caused by electrons captured in a magnetic trap generating the continuum) is quenched. As result, a fast drift burst appears in absorption, and the zebra pattern becomes visible on the low background emission. This zebra pattern is generated by a group of electrons with a nonequilibrium distribution over transverse velocities. In the absence of the beam the pattern is invisible against the background of the stronger continuum. It is shown that the mechanism is sensitive to the distribution parameters of the different electron ensembles. Therefore the effect in dynamic radio spectra is comparatively rare but its proper existence underlines that the simultaneous presence of different ensembles of electrons in the flaring corona can be quite a frequent situation. This can explain some problems in deconvolving X-ray photon spectra to electron energy spectra.

Grid integration of robotic telescopes

AbstractRobotic telescopes and grid technology have made significant progress in recent years. Both innovations offer important advantages over conventional technologies, particularly in combination with one another. Here, we introduce robotic telescopes used by the Astrophysical Institute Potsdam as ideal instruments for building a robotic telescope network. We also discuss the grid architecture and protocols facilitating the network integration that is being developed by the German AstroGrid‐D project. Finally, we present three user interfaces employed for this purpose. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

On Solar Intermediate Drift Radio Bursts at Decimeter and Meter Wavelength

Fiber – or intermediate drift – bursts are a continuum fine structure in some complex solar radio events. We present the analysis of such bursts in the X17 flare on 28 Oct. 2003. Based on the whistler wave model of fiber bursts we derive the 3D magnetic field structures that carry the radio sources in different stages of the event and obtain insight into the energy release evolution in the main flare phase, the related paths of nonthermal particle propagation in the corona, and the involved magnetic field structures. Additionally, we test the whistler wave model of fiber bursts for the meter and the decimeter wave range. Radio spectral data (Astrophysikalisches Institut Potsdam, Astronomical Observatory Ondřejov) show a continuum with fibers for ≈ 6 min during the main flare phase. Radio imaging data (Nancay Radio Heliograph) yield source centroid positions of the fibers at three frequencies in the spectrometer band. We compare the radio positions with the potential coronal magnetic field extrapolated from SOHO/MDI data. Given the detected source site configuration and evolution, and the change of the fiber burst frequency range with time, we can also extract those coronal flux tubes where the high-frequency fiber bursts are situated even without decimeter imaging data. To this aim we use a kinetic simulation of whistler wave growth in sample flux tubes modeled by selected potential field lines and a barometric density model. The whistler wave model of fiber bursts accurately explains the observations on 28 Oct. 2003. A laterally extended system of low coronal loops is found to guide the whistler waves. It connects several neighboring active regions including the flaring AR 10486. For varying source sites the fiber bursts are emitted at the fundamental mode of the plasma frequency over the whole range (1200 – 300 MHz). The present event can be understood without assuming two different generation mechanisms for meter and decimeter wave fiber bursts. It gives new insight into particle acceleration and propagation in the low flare and post-CME corona.

Radio burst from converging separatrices

Context. In a previous paper on the X17 flare October 28, 2003, we found, among other radio flare sources, one displaced at ≈ 0.2 $R_\odot$ north of the flaring AR 10486, away from the main H α and hard X-ray flare emission. The source came to our attention due to its timing, its spatial displacement from the flaring active region, and due to the behavior of the radio spectral fine structure sources which are embedded in the continuum emission. We speculated that the source is situated at a separator of coronal magnetic flux systems. Aims. Here we analyze the topology of the potential coronal magnetic field extrapolated from SOHO-MDI data near the source site of this meter-decimeter radio continuum. Methods. Using the Source Method for magnetic field modeling, and the displacement gradient of the field lines as a connectivity measure, we give a description of the critical field structure. We compare it with the Nancay Radio Heliograph source positions of the continuum which have been classified by the spectral data of Astrophysical Institute Potsdam. Results. We find that the radio source occurs near the contact of three separatrix surfaces between magnetic flux cells. There are other separatrix surfaces in the field which are not distinguished by a strong radio source during the analyzed flare. Conclusions. This is the first evidence for the occurence of a strong coronal radio burst continuum source at such coronal magnetic field structures.

Internal kinematics of modelled interacting disc galaxies

Astrophysikalisches Institut Potsdam, An der Sternwarte 16, D-14482 Potsdam, Germany-/-Abstract. We present an investigation of galaxy-galaxy interactions and their effects on the velocity fields of discgalaxies in combined N-body/hydrodynamic simulations, which include cooling, star formation with feedback, andgalactic winds. Rotation curves (RCs) of the gas are extracted from these simulations in a way that follows theprocedure applied to observations of distant, small, and faint galaxies as closely as possible. We show that galaxy-galaxy mergers and fly-bys disturb the velocity fields significantly and hence the RCs of the interacting galaxies,leading to asymmetries and distortions in the RCs. Typical features of disturbed kinematics are significantly risingor falling profiles in the direction of the companion galaxy and pronounced bumps in the RCs. In addition, tidaltails can leave strong imprints on the rotation curve. All these features are observable for intermediate redshiftgalaxies, on which we focus our investigations. We use a quantitative measure for the asymmetry of rotation curvesto show that the appearance of these distortions strongly depends on the viewing angle. We also find in this waythat the velocity fields settle back into relatively undisturbed equilibrium states after unequal mass mergers andfly-bys. About 1 Gyr after the first encounter, the RCs show no severe distortions anymore. These results areconsistent with previous theoretical and observational studies. As an illustration of our results, we compare oursimulated velocity fields and direct images with rotation curves from VLT/FORS spectroscopy and ACS imagesof a cluster at z=0.53 and find remarkable similarities.Key words. Galaxies: kinematics and dynamics - Galaxies: interactions - Methods: numerical

The GLE on Oct. 28, 2003 – radio diagnostics of relativistic electron and proton injection

Timing discrepancies between signatures of accelerated particles at the sun and the arrival times of the particles at near-earth detectors are a matter of fundamental interest for space-weather applications. The solar injection times of various components of energetic particles were derived by Klassen et al. (2005, JGR, 110, A09S04) for the October 28, 2003, X-class/ γ -ray flare in NOAA AR 10486. This flare occured in connection with a fast halo coronal mass ejection and a neutron monitor-observed ground level event (GLE). We used radio (Astrophysikalisches Institut Potsdam, $\emph{WIND}$, Nancay Multifrequency Radio Heliograph), H α (Observatorium Kanzelhohe), $\emph{RHESSI}$, $\emph{SOHO}$ (EIT, LASCO, MDI), and $\emph{TRACE}$ data to study the associated chromospheric and low coronal phenomena. We identify three source sites of accelerated particles in this event. Firstly, there is a source in projection 0.3 $R_\odot$ away from AR 10486, which is the site of the reconnection outflow termination, as revealed by a termination shock signature in the dynamic radio spectrum. Secondly, there is the extended current sheet above a giant coronal postflare loop system in the main flare phase. Thirdly, there is a source situated on a magnetic separatrix surface between several magnetic arcades and neighbouring active regions. This source is 0.2 $R_\odot$ away from AR 10486 and acts during onset and growth of high energy proton injection in space. It is not clear if this source is related to the acceleration of protons, or if it only confirms that energetic particles penetrate a multistructure magnetic loop system after being previously accelerated near the main HXR- and γ -ray sources. The result is in favour of energetic particle acceleration in the low corona (<0.5 $R_\odot$ above the photosphere) and in contrast to acceleration of the relativistic particles at remotely propagating shock waves.

Observations of the coronal dynamics associated with solar radio spike burst emission

We present the results of an analysis of multi-wavelength data for a solar radio spike burst event which was observed on 1997 November 14 by the Solar Radio Spectrometers of the Astrophysikalisches Institut Potsdam (AIP). Using radio imaging data from the Nancay Radioheliograph we are able to determine the location of the spike burst emission sites in relation to the associated flare and its coronal environment as seen in images from the Yohkoh Soft X-ray Telescope (SXT), Hard X-ray Telescope (HXT) and the Solar and Heliospheric Observatory (SOHO) Extreme ultraviolet Imaging Telescope (EIT). For this event we find that the spike burst emission originated high in the corona, ~122 Mm above the soft X-ray and hard X-ray emitting regions of the associated (near-limb) flaring region. Using imaging data from SXT, HXT, and EIT we are also able to show, for the first time, the location of a solar radio spike burst in relation to the dynamics of coronal structures. We find that as an earlier flare-associated coronal mass ejection (CME) in the vicinity expanded outwards it appeared to compress the magnetic field structures at its flanks (associated with highly inclined coronal loops at the periphery of the active region). The radio spike bursts appeared at the time and in the vicinity of the compression of the coronal field. The compression presumably led to reconnection of the coronal magnetic field structures, particle acceleration and the radio spike burst emission signatures. For the specific event we analyse we find that the spike burst emission is associated with secondary flare energy release induced by an earlier flare-associated CME. These observations also provide evidence for a new category of sympathetic flaring where a large flare-associated coronal mass ejection compresses adjacent magnetic structures leading to nearby, but remote, small-scale flaring.

STELLA and RoboTel – a prototype for a robotic network?

AbstractRobotic telescopes are more and more commonly used in today's astronomical research. In fact, several facilities are spread around the globe, already forming a loose net. A big leap forward would lie in the capabilities to share observations between different telescopes. One gains immediately weather independence and the possibility of continuous observations from a working network. In this paper, the three robotic telescope operated under the hood of the Astrophysical Institute Potsdam are introduced, the potential of a robotic telescope network are sketched out and principle hints on accomplishing such a network are outlined. (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

The Production of Near-Relativistic Electrons by CME-Driven Shocks

The solar sources of near-relativistic 30 keV) electron events observed at 1 AU are poorly understood. In general, the solar injection times deduced from the observed 1 AU onset times and assumed 1.2 AU travel distances yield injection times about 10 minutes after the associated flare impulsive phases and type III radio burst times. One interpretation is that the apparent delays occur in the interplanetary medium, probably due to scattering of the electrons. If the injection times are delayed from the impulsive phases, the electron acceleration might take place in CME-driven shocks. Here a large number of electron events observed with the UC/Berkeley 3DP detector on the Wind spacecraft are compared with CMEs observed by the Lasco coronagraph on SOHO and with type II bursts observed by the 40 to 800 MHz radio receiver at the Astrophysikalisches Institut Potsdam (AIP) and by the 20 kHz to 14 MHz WAVES instrument on the Wind spacecraft. The acceleration of at least some of the electron events is not consistent with the shock hypothesis.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Solar type IV burst spectral fine structures

The fine structures (FS) of solar type IV radio bursts are of principal interest for flare plasma diagnostics in the low corona. In this paper we give an observational (Part I) and theoretical (Paper II) treatment of broad band radio pulsations (BBP) and zebra patterns (ZP) in a well observed flaring sigmoidal loop system of AR 7792 on 25 October 1994. We present comprehensive meter-decimeter radio spectral (Astrophysical Institute Potsdam, AIP) and meter wave heliographic (Nancay Radio Heliograph of Paris-Meudon Observatory, NRH) observations. Spectral and spatial properties of FS elements (one pulsation pulse, one single zebra stripe) as well as a statistical analysis for the whole fine structure event are presented. The source sites are compared with soft X-ray images of the flare, and with force-free extrapolated coronal magnetic fields. Both FS sources occur in a common diverging loop structure with a turning height of about 70 Mm. The BBP source is shown to appear (if seen along the loop axis) nearer to the injection site of the electrons than the ZP source. BBP do show high frequency drift (-250 MHz s - 1 ). At a given frequency, the projected source speed is 1.1 x 10 5 km s - 1 . For ZP, we find a good correlation between the inclination of a single zebra stripe to the heliographic observing frequency level in the dynamic spectrogram, and the speed of the simultaneously observed projected source motion at this frequency. The direction of the source motion at a given frequency is on average found to be perpendicular between BBP and ZP sources. During a time interval of 90 s the BBP source consists in its lower part (higher observing frequencies) of a widely spaced double source. Despite a source distance of 360 Mm both subsources are highly correlated and thus probably simultaneously driven. We come to the conclusion that both fine structures are emitted during repeated electron beam injection into an asymmetric magnetic trap configuration between a footpoint in the leading spot of AR 7792 and a trailing more dispersed footpoint. In Paper II we will show that the specifications derived from the data allow for selecting one out of several competing fine structure models which explains the simultaneous formation of BBP and ZP in the same loop structure.

ROSITA

AbstractThe Max‐Planck‐Institut für extraterrestrische Physik, the Astrophysikalisches Institut Potsdam, and the Institut für Astronomie und Astrophysik of the university of Tübingen, together with European cooperation partners and ESA, plan to install an X‐ray telescope on the International Space Station (ISS). The mission ROSITA (ROentgen Survey with an Imaging Telescope Array) will perform the first imaging all‐sky survey in the medium energy X‐ray range up to 10 keV with an unprecedented spectral and angular resolution. The main scientific goals are (1) to detect systematically all obscured accreting Black Holes in nearby galaxies and altogether about 50,000 AGN in the 2‐10 keV band, (2) to detect the hot intergalactic medium of several ten thousand galaxy clusters, and (3) to study in detail the physics of galactic X‐ray source populations, like pre‐main sequence stars, supernova remnants, and X‐ray binaries. In the hard X‐ray band (above 2 keV) the ROSITA survey will have a hundred times higher sensitivity and a hundred times better angular resolution than the last all‐sky survey in this band, which was performed about 25 years ago. In the soft band (0.5‐2 keV) the ROSITA survey will be more sensitive and have a substantially better energy and also angular resolution than the ROSAT all‐sky survey. The telescope will consist of seven 27‐fold nested Wolter‐1 mirror systems, the type already flown on ABRIXAS, and a novel detector system currently being developed by MPE on the basis of the successful XMM pn‐CCD technology. Major improvements of the new camera are a higher time and energy resolution.