Category: Research

Plate Archive

Two major sky patrol projects were carried out by the Dr. Remeis-Observatory (Bamberg). The Northern sky was monitored from 1926 to 1939 in Bamberg, whereas monitoring the Southern Sky was carried out between 1962 and 1976 from Boyden Observatory (South Africa), Mount John (New Zeeland) and San Miguel Observatory (Argentina). In a DFG funded collaboration with the Hamburger Sternwarte and the Leibniz Institute for Astrophysics Potsdam the archived plates have been digitized with high resolution scanners and being calibrated and integrated into the online archive APPLAUSE. Data relase 3 took place in October 2018.

The Northern Sky Patrol

Fig .1: The Ernostar-camera used for the Northern Sky patrol in Bamberg (1928-1939). Image courtesy: Remeis observatory

The Bamberg Northern Sky Survey was part of an observational programme initiated by Paul Guthnick to study variable stars in the Northern hemisphere. Three German observatories teamed up for this task: Berlin-Babelsberg (lead by Guthnick), Sonneberg (C. Hoffmeister) and the Dr. Remeis-Observatory in Bamberg (E. Zinner). The intention was to cover the Sky devided in 30 degree zones with identical Ernostar telescopes (aperture 13.5 cm, focal length 24 cm, see Fig.1) and 16 x 16cm photographic plates covering 28 degrees at a plate scale of 859 “/mm. The task was shared by the three observatories by assigning different sky areas to each of them. The Bamberg zones were at declinations -4 degrees (R.A: 1h, 3h, … 23h); +24 (0h, 2h, … 22h); +53 (0h, 2h, … 22h). Since 1935 the Bamberg staff had to take care of the Babelsberg fields as well because the Babelsberg observatroy left the project. The second world war put an end to the project in 1939. About 6500 project plates taken between 1928 and 1939 in Bamberg have been archived.

After the second world war: Observing the Northern Sky from Bamberg

Figure 2: Dogmar camera (left) and Aero Ektar camera (right). Image courtesy: Remeis observatory

In addition to the work horse Ernostar several smaller cameras have been used in Bamberg: From 1931 to 1953 a Tessar (aperture: 3cm, focal length: 14cm, plate scale 1528″/mm) produced 2500 plates. After the second world war it was replaced by a larger one (aperture: 9mm) operated from 1953 to 1963, more than 1000 plates are archived. From 1950 to 1963 a 11cm Dogmar (f=40cm, see Fig. 2) delivered more than 1000 plates ). In preparation for the southern survey new instruments were bought at the end of the 1950s. In preparation for a Southern Survey several cameras were tested and multiple cameras were adjusted on a single mount. Finally, it was decided to buy 20 Aero Ektar cameras (see Fig. 2) for the southern survey.

The Southern Sky patrol of the Dr. Remeis-Sternwarte

The Southern Sky patrol was carried out between 1963 and 1976 from Boyden Observatory (South Africa), Mount John (New Zeeland) and San Miguel Observatory (Argentina) as show in Fig. 3. All southern stations were equipped with identical Aero Ektar (aperture: 10cm, focal length: 61cm, plate scale: 388″/mm)cameras. The major southern station operated by Bamberg staff was set up at Boyden observatory in South Africa, which was equipped with 10 cameras and operated from 1963 to 1972 (see Fig. 4), while 4 cameras were operated from 1967 to 1976 at Mount John station and 6 at San Miguel from 1969-1972. A total of 22000 plates of the southern sky were obtained.

Figure 3: Location of the stations of the Bamberg Southern Sky patrol. Image courtesy: Remeis observatory

Figure 4: Ten Aero Ektar objectives of the southern survey mounted at Boyden station. Image courtesy: Remeis observatory

Atomic Physics

K-shell transitions in astrophysically abundant metals and L-shell transitions in Fe group elements show characteristic signatures in the soft X-ray spectrum in the energy range 0.1–10 keV. These signatures have great diagnostic value for plasma parameters such as electron and ion temperatures and densities, elemental abundances, and velocities of the observed material. These signatures can thus help understand the physics controlling the energetic processes in astrophysical sources. This diagnostic power increases with advances in spectral resolution and effective area of the employed X-ray observatories. However, to make optimal use of the diagnostic potential – whether through global spectral modeling or through diagnostics from local modeling of individual lines – the underlying atomic physics has to be complete and well known. With the next generation of soft X-ray observatories featuring micro-calorimeters such as the calorimeter on XARM or the X-IFU on Athena, broadband high-resolution spectroscopy with large effective area will become more commonly available in the next decade. With these spectrometers, the accuracy of the plasma parameters derived from spectral modeling will be limited by the uncertainty of the reference atomic data rather than by instrumental factors. This is sometimes already the case for the high-resolution grating observations with Chandra-HETG and XMM-Newton-RGS. To take full advantage of the measured spectra, assessment of the accuracy of and improvements to the available atomic reference data are therefore important.

Credit: Natalie Hell

The required atomic physics data essentially cover all known atomic physics properties and processes, including energy levels, transition wavelengths and rates, and cross sections for collisional ionization and excitation, autoionization, dielectronic recombination, photoionization and -excitation, radiative recombination, and charge exchange for all of these levels. These rates and cross sections need to be known for the full range of ions from neutral atoms to highly charged ions, where especially the near-neutral ions show a highly complex level structure. The bulk of the data therefore usually stems from theoretical calculations, especially for weak and heavily blended spectral features. These data need to be assessed both through comparisons between calculations, but more importantly by benchmarking the calculations through dedicated measurements in the laboratory. Finally, the data need to be made available and easily accessible to the astrophysics community through comprehensive atomic physics databases. These databases serve as look-up tables for specific parameter values, e.g., to determine temperatures from individual line ratios, on the one hand and to feed physical plasma models on the other hand. Remeis observatory is involved with several projects covering multiple of these aspects. These include a close collaboration with the developers of AtomDB, an atomic physics database providing a compilation of reference values as well as spectral models focused on collisionally ionized plasmas in- and outside of thermal equilibrium. This effort also includes a push to not only tag each reference value with a measure for its estimated accuracy, but also to make it possible to take such uncertainties of the model into account during spectral fits. Sophisticated routines are being developed for automated (and legible) adding of line labels, drawn from a database, to spectral plots in order to aid with line identification.

Source: https://ebit.llnl.gov/

Additionally, in order to get ready for upcoming X-ray spectroscopy missions, the observatory has a leading role in initiating a coordinated effort in Europe to identify the requirements these missions make on the accuracy and completeness of atomic reference data and to raise awareness in the community for current issues and shortcomings that still need to be addressed. This effort includes a strong collaboration with the EBIT group at LLNL, whose dedicated laboratory astrophysics program has a long and successful history of providing atomic physics reference data and benchmarks for theoretical calculations by measuring these parameters in the well-controlled environment of an Electron Beam Ion Trap using high-resolution spectrometers.

Absorption in the interstellar medium

X-rays produced by an astronomical source are passing through the interstellar medium of our Galaxy. While the interstellar medium is almost a vacuum, it does contain some material – gas, molecules, and dust – which can absorb the X-rays. If we want to study the sources, i.e., if we want to measure their spectral shape in order to learn about their physics, we need to correct for these effects of absorption. In collaboration with others we have developed the de facto standard model for the absorption of X-rays in the interstellar medium. The first version of this model, called tbabs, was published by Wilms, Allen, and McCray (2000, ApJ 542, 914). Since then we have continued to update and improve the model. The newest version of the model can be found here, it is also distributed with the newest releases of the standard X-ray astronomy modeling packages XSPEC and isis.

EXTraS

The EXTraS project makes use of data obtained by XMM-Newton, an ESA science mission funded by ESA Member States and the USA (NASA). EXTraS is funded within the EU/FP7-Cooperation Space framework and is carried out by a collaboration including INAF (Italy), IUSS (Italy), CNR/IMATI (Italy), University of Leicester (UK), MPE (Germany) and ECAP (Germany). It harvests the hitherto unexplored temporal domain information buried in the serendipitous data collected by the European Photon Imaging Camera (EPIC) onboard the XMM-Newton mission since its launch. This includes a search for fast transients, missed by standard image analysis, and a search and characterization of variability in hundreds of thousands of sources. The ECAP/Remeis group worked on an automated classification scheme for new transient sources in the EXTraS project. This included an automated spectral fitting algorithm, catalogue crossmatching tools and machine learning software (performed in R; randomForest (Breiman, 2001)).

ATHENA

ESA’s Advanced Telescope for High-Energy Astrophysics (ATHENA) is a future X-ray telescope to be launched in 2031. It is the second large class mission within the European Space Agency Cosmic Vision 2015-2025 program. The aim of ATHENA is the science of the Hot and Energetic Universe, especially the study of the emission from hot plasmas, the search for missing baryons, and the study and evolution of the large scale structure and black holes (http://www.the-athena-x-ray-observatory.eu/).

(Image Credit: MPE and ATHENA Team)

ATHENA will carry two detectors, the Wide Field Imager (WFI) and the X-ray Integral Field Unit (X-IFU). Our team is part of both instrument consortia, performing simulations with the SIXTE end-to-end simulator developed at the Remeis Observatory.

Wide Field Imager (WFI)

The Wide Field Imager is a newly developed DEPFET detector, whose development is lead by the Max Planck institute for Extraterrestrial Physics (MPE) in Munich. The WFI detector consists of 4 large detector chips, allowing for a large field of view (40′ x 40′) and a fast chip to observe bright X-ray sources. More details on the detector development can be found on the official MPE page here: http://www.mpe.mpg.de/ATHENA-WFI/

X-ray Integral Field Unit (X-IFU)

The X-ray Integral Field Unit is a microcalorimeter array using the technology of Transition Edge Sensors (TES) at sub-Kelvin temperatures in order to achieve an unprecedented energy resolution of 2.5 eV at X-ray energies up to 7 keV. The official webpage gives more details on the science and the hardware development: http://x-ifu.irap.omp.eu/

eROSITA

eROSITA is the main instrument of the upcoming Spektrum-Roentgen-Gamma mission (SRG). SRG is expected to be launched on 21 June 2019 from Baikonur into an orbit around the Lagrange Point L2 in a distance of about 1.5 million km from Earth. The main scientific question eROSITA will help to answer is dark energy. Current cosmological models show that the universe consists of about 30% matter (most of which is also dark) and 70% dark energy. While the nature of this dark matter has been studied in the last decades in detail, the nature of the dark energy remains elusive. A way to study dark energy is to study the number density and distribution of galaxy clusters – the largest structures in the universe. Their distribution and evolution depends strongly on the cosmological parameters and the influence of the dark energy. eROSITA will therefore perform the first complete all-sky survey in the energy range from 0.1 to 10 keV with high spectral and angular resolution. eROSITA is expected to find up to 100.000 galaxy clusters and 3 Million Active Galactic Nuclei (AGN). eROSITA consists of 7 identical Wolter telescopes with 54 nested mirror shells. Each telescope uses a framestore CCD sensor with 384×384 pixels. Our team is responsible for the development of the preprocessing software (decoding of the telemetry, processing the data, and storage in the archive) and the near real time analysis (NRTA) to assess the health of the instrument and take a first look at the scientific content of the data, as well as the development of the SIXTE simulation software for the mission.

Simulation of 6 months of the eROSITA survey in Galactic coordinates. The image is not exposure corrected. It shows the two survey poles (bright spots) as well as a large number of point sources.

Software

In the following a short list of the most important software we develop is given. A full list of git archives showing the most recent development versions of the software can be found here.

Interactive-Spectral-Interpretation-System (ISIS)

The ISIS software is frequently used for X-ray data analysis software. It is being developed by the MIT and further information can be at their homepage. In order to provide a larger suite of high-level functions to this software, we started the “The Remeis ISISscripts”, which by now contains a large collection of useful ISIS functions. These functions range from general SLang functions for array manipulation or adaptive integration routines, to parallel fitting functions (together with the Remeis SLmpi module) or powerful plotting routines. More information and an explanation on how to download these scripts can be found on our isisscripts-homepage.

The SIXTE end-to-end simulator

The end-to-end simulator SIXTE is developed here for simulating the detector performance of future X-ray missions. Currently most development is done for Athena and eROSITA. The software is written in C, with contributions from different people and institutes. A full description of the simulator can be found on the dedicated homepage.

SIXTE-Simulation of M82 with the Athena X-IFU (Credits: Thomas Dauser and Athena X-IFU Team)

Near Real-Time Analysis Software (NRTA) for eROSITA

Supernova Remnant Impact on Star Formation

Although gravitation is considered to be the driving mechanism for the formation of stars out of the densest cores in molecular clouds, observations have shown that gravitation alone is often not sufficient, but additional compression by shocks like in SNRs seems to be necessary. In a systematic search using archival data and dedicated follow-up observations, we have found candidates for young stellar objects (YSOs) inside Galactic SNRs. Using these objects we study of the impact of SNR shocks on YSOs and their discs and envelopes.

Supernova Remnants and Superbubbles

Stars emit light because they generate energy in thermonuclear burning. Massive stars ionise the ambient medium and inject matter and energy to the ISM through their strong radiation and stellar winds. At the end of the life of a massive star, its core collapses resulting in an explosion called a supernova: a strong shock arises that ejects the outer layers outwards. A combination of stellar winds of massive stars and one or multiple supernova explosions creates an interstellar structure called superbubbles. Supernova remnants (SNRs) and superbubbles are powered by strong shock waves and emit X-rays from thermal hot thin plasma and from non-thermal processes related to shocks. We study the emission of the shocked interstellar gas, ejecta expelled in supernova explosions, and particles accelerated in the strong interstellar shock waves using multiwavelength data.

SNR CTB109 (Radio continuum of CGPS with XMM-Newton contours, right: XMM-Newton with CO and IR contours). Copyright: M. Sasaki.

XMM-Newton First Light image, showing the LMC superbubble 30 Dor C. Credit: MPE.

X-ray Source Population in Nearby Galaxies

If a white dwarf, a neutron star, or a black hole, which are created at the end of the life of a star, forms a binary system with another star, it accretes matter from its companion, thus producing bright X-ray emission. Owing to the different types of companion stars, different populations of these accreting white dwarfs or X-ray binaries in galaxies correspond to different stellar populations, thus different star formation histories in the galaxies. We study the X-ray source populations in nearby galaxies using both archival and proprietary X-ray data in combination with data from radio, infrared, and optical observations.

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