2014, Schönherr, G., Schwarm, F., Falkner, S., Becker, P., Wilms, J., Dauser, T., Wolff, M.T., Wolfram, K., West, B., Pottschmidt, K., Kretschmar, P., Ferrigno, C., Klochkov, D., Nishimura, O., Kreykenbohm, I., Caballero, I., Staubert, R.

The emission characteristics of X-ray pulsars are governed by magnetospheric accretion within the Alfvén radius, leading to a direct coupling of accretion column properties and interactions at the magnetosphere. The complexity of the physical processes governing the formation of radiation within the accreted, strongly magnetized plasma has led to several sophisticated theoretical modelling efforts over the last decade, dedicated to either the formation of the broad band continuum, the formation of cyclotron resonance scattering features (CRSFs) or the formation of pulse profiles. While these individual approaches are powerful in themselves, they quickly reach their limits when aiming at a quantitative comparison to observational data. Too many fundamental parameters, describing the formation of the accretion columns and the systems' overall geometry are unconstrained and different models are often based on different fundamental assumptions, while everything is intertwined in the observed, highly phase-dependent spectra and energy-dependent pulse profiles. To name just one example: the (phase variable) line width of the CRSFs is highly dependent on the plasma temperature, the existence of B-field gradients (geometry) and observation angle, parameters which, in turn, drive the continuum radiation and are driven by the overall two-pole geometry for the light bending model respectively. This renders a parallel assessment of all available spectral and timing information by a compatible across-models-approach indispensable. In a collaboration of theoreticians and observers, we have been working on a model unification project over the last years, bringing together theoretical calculations of the Comptonized continuum, Monte Carlo simulations and Radiation Transfer calculations of CRSFs as well as a General Relativity (GR) light bending model for ray tracing of the incident emission pattern from both magnetic poles. The ultimate goal is to implement a unified fitting model for phase-resolved spectral and timing data analysis. We present the current status of this project.

2014, Schwarm, F.-W., Schönherr, G., Kühnel, M., Wilms, J.

X-ray binary systems consisting of a mass donating optical star and a highly magnetized neutron star, under the right circumstances, show quantum mechanical absorption features in the observed spectra called cyclotron resonant scattering features (CRSFs). We have developed a simulation to model CRSFs using Monte Carlo methods. We calculate Green's tables which can be used to imprint CRSFs to arbitrary X-ray continua. Our simulation keeps track of scattering parameters of individual photons, extends the number of variable parameters of previous works, and allows for more flexible geometries. Here we focus on the influence of bulk velocity of the accreted matter on the CRSF line shapes and positions.

2015, Wallrabe, Ulrike, Brunne, Jens, Treffer, Alexander, Grunwald, Ruediger, Bellouard, Yves

We report on the design, fabrication and testing of novel types of low-dispersion axicons for the adaptive shaping of ultrashort laser pulses. An overview is given on the basic geometries and operating principles of our purely reflective adaptive MEMS-type devices based on thermal or piezoelectric actuation. The flexible formation of nondiffracting beams at pulse durations down to a few oscillations of the optical field enables new applications in optical communication, pulse diagnostics, laser-matter interaction and particle manipulation. As an example, we show first promising results of adaptive autocorrelation. The combination of excellent pulse transfer, self-reconstruction properties and propagation invariance of nondiffracting beams with an adaptive approach promises to extend the field of practical applications significantly.

2014, Hubrig, S., Ilyin, I., Schöller, M., Cowley, C.R., Castelli, F., Stelzer, B., Gonzalez, J.-F., Wolff, B.

We report on the status of our spectropolarimetric studies of Herbig Ae/Be stars carried out during the last years. The magnetic field geometries of these stars, investigated with spectropolarimetric time series, can likely be described by centred dipoles with polar magnetic field strengths of several hundred Gauss. A number of Herbig Ae/Be stars with detected magnetic fields have recently been observed with X-shooter in the visible and the near-IR, as well as with the high-resolution near-IR spectrograph CRIRES. These observations are of great importance to understand the relation between the magnetic field topology and the physics of the accretion flow and the accretion disk gas emission.

2014, Cowley, C.R., Castelli, J., Hubrig, S.

We present here the most recent abundance analysis of this Herbig Ae system based on high-resolution UVES and HARPS spectra and the results of our magnetic field measurements using high-resolution spectra obtained with HARPSpol.

2015, Schäfer, Jan, Bonaventura, Zdeněk, Foest, Rüdiger

Recently, laser schlieren deflectometry (LSD) had been successfully employed as a temperature measurement method to reveal the heat convection generated by micro filaments of a self-organized non-thermal atmospheric plasma jet. Based on the theory of the temperature measurements using LSD, in this work, three approaches for an application of the method are introduced: (i) a hyperbolic-like model of refractive index is applied which allows an analytical theory for the evaluation of the deflection angle to be developed, (ii) a Gaussian shape model for the filament temperature is implemented which is analyzed numerically and (iii) an experimental calibration of the laser deflection with a gas mixture of helium and argon is performed. Thus, these approaches demonstrate that a universal relation between the relative maximum temperature of the filament core (T1/T0) and a the maximum deflection angle δ1 of the laser beam can be written as T1/T0=(1 − δ1/δ0)−1, where δ0 is a parameter that is defined by the configuration of the experiment and by the assumed model for the shape of the temperature profile.

2014, Kühnel, M., Müller, S., Kreykenbohm, I., Fürst, F., Pottschmidt, K., Rothschild, R.E., Caballero, I., Grinberg, V., Schönherr, G., Shrader, C., Klochkov, D., Staubert, R., Ferrigno, C., Torrejón, J.-M., Martínez-Núñez, S., Wilms, J.

In a former publication, we have analyzed the transient neutron star X-ray binary GRO J1008-57 using all available RXTE-, Swift-, and Suzaku-data. As we have found, the source's spectral components, i.e., a power-law with high exponential cutoff and a black-body, are strongly correlated with the hard X-ray flux (15-50 keV). We update the analytical description of these dependence, including a change in the photon index behaviour from a flat to a logarithmic function. The flux, where the change occurs, is consistent with the onset of the black-body emission. Thus, a change of the accretion state always occurs in GRO J1008-57 at a particular flux level.

2015, Harndt, Susanna, Kaufmann, Christian A., Lux-Steiner, Martha C., Klenk, Reiner, Nürnberg, Reiner

The influence of absorber grain boundaries on the photocurrent transport in chalcopyrite based thin film solar cells has been calculated using a two dimensional numerical model. Considering extreme cases, the variation in red response is more expressed than in one dimensional models. These findings may offer an explanation for the strong influence of buffer layer preparation on the spectral response of cells with small grained absorbers.