Observability of characteristic binary-induced structures in circumbinary disks

Context: A substantial fraction of protoplanetary disks forms around stellar binaries. The binary system generates a time-dependent non-axisymmetric gravitational potential, inducing strong tidal forces on the circumbinary disk. This leads to a change in basic physical properties of the circumbinary disk, which should in turn result in unique structures that are potentially observable with the current generation of instruments. Aims: The goal of this study is to identify these characteristic structures, to constrain the physical conditions that cause them, and to evaluate the feasibility to observe them in circumbinary disks. Methods: To achieve this, at first two-dimensional hydrodynamic simulations are performed. The resulting density distributions are post-processed with a 3D radiative transfer code to generate re-emission and scattered light maps. Based on these, we study the influence of various parameters, such as the mass of the stellar components, the mass of the disk and the binary separation on observable features in circumbinary disks. Results: We find that the Atacama Large (sub-)Millimetre Array (ALMA) as well as the European Extremely Large Telescope (E-ELT) are capable of tracing asymmetries in the inner region of circumbinary disks which are affected most by the binary-disk interaction. Observations at submillimetre/millimetre wavelengths will allow the detection of the density waves at the inner rim of the disk and the inner cavity. With the E-ELT one can partially resolve the innermost parts of the disk in the infrared wavelength range, including the disk's rim, accretion arms and potentially the expected circumstellar disks around each of the binary components

Multi-scale simulations of black hole accretion in barred galaxies: Self-gravitating disk models

Due to the non-axisymmetric potential of the central bar, barred spiral galaxies form, in addition to their characteristic arms and bar, a variety of structures within the thin gas disk, like nuclear rings, inner spirals and dust-lanes. These structures in the inner kiloparsec are most important to explain and understand the rate of black hole feeding. The aim of this work is to investigate the influence of stellar bars in spiral galaxies on the thin self-gravitating gas disk. We focus on the accretion of gas onto the central supermassive black hole and its time-dependent evolution. We conduct multi-scale simulations simultaneously resolving the galactic disk and the accretion disk around the central black-hole. We vary in all simulations the initial gas disk mass. As additional parameter we choose either the gas temperature for isothermal simulations or the cooling timescale in case of non-isothermal simulations. Accretion is either driven by a gravitationally unstable or clumpy accretion disk or by energy dissipation in strong shocks. Most simulations show a strong dependence of the accretion rate at the outer boundary of the central accretion disk ($r< 300~\mathrm{pc}$) on the gas flow at kiloparsec scales. The final black hole masses reach up to $\sim 10^9 M_\odot$ after $1.6~\mathrm{Gyr}$. Our models show the expected influence of the Eddington limit and a decline in growth rate at the corresponding sub-Eddington limit

Hochauflösende Verfahren zur numerischen Berechnung von strahlungsgetriebenen Scheibenwinden

In dieser Arbeit wird das dreidimensionale System der gasdynamischen Gleichungen in allgemein krummlinig-orthogonalen Koordinaten formuliert und auf zwei Raumdimensionen reduziert, indem nur Probleme mit bestimmten Symmetrien betrachtet werden. Zur Lösung der so erhaltenen hyperbolischen Erhaltungsgleichungen wird ein neues numerisches Verfahren für krummlinige Gitter entwickelt. Umfangreiche Tests belegen, dass die mit dieser Methode gewonnenen Resultate eine im Vergleich mit anderen Verfahren mindestens ebenso gute Approximation für die tatsächlichen Lösungen darstellen. Mit Hilfe des neuen numerischen Verfahrens wird die Dynamik der strahlungsgetriebenen Scheibenwinde untersucht. Es werden stationäre Lösungen für bestimmte Einflussrandbedingungen gefunden. Außerdem wird untersucht, inwiefern die Resultate von der künstlichen Viskosität des Verfahrens abhängen. Berechnungen auf sphärischen und zylindrischen Gittern ergeben kleine Unterschiede in den Lösungen in Abhängigkeit von der jeweiligen Geometrie

Composição musical para a liturgia luterana no Brasil: relato de experiência

Este relato de experiência reúne ideias sobre composição musical, que poderão servir como base para estudos nas áreas de Música e Teologia Prática, em especial, para o culto e suas moldagens litúrgicas, no contexto da Igreja Evangélica de Confissão Luterana no Brasil (IECLB)

Editorial

Editorial 2020/01