The magnetic field in the Sun undergoes a cyclic modulation with a
reversal typically every 11 years due to a dynamo operating under the
surface. Also, other solar-like stars exhibit magnetic activity, most of
them with much higher levels compared to the Sun. Some of these stars
show cyclic modulation of their activity similar to the Sun. The
rotational dependence of activity and cycle length suggests a common
underlying dynamo mechanism.Here we present results of 3D MHD convective
dynamo simulations of slowly and rapidly rotating solar-type stars,
where the interplay between convection and rotation self-consistently
drives a large-scale magnetic field. With the help of the test-field
method, we are able to measure the turbulent transport coefficients in
these simulations and therefore get insights about the dynamo mechanism
operating in these simulations. It allows us to derive a scaling of the
cycle period with the relevant effects of the dynamo.We discuss how
magnetic helicity is a key quantity connecting the stellar convection
zone with the stellar surface and stellar coronae. Magnetic helicity is
produced in the convection zone of stars via a dynamo in the presence of
convection and rotation. At the surface, it plays an important role in
the formation process of active regions. In the corona, it is believed
to be essential for the release of energy leading to the eruption of
plasma via coronal mass ejections and is thought to play an important
role in the heating process of the coronal plasma. Numerical simulations
of stellar convection zones and the solar corona allow us to investigate
We investigate the effect of vibrational degrees of freedom on the thermoelectric transport through a single level quantum dot described by the spinless Anderson-Holstein impurity model. To study the effects of strong electron-phonon coupling in the linear response regime, we use the nonperturbative numerical renormalization group approach. We also compare our results, at weak to intermediate coupling, with those obtained by employing the functional renormalization group method, finding good agreement in this parameter regime. When applying a gate voltage at finite temperatures, the inelastic scattering processes, induced by phonon-assisted tunneling, result in an interesting interplay between electrical and thermal transport. We explore different parameter regimes and identify situations for which the thermoelectric power as well as the dimensionless figure of merit are significantly enhanced. By applying the functional renormalization group on the Keldysh contour, we further study the nonlinear thermoelectric transport in scenarios, in which the vibrating molecule is coupled to reservoirs held at different temperatures and chemical potentials.
Das Institut für Astrophysik bietet in unregelmäßigen Abständen öffentliche Führungen mit Beobachtungsmöglichkeit am 50-cm-Spiegelteleskop an. Während der Führungen werden die Forschungs- und Ausbildungseinrichtungen des Instituts vorgestellt und, bei klarem Himmel, eindrucksvolle Himmelsobjekte (z. B. Mond, Planeten, Gasnebel, Sternhaufen, Galaxien) im Fernrohr gezeigt. Die Führungen werden durch eine halbstündige Präsentation zu einem aktuellen Thema aus der astronomischen Forschung ergänzt.
Am 23. Februar 2018 bedeckt der Mond von 17:52 bis 18:57 Uhr den hellen Fixstern Aldebaran. Der Ein- und Austritt können bei klarem Himmel live am Teleskop beobachtet werden. In einem begleitenden Vortrag zum Thema "Sternbdeckungen, Finsternisse, Zeitbestimmung und die Bahn des Mondes" wird das Ereignis näher erläutert.
As of today more than 2700 exoplanetary systems containing over 3700 planets
have been discovered from the ground or the Kepler space mission. Many systems
display orbital dynamics quite different from our own Solar System. An important
role is played by the interaction of the growing planet with the ambient disk
that will change the orbital elements of a planet.
In the talk I will review the important results on the physics of disk driven
migration, and will then focus on recent developments on the migration of massive
planets in the so called type II migration regime, and in turbulent disks.
Here we present recent highlights from the minor planet research group of the Konkoly Observatory, all related to photometric observations of main-belt asteroids and Trans-Neptunian Objects (TNOs) with novel techniques that appeared in the last few years. First, the ecliptic survey of the NASA Kepler space telescope, known as the K2 mission, opened a whole new avenue of obtaining unbiased rotational properties of minor planets. For this, a new observing strategy had to be developed for Kepler, optimizing the data acquisition for the uninterrupted ~80 days of observations of moving objects in the fixed field of view in the ecliptic plane. Our results include statistically meaningful samples of rotational properties of main-belt asteroids, Jovian Trojan asteroids and several TNOs and Uranian small irregular moons. We also demonstrate the power of combining K2, Spitzer and HST observations for full characterization of distant icy bodies in the outer regions of the Solar System. Second, our group has actively taken part in TNO occultation observations, of which the highlight is the discovery of the rings of Haumea. For this, critical observations were made with a high-end ultrasensitive EMCCD camera, one that is capable of fast photometry of faint targets. We briefly discuss the advantages of the EMCCD technique in respect to traditional CCD photometry