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Seminare am MPS

ESPOS

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ESP Online Seminar: What can numerical simulations tell us about the mechanism of solar and stellar activity? (J. Warnecke)

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 this process. [mehr]

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Planetary Group Seminar: The evolution of planets in disks (W. Kley)

  • Datum: 02.03.2018
  • Uhrzeit: 11:00 - 12:00
  • Vortragender: Willhelm Kley
  • University of Tübingen, Institute for Astronomics & Astrophysics
  • Ort: MPS
  • Raum: Auditorium
  • Gastgeber: Urs Mall

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. [mehr]

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MPS Seminar: Minor planet photometric investigations: novel techniques from space and the ground (L.L. Kiss)

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 [mehr]

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Planetary Group Seminar: Interstellar dust and the heliosphere (V. Sterken)

Interstellar dust (ISD) from the local interstellar cloud traverses the solar system at 26 km/s, owing to the relative motion of the Sun and the cloud. These particles are messengers from interstellar space that can be studied in situ with dust detectors on space missions. In 1993, the first such ISD particles were detected using the Ulysses cosmic dust detector. The mission provided a total of 16 years of ISD data and thus covered almost one Hale cycle. This is important since the dust trajectories are shaped by the solar radiation pressure, gravity and Lorentz force (as they are charged and move through the interplanetary magnetic field that changes throughout the solar cycle). Interpretation of these data is done using monte carlo simulations of dust trajectories, which allows us to constrain the particle properties and it teaches us about the role of the heliosphere. Finally, in 2006, Stardust brought a few samples of interstellar dust material back to Earth, and in 2016, the Cassini mission provided the first time-of-flight mass spectra of 36 ISD impacts on the Cassini Cosmic Dust Analyzer. In this talk, we review the latest developments in the study of “local” interstellar dust with astronomical, in-situ, and sample return techniques. The dynamics of the ISD as it moves through the heliosphere will be explained and finally, we elaborate on what we can gain from computer simulations and spacecraft data for constraining both the ISD properties as well as for studying the heliosphere. [mehr]

 
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