KIS Astrophysical Colloquium 2017
The colloquium usually takes place on Thursdays at 11:30 if not stated otherwise.
|March 23||Ansgar Reiners, Universität Göttingen:
Exoplanets and solar convection: Motivating advances in high accuracy spectroscopy
|Extrasolar planet research has matured from lucky discovery mode to planet characterization and the systematic search for planetary systems. Among the major drivers today is the search for planets around low-mass stars, which include our immediate neighborhood where discoveries inspired groundbreaking ideas like sending spaceprobes to Proxima b. One of the limitations for current and next generation planet surveys is the moving stellar plasma that can introduce Doppler shifts far larger than the radial velocity signal from planets. This convective blueshift is difficult to study on other stars, but a lot can be learned from the Sun. I will give an overview about exoplanetary research and spectrograph development, and I will show how Doppler programs provide (even more) motivation for high accuracy solar spectroscopy.|
|April 4|| Reza Rezai, Instituto de Astrofisica de Canarias:
Structure of sunspot light bridges in the chromosphere and transition region
|Light bridges are elongated structures with enhanced intensity embedded in sunspot umbra and pores. Using IRIS spectral data, we study properties of a sample of 60 light bridges in the chromosphere and transition region. Traces of photospheric light bridges are found in the near ultra violet Mg II h and k lines as well as in the far ultra violet emission lines of the O I, C II, Si IV and O IV. These set of spectral lines cover the entire chromosphere and lower part of the transition region. We created a sample of mean values for the continuum and line intensities, line shifts and widths. A majority of photospheric light bridges in our sample have an associated enhanced emission in the chromosphere and transition region. In most cases, morphology of light bridges in the chromosphere and transition region are similar to the photospheric light bridge such that a 1-1 correspondence can be established. We measured a systematic shift between position of the light bridges in the transition region and photosphere, which illustrates the three-dimensional structure of light bridges, where the Si IV signal originates from about 3.5 Mm above the photosphere. The line widths increases with the formation temperature in the light bridge atmosphere, similar to quiet Sun. The line profiles have distinctly different shapes in the light bridge and nearby umbra suggesting that the umbral scattered light does not play an important role. Light bridges show red shift in the chromosphere and the transition region. We find the observed co-temporal and co-spatial emission enhancements above photospheric light bridges is a systematic phenomena suggesting that light bridges extend well beyond the photospheric boundary.|
|April 20||Jorge Sanchez Almeida, Instituto de Astrofisica de Canarias, Spain:
What are galaxies feeding from?
|May 4||Alexei Pevtsov, National Solar Observatory, Boulder, USA:
|June 22||Robert Jedicke, University of Hawaii, USA:
Super catastrophic disruption of asteroids at small perihelion distances
|Most near-Earth objects (NEOs) were derived from the asteroid belt as small objects that drifted via non-gravitational thermal forces into resonant escape routes that then push them onto planet-crossing orbits. The dynamics of how these objects evolve in the inner solar system is well understood and has been used to predict the orbital nature and size-frequency distribution of the NEO population. However, as NEO discoveries have increased problems have emerged with the existing NEO models. For example, many NEOs should be on orbits that closely approach the Sun yet few have been discovered. In addition, even though the NEO population is roughly an even mix of low-albedo (<10%) and high-albedo (>10%) asteroids, the characterized NEOs with small perihelion distances show a strong preference for high albedos. Our new NEO model shows that the deficit is likely produced by the super-catastrophic disruption of a substantial fraction of the small and mid-sized NEOs when they reach perihelion distances of a few tens of solar radii.|
|June 29||Zdzislaw Musielak, University of Texas at Arlington, USA:
|February 9||Prof. Dr. Dagmar Schmauks, Technical University, Berlin:
Extra-Terrestrial Life in Science Fiction
| Deutsch Ein erkenntnistheoretischer Aspekt von Science Fiction ist ihr Versuch, unsere erd-, gattungs-, kultur- und epochenspezifischen Vorurteile zu erhellen, also sozusagen eine Außenansicht der Welt des homo sapiens zu bieten. Ein grundlegendes Thema hierbei ist das Zusammentreffen mit außerirdischen Lebensformen. Schlichte Autoren kombinieren nur bekannte Fakten neu, so dass die Außerirdischen irdischen Kraken ähneln oder Stielaugen besitzen. Kreativere Autoren hingegen entwerfen Lebewesen, die kein Vorbild in der irdischen Evolution haben. Einfache Lebensformen werden oft unabsichtlich oder gezielt ausgerottet (schließlich hat sich der Mensch schon öfters als „invasiver Neobiont“ erwiesen). Intelligente Außerirdische sind aus dramaturgischen Gründen oft technologisch weit überlegen, was meist zu spektakulären Kämpfen und selten zu friedlicher Koexistenz führt. Die interessantesten Visionen entwerfen Lebewesen, die eine ganz andere Biologie besitzen (etwa silizium-basiert), die keine Individuen in unserem Sinne sind (etwa Lems Gallert-Ozean Solaris) oder die gar nicht auf Planeten leben (Hoyles Schwarze Wolke). Kontaktversuche mit Außerirdischen sind ein Prüfstein jeder Kommunikationstheorie. Optimistische Texte beschreiben Telepathie oder universelle Übersetzungscomputer, andere machen interessante Vorschläge für den Aufbau gegenseitiger Verständigung. Abschließend werden mögliche Vorteile und Gefahren kosmischer Kontakte skizziert. Und vielleicht sollten wir uns erst einmal um bessere Kontakte mit unseren intelligenten Mitgeschöpfen auf der Erde bemühen?
English An epistemological aspect of science fiction is its attempt to elucidate our prejudices related to earth, species, culture, and epoch, thus delivering an external view on the world of homo sapiens. One basic topic is in the contact with extraterrestrial lifeforms. Simple writers only combine known facts, so that the aliens resemble terrestrial octopuses or possess stalk eyes. More creative authors, however, design creatures without example in terrestrial evolution. Primitive extraterrestrial lifeforms are often exterminated inadvertently or purposefully (after all, humans on earth have already proved themselves to be “invasive neobiota”). Due to dramaturgical reasons, intelligent aliens frequently possess a highly superior technology, usually leading to spectacular battles and rarely to friendly coexistence. The most interesting visions describe living beings that have a completely different biology (such as silicon-based), that are not individuals in our sense (Lems gelatinous ocean Solaris) or are not bound to planets (Hoyles Black Cloud). Contact attempts with extraterrestrials are a touchstone of every communication theory. Optimistic texts describe telepathy or universal translation computers, while others make interesting suggestions for building up mutual understanding. Finally, some possible advantages and dangers of cosmic contacts are sketched. And maybe we should initially try to improve our contacts with our intelligent fellow creatures on earth?
|March 2||Travis Metcalfe, Space Science Institute, Boulder, USA:
A stellar context for the solar activity cycle
|Precise photometry from the Kepler space telescope allows not only the measurement of rotation in solar-type field stars, but also the determination of reliable masses and ages from asteroseismology. These critical data have recently provided the first opportunity to calibrate rotation-age relations for stars older than the Sun. The evolutionary picture that emerges is surprising: beyond middle-age the efficiency of magnetic braking is dramatically reduced, implying a fundamental change in angular momentum loss beyond a critical Rossby number (Ro~2). We have compiled chromospheric activity measurements for the sample of Kepler asteroseismic targets that were used to establish the new rotation-age relations. We use these data along with a sample of well-characterized solar analogs from the Mount Wilson HK survey to develop a qualitative scenario connecting the evolution of chromospheric activity to a fundamental shift in the character of differential rotation. We conclude that the Sun may be in a transitional evolutionary phase, and that its magnetic cycle might represent a special case of stellar dynamo theory.|