December 2011

15/12/11 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — Measuring the Cosmos
Marc Reid (CfA Harvard)

Abstract

Over 2000 years ago, Hipparcus measured the distance to the Moon by triangulation from two locations across the Mediterranean Sea. However, determining distances to stars proved much more difficult. Many of the best scientists of the 16th through 18th centuries attempted to measure stellar parallax, not only to determine the scale of the cosmos but also to test Heliocentric cosmologies. While these efforts failed, along the way they led to many discoveries, including atmospheric refraction, precession, and aberration of light. It was not until the 19th century that Bessel measured the first stellar parallax. Distance measurement in astronomy remained a difficult problem even into the early 20th century, when the nature of galaxies ("spiral nebulae") was still debated. While we now know the distances of galaxies at the edge of the Universe, we have only just begun to measure distances accurately throughout the Milky Way. Using the Very Long Baseline Array, we now can achieve positional accuracy approaching 10 micro-arcseconds! I will present new results on parallaxes and motions of star forming regions and the black hole at the center of the Milky Way. These measurements address the nature of the spiral structure, size, rotation speed, and mass of the Milky Way.
08/12/11 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — Weak lensing: revealing the dark side of the universe
Rachel Mandelbaum
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Abstract

Weak gravitational lensing, the deflection of light from distant galaxies due to all intervening mass along the line of sight, is one of the most direct ways to observe dark matter. As a result, in the past decade, weak lensing has become a very important tool both for constraining cosmological parameters and for revealing the connection between galaxies and dark matter. I will begin by reviewing some recent, significant observational advances related to both galaxies and cosmology that were made possible by weak lensing. Next, I will outline some of the challenges and opportunities facing the lensing community in existing and upcoming imaging surveys. I will conclude with some perspective on how these challenges will be addressed to do ground-breaking work in the fields of cosmology, galaxy formation, and galaxy cluster formation and evolution with weak lensing observations in the next decade.

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01/12/11 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — Observational constraints on the critical metallicity for low mass star formation
Piercarlo Bonifacio (Observatoire de Paris)

Abstract

The Universe emerged from the Big Bang with a very simple chemical composition: hydrogen, helium and traces of lithium. The first stars that formed had this chemical composition, however, from the theoretical point of view only very massive stars should have formed, due to the lack of efficient cooling mechanisms that allow the formation of low mass stars. Thus there should exist a critical metallicity, below which no low-mass stars, that are long-lived and may still be observed at the present time, can be formed. To put observational constraints on this critical metallicity we have to search for extremely metal-poor stars and derive the metal-weak tail of the metallicity distribution function. The critical metallicity should manifest itself as a sharp drop in the MDF. In this search one finds many extremely metal-poor stars (EMP) that hold in their atmospheres the fossil record of the chemical composition of the early phases of the Galactic evolution. The chemical analysis of such objects provides important constraints on these early phases and especially on the masses of their progenitors that produced the metals observed in their atmospheres. To pursue this objective it is necessary to treat large amounts of data. With an automatic procedure, we analysed objects with colours of Turn-Off stars from the Sloan Digital Sky Survey to select a sample of candidate EMP stars. During the French-Italian X-Shooter GTO, used as a pilot programme, we observed a small sample of these candidates. We could confirm the low metallicity of our sample of stars, and we succeeded in finding the present record metal-poor star: SDSS J102915+172927 with [M/H]=-5, Z<= 6.9x10^{-7}. This star shows no enhancement of CNO elements, as do the previously found extremely iron-poor stars and, surprisingly, shows no lithium.

November 2011

24/11/11 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — Astronomy at the very edge of black holes
Giovanni Miniutti (CSIC/INTA, Madrid)

Abstract

Accretion onto black holes can liberate a significant fraction of the rest mass energy as radiation and/or relativistic jets. It powers both X-ray binaries and active galaxies. Most of the power is dissipated in the immediate vicinity of the central black hole. Irradiation of the flow produces a characteristic reflection spectrum which, through relativistic blurring, carries imprints of the effects of strong gravity. X-ray observations probe the innermost regions of the accretion flow via X-ray spectra and variability. I will review our current understanding of the phenomena associated with the X-ray emission in accreting black holes and discuss past and most recent observational and theoretical results in the field.
17/11/11 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — The Sun's magnetic surface
Henk Spruit (MPA)

Abstract

The magnetic field of the Sun is generated in its convective envelope. It is often considered a manifestation of 'the interaction between magnetic fields and turbulent convection'. In the first part of the talk I'll review some observations, old and new, which show that such a turbulent interaction picture fits the observations poorly. The observations, complemented with numerical work, lead to a considerably different conceptual picture of the solar cycle. In a second part I briefly review some spectacular recent successes in realistic numerical simulations of magnetic structures at the solar surface, which have greatly boosted confidence in our ability to reproduce observables with realistic radiative MHD simulations. In the third I discuss the (controversial) possibility that variations of the Sun's magnetic field might have an influence on climate.
10/11/11 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — Tracing the growth of the first black holes
Marta Volonteri (University of Michigan)

Abstract

Massive black holes, weighing millions to billions of solar masses, powered luminous quasars within the first billion years of the Universe. The first massive black holes must therefore have formed around the time the first stars and galaxies formed, at the end of the cosmic Dark Ages. In this talk I will discuss our recent simulations that trace the evolution of massive black holes in the first billion years of the Universe, and review possible strategies for testing our understanding of this early evolution.
03/11/11 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — Cosmology from ACT: the small-scale CMB
Joanna Dunkley (Oxford University)

Abstract

The Atacama Cosmology Telescope has mapped the microwave sky to arc minute scales. I will present recent results from ACT on the angular power spectrum of the Cosmic Microwave Background fluctuations, measuring primordial acoustic oscillations well into the Silk damping tail. I will also describe the extraction of a gravitational lensing signal from the observations, and the detection of galaxy clusters via the Sunyaev-Zeldovich (SZ) effect. I will describe the implications of these various measurements for cosmology, and discuss prospects for the upcoming ACTPol experiment.

October 2011

28/10/11 (Friday)
11:00, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Martin Elvis (Harvard-Smithsonian Center for Astrophysics)
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Abstract

Supermassive black holes pass through several 'ages' - birth, rapid growth at high redshift, moderate growth as quasars, merger growth, and slow growth as radio galaxies and Seyferts, and finally a turn-off. Downsizing of active black holes toward the present means that turned off quasars remain quiescent, a kind of "quasar death". Most of this life cycle is very poorly known, with only the quasar phase well studied. I will describe our new studies, based on both the COSMOS and the SDSS DR5 quasar samples, which shed light on this quasar death phase, as well as adding new complexity to the quasar and merger growth phases. These studies include a careful examination of the Mass-Luminosity plane for quasars, and the nature of 'intrinsically red' quasars based on joint optical and X-ray observations.

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13/10/11 (Thursday)
16:15, *** EXCEPTIONALLY IN THE MPE NEW SEMINAR ROOM, 1.1.18b *** | ESO Garching
Munich Joint Astronomy Colloquium
Talk — A Holistic Study of Supernovae
Alicia M. Soderberg (Harvard Univ., Cambridge MA)

Abstract

Throughout history, observational supernova studies have focused almost exclusively on their strong optical emission powered by the radioactive decay of Nickel-56. Yet many of the leading breakthroughs in our understanding of supernovae and their progenitors have been enabled by observations at other wavelengths. For example, through the combination of radio, optical, X-ray and gamma-ray observations, we now know that less than 0 .1 percent of all core-collapse supernovae require "central engines" (compact accreting sources) to power associated gamma-ray bursts. As I will discuss, it is the growing sample of radio and X-ray observations of nearby supernovae that are enabling rapid progress in revealing the nature of the GRB-SN connection. The fundamental question at this stage is clearly: which key progenitor property enables such a small fraction of massive star explosions to give rise to relativistic ejecta, and in turn, GRBs? While progenitor mass, metallicity, and binarity are among the most popular explanations, I will discuss how panchromatic observations (radio through gamma-rays) of supernovae and their environments shed light on this puzzle.
06/10/11 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — High redshift ULIRGs and the formation of massive galaxies
Scott Chapman (IoA, Cambridge, UK)
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Abstract

Studying ultraluminous galaxies (ULIRGs) at early times (z>2) provides insight into the formative phases of massive galaxies around us today. While the filed has become a relatively mature science, there remain various aspects of this field that are still mired in uncertainty, and new facilities offer possibilities for great leaps forward in our understanding. I will provide an overview of this exciting field, and present new avenues of research into high-z ULIRGs which are significantly pushing our understanding of the population. These include Herschel-HerMES, the South Pole Telescope (SPT), our recently completed IRAM-PdBI survey of CO 50 high-z SMGs (Bothwell et al. 2011), and the CDFS-LESS survey with LABOCA and its followup.

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September 2011

29/09/11 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — Comets, charge exchange, and a novel look at the X-ray universe
Konrad Dennerl (MPE)

Abstract

The discovery of cometary X-ray emission in 1996 with ROSAT has revealed the importance of a fundamental process for the generation of X-rays which was overlooked for a long time: charge exchange, a process where X-rays are not produced by hot electrons, but by ions picking up electrons from cold gas. It has also provided a conceptual breakthrough for the understanding of the soft X-ray background, and has opened up entirely new fields of X-ray studies. The talk will attempt to put the various aspects of the study of charge exchange reactions into a broader historical context, with special emphasis on X-ray astrophysics, where cometary X-rays may have stimulated a novel look at our universe.
22/09/11 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — Dark Matter, Dwarf Galaxies, and Massive Failures n the Halo of the Milky Way
James Bullock (University of California)

Abstract

The favored dark energy plus cold dark matter (LCDM) model of cosmology predicts that the Milky Way should be surrounded by thousands of dark matter satellite clumps, in great excess of the observed count of Galactic dwarf satellite galaxies. This mismatch is known as the "missing satellite problem". Recent discoveries in the Sloan Digital Sky Survey have revealed a new population of ultra-faint dwarf satellites, motivating excitement within the community that some "missing" LCDM satellites are finally being found. Unfortunately for the theory, the situation is not quite so rosy once the dynamical masses of the known satellites are considered. Specifically, the majority of the most massive dark matter satellites predicted to exist are too dense to host any of the bright satellite galaxies of the Milky Way. This poses a serious puzzle theoretically: either galaxy formation becomes effectively stochastic on scales smaller than ~0.1 L* or the central densities of dark matter subhalos are significantly lower than predicted in dissipationless simulations. I discuss some possible solutions to this puzzle from the standpoint of baryonic physics and non-standard dark matter physics.
15/09/11 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — Massive Stars: From the VLT to the ELTs
Chris Evans (Royal Observatory, Edinburgh)

Abstract

Massive stars play a key role in the dynamical and chemical evolution of star-forming galaxies, via their intense stellar winds, UV radiation fields, and explosive deaths. To develop realistic tools to analyse integrated-light observations of distant galaxies, we first need to calibrate the models via study of stars closer to home. To this end, I will present first results from the VLT-FLAMES Tarantula Survey, which has obtained multi-epoch spectroscopy of the massive-star population of 30 Doradus, the richest stellar nursery in the Local Group. Looking ahead, I will also discuss the exciting potential of the future Extremely Large Telescopes (ELTs), which will enable direct abundance estimates for individual stars in galaxies across a large volume of the local Universe.

June 2011

16/06/11 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — Achievements and challenges in star formation
Richard de Grijs (Peking University)
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Abstract

What has been the most profound discovery, progress or idea that has emerged in astronomy over the last decade? And what will be the most important challenge in astronomical research in the next decade? These questions are at the heart of our discipline, but we rarely venture outside of our own niche areas. I will attempt to focus on the broad picture underlying the field of star formation and discuss the requisite conditions for sustained progress in this field, aided by recent achievements in the context of my group's star cluster research.

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09/06/11 (Thursday)
16:15, *** EXCEPTIONALLY IN THE MPE NEW SEMINAR ROOM, 1.1.18b *** | ESO Garching
Munich Joint Astronomy Colloquium
Talk — The Turbulent-Fragmentation Model of Star Formation
Paolo Padoan (ICREA - ICC, University of Barcelona)

May 2011

19/05/11 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — Stars: The End
Albert Zijlstra (Jodrell Bank)
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Abstract

Planetary nebulae reflect the death throes of Sun-like stars. During their final phase of nuclear burning, between 20% and 80% of the mass of the star is ejected through a 'super'-wind. The ejection processdetermines the white dwarf mass distribution, and is the origin of up to half of the gas and dust in the ISM. The cause, evolution and composition of this catastrophic mass loss is still a matter of debate. Observations of planetary nebulae and their progeny, AGB stars, provide important constraints on the superwind and its origin. This talk will discuss mass loss in RGB and AGB stars, including the fate of iron, the formation process of PAHs, and the formation and destruction of dust disks. Observations of planetary nebulae in the Galactic Bulge provide surprising results on the binary stellar population of the Galactic Bulge.

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March 2011

31/03/11 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — Solar magnetism: complexity, simplicity, and a bad conscience
Manfred Schuessler (MPI f. Sonnenforschung)
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February 2011

17/02/11 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — Planck's early results on Sunyaev-Zel'dovich clusters
Nabila Aghanim (IAS, Orsay)
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January 2011

27/01/11 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — Radiation feedback in high and low mass star and planet formation
Barbara Ercolano (Cluster/TUM/LMU)
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