The Red MSX Source Survey

Lunch Colloquium
Dr. James Urquhart
ORATED
MPIfR

Here we describe the Red MSX Source (RMS) survey which is the largest, systematic, galaxy-wide search for massive young stellar objects (MYSOs) yet undertaken. Mid-IR bright point sources from the MSX satellite survey have been followed-up with ground-based radio, millimetre, and infrared observations to identify the contaminating sources and characterise the MYSOs and UCH II regions. With initial classification now complete the distribution of sources in the galaxy will be discussed, as well as some programmes being developed to exploit our sample.

Non-equilibrium chemistry in the shocked inner winds of AGB stars: a close look at the carbon star IRC+10216

Main Colloquium
Dr. Isabelle Cherchneff
ORATED
Universität Basel

The wind of Asymptotic Giant Branch stars develops in the dust formation zone (i.e., the inner wind). This narrow region above the stellar photosphere is crossed by periodic shocks induced by the pulsation of the star. The postshock gas is characterised by an active chemistry which destroys and produces molecules, in particular chemical species that are not present in the photosphere. We will present new results for the carbon star IRC+10216 based on the modelling of its inner wind, which includes the formation of water, hydrocarbons, aromatics, hydrides, halogens and phosphorous-bearing molecules. The results will be compared to the latest data from Herschel. Finally, prescriptions for dust formation in carbons stars will be discussed from the synthesis of dust molecular precursors in these shocked gas layers.

A giant polar structure of streams, globular clusters and satellite galaxies around the Milky Way

Lunch Colloquium
Marcel Pawlowski
ORATED
AIfA

It has been known for a long time that the satellite galaxies of the Milky Way (MW) show a significant amount of phase-space correlation: they are distributed in a highly inclined Disc of Satellites (DoS). Suggested explanations include the infall of groups of dwarf galaxies, their accretion along filaments or a tidal origin. We extend the previous studies on the DoS by analyzing for the first time the orientations of streams of stars and gas, and the distributions of globular clusters within the halo of the MW. It is shown that the spatial distribution of MW globular clusters classified as young halo clusters is similar to the DoS and that half of the analyzed streams align well with the DoS. The observed clustering of streams is extremely improbable (0.3 per cent) when assuming isotropy. These findings demonstrate that an isotropic infall of cosmological sub-structure components onto the MW is essentially ruled out. Either a large number of infalling objects had to be highly correlated, or their majority had to be formed as a single population, as is possible only in tidal material. The existence of a disc-like distribution of subsystems (satellite galaxies, globular clusters and streams), spreading from Galactocentric distances as small as 10 kpc out to 250 kpc, becomes established beyond reasonable doubt. The potential consequences of this realization are severe. If all the satellite galaxies and young halo globular clusters are of tidal origin, then the MW does not have any luminous dark-matter substructures and the missing satellites problem becomes a catastrophic failure.

Jets and lobes of radio galaxies: insights from radio and X-ray data

Special Colloquium
Dharam V. Lal
ORATED
Harvard-Smithsonian Center for Astrophysics

The brightest and most numerous discrete radio sources in the sky, radio galaxies and quasars, are powered by twin jets of plasma which emerge at relativistic speeds from very small regions at the centre of large elliptical galaxies, powered by mass infall on to supermassive black holes. The jets can carry material out to very large distances (upto many hundreds of kpcs) where it forms balloon-like lobes. Groups and clusters commonly contain radio galaxies, which eject large amounts of energy into their external environments. Its influence is to regulate gas cooling and galaxy evolution by an amount, which depends on energy ejected, mixing, and entrainment. Until recently, due to the absence of high resolution and high sensitivity X-ray facilities, it has been impossible to make definite statements about the energy or the nature of the matter supplied by the jets, or the dynamics of the lobes as they expand into the external medium. This has meant that crucial questions about the generation of radio sources and their effect on their environment have gone unanswered. The situation has been revolutionized by the launch at the start of this decade of a new generation of X-ray observatories, Chandra and XMM-Newton. In this seminar, we present (i) the broad classification of AGN with a multi-wavelength approach, paying particular attention to the radio and X-ray band which carries precious information on the innermost regions of AGN. We will also discuss (ii) our recent results, i.e., the importance of jet/environment interactions for both radio-source structure and the properties of the surrounding gas, including multi-wavelength SED of the jet using Chandra/X-ray observations of radio galaxies and the prospects for future work.

High-energy cosmic rays and the impact of astrophysical magnetic fields

Main Colloquium
Prof. Dr. Julia Becker
ORATED
Ruhr-Universität Bochum

Since the discovery of cosmic rays in balloon experiments performed by Victor Hess in 1912, the origin of the hadronic particle component from the cosmos has been discussed. No definite answer can be given as of today, since the scrambeling of the direction of the charged particles does not allow for a simple reconstruction of the original direction. In this talk, the theoretical arguments for possible cosmic ray sources and experimental indications will be reviewed. In particular, supernova remnants as a strong source candidate for Galactic cosmic rays will be discussed: Electromagnetic fields play a crucial role both for the acceleration of the cosmic rays and their transport through the galaxy. The model of supernova remants being the sources of cosmic rays is tested for different recent measurements, e.g. concerning PAMELA, ATIC, Fermi, WMAP and IceCube data.

Infrared interferometry for AGN science

Lunch Colloquium
Dr. Makoto Kishimoto
ORATED
MPIfR

The speaker has been indulging himself into AGN infrared interferometry a bit too much. But he has recently been given an opportunity to give a review talk in an ESO VLTI conference, and wishes to give the same up-to-date information to the people at MPIfR on the front line of the exploitation of Keck and VLT interferometers for AGN science. This is on the new exploration of the innermost dusty region around supermassive black holes on milli-arcsecond scales, corresponding to sub-pc scales in nearby galaxies. The field is now beginning to quantify the radial structure of the inner dusty accreting material directly. Starting from some historical aspects, the new information as being obtained and the resulting scientific outcome will be shared with the audience.

LOFAR activities in Sweden

Special Colloquium
Dr. T. D. Carozzi
ORATED
Onsala Space Observatory, Chalmers, Sweden

With the recent official opening of the LOFAR station at the Onsala Space Observatory in Sweden, the current incarnation of the International LOFAR telescope (ILT) is now complete. Although one of the smaller countries in the ILT, we plan to play an active role in various aspects of LOFAR. I will first present details of the Onsala station itself. Then I will show some of the work we have done on modeling the LOFAR station beams, including polarimetry, and how to assess the polarimetric quality of LOFAR configurations. This beam modeling work has recently become very important as it was realized that the basic definitions and geometries for it are currently not in the main LOFAR data reduction pipeline. I finish by outlining some initial attempts to exploit the new possibilities of the LOFAR design for new types of radio astronomical observations: in particular I will talk about the possibility of directly measuring the orbital angular momentum emitted by radio sources.

Merger Shocks in Clusters of Galaxies

Main Colloquium
Prof. Craig Sarazin
ORATED
University of Virginia, Charlottesville, USA

Clusters of galaxies are the largest relaxed bound systems in the Universe. They form hierarchically by the merger of smaller clusters and groups. Major cluster mergers are the most energetic events which have occurred in the Universe since the Big Bang. Cluster mergers drive shocks into the intracluster medium; these shocks increase the temperature, pressure, and entropy of the intracluster medium (ICM), and are the main heating source for the ICM. The same shocks can generate turbulence in the ICM, and may (re)accelerate relativistic electrons and ions. Diffuse radio sources (radio relic and halos) are seen in clusters which do, indeed, seem to be related to cluster merger shocks. I will present new results on merger shocks in clusters galaxies, including Chandra, XMM-Newton, Swift, and Suzaku X-ray observations which allow us to determine the properties of the shocks. The efficiency of shock particle acceleration can be derived by comparing the merger shocks and resulting radio relics. X-ray observations give limits on the nonthermal Inverse Compton emission by the relativistic electrons in the radio halos and relics. I will also present new results from high spatial resolution Sunyaev-Zel’dovich (SZ) imaging for clusters using the MUSTANG detector on the Green Bank Telescope (GBT). Because the thermal SZ effect measures the integrated pressure along the line of sight, these images have proven to be very useful for detecting merger shocks in clusters.

Satellite galaxies and high-velocity clouds

Special Colloquium
Sylvia Plöckinger
ORATED
Universität Wien

Galaxies like the Milky Way Galaxy (MWG) are not isolated systems but are continuously interacting with their environment. Gas packages from the galactic disk can be ejected by the energy of cumulative supernovae explosions, but also accretion is observed, either due to in-falling pure gas clouds or systems of both stars and gas, like dwarf satellite galaxies which are spiraling into their host galaxy (”minor merger”). Other systems that can be used to determine the existence of dark matter sub-halos around the MWG are High Velocity Clouds (HVCs). These pure gas clouds are reaching very high velocities (up to more than 400 km/s) on their way to the galaxy center, which means that these systems are facing ram pressure due to interactions with the hot gaseous halo around the galaxy. We performed a series of 3D hydrodynamical simulations using the FLASH Code V3.2 and found that both HVCs and dwarf galaxies do not necessarily need a dark matter halo to keep their material bound. We solve for the self-gravity with a multi-grid Poisson solver and find that also pure gas clouds during the simulation time of 100 Myrs, with galacto-centric distances between 20 and 50 kpc lose only a few percent of their initial mass. First results of our TDG simulations show good agreement with previous simulations of other authors, which focused on the large scale evolution of interacting galaxies. Dwarf galaxies in our runs can survive the simulation time of 300 Myrs, if their distance to the mass center of the interacting galaxies around 75 kpc, while systems which are much closer, suffer from the tidal field and get disrupted faster.

Probing the Microscopic with the Macroscopic: from Properties of Star Cluster Systems to Properties of Cluster-Forming Regions

Lunch Colloquium
Dr. Genevieve Parmentier
ORATED
Astronomisches Rechen-Institut, Heidelberg

Studying how gas expulsion out of forming star clusters shapes the properties of young cluster systems constitutes a powerful probe into the properties of cluster-forming regions (CFRgs). I show that, in combination with an external tidal field, the CFRg mass-radius relation rules cluster infant weight-loss as a function of cluster mass. The observational constraint of a time-invariant slope for the power-law young cluster mass function is robustly satisfied by CFRgs with a constant mean volume density. This conclusion is consistent with star formation a process driven by a volume density threshold. As a result, properties of molecular clumps and CFRgs get dissociated. This allows to understand the massive star formation limit in the molecular clump mass-radius space.

Pulsar single-pulse studies with LOFAR

Main Colloquium
Dr. Vladislav Kondratiev
ORATED
ASTRON

Rotation-powered pulsars display a variety of observational phenomena both in their integrated profiles and individual pulses, usually observed as a change in intensity and profile shape on different time scales from seconds (nulling) to microseconds and lower (giant pulses). All these phenomena are mostly studied at radio frequencies above 1 GHz, where combination of pulsar spectra, effects related to interstellar propagation and sky temperature makes 1-2 GHz band an ideal for pulsar observations. However, remarkably for the past few years at the very low frequencies < 30 MHz several pulsars were reported to show occasional bright narrow-band individual pulses. They were first identified by Ul’yanov et al. (2006) and termed ”anomalously intensive pulses”. Recent LOFAR low-frequency observations of these pulsars allowed us to study this phenomenon in more detail taking advantage of LOFAR’s large fractional band and sensitivity. In my talk I will briefly give a review of giant pulses and anomalously intensive pulses and present the latest results of our single-pulse studies with LOFAR. I will argue that these low-frequency pulses are intrinsic to the pulsar emission mechanism itself rather than being due to propagation effects and will discuss the relation of this phenomenon to other single-pulse phenomena like giant pulses.

Physics and Kinematics of the Parsec Scale Jet of the Quasar 3C345

Lunch Colloquium
Dr. Frank Schinzel
ORATED
MPIfR

The quasar 3C 345 is one of the archetypical examples of an AGN featuring a complex parsec-scale jet with a pronounced helical morphology and a range of distinct emitting regions moving at apparent superluminal speeds. I am going to present recent results from a study of the long-term jet evolution of more than 20 distinct regions embedded in the jet monitored over a period of over 30 years. This study provides evidence for the existence of a slowly evolving pattern lit up by passages of plasma condensations ejected during high activity states. Special attention will be given to the onset of a new active state that began in 2008 which has been observed from radio through gamma-rays. The combined study of the evolution of gamma-ray, optical, and parsec-scale radio emission indicate similar physical origins and provide evidence for shock-shock interactions, while questioning some of the proposed scenarios for production of high energy emission.

Gaseous Halos in Spiral Galaxies

Special Colloquium
Dr. Peter Kamphuis
ORATED
Ruhr-Universität Bochum

The properties of gas in the halos of galaxies constrain global models of the interstellar medium. Studies of the extra-planar ionized hydrogen as well as the neutral hydrogen have shown that gaseous halos can improve our understanding of the disk-halo interaction, accretion from the IGM and global magnetic fields; these are key elements in galaxy evolution. Kinematical information is of particular interest since it provides clues to the origin of the gas and helps to disentangle projection effects. Such kinematical studies have shown that the rotational velocities of the gas in massive spiral galaxies decline with increasing distance to the mid-plane, the so-called lagging halos. However, whether all gaseous halos contain such a ’lag’ as well as what is the origin of this vertical gradient in the rotational velocities remain open questions. Multi-wavelength studies could be key in solving these problems. In particular, X-ray observations can provide us with the physical conditions present in these halos. Currently large multi-wavelength surveys are undertaken to obtain the properties of gaseous halos for large samples of galaxies. This will, for the first time, provide us with the data to correlate halo properties with global galaxy properties.

Generation of Magnetic Field in Cosmic Structure

Main Colloquium
Dr. Francesco Miniati
ORATED
ETH Zürich

Magnetic fields are a common feature of cosmic bodies, including planets, stars and young galaxies and even the largest structures of the universe. Recent experiments based on gamma-ray observations of distant blazars suggest that even void of galaxies are permeated with magnetic fields, with strengths ge 10^{-18} G or so, which are extremely difficult to explain with astrophysical processes. After a brief review of observations, I will focus on a “resistive” mechanism for the generation of intergalactic magnetic fields before the end of re-ionization. In this model, magnetic field is generated by the streaming of cosmic-ray particles produced by the same galaxies and stars that are also responsible for the re-ionization of the universe. I will describe the model and present numerical simulations of structure formation that include self-consistently the resistive source of magnetic field. Finally, I will present novel plasma experiments that exploit the scaling relations of hydrodynamics to reproduce the relevant protogalactic shocks conditions in a laboratory chamber. We have applied this experiments to study the generation of magnetic fields in protogalaxies by the Biermann’s battery mechanism. I will show results of the experiment and the fascinating quantitative agreement with predictions from simulations of structure formation.

Project BEACON! (or: How I learned to stop worrying and love general relativity)

Lunch Colloquium
Dr. Paulo Freire
ORATED
MPIfR

In this talk I present project BEACON, which has just been funded with a 1.9 Million Euro Consolidator award from the European Research Council. I describe the theoretical motivation of the project and its aims: to carry out the most stringent tests of gravitational theories ever made by timing binary pulsars. To do this, we are now in the process of building a new ultra-broadband receiver and coherent dedispersion systems for the Effelsberg telescope, which will yield revolutionary improvements in pulsar timing precision. I will also discuss some preliminary results that show that, even at the start of our project, our tests already exclude all natural versions of the Tensor Vector scalar theories of gravity, a relativistic formulation of Modified Newtonian Dynamics (MOND). These preliminary findings indicate that, within our experimental precision, General Relativity provides the correct description of gravity.

From Spherical Cows to Modified Newtonian Gravity

Special Colloquium
Dr. Robert L. Dickman
ORATED
National Radio Astronomy Observatory, USA

In 1983, M. Milgrom pointed out that a seemingly simple modification of the Newton force law – which he termedi Modified Newtonian Dynamics (MOND) – could explain galactic rotation curves without the need to invoke the presence of dark matter. With the passage of time, MOND has become increasingly compelling as an economical modeling tool for galaxy rotation curves, and is now also recognized to predict a number of other regularities in the behavior of disk and ellipsoidal galactic systems (such as the Fisher-Tully and Faber Jackson relations). MOND is nonlinear in the gravitational potential. In its Lagrangian formulation, this nonlinearity is encoded by the ratio of total gravitational acceleration to a new fundamental acceleration scale, ao and under certain conditions, a system in equilibrium whose internal acceleration is below ao may exhibit novel properties whose presence depends on the magnitude of the external gravitational field in which the system lies. This so-called ”external field effect” (EFE) can lead to phenomena that include morphological elongations as well as amplifications of the internal gravitational field. Equally important, these signature effects can be suppressed by a sufficiently strong external gravitational field. The rarity of suitably simple test objects – ”spherical cows” – and the smallness of Milgrom’s constant, ao, have made it very difficult to test MOND’s EFE predictions observationally. Recently developed observational capabilities, In this talk I will review various predictions that MOND makes via the EFE, and will discuss some recent observational results as well as their potential implications.

Geodetic VLBI and the 100 m telescope

Lunch Colloquium
Dr. Axel Nothnagel
ORATED
Institute of Geodesy and Geoinformation, University of Bonn

Radio telescope coordinates, Earth rotation variations and quasar positions are the primary results of geodetic and astrometric Very Long Baseline Interferometry (VLBI) observations. Pairs or networks of radio telescopes simultaneously observe quasars and other extra-galactic radio sources recording the noise patterns emitted by the radio sources. The observing schedule is quite different to astronomical ones because geodesists observe many quasars repeatedly for only 40 - 200 seconds each. The recordings are subsequently employed to determine the group delay observables in a correlation and fringe fitting process. Data analysis then provides a variety of highly precise and unique geodetic, geophysical and astrometric results. Radio source positions define a quasi-inertial reference frame, the only one which is available today. Radio telescope coordinates and velocities are used to establish and maintain a terrestrial reference frame for geodetic and geophysical studies. Although the Effelsberg 100 m telescope participates in geodetic sessions only twice a year, it provides an invaluable contribution to studies of tectonic stability in central Europe. However, the enormous size of the telescope requires a detailed analysis of its deformation characteristics.

The multiphase extraplanar medium in spiral galaxies

Main Colloquium
Dr. George Heald
ORATED
ASTRON

The continuing evolution of galaxies is linked with their connection to the external environment. Through mergers, interactions, and accretion, the structure and contents of galaxies’ interstellar media can be strongly altered. The extraplanar region in spiral galaxies is the interface between the star-forming disk and the environment. The structure and kinematics of the baryonic material in this interface region are vital clues to the relative importance of various processes, such as cold gas accretion and galactic fountains, in determining the history of galaxies. The strength and morphology of the magnetic fields in these regions may also be crucial to understanding the connection to the intergalactic medium. In this talk, I will describe results from two surveys that are shedding light on these issues: the recently completed WSRT Hydrogen Accretion in LOcal GAlaxieS (HALOGAS) Survey, and the WSRT-SINGS Survey. HALOGAS is the first systematic investigation of cold gas accretion in nearby spiral galaxies. It consists of deep (120 hours) WSRT observations of 22 edge-on and moderately-inclined nearby galaxies, and reveals the presence of kinematically lagging extraplanar gas, and counterparts to the Milky Way’s high velocity clouds. The WSRT-SINGS Survey provides high-quality polarimetric data for a partially overlapping galaxy sample (derived from SINGS), and has led to a common model of the magnetic field morphology in spiral galaxies. I will conclude the talk by describing directions for future work in both areas, to be pursued with upcoming telescopes such as LOFAR, as well as the Square Kilometre Array.

TBA

Lunch Colloquium
Dr. Sambaran Banerjee
ORATED
AIfA

Among the most explored directions in the study of dense stellar systems is the investigation of the effects of the retention of supernova remnants, especially that of the massive stellar remnant black holes (BH), in star clusters. By virtue of their eventual high central concentration, these stellar mass BHs potentially invoke a wide variety of physical phenomena, the most important ones being emission of gravitational waves (GW), formation of X-ray binaries and modification of the dynamical evolution of the cluster. We propose, for the first time, that rapid removal of stars from the outer parts of a cluster by the strong tidal field in the inner region of our Galaxy can unveil its BH sub-cluster, which appears like a star cluster that is gravitationally bound by an invisible mass. We study the formation and properties of such systems through direct N-body computations and estimate that they can be present in significant numbers in the inner region of the Milky Way. We call such objects ``dark star clusters' (DSCs) as they appear dimmer than normal star clusters of similar mass and they comprise a predicted new class of entities. The finding of DSCs will robustly cross-check BH-retention; they will not only constrain the uncertain natal kicks of BHs, thereby the widely-debated theoretical models of BH-formation, but will also pin-point star clusters as potential sites for GW emission for forthcoming ground-based detectors such as the ``Advanced LIGO'. Finally, we also discuss the relevance of DSCs for the nature of IRS 13E; a highly controversial stellar association close to the Galactic center. [Submitted; Authors: Sambaran Banerjee and Pavel Kroupa]

New methods and tools for specifying the Milky Way's magnetic field structure, and some implications for very high energy CR pro

Special Colloquium
Prof. Philipp Kronberg
ORATED
University of Toronto, Canada

I describe two new RM analyses for specifying the average magnetic field geometry in the Milky Way. The first results reveal that, within   1.5 kpc of the Galactic mid-plane near the Sun, a ``grand magnetic design’’ is now clearly indicated in RM’s (Kronberg & Newton-McGee 2011). The Milky Way disk’s magnetic structure appears similar to other grand design spiral galaxies when seen with similar linear resolution. A second paper (Pshirkov et al 2011) uses the same all-sky Faraday RM (l,b) data to generate mathematical model templates for the halo + disk magnetic field. These two studies will help to define the environment for HE CR propagation, and to ultimately understand their energy-dependent anisotropies.

Mopra and the Central Molecular Zone / Astronomy in Antarctica

Special Colloquium
Prof. Michael G. Burton
ORATED
University of New South Wales, Sydney, Australia

Mopra and the Central Molecular Zone: The Central Molecular Zone (or CMZ) holds the greatest collection of moleculari gas in our Galaxy, an environment which is denser, warmer and more turbulent than the molecular medium found in the spiral arms. It also provides us a panoramic view of what a galactic nucleus may look like. The Mopra telescope has been used to undertake a multiple molecular line mapping survey of the CMZ, mapping the distribution of 18 molecular lines across it. This talk will overview this fascinating new data set, and some of the interesting avenues of investigation it opens. Astronomy in Antarctica: A rich range of astrophysical endeavours are now underway in Antarctica, ranging from neutrino telescope to cosmic microwave background studies to traditional optical / IR / mm astronomy. Astronomy is now underway at 4 Antarctic plateau stations as well as from long duration ballooning around the coast. This brief talk will overview some of this activity, and opportunities that the clear, cold, dry and stable conditions of the high plateau present for future study of the cosmos.

TBA

Lunch Colloquium
Dr. Matthias Maercker
ORATED
AIfA

After careful planning for over a decade, ALMA has started real science operations in the end of September with the first batch of accepted early science proposals. A total of 919 proposal were submitted, of which 112 high-priority proposals will be scheduled to be observed. 35 of these are from Europe. Already now, ALMA meets and exceeds the requirements set for early science, and the observations are certain to increase our knowledge of the universe as seen at millimetre and submillimetre wavelengths. With the first observations underway, preparations are ongoing for the next cycle of proposals with a larger array. I will give an update on the current status of the ALMA early science array, the outcome of the proposal review, and the observations, as well as a preview of the plans for Cycle 1.

Searching for radio pulsars, just about everywhere!

Lunch Colloquium
Dr. Ralph Eatough
ORATED
MPIfR

In this talk I will summarize the work being done at the MPIfR, in collaboration with various international partners, on searching for radio pulsars. Finding more pulsars elucidates the properties of their Galactic population, and also offers the possibility of uncovering new and extreme phenomena in neutron-star astrophysics. New all-sky pulsar surveys, enabled by recent hardware upgrades, are underway at both the Effelsberg and Parkes observatories. Already, three new pulsars have been discovered at Effelsberg, and a further twelve have been identified in a deep survey of the Galactic plane at Parkes. In addition, over the last year, 10 pulsars have been discovered by re- analyzing archival data from the Parkes multi-beam pulsar survey (PMPS) using Einstein@home; a massive distributed computing project. The Einstein@home analysis of the PMPS is the most sensitive search for highly relativistic binary pulsars (e.g. coalescing NS-NS or NS-BH systems), but to date, none of the target systems have been found. Possible reasons for the non-detection and detection techniques, such as artificial neural networks, that may aid in future searches for such systems will be discussed.

Molecular Tracers of Turbulent Shocks and Large Scale Collapse Modes in Star Forming Regions

Special Colloquium
Andy Pon
ORATED
University of Victoria, Canada

Molecular clouds exhibit large linewidths, which are usually interpreted as being due to supersonic turbulence. This turbulence plays a key role in many theories of star formation, as it is believed to help support and fragment molecular clouds. Simulations of such turbulence, however, show that this turbulence should decay rapidly through shocks and there has been little work done in determining how this dissipated energy leaves a molecular cloud and whether there would be any observable signature of this turbulent dissipation. I will describe recent work that I have been involved with in determining the dominant cooling mechanisms of slow, C-type shocks. We have run models of C-type shocks, based on the code of Kaufman & Neufeld (1996), for densities ranging from 102.5 to 103.5 cm-3 and velocities of 2 and 3 km/s. By combining these shock models with estimates for the rate of turbulent energy dissipation in nearby molecular clouds (Basu & Murali 2001), we produce synthetic CO spectra and predict those line emissions that will be observable with current and upcoming observational facilities such as Herschel, ALMA, APEX, and CCAT. In particular, we find that the CO J = 6-5 and 7-6 lines are powerful shock tracers. I will also be talking about a second project that I have been involved with in determining how the ratio of local to global collapse times varies between molecular clouds with different geometries.

The Cosmological Impact of Blazars: from Plasma Instabilities to Structure Formation

Main Colloquium
Dr. Christoph Pfrommer
ORATED
Institut fuer Theoretische Astrophysik, Heidelberg

The endeavors of imaging atmospheric Cherenkov telescopes have recently revealed a plethora of blazars that populate the extragalactic gamma-ray sky at TeV energies. Blazars are a subclass of accreting super-massive black holes with powerful relativistic outflows directed at us, allowing us to detect the Doppler-boosted radiation. The Universe is opaque to extragalactic TeV-gamma rays because they annihilate and pair produce on the extragalactic background light. The resulting ultra-relativistic pairs are commonly assumed to lose energy primarily through inverse Compton scattering of cosmic microwave background photons, reprocessing the original emission from TeV to GeV energies. However, I will argue that this is not the case; powerful plasma instabilities driven by the highly anisotropic nature of the ultra-relativistic pair distribution provide a plausible way to dissipate the kinetic energy of the TeV-generated pairs locally, heating the intergalactic medium (IGM). This has important implications for origin of the extragalactic gamma-ray background and recent estimates of intergalactic magnetic field strengths from blazar spectra. It also significantly alters the thermal history of the IGM, imprinting a unique signal into the Lyman-alpha forest. Finally, the substantially increased temperatures of the IGM have dramatic consequences for the thermodynamic structure of forming galaxy groups and dwarf galaxies. This may help resolve the ”missing satellite problem” in the Milky Way and the ”void phenomenon” of the low observed abundances of dwarf satellites compared to cold dark matter simulations and may bring the observed early star formation histories into agreement with galaxy formation models.

Probing the First Stars and Black Holes in the Early Universe with the Dark Ages Radio Explorer (DARE).

Special Colloquium
Jack Burns
ORATED
University of Colorado Boulder

A concept for a new space-based cosmology mission called the Dark Ages Radio Explorer (DARE) will be presented in this talk. DARE’s science objectives include (1) When did the first stars form? (2) When did the first accreting black holes form? (3) When did Reionization begin? (4) What surprises does the end of the Dark Ages hold (e.g., Dark Matter decay)? DARE will use the highly-redshifted hyperfine 21-cm transition from neutral hydrogen to track the formation of the first luminous objects by their impact on the intergalactic medium during the end of the Dark Ages and during Cosmic Dawn (redshifts z=11–35). It will measure the sky-averaged spin temperature of neutral hydrogen at the unexplored epoch 80-420 million years after the Big Bang, providing the first evidence of the earliest stars and galaxies to illuminate the cosmos and testing our models of galaxy formation. DARE’s approach is to measure the expected spectral features in the sky-averaged, redshifted 21-cm signal over a radio bandpass of 40-120 MHz. DARE orbits the Moon for a mission lifetime of 3 years and takes data above the lunar farside, the only location in the inner solar system proven to be free of human-generated radio frequency interference and any significant ionosphere. The science instrument is composed of a low frequency radiometer, including electrically-short, tapered, bi-conical dipole antennas, a receiver, and a digital spectrometer. The smooth frequency response of the antennas and the differential spectral calibration approach using a Markov Chain Monte Carlo technique will be applied to detect the weak cosmic 21-cm signal in the presence of the intense solar system and Galactic foreground emissions.

Dynamics in young star clusters: From planets to massive stars

Special Colloquium
Dr. Christoph Olczak
ORATED
Astronomisches Rechenzentrum, Heidelberg

The young star clusters we observe today are the building blocks of a new generation of stars and planets in our Galaxy and beyond. Despite their fundamental role we still lack knowledge about the initial conditions under which star clusters form and the impact of these often harsh environments on the formation and evolution of their stellar and substellar members. I will demonstrate the vital role numerical simulations play to uncover both key issues. Using dynamical models of different star cluster environments – from NGC 2024 to the Orion Nebula Cluster (ONC) and to the Arches cluster – I will show the huge variety of effects stellar interactions potentially have: they can prevent or trigger planet formation, modify the disk structure, affect the stellar multiplicity, and - fortunately - leave characteristic signatures that can be traced observationally. Moreover, I will present a recently developed very efficient measure of mass segregation in stellar systems. Its application to realistic numerical models of young star clusters shows that mass segregation occurs rapidly even for spherical systems without substructure. This finding is a critical step to resolve the controversial debate on mass segregation in young star clusters andi provides strong constraints on their initial conditions.

Structure of Hot Molecular Cores

Lunch Colloquium
Dr. Rainer Rolffs
ORATED
MPIfR

Hot molecular cores are a transient phase of high-mass star formation, after heating up the surrounding molecular gas, but before ionizing it. In this talk, which I held as my PhD defense in Cologne, I will give an introduction to high-mass star formation, present the observations and analysis methods (APEX and Herschel observations with spherical radiative transfer modeling and VLA and SMA observations with 3-d modeling), and highlight some results of my thesis. These include the large mass of hot molecular gas, the internal heating mechanism aided by diffusion of radiation, the reversal of infall in the central region, and the centrally flat density distribution. All can be explained by increased central pressure caused by feedback from young massive stars in a high-column-density environment.

Stellar Spectroscopy Unleashed - ELTs and Red Supergiants in the Coma Cluster

Main Colloquium
Prof. Dr. Rolf Peter Kudritzki
ORATED
Institute of Astronomy, Hawaii

The determination of the chemical composition and distances of galaxies is crucial for constraining the theory of galaxy formation and evolution in a dark energy and cold dark matter dominated universe. However, the standard techniques to obtain information about the chemical composition and distances of star forming galaxies are subject to large systematic uncertainties which are poorly understood. As an alternative, I introduce a new method, which will use low resolution J-band spectroscopy of individual red supergiant stars (RSGs) in distant galaxies. Using Mauna Kea IRTF SpeX low resolution spectra of Milky Way RSGs and MARCS model atmospheres we have demonstrated that our analysis method allows individual metallicities and alpha/Fe ratios to be determined with an accuracy of about 0.1 dex (Davies, Kudritzki, Figer, 2010, MNRAS 407, 1203). The extension of the method to star forming galaxies beyond the Local Group with MOS devices at large telescopes such as MOSFIRE/Keck and KMOS/VLT is straightforward. This new method will gain tremendous momentum with the next generation of ELTs and AO supported MOS instruments like IRMS at the TMT and EAGLE at the E-ELT, since the limiting magnitude in the diffraction limit case increases with the fourth power of the telescope diameter. We have shown that we can reach individual RSGs in galaxies as distant as the Coma Cluster (Evans, Davies, Kudritzki et al., 2011, A&A 527, 50). I will also discuss the potential of observing the integrated light of Super Star Clusters (SSCs). The J-band light of these objects is entirely dominated by RSGs as soon as the cluster age is larger than 8 Myr (Gazak, Kudritzki, Davies, 2011, in prep.). This allows for the determination of accurate detailed chemical composition by simple population synthesis techniques. Because of the enormous brightness of SSCs in the J-band an enormous volume of the local universe can be studied in this way.

The High Time Resolution Universe Survey and its Jewels

Main Colloquium
Prof. Matthew Bailes
ORATED
Swinburne University of Technology, Australia

The High Time Resolution Universe Survey for pulsars and fast transients is a very ambitious survey of the Southern sky with new digital spectrometers with a fast read-out time being performed by a collaboration from Australia, Germany (MPIfR), Italy and the UK. A complementary sister survey is underway at the Effelsberg 100m for the Northern sky. When completed the survey will have recorded almost 1 petabyte of data and (we believe) have discovered some 600+ pulsars including a large number of millisecond pulsars, sources of single pulses of emission and hopefully systems useful for testing theories of relativistic gravity. I will describe the (inexpensive) hardware used for survey based on the CASPER toolkit, how the data have been processed, radical new techniques for radio frequency interference excision and some of the remarkable systems being discovered, including the much-publicised “Diamond Planet” pulse recently published in Science. I will also demonstrate how GPU-based computers can exhaustively search these data for accelerated pulsars in the near future and hopefully find the first pulsar-black hole binary.

Astrometry Lost and Regained: From a modest experiment in Copenhagen in 1925 to the Hipparcos and Gaia space missions

Special Colloquium
Dr. Erik Hoeg
ORATED
Niels Bohr Institute, Copenhagen

Technological and scientific developments during the past century made a new branch of astronomy flourish, i.e. astrophysics, and resulted in our present deep understanding of the whole Universe. But this brought astrometry almost to extinction because it was considered to be dull and old-fashioned, especially by young astronomers. Astrometry is the much older branch of astronomy, in fact 2000 years of age, which performs accurate measurements of positions, motions and distances of stars and other celestial bodies. Astrometric data are of great scientific and practical importance for investigation of celestial phenomena and also for control of telescopes and satellites and for monitoring of Earth rotation. Our main subject is the development during the 20th century which finally made astrometry flourish as an integral part of astronomy through the success of the Hipparcos astrometric satellite, soon to be followed by the even more powerful Gaia mission. The Hipparcos mission approved in 1980 was based on photoelectric detectors measuring one star at a time. In 1992 CCD detectors were introduced in the Roemer mission proposal which could measure ten thousands of stars simultaneously, still in a rotating satellite performing a systematic scan of the entire sky. During 1993-97 an interferometric option, GAIA, was also studied, but the Roemer option with direct imaging on CCDs was much better and is therefore used in the Gaia mission.

A multiwavelength view of the microquasar Cyg X-1: spectral variability, Gamma-ray polarisation, and jets

Special Colloquium
Victoria Grinberg
ORATED
Dr Remeis Observatory & ECAP, Bamberg/Erlangen

Discovered in 1965, the microquasar Cygnus X-1 is a persistent high mass X-ray binary, consisting of an O-type supergiant and a stellar mass black hole, and therefore one of those system which are often considered as downscaled versions of AGN, an analogy supported in Cyg X-1 by observations of radio jets. The size and proximity of such systems allow us to assess phenomena on time-scales which are not accessible in their supermassive siblings. Cyg X-1 shows distinct X-ray states, characterised by X-ray spectral and timing properties, as well as correlated radio behaviour. It is the target of coordinated multiwavelength studies, e.g. simultaneous mid-infrared, X-ray and radio observations, as well as of two large monitoring campaigns in X-ray/radio and Gamma-rays: the bi-weekly RXTE/AMI monitoring campaign (1998-today) and the INTEGRAL Key Programme (2007-today). The multiwavelength snapshots and long term high energy variability studies are complementary approaches with the ultimate goal to understand the inflow/outflow connection for black holes on all mass-scales. Additionally, all INTEGRAL data of Cyg X-1 have been used to constrain, for the first time, the Gamma-ray polarisation of an X-ray binary: we find a significant polarisation signal in the so-called hard tail above 400 keV and therefore further the notion that this emission component is produced in jets.

IRAS 16293-2422: a very young FU Orionis analog entering a phase of enhanced accretion?

Lunch Colloquium
Prof. Laurent Loinard
ORATED


Multi-epoch (Expanded) Very Large Array observations have revealed that one of the protostars in the very young system IRAS 16293-2422 expelled a bipolar pair of ionized ejecta in early 2006, and underwent another (possibly one-sided) ejection in 2011. A reanalysis of archival Sub-Millimeter Array observations further reveals a 40% increase in mass accretion rate associated with the 2006 ejection event. This observation provides unambiguous empirical evidence for a direct (presumably magnetic) coupling between accretion and ejection processes during the earliest stages of stellar evolution. It also validates the frequently made assumption that the accretion history of young stellar objects can be reconstructed from the fossil record of their ejection past imprinted in their outflow systems. The excess mass accreted during the accretion/ejection episode experienced by IRAS 16293-2422 in 2006 was roughly three times the mass ejected during the same timespan, in good agreement with theoretical expectations. IRAS 16293-2422 has been regularly monitored at radio wavelengths ever since the late 1980s, and the 2006 and 2011 events are the only recorded ejections so far. It appears that this source is currently undergoing a burst of accretion/ejection, analogous (albeit less extreme) to those suffered by the more evolved FU Orionis objects.

X-ray emission from cool stars

Main Colloquium
Dr. Jan Robrade
ORATED
Hamburger Sternwarte

X-ray emission from cool stars is produced by several million degree plasma in their outer atmospheric layer, the corona. Actually the Sun, a slightly aged cool star, was the first astrophysical source detected in X-rays, but coronae are ubiquitous on stars with spectral types from late A to the end of the main sequence. Its generation is connected to magnetic activity driven by dynamo processes operating in the stellar interior. X-ray astronomy strongly contributes to our understanding of the underlying astrophysical processes like magnetic field generation or energy release and their evolution throughout the stellar life time. I review basic properties of stellar X-ray emission and highlight some phenomena related to magnetic activity in cool stars. In this context I present results from observations with the X-ray missions XMM-Newton and Chandra; going from young pre-main sequence stars over the hot and cool stellar extremes in the regime of magnetic activity to stars that are similar to our Sun.

The space radio telescope Radioastron is successfully launched and deployed

Special Colloquium
Dr. Yuri Kovalev
ORATED
NRAO Green Bank & Lebedev Physical Institute, Moscow

If you want to learn more about the current status, recent events, and future plans for tests, fringe search and science observations to be done with the ground-space VLB interferometer Radioastron, welcome to my talk.

Jet dynamics, stability, and energy transport

Special Colloquium
Dr. Manuel Perucho
ORATED
University of Valencia, Spain

Relativistic jets are a common feature of compact objects accreting matter. One of their most remarkable features is their long-term stability. In the case of extragalactic jets, they propagate up to nine orders of magnitude in distance. In the case of microquasar jets, the environmental conditions and the jet power are crucial for the jets to reach parsec scales and be detected by radio telescopes in the form of radio blobs. In this talk, I will review the main results from numerical simulations that have allowed to us to learn about the basic dynamics of relativistic jets. I will pay special attention to the stability properties and possible causes of disruption of both extragalactic and microquasar jets. At the end of my talk, I will show how using very-long-term relativistic simulations can change our view on how AGNs feedback their host clusters.

The Ionized Interstellar Medium on Scales < 100 AU: Blobs, Clouds, or Spaghetti?

Main Colloquium
Dr. William A. Coles
ORATED
University of California, San Diego

The IISM can be studied directly with imaging spectroscopy on relatively large scales, and less directly with various radio propagation techniques on much smaller scales. The two “scale windows” touch around 10 AU. In the small scale regime it has been the practice to model the IISM as homogeneous, isotropic, Kolmogorov turbulence. It is becoming apparent that none of these assumptions is valid. I will discuss the evidence for this suggestion and show some (relatively) new observations suggesting that a model of flux ropes, not unlike the structure of a coronal mass ejection, might be more appropriate. The case is far from closed - this discussion will be characterized (like much work on turbulence) by sparse observations, hand-waving physics, and wildly-speculative interpretation.

Studying the Fomalhaut debris disk with infrared interferometry

Main Colloquium
Dr. Olivier Absil
ORATED
Liege University, Belgium

In this talk, I will describe two recent studies carried out with infrared interferometry to characterise the planetary system around Fomalhaut, and its debris disk in particular. In the first study, we aimed to determine whether the debris disk is located within the equatorial plane of the stellar photosphere, in an attempt to improve our understanding of spin-orbit misalignements in planetary systems in general. We measured the orientation of the rotationnally-distorted stellar photosphere using micro-arcsecond precision VLTI/AMBER spectro-astrometry within the Br-gamma line. The derived position angle is in perfect agreement with the position angle of the cold debris disk measured in visible and sub-millimeter images. We discuss the implications of this result on our understanding of the dust grain properties in the Fomalhaut disk. In the second study, we aimed at characterising the dust content of the innermost part of the debris disk. We used archival high-precision K-band visibility measurements with VLTI/VINCI and obtained N-band nulling observations with the Keck Interferometer Nuller. We report a significant excess emission at K band, and a marginal excess emission at N band, that we attempt to reproduce with a 2D debris disk model. A comprehensive Bayesian analysis of the main disk parameters is performed to derive most-probable values. Our analysis points towards a very compact ring of hot dust close to the sublimation radius as the origin of the reported excess emission.

Towards an Understanding of Gas Accretion and Star Formation in Galaxies

Main Colloquium
Dr. Guinevere Kauffmann
ORATED
Max-Planck-Institut für Astrophysik, Garching bei München

The GALEX Arecibo SDSS Survey (GASS) is an ongoing large targeted survey at Arecibo, home to world’s largest single-dish radio telescope. GASS is designed to measure the neutral hydrogen content of a representative sample of sim 1000 massive galaxies, uniformly selected from the SDSS spectroscopic and GALEX imaging surveys. A sister survey COLD GASS is being cunducted at the IRAM 30m telescope to better understand the connection between atomic and moelcular gas and star formation in the same galaxies. I will discuss recent results from both surveys, highlighting how the outer disks of spiral galaxies like our own Milky Way are still being assembled at the present day.

A Story of Three Galaxies: The Truth About Giant Ellipticals

Main Colloquium
Prof. Dr. William E. Harris
ORATED
McMaster University, Canada

Giant elliptical galaxies may have the most complex formation histories. Use of the Hubble Telescope cameras has allowed us to probe the composition of the outer parts of the nearest gE’s by direct resolution into stars. For these few keystone objects, we can construct true distribution functions of metallicity and age. These are revealing some surprises, and add essential pieces of data to the more normal but much cruder measurements from integrated light.

Wild at Heart: The Particle Astrophysics of the Galactic Centre and the Fermi Bubbles

Main Colloquium
Dr. Roland Crocker
ORATED
MPI für Kernphysik, Heidelberg

I describe the high-energy astrophysics of the inner  200 pc of the Galaxy. This is ultimately driven by the on-going massive star formation that occurs in this region. Our recent modelling shows that the supernovae exploding here every few thousand years inject enough power to i) sustain the steady-state, in situ population of cosmic rays (CRs) required to generate the region’s non-thermal radio and diffuse TeV gamma-ray emission (as observed by the HESS telescope); ii) drive a powerful wind that advects non-thermal particles out of the inner GC; iii) accelerate the CR protons and heavier ions which, continuously advected to very large scales (up to  10 kpc) above and below the plane over timescales approaching the age of the Galaxy, generate the very-extended regions of hard-spectrum gamma-ray emission recently detected by the Fermi telescope (and corresponding microwave structures detected by WMAP – the ”Fermi bubbles” and ”WMAP haze”). Our modelling bounds the magnetic field amplitude in the inner few degrees of the Galaxy to the range 60< B/microG < 400 and predicts a region of very extended  TeV gamma-ray and neutrino emission surrounding the GC, the latter constituting a very promising source for a future, km3-class Northern Hemisphere neutrino telescope.

Modified Gravity Or Dark Matter?

Special Colloquium
Prof. Dr. John Moffat
ORATED
Perimeter Institute for Theoretical Physics, Canada

Modified Gravity (MOG) has been used successfully to explain the rotation curves of galaxies, the motion of galaxy clusters, the Bullet Cluster, and cosmological observations without the use of dark matter. We review the main theoretical ideas and applications of the theory to astrophysical and cosmological data.

Nature, formation, and evolution of High Mass X-ray Binaries

Main Colloquium
Dr. Sylvain Chaty
ORATED
University Paris Diderot

I will describe the nature, formation and evolution of the 3 kinds of high mass X-ray binaries: HMXBs hosting Be star, accreting the wind from supergiants, and accreting through Roche lobe filling supergiants. A wealth of new observations, from the high-energy side (mainly INTEGRAL satellite), completed by multi-wavelength observations (mainly optical/near-infrared/mid-infrared from ESO), has shown that a new population of supergiant HMXBs has been recently revealed. New observations even suggest the existence of evolutionary links between Be and stellar wind accreting supergiant X-ray binaries. I will describe observational facts about these different categories of HMXBs, discuss the different models of accretion in these sources (e.g. transitory disk vs clumpy wind), show the evidences of a link between these different kinds of HMXBs, and finally include comparisons with population synthesis models.

The central parsecs of active galactic nuclei in the infrared

Main Colloquium
Dr. Almudena Prieto
ORATED
Max-Planck-Institut für Astronomie, Heidelberg

The use of adaptive optics and interferometer techniques in the IR has proven to be extremely powerful in penetrating and resolving the central parsecs of the brightest galaxies. Two main results that have emerged from the study of the nearest active galactic nuclei using those techniques will be reviewed: 1) Within scales of a few parsecs, some AGN show with unprecedented detail nuclear channels through which material seems to be driven towards the very centre, others however show a “clean” central environment. At the very center, a compact region of about 2 pc size is resolved in the best studied cases, for most cases the spatial scales achived limit the nuclear torus to less than 10 pc in size, 2) Sub-arcsec spectral energy distributions of these cores, spanning the UV - radio range, show very different from those currently in use and based on larger aperture data: the shape of the spectral energy distribution is different and the bolometric luminosity largely overestimated. The implications from these differences will be discussed.

Binary black hole coalescences in numerical relativity

Main Colloquium
Prof. Dr. Luciano Rezzolla
ORATED
MPI for Gravitational Physics, Albert Einstein Institute, Golm

Recent years have seen a major progress in numerical relativity and the solution of the simplest and yet among the most challenging problems in classical general relativity: that of the evolution of two black holes interacting only gravitationally. I will review the results obtained so far and also the impact these have in gravitational-wave detection, in astrophysics and in cosmology. Finally, I will comment on how to go from a ”knowledge” of the properties of this process to an ”understanding” of the physics of black hole spacetimes.

MeerKAT, the South African SKA Precursor

Main Colloquium
Dr. Roy Booth
ORATED
Hartebeesthoek Radio Astronomy Observatory, South Africa

MeerKAT is designed to be the most sensitive array in the Southern Hemisphere. It will consist of 64 x 13.5m offset Gregorian antennas and operate over a frequency range of 0.59 to 14.5 GHz. It is hoped that it will become operational between 2014 and 2016. A call for Large Survey project proposals for the array produced 20 proposals involving 730 individuals (500 unique), requesting more than 10 years observing time. A subsequent TAC meeting reduced these proposals by a factor of 2 and a time allocation of 5 years. I will discuss the developments in RSA leading up to MeerKAT, and review the proposed science. I will also introduce a proposal for an African VLBI Network which could operate with the EVN and other VLBI arrays.

Flugzeugastronomie mit GREAT

Main Colloquium
Dr. Stefan Heyminck
ORATED
MPI für Radioastronomie

Auf Wunsch vieler Mitarbeiter werden wir unseren Einsatz auf dem Flugzeugobservatorium SOFIA noch einmal (und auf Deutsch) vorstellen. Dieses Mal mit mehr Augenmerk auf die Vorbereitung des Instruments im Labor und den Betrieb im Flug; unterlegt mit Filmsequenzen der NASA zu den einzelnen Phasen.

Ab initio calculation of the Hoyle state

Main Colloquium
Prof. Dr. Ulf Meissner
ORATED
HISKP

The Hoyle state plays a crucial role in the hydrogen burning of stars heavier than our sun and in the production of carbon and other elements necessary for life. This excited state of the carbon-12 nucleus was postulated by Hoyle as a necessary ingredient for the fusion of three alpha particles to produce carbon at stellar temperatures. Although the Hoyle state was seen experimentally more than a half century ago, nuclear theorists have not yet uncovered the nature of this state from first principles. I report the first ab initio calculation of the low-lying states of carbon-12 using supercomputer lattice simulations and a theoretical framework known as effective field theory. In addition to the ground state and excited spin-2 state, we find a resonance at -85(3) MeV with all of properties of the Hoyle state and in agreement with he experimentally observed energy. These lattice simulations provide insight into the structure of this unique state and new clues as to the amount of fine-tuning needed in nature for the production of carbon in stars.

Airborne FIR Astronomy with SOFIA: First Science Flight with GREAT

Main Colloquium
Dr. Rolf Güsten
ORATED
MPIfR Bonn

The Stratospheric Observatory for Infrared Astronomy (SOFIA) has completed the Commissioning and Science Demonstration phase with the two first-light instruments FORCAST (Cornell) and GREAT, and is now executing Basic Science with community involvement. GREAT, the heterodyne spectrometer build by MPIfR and the University of Cologne, in cooperation with MPS and DLR-PF, successfully performed its first science flights in early April. We will introduce SOFIA, the observatory and its operation, and describe the design and performance of the GREAT instrument. We will highlight the scientific potential of airborne far-infrared astronomy, and present first results derived from the GREAT early science flights.

Massive field stars as runaways

Main Colloquium
Dr. Vasilii V. Gvaramadze
ORATED
Sternberg Astronomical Institute, Moscow State University

The large separation (hundreds parsecs) of some massive stars from known young star clusters and OB associations is often interpreted as an indication that the field can produce stars as massive as those born in clusters. An obvious alternative to this interpretation is that the massive field stars were actually formed in a clustered environment and subsequently ejected from their birth sites via dynamical processes. To prove the runaway nature of the massive field stars, we used the archival data of the Midcourse Space Experiment (MSX) satellite and the Spitzer Space Telescope to search for bow shocks (the natural attributes of supersonically moving objects) around isolated OB stars in the Milky Way and the Magellanic Clouds. We detected dozens of bow shocks. The geometry of the bow shocks allow us to infer the direction of stellar motion, thereby determining the possible parent clusters even for those field OB stars whose proper motions are still not available or measured with a low significance.

From V838 Mon to V1309 Sco: a story on stellar mergers

Special Colloquium
Dr. Romuald Tylenda
ORATED
N. Copernicus Astronomical Centre

V838 Mon erupted in 2002 and quickly raised a wide interest, partly because of its spectacular light echo but mostly because of its behaviour during and after the eruption. Astrophysicist quickly realised (at least some of them) that it could not be a classical nova. The eruption lasted  3 months, during which the object attained a luminosity of  106 L_isun and, what was most important, the object became very cool and for a few months it practically disappeared from the optical (remaining very luminous in the infrared). For many years I have been trying to convince astrophysisicts that eruptions of this type result from stellar collisions and mergers. Other objects of the V838 Mon type (also named as “red novae” or "optical transients”) are M31 RV (erupted in 1989), V4332 Sgr (1994), M85OT2006, NGC300OT2008 and V1309 Sco (2008). The latter object turned out to be a rosetta stone in the subject. Due to its position on the sky (3 degrees from the Galactic centre) the object has been monitored by the OGLE project since 2001. The light curve of the progenitor evidently shows that this was a contact binary, whose orbital period was systematically decreasing up to the merger of the system, which started in March 2008, i.e. 6 months before the discovery of the V1309 Sco eruption.

Super-Earth & Life: a fascinating puzzle

Main Colloquium
Dr. Lisa Kaltenegger
ORATED
MPI für Astronomie

The first Super-Earths have recently been discovered. This number will raise significantly when Kepler planetary candidates will be confirmed. We show models for rocky Super-Earth atmospheres and derive detectable spectroscopic features that can indicate habitable environments in transmission and emergent spectra for future space- and ground based telescopes like the James Webb Space Telescope. What does it take for super-Earths to support life? As a specific example, we show under which condition the recently discovered M-dwarf planet Gl581 d is potentially habitable. This talk will focus on the cross-disciplinary connection between planetary science, biology and astronomy and explore its remotely detectable features in a planet’s atmosphere. The observational features of the planet are used to derive observable quantities to examine if our concept of habitability is correct and how we can find the first habitable new worlds in the sky.

Non-standard applications of VLBI: pulsar scattering and transient detection

Main Colloquium
Dr. Walter Brisken
ORATED
NRAO, Socorro

This talk will have two parts. First I will desribe an experiment to image the scattering disk of pulsar B0834+06 using a global VLBI array at 327 MHz. The technique of VLBI was adapted to the study of scintillation arcs for this work. Some unexpected ties to astrometry will be presented. Second, I will describe the commensal VFASTR transient search project. The DiFX software correlator used for processing VLBA data in Socorro has been augmented with a transient detector that makes use of autocorrelations delivered independently by each of the antennas being correlated that are all looking in the same direction. The multi-antenna approach offers RFI rejection and the ability to image and perform astrometry on candidate events.

From the filamentary structure of the ISM to prestellar cores to the stellar IMF: First results from the Herschel Gould Belt Sur

Main Colloquium
Dr. Philippe Andre
ORATED
CEA, Saclay, France

The Herschel Space Observatory provides a unique opportunity to improve our global understanding of the earliest phases of star formation. I will present an overview of the first results from the Gould Belt survey, one of the largest key projects with Herschel. The immediate objective of this SPIRE/PACS imaging survey is to obtain complete samples of nearby prestellar cores and Class 0 protostars with well characterized luminosities, temperatures, and density profiles, as well as robust core mass functions in a variety of environments. The main scientific goal is to elucidate the physical mechanisms responsible for the formation of prestellar cores out of the diffuse interstellar medium. Our early findings confirm the existence of a close relationship between the prestellar core mass function (CMF) and the stellar initial mass function (IMF). The Herschel images also reveal a rich network of filaments in every interstellar cloud and suggest an intimate connection between the filamentary structure of the ISM and the formation process of prestellar cores. Remarkably, filaments are omnipresent even in unbound, non-star-forming complexes and seem to be characterized by a narrow distribution of widths around sim 0.1 pc. This characteristic width approximately corresponds to the sonic scale below which interstellar turbulence becomes subsonic in diffuse gas, supporting the view that the filaments may form as a result of the dissipation of large-scale turbulence. In active star-forming regions, most of the prestellar cores identified with Herschel are located within gravitationally unstable filaments above a critical threshold sim 15 Msun/pc in mass per unit length or sim 150 Msun/pc2 in gas surface density. Altogether, the Herschel results favor a scenario in which interstellar filaments and prestellar cores represent two fundamental steps in the star formation process: First, large-scale magneto-hydrodynamic turbulence generates a complex web of filaments in the ISM; second, the densest filaments fragment and develop prestellar cores (and ultimately protostars) via gravitational instability.

A panchromatic view of massive star feedback and triggered star formation in the Carina Nebula

Main Colloquium
Prof. Thomas Preibisch
ORATED
Universitäts-Sternwarte Muenchen

I will present results of a recent deep multi-wavelength study of the Great Nebula in Carina. The Carina Nebula contains some of the most massive and luminous stars in our Galaxy and is an ideal site to study in detail the physics of violent massive star formation and the resulting feedback effects, i.e. cloud dispersal and triggering of star formation. With a distance of 2.3 kpc, it constitutes our best bridge between nearby regions like Orion and the much more massive, but also more distant extragalactic starburst systems like 30 Doradus. Our new X-ray and infrared data reveal, for the first time, the full low-mass stellar population in the Carina Nebula, and allow us to study the ages, mass function, and disk properties of the young stars. With sub-mm observations we also probed the morphology of the cold dusty molecular clouds throughout the complex and studied the interaction between massive stars and clouds. A detailed comparison of these observational data to numerical radiation-hydrodynamic simulations of stellar feedback will show how the ionizing radiation and stellar winds disperse the clouds and trigger the formation of a new generation of stars.

First results of the Planck mission: the early cluster science

Main Colloquium
Dr. Jean-Baptiste Melin
ORATED
CEA, Saclay, France

In January 2011, the Planck collaboration has released the first results of the mission. These results are based on the first 10 months of survey data (allowing for a full sky coverage). They already answer many questions related to galactic and extragalactic physics. I’ll give a brief overview of them and will then focus on cluster science. I’ll present the early cluster sample and detailed multi-wavelength analyses that have shed new light on the structure formation process in the Universe.

Supermassive Black Holes: Singles, Binaries, and Escapees

Main Colloquium
Dr. Stefanie Komossa
ORATED
MPIfR

There is now growing evidence that supermassive black holes reside at the centres of most galaxies, and that there is an intimate link between their formation and evolution and that of their host galaxies. Throughout the history of the universe, galaxies will merge frequently with each other, forming binary black holes at their centres, and an active search for these binaries is currently ongoing. During the final coalescence of the two black holes, linear momentum imparted by gravitational waves produces a kick, and the newly formed single black hole will recoil from the centre of its host galaxy. The presence of supermassive binary black holes and recoiling black holes has a wealth of astrophysical implications which are currently being explored including consequences for structure formation in the early universe and black hole growth, for unified models and the evolution of active galaxies, and for black hole - galaxy scaling relations. I will give an overview of the observations and predicted electromagnetic signatures of massive black hole binaries and recoiling black holes, including future schemes to search for electromagnetic counterparts to their gravitational wave signals, and I will discuss astrophysical implications.

Wide-angle outflow and jet in the massive protostar Cep A HW2

Main Colloquium
Prof. José-María Torrelles
ORATED
Institut d'Estudis Espacials de Catalunya-CSIC, Barcelona, Spain

We present five epochs of VLBI water maser observations around the massive protostar Cepheus A HW2 with 0.4 mas (0.3 AU) resolution. The main goal of these observations was to follow the evolution of the remarkable water maser linear/arcuate structures found in earlier VLBI observations. Comparing the data of our new epochs of observation with those observed five years before, we find that at “large” scales of > 1”(700 AU) the main regions of maser emission persist, implying that both the surrounding medium and the exciting sources of the masers have been relatively stable during that time span. However, at smaller scales of < 0.1”(70 AU) we see large changes in the maser structures, particularly in the expanding arcuate structures R4 and R5. R4 traces a nearly elliptical patchy ring of sim 70 mas size (50 AU) with expanding motions of sim 5 mas/yr (15 km/s). This structure is probably driven by the wind of a still unidentified YSO located at the centre of the ring (sim 0.18” south of HW2). On the other hand, the R5 expanding bubble structure (driven by the wind of a previously identified YSO located sim 0.6” south of HW2) is currently dissipating in the circumstellar medium and losing its previous degree of symmetry, indicating a very short-lived event. In addition, our results reveal, at scales of sim 1” (700 AU), the simultaneous presence of a relatively slow (sim 10–70 km/s) wide-angle outflow (opening angle of sim 102 deg, traced by the masers, and the fast (sim 500 km/s) highly collimated radio jet associated with HW2 (opening angle of sim 15 deg, previously observed with the VLA. This simultaneous presence of a wide-angle outflow and a highly collimated jet associated with a massive protostar is similar to what is found in some low-mass YSOs. There are indications that the primary wind(s) from HW2 could be rotating. The implications of these results in the study of the formation of high-mass stars are discussed.

Investigating Class I/II YSOs in L1641 through a combined optical/IR spectroscopy

Special Colloquium
Dr. Alessio Caratti o Garatti
ORATED
Dublin Institute for Advanced Studies

Low mass Young Stellar Objects (YSOs) are usually classified by the shape of their Spectral Energy Distribution (SED) into an empirical evolutionary sequence, which forms the basis of our understanding of the YSO formation process. In recent years, this classification has shown limitations in providing precise information on the YSO real evolutionary state. For instance geometrical effects have led to mis-classifications between Class I and II objects. I will present an in-depth study of a flux-limited sample of 27 Class I and II YSOs in L1641, based on low-resolution spectroscopy and photometry, ranging from optical to mid-IR wavelengths. The aim of this survey is to investigate the nature of these sources, deriving the main physical parameters from their spectra. Although Class I objects in our sample do not have bolometric luminosities dominated by accretion (Lacc/Lbol 0.3), we find that, on average, they are typically younger than CTTs. Similarly, we infer that the youngest objects have the highest accretion rates. Most notably, one of the targets shows a strong outburst, originated from an increase in the mass accretion rate onto the source. Its mass accretion rate is about 2 order of magnitudes larger than the typical accretion rates of Class I YSOs, likely suggesting that YSO accretion might happen in bursts.

High-precision VLBI astrometry of AGN jets

Main Colloquium
Dr. Ivan Marti-Vidal
ORATED
Onsala Space Observatory, Sweden

VLBI observations provide, by far, the highest angular resolution achievable with the present technology. However, an important piece of information is lost after the visibility calibration: the absolute sky coordinates in the images of the observed sources. Hence, it is impossible to perform a reliable study of the absolute kinematics in AGN jets. It is also difficult to study chromatic effects in AGN, unless clear optically-thin components are detected at all the observing frequencies (only a small subset of structure-rich AGN jets reliably fulfill this condition). This drawback can be partially overcomed using differential astrometry, based on the difference of observed phase delays from nearby sources (basically, phase-referencing). I will present results of a phase-referencing VLBI monitoring of a sample of AGN jets (the S5 polar cap sample and the nucleus of galaxy M81), at several frequencies during more than a decade. On the one hand, simultaneous differential astrometry between all the S5 polar-cap sources allows to “convert” differential astrometry into absolute astrometry, based on the redundant information in the relative position between all the possible source pairs. On the other hand, an intense observing campaign of supernova SN1993J, phase-referenced to the AGN in its host galaxy M81, allows to study with detail the astrometric and geometric evolution of the AGN at several frequencies in the coordiante frame of M81.

High-frequency flares in blazars and the physics of plasma jets

Main Colloquium
Dr. Jörg Rachen
ORATED
MPI für Astrophysik, Garching

Blazars are the perfect laboratories for non-thermal processes in the universe. Their emission spectrum extends over almost 20 orders of magnitude in frequency, and is strongly variable, in particular at high energies, with intrinsic time scales down to less than one day. Understanding the properties of blazar spectra and their flaring behavior could be the key to many interesting questions of astrophysics, including the physics of relativistic plasmas, particle acceleration, high energy particle interactions, and the way how plasma jets are launched in the vicinity of black holes. In this talk, I will focus on the discussion of radio-submillimeter spectra and their time evolution in flares. In the light of many excellent data from recent flux monitoring programs, in particular the MPIfR/IRAM based F-GAMMA programme, I will give a critical discussion of some of the current theoretical paradigms for the physics of blazars, and present some often neglected, but still promising alternative views. Finally, I will explore the potential of the Planck Surveyor Mission, which has just released first data on compact sources, among them many blazars, for the near future of this field.

Jets from Spinning Black Holes in Active Galactic Nuclei

Main Colloquium
Ioana Dutan
ORATED
MPI fuer Radioastronomie

Relativistic jets are highly collimated plasma outflows that can be present in extragalactic radio sources, which are associated with active galactic nuclei (AGN). Observations give strong support for the idea that a supermassive black hole, surrounded by an accretion disk, is harbored in the center of an AGN. The jet power can be generally provided by the accretion disk, by the black hole rotation, or both. Such powerful jets can also be sites of the origin of ultra-high-energy cosmic rays (UHECRs). The main aim of the speaker’s research was to improve the current understanding of the mechanisms of jet formation from rapidly-spinning black holes in the framework of General Relativity and General Relativistic Magnetohydrodynamics, as well as the production of UHECRs in AGN jets. The speaker will present (i) a “Magnetic Connection Model for Launching Relativistic Jets from Kerr Black Holes,” (ii) a model for “Ultra-High-Energy Cosmic Ray Contribution from the Spin-Down Power of Black Holes,” and (iii) “General Relativistic Magnetohydrodynamic Simulation of Jet Formation from Kerr Black Holes.”

Fitting along the Fundamental Plane: New comparisons of jet physics across the black hole mass scale

Main Colloquium
Dr. Sera Markoff
ORATED
University of Amsterdam

Correlations between the radio and X-ray bands in the hard state of black hole X-ray binaries have led to the discovery of the so-called Fundamental Plane (FP) of black hole accretion, linking accretion-driven radiative attributes to black hole mass. Although this discovery has provided tight constraints on radiative efficiencies, there is still significant degeneracy in terms of understanding the governing physics involved. After a brief summary of the FP phenomenology and implications, I will present several new results exploring the processes that drive this relation over several orders of magnitude in black hole mass. In particular, I will focus on how we can exploit the FP to learn more about the relationship between the accretion flow and the jets near their launch point, as well as the structures leading to particle acceleration further out.

Polar Disk Galaxies as a new way to study galaxy formation: the case of NGC4650A

Main Colloquium
Dr. Enrichetta Iodice
ORATED
Astronomical Observatory of Capodimonte

NGC4650A is considered the prototype of the class of wide Polar Ring Galaxies (PRGs): this is a peculiar object composed by a central spheroidal component, the host galaxy, and an extended disk made up by gas, stars and dust, which orbits nearly perpendicular to the plane of the central galaxy. This object is one of the best-investigated PRGs: the existence of two decoupled components of the angular momentum let this object the ideal laboratory i) to study gravitational interactions and merging and ii) to constrain the 3D shape of its dark matter halo. In view of these applications, I would like to review the latest and most important results in these fields, in particular, I would like to show how by studying the observed structure, metallicity and dynamics of the polar disks we can constrain i) the formation scenario, which turns to be consistent with a polar disk formed by accretion of cold gas from cosmic web filaments; and ii) the dark halo content and shape, by using different dynamical traces (stars and gas) along the equatorial and meridian plane.

Galactic dark mater and mysterious transient radio events

Main Colloquium
Prof. Dr. Theo Nieuwenhuizen
ORATED
University of Amsterdam

Recently, Ofek et al (ApJ 711, 517, 2010) observed a mysterious class of ’long duration radio transients’, lasting more than 30 minutes but less than several days, that have ther a counterpart in the near-infrared, visible or X-ray spectrum nor a quiescent radio state. The event rate is large, some 1000 /deg2 yr and they can be bright, > 1 Jy. The theory of gravitational hydrodynamics says that after the recombination all gas fragmented into Jeans clumps of some 600.000 solar masses. Due to viscosity they fragmented into micro brown dwarfs (mBDs) of earth mass, turning them into Jeans clusters of almost a trillion mBDs. These mBDs have been observed in quasar microlensing and possible in extreme scattering events in radio. The Galaxy contains a few million Jeans clusters, that within isothermal modeling explain the flattening of the rotation curves. The mysterious radio events of Ofek et al. are interpreted as mBD mergers. Within isothermal modeling the observed frequency and intensity of the events come out reasonably. The ’true’ (i.e. non-baryonic) dark matter is studied by modeling lensing properties of the galaxy cluster Abell 1689 by isothermal fermions. The best candidate turns out to the neutrino with mass 1.5 eV/c2; this will be tested in the KATRIN experiment in Karlruhe in 2015. In this picture galactic dark matter consists of baryons and cluster dark matter of neutrinos, while cold dark matter has no reason to exist.

Faraday rotation in active galactic nuclei

Special Colloquium
Dr. Talvikki Hovatta
ORATED
Aalto University Metsähovi Radio Observatory

Polarimetric observations of active galactic nuclei jets enable studies of the magnetic field structure in the sources. Polarized waves are affected by Faraday rotation when they propagate through non-radiating plasma. By studying the Faraday rotation we will learn about the intrinsic magnetic field structure in the jets and about the plasma properties in and around the source. I will show preliminary results of a large Faraday rotation survey conducted within the MOJAVE project. In 2006, 193 sources were observed with the VLBA at four frequencies. We have produced rotation measure (RM) maps of all the sources with significant polarized emission resulting in a total of 172 RM maps. The large sample enables statistical studies of Faraday rotation in AGN. In addition, I will talk about a few individual sources which show interesting Faraday rotation structures.