H. Beuther

Max Planck Institute for Astronomy, Heidelburg, Baden-Württemberg, Germany

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Publications (233)657.8 Total impact

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    ABSTRACT: We present new Plateau de Bure Interferometer observations of a region in the filamentary infrared-dark cloud (IRDC) G011.11-0.12 containing young, star-forming cores. In addition to the 3.2mm continuum emission from cold dust, we map this region in the N$_2$H$^+$(1-0) line to trace the core kinematics with an angular resolution of 2" and velocity resolution of 0.2km s$^{-1}$. These data are presented in concert with recent {\em Herschel} results, single-dish N$_2$H$^+$(1-0) data, SABOCA 350$\mu$m continuum data, and maps of the C$^{18}$O (2-1) transition obtained with the IRAM 30m telescope. We recover the star-forming cores at 3.2mm continuum, while in N$_2$H$^+$ they appear at the peaks of extended structures. The mean projected spacing between N$_2$H$^+$ emission peaks is 0.18pc, consistent with simple isothermal Jeans fragmentation. The 0.1pc-sized cores have low virial parameters on the criticality borderline, while on the scale of the whole region, we infer that it is undergoing large-scale collapse. The N$_2$H$^+$ linewidth increases with evolutionary stage, while CO isotopologues show no linewidth variation with core evolution. Centroid velocities of all tracers are in excellent agreement, except in the starless region where two N$_2$H$^+$ velocity components are detected, one of which has no counterpart in C$^{18}$O. We suggest that gas along this line of sight may be falling into the quiescent core, giving rise to the second velocity component, possibly connected to the global collapse of the region.
    11/2014;
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    ABSTRACT: Context: How do molecular clouds form out of the atomic phase? And what are the relative fractions of carbon in the ionized, atomic and molecular phase? These are questions at the heart of cloud and star formation. Methods: Using multiple observatories from Herschel and SOFIA to APEX and the IRAM 30m telescope, we mapped the ionized, atomic and molecular carbon ([CII]@1900GHz, [CI]@492GHz and C18O(2-1)@220GHz) at high spatial resolution (12"-25") in four young massive infrared dark clouds (IRDCs). Results: The three carbon phases were successfully mapped in all four regions, only in one source the [CII] line remained a non-detection. Both the molecular and atomic phases trace the dense structures well, with [CI] also tracing material at lower column densities. [CII] exhibits diverse morphologies in our sample, from compact to diffuse structures probing the cloud environment. In at least two out of the four regions, we find kinematic signatures strongly indicating that the dense gas filaments have formed out of a dynamically active and turbulent atomic/molecular cloud, potentially from converging gas flows. The atomic-to-molecular carbon gas mass ratios are low between 7% and 12% with the lowest values found toward the most quiescent region. In the three regions where [CII] is detected, its mass is always higher by a factor of a few than that of the atomic carbon. The ionized carbon emission depends as well on the radiation field, however, we also find strong [CII] emission in a region without significant external sources, indicating that other processes, e.g., energetic gas flows can contribute to the [CII] excitation as well.
    10/2014;
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    ABSTRACT: Context: The initial conditions for the gravitational collapse of molecular cloud cores and the subsequent birth of stars are still not well constrained. The characteristic cold temperatures (about 10 K) in such regions require observations at sub-millimetre and longer wavelengths. The Herschel Space Observatory and complementary ground-based observations presented in this paper have the unprecedented potential to reveal the structure and kinematics of a prototypical core region at the onset of stellar birth. Aims: This paper aims to determine the density, temperature, and velocity structure of the star-forming Bok globule CB 17. This isolated region is known to host (at least) two sources at different evolutionary stages: a dense core, SMM1, and a Class I protostar, IRS. Methods: We modeled the cold dust emission maps from 100 micron to 1.2 mm with both a modified blackbody technique to determine the optical depth-weighted line-of-sight temperature and column density and a ray-tracing technique to determine the core temperature and volume density structure. Furthermore, we analysed the kinematics of CB17 using the high-density gas tracer N2H+. Results: From the ray-tracing analysis, we find a temperature in the centre of SMM1 of 10.6 K, a flat density profile with radius 9500 au, and a central volume density of n(H) = 2.3x10^5 cm-3. The velocity structure of the N2H+ observations reveal global rotation with a velocity gradient of 4.3 km/s/pc. Superposed on this rotation signature we find a more complex velocity field, which may be indicative of differential motions within the dense core. Conclusions: SMM is a core in an early evolutionary stage at the verge of being bound, but the question of whether it is a starless or a protostellar core remains unanswered.
    Astronomy and Astrophysics 09/2014; 569. · 5.08 Impact Factor
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    ABSTRACT: In the low-mass regime, it is found that the gas-phase abundances of C-bearing molecules in cold starless cores rapidly decrease with increasing density, as the molecules form mantles on dust grains. We study CO depletion in 102 massive clumps selected from the ATLASGAL 870 micron survey, and investigate its correlation with evolutionary stage and with the physical parameters of the sources. Moreover, we study the gradients in [12C]/[13C] and [18O]/[17O] isotopic ratios across the inner Galaxy, and the virial stability of the clumps. We use low-J emission lines of CO isotopologues and the dust continuum emission to infer the depletion factor fD. RATRAN one-dimensional models were also used to determine fD and to investigate the presence of depletion above a density threshold. The isotopic ratios and optical depth were derived with a Bayesian approach. We find a significant number of clumps with a large fD, up to ~20. Larger values are found for colder clumps, thus for earlier evolutionary phases. For massive clumps in the earliest stages of evolution we estimate the radius of the region where CO depletion is important to be a few tenths of a pc. Clumps are found with total masses derived from dust continuum emission up to ~20 times higher than the virial mass, especially among the less evolved sources. These large values may in part be explained by the presence of depletion: if the CO emission comes mainly from the low-density outer layers, the molecules may be subthermally excited, leading to an overestimate of the dust masses. CO depletion in high-mass clumps seems to behave as in the low-mass regime, with less evolved clumps showing larger values for the depletion than their more evolved counterparts, and increasing for denser sources. The C and O isotopic ratios are consistent with previous determinations, and show a large intrinsic scatter.
    07/2014;
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    ABSTRACT: The APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) is the largest and most sensitive systematic survey of the inner Galactic plane in the submillimetre wavelength regime. The observations were carried out with the Large APEX Bolometer Camera (LABOCA), an array of 295 bolometers observing at 870\,$\mu$m (345 GHz). Aim: In this research note we present the compact source catalogue for the 280\degr\ $ <\ell <$ 330\degr\ and 21\degr\ $ <\ell <$ 60\degr\ regions of this survey. Method: The construction of this catalogue was made with the source extraction routine \sex\ using the same input parameters and procedures used to analyse the inner Galaxy region presented in an earlier publication (i.e., 330\degr\ $ <\ell <$ 21\degr). Results: We have identified 3523 compact sources and present a catalogue of their properties. When combined with the regions already published this provides a comprehensive and unbiased database of ~10163 massive, dense clumps located across the inner Galaxy.
    06/2014;
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    ABSTRACT: Numerical simulations have explored the possibility to form molecular clouds through either a quasi-static, self-gravitating mechanism or the collision of gas streams or lower-density clouds. They also quantitatively predict the distribution of matter at the transition from atomic to molecular gases. We aim to observationally test these models by studying the environment of W43, a molecular cloud complex near the tip of the Galactic long bar. Using Galaxy-wide HI and 12CO surveys we searched for gas flowing toward the W43 molecular cloud complex. We also estimated the HI and H2 mass surface densities to constrain the transition from atomic to molecular gas around and within W43. We found 3 cloud ensembles within the position-velocity diagrams of 12CO and HI gases. They are separated by 20km/s along the line of sight and extend into the 13CO velocity structure of W43. Since their velocity gradients are consistent with free-fall, they could be nearby clouds attracted by, and streaming toward, the W43 10^7Msun potential well. We show that the HI surface density, Sigma_HI=45-85Msun/pc2, does not reach any threshold level but increases when entering the 130pc-wide molecular complex previously defined. This suggests that an equilibrium between H2 formation and photodissociation has not yet been reached. The H2-to-HI ratio measured over the W43 region and its surroundings, R_H2~3.5, is high, indicating that most of the gas is already in molecular form in W43 and in structures several hundreds of parsecs downstream along the Scutum-Centaurus arm. The W43 molecular cloud complex may have formed, and in fact may still be accreting mass from the agglomeration of clouds. Already in the molecular-dominated regime, most of these clouds are streaming from the Scutum-Centaurus arm. This is in clear disagreement with quasi-static and steady-state models of molecular cloud formation.
    04/2014;
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    ABSTRACT: The massive infrared dark cloud G0.253+0.016 projected 45pc from the Galactic centre contains ~10^5Msun of dense gas whilst being mostly devoid of observed star-formation tracers. To scrutinise the physical properties, dynamics and structure of this cloud with reference to its star-forming potential, we have carried out a concerted SMA and IRAM 30m study of this cloud in dust continuum, CO isotopologues, shock tracing molecules, as well as H$_2$CO to trace the gas temperature. We detect and characterise the dust cores within G0.253+0.016 at ~1.3 mm and find that the kinetic temperature of the gas is >320K on size-scales of ~0.15 pc. Analysis of the position-velocity diagrams of our observed lines show broad linewidths and strong shock emission in the south of the cloud, indicating that G0.253+0.016 is colliding with another cloud at v(LSR)~70 km/s. We confirm via an analysis of the observed dynamics in the CMZ that it is an elongated structure, orientated with Sgr B2 closer to the Sun, however our results suggest that the actual geometry may be more complex than an elliptical ring. We find that the column density PDF of G0.253+0.016 is log-normal with no discernible power-law tail, consistent with little star formation, and that its width can be explained in the framework of theory predicting the density structure of clouds created by supersonic, magnetised turbulence. We also present the delta-variance spectrum of this region, and show it is consistent with that expected for clouds with no star formation. Using G0.253+0.016 as a test-bed of the conditions required for star formation in a different physical environment to that of nearby clouds, we also conclude that there is not one column density threshold for star formation, but instead this value is dependant on the local physical conditions. [Abbrv.]
    04/2014;
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    ABSTRACT: We investigate the physical and chemical processes at work during the formation of a massive protostar based on the observation of water in an outflow from a very young object previously detected in H2 and SiO in the IRAS 17233-3606 region. We estimated the abundance of water to understand its chemistry, and to constrain the mass of the emitting outflow. We present new observations of shocked water obtained with the HIFI receiver onboard Herschel. We detected water at high velocities in a range similar to SiO. We self-consistently fitted these observations along with previous SiO data through a state-of-the-art, one-dimensional, stationary C-shock model. We found that a single model can explain the SiO and H2O emission in the red and blue wings of the spectra. Remarkably, one common area, similar to that found for H2 emission, fits both the SiO and H2O emission regions. This shock model subsequently allowed us to assess the shocked water column density, N(H2O)=1.2x10^{18} cm^{-2}, mass, M(H2O)=12.5 M_earth, and its maximum fractional abundance with respect to the total density, x(H2O)=1.4x10^{-4}. The corresponding water abundance in fractional column density units ranges between 2.5x10^{-5} and 1.2x10^{-5}, in agreement with recent results obtained in outflows from low- and high-mass young stellar objects.
    03/2014;
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    ABSTRACT: Throughout the Milky Way, molecular clouds typically appear filamentary, and mounting evidence indicates that this morphology plays an important role in star formation. What is not known is to what extent the dense filaments most closely associated with star formation are connected to the surrounding diffuse clouds up to arbitrarily large scales. How are these cradles of star formation linked to the Milky Way's spiral structure? Using archival Galactic plane survey data, we have used multiple datasets in search of large-scale, velocity-coherent filaments in the Galactic plane. In this paper, we present our methods employed to identify coherent filamentary structures first in extinction and confirmed using Galactic Ring Survey data. We present a sample of seven Giant Molecular Filaments (GMFs) that have lengths of order ~100pc, total masses of 10$^4$ - 10$^5$M$_{\odot}$, and exhibit velocity coherence over their full length. The GMFs we study appear to be inter-arm clouds and may be the Milky Way analogues to spurs observed in nearby spiral galaxies. We find that between 2 and 12% of the total mass (above ~10$^{20}$ cm$^{-2}$) is "dense" (above 10$^{22}$ cm$^{-2}$), where filaments near spiral arms in the Galactic midplane tend to have higher dense gas mass fractions than those further from the arms.
    03/2014;
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    ABSTRACT: The mid- and far-infrared view on high-mass star formation, in particular with the results from the Herschel space observatory, has shed light on many aspects of massive star formation. However, these continuum studies lack kinematic information. We study the kinematics of the molecular gas in high-mass star-forming regions. We complemented the PACS and SPIRE far-infrared data of 16 high-mass star-forming regions from the Herschel key project EPoS with N2H+ molecular line data from the MOPRA and Nobeyama 45m telescope. Using the full N2H+ hyperfine structure, we produced column density, velocity, and linewidth maps. These were correlated with PACS 70micron images and PACS point sources. In addition, we searched for velocity gradients. For several regions, the data suggest that the linewidth on the scale of clumps is dominated by outflows or unresolved velocity gradients. IRDC18454 and G11.11 show two velocity components along several lines of sight. We find that all regions with a diameter larger than 1pc show either velocity gradients or fragment into independent structures with distinct velocities. The velocity profiles of three regions with a smooth gradient are consistent with gas flows along the filament, suggesting accretion flows onto the densest regions. We show that the kinematics of several regions have a significant and complex velocity structure. For three filaments, we suggest that gas flows toward the more massive clumps are present.
    01/2014;
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    ABSTRACT: Understanding the chemical evolution of young (high-mass) star-forming regions is a central topic in star formation research. Chemistry is employed as a unique tool 1) to investigate the underlying physical processes and 2) to characterize the evolution of the chemical composition. We observed a sample of 59 high-mass star-forming regions at different evolutionary stages varying from the early starless phase of infrared dark clouds to high-mass protostellar objects to hot molecular cores and, finally, ultra-compact HII regions at 1mm and 3mm with the IRAM 30m telescope. We determined their large-scale chemical abundances and found that the chemical composition evolves along with the evolutionary stages. On average, the molecular abundances increase with time. We modeled the chemical evolution, using a 1D physical model where density and temperature vary from stage to stage coupled with an advanced gas-grain chemical model and derived the best-fit chi^2 values of all relevant parameters. A satisfying overall agreement between observed and modeled column densities for most of the molecules was obtained. With the best-fit model we also derived a chemical age for each stage, which gives the timescales for the transformation between two consecutive stages. The best-fit chemical ages are ~10,000 years for the IRDC stage, ~60,000 years for the HMPO stage, ~40,000 years for the HMC stage, and ~10,000 years for the UCHII stage. The total chemical timescale for the entire evolutionary sequence of the high-mass star formation process is on the order of 10^5 years, which is consistent with theoretical estimates. Furthermore, based on the approach of a multiple-line survey of unresolved data, we were able to constrain an intuitive and reasonable physical and chemical model. The results of this study can be used as chemical templates for the different evolutionary stages in high-mass star formation.
    Astronomy and Astrophysics 01/2014; 563. · 5.08 Impact Factor
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    ABSTRACT: The formation processes and the evolutionary stages of high-mass stars are poorly understood compared to low-mass stars. Large-scale surveys are needed to provide an unbiased census of high column density sites which can potentially host precursors to high-mass stars. Here we use the ATLASGAL survey covering 420 sq. degree of the Galactic plane at 870 micron; and use the MRE-GLC method to identify the population of embedded sources throughout the inner Galaxy. We identify in total 10952 compact sub-millimeter sources with fluxes above 5 sigma. Completeness tests show that our catalogue is 97% complete above 5 sigma and >99% complete above 7 sigma. We correlate this sample with mid-infrared point source catalogues (MSX at 21.3 micron and WISE at 22 micron) and determine a lower limit of ~33% that are associated with embedded protostellar objects. We note that the proportion of clumps associated with mid-infrared sources increases with increasing flux density, achieving a rather constant fraction of ~75% of all clumps with fluxes over 5 Jy/beam being associated with star-formation. Examining the source counts as a function of Galactic longitude we are able to identify the most prominent star forming regions in the Galaxy. From the fraction of the likely massive quiescent clumps (~25%) we estimate a formation time-scale of ~7.25+/-2.50 x 10^4~yr for the deeply embedded phase before the emergence of luminous YSOs. Such a short duration for the formation of high-mass stars in massive clumps clearly proves that the earliest phases have to be dynamic with supersonic motions.
    12/2013;
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    ABSTRACT: In order to investigate whether the feedback produced by photo-ionisation has an important effect on the geometry of the circumstellar dust and gas around forming massive stars, we have observed the luminous southern embedded star AFGL 4176 in transitions of NH3 and the hydrogen recombination line H68α. We present our preliminary results, which show a compact H ii region embedded in a parsec-scale (radius ̃ 0.7 pc) rotating envelope/torus. In addition, the H ii region is found to be offset from the centre of the envelope, and the velocity gradient in the ionised gas is not aligned with the rotation axis of the envelope, suggesting complex dynamics and multiplicity.
    11/2013;
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    ABSTRACT: The Atacama Pathfinder Experiment (APEX) telescope is ideally located to observe the inner part of our Galaxy. With its good sensitivity, the LABOCA bolometer array can map hundreds of square degrees at
    11/2013;
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    ABSTRACT: Understanding the chemical evolution of young (high-mass) star-forming regions is a central topic in star formation research. The chemistry plays two main roles here: to study the evolution from simple to complex molecules, and to investigate the underlying physical processes. With these aims in mind, we observed a diverse sample of 60 high-mass star-forming regions in different evolutionary stages. In the early phase, quiescent Infrared Dark Clouds (IRDCs), consisting of cold and dense gas and dust, and emitting mainly at (sub-)millimeter wavelength, are formed. In the next phase, the so called High Mass Protostellar Objects (HMPOs) form, which host a central, likely still accreting protostar and already show emission at mid-infrared wavelengths. In the Hot Molecular Core phase (HMC) the central source heats up the surrounding environment, evaporating molecular-rich ices, which gives rise to a rich chemistry leading to complex molecules such as long carbon chains. Finally the UV-radiation from the embedded protostars ionizes the gas around and forms an Ultra Compact HII (UCHII) region. In these objects many of the previously formed complex molecules are not longer detected as they got destroyed by the ionizing radiation. For our observations, we used the IRAM 30m telescope with the total bandpass of 16 GHz and good spectral resolution (̃0.3/0.7 km/s at 1/3 mm). We derived their large-scale chemical abundances, assuming LTE and optically thin emission. To set these results into context, we model the chemical evolution in such environments with a state-of-the-art chemical model. This enables us to put constraints on the chemical evolution, the age and parameters such as the temperature and the density of the molecular clouds.
    11/2013;
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    ABSTRACT: We provide the photometric JHKs catalogs used in this paper. The observations are carried out with LUCI1 at the LBT. The photometry is calibrated with 2MASS. For each star the photometric completeness derived from our two dimensional completeness analysis is given. The three files give the JHKs matched, HK matched and K-only catalogs. These 3 catalogs are used in the different sections of the paper. (3 data files).
    VizieR Online Data Catalog. 11/2013;
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    ABSTRACT: Embedded clusters like W3 Main are complex and dynamically evolving systems that represent an important phase of the star formation process. We aim at the characterization of the entire stellar content of W3 Main in a statistical sense to identify possible differences in evolutionary phase of the stellar populations and find clues about the formation mechanism of this massive embedded cluster. Methods. Deep JHKs imaging is used to derive the disk fraction, Ks-band luminosity functions and mass functions for several subregions in W3 Main. A two dimensional completeness analysis using artificial star experiments is applied as a crucial ingredient to assess realistic completeness limits for our photometry. We find an overall disk fraction of 7.7 $\pm$ 2.3%, radially varying from 9.4 $\pm$ 3.0 % in the central 1 pc to 5.6 $\pm$ 2.2 % in the outer parts of W3 Main. The mass functions derived for three subregions are consistent with a Kroupa and Chabrier mass function. The mass function of IRSN3 is complete down to 0.14 Msun and shows a break at M $\sim$ 0.5 Msun. We interpret the higher disk fraction in the center as evidence for a younger age of the cluster center. We find that the evolutionary sequence observed in the low-mass stellar population is consistent with the observed age spread among the massive stars. An analysis of the mass function variations does not show evidence for mass segregation. W3 Main is currently still actively forming stars, showing that the ionizing feedback of OB stars is confined to small areas ($\sim$ 0.5 pc). The FUV feedback might be influencing large regions of the cluster as suggested by the low overall disk fraction.
    Astronomy and Astrophysics 10/2013; · 5.08 Impact Factor
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    ABSTRACT: In the last decade, we have started to spatially resolve the relatively small gas and dust condensations in high-mass star-forming regions that will eventually become a massive star or system. We call these condensations of sizes on the order of 0.01 pc “cores”, and by estimating their masses we can construct the so-called Core Mass Function (CMF) of a region, to compare with the IMF and try to determine the evolutionary process from core to star. For massive star-forming regions, the relationship between the CMF and the IMF is not yet well understood. This is, among other factors, due to the fact that there are not many massive CMF determined. Even then, some of those few CMF seem to tell a story of evolution, by presenting different slopes than that of the Salpeter IMF while others, seem to be very similar to the IMF. In this work we show CMFs obtained for a group of massive star-forming regions with SMA and PdBI observations. These CMFs show different slopes, and we explain the possible significance this has on the evolution of the cores.
    10/2013;
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    ABSTRACT: We observed molecular clouds in the giant star forming region W43. For this project we used the IRAM 30m telescope to observe the molecular emission lines 13CO (2-1) and C18O (2-1), that trace the mid-density (n~103cm-3) molecular gas. The lines were observed with the HERA receiver and the VESPA backend. At the observed frequencies the IRAM 30m has a beam size of 11.7". We include two FITS files containing the data-cubes (pos-pos-vel) of the 13CO and C18O emission lines of the W43 complex. We used equatorial coordinates for the spatial dimensions and vlsr for the spectral dimension. The pixel size is 5.9" in spatial dimension and the spectral resolution is 0.16km/s. All values are in K. The data-cubes span an area of about 1x1.5° (RAxDec) around the center of the maps at 18:46:54.4 -02:14:11 (EQ=J2000) and the velocity range from 30 to 130km/s and include the complete W43 complex and several fore- and background clouds. (2 data files).
    VizieR Online Data Catalog. 10/2013;
  • H. Beuther, H. Linz, Th. Henning
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    ABSTRACT: NGC 7538 IRS1 was observed, together with NGC 7538S, in a shared-track mode in A configuration on February 27, 2012, with the PdBI at 843um in its most extended configuration. (2 data files).
    VizieR Online Data Catalog. 10/2013;

Publication Stats

2k Citations
657.80 Total Impact Points

Institutions

  • 2006–2014
    • Max Planck Institute for Astronomy
      Heidelburg, Baden-Württemberg, Germany
  • 2003–2012
    • Harvard-Smithsonian Center for Astrophysics
      • Smithsonian Astrophysical Observatory
      Cambridge, Massachusetts, United States
  • 2011
    • Leiden University
      Leyden, South Holland, Netherlands
  • 2009
    • University of Virginia
      • Department of Astronomy
      Charlottesville, Virginia, United States
  • 2008
    • Nanjing University
      • Department of Astronomy
      Nan-ching, Jiangsu Sheng, China
    • University of Toledo
      Toledo, Ohio, United States
  • 2002–2006
    • Max Planck Institute for Radio Astronomy
      Bonn, North Rhine-Westphalia, Germany