Excellence Cluster Origin and Structure of the Universe

Garching bei München, Germany

Excellence Cluster Origin and Structure of the Universe

Garching bei München, Germany
SEARCH FILTERS
Time filter
Source Type

Ercolano B.,Universitats Sternwarte Munich | Ercolano B.,Excellence Cluster Origin and Structure of the Universe | Owen J.E.,Institute for Advanced Study
Monthly Notices of the Royal Astronomical Society | Year: 2016

Photoevaporation of protoplanetary discs by high-energy radiation from the central young stellar object is currently the favourite model to explain the sudden dispersal of discs from the inside out. While several theoretical works have provided a detailed pictured of this process, the direct observational validation is still lacking. Emission lines produced in these slow-moving protoplanetary disc winds may bear the imprint of the wind structure and thus provide a potential diagnostic of the underlying dispersal process. In this paper, we primarily focus on the collisionally excited neutral oxygen line at 6300 Å. We compare our models predictions to observational data and demonstrate a thermal origin for the observed blueshifted low-velocity component of this line from protoplanetary discs. Furthermore, our models show that while this line is a clear tell-tale sign of a warm, quasi-neutral disc wind, typical of X-ray photoevaporation, its strong temperature dependence makes it unsuitable to measure detailed wind quantities like mass-loss rate. © 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Lapidus K.,TU Munich | Lapidus K.,Excellence Cluster Origin and Structure of the Universe
AIP Conference Proceedings | Year: 2016

We discuss recent advances of the HADES collaboration in the sector of in-medium strangeness physics, in particular the measurement of neutral kaons produced in proton-niobium reactions at 3.5 GeV. © 2016 AIP Publishing LLC.


Gasik P.,TU Munich | Gasik P.,Excellence Cluster Origin and Structure of the Universe
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2017

A large Time Projection Chamber (TPC) is the main device for tracking and charged-particle identification in the ALICE experiment at the CERN LHC. After the second long shutdown in 2019–2020, the LHC will deliver Pb beams colliding at an interaction rate up to 50 kHz, which is about a factor of 100 above the present read-out rate of the TPC. To fully exploit the LHC potential the TPC will be upgraded based on the Gas Electron Multiplier (GEM) technology. A prototype of an ALICE TPC Outer Read-Out Chamber (OROC) was equipped with twelve large-size GEM foils as amplification stage to demonstrate the feasibility of replacing the current Multi Wire Proportional Chambers with the new technology. With a total area of ∼0.76 m2 it is the largest GEM-based detector built to date. The GEM OROC was installed within a test field cage and commissioned with radioactive sources. © 2016 Elsevier B.V.


Ercolano B.,Universitats Sternwarte Munich | Ercolano B.,Excellence Cluster Origin and Structure of the Universe | Mayr D.,Universitats Sternwarte Munich | Owen J.E.,Canadian Institute for Theoretical Astrophysics | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

We analyse current measurements of accretion rates on to pre-main-sequence stars as a function of stellar mass, and conclude that the steep dependence of accretion rates on stellar mass is real and not driven by selection/detection threshold, as has been previously feared. These conclusions are reached by means of statistical tests including a survival analysis which can account for upper limits. The power-law slope of the M-M* relation is found to be in the range of 1.6-1.9 for young stars with masses lower than 1 M⊙ The measured slopes and distributions can be easily reproduced by means of a simple disc model which includes viscous accretion and X-ray photoevaporation. We conclude that the M-M* relation in pre-main-sequence stars bears the signature of disc dispersal by X-ray photoevaporation, suggesting that the relation is a straightforward consequence of disc physics rather than an imprint of initial conditions. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Niederhofer F.,Excellence Cluster Origin and Structure of the Universe | Niederhofer F.,Universitats Sternwarte Munich | Georgy C.,Keele University | Bastian N.,Liverpool John Moores University | Ekstrom S.,University of Geneva
Monthly Notices of the Royal Astronomical Society | Year: 2015

We use the Geneva SYCLIST isochrone models that include the effects of stellar rotation to investigate the role that rotation has on the resulting colour-magnitude diagram of young and intermediate age clusters. We find that if a distribution of rotation velocities exists within the clusters, rotating stars will remain on the main sequence for longer, appearing to be younger than non-rotating stars within the same cluster. This results in an extended main sequence turn-off(eMSTO) that appears at young ages (~30 Myr) and lasts beyond 1 Gyr. If this eMSTO is interpreted as an age spread, the resulting age spread is proportional to the age of the cluster, i.e. young clusters (<100 Myr) appear to have small age spreads (tens of Myr) whereas older clusters (~1 Gyr) appear to have much large spreads, up to a few hundred Myr. We compare the predicted spreads for a sample of rotation rates to observations of young and intermediate age clusters, and find a strong correlation between the measured 'age spread' and the age of the cluster, in good agreement with models of stellar rotation. This suggests that the 'age spreads' reported in the literature may simply be the result of a distribution of stellar rotation velocities within clusters. © 2015 The Authors.


Ercolano B.,Universitats Sternwarte Munich | Ercolano B.,Excellence Cluster Origin and Structure of the Universe | Rosotti G.,Universitats Sternwarte Munich | Rosotti G.,Excellence Cluster Origin and Structure of the Universe | Rosotti G.,Institute of Astronomy
Monthly Notices of the Royal Astronomical Society | Year: 2015

We investigate the influence of photoevaporation of protoplanetary discs on the final distribution of exoplanets semimajor axis distances.We model giant planet migration in viscous discs affected by photoevaporation driven by either pure EUV or soft X-ray radiation (XEUV). We show that the final exoplanet distributions are strongly dependant on the choice of the photoevaporation model. In particular, we find that XEUV is more efficient than pure EUV radiation at parking planets at approximately 1-2 au distance from their central star, hence roughly reproducing the observed peak in the exoplanets semimajor axis distributions. We note however that a more quantitative comparison with the observations is hindered by the oversimplified treatment of planetary accretion, which severely affectsmigration rates. For this reason, caution should be used when using these models to constrain details of disc clearing and/or migration from the observations. Nevertheless our results indicate that disc dispersal by photoevaporation may be the main driver of the features in the exoplanets semimajor axis distribution observed by recent surveys. © 2015 The Authors.


Lorenz E.,Max Planck Institute for Physics | Wagner R.,Excellence Cluster Origin and Structure of the Universe
European Physical Journal H | Year: 2012

Very-high energy (VHE) gamma quanta contribute only a minuscule fraction - below one per million - to the flux of cosmic rays. Nevertheless, being neutral particles they are currently the best "messengers" of processes from the relativistic/ultra-relativistic Universe because they can be extrapolated back to their origin. The window of VHE gamma rays was opened only in 1989 by the Whipple collaboration, reporting the observation of TeV gamma rays from the Crab nebula. After a slow start, this new field of research is now rapidly expanding with the discovery of more than 150 VHE gamma-ray emitting sources. Progress is intimately related with the steady improvement of detectors and rapidly increasing computing power. We give an overview of the early attempts before and around 1989 and the progress after the pioneering work of the Whipple collaboration. The main focus of this article is on the development of experimental techniques for Earth-bound gamma-ray detectors; consequently, more emphasis is given to those experiments that made an initial breakthrough rather than to the successors which often had and have a similar (sometimes even higher) scientific output as the pioneering experiments. The considered energy threshold is about 30 GeV. At lower energies, observations can presently only be performed with balloon or satellite-borne detectors. Irrespective of the stormy experimental progress, the success story could not have been called a success story without a broad scientific output. Therefore we conclude this article with a summary of the scientific rationales and main results achieved over the last two decades. © EDP Sciences, Springer-Verlag 2012.


Arnold O.,TU Munich | Arnold O.,Excellence Cluster Origin and Structure of the Universe
Journal of Physics: Conference Series | Year: 2016

We present a two-particle correlation measurement of proton- and of Λp-pairs, measured with the HADES detector in p+Nb reactions at a kinetic beam energy of 3.5 GeV. The proton-proton correlation function is used to extract the size of the region of homogeneity. Using this information together with a UrQMD transport simulation opens the possibility to study the interaction of Λp pairs in terms of spin average scattering length and effective range.


Epple E.,Excellence Cluster Origin and Structure of the Universe | Epple E.,TU Munich | Fabbietti L.,Excellence Cluster Origin and Structure of the Universe | Fabbietti L.,TU Munich
Physical Review C - Nuclear Physics | Year: 2015

In this work we question the hypothesis that the previously reported structure X(2265) in p+p data is due to the kaonic nuclear bound state "ppK-". We will show that it is rather unlikely that X(2265), as reported by the DISTO collaboration, corresponds to a kaonic nuclear bound state. The main argument is based on the repetition of the DISTO analysis applied to a HADES data sample, which contains p+p reactions at 3.5 GeV. We further discuss many aspects in connection with the pK+Λ final state and the Λ(1405) resonance. The results point to possible problems in the interpretation of the DISTO data. © 2015 American Physical Society.


Epple E.,Excellence Cluster Origin and Structure of the Universe | Epple E.,TU Munich
EPJ Web of Conferences | Year: 2014

The HADES collaboration has searched for the anti-kaonic nuclear cluster "ppK-" in p+p collisions by its decay into pΛ. In the course of this analysis several cross checks had to be performed. This report discusses two examples thereof. In one test it was checked whether the presence of background events could introduce a bias on the applied partial wave analysis. The second item discussed here is the extraction of the total pK+Λ production cross section necessary to derive the absolute upper limit on the "ppK-" production cross section. © Owned by the authors, published by EDP Sciences, 2014.

Loading Excellence Cluster Origin and Structure of the Universe collaborators
Loading Excellence Cluster Origin and Structure of the Universe collaborators