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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.

Ercolano B.,Universitats Sternwarte Munich | Ercolano B.,Excellence Cluster Origin and Structure of the Universe | Koepferl C.,Max Planck Institute for Astronomy | Owen J.,Institute for Advanced Study | Robitaille T.,Max Planck Institute for Astronomy
Monthly Notices of the Royal Astronomical Society | Year: 2015

By means of radiative transfer simulation, we study the evolution of the far-infrared colours of protoplanetary discs undergoing inside-out dispersal, often referred to as transition discs. We show that a brightening of the mid- and far-infrared emission from these objects is a natural consequence of the removal of the inner disc. Our results can fully explain recent observations of transition discs in the Chamaleon and Lupus star-forming regions from the Herschel Gould Belt Survey, which shows a higher median for the 70 μm (Herschel PACS 1) band of known transition objects compared with primordial discs. Our theoretical results hence support the suggestion that the 70 μmband may be a powerful diagnostic for the identification of transition discs from photometry data, provided that the inner hole is larger than tens of au, depending on spectral type. Furthermore, we show that a comparison of photometry in the K, 12 μm and 70 μm bands to model tracks can provide a rough, but quick estimate of the inner hole size of these objects, provided their inclination is below ~85° and the inner hole size is again larger than tens of au. © 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

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.

Diehl R.,Max Planck Institute for Extraterrestrial Physics | Lang M.G.,Max Planck Institute for Extraterrestrial Physics | Martin P.,Max Planck Institute for Extraterrestrial Physics | Ohlendorf H.,Max Planck Institute for Extraterrestrial Physics | And 7 more authors.
Astronomy and Astrophysics | Year: 2010

Context. The Scorpius-Centaurus association is the most-nearby group of massive and young stars. As nuclear-fusion products are ejected by massive stars and supernovae into the surrounding interstellar medium, the search for characteristic γ-rays from radioactivity is one way to probe the history of activity of such nearby massive stars on a My time scale through their nucleosynthesis. 26Al decays with a radioactivity lifetime t∼1 My, 1809 keV γ-rays from its decay can be measured with current γ-ray telescopes. Aims.We aim to identify nucleosynthesis ejecta from the youngest subgroup of Sco-Cen stars, and interpret their location and bulk motion from 26Al observations with INTEGRAL's γ-ray spectrometer SPI. Methods. Following earlier 26Al γ-ray mapping with NASA's Compton observatory, we test spatial emission skymaps of 26Al for a component which could be attributed to ejecta from massive stars in the Scorpius-Centaurus group of stars. Such a model fit of spatial distributions for large-scale and local components is able to discriminate 26Al emission associated with Scorpius-Centaurus, in spite of the strong underlying nucleosynthesis signal from the Galaxy at large. Results. We find an 26Al γ-ray signal above 5s significance, which we associate with the locations of stars of the Sco-Cen group. The observed flux of 6 × 10-5 ph cm-2 s -1 corresponds to ∼1.1 × 10-4 M⊙ of 26Al. This traces the nucleosynthesis ejecta of several massive stars within the past several million years. Conclusions.We confirm through direct detection of radioactive 26Al the recent ejection of massive-star nucleosynthesis products from the Sco-Cen association. Its youngest subgroup in Upper Scorpius appears to dominate 26Al contributions from this association. Our 26Al signal can be interpreted as a measure of the age and richness of this youngest subgroup. We also estimate a kinematic imprint of these nearby massive-star ejecta from the bulk motion of 26Al and compare this to other indications of Scorpius-Centaurus massive-star activity. © 2010 ESO.

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.

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