Results for "A. Chiavassa"

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Atmospheric dynamics of red supergiant stars and InterferometryFeb 11 2008We developed a 3D pure LTE radiative transfer code to derive observables expected for RSGs, with emphasis on small scale structures, from radiative-hydrodynamic (RHD) simulations of red supergiant stars (RSGs) carried out with CO5BOLD (Freytag et al. ... More
Red supergiant star studies with CO5BOLD and Optim3DMay 28 2013May 29 2013We describe recent work focused towards a better understanding of red supergiant stars using 3D radiative-hydrodynamics (RHD) simulations with CO5BOLD. A small number of simulations now exist that span up to seven years of stellar time, at various numerical ... More
Pathways for Observing Stellar Surfaces Using 3D Hydrodynamical Simulations of Evolved StarsDec 11 2015Evolved stars are among the largest and brightest stars and they are ideal targets for the new generation of sensitive, high resolution instrumentation that provides spectrophotometric, interferometric, astrometric, and imaging observables. The interpretation ... More
3D hydrodynamical simulations of evolved stars and observations of stellar surfacesOct 14 2014Evolved stars are among the largest and brightest stars and they are ideal targets for the new generation of sensitive, high resolution instrumentation that pro- vides spectrophotometric, interferometric, astrometric, and imaging observables. The interpretation ... More
Stellar granulation and interferometryJul 28 2015Stars are not smooth. Their photosphere is covered by a granulation pattern associated with the heat transport by convection. The convection-related surface structures have different size, depth, and temporal variations with respect to the stellar type. ... More
Atmospheric dynamics of red supergiant stars and applications to InterferometryFeb 11 2008We have written a 3D radiative transfer code that computes emerging spectra and intensity maps. We derive from radiative hydrodynamic (RHD) simulations of RSG stars carried out with CO5BOLD (Freytag et al. 2002) observables expected for red supergiant ... More
Radiative hydrodynamics simulations of red supergiant stars. IV gray versus non-gray opacitiesSep 16 2011Red supergiants are massive evolved stars that contribute extensively to the chemical enrichment of our Galaxy. It has been shown that convection in those stars gives rise to large granules that cause surface inhomogeneities and shock waves in the photosphere. ... More
Radiative hydrodynamics simulations of red supergiant stars: I. interpretation of interferometric observationsJul 10 2009Context. It has been suggested that convection in Red Supergiant (RSG) stars gives rise to large-scale granules causing observable surface inhomogeneities. This convection is also extremely vigorous, and suspected to be one of the causes of mass-loss ... More
Three-dimensional hydrodynamical simulations of red giant stars: semi-global models for the interpretation of interferometric observationsSep 09 2010Context. Theoretical predictions from models of red giant branch stars are a valuable tool for various applications in astrophysics ranging from galactic chemical evolution to studies of exoplanetary systems. Aims. We use the radiative transfer code OPTIM3D ... More
Accurate effective temperatures of the metal-poor benchmark stars HD 140283, HD 122563 and HD 103095 from CHARA interferometryJan 10 2018Large stellar surveys of the Milky Way require validation with reference to a set of "benchmark" stars whose fundamental properties are well-determined. For metal-poor benchmark stars, disagreement between spectroscopic and interferometric effective temperatures ... More
Science with MATISSESep 20 2016We present an overview of the scientific potential of MATISSE, the Multi Aperture mid-Infrared SpectroScopic Experiment for the Very Large Telescope Interferometer. For this purpose we outline selected case studies from various areas, such as star and ... More
Evolution of the cosmic ray anisotropy above 10^{14} eVJan 18 2009The amplitude and phase of the cosmic ray anisotropy are well established experimentally between 10^{11} eV and 10^{14} eV. The study of their evolution into the energy region 10^{14}-10^{16} eV can provide a significant tool for the understanding of ... More
Near-infrared spectro-interferometry of Mira variables and comparisons to 1D dynamic model atmospheres and 3D convection simulationsJan 11 2016We obtained a total of 20 near-infrared K-band spectro-interferometric snapshot observations of the Mira variables o Cet, R Leo, R Aqr, X Hya, W Vel, and R Cnc with a spectral resolution of about 1500. We compared observed flux and visibility spectra ... More
Transiting exoplanets and magnetic spots characterized with optical interferometryOct 20 2014Nov 24 2014Stellar activity causes difficulties in the characterization of transiting exoplanets. Studies have been performed to quantify its impact on infrared interferometry, but not in the visible domain, which however allows reaching better angular resolution ... More
The proton-air inelastic cross-section measurement at $\sqrt{s} \approx $ 2 TeV from EAS-TOP experimentDec 09 2010The proton-air inelastic cross section value \sigmapairin=338$\pm$21({\it stat})$\pm$19({\it syst})-28({\it syst}) mb at $\sqrt{s} \approx $ 2 TeV has been measured by the EAS-TOP Extensive Air Shower experiment. The absorption length of cosmic ray proton ... More
The Stagger-grid: A grid of 3D stellar atmosphere models V. Synthetic stellar spectra and broad-band photometryJan 05 2018Context. The surface structures and dynamics of cool stars are characterized by the presence of convective motions and turbulent flows which shape the emergent spectrum. Aims. We used realistic three-dimensional radiative hydrodynamical simulations from ... More
Radiative hydrodynamics simulations of red supergiant stars: II. simulations of convection on Betelgeuse match interferometric observationsMar 06 2010Context. The red supergiant (RSG) Betelgeuse is an irregular variable star. Convection may play an important role in understanding this variability. Interferometric observations can be interpreted using sophisticated simulations of stellar convection. ... More
Three-dimensional interferometric, spectrometric, and planetary views of ProcyonJan 16 2012We used a new realistic 3D radiative-hydrodynamical model atmosphere of Procyon generated with the Stagger Code and synthetic spectra computed with the radiative transfer code Optim3D to re-analyze interferometric and spectroscopic data from the optical ... More
The convective photosphere of the red supergiant CE Tau. I. VLTI/PIONIER H-band interferometric imagingFeb 16 2018Context. Red supergiant stars are one of the latest stages in the evolution of massive stars. Their photospheric convection may play an important role in the launching mechanism of their mass loss; however, its characteristics and dynamics are still poorly ... More
A new view on exoplanet transits: Transit of Venus described using three-dimensional solar atmosphere Stagger-grid simulationsJan 25 2015Stellar activity and, in particular, convection-related surface structures, potentially cause fluctuations that can affect the transit light curves. Surface convection simulations can help the interpretation of ToV. We used realistic three-dimensional ... More
3D hydrodynamical model atmospheres: a tool to correct radial velocities and parallaxes for GaiaNov 23 2011Nov 28 2011Convection plays an essential role in the emerging intensity for many stars that will be observed by Gaia. Convective-related surface structures affect the shape, shift, and asymmetry of absorption lines, the phocentric and photometric variability causing ... More
VLTI/AMBER spectro-interferometry of the late-type supergiants V766 Cen (=HR 5171 A), sigma Oph, BM Sco, and HD 206859Oct 06 2016We add four warmer late-type supergiants to our previous spectro-interferometric studies of red giants and supergiants. V766 Cen (=HR 5171 A) is found to be a high-luminosity log(L/L_sun)=5.8+-0.4 source of Teff 4290+-760 K and radius 1490+-540 Rsun located ... More
Time domain numerical modeling of wave propagation in 2D heterogeneous porous mediaDec 15 2010Mar 18 2011This paper deals with the numerical modeling of wave propagation in porous media described by Biot's theory. The viscous efforts between the fluid and the elastic skeleton are assumed to be a linear function of the relative velocity, which is valid in ... More
Fundamental parameters of 16 late-type stars derived from their angular diameter measured with VLTI/AMBERJun 14 2013Thanks to their large angular dimension and brightness, red giants and supergiants are privileged targets for optical long-baseline interferometers. Sixteen red giants and supergiants have been observed with the VLTI/AMBER facility over a two-years period, ... More
Wave propagation across acoustic / Biot's media: a finite-difference methodSep 15 2011Apr 06 2012Numerical methods are developed to simulate the wave propagation in heterogeneous 2D fluid / poroelastic media. Wave propagation is described by the usual acoustics equations (in the fluid medium) and by the low-frequency Biot's equations (in the porous ... More
Hydrogenation at low temperatures does not always lead to saturation: the case of HNCOFeb 11 2015Context. It is generally agreed that hydrogenation reactions dominate chemistry on grain surfaces in cold, dense molecular cores, saturating the molecules present in ice mantles. Aims. We present a study of the low temperature reactivity of solid phase ... More
Measuring stellar granulation during planet transitsSep 28 2016Stellar activity and convection-related surface structures might cause bias in planet detection and characterization that use these transits. Surface convection simulations help to quantify the granulation signal. We used realistic three-dimensional radiative ... More
The thermal reactivity of HCN and NH3 in interstellar ice analoguesOct 26 2012HCN is a molecule central to interstellar chemistry, since it is the simplest molecule containing a carbon-nitrogen bond and its solid state chemistry is rich. The aim of this work was to study the NH3 + HCN -> NH4+CN- thermal reaction in interstellar ... More
Long-term spectropolarimetric monitoring of the cool supergiant BetelgeuseFeb 05 2013We report on a long-term monitoring of the cool supergiant Betelgeuse, using the NARVAL and ESPaDOnS high-resolution spectropolarimeters, respectively installed at Telescope Bernard Lyot (Pic du Midi Observatory, France) and at the Canada-France-Hawaii ... More
The Stagger-grid: A Grid of 3D Stellar Atmosphere Models - I. Methods and General PropertiesFeb 11 2013Jul 12 2013We present the Stagger-grid, a comprehensive grid of time-dependent, 3D hydrodynamic model atmospheres for late-type stars with realistic treatment of radiative transfer, covering a wide range in stellar parameters. This grid of 3D models is intended ... More
Radiative hydrodynamics simulations of red supergiant stars. III. Spectro-photocentric variability, photometric variability, and consequences on Gaia measurementsDec 23 2010Context. It has been shown that convection in red supergiant stars gives rise to large granules causing surface inhomogeneities together with shock waves in the photosphere. The resulting motion of the photocenter (on time scales ranging from months to ... More
VLTI/AMBER spectro-interferometric imaging of VX Sgr's inhomogenous outer atmosphereNov 23 2009Nov 24 2009Aims. We aim to explore the photosphere of the very cool late-type star VX Sgr and in particular the existence and characterization of molecular layers above the continuum forming photosphere. Methods. We obtained interferometric observations with the ... More
VLTI-GRAVITY measurements of cool evolved stars: I. Variable photosphere and extended atmosphere of the Mira star R PegMay 14 2018Dynamic model atmospheres of Mira stars predict variabilities in the photospheric radius and in atmospheric molecular layers which are not yet strongly constrained by observations. Here we measure the variability of the oxygen-rich Mira star R Peg. We ... More
The close circumstellar environment of Betelgeuse - III. SPHERE/ZIMPOL visible polarimetry of the inner envelope and photosphereNov 13 2015The physical mechanism through which the outgoing material of massive red supergiants is accelerated above the escape velocity is unclear. Thanks to the transparency of its circumstellar envelope, the nearby red supergiant Betelgeuse gives the opportunity ... More
What causes the large extensions of red-supergiant atmospheres? Comparisons of interferometric observations with 1-D hydrostatic, 3-D convection, and 1-D pulsating model atmospheresJan 07 2015We present the atmospheric structure and the fundamental parameters of three red supergiants, increasing the sample of RSGs observed by near-infrared spectro-interferometry. Additionally, we test possible mechanisms that may explain the large observed ... More
New detectors of the Experimental complex NEVOD for multicomponent EAS detectionDec 30 2016Experimental complex (EC) NEVOD includes a number of unique experimental facilities for studies of main components of cosmic rays on the Earth's surface. The complex is used for the basic research of CR flux characteristics and their interactions in the ... More
Investigation on the energy and mass composition of cosmic rays using LOPES radio dataSep 10 2013The sensitivity to the mass composition as well as the reconstruction of the energy of the primary particle are explored here by leveraging the features of the radio lateral distribution function. For the purpose of this analysis, a set of events measured ... More
Mass sensitivity in the radio lateral distribution functionJul 31 2013Measuring the mass composition of ultra-high energy cosmic rays is one of the main tasks in the cosmic rays field. Here we are exploring the composition signature in the coherent electromagnetic emission from extensive air showers, detected in the MHz ... More
Biot-JKD model: simulation of 1D transient poroelastic waves with fractional derivativesJul 02 2012Dec 11 2012A time-domain numerical modeling of Biot poroelastic waves is presented. The viscous dissipation occurring in the pores is described using the dynamic permeability model developed by Johnson-Koplik-Dashen (JKD). Some of the coefficients in the Biot-JKD ... More
Investigation of the radio wavefront of air showers with LOPES measurements and CoREAS simulations (ARENA 2014)Jul 28 2015We investigated the radio wavefront of cosmic-ray air showers with LOPES measurements and CoREAS simulations: the wavefront is of approximately hyperbolic shape and its steepness is sensitive to the shower maximum. For this study we used 316 events with ... More
Improved absolute calibration of LOPES measurements and its impact on the comparison with REAS 3.11 and CoREAS simulationsJul 27 2015Dec 18 2015LOPES was a digital antenna array detecting the radio emission of cosmic-ray air showers. The calibration of the absolute amplitude scale of the measurements was done using an external, commercial reference source, which emits a frequency comb with defined ... More
Reconstruction of the energy and depth of maximum of cosmic-ray air-showers from LOPES radio measurementsAug 11 2014LOPES is a digital radio interferometer located at Karlsruhe Institute of Technology (KIT), Germany, which measures radio emission from extensive air showers at MHz frequencies in coincidence with KASCADE-Grande. In this article, we explore a method (slope ... More
Comparing LOPES measurements of air-shower radio emission with REAS 3.11 and CoREAS simulationsSep 19 2013Dec 18 2015Cosmic ray air showers emit radio pulses at MHz frequencies, which can be measured with radio antenna arrays - like LOPES at the Karlsruhe Institute of Technology in Germany. To improve the understanding of the radio emission, we test theoretical descriptions ... More
Vectorial Radio Interferometry with LOPES 3DAug 12 2013One successful detection technique for high-energy cosmic rays is based on the radio signal emitted by the charged particles in an air shower. The LOPES experiment at Karlsruhe Institute of Technology, Germany, has made major contributions to the evolution ... More
LOPES 3D - vectorial measurements of radio emission from cosmic ray induced air showersMar 28 2013LOPES 3D is able to measure all three components of the electric field vector of the radio emission from air showers. This allows a better comparison with emission models. The measurement of the vertical component increases the sensitivity to inclined ... More
Comparison of LOPES data and CoREAS simulations using a full detector simulation (ICRC2013)Aug 12 2013The LOPES experiment at the Karlsruhe Institute of Technology, Germany, has been measuring radio emission of air showers for almost 10 years. For a better understanding of the emission process a detailed comparison of data with simulations is necessary. ... More
Scientific rationale for Uranus and Neptune in situ explorationsAug 01 2017The ice giants Uranus and Neptune are the least understood class of planets in our solar system but the most frequently observed type of exoplanets. Presumed to have a small rocky core, a deep interior comprising ~70% heavy elements surrounded by a more ... More
Wave simulation in 2D heterogeneous transversely isotropic porous media with fractional attenuation: a Cartesian grid approachApr 01 2015A time-domain numerical modeling of transversely isotropic Biot poroelastic waves is proposed in two dimensions. The viscous dissipation occurring in the pores is described using the dynamic permeability model developed by Johnson-Koplik-Dashen (JKD). ... More
The 2010 Interferometric Imaging Beauty ContestJul 26 2010We present the results of the fourth Optical/IR Interferometry Imaging Beauty Contest. The contest consists of blind imaging of test data sets derived from model sources and distributed in the OI-FITS format. The test data consists of spectral data sets ... More
Ankle-like Feature in the Energy Spectrum of Light Elements of Cosmic Rays Observed with KASCADE-GrandeApr 26 2013Recent results of the KASCADE-Grande experiment provided evidence for a mild knee-like structure in the all-particle spectrum of cosmic rays at $E = 10^{16.92 \pm 0.10} \, \mathrm{eV}$, which was found to be due to a steepening in the flux of heavy primary ... More
Energy spectra of KASCADE-Grande based on shower size measurements and different hadronic interaction modelsSep 17 2013KASCADE-Grande is dedicated for investigations of cosmic-ray air showers in the primary energy range from 10 PeV to 1 EeV. The multi-detector system allows us to reconstruct charged particles, electron and muon numbers for individual air showers with ... More
Study of the muon content of very high-energy EAS measured with the KASCADE-Grande observatoryAug 14 2013The KASCADE-Grande detector is an air-shower array devoted to the study of primary cosmic rays with very high-energies (E = 10^{16} - 10^{18} eV). The instrument is composed of different particle detector systems suitable for the detailed study of the ... More
High-energy cosmic rays measured with KASCADE-GrandeAug 07 2013The detection of high-energy cosmic rays above a few hundred TeV is realized by the observation of extensive air-showers. By using the multi-detector setup of KASCADE-Grande, energy spectrum, elemental composition, and anisotropies of high-energy cosmic ... More
KASCADE-Grande Limits on the Isotropic Diffuse Gamma-Ray Flux between 100 TeV and 1 EeVOct 08 2017KASCADE and KASCADE-Grande were multi-detector installations to measure individual air showers of cosmic rays at ultra-high energy. Based on data sets measured by KASCADE and KASCADE-Grande, 90% C.L. upper limits to the flux of gamma-rays in the primary ... More
Multi-epoch VLTI-PIONIER imaging of the supergiant V766 Cen: Image of the close companion in front of the primarySep 27 2017The star V766 Cen (=HR 5171A) was originally classified as a yellow hypergiant but lately found to more likely be a 27-36 Msun red supergiant (RSG). Recent observations indicated a close eclipsing companion in the contact or common-envelope phase. Here, ... More
Evolution of the magnetic field of Betelgeuse from 2009 - 2017Apr 05 2018Betelgeuse is an M-type supergiant that presents a circularly polarized (Stokes V) signal in its line profiles, interpreted in terms of a surface magnetic field. The weak circular polarization signal has been monitored over 7.5 years in order to follow ... More
Numerical modeling of 1-D transient poroelastic waves in the low-frequency rangeNov 30 2007Apr 29 2008Propagation of transient mechanical waves in porous media is numerically investigated in 1D. The framework is the linear Biot's model with frequency-independant coefficients. The coexistence of a propagating fast wave and a diffusive slow wave makes numerical ... More
A time-domain numerical method for Biot-JKD poroelastic waves in 2D heterogeneous mediaOct 01 2012An explicit finite-difference scheme is presented for solving the two-dimensional Biot equations of poroelasticity across the full range of frequencies. The key difficulty is to discretize the Johnson-Koplik-Dashen (JKD) model which describes the viscous ... More
Sensitivity of KASCADE-Grande data to hadronic interaction modelsSep 24 2010KASCADE-Grande is a large detector array dedicated for studies of high-energy cosmic rays in the primary energy range from 100 TeV to 1 EeV. The multi-detector concept of the experimental set-up offers the possibility to measure simultaneously various ... More
Cosmic Ray Measurements with the KASCADE-Grande ExperimentJun 21 200914 KASCADE-Grande reports submitted to the 31st International Cosmic Ray Conference, Lodz, Poland, July 2009
Longitudinal EAS-Development Studies in the Air-Shower Experiment KASCADE-GrandeOct 13 2010A large area (128 m^2) Muon Tracking Detector (MTD), located within the KASCADE experiment, has been built with the aim to identify muons (E_mu > 0.8 GeV) and their directions in extensive air showers by track measurements under more than 18 r.l. shielding. ... More
The close circumstellar environment of Betelgeuse. IV. VLTI/PIONIER interferometric monitoring of the photosphereFeb 16 2016Mar 30 2016Context. The mass-loss mechanism of cool massive evolved stars is poorly understood. The proximity of Betelgeuse makes it an appealing target to study its atmosphere, map the shape of its envelope, and follow the structure of its wind from the photosphere ... More
The EEE ProjectJul 04 2006The new experiment ``Extreme Energy Events'' (EEE) to detect extensive air showers through muon detection is starting in Italy. The use of particle detectors based on Multigap Resistive Plate Chambers (MRPC) will allow to determine with a very high accuracy ... More
A comparison of the cosmic-ray energy scales of Tunka-133 and KASCADE-Grande via their radio extensions Tunka-Rex and LOPESOct 26 2016Oct 27 2016The radio technique is a promising method for detection of cosmic-ray air showers of energies around $100\,$PeV and higher with an array of radio antennas. Since the amplitude of the radio signal can be measured absolutely and increases with the shower ... More
Semi-analytical and numerical methods for computing transient waves in 2D acoustic / poroelastic stratified mediaFeb 09 2012Apr 18 2012Wave propagation in a stratified fluid / porous medium is studied here using analytical and numerical methods. The semi-analytical method is based on an exact stiffness matrix method coupled with a matrix conditioning procedure, preventing the occurrence ... More
The Stagger-grid: A grid of 3D stellar atmosphere models - IV. Limb darkening coefficientsMar 14 2014Oct 06 2014We compute the emergent stellar spectra from the UV to far infrared for different viewing angles using realistic 3D model atmospheres for a large range in stellar parameters to predict the stellar limb darkening. We have computed full 3D LTE synthetic ... More
The convection of close red supergiant stars observed with near-infrared interferometryDec 10 2015Our team has obtained observations of the photosphere of the two closest red supergiant stars Betelgeuse ($\alpha$ Ori) and Antares ($\alpha$ Sco) using near infrared interferometry. We have been monitoring the photosphere of Betelgeuse with the VLTI/PIONIER ... More
Analytical solution to the Riemann problem of 1D elastodynamics with general constitutive lawsAug 09 2016Under the hypothesis of small deformations, the equations of 1D elastodynamics write as a 2 x 2 hyperbolic system of conservation laws. Here, we study the Riemann problem for convex and nonconvex constitutive laws. In the convex case, the solution can ... More
Direct imaging with a hypertelescope of red supergiant stellar surfacesAug 11 2011High angular resolution images obtained with a hypertelescope can strongly constrain the radiative-hydrodynamics simulations of red supergiant (RSG) stars, in terms of intensity contrast, granulation size and temporal variations of the convective motions ... More
Plane-strain waves in nonlinear elastic solids with softeningMar 06 2019Propagation of elastic waves in damaged media (concrete, rocks) is studied theoretically and numerically. Such materials exhibit a nonlinear behavior, with long-time softening and recovery processes (slow dynamics). A constitutive model combining Murnaghan ... More
Detection of extensive air showers with the NEVOD-EAS cluster type detectorDec 30 2016A new cluster type shower array NEVOD-EAS is designed for estimating the size, axis position and arrival direction of extensive air showers registered by the Cherenkov water detector NEVOD and coordinate detector DECOR (Moscow, Russia). In 2015-2016, ... More
Ultraviolet Spectropolarimetry as a Tool for Understanding the Diversity of Exoplanetary AtmospheresMar 14 2019The polarization state of starlight reflected by a planetary atmosphere uniquely reveals coverage, particle size, and composition of aerosols as well as changing cloud patterns. It is not possible to obtain a comparable level of detailed from flux-only ... More
Discovery of a complex linearly polarized spectrum of Betelgeuse dominated by depolarization of the continuumMay 16 2016May 17 2016Betelgeuse is an M supergiant that harbors spots and giant granules at its surface and presents linear polarization of its continuum. We have previously discovered linear polarization signatures associated with individual lines in the spectra of cool ... More
Grown-up stars physics with MATISSEJul 08 2016MATISSE represents a great opportunity to image the environment around massive and evolved stars. This will allow one to put constraints on the circumstellar structure, on the mass ejection of dust and its reorganization , and on the dust-nature and formation ... More
Ultraviolet Spectropolarimetry as a Tool for Understanding the Diversity of Exoplanetary AtmospheresMar 14 2019Mar 15 2019The polarization state of starlight reflected by a planetary atmosphere uniquely reveals coverage, particle size, and composition of aerosols as well as changing cloud patterns. It is not possible to obtain a comparable level of detailed from flux-only ... More
Benchmark stars for Gaia: fundamental properties of the Population II star HD140283 from interferometric, spectroscopic and photometric dataOct 17 2014Dec 15 2014We determined the fundamental properties of HD 140283 by obtaining new interferometric and spectroscopic measurements and combining them with photometry from the literature. The interferometric measurements were obtained using the visible interferometer ... More
CRIRES high-resolution infrared spectroscopy of the long-period Cepheid l CarAug 24 2018The dynamical structure of the atmosphere of Cepheids has been well studied in the optical. Several authors have found very interesting spectral features in the J band, but little data have been secured beyond 1.6 um. However, such observations can probe ... More
Fundamental properties of the Population II fiducial stars HD 122563 and Gmb 1830 from CHARA interferometric observationsJul 25 2012We have determined the angular diameters of two metal-poor stars, HD 122563 and Gmb 1830, using CHARA and Palomar Testbed Interferometer observations. For the giant star HD 122563, we derive an angular diameter theta_3D = 0.940 +- 0.011 milliarcseconds ... More
Radar reflection off extensive air showersOct 04 2012We investigate the possibility of detecting extensive air showers by the radar technique. Considering a bistatic radar system and different shower geometries, we simulate reflection of radio waves off the static plasma produced by the shower in the air. ... More
Imaging the heart of astrophysical objects with optical long-baseline interferometryApr 19 2012The number of publications of aperture-synthesis images based on optical long-baseline interferometry measurements has recently increased due to easier access to visible and infrared interferometers. The interferometry technique has now reached a technical ... More
The Tunka-133 EAS Cherenkov light array: status of 2011Jan 10 2012A new EAS Cherenkov light array, Tunka-133, with ~1 km^2 geometrical area has been installed at the Tunka Valley (50 km from Lake Baikal) in 2009. The array permits a detailed study of cosmic ray energy spectrum and mass composition in the energy range ... More
Cryogenic Characterization of FBK RGB-HD SiPMsMay 19 2017Sep 12 2017We report on the cryogenic characterization of Red Green Blue - High Density (RGB-HD) SiPMs developed at Fondazione Bruno Kessler (FBK) as part of the DarkSide program of dark matter searches with liquid argon time projection chambers. A dedicated setup ... More
The close circumstellar environment of Betelgeuse - II. Diffraction-limited spectro-imaging from 7.76 to 19.50 microns with VLT/VISIRJun 24 2011Context: Mass-loss occurring in red supergiants (RSGs) is a major contributor to the enrichment of the interstellar medium in dust and molecules. The physical mechanism of this mass loss is however relatively poorly known. Betelgeuse is the nearest RSG, ... More
Phase Closure Image Reconstruction for Future VLTI InstrumentationOct 02 2008Classically, optical and near-infrared interferometry have relied on closure phase techniques to produce images. Such techniques allow us to achieve modest dynamic ranges. In order to test the feasibility of next generation optical interferometers in ... More
Planet transit and stellar granulation detection with interferometryApr 28 2014Aims. We used realistic three-dimensional (3D) radiative hydrodynamical (RHD) simulations from the Stagger-grid and synthetic images computed with the radiative transfer code Optim3D to provide interferometric observables to extract the signature of stellar ... More
<3D> NLTE line formation in the atmospheres of red supergiantsMar 19 2013Red supergiants with their enormous brightness at J-band are ideal probes of cosmic chemical composition. It is therefore crucial to have realistic models of radiative transfer in their atmospheres, which will permit determination of abundances accurate ... More
The High-Resolution Transmission Spectrum of HD 189733b Interpreted with Atmospheric Doppler Shifts from Three-Dimensional General Circulation ModelsOct 14 2018The interplay of rotation and energy redistribution in the atmospheres of hot Jupiters produces complex wind patterns affecting the shape and shift of spectral lines. This signature is detectable at high spectral resolution, however no direct comparison ... More
Properties of the CO and H$_2$O MOLsphere of the red supergiant Betelgeuse from VLTI/AMBER observationsAug 13 2014Oct 02 2014Context. Betelgeuse is the closest red supergiant (RSG); therefore, it is well suited for studying the complex processes in its atmosphere that lead to the chemical enrichment of the interstellar medium. Aims. We intend to investigate the shape and composition ... More
The High-Resolution Transmission Spectrum of HD 189733b Interpreted with Atmospheric Doppler Shifts from Three-Dimensional General Circulation ModelsOct 14 2018Apr 04 2019The signature of wind patterns caused by the interplay of rotation and energy redistribution in hot Jupiters is detectable at high spectral resolution, yet no direct comparison has been attempted between predictions from general circulation models (GCMs) ... More
GW150914: First search for the electromagnetic counterpart of a gravitational-wave event by the TOROS collaborationJul 26 2016We present the results of the optical follow-up conducted by the TOROS collaboration of the first gravitational-wave event GW150914. We conducted unfiltered CCD observations (0.35-1 micron) with the 1.5-m telescope at Bosque Alegre starting ~2.5 days ... More
Milli-arcsecond astrophysics with VSI, the VLTI spectro-imager in the ELT eraJan 17 2008Nowadays, compact sources like surfaces of nearby stars, circumstellar environments of stars from early stages to the most evolved ones and surroundings of active galactic nuclei can be investigated at milli-arcsecond scales only with the VLT in its interferometric ... More
SPIDAST: a new modular software to process spectro-interferometric measurementsApr 05 2013Extracting stellar fundamental parameters from SPectro-Interferometric (SPI) data requires reliable estimates of observables and with robust uncertainties (visibility, triple product, phase closure). A number of fine calibration procedures is necessary ... More
The temperatures of Red SupergiantsFeb 12 2013We present a re-appraisal of the temperatures of Red Supergiants (RSGs) using their optical and near-infrared spectral energy distributions (SEDs). We have obtained data of a sample of RSGs in the Magellanic Clouds using VLT+XSHOOTER, and we fit MARCS ... More
An edge-on translucent dust disk around the nearest AGB star L2 Puppis - VLT/NACO spectro-imaging from 1.04 to 4.05 microns and VLTI interferometryApr 11 2014As the nearest known AGB star (d=64pc) and one of the brightest (mK-2), L2 Pup is a particularly interesting benchmark object to monitor the final stages of stellar evolution. We report new lucky imaging observations of this star with the VLT/NACO adaptive ... More
Muon Counting using Silicon Photomultipliers in the AMIGA detector of the Pierre Auger ObservatoryMar 17 2017Oct 04 2017AMIGA (Auger Muons and Infill for the Ground Array) is an upgrade of the Pierre Auger Observatory designed to extend its energy range of detection and to directly measure the muon content of the cosmic ray primary particle showers. The array will be formed ... More
The GALAH Survey: Accurate Radial Velocities and Library of Observed Stellar Template SpectraApr 17 2018Sep 06 2018GALAH is a large-scale magnitude-limited southern stellar spectroscopic survey. Its second data release (GALAH DR2) provides values of stellar parameters and abundances of 23 elements for 342,682 stars (Buder et al.). Here we add a description of the ... More
Lateral Distribution of the Radio Signal in Extensive Air Showers Measured with LOPESOct 26 2009The antenna array LOPES is set up at the location of the KASCADE-Grande extensive air shower experiment in Karlsruhe, Germany and aims to measure and investigate radio pulses from Extensive Air Showers. The coincident measurements allow us to reconstruct ... More
Cosmic Ray Measurements with LOPES: Status and Recent Results (ARENA 2012)Jan 11 2013LOPES is a digital antenna array at the Karlsruhe Institute of Technology, Germany, for cosmic-ray air-shower measurements. Triggered by the co-located KASCADE-Grande air-shower array, LOPES detects the radio emission of air showers via digital radio ... More
Testing Hadronic Interactions at Ultrahigh Energies with Air Showers Measured by the Pierre Auger ObservatoryOct 26 2016Oct 31 2016Ultrahigh energy cosmic ray air showers probe particle physics at energies beyond the reach of accelerators. Here we introduce a new method to test hadronic interaction models without relying on the absolute energy calibration, and apply it to events ... More
LOPES 3D reconfiguration and first measurementsMar 28 2013The Radio detection technique of high-energy cosmic rays is based on the radio signal emitted by the charged particles in an air shower due to their deflection in the Earth's magnetic field. The LOPES experiment at Karlsruhe Institute of Technology, Germany ... More