A5033421182- Stellar, planetary, and galactic studies
- Astronomy and Astrophysical Research
- Astrophysics and Star Formation Studies
- Astro and Planetary Science
- Solar and Space Plasma Dynamics
- Adaptive optics and wavefront sensing
- Gamma-ray bursts and supernovae
- Atmospheric Ozone and Climate
- Astronomical Observations and Instrumentation
- Geophysics and Gravity Measurements
- Semiconductor Quantum Structures and Devices
- Atmospheric and Environmental Gas Dynamics
- Ionosphere and magnetosphere dynamics
- Advanced Semiconductor Detectors and Materials
- Chalcogenide Semiconductor Thin Films
- Spectroscopy and Laser Applications
- Gas Dynamics and Kinetic Theory
- Geomagnetism and Paleomagnetism Studies
- Mathematics and Applications
- Scientific Research and Discoveries
- Space Exploration and Technology
- Climate variability and models
- Solar Radiation and Photovoltaics
- Meteorological Phenomena and Simulations
- Astronomical and nuclear sciences
Uppsala University
2015-2024
Max Planck Institute for Astronomy
2018
Max Planck Society
2018
Centre de Recherche Astrophysique de Lyon
2007-2015
École Normale Supérieure de Lyon
2007-2015
Université Claude Bernard Lyon 1
2007-2015
Centre National de la Recherche Scientifique
2007-2015
Astronomical Observatory of Capodimonte
2010-2011
National Institute for Astrophysics
2011
University of Göttingen
2009
Within the next few years, GAIA and several instruments aiming at imag- ing extrasolar planets will see first light. In parallel, low mass are being searched around red dwarfs which offer more favourable conditions, both for radial velocity de- tection transit studies, than solar-type stars. Authors of model atmosphere code has allowed detection water vapour in Hot Jupiters re- view recent advancement modelling stellar to substellar transition. The revised solar oxygen abundances cloud allow...
We present VLT-UVES Li abundances for 28 halo dwarf stars between [Fe/H]=-2.5 and -3.5, 10 of which have [Fe/H]<-3. Four different T_eff scales been used. Direct Infrared Flux Method (IRFM) has used on the basis 2MASS infrared photometry. H_alpha wings fitted against synthetic grids computed by means 1D LTE atmosphere models, assuming self-broadening theories. Finally, a grid profiles 3D hydrodynamical models. The I doublet at 670.8 nm to measure A(Li) NLTE spectral syntheses. An analytical...
Three-dimensional numerical simulations with COBOLD, a new radiation hydrodynamics code, result in dynamic, thermally bifurcated model of the non-magnetic chromosphere quiet Sun. The 3D includes middle and low chromosphere, photosphere, top convection zone, where acoustic waves are excited by convective motions. While propagate upwards, they steepen into shocks, dissipate, deposit their mechanical energy as heat chromosphere. Our show for first time complex structure chromospheric layers,...
Context. The solar oxygen abundance has undergone a major downward revision in the past decade, most noticeable one being update including 3D hydrodynamical simulations to model photosphere. Up now, such an analysis only been carried out by group using radiation-hydrodynamics code.
The observed irregular brightness fluctuations of the well-known red supergiant Betelgeuse (α Ori, M2 Iab) have been attributed by M. Schwarzschild (1975) to changing granulation pattern formed only a few giant convection cells covering surface this star. structure revealed modern interferometric methods appears be generally consistent with explanation as large-scale granular intensity fluctuations. data can modeled equally well assuming presence (up 3) unresolved hot or cool spots on...
We present the first grid of mean three-dimensional (3D) spectra for pure-hydrogen (DA) white dwarfs based on 3D model atmospheres. use CO5BOLD radiation-hydrodynamics simulations instead mixing-length theory treatment convection. The cover effective temperature range 6000 < Teff (K) 15 000 and surface gravity 7 log g 9 where large majority DAs with a convective atmosphere are located. rely horizontally averaged structures (over constant Rosseland optical depth) to compute ⟨3D⟩ spectra. It...
Context. Winds of asymptotic giant branch stars are assumed to be driven by radiation pressure on dust. Previously, this process has been modeled with detailed time-dependent simulations atmospheres and winds assuming spherically symmetric flows. In such models kinetic energy is injected a variable inner boundary ("piston") simulating the effects stellar pulsation. However, dynamical processes in these – convection pulsations actually three-dimensional.
Observationally, spectra of brown dwarfs indicate the presence dust in their atmospheres while theoretically it is not clear what prevents from settling and disappearing regions spectrum formation. Consequently, standard models have to rely on ad hoc assumptions about mechanism that keeps grains aloft atmosphere. We apply hydrodynamical simulations develop an improved physical understanding mixing properties macroscopic flows M dwarf atmospheres, particular influence underlying convection...
Context. Observations of asymptotic giant branch (AGB) stars with increasing spatial resolution reveal new layers complexity atmospheric processes on a variety scales.
We present two epochs of MPG/ESO 2.2 m GROND simultaneous six-band (r'i'z' JHK) photometric monitoring the closest known L/T transition brown dwarf binary WISE J104915.57−531906.1AB. report here first resolved variability both T0.5 and L7.5 components. obtained 4 hr focused observations on night 2013 April 22 (UT), as well defocused (unresolved) 16 (UT). note a number robust trends in our light curves. The r' i' curves appear to be anti-correlated with z' H for component unresolved curve. In...
<i>Context. <i/>It has been proposed that convection in red supergiant (RSG) stars produces large-scale granules causing observable surface inhomogeneities. This is also extremely vigorous and suspected to be one of the main causes mass-loss RSGs. It should thus understood detail. Evidence accumulated asymmetries photospheres RSGs, but detailed studies granulation are still lacking. Interferometric observations provide an innovative way addressing this question, they often interpreted using...
Context. It has been shown that convection in red supergiant stars gives rise to large granules causing surface inhomogeneities together with shock waves the photosphere. The resulting motion of photocenter (on time scales ranging from months years) could possibly have adverse effects on parallax determination Gaia. Aims. We explore impact granulation photocentric and photometric variability. quantify these order better characterize error altering parallax. Methods. use 3D...
Context. The red supergiant (RSG) Betelgeuse is an irregular variable star. Convection may play important role in understanding this variability. Interferometric observations can be interpreted using sophisticated simulations of stellar convection. Aims. We compare the visibility curves and closure phases obtained from our 3D simulation RSG convection with CO5BOLD to various interferometric optical H band order characterize measure pattern on Methods. use radiative-hydrodynamics (RHD)...
Red supergiants are massive evolved stars that contribute extensively to the chemical enrichment of our Galaxy. It has been shown convection in those gives rise large granules cause surface inhomogeneities and shock waves photosphere. The understanding their dynamics is crucial unveil unknown mass-loss mechanism, composition stellar parameters. We present a new generation red simulations with more sophisticated opacity treatment done 3D radiative- hydrodynamics CO5BOLD. In code, coupled...
Within the next few years, several instruments aiming at imaging extrasolar planets will see first light. In parallel, low mass are being searched around red dwarfs which offer more favorable conditions, both for radial velocity detection and transit studies, than solar-type stars. We review recent advancements in modeling stellar to substellar transition. The revised solar oxygen abundances cloud models allow reproduce photometric spectroscopic properties of this transition a degree never...
The $s$-process nucleosynthesis in Asymptotic Giant Branch (AGB) stars depends on the modeling of convective boundaries. We present models and s-process simulations that adopt a treatment boundaries based results hydrodynamic theory mixing due to gravity waves vicinity Hydrodynamics suggest presence boundary (CBM) at bottom thermal pulse-driven zone. Similarly, convection-induced processes are proposed for below envelope during third dredge-up where 13C pocket s process AGB forms. In this...
Aims. This research has two main goals. First, we present the atmospheric structure and fundamental parameters of three red supergiants (RSGs), increasing sample RSGs observed by near-infrared spectro-interferometry. Additionally, test possible mechanisms that may explain large extensions RSGs.