A5052401672- Stellar, planetary, and galactic studies
- Astronomy and Astrophysical Research
- Astrophysics and Star Formation Studies
- Astro and Planetary Science
- Solar and Space Plasma Dynamics
- Atmospheric Ozone and Climate
- Astronomical Observations and Instrumentation
- Geophysics and Gravity Measurements
- Gamma-ray bursts and supernovae
- Astronomical and nuclear sciences
- Adaptive optics and wavefront sensing
- Spectroscopy and Laser Applications
- History and Developments in Astronomy
- Geomagnetism and Paleomagnetism Studies
- Atmospheric and Environmental Gas Dynamics
- Scientific Research and Discoveries
- Ionosphere and magnetosphere dynamics
- Calibration and Measurement Techniques
- Solar Radiation and Photovoltaics
- Galaxies: Formation, Evolution, Phenomena
- Fluid Dynamics and Turbulent Flows
- Solar Thermal and Photovoltaic Systems
- Cosmology and Gravitation Theories
- Aeolian processes and effects
- Meteorological Phenomena and Simulations
Heidelberg University
2015-2024
Max Planck Institute for Astronomy
2012-2024
Heidelberg University
2023
Galaxies, Etoiles, Physique et Instrumentation
2011-2022
Centre National de la Recherche Scientifique
2011-2022
Université Paris Sciences et Lettres
2016-2022
Université Paris Cité
2009-2020
Observatoire de Paris
2005-2020
Max Planck Society
1997-2018
Délégation Paris 7
2008-2017
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...
The Gaia-ESO Survey is obtaining high-quality spectroscopic data for about 10^5 stars using FLAMES at the VLT. UVES high-resolution spectra are being collected 5000 FGK-type stars. These analyzed in parallel by several state-of-the-art methodologies. Our aim to present how these analyses were implemented, discuss their results, and describe a final recommended parameter scale defined. We also precision (method-to-method dispersion) accuracy (biases with respect reference values) of...
Context. The chemical composition of the Sun is required in context various studies astrophysics, among them calculation standard solar models (SSMs) used to describe evolution from pre-main-sequence its present age. Aims. In this work, we provide a critical re-analysis abundances and corresponding SSMs. Methods. For photospheric values, employed new high-quality observational data collected with IAG facility, state-of-the art non-equilibrium modelling, oscillator strengths, different...
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.
<i>Context. <i/>The detailed chemical abundances of extremely metal-poor (EMP) stars are key guides to understanding the early evolution Galaxy. Most existing data, however, treat giant that may have experienced internal mixing later.<i>Aims. <i/>We aim compare results for giants with new, accurate all observable elements in 18 EMP turnoff stars.<i>Methods. <i/>VLT/UVES spectra at <i>R<i/> ~ 45 000 and <i>S<i/>/<i>N<i/> 130 per pixel ( 330-1000 nm) analysed OSMARCS model atmospheres...
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...
The 4MOST consortium is currently halfway through a Conceptual Design study for ESO with the aim to develop wide-field (>3 square degree, goal >5 degree), high-multiplex (>1500 fibres, 3000 fibres) spectroscopic survey facility an 4m-class telescope (VISTA). will run permanently on perform 5 year public yielding more than 20 million spectra at resolution R~5000 ({\lambda}=390-1000 nm) and 2 R~20,000 (395-456.5 nm & 587-673 nm). design especially intended complement three key all-sky,...
<i>Context. <i/>Solar-like oscillations have been observed in numerous red giants from ground and space. An important question arises: could we expect to detect non-radial modes probing the internal structure of these stars?<i>Aims. <i/>We investigate under what physical circumstances be observable giants; would their amplitudes, lifetimes heights power spectrum (PS)?<i>Methods. <i/>Using a non-adiabatic pulsation code including non-local time-dependent treatment convection, compute...
Context. In the course of Turn Off Primordial Stars (TOPoS) survey, aimed at discovering lowest metallicity stars, we have found several carbon-enhanced metal-poor (CEMP) stars. These stars are very common among extremely low and provide important clues to star formation processes. We here present our analysis six CEMP
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...
We present preliminary asteroseismic results from Kepler on three G-type stars. The observations, made at one-minute cadence during the first 33.5d of science operations, reveal high signal-to-noise solar-like oscillation spectra in all stars: About 20 modes may be clearly distinguished each star. discuss appearance spectra, use frequencies and frequency separations to provide radii, masses ages stars, comment light these prospects for inference other solar-type stars that will observe.
Context. The discovery and chemical analysis of extremely metal-poor stars permit a better understanding the star formation first generation Universe emerging from Big Bang.
Carbon-enhanced metal poor stars (CEMP) form a significant proportion of the metal-poor stars, their origin is not well understood. Three very C-rich turnoff were selected from SDSS survey, observed with ESO VLT (UVES) to precisely determine element abundances. In (unlike giants) carbon abundance has been affected by mixing deep layers and therefore easier interpret. The analysis was performed 1D LTE static model atmospheres. When available, non-LTE corrections applied classical 3D effects...
4MOST is a wide-field, high-multiplex spectroscopic survey facility under development for the VISTA telescope of European Southern Observatory (ESO). Its main science drivers are in fields galactic archeology, high-energy physics, galaxy evolution and cosmology. will particular provide complements to large area surveys coming from space missions like Gaia, eROSITA, Euclid, PLATO ground-based facilities VISTA, VST, DES, LSST SKA. The baseline concept features 2.5 degree diameter field-of-view...
The space-borne missions have provided us with a wealth of high-quality observational data that allows for seismic inferences stellar interiors. This requires the computation precise and accurate theoretical frequencies, but imperfect modeling uppermost layers introduces systematic errors. To overcome this problem, an empirical correction has been introduced by Kjeldsen et al. (2008, ApJ, 683, L175) is now commonly used inferences. Nevertheless, we still lack physical justification allowing...
Context.Line asymmetries are generated by convective Doppler shifts in stellar atmospheres, especially metal-poor stars, where motions penetrate to higher atmospheric levels. Such usually neglected abundance analyses. The determination of the isotopic ratio is prone suffering from such asymmetries, as contribution 6Li a slight blending reinforcement red wing each component corresponding 7Li line, with respect its blue wing.
CONTEXT: In recent years, the solar chemical abundances have been studied in considerable detail because of discrepant values metallicity inferred from different indicators, i.e., on one hand, "sub-solar" photospheric resulting spectroscopic composition analyses with aid 3D hydrodynamical models atmosphere, and, other high by helioseismology. AIMS: After investigating oxygen abundance using a CO5BOLD model previous work, we undertake similar approach studying nitrogen, since this element...
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...
The origin of carbon-enhanced metal-poor stars enriched with both s and r elements is highly debated. Detailed abundances these types are crucial to understand the nature their progenitors. aim this investigation study in detail SDSS J1349-0229, J0912+0216 J1036+1212, three dwarf CEMP stars, selected from Sloan Digital Sky Survey. Using high resolution VLT/UVES spectra (R ~ 30 000) we determine for Li, C, N, O, Na, Mg, Al, Ca, Sc, Ti, Cr, Mn, Fe, Co, Ni 21 neutron-capture elements. We made...