Publications (44)
Systematic investigation of chemical abundances derived using IR spectra obtained with GIANO
E. Caffau, P. Bonifacio, E. Oliva +10
Detailed chemical abundances of Galactic stars are needed in order to improve our knowledge of the formation and evolution of our galaxy, the Milky Way. We took advantage of the GI…
Non-LTE line formation of Fe in late-type stars IV: Modelling of the solar centre-to-limb variation in 3D
K. Lind, A. M. Amarsi, M. Asplund +7
Our ability to model the shapes and strengths of iron lines in the solar spectrum is a critical test of the accuracy of the solar iron abundance, which sets the absolute zero-point…
Exoplanetary atmospheric sodium revealed by the orbital motion. Narrow-band transmission spectroscopy of HD 189733b with UVES
S. Khalafinejad, C. von Essen, H. J. Hoeijmakers +8
During primary transits, the spectral signatures of an exoplanet atmosphere can be measured using transmission spectroscopy. The goal of this work is to accurately measure the atom…
Three-dimensional surface convection simulations of metal-poor stars -- The effect of scattering on the photospheric temperature stratification
R. Collet, W. Hayek, M. Asplund +3
Three-dimensional (3D) radiative hydrodynamic model atmospheres of metal-poor late-type stars are characterized by cooler upper photospheric layers than their 1D counterparts. This…
Women Scientists Who Made Nuclear Astrophysics
C. V. Hampton, M. Lugaro, P. Papakonstantinou +24
Female role models reduce the impact on women of stereotype threat, i.e., of being at risk of conforming to a negative stereotype about one's social, gender, or racial group. This…
The Barium Isotopic Abundance in the Metal-Poor Star HD140283
R. Collet, M. Asplund, P. E. Nissen
We derive the mixture of odd to even barium isotopes in the atmosphere of the metal-poor subgiant HD140283 from the analysis of the Ba II transition at 455.4 nm in a high-resolutio…
Bisectors of the HARPS Cross-Correlation-Function. The dependence on stellar atmospheric parameters
O. Basturk, T. H. Dall, R. Collet +2
Bisectors of the HARPS cross-correlation function (CCF) can discern between planetary radial-velocity (RV) signals and spurious RV signals from stellar magnetic activity variations…
A probable stellar solution to the cosmological lithium discrepancy
A. J. Korn, F. Grundahl, O. Richard +5
The measurement of the cosmic microwave background has strongly constrained the cosmological parameters of the Universe. When the measured density of baryons (ordinary matter) is c…
Asymmetries on red giant branch surfaces from CHARA/MIRC optical interferometry
A. Chiavassa, R. Norris, M. Montargès +14
Context. Red giant branch (RGB) stars are very bright objects in galaxies and are often used as standard candles. Interferometry is the ideal tool to characterize the dynamics and…
Non-LTE line formation of Fe in late-type stars - III. 3D non-LTE analysis of metal-poor stars
A. M. Amarsi, K. Lind, M. Asplund +2
As one of the most important elements in astronomy, iron abundance determinations need to be as accurate as possible. We investigate the accuracy of spectroscopic iron abundance an…
Granulation signatures in the spectrum of the very metal-poor red giant HD122563
I. Ramirez, R. Collet, D. L. Lambert +2
A very high resolution (R=200,000), high signal-to-noise ratio (S/N=340) blue-green spectrum of the very metal-poor ([Fe/H]=-2.6) red giant star HD122563 has been obtained by us at…
The chemical composition of red giants in 47 Tucanae. II. Magnesium isotopes and pollution scenarios
A. O. Thygesen, L. Sbordone, H. -G. Ludwig +6
The phenomenon of multiple populations in globular clusters is still far from understood, with several proposed mechanisms to explain the observed behaviour. The study of elemental…
Sulphur abundances in halo giants from the [S I] line at 1082 nm and the S I triplet around 1045 nm
H. Jönsson, N. Ryde, P. E. Nissen +4
It is still debated whether or not the Galactic chemical evolution of sulphur in the halo followed the constant or flat trend with [Fe/H], ascribed to the result of explosive nucle…
Iron and s-elements abundance variations in NGC5286: comparison with anomalous globular clusters and Milky Way satellites
A. F. Marino, A. P. Milone, A. I. Karakas +13
We present a high resolution spectroscopic analysis of 62 red giants in the Milky Way globular cluster NGC5286. We have determined abundances of representative light proton-capture…
The chemical composition of red giants in 47 Tucanae I: Fundamental parameters and chemical abundance patterns
A. O. Thygesen, L. Sbordone, S. Andrievsky +9
Context: The study of chemical abundance patterns in globular clusters is of key importance to constrain the different candidates for intra-cluster pollution of light elements. Aim…
3D LTE spectral line formation with scattering in red giant stars
W. Hayek, M. Asplund, R. Collet +1
We investigate the effects of coherent isotropic continuum scattering on the formation of spectral lines in local thermodynamic equilibrium (LTE) using 3D hydrodynamical and 1D hyd…
Three-dimensional models of metal-poor stars
R. Collet
I present here the main results of recent realistic, 3D, hydrodynamical simulations of convection at the surface of metal-poor red giant stars. I discuss the application of these c…
Three-dimensional hydrodynamical simulations of red giant stars: semi-global models for the interpretation of interferometric observations
A. Chiavassa, R. Collet, L. Casagrande +1
Context. Theoretical predictions from models of red giant branch stars are a valuable tool for various applications in astrophysics ranging from galactic chemical evolution to stud…
The 3D non-LTE solar nitrogen abundance from atomic lines
A. M. Amarsi, N. Grevesse, J. Grumer +3
Nitrogen is an important element in various fields of stellar and Galactic astronomy, and the solar nitrogen abundance is crucial as a yardstick for comparing different objects in…
Effective temperature determinations of late-type stars based on 3D non-LTE Balmer line formation
A. M. Amarsi, T. Nordlander, P. S. Barklem +3
Hydrogen Balmer lines are commonly used as spectroscopic effective temperature diagnostics of late-type stars. However, the absolute accuracy of classical methods that are based on…
Radiative transfer with scattering for domain-decomposed 3D MHD simulations of cool stellar atmospheres
W. Hayek, M. Asplund, M. Carlsson +5
We present the implementation of a radiative transfer solver with coherent scattering in the new BIFROST code for radiative magneto-hydrodynamical (MHD) simulations of stellar surf…
The Stagger-grid: A Grid of 3D Stellar Atmosphere Models - I. Methods and General Properties
Z. Magic, R. Collet, M. Asplund +5
We 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…
Three-dimensional interferometric, spectrometric, and planetary views of Procyon
A. Chiavassa, L. Bigot, P. Kervella +5
We 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 Opti…
Chemical Homogeneity in Collinder 261 and Implications for Chemical Tagging
G. M. De Silva, K. C. Freeman, M. Asplund +3
This paper presents abundances for 12 red giants of the old open cluster Collinder 261 based on spectra from VLT/UVES. Abundances were derived for Na, Mg, Si, Ca, Mn, Fe, Ni, Zr an…
Chemical abundances in the multiple sub-giant branch of 47 Tucanae: insights on its faint sub-giant branch component
A. F. Marino, A. P. Milone, L. Casagrande +8
The globular cluster 47 Tuc exhibits a complex sub-giant branch (SGB) with a faint-SGB comprising only about the 10% of the cluster mass and a bright-SGB hosting at least two disti…
The Galactic chemical evolution of oxygen inferred from 3D non-LTE spectral line formation calculations
A. M. Amarsi, M. Asplund, R. Collet +1
We revisit the Galactic chemical evolution of oxygen, addressing the systematic errors inherent in classical determinations of the oxygen abundance that arise from the use of one d…
Atomic Diffusion and Mixing in Old Stars I. VLT/FLAMES-UVES Observations of Stars in NGC 6397
A. J. Korn, F. Grundahl, O. Richard +5
We present a homogeneous photometric and spectroscopic analysis of 18 stars along the evolutionary sequence of the metal-poor globular cluster NGC 6397 ([Fe/H] = -2), from the main…
New Abundances for Old Stars - Atomic Diffusion at Work in NGC 6397
A. J. Korn, F. Grundahl, O. Richard +5
A homogeneous spectroscopic analysis of unevolved and evolved stars in the metal-poor globular cluster NGC 6397 with FLAMES-UVES reveals systematic trends of stellar surface abunda…
Inelastic O+H collisions and the OI 777nm solar centre-to-limb variation
A. M. Amarsi, P. S. Barklem, M. Asplund +2
The OI 777 nm triplet is a key diagnostic of oxygen abundances in the atmospheres of FGK-type stars; however it is sensitive to departures from local thermodynamic equilibrium (LTE…
The solar carbon, nitrogen, and oxygen abundances from a 3D LTE analysis of molecular lines
A. M. Amarsi, N. Grevesse, M. Asplund +1
Carbon, nitrogen, and oxygen are the fourth, sixth, and third most abundant elements in the Sun. Their abundances remain hotly debated due to the so-called solar modelling problem…
Observational constraints on the origin of the elements II. 3D non-LTE formation of Ba ii lines in the solar atmosphere
A. J. Gallagher, M. Bergemann, R. Collet +5
Context. The pursuit of more realistic spectroscopic modelling and consistent abundances has led us to begin a new series of papers designed to improve current solar and stellar ab…
Fundamental properties of the Population II fiducial stars HD 122563 and Gmb 1830 from CHARA interferometric observations
O. L. Creevey, F. Thévenin, T. S. Boyajian +17
We 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,…
3D non-LTE line formation of neutral carbon in the Sun
A. M. Amarsi, P. S. Barklem, R. Collet +2
Carbon abundances in late-type stars are important in a variety of astrophysical contexts. However C i lines, one of the main abundance diagnostics, are sensitive to departures fro…
Beyond 1D: spectral line formation with 3D hydrodynamical model atmospheres of red giants
R. Collet, M. Asplund, R. Trampedach
We present the results of realistic, 3D, hydrodynamical, simulations of surface convection in red giant stars with varying effective temperatures and metallicities. We use the conv…
Non-LTE oxygen line formation in 3D hydrodynamic model stellar atmospheres
A. M. Amarsi, M. Asplund, R. Collet +1
The OI 777 nm lines are among the most commonly used diagnostics for the oxygen abundances in the atmospheres of FGK-type stars. However, they form in conditions that are far from…
Lithium abundances of halo dwarfs based on excitation temperatures. II. NLTE
A. Hosford, A. E. Garcia Perez, R. Collet +3
One of the most important factors in determining the stellar lithium abundance is the effective temperature. In a previous study by the authors, new effective temperatures Teff for…
High-precision abundances of elements in Kepler LEGACY stars. Verification of trends with stellar age
P. E. Nissen, V. Silva Aguirre, J. Christensen-Dalsgaard +3
HARPS-N spectra with S/N > 250 and MARCS model atmospheres were used to derive abundances of C, O, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni, Zn, and Y in ten stars from the Kepler LEGACY…
Measuring stellar granulation during planet transits
A. Chiavassa, A. Caldas, F. Selsis +6
Stellar activity and convection-related surface structures might cause bias in planet detection and characterization that use these transits. Surface convection simulations help to…
High Precision Differential Abundance Measurements in Globular Clusters: Chemical Inhomogeneities in NGC 6752
David Yong, Jorge Melendez, Frank Grundahl +9
We report on a strictly differential line-by-line analysis of high quality UVES spectra of bright giants in the metal-poor globular cluster NGC 6752. We achieved high precision dif…
Simulations of the solar near-surface layers with the CO5BOLD, MURaM, and Stagger codes
B. Beeck, R. Collet, M. Steffen +6
Radiative hydrodynamic simulations of solar and stellar surface convection have become an important tool for exploring the structure and gas dynamics in the envelopes and atmospher…
3D hydrodynamical model atmospheres: a tool to correct radial velocities and parallaxes for Gaia
A. Chiavassa, L. Bigot, F. Thevenin +4
Convection 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 asymme…
The Stagger-grid: A grid of 3D stellar atmosphere models V. Synthetic stellar spectra and broad-band photometry
A. Chiavassa, L. Casagrande, R. Collet +4
Context. 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 u…
A new view on exoplanet transits: Transit of Venus described using three-dimensional solar atmosphere Stagger-grid simulations
A. Chiavassa, C. Pere, M. Faurobert +5
Stellar activity and, in particular, convection-related surface structures, potentially cause fluctuations that can affect the transit light curves. Surface convection simulations…
Abundance Analysis of the Halo Giant HD122563 with Three-Dimensional Model Stellar Atmospheres
R. Collet, A. Nordlund, M. Asplund +2
We present a preliminary local thermodynamic equilibrium (LTE) abundance analysis of the template halo red giant HD122563 based on a realistic, three-dimensional (3D), time-depende…