An in-depth spectroscopic examination of molecular bands from 3D hydrodynamical model atmospheres

Gallagher, A. J.; Caffau, E.; Bonifacio, P.; Ludwig, H.‐G.; Steffen, M.; Spite, M.

doi:10.1051/0004-6361/201628602

Cited by 41 publications

(58 citation statements)

References 29 publications

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“…For Li, a signal-to-noise (S/N) ratio of approximately 70 in the range implies A(Li) < 1.3, at 3σ, using the 3D-NLTE formula of Sbordone et al (2010); this put the stars in the Li-meltdown region. The 3D corrections for the G-band would increase A(C) by approximately 0.05 dex (see Gallagher et al 2016). However, the spectrum is consistent with the presence of a line corresponding to the above Zn abundance and shifted to the blue by 4.6 km s −1 .…”

Section: Analysis and Resultsmentioning

confidence: 70%

TOPoS

Caffau

Bonifacio

Spite

et al. 2016

A&A

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Aims. One of the primary objectives of the TOPoS survey is to search for the most metal-poor stars. Our search has led to the discovery of one of the most iron-poor objects known, SDSS J092912.32+023817.0. This object is a multiple system, in which two components are clearly detected in the spectrum. Methods. We have analysed 16 high-resolution spectra obtained using the UVES spectrograph at the ESO 8.2 m VLT telescope to measure radial velocities and determine the chemical composition of the system. Results. Cross correlation of the spectra with a synthetic template yields a double-peaked cross-correlation function (CCF) for eight spectra, and in one case there is evidence for the presence of a third peak. Chemical analysis of the spectrum obtained by averaging all the spectra for which the CCF showed a single peak found that the iron abundance is [Fe/H] = −4.97. The system is also carbon enhanced with [C/Fe] = +3.91 (A(C) = 7.44). From the permitted oxygen triplet we determined an upper limit for oxygen of [O/Fe] < +3.52 such that C/O > 1.3. We are also able to provide more stringent upper limits on the Sr and Ba abundances ([Sr/Fe] < +0.70, and [Ba/Fe] < +1.46, respectively).

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Section: Analysis and Resultsmentioning

confidence: 70%

TOPoS

Caffau

Bonifacio

Spite

et al. 2016

A&A

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“…They were computed from 3D synthetic spectra based on a CO 5 BOLD (Freytag et al 2012) model atmosphere from the Cosmological Impact of the First STars (CIFIST; Ludwig et al 2009) grid, using the latest version of Linfor3D 5 (Gallagher et al 2016a). A grid of 1D synthetic spectra -based on 1D LHD models (Caffau & Ludwig 2007) computed with the same micro-physics as the 3D models -were fit to the 3D synthetic profiles to determine the 3D correction (see Gallagher et al 2016b).…”

Section: Spectral Analysis and Abundance Measurementsmentioning

confidence: 99%

“…We define a 3D correction, ∆ 3D , with the formalism given by Gallagher et al (2016b), i.e., ∆ 3D = A(X) 3D −A(X) 1D , where the 1D synthesis is computed from LHD model atmospheres. We computed 3D profiles of CH and OH using the absolute carbon and oxygen abundances derived from the 1D non-LTE computations of the A26, page 4 of 8 For the G-band we found a 3D correction of -0.28 dex.…”

Section: -3d Computationsmentioning

confidence: 99%

“…In fact, owing to the low C/O ratio in the atmosphere of a typical metal-poor star like HD 84937, the OH lines are mainly formed in the most external regions of the atmosphere, which are about 300 K cooler in the 3D model than in the 1D model (see Fig. 1 in Gallagher et al 2016b, for a metallicity of -2). In this case, the 3D correction reaches −0.72 dex.…”

Section: -3d Computationsmentioning

confidence: 99%

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Abundances of the light elements from UV (HST) and red (ESO) spectra in the very old star HD 84937

Spite

Peterson

Gallagher

et al. 2017

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Aims. In order to provide a better basis for the study of mechanisms of nucleosynthesis of the light elements beyond hydrogen and helium in the oldest stars, the abundances of C, O, Mg, Si, P, S, K, and Ca have been derived from UV-HST and visible-ESO high resolution spectra in the old, very metal-poor star HD 84937, at a metallicity that is 1/200 that of the Sun's. For this halo main-sequence turnoff star, the abundance determination of P and S are the first published determinations. Methods. The LTE profiles of the lines were computed and fitted to the observed spectra. Wherever possible, we compared the abundances derived from the UV spectrum to abundances derived from the visible or near-infrared spectra, and also corrected the derived abundances for non-LTE effects. Three-dimensional (3D) CO 5 BOLD model atmospheres have been used to determine the abundances of C and O from molecular CH and OH bands. Results. The abundances of these light elements relative to iron in HD 84937 are found to agree well with the abundances of these elements in classical metal-poor stars. Our HD 84937 carbon abundance determination points toward a solar (or mildly enhanced above solar) value of [C/Fe]. The modest overabundance of the α elements of even atomic number Z, typical of halo turnoff stars, is confirmed in this example. The odd-Z element P is found to be somewhat deficient in HD 84937, at [P/Fe] = −0.32, which is again consistent with the handful of existing determinations for turnoff stars of such low metallicity. We show that the abundance of oxygen, deduced from the OH band from 3D computations, is not compatible with the abundance deduced from the red oxygen triplet. This incompatibility is explained by the existence of a chromosphere heating the shallow layers of the atmosphere where the OH band, in 3D computations, is mainly formed. Conclusions. The abundance ratios are compared to the predictions of models of galactic nucleosynthesis and evolution.

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“…In the first paper in this series, (Gallagher et al 2016a, henceforth Paper I), we recently published a grid of 3D A(C) corrections for several dwarf star models. They were computed by fitting 1D synthetic G-band profiles to 3D G-band profiles, essentially treating the 3D synthetic profiles as observed data of known A(C).…”

Section: Introductionmentioning

confidence: 99%

An in-depth spectroscopic examination of molecular bands from 3D hydrodynamical model atmospheres

Gallagher

Caffau

Bonifacio

et al. 2017

A&A

Self Cite

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Context. Tighter constraints on metal-poor stars we observe are needed to better understand the chemical processes of the early Universe. Computing a stellar spectrum in 3D allows one to model complex stellar behaviours, which cannot be replicated in 1D. Aims. We examine the effect that the intrinsic CNO abundances have on a 3D model structure and the resulting 3D spectrum synthesis. Methods. Model atmospheres were computed in 3D for three distinct CNO chemical compositions using the CO 5 BOLD model atmosphere code, and their internal structures were examined. Synthetic spectra were computed from these models using Linfor3D and they were compared. New 3D abundance corrections for the G-band and a selection of UV OH lines were also computed. Results. The varying CNO abundances change the metal content of the 3D models. This had an effect on the model structure and the resulting synthesis. However, it was found that the C/O ratio had a larger effect than the overall metal content of a model. Conclusions. Our results suggest that varying the C/O ratio has a substantial impact on the internal structure of the 3D model, even in the hot turn-off star models explored here. This suggests that bespoke 3D models, for specific CNO abundances should be sought. Such effects are not seen in 1D at these temperature regimes.

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An in-depth spectroscopic examination of molecular bands from 3D hydrodynamical model atmospheres

Cited by 41 publications

References 29 publications

TOPoS

TOPoS

Abundances of the light elements from UV (HST) and red (ESO) spectra in the very old star HD 84937

An in-depth spectroscopic examination of molecular bands from 3D hydrodynamical model atmospheres

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