How summit calderas collapse on basaltic volcanoes: New insights from the April 2007 caldera collapse of Piton de la Fournaise volcano

International audienceIn April 2007, Piton de la Fournaise volcano experienced a caldera collapse during its largest historical eruption. We present here a structural analysis both of the caldera and the surrounding area, and precise GPS data recorded with a dense GPS network specifically dedicated to the analysis of deformation related to the summit collapse structures. Despite a collapse of more than 300 m in the central zone, the geometry of the new caldera is similar in map view to that of the pre-existing collapsed structure, which was formed from the coalescence of several pit craters. The caldera shows an asymmetric inner geometry with sub-vertical walls in the NW quadrant and steep scarps composed of inward tilted blocks in the southern half. The presence of preserved polished surfaces on the lower part of the sub-vertical scarp indicates that it corresponds to the caldera north-western ring fault. The April 2007 caldera collapse led to the development and the reactivation of concentric fractures on the caldera rim, mostly along the southern limit of the caldera. GPS data show that fractures result from radial extensional stresses that are restricted within the first tens of meters of the caldera edge. GPS data also reveal that the caldera collapse was coeval with a centripetal deflation, whose magnitude is largest along the southern half of the caldera. The displacements recorded by GPS result from both a general deflation, due to magma withdrawal from Piton de la Fournaise's summit magma chamber, and additional local effects related to the caldera collapse. Comparison of the caldera collapses at Piton de la Fournaise, Miyakejima and Fernandina reveals striking similarities, with cyclic seismic signals accompanying small-scale deflation–inflation cycles. This strongly suggests a common mode of collapse. Hence, we propose a unifying model of caldera collapse in basaltic setting, in which the inward deflation due to magma withdrawal from the magma chamber prevents the collapse of the caldera roof until the gravitational stress acting on the rock column above the magma chamber exceeds the shear strength along pre-existing ring faults. The downward displacement stops when the pressure increase into the magma chamber is able to again sustain the rock column. The succession of (1) inward deflation that prevents the collapse, (2) collapse due to gravitational stress and (3) stopping of the downward motion is repeated many times. The frequency of the cycles is influenced by the rate of magma withdrawal and by the amount of intrusion of magma along the ring faults

The Belgian repository of fundamental atomic data and stellar spectra (BRASS). I. Cross-matching atomic databases of astrophysical interest

Fundamental atomic parameters, such as oscillator strengths, play a key role in modelling and understanding the chemical composition of stars in the universe. Despite the significant work underway to produce these parameters for many astrophysically important ions, uncertainties in these parameters remain large and can propagate throughout the entire field of astronomy. The Belgian repository of fundamental atomic data and stellar spectra (BRASS) aims to provide the largest systematic and homogeneous quality assessment of atomic data to date in terms of wavelength, atomic and stellar parameter coverage. To prepare for it, we first compiled multiple literature occurrences of many individual atomic transitions, from several atomic databases of astrophysical interest, and assessed their agreement. Several atomic repositories were searched and their data retrieved and formatted in a consistent manner. Data entries from all repositories were cross-matched against our initial BRASS atomic line list to find multiple occurrences of the same transition. Where possible we used a non-parametric cross-match depending only on electronic configurations and total angular momentum values. We also checked for duplicate entries of the same physical transition, within each retrieved repository, using the non-parametric cross-match. We report the cross-matched transitions for each repository and compare their fundamental atomic parameters. We find differences in log(gf) values of up to 2 dex or more. We also find and report that ~2% of our line list and Vienna Atomic Line Database retrievals are composed of duplicate transitions. Finally we provide a number of examples of atomic spectral lines with different log(gf) values, and discuss the impact of these uncertain log(gf) values on quantitative spectroscopy. All cross-matched atomic data and duplicate transitions are available to download at brass.sdf.org.Comment: 18 pages, 12 figures, 9 tables. Accepted for publication in A&

Titans metal-poor reference stars II. Red giants and CEMP stars

Representative samples of F-, G-, K-type stars located out of the Solar Neighbourhood has started to be available in spectroscopic surveys. The fraction of metal-poor ([Fe/H]~$\lesssim -0.8$~dex) giants becomes increasingly relevant to far distances. In metal-poor stars, effective temperatures ($T_{\mathrm{eff}}$) based on LTE spectroscopy and on former colour-$T_{\mathrm{eff}}$ relations of still wide use have been reported to be inaccurate. It is necessary to re-calibrate chemical abundances based on these $T_{\mathrm{eff}}$ scales in the multiple available surveys to bring them to the same standard scale for their simultaneous use. For that, a complete sample of standards is required, which so far, is restricted to a few stars with quasi-direct $T_{\mathrm{eff}}$ measurements. We aim at providing a legacy sample of metal-poor standards with proven accurate atmospheric parameters. We add 47 giants to the sample of metal-poor dwarfs of Giribaldi et al. 2021, thereby constituting the Titans metal-poor reference stars. $T_{\mathrm{eff}}$ was derived by 3D non-LTE H$\alpha$ modelling, whose accuracy was tested against interferometry and InfraRed Flux Method (IRFM). Surface gravity (log $g$) was derived by fitting Mg~I~b triplet lines, whose accuracy was tested against asteroseismology. Metallicity was derived using Fe II lines, which was verified to be identical to the [Fe/H] derived from non-LTE spectral synthesis. $T_{\mathrm{eff}}$ from 3D non-LTE H$\alpha$ is equivalent to interferometric and IRFM temperatures within a $\pm$46~K uncertainty. We achieved precision of $\sim$50~K for 34 stars with spectra with the highest S/N. For log $g$, we achieved a total uncertainty of $\pm$0.15~dex. For [Fe/H], we obtained a total uncertainty of $\pm$0.09~dex. We find that the ionization equilibrium of Fe lines under LTE is not valid in metal-poor giants.Comment: Accepted in A&

The surface composition of six newly discovered chemically peculiar stars. Comparison to the HgMn stars μ\mu Lep and β\beta Scl and the superficially normal B star ν\nu Cap

We report on a detailed abundance study of six bright, mostly southern, slowly rotating late B stars: HD~1279 (B8III), HD~99803 (B9V), HD~123445 (B9V), HD~147550 (B9V), HD~171961 (B8III) and HD~202671 (B5II/III), hitherto reported as normal stars. We compare them to the two classical HgMn stars $\mu$ Lep and $\beta$ Scl and to the superficially normal star, $\nu$ Cap. In the spectra of the six stars, the \ion{Hg}{2} line at 3984 \AA\ line is clearly seen and numerous lines of P, Ti, Mn, Fe, Ga, Sr, Y, and Zr appear to be strong absorbers. A comparison of newly acquired and archival spectra of these objects with a grid of synthetic spectra for selected unblended lines reveals large overabundances of P, Ti, Cr, Mn, Sr, Y, Zr, Ba, Pt and Hg and underabundances of He, Mg, Sc and Ni. The effective temperatures, surface gravities, low projected rotational velocities and the peculiar abundance patterns of the six investigated stars show that they are new chemically peculiar stars, mostly new HgMn stars, and are reclassified as such. The evolutionary status of these stars has been inferred and their ages and masses estimated. The two most massive objects, HD~1279 and HD~202671, might have evolved away from the main-sequence recently, the other stars are main-sequence objects. HD~99803A is a sharp lined HgMn star with grazing eclipses; from TESS and MASCARA photometry we determine an orbital period of $P_{\rm orb} = 26.12022 \pm 0.00004$\,d.Comment: 54 pages, accepted in The Astronomical Journal. arXiv admin note: substantial text overlap with arXiv:1908.0502

Stellar Astrophysics and Exoplanet Science with the Maunakea Spectroscopic Explorer (MSE)

The Maunakea Spectroscopic Explorer (MSE) is a planned 11.25-m aperture facility with a 1.5 square degree field of view that will be fully dedicated to multi-object spectroscopy. A rebirth of the 3.6m Canada-France-Hawaii Telescope on Maunakea, MSE will use 4332 fibers operating at three different resolving powers (R ~ 2500, 6000, 40000) across a wavelength range of 0.36-1.8mum, with dynamical fiber positioning that allows fibers to match the exposure times of individual objects. MSE will enable spectroscopic surveys with unprecedented scale and sensitivity by collecting millions of spectra per year down to limiting magnitudes of g ~ 20-24 mag, with a nominal velocity precision of ~100 m/s in high-resolution mode. This white paper describes science cases for stellar astrophysics and exoplanet science using MSE, including the discovery and atmospheric characterization of exoplanets and substellar objects, stellar physics with star clusters, asteroseismology of solar-like oscillators and opacity-driven pulsators, studies of stellar rotation, activity, and multiplicity, as well as the chemical characterization of AGB and extremely metal-poor stars.Comment: 31 pages, 11 figures; To appear as a chapter for the Detailed Science Case of the Maunakea Spectroscopic Explore

The SAPP pipeline for the determination of stellar abundances and atmospheric parameters of stars in the core program of the PLATO mission

We introduce the SAPP (Stellar Abundances and atmospheric Parameters Pipeline), the prototype of the code that will be used to determine parameters of stars observed within the core program of the PLATO space mission. The pipeline is based on the Bayesian inference and provides effective temperature, surface gravity, metallicity, chemical abundances, and luminosity. The code in its more general version has a much wider range of potential applications. It can also provide masses, ages, and radii of stars and can be used with stellar types not targeted by the PLATO core program, such as red giants. We validate the code on a set of 27 benchmark stars that includes 19 FGK-type dwarfs, 6 GK-type subgiants, and 2 red giants. Our results suggest that combining various observables is the optimal approach, as this allows the degeneracies between different parameters to be broken and yields more accurate values of stellar parameters and more realistic uncertainties. For the PLATO core sample, we obtain a typical uncertainty of 27 (syst.) ± 37 (stat.) K for Teff, 0.00 ± 0.01 dex for log g, 0.02 ± 0.02 dex for metallicity [Fe/H], −0.01 ± 0.03 R⊙ for radii, −0.01 ± 0.05 M⊙ for stellar masses, and −0.14 ± 0.63 Gyr for ages. We also show that the best results are obtained by combining the νmax scaling relation with stellar spectra. This resolves the notorious problem of degeneracies, which is particularly important for F-type stars

Transfert de rayonnement hors ETL pour l'étude des photosphères et des chromosphères stellaires : applications aux atomes du magnésium, du calcium et du fer dans les étoiles tardives.

The stellar abundance analysis frequently relies on the local thermodynamic equilibrium (LTE) assumption for spectral line formation. This assumption is not always appropriate, in particular, for metal-poor and/or evolved stars. To better understand these stars and contrain their impacts in the chemical enrichment of the Galaxy, it is necessary to use a non-LTE (NLTE) description more realistic but also more complex to built up. My thesis work consisted in constructing model atoms from the most recent atomic databases for two α-elements: the magnesium and the calcium. These elements are astrophysically interesting because they permit us to characterize the chemical enrichment of stellar populations. I therefore developed a model atom construction code, FORMATO, to study the NLTE formation of spectral lines. I used these models for computing a grid of NLTE corrections to apply to the equivalent widths of the principal spectral lines of these elements, whose several will be observed by the Gaia mission, for giants and super-giants. I also applied these results to the NLTE limb-darkening laws for the CaII IR triplet which permit to determine, for the first time, the chromospheric extent of the red giant β Cet, using interferometric observations (VEGA@CHARA). Finally, in the context of the Carina Project, I highlighted NLTE effects on ionization equilibrium of iron (~0,1 dex) in a sample of 44 red giant stars in the Carina dSph galaxy, thanks to a comparative study between FeI and FeII lines in LTE and NLTE.L'analyse des abondances stellaires suppose souvent que les raies spectrales se forment à l'équilibre thermodynamique local (ETL). Cette hypothèse n'est pas toujours appropriée notamment pour les étoiles pauvres en métaux et/ou évoluées. Pour mieux comprendre ces étoiles et appréhender leur rôle dans l'enrichissement chimique de la Galaxie, il est devenu nécessaire d'adopter une description hors ETL (HETL) plus réaliste mais aussi plus complexe à mettre en oeuvre. Mon travail de thèse a consisté à construire des modèles d'atomes à partir des bases de données de physique atomique les plus récentes pour deux éléments α : le magnésium et le calcium. Ils ont un intérêt astrophysique important car ils permettent de caractériser l'enrichissement chimique des populations stellaires. J'ai donc développé un code de construction de modèles d'atomes, FORMATO, pour l'étude des raies spectrales HETL. J'ai utilisé ces modèles pour calculer une grille de corrections HETL à appliquer sur les largeurs équivalentes des principales raies de ces éléments, dont certaines seront observées par la mission Gaia, pour des géantes et des super- géantes. J'ai aussi appliqué ces résultats pour calculer des lois d'assombrissement centre-bord HETL pour le triplet IR du CaII qui ont permis de déterminer, pour la première fois, l'extension chromosphérique de la géante β Cet, grâce à des mesures interférométriques (VEGA@CHARA). Enfin, dans le cadre du Carina Project, j'ai mis en évidence des effets HETL sur l'équilibre d'ionisation du fer (~0,1 dex) dans un échantillon de 44 géantes rouges de la galaxie dSph Carina, en s'appuyant sur une étude comparée des raies du FeI et FeII à l'ETL et HETL

BACCHUS: Brussels Automatic Code for Characterizing High accUracy Spectra

BACCHUS (Brussels Automatic Code for Characterizing High accUracy Spectra) derives stellar parameters (Teff, log g, metallicity, microturbulence velocity and rotational velocity), equivalent widths, and abundances. The code includes on the fly spectrum synthesis, local continuum normalization, estimation of local S/N, automatic line masking, four methods for abundance determinations, and a flagging system aiding line selection. BACCHUS relies on the grid of MARCS model atmospheres, Masseron's model atmosphere thermodynamic structure interpolator, and the radiative transfer code Turbospectrum (ascl:1205.004).info:eu-repo/semantics/publishe

NLTE Iron abundance determination in Red Giants

Our aim is to perform Non-LTE iron abundance calculations on a sample of Kepler red giants with reliable fundamental atmospheric parameters from asteroseismology, specifically log g, in order to calibrate for unknown atomic collisional effects with neutral hydrogen for which quantum mechanical data does not yet exist. Preliminary results show better mutual agreement between FeI and FeII lines as compared to LTE, as well as less FeI abundance dispersion than that of previous work.info:eu-repo/semantics/publishe

Transfert de rayonnement hors ETL pour l'étude des photosphères et des chromosphères stellaires (applications aux atomes du magnésium, du calcium et du fer dans les étoiles tardives)

L'analyse des abondances stellaires suppose souvent que les raies spectrales se forment à l'équilibre thermodynamique local (ETL). Cette hypothèse n'est pas toujours appropriée, notamment pour les étoiles pauvres en métaux et/ou évoluées. Pour mieux comprendre ces étoiles et appréhender leur rôle dans l enrichissement chimique de la Galaxie, il est devenu nécessaire d'adopter une description hors ETL (HETL) plus réaliste mais aussi plus complexe à mettre en œuvre. Mon travail de thèse a consisté à construire des modèles d'atomes à partir des bases de données de physique atomique les plus récentes pour deux éléments a : le magnésium et le calcium. Ils ont un intérêt astrophysique important car ils permettent de caractériser l'enrichissement chimique des populations stellaires. J'ai donc développé un code de construction de modèles d'atomes, FORMATO, pour l'étude des raies spectrales HETL. J'ai utilisé ces modèles pour calculer une grille de corrections HETL à appliquer sur les largeurs équivalentes des principales raies de ces éléments, dont certaines seront observées par la mission Gaia, pour des géantes et des super-géantes. J'ai aussi appliqué ces résultats pour calculer des lois d'assombrissement centre-bord HETL pour le triplet IR du CaII qui ont permis de déterminer, pour la première fois, l'extension chromosphérique de la géante b Cet, grâce à des mesures interférométriques (VEGA@CHARA). Enfin, dans le cadre du Carina Project, j'ai mis en évidence des effets HETL sur l'équilibre d'ionisation du fer (~0,1 dex) dans un échantillon de 44 géantes rouges de la galaxie dSph Carina, en m'appuyant sur une étude comparée des raies du FeI et FeII ETL et HETL.The stellar abundance analyses frequently relies on the local thermodynamic equilibrium (LTE) assumption for spectral line formation. This assumption is not always appropriate, in particular for metal-poor and/or evolved stars. To better understand these stars and comprehend their impacts on the chemical enrichment of the Galaxy, it is necessary to use a non-LTE (NLTE) description which is more realistic but also more complex to build up. My thesis work consisted in constructing model atoms from the most recent atomic databases for two a-elements: the magnesium and the calcium. These elements are astrophysically interesting because they permit us to characterize the chemical enrichment of stellar populations. I therefore developed a model atom construction code, FORMATO, to study the NLTE formation of spectral lines. I used these models to compute a grid of NLTE corrections to be applied to the equivalent widths of the main spectral lines of these elements, some of which will be observed by the Gaia mission, for giants and super-giants. I also applied these results to the NLTE limb-darkening laws for the CaII IR triplet which has permitted to determine, for the first time, the chromospheric extent of the red giant b Cet, using interferometric observations (VEGA@CHARA). Finally, in the context of the Carina Project, I highlighted NLTE effects on ionization equilibrium of iron (~0,1 dex) in a sample of 44 red giant stars in the Carina dSph galaxy, thanks to a comparative study between FeI and FeII lines in LTE and NLTE.NICE-BU Sciences (060882101) / SudocSudocFranceF