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Accretion of the anomalous CR2 chondrite Northwest Africa 14674: Implications for the complexities of the CR parent bodies
No full textInternational audienceAn understanding of the differences between ungrouped, or anomalous, and normal carbonaceous chondrites could provide information on the population of parent bodies required to explain a chondrite group and on first solid accretion and evolution in the outer protoplanetary disk. The CR chondrites are key in this respect, as they display a unique formation history that distinguishes them from other groups. They are known to have formed between 4.1 and 4.6 Myr after CAI, with two generations of chondrules. Northwest Africa (NWA) 14674 is a CR2 anomalous (CR2-an) chondrite with very similar oxygen isotope composition, dark inclusion (DI) content, and serpentine-magnetite matrix to Al Rais (CR2-an). Both are petrologic subtype 2.3 with fresh magnesian olivine, and partly altered ferroan olivine, pyroxene, and metal. Additionally, NWA 14674 contains residual GEMS-like material at the nanoscale within preserved moderately altered areas. DI and matrix in NWA 14674 are mineralogically similar but they have different fabrics, and matrix is more porous than both DI and fine-grained rims (FGR). Matrix has aligned framboidal magnetite aggregates swathing the chondrules, suggesting slight compaction of the chondrite. Some DI have inner chondrule fragments and concentric layers richer and poorer in magnetite, indicating formation as accretionary pellets and lapilli: they are pebbles rather than clasts. The framboidal magnetite abundance is consistent with an alkaline alteration fluid potentially due to NH3 ice mixed with the more common water ice, which implies late distal accretion. Comparison with the CR chondrites Bells (regolith-like) and NWA 801 (with high-pressure clasts) indicates that a complex history involving inward drift, disruption of the grandparent body, and reaccretion of debris along with chondrules, DI pebbles, and dust is required to explain CR chondrite formation. The diverse facies observed in CR chondrites may be explained by the formation of relatively large parent bodies, comprising distinct layers (core to regolith). Some material has been inherited from a chondritic protoplanet that formed during the oligarchic growth phase of planetary formation. Subsequently, this initial body underwent disruption and partial reaccretion into the CR parent body
Magnetic field morphologies in convective zones influenced by a turbulent surface layer
No full textInternational audienceContext. The magnetism of low-mass stars can have a significant impact on their activity and therefore the detection of exoplanets and their properties. Spectropolarimetric observations show that many low-mass stars possess large-scale poloidal magnetic fields with a considerable dipole component, which in some cases exhibit temporal dynamics (cycles or reversals). Although it is widely accepted that magnetic fields of low-mass stars are generated by the dynamo process (i.e., stretching and twisting of magnetic field lines by helical motions in stellar convective envelopes), numerical dynamo simulations show that it is hard to reproduce coherent oscillations of large-scale magnetic fields with a dipolar symmetry as observed for the Sun when turbulent and compressible regimes are explored.Aims. Modeling stellar dynamos is a real challenge, as it requires taking into account various interacting physical effects that develop on different scales of time and length. Most previous 3D numerical studies partially avoided this problem by considering a numerical domain with low density stratification, which may correspond to neglecting surface effects where density drops considerably. Our work aims to address this question.Methods. We performed three-dimensional direct numerical simulations of convective dynamos in extreme parameter regimes of both strong turbulence and strong density stratification using the community-tested numerical software MagIC. The dynamics in such systems, particularly the dominance of the Coriolis effects, depend on the depth of the fluid layer. Our strongly stratified dynamo simulations exhibit rotationally influenced large-scale convective motions surrounded by a turbulent compressible surface layer.Results. We find complex time variations of the magnetic field with flow regimes of a predominantly dipolar configuration with respect to the few large-scale harmonics that would be captured by spectropolarimetry. In such regimes, the turbulent surface layer induces a global magnetic pumping mechanism, transporting the magnetic energy into the deep interiors of our dynamo model. We find that the dipole magnetic fields are in regimes of transition between solar- and anti-solar differential rotation and that they interact dynamically with it.Conclusions. The spatial distribution and temporal behavior of the large-scale fields is consistent with observations of low-mass stars, which suggests magnetic pumping could promote time-dependent magnetic fields with a similar dipolar symmetry as observed for the Sun and other solar-like stars. Our results suggest a parameter path in which dynamo models with complex multiscale dynamics should be explored
Direct imaging of active galactic nucleus outflows and their origin with the 23 m Large Binocular Telescope
No full textInternational audienceActive galactic nuclei (AGNs) are a key component of galaxy evolution due to feedback on the host from its supermassive black hole. The morphology of warm, in-and outflowing dusty material can reveal the nature of the onset of feedback, AGN feeding, and the unified model of AGN. Here we use the Large Binocular Telescope Interferometer (LBTI) to image the dense, obscuring disk and extended dusty outflow region of NGC 1068. In Fizeau imaging mode the LBTI synthesizes the equivalent resolution of a 22.8 m telescope. The 8.7 µm Fizeau images of NGC 1068 have an effective resolution of 47 × 90 mas (3.3 × 6.2 pc) in a 5" field of view after performing PSF deconvolution techniques described here. This is the only extragalactic source to be Fizeau imaged using the LBTI, and the images bridge the scales measured with the Very Large Telescope Interferometer (VLTI; 0.5-5 pc) and those of single telescopes such as JWST and Keck (> 15 pc). The images detect and spatially resolve the low surface brightness mid-infrared (MIR) features in the AGN disk/wind region that are over-resolved by the VLTI. The images show strong correlation between MIR dust emission and nearinfrared (NIR) emission of highly excited atomic lines observed by SINFONI. Such LBTI imaging is a precursor to infrared imaging using the upcoming generation of extremely large telescopes, with angular resolutions up to 6x better than JWST, the largest space telescope in orbit
Constraints on cosmology and baryonic feedback with joint analysis of Dark Energy Survey Year 3 lensing data and ACT DR6 thermal Sunyaev-Zel'dovich effect observations
No full textInternational audienceWe present a joint analysis of weak gravitational lensing (shear) data obtained from the first three years of observations by the Dark Energy Survey and thermal Sunyaev-Zel'dovich (tSZ) effect measurements from a combination of Atacama Cosmology Telescope (ACT) and Planck data. A combined analysis of shear (which traces the projected mass) with the tSZ effect (which traces the projected gas pressure) can jointly probe both the distribution of matter and the thermodynamic state of the gas, accounting for the correlated effects of baryonic feedback on both observables. We detect the sheartSZ cross-correlation at a 21 significance, the highest to date, after minimizing the bias from cosmic infrared background leakage in the tSZ map. By jointly modeling the small-scale shear auto-correlation and the sheartSZ cross-correlation, we obtain and , results consistent with primary CMB analyses from Planck and P-ACT. We find evidence for reduced thermal gas pressure in dark matter halos with masses , supporting predictions of enhanced feedback from active galactic nuclei on gas thermodynamics. A comparison of the inferred matter power suppression reveals a tension with hydrodynamical simulations that implement mild baryonic feedback, as our constraints prefer a stronger suppression. Finally, we investigate biases from cosmic infrared background leakage in the tSZ-shear cross-correlation measurements, employing mitigation techniques to ensure a robust inference. Our code is publicly available on GitHub
Euclid preparation. Constraining parameterised models of modifications of gravity with the spectroscopic and photometric primary probes
No full textInternational audienceThe Euclid mission has the potential to understand the fundamental physical nature of late-time cosmic acceleration and, as such, of deviations from the standard cosmological model, LCDM. In this paper, we focus on model-independent methods to modify the evolution of scalar perturbations at linear scales. We consider two approaches: the first is based on the two phenomenological modified gravity (PMG) parameters, and , which are phenomenologically connected to the clustering of matter and weak lensing, respectively; and the second is the effective field theory (EFT) of dark energy and modified gravity, which we use to parameterise the braiding function, , which defines the mixing between the metric and the dark energy field. We discuss the predictions from spectroscopic and photometric primary probes by Euclid on the cosmological parameters and a given set of additional parameters featuring the PMG and EFT models. We use the Fisher matrix method applied to spectroscopic galaxy clustering (GCsp), weak lensing (WL), photometric galaxy clustering (GCph), and cross-correlation (XC) between GCph and WL. For the modelling of photometric predictions on nonlinear scales, we use the halo model to cover two limits for the screening mechanism: the unscreened (US) case, for which the screening mechanism is not present; and the super-screened (SS) case, which assumes strong screening. We also assume scale cuts to account for our uncertainties in the modelling of nonlinear perturbation evolution. We choose a time-dependent form for , with two fiducial sets of values for the corresponding model parameters at the present time, , and two forms for , with one fiducial set of values for each of the model parameters, and . (Abridged
The effects of the spin and quadrupole moment of SgrA* on the orbits of S stars
No full textInternational audienceMeasuring the astrometric and spectroscopic data of stars orbiting the central black hole in our galaxy (Sgr A*) offers a promising way to measure relativistic effects. In principle, the "no-hair" theorem can be tested at the Galactic Center by monitoring the orbital precession of S-stars due to the angular momentum (spin) and quadrupole moment of Sgr A*. Closer-in stars, more strongly affected by the black hole's rotation, may be required. GRAVITY+ could detect such stars that are currently too faint for GRAVITY. We aim to analytically and numerically characterize orbital reorientations induced by spin-related effects of Sgr A* up to the second post-Newtonian (2PN) order. We use the two-timescale method to derive the 2PN analytical expressions of the secular evolution of the orbital parameters that are related to the observer. To study the interaction between the orbital and spin orientations, we introduce observer-independent quantities that offer insight into the Kerr geometry. We also use the post-Newtonian code OOGRE to simulate hypothetical stars orbiting closer to Sgr A*, where spin and quadrupole effects are stronger. This enables comparison with our analytical predictions. We exhibit three orbital-timescale precession rates that encode the in-plane pericenter shift and the out-of-plane redirection of the osculating ellipse. We provide the 2PN expressions of these precession rates and express the orbit-integrated associated angular shifts of the pericenter and of the ellipse axes. We relate these orbital-timescale precession rates to the secular-timescale precession of the orbital angular momentum around the black hole spin axis. We consider that the theoretical insight we provide in this article will be useful in constraining the spin effect of Sgr A* with GRAVITY+ observations
3D Monte Carlo Radiative Transfer for Parameter Retrieval in Planetary Atmospheres
No full textInternational audienceRetrieving planetary atmospheric parameters from observational data is particularly challenging under large observation angles, in thick and highly scattering media (such as Titan and Venus), and in the presence of horizontal heterogeneities, like clouds and hazes. Traditional radiative transfer models, often based on plane-parallel or pseudo-spherical approximations, typically assume horizontally homogeneous layers, which limits their applicability in such scenarios.To overcome these limitations, we have developed a novel 3D radiative transfer solver, htrdr-planets, based on the Monte Carlo method that solves models considering spherical and heterogeneous atmospheres[1]. This solver leverages recent advances from the computer graphics and statistical physics communities to ensure computational efficiency.htrdr-planets supports arbitrary ground geometry, represented as triangular meshes with user-defined surface materials, and atmospheric properties defined on unstructured tetrahedral meshes. Gas absorption is modeled using the k-distribution method, and multiple aerosol and cloud populations with their own radiative properties can be described on separate spatial grids.Critically, we address the need for gradients (i.e., sensitivities) in parameter retrieval. Since conventional finite-difference methods are inefficient or infeasible with Monte Carlo, we differentiate the Monte Carlo estimator itself [2]. By reusing the same radiative paths, we construct a Monte Carlo estimator that computes both the radiance and its gradient with respect to atmospheric and surface parameters at negligible additional time cost.We apply this method to Titan and Venus, producing spatially resolved maps of sensitivity with respect to scattering, absorption, and surface-reflection properties. This framework enables retrievals in geometrically complex cases that defy traditional models, including Titan’s polar cloud structure and haze distribution, using Cassini and JWST datasets. This work is supported by the Agence National de la Recherche (ANR) through the RaD3-net project (ANR-21-CE49-0020-01).[1] htrdr-planets, https://www.meso-star.com/projects/htrdr/htrdr.html[2] He, Zili, et al. "Simultaneous Estimation of Radiance and its Sensitivities to Radiative Properties in a Spherical-Heterogeneous Atmospheric Radiative Transfer Model by Monte Carlo: Application to Titan." (Submitted to Journal of Quantitative Spectroscopy and Radiative Transfer.
A reversed Monte Carlo radiative transfer model for Titan PCM
No full textInternational audienceTitan and particularly its thick atmosphere, unique among solar system objects, has been a center of interest for many decades. Titan's atmosphere has been thoroughly studied, notably with the use of Global Climate Models (GCM) (Lebonnois et al. 2012; Lora et al. 2015; de Batz de Trenquelléon et al. 2025a; de Batz de Trenquelléon et al. 2025b). All of them currently consider a plane-parallel atmosphere for the radiative transfer calculation (Lora et al. 2015; de Batz de Trenquelléon et al. 2025a). However, this assumption has limitations in the case of Titan
FLRW embeddings in , differential geometry and conformal photon propagator
No full textInternational audienceThis paper introduces differential-geometric methods to study -dimensional locally conformally flat spaces as submanifolds in . We derive explicit formulas relating intrinsic and ambient differential-geometric objects, including curvature tensors, the codifferential and laplacian operators. We apply this approach to Friedmann-Lemaître-Robertson-Walker (FLRW) spaces using newfound embedding formulas, obtaining new and simplified expressions for the photon propagator in four dimensions
GWTC-4.0: An Introduction to Version 4.0 of the Gravitational-Wave Transient Catalog
No full textInternational audienceThe Gravitational-Wave Transient Catalog (GWTC) is a collection of short-duration (transient) gravitational wave signals identified by the LIGO-Virgo-KAGRA Collaboration in gravitational-wave data produced by the eponymous detectors. The catalog provides information about the identified candidates, such as the arrival time and amplitude of the signal and properties of the signal's source as inferred from the observational data. GWTC is the data release of this dataset and version 4.0 extends the catalog to include observations made during the first part of the fourth LIGO-Virgo-KAGRA observing run up until 2024 January 31. This paper marks an introduction to a collection of articles related to this version of the catalog, GWTC-4.0. The collection of articles accompanying the catalog provides documentation of the methods used to analyze the data, summaries of the catalog of events, observational measurements drawn from the population, and detailed discussions of selected candidate