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Impact of the ambipolar diffusion in the structuration of the magnetic Rayleigh Taylor instability with oblique magnetic field
No full textInternational audienceAims: We investigate the impact of ambipolar diffusion on the development of the Rayleigh-Taylor instability (RTI) with an oblique magnetic field in the incompressible limit.Methods: We developed a general bi-fluid framework comprising charges and neutrals with the specific feature of differing gravity between charges and neutrals. We derived the perturbed magnetohydrodynamic (MHD) equations and obtained an analytic dispersion relation for an oblique magnetic field. The growth rate was then evaluated using a numerical integration of the dispersion relation. In particular, we focussed on the anisotropy in the mode growth induced ambipolar diffusion.Results: In contrast to the case of a magnetic field within the interface, an oblique magnetic field is much less restrictive with respect to the wavenumbers that can develop; rather than a sharp cut-off, it results in a selection of preferred scales for mode growth. The presence of a second neutral fluid that is insensitive to gravity tends to amplify the anisotropy in the possible direction of the instability development. In particular, we show that this effect is maximal when the coupling is in an intermediate range between full and no charge-neutral coupling, specifically in the region where the ambipolar diffusion is highest
Broadband polarized radio emission detected from Starlink satellites below 100 MHz with NenuFAR
No full textInternational audienceAims. We evaluate the impact of Starlink satellites on low-frequency radio astronomy below 100 MHz. We focus on challenges of the data processing and on scientific goals.Methods. We conducted 40 hours of imaging observations using NenuFAR in the 30.8–78.3 MHz range. Observations included both the targeted tracking of specific satellites based on orbital predictions and the untargeted searches focused on high-elevation regions of the sky. Images in total intensity and polarimetry were obtained, and full Stokes dynamic spectra were generated for several hundred directions within the field of view. The detected signals were cross-matched with satellite orbital data to confirm the satellite associations. We performed detailed analyses of the observed spectra, polarization, and temporal characteristics to investigate the origin and properties of the detected emissions.Results. We detected broadband emissions from Starlink satellites, predominantly between 54–66 MHz, with flux densities exceeding 500 Jy. These signals are highly polarized and unlikely to originate from ground-based radio frequency interference or reflected astronomical sources. Instead, they are likely intrinsic to the satellites, and distinct differences in the emission properties are observed for the different satellite generations. These findings highlight significant challenges to the data processing and scientific discoveries at these low frequencies and emphasize the need for effective mitigation strategies, in particular, through collaboration between astronomers and satellite operators
The Atacama Cosmology Telescope: DR6 Power Spectrum Foreground Model and Validation
No full textInternational audienceWe discuss the model of astrophysical emission at millimeter wavelengths used to characterize foregrounds in the multi-frequency power spectra of the Atacama Cosmology Telescope (ACT) Data Release 6 (DR6), expanding on Louis et al. (2025). We detail several tests to validate the capability of the DR6 parametric foreground model to describe current observations and complex simulations, and show that cosmological parameter constraints are robust against model extensions and variations. We demonstrate consistency of the model with pre-DR6 ACT data and observations from Planck and the South Pole Telescope. We evaluate the implications of using different foreground templates and extending the model with new components and/or free parameters. In all scenarios, the DR6 CDM and CDM+ cosmological parameters shift by less than relative to the baseline constraints. Some foreground parameters shift more; we estimate their systematic uncertainties associated with modeling choices. From our constraint on the kinematic Sunyaev-Zel'dovich power, we obtain a conservative limit on the duration of reionization of , assuming a reionization midpoint consistent with optical depth measurements and a minimal low-redshift contribution, with varying assumptions for this component leading to tighter limits. Finally, we analyze realistic non-Gaussian, correlated microwave sky simulations containing Galactic and extragalactic foreground fields, built independently of the DR6 parametric foreground model. Processing these simulations through the DR6 power spectrum and likelihood pipeline, we recover the input cosmological parameters of the underlying cosmic microwave background field, a new demonstration for small-scale CMB analysis. These tests validate the robustness of the ACT DR6 foreground model and cosmological parameter constraints
How to Model and QuantifyInterference in Multicore SpaceFlight Software
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Guide simplifié - Gestion des données de vos recherches à l'usage des porteurs de projets
No full textCe document vise à synthétiser les recommandations pour une meilleure gestion des données desprojets de recherche. Il balaye de façon succincte les différentes facettes d'une bonne gestion des données de recherche lors d'un projetInternational audienceNachricht an die Projektträger.Dieses Dokument soll die Empfehlungen für eine bessere Verwaltung der Daten von Forschungsprojekten zusammenfassen. Dies ist mein Vorschlag, um Ihnen das Leben leichter zu machen.Vier Seiten, auf denen die verschiedenen Aspekte des Datenmanagements abgehandelt werden, gefolgt von einer Seite mit Ressourcen - keine Ausrede, um sie nicht zu lesen!Sie können zur Verbesserung beitragen, indem Sie uns Feedback geben.Verwaltung Ihrer Forschungsdaten für ProjektträgerMessage for project leaders.This document aims to summarise the recommendations for better data management in research projects.This is my proposal to make your life easier.Four pages covering the various aspects of data management, followed by a page of resources - no excuse not to read them!You can contribute to its improvement by giving us feedback.Managing your research data for use by project sponsorsMessage à destination des porteurs de projets.Ce document vise à synthétiser les recommandations pour une meilleure gestion des données des projets de recherche. Ceci est ma proposition pour vous faciliter la vie.Quatre pages pour balayer les différents aspects de la gestion des données suivies d'une page de ressources, aucune excuse pour ne pas les lire !Vous pouvez contribuer à son amélioration en nous faisant des retours.Gestion des données de vos recherches à l'usage des porteurs de projet
The ESO SupJup Survey: VII. Clouds and line asymmetries in CRIRES<sup>+</sup> J-band spectra of the Luhman 16 binary
No full textInternational audienceContext. Brown dwarfs at the L–T transition likely experience an inhomogeneous clearing of the clouds in their atmospheres. The resulting surface of thin and thick cloudy patches has been put forward to explain the observed variability, J-band brightening, and re-emergence of FeH absorption. Aims. We studied the closest binary brown dwarfs, Luhman 16A and B, in an effort to constrain their chemical and cloud compositions. As this binary consists of an L7.5 and a T0.5 component, we gain insight into the atmospheric properties at the L–T transition. Methods. As part of the ESO SupJup Survey, we observed Luhman 16AB at high spectral resolution in the J band (1.1–1.4 μm) using CRIRES+. To analyse the spectra, we employed an atmospheric retrieval framework, coupling the radiative transfer code petitRADTRANS with the MultiNest sampling algorithm. Results. For both objects, we report detections of H2O, K, Na, FeH, and, for the first time in the J band, hydrogen fluoride (HF). The K doublet at 1250 nm shows asymmetric absorption in the blue line wings, which are reproduced via pressure- and temperature-dependent shifts in the line cores. We find evidence of clouds in both spectra and place constraints on an FeH depletion in the Luhman 16A photosphere. The inferred over-abundance of FeH for Luhman 16B is in contradiction with its predicted rainout into iron clouds. A two-column model, which emulates the patchy surface expected at the L–T transition, is weakly preferred (~1.8σ) for component B but disfavoured for A (~5.5σ). Conclusions. The results suggest a uniform surface on Luhman 16A, which is in good agreement with the reduced variability observed for this L-type component. While the presented evidence is not sufficient to allow us to draw conclusions about any inhomogeneity on Luhman 16B, future observations covering a broader wavelength range could help us test the cloud-clearing hypothesis
Comment l'informatique interactive révolutionna l'astronomie solaire dans la décennie 1980
No full textNous présentons dans cet article comment l'arrivée de l'informatique interactive ou conversationnelle à l'observatoire de Meudon en 1981 révolutionna les traitements de données, en particulier en astronomie solaire, où la grande abondance de photons (par rapport à l'astronomie nocturne) génère un grand volume de données sous forme de séquences temporelles d'images ou de spectro images
Euclid preparation LXX. Forecasting detection limits for intracluster light in the Euclid Wide Survey
No full textInternational audienceThe intracluster light (ICL) permeating galaxy clusters is a tracer of the cluster's assembly history, and potentially a tracer of their dark matter structure. In this work we explore the capability of the Euclid Wide Survey to detect ICL using H-band mock images. We simulate clusters across a range of redshifts (0.3-1.8) and halo masses (- M), using an observationally motivated model of the ICL. We identify a 50-200 kpc circular annulus around the brightest cluster galaxy (BCG) in which the signal-to-noise ratio (S/N) of the ICL is maximised and use the S/N within this aperture as our figure of merit for ICL detection. We compare three state-of-the-art methods for ICL detection, and find that a method that performs simple aperture photometry after high-surface brightness source masking is able to detect ICL with minimal bias for clusters more massive than M. The S/N of the ICL detection is primarily limited by the redshift of the cluster, driven by cosmological dimming, rather than the mass of the cluster. Assuming the ICL in each cluster contains 15% of the stellar light, we forecast that Euclid will be able to measure the presence of ICL in up to clusters of >10^{14.2} M between and 1.5 with a S/N>3. Half of these clusters will reside below and the majority of those below will be detected with a S/N >20. A few thousand clusters at M. Euclid will detect the ICL at more than 500 kpc distance from the BCG, up to , in several hundred of these massive clusters over its large survey volume
3D MHD simulations of runaway pulsars in core collapse supernova remnants
No full textInternational audiencePulsars are one of the possible final stages in the evolution of massive stars. If a supernova explosion is anisotropic, it can give the pulsar a powerful kick, propelling it to supersonic speeds. The resulting pulsar wind nebula is significantly reshaped by its interaction with the surrounding medium as the pulsar moves through it. First, the pulsar crosses the supernova remnant, followed by the different layers of circumstellar medium formed during different stages of the progenitor star s evolution. We aim to investigate how the evolutionary history of massive stars shapes the bow shock nebulae of runaway kicked pulsars, and how these influences in turn affect the dynamics and non-thermal radio emission of the entire pulsar remnant. We perform three-dimensional magnetohydrodynamic simulations using the PLUTO code to model the pulsar wind nebula generated by a runaway pulsar in the supernova remnant of a red supergiant progenitor, and derive its non-thermal radio emission. The supernova remnant and the pre-supernova circumstellar medium of the progenitor strongly confine and reshape the pulsar wind nebula of the runaway pulsar, bending its two side jets inwards and giving the nebula an arched shape for an observer perpendicular to the jets and the propagation direction, as observed around PSR J1509 5850 and Gemina. We perform the first classical 3D model of a pulsar moving inward through its supernova ejecta and circumstellar medium, inducing a bending of its polar jet that turns into characteristic radio synchrotron signature. The circumstellar medium of young runaway pulsars has a significant influence on the morphology and emission of pulsar wind nebulae, whose comprehension requires a detailed understanding of the evolutionary history of the progenitor star
Fermionic sub-GeV Dark Matter from evaporating Primordial Black Holes at DarkSide-50
No full textInternational audienceWe present a search for boosted dark matter from Primordial Black Holes (PBH) evaporation using the DarkSide-50 ionization-signal-only dataset corresponding to the experiment's () exposure. We focus on evaporation of PBHs with masses in the range [] g producing Dirac fermionic dark matter particles with sub-GeV kinetic energy. These relativistic particles, with energies up to hundreds of MeV, can generate detectable signals for masses below MeV. The absence of a signal enables setting complementary limits to those derived from cosmological observations and direct detection searches for cosmic ray-boosted dark matter