Laboratoire Univers et Particules de Montpellier

A large proportion of observed white dwarfs show evidence of debris disks, remnants of the former planetary systems, and/or signatures of heavy elements in their atmospheres, induced by the accretion of planetary matter onto their surfaces. The observed abundances are the result of the balance between the accretion flux and the dilution of this planetary material by internal transport processes. A recent study showed that more massive DA white dwarfs are less polluted than smaller mass ones. It was suggested that the reason could be related to the formation of planetary systems when these stars were on the main sequence. The aim of this work is to test how internal dilution processes, including thermohaline convection, change with white dwarf masses, and whether such an effect could account for variations in the observed pollution. We computed the efficiency of atomic diffusion and thermohaline convection after the accretion of heavy elements onto white dwarfs using static DA models with various masses, effective temperatures, and hydrogen contents. We confirm that thermohaline convection is always more efficient in diluting accreted elements than atomic diffusion, as previously shown in the literature. However, we find that element dilution by thermohaline convection is less efficient in massive white dwarfs than in smaller mass ones, due to their larger internal density. We showed that the differences in observed heavy element pollution in white dwarfs according to their masses cannot be explained by the dilution induced by atomic diffusion and thermohaline mixing alone. Indeed, the pollution by planetary system accretion should be more easily detectable in massive white dwarfs than in low-mass ones. We discuss other processes that should be taken into account before drawing any conclusion about the occurrences of planetary systems according to the mass of the star on the main sequence.

A bstract The existence of an eV-scale sterile neutrino has been proposed to explain several anomalous experimental results obtained over the course of the past 25 years. The first search for such a sterile neutrino conducted with data from KM3NeT/ORCA — a water Cherenkov neutrino telescope under construction at the bottom of the Mediterranean Sea — is reported in this paper. GeV-scale atmospheric neutrino oscillations are measured by reconstructing the energy and arrival direction of up-going neutrinos that have traversed the Earth. This study is based on a data sample containing 5828 neutrino candidates collected with 6 detection units (5% of the complete detector), corresponding to an exposure of 433 kton-years. From the expected effect of an eV-scale sterile neutrino on the first ν μ → ν τ standard oscillation maximum, simultaneous constraints are put on the magnitude of the U μ 4 and U τ 4 mixing elements assuming $$ \Delta {m}_{41}^2\ge 1 $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>Δ</mml:mi> <mml:msubsup> <mml:mi>m</mml:mi> <mml:mn>41</mml:mn> <mml:mn>2</mml:mn> </mml:msubsup> <mml:mo>≥</mml:mo> <mml:mn>1</mml:mn> </mml:math> eV 2 . The results are compatible with the absence of mixing between active neutrinos and a sterile state, with | U μ 4 | 2 &lt; 0.138 and | U τ 4 | 2 &lt; 0.076 at a 90% confidence level. Such constraints are compatible with the results reported by other long-baseline experiments, and indicate that with KM3NeT/ORCA it is possible to bring crucial contributions to sterile neutrino searches in the coming years.

Ground-based surveys such as the Vera C. Rubin Observatory's Legacy Survey of Space and Time require photometric calibration that is both long-term stable and spatially uniform at the sub-per cent level, even during non-photometric conditions. Achieving this precision motivates new approaches to characterize atmospheric transmission, particularly to mitigate grey extinction from clouds. The StarDICE experiment aims to establish a metrology chain linking laboratory standards to astrophysical fluxes with 1 mmag accuracy in the $\textit{griz}$ bands, a goal for which controlling variable atmospheric effects is essential. We present a method that corrects photometric measurements using simultaneous radiometric information from an infrared thermal camera. The grey-extinction model is fit on an image-by-image basis using thermal radiance excess and the difference between synthetic and instrumental fluxes of calibration stars, without requiring assumptions about the spatial structure of extinction. The method relies on a forward model that incorporates environmental monitoring, radiative-transfer simulations, and Gaia DR3 stellar catalogues. Using data from a remote observing system that repeatedly monitored two fields under diverse atmospheric conditions, we show that the corrections reduce residuals between corrected and reference magnitudes and produce extinction maps with 2-arcmin resolution and ~0.01 mag accuracy. Using this technique, we can recover data acquired under non-photometric conditions with a precision comparable to data obtained under photometric conditions. For the most affected exposures, the mean absolute error improves from 0.64 to 0.11 mag, and temporal extinction variations can be reduced to 0.025 mag per source. We discuss the implications of this technique for future surveys and outline directions for further refinement.

ABSTRACT The COSMOS-Web Lens Survey (COWLS) presents the first systematic search for strong gravitational lenses in the COSMOS-Web field using data from the James Webb Space Telescope (JWST). Using high-resolution NIRCam imaging, we visually inspected over 42 660 galaxies and identified over 400 lensing candidates. Here, we report the 17 most obvious and spectacular strong lensing systems, distinguished by large Einstein rings, arcs, and distinct lens and source colours. These diverse lenses, identified only through visual inspection of lens-light-subtracted images, represent the extremes of lens parameter space. Exceptionally high signal-to-noise, multiwavelength imaging enables unprecedented lensing analysis, including ‘HST-dark’ source galaxies that are also invisible in deeper but bluer JWST wavebands: enabling clean deblending between the lens and the source. Some sources exhibit dramatic morphological changes across wavelengths, and patterns of dust absorption within lenses. No other current facility, including the Hubble Space Telescope, can discover or image such lenses with comparable detail. We estimate that JWST uncovers a new spectacular lens approximately every 10 to 12 NIRCam pointings, suggesting that over 40 similar lenses remain undiscovered within its first three years of observations. All COWLS data are publicly available on GitHub.

ABSTRACT The goal of this work is to estimate the Hubble constant $H_0$ through the time-delay cosmographic study of the quadruply lensed, variable quasi-stellar objects (QSO) SDSSJ1433+6007. We combine multifilter, archival Hubble Space Telescope data for lens modelling with a dedicated 3-yr long time-delay monitoring campaign using the 2.1 m Fraunhofer telescope at the Wendelstein Observatory. The lens modelling is performed with the public lenstronomy python package individually for the infrared data, utilizing the higher resolution of the optical data to constrain image positions a priori. This approach revealed two luminous contaminants in one of the near-infrared exposures, which would bias the lensing potentials and cosmological inference if left unaccounted. After masking these contaminants, we repeated the modelling and combined the lens posteriors, obtaining a constraint on the Fermat potential with a statistical uncertainty of $2.6\, {{\rm per\ cent}}$. The g′-band Wendelstein light-curve data are reduced and then analysed using a free-knot spline fitting method implemented in the public python pycs3 tools, accounting for microlensing correction. We obtain a precision of $6.5\, {{\rm per\ cent}}$ for the time delays between the QSO images. By combining the posteriors for the Fermat potential differences and time delays, and assuming a flat Lambda-cold dark matter cosmology, we infer a Hubble constant of $H_0=71.7^{+3.9}_{-3.6}\, {\rm{km}}\,{\mathrm{Mpc}^{-1}~\mathrm{s}^{-1}}$, achieving $5.3\, {{\rm per\ cent}}$ purely statistical uncertainty for this single system. Complementary observations and further study are required to address the systematic errors fully.

Observations of our Galaxy at very-high and ultra-high photon energies have revealed a rich population of sources, many of which have significant angular extension and/or are positionally coincident with energetic pulsars. We assessed whether the properties of these gamma-ray emitters are consistent with the predictions of a model for the non-thermal leptonic emission of a pulsar wind nebula expanding within a supernova remnant, including the possibility of particle escape across the different components of the system up to the ambient medium. We used a multi-zone model framework that describes the transport and radiation of a population of ultra-relativistic electron-positron pairs. The dynamics of the system is retrieved from numerical hydrodynamics simulations, which allows to follow the evolution through advanced stages. Model predictions for typical parameter setups are compared to source catalogs issued by the H.E.S.S. and LHAASO collaborations. If particles remain confined in the nebula, 1-100TeV emission is only partially consistent with the properties of observed sources in terms of surface brightness, angular extent, and photon index. In particular, the systems spend a long time in a bright and soft state that has no equivalent in observations. Conversely, including the possibility of energy-dependent particle escape across the object results in a much better agreement, both in the 1-10TeV range explored with H.E.S.S. or LHAASO-WCDA, and in the 20-100TeV range explored by LHAASO-KM2A. Emission components with intermediate to low brightnesses and large to very large sizes result from particles trapped in the remnant or escaped in the surrounding medium. Particle escape, clearly seen in the form of misaligned jets or halos around middle-aged pulsars, is a very important process in much younger systems with 1-100kyr ages, and shapes their appearance as TeV/PeV sources.

The HeH+ ion was the first molecule to form in the early Universe, and its comparatively large dipole moment renders it a potential coolant, relevant during the epoch of first star formation. The main destruction mechanisms under primordial conditions are recombination with free electrons and chemical reactions with hydrogen atoms. The latter process was believed to be slow at low temperatures, owing to a barrier forming along the reaction coordinate. Here we present a joint experimental and theoretical study of the reaction HeH+ + D → HD+ + He that confirms the very recent proposition that the reaction is, in fact, barrierless and fast at low collision energies. The present evidence suggests that previous studies underestimated the low-temperature rate coefficient significantly because of an artifact in a widely used potential energy surface, and calls for a reassessment of the helium chemistry in the early Universe.

Sharp features in the primordial power spectrum are a natural prediction of many UV-complete models of inflation. The authors use dedicated N-body simulations to demonstrate that features consistent with CMB constraints persist throughout the nonlinear regime of structure formation and thus may play a role in explaining tensions between the CMB and observations of the late-time matter distribution. While further numerical work is necessary to resolve the degeneracy with other effects, this study is a pioneering foundation for future research.

We compare forecasts for the abundance and properties of strong gravitational lenses in the COSMOS-Web survey, a $0.54$ deg$^2$ survey of the COSMOS field using the NIRCam and MIRI instruments aboard JWST, with the first catalogue of strong lens candidates identified in the observed NIRCam data, COWLS. We modify the lenspop package to produce a forecast for strong lensing in COSMOS-Web. We add a new mock galaxy catalogue to use as the source population, as well as the COSMOS-Web survey specifications, including the transmission data for the four NIRCam filters used. We forecast 107 strong lenses can be detected in COSMOS-Web across all bands, assuming complete subtraction of the lens galaxy light. The majority of the lenses are forecast to have small Einstein radii ($\theta_{\rm E} < 1$ arcsecond) and lie at redshifts between $0 < z <2$, whilst the source redshift distribution peaks at $z\sim 3$ and has a long tail extending up to $z \sim 11$, unambiguously showing that strong lensing in JWST can probe the entirety of the epoch of reionisation. We compare our forecast with the distributions of Einstein radii, lens photometric redshifts, and lens and source magnitudes in the observed lenses, finding that whilst the forecast and observed Einstein radii distributions match, the redshifts and magnitudes do not. The observed lens redshift distribution peaks at a slightly lower redshift than the forecast one, whilst the lens magnitudes are systematically brighter in the observed data than in the forecast.

Context. In a recent paper, we presented circularly polarised radio bursts detected by the Five-hundred-meter Aperture Spherical radio Telescope (FAST) from the flare star AD Leo over 2–3 December 2021. These bursts have been attributed to the electron cyclotron maser (ECM) instability. Aims. In that context, we have adopted two independent and complementary approaches, inspired by the study of auroral radio emissions from Solar System planets. Our goal is to constrain, for the first time, the source location (magnetic shell, height) and the energy of the emitting electrons. Methods. These two approaches consist of (i) modelling the overall occurrence of the emission with the ExPRES code and (ii) fitting the drift rate of the fine structures observed by FAST. Results. We obtained consistent results, pointing at 20–30 keV electrons on magnetic shells with an apex at 2–10 stellar radii. The emission polarisation observed by FAST and the magnetic topology of AD Leo appear to favour X-mode emission from the southern magnetic hemisphere, allowing us to set constraints on the plasma density scale height in the star’s atmosphere. Conclusions. We demonstrate that sensitive radio observations with high time-frequency resolutions, coupled with modelling tools such as ExPRES, along with analytical calculations and stellar magnetic field measurements, allow us to remotely probe stellar radio environments. We provide elements of comparison with Solar System radio bursts (Jovian and Solar), establish hypotheses about the driver of AD Leo’s radio bursts, and discuss the perspectives of future observations, particularly at very low frequencies (&lt;100 MHz).