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Auto-calibration and performance monitoring of GRAVITY+ Adaptive Optics system with physics-based methods and inverse problem approaches
No full textInternational audienceIn 2024/2025, the GRAVITY+ Adaptive Optics (GPAO) project installed four extreme AO systems on the 8-meter UTs of the Very Large Telescope: 43x43 deformable mirrors (DM, 1432 actuators), 40x40 (1240 sub-apertures (SA)) visible and 30x30 (704 SA) laser guide star Shack-Hartmann wavefront sensors (SH-WFS) with 9x9 (60 SA) infrared or 2x2 (12 SA) visible SH-WFSs for low order sensing. These subsystems are distributed across the entire infrastructure (pupil in M2 rotating with elevation ; DM in Coudé train wobbling and rotating with azimuth ; WFSs fixed on the ground ; science focal plane in the interferometric laboratory 150 meters away). GPAO’s complexity prefigures that of the AO systems of future giant telescopes: numerous modes, many moving components, and the need to operate robustly in a broad range of magnitudes and turbulence conditions. GPAO successfully achieved these goals thanks to a complete re-design of the tools available in the Standard Platform for Adaptive optics Real Time Applications (SPARTA, from ESO) and the development of new, versatile methods based on physical modelling and inverse problem approaches. In this work we present the five main modules and their on-sky performances: (i) the Pseudo-Synthetic Interaction Matrix (PSIM) module, in charge to numerically (and quickly) compensate the system rotation, which includes a physical model of the ALPAO DM influence functions, (ii) the innovative estimators of WFS/DM lateral mis-registrations for the instrument bootstrapping through the turbulence in open loop and its auto-alignment in closed loop, (iii) a robust spot monitor for faint star detection and centering during the automatic acquisition sequence and for the update of the weighted center of gravity in closed loop, (iv) the atmospheric and performance monitor made versatile to the different GPAO modes and augmented with an innovative multi-layer profiler for wind estimation, and (v) a pupil monitor that offers a fine positioning of the photometric pupil, its orientation and magnification
Resonant capture of Saturn’s arcs
No full textInternational audienceObtained images from the Cassini spacecraft have unveiled several small satellites in the vicinity of Mimas’ orbit: Aegaeon, Methone and Anthe. Methone and Anthe are situated within arcs of material, while Aegaeon orbits within an arc near the inner edge of Saturn’s G ring. The presence of these arcs and moons is consistent with their confinement by corotation eccentric resonance (CER) with Mimas. Aegaeon is captured in an inner 7 : 6 mean motion resonance with Mimas, while Methone and Anthe are, respectively, captured in outer 14 : 15 and 10 : 11 resonances with Mimas. Here, we estimate the probabilities of capturing these small satellites into their respective CERs with Mimas as the orbit of the latter evolves through tidal effects. We will discuss the potential implications of this work, in particular the constraints it may provide on Mimas’ orbital evolution. This article is part of the theme issue ‘Major advances in planetary sciences thanks to stellar occultations’
On the origin of ~ 100 TeV neutrinos from the Seyfert galaxy NGC 7469
No full textInternational audienceThe origin of TeV-PeV neutrinos detected by IceCube remains largely unknown. The most significant individual neutrino source is the close-by Seyfert galaxy NGC 1068 at 4.2 level with a soft spectral index. Another notable candidate is the Seyfert galaxy NGC 7469, which has been recently proposed as a potential neutrino emitter. The likelihood fit of the IceCube data for this source returned a very hard spectral index of ~ 1.9 and the excess is dominated by two high-energy events, issued as two neutrino alerts IC220424A and IC230416A. The energies of the two neutrinos are estimated to be 100-200 TeV, implying a maximum proton energy > 2 PeV, significantly higher than that in NGC 1068. The lack of lower-energy neutrinos from NGC 7469 also suggests a neutrino spectrum harder than that of NGC 1068. In this paper, we analyze the Fermi-LAT observations of NGC 7469, which yield non-detection. By requiring the cascade flux accompanying neutrino production not to exceed the upper limit of the GeV flux, the size of the neutrino-emitting region can be constrained when the neutrino flux takes a high value of the allowed range. We suggest that protons are accelerated to PeV energies via turbulence or magnetic reconnection in the corona of NGC 7469 and interact with OUV photons from the accretion disk and X-rays from the corona through the process, producing neutrinos with energy of 100-200 TeV. In the turbulence acceleration scenario, the required maximum proton energy can be achieved with a magnetization parameter close to unity (), while in the reconnection scenario, a magnetization parameter with is needed. In both scenarios, a pair dominated composition for the corona is preferred. The difference in the neutrino spectrum between NGC 7469 and NGC 1068 could be due to a different magnetization despite that they belong to the same type of AGN
The Disks In Scorpius–Centaurus Survey (DISCS). I. Four Newly Resolved Debris Disks in Polarized Intensity Light
No full textInternational audienceThe presence of infrared excesses around stars directly correlates with spatially resolved imaging detections of circumstellar disks at both millimeter and optical/near-infrared wavelengths. High-contrast imagers have resolved dozens of circumstellar disks with scattered light polarimetric imaging. Many of these detections are members of the Scorpius–Centaurus OB association, demonstrating it to be a rich sample for investigating planetary system architectures and planet–disk interactions. With the goal of expanding the sample of directly imaged debris disks in Scorpius–Centaurus, we conducted the Disks In Scorpius–Centaurus Survey, leveraging knowledge of high-IR excesses and the power of high-contrast polarimetric differential imaging. In combination with the GPIES polarimetric disk survey, we observe seven new Scorpius–Centaurus targets to achieve a 60% complete survey of debris disks with IR excesses exceeding 2.5 × 10 −4 , resolving four new debris disks. HD 98363, HD 109832, and HD 146181 are resolved for the first time, and HD 112810 is resolved for the first time in polarized intensity. We identify morphological structures that may be indications of planet–disk interactions. We place the systems in the greater context of resolved debris disks, identifying order of magnitude differences in scattered light contrast for a given IR excess, implying gaps in our understanding of the smallest and largest dust grains of a system. We conclude that while thermal emission measurements are correlated with scattered light detection, they poorly predict the magnitude of scattered light brightness. We also establish Scorpius–Centaurus debris disks as critical benchmarks in understanding the properties of disks in the scattering regime
Search for β-delayed fission of 178 Au g,m and an updated systematics in the region of neutron-deficient nuclei
No full textInternational audienceA search for a β-delayed fission (βDF) decay branch of isomerically pure samples of 178 Augand 178 Aum has been performed at the ISOLDE-CERN facility. Two complementary detectionsystems capable of registering α decays and fission fragments, the ISOLDE Decay Station and theASET (Alpha SETup), were used. Despite very high statistics of produced 178 Au nuclei, no fissionfragments were detected. Upper limits of βDF probabilities of PβDF (178 Aug ) < 1.11(2) × 10−8 andPβDF (178 Aum ) < 9.7(2) × 10−9 were determined. Corresponding lower limits of βDF partial half-lives were deduced as well, and the results are discussed in the context of experimental systematicsof βDF in the neutron-deficient region of the nuclear chart
Detecting gravitational lensing by matter currents
No full textInternational audienceWe explore the observational prospects for detecting gravitational lensing induced by cosmological matter currents, a relativistic correction to the standard scalar lensing effect arising from the motion of matter. We propose to isolate this contribution by cross-correlating the weak-lensing convergence field with a reconstructed cosmic momentum field inferred from galaxy surveys. Using numerical simulations, we demonstrate that this reconstructed momentum field is uncorrelated with the scalar lensing signal, enabling a clean separation of the gravitomagnetic component. We then forecast the detectability of this signal for upcoming wide-field galaxy and weak-lensing surveys, showing that a statistically significant detection may be achievable under realistic observational conditions. Such a measurement would provide the first direct probe of the large-scale cosmic momentum field, offering a novel test of general relativity and Lorentz invariance on cosmological scales
Quantitative estimates of the magnetic flux variations in the inner magnetosphere during an intense storm.
No full textInternational audienceIn the present study, we analyzed the Earth's magnetospheric dynamics in response to the intense geomagnetic storm of 19th December 2015, marked by a substantial decrease in the SYM-H index to -188 nT. We focushere on the variations of the magnetic flux content (MFC) within closed magnetic shells in the inner magnetosphe up to a distance roughly corresponding to the magnetopause. During this event, we had the chance to have observations on the dayside and on the nightside and at different distances in the magnetosphere (OMNI, Van Allen Probes, GOES, THEMIS, MMS, Cluster). Using these various observations together with the Tsyganenko T96 model, we estimated the MFC in the inner magnetosphere. It is found that in comparison to pre-storm conditions, MCF decreased during SSC by 17% and in the main phase by 27% but it gradually rebounded (swelled) during 3 following days of the recovery phase reducing the decrease to 22%, 14% and 8% respectively. The importance of storm-time magnetospheric dynamics in the field of space weather forecasting is emphasized by these findings and calls for further studies
Euclid: Exploring observational systematics in cluster cosmology -- a comprehensive analysis of cluster counts and clustering
No full textInternational audienceThis study explores the impact of observational and modelling systematic effects on cluster number counts and cluster clustering and provides model prescriptions for their joint analysis, in the context of the \Euclid survey. Using 1000 \Euclid-like cluster catalogues, we investigate the effect of systematic uncertainties on cluster summary statistics and their auto- and cross-covariance, and perform a likelihood analysis to evaluate their impact on cosmological constraints, with a focus on the matter density parameter and on the power spectrum amplitude . Combining cluster clustering with number counts significantly improves cosmological constraints, with the figure of merit increasing by over 300% compared to number counts alone. We confirm that the two probes are uncorrelated, and the cosmological constraints derived from their combination are almost insensitive to the cosmology dependence of the covariance. We find that photometric redshift uncertainties broaden cosmological posteriors by 20--30%, while secondary effects like redshift-space distortions (RSDs) have a smaller impact on the posteriors -- 5% for clustering alone, 10% when combining probes -- but can significantly bias the constraints if neglected. We show that clustering data below Mpc provides additional constraining power, while scales larger than acoustic oscillation scale add almost no information on and parameters. RSDs and photo- uncertainties also influence the number count covariance, with a significant impact, of about 15--20%, on the parameter constraints
The Geometry of Qubit Decoherence: Linear vs. Nonlinear Dynamics in the Bloch Ball
No full textInternational audienceWe present two complementary approaches to the GKSL equation for an open qubit. The first, based on linearity, yields solutions illustrated by mixed states trajectories in the Bloch ball, including non-random asymptotic fixed points, and exceptional points. The second, exploiting the SU(2) symmetry, leads to a nonlinear dynamical system that separates angular dynamics from radial dissipation. This symmetry-based perspective offers a promising route toward generalisation to open qudits
Fuzzy dark matter dynamical friction: Defying galactic cannibalism of globular clusters
No full textInternational audienceWe present a new implementation of fuzzy dark matter (FDM) dynamical friction within the galpy framework, enabling orbital integrations of globular clusters (GCs) across a broad range of halo-to-GC mass ratios and boson masses. In this alternative DM scenario, dynamical friction is reduced or even suppressed by heating induced by FDM density granules. We further quantify the role of baryons and solitonic cores, natural consequences of FDM in galaxies, on the efficiency of orbital decay and the long-term survival of GCs. The most significant deviations from the cold DM (CDM) paradigm arise in the dwarf-galaxy regime, where FDM dynamical friction can stall the inspiral of GCs over a Hubble time, thereby preventing their sinking into galactic centers and halting the canonical galactic cannibalism of clusters. Importantly, our FDM-only friction model should be regarded as a conservative lower bound, since the inclusion of realistic FDM cores can only strengthen the survival of GCs through core stalling. This stalling mechanism not only preserves in-situ populations that would otherwise be erased in CDM, but also strongly suppresses the mixing of in-situ and ex-situ clusters, yielding a bimodal radial distribution of GCs. Our results show that the demographics of GC systems encode a distinct dynamical signature of FDM in dwarfs. These predictions open a new pathway to constrain the boson mass parameter with upcoming Euclid DR1 observations of extragalactic GCs, while simultaneously offering a natural explanation for the long-standing Fornax timing problem