HAL-OBSPM
Not a member yet
37663 research outputs found
Sort by
Innermost stable circular orbit of arbitrary-mass compact binaries at fourth post-Newtonian order
No full textInternational audienceWe compute by means of post-Newtonian (PN) methods the innermost stable circular orbit (ISCO) of arbitrary-mass (in particular, comparable-mass) compact binaries. Two methods are used with equivalent results: dynamical perturbation of the conservative equations of motion in harmonic coordinates, and dynamical perturbation of the conservative Hamiltonian in ADM coordinates. The perturbation of the non-local tail term at 4PN order in both approaches is carefully investigated. Our final gauge invariant result for the location of the ISCO at 4PN order is close to the numerical value of the ISCO shift computed by the gravitational self-force (GSF) approach in the small mass-ratio limit, and is also in good agreement with the full numerical-relativity calculation in the case of equal masses. The PN method followed here is considered in standard Taylor-expanded form, without any resummation techniques applied. As a complement, we also compute explicitly the gauge transformation from harmonic coordinates to ADM coordinates up to 4PN order, including the tail contribution therein
<i>Euclid</i>: Early Release Observations – The intracluster light and intracluster globular clusters of the Perseus cluster
No full textInternational audienceWe study the intracluster light (ICL) and intracluster globular clusters (ICGCs) in the nearby Perseus cluster of galaxies using Euclid's Early Release Observations. By modelling the isophotal and iso-density contours, we mapped the distributions and properties of the ICL and ICGCs out to radii of 200-600 kpc (up to ∼ 1 3 of the virial radius, depending on the parameter) from the brightest cluster galaxy (BCG). We find that the central 500 kpc of the Perseus cluster hosts 70 000 ± 2800 globular clusters, and 1.7 × 10 12 L ⊙ of diffuse light from the BCG+ICL in the near-infrared H E . This accounts for 38 ± 6% of the cluster's total stellar luminosity within this radius. The ICL and ICGCs share a coherent spatial distribution which suggests that they have a common origin or that a common potential governs their distribution. Their contours on the largest scales (>200 kpc) are not centred on the BCG's core, but are instead offset westwards by 60 kpc towards several luminous cluster galaxies. This offset is opposite to the displacement observed in the gaseous intracluster medium. The radial surface brightness profile of the BCG+ICL is best described by a double Sérsic model, with 68 ± 4% of the H E light contained in the extended, outer component. The transition between these components occurs at ≈60 kpc, beyond which the isophotes become increasingly elliptical and off-centred. Furthermore, the radial ICGC number density profile closely follows the profile of the ⋆ This paper is published on behalf of the Euclid Consortium.</div
The ANTARES detector: two decades of neutrino searches in the Mediterranean Sea
No full textInternational audienceInterest for studying cosmic neutrinos using deep-sea detectors has increase after the discovery of a diffuse flux of cosmic neutrinos by the IceCube collaboration and the possibility of wider multi-messenger studies with the observations of gravitational waves. The ANTARES detector was the first neutrino telescope in seawater, operating successfully in the Mediterranean Sea for more than a decade and a half. All challenges related to the operation in the deep sea were accurately addressed by the collaboration. Deployment and connection operations became smoother over time; data taking and constant re-calibration of the detector due to the variable environmental conditions were fully automated. A wealth of results on the subject of astroparticle physics, particle physics and multi-messenger astronomy have been obtained, despite the relative modest size of the detector, paving the way to a new generation of larger undersea detectors. This review summarizes the efforts by the ANTARES collaboration that made the possibility to operate neutrino telescopes in seawater a reality and the results obtained in this endeavor
Abundances of refractory ions in Beta Pictoris exocomets
No full textInternational audienceβ Pictoris is a young A5V star known for harbouring a large number of cometary-like objects (or exocomets) that frequently transit the star and create variable absorption signatures in its spectrum. The physical and chemical properties of these exocomets can be probed by the recently introduced curve of growth approach, which enables column densities measurements in cometary tails using absorption measurements in numerous spectral lines. Through this approach, we present a new study of archival spectra of β Pic obtained with the Hubble Space Telescope, the HARPS spectrograph, and at the Mont John University Observatory aimed at constraining the abundance of refractory ions in β Pic exocomets. We studied 29 individual objects, all of which were observed in Fe II lines (used as a reference ion) and at least one other species (e.g. Ni II, Ca II, Cr II). We find that the refractory composition of β Pic exocomets is stable overall, especially for singly ionised species, and consistent with solar abundances. This outcome validates the use of the curve of growth approach to study exocometary composition. We also show that some ions, such as Ca II, are significantly depleted compared to solar abundances, which allowed us to constrain the typical ionisation state in β Pic exocomets. We find that most refractory elements (e.g. Mg, Ni, Fe) are split into similar fractions between their first and second ionisation states, with the exception of Ca, which is mostly ionised twice. A strong correlation between the Al III/Fe II ratio and radial velocity is also found, showing that the most redshifted exocomets tend to be more ionised. These results open the way for further modelling of exocomets in order to unveil their composition and the physical processes that affect their tails
Pluto’s atmosphere gas and haze composition from JWST/MIRI spectroscopy
No full textInternational audienceContext: Pluto possesses a tenuous, time-variable, N2-dominated atmosphere, with extensive haze. Previous spectroscopic observations from the ground at near-infrared (NIR) and submillimeter (submm) wavelengths and New Horizons in the ultraviolet (UV) have revealed a Titan-like atmosphere with rich N2-CH4 photochemistry. The mid-infrared (MIR) range of Pluto’s spectrum, however, has remained out of reach thus far.Aims. Taking advantage of JWST sensitivity, our goal is to obtain new insights into Pluto’s atmospheric gas and haze composition using mid-IR spectroscopy.Methods. In May 2023, we used JWST/MIRI MRS to acquire a high signal-to-noise (S/N) spectrum of Pluto over 4.9–27 μm, finally opening up the MIR spectral range for Pluto. The data were analyzed with a standard radiative transfer code, including the solar and thermal components, and the gas and haze emission, using gas vertical distributions from photochemical models as templates.Results. The Pluto spectrum consists of the superposition of solar light reflected off Pluto’s surface, surface thermal emission, gas thermal and non-thermal emission, and haze emission. The solar reflected component shows absorption by CH4, CH3D, and C2H4 surface ices. Spectral signatures of C2H6, C2H2, CH3C2H, and C4H2 gases are strongly detected over 12–16 μm, broadly probing the stratopause region (altogether spanning 15–100 km). Unexpectedly, we also detect fluorescence (non-LTE) emission from gas CH4 (ν4 and hot bands) and CH3D (ν6 band) in the 7–9 μm range, indicating excitation temperatures that are much higher than Pluto’s atmosphere kinetic temperature. The C2H6 abundance agrees very well with photochemical models, but those of CH3C2H, and C4H2 are about five and ten times lower than model predictions, respectively. The C2H2 12.9–14.7 μm emission (ν5) is imperfectly fit and may point to a less steep C2H2 profile than in model predictions or (perhaps more likely) to non-LTE effects on this band. Remarkably, C2HD is detected at 14.75 μm, yielding a (D/H)C2H2 ratio equal to (3±1) terrestrial. Also, HCN has been tentatively observed and upper limits on several other gases (C2H4, C3H8, C6H6, HC3N, and CO2) are obtained. The haze emission is clearly present over 13–20 μm and characterized by emission peaks at 15.45 μm, 14.58 μm, and maybe 13.60 μm. The haze spectrum is very different from Titan’s and points to the presence of pure or mixed ices (e.g., C4H2, C6H6), as previously proposed.Conclusions: The spectacular JWST MIRI spectrum is giving us a new look at Pluto’s atmosphere. An improved non-LTE modeling of the fluorescent emissions (CH4, CH3D, and possibly C2H2) and of the ice features is expected to yield a broader view of Pluto’s D/H ratio in different gases (CH4, C2H2) and phases (gas and solid). This would bear key information on Pluto’s ice origin and evolution
Satellite system around the spiral galaxy NGC 5965
No full textWe have constituted a catalog of isolated giant galaxies surrounded by dwarf galaxies. From that catalog we have chosen to study the system of NGC 5965 and its fourteen companion galaxies.We have analysed the structure of the NGC 5965 system and its internal motions by a new statistical deprojection method using pairs of satellites, which allows us to identify a disk structure despite the absence of 3 among 6 phase-space coordinates and to obtain a statistical measurement of its thickness. This method is validated using numerical simulations.We find that eleven among the companion galaxies are, with a high probability, bound satellites lying in a disk-like structure of radius 1 Mpc and thickness Mpc, two are unbound or out of plane and one is probably an interloper at cosmological distance.We have found evidence that NGC 5965, a ( Mpc) distant galaxy, is surrounded by a low thickness disk-like system of satellites whose rotation velocity is constant up to about 200 kpc, then decreases beyond according to a Kepler law, up to 1 Mpc from the main galaxy
Search for QCD coupled axion dark matter with the MICROSCOPE space experiment
No full textInternational audienceAxion dark matter coupled via QCD induces a non-zero differential acceleration between test masses of different composition. Tests of the equivalence principle, like the recent MICROSCOPE space mission, are sensitive to such a signal. We use the final released data of the MICROSCOPE experiment, to search for this effect. We find no positive signal consistent with the dark matter model, and set upper limits on the axion-gluon coupling that improve existing laboratory bounds by up to two orders of magnitude for axion masses in the eV to eV range
Constraints on primordial non-Gaussianity from Planck PR4 data
No full textInternational audienceWe perform the first bispectrum analysis of the final Planck release temperature and E-polarization CMB data, called PR4. We use the binned bispectrum estimator pipeline that was also used for the previous Planck releases as well as the integrated bispectrum estimator. We test the standard primordial (local, equilateral and orthogonal) and secondary (lensing, unclustered point sources and CIB) bispectrum shapes. The final primordial results of the full T+E analysis are , and . These results are consistent with previous Planck releases, but have slightly smaller error bars than in PR3, up to smaller for orthogonal. They represent the best Planck constraints on primordial non-Gaussianity. The lensing and point source bispectra are also detected, consistent with PR3. We perform several validation tests and find in particular that the 600 simulations, used to determine the linear correction term and the error bars, have a systematically low lensing bispectrum. We show however that this has no impact on our results
Euclid Quick Data Release (Q1) The Strong Lensing Discovery Engine B -- Early strong lens candidates from visual inspection of high velocity dispersion galaxies
No full textInternational audienceWe present a search for strong gravitational lenses in Euclid imaging with high stellar velocity dispersion ( km/s) reported by SDSS and DESI. We performed expert visual inspection and classification of \Euclid images. We discovered 38 grade A and 40 grade B candidate lenses, consistent with an expected sample of 32. Palomar spectroscopy confirmed 5 lens systems, while DESI spectra confirmed one, provided ambiguous results for another, and help to discard one. The \Euclid automated lens modeler modelled 53 candidates, confirming 38 as lenses, failing to model 9, and ruling out 6 grade B candidates. For the remaining 25 candidates we could not gather additional information. More importantly, our expert-classified non-lenses provide an excellent training set for machine learning lens classifiers. We create high-fidelity simulations of \Euclid lenses by painting realistic lensed sources behind the expert tagged (non-lens) luminous red galaxies. This training set is the foundation stone for the \Euclid galaxy-galaxy strong lensing discovery engine
Aurore boréale des 10 et 11 Mai 2024 visible dans les Alpes et observée par les caméras panoramiques et automatiques de haute montagne
No full textL’archive ZIP ci jointe contient des images de l’aurore boréale des 10 et 11 Mai 2024 prises par des caméras panoramiques et automatiques de haute montagne situées dans les Alpes françaises, suisses et italiennes, au cours du maximum d’activité solaire du cycle 25. L’activité géomagnétique (G5 ou Kp9) des 10-11 Mai est classée en 7ème position depuis 70 ans (époque du maximum du cycle 19), tandis que la surface tachée de la région solaire AR3664, dont les éruptions et éjections de masse coronale sont à l’origine de cette activité, était assez exceptionnelle