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A high geometric albedo and small size of the Haumea cluster member (24835) 1995 SM55 from a stellar occultation and photometric observations
No full textTrans-Neptunian objects (TNOs) are among the most ancient bodies of the solar system. Understanding their physical properties is key to constraining their origin and the evolution of the outer regions beyond Neptune. Stellar occultations provide highly accurate size and shape information. (24835) 1995 SM55 is one of the few members of the Haumea cluster and thus of particular interest. We aimed to determine its projected size, absolute magnitude, and geometric albedo, and to compare these with Haumea. A stellar occultation on 25 February 2024 was observed from five sites, with seven positive detections and 33 negative chords. An elliptical fit to the occultation chords yields semi-axes of km, giving an area-equivalent diameter of km, smaller than the 250 km upper limit from Herschel thermal data. Photometry provides an absolute magnitude , a phase slope of mag/deg, and a . The rotational variability has an amplitude mag, but the period remains uncertain. Combining occultation and photometry, we derive a geometric albedo , one of the highest values measured for a TNO. This value is slightly higher than that of Haumea, consistent with the interpretation that 1995 SM55 belongs to the Haumea cluster
In-situ measurement of surface reaction probabilities in low-pressure plasmas
No full textInternational audienceSurface-catalysed recombination is often the dominant loss process for reactive atoms and free radicals created in low-pressure plasmas in molecular gases. However, ab-initio theoretical methods to estimate the rates of these processes are far from mature, in part due to the complexity of the chemical composition and morphology of surfaces subjected to energetic ion bombardment. Therefore, reliable in-situ measurements are essential to understand the chemical kinetics of these systems. A number of experimental techniques to measure surface reaction rates have been developed, and will be reviewed in this talk. However, analysis of these experimental results has historically relied on simplifying assumptions, notably that of constant surface reaction probability, . However, high-quality data from improved experimental techniques combined with systematic measurements in simplified model systems has shown that this assumption is far from correct in many circumstances. More sophisticated surface models are therefore necessary
Rejection of wavefront aberrations in an atomic gradiometer
No full textOne of the main residual limitations of inertial sensors based on atom interferometry stems from laser beam distortions, which cause parasitic phase shifts and non-homogeneous matter-light couplings. Here we present numerical simulations, accompanied by analytical calculations, which quantify the impact of these effects in a cold atom gradiometer. We demonstrate that the propagation of interferometric laser beam aberrations, combined with initial asymmetry and significant time-of-flight expansion of the the two atomic sources, limit the common-mode rejection of phase noise in a differential configuration. The resulting deviations in gravitational acceleration and its gradient are within reach of current experimental devices. Our study allows us to evaluate the surface quality requirements for retroreflective optics in cold-atom gradiometers of various baselines, and can be extended to other sensors based on different interferometer geometries
Dust populations from 30 to 1000 au in the debris disk of HD 120326
No full textInternational audienceContext. To date, more than a hundred debris disks have been spatially resolved. Among them, the young system HD 120326 stands out, displaying different disk substructures on both intermediate (30–150 au) and large (150–1000 au) scales. Aims. We present new VLT/SPHERE (1.0–1.8 μm) and ALMA (1.3 mm) data of the debris disk around HD 120326. By combining them with archival HST/STIS (0.2–1.0 μm) and archival SPHERE data, we have been able to examine the morphology and photometry of the debris disk, along with its dust properties. Methods. We present the open-access code MoDiSc (Modeling Disks in Scattered light) to model the inner belt jointly using the SPHERE polarized and total intensity observations. Separately, we modeled the ALMA data and the spectral energy distribution (SED). We combined the results of both these analyses with the STIS data to determine the global architecture of HD 120326. Results. For the inner belt, identified as a planetesimal belt, we derived a semi-major axis of 43 au, fractional luminosity of 1.8 × 10 −3 , and maximum degree of polarization of 51% ± 6% at 1.6 μm. The spectral slope of its reflectance spectrum is red between 1.0 and 1.3 μm and gray between 1.3 and 1.8 μm. Additionally, the SPHERE data show that there could be a halo of small particles or a second belt at distances ≤150 au. Using ALMA, we derived in the continuum (1.3 mm) an integrated flux of 561 ± 20 μJy. We did not detect any 12 CO emission. At larger separations (>150 au), we highlight a spiral-like feature spanning hundreds of astronomical units in the STIS data. Conclusions. Further data are needed to confirm and better constrain the dust properties and global morphology of HD 120326
Optical emission line properties of eROSITA-selected SDSS-V galaxies
No full textInternational audienceWe present and discuss optical emission line properties obtained from the analysis of spectra obtained in the Sloan Digital Sky Survey (SDSS) for an X-ray-selected sample of 3684 galaxies (0.002 < z < 0.55) that were drawn from the eRASS1 catalog. We modeled the SDSS-V DR19 spectra using the NBURSTS full spectrum-fitting technique with E-MILES simple stellar population models and emission line templates to decompose the broad and narrow emission line components for a correlation with the X-ray properties. We placed the galaxies on the Baldwin-Phillips-Terlevich (BPT) diagram to diagnose their dominant excitation mechanism. We show that the consistent use of the narrow component fluxes shifts most galaxies systematically and significantly upward to the active galactic nucleus (AGN) region in the BPT diagram. On this basis, we confirm the dependence of the position of a galaxy in the BPT diagram on its (0.2 − 2.3 keV) X-ray/Hα flux ratio. We also verified the correlation between the X-ray luminosity and the emission line luminosities of the narrow [O III]λ5007 and broad Hα component and the relations between the supermassive black hole mass, the X-ray luminosity, and the velocity dispersion of the stellar component (σ*) on the base of the unique sample of optical spectroscopic follow-up of X-ray sources detected by eROSITA. These results highlight the importance of emission line decomposition in the AGN classification and refine the connection between X-ray emission and optical emission line properties in galaxies.Key words: line: profiles / methods: data analysis / techniques: spectroscopic / galaxies: nuclei⋆⋆ These authors contributed equally to this work
Helioseismic inference of the solar radiative opacity
No full textInternational audienceThe Sun is the most studied of all stars, and thus constitutes a benchmark for stellar models. However, our vision of the Sun is still incomplete, as illustrated by the current debate on its chemical composition. The problem reaches far beyond chemical abundances and is intimately linked to microscopic and macroscopic physical ingredients of solar models such as radiative opacity, for which experimental results have been recently measured that still await theoretical explanations. We present opacity profiles derived from helioseismic inferences and compare them with detailed theoretical computations of individual element contributions using three different opacity computation codes, in a complementary way to experimental results. We find that our seismic opacity is about 10% higher than theoretical values used in current solar models around 2 million degrees, but lower by 35% than some recent available theoretical values. Using the Sun as a laboratory of fundamental physics, we show that quantitative comparisons between various opacity tables are required to understand the origin of the discrepancies between reported helioseismic, theoretical and experimental opacity values
Euclid preparation. Cosmology Likelihood for Observables in Euclid (CLOE). 4: Validation and Performance
No full textInternational audienceThe Euclid satellite will provide data on the clustering of galaxies and on the distortion of their measured shapes, which can be used to constrain and test the cosmological model. However, the increase in precision places strong requirements on the accuracy of the theoretical modelling for the observables and of the full analysis pipeline. In this paper, we investigate the accuracy of the calculations performed by the Cosmology Likelihood for Observables in Euclid (CLOE), a software able to handle both the modelling of observables and their fit against observational data for both the photometric and spectroscopic surveys of Euclid, by comparing the output of CLOE with external codes used as benchmark. We perform such a comparison on the quantities entering the calculations of the observables, as well as on the final outputs of these calculations. Our results highlight the high accuracy of CLOE when comparing its calculation against external codes for Euclid observables on an extended range of operative cases. In particular, all the summary statistics of interest always differ less than from the chosen benchmark, and CLOE predictions are statistically compatible with simulated data obtained from benchmark codes. The same holds for the comparison of correlation function in configuration space for spectroscopic and photometric observables
Flux-driven turbulent transport using penalisation in the Hasegawa-Wakatani system
No full textInternational audienceFirst numerical results from the newly developed pseudo-spectral code P-FLARE (Penalised FLux-driven Algorithm for REduced models) are presented. This flux-driven turbulence/transport code uses a pseudo-spectral formulation with the penalisation method to impose radial boundary conditions. Its concise, flexible structure allows implementing various quasi-two-dimensional reduced fluid models in flux-driven formulation. Here, results from simulations of the modified Hasegawa–Wakatani system are discussed, where particle transport and zonal flow formation, together with profile relaxation, are studied. It is shown that coupled spreading/profile relaxation that one obtains for this system is consistent with a simple one-dimensional model of coupled spreading/transport equations. Then, the effect of a particle source is investigated, which results in the observation of sandpile-like critical behaviour. The model displays profile stiffness for certain parameters, with very different input fluxes resulting in very similar mean density gradients. This is due to different zonal flow levels around the critical value for the control parameter (i.e. the ratio of the adiabaticity parameter to the mean gradient) and the existence for this system of a hysteresis loop for the transition from two-dimensional turbulence to a zonal flow dominated state
Contact binary asteroid (153201) 2000 WO107: Rotation, shape model, and density
No full textInternational audienceContext. The spectral properties and albedo of near-Earth asteroid (153201) 2000 WO107 are consistent with a taxonomic type M. This implies that it might have a high metal abundance and higher density.Aims. We combined different methods to investigate the asteroid rotation, determine its shape, and use it to estimate its density.Methods. We carried out photometric observations of the asteroid during the 2020 apparition. We then created a program to simulate the light curves, and used it within a Markov chain Monte Carlo (MCMC) algorithm to reconstruct the asteroid shape model from the observational data. The Goldstone radar observations of the asteroid were used as an additional constraint on the asteroid model in the MCMC algorithm. The estimated shape and rotation rate of the contact binary were used to compute its density.Results. The photometric observations of (153201) 2000 WO107 obtained at a wide range of the phase angles from 5 to 68 degrees in the time interval of November 28 – December 8, 2020, show light curves typical for contact binary asteroids, which agrees with the results of the radar data. The light curves have a maximum amplitude of up to 1.24 mag. The best-fit modeled shape of the asteroid is composed of two ellipsoidal lobes with axes of 0.68 × 0.38 × 0.36 km and 0.44 × 0.42 × 0.16 km. Its sidereal rotation period is determined to be 5.017 ± 0.002 h. The most probable solution for the angular velocity vector of the asteroid indicates ecliptic coordinates of λ = 96° ± 8° and β = −78° ± 1°, but another less probable solution of around λ = 286° ± 11°, β = −76° ± 2° cannot be disregarded. The estimated density of the asteroid ρ = 4.80−0.63+0.34 g/cm3 is consistent with a possible metallic composition. From the orbital simulation of this potentially hazardous asteroid, we find that its integral probability of colliding with the Earth in the next 10 000 years is 7 · 10−5
ZTF SNe Ia DR2: Towards cosmology-grade ZTF supernova light curves using scene modeling photometry
No full textInternational audienceThe Zwicky Transient Facility (ZTF) is conducting a wide-field survey of the northern sky in three optical bands and the collaboration cosmology working group has released 3628 spectroscopically confirmed Type Ia supernovae (SNe Ia) discovered during its first 2.5 years of operation. This "ZTF SN Ia DR2" sample is the largest SN Ia dataset to date. Fully exploiting this dataset to improve understanding of the properties of dark energy requires a photometric accuracy of O(0.1%). This can be achieved using Scene Modeling Photometry (SMP), which is optimal to extract a transient signal (SN) from a complex background (its host), while ensuring a common flux estimator with nearby stars used as calibration reference. In this paper, we present the status of the SMP development and use it to assess the precision and accuracy of the ZTF SN Ia DR2 force photometry light curves. We reach a repeatability of the star observations better than 1%. However, we have identified a new sensor effect, dubbed "pocket-effect", which distorts the Point Spread Function (PSF) in a flux-dependent manner leading to non-linearities in the photometry of a few percent. Correcting for this effect requires time- and sensor-dependent corrections to be applied at the pixel level, which is currently under development. This effects affects all light curve releases to date -- both from forced photometry and scene modelling preventing ZTF SN Ia DR2 to be used for accurate cosmological inference. Comparing the SMP and forced photometry measurements, we find that stretch and color estimated from both processings are consistent, aside from a 10 mmag shift in color. This assess the robustness of results presented as part of the the ZTF SN Ia DR2 release. The absolute calibration however shifts by 90 mmag. A reprocessing of the full ZTF SN Ia DR2 dataset using the SMP method is currently in progress