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ALMA-IMF: XVII. Census and lifetime of high-mass prestellar cores in 14 massive protoclusters
No full textInternational audienceContext. High-mass prestellar cores are extremely rare. Until recently, the search for such objects has been hampered by small sample sizes, leading to large ambiguities in their lifetimes and hence the conditions in the cores in which high-mass stars (≳8 M⊙) form. Aims. Here we leverage the large sample (~580 cores) detected in the ALMA-IMF survey to identify both protostellar and prestellar cores to estimate their relative lifetimes. Methods. We used CO and SiO outflows to identify protostellar cores. We present a new automated method based on aperture line emission and background subtraction to systematically detect outflows associated with each of the 141 most massive cores. Massive cores that are not driving an outflow in either tracer are identified as prestellar. After careful scrutiny of the sample, we derived statistical lifetime estimates for the prestellar phase. Results. Our automated method allows the efficient detection of CO and SiO outflows and has a performance efficiency similar to that of more cumbersome classical techniques. We identified 30 likely prestellar cores with M≳ 8 M⊙, of which 12 have core masses M≳ 16 M⊙. The latter group contains the best candidates for high-mass star precursors. Moreover, most of these 12 high-mass prestellar cores are located inside the crowded central regions of the protoclusters, where most high-mass stars are expected to form. Using the relative ratios of prestellar to protostellar cores, and assuming a high-mass protostellar lifetime of 300 kyr, we derive a prestellar core lifetime of 120 kyr to 240 kyr for cores with masses 8 M⊙ < M < 16 M⊙. For 30 M⊙ < M < 55 M⊙, the lifetimes range from 50 kyr to 100 kyr. The spread in timescales reflects different assumptions for scenarios for the mass reservoir evolution. These timescales are remarkably long compared to the 4 kyr to 15 kyr free-fall time of the cores. Hence, we suggest that high-mass cores live ~10 to 30 free-fall times, with a tentative trend of a slight decrease with core mass. Such high ratios suggest that the collapse of massive cores is slowed down by non-thermal support of turbulent, magnetic or rotational origin at or below the observed scale
Quantum Stark widths of N IV-V and O IV spectral lines
No full textInternational audienceIn this paper, we report new quantum Full Widths at Half Maximum (FWHM) intensities for 24 spectral lines corresponding to various nitrogen and oxygen ions, including 13 N IV, 4 N V and 7 O IV lines. The majority of the spectral lines examined were recently identified in the CASPEC and UVES spectra of the O(He) star JL9, which is a hot hydrogen-deficient pre-white dwarf (pre-WD). These recent findings motivate us to compute their Stark widths in order to address the gaps in the STARK-B database. Part of the present quantum results are compared to the available theoretical and experimental data. Our quantum method, which was developed years ago and has consistently yielded reliable results compared to other approaches, can serve as a valuable tool to clarify the discrepancies observed for certain spectral lines. Additionally, the results obtained can be applied to determine elemental abundances, calculate stellar opacity, interpret and model stellar spectra, analyze observed spectra in such stars, estimate radiative transfer through stellar plasmas, and more. A portion of the current results will also be incorporated into the STARK-B database of Stark broadening parameters. Prior to evaluating the Stark widths, two computational steps were performed: first, the atomic structure was calculated, followed by the electron–ion collision calculations. We present our results for these spectral lines at various temperatures and densities
The Ganymede Laser Altimeter (GALA) on the Jupiter Icy moons Explorer (JUICE) Mission
No full textInternational audienceThe Ganymede Laser Altimeter (GALA) on the Jupiter Icy Moons Explorer (JUICE) mission, is in charge of a comprehensive geodetic mapping of Europa, Ganymede, and Callisto on the basis of Laser range measurements. While multiple topographic profiles will be obtained for Europa and Callisto during flybys, GALA will provide a high-resolution global shape model of Ganymede while in orbit around this moon based on at least 600 million range measurements from altitudes of 500 km and 200 km above the surface. By measuring the diurnal tidal deformation of Ganymede, which crucially depends on the decoupling of the outer ice shell from the deeper interior by a liquid water ocean, GALA will obtain evidence for (or against) a subsurface ocean on Ganymede and will provide constraints on the ice shell thickness above the ocean. In combination with other instruments, it will characterize the morphology of surface units on Ganymede, Europa, and Callisto providing not only topography but also measurements of surface roughness on the scale of the laser footprint, i.e. at a scale of about 50 m from 500 km altitude, and albedo values at the laser wavelength of 1064 nm. GALA is a single-beam laser altimeter, operating at a nominal frequency of 30 Hz, with a capability of reaching up to 48 Hz. It uses a Nd:YAG laser to generate pulses with pulse lengths of 5.5 ± 2.5 ns. The return pulse is detected by an Avalanche Photo Diode (APD) with 100 MHz bandwidth and the signal is digitized at a sampling rate of 200 MHz providing range measurements with a sub-sample resolution of 0.1 m. Research institutes and industrial partners from Germany, Japan, Switzerland and Spain collaborated to build the instrument. JUICE, conducted under responsibility of the European Space Agency (ESA), was successfully launched in April 2023 and is scheduled for arrival at the Jupiter system in July 2031. The nominal science mission including multiple close flybys at Europa, Ganymede, and Callisto, as well as the final Ganymede orbit phase will last from 2031 to 2035. In May 2023 GALA has completed its Near-Earth Commissioning, showing full functionality of all units. Here we summarize the scientific objectives, instrument design and implementation, performance, and operational aspects of GALA
On the polarimetric response of the Nançay Radio Telescope and its impact on precision pulsar timing
No full textInternational audienceIn \citet{Guillemot2023} we presented a new method for calibrating pulsar observations conducted with the Nançay decimetric Radio Telescope (NRT), which significantly improved NRT polarimetric measurements and pulsar timing quality for data taken after this method was developed, in November 2019. Results hinted at a dependence of the polarimetric response of the NRT on the observed direction. We investigated this potential dependence, since unaccounted variations of the instrumental response could degrade polarimetric measurements. Additionally, we aimed to develop a method for properly calibrating NRT pulsar observations conducted before November 2019. We conducted three series of observations of bright pulsars over wide declination ranges, in a special observation mode in which the feed horn rotates by 180 degrees across the observation, enabling us to determine the full polarimetric response of the NRT while modeling potential variations of calibration parameters with hour angle and declination. In addition, we used the METM technique to improve the calibration of pre-November 2019 data. From the analysis of the series of observations of bright pulsars with horn rotation, we found that the polarimetric response of the NRT does not appear to vary with hour angle or declination. On the other hand, the new METM-based calibration method appears to significantly improve the calibration of pre-November 2019 data. By analyzing NRT data on a selection of millisecond pulsars we found that the new polarimetric profiles are more homogeneous, they generally have larger signal-to-noise ratios, and found that the TOA data for these MSPs are more accurate and contain lower levels of noise, especially when combining the new calibration method with the \textit{Matrix Template Matching} (MTM) method for extracting TOAs from pulsar observations
MINCE III. Detailed chemical analysis of the UVES sample
No full textInternational audienceContext . The Measuring at Intermediate Metallicity Neutron-Capture Elements (MINCE) project aims to provide high-quality neutron-capture abundances measurements for several hundred stars at an intermediate metallicity of −2.5 < [Fe/H] < −1.5. This project will shed light on the origin of the neutron-capture elements and the chemical enrichment of the Milky Way. Aims . The goal of this work is to chemically characterize the second sample of the MINCE project and compare the abundances with the galactic chemical evolution model at our disposal. Methods . We performed a standard abundance analysis based on one-dimensional (1D) local thermodynamic equilibrium (LTE) model atmospheres based on high-resolution and high-signal-to-noise-ratio (S/N) spectra from Ultraviolet and Visual Echelle Spectrograph (UVES). Results . We provide the kinematic classification (i.e., thin disk, thick disk, thin-to-thick disk, halo, Gaia Sausage Enceladus, Sequoia) of 99 stars and the atmospheric parameters for almost all stars. We derived the abundances for light elements (from Na to Zn) and neutron-capture elements (Rb, Sr, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, and Eu) for a subsample of 32 stars in the metallicity range of −2.5 < [Fe/H] < −1.00. In the subsample of 32 stars, we identified eight active stars exhibiting (inverse) P-Cygni profile and one Li-rich star, CD 28-11039. We find a general agreement between the chemical abundances and the stochastic model computed for the chemical evolution of the Milky Way halo for elements Mg, Ca, Si, Ti, Sc, Mn, Co, Ni, Zn, Rb, Sr, Y, Zr, Ba, La, and Eu . Conclusions . The MINCE project has already significantly increased the number of neutron-capture elements measurements in the intermediate metallicity range. The results from this sample are in perfect agreement with the previous MINCE sample. The good agreement between the chemical abundances and the chemical evolution model of the Galaxy supports the nucleosynthetic processes adopted to describe the origin of the n-capture elements
Infrared radiometric image classification and segmentation of cloud structures using a deep-learning framework from ground-based infrared thermal camera observations
No full textInternational audienceAbstract. Infrared thermal cameras offer reliable means of assessing atmospheric conditions by measuring the downward radiance from the sky, facilitating their usage in cloud monitoring endeavors. The precise identification and detection of clouds in images pose great challenges stemming from the indistinct boundaries inherent to cloud formations. Various methodologies for segmentation have been previously suggested. Most of them rely on color as the distinguishing criterion for cloud identification in the visible spectral domain and thus lack the ability to detect cloud structures in gray-scaled images with satisfying accuracy. In this work, we propose a new complete deep-learning framework to perform image classification and segmentation with convolutional neural networks. We demonstrate the effectiveness of this technique by conducting a series of tests and validations based on self-captured infrared sky images. Our findings reveal that the models can effectively differentiate between image types and accurately capture detailed cloud structure information at the pixel level, even when trained with a single binary ground-truth mask per input sample. The classifier model achieves an excellent accuracy of 99 % in image type distinction, while the segmentation model attains a mean pixel accuracy of 95 % in our dataset. We emphasize that our framework exhibits strong viability and can be used for infrared thermal ground-based cloud monitoring operations over extended durations. We expect to take advantage of this framework for astronomical applications by providing cloud cover selection criteria for ground-based photometric observations within the StarDICE experiment. </p
Possible evidence for the 478 keV emission line from Be decay during the outburst phases of V1369 Cen
No full textInternational audienceAfter decades of uncertainty about the origin of lithium, recent evidence suggests Galactic novae as its main astrophysical source. In this work, we present possible evidence for the first detection of the Be line at 478 keV, observed with the INTEGRAL satellite. The emission is temporally and spatially coincident with the outburst of the bright nova V1369 Cen, and line significance ranges from 2.5 to 1.9, depending on the detection methodology. A bootstrap analysis, assuming a fixed FWHM of 8 keV, provides a flux of ph/cm/s centered at 479.0 2.5 keV, with a 2.5 significant excess. This flux implies a total Be mass of M at the distance determined using several indicators including the {\em Gaia} satellite. For a nova ejected mass estimated from radio observations, this result implies a Be=Li yield corresponding to . This value is comparable to those measured in a dozen novae through optical observations. Crucially, we confirm optically derived Li yields and demonstrate the groundbreaking potential of using gamma-ray data to measure Li abundances
Radiometer Calibration using Machine Learning
No full textInternational audienceRadiometers are crucial instruments in radio astronomy, forming the primary component of nearly all radio telescopes. They measure the intensity of electromagnetic radiation, converting this radiation into electrical signals. A radiometer's primary components are an antenna and a Low Noise Amplifier (LNA), which is the core of the ``receiver'' chain. Instrumental effects introduced by the receiver are typically corrected or removed during calibration. However, impedance mismatches between the antenna and receiver can introduce unwanted signal reflections and distortions. Traditional calibration methods, such as Dicke switching, alternate the receiver input between the antenna and a well-characterised reference source to mitigate errors by comparison. Recent advances in Machine Learning (ML) offer promising alternatives. Neural networks, which are trained using known signal sources, provide a powerful means to model and calibrate complex systems where traditional analytical approaches struggle. These methods are especially relevant for detecting the faint sky-averaged 21-cm signal from atomic hydrogen at high redshifts. This is one of the main challenges in observational Cosmology today. Here, for the first time, we introduce and test a machine learning-based calibration framework capable of achieving the precision required for radiometric experiments aiming to detect the 21-cm line
Search for high energy 5.5 MeV solar axions with the complete Borexino dataset
No full textInternational audienceA search for solar axions and axion-like particles produced in the reaction was performed using the complete dataset of the Borexino detector (3995 days of measurement live-time). The following interaction processes have been considered: axion decay into two photons , inverse Primakoff conversion on nuclei ), the Compton conversion of axions to photons and the axio-electric effect ). Model-independent limits on axion-photon (), axion-electron (), and isovector axion-nucleon () couplings are obtained: and at 1 MeV (90% c.l.). The Borexino results exclude new large regions of , and coupling constants and axion masses , and leads to constraints on the products and for the KSVZ- and the DFSZ-axion models
Rapport de conjoncture de la Section 17 "SYSTÈME SOLAIRE ET UNIVERS LOINTAIN" du Comité National de la Recherche Scientifique - Mandature 2021-2025
No full textCe rapport s'adresse à un lectorat non expert de la discipline Astrophysique, souhaitant avoir un aperçu de l'évolution de notre communauté de recherche au sein de CNRS INSU (Institut National des Sciences de l'Univers, également appelé CNRS Terre & Univers) sur la période 2022-2024. Il présente un résumé thématique et méthodologique de nos activités, un panorama de la structuration actuelle de notre communauté, ainsi qu'un bilan des recrutements et des promotions. Il est fondé sur le travail de la section 17, lequel comprend les concours de recrutement, les recrutements contractuels RQTH, la carrière (évaluation, promotion, éméritat, demande de rattachement à la section ou de détachement de celle-ci, changement d'affectation et RIPEC C3) des personnels de recherche rattachés à la section 17 ; l'évaluation des structures rattachées à la section 17 ; les propositions pour les médailles d'argent et de bronze du CNRS ; les demandes d'accueil en délégation au CNRS ; les écoles thématiques