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Cassini CAPS‐ELS Observations of Low‐Energy Electron Beams Within Enceladus Mid‐Latitude Flux Tubes
No full textInternational audienceAbstract The electrodynamic interaction between Saturn's magnetosphere and Enceladus accelerates electrons along magnetic field lines. These electrons propagate inside magnetic flux tubes connecting the moon to the giant planet, generating distinctive auroral hiss and auroral footprint signatures, both previously observed by the Cassini spacecraft. In this study, we analyze low‐energy electron measurements made during multiple mid‐latitude crossings of magnetic flux tubes connected to Enceladus' wake. We show that the properties of the observed electrons are consistent with those of electrons inducing Enceladus' auroral hiss, and discuss the physical processes responsible for their pitch‐angle distributions and acceleration. Field‐aligned electron beams have very different properties from those triggering the Enceladus ultraviolet footprint, with a much lower characteristic energy and energy flux. Observations of electron beams resulting from the moon‐magnetosphere interactions up to 30° downstream of the moon reveal that the coupling system between Enceladus and Saturn is significantly more extended than previously anticipated
Enabling Blind and Visually Impaired Individuals to Pursue Careers in Science: Make Science more accessible to blind and visually impaired individuals
No full textInternational audienceSF2A annual conferenceBlind and Visually Impaired (BVI) Individuals face significant challenges in science due to the discipline's reliance on visual elements such as graphs, diagrams, and laboratory work. Traditional learning materials, such as Braille and large-print textbooks, are often scarce or delayed, while practical experiments are rarely adapted for accessibility. Additionally, mainstream educators lack the training to effectively support BVI students, and Teachers for the Visually Impaired (TVIs) often lack scientific expertise. As a result, BVI individuals remain underrepresented in scientific jobs, reinforcing a cycle of exclusion. However, technological advancements and inclusive initiatives are opening new opportunities. Outreach programs aim to make science engaging and accessible for BVI individuals through multi-sensory learning experiences. Hands-on involvement in these activities fosters confidence and interest in scientific careers. Beyond sparking interest, equipping BVI students with the right tools and skills is crucial for their academic success. Early exposure to assistive technologies enables BVI students to navigate scientific studies independently. Artificial Intelligence (AI) tools further enhance accessibility by converting visual data into descriptive text and providing interactive assistance. Several learning sessions demonstrated the effectiveness of these interventions, with participants successfully integrating into university-level science programs. Educating BVI and their teachers on these tools and good pratices is the aim of our project AccesSciencesDV. Research careers offer promising opportunities for BVI, especially in computational fields. By leveraging coding, data analysis, and AI-driven tools, BVI researchers can conduct high-level scientific work without relying on direct visual observations. The presence of BVI scientists enriches research environments
Broad Iron Line as a Relativistic Reflection from Warm Corona in AGN
No full textInternational audienceWe present that the broad feature usually observed in X-ray spectra can be explained by a ray-traced emission from a two-slab system containing a dissipative, warm corona on top of an accretion disk in an AGN. Such an accretion flow is externally illuminated by X-ray radiation from a lamp located above a central SMBH. Thermal lines from highly ionized iron ions (FeXXV and FeXXVI), caused by both internal heating and reflection from the warm corona, can be integrated into an observed broad line profile due to the close vicinity of the SMBH. We investigate the dependence of the broad line profile by varying the SMBH spin parameter, viewing angle, lamp height, and dissipation factor. Our results introduce a new method to probe properties of the warm corona using high-resolution spectroscopic measurements. We use the photoionization code TITAN to compute local ion populations and emission line profiles, and the ray-tracing code GYOTO to include relativistic effects on the outgoing X-ray spectrum. In our models, the temperature of the inner atmosphere covering the disk can reach values of 10^7 - 10^8 K due to internal warm corona dissipation and external illumination, which is adequate for generating the highly ionized iron lines. These lines can undergo significant gravitational redshift near the black hole, leading to a prominent spectral feature centered around 6.4 keV. For all computed models, the relativistic corrections shift highly ionized iron lines to the X-ray region, usually attributed to fluorescent emission from the illuminated skin of an accretion disk. Hence, in the case of a warm corona covering the inner disk regions, the resulting theoretical line profile under strong gravity is a sum of different iron line transitions, and those originating from highly ionized iron contribute the most to the observed total line profile in AGN
Search for complex nitriles in Titan’s stratosphere
No full textInternational audience) Introduction: The atmosphere of Titan is known to host a complex organic chemistry [1,2,3]. From the Voyager missions, and later the Cassini-Huygens mission, several hydrocarbons and nitriles have been detected and their seasonal variations have been monitored during a period of one Titan season (30 years). Photochemical models that have also predicted the presence of other minor species, among which some have infrared transitions in the 5-25 mm spectral range. We have observed Titan with IRTF/TEXES in September 2022, searching for two complex nitriles C4H3N and C4H7N. We published an analysis of the data with the support of updated spectroscopic databases (like in HITRAN and GEISA) and new data from recent laboratory work [4].2) Photochemistry: Cyanopropyne (CH3C3N) was detected in the mm range with Alma [5], in band 6 (∼230 – 272 GHz). We have selected to search for cyanopropyne (C4H3N) because it has a strong band (n10) with a Q-branch at 499 cm-1 [6]. We have used a photochemical model previously applied to Titan, Pluto and Triton [7a] to simulate the profile of CH3C3 Dominant formation is through reaction of C2N with ethylene (C2H4), reactions of CN with methylacetylene (CH3C2H) and allene (CH2CCH2), and the recombination of CH3C3NH+, while below 900 km the dominant CH3C3N loss mechanism is photolysis. The measured cross sections allow for decreased uncertainties in the photolysis of CH3C3N [7b]. The simulations suggest a C4H3N abundance of a few 10-10 in the stratosphere. Isobutyronitrile (C3H7CN) has not yet been detected, but has a band at 538 cm-1; production is dominated by the C2H4CN + CH3 and CN + C3H8 reactions and loss is driven by photodissociation. Its present upper limit is ~10-7 in the thermosphere and ~10-11 in the stratosphere. 3) ObservationsWe observed Titan in September 2022 using the TEXES thermal infrared imaging spectrometer at the Infrared Telescope Facility (Mauna Kea, Hawaii) to search for C4H3N and C4H7N in the 20-micron region and to monitor the infrared signatures of hydrogen cyanide (HCN) and cyanoacetylene (HC3N), along with acetylene (C2H2 and C2HD).The TEXES data were also used for a study of the variations of HCN and HC3N and for a retrieval of D/H from C2HD/C2H2.4) Spectroscopic data:Absorption coefficients and absorption cross-sections have been obtained for the two noncyclic cyanopropyne (CH3C3N) and the isobutyronitrile (i-C3H7CN) organic molecules at room temperature. The gas phase spectra of the nitriles were recorded between 160 and 3500 cm-1 using an infrared Fourier transform spectrometer. The spectral resolution was 0.056 cm-1. For the 18-20 μm spectral region an additional resolution of 0.01 cm-1 was used. Among the various absorption bands observed, some, as the ν10 band of cyanopropyne around 500 cm-1, are particularly interesting for detecting and quantifying these molecules in astrophysical objects other than Titan.The retrieved absorption cross-sections were used in radiative transfer simulations of the observations using the PSG radiative transfer code by [9] and a radiative code for Titan used in analyzing CIRS data. We published the results and perspectives [4].5) TEXES analysis results499 cm-1 range: with current TEXES data, we derive an upper limit for cyanopropyne of about 3×10-9 (Fig. 1). The C2HD line intensity is in reasonable agreement with the nominal value of C2H2 at the equator (2.5×10-6), with D/H = 5×10-4. The HC3N band is not visible because the value at the equator (3×10-10) is too low (detection limit: around 10-9; [1,2]). 538 cm-1 range: The upper limit of isobutyronitrile is around 3×10-7. The band is weak and there is no apparent structure. Even with a resolution of 0.01 cm-1, the instrumental spectrum is not resolved. The C2HD is consistent with the nominal value C2H2 = 2.5×10-6 with D/H = 5×10-4. 746 and 1247 cm-1 ranges: TEXES data appear to be in good agreement with CIRS measurements and the nominal model for the continuum and the band wings. In the future, we plan to investigate the Cassini/CIRS large averages in order to search for the nitriles in the FP1 and FP3 spectral ranges. 6) Conclusions and future prospectsThe spectroscopic data covering both FIR and MIR are available and should allow future quantitative detection of these two molecules. They will be included in the 2024 update of HITRAN. Measurements at lower temperature and pressure should also be performed since they will improve the quality of the detection in astrophysical object such as the stratosphere of Titan. Although no detection was achieved with these observations, we plan to use the new laboratory data in conjunction with larger telescopes in the future, like the 8-m telescope Gemini, to improve the limit of detection. Such observations should provide significant insights in our understanding of the Titan nitrile chemistry, in particular for C4Hx species.References[1] Coustenis, A., 2021. In Read, P. (Ed.), Oxford Research Encyclopedia of Planetary Science. Oxford University Press. [2] Nixon, C., 2024. ACS Earth and Space Chemistry 8 (3), 406-456. [3] Waite et al., 2007. Science 316, 870. [4] Jacquemart et al., 2025. JQSRT 2025, 109466. [5] Thelen et al., 2020. https://arxiv.org/pdf/2010.08654.pdf [6] Cerceau, F., et al., 1985. Icarus 62, pp. 207–220. [7] a. Lavvas et al. 2021 Astr. 5, 289-297; b. Lammarre et al. 2016, JQSRT 182, 286-295 [8] Coustenis et al., 1993. Icarus, 102, 240−260. [9] Villanueva et al., 2018. https://arxiv.org/abs/1803.02008 Figure 1: simulations and results for cyanopropyne in the region around 500 cm-1. Figure 2: simulations and results for isobutyronitrile in the region around 538 cm-1
Mapping the world's inland surface waters: an upgrade to the Global Lakes and Wetlands Database (GLWD v2)
No full textInternational audienceIn recognition of the importance of inland waters, numerous datasets mapping their extents, types, or changes have been created using sources ranging from historical wetland maps to real-time satellite remote sensing. However, differences in definitions and methods have led to spatial and typological inconsistencies among individual data sources, confounding their complementary use and integration. The Global Lakes and Wetlands Database (GLWD), published in 2004, with its globally seamless depiction of 12 major vegetated and non-vegetated wetland classes at 1 km grid cell resolution, has emerged over the last few decades as a foundational reference map that has advanced research and conservation planning addressing freshwater biodiversity, ecosystem services, greenhouse gas emissions, land surface processes, hydrology, and human health. Here, we present a new iteration of this map, termed GLWD version 2, generated by harmonizing the latest ground- and satellite-based data products into one single database. Following the same design principle as its predecessor, GLWD v2 aims to avoid double counting of overlapping surface water features while differentiating between natural and non-natural lakes, rivers of multiple sizes, and several other wetland types. The classification of GLWD v2 incorporates information on seasonality (i.e., permanent vs. intermittent vs. ephemeral); inundation vs. saturation (i.e., flooding vs. waterlogged soils), vegetation cover (e.g., forested swamps vs. non-forested marshes), salinity (e.g., salt pans), natural vs. non-natural origins (e.g., rice paddies), and stratification of landscape position and water source (e.g., riverine, lacustrine, palustrine, coastal/marine). GLWD v2 represents 33 wetland classes and – including all intermittent classes – depicts a maximum of 18.2 ×106 km2 of wetlands (13.4 % of the global land area excluding Antarctica). The spatial extent of each class is provided as the fractional coverage within each grid cell at a resolution of 15 arcsec (approximately 500 m at the Equator), with cell fractions derived from input data at resolutions as small as 10 m. The upgraded GLWD v2 offers an improved representation of inland surface water extents and their classification for contemporary conditions (∼ 1984–2020). Despite being a static map, it includes classes that denote intrinsic temporal dynamics. GLWD v2 is designed to facilitate large-scale hydrological, ecological, biogeochemical, and conservation applications, aiming to support the study and protection of wetland ecosystems around the world. The GLWD v2 database is available at https://doi.org/10.6084/m9.figshare.28519994 (Lehner et al., 2025)
Statistical Analysis of the Rotation Induced Decay of the Contrast in an Onboard Atom Interferometer
No full textInternational audienceWe present a statistical analysis of the measurement noise of an atom interferometer under large phase and contrast noise caused by rotation fluctuations. The extraction of the standard deviation of the contrast fluctuations out of transition probability measurements allows us to determine the level of rotation noise applied to the onboard instrument. We include an experimental validation of the method
Enabling Early Transient Discovery in LSST via Difference Imaging with DECam
No full textInternational audienceWe present SLIDE, a pipeline that enables transient discovery in data from the Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST), using archival images from the Dark Energy Camera as templates for difference imaging. We apply this pipeline to the recently released Data Preview 1 (DP1; the first public release of Rubin commissioning data) and search for transients in the resulting difference images. The image subtraction, photometry extraction, and transient detection are all performed on the Rubin Science Platform. We demonstrate that SLIDE effectively extracts clean photometry by circumventing poor or missing LSST templates. We identified 29 previously unreported transients, 12 of which would not have been detected based on the DP1 DiaObject catalog. SLIDE will be especially useful for transient analysis in the early years of LSST, when template coverage will be largely incomplete or when templates may be contaminated by transients present at the time of acquisition. We present multiband light curves for a sample of known transients, along with new transient candidates identified through our search. Finally, we discuss the prospects of applying this pipeline during the main LSST survey. Our pipeline is broadly applicable and will support studies of all transients with slowly evolving phases
Cometary observations in light-polluted environments: a case study of interstellar comet 2I/Borisov
No full textInternational audienceAbstract Comets and asteroids have long captured human curiosity, and until recently, all documented examples belonged to our Solar System. That changed with the discovery of the first known interstellar object, 1I/2017 U1 (‘Oumuamua), in 2017. Two years later, on August 30, 2019, Gennady Borisov discovered a second interstellar object, 2019 Q4, which was officially designated 2I/Borisov. From its initial images, the object’s diffuse appearance hinted at its cometary nature. To better understand the photometric evolution of comet 2I/Borisov as it traveled through the inner Solar System, we compiled observations using medium-sized telescopes. This data is crucial for gaining insights into its size and composition, as well as how such objects, after millions of years in interstellar space, behave when exposed to the Sun’s radiation. Given that 2I/Borisov is the first interstellar comet ever observed, constraining its behavior is of great scientific interest. In this paper, we present photometric data gathered from observatories in Crimea and Catalonia, highlighting the importance of systematic photometric studies of interstellar objects using meter-class telescopes. Our observations showed a steady increase in the comet’s brightness as it approached perihelion, likely due to the slow sublimation of ices. Over the five-month pre-perihelion observation period, we did not detect any significant changes in magnitude. The analysis of observations reveals a steady increase in comet 2I/Borisov brightness as it approached perihelion, likely due to the sublimation of ices, with no observable outbursts during the five-month pre-perihelion period. Additionally, we discuss the challenges in ground-based observation of comets posed by light pollution today, particularly in urban areas, where visual observations are severely limited. Using sample surface brightness measurements, we demonstrate the impact of light pollution and outline the importance of systematic photometric studies for interstellar objects
Blind deconvolution and reconstruction of complex point spread functions
No full textInternational audienceThe emergence of extreme adaptive optics (AO) systems in the last two decades pushed to unprecedented limits the resolution achievable by ground-based telescopes. Nonetheless, despite the always increasing performances of AO systems, the correction is never perfect, still degrading the images compared to the theoretical limits of the telescope pupil. Using a reference point spread function (PSF) obtained by simulation or by pointing a bright star is not always sufficient due to the random nature of the turbulence. The only solution is thus to extract and reconstruct the AO-PSF directly from the data of interest, a problem known as blind deconvolution. In recent years, marginal approaches emerged, based on a parametric modelling of the AO-PSF with a limited number of physical parameters. These methods correctly grasp the global structure of AO-PSFs (such as full width at half maximum or the AO-cutoff frequency), but they produce perfect PSF that fail at fitting the complex structures of real AO-PSFs such as coherent speckles or multi-lobbed cores in presence of low wind effect or motion blur. With pupil segmented in multiple mirrors and fragmented by the large structures holding the secondary mirror, AO-PSFs of giant telescopes will even more suffer from these effects. To achieve the theoretical performances, it will be necessary to retrieve the 2D image of the AO-PSF in its full complexity. In this work, we present our blind deconvolution method that reconstructs the AO-PSF directly in the data of interest in the presence of sharp-edge objects, such as resolved asteroids, without any prior on the instrument. The PSF faint extensions are reconstructed with a robust penalization optimization, discarding outliers on-the-fly such as cosmic rays or defective pixels. Our methods is successfully applied to a variety of real AO-systems and simulated ELT PSFs