Jerome Berthier

Context . Large photometric surveys provide sparse multiband photometry for millions of Solar System objects (SSOs), offering an opportunity to jointly constrain their physical and compositional properties. However, current phase-function models do not account for rotational variability, limiting their ability to retrieve accurate parameters. Similarly, methods that recover shape and rotational parameters remain both computationally and observationally expensive, making the extraction of such properties prohibitive at scale. Aims . We aim to develop a model capable of simultaneously retrieving the absolute magnitude, phase parameters, spin state, and shape proportions of SSOs from sparse photometric data, while remaining computationally efficient for large datasets. Methods . We introduce the Shape, orientation, and colors-combined approach for asteroids (SOCCA), which extends the HG ₁ G ₂ formalism by incorporating the projected surface of a rotating triaxial ellipsoid. The model jointly fits multiband photometry and includes a dedicated treatment of rotational period determination. Results . We implemented the model on a ten-year Legacy Survey of Space and Time (LS ST) simulation as well as on real data of the asteroid (45) Eugenia for validation purposes. SOCCA significantly improves the fit to photometric data, reducing the mean residuals to half, compared to previous models. It retrieves the absolute magnitude with a scatter about three times smaller than existing approaches and improves the determination of phase parameters by a similar factor. It also recovers the sidereal rotation period, spin-axis orientation, and the axis ratios of the best fitting ellipsoid. The inclusion of shape and rotation increases the number of physically meaningful solutions by ~10–20% per filter, leading to an overall success rate of 53%. Conclusions . By combining phase, shape, and rotational information in a single model, SOCCA provides a more complete physical description of SSOs from sparse photometry. Its performance and scalability make it well suited for current and upcoming large surveys such as the Zwicky Transient Facility and the recently launched LS ST.

Context . Detecting and characterizing the atmosphere of rocky planets in the habitable zone is a key objective of exoplanet research in the era of JWST and the upcoming E-ELT. Spectroscopy of a planetary transit is the primary method of obtaining a transmission spectrum of an exoplanetary atmosphere. A lunar eclipse is a natural proxy for an Earth transit, offering a unique opportunity to study Earth’s atmosphere as if it were an exoplanet. Aims . This work aims to derive the empirical, wavelength-dependent effective height of Earth’s atmosphere in the near-infrared, spanning the Y to K bands. Methods . During a lunar eclipse, the penumbra – the region where the Sun is partially occulted by the Earth – contains the signature of the transmission spectrum of the atmosphere along Earth’s limb. The high-resolution (R=70 000) SPIRou spectrograph at CFHT was used to collect spectra during and after the November 19, 2021 eclipse. Two distinct methods, using either one or two penumbral spectra, were employed to derive the effective height of the atmosphere. Each method was evaluated in the context of distinct astrometric and spectrophotometric approaches. Results . The derived effective height spans 964 to 2498 nm and shows the absorption bands of H ₂ O, O ₂ , CH ₄ , and CO ₂ peaking at up to 29.6 km at a spectral resolution of R=70 000, including a 12.7 km offset defining a reference altitude taken from a transit model. The uncertainty assessed from individual penumbra observations and from uncertainties on telluric lines correction and Moon reflectance is found to be 3 σ ≈ 3.6 km. Heights are up to 25.1 km at a convolved resolution of R=1000. Conclusions . The measured heights are in good agreement with theoretical predictions. The high-resolution wavelength-dependent effective heights are made publicly available to the community.

Context . Understanding the rotational periods of asteroids is crucial for gaining insights into their internal structures, compositions, and collisional histories. NASA’s Kepler Space Telescope, during its K2 extension (2014-2018), serendipitously observed numerous asteroids while surveying the ecliptic plane, providing a unique photometric dataset. Aims . By analyzing photometric data from the K2 mission, we aimed to determine the rotational periods of asteroids that crossed Kepler ’s field of view, focusing on objects with an apparent magnitude of 19 or brighter that appeared in the Kepler target pixel files at least ten times. Methods . We developed an algorithm to identify asteroid crossings in the Kepler data and extract photometric light curves. The Lomb–Scargle periodogram method was employed to determine the rotational periods from the extracted light curves due to its robustness in handling unevenly sampled data. Noise and systematic errors were mitigated through photometric corrections using co-trending basis vectors. Results . We extracted and analyzed 4,596 light curves from 2,418 asteroids observed during the Kepler /K2 mission. This allowed us to compute rotation periods for 559 asteroids. We found that 375 of these asteroids had previously known periods. The rotation periods determined for 295 of the asteroids in this study agree with existing asteroid rotation periods from the literature, validating our approach. We report new rotation periods and their light curve amplitudes for 184 asteroids, expanding the catalog of known asteroid rotation periods. Conclusions . The analysis of rotation periods from the Kepler K2 mission data has provided valuable insights into the physical characteristics of main-belt asteroids. Our results are consistent with existing data and expand the catalog of known asteroid rotation periods. These findings contribute to our understanding of asteroid dynamics and will aid future research in planetary science and asteroid exploration.

Context. No less than 15% of large asteroids (with diameters greater than 140 km) have satellites. The commonly accepted mechanism for their formation is post-impact reaccumulation. However, the detailed physical and dynamical properties of these systems are not well understood, and many of them have not been studied in detail. Aims. We studied the population of large binary asteroid systems, in part through the characterization of (283) Emma and (762) Pulcova. To do so, we compared the gravitational fields predicted from the shape of the primary body with the non-Keplerian gravitational components identified in orbital models of the satellites of each system. We contextualize these systems in the greater population of large binary systems, thus providing clues to asteroid satellite formation. Methods. We reduced all historical high angular resolution adaptive optics (AO) images from ground-based telescopes to conduct astrometric and photometric measurements of each system’s components. We then determined orbital solutions for each system using the genoid algorithm. We modeled the shapes of the system primaries using light curve-inversion techniques scaled with stellar occultations and AO images, and we developed internal structure models using SHTOOLS. Finally, we compared the distribution of the physical and orbital properties of the known binary asteroid systems. Results. We find a very low residual orbital solution for Emma with a gravitational quadrupole J₂ value that is significantly lower than expected from the shape model, implying that Emma has a significantly nonhomogeneous internal structure, and an overall bulk density of 0.9 ± 0.3 g cm-3⁻³. The circular co-planar orbit of Pulcova’s satellite leaves substantial ambiguity in the orbital solution. We also find that the differences between these systems reflect an overall dichotomy within the population of large binary systems, with a strong correlation between primary elongation and satellite eccentricity observed in one group. Conclusions. We determine that there may be two distinct formation pathways influencing the end-state dichotomy in these binary systems, and that (762) Pulcova and (283) Emma belong to the two separate groups.

The current standard model of cosmology successfully describes a variety of measurements, but the nature of its main ingredients, dark matter and dark energy, remains unknown. Euclid is a medium-class mission in the Cosmic Vision 2015–2025 programme of the European Space Agency (ESA) that will provide high-resolution optical imaging, as well as near-infrared imaging and spectroscopy, over about 14 000 deg² of extragalactic sky. In addition to accurate weak lensing and clustering measurements that probe structure formation over half of the age of the Universe, its primary probes for cosmology, these exquisite data will enable a wide range of science. This paper provides a high-level overview of the mission, summarising the survey characteristics, the various data-processing steps, and data products. We also highlight the main science objectives and expected performance.

Context. Large sky surveys provide numerous non-targeted observations of small bodies of the Solar System. The upcoming LSST of the Vera C. Rubin Observatory will be the largest source of small body photometry in the next decade. With non-coordinated epochs of observation, colors – and therefore taxonomy and composition – can only be computed by comparing absolute magnitudes obtained in each filter by solving the phase function (evolution of brightness of the small body against the solar phase angle). Current models in use in the community (HG, HG₁₂^*, and HG₁G₂), however, fail to reproduce the long-term photometry of many targets due to the change in the aspect angle between apparitions. Aims. We aim to derive a generic yet simple phase function model accounting for the variable geometry of the small bodies over multiple apparitions. Methods. As a spinoff of the HG₁ G₂ model, we propose the sHG₁G₂ phase function model in which we introduce a term describing the brightness changes due to spin orientation and polar oblateness. We applied this new model to 13 245 908 observations of 122 675 Solar System objects (SSOs). These observations were acquired in the g and r filters with the Zwicky Transient Facility between November 1, 2019 and December 1, 2023. We retrieved them and implemented the new sHG₁G₂ model in FINK, a broker of alerts designed for the LSST. Results. The sHG₁G₂ model leads to smaller residuals than other phase function models, providing a better description of the photometry of asteroids. We determined the absolute magnitude, H, and phase function coefficients (G₁, G₂) in each filter, the spin orientation (α₀, δ₀), and the polar-to-equatorial oblateness, R, for 95 593 SSOs, which constitutes about a tenfold increase in the number of characterized objects compared to the current census. Conclusions. The application of the sHG₁ G₂ model to ZTF alert data using the FINK broker shows that the model is appropriate for extracting physical properties of asteroids from multi-band and sparse photometry, such as the forthcoming LSST survey.

Context. Gravitational waves from black-hole (BH) merging events have revealed a population of extra-galactic BHs residing in short-period binaries with masses that are higher than expected based on most stellar evolution models – and also higher than known stellar-origin black holes in our Galaxy. It has been proposed that those high-mass BHs are the remnants of massive metal-poor stars. Aims. Gaia astrometry is expected to uncover many Galactic wide-binary systems containing dormant BHs, which may not have been detected before. The study of this population will provide new information on the BH-mass distribution in binaries and shed light on their formation mechanisms and progenitors. Methods. As part of the validation efforts in preparation for the fourth Gaia data release (DR4), we analysed the preliminary astrometric binary solutions, obtained by the Gaia Non-Single Star pipeline, to verify their significance and to minimise false-detection rates in high-mass-function orbital solutions. Results. The astrometric binary solution of one source, Gaia BH3, implies the presence of a 32.70 ± 0.82 M_⊙ BH in a binary system with a period of 11.6 yr. Gaia radial velocities independently validate the astrometric orbit. Broad-band photometric and spectroscopic data show that the visible component is an old, very metal-poor giant of the Galactic halo, at a distance of 590 pc. Conclusions. The BH in the Gaia BH3 system is more massive than any other Galactic stellar-origin BH known thus far. The low metallicity of the star companion supports the scenario that metal-poor massive stars are progenitors of the high-mass BHs detected by gravitational-wave telescopes. The Galactic orbit of the system and its metallicity indicate that it might belong to the Sequoia halo substructure. Alternatively, and more plausibly, it could belong to the ED-2 stream, which likely originated from a globular cluster that had been disrupted by the Milky Way.

Context. Strongly lensed quasars are fundamental sources for cosmology. TheGaiaspace mission covers the entire sky with the unprecedented resolution of 0.18″ in the optical, making it an ideal instrument to search for gravitational lenses down to the limiting magnitude of 21. Nevertheless, the previousGaiaData Releases are known to be incomplete for small angular separations such as those expected for most lenses.Aims. We present the Data Processing and Analysis Consortium GravLens pipeline, which was built to analyse allGaiadetections around quasars and to cluster them into sources, thus producing a catalogue of secondary sources around each quasar. We analysed the resulting catalogue to produce scores that indicate source configurations that are compatible with strongly lensed quasars.Methods. GravLens uses the DBSCAN unsupervised clustering algorithm to detect sources around quasars. The resulting catalogue of multiplets is then analysed with several methods to identify potential gravitational lenses. We developed and applied an outlier scoring method, a comparison between the average BP and RP spectra of the components, and we also used an extremely randomised tree algorithm. These methods produce scores to identify the most probable configurations and to establish a list of lens candidates.Results. We analysed the environment of 3 760 032 quasars. A total of 4 760 920 sources, including the quasars, were found within 6″ of the quasar positions. This list is given in theGaiaarchive. In 87% of cases, the quasar remains a single source, and in 501 385 cases neighbouring sources were detected. We propose a list of 381 lensed candidates, of which we identified 49 as the most promising ones. Beyond these candidates, the associate tables in this Focused Product Release allow the entire community to explore the uniqueGaiadata for strong lensing studies further.

In the absence of any visible solid surface, the rotation period of the giant planets has been inferred from periodic phenomena tied to the magnetic field produced in their deep interior. The main method relied on remote radio auroral observations, sometimes complemented by in situ magnetic measurements. For Uranus, such measurements acquired during the Voyager 2 flyby in 1986 yielded a rotation period of 17.24±0.01h¹. This fundamental planetary parameter, referenced since then by the International Astronomical Union, is the basis of the Uranian longitude model². Still, the period uncertainty limits its validity to a few years, after which the orientation of the magnetic axis was lost. Here, we use a novel approach, based on the long term (2011-2022) tracking of Uranus’ magnetic poles from Hubble Space Telescope images of its ultraviolet aurorae, to achieve a new rotation period of 17.247864±0.000010h. It is consistent with, although 28s longer than, the Voyager 2 period. This much more precise determination leads to a new longitude model now valid over decades, from before the Voyager 2 epoch up to the arrival of any future Uranus mission. It also has strong direct implications on formation scenarios, interior models, dynamo theories and studies of the magnetosphere. This novel approach stands as an alternate method to determine the rotation rate of any object hosting a magnetosphere and rotationally modulated aurorae, in our solar system and beyond.