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Compte rendu du congrès général 2025 de la SFP à Troyes
No full textLe 27e congrès général de la Société Française de Physique s’est déroulé du 30 juin au 4 juillet 2025 à l’Université de Technologie de Troyes, dans cette belle ville champenoise. Cette édition est une première, puisque c’est la première fois qu’un congrès général de la SFP se tient dans une université de technologie
X TrA through the eyes of MATISSE: More evidence of clumpy molecular layers around C-type asymptotic giant branch stars
No full textAims. The goal of this study is to further the understanding of the wind formation mechanism in asymptotic giant branch (AGB) stars through the analysis of the close environment (within a few stellar radii) of the carbon star X TrA.
Methods. X TrA was observed for the first time with the Mid-Infrared SpectroScopic Experiment instrument (MATISSE) in the L and N bands in low spectral resolution mode (R=30), and its close surroundings were mapped in specific wavelength ranges corresponding to specific molecules (C2H2 and HCN, at 3.1 and 3.8 μm) and dust (amorphous carbon and, for example, SiC at 11.3 μm), via image reconstruction techniques.
Results. The angular diameter of the star ranges from 10 mas in the L band pseudo-continuum (3.5 μm) to 20 mas at 3.1 and 11.3 μm. The reconstructed images show some mild elongated features (along the east-west direction) and asymmetric protrusions, which are most evident around 3.1 μm. Imaging results highlight the clumpy nature of the circumstellar environment, starting from the photospheric region up to more distant layers.
Conclusions. The angular diameters found for X TrA in the image data are in agreement with previous photospheric diameter estimates (following VLTI/MIDI 8–13 μm observations), and their wavelength dependence is similar to values found for other carbon stars observed with MATISSE (R Scl and V Hya). The 3.1 μm images presented here show highly asymmetric features, another case of a C-rich star with irregular morphologies close to the stellar disk; this supports the notion that the C2H2 + HCN abundance distribution usually originates from a clumpy layer around carbon stars
The ALMA survey to Resolve exoKuiper belt Substructures (ARKS)
No full textContext. ExoKuiper belts around young A-type stars often host CO gas, whose origin is still unclear. The ALMA survey to Resolve exoKuiper belt Substructures (ARKS) includes six of these gas-bearing belts, to characterise their dust and gas distributions and investigate the gas origin.
Aims. As part of ARKS, we observed the gas-rich system HD 121617 with a 0⋅′′ 12 (14 au) resolution and discovered an arc of enhanced dust density. In this paper, we analyse in detail the dust and gas distributions and the gas kinematics of this system.
Methods. We extracted radial and azimuthal profiles of the dust (in the millimetre and near-infrared) and gas emission (12CO and 13CO) from reconstructed images. To constrain the morphology of the arc, we fitted an asymmetric model to the dust emission. To characterise the gas kinematics, we fitted a Keplerian model to the velocity map and extracted the gas azimuthal velocity profile by deprojecting the data.
Results. We find that the dust arc is narrow (1–5 au wide at a radius of 75 au), azimuthally extended with a full width at half maximum of ~90°, and asymmetric; the emission is more azimuthally compact in the direction of the system’s rotation, and represents 13% of the total dust mass (0.2 M⊕). From analysis of the scattered light and CO images, we conclude that the arc is much less pronounced or absent for small grains and gas. Finally, we find strong non-Keplerian azimuthal velocities at the inner and outer wings of the ring, as was expected due to strong pressure gradients.
Conclusions. The dust arc resembles the asymmetries found in protoplanetary discs, often interpreted as the result of dust trapping in vortices. If the gas disc mass is high enough (≳20 M⊕, requiring a primordial gas origin), both the radial confinement of the ring and the azimuthal arc may result from dust grains responding to gas drag. Alternatively, it could result from planet-disc interactions via mean motion resonances. Further studies should test these hypotheses and may provide a dynamical gas mass estimate in this CO-rich exoKuiper belt
X-ray properties of RR Lyrae and Cepheid variables from eROSITA
No full textWe present a search for X-ray counterparts to RR Lyrae and Cepheid variables using data from the first eROSITA all-sky survey. We identify seven RR Lyrae and eight Cepheid variables with positional matches to X-ray sources. While most Cepheid associations appear reliable, the RR Lyrae matches are predominantly spurious. Only one source, OGLE-BLG-RRLYR-00252, appears to be a plausible RR Lyrae detection, potentially representing the first observational evidence of X-ray emission from a star of this type. Its inferred luminosity suggests that RR Lyrae stars are intrinsically at least two orders of magnitude fainter in X-rays than the brightest Cepheids. We also observe a tentative increase in X-ray luminosity with pulsation period among classical Cepheids, and higher luminosities in type II Cepheids at comparable periods. These trends may reflect intrinsic differences in atmospheric structure and shock efficiency, offering new insight into the mechanisms driving high-energy emission in pulsating stars
Boosting decision trees for the selection of main belt asteroids in planetary ephemerides: An alternative model
No full textContext. One of the main bottlenecks in assessing the accuracy of the Mars orbit is the unknown value of the asteroids in the main asteroid belt. A modeling with 343 asteroids as point masses is used today, with the relative masses fit to observational data.
Aims. We propose an innovative method for reducing the number of asteroids implemented as point masses, which in turn reduces the number of parameters to be fit without a significant degradation of the postfit residuals.
Methods. We used boosting decision trees to obtain a ranking by relative importance of the 343 asteroids of the current main belt modeling.
Results. We were able to remove more than 100 of these asteroids without significantly degrading the postfit residuals and with a significant improvement of the uncertainties. Furthermore, we verified that the postfit masses found with the new modeling (INPOP25c) are consistent with respect to the mass estimation from an independent approach by means of the albedo properties of the asteroids
Null infinity as
No full textThis paper studies the quantization of the future null infinity () of an asymptotically flat spacetime. Based on the observation by Ashtekar and Speziale that can be regarded as an extremal weakly isolated horizon, we extend the quantization framework developed for weakly isolated horizon to quantize . We first show that the symplectic structure of is equivalent to the sum of the symplectic structures of two SU(2) Chern–Simons theories with opposite levels. Based on this observation, we apply Chern–Simons quantization approach to quantize . Finally, we compute the entropy of by counting the microstates, showing that it is proportional to the area of , a spacelike cross-section of . Our result is consistent with the universal entropy formula in the framework of (weakly) isolated horizon
Quasinormal spectra of a wormhole family: overtone features and a parameter-controlled redshift
No full textThough investigated extensively in the past, we take a detailed relook at the study of quasinormal modes (QNM) in a known family of wormholes (ultrastatic (), as well as spacetimes with different, non-constant ), which includes the familiar Bronnikov–Ellis spacetime as a special case. Our focus here is to go beyond the fundamental mode and obtain some of the QNM overtones using a suitable numerical scheme. Scalar and axial gravitational QNMs including two or three overtones are obtained for the family of ultrastatic geometries and their parameter dependencies are shown explicitly. Further, we comment on how (a) the overtones may influence the time-domain profile in a perturbation and (b) in what sense, the use of overtones may help in distinguishing between different geometries within the family. Finally, we show how an effect somewhat similar to the so-called ‘environment induced redshift’ of QNMs, introduced recently (Pezzella et al. in Phys Rev D 111:064026, 2025), may be obtained for spacetimes with non-constant , via an appropriate tuning of available metric parameters which systematically modify the shapes of the effective potentials arising in the perturbation equations
Quasinormal modes and greybody factors of black holes corrected by nonlinear electrodynamics
No full textCan models that are degenerate in electromagnetic observations (i.e., having identical shadows) be distinguished by their dynamical behaviors and quantum radiation properties? To address this question, this paper considers a unique charged black hole with logarithmic term corrections in NED (Mazharimousavi in Phys Lett B 841:137948, 2023, https://doi.org/10.1016/j.physletb.2023.13794
The coupled tidal evolution of the moons and spins of warm exoplanets
No full textContext. The Solar System giant planets harbor a wide variety of moons. Among them, the largest moons have moon-to-planet mass ratios of the order of 10−4. Moons around exoplanets are plausibly similarly abundant, even though most of them are likely too small to be easily detectable with modern instruments. Moons are known to affect the long-term dynamics of the spin of their host planets; however, their influence on warm exoplanets (i.e. with moderately short periods of about 10 to 200 days), which undergo significant star–planet tidal dissipation, is still unclear.
Aims. Here, we study the coupled dynamical evolution of exomoons and the spin dynamics of their host planets, focusing on warm exoplanets.
Methods. Analytical criteria give the relevant dynamical regimes at play as a function of the system’s parameters. Possible evolution tracks mostly depend on the hierarchy of timescales between the star–planet and the moon-planet tidal dissipations. We illustrate the variety of possible trajectories using self-consistent numerical simulations.
Results. We find two principal results: i) Due to star–planet tidal dissipation, a substantial fraction of warm exoplanets naturally evolve through a phase of instability for the moon’s orbit (the ‘Laplace plane’ instability). Many warm exoplanets may have lost their moon(s) through this process. ii) Surviving moons slowly migrate inwards due to the moon-planet tidal dissipation until they are disrupted below the Roche limit. During their last migration stage, moons – even small ones – eject planets from their tidal spin equilibrium. Planets can then converge back to this equilibrium or adopt a new one with a low or high obliquity. Additionally, before their disruption, massive exomoons (with moon-to-planet mass ratios of the order of 10−2) can maintain their planet in a long-lived high-obliquity state.
Conclusions. The loss of moons through the Laplace plane instability may contribute to disfavor the detection of moons around close-in exoplanets. Moreover, moons (even those that have been lost) play a critical role in the final obliquities of warm exoplanets. Hence, the existence of exomoons poses a serious challenge in predicting the present-day obliquities of observed exoplanets
Consensus-based algorithm for the nonparametric detection of star clusters (CANDiSC)
No full textContext. The VISTA Variables in the Vía Láctea (VVV) and its eXtension (VVVX) are near-infrared surveys mapping the Galactic bulge and adjacent disk. These datasets have enabled the discovery of numerous star clusters obscured by high and spatially variable extinction. However, most previous searches relied on visual inspection of individual tiles, which is inefficient and biased against faint or low-density systems.
Aims. We aim to develop an automated, homogeneous algorithm for systematic cluster detection across different surveys. Here, we aim to apply our method to VVVX data covering low-latitude regions of the Galactic bulge and disk, affected by extinction and crowding.
Methods. We introduce the Consensus-based Algorithm for Nonparametric Detection of Star Clusters (CANDiSC), which integrates kernel-density estimation (KDE), Density-Based Spatial Clustering of Applications with Noise (DBSCAN), and nearest-neighbor density estimation (NNDE) within a consensus framework. A stellar overdensity is classified as a candidate if identified by at least two of these methods. We applied CANDiSC to 680 tiles in the VVVX PSF photometric catalogue, covering ≈ 1100, deg2.
Results. We detect 163 stellar overdensities, of which 118 are known clusters. Cross-matching with recen catalogues yields five additional matches, leaving 40 likely new candidates absent from existing compilations. The estimated false-positive rate is below 5%.
Conclusions. CANDiSC offers a robust and scalable approach for detecting stellar clusters in deep, near-infrared surveys, successfully recovering known systems and revealing new candidates in the obscured and crowded regions of the Galactic plane