arXiv subjects

S. Mercier

Publications and source records attributed to S. Mercier.

4 recordsLinked to original sources

arXiv2025

MANGOS II: Five new giant planets orbiting low-mass stars

Giant planets orbiting low-mass stars on short orbits present a conundrum, as in the most extreme cases their existence cannot be reconciled with current models of core accretion. Therefore, surveys dedicated to finding these rare planets have a key role to play by growing the sample to overcome small number statistics. In this work we present MANGOS, a programme dedicated to the search for giant objects (planets, brown dwarfs, and low-mass stars) orbiting M dwarfs. We report on the discovery of five new giant planets (TOI-3288 Ab, TOI-4666 b, TOI-5007 b, TOI-5292 Ab, TOI-5916 b) first detected by TESS, and confirmed using ground-based photometry and spectroscopy. The five planets have radii in the range 0.99-1.12 $\mathrm{R_{Jup}}$, masses between 0.49--1.69~$\mathrm{M_{Jup}}$, and orbital periods between 1.43 and 2.91 days. We reveal that TOI-3288 and TOI-5292 are wide binaries, and in the case of TOI-5292 we are able to characterise both stellar components. We demonstrate that the planets presented are suitable for further characterisation of their obliquities and atmospheres. We detect a small but significant eccentricity for TOI-5007 b, although for this to be more robust, more observations are needed to fully sample the orbit. Finally, we reveal a correlation between stellar metallicity and planet bulk density for giant planets orbiting low-mass stars.

astro-ph.EP↗

arXiv2025

The effect of stellar magnetic activity on measurements of morning and evening asymmetry of planetary terminator

Differences in the ingress and egress shapes of transit light curves can indicate morning-evening temperature contrasts on transiting planets. Here, we pinpoint an alternative mechanism that can introduce asymmetries in transit light curves, potentially affecting the accurate determination of morning-evening differences. Small-scale magnetic field concentrations on the surfaces of the host star affect the visibility of stellar limb regions, making them brighter relative to the non-magnetic case. A difference in magnetization between the star's western and eastern limbs can thus create an asymmetry in limb brightness and, consequently, an asymmetry between transit ingress and egress. We model the limb darkening and stellar limb asymmetry in solar-like stars using the 3D radiative MHD code MURaM to simulate magnetized stellar atmospheres and the MPS-ATLAS code to synthesize spectra using ray-by-ray approach. Our results show that ingress-egress depth differences can reach up to 600 ppm for a 10000 ppm transit at 600 nm, depending on the magnetization of the stellar limbs--significantly interfering with planetary signals. Observations of the Sun show that such concentrations are often not accompanied by spots and do not manifest in photometric variability, indicating that even photometrically quiet stars can produce such asymmetries. However, planetary and stellar asymmetries exhibit distinct wavelength dependencies, which we propose to leverage for disentangling them.

astro-ph.SR↗

arXiv2024

The ANTARESS workflow I. Optimal extraction of spatially resolved stellar spectra with high-resolution transit spectroscopy

High-resolution spectrographs open a detailed window onto the atmospheres of stars and planets. As the number of systems observed with different instruments grows, it is crucial to develop a standard in analyzing spectral time series of exoplanet transits and occultations, for the benefit of reproducibility. Here, we introduce the ANTARESS workflow, a set of methods aimed at processing high-resolution spectroscopy datasets in a robust way and extracting accurate exoplanetary and stellar spectra. While a fast preliminary analysis can be run on order-merged 1D spectra and cross-correlation functions (CCFs), the workflow was optimally designed for extracted 2D echelle spectra to remain close to the original detector counts, limit the spectral resampling, and propagate the correlated noise. Input data from multiple instruments and epochs were corrected for relevant environmental and instrumental effects, processed homogeneously, and analyzed independently or jointly. In this first paper, we show how planet-occulted stellar spectra extracted along the transit chord and cleaned from planetary contamination provide a direct comparison with theoretical stellar models and enable a spectral and spatial mapping of the photosphere. We illustrate this application of the workflow to archival ESPRESSO data, using the Rossiter-McLaughlin effect Revolutions (RMR) technique to confirm the spin-orbit alignment of HD\,209458b and unveil biases in WASP-76b's published orbital architecture. Because the workflow is modular and its concepts are general, it can support new methods and be extended to additional spectrographs to find a range of applications beyond the proposed scope. In a companion paper, we will present how planet-occulted spectra can be processed further to extract and analyze planetary spectra decontaminated from the star, providing clean and direct measurements of atmospheric properties.

astro-ph.EP↗

arXiv2022

Fill in Fabrics: Body-Aware Self-Supervised Inpainting for Image-Based Virtual Try-On

Previous virtual try-on methods usually focus on aligning a clothing item with a person, limiting their ability to exploit the complex pose, shape and skin color of the person, as well as the overall structure of the clothing, which is vital to photo-realistic virtual try-on. To address this potential weakness, we propose a fill in fabrics (FIFA) model, a self-supervised conditional generative adversarial network based framework comprised of a Fabricator and a unified virtual try-on pipeline with a Segmenter, Warper and Fuser. The Fabricator aims to reconstruct the clothing image when provided with a masked clothing as input, and learns the overall structure of the clothing by filling in fabrics. A virtual try-on pipeline is then trained by transferring the learned representations from the Fabricator to Warper in an effort to warp and refine the target clothing. We also propose to use a multi-scale structural constraint to enforce global context at multiple scales while warping the target clothing to better fit the pose and shape of the person. Extensive experiments demonstrate that our FIFA model achieves state-of-the-art results on the standard VITON dataset for virtual try-on of clothing items, and is shown to be effective at handling complex poses and retaining the texture and embroidery of the clothing.

cs.CV↗