Neda Heidari

Context. Exoplanetary magnetic fields govern atmospheric escape and circulation but have eluded detection in close-in planets. In the ultra-hot Jupiter KELT-9b, atmospheric dynamo is predicted to generate atmospheric fields of 400−4000 G. Aims. We searched for the circular polarization in atomic lines that a magnetic field would imprint, through the Zeeman effect, on the transmission spectrum of KELT-9b. Methods. We observed three transits with SPIRou at the CFHT, on 07 September 2025 and 03 and 06 July 2026, and applied least squares deconvolution to 1398 atomic lines to map the transit-averaged Stokes V and null spectra against the orbital semi-amplitude, K _p , and systemic velocity, v _sys . Results. The 2025 transit shows a Stokes V signature of V / I _c = 9.3 × 10 ⁻⁵ at K _p = 219 ± 11 km s ⁻¹ , v = −34.0 ± 1.2 km s ⁻¹ , close to the expected planetary velocity. Its false-alarm probability is 1.9 × 10 ⁻⁴ , and thus it is formally a marginal detection. Both 2026 transits are of comparable sensitivity but neither exhibits a signal at that location, setting 3 σ limits of 4.9 and 6.0 × 10 ⁻⁵ ; the 2025 amplitude would have been recovered at 4.9 σ and 4.0 σ . Conclusions. The 2025 signature is robust to the tests we applied to it but qualifies as a marginal detection at best. Spurious signals of comparable strengths occur elsewhere in our Stokes V and null maps, and we cannot rule out that our marginal detection is excess noise. It is not reproduced ten months later.

We present a comprehensive reanalysis of two star-planet systems: TOI-4438, an M3.5V star hosting a mini-Neptune in a 7.4-day orbit, and TOI-442, an M1V star with a 4-day period planet located within the hot Neptune desert. Both systems were originally identified as transiting planet candidates by the Transiting Exoplanet Survey Satellite (TESS) and subsequently validated through the radial velocity (RV) method. Our work incorporates new TESS transit data and high-resolution spectroscopy from the SPIRou near-infrared spectropolarimeter. We detected a persistent and relatively strong Zeeman signature in TOI-442, while TOI-4438 exhibits weaker and intermittent magnetic activity, and we inferred the stellar rotation periods of both stars from the variability of the longitudinal magnetic field. We jointly fit photometry and RV models for each system. For TOI-4438 b we combined archival CARMENES data with 81 SPIRou observations and five TESS sectors. This yielded a refined planetary mass of M _p = 4.11 ^+0.40 _−0.38 M _⊕ and a radius of R _p = 2.40 ^+0.09 _−0.10 R _⊕ , consistent with the previous estimate within 1.1 σ while improving by 53% the precision on the mass and 22% on the radius. For TOI-442 b, we added 29 SPIRou RV measurements to an extensive archival dataset, significantly extending the temporal baseline. Incorporating this with a new TESS sector, we tighten the constraints on the planetary mass to M _p = 28.38 ^+0.77 _−0.73 M _⊕ and radius to R _p = 4.25 ^+0.10 _−0.08 R _⊕ , which agrees with the previous values within 1.5 σ and improves the precisions by 46 and 67%, respectively. We found no clear signs of additional planets in the currently available RV data, although we detected a single-transit event in the TOI-4438 light curve. We compared various RV models and found that those accounting for stellar variability-induced signals yield improved constraints on the planetary parameters.

Context . Following the 2022 alert of a TESS object of interest transiting TOI-5624 (a G7 V star ∼ 100 pc away), a CHEOPS campaign in 2023 detected four planetary signals at P _b ≈ 3.4, P _c ≈ 7.9, P _d ≈ 13.7, and P _e ≈ 21.5 days. These signals were later confirmed by additional TESS and CHEOPS photometry in 2024-2025. Aims . By using TESS and CHEOPS photometry, along with HARPS-N and SOPHIE high-resolution spectra, we determined the planet properties and performed a dynamical analysis of the system. Methods . After analysing the photometric data, we extracted and modelled the radial velocity (RV) time series using two independent methodologies, both within a Markov chain Monte Carlo framework. We further integrated the N -body equations of motion, while simultaneously fitting the transit times and the detrended RVs, to dynamically characterise the system. Results . We present the discovery of four transiting sub-Neptunes with radii of R _b = 2.314 ± 0.035 R _⊕ , R _c = 2.474 ± 0.042 R _⊕ , R _d = 3.584 _−0.050 ^+0.051 R _⊕ , and R _e = 3.247 _−0.043 ^+0.042 R _⊕ , along with masses of M _b = 9.4 ± 1.4 M _⊕ , M _c = 4.8 ± 1.9 M _⊕ , Md = 4.9 ± 2.2 M _⊕ , and M _e = 8.9 _−3.0 ^+2.9 M _⊕ . Our photometric analysis revealed that the outermost transiting planet TOI-5624e shows significant transit-timing variations (TTVs). Indeed, we found a robust Keplerian signal in the RV time series close to the 2:1 period commensurability with TOI-5624 e, which explains the TTV pattern exhibited by TOI-5624 e according to our dynamical analysis. We labelled this non-transiting planet as TOI-5624 f and determined its minimum mass to be M _f sin i _f = 13.0 ± 3.7 M _⊕ . Conclusions . Among the known systems hosting more than four planets, the remarkable precision with which the radii have been measured (3σ) of the mass for at least three planets has previously been reached only for TRAPPIST-1. Additional photometric observations will enable a better sample of the TTV modulation and a more robust dynamical determination of the masses.

We present the TESS-based discoveries of planetary systems orbiting the late G dwarfs TOI-2494 and TOI-5143, each of which harbors a hot giant planet and a smaller interior planet. TOI-2494 hosts a transiting mini-Neptune ( P = 2.41 days, R P = 2.3 5 − 0.15 + 0.16 R _⊕ ) and a hot Saturn ( P = 8.38 days) with grazing transits, while TOI-5143 hosts a transiting mini-Neptune ( P = 2.38 days, R P = 2.7 3 − 0.17 + 0.19 R _⊕ ) and a hot Jupiter ( P = 5.21 days) with grazing transits. We measure the masses of TOI-2494 c (80 ± 19 M _⊕ ) and TOI-5143 c (208 ± 14 M _⊕ ), place upper limits on the masses of the smaller planets, and explore the architectures of the planetary systems. TOI-2494 c and TOI-5143 c join a small but growing number of short-period giant planets known to be flanked by smaller companions. While the absence of close neighbors to most hot Jupiters would be consistent with disruptive dynamical evolution, the presence of nearby small planets in some hot Jupiter systems points to a separate, dynamically quiet formation pathway. In support of this conclusion, we present preliminary evidence that hot giant planets with small nearby companions tend to have low mutual orbital inclinations, consistent with the mutual inclination distribution of the dynamically quiet population of compact systems of multiple super-Earths and mini-Neptunes.

Surmonter l'impact de l'activité stellaire sur la détection et caractérisation d'exoplanètes : application au suivi de candidats TESS avec le spectrographe SOPHIE: Les exoplanètes de faible masse, c'est-à-dire celles ayant une masse inférieure à 30 masses terrestres, ont des compositions très différentes.Leur densité apparente, obtenue à partir de la vitesse radiale et des données photométriques, va des super-Terres rocheuses massives avec un noyau riche en fer aux "super-puffs", des objets de faible densité avec des atmosphères gazeuses épaisses.Les compositions très diversifiées de ces planètes soulèvent plusieurs questions pour les théories de perte atmosphérique et de formation planétaire.Notre capacité à y répondre est actuellement limitée par le nombre restreint de planètes de faible masse dont les propriétés fondamentales ont été précisément caractérisées.L'objectif de cette thèse est d'étudier la diversité des compositions des planètes de faible masse, en augmentant l'échantillon de planètes précisément caractérisées et en faisant le lien entre les observations et les trajectoires de formation de ces corps.Plus particulièrement, dans cette thèse, je surmonte deux défis : 1. les limitations instrumentales, en améliorant la réduction et le traitement des données et (2) la détection de planètes de faible masse et leur caractérisation.Lorsque l'on utilise la méthode des vitesses radiales, un système de réduction de données très précis et capable de traiter les éventuelles sources d'erreurs systématiques est nécessaire pour atteindre la limite instrumentale.Je me suis donc d'abord concentrée sur la résolution de problèmes et l'amélioration du logiciel de réduction de données SOPHIE (DRS). J'ai mis à jour le code de la DRS vers la dernière version du logiciel Python et y ai ajouté plusieurs nouvelles fonctionnalités, notamment corriger de l'effet de dispersion atmosphérique, fixer le nombre de lignes de masque à différentes époques, optimiser la variation à long terme à partir du point zéro, optimiser la détection de détection des spectres contaminer par le spectre du Soleil et la corriger de la contamination de fond de la lampe d'étalonnage. Ces améliorations logicielles ont permis de réduire de 22 cm/s en moyenne la dispersion des mesures en VRs, et de 18,57 m/s en moyenne la dispersion de la mesure de la largeur à mi-hauteur des raies (voir le chapitre 2 de cette thèse). Ensuite, j'ai entrepris la détection et la caractérisation de planète de faible masse.D'une part, j'ai analysé les données photométriques disponibles et les vitesses radiales des cibles du sous-programme 1 de SOPHIE (SP1), un programme dédié à la détections de planètes de faible masse. Mon objectif principal, grâce à l'analyse des données spectroscopiques, était de détecter des signaux périodiques significatifs dans les données de vitesse radiale et d'étudier une variété d'indicateurs d'activité stellaire, afin d'aider à confirmer la nature du signal. D'autre part, l'analyse photométrique m'a permis I) d'explorer la possible détection d'un nouveau signal planétaire dans les données TESS; II) d'étudier les variations probables de VR induites par l'activité; III) d'évaluer l'activité des étoiles hôtes des candidats planètes SOPHIE. Ces travaux ont conduit à la découverte de deux planètes en transit et de plusieurs candidats, et ont permis d'éliminer certains faux positifs (voir le chapitre 3 de cette thèse). Enfin, j'ai fait une étude générale des planètes de faible masse.J'y discute certaines questions clés de la science des exoplanètes, et de la manière dont les instruments et méthodes actuels et futurs aideront à y répondre (voir chapitre 4). Les techniques développées et les résultats rassemblés dans cette thèse contribueront grandement à la détection précise et à la bonne caractérisation des futures planètes détectées par SOPHIE. Les futures découvertes de planètes de faible masse contribueront à une meilleure compréhension de cette population.

We present the characterisation of the TOI-6041 system, a bright ( V = 9.84 ± 0.03) G7-type star hosting at least two planets. The inner planet, TOI-6041 b, is a warm Neptune with a radius of 4.55 _−0.17 ^+0.18 R _⊕ , initially identified as a single-transit event in TESS photometry. Subsequent observations with TESS and CHEOPS revealed additional transits, enabling the determination of its 26.04945 _−0.00034 ^+0.00033 orbital period and the detection of significant transit-timing variations (TTVs), exhibiting a peak-to-peak amplitude of about 1 hour. Radial-velocity (RV) measurements obtained with the APF spectrographs allowed us to place a 3 σ upper mass limit of 28.9 M _⊕ on TOI-6041 b. In addition, the RV data reveal a second companion, TOI-6041 c, on an 88 d orbit, with a minimum mass of 0.25 M _Jup . A preliminary TTV analysis suggested that the observed variations could be caused by gravitational perturbations from planet c; however, reproducing the observed amplitudes requires a relatively high eccentricity of about 0.3 for that planet. Our dynamical stability analysis indicates that such a configuration is dynamically viable and places a 1 σ upper limit on the mass of TOI-6041 c at 0.8 M _Jup . An alternative is the presence of a third, low-mass planet located between planets b and c, or on an inner orbit relative to planet b – particularly near a mean-motion resonance with planet b – which could account for the observed variations. These findings remain tentative, and further RV and photometric observations are essential in to better constrain the mass of planet b and to refine the TTV modeling, thereby improving our understanding of the system’s dynamical architecture.

Context. In the search for exoplanets using radial velocities (RV), stellar activity has become one of the main limiting factors for detectability. Fortunately, activity-induced RV signals are wavelength-dependent or chromatic, unlike planetary signals. This study exploits the broad spectral coverage provided by the combined use of SOPHIE and SPIRou velocimeters to investigate the chromatic nature of the activity signal of the highly active M dwarf EV Lac. Aims. We aim to understand the origin of the strong wavelength dependence (chromaticity) observed in the RV signal of EV Lac by selecting spectral lines based on physical properties. In particular, we explore the impact of starspots by defining the contrast effect at the level of individual lines. The Zeeman effect is also considered in this study. Methods. SPIRou and SOPHIE spectra were reduced using the line-by-line (LBL) method. We performed custom RV calculations, using groups of spectral lines selected for their sensitivity to either the spot-to-photosphere contrast or the Zeeman effect. The sensitivity of each line to the spot is defined using a two-temperature model based on PHOENIX spectra, while Landé factors were used to quantify Zeeman sensitivity. Results. We find that the spectral lines are distributed in two distinct families of contrasts, producing anti-correlated RV signals. This leads to a partial cancellation of the total RV signal, especially at longer wavelengths and provides a natural explanation for the strong chromaticity observed in EV Lac. This sign-reversal effect is demonstrated here, for the first time, on empirical data. Building on this discovery, we propose a new approach to constraining spot temperatures and to mitigating stellar activity. This will open up promising avenues for improving activity corrections and enhancing the detection of exoplanets around active M dwarfs.

Context. The search for exoplanets around nearby M dwarfs represents a crucial milestone in the census of planetary systems in the vicinity of our Solar System. Aims. Since 2018 our team has been conducting a blind search program for planets around nearby M dwarfs with the near-IR spectro-polarimeter and velocimeter SPIRou at the Canada-France-Hawaii Telescope and with the optical velocimeter SOPHIE at the Haute-Provence Observatory in France. The aim of this paper is to present our results on Gl 410, a 0.55 M_⊙ 480 ± 150 Myr old active M dwarf distant 12 pc. Methods. We searched for planetary companions using radial velocities (RVs). We used the line-by-line (LBL) technique to measure the RVs with SPIRou and the template matching method with SOPHIE. Three different methods were employed, two based on principal component analysis (PCA), to clean the SPIRou RVs for systematics. We applied Gaussian processes (GP) modeling to correct the SOPHIE RVs for stellar activity. The ℓ₁ and apodized sine periodogram analysis was used to search for planetary signals in the SPIRou data taking into account activity indicators. We analyzed TESS data and searched for planetary transits. Results. We report the detection of a M sin(i) = 8.4 ± 1.3 M_⊕ sub-Neptune planet at a period of 6.020 ± 0.004 days in circular orbit with SPIRou. The same signal, although with lower significance, was also retrieved in the SOPHIE RV data after correction for activity using a GP trained on SPIRou’s longitudinal magnetic field (B_ℓ) measurements. The TESS data indicate that the planet is not transiting. Within the SPIRou wPCA RVs, we find tentative evidence for two additional planetary signals at 2.99 and 18.7 days. Conclusions. Infrared RVs are a powerful method to detect extrasolar planets around active M dwarfs. Care should be taken, however, to correct or filter systematics generated by residuals of the telluric correction or small structures in the detector plane. The LBL technique combined with PCA offers a promising way to reach this objective. Further monitoring of Gl 410 is necessary.

Context. Wind dynamics play a pivotal role in governing transport processes within planetary atmospheres, influencing atmospheric chemistry, cloud formation, and the overall energy budget. Understanding the strength and patterns of winds is crucial for comprehensive insights into the physics of ultra-hot-Jupiter atmospheres. Current research has proposed different mechanisms that limit wind speeds in these atmospheres. Aims. This study focuses on unraveling the wind dynamics and the chemical composition in the atmosphere of the ultra-hot Jupiter TOI-1518 b. Methods. Two transit observations using the high-resolution (R_λ ∼ 85 000) optical (spectral coverage between 490 and 920 nm) spectrograph MAROON-X were obtained and analyzed to explore the chemical composition and wind dynamics using the cross-correlation techniques, global circulation models (GCMs), and atmospheric retrieval. Results. We report the detection of 14 species in the atmosphere of TOI-1518 b through cross-correlation analysis. VO was detected only with the new HyVO line list, whereas TiO was not detected. Additionally, we measured the time-varying cross-correlation trails for six different species, compared them with predictions from GCMs, and conclude that a strong drag is slowing the winds in TOI-1518 b’s atmosphere (τ_drag ≈ 10³−10⁴ s). We find that the trails are species dependent. Fe+ favors stronger drag than Fe, which we interpret as a sign of magnetic effects being responsible for the observed strong drag. Furthermore, we show that Ca+ probes layers above the Roche lobe, leading to a qualitatively different trail than the other species. Finally, We used a retrieval analysis to further characterize the abundances of the different species detected. Our analysis is refined thanks to the updated planetary mass of 1.83 ± 0.47 M_Jup we derived from new Sophie radial-velocity observations. We measure an abundance of Fe of log₁₀ Fe = −4.88_−0.76^+0.63 corresponding to 0.07 to 1.62 solar enrichment. For the other elements, the retrievals appear to be biased, probably due to the different K_p/V_sys shifts between Fe and the other elements, which we demonstrate for the case of VO.