arXiv subjects

D. Mounzer

Publications and source records attributed to D. Mounzer.

6 recordsLinked to original sources

arXiv2026

Precise measurement of WASP-31 b's Rossiter-McLaughlin effect and characterization of the planet transmission spectra

Context. Hot Jupiters are ideal natural laboratories to investigate atmospheric composition and dynamics. However, high-resolution transmission spectroscopy is currently limited by our capability of removing planet-occulted line-distortion (POLD) contamination from the signal. Aims. In this paper, we aim to characterize the transmission spectrum of WASP-31 b from two and a half transits observed with the ESPRESSO spectrograph at the VLT. Methods. The Rossiter-McLaughlin (RM) signature was analyzed using the RM "revolutions" method. Before extracting the transmission spectrum of the planet, we corrected the dataset for telluric lines using molecfit and further modeled the POLD deformations using EvE. Results. We confirm the planet low sky-projected spin-orbit angle from previous studies and further refine its value to $\lambda = -0.09^{+0.31}_{-0.32}$ deg. We do not detect any species (including previously detected species such as K or CrH) in the planetary atmosphere. In most cases the non-detections are due to the strong POLDs contamination or lack of observable lines in the ESPRESSO wavelength range, and so previous detections cannot be ruled out. Conclusions. Planet-occulted line-distortion contamination continues to be the main limitation of high-resolution transmission spectroscopy for species present in both the star and the planet, hindering atmospheric detections even with state-of-the-art models, in particular for planets with a low sky-projected spin-orbit angle. Developing advanced techniques to isolate planetary signatures is of utmost importance in the advent of ELT-like observations.

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arXiv2025

The ESPRESSO transmission spectrum of HD$\,$189733$\,$b : Extracting the planetary sodium and lithium signatures amid stellar contamination

While transmission spectroscopy has allowed us to detect many atomic and molecular species in exoplanet atmospheres, the improvement in resolution and signal-to-noise ratio enabled us to become sensitive to planet-occulted line distortions (POLDs) in the spectrum that are induced by center-to-limb variations and the Rossiter-McLaughlin effect. POLDs can bias the interpretation of the transmission spectrum, and it is difficult to correct for them with stellar models. We analyzed two ESPRESSO transits (R $\sim$ 140$\,$000) of the archetypal hot Jupiter HD$\,$189733$\,$b. The transmission spectrum of this aligned system is heavily affected by POLDs, stellar activity, and instrumental effects. It is therefore a challenging study case of how to account for these effects when the planetary signal is retrieved from chemical species through transmission spectroscopy. We confirm the previous detections of the sodium doublet signature in the upper atmosphere of HD$\,$189733$\,$b. When we accounted for POLDs and isolated the planetary signal from uncorrected stellar residuals, we found a shallower (0.432 $\pm$ 0.027 %) and more strongly blueshifted (-7.97 $\pm$ 0.28 km/s) signal. We attempted to reinterpret the other high-resolution sodium studies of this system in light of our results. We suggest that the POLDs and stellar activity are insufficiently corrected for in all analyses, including ours. We also detected a planetary lithium signature of 0.102 $\pm$ 0.016 % (6.4$\sigma$) at a blueshift of -2.4 $\pm$ 1.8 km/s.

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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.

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arXiv2023

DREAM: III.A helium survey in exoplanets on the edge of the hot Neptune desert with GIANO-B@TNG

The population of close-in exoplanets features a desert of hot Neptunes whose origin is uncertain. These planets may have lost their atmosphere, eroding into mini-Neptunes and super-Earths. Direct observations of evaporating atmospheres are essential to derive mass-loss estimates and constrain this scenario. The metastable 1083.3nm HeI triplet represents a powerful diagnostic of atmospheric evaporation since it traces the hot gas in extended exoplanet atmospheres, is observable from the ground, and is weakly affected by interstellar medium absorption. We conducted a uniform HeI transmission spectroscopy survey, focusing on 9 planets located at the edges of the Neptunian desert, aiming to gain insights into the role of photo-evaporation in its formation. We observed one transit per planet using the high-resolution, near-infrared spectrograph GIANO-B on the Telescopio Nazionale Galileo. We focused our analysis on the HeI triplet by computing high-resolution transmission spectra. We then employed the p-winds model to interpret the observed transmission spectra. We found no sign of planetary absorption in the HeI triplet in any of the investigated targets. We thus provided 3sigma upper-limit estimations on the thermosphere absorption, temperature, and mass loss, and combined them with past measurements to search for correlations with parameters thought to be drivers in the formation of the HeI triplet. Our results strengthen the importance of performing homogeneous surveys and analyses to bring clarification in the HeI detection and hence in the Neptunian desert origin. Our findings corroborate the literature expectations that the HeI absorption signal correlates with the stellar mass and the received XUV flux. However, these trends seem to disappear in terms of mass-loss rates; further studies are essential to shed light on this aspect and to understand better the photo-evaporation process.

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arXiv2023

Hot Exoplanet Atmospheres Resolved with Transit Spectroscopy (HEARTS) VIII. Nondetection of sodium in the atmosphere of the aligned planet KELT-10b

We searched for potential atmospheric species in KELT-10b, focusing on sodium doublet lines (Na i; 589 nm) and the Balmer alpha line (H $\alpha$; 656 nm) in the transmission spectrum. Furthermore, we measured the planet-orbital alignment with the spin of its host star. We used the Rossiter-McLaughlin Revolutions technique to analyze the local stellar lines occulted by the planet during its transit. We used the standard transmission spectroscopy method to probe the planetary atmosphere, including the correction for telluric lines and the Rossiter-McLaughlin effect on the spectra. We analyzed two new light curves jointly with the public photometry observations. We do not detect signals in the Na i and H $\alpha$ lines within the uncertainty of our measurements. We derive the 3-sigma upper limit of excess absorption due to the planetary atmosphere corresponding to equivalent height Rp to 1.8Rp (Na i) and 1.9Rp (H $\alpha$). The analysis of the Rossiter-McLaughlin effect yields the sky-projected spin-orbit angle of the system $\lambda$ = -5.2 $\pm$ 3.4 and the stellar projected equatorial velocity $v_{eq} \sin{i_\star}$ = 2.58 $\pm$ 0.12 km/s. Photometry results are compatible within 1 -sigma with previous studies. We found no evidence of Na i and H $\alpha$, within the precision of our data, in the atmosphere of KELT-10b. Our detection limits allow us to rule out the presence of neutral sodium or excited hydrogen in an escaping extended atmosphere around KELT-10b. We cannot confirm the previous detection of Na i at lower altitudes with VLT/UVES. We note, however, that the Rossiter-McLaughlin effect impacts the transmission spectrum on a smaller scale than the previous detection with UVES. Analysis of the planet-occulted stellar lines shows the sky-projected alignment of the system, which is likely truly aligned due to tidal interactions of the planet with its cool (Teff < 6250 K) host star.

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arXiv2022

Detection of barium in the atmospheres of the ultra-hot gas giants WASP-76b and WASP-121b

High-resolution spectroscopy studies of ultra-hot Jupiters have been key in our understanding of exoplanet atmospheres. Observing into the atmospheres of these giant planets allows for direct constraints on their atmospheric compositions and dynamics while laying the groundwork for new research regarding their formation and evolution environments. Two of the most well-studied ultra-hot Jupiters are WASP-76b and WASP-121b, with multiple detected chemical species and strong signatures of their atmospheric dynamics. We take a new look at these two exceptional ultra-hot Jupiters by reanalyzing the transit observations taken with ESPRESSO at the Very Large Telescope and attempt to detect additional species. To extract the planetary spectra of the two targets, we corrected for the telluric absorption and removed the stellar spectrum contributions. We then exploited new synthetic templates that were specifically designed for ultra-hot Jupiters in combination with the cross-correlation technique to unveil species that remained undetected by previous analyses. We add a novel detection of Ba+ to the known atmospheric compositions of WASP-76b and WASP-121b, the heaviest species detected to date in any exoplanetary atmosphere, with additional new detections of Co and Sr+ and a tentative detection of Ti+ for WASP-121b. We also confirm the presence of Ca+, Cr, Fe, H, Li, Mg, Mn, Na, and V on both WASP-76b and WASP-121b, with the addition of Ca, Fe+, and Ni for the latter. Finally, we also confirm the clear asymmetric absorption feature of Ca+ on WASP-121b, with an excess absorption at the bluer wavelengths and an effective planet radius beyond the Roche lobe. This indicates that the signal may arise from the escape of planetary atmosphere.

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