Dr. Astudillo-Defru, Nicola

Distinguishing classes within substellar objects and understanding their formation and evolution need larger samples of substellar companions such as exoplanets, brown dwarfs, and low-mass stars. In this paper, we look for substellar companions using radial velocity surveys of FGK stars with the SOPHIE spectrograph at the Observatoire de Haute-Provence. We assign here the radial velocity variations of 27 stars to their orbital motion induced by low-mass companions. We also constrained their plane-of-the-sky motion using HIPPARCOS and Gaia Data Release 1 measurements, which constrain the true masses of some of these companions. We report the detection and characterization of six cool Jupiters, three brown dwarf candidates, and 16 low-mass stellar companions. We additionally update the orbital parameters of the low-mass star HD 8291 B, and we conclude that the radial velocity variations of HD 204277 are likely due to stellar activity despite resembling the signal of a giant planet. One of the new giant planets, BD+631405 b, adds to the population of highly eccentric cool Jupiters, and it is presently the most massive member. Two of the cool Jupiter systems also exhibit signatures of an additional outer companion. The orbital periods of the new companions span 30 days to 11.5 yr, their masses 0.72 MJ–0.61 M, and their eccentricities 0.04–0.88. These discoveries probe the diversity of substellar objects and low-mass stars, which will help constrain the models of their formation and evolution.

WASP-127b is one of the puffiest exoplanets found to date, with a mass of only 3.4 Neptune masses, but a radius larger than that of Jupiter. It is located at the border of the Neptune desert, which describes the lack of highly irradiated Neptune-sized planets, and which remains poorly understood. Its large scale height and bright host star make the transiting WASP-127b a valuable target to characterise in transmission spectroscopy. We used combined EulerCam and TESS light curves to recalculate the system parameters. Additionally, we present an in-depth search for sodium in four transit observations of WASP-127b, obtained as part of the Hot Exoplanet Atmosphere Resolved with Transit Spectroscopy (HEARTS) survey with the High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph. Two nights from this dataset were analysed independently by another team. The team claimed a detection of sodium that is incompatible with previous studies of data from both ground and space. We show that this strong sodium detection is due to contamination from telluric sodium emissions and the low signal-to-noise ratio in the core of the deep stellar sodium lines. When these effects are properly accounted for, the previous sodium signal is reduced to an absorption of 0.46 ± 0.20% (2.3σ), which is compatible with analyses of WASP-127b transits carried out with other instruments. We can fit a Gaussian to the D2 line, but the D1 line was not detected. This indicates an unusual line ratio if sodium exists in the atmosphere. Follow-up of WASP-127 at high resolution and with high sensitivity is required to firmly establish the presence of sodium and analyse its line shape.

Context. High-resolution transmission spectroscopy has allowed for in-depth information on the composition and structure of exoplanetary atmospheres to be garnered in the last few years, especially in the visible and in the near-infrared. Many atomic and molecular species have been detected thanks to data gathered from state-of-the-art spectrographs installed on large ground-based telescopes. Nevertheless, the Earth daily cycle has been limiting observations to exoplanets with the shortest transits. Aims. The inflated sub-Saturn KELT-11 b has a hot atmosphere and orbits a bright evolved subgiant star, making it a prime choice for atmospheric characterization. The challenge lies in its transit duration – of more than 7 h – which can only be covered partially or without enough out-of-transit baselines when observed from the ground. Methods. To overcome this constraint, we observed KELT-11 b with the HARPS spectrograph in series of three consecutive nights, each focusing on a different phase of the planetary orbit: before, during, and after the transit. This allowed us to gather plenty of out-of-transit baseline spectra, which was critical to build a spectrum of the unocculted star with sufficient precision. Telluric absorption lines were corrected using the atmospheric transmission code MOLECFIT. Individual high-resolution transmission spectra were merged to obtain a high signal-to-noise transmission spectrum to search for sodium in KELT-11 b’s atmosphere through the ~5900 Å doublet. Results. Our results highlight the potential for independent observations of a long-transiting planet over consecutive nights. Our study reveals a sodium excess absorption of 0.28 ± 0.05% and 0.50 ± 0.06% in the Na D1 and D2 lines, respectively. This corresponds to 1.44 and 1.69 times the white-light planet radius in the line cores. Wind pattern modeling tends to prefer day-to-night side winds with no vertical winds, which is surprising considering the planet bloatedness. The modeling of the Rossiter-Mclaughlin effect yields a significantly misaligned orbit, with a projected spin-orbit angle of λ = −77.86−2.26+2.36∘. Conclusions. Belonging to the under-studied group of inflated sub-Saturns, the characteristics of KELT-11 b – notably its extreme scale height and long transit – make it an ideal and unique target for next-generation telescopes. Our results as well as recent findings from HST, TESS, and CHEOPS observations could make KELT-11 b a benchmark exoplanet in atmospheric characterization.