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Ultra-hot Jupiters showcase extreme atmospheric conditions, including molecular dissociation, ionisation, and significant day-to-night temperature contrasts. Their close proximity to host stars subjects them to intense stellar irradiation, driving high temperatures where hydride ions (H\\(^-\\)) significantly contribute to opacity, potentially obscuring metal features in near-infrared transmission spectra. We investigate the atmosphere of WASP-189b, targeting atomic, ionic, and molecular species (H, He, Fe, Ti, V, Mn, Na, Mg, Ca, Cr, Ni, Y, Ba, Sc, Fe\\(^+\\), Ti\\(^+\\), TiO, H\\(_2\\)O, CO, and OH), focusing on (i) the role of H\\(^-\\) as a source of continuum opacity, and (ii) the relative hydride-to-Fe abundance using joint optical and near-infrared data. We present two transits of WASP-189b gathered simultaneously in the optical with HARPS and near-infrared with NIRPS, supported by photometric light curves from EulerCam and ExTrA. Transmission spectra were analysed via cross-correlation to detect absorption features and enhance the signal-to-noise ratio. Atmospheric retrievals quantified relative abundances by fitting overall metallicity and proxies for TiO, H\\(^-\\), and e\\(^-\\). Only atomic iron is detected in HARPS data (S/N ~5.5), but not in NIRPS, likely due to H\\(^-\\) continuum dampening. Retrievals on HARPS-only and HARPS+NIRPS suggest the hydride-to-Fe ratio exceeds equilibrium predictions by about 0.5 dex, hinting at strong hydrogen ionisation. Including NIRPS data helps constrain H\\(^-\\) abundance and set an upper limit on free electron density, unconstrained in HARPS-only data. These results emphasise H\\(^-\\) as a significant continuum opacity source impeding detection of planetary absorption features in WASP-189b's near-infrared transmission spectrum.

In this work we present the discovery and confirmation of two hot Jupiters orbiting red-giant stars, TOI-4377 b and TOI-4551 b, observed by TESS in the southern ecliptic hemisphere and later followed-up with radial-velocity (RV) observations. For TOI-4377 b we report a mass of \\(0.957^{+0.089}_{-0.087} \\ M_\\mathrm{J}\\) and a inflated radius of \\(1.348 \\pm 0.081 \\ R_\\mathrm{J}\\) orbiting an evolved intermediate-mass star (\\(1.36 \\ \\mathrm{M}_\\odot\\), \\(3.52 \\ \\mathrm{R}_\\odot\\); TIC 394918211) on a period of of \\(4.378\\) days. For TOI-4551 b we report a mass of \\(1.49 \\pm 0.13 \\ M_\\mathrm{J}\\) and a radius that is not obviously inflated of \\(1.058^{+0.110}_{-0.062} \\ R_\\mathrm{J}\\), also orbiting an evolved intermediate-mass star (\\(1.31 \\ \\mathrm{M}_\\odot\\), \\(3.55 \\ \\mathrm{R}_\\odot\\); TIC 204650483) on a period of \\(9.956\\) days. We place both planets in context of known systems with hot Jupiters orbiting evolved hosts, and note that both planets follow the observed trend of the known stellar incident flux-planetary radius relation observed for these short-period giants. Additionally, we produce planetary interior models to estimate the heating efficiency with which stellar incident flux is deposited in the planet's interior, estimating values of \\(1.91 \\pm 0.48\\%\\) and \\(2.19 \\pm 0.45\\%\\) for TOI-4377 b and TOI-4551 b respectively. These values are in line with the known population of hot Jupiters, including hot Jupiters orbiting main sequence hosts, which suggests that the radii of our planets have reinflated in step with their parent star's brightening as they evolved into the post-main-sequence. Finally, we evaluate the potential to observe orbital decay in both systems.

Ultra-hot Jupiters (UHJs), rendering the hottest planetary atmospheres, offer great opportunities of detailed characterisation with high-resolution spectroscopy. MASCARA-4 b is a recently discovered close-in gas giant belonging to this category. In order to refine system and planet parameters, we carried out radial velocity measurements and transit photometry with the CORALIE spectrograph and EulerCam at the Swiss 1.2m Euler telescope. We observed two transits of MASCARA-4 b with the high-resolution spectrograph ESPRESSO at ESO's Very Large Telescope. We searched for atomic, ionic, and molecular species via individual absorption lines and cross-correlation techniques. These results are compared to literature studies on UHJs characterised to date. With CORALIE and EulerCam observations, we updated the mass of MASCARA-4 b (1.675 +/- 0.241 Jupiter masses) as well as other system and planet parameters. In the transmission spectrum derived from ESPRESSO observations, we resolve excess absorption by H\\(\\alpha\\), H\\(\\beta\\), Na D1 & D2, Ca+ H & K, and a few strong individual lines of Mg, Fe and Fe+. We also present the cross-correlation detection of Mg, Ca, Cr, Fe and Fe+. The absorption strength of Fe+ significantly exceeds the prediction from a hydrostatic atmospheric model, as commonly observed in other UHJs. We attribute this to the presence of Fe+ in the exosphere due to hydrodynamic outflows. This is further supported by the positive correlation of absorption strengths of Fe+ with the H\\(\\alpha\\) line. Comparing transmission signatures of various species in the UHJ population allows us to disentangle the hydrostatic regime (as traced via the absorption by Mg and Fe) from the exospheres (as probed by H\\(\\alpha\\) and Fe+) of the strongly irradiated atmospheres.

We report the discovery of three transiting low-mass companions to aged stars: a brown dwarf (TOI-2336b) and two objects near the hydrogen burning mass limit (TOI-1608b and TOI-2521b). These three systems were first identified using data from the Transiting Exoplanet Survey Satellite (TESS). TOI-2336b has a radius of \\(1.05\\pm 0.04\\ R_J\\), a mass of \\(69.9\\pm 2.3\\ M_J\\) and an orbital period of 7.71 days. TOI-1608b has a radius of \\(1.21\\pm 0.06\\ R_J\\), a mass of \\(90.7\\pm 3.7\\ M_J\\) and an orbital period of 2.47 days. TOI-2521b has a radius of \\(1.01\\pm 0.04\\ R_J\\), a mass of \\(77.5\\pm 3.3\\ M_J\\) and an orbital period of 5.56 days. We found all these low-mass companions are inflated. We fitted a relation between radius, mass and incident flux using the sample of known transiting brown dwarfs and low-mass M dwarfs. We found a positive correlation between the flux and the radius for brown dwarfs and for low-mass stars that is weaker than the correlation observed for giant planets. We also found that TOI-1608 and TOI-2521 are very likely to be spin-orbit synchronized, leading to the unusually rapid rotation of the primary stars considering their evolutionary stages. Our estimates indicate that both systems have much shorter spin-orbit synchronization timescales compared to their ages. These systems provide valuable insights into the evolution of stellar systems with brown dwarf and low-mass stellar companions influenced by tidal effects.

While the sample of confirmed exoplanets continues to increase, the population of transiting exoplanets around early-type stars is still limited. These planets allow us to investigate the planet properties and formation pathways over a wide range of stellar masses and study the impact of high irradiation on hot Jupiters orbiting such stars. We report the discovery of TOI-615b, TOI-622b, and TOI-2641b, three Saturn-mass planets transiting main sequence, F-type stars. The planets were identified by the Transiting Exoplanet Survey Satellite (TESS) and confirmed with complementary ground-based and radial velocity observations. TOI-615b is a highly irradiated (\\(\\sim\\)1277 \\(F_{\\oplus}\\)) and bloated Saturn-mass planet (1.69$^{+0.05}_{-0.06}$$R_{Jup}\\( and 0.43\\)^{+0.09}_{-0.08}$$M_{Jup}\\() in a 4.66 day orbit transiting a 6850 K star. TOI-622b has a radius of 0.82\\)^{+0.03}_{-0.03}$$R_{Jup}\\( and a mass of 0.30\\)^{+0.07}_{-0.08}\\(~\\)M_{Jup}\\( in a 6.40 day orbit. Despite its high insolation flux (\\)\\sim\\(600 \\)F_{\\oplus}\\(), TOI-622b does not show any evidence of radius inflation. TOI-2641b is a 0.39\\)^{+0.02}_{-0.04}$$M_{Jup}\\( planet in a 4.88 day orbit with a grazing transit (b = 1.04\\)^{+0.05}_{-0.06 }\\() that results in a poorly constrained radius of 1.61\\)^{+0.46}_{-0.64}$$R_{Jup}\\(. Additionally, TOI-615b is considered attractive for atmospheric studies via transmission spectroscopy with ground-based spectrographs and \\)\\textit{JWST}$. Future atmospheric and spin-orbit alignment observations are essential since they can provide information on the atmospheric composition, formation and migration of exoplanets across various stellar types.

We report the discovery of a 1.32\\(^{+0.10}_{-0.10}\\) \\(\\mathrm{M_{\\rm Jup}}\\) planet orbiting on a 75.12 day period around the G3V \\(10.8^{+2.1}_{-3.6}\\) Gyr old star TOI-5542 (TIC 466206508; TYC 9086-1210-1). The planet was first detected by the Transiting Exoplanet Survey Satellite (TESS) as a single transit event in TESS Sector 13. A second transit was observed 376 days later in TESS Sector 27. The planetary nature of the object has been confirmed by ground-based spectroscopic and radial velocity observations from the CORALIE and HARPS spectrographs. A third transit event was detected by the ground-based facilities NGTS, EulerCam, and SAAO. We find the planet has a radius of 1.009\\(^{+0.036}_{-0.035}\\) \\(\\mathrm{R_{\\rm Jup}}\\) and an insolation of 9.6\\(^{+0.9}_{-0.8}\\) \\(S_{\\oplus}\\), along with a circular orbit that most likely formed via disk migration or in situ formation, rather than high-eccentricity migration mechanisms. Our analysis of the HARPS spectra yields a host star metallicity of [Fe/H] = \\(-\\)0.21\\(\\pm\\)0.08, which does not follow the traditional trend of high host star metallicity for giant planets and does not bolster studies suggesting a difference among low- and high-mass giant planet host star metallicities. Additionally, when analyzing a sample of 216 well-characterized giant planets, we find that both high masses (4 \\(\\mathrm{M_{\\rm Jup}}\\) \\(\\) 10 days) and hot (P \\(<\\) 10 days) giant planets are preferentially located around metal-rich stars (mean [Fe/H] \\(>\\) 0.1). TOI-5542b is one of the oldest known warm Jupiters and it is cool enough to be unaffected by inflation due to stellar incident flux, making it a valuable contribution in the context of planetary composition and formation studies.

We present the characterization of two planetary systems orbiting the M dwarfs TOI-4336 A (M3.5V) and TOI-4342 (M0V), each hosting two transiting planets previously validated with TESS and ground-based observations. We refined the photometry of the TOI-4342 system using TESS and LCOGT data, and characterized the host stars with NIRPS and ESPRESSO spectroscopy. High-precision ESPRESSO radial velocities allowed us to constrain the planetary masses and investigate their potential compositions. The TOI-4336 A system is composed of a sub-Neptune with a period of 16.34 days, a radius of \\(2.14 0.08\\) Re, and a mass of \\(3.33 0.36\\) Me, along with an inner super-Earth on a 7.59-day orbit with a radius of \\(1.25 0.07\\) Re and a mass of \\(1.55 0.13\\) Me. The TOI-4342 system hosts two sub-Neptunes of similar sizes (\\(2.33 0.09\\) Re and \\(2.35 0.09\\) Re), with periods of 5.54 and 10.69 days. Their masses are measured to be \\(7.3 1.3\\) Me and \\(4.8 1.4\\) Me, respectively. The RVs also reveal a planet candidate around TOI-4342, likely non-transiting, with a period of 47.5 days and a minimum mass of \\(17.8 3.0\\) Me. With precise radii and masses, we derived bulk densities and explored possible compositions. The TOI-4336 A sub-Neptune and super-Earth have densities of \\(1.87 0.30\\) and \\(4.35 0.79\\) g cm\\(^-3\\), while the two similar-sized sub-Neptunes in TOI-4342 show distinct densities of \\(3.18 0.67\\) and \\(2.01 0.63\\) g cm\\(^-3\\). All four planets are excellent targets for future atmospheric characterization with JWST, and their multi-planet nature makes them especially interesting for comparative planetology. Notably, TOI-4336 A b stands out as one of the best-known targets in its size and temperature regime, with a TSM of 138, comparable to benchmark planets such as K2-18 b and LHS 1140 b.

Neutral sodium (Na I) is an alkali metal with a favorable absorption cross section such that tenuous gases are easily illuminated at select transiting exoplanet systems. We examine both the time-averaged and time-series alkali spectral flux individually, over 4 nights at a hot Saturn system on a \\(\\) 2.8 day orbit about a Sun-like star WASP-49 A. Very Large Telescope/ESPRESSO observations are analyzed, providing new constraints. We recover the previously confirmed residual sodium flux uniquely when averaged, whereas night-to-night Na I varies by more than an order of magnitude. On HARPS/3.6-m Epoch II, we report a Doppler redshift at \\(v_ NaD =\\) +9.7 \\(\\) 1.6 km/s with respect to the planet's rest frame. Upon examining the lightcurves, we confirm night-to-night variability, on the order of \\(\\) 1-4 % in NaD rarely coinciding with exoplanet transit, not readily explained by stellar activity, starspots, tellurics, or the interstellar medium. Coincident with the \\(\\)+10 km/s Doppler redshift, we detect a transient sodium absorption event dF\\(_NaD\\)/F\\(_\\) = 3.6 \\(\\) 1 % at a relative difference of \\( F_NaD (t) \\) 4.4 \\(\\) 1 %, enduring \\( t_NaD \\) 40 minutes. Since exoplanetary alkali signatures are blueshifted due to the natural vector of radiation pressure, estimated here at roughly \\(\\) -5.7 km/s, the radial velocity is rather at +15.4 km/s, far larger than any known exoplanet system. Given that the redshift magnitude v\\(_\\) is in between the Roche limit and dynamically stable satellite orbits, the transient sodium may be a putative indication of a natural satellite orbiting WASP-49 A b.

Ultra-hot Jupiters like WASP-121b provide unique laboratories for studying atmospheric chemistry and dynamics under extreme irradiation. Constraining their composition and circulation is key to tracing planet formation pathways. We present a comprehensive characterisation of WASP-121b using high-resolution transit spectroscopy from HARPS, NIRPS, and CRIRES+ across nine transits, complemented by five TESS sectors, two EulerCam light curves simultaneous with HARPS/NIRPS, and an extensive RV dataset refining orbital parameters. Cross-correlation detects Fe, CO, and V with SNRs of 5.8, 5.0, and 4.7, respectively. Retrieval analysis constrains H\\(_2\\)O to \\(-6.52^{+0.49}_{-0.68}\\) dex, though its signal might be muted by the H\\(^-\\) continuum. We measure volatile/refractory ratios, key to uncover planetary chemistry, evolution, and formation. Retrieved values align with solar composition in chemical equilibrium, suggesting minimal disequilibrium chemistry at the probed pressures (around \\(10^{-4}\\)-\\(10^{-3}\\) bar). We update WASP-121b's orbital parameters analysing its largest RV dataset to date. Comparing orbital velocities from RVs and atmospheric retrieval reveals a non-zero circulation offset, \\(\\mathrm{\\Delta K}_{\\mathrm{p}} = -15 \\pm 3 \\ \\mathrm{km}\\mathrm{s}^{-1}\\) (assuming \\(\\mathrm{M}_{\\star} = 1.38 \\pm 0.02 \\ \\mathrm{M}_{\\odot}\\)), consistent with drag-free or weak-drag 3D GCM predictions, though sensitive to stellar mass. These results provide new constraints on WASP-121b's thermal structure, dynamics, and chemistry, underscoring the power of multi-instrument and multi-wavelength high-resolution spectroscopy to probe exoplanet atmospheres.

We report the discovery of five transiting companions near the hydrogen-burning mass limit in close orbits around main sequence stars originally identified by the Transiting Exoplanet Survey Satellite (TESS) as TESS Objects of Interest (TOIs): TOI-148, TOI-587, TOI-681, TOI-746, and TOI-1213. Using TESS and ground-based photometry as well as radial velocities from the CORALIE, CHIRON, TRES, and FEROS spectrographs, we found the companions have orbital periods between 4.8 and 27.2 days, masses between 77 and 98 \\(\\mathrm{M_{Jup}}\\), and radii between 0.81 and 1.66 \\(\\mathrm{R_{Jup}}\\). These targets have masses near the uncertain lower limit of hydrogen core fusion (\\(\\sim\\)73-96 \\(\\mathrm{M_{Jup}}\\)), which separates brown dwarfs and low-mass stars. We constrained young ages for TOI-587 (0.2 \\(\\pm\\) 0.1 Gyr) and TOI-681 (0.17 \\(\\pm\\) 0.03 Gyr) and found them to have relatively larger radii compared to other transiting companions of a similar mass. Conversely we estimated older ages for TOI-148 and TOI-746 and found them to have relatively smaller companion radii. With an effective temperature of 9800 \\(\\pm\\) 200 K, TOI-587 is the hottest known main-sequence star to host a transiting brown dwarf or very low-mass star. We found evidence of spin-orbit synchronization for TOI-148 and TOI-746 as well as tidal circularization for TOI-148. These companions add to the population of brown dwarfs and very low-mass stars with well measured parameters ideal to test formation models of these rare objects, the origin of the brown dwarf desert, and the distinction between brown dwarfs and hydrogen-burning main sequence stars.