Paolo Giacobbe

Aims . We aim to constrain the dynamical masses of the four confirmed transiting planets orbiting the infant (20 ± 10 Myr) star V1298 Tau (orbital periods P _b ∼ 24.1 d, P _c ∼ 8.2 d, P _d ∼ 12.4 d, and P _e ∼ 48.7 d), through a new analysis of a homogeneous radial-velocity dataset. This system is a key benchmark for testing formation and early-stage evolutionary models of planets. Methods . We analysed more than 380 high-resolution spectra collected with the HARPS-N spectrograph over a time span of 4.5 yr. To account for dominant stellar activity and transit-timing-derived planet–planet interactions, we analysed radial velocities extracted using two different approaches and combined N -body simulations with multi-dimensional Gaussian-process regression. We tested a set of spectroscopic and photometric activity diagnostics to mitigate the variability due to the stellar magnetic activity in the radial-velocity time series. Results . The mass determinations are sensitive to the choice of the radial-velocity extraction method and activity diagnostics. For some specific models, we measured masses with a significance of 3.5–4 σ for planets b (0.52 _−0.14 ^+0.12 , 0.65 _−0.18 ^+0.21 , 0.67 _−0.19 ^+0.16 , and 0.78 _−0.20 ^+0.19 M _Jup ) and e (0.40 _−0.13 ^+0.14 , 0.66 _−0.18 ^+0.17 , and 0.71 _−0.22 ^+0.18 M _Jup ). These values are compatible with masses of giant planets and are notably higher than those recently derived from transit timing variations alone, which indicate that these are low-density ‘super-puffy’ planets. Injection-and-recovery simulations moderately support this conclusion for planet b. For planets c and d, we primarily provide updated upper mass limits. Conclusions . Our analysis represents an exploratory study to address the complex issue of mass measurement in a multi-planetary system characterised by high levels of stellar activity. While firm conclusions cannot be drawn for V1298 Tau, in a few cases our results leave open the possibility that planet b in particular is a massive giant rather than a sub-Neptune progenitor. This dichotomy may be solved by combining radial velocities and transit time variations in a more complex photo-dynamical modelling, with a larger sample of transits than currently available.

Among the different classes of exoplanets, ultra-hot Jupiters represent prime laboratories for atmospheric characterisation. With an equilibrium temperature of ~2300 K, KELT-20b/MASCARA-2b (HD 185603 b) is a well-studied ultra-hot Jupiter, for which several atomic species have already been detected in both transmission and emission spectroscopy. Nevertheless, important open questions remain regarding the completeness of the chemical inventory and the interpretation of spurious aliasing signals that may mimic genuine atmospheric signatures. In addition, asymmetries in the detected signals across transits can encode valuable information on the spatial structure and dynamics of the planetary atmosphere. In this work, we analyse seven transits of KELT-20b/MASCARA-2b observed with the high-resolution spectrograph HARPS-N at the Telescopio Nazionale Galileo. We apply the cross-correlation function technique to a large set of atomic and ionic species, accounting for aliasing effects that can lead to false detections. We confirm previous detections of H I , Na I , Mg I , Cr I , Fe I , and Fe II , and tentatively detect Cr II . We further report new detections of K I , Ca I , V I , Mn I , and Ba II , and a tentative detection of Pr I in the planetary atmosphere. By performing a phase-resolved analysis and splitting the transit into pre- and post-mid-transit phases, we investigate longitudinal variations in the detected signals. For several species, we observe a double-peaked structure in the K _p – V _sys maps, notably in Ca I , V I , Cr I , and Fe I , consistent with absorption arising from two distinct atmospheric limbs of the planet.

Hot Neptunes are close-in exoplanets that occupy a sparsely populated region of parameter space known as the hot Neptune desert. Their presence in this extreme environment is puzzling as it implies a complex history involving intense stellar radiation, atmospheric loss, and unique migration patterns that differ from more conventional Neptunes at larger orbital periods. We are running an observational programme aimed at enlarging the number of close-in Neptune-sized planets, with well-measured physical and orbital parameters. It contributes to the compilation of a statistically significant sample that will aid in clarifying the formation and migration pathways characterising this class of exoplanets. We used currently available TESS photometry, along with new (HARPS-N) and archival (HIRES) high-precision radial-velocity measurements, to review the main properties of the planetary systems TOI-1272 and TOI-1694 by means of joint-fit analyses. In the case of TOI-1272, this included Gaussian-process regressions for carefully modelling stellar activity. Our final estimates of the parameters of the two systems are consistent with previous measurements but have smaller uncertainties. We identified the radial-velocity variation of TOI-1272 found in the HIRES data as stellar activity, rather than planetary in nature and, therefore, we rejected the non-transiting planet TOI-1272,c. This opens up the possibility that TOI-1272,b's eccentricity is the result of high-eccentricity migration. The larger store of data at our disposal also allowed us to point out that both TOI-1694,b and TOI-1694,c move on slightly eccentric orbits. The current orbital architecture of TOI-1694 suggests a history of migration driven by both disc and dynamical interactions.

Since the discovery of the first exoplanet, significant efforts have been made to characterise their atmospheres. Ultra-hot Jupiters (UHJs) are of particular interest due to their extended and hot atmospheres. Although previous studies have focused on the detection of atomic species at optical wavelengths, near-infrared (NIR) observations offer the potential to detect molecules. In our study, we applied the cross-correlation technique to NIR transmission spectra from The analysis focuses on the search for H_2O, CO, CO_2, CH_4, HCN, and FeH molecular signals in the atmospheres of four UHJs: HAT-P-57 b, KELT-17 b, KELT-21 b, and WASP-189 b. For the first time, we report results on the NIR transmission spectra of KELT-17b, KELT-21b, and WASP-189b. We report a tentative detection (3.8σ) of H_2O in HAT-P-57 b and a detection (5.3σ) of FeH in KELT-17 b, which is the third FeH detection ever in a UHJ and with the lowest equilibrium temperature. No molecular signals were found in KELT-21b and WASP-189b, or for other molecules in HAT-P-57b and KELT-17b. The cross-correlation results for HAT-P-57 b, KELT-17 b, KELT-21 b, and WASP-189 b in transmission align with the species detected in the UHJ population. This work underscores the need for further observations to confirm and expand the transmission study of UHJs in the NIR, and the capabilities of high-resolution spectrographs on 4-m-class telescopes.

Context. The study of the atmosphere of ultra-hot Jupiters (UHJs) with equilibrium temperatures ≥2000 K provides valuable insights into atmospheric physics under such extreme conditions. Aims. We aim to characterise the dayside thermal spectrum of the UHJ WASP-76 b and investigate its properties. We analysed data gathered with three high-resolution spectrographs: specifically two nights with simultaneous observations of HARPS-N and GIANO-B, and four nights of publicly available ESPRESSO optical spectra. We observed the planet’s dayside, covering orbital phases between quadratures (0.25 < ϕ < 0.75). Methods. We performed a homogeneous analysis of the GIANO-B, HARPS-N, and ESPRESSO data and co-added the signal of thousands of planetary lines through cross-correlation with simulated spectra of the planetary atmosphere. Results. We report the detection of CO in the dayside atmosphere of WASP-76 b with a signal-to-noise ratio (S/N) of 10.4 in the GIANO-B spectra. In addition, we detect Fe I in both the HARPS-N and ESPRESSO datasets, with S/N values of 3.5 and 6.2, respectively. A signal from Fe I is also identified in one of the two GIANO-B observations, with an S/N of 4.0. Interestingly, a qualitatively similar pattern – with a weaker detection in one epoch compared to the other – is also observed in the two HARPS-N nights. The GIANO-B results are, therefore, consistent with those obtained with HARPS-N. Finally, we compared our strongest detections of CO (GIANO-B) and Fe I (ESPRESSO), with predictions from global circulation models (GCM). Both cross-correlation and likelihood analyses favour the GCM that includes atmospheric dynamics over a static (no-dynamics) model when applied to the ESPRESSO data. This study adds to the growing body of literature employing GCMs to interpret high-resolution spectroscopic measurements of exoplanet atmospheres.

Context. Hot Jupiters are among the most suitable targets for atmospheric studies. Expanding the number of hot gaseous giant planets with atmospheric characterisations can improve our understanding of the chemical-physical properties of their atmospheres, as well as the formation and evolution of these extreme planets. Aims. In this work, we use high-resolution spectroscopy in the near-infrared (NIR) to search for chemical signatures in the atmospheres of the two hot Jupiters KELT-8 b (T_eq = 1675₋₅₅⁺⁶¹ K) and KELT-23 Ab (T_eq = 1561 ± 20 K) and present a first characterisation of their atmospheric properties. Methods. We measured the transmission spectrum of each target with the near-infrared (NIR) high-resolution spectrograph GIANO-B at the TNG. We searched for atmospheric signals by cross-correlating the data with synthetic transmission spectra. To characterise the chemical-physical properties of the atmospheres of both planets, we ran two different atmospheric retrievals for each dataset: a retrieval assuming chemical equilibrium and a ‘free-chemistry’ retrieval, in which the abundance of each molecule could vary freely. Results. We detect water vapour (H₂O) in the atmospheres of both KELT-8 b and KELT-23 Ab with a signal-to-noise ratio of S/N = 6.6 and S/N = 4.2, respectively. The two retrievals indicate a water-rich atmosphere for both targets. In the case of KELT-8 b, we determine a water volume mixing ratio of log₁₀ (VMRH₂O) = −2.07_−0.72^+0.53, a metallicity of [M/H = 0.77_−0.89^+0.61 dex, and a sub-solar C/O ratio (C/O ≤0.30, at 2 σ). For KELT-23 Ab, we find log₁₀ (VMRH₂O) = −2.26_−1.24^+0.75, [M/H]= −0.42_−1.35^+1.56 dex, and C/O ratio ≤0.78 (at 2 σ). The constraints on the metallicity and C/O ratio are based on the assumption of chemical equilibrium. Comparing these atmospheric chemical properties with those of the host stars, we suggest that for both planets, the accretion of gaseous material occurred within the H₂O snowline in a pebble-rich disk enriched in oxygen due to sublimation of water ice from the inward-drifting pebbles. Conclusions. We investigated the atmospheres of KELT-8 b and KELT-23 Ab for the first time, finding water vapour in both of them and placing first constraints on their properties. These two planets are promising targets for future high- and low-resolution observations.

High-resolution transmission spectroscopy of the warm gas giant WASP-69 b has revealed the presence of H₂O, CO, CH₄, NH₃, and C₂H₂ in its atmosphere. This study investigates the impact of vertical diffusion and photochemistry on its atmospheric composition, with a focus on the detected species plus HCN and CO₂, to constrain the atmospheric C/O ratio. We utilize nonequilibrium gas-phase simulations to conduct a parameter study for vertical diffusion strength, local gas temperature, and C/O ratio. Our results indicate that a carbon-rich atmosphere enhances CH₄ and C₂H₂ concentrations, while NH₃ undergoes chemical conversion into HCN in carbon-rich, high-temperature environments. Consequently, HCN is abundantly produced in such atmospheres, though its strong spectral features remain undetected in WASP-69 b. Photochemical production of HCN and C₂H₂ is highly sensitive to vertical diffusion strength, with weaker diffusion resulting in higher concentrations. Cross-correlation of synthetic spectra with observed data shows that models with C/O = 2 best match observations, but models with C/O = 0.55 and 0.9 lead to statistically equivalent fits, leaving the C/O ratio unconstrained. We highlight the importance of accurately modeling NH₃ quenching at pressures greater than 100 bars. Models for WASP-69 b capped at 100 bars bias cross-correlation fits toward carbon-rich values. We suggest that if the atmosphere of WASP-69 b is indeed carbon-rich with a solar metallicity, future observations should reveal the presence of HCN.

The neutral sodium resonance doublet (Na I D) has been detected in the upper atmosphere of several close-in gas giants, through high-resolution transmission spectroscopy. We aim to investigate whether its variability is linked to the planets’ properties, the data quality, or the accuracy of the system parameters used. Using the public code SLOPpy, we extracted the transmission spectrum in the Na I D region of ten gas giants for which a large number of HARPS-N observations are available. We modelled the absorption signals found, performing an MCMC analysis, and converted the measured absorption depth to the corresponding atmospheric height over which most sodium absorption occurs. While two targets (GJ 436 b and KELT-7 b) show no Na I D feature, we found variability in the transmission spectrum of the other targets. Three of them (HD 209458 b, WASP-80 b, and WASP-127 b) present absorption on only some nights, while in the other five targets (HD 189733 b, KELT-9 b, KELT-20 b, WASP-69 b, and WASP-76 b), a significant absorption signal is present on most of the nights analysed. Except for WASP-69 b, the measured absorption depths lead to a ratio of the two Na I D depths that is compatible with or slightly larger than one. As was expected from literature, the relative atmospheric height follows an empirical exponential trend as a function of a scaled product of the planet’s equilibrium temperature and surface gravity. We confirm the sodium detection on HD 189733 b, KELT-9 b, KELT-20 b, WASP-69 b, and WASP-76 b. The signal detected in WASP- 127 b requires further observations for definitive confirmation. We exclude a planetary origin for the signals found on HD 209458 b and WASP-80 b. The sodium absorption variability does not appear to be related to planetary properties, but rather to data quality, sub-optimal data treatment, or stellar activity.

High-resolution transmission spectroscopy of the warm gas-giant WASP-69b has revealed the presence of H2O, CO, CH4, NH3, and C2H2 in its atmosphere. This study investigates the impact of vertical diffusion and photochemistry on its atmospheric composition, with a focus on the detected species plus HCN and CO2, to constrain the atmospheric C/O ratio. We utilize non-equilibrium gas-phase simulations to conduct a parameter study for vertical diffusion strength, local gas temperature, and C/O ratio. Our results indicate that a carbon-rich atmosphere enhances CH4 and C2H2 concentrations, while NH3 undergoes chemical conversion into HCN in carbon-rich, high-temperature environments. Consequently, HCN is abundantly produced in such atmospheres, though its strong spectral features remain undetected in WASP-69b. Photochemical production of HCN and C2H2 is highly sensitive to vertical diffusion strength, with weaker diffusion resulting in higher concentrations. Cross-correlation of synthetic spectra with observed data shows that models with C/O=2 best match observations, but models with C/O=0.55 and 0.9 lead to statistically equivalent fits, leaving the C/O ratio unconstrained. We highlight the importance of accurately modeling NH3 quenching at pressures greater than 100 bars. Models for WASP-69b capped at 100 bars bias cross-correlation fits towards carbon-rich values. We suggest that if the atmosphere of WASP-69b is indeed carbon-rich with a solar metallicity, future observations should reveal the presence of HCN.