Antonino Francesco Lanza

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.

The third Gaia data release (GDR3) includes the gdr3_rotmod catalogue of 474 026 stars with variability attributed to magnetic activity, analogous to that observed in the Sun and arising from rotational modulation induced by spots and faculae. These stars are expected to exhibit flaring activity driven by magnetic reconnection processes. We aim to demonstrate that stellar flares can be reliably identified and characterised in the sparsely sampled Gaia photometric time series. We develop and validate a dedicated flare-detection pipeline that exploits simultaneous multi-band photometry in the G , G _BP , and G _RP bands. The algorithm identifies outliers associated with a concurrent increase in brightness and blueing of the stellar colour. It also applies consistency criteria to distinguish genuine flare events from instrumental or calibration artefacts. Applying this method to the gdr3_rotmod catalogue, we detected 3217 flares occurring on 2818 stars out of 474 026 analysed sources. All events are provided in a dedicated catalogue together with their photometric amplitudes. For a subset of 348 flares, we estimated the effective temperature using a black-body approximation and we identified 29 hyper-flares with amplitudes A ( G ) ≥ 0.75 mag, which occur preferentially in M dwarfs. Despite the sparse temporal sampling of Gaia , our results demonstrate that its multi-band photometry and spectrophotometric information enable the robust detection of flares and the basic characterisation of their properties across an all-sky stellar sample. This work establishes the methodological foundation for future Gaia flare catalogues and provides a homogeneous, complementary view of stellar flaring activity alongside high-cadence missions such as Kepler and TESS.

Context . The architecture of our Solar System, with inner small planets (ISPs) and outer giants, may or may not be common. Understanding whether a correlation exists between ISPs and outer cold giants is key to evaluating how common systems with a similar architecture to our own are. Aims . This study aims to build a large, homogeneous sample of systems hosting cold Jupiters (CJs, a _peri > 1 au, m sin i > 0.1 M _J ) detected via radial velocities (RVs), and to assess the presence of additional ISPs ( P < 400 d, 3 ≤ m sin i ≤ 31.7 M _⊕ ), studying the correlation between these two types of objects. Methods . We selected 137 stars known to host a CJ, including 23 that also harbour a hot Jupiter and were treated separately. Data from various instruments were compiled, including unpublished data gathered with the High Accuracy Radial velocity Planet Searcher for the Northern hemisphere (HARPS-N) within the Global Architectures of Planetary Systems (GAPS) programme, and consistently fitted using PyORBIT. We derived RV detection maps and calculated occurrence rates for ISPs, cross-validating results with two independent codes. The sample was divided into subgroups to evaluate how system parameters influence planet occurrence. Results . We confirmed the 213 already known planets in the 137 systems and also identified six new candidates. We divided them, based on mass and period, into Neptunes (10 < m sin i < 31.7 M _⊕ ) and super-Earths (3 < m sin i ≤ 10 M _⊕ ), and into hot (1 ≤ P ≤ 10 d), warm (10 < P ≤ 100 d), and cool (100 < P ≤ 400 d). We found occurrences of ~5%, ~13%, and ~12% for hot, warm, and cool Neptunes, respectively, and ~11% and ~16% for hot and warm super-Earths, respectively. Systems with dynamically stable inner regions show higher rates of small planets. These findings are consistent with previous studies showing no strong correlation between ISPs and CJs at average stellar metallicity and mass, and suggest that hot Jupiters may be more commonly associated with external giants.

The astrometric measurements provided by the Gaia space mission represent a key advancement in the search for and characterisation of exoplanets, helping in particular to solve the mass degeneracy intrinsic to the radial velocity (RV) method. The fact that a fraction of astrophysical false positives contaminates the current catalogue of astrometric candidate solutions requires an RV follow-up to validate and confirm such candidates. Within the Global Architecture of Planetary Systems (GAPS) programme, we observed a selected sample of 14 stars with Gaia astrometric solutions compatible with the presence of a sub-stellar companion. The immediate aim of this survey is to identify astrophysical false positives and provide the first RV validation and confirmation of the remaining candidates. We analysed data collected with the HARPS-N spectrograph to identify stellar binary systems from the spectral cross correlation function profiles. The remaining astrometric candidates were characterised via Markov chain Monte Carlo analysis searching for the best-fit RV solution. Among the stars in our sample with astrometric candidate solutions, we identify six as originating from close binary companions mimicking the astrometric motion of distant sub-stellar companions, from which we can estimate an updated value of 43_ -11 ^ +13 % for the binary contamination fraction in the Gaia DR3 catalogue of astrometric candidates. We validate and confirm the remaining eight solutions, corresponding to giant and brown dwarf companions with minimum masses between 8 and 62 M_ Jup and semi-major axes between 0.76 and 1.42 au, providing the first RV characterisation for six of these candidates and updated orbital solutions for two previously confirmed ones.

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.

Close-in substellar companions experience strong tidal and magnetic interactions with their host stars and are therefore subject to fast orbital evolution. Moreover, due to the strong irradiation of their surface, they exhibit orbital phase modulations of significant amplitudes, allowing their atmospheric radiative properties to be characterised . In particular, this means that companions can be detected and characterised even in the absence of transits. The solar-type pulsator KIC 9139163 exhibits, in its light curve, a stable 0.6-day modulation for which the best explanation is the presence of a close-in non-transiting companion that we therefore attempt to characterise. We combined and TESS photometric data with spectroscopic observations obtained with the High Accuracy Radial velocity Planet Searcher for the Northern hemisphere (HARPS-N). We validated the KIC 9139163 surface stellar rotation period and we used the HARPS-N spectra to refine the stellar modelling. The analysis of the radial velocities obtained with HARPS-N provides a companion mass M_p _⊕. Kepler i = 7.3 ± 1.4 , M Using a joint grid fitting of the and TESS phase curves with an ultra-hot exoplanet model, we inferred a planetary radius of 2.43 ± 0.14 , Kepler R _⊕, which, combined with the measured mass and retrieved inclination, implies a bulk density consistent with a hot water-rich world. This places the non-transiting companion candidate of KIC 9139163 within the Neptunian desert, a regime where planets are expected either to have lost their primordial hydrogen or helium envelopes or to harbour metal-enriched atmospheres. We further detected significant variations in amplitude between the and TESS phase curves, obtained six years apart, as well as a secular increase in amplitude over the baseline. Our joint fit favours a model with two distinct longitudinal cloud offsets over a single-offset scenario. Both datasets indicate a moderate-to-high geometric albedo and low-to-moderate heat redistribution. The opposite phase offsets observed in the and TESS datasets suggest a time-variable longitudinal brightness distribution, potentially driven by evolving cloud properties or changes in scattering behaviour. Kepler Kepler Kepler Nevertheless, given the larger noise level and contamination affecting the TESS photometry, this interpretation remains tentative. These results point towards a dynamic and evolving reflective component in the atmosphere of the candidate planet. While making KIC 9139163 an interesting candidate for future ground follow-ups, it also suggests that searching for other non-transiting planets around fast stellar rotators in space-borne photometric surveys might provide new insights into the physics of the Neptunian planets located in the desert.

The measurement of the spin-orbit obliquity, that is, the angle between the orbital axis of a planet and the stellar spin axis, provides crucial insights into how planets form and migrate. Observations of young transiting planets, which have not yet experienced significant tidal alterations, offer a unique opportunity to study the planets’ original obliquity configuration. We observed the warm Saturn-sized TOI-837 b (member of the 35 Myr old open cluster IC 2602) in transit using ESPRESSO at VLT, collecting high-precision radial velocities to measure the Rossiter-McLaughlin effect. We found a sky-projected obliquity of λ = 341.1 _−2.5 ^+2.3 deg. Using our knowledge of the stellar rotation period (3.00 ± 0.02 d), we estimated a true obliquity of ψ = 25.9 _−6.3 ^+7.5 deg, which indicates prograde motion and suggests a mildly misaligned orbit. This places TOI-837 b as the first planet younger than 100 Myr with accessible ψ incompatible with an aligned orbit. Together with the primordial circular orbit of TOI-837 b and the presence of a bound stellar companion, this mild misalignment favours the possibility of a primordial obliquity excitation (secular torque on the protoplanetary disc) followed by disc-driven migration, rather than high-eccentricity migration after formation.

Theory predicts that a planet with a sufficiently strong magnetic field orbiting close to its host star could induce star-planet magnetic interactions. This is potentially observable as an optical or radio stellar activity signal synchronised with the planet’s orbital period. We analyze 18 years of high-resolution optical spectroscopy of GJ 436, a low mass star orbited by a Neptune-sized exoplanet on a polar eccentric orbit. Stellar activity indicators show enhancements at a period corresponding to the exoplanet orbit, modulated by stellar rotation, and the star’s 8-year magnetic cycle. We interpret this as a signal of star-planet magnetic interaction. Using a geometric model, we reproduce these periods if GJ 436 b has a magnetic field strength of 6 to 110 Gauss.

Context. M dwarfs are the most abundant stars in the Galaxy and exhibit diverse magnetic behaviours. While understanding their large-scale magnetic fields is essential for investigating stellar dynamos and assessing the impact of magnetic activity on planetary environments, their magnetic properties and long-term variability remain poorly characterised. Aims. Our aim was to characterise the large-scale magnetic fields of six M dwarfs in the southern PLATO field, with rotation periods ranging from approximately 1 to 17 days and masses between 0.26 and 0.64 M _⊙ . Five of these stars are partially convective, while one is fully convective. These targets extend the mass–rotation diagram into previously unsampled regions. Methods. We analysed TESS light curves to determine accurate rotation periods and optimise phase coverage for our spectropolarimetric observations. SPIRou data were reduced to obtain least-squares deconvolution (LSD) profiles and longitudinal field measurements, while synthetic spectra fitting yielded small-scale field strengths. We then applied ZDI to reconstruct the large-scale magnetic topologies of the six targets. Results. We report a wide diversity of magnetic topologies among the six M dwarfs, with three main results: (1) Rapidly rotating ( P _rot < 2 d) early M dwarfs can generate dipole-dominated magnetic fields of moderate intensity, similar to those of less massive mid-M dwarfs; (2) Rapidly rotating mid-M dwarfs can generate non-axisymmetric large-scale magnetic fields featuring a significant toroidal component; (3) We report a moderately rotating ( P _rot ∼ 17 d) early M dwarf featuring a surprisingly weak large-scale magnetic field. Conclusions. Our findings further highlight the diversity of magnetic field configurations among M dwarfs, including in previously unexplored regions of parameter space. Long-term monitoring of our sample is crucial in order to distinguish persistent features from variability-driven excursions and to characterise the long-term evolution of their surface magnetic fields. Complementary PLATO photometry, including flare and spot-induced variability analyses, will be essential to link surface activity with magnetic properties.

Context. Precise mass and radius measurements of small, transitional exoplanets, such as super-Earths and sub-Neptunes, are essential to constrain their bulk density and formation history, serving as prerequisites for atmospheric characterization. Aims. The ArMS Large Programme, carried out within GAPS using the HARPS-N spectrograph at the Telescopio Nazionale Galileo, aims to confirm and characterize transitional planets in the radius valley through high-precision radial-velocity (RV) measurements. The ultimate goal is to identify ideal targets for atmospheric follow-up observations with next-generation facilities such as the James Webb Space Telescope and the future ESA Ariel satellite. We present the first mass determination of a sub-Neptune planet using data entirely collected within the ArMS programme, focusing on the validated planet TOI-4602 b. Methods. We monitored TOI-4602, which hosts a close-in validated sub-Neptune (P ∼ 3.98 d) detected by the Transiting Exoplanet Survey Satellite (TESS), searching for planet-induced RV variations. We then performed a joint analysis of these RV measurements together with the TESS photometric data. Results. We determined that TOI-4602 b is a sub-Neptune with a radius of R _p = 2.5 ± 0.2 R _⊕ and a mass of M _p = 5.5 ± 0.9 M _⊕ . The resulting bulk density ( ρ _p = 2.1 ± 0.6 g cm ⁻³ ) and atmospheric evolution modelling suggest the planet is retaining a tenuous envelope while evolving towards a bare core, consistent with a position immediately above the radius valley. Conclusions. Given its bright (V = 8.4) and quiet host star and the high transmission spectroscopy metric (TSM) value (140 ± 54), TOI-4602 b is a prime target for atmospheric characterization. Simulated retrievals indicate that JWST and Ariel can effectively constrain its atmospheric composition, offering a unique window into the physical processes driving the sub-Neptune to super-Earth transition.