arXiv subjects

A. Ghedina

Publications and source records attributed to A. Ghedina.

At least 19 recordsLinked to original sources

arXiv2026

Refined parameters, formation, and dynamical stability of the wild exoplanet system K2-312=HD 80653

The architecture of planetary systems hosting ultra-short-period (USP) planets is a key diagnostic for understanding formation and migration scenarios. The presence of outer giant companions in these systems is of particular interest to test theories regarding dynamical effects and pebble accretion. We present an extended radial velocity (RV) monitoring of the bright star K2-312=HD80653, known to host a rocky USP super-Earth ($P_b=0.720$d). Previous studies identified a long-term trend and subsequently a Keplerian signal due to an outer highly eccentric giant planet, K2-312c. We aim to refine the orbital parameters of K2-312c by precisely monitoring its periastron passage and to model the formation and dynamical evolution of the system. We analyzed a set of 237 HARPS-N high-resolution spectra, extending the observation baseline of previous literature by almost 4 years. We performed a joint analysis of the RVs together with K2 and TESS photometry to refine the ephemerides and properties of the two planets. To account for stellar activity, we coupled the Keplerian models with a Gaussian processes regression. K2-312c is a cold Jupiter on a wide orbit (orbital period refined to $P_c=871.32$d), with a minimum mass of Msin(i)$\sim5 M_{Jup}$ and a refined eccentricity of $e_c \sim 0.85$. It is among the most eccentric cold Jupiters known in multi-planet systems, and the only one that is highly eccentric and has a USP planet companion. Our simulations suggest that planet-planet scattering between two giant planets could have driven K2-312c to its current high eccentricity, ejected the other giant, and still allowed for the survival of K2-312b. The extended observation baseline further allowed us to identify the stellar rotation period and a long activity cycle, while a new K2 reduction improved the significance of the secondary eclipse detection for K2-312b.

astro-ph.EP↗

arXiv2026

The GAPS programme at TNG: LXXVI. TOI-1533: a compact system hosting a super-Neptune-mass pair with disparate radii

The present-day architecture of planetary systems contains information about their formation and migration histories. The origin of hot Jupiters (HJs, P $\lesssim$ 10 d, $R_{\rm p} > 8 R_\oplus$) has long been a matter of debate. While most of them are found to be ``lonely'', there is a rare population of HJs hosting small companions on inner orbits (eight known as of May 2026). Their peculiar architecture suggests a gentle disc-migration mechanism. In this study, we present the discovery and characterisation of the multi-planet system TOI-1533, comprising an inner sub-Neptune (TOI-1533 b, $P_{\rm orb} = 3.63$ d, $R_{\rm p} = 3.15 R_\oplus$) and an outer hot giant planet (TOI-1533 c, $P_{\rm orb} = 8.06$ d, $R_{\rm p} > 7.5 R_\oplus$) with substantial H/He by mass ($ρ_{\rm p} < 0.48$ g cm$^{-3}$), both transiting an active K-dwarf star ($T_{\rm eff} \approx$ 5130 K; $V$ (mag) $\approx$ 11). Our joint modelling of stellar activity and planetary signals from radial velocities (HARPS-N) and transits (TESS) allows us to detect their Keplerian signals (approximately $10~σ$) and to isolate the stellar modulation. The inclusion of simultaneous photometry in the multi-dimensional Gaussian processes formalism was a fundamental addition to the spectroscopic activity indicators, enabling the disentanglement of stellar activity from planetary signals. The mass ratio of the two confirmed planets ($M_{\rm b} / M_{\rm c}$ about 0.8), together with the super-Neptune mass of the large outer companion ($M_{\rm c} \approx 40 M_\oplus$), makes this system unusual compared to the other few HJs with low-mass inner companions.

astro-ph.EP↗

arXiv2026

The GAPS Programme with HARPS-N at TNG LXXVII. Occurrence rates of small close-in planets in the presence of cold Jupiters

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 > 1 au, msini > 0.1 M$_J$) detected via radial velocities (RVs), and to assess the presence of additional ISPs (P < 400 d, 3 < msini < 31.7 M$_{\oplus}$), studying the correlation between these two types of objects. Methods. We selected 137 stars known to host a CJ, including 23 which also harbor a hot Jupiter and were treated separately. Data from various instruments were compiled, including unpublished data gathered with HARPS-N within the GAPS program, 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$_{\oplus}$) and Super-Earths (3 < m sin i < 10 M$_{\oplus}$), 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 HJs may be more commonly associated with external giants.

astro-ph.EP↗

arXiv2025

A Decade of Solar High-Fidelity Spectroscopy and Precise Radial Velocities from HARPS-N

We recently released 10 years of HARPS-N solar telescope and the goal of this manuscript is to present the different optimisations made to the data reduction, to describe data curation, and to perform some analyses that demonstrate the extreme RV precision of those data. By analysing all the HARPS-N wavelength solutions over 13 years, we bring to light instrumental systematics at the 1 m/s level. After correction, we demonstrate a peak-to-peak precision on the HARPS-N wavelength solution better than 0.75 m/s over 13 years. We then carefully curate the decade of HARPS-N re-reduced solar observations by rejecting 30% of the data affected either by clouds, bad atmospheric conditions or well-understood instrumental systematics. Finally, we correct the curated data for spurious sub-m/s RV effects caused by erroneous instrumental drift measurements and by changes in the spectral blaze function over time. After curation and correction, a total of 109,466 HARPS-N solar spectra and respective RVs over a decade are available. The median photon-noise precision of the RV data is 0.28 m/s and, on daily timescales, the median RV rms is 0.49 m/s, similar to the level imposed by stellar granulation signals. On 10-year timescales, the large RV rms of 2.95 m/s results from the RV signature of the Sun's magnetic cycle. When modelling this long-term effect using the Magnesium II activity index, we demonstrate a long-term RV precision of 0.41 m/s. We also analysed contemporaneous HARPS-N and NEID solar RVs and found the data from both instruments to be of similar quality and precision, with an overall RV differece rms of 0.79 m/s. This decade of high-cadence HARPS-N solar observations with short- and long-term precision below 1 m/s represents a crucial dataset to further understand stellar activity signals in solar-type stars , and to advance other science cases requiring such an extreme precision.

astro-ph.SR↗

arXiv2025

Discovery of a multi-planetary system orbiting the aged Sun-like star HD 224018

In 2016, Kepler/K2 detected a system of two sub-Neptunes transiting the star HD 224018, one of them showing a mono-transit event. In 2017, we began a spectroscopic follow-up with HARPS-N to measure the dynamical masses of the planets using radial velocities, and collected additional transit observations using CHEOPS. We measured the fundamental physical parameters of the host star, which is an ``old Sun'' analogue. We analysed radial velocities and photometric time series, also including data by TESS, to provide precise ephemerides, radii, masses, and bulk densities of the two planets, and possibly modeling their internal structure and composition. The system turned out to be more crowded than shown by K2. Radial velocities revealed the presence of two additional bodies: a candidate cold companion on an eccentric orbit with a minimum mass nearly half that of Jupiter (eccentricity $0.60^{+0.07}_{-0.08}$; semi-major axis 8.6$^{+1.5}_{-1.6}$ au), and an innermost super-Earth (orbital period 10.6413$\pm$0.0028 d; mass 4.1$\pm$0.8 Me) for which we discovered previously undetected transit events in K2 photometry. TESS revealed a second transit of one of the two companions originally observed by K2. This allowed us to constrain its orbital period to a grid of values, the most likely being $\sim$138 days, which would imply a mass less than 9 Me, at a 3$σ$ significance level. Given the level of precision of our measurements, we were able to constrain the internal structure and composition of the second-most distant planet from the host star, a warm sub-Neptune with a bulk density of 3.9$\pm$0.5 g/cm$^{3}$. HD 224018 hosts three close-in transiting planets in the super-Earth-to-sub-Neptune regime, and a candidate cold and eccentric massive companion. Additional follow-up is needed to better characterise the physical properties of the planets and their architecture.

astro-ph.EP↗

arXiv2025

Evidence for optical pulsations from a redback millisecond pulsar

Recent detections of optical pulsations from both a transitional and an accreting millisecond pulsar have revealed unexpectedly bright signals, suggesting that the presence of an accretion disk enhances the efficiency of optical emission, possibly via synchrotron radiation from accelerated particles. In this work, we present optical observations of the redback millisecond pulsar PSR J2339-0533, obtained with the SiFAP2 photometer mounted on the Telescopio Nazionale Galileo. Data accumulated during the campaign with the longest exposure time (12 hr) suggest that its $\sim$18 mag optical counterpart exhibits pulsations at the neutron star's spin frequency. This candidate signal was identified by folding the optical time series using the pulsar ephemeris derived from nearly simultaneous observations with the 64-m Murriyang (Parkes) radio telescope. The detection significance of the candidate optical signal identified in those data lies between 2.9 and 3.5 $σ$, depending on the statistical test employed. The pulsed signal has a duty cycle of $\approx 1/32$, and the de-reddened pulsed magnitude in the V band is $(26.0 \pm 0.6)$ mag. At a distance of 1.7 kpc, this corresponds to a conversion efficiency of $\sim 3 \times 10^{-6}$ of the pulsar's spin-down power into pulsed optical luminosity, comparable to values observed in young, isolated pulsars like the Crab, but 50-100 times lower than in disk-accreting millisecond pulsars. If confirmed, these findings suggest that optical pulsations arise independently of an accretion disk and support the notion that such disks boost the optical emission efficiency.

astro-ph.HE↗

arXiv2025

The GAPS Programme at TNG. LXIX.The Dayside of WASP-76b revealed by GIANO-B, HARPS-N and ESPRESSO: Evidence for Three-Dimensional Atmospheric Effects

The study of the atmosphere of ultra-hot Jupiters (UHJs) with equilibrium temperature $\geq$2000 K provides valuable insights into atmospheric physics under such extreme conditions. We aim to characterise the dayside thermal spectrum of the UHJ WASP-76b 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). 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. We report the detection of CO in the dayside atmosphere of WASP-76b 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 of 3.5 and 6.2, respectively. A signal from Fe I is also identified in one of the two GIANO-B observations, with a 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 (GCMs). 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.

astro-ph.EP↗

arXiv2025

In-depth characterization of the Kepler-10 three-planet system with HARPS-N radial velocities and Kepler transit timing variations

The old G3V star Kepler-10 is known to host two transiting planets, the ultra-short-period super-Earth Kepler-10b ($P=0.837$ d; $R_{\rm p}=1.47~\rm R_\oplus$) and the long-period sub-Neptune Kepler-10c ($P=45.294$ d; $R_{\rm p}=2.35~\rm R_\oplus$), and a non-transiting planet that causes variations in the Kepler-10c transit times. Measurements of the mass of Kepler-10c in the literature have shown disagreement, depending on the radial-velocity dataset and/or the modeling technique used. Here we report on the analysis of almost 300 high-precision radial velocities gathered with the HARPS-N spectrograph at the Telescopio Nazionale Galileo over $\sim11$~years, and extracted with the YARARA-v2 tool, which corrects for possible systematics and/or low-level activity variations at the spectrum level. To model these radial velocities, we used three different noise models and various numerical techniques, which all converged to the solution: $M_{\rm p, b}=3.24 \pm 0.32~\rm M_\oplus$ (10$σ$) and $ρ_{\rm p, b}=5.54 \pm 0.64~\rm g\;cm^{-3}$ for planet b; $M_{\rm p, c}=11.29 \pm 1.24~\rm M_\oplus$ (9$σ$) and $ρ_{\rm p, c}=4.75 \pm 0.53~\rm g\;cm^{-3}$ for planet c; and $M_{\rm p, d}\sin{i}=12.00 \pm 2.15~\rm M_\oplus$ (6$σ$) and $P=151.06 \pm 0.48$ d for the non-transiting planet Kepler-10d. This solution is further supported by the analysis of the Kepler-10c transit timing variations and their simultaneous modeling with the HARPS-N radial velocities. While Kepler-10b is consistent with a rocky composition and a small or no iron core, Kepler-10c may be a water world that formed beyond the water snowline and subsequently migrated inward.

astro-ph.EP↗

arXiv2024

The GAPS Programme at TNG. LXV. Precise density measurement of TOI-1430 b, a young planet with an evaporating atmosphere

Small-sized exoplanets in tight orbits around young stars (10-1000 Myr) give us the opportunity to investigate the mechanisms that led to their formation, the evolution of their physical and orbital properties and, especially, of their atmospheres. Thanks to the all-sky survey carried out by TESS, many of these exoplanets have been discovered and have subsequently been characterized with dedicated follow-up observations. In the context of a collaboration among the GAPS, TKS and CPS teams, we measured with a high level of precision the mass and the radius of TOI-1430 b, a young (~700 Myr) exoplanet with an escaping He atmosphere orbiting the K-dwarf star HD 235088 (TOI-1430). By adopting appropriate stellar parameters, which were measured in this work, we were able to simultaneously model the signals due to strong stellar activity and the transiting planet TOI-1430 b in both photometric and spectroscopic series. This allowed us to measure the density of the planet with high precision, and reconstruct the evolution of its atmosphere. TOI-1430 is an active K-dwarf star born 700+/-150 Myr ago and rotates in ~12 d. It hosts a mini-Neptune whose orbital period is Pb=7.434133+/-0.000004 d. Thanks to long-term monitoring of this target performed with TESS, HARPS-N, HIRES, and APF, we estimated a radius Rb=1.98+/-0.07 $R_{\oplus}$, a mass Mb=4.2+/-0.8 $M_{\oplus}$, and thus a planetary density $ρ$b=0.5+/-0.1 $ρ_{\oplus}$. TOI-1430 b is hence a low-density mini-Neptune with an extended atmosphere, at the edge of the radius gap. Because this planet is known to have an evaporating atmosphere of He, we reconstructed its atmospheric history. Our analysis supports the scenario in which, shortly after its birth, TOI-1430 b may have been super-puffy, with a radius 5x-13x and a mass 1.5x-2x that of today; in ~200 Myr from now, TOI-1430 b should lose its envelope, showing its Earth-size core.

astro-ph.EP↗

arXiv2024

The GAPS programme at TNG -- LXIII. Photo-evaporating puzzle: Exploring the enigmatic nature of TOI-5398 b atmospheric signal

Atmospheric characterization is key to understanding exoplanetary systems, offering insights into the planets current and past conditions. By analyzing key lines like H alpha and the He I triplet, we can trace the evolution of planets through atmospheric photo-evaporation. While ultra-hot Jupiters have been the focus for years, attention is shifting toward smaller, colder planets, which are more challenging to study due to weaker signals, requiring more precise techniques. This study aims to characterize the atmosphere of TOI-5398 b, a warm Saturn with a 10.59-day orbit around a young (650 Myr) G-type star. The system also hosts a smaller inner planet, TOI-5398 c, with a 4.77-day orbit. Both planets are ideal for atmospheric studies due to their proximity to the host star, which drives strong photo-evaporation, especially in planet b, whose high transmission spectroscopy metric (288) makes it a prime target. We analyzed data from a transit observed with the HARPS-N and GIANO-B high-resolution spectrographs, using cross-correlation and single-line analysis to search for atomic species. During this observation, planet c was also transiting, so we investigated the source of the signals. Based on photo-evaporation models, we attribute the signal mainly to planet b, which is expected to lose more mass. We detected H alpha and He I triplets, key markers of photo-evaporation, corresponding to atmospheric heights of 2.33 Rp and 1.65 Rp, respectively. The ATES models supported our observations, predicting a similar He I absorption for planet b and suggesting an He/H ratio of 1/99. Additionally, we detected an Na I doublet via single-line analysis, though cross-correlation did not reveal other atomic species.

astro-ph.EP↗

arXiv2024

The GAPS programme at TNG LX Atmospheric characterisation of KELT-9 b via single-line analysis: Detection of six H I Balmer lines, Na I, Ca I, Ca II, Fe I, Fe II, Mg I, Ti II, Sc II, and Cr II

We analysed six primary transits of the ultra-hot Jupiter KELT-9,b obtained with the HARPS-N high-resolution spectrograph in the context of the Global Architecture of Planetary Systems (GAPS2) project, to characterise the atmosphere via single-line analysis. We extracted the transmission spectrum of each individual line by comparing the master out-of-transit spectrum with the in-transit spectra and computing the weighted average of the tomography in the planet reference frame. We corrected for the centre-to-limb variation and the Rossiter-McLaughlin effect by modelling the region of the star disc obscured by the planet during the transit and subtracting it from the master-out spectrum. We detected all six observable lines of the Balmer series within the HARPS-N wavelength range, from H$α$ to H$ζ$, with a significance exceeding 5$σ$. We focussed on metal species, detecting Na I, Ca I, Ca II, Fe I, Fe II, Mg I, Ti II, Sc II, and Cr II lines. This is the first detection in the atmosphere of an exoplanet of H$ε$ and H$ζ$ lines, as well as of individual lines of Sc II and Cr II. Our detections are supported by a comparison with published synthetic transmission spectra of KELT-9b obtained accounting for non-local thermodynamic equilibrium effects. The results underline the presence of a systematic blueshift due to night-side to day-side winds. The single-line analysis allowed us not only to assess the presence of atomic species in the atmosphere of KELT-9 b, but also to further characterise the local stratification of the atmosphere. Coupling the height distribution of the detected species with the velocity shift retrieved, we acknowledged the height distribution of night-side to day-side winds. Moreover, the study of the rotational broadening of different species supports the prediction of a tidally locked planet rotating as a rigid body.

astro-ph.EP↗

arXiv2024

The Mean Longitudinal Magnetic Field and its Uses in Radial-Velocity Surveys

This work focuses on the analysis of the mean longitudinal magnetic field as a stellar activity tracer in the context of small exoplanet detection and characterisation in radial-velocity (RV) surveys. We use SDO/HMI filtergrams to derive Sun-as-a-star magnetic field measurements, and show that the mean longitudinal magnetic field is an excellent rotational period detector and a useful tracer of the solar magnetic cycle. To put these results into context, we compare the mean longitudinal magnetic field to three common activity proxies derived from HARPS-N Sun-as-a-star data: the full-width at half-maximum, the bisector span and the S-index. The mean longitudinal magnetic field does not correlate with the RVs and therefore cannot be used as a one-to-one proxy. However, with high cadence and a long baseline, the mean longitudinal magnetic field outperforms all other considered proxies as a solar rotational period detector, and can be used to inform our understanding of the physical processes happening on the surface of the Sun. We also test the mean longitudinal magnetic field as a "stellar proxy" on a reduced solar dataset to simulate stellar-like observational sampling. With a Gaussian Process regression analysis, we confirm that the solar mean longitudinal magnetic field is the most effective of the considered indicators, and is the most efficient rotational period indicator over different levels of stellar activity. This work highlights the need for polarimetric time series observations of stars.

astro-ph.SR↗

arXiv2024

Confronting compositional confusion through the characterisation of the sub-Neptune orbiting HD 77946

We report on the detailed characterization of the HD 77946 planetary system. HD 77946 is an F5 ($M_*$ = 1.17 M$_{\odot}$, $R_*$ = 1.31 R$_{\odot}$) star, which hosts a transiting planet recently discovered by NASA's Transiting Exoplanet Survey Satellite (TESS), classified as TOI-1778 b. Using TESS photometry, high-resolution spectroscopic data from HARPS-N, and photometry from CHEOPS, we measure the radius and mass from the transit and RV observations, and find that the planet, HD 77946 b, orbits with period $P_{\rm b}$ = $6.527282_{-0.000020}^{+0.000015}$ d, has a mass of $M_{\rm b} = 8.38\pm{1.32}$M$_\oplus$, and a radius of $R_{\rm b} = 2.705_{-0.081}^{+0.086}$R$_\oplus$. From the combination of mass and radius measurements, and the stellar chemical composition, the planet properties suggest that HD 77946 b is a sub-Neptune with a $\sim$1\% H/He atmosphere. However, a degeneracy still exists between water-world and silicate/iron-hydrogen models, and even though interior structure modelling of this planet favours a sub-Neptune with a H/He layer that makes up a significant fraction of its radius, a water-world composition cannot be ruled out, as with $T_{\rm eq} = 1248^{+40}_{-38}~$K, water may be in a supercritical state. The characterisation of HD 77946 b, adding to the small sample of well-characterised sub-Neptunes, is an important step forwards on our journey to understanding planetary formation and evolution pathways. Furthermore, HD 77946 b has one of the highest transmission spectroscopic metrics for small planets orbiting hot stars, thus transmission spectroscopy of this key planet could prove vital for constraining the compositional confusion that currently surrounds small exoplanets.

astro-ph.EP↗

arXiv2024

The GAPS Programme at TNG: LIV. A HeI survey of close-in giant planets hosted by M-K dwarf stars with GIANO-B

Atmospheric escape plays a fundamental role in shaping the properties of exoplanets. The metastable near-infrared helium triplet at 1083.3 nm (HeI) is a powerful proxy of extended and evaporating atmospheres. We used the GIARPS (GIANO-B+HARPS-N) observing mode of the Telescopio Nazionale Galileo to search for HeI absorption in the upper atmosphere of five close-in giant planets hosted by the K and M dwarf stars of our sample, namely WASP-69b, WASP-107b, HAT-P-11b, GJ436b, and GJ3470b. We focused our analysis on the HeI triplet by performing high-resolution transmission spectroscopy. When nightly variability in the HeI absorption signal was identified, we investigated the potential influence of stellar magnetic activity by searching for variations in the H$α$. We spectrally resolve the HeI triplet and confirm the published detections for WASP-69b (3.91$\pm$0.22%, 17.6$σ$), WASP-107b (8.17$^{+0.80}_{-0.76}$%, 10.5$σ$), HAT-P-11b (1.36$\pm$0.17%, 8.0$σ$), and GJ3470b (1.75$^{+0.39}_{-0.36}$%, 4.7$σ$). We do not find evidence of extra absorption for GJ436b. We observe night-to-night variations in the HeI absorption signal for WASP-69b, associated with variability in H$α$, which likely indicates the influence of stellar activity. Additionally, we find that the HeI signal of GJ3470b originates from a single transit, thereby corroborating the discrepancies in the existing literature. An inspection of the H$α$ reveals an absorption signal during the same transit. By combining our findings with previous analyses of GIANO-B HeI measurements of planets around K dwarfs, we explore potential trends with planetary/stellar parameters that are thought to affect the HeI absorption. Our analysis is unable to identify clear patterns, emphasising the need for further measurements and the exploration of additional potential parameters that might influence HeI absorption.

astro-ph.EP↗

arXiv2024

The GAPS Programme at TNG. XXX: Characterization of the low-density gas giant HAT-P-67 b with GIARPS

HAT-P-67 b is one of the lowest-density gas giants known to date, making it an excellent target for atmospheric characterization through the transmission spectroscopy technique. In the framework of the GAPS large programme, we collected four transit events, with the aim of studying the exoplanet atmosphere and deriving the orbital projected obliquity. We exploited the high-precision GIARPS observing mode of the TNG, along with additional archival TESS photometry, to explore the activity level of the host star. We performed transmission spectroscopy, both in the VIS and in the nIR wavelength range, and analysed the RML effect both fitting the RVs and the Doppler shadow. Based on the TESS photometry, we redetermined the transit parameters of HAT-P-67 b. By modelling the RML effect, we derived a sky-projected obliquity of ($2.2\pm0.4$)° indicating an aligned planetary orbit. The chromospheric activity index $\log\,R^{\prime}_{\rm HK}$, the CCF profile, and the variability in the transmission spectrum of the H$α$ line suggest that the host star shows signatures of stellar activity and/or pulsations. We found no evidence of atomic or molecular species in the VIS transmission spectra, with the exception of pseudo-signals corresponding to Cr I, Fe I, H$α$, Na I, and Ti I. In the nIR range, we found an absorption signal of the He I triplet of 5.56$^{+0.29}_{-0.30}$%(19.0$σ$), corresponding to an effective planetary radius of $\sim$3$R_p$ (where $R_p\sim$2$R_J$) which extends beyond the planet's Roche Lobe radius. Owing to the stellar variability, together with the high uncertainty of the model, we could not confirm the planetary origin of the signals found in the optical transmission spectrum. On the other hand, we confirmed previous detections of the infrared He I triplet, providing a 19.0$σ$ detection. Our finding indicates that the planet's atmosphere is evaporating.

astro-ph.EP↗

arXiv2024

The GAPS Programme at TNG LV. Multiple molecular species in the atmosphere of HAT-P-11 b and review of the HAT-P-11 planetary system

The atmospheric characterisation of hot and warm Neptune-size exoplanets is challenging due to their small radius and atmospheric scale height. The warm-Neptune HAT-P-11b is a remarkable target for such characterisation due to the large brightness of its host star (V=9.46 mag; H=7.13 mag). The aims of this work are to review the main physical and architectural properties of the HAT-P-11 planetary system, and to probe the presence of 8 molecular species in the atmosphere of HAT-P-11b at high spectral resolution in the near-infrared. The planetary system was reviewed by analysing transits and occultations of HAT-P-11b from the Kepler data set as well as HIRES at Keck archival radial-velocity (RV) data. We modelled the latter with Gaussian-process regression and a combined quasi-periodic and squared-exponential kernel to account for stellar variations on both (short-term) rotation and (long-term) activity-cycle timescales. In order to probe the atmospheric composition of HAT-P-11b, we observed 4 transits of this target with GIANO-B at TNG. We find that the long-period ($P\sim9.3$ years) RV signal previously attributed to planet HAT-P-11c is more likely due to the stellar magnetic activity cycle. Nonetheless, the Hipparcos-Gaia difference in the proper-motion anomaly suggests that an outer-bound companion might still exist. For HAT-P-11b, we measure a radius $R_{\rm p}=0.4466\pm0.0059\,R_{\rm J}$, a mass $M_{\rm p}=0.0787\pm0.0048\,M_{\rm J}$, and an eccentricity $e=0.2577^{+0.0033}_{-0.0025}$, in accordance with values in the literature. Probing its atmosphere, we detect $NH_3$ (S/N$=5.3$, significance$=5.0σ$) and confirm the presence of $H_2O$ (S/N$=5.1$, significance$=3.4σ$). We also tentatively detect the signal of $CO_2$ (S/N$=3.0$, significance$=3.2σ$) and $CH_4$ (S/N$=4.8$, significance$=2.6σ$), whose presence need to be confirmed by further observations.

astro-ph.EP↗

arXiv2023

The GAPS Programme at TNG L -- TOI-4515 b: An eccentric warm Jupiter orbiting a 1.2 Gyr-old G-star

Context. Different theories have been developed to explain the origins and properties of close-in giant planets, but none of them alone can explain all of the properties of the warm Jupiters (WJs, Porb = 10 - 200 days). One of the most intriguing characteristics of WJs is that they have a wide range of orbital eccentricities, challenging our understanding of their formation and evolution. Aims. The investigation of these systems is crucial in order to put constraints on formation and evolution theories. TESS is providing a significant sample of transiting WJs around stars bright enough to allow spectroscopic follow-up studies. Methods. We carried out a radial velocity (RV) follow-up study of the TESS candidate TOI-4515 b with the high-resolution spectrograph HARPS-N in the context of the GAPS project, the aim of which is to characterize young giant planets, and the TRES and FEROS spectrographs. We then performed a joint analysis of the HARPS-N, TRES, FEROS, and TESS data in order to fully characterize this planetary system. Results. We find that TOI-4515 b orbits a 1.2 Gyr-old G-star, has an orbital period of Pb = 15.266446 +- 0.000013 days, a mass of Mb = 2.01 +- 0.05 MJ, and a radius of Rb = 1.09 +- 0.04 RJ. We also find an eccentricity of e = 0.46 +- 0.01, placing this planet among the WJs with highly eccentric orbits. As no additional companion has been detected, this high eccentricity might be the consequence of past violent scattering events.

astro-ph.EP↗

arXiv2023

The GAPS programme at TNG XLIX. TOI-5398, the youngest compact multi-planet system composed of an inner sub-Neptune and an outer warm Saturn

Short-period giant planets are frequently found to be solitary compared to other classes of exoplanets. Small inner companions to giant planets with $P \lesssim$ 15 days are known only in five compact systems: WASP-47, Kepler-730, WASP-132, TOI-1130, and TOI-2000. Here, we report the confirmation of TOI-5398, the youngest compact multi-planet system composed of a hot sub-Neptune (TOI-5398 c, $P_{\rm c}$ = 4.77271 days) orbiting interior to a short-period Saturn (TOI-5398 b, $P_{\rm b}$ = 10.590547 days) planet, both transiting around a 650 $\pm$ 150 Myr G-type star. As part of the GAPS Young Object project, we confirmed and characterised this compact system, measuring the radius and mass of both planets, thus constraining their bulk composition. Using multidimensional Gaussian processes, we simultaneously modelled stellar activity and planetary signals from TESS Sector 48 light curve and our HARPS-N radial velocity time series. We have confirmed the planetary nature of both planets, TOI-5398 b and TOI-5398 c, alongside a precise estimation of stellar parameters. Through the use of astrometric, photometric, and spectroscopic observations, our findings indicate that TOI-5398 is a young, active G dwarf star (650 $\pm$ 150 Myr), with a rotational period of $P_{\rm rot}$ = 7.34 days. The transit photometry and radial velocity measurements enabled us to measure both the radius and mass of planets b, $R_b = 10.30\pm0.40 R_{\oplus}$, $M_b = 58.7\pm5.7 M_{\oplus}$, and c, $R_c = 3.52 \pm 0.19 R_{\oplus}$, $M_c = 11.8\pm4.8 M_{\oplus}$. TESS observed TOI-5398 during sector 48 and no further observations are planned in the current Extended Mission, making our ground-based light curves crucial for ephemeris improvement. With a Transmission Spectroscopy Metric value of around 300, TOI-5398 b is the most amenable warm giant (10 < $P$ < 100 days) for JWST atmospheric characterisation.

astro-ph.EP↗