arXiv subjects

S. Desidera

Publications and source records attributed to S. Desidera.

At least 55 records · Page 3Linked to original sources

arXiv2024

SPHERE RefPlanets: Search for epsilon Eridani b and warm dust

We carried out very deep VLT/SPHERE imaging polarimetry of the nearby system Eps Eri based on 38.5 hours of integration time with a 600 - 900 nm broadband filter to search for polarized scattered light from a planet or from circumstellar dust using AO, coronagraphy, high precision differential polarimetry, and angular differential imaging. We have improved several data reduction and post-processing techniques and also developed new ones to further increase the sensitivity of SPHERE/ZIMPOL. The data provide unprecedented contrast limits, but no significant detection of a point source or an extended signal from circumstellar dust. For each observing epoch, we obtained a point source contrast for the polarized intensity between $2\cdot 10^{-8}$ and $4\cdot 10^{-8}$ at the expected separation of the planet Eps Eri b of 1'' near quadrature phase. The polarimetric contrast limits are about six to 50 times better than the intensity limits because polarimetric imaging is much more efficient in speckle suppression. Combining the entire 14-month data set to the search for a planet moving on a Keplerian orbit with the K-Stacker software further improves the contrast limits by a factor of about two, to about $8 \cdot 10^{-9}$ at 1''. This would allow the detection of a planet with a radius of about 2.5 Jupiter radii. The surface brightness contrast limits achieved for the polarized intensity from an extended scattering region are about 15 mag arcsec$^{-2}$ at 1'', or up to 3 mag arcsec$^{-2}$ deeper than previous limits. For Eps Eri, these limits exclude the presence of a narrow dust ring and they constrain the dust properties. This study shows that the polarimetric contrast limits for reflecting planets with SPHERE/ZIMPOL can be improved to a level $<10^{-8}$ simply by collecting more data over many nights and using the K-Stacker software.

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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.

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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.

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arXiv2024

Orbital obliquity of the young planet TOI-5398 b and the evolutionary history of the system

Multi-planet systems exhibit remarkable architectural diversity. However, short-period giant planets are typically isolated. Compact systems like TOI-5398, with an outer close-orbit giant and an inner small-size planet, are rare among systems containing short-period giants. TOI-5398's unusual architecture coupled with its young age (650 $\pm$ 150 Myr) make it a promising system for measuring the original obliquity between the orbital axis of the giant and the stellar spin axis in order to gain insight into its formation and orbital migration. We collected in-transit (plus suitable off-transit) observations of TOI-5398 b with HARPS-N at TNG on March 25, 2023, obtaining high-precision radial velocity time series that allowed us to measure the Rossiter-McLaughlin (RM) effect. By modelling the RM effect, we obtained a sky-projected obliquity of $λ= 3.0^{+6.8}_{-4.2}$ deg for TOI-5398 b, consistent with the planet being aligned. With knowledge of the stellar rotation period, we estimated the true 3D obliquity, finding $ψ= (13.2\pm8.2)$ deg. Based on theoretical considerations, the orientation we measure is unaffected by tidal effects, offering a direct diagnostic for understanding the formation path of this planetary system. The orbital characteristics of TOI-5398, with its compact architecture, eccentricity consistent with circular orbits, and hints of orbital alignment, appear more compatible with the disc-driven migration scenario. TOI-5398, with its relative youth (compared with similar compact systems) and exceptional suitability for transmission spectroscopy studies, presents an outstanding opportunity to establish a benchmark for exploring the disc-driven migration model.

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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.

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arXiv2024

TASTE V. A new ground-based investigation of orbital decay in the ultra-hot Jupiter WASP-12b

The discovery of the first transiting hot Jupiters (HJs; giant planets on orbital periods shorter than $P\sim10$ days) was announced more than twenty years ago. As both ground- and space-based follow-up observations are piling up, we are approaching the temporal baseline required to detect secular variations in their orbital parameters. In particular, several recent studies focused on constraining the efficiency of the tidal decay mechanism to better understand the evolutionary time scales of HJ migration and engulfment. This can be achieved by measuring a monotonic decrease of orbital period $\mathrm{d}P/\mathrm{d}t<0$ due to mechanical energy being dissipated by tidal friction. WASP-12b was the first HJ for which a tidal decay scenario appeared convincing, even though alternative explanations have been hypothesized. Here we present a new analysis based on 28 unpublished high-precision transit light curves gathered over a twelve-year baseline and combined with all the available archival data, and an updated set of stellar parameters from HARPS-N high-resolution spectra, which are consistent with a main sequence scenario, close to the hydrogen exhaustion in the core. Our values of $\mathrm{d}P/\mathrm{d}t$ = $-30.72 \pm 2.67$ and $Q_{\ast}^{'}$ = $(2.13 \pm 0.18) \times 10^{5}$ are statistically consistent with previous studies, and indicate that WASP-12 is undergoing fast tidal dissipation. We additionally report the presence of an excess scatter in the timing data and discuss its possible origin.

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arXiv2024

Implications of the discovery of AF Lep b: The mass-luminosity relation for planets in the $β$ Pic Moving Group and the L-T transition for young companions and free-floating planets

Dynamical masses of young planets aged between 10 and 200 Myr detected in imaging play a crucial role in shaping models of giant planet formation. Regrettably, only a few such objects possess these characteristics. Furthermore, the evolutionary pattern of young sub-stellar companions in near-infrared colour-magnitude diagrams might diverge from free-floating objects, possibly due to differing formation processes. The recent identification of a giant planet around AF Lep, part of the beta Pic moving group (BPMG), encouraged us to re-examine these points. We considered updated dynamical masses and luminosities for the sub-stellar objects in the BPMG. In addition, we compared the properties of sub-stellar companions and free-floating objects in the BPMG and other young associations remapping the positions of the objects in the colour-magnitude diagram into a dustiness-temperature plane. We found that cold-start evolutionary models do not reproduce the mass-luminosity relation for sub-stellar companions in the BPMG. This aligns rather closely with predictions from 'hot start' scenarios and is consistent with recent planet formation models. We obtain rather good agreement with masses from photometry and the remapping approach compared to actual dynamical masses. We also found a strong suggestion that the near-infrared colour-magnitude diagram for young companions is different from that of free-floating objects belonging to the same young associations. If confirmed by further data, this last result would imply that cloud settling - which likely causes the transition between L and T spectral type - occurs at a lower effective temperature in young companions than in free-floating objects. This might tentatively be explained with a different chemical composition.

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arXiv2024

Stellar companions and Jupiter-like planets in young associations

Recently, combining high-contrast imaging and space astrometry we found that Jupiter-like (JL) planets are frequent in the beta Pic moving group (BPMG) around those stars where their orbit can be stable, prompting further analysis and discussion. We broaden our previous analysis to other young nearby associations to determine the frequency, mass, and separation of companions in general and JL in particular and their dependencies on the mass and age of the associations. We collected available data about companions including those revealed by visual observations, eclipses, spectroscopy, and astrometry. We determined search completeness and found that it is very high for stellar companions, while completeness corrections are still large for JL companions. Once these corrections are included, we found a high frequency of companions, both stellar (>0.52+/-0.03) and JL (0.57+/-0.11). The two populations are separated by a gap that corresponds to the brown dwarf desert. Within the population of massive companions, we found trends in frequency, separation, and mass ratios with stellar mass. Planetary companions pile up in the region just outside the ice line and we found them to be frequent once completeness was considered. The frequency of JL planets decreases with the overall mass and possibly the age of the association. We tentatively identify the two populations as due to disk fragmentation and core accretion, respectively. The distributions of stellar companions with a semi-major axis <1000 au is well reproduced by a simple model of formation by disk fragmentation. The observed trends with stellar mass can be explained by a shorter but much more intense phase of accretion onto the disk of massive stars and by a more steady and prolonged accretion on solar-type stars. Possible explanations for the trends in the population of JL planets with association mass and age are briefly discussed.

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arXiv2024

The GAPS Programme at TNG. LIII. New insights on the peculiar XO-2 system

Planets in binary systems are a fascinating and yet poorly understood phenomenon. Since there are only a few known large-separation systems in which both components host planets, characterizing them is a key target for planetary science. In this paper, we aim to carry out an exhaustive analysis of the interesting XO-2 system, where one component appears to be a system with only one planet, while the other has at least three planets. Over the last 9 years, we have collected 39 spectra of XO-2N and 106 spectra of XO-2S with the High Accuracy Radial velocity Planet Searcher for the Northern emisphere (HARPS-N) in the framework of the Global Architecture of Planetary Systems project, from which we derived precise radial velocity and activity indicator measurements. Additional spectroscopic data from the High Resolution Echelle Spectrometer and from the High Dispersion Spectrograph, and the older HARPS-N data presented in previous papers, have also been used to increase the total time span. We also used photometric data from TESS to search for potential transits that have not been detected yet. For our analysis, we mainly used PyORBIT, an advanced Python tool for the Bayesian analysis of RVs, activity indicators, and light curves. We found evidence for an additional long-period planet around XO-2S and characterized the activity cycle likely responsible for the long-term RV trend noticed for XO-2N. The new candidate is an example of a Jovian analog with $m\sin i \sim 3.7$ M$_J$, $a \sim 5.5$ au, and $e = 0.09$. We also analyzed the stability and detection limits to get some hints about the possible presence of additional planets. Our results show that the planetary system of XO-2S is at least one order of magnitude more massive than that of XO-2N. The implications of these findings for the interpretation of the previously known abundance difference between components are also discussed.

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arXiv2023

First light of VLT/HiRISE: High-resolution spectroscopy of young giant exoplanets

A major endeavor of this decade is the direct characterization of young giant exoplanets at high spectral resolution to determine the composition of their atmosphere and infer their formation processes and evolution. Such a goal represents a major challenge owing to their small angular separation and luminosity contrast with respect to their parent stars. Instead of designing and implementing completely new facilities, it has been proposed to leverage the capabilities of existing instruments that offer either high contrast imaging or high dispersion spectroscopy, by coupling them using optical fibers. In this work we present the implementation and first on-sky results of the HiRISE instrument at the very large telescope (VLT), which combines the exoplanet imager SPHERE with the recently upgraded high resolution spectrograph CRIRES using single-mode fibers. The goal of HiRISE is to enable the characterization of known companions in the $H$ band, at a spectral resolution of the order of $R = λ/Δλ= 100\,000$, in a few hours of observing time. We present the main design choices and the technical implementation of the system, which is constituted of three major parts: the fiber injection module inside of SPHERE, the fiber bundle around the telescope, and the fiber extraction module at the entrance of CRIRES. We also detail the specific calibrations required for HiRISE and the operations of the instrument for science observations. Finally, we detail the performance of the system in terms of astrometry, temporal stability, optical aberrations, and transmission, for which we report a peak value of $\sim$3.9% based on sky measurements in median observing conditions. Finally, we report on the first astrophysical detection of HiRISE to illustrate its potential.

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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.

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arXiv2023

Binary planet formation through tides

The search for satellites around exoplanets represents one of the greatest challenges in advancing the characterization of planetary systems. Currently, we can only detect massive satellites, which resemble additional planetary companions rather than rocky moons. It is not yet well understood whether such substellar pairs, known as binary planets, are common or how they form. In this study, we investigated the formation scenario for binary planets resulting from tidal dissipation during close encounters in the gravitational instability scenario. We conducted seven sets of simulations, varying the number of initial planets injected into the system from two to five, as well as the amount of energy lost due to tides. Our results demonstrate that this formation mechanism is quite efficient in producing binary planets, with an average occurrence rate for the simulated systems of 14.3%. Additionally, we present the distribution of relevant physical parameters (semi-major axis, eccentricity, mass ratios, and formation time) for planet-planet pairs. We also provide comprehensive statistics for single planets and planet-planet pairs.

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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.

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arXiv2023

Photometric follow-up of the 20 Myr-old multi-planet host star V1298~Tau with CHEOPS and ground-based telescopes

V1298 Tau hosts at least four planets. Since its discovery, this system has been a target of intensive photometric and spectroscopic monitoring. The characterisation of its architecture and planets' fundamental properties turned out to be very challenging so far. The determination of the orbital ephemeris of the outermost planet V1298 Tau $e$ remains an open question. Only two transits have been detected so far by $Kepler/K2$ and TESS, allowing for a grid of reference periods to be tested with new observations, without excluding the possibility of transit timing variations. Observing a third transit would allow to better constrain the orbital period, and would also help determining an accurate radius of V1298 Tau $e$ because the former transits showed different depths. We observed V1298 Tau with the CHEOPS space telescope to search for a third transit of planet $e$ within observing windows that have been selected in order to test three of the shortest predicted orbital periods. We also collected ground-based observations to verify the result found with CHEOPS. We reanalysed $Kepler/K2$ and TESS light curves to test how the results derived from these data are affected by alternative photometric extraction and detrending methods. We report the detection with CHEOPS of a transit that could be attributed to V1298 Tau $e$. If so, that result implies that the orbital period calculated from fitting a linear ephemeris to the three available transits is close to $\sim45$ days. Results from the ground-based follow-up marginally support this possibility. We found that $\textit{i}$) the transit observed by CHEOPS has a longer duration compared to that of the transits observed by $Kepler/K2$ and TESS; $\textit{ii}$) the transit observed by TESS is $>30\%$ deeper than that of $Kepler/K2$ and CHEOPS, and deeper than the measurement previously reported in the literature, according to our reanalysis.

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arXiv2023

A super-massive Neptune-sized planet

Neptune-sized planets exhibit a wide range of compositions and densities, depending onf cators related to their formation and evolution history, such as the distance from their host stars and atmospheric escape processes. They can vary from relatively low-density planets with thick hydrogen-helium atmospheres to higher-density planets with a substantial amount of water or a rocky interior with a thinner atmosphere, such as HD 95338 b, TOI-849 b and TOI-2196 b. The discovery of exoplanets in the hot-Neptune desert, a region close to the host stars with a deficit of Neptune-sized planets, provides insights into the formation and evolution of planetary systems, including the existence of this region itself. Here we show observations of the transiting planet TOI-1853 b, which has a radius of 3.46 +- 0.08 Earth radii and orbits a dwarf star every 1.24 days. This planet has a mass of 73.2 +- 2.7 Earth masses, almost twice that of any other Neptune-sized planet known so far, and a density of 9.7 +- 0.8 grams per cubic centimetre. These values place TOI-1853 b in the middle of the Neptunian desert and imply that heavy elements dominate its mass. The properties of TOI-1853 b present a puzzle for conventional theories of planetary formation and evolution, and could be the result of several proto-planet collisions or the final state of an initially high-eccentricity planet that migrated closer to its parent star.

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arXiv2023

Multiples among B stars in the Scorpius-Centaurus association

We discuss the properties of companions to B stars in the Scorpius-Centaurus association (age ~15 Myr, 181 B-stars). We gathered available data combining high contrast imaging samples with evidence of companions from Gaia, from eclipsing binaries, and from spectroscopy. We evaluated the completeness of the binary search and estimated the mass and semi-major axis for all detected companions. These data provide a complete sample of stellar secondaries for separation >3 au, and they are highly informative as to closer companions. We found evidence for 200 companions around 181 stars. The fraction of single star is 15.2\pm 4.1% for stars with M_A>3.5 Msun while it is 31.5\pm 5.9% for lower-mass stars. The median semi-major axis of the orbits of the companions is smaller for B than in A stars, confirming a turn-over previously found for OB stars. The mass distribution of the very wide (a>1000 au) and closer companions is different. Very few companions of massive stars M_A>5.0 Msun have a mass below solar and even fewer are M stars with a semi-major axis <1000 au. The scarcity of low-mass companions extends throughout the whole sample. Most early B stars are in compact systems with massive secondaries, while lower-mass stars are mainly in wider systems with a larger spread in mass ratios. We interpret our results as the formation of secondaries with a semi-major axis <1000 au (about 80% of the total) by fragmentation of the disk of the primary and selective mass accretion on the secondaries. The observed trends with primary mass may be explained by a more prolonged phase of accretion episodes on the disk and by a more effective inward migration. We detected twelve new stellar companions from the BEAST survey and of a new BD companion at 9.6 arcsec from HIP74752 using Gaia data, and we discuss the cases of possible BD and low-mass stellar companions to HIP59173, HIP62058, and HIP64053.

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arXiv2023

The GAPS program at TNG XLVII: The unusual formation history of V1298 Tau

Observational data from space and ground-based campaigns reveal that the 10-30 Ma old V1298 Tau star hosts a compact and massive system of four planets. Mass estimates for the two outer giant planets point to unexpectedly high densities for their young ages. We investigate the formation of these two outermost giant planets, V1298 Tau b and e, and the present dynamical state of V1298 Tau's global architecture to shed light on the history of this young and peculiar extrasolar system. We perform detailed N-body simulations to explore the link between the densities of V1298 Tau b and e and their migration and accretion of planetesimals within the native circumstellar disk. We combine N-body simulations and the normalized angular momentum deficit (NAMD) analysis to characterize V1298 Tau's dynamical state and connect it to the formation history of the system. We search for outer planetary companions to constrain V1298 Tau's architecture and the extension of its primordial circumstellar disk. The high densities of V1298 Tau b and e suggest they formed quite distant from their host star, likely beyond the CO$_2$ snowline. The higher nominal density of V1298 Tau e suggests it formed farther out than V1298 Tau b. The current architecture of V1298 Tau is not characterized by resonant chains. Planet-planet scattering with an outer giant planet is the most likely cause for the instability, but our search for outer companions using SPHERE and GAIA observations excludes only the presence of planets more massive than 2 M$_\textrm{J}$. The most plausible scenario for V1298 Tau's formation is that the system is formed by convergent migration and resonant trapping of planets born in a compact and plausibly massive disk. The migration of V1298 Tau b and e leaves in its wake a dynamically excited protoplanetary disk and creates the conditions for the resonant chain breaking by planet-planet scattering.

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arXiv2023

An imaged 15Mjup companion within a hierarchical quadruple system

Since 2019, the direct imaging B-star Exoplanet Abundance Study (BEAST) at SPHERE@VLT has been scanning the surroundings of young B-type stars in order to ascertain the ultimate frontiers of giant planet formation. Recently, the $17^{+3}_{-4}$ Myr HIP 81208 was found to host a close-in (~50 au) brown dwarf and a wider (~230 au) late M star around the central 2.6Msun primary. Alongside the continuation of the survey, we are undertaking a complete reanalysis of archival data aimed at improving detection performances so as to uncover additional low-mass companions. We present here a new reduction of the observations of HIP 81208 using PACO ASDI, a recent and powerful algorithm dedicated to processing high-contrast imaging datasets, as well as more classical algorithms and a dedicated PSF-subtraction approach. The combination of different techniques allowed for a reliable extraction of astrometric and photometric parameters. A previously undetected source was recovered at a short separation from the C component of the system. Proper motion analysis provided robust evidence for the gravitational bond of the object to HIP 81208 C. Orbiting C at a distance of ~20 au, this 15Mjup brown dwarf becomes the fourth object of the hierarchical HIP 81208 system. Among the several BEAST stars which are being found to host substellar companions, HIP 81208 stands out as a particularly striking system. As the first stellar binary system with substellar companions around each component ever found by direct imaging, it yields exquisite opportunities for thorough formation and dynamical follow-up studies.

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