arXiv subjects

M. Cecconi

Publications and source records attributed to M. Cecconi.

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.

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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$\alpha$. We spectrally resolve the HeI triplet and confirm the published detections for WASP-69b (3.91$\pm$0.22%, 17.6$\sigma$), WASP-107b (8.17$^{+0.80}_{-0.76}$%, 10.5$\sigma$), HAT-P-11b (1.36$\pm$0.17%, 8.0$\sigma$), and GJ3470b (1.75$^{+0.39}_{-0.36}$%, 4.7$\sigma$). We do not find evidence of extra absorption for GJ436b. We observe night-to-night variations in the HeI absorption signal for WASP-69b, associated with variability in H$\alpha$, which likely indicates the influence of stellar activity. Additionally, we find that the HeI signal of GJ3470b originates from a single transit, thereby corroborating the discrepancies in the existing literature. An inspection of the H$\alpha$ 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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arXiv2023

The GAPS programme at TNG LII. Spot modeling of V1298 Tau using SpotCCF tool

The intrinsic variability due to the magnetic activity of young active stars is one of the main challenges in detecting and characterising exoplanets. We present a method able to model the stellar photosphere and its surface inhomogeneities (starspots) in young/active and fast-rotating stars, based on the cross-correlation function (CCF) technique, to extract information about the spot configuration of the star. Within the Global Architecture of Planetary Systems (GAPS) Project at the Telescopio Nazionale Galileo, we analysed more than 300 spectra of the young planet-hosting star V1298 Tau provided by HARPS-N high-resolution spectrograph. By applying the SpotCCF model to the CCFs we extracted the spot configuration (latitude, longitude and projected filling factor) of this star, and also provided the new RVs time series of this target. We find that the features identified in the CCF profiles of V1298 Tau are modulated by the stellar rotation, supporting our assumption that they are caused by starspots. The analysis suggests a differential rotation velocity of the star with lower rotation at higher latitudes. Also, we find that SpotCCF provides an improvement in RVs extraction with a significantly lower dispersion with respect to the commonly used pipelines, with consequent mitigation of the stellar activity contribution modulated with stellar rotation. A detection sensitivity test, by the direct injection of a planetary signal into the data, confirmed that the SpotCCF model improves the sensitivity and ability to recover planetary signals. Our method enables the modelling of the stellar photosphere, extracting the spot configuration of young/active and rapidly rotating stars. It also allows for the extraction of optimised RV time series, thereby enhancing our detection capabilities for new exoplanets and advancing our understanding of stellar activity.

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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

The GAPS Programme at TNG XLII. A characterisation study of the multi-planet system around the 400 Myr-old star HD 63433 (TOI-1726)

For more than two years, we monitored with the HARPS-N spectrograph the 400 Myr-old star HD\,63433, which hosts two close-in (orbital periods $P_b\sim7.1$ and $P_c\sim20.5$ days) sub-Neptunes detected by the TESS space telescope, and it was announced in 2020. Using radial velocities and additional TESS photometry, we aim to provide the first measurement of their masses, improve the measure of their size and orbital parameters, and study the evolution of the atmospheric mass-loss rate due to photoevaporation. We tested state-of-the-art analysis techniques and different models to mitigate the dominant signals due to stellar activity that are detected in the radial velocity time series. We used a hydro-based analytical description of the atmospheric mass-loss rate, coupled with a core-envelope model and stellar evolutionary tracks, to study the past and future evolution of the planetary masses and radii. We derived new measurements of the planetary orbital periods and radii ($P_b=7.10794\pm0.000009$ d, $r_b=2.02^{+0.06}_{-0.05}$ $R_{\oplus}$; $P_c=20.54379\pm0.00002$ d, $r_c=2.44\pm0.07$ $R_{\oplus}$), and determined mass upper limits ($m_b\lesssim$11 $M_{\oplus}$; $m_c\lesssim$31 $M_{\oplus}$; 95$\%$ confidence level), with evidence at a 2.1--2.7$\sigma$ significance level that HD\,63433\,c might be a dense mini-Neptune with a Neptune-like mass. For a grid of test masses below our derived dynamical upper limits, we found that HD\,63433\,b has very likely lost any gaseous H-He envelope, supporting HST-based observations that are indicative of there being no ongoing atmospheric evaporation. HD\,63433\,c will keep evaporating over the next $\sim$5 Gyr if its current mass is $m_c\lesssim$15 $M_{\oplus}$, while it should be hydrodynamically stable for higher masses.

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arXiv2022

Investigating the origin of optical and X-ray pulsations of the transitional millisecond pulsar PSR J1023+0038

PSR J1023+0038 is the first millisecond pulsar that was ever observed as an optical and UV pulsar. So far, it is the only optical transitional millisecond pulsar. The rotation- and accretion-powered emission mechanisms hardly individually explain the observed characteristics of optical pulsations. A synergistic model, combining these standard emission processes, was proposed to explain the origin of the X-ray/UV/optical pulsations. We study the phase lag between the pulses in the optical and X-ray bands to gain insight into the physical mechanisms that cause it. We performed a detailed timing analysis of simultaneous or quasi-simultaneous observations in the X-ray band, acquired with the XMM-Newton and NICER satellites, and in the optical band, with the fast photometers SiFAP2 (mounted at the 3.6 m Telescopio Nazionale Galileo) and Aqueye+ (mounted at the 1.8 m Copernicus Telescope). We estimated the time lag of the optical pulsation with respect to that in the X-rays by modeling the folded pulse profiles with two harmonic components. Optical pulses lag the X-ray pulses by $\sim$ 150 $\mu$s in observations acquired with instruments (NICER and Aqueye+) whose absolute timing uncertainty is much smaller than the measured lag. We also show that the phase lag between optical and X-ray pulsations lies in a limited range of values, $\delta \phi \in$ (0 $-$ 0.15), which is maintained over timescales of about five years. This indicates that both pulsations originate from the same region, and it supports the hypothesis of a common emission mechanism. Our results are interpreted in the shock-driven mini pulsar nebula scenario. This scenario suggests that optical and X-ray pulses are produced by synchrotron emission from the shock that formed within a few light cylinder radii away ($\sim$ 100 km) from the pulsar, where its striped wind encounters the accretion disk inflow.

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arXiv2021

Twenty-year monitoring of the surface magnetic fields of chemically peculiar stars

Magnetic chemically peculiar stars of the main sequence can present rotational periods as long as many decades. Here we report the results of an observational campaign started in 2001 aimed at establishing these very long periods from the variability of the integrated magnetic field modulus, the so-called surface magnetic field $B_s$, as measured from the Zeeman splitting of the Fe{\sc ii}\,6149.258\,{\AA} spectral line. Thirty-six stars have been monitored with various high-resolution spectrographs at different telescopes, totalling 412 newly collected spectra. To improve the phase coverage, we have also exploited all public archives containing high-resolution spectra, many not yet published. On the basis of these new $B_s$ variability curves, we 1) confirm or revisit the periods of 24 stars, 2) extend the lower limits to the periods of HD\,55719 ($P > 38$\,yr), HD\,165474 ($P > 27$\,yr), HD\,177765 ($P > 37$\,yr), 3) establish for the first time the periods of HD\,29578 ($P = 10.95$\,yr), HD\,47103 ($P = 17.683$\,d), HD\,150562 ($P = 5.7$\,yr), HD\,216018 ($P = 34.044$\,d), and 4) set lower limits to the periods of HD\,75445 ($P >> 14$\,yr), HD\,110066 ($P >> 29$\,yr), HD\,116114 ($P > 48$\,yr), and HD\,137949 ($P > 27$\,yr). As to $\gamma$\,Equ, whose period must exceed 90 years, we point out a clear decrease in the field modulus, the maximum of which coincides within the uncertainties with the minimum of the variation in the integrated longitudinal field.

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arXiv2021

Estimating Magnetic Filling Factors From Simultaneous Spectroscopy and Photometry: Disentangling Spots, Plage, and Network

State of the art radial velocity (RV) exoplanet searches are limited by the effects of stellar magnetic activity. Magnetically active spots, plage, and network regions each have different impacts on the observed spectral lines, and therefore on the apparent stellar RV. Differentiating the relative coverage, or filling factors, of these active regions is thus necessary to differentiate between activity-driven RV signatures and Doppler shifts due to planetary orbits. In this work, we develop a technique to estimate feature-specific magnetic filling factors on stellar targets using only spectroscopic and photometric observations. We demonstrate linear and neural network implementations of our technique using observations from the solar telescope at HARPS-N, the HK Project at the Mt. Wilson Observatory, and the Total Irradiance Monitor onboard SORCE. We then compare the results of each technique to direct observations by the Solar Dynamics Observatory (SDO). Both implementations yield filling factor estimates that are highly correlated with the observed values. Modeling the solar RVs using these filling factors reproduces the expected contributions of the suppression of convective blueshift and rotational imbalance due to brightness inhomogeneities. Both implementations of this technique reduce the overall activity-driven RMS RVs from 1.64 m/s to 1.02 m/s, corresponding to a 1.28 m/s reduction in the RMS variation. The technique provides an additional 0.41 m/s reduction in the RMS variation compared to traditional activity indicators.

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arXiv2021

The obliquity and atmosphere of the ultra-hot Jupiter TOI-1431b (MASCARA-5b): A misaligned orbit and no signs of atomic ormolecular absorptions

Ultra-hot Jupiters are defined as giant planets with equilibrium temperatures larger than 2000 K. Most of them are found orbiting bright A-F type stars, making them extremely suitable objects to study their atmospheres using high-resolution spectroscopy. Recent studies show a variety of atoms and molecules detected in the atmospheres of this type of planets. Here we present our analysis of the newly discovered ultra-hot Jupiter TOI-1431b/MASCARA-5b, using two transit observations with the HARPS-N spectrograph and one transit observation with the EXPRES spectrograph. Analysis of the Rossiter-McLaughlin effect shows that the planet is in a polar orbit, with a projected obliquity $ \lambda = -155^{+20}_{-10}$ degrees. Combining the nights and applying both cross-correlation methods and transmission spectroscopy, we find no evidences of CaI, FeI, FeII, MgI, NaI, VI, TiO, VO or H$\alpha$ in the atmosphere of the planet. Our most likely explanation for the lack of atmospheric features is the large surface gravity of the planet.

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arXiv2021

TOI-1634 b: an Ultra-Short Period Keystone Planet Sitting Inside the M Dwarf Radius Valley

Studies of close-in planets orbiting M dwarfs have suggested that the M dwarf radius valley may be well-explained by distinct formation timescales between enveloped terrestrials, and rocky planets that form at late times in a gas-depleted environment. This scenario is at odds with the picture that close-in rocky planets form with a primordial gaseous envelope that is subsequently stripped away by some thermally-driven mass loss process. These two physical scenarios make unique predictions of the rocky/enveloped transition's dependence on orbital separation such that studying the compositions of planets within the M dwarf radius valley may be able to establish the dominant physics. Here, we present the discovery of one such keystone planet: the ultra-short period planet TOI-1634 b ($P=0.989$ days, $F=121 F_{\oplus}$, $r_p = 1.790^{+0.080}_{-0.081} R_{\oplus}$) orbiting a nearby M2 dwarf ($K_s=8.7$, $R_s=0.45 R_{\odot}$, $M_s=0.50 M_{\odot}$) and whose size and orbital period sit within the M dwarf radius valley. We confirm the TESS-discovered planet candidate using extensive ground-based follow-up campaigns, including a set of 32 precise radial velocity measurements from HARPS-N. We measure a planetary mass of $4.91^{+0.68}_{-0.70} M_{\oplus}$, which makes TOI-1634 b inconsistent with an Earth-like composition at $5.9\sigma$ and thus requires either an extended gaseous envelope, a large volatile-rich layer, or a rocky portion that is not dominated by iron and silicates to explain its mass and radius. The discovery that the bulk composition of TOI-1634 b is inconsistent with that of the Earth favors the gas-depleted formation mechanism to explain the emergence of the radius valley around M dwarfs with $M_s\lesssim 0.5 M_{\odot}$.

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arXiv2021

Optical and ultraviolet pulsed emission from an accreting millisecond pulsar

Millisecond spinning, low magnetic field neutron stars are believed to attain their fast rotation in a 0.1-1 Gyr-long phase during which they accrete matter endowed with angular momentum from a low-mass companion star. Despite extensive searches, coherent periodicities originating from accreting neutron star magnetospheres have been detected only at X-ray energies and in ~10% of the presently known systems. Here we report the detection of optical and ultraviolet coherent pulsations at the X-ray period of the transient low mass X-ray binary system SAX J1808.4-3658, during an accretion outburst that occurred in August 2019. At the time of the observations, the pulsar was surrounded by an accretion disc, displayed X-ray pulsations and its luminosity was consistent with magnetically funneled accretion onto the neutron star. Current accretion models fail to account for the luminosity of both optical and ultraviolet pulsations; these are instead more likely driven by synchro-curvature radiation in the pulsar magnetosphere or just outside of it. This interpretation would imply that particle acceleration can take place even when mass accretion is going on, and opens up new perspectives in the study of coherent optical/UV pulsations from fast spinning accreting neutron stars in low-mass X-ray binary systems.

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arXiv2020

Separating planetary reflex Doppler shifts from stellar variability in the wavelength domain

Stellar magnetic activity produces time-varying distortions in the photospheric line profiles of solar-type stars. These lead to systematic errors in high-precision radial-velocity measurements, which limit efforts to discover and measure the masses of low-mass exoplanets with orbital periods of more than a few tens of days. We present a new data-driven method for separating Doppler shifts of dynamical origin from apparent velocity variations arising from variability-induced changes in the stellar spectrum. We show that the autocorrelation function (ACF) of the cross-correlation function used to measure radial velocities is effectively invariant to translation. By projecting the radial velocities on to a subspace labelled by the observation identifiers and spanned by the amplitude coefficients of the ACF's principal components, we can isolate and subtract velocity perturbations caused by stellar magnetic activity. We test the method on a 5-year time sequence of 853 daily 15-minute observations of the solar spectrum from the HARPS-N instrument and solar-telescope feed on the 3.58-m Telescopio Nazionale Galileo. After removal of the activity signals, the heliocentric solar velocity residuals are found to be Gaussian and nearly uncorrelated. We inject synthetic low-mass planet signals with amplitude $K=40$ cm s$^{-1}$ into the solar observations at a wide range of orbital periods. Projection into the orthogonal complement of the ACF subspace isolates these signals effectively from solar activity signals. Their semi-amplitudes are recovered with a precision of $\sim~6.6$ cm s$^{-1}$, opening the door to Doppler detection and characterization of terrestrial-mass planets around well-observed, bright main-sequence stars across a wide range of orbital periods.

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arXiv2020

Three Years of HARPS-N High-Resolution Spectroscopy and Precise Radial Velocity Data for the Sun

The solar telescope connected to HARPS-N has been observing the Sun since the summer of 2015. Such high-cadence, long-baseline data set is crucial for understanding spurious radial-velocity signals induced by our Sun and by the instrument. On the instrumental side, this data set allowed us to detect sub-\ms\,systematics that needed to be corrected for. The goal of this manuscript is to i) present a new data reduction software for HARPS-N, ii) demonstrate the improvement brought by this new software on the first three years of the HARPS-N solar data set, and iii) release all the obtained solar products, from extracted spectra to precise radial velocities. To correct for the instrumental systematics observed in the data reduced with the current version of the HARPS-N data reduction software (DRS version 3.7), we adapted the newly available ESPRESSO DRS (version 2.2.3) to HARPS-N and developed new optimized recipes for the spectrograph. We then compared the first three years of HARPS-N solar data reduced with the current and new DRS. The most significant improvement brought by the new DRS is a strong decrease in the day-to-day radial-velocity scatter, from 1.27 to 1.07\ms; this is thanks to a more robust method to derive wavelength solutions, but also to the use of calibrations closer in time. The newly derived solar radial-velocities are also better correlated with the chromospheric activity level of the Sun on the long-term, with a Pearson correlation coefficient of 0.93 compared to 0.77 before, which is expected from our understanding of stellar signals. Finally, we also discuss how HARPS-N spectral ghosts contaminate the measurement of the calcium activity index, and present an efficient technique to derive an index free of instrumental systematics. This paper presents a new data reduction software for HARPS-N, and demonstrates its improvements [...]

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arXiv2020

Detection Limits of Low-mass, Long-period Exoplanets Using Gaussian Processes Applied to HARPS-N Solar RVs

Radial velocity (RV) searches for Earth-mass exoplanets in the habitable zone around Sun-like stars are limited by the effects of stellar variability on the host star. In particular, suppression of convective blueshift and brightness inhomogeneities due to photospheric faculae/plage and starspots are the dominant contribution to the variability of such stellar RVs. Gaussian process (GP) regression is a powerful tool for statistically modeling these quasi-periodic variations. We investigate the limits of this technique using 800 days of RVs from the solar telescope on the High Accuracy Radial velocity Planet Searcher for the Northern hemisphere (HARPS-N) spectrograph. These data provide a well-sampled time series of stellar RV variations. Into this data set, we inject Keplerian signals with periods between 100 and 500 days and amplitudes between 0.6 and 2.4 m s$^{-1}$. We use GP regression to fit the resulting RVs and determine the statistical significance of recovered periods and amplitudes. We then generate synthetic RVs with the same covariance properties as the solar data to determine a lower bound on the observational baseline necessary to detect low-mass planets in Venus-like orbits around a Sun-like star. Our simulations show that discovering planets with a larger mass ($\sim$ 0.5 m s$^{-1}$) using current-generation spectrographs and GP regression will require more than 12 yr of densely sampled RV observations. Furthermore, even with a perfect model of stellar variability, discovering a true exo-Venus ($\sim$ 0.1 m s$^{-1}$) with current instruments would take over 15 yr. Therefore, next-generation spectrographs and better models of stellar variability are required for detection of such planets.

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arXiv2020

The GAPS Programme at TNG -- XXV. Stellar atmospheric parameters and chemical composition through GIARPS optical and near-infrared spectra

The detailed chemical composition of stars is important in many astrophysical fields, among which the characterisation of exoplanetary systems. Previous studies seem to indicate an anomalous chemical pattern of the youngest stellar population in the solar vicinity with a sub-solar metal content. This can influence various observational relations linking the properties of exoplanets to the characteristics of the host stars, for example the giant planet-metallicity relation. In this framework, we aim to expand our knowledge of the chemical composition of intermediate-age stars and understand whether these peculiarities are real or related to spectroscopic analysis techniques. We analysed high-resolution optical and near-infrared GIARPS spectra of intermediate-age stars (< 700Myr). To overcome issues related to the young ages of the stars, we applied a new spectroscopic method that uses titanium lines to derive the atmospheric parameters, in particular surface gravities and microturbulence velocity parameter. We also derived abundances of 14 different atomic species. The lack of systematic trends between elemental abundances and effective temperatures validates our method. However, we observed that the coolest (<5400 K) stars in the sample, display higher abundances for the Cr II, and for high-excitation potential C I lines. We found a positive correlation between the higher abundances measured of C I and Cr II and the activity index logR$_{HK}$. Instead, we found no correlations between the C abundances obtained from CH molecular band at 4300\AA, and both effective temperatures and activity. Thus, we suggest that these are better estimates for C abundances in young and cool stars. Finally, we found an indication of an increasing abundance ratio [X/H] with the condensation temperature for HD167389, indicating possible episodes of planet engulfment.

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arXiv2020

The GAPS programme at TNG XXII. The GIARPS view of the extended helium atmosphere of HD189733 b accounting for stellar activity

Exoplanets orbiting very close to their host star are strongly irradiated. This can lead the upper atmospheric layers to expand and evaporate into space. The metastable helium (HeI) triplet at 1083.3nm has recently been shown to be a powerful diagnostic to probe extended and escaping exoplanetary atmosphere. We perform high-resolution transmission spectroscopy of the transiting hot Jupiter HD189733b with the GIARPS (GIANO-B + HARPS-N) observing mode of the Telescopio Nazionale Galileo, taking advantage of the simultaneous optical+near infrared spectral coverage to detect HeI in the planet's extended atmosphere and to gauge the impact of stellar magnetic activity on the planetary absorption signal. Observations were performed during five transit events of HD189733b. By comparison of the in- and out-of-transit GIANO-B observations we compute high-resolution transmission spectra, on which we perform equivalent width measurements and light-curves analyses to gauge the excess in-transit absorption in the HeI triplet. We detect an absorption signal during all five transits. The mean in-transit absorption depth amounts to 0.75+/-0.03%. We detect night-to-night variations in the HeI absorption signal likely due to the transit events occurring in presence of stellar surface inhomogeneities. We evaluate the impact of stellar-activity pseudo-signals on the true planetary absorption using a comparative analysis of the HeI and the H$\alpha$ lines. We interpret the time-series of the HeI absorption lines in the three nights not affected by stellar contamination -exhibiting a mean in-transit absorption depth of 0.77+/-0.04%- using a 3-d atmospheric code. Our simulations suggest that the helium layers only fill part of the Roche lobe. Observations can be explained with a thermosphere heated to $\sim$12000 K, expanding up to $\sim$1.2 planetary radii, and losing $\sim$1 g/s of metastable helium.

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arXiv2020

The lowest frequency Fast Radio Bursts: Sardinia Radio Telescope detection of the periodic FRB 180916 at 328 MHz

We report on the lowest-frequency detection to date of three bursts from the fast radio burst FRB 180916, observed at 328 MHz with the Sardinia Radio Telescope (SRT). The SRT observed the periodic repeater FRB 180916 for five days from 2020 February 20 to 24 during a time interval of active radio bursting, and detected the three bursts during the first hour of observations; no more bursts were detected during the remaining ~ 30 hours. Simultaneous SRT observations at 1548 MHz did not detect any bursts. Burst fluences are in the range 37 to 13 Jy ms. No relevant scattering is observed for these bursts. We also present the results of the multi-wavelength campaign we performed on FRB 180916, during the five days of the active window. Simultaneously with the SRT observations, others with different time spans were performed with the Northern Cross at 408 MHz, with XMM-Newton, NICER, INTEGRAL, AGILE, and with the TNG and two optical telescopes in Asiago, which are equipped with fast photometers. XMM-Newton obtained data simultaneously with the three bursts detected by the SRT, and determined a luminosity upper limit in the 0.3-10 keV energy range of ~$10^{45}$ erg/s for the burst emission. AGILE obtained data simultaneously with the first burst and determined a fluence upper limit in the MeV range for millisecond timescales of $ 10^{-8}$ erg cm$^{-2}$.Our results show that absorption from the circumburst medium does not significantly affect the emission from FRB 180916, thus limiting the possible presence of a superluminous supernova around the source, and indicate that a cutoff for the bursting mechanism, if present, must be at lower frequencies. Our multi-wavelength campaign sensitively constrains the broadband emission from FRB 180916, and provides the best limits so far for the electromagnetic response to the radio bursting of this remarkable source of fast radio bursts.

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arXiv2020

The GAPS Programme at TNG XXI -- A GIARPS case-study of known young planetary candidates: confirmation of HD 285507 b and refutation of AD Leo b

The existence of hot Jupiters is still not well understood. Two main channels are thought to be responsible for their current location: a smooth planet migration through the proto-planetary disk or the circularization of an initial high eccentric orbit by tidal dissipation leading to a strong decrease of the semimajor axis. Different formation scenarios result in different observable effects, such as orbital parameters (obliquity/eccentricity), or frequency of planets at different stellar ages. In the context of the GAPS Young-Objects project, we are carrying out a radial velocity survey with the aim to search and characterize young hot-Jupiter planets. Our purpose is to put constraints on evolutionary models and establish statistical properties, such as the frequency of these planets from a homogeneous sample. Since young stars are in general magnetically very active, we performed multi-band (visible and near-infrared) spectroscopy with simultaneous GIANO-B + HARPS-N (GIARPS) observing mode at TNG. This helps to deal with stellar activity and distinguish the nature of radial velocity variations: stellar activity will introduce a wavelength-dependent radial velocity amplitude, whereas a Keplerian signal is achromatic. As a pilot study, we present here the cases of two already claimed hot Jupiters orbiting young stars: HD285507 b and AD Leo b. Our analysis of simultaneous high-precision GIARPS spectroscopic data confirms the Keplerian nature of HD285507's radial velocities variation and refines the orbital parameters of the hot Jupiter, obtaining an eccentricity consistent with a circular orbit. On the other hand, our analysis does not confirm the signal previously attributed to a planet orbiting AD Leo. This demonstrates the power of the multi-band spectroscopic technique when observing active stars.

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