arXiv subjects

A. F. M. Fiorenzano

Publications and source records attributed to A. F. M. Fiorenzano.

16 recordsLinked to original sources

arXiv2024

The GAPS Programme at TNG. LXI. Atmospheric parameters and elemental abundances of TESS young exoplanet host stars

The study of exoplanets at different evolutionary stages can shed light on their formation, migration, and evolution. The determination of exoplanet properties depends on the properties of their host stars. It is therefore important to characterise the host stars for accurate knowledge on their planets. Our final goal is to derive, in a homogeneous and accurate way, the stellar atmospheric parameters and elemental abundances of ten young TESS transiting planet-hosting GK stars followed up with the HARPS-N at TNG spectrograph within the GAPS programme. We derived stellar kinematic properties, atmospheric parameters, and abundances of 18 elements. Lithium line measurements were used as approximate age estimations. We exploited chemical abundances and their ratios to derive information on planetary composition. Elemental abundances and kinematic properties are consistent with the nearby Galactic thin disk. All targets show C/O<0.8 and 1.0<Mg/Si<1.5, compatible with silicate mantles made of a mixture of pyroxene and olivine assemblages. The Fe/Mg ratios, with values of $\sim$0.7-1.0, show a propensity for the planets to have big (iron) cores. All stars hosting very low-mass planets show Mg/Si values consistent with the Earth values, thus demonstrating their similar mantle composition. Hot Jupiter host stars show a lower content of O/Si, which could be related to the lower presence of water content. We confirm a trend found in the literature between stellar [O/Fe] and total planetary mass, implying an important role of the O in shaping the mass fraction of heavy elements in stars and their disks. The detailed host star abundances provided can be employed for further studies on the composition of the planets within the current sample, when their atmospheres will be exploited.

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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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arXiv2022

The GAPS Programme at TNG: XXXVI. Measurement of the Rossiter-McLaughlin effect and revising the physical and orbital parameters of the HAT-P-15, HAT-P-17, HAT-P-21, HAT-P-26, HAT-P-29 eccentric planetary systems

Aim: We aim to refine the orbital and physical parameters and determine the sky-projected planet orbital obliquity of five eccentric transiting planetary systems: HAT-P-15, HAT-P-17, HAT-P-21, HAT-P-26, and HAT-P-29. Each of the systems hosts a hot Jupiter, except for HAT-P-26 which hosts a Neptune-mass planet. Methods: We observed transit events of these planets with the HARPS-N spectrograph, obtaining high-precision radial velocity measurements that allow us to measure the Rossiter-McLaughlin effect for each of the target systems. We used these new HARPS-N spectra and archival data, including those from Gaia, to better characterise the stellar atmospheric parameters. The photometric parameters for four of the hot Jupiters were recalculated using 17 new transit light curves, obtained with an array of medium-class telescopes, and data from the TESS space telescope. HATNet time-series photometric data were checked for the signatures of rotation periods of the target stars and their spin axis inclination. Results: From the analysis of the Rossiter-McLaughlin effect, we derived a sky-projected obliquity of 13, -26.3, -0.7, -26 degree for HAT-P-15b, HAT-P-17b, HAT-P-21b and HAT-P-29b, respectively. Due to the quality of the data, we were not able to well constrain the sky-projected obliquity for HAT-P-26b, although a prograde orbit is favoured. The stellar activity of HAT-P-21 indicates a rotation period of 15.88 days, which allowed us to determine its true misalignment angle (25 degree). Our new analysis of the physical parameters of the five exoplanetary systems returned values compatible with those existing in the literature. Using TESS and the available transit light curves, we reviewed the orbital ephemeris for the five systems and confirmed that the HAT-P-26 system shows transit timing variations, which may tentatively be attributed to the presence of a third body.

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arXiv2022

The GAPS Programme at TNG XL: A puffy and warm Neptune-sized planet and an outer Neptune-mass candidate orbiting the solar-type star TOI-1422

We investigate the exoplanet candidate TOI-1422b, which was discovered by the TESS space telescope around the high proper-motion G2V star TOI-1422 ($V=10.6$ mag), 155pc away, with the primary goal of confirming its planetary nature and characterising its properties. We monitored TOI-1422 with the HARPS-N spectrograph for 1.5 years to precisely quantify its radial velocity variation. The radial velocity measurements are analyzed jointly with TESS photometry and we also check for blended companions through high-spatial resolution images using the AstraLux instrument. We estimate that the parent star has a radius and a mass of $R^*=1.019_{-0.013}^{+0.014} R_{\odot}$, $M^*=0.981_{-0.065}^{+0.062} M_{\odot}$, respectively. Our analysis confirms the planetary nature of TOI-1422b and also suggests the presence of a Neptune-mass planet on a more distant orbit, the candidate TOI-1422c, which is not detected in TESS light curves. The inner planet, TOI-1422b, orbits on a period $P_{\rm b}=12.9972\pm0.0006$ days and has an equilibrium temperature $T_{\rm eq, b}=867\pm17$ K. With a radius of $R_{\rm b}=3.96^{+0.13}_{-0.11} R_{\oplus}$, a mass of $M_{\rm b}=9.0^{+2.3}_{-2.0} M_{\oplus}$ and, consequently, a density of $ρ_{\rm b}=0.795^{+0.290}_{-0.235}$ g cm$^{-3}$, it can be considered a warm Neptune-size planet. Compared to other exoplanets of similar mass range, TOI-1422b is among the most inflated ones and we expect this planet to have an extensive gaseous envelope that surrounds a core with a mass fraction around $10\%-25\%$ of the total mass of the planet. The outer non-transiting planet candidate, TOI-1422c, has an orbital period of $P_{\rm c}=29.29^{+0.21}_{-0.20}$ days, a minimum mass, $M_{\rm c}\sin{i}$, of $11.1^{+2.6}_{-2.3} M_{\oplus}$, an equilibrium temperature of $T_{\rm eq, c}=661\pm13$ K and, therefore, if confirmed, it could be considered as another warm Neptune.

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arXiv2022

The GAPS Programme with HARPS-N at TNG. XXXVII. A precise density measurement of the young ultra-short period planet TOI-1807 b

Great strides have been made in recent years in the understanding of the mechanisms involved in the formation and evolution of planetary systems; despite this, many observational facts still do not have an explanation. A great contribution to the study of planetary formation processes comes from the study of young, low-mass planets, with short orbital periods. In the last years, the TESS satellite has identified many planets of this kind, and their characterization is mandatory to understand how they formed and evolved. Within the framework of the GAPS project, we performed the validation and characterization of the ultra-short period planet (USPP) TOI-1807b, orbiting its young host star BD+39 2643 (~300 Myr) in only 13 hours. This is the youngest USPP discovered so far. Thanks to a joint modeling of the stellar activity and planetary signals in the TESS light curve and in HARPS-N radial-velocity measurements, combined with accurate estimation of stellar parameters, we validated the planetary nature of TOI-1807b and measured its orbital and physical parameters. By using astrometric, photometric, and spectroscopic observations we found that BD+39 2643 is a young, active K dwarf star, member of a 300+/-80 Myr old moving group and that it rotates in Prot=8.8+/-0.1 days. This star hosts an USPP with an orbital period of only P_b=0.54937+/-0.00001 d. Thanks to the exquisite photometric and spectroscopic series, and the accurate information on the stellar activity, we measured both the radius and the mass of TOI-1807b with high precision, obtaining R_b=1.37+/-0.09 R_Earth and M_b=2.57+/-0.50 M_Earth. These planet parameters correspond to a rocky planet with an Earth-like density and no extended H/He envelope. From the analysis of the age-R_P distribution for planets with well measured ages, we inferred that TOI-1807b may have already lost a large part of its atmosphere during its 300 Myr life.

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arXiv2022

The GAPS Programme with HARPS-N at TNG. XXXV. Fundamental properties of transiting exoplanet host stars

Exoplanetary properties depend on stellar properties: to know the planet with accuracy and precision it is necessary to know the star as accurately and precisely as possible. Our immediate aim is to characterize in a homogeneous and accurate way a sample of 27 transiting planet-hosting stars observed within the GAPS program. We determined stellar parameters (effective temperature, surface gravity, rotational velocity) and abundances of 26 elements (Li,C,N,O,Na,Mg,Al,Si,S,Ca,Sc,Ti,V,Cr,Fe,Mn,Co,Ni,Cu,Zn,Y,Zr,Ba,La,Nd,Eu). Our study is based on high-resolution HARPS-N@TNG and FEROS@ESO spectra and uniform techniques. We derived kinematic properties from Gaia data and estimated for the first time in exoplanet host stars ages using elemental ratios as chemical clocks. Teff of our stars is of 4400-6700 K, while [Fe/H] is within -0.3 and 0.4 dex. Lithium is present in 7 stars. [X/H] and [X/Fe] abundances vs [Fe/H] are consistent with the Galactic Chemical Evolution. The dependence of [X/Fe] with the condensation temperature is critically analyzed with respect to stellar and kinematic properties. All targets with measured C and O abundances show C/O<0.8, compatible with Si present in rock-forming minerals. Most of targets show 1.0<Mg/Si<1.5, compatible with Mg distributed between olivine and pyroxene. HAT-P-26, the target hosting the lowest-mass planet, shows the highest Mg/Si ratio. From our chemo-dinamical analysis we find agreement between ages and position within the Galactic disk. We note a tendency for higher density planets to be around metal-rich stars and hints of higher stellar abundances of some volatiles for lower mass planets. We cannot exclude that part of our results could be also related to the location of the stars within the Galactic disk. We trace the planetary migration scenario from the composition of the planets related to the chemical composition of the hosting stars

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arXiv2022

The GAPS Programme at TNG XXXIII. HARPS-N detects multiple atomic species in emission from the dayside of KELT-20b

The detection of lines in emission in planetary atmospheres provides direct evidence of temperature inversion. We confirm the trend of ultra-hot Jupiters orbiting A-type stars showing temperature inversions on their daysides, by detecting metals emission lines in the dayside of KELT-20b. We first detect the planetary emission by using the G2 stellar mask of the HARPS-N pipeline, which is mainly composed of neutral iron lines, as a template. Using neutral iron templates, we perform a retrieval of the atmospheric temperature-pressure profile of the planet, confirming a thermal inversion. Then we create models of planetary emission of different species using the retrieved inverted temperature-pressure profile. By using the cross-correlation technique, we detect FeI, FeII and CrI at signal-to-noise ratio levels of 7.1, 3.9 and 3.6, respectively. The latter is detected for the first time in emission in the atmosphere of an exoplanet. Contrary to FeI, FeII and CrI are detected only after the occultation and not before, hinting for different atmospheric properties in view on the pre- and post- occultation orbital phases. A further retrieval of the temperature-pressure profile performed independently on the pre- and post- occultation phases, while not highly significant, points to a steeper thermal inversion in the post-occultation.

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arXiv2021

The GAPS Programme with HARPS-N at TNG. XXXI. The WASP-33 system revisited with HARPS-N

[abridged] We analyse four transits of WASP-33b observed with the optical high-resolution HARPS-N spectrograph to confirm its nodal precession, study its atmosphere and investigate the presence of star-planet interactions.We extract the mean line profiles of the spectra by using the LSD method, and analyse the Doppler shadow and the RVs. We also derive the transmission spectrum of the planet, correcting it for the stellar contamination due to rotation, CLV and pulsations. We confirm the previously discovered nodal precession of WASP-33b, almost doubling the time coverage of the inclination and projected spin-orbit angle variation. We find that the projected obliquity reached a minimum in 2011 and use this constraint to derive the geometry of the system, in particular its obliquity at that epoch ($ε=113.99^{\circ}\pm 0.22^{\circ}$) and the inclination of the stellar spin axis ($i_{\rm s}=90.11^{\circ}\pm 0.12^{\circ}$), as well as the gravitational quadrupole moment of the star $J_2=(6.73\pm 0.22)\times 10^{-5}$. We present detections of H$α$ and H$β$ absorption in the atmosphere of the planet with a contrast almost twice smaller than previously detected in the literature. We also find evidence for the presence of a pre-transit signal, which repeats in all four analysed transits. The most likely explanation lies in a possible excitation of a stellar pulsation mode by the presence of the planetary companion. Future common analysis of all available datasets in the literature will help shedding light on the possibility that the observed Balmer lines transit depth variations are related to stellar activity and/or pulsation, and to set constraints on the energetics possibly driving atmospheric escape. A complete orbital phase coverage of WASP-33b with high-resolution spectroscopic (spectro-polarimetric) observations could help understanding the nature of the pre-transit signal.

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arXiv2020

The GAPS Programme at TNG -- XXIV. An eccentric Neptune-mass planet near the inner edge of the BD-11 4672 habitable zone

With the growth of comparative exoplanetology, it is increasingly clear that investigating the relationships between inner and outer planets plays a key role in discriminating between competing formation and evolution models. To do so, it is important to probe the inner region of systems hosting long-period giants in search for undetected lower-mass planetary companions. In this work we present our results on the K-dwarf star BD-11~4672, already known to host a long-period giant planet, as the first output of a subsample of the GAPS programme specifically aimed at assessing the impact of inefficient migration of planets formed beyond the snowline by searching for Neptune-mass and super-Earths planetary companions of known longer-period giants. The high-precision HARPS-N observations of BD-11~4672 are used in conjunction with literature time series in order to search for additional inner planetary signals to be fitted using differential evolution Markov chain Monte Carlo. The long-term stability of the new orbital solutions is tested by N-body dynamical simulations. We report the detection of BD-11~4672~c, a new Neptune-mass planet with an orbital period of $74.20_{-0.08}^{+0.06}\,\rm{d}$, eccentricity $0.40_{-0.15}^{+0.13}$, semimajor axis $0.30\pm0.01\,\rm{au}$ and minimum mass $15.37_{-2.81}^{+2.97}\,M_\oplus$ orbiting slightly outside the inner edge of the optimistic circumstellar habitable zone. In order to assess its impact on the dynamical stability of the habitable zone we compute the angular momentum deficit of the system, showing that planet c has a severe negative impact on the stability of possible additional lower-mass temperate planets. The BD-11~4672 system is notable for its architecture, hosting both a long-period giant planet and an inner lower-mass planet, the latter being also among the most eccentric Neptune-mass planets known at similar periods.

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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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arXiv2019

The GAPS Programme with HARPS-N at TNG XIX. Atmospheric Rossiter-McLaughlin effect and improved parameters of KELT-9b

In the framework of the GAPS project, we observed the planet-hosting star KELT-9 (A-type star, VsinI$\sim$110 km/s) with the HARPS-N spectrograph at the TNG. In this work we analyse the spectra and the extracted radial velocities (RVs), to constrain the physical parameters of the system and to detect the planetary atmosphere of KELT-9b. We extracted from the high-resolution optical spectra the mean stellar line profiles with an analysis based on the Least Square Deconvolution technique. Then, we computed the stellar RVs with a method optimized for fast rotators, by fitting the mean stellar line profile with a purely rotational profile instead of using a Gaussian function. The new spectra and analysis led us to update the orbital and physical parameters of the system, improving in particular the value of the planetary mass to $M_{\rm p}=2.88\pm0.35\,M_{\rm Jup}$. We discovered an anomalous in-transit RV deviation from the theoretical Rossiter-McLaughlin effect solution, calculated from the projected spin-orbit angle $λ=-85.78\pm0.46$ degrees measured with Doppler tomography. We prove that this deviation is caused by the planetary atmosphere of KELT-9b, thus we name this effect Atmospheric Rossiter-McLaughlin effect. By analysing the magnitude of the RV anomaly, we obtained information on the extension of the planetary atmosphere as weighted by the model used to retrieve the stellar mean line profiles, which is up to $1.22\pm0.02\,R_{\rm p}$. The Atmospheric Rossiter-McLaughlin effect will be observable for other exoplanets whose atmosphere has non-negligible correlation with the stellar mask used to retrieve the RVs, in particular ultra-hot Jupiters with iron in their atmosphere. The duration and amplitude of the effect will depend not only on the extension of the atmosphere, but also on the in-transit planetary RVs and on the projected rotational velocity of the parent star.

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arXiv2018

Eyes on K2-3: A system of three likely sub-Neptunes characterized with HARPS-N and HARPS

M-dwarf stars are promising targets for identifying and characterizing potentially habitable planets. K2-3 is a nearby (45 pc), early-type M dwarf hosting three small transiting planets, the outermost of which orbits close to the inner edge of the stellar (optimistic) habitable zone. The K2-3 system is well suited for follow-up characterization studies aimed at determining accurate masses and bulk densities of the three planets. Using a total of 329 radial velocity measurements collected over 2.5 years with the HARPS-N and HARPS spectrographs and a proper treatment of the stellar activity signal, we aim to improve measurements of the masses and bulk densities of the K2-3 planets. We use our results to investigate the physical structure of the planets. We analyse radial velocity time series extracted with two independent pipelines by using Gaussian process regression. We adopt a quasi-periodic kernel to model the stellar magnetic activity jointly with the planetary signals. We use Monte Carlo simulations to investigate the robustness of our mass measurements of K2-3\,c and K2-3\,d, and to explore how additional high-cadence radial velocity observations might improve them. Despite the stellar activity component being the strongest signal present in the radial velocity time series, we are able to derive masses for both planet b ($M_{\rm b}=6.6\pm1.1$ $M_{\rm \oplus}$) and planet c ($M_{\rm c}=3.1^{+1.3}_{-1.2}$ $M_{\rm \oplus}$). The Doppler signal due to K2-3\,d remains undetected, likely because of its low amplitude compared to the radial velocity signal induced by the stellar activity. The closeness of the orbital period of K2-3\,d to the stellar rotation period could also make the detection of the planetary signal complicated. [...]

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arXiv2016

The GAPS programme with HARPS-N at TNG XI. Pr~0211 in M~44: the first multi-planet system in an open cluster

Open cluster (OC) stars share the same age and metallicity, and, in general, their age and mass can be estimated with higher precision than for field stars. For this reason, OCs are considered an important laboratory to study the relation between the physical properties of the planets and those of their host stars, and the evolution of planetary systems. We started an observational campaign within the GAPS collaboration to search for and characterize planets in OCs We monitored the Praesepe member Pr0211 to improve the eccentricity of the Hot-Jupiter (HJ) already known to orbit this star and search for additional planets. An eccentric orbit for the HJ would support a planet-planet scattering process after its formation. From 2012 to 2015, we collected 70 radial velocity (RV) measurements with HARPS-N and 36 with TRES of Pr0211. Simultaneous photometric observations were carried out with the robotic STELLA telescope in order to characterize the stellar activity. We discovered a long-term trend in the RV residuals that we show to be due to the presence of a second, massive, outer planet. Orbital parameters for the two planets are derived by simultaneously fitting RVs and photometric light curves, with the activity signal modelled as a series of sinusoids at the rotational period of the star and its harmonics. We confirm that Pr0211b has a nearly circular orbit ($e = 0.02 \pm 0.01$), with an improvement of a factor two with respect to the previous determination of its eccentricity, and estimate that Pr0211c has a mass $M_p\sin i = 7.9 \pm 0.2 M_J$, a period $P>$3500 days and a very eccentric orbit ($e>$0.60). Such peculiar systems may be typical of open clusters if the planet-planet scattering phase leading to the formation of HJs is caused by stellar encounters rather than unstable primordial orbits. Pr0211 is the first multi-planet system discovered around an OC star. (abridged)

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arXiv2015

The HARPS-N Rocky Planet Search I. HD219134b: A transiting rocky planet in a multi-planet system at 6.5 pc from the Sun

We present here the detection of a system of four low-mass planets around the bright (V=5.5) and close-by (6.5 pc) star HD219134. This is the first result of the Rocky Planet Search program with HARPS-N on the TNG in La Palma. The inner planet orbits the star in 3.0937 +/-0.0004 days, on a quasi-circular orbit with a semi-major axis of 0.0382 +/- 0.0003 AU. Spitzer observations allowed us to detect the transit of the planet in front of the star making HD219134b the nearest known transiting planet to date. From the amplitude of the radial-velocity variation (2.33 +/- 0.24 m/s) and observed depth of the transit (359 +/- 38 ppm), the planet mass and radius are estimated to be 4.46 +/- 0.47 M_{\oplus} and 1.606 +/- 0.086 R_{\oplus} leading to a mean density of 5.89 +/- 1.17 g/cc, suggesting a rocky composition. One additional planet with minimum mass of 2.67 +/- 0.59 M_{\oplus} moves on a close-in, quasi-circular orbit with a period of 6.765 +/- 0.005 days. The third planet in the system has a period of 46.78 +/- 0.16 days and a minimum mass of 8.7 +/- 1.1 M{\oplus}, at 0.234 +/- 0.002 AU from the star. Its eccentricity is 0.32 +/- 0.14. The period of this planet is close to the rotational period of the star estimated from variations of activity indicators (42.3 +/- 0.1 days). The planetary origin of the signal is, however, the preferred solution as no indication of variation at the corresponding frequency is observed for activity-sensitive parameters. Finally, a fourth additional longer-period planet of mass of 62 +/- 6 M_{\oplus} orbits the star in 1190 days, on an eccentric orbit (e=0.27 +/- 0.11) at a distance of 2.14 +/- 0.27 AU.

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arXiv2015

The GAPS Programme with HARPS-N at TNG. VII. Putting exoplanets in the stellar context: magnetic activity and asteroseismology of $τ$ Bootis A

Aims. We observed the $τ$ Boo system with the HARPS-N spectrograph to test a new observational strategy aimed at jointly studying asteroseismology, the planetary orbit, and star-planet magnetic interaction. Methods. We collected high-cadence observations on 11 nearly consecutive nights and for each night averaged the raw FITS files using a dedicated software. In this way we obtained spectra with a high signal-to-noise ratio, used to study the variation of the CaII H&K lines and to have radial velocity values free from stellar oscillations, without losing the oscillations information. We developed a dedicated software to build a new custom mask that we used to refine the radial velocity determination with the HARPS-N pipeline and perform the spectroscopic analysis. Results. We updated the planetary ephemeris and showed the acceleration caused by the stellar binary companion. Our results on the stellar activity variation suggest the presence of a high-latitude plage during the time span of our observations. The correlation between the chromospheric activity and the planetary orbital phase remains unclear. Solar-like oscillations are detected in the radial velocity time series: we estimated asteroseismic quantities and found that they agree well with theoretical predictions. Our stellar model yields an age of $0.9\pm0.5$ Gyr for $τ$ Boo and further constrains the value of the stellar mass to $1.38\pm0.05$ M$_\odot$.

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arXiv2014

Characterization of the Kepler-101 planetary system with HARPS-N. A hot super-Neptune with an Earth-sized low-mass companion

We report on the characterization of the Kepler-101 planetary system, thanks to a combined DE-MCMC analysis of Kepler data and forty radial velocities obtained with the HARPS-N spectrograph. This system was previously validated by Rowe et al. (2014) and is composed of a hot super-Neptune, Kepler-101b, and an Earth-sized planet, Kepler-101c. These two planets orbit the slightly evolved and metal-rich G-type star in 3.49 and 6.03 days, respectively. With mass $M_{\rm p}=51.1_{-4.7}^{+5.1}~M_{\oplus}$, radius $R_{\rm p}=5.77_{-0.79}^{+0.85}~R_{\oplus}$, and density $ρ_{\rm p}=1.45_{-0.48}^{+0.83} \rm g\;cm^{-3}$, Kepler-101b is the first fully-characterized super-Neptune, and its density suggests that heavy elements make up a significant fraction of its interior; more than $60\%$ of its total mass. Kepler-101c has a radius of $1.25_{-0.17}^{+0.19}~R_{\oplus}$, which implies the absence of any H/He envelope, but its mass could not be determined due to the relative faintness of the parent star for highly precise radial-velocity measurements ($K_{\rm p}=13.8$) and the limited number of radial velocities. The $1~σ$ upper limit, $M_{\rm p} < 3.8~M_{\oplus}$, excludes a pure iron composition with a $68.3\%$ probability. The architecture of the Kepler-101 planetary system - containing a close-in giant planet and an outer Earth-sized planet with a period ratio slightly larger than the 3:2 resonance - is certainly of interest for planet formation and evolution scenarios. This system does not follow the trend, seen by Ciardi et al. (2013), that in the majority of Kepler systems of planet pairs with at least one Neptune-size or larger planet, the larger planet has the longer period.

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