arXiv subjects

M. Esposito

Publications and source records attributed to M. Esposito.

At least 55 records · Page 3Linked to original sources

arXiv2019

HD219666b: A hot-Neptune from TESS Sector 1

We report on the confirmation and mass determination of a transiting planet orbiting the old and inactive G7 dwarf star HD219666 (Mstar = 0.92 +/- 0.03 MSun, Rstar = 1.03 +/- 0.03 RSun, tau_star = 10 +/- 2 Gyr). With a mass of Mb = 16.6 +/- 1.3 MEarth, a radius of Rb = 4.71 +/- 0.17 REarth, and an orbital period of P ~ 6 days, HD219666b is a new member of a rare class of exoplanets: the hot-Neptunes. The Transiting Exoplanet Survey Satellite (TESS) observed HD219666 (also known as TOI-118) in its Sector 1 and the light curve shows four transit-like events, equally spaced in time. We confirmed the planetary nature of the candidate by gathering precise radial-velocity measurements with HARPS@ESO3.6m. We used the co-added HARPS spectrum to derive the host star fundamental parameters (Teff = 5527 +/- 65 K, log g = 4.40 +/- 0.11 (cgs), [Fe/H]= 0.04 +/- 0.04 dex, log R'HK = -5.07 +/- 0.03), as well as the abundances of many volatile and refractory elements. The host star brightness (V = 9.9) makes it suitable for further characterisation by means of in-transit spectroscopy. The determination of the planet orbital obliquity, along with the atmospheric metal-to-hydrogen content and thermal structure could provide us with important clues on the formation mechanisms of this class of objects.

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arXiv2019

K2-290: a warm Jupiter and a mini-Neptune in a triple-star system

We report the discovery of two transiting planets orbiting K2-290 (EPIC 249624646), a bright (V=11.11) late F-type star residing in a triple-star system. It was observed during Campaign 15 of the K2 mission, and in order to confirm and characterise the system, follow-up spectroscopy and AO imaging were carried out using the FIES, HARPS, HARPS-N, and IRCS instruments. From AO imaging and Gaia data we identify two M-dwarf companions at a separation of $113 \pm 2$ AU and $2467_{-155}^{+177}$ AU. From radial velocities, K2 photometry, and stellar characterisation of the host star, we find the inner planet to be a mini-Neptune with a radius of $3.06 \pm 0.16 R_{\oplus}$ and an orbital period of $P = 9.2$ days. The radius of the mini-Neptune suggests that the planet is located above the radius valley, and with an incident flux of $F\sim 400 F_{\oplus}$, it lies safely outside the super-Earth desert. The outer warm Jupiter has a mass of $0.774\pm 0.047 M_{\rm J}$ and a radius of $1.006\pm 0.050R_{\rm J}$, and orbits the host star every 48.4 days on an orbit with an eccentricity $e<0.241$. Its mild eccentricity and mini-Neptune sibling suggest that the warm Jupiter originates from in situ formation or disk migration.

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arXiv2018

Detection and characterization of an ultra-dense sub-Neptune planet orbiting the Sun-like star HD 119130

We present the discovery and characterization of a new transiting planet from Campaign 17 of the Kepler extended mission K2. HD 119130 b is a warm sub-Neptune on a 17-d orbit around a bright (V = 9.9 mag) solar-like G3 V star with a mass and radius of $M_\star = 1.00\pm0.03\,\mathrm{M_\odot}$ and $R_\star = 1.09\pm0.03\,\mathrm{R_\odot}$, respectively. We model simultaneously the K2 photometry and CARMENES spectroscopic data and derive a radius of $R_\mathrm{p} = 2.63_{-0.10}^{+0.12}\,\mathrm{R_\oplus}$ and mass of $M_\mathrm{p} = 24.5_{-4.4}^{+4.4}\,\mathrm{M_\oplus}$, yielding a mean density of $ρ_\mathrm{p} = 7.4_{-1.5}^{+1.6}\,\mathrm{g\,cm^{-3}}$, which makes it one of the densest sub-Neptune planets known to date. We also detect a linear trend in radial velocities of HD 119130 ($\dotγ_{\rm RV}= -0.40^{+0.07}_{-0.07}\,\mathrm{m\,s^{-1}\,d^{-1}}$) that suggests a long-period companion with a minimum mass on the order of $33\,\mathrm{M_\oplus}$. If confirmed, it would support a formation scenario of HD 119130 b by migration caused by Kozai-Lidov oscillations.

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arXiv2018

The GAPS Programme with HARPS-N at TNG XVIII. Two new giant planets around the metal-poor stars HD 220197 and HD 233832

Statistical studies of exoplanets have shown that giant planets are more commonly hosted by metal-rich dwarf stars than low-metallicity ones, while such a correlation is not evident for lower-mass planets. The search for giant planets around metal-poor stars and the estimate of their occurrence $f_p$ is an important element in providing support to models of planet formation. We present results from the HARPS-N search for giant planets orbiting metal-poor ($-1.0\leq[Fe/H]\leq-0.5$ dex) stars in the northern hemisphere complementing a previous HARPS survey on southern stars in order to update the estimate of $f_p$. High-precision HARPS-N observations of 42 metal-poor stars are used to search for planetary signals to be fitted using differential evolution MCMC single-Keplerian models. We then join our detections to the results of the previous HARPS survey on 88 metal-poor stars to provide a preliminar estimate of the two-hemisphere $f_p$. We report the detection of two new giant planets around HD 220197 and HD 233832. The first companion has M$\sin{i}=0.20_{-0.04}^{+0.07}$ M$_{\rm Jup}$ and orbital period of $1728_{-80}^{+162}$ days, and for the second companion we find two solutions of equal statistical weight having periods $2058_{-40}^{+47}$ and $4047_{-117}^{+91}$ days and minimum masses of $1.78_{-0.06}^{+0.08}$ and $2.72_{-0.23}^{+0.23}$ M$_{\rm Jup}$, respectively. Joining our two detections with the three from the southern survey we obtain a preliminary and conservative estimate of global frequency of $f_p=3.84_{-1.06}^{+2.45}\%$ for giant planets around metal-poor stars. The two new giant planets orbit dwarf stars at the metal-rich end of the HARPS-N metal-poor sample, corroborating previous results suggesting that giant planet frequency still is a rising function of host star [Fe/H]. We also note that all detections in the overall sample are giant long-period planets.

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arXiv2018

TESS's first planet: a super-Earth transiting the naked-eye star $π$ Mensae

We report on the confirmation and mass determination of Pi Men c, the first transiting planet discovered by NASA's TESS space mission. Pi Men is a naked-eye (V=5.65 mag), quiet G0 V star that was previously known to host a sub-stellar companion (Pi Men b) on a long-period (Porb = 2091 days), eccentric (e = 0.64) orbit. Using TESS time-series photometry, combined with Gaia data, published UCLES@AAT Doppler measurements, and archival HARPS@ESO-3.6m radial velocities, we found that Pi Men c is a close-in planet with an orbital period of Porb = 6.27 days, a mass of Mc = 4.52 +/- 0.81 MEarth, and a radius of Rc = 2.06 +/- 0.03 REarth. Based on the planet's orbital period and size, Pi Men c is a super-Earth located at, or close to, the radius gap, while its mass and bulk density suggest it may have held on to a significant atmosphere. Because of the brightness of the host star, this system is highly suitable for a wide range of further studies to characterize the planetary atmosphere and dynamical properties. We also performed an asteroseismic analysis of the TESS data and detected a hint of power excess consistent with the seismic values expected for this star, although this result depends on the photometric aperture used to extract the light curve. This marginal detection is expected from pre-launch simulations hinting at the asteroseismic potential of the TESS mission for longer, multi-sector observations and/or for more evolved bright stars.

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arXiv2018

K2-140b and K2-180b - Characterization of a hot Jupiter and a mini-Neptune from the K2 mission

We report the independent discovery and characterization of two K2 planets: K2-180b, a mini-Neptune-size planet in an 8.9-day orbit transiting a V = 12.6 mag, metal-poor ([Fe/H] =$-0.65\pm0.10$) K2V star in K2 campaign 5; K2-140b, a transiting hot Jupiter in a 6.6-day orbit around a V = 12.6 mag G6V ([Fe/H] = $+0.10\pm0.10$) star in K2 campaign 10. Our results are based on K2 time-series photometry combined with high-spatial resolution imaging and high-precision radial velocity measurements. We present the first mass measurement of K2-180b. K2-180b has a mass of $M_\mathrm{p}=11.3\pm1.9$ ${M_{\oplus}}$ and a radius of $R_\mathrm{p}=2.2\pm0.1$ ${R_{\oplus}}$ , yielding a mean density of $ρ_\mathrm{p}=5.6\pm1.9\,g\,cm^{-3}$, suggesting a rock composition. Given its radius, K2-180b is above the region of the so-called `planetary radius gap'. K2-180b is in addition not only one of the densest mini-Neptune-size planets, but also one of the few mini-Neptune-size planets known to transit a metal-poor star. We also constrain the planetary and orbital parameters of K2-140b and show that, given the currently available Doppler measurements, the eccentricity is consistent with zero, contrary to the results of a previous study.

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arXiv2018

Super-Earth of 8 Mearth in a 2.2-day orbit around the K5V star K2-216

The KESPRINT consortium identified K2-216 as a planetary candidate host star in the K2 space mission Campaign 8 field with a transiting super-Earth. The planet has recently been validated as well. Our aim was to confirm the detection and derive the main physical characteristics of K2-216b, including the mass. We performed a series of follow-up observations: high resolution imaging with the FastCam camera at the TCS, the Infrared Camera and Spectrograph at Subaru, and high resolution spectroscopy with HARPS (ESO, La Silla), HARPS-N (TNG), and FIES (NOT). The stellar spectra were analyzed with the SpecMatch-Emp and SME codes to derive the stellar fundamental properties. We analyzed the K2 light curve with the Pyaneti software. The radial-velocity measurements were modelled with both a Gaussian process (GP) regression and the floating chunk offset (FCO) technique to simultaneously model the planetary signal and correlated noise associated with stellar activity. Imaging confirms that K2-216 is a single star. Our analysis discloses that the star is a moderately active K5V star of mass 0.70+/-0.03 Msun and radius 0.72+/-0.03 Rsun. Planet b is found to have a radius of 1.75+0.17-0.10 Rearth and a 2.17-day orbit in agreement with previous results. We find consistent results for the planet mass from both models: 7.4+/-2.2 Mearth from the GP regression, and 8.0+/-1.6 Mearth from the FCO technique, which implies that this planet is a super-Earth. The planet parameters put planet b in the middle of, or just below, the gap of the radius distribution of small planets. The density is consistent with a rocky composition of primarily iron and magnesium silicate. In agreement with theoretical predictions, we find that the planet is a remnant core, stripped of its atmosphere, and is one of the largest planets found that has lost its atmosphere.

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arXiv2018

K2-260 b: a hot Jupiter transiting an F star, and K2-261 b: a warm Saturn around a bright G star

We present the discovery and confirmation of two new transiting giant planets from the Kepler extended mission K2. K2-260 b is a hot Jupiter transiting a $V=12.7$ F6V star in K2 Field 13, with a mass and radius of $M_{\star}=1.39_{-0.06}^{+0.05} M_{\odot}$ and $R_{\star}=1.69 \pm 0.03 R_{\odot}$. The planet has an orbital period of $P=2.627$ days, and a mass and radius of $M_P=1.42^{+0.31}_{-0.32} M_J$ and $R_P=1.552^{+0.048}_{-0.057} R_J$. This is the first K2 hot Jupiter with a detected secondary eclipse in the Kepler bandpass, with a depth of $71 \pm 15$ ppm, which we use to estimate a geometric albedo of $A_g\sim0.2$. We also detected a candidate stellar companion at 0.6" from K2-260; we find that it is very likely physically associated with the system, in which case it would be an M5-6V star at a projected separation of $\sim400$ AU. K2-261 b is a warm Saturn transiting a bright ($V=10.5$) G7IV/V star in K2 Field 14. The host star is a metal-rich ([Fe/H]$=0.36 \pm 0.06$), mildly evolved $1.10_{-0.02}^{+0.01} M_{\odot}$ star with $R_{\star}=1.65 \pm 0.04 R_{\odot}$. Thanks to its location near the main sequence turn-off, we can measure a relatively precise age of $8.8_{-0.3}^{+0.4}$ Gyr. The planet has $P=11.633$ days, $M_P=0.223 \pm 0.031 M_J$, and $R_P=0.850^{+0.026}_{-0.022} R_J$, and its orbit is eccentric ($e=0.39 \pm 0.15$). Its brightness and relatively large transit depth make this one of the best known warm Saturns for follow-up observations to further characterize the planetary system.

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arXiv2018

The GAPS Programme with HARPS-N at TNG XVII. Line profile indicators and kernel regression as diagnostics of radial-velocity variations due to stellar activity in solar-like stars

Stellar activity is the ultimate source of radial-velocity (RV) noise in the search for Earth-mass planets orbiting late-type main-sequence stars. We analyse the performance of four different indicators and the chromospheric index $\log R'_{\rm HK}$ in detecting RV variations induced by stellar activity in 15 slowly rotating ($v\sin i \leq 5$ km/s), weakly active ($\log R'_{\rm HK} \leq -4.95$) solar-like stars observed with the high-resolution spectrograph HARPS-N. We consider indicators of the asymmetry of the cross-correlation function (CCF) between the stellar spectrum and the binary weighted line mask used to compute the RV, that is the bisector inverse span (BIS), $ΔV$, and a new indicator $V_{\rm asy(mod)}$ together with the full width at half maximum (FWHM) of the CCF. We present methods to evaluate the uncertainties of the CCF indicators and apply a kernel regression (KR) between the RV, the time, and each of the indicators to study their capability of reproducing the RV variations induced by stellar activity. The considered indicators together with the KR prove to be useful to detect activity-induced RV variations in $47 \pm 18$ percent of the stars over a two-year time span when a significance (two-sided p-value) threshold of one percent is adopted. In those cases, KR reduces the standard deviation of the RV time series by a factor of approximately two. The BIS, the FWHM, and the newly introduced $V_{\rm asy(mod)}$ are the best indicators, being useful in $27 \pm 13$, $13 \pm 9$, and $13 \pm 9$ percent of the cases, respectively. The relatively limited performances of the activity indicators are related to the very low activity level and $v\sin i$ of the considered stars. For the application of our approach to sun-like stars, a spectral resolution of at least $10^5$ and highly stabilized spectrographs are recommended.

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arXiv2018

The GAPS Programme with HARPS-N at TNG XVI: Measurement of the Rossiter-McLaughlin effect of the transiting planetary systems HAT-P-3, HAT-P-12, HAT-P-22, WASP-39 and WASP-60

We characterised five transiting planetary systems (HAT-P-3, HAT-P-12, HAT-P-22, WASP-39 and WASP-60) and determined their sky-projected planet orbital obliquity through the measurement of the RM effect. We used HARPS-N high-precision radial velocity measurements, gathered during transit events, to measure the RM effect in the target systems and determine the sky-projected angle between the planetary orbital plane and the stellar equator. The characterisation of stellar atmospheric parameters was performed exploiting the HARPS-N spectra, using line equivalent width ratios, and spectral synthesis methods. Photometric parameters of the five transiting exoplanets were re-analysed through 17 new light curves, obtained with an array of medium-class telescopes, and other light curves from the literature. Survey-time-series photometric data were analysed for determining the rotation periods of the five stars and their spin inclination. From the analysis of the RM effect we derived a sky-projected obliquity of 21.2 degree, -54 degree, -2.1 degree, 0 degree and -129 degree for HAT-P-3b, HAT-P-12b, HAT-P-22b, WASP-39b and WASP-60b, respectively. The latter value indicates that WASP-60b is moving on a retrograde orbit. These values represent the first measurements of λfor the five exoplanetary systems under study. The stellar activity of HAT-P-22 indicates a rotation period of 28.7 days, which allowed us to estimate the true misalignment angle of HAT-P-22b, ψ=24 degree. The revision of the physical parameters of the five exoplanetary systems returned values that are fully compatible with those existing in the literature. The exception to this is the WASP-60 system, for which, based on higher quality spectroscopic and photometric data, we found a more massive and younger star and a larger and hotter planet.

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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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arXiv2017

HADES RV Programme with HARPS-N at TNG. VII. Rotation and activity of M-Dwarfs from time-series high-resolution spectroscopy of chromospheric indicators

We aim to investigate the presence of signatures of magnetic cycles and rotation on a sample of 71 early M-dwarfs from the HADES RV programme using high-resolution time-series spectroscopy of the Ca II H & K and Halpha chromospheric activity indicators, the radial velocity series, the parameters of the cross correlation function and the V-band photometry. We used mainly HARPS-N spectra, acquired over four years, and add HARPS spectra from the public ESO database and ASAS photometry light-curves as support data, extending the baseline of the observations of some stars up to 12 years. We provide log(R'hk) measurements for all the stars in the sample, cycle length measurements for 13 stars, rotation periods for 33 stars and we are able to measure the semi-amplitude of the radial velocity signal induced by rotation in 16 stars. We complement our work with previous results and confirm and refine the previously reported relationships between the mean level of chromospheric emission, measured by the log(R'hk), with the rotation period, and with the measured semi-amplitude of the activity induced radial velocity signal for early M-dwarfs. We searched for a possible relation between the measured rotation periods and the lengths of the magnetic cycle, finding a weak correlation between both quantities. Using previous v sin i measurements we estimated the inclinations of the star's poles to the line of sight for all the stars in the sample, and estimate the range of masses of the planets GJ 3998 b and c (2.5 - 4.9 Mearth and 6.3 - 12.5 Mearth), GJ 625 b (2.82 Mearth), GJ 3942 b (7.1 - 10.0 Mearth) and GJ 15A b (3.1 - 3.3 Mearth), assuming their orbits are coplanar with the stellar rotation.

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arXiv2017

The RoPES project with HARPS and HARPS-N. I. A system of super-Earths orbiting the moderately active K-dwarf HD 176986

We report the discovery of a system of two super-Earths orbiting the moderately active K-dwarf HD 176986. This work is part of the RoPES RV program of G- and K-type stars, which combines radial velocities (RVs) from the HARPS and HARPS-N spectrographs to search for short-period terrestrial planets. HD 176986 b and c are super-Earth planets with masses of 5.74 and 9.18 M$_{\oplus}$, orbital periods of 6.49 and 16.82 days, and distances of 0.063 and 0.119 AU in orbits that are consistent with circular. The host star is a K2.5 dwarf, and despite its modest level of chromospheric activity (log(R'hk) = - 4.90 +- 0.04), it shows a complex activity pattern. Along with the discovery of the planets, we study the magnetic cycle and rotation of the star. HD 176986 proves to be suitable for testing the available RV analysis technique and further our understanding of stellar activity.

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arXiv2017

HADES RV Programme with HARPS-N at TNG VI. GJ 3942 b behind dominant activity signals

Short- to mid-term magnetic phenomena on the stellar surface of M-type stars cannot only resemble the effects of planets in radial velocity data, but also may hide them. We analyze 145 spectroscopic HARPS-N observations of GJ 3942 taken over the past five years and additional photometry to disentangle stellar activity effects from genuine Doppler signals as a result of the orbital motion of the star around the common barycenter with its planet. To achieve this, we use the common methods of pre-whitening, and treat the correlated red noise by a first-order moving average term and by Gaussian-process regression following an MCMC analysis. We identify the rotational period of the star at 16.3 days and discover a new super-Earth, GJ 3942 b, with an orbital period of 6.9 days and a minimum mass of 7.1 Me. An additional signal in the periodogram of the residuals is present but we cannot claim it to be related to a second planet with sufficient significance at this point. If confirmed, such planet candidate would have a minimum mass of 6.3 Me and a period of 10.4 days, which might indicate a 3:2 mean-motion resonance with the inner planet.

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arXiv2017

X-shooter spectroscopy of young stellar objects in Lupus: Lithium, iron, and barium elemental abundances

With the purpose of performing a homogeneous determination of elemental abundances for members of the Lupus T association, we analyzed three chemical elements: lithium, iron, and barium. The aims were: to derive the Li abundance for ~90% of known class II stars in the Lupus I, II, III, IV clouds; to perform chemical tagging of a region where few Fe abundance measurements have been obtained in the past, and no determination of the Ba content has been done up to now. We also investigated possible Ba enhancement, as this element has become increasingly interesting in the last years following the evidence of Ba over-abundance in young clusters, the origin of which is still unknown. Using X-shooter@VLT, we analyzed the spectra of 89 cluster members, both class II and III stars. We measured the strength of the Li line and derived the abundance of this element through equivalent width measurements and curves of growth. For six class II stars we also measured the Fe and Ba abundances using the spectral synthesis and the code MOOG. The veiling contribution was taken into account for all three elements. We find a dispersion in the strength of the Li line at low Teff and identify three targets with severe Li depletion. The nuclear age inferred for these highly Li-depleted stars is around 15 Myr, which exceeds the isochronal one. As in other star-forming regions, no metal-rich members are found in Lupus, giving support to a recent hypothesis that the Fe abundance distribution of most of the nearby young regions could be the result of a common and widespread star formation episode involving the Galactic thin disk. We find that Ba is over-abundant by ~0.7 dex with respect to the Sun. Since current theoretical models cannot reproduce this Ba abundance pattern, we investigated whether this unusually large Ba content might be related to effects due to stellar parameters, stellar activity, and accretion.

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arXiv2017

The GAPS Programme with HARPS-N@TNG XIV. Investigating giant planet migration history via improved eccentricity and mass determination for 231 transiting planets

We carried out a Bayesian homogeneous determination of the orbital parameters of 231 transiting giant planets (TGPs) that are alone or have distant companions; we employed DE-MCMC methods to analyse radial-velocity (RV) data from the literature and 782 new high-accuracy RVs obtained with the HARPS-N spectrograph for 45 systems over 3 years. Our work yields the largest sample of systems with a transiting giant exoplanet and coherently determined orbital, planetary, and stellar parameters. We found that the orbital parameters of TGPs in non-compact planetary systems are clearly shaped by tides raised by their host stars. Indeed, the most eccentric planets have relatively large orbital separations and/or high mass ratios, as expected from the equilibrium tide theory. This feature would be the outcome of high-eccentricity migration (HEM). The distribution of $α=a/a_R$, where $a$ and $a_R$ are the semi-major axis and the Roche limit, for well-determined circular orbits peaks at 2.5; this also agrees with expectations from the HEM. The few planets of our sample with circular orbits and $α>5$ values may have migrated through disc-planet interactions instead of HEM. By comparing circularisation times with stellar ages, we found that hot Jupiters with $a < 0.05$ au have modified tidal quality factors $10^{5} < Q'_p < 10^{9}$, and that stellar $Q'_s > 10^{6}-10^{7}$ are required to explain the presence of eccentric planets at the same orbital distance. As a by-product of our analysis, we detected a non-zero eccentricity for HAT-P-29; we determined that five planets that were previously regarded to have hints of non-zero eccentricity have circular orbits or undetermined eccentricities; we unveiled curvatures caused by distant companions in the RV time series of HAT-P-2, HAT-P-22, and HAT-P-29; and we revised the planetary parameters of CoRoT-1b.

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arXiv2017

The GAPS Programme with HARPS-N at TNG XV. A substellar companion around a K giant star identified with quasi-simultaneous HARPS-N and GIANO measurements

Context. Identification of planetary companions of giant stars is made difficult because of the astrophysical noise, that may produce radial velocity (RV) variations similar to those induced by a companion. On the other hand any stellar signal is wavelength dependent, while signals due to a companion are achromatic. Aims. Our goal is to determine the origin of the Doppler periodic variations observed in the thick disk K giant star TYC 4282-605-1 by HARPS-N at the Telescopio Nazionale Galileo (TNG) and verify if they can be due to the presence of a substellar companion. Methods. Several methods have been used to exclude the stellar origin of the observed signal including detailed analysis of activity indicators and bisector and the analysis of the photometric light curve. Finally we have conducted an observational campaign to monitor the near infrared (NIR) RV with GIANO at the TNG in order to verify whether the NIR amplitude variations are comparable with those observed in the visible. Results. Both optical and NIR RVs show consistent variations with a period at 101 days and similar amplitude, pointing to the presence of a companion orbiting the target. The main orbital properties obtained for our giant star with a derived mass of M=0.97+-0.03M_sun are M_Psini=10.78+-0.12MJ;P=101.54+-0.05days;e=0.28+-0.01 and a=0.422+-0.009AU. The chemical analysis shows a significant enrichment in the abundance of Nai, Mgi, Ali and S i while the rest of analyzed elements are consistent with the solar value demonstrating that the chemical composition corresponds with an old K giant (age = 10.1 Gyr) belonging to local thick disk. Conclusions. We conclude that the substellar companion hypothesis for this K giant is the best explanation for the observed periodic RV variation. This study also shows the high potential of multi-wavelength RV observations for the validation of planet candidates.

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arXiv2017

HADES RV Programme with HARPS-N at TNG: V. A super-Earth on the inner edge of the habitable zone of the nearby M-dwarf GJ 625

We report the discovery of a super-Earth orbiting at the inner edge of the habitable zone of the star GJ 625 based on the analysis of the radial-velocity (RV) time series from the HARPS-N spectrograph, consisting in 151 HARPS-N measurements taken over 3.5 yr. GJ 625 b is a planet with a minimum mass M sin $i$ of 2.82 $\pm$ 0.51 M$_{\oplus}$ with an orbital period of 14.628 $\pm$ 0.013 days at a distance of 0.078 AU of its parent star. The host star is the quiet M2 V star GJ 625, located at 6.5 pc from the Sun. We find the presence of a second radial velocity signal in the range 74-85 days that we relate to stellar rotation after analysing the time series of Ca II H\&K and H$α$ spectroscopic indicators, the variations of the FWHM of the CCF and and the APT2 photometric light curves. We find no evidence linking the short period radial velocity signal to any activity proxy.

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