arXiv subjects

J. Maldonado

Publications and source records attributed to J. Maldonado.

At least 73 records · Page 4Linked to original sources

arXiv2020

Testing the Spectroscopic Extraction of Suppression of Convective Blueshift

Efforts to detect low-mass exoplanets using stellar radial velocities (RVs) are currently limited by magnetic photospheric activity. Suppression of convective blueshift is the dominant magnetic contribution to RV variability in low-activity Sun-like stars. Due to convective plasma motions, the magnitude of RV contributions from the suppression of convective blueshift is related to the depth of formation of photospheric spectral lines of a given species used to compute the RV time series. Meunier et al. (2017), used this relation to demonstrate a method for spectroscopic extraction of the suppression of convective blueshift in order to isolate RV contributions, including planetary RVs, that contribute equally to the timeseries for each spectral line. Here, we extract disk-integrated solar RVs from observations over a 2.5 year time span made with the solar telescope integrated with the HARPS-N spectrograph at the Telescopio Nazionale Galileo (La Palma, Canary Islands, Spain). We apply the methods outlined by Meunier et al. (2017). We are not, however, able to isolate physically meaningful contributions of the suppression of convective blueshift from this solar dataset, potentially because our dataset is from solar minimum when the suppression of convective blueshift may not sufficiently dominate activity contributions to RVs. This result indicates that, for low-activity Sun-like stars, one must include additional RV contributions from activity sources not considered in the Meunier et al. (2017) model at different timescales as well as instrumental variation in order to reach the sub-meter per second RV sensitivity necessary to detect low-mass planets in orbit around Sun-like 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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arXiv2019

HR 10: A main-sequence binary with circumstellar envelopes around both components. Discovery and analysis

This paper is framed within a large project devoted to studying the presence of circumstellar material around main sequence stars, and looking for exocometary events. The work concentrates on HR 10 (A2 IV/V), known for its conspicuous variability in the circumstellar narrow absorption features of Ca II K and other lines, so far interpreted as $β$ Pic-like phenomena, within the falling evaporating body scenario. The main goal of this paper is to carry out a thorough study of HR 10 to find the origin of the observed variability, determine the nature of the star, its absolute parameters, and evolutionary status. Interferometric near-infrared (NIR) observations, multi-epoch high-resolution optical spectra spanning a time baseline of more than 32 years, and optical and NIR photometry, together with theoretical modelling, were used to tackle the above objectives. Our results reveal that HR 10 is a binary. The narrow circumstellar absorption features superimposed on the photospheric Ca II K lines -- and lines of other species -- can be decomposed into two or more components, the two deep ones tracing the radial velocity of the individual stars, which implies that their origin cannot be ascribed to transient exocometary events, their variability being fully explained by the binarity of the object. There does not appear to be transient events associated with potential exocomets. Each individual star holds its own circumstellar shell and there are no traces of a circumbinary envelope. The combined use of the interferometric and radial velocity data leads to a complete spectrometric and orbital solution for the binary, the main parameters being: an orbital period of 747.6 days, eccentricities of the orbits around the centre of mass 0.25 (HR 10-A), 0.21 (HR 10-B) and a mass ratio of q=M$_{\rm B}$/M$_{\rm A}$=0.72-0.84. The stars are slightly off the main sequence, the binary being $\sim530$ Myr old.

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arXiv2019

Temporal evolution and correlations of optical activity indicators measured in Sun-as-a-star observations

(Abridged) We perform a detailed study of the main optical activity indicators (Ca II H & K, Balmer lines, Na I D$_{\rm 1}$ D$_{\rm 2}$, and He I D$_{\rm 3}$) measured for the Sun using the data provided by the HARPS-N solar-telescope feed at the Telescopio Nazionale Galileo. The value of the solar rotation period is found in all the activity indicators, with the only exception being H$δ$. The derived values vary from 26.29 days (H$γ$ line) to 31.23 days (He I). From an analysis of sliding periodograms we find that in most of the activity indicators the spectral power is split into several "bands" of periods around 26 and 30 days, that might be explained by the migration of active regions between the equator and a latitude of $\sim$ 30$^{\circ}$, spot evolution or a combination of both effects. In agreement with previous works a typical lifetime of active regions of $\sim$ ten rotation periods is inferred from the pooled variance diagrams. We find that H$α$, H$β$, H$γ$, H$ε$, and He I show a significant correlation with the S index. Significant correlations between the contrast, bisector span, and the heliocentric radial velocity with the activity indexes are also found. We show that the full width at half maximum, the bisector, and the disc-integrated magnetic field correlate with the radial velocity variations. The correlation of the S index and H$α$ changes with time, increasing with larger sun spot numbers and solar irradiance. A similar tendency with the S index - radial velocity correlation is also present in the data. Our results are consistent with a scenario in which higher activity favours the correlation between the S index and the H$α$ activity indicators and between the S index and radial velocity variations.

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arXiv2019

Three years of Sun-as-a-star radial-velocity observations on the approach to solar minimum

The time-variable velocity fields of solar-type stars limit the precision of radial-velocity determinations of their planets' masses, obstructing detection of Earth twins. Since 2015 July we have been monitoring disc-integrated sunlight in daytime using a purpose-built solar telescope and fibre feed to the HARPS-N stellar radial-velocity spectrometer. We present and analyse the solar radial-velocity measurements and cross-correlation function (CCF) parameters obtained in the first 3 years of observation, interpreting them in the context of spatially-resolved solar observations. We describe a Bayesian mixture-model approach to automated data-quality monitoring. We provide dynamical and daily differential-extinction corrections to place the radial velocities in the heliocentric reference frame, and the CCF shape parameters in the sidereal frame. We achieve a photon-noise limited radial-velocity precision better than 0.43 m s$^{-1}$ per 5-minute observation. The day-to-day precision is limited by zero-point calibration uncertainty with an RMS scatter of about 0.4 m s$^{-1}$. We find significant signals from granulation and solar activity. Within a day, granulation noise dominates, with an amplitude of about 0.4 m s$^{-1}$ and an autocorrelation half-life of 15 minutes. On longer timescales, activity dominates. Sunspot groups broaden the CCF as they cross the solar disc. Facular regions temporarily reduce the intrinsic asymmetry of the CCF. The radial-velocity increase that accompanies an active-region passage has a typical amplitude of 5 m s$^{-1}$ and is correlated with the line asymmetry, but leads it by 3 days. Spectral line-shape variability thus shows promise as a proxy for recovering the true radial velocity.

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arXiv2019

The HADES RV Programme with HARPS-N at TNG XI. GJ 685 b: a warm super-Earth around an active M dwarf

Small rocky planets seem to be very abundant around low-mass M-type stars. Their actual planetary population is however not yet precisely understood. Currently several surveys aim to expand the statistics with intensive detection campaigns, both photometric and spectroscopic. We analyse 106 spectroscopic HARPS-N observations of the active M0-type star GJ 685 taken over the past five years. We combine these data with photometric measurements from different observatories to accurately model the stellar rotation and disentangle its signals from genuine Doppler planetary signals in the RV data. We run an MCMC analysis on the RV and activity indexes time series to model the planetary and stellar signals present in the data, applying Gaussian Process regression technique to deal with the stellar activity signals. We identify three periodic signals in the RV time series, with periods of 9, 24, and 18 d. Combining the analyses of the photometry of the star with the activity indexes derived from the HARPS-N spectra, we identify the 18 d and 9 d signals as activity-related, corresponding to the stellar rotation period and its first harmonic respectively. The 24 d signals shows no relations with any activity proxy, so we identify it as a genuine planetary signal. We find the best-fit model describing the Doppler signal of the newly-found planet, GJ 685\,b, corresponding to an orbital period $P_b = 24.160^{+0.061}_{-0.047}$ d and a minimum mass $M_P \sin i = 9.0^{+1.7}_{-1.8}$ M$_\oplus$. We also study a sample of 70 RV-detected M-dwarf planets, and present new statistical evidence of a difference in mass distribution between the populations of single- and multi-planet systems, which can shed new light on the formation mechanisms of low-mass planets around late-type stars.

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arXiv2019

Connecting substellar and stellar formation. The role of the host star's metallicity

Most of our current understanding of the planet formation mechanism is based on the planet metallicity correlation derived mostly from solar-type stars harbouring gas-giant planets. To achieve a far more reaching grasp on the substellar formation process we aim to analyse in terms of their metallicity a diverse sample of stars (in terms of mass and spectral type) covering the whole range of possible outcomes of the planet formation process (from planetesimals to brown dwarfs and low-mass binaries). Our methodology is based on the use of high-precision stellar parameters derived by our own group in previous works from high-resolution spectra by using the iron ionisation and equilibrium conditions. All values are derived in an homogeneous way, except for the M dwarfs where a methodology based on the use of pseudo equivalent widths of spectral features was used. Our results show that as the mass of the substellar companion increases the metallicity of the host star tendency is to lower values. The same trend is maintained when analysing stars with low-mass stellar companions and a tendency towards a wide range of host star's metallicity is found for systems with low mass planets. We also confirm that more massive planets tend to orbit around more massive stars. The core-accretion formation mechanism for planet formation achieves its maximum efficiency for planets with masses in the range 0.2 and 2 M$_{\rm Jup}$. Substellar objects with higher masses have higher probabilities of being formed as stars. Low-mass planets and planetesimals might be formed by core-accretion even around low-metallicity stars.

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arXiv2019

HADES RV Programme with HARPS-N at TNG. X. The non-saturated regime of the stellar activity-rotation relationship for M-Dwarfs

Aims. We aim to extend the relationship between X-ray luminosity (Lx) and rotation period (Prot) found for main-sequence FGK stars and test whether it also holds for early-M dwarfs, especially in the non-saturated regime (Lx α P_{rot}^{-2}) which corresponds to slow rotators. Methods. We use the luminosity coronal activity indicator (Lx) of a sample of 78 early-M dwarfs with masses in the range from 0.3 to 0.75 Msun from the HArps-N red Dwarf Exoplanet Survey (HADES) radial velocity (RV) programme collected from ROSAT and XMM-Newton. The determination of the rotation periods (P_{rot}) was done by analysing time-series of high-resolution spectroscopy of the Ca ii H & K and Hα activity indicators. Our sample principally covers the slow rotation regime with rotation periods from 15 to 60 days. Results. Our work extends to the low mass regime the observed trend for more massive stars showing a continuous shift of the Lx/Lbol vs. Prot power-law towards longer rotation period values and includes the determination, in a more accurate way, of the value of the rotation period at which the saturation occurs (P_{sat}) for M dwarf stars. Conclusions. We conclude that the relations between coronal activity and stellar rotation for FGK stars also hold for early-M dwarfs in the non-saturated regime, indicating that the rotation period is sufficient to determine the ratio Lx/Lbol.

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arXiv2019

HARPS-N Solar Radial-Velocity Variations Are Dominated By Large, Bright Magnetic Regions

State of the art radial-velocity (RV) exoplanet searches are currently limited by RV signals arising from stellar magnetic activity. We analyze solar observations acquired over a 3-year period during the decline of Carrington Cycle 24 to test models of RV variation of Sun-like stars. A purpose-built solar telescope at the High Accuracy Radial velocity Planet Searcher for the Northern hemisphere (HARPS-N) provides disk-integrated solar spectra, from which we extract RVs and $\log{R'_{\rm HK}}$. The Solar Dynamics Observatory (SDO) provides disk-resolved images of magnetic activity. The Solar Radiation and Climate Experiment (SORCE) provides near-continuous solar photometry, analogous to a Kepler light curve. We verify that the SORCE photometry and HARPS-N $\log{R'_{\rm HK}}$ correlate strongly with the SDO-derived magnetic filling factor, while the HARPS-N RV variations do not. To explain this discrepancy, we test existing models of RV variations. We estimate the contributions of the suppression of convective blueshift and the rotational imbalance due to brightness inhomogeneities to the observed HARPS-N RVs. We investigate the time variation of these contributions over several rotation periods, and how these contributions depend on the area of active regions. We find that magnetic active regions smaller than $60 \ \rm Mm^2$ do not significantly suppress convective blueshift. Our area-dependent model reduces the amplitude of activity-induced RV variations by a factor of two. The present study highlights the need to identify a proxy that correlates specifically with large, bright magnetic regions on the surfaces of exoplanet-hosting stars.

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arXiv2019

HADES RV program with HARPS-N at TNG. IX. A super-Earth around the M dwarf Gl686

The HArps-n red Dwarf Exoplanet Survey is providing a major contribution to the widening of the current statistics of low-mass planets, through the in-depth analysis of precise radial velocity measurements in a narrow range of spectral sub-types. As part of that program, we obtained radial velocity measurements of Gl 686, an M1 dwarf at d = 8.2 pc. The analysis of data obtained within an intensive observing campaign demonstrates that the excess dispersion is due to a coherent signal, with a period of 15.53 d. Almost simultaneous photometric observations were carried out within the APACHE and EXORAP programs to characterize the stellar activity and to distinguish periodic variations related to activity from signals due to the presence of planetary companions, complemented also with ASAS photometric data. We took advantage of the available radial velocity measurements for this target from other observing campaigns. The analysis of the radial velocity composite time series from the HIRES, HARPS and HARPS-N spectrographs, consisting of 198 measurements taken over 20 years, enabled us to address the nature of periodic signals and also to characterize stellar physical parameters (mass, temperature, and rotation). We report the discovery of a super-Earth orbiting at a distance of 0.092 AU from the host star Gl 686. Gl 686 b has a minimum mass of 7.1 +/- 0.9 MEarth and an orbital period of 15.532 +/- 0.002 d. The analysis of the activity indexes, correlated noise through a Gaussian process framework and photometry, provides an estimate of the stellar rotation period at 37 d, and highlights the variability of the spot configuration during the long timespan covering 20 yrs. The observed periodicities around 2000 d likely point to the existence of an activity cycle.

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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

GIARPS: commissioning and first scientific results

GIARPS (GIAno \& haRPS) is a project devoted to have on the same focal station of the Telescopio Nazionale Galileo (TNG) both high resolution spectrographs, HARPS-N (VIS) and GIANO-B (NIR), working simultaneously. This could be considered the first and unique worldwide instrument providing cross-dispersed echelle spectroscopy at a resolution of 50,000 in the NIR range and 115,000 in the VIS and over in a wide spectral range ($0.383 - 2.45\ μ$m) in a single exposure. The science case is very broad, given the versatility of such an instrument and its large wavelength range. A number of outstanding science cases encompassing mainly extra-solar planet science starting from rocky planets search and hot Jupiters to atmosphere characterization can be considered. Furthermore both instruments can measure high precision radial velocities by means the simultaneous thorium technique (HARPS-N) and absorbing cell technique (GIANO-B) in a single exposure. Other science cases are also possible. GIARPS, as a brand new observing mode of the TNG started after the moving of GIANO-A (fiber fed spectrograph) from Nasmyth-A to Nasmyth-B where it was re-born as GIANO-B (no more fiber feed spectrograph). The official Commissioning finished on March 2017 and then it was offered to the community. Despite the work is not finished yet. In this paper we describe the preliminary scientific results obtained with GIANO-B and GIARPS observing mode with data taken during commissioning and first open time observations.

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arXiv2018

Multi-band high resolution spectroscopy rules out the hot Jupiter BD+20 1790b - First data from the GIARPS Commissioning

Context. Stellar activity is currently challenging the detection of young planets via the radial velocity (RV) technique. Aims. We attempt to definitively discriminate the nature of the RV variations for the young active K5 star BD+20 1790, for which visible (VIS) RV measurements show divergent results on the existence of a substellar companion. Methods. We compare VIS data with high precision RVs in the near infrared (NIR) range by using the GIANO - B and IGRINS spectrographs. In addition, we present for the first time simultaneous VIS-NIR observations obtained with GIARPS (GIANO - B and HARPS - N) at Telescopio Nazionale Galileo (TNG). Orbital RVs are achromatic, so the RV amplitude does not change at different wavelengths, while stellar activity induces wavelength-dependent RV variations, which are significantly reduced in the NIR range with respect to the VIS. Results. The NIR radial velocity measurements from GIANO - B and IGRINS show an average amplitude of about one quarter with respect to previously published VIS data, as expected when the RV jitter is due to stellar activity. Coeval multi-band photometry surprisingly shows larger amplitudes in the NIR range, explainable with a mixture of cool and hot spots in the same active region. Conclusions. In this work, the claimed massive planet around BD+20 1790 is ruled out by our data. We exploited the crucial role of multi- wavelength spectroscopy when observing young active stars: thanks to facilities like GIARPS that provide simultaneous observations, this method can reach its maximum potential.

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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 HADES RV Programme with HARPS-N@TNG VIII. Gl15A: A multiple wide planetary system sculpted by binary interaction

We present 20 years of radial velocity (RV) measurements of the M1 dwarf Gl15A, combining 5 years of intensive RV monitoring with the HARPS-N spectrograph with 15 years of archival HIRES/Keck RV data. We carry out an MCMC-based analysis of the RV time series, inclusive of Gaussian Process (GP) approach to the description of stellar activity induced RV variations. Our analysis confirms the Keplerian nature and refines the orbital solution for the 11.44-day period super Earth, Gl15A\,b, reducing its amplitude to $1.68^{+0.17}_{-0.18}$ m s$^{-1}$ ($M \sin i = 3.03^{+0.46}_{-0.44}$ M$_\oplus$), and successfully models a long-term trend in the combined RV dataset in terms of a Keplerian orbit with a period around 7600 days and an amplitude of $2.5^{+1.3}_{-1.0}$ m s$^{-1}$, corresponding to a super-Neptune mass ($M \sin i = 36^{+25}_{-18}$ M$_\oplus$) planetary companion. We also discuss the present orbital configuration of Gl15A planetary system in terms of the possible outcomes of Lidov-Kozai interactions with the wide-separation companion Gl15B in a suite of detailed numerical simulations. In order to improve the results of the dynamical analysis, we derive a new orbital solution for the binary system, combining our RV measurements with astrometric data from the WDS catalogue. The eccentric Lidov-Kozai analysis shows the strong influence of Gl15B on the Gl15A planetary system, which can produce orbits compatible with the observed configuration for initial inclinations of the planetary system between $75^\circ$ and $90^\circ$, and can also enhance the eccentricity of the outer planet well above the observed value, even resulting in orbital instability, for inclinations around $0^\circ$ and $15^\circ - 30^\circ$. The Gl15A system is the multi-planet system closest to Earth, at $3.57$ pc, and hosts the longest period RV sub-jovian mass planet discovered so far.

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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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arXiv2018

The co-existence of hot and cold gas in debris discs

Debris discs have often been described as gas-poor discs as the gas-to-dust ratio is expected to be considerably lower than in primordial,protoplanetary discs. However, recent observations have confirmed the presence of a non-negligible amount of cold gas in the circumstellar (CS) debris discs around young main-sequence stars.This cold gas has been suggested to be related to the outgassing of planetesimals and cometary-like objects. The aim of the paper is to investigate the presence of hot gas in the surroundings of stars bearing cold-gas debris discs. High-resolution optical spectra of all currently known cold-gas-bearing debris-disc systems, with the exception of $β$ Pic and Fomalhaut, have been obtained from different observatories.We have analysed the Ca II H & K and the Na I D lines searching for non-photospheric absorptions of CS origin, usually attributed to cometary-like activity. Narrow, stable Ca II and/or Na I absorption features have been detected superimposed to the photospheric lines in 10 out of the 15 observed cold-gas-bearing debris disc.Features are found at the radial velocity of the stars, or slightly blue- or red-shifted, and/or at the velocity of the local interstellar medium (ISM). Some stars also present transient variable events or absorptions extended towards red wavelengths. These are the first detections of such Ca II features in 7 out of the 15 observed stars. In some of these stars, results suggest that the stable and variable absorptions arise from relatively hot gas located in the CS close-in environment. This hot gas is detected in at least ~80%, of edge-on cold-gas-bearing debris discs, while in only ~10% of the discs seen close to face-on. We interpret this as a geometrical effect, and suggest that the non-detection of hot gas absorptions is due to the disc inclination rather than to the absence of the hot-gas component.

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