Search

Context. The intrinsic variability due to the magnetic activity of young active stars is one of the main challenges in detecting and characterising exoplanets. The stellar activity is responsible for jitter effects observed both in photometric and spectroscopic observations that can impact our planetary detection sensitivity. Aims. We present a method able to model the stellar photosphere and its surface inhomogeneities (starspots) in young, active, and fast-rotating stars based on the cross-correlation function (CCF) technique, and we extract information about the spot configuration of the star. Methods. We developed Spot CCF, a tool able to model the deformation of the CCF profile due to the presence of multiple spots on the stellar surface. Within the Global Architecture of Planetary Systems (GAPS) Project at the Telescopio Nazionale Galileo, we analysed more than 300 spectra of the young planet-hosting star V1298 Tau provided by the HARPS-N high-resolution spectrograph. By applying the SpotCCF model to the CCFs, we extracted the spot configuration (latitude, longitude, and projected filling factor) of this star, and provide a new radial velocity (RV) time series for this target. Results. We find that the features identified in the CCF profiles of V1298 Tau are modulated by the stellar rotation, supporting our assumption that they are caused by starspots. The analysis suggests a differential rotation velocity of the star with lower rotation at higher latitudes. Also, we find that SpotCCF provides an improvement in RV extraction, with a significantly lower dispersion with respect to the commonly used pipelines. This allows mitigation of the stellar activity contribution modulated with stellar rotation. A detection sensitivity test, involving the direct injection of a planetary signal into the data, confirms that the SpotCCF model improves the sensitivity and ability to recover planetary signals. Conclusions. Our method enables us to model the stellar photosphere and extract the spot configuration of young, active, and rapidly rotating stars. It also allows the extraction of optimised RV time series, thereby enhancing our detection capabilities for new exoplanets and advancing our understanding of stellar activity. [ABSTRACT FROM AUTHOR]

The nearby mid-K dwarf HIP 66074 was recently identified as host to a candidate super-Jupiter companion on a ∼300 day, almost edge-on, orbit, based on Gaia Data Release 3 (DR3) astrometry. Initial attempts at confirming the planetary nature of the signal based on publicly available radial-velocity (RV) observations uncovered an intriguing conundrum: the inferred RV semi-amplitude appears to be a factor of 15 smaller than the one predicted based on the Gaia solution (corresponding to a 7-MJup companion on a close to edge-on orbit). We present the results of intensive RV monitoring of HIP 66074 with the HARPS-N spectrograph. We detected the companion at the Gaia period, but with an extremely eccentric orbit (e = 0.948 ± 0.004), a semi-amplitude K = 93.9−7.0+9.4 m s−1, and a minimum mass mb sin ib = 0.79 ± 0.05 MJup. We used detailed simulations of Gaia astrometry with the DR3 time-span to show that the conundrum can be fully resolved by taking into account the combination of the initially sub-optimal RV sampling and systematic biases in the Gaia astrometric solution, which include an underestimation of the eccentricity and incorrect identification of orbital inclination, which has turned out to correspond to a close to face-on configuration (i ≲ 13°). With an estimated mass in the approximate range of 3 − 7 MJup, we find that HIP 66074b (≡Gaia-3b) is the first exoplanet candidate astrometrically detected by Gaia to be successfully confirmed based on RV follow-up observations. [ABSTRACT FROM AUTHOR]

We characterize twelve young stellar objects (YSOs) located in the Lupus I region, spatially overlapping with the Upper Centaurus Lupus (UCL) sub-stellar association. The aim of this study is to understand whether the Lupus I cloud has more members than what has been claimed so far in the literature and gain a deeper insight into the global properties of the region. We selected our targets using the Gaia DR2 catalog based on their consistent kinematic properties with the Lupus I bona fide members. In our sample of twelve YSOs observed by X-shooter, we identified ten Lupus I members. We could not determine the membership status of two of our targets, namely Gaia DR2 6014269268967059840 and 2MASS J15361110-3444473 due to technical issues. We found out that four of our targets are accretors, among them, 2MASS J15551027-3455045, with a mass of ∼0.03 M⊙, is one of the least massive accretors in the Lupus complex identified to date. Several of our targets (including accretors) are formed in situ and off-cloud with respect to the main filaments of Lupus I; hence, our study may hint that there are diffused populations of M dwarfs around Lupus I main filaments. In this context, we would like to emphasize that our kinematic analysis with Gaia catalogs played a key role in identifying the new members of the Lupus I cloud. [ABSTRACT FROM AUTHOR]

Aims. We present a novel method for studying the thermal emission of exoplanets as a function of orbital phase at very high spectral resolution, and use it to investigate the climate of the ultra-hot Jupiter KELT-9b. Methods. We combine three nights of HARPS-N and two nights of CARMENES optical spectra, covering orbital phases between quadratures (0.25 < φ < 0.75), when the planet shows its day-side hemisphere with different geometries. We co-add the signal of thousands of Fe I lines through cross-correlation, which we map to a likelihood function. We investigate the phase-dependence of two separate observable quantities, namely (i) the line depths of Fe I and (ii) their Doppler shifts, introducing a new method that exploits the very high spectral resolution of our observations. Results. We confirm a previous detection of Fe I emission, and demonstrate a precision of 0.5 km s−1 on the orbital properties of KELT-9b when combining all nights of observations. By studying the phase-resolved Doppler shift of Fe I lines, we detect an anomaly in the planet's orbital radial velocity well-fitted with a slightly eccentric orbital solution (e = 0.016 ± 0.003, ω = 150−11+13°, 5σ preference). However, we argue that this anomaly is caused by atmospheric circulation patterns, and can be explained if neutral iron gas is advected by day-to-night atmospheric wind flows of the order of a few km s−1. We additionally show that the Fe I emission line depths are symmetric around the substellar point within 10° (2σ), possibly indicating the lack of a large hot-spot offset at the altitude probed by neutral iron emission lines. Finally, we do not obtain a significant preference for models with a strong phase-dependence of the Fe I emission line strength. We show that these results are qualitatively compatible with predictions from general circulation models (GCMs) for ultra-hot Jupiter planets. Conclusions. Very high-resolution spectroscopy phase curves are of sufficient sensitivity to reveal a phase dependence in both the line depths and their Doppler shifts throughout the orbit. They constitute an under-exploited treasure trove of information that is highly complementary to space-based phase curves obtained with HST and JWST, and open a new window onto the still poorly understood climate and atmospheric structure of the hottest planets known to date. [ABSTRACT FROM AUTHOR]

Context. Detecting and characterising exoworlds around very young stars (age ≤10 Myr) are key aspects of exoplanet demographic studies, especially for understanding the mechanisms and timescales of planet formation and migration. Any reliable theory for such physical phenomena requires a robust observational database to be tested. However, detection using the radial velocity method alone can be very challenging because the amplitude of the signals caused by the magnetic activity of such stars can be orders of magnitude larger than those induced even by massive planets. Aims. We observed the very young (~2 Myr) and very active star V830 Tau with the HARPS-N spectrograph between October 2017 and March 2020 to independently confirm and characterise the previously reported hot Jupiter V830 Tau b (Kb = 68 ± 11 m s−1; mb sin ib = 0.57 ± 0.10 MJup; Pb = 4.927 ± 0.008 d). Methods. Because of the observed ~1 km s−1 radial velocity scatter that can clearly be attributed to the magnetic activity of V830 Tau, we analysed radial velocities extracted with different pipelines and modelled them using several state-of-the-art tools. We devised injection-recovery simulations to support our results and characterise our detection limits. The analysis of the radial velocities was aided by a characterisation of the stellar activity using simultaneous photometric and spectroscopic diagnostics. Results. Despite the high quality of our HARPS-N data and the diversity of tests we performed, we were unable to detect the planet V830 Tau b in our data and cannot confirm its existence. Our simulations show that a statistically significant detection of the claimed planetary Doppler signal is very challenging. Conclusions. It is important to continue Doppler searches for planets around young stars, but utmost care must be taken in the attempt to overcome the technical difficulties to be faced in order to achieve their detection and characterisation. This point must be kept in mind when assessing their occurrence rate, formation mechanisms, and migration pathways, especially without evidence of their existence from photometric transits. [ABSTRACT FROM AUTHOR]

Substellar companions at wide separation around stars hosting planets or brown dwarfs (BDs) yet close enough for their formation in the circumstellar disc are of special interest. In this Letter we report the discovery of a wide (projected separation ~1600:0, or 2400AU, and position angle 114.61°) companion of the GQLup A-B system, most likely gravitationally bound to it. A VLT/Xshooter spectrum shows that this star, 2MASS J15491331-3539118, is a bonafide low-mass (~0.15 M⊙) young stellar object (YSO) with stellar and accretion/ejection properties typical of Lupus YSOs of similar mass, and with kinematics consistent with that of the GQLup A-B system. A possible scenario for the formation of the triple system is that GQLupA and 2MASS J15491331-3539118 formed by fragmentation of a turbulent core in the Lup I filament, while GQLup B, the BD companion of GQLupA at 000:7, formed in situ by the fragmentation of the circumprimary disc. The recent discoveries that stars form along cloud filaments would favour the scenario of turbulent fragmentation for the formation of GQLupA and 2MASS J15491331-3539118. [ABSTRACT FROM AUTHOR]

Aims. In the framework of the GAPS project, we observed the planet-hosting star KELT-9 (A-type star, v sin i ~ 110 km s−1) with the HARPS-N spectrograph at the Telescopio Nazionale Galileo. In this work we analyse the spectra and the extracted radial velocities to constrain the physical parameters of the system and to detect the planetary atmosphere of KELT-9b. Methods. We extracted the mean stellar line profiles from the high-resolution optical spectra via an analysis based on the least-squares deconvolution technique. Then we computed the stellar radial velocities with a method optimised for fast rotators by fitting the mean stellar line profile with a purely rotational profile instead of using a Gaussian function. Results. 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 Mp = 2.88 ± 0.35 MJup. We discovered an anomalous in-transit radial velocity deviation from the theoretical Rossiter-McLaughlin effect solution, calculated from the projected spin-orbit angle λ = −85.78 ± 0.46 degrees measured with Doppler tomography. We prove that this deviation is caused by the planetary atmosphere of KELT-9b, thus we call this effect Atmospheric Rossiter-McLaughlin effect. By analysing the magnitude of the radial velocity 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 ± 0.02 Rp. Conclusions. 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 radial velocities, in particular ultra-hot Jupiters with iron in their atmospheres. The duration and amplitude of the effect will depend not only on the extension of the atmosphere, but also on the in-transit planetary radial velocities and on the projected rotational velocity of the parent star. [ABSTRACT FROM AUTHOR]

Aims. We 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 ∝ Prot−2 $L_{\textrm{x}} \propto P_{\textrm{rot}}^{-2}$ L x ∝ 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 M⊙ 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 (Prot) 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 versus Prot power law towards longer rotation period values, and includes a more accurate way to determine the value of the rotation period at which the saturation occurs (Psat) 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. [ABSTRACT FROM AUTHOR]

Context. Statistical studies of exoplanets have shown that giant planets are more commonly hosted by metal-rich dwarf stars than low-metallicity stars, while no such correlation is evident for lower mass planets. The search for giant planets around metal-poor stars and the estimate of their occurrence fp is an important element in providing support to models of planet formation. Aims. We present results from the HARPS-N search for giant planets orbiting metal-poor (− 1.0 ≤[Fe/H] ≤−0.5 dex) stars in the northern hemisphere, complementing a previous HARPS survey on southern stars in order to update the estimate of fp. Methods. High-precision HARPS-N observations of 42 metal-poor stars were used to search for planetary signals to be fitted using differential evolution Markov chain Monte Carlo single-Keplerian models. We then joined our detections to the results of the previous HARPS survey on 88 metal-poor stars to provide a preliminary estimate of the two-hemisphere fp. Results. 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 $\sin{i}=0.20_{-0.04}^{+0.07}$ sin i = 0.20 − 0.04 + 0.07 MJup and an orbital period of 1728−80+162 $1728_{-80}^{+162}$ 1728 − 80 + 162 days, and for the second companion, we find two solutions of equal statistical weight with periods of 2058−40+47 $2058_{-40}^{+47}$ 2058 − 40 + 47 and 4047−117+91 $4047_{-117}^{+91}$ 4047 − 117 + 91 days and minimum masses of 1.78−0.06+0.08 $1.78_{-0.06}^{+0.08}$ 1.78 − 0.06 + 0.08 and 2.72−0.23+0.23 $2.72_{-0.23}^{+0.23}$ 2.72 − 0.23 + 0.23 MJup, respectively. Joining our two detections with the three from the southern survey, we obtain a preliminary and conservative estimate of the global frequency of fp = 3.84 −1.06+2.45% $f_p=3.84_{-1.06}^{+2.45}\%$ f p = 3.84 − 1.06 + 2.45 % for giant planets around metal-poor stars. Conclusions. The two new giant planets orbit dwarf stars at the metal-rich end of the HARPS-N metal-poor sample. This corroborates previous results that suggested that giant planet frequency is still a rising function of the host star [Fe/H]. We also note that all detections in the overall sample are giant long-period planets. [ABSTRACT FROM AUTHOR]

Context. The measurement of the orbital obliquity of hot Jupiters with different physical characteristics can provide clues to the mechanisms of migration and orbital evolution of this particular class of giant exoplanets. Aims. We aim to derive the degree of alignment between planetary orbit and stellar spin angular momentum vectors and look for possible links with other orbital and fundamental physical parameters of the star-planet system. We focus on the characterisation of five transiting planetary systems (HAT-P-3, HAT-P-12, HAT-P-22, WASP-39, and WASP-60) and the determination of their sky-projected planet orbital obliquity through the measurement of the Rossiter-McLaughlin effect. Methods. We used HARPS-N high-precision radial velocity measurements, gathered during transit events, to measure the Rossiter- McLaughlin effect in the target systems and determine the sky-projected angle between the planetary orbital plane and stellar equator. The characterisation of stellar atmospheric parameters was performed by 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. Results. From the analysis of the Rossiter-McLaughlin effect we derived a sky-projected obliquity of λ = 21:2° ± 8:7°, λ = -54° +41° -13° , λ = -2:1° ± 3:0°, λ = 0° ± 11°, and λ = -129° ± 17° for HAT-P-3 b, HAT-P-12 b, HAT-P-22 b, WASP-39 b, and WASP-60 b, respectively. The latter value indicates that WASP-60 b is moving on a retrograde orbit. These values represent the first measurements of λ for the five iexoplanetary systems under study. The stellar activity of HAT-P-22 indicates a rotation period of 28:7 ± 0:4 days, which allowed us to estimate the true misalignment angle of HAT-P-22 b, ψ= 24° ± 18°. 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. [ABSTRACT FROM AUTHOR]

Context. Identification of planetary companions of giant stars is made difficult because of the astrophysical noise, that may produce radial velocity 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) radial velocity 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 radial velocities 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⊙ are MPsini = 10.78 ± 0.12MJ; P = 101.54 ± 0.05 days; e = 0.28 ± 0.01 and a = 0.422 ± 0.009 AU. The chemical analysis shows a significant enrichment in the abundance of Na i, Mg i, Al i and Si 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 radial velocity variation. This study also shows the high potential of multi-wavelength radial velocity observations for the validation of planet candidates. [ABSTRACT FROM AUTHOR]

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 of 151 HARPS-N measurements taken over 3.5 yr. GJ 625 b is a planet with a minimum mass Msin i of 2.82 ± 0.51 M⊕ with an orbital period of 14.628 ± 0.013 days at a distance of 0.078 AU from 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 Hα spectroscopic indicators, the variations of the FWHM of the CCF, and the APT2 photometric light curves. We find no evidence linking the short-period radial-velocity signal to any activity proxy. [ABSTRACT FROM AUTHOR]

Aims. 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: 1) to derive the lithium abundance for the almost complete sample (~ 90%) of known class II stars in the Lupus I, II, III, and IV clouds; 2) to perform chemical tagging of a region where few iron abundance measurements have been obtained in the past, and no determination of the barium content has been done up to now. We also investigated possible barium enhancement at the very young age of the region, as this element has become increasingly interesting in the last few years following the evidence of barium over-abundance in young clusters, the origin of which is still unknown. Methods. Using the X-shooter spectrograph mounted on the Unit 2 (UT2) at the Very Large Telescope (VLT), we analyzed the spectra of 89 cluster members, both class II (82) and class III (7) stars. We measured the strength of the lithium line at λ6707.8 Å and derived the abundance of this element through equivalent width measurements and curves of growth. For six class II stars we also derived the iron and barium abundances using the spectral synthesis method and the code MOOG. The veiling contribution was taken into account in the abundance analysis for all three elements. Results. We find a dispersion in the strength of the lithium line at low effective temperatures and identify three targets with severe Li depletion. The nuclear age inferred for these highly lithium-depleted stars is around 15 Myr, which exceeds by an order of magnitude the isochronal one. We derive a nearly solar metallicity for the members whose spectra could be analyzed. We find that Ba is over-abundant by ~ 0.7 dex with respect to the Sun. Since current theoretical models cannot reproduce this abundance pattern, we investigated whether this unusually large Ba content might be related to effects due to stellar parameters, stellar activity, and accretion. Conclusions. We are unable to firmly assess whether the dispersion in the lithium content we observe is a consequence of an age spread. As in other star-forming regions, no metal-rich members are found in Lupus, giving support to a recent hypothesis that the iron 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. Among the possible causes or sources for Ba enhancement examined here, none is sufficient to account for the over-abundance of this element at a ~ 0.7 dex level. [ABSTRACT FROM AUTHOR]

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 differential evolution Markov chain Monte Carlo 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 planetary migration from highly eccentric orbits excited by planetplanet scattering, Kozai-Lidov perturbations, or secular chaos. The distribution of α = a/aR, where a and aR are the semi-major axis and the Roche limit, for well-determined circular orbits peaks at 2.5; this agrees with expectations from the high-eccentricity migration (HEM), although it might not be limited to this migration scenario. 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 105 ≾ Qp' ≿ 109, and that stellar Q0s & 106-107 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 e = 0:104-0:018+0:021 for HAT-P-29; we determined that five planets that were previously regarded to be eccentric or to have hints of non-zero eccentricity, namely CoRoT-2b, CoRoT-23b, TrES-3b, HAT-P-23b, and WASP-54b, 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; we significantly improved the orbital parameters of the long-period planet HAT-P-17c; and we revised the planetary parameters of CoRoT-1b, which turned out to be considerably more inflated than previously found. [ABSTRACT FROM AUTHOR]

Context: The orbital obliquity of planets with respect to the rotational axis of their host stars is a relevant parameter for the characterization of the global architecture of planetary systems and a key observational constraint to discriminate between different scenarios proposed to explain the existence of close-in giant planets. Aims: In the framework of the GAPS project, we conduct an observational programme aimed at determinating the orbital obliquity of known transiting exoplanets. The targets are selected to probe the obliquity against a wide range of stellar and planetary physical parameters. Methods: We exploit high-precision radial velocity (RV) measurements, delivered by the HARPS-N spectrograph at the 3.6 m Telescopio Nazionale Galileo, to measure the Rossiter-McLaughlin (RM) effect in RV time-series bracketing planet transits, and to refine the orbital parameters determinations with out-of-transit RV data. We also analyse new transit light curves obtained with several 1-2 m class telescopes to better constrain the physical fundamental parameters of the planets and parent stars. Results: We report here on new transit spectroscopic observations for three very massive close-in giant planets: WASP-43 b, HAT-P-20 b and Qatar-2 b (Mp = 2.00, 7.22, 2.62 MJ; a = 0.015, 0.036, 0.022 AU, respectively) orbiting dwarf K-type stars with effective temperature well below 5000 K (Teff = 4500 ± 100, 4595 ± 45, 4640 ± 65 K respectively). These are the coolest stars (except for WASP-80) for which the RM effect has been observed so far. We find λ = 3.5 ± 6.8 deg for WASP-43 b and λ = -8.0 ± 6.9 deg for HAT-P-20 b, while for Qatar-2, our faintest target, the RM effect is only marginally detected, though our best-fit value λ = 15 ± 20 deg is in agreement with a previous determination. In combination with stellar rotational periods derived photometrically, we estimate the true spin-orbit angle, finding that WASP-43 b is aligned while the orbit of HAT-P-20 b presents a small but significant obliquity (Ψ = 36-12+10 deg). By analyzing the CaII H&K chromospheric emission lines for HAT-P-20 and WASP-43, we find evidence for an enhanced level of stellar activity that is possibly induced by star-planet interactions. [ABSTRACT FROM AUTHOR]

The mass accretion rate, Ṁacc, is a key quantity for the understanding of the physical processes governing the evolution of accretion discs around young low-mass (M≱2.0 M⊆) stars and substellar objects (YSOs). We present here the results of a study of the stellar and accretion properties of the (almost) complete sample of class II and transitional YSOs in the Lupus I, II, III and IV clouds, based on spectroscopic data acquired with the VLT/X-shooter spectrograph. Our study combines the dataset from our previous work with new observations of 55 additional objects. We have investigated 92 YSO candidates in total, 11 of which have been definitely identified with giant stars unrelated to Lupus. The stellar and accretion properties of the 81 bona fide YSOs, which represent more than 90% of the whole class II and transition disc YSO population in the aforementioned Lupus clouds, have been homogeneously and self-consistently derived, allowing for an unbiased study of accretion and its relationship with stellar parameters. The accretion luminosity, Lacc, increases with the stellar luminosity, L*, with an overall slope of ~1.6, similar but with a smaller scatter than in previous studies. There is a significant lack of strong accretors below L* 0.1 L⊆, where Lacc is always lower than 0.01 L*. We argue that the Lacc - L* slope is not due to observational biases, but is a true property of the Lupus YSOs. The log Ṁacc - log M* correlation shows a statistically significant evidence of a break, with a steeper relation for M≱0.2 M⊆ and a flatter slope for higher masses. The bimodality of the Ṁacc - M* relation is confirmed with four different evolutionary models used to derive the stellar mass. The bimodal behaviour of the observed relationship supports the importance of modelling self-gravity in the early evolution of the more massive discs, but other processes, such as photo-evaporation and planet formation during the YSO's lifetime, may also lead to disc dispersal on different timescales depending on the stellar mass. The sample studied here more than doubles the number of YSOs with homogeneously and simultaneously determined Lacc and luminosity, Lline, of many permitted emission lines. Hence, we also refined the empirical relationships between Lacc and Lline on a more solid statistical basis. [ABSTRACT FROM AUTHOR]

Aims. For more than 1.5 years we spectroscopically monitored the star KELT-6 (BD+31 2447), which is known to host the transiting hot-Saturn KELT-6 b, because a previously observed long-term trend in radial velocity time series suggested that there is an outer companion. Methods. We collected a total of 93 new spectra with the HARPS-N and TRES spectrographs. A spectroscopic transit of KELT-6 b was observed with HARPS-N, and simultaneous photometry was obtained with the IAC-80 telescope. Results. We proved the existence of an outer planet with a mininum mass Mpsin i = 3.71 ± 0.21 ... and a moderately eccentric orbit (e = 0.21-0.036+0.039) of period P ~ 3.5 years. We improved the orbital solution of KELT-6 b and obtained the first measurement of the Rossiter-McLaughlin effect, showing that the planet has a likely circular, prograde, and slightly misaligned orbit with a projected spin-orbit angle of λ = -36 ± 11 degrees. We improved the KELT-6 b transit ephemeris from photometry and provide new measurements of the stellar parameters. KELT-6 appears as an interesting case for studying the formation and evolution of multi-planet systems. [ABSTRACT FROM AUTHOR]

Context. Orbital obliquity is thought to be a fundamental parameter in tracing the physical mechanisms that cause the migration of giant planets from the snow line down to roughly 10-2 au from their host stars.We are carrying out a large programme to estimate the spin-orbit alignment of a sample of transiting planetary systems to study what the possible configurations of orbital obliquity are and whether they correlate with other stellar or planetary properties. Aims. We determine the true and the projected obliquity of HAT-P-36 and WASP-11/HAT-P-10 systems, respectively, which are both composed of a relatively cool star (with effective temperature Teff < 6100 K) and a hot-Jupiter planet. Methods. Thanks to the high-resolution spectrograph HARPS-N, we observed the Rossiter-McLaughlin effect for both systems by acquiring precise (3-8ms-1) radial-velocity measurements during planetary transit events. We also present photometric observations comprising six light curves that cover five transit events, which were obtained using three medium-class telescopes. One transit of WASP-11/HAT-P-10 was followed simultaneously from two observatories. The three transit light curves of HAT-P-36 b show anomalies that are attributable to starspot complexes on the surface of the parent star, in agreement with the analysis of its spectra that indicates moderate activity (log R'HK = -4.65 dex). By analysing the complete HATNet data set of HAT-P-36, we estimated the stellar rotation period by detecting a periodic photometric modulation in the light curve caused by star spots, obtaining Prot = 15.3±0.4 days, which implies that the inclination of the stellar rotational axis with respect to the line of sight is i* = 65° ± 34°. Results. We used the new spectroscopic and photometric data to revise the main physical parameters and measure the sky-projected misalignment angle of the two systems. We found λ = -14° ± 18° for HAT-P-36 and λ = 7° ± 5° for WASP-11/HAT-P-10, indicating in both cases a good spin-orbit alignment. In the case of HAT-P-36, we were also able to estimate an upper limit of its real obliquity, which turned out to be ψ < 63 degrees. [ABSTRACT FROM AUTHOR]

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 Ca II 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 ± 0.5 Gyr for τ Boo and further constrains the value of the stellar mass to 1.38 ± 0.05 M⊙. [ABSTRACT FROM AUTHOR]

Context. Low-mass stars have been recognised as promising targets in the search for rocky, small planets with the potential of supporting life. As a consequence, Doppler search programmes using high-resolution spectrographs like HARPS or HARPS-N are providing huge quantities of optical spectra of M dwarfs. However, determining the stellar parameters of M dwarfs using optical spectra has proven to be challenging. Aims. We aim to calibrate empirical relationships to determine accurate stellar parameters for early-M dwarfs (spectral types M0- M4.5) using the same spectra as those that are used for radial velocity determinations, without the necessity of acquiring IR spectra or relying on atmospheric models and/or photometric calibrations. Methods. Our methodology consists of using ratios of pseudo-equivalent widths of spectral features as a temperature diagnostic, a technique frequently used in solar-type stars. Stars with effective temperatures obtained from interferometric estimates of their radii are used as calibrators. Empirical calibrations for the spectral type are also provided. Combinations of features and ratios of features are used to derive calibrations for the stellar metallicity. Our methods are then applied to a large sample of M dwarfs that are currently being observed in the framework of the HARPS GTO search for extrasolar planets. The derived temperatures and metallicities are used together with photometric estimates of mass, radius, and surface gravity to calibrate empirical relationships for these parameters. Results. A long list of spectral features in the optical spectra of early-M dwarfs was identified. This list shows that the pseudo-equivalent width of roughly 43% of the features is strongly anticorrelated with the e ective temperature. The correlation with the stellar metallicity is weaker. A total of 112 temperature sensitive ratios were identified and calibrated over the range 3100-3950 K, providing e ective temperatures with typical uncertainties of about 70 K. Eighty-two ratios of pseudo-equivalent widths of features were calibrated to derive spectral types within 0.5 subtypes for stars with spectral types between K7V and M4.5V. We calibrated 696 combinations of the pseudo-equivalent widths of individual features and temperature-sensitive ratios for the stellar metallicity over a metallicity range from -0.54 to +0.24 dex, with estimated uncertainties in the range of 0.07-0.10 dex. We provide our own empirical calibrations for stellar mass, radius, and surface gravity. These parameters depend on the stellar metallicity. For a given e ective temperature, lower metallicities predict lower masses and radii as well as higher gravities. [ABSTRACT FROM AUTHOR]

Context. Young, close stars are ideal targets for searching planets using the direct imaging technique. The determination of stellar parameters is crucial for the interpretation of imaging survey results, particularly since the luminosity of substellar objects has a strong dependence on system age. Aims. We have conducted a large program with NaCo at the VLT to search for planets and brown dwarfs in wide orbits around 86 stars. A large fraction of the targets observed with NaCo were poorly investigated in the literature. We performed a study to characterize the fundamental properties (age, distance, and mass) of the stars in our sample. To improve target age determinations, we compiled and analyzed a complete set of age diagnostics. Methods. We measured spectroscopic parameters and age diagnostics using dedicated observations acquired with FEROS and CORALIE spectrographs at La Silla Observatory. We also made extensive use of archival spectroscopic data and the results that are available in the literature. Additionally, we exploited photometric time-series, which are available in ASAS and Super-WASP archives, to derive a rotational period for a large fraction of our program stars. Results. We provided updated characterization of all the targets observed in the VLT NaCo Large program, a survey designed to probe the occurrence of exoplanets and brown dwarfs in wide orbits. The median distance and age of our program stars are 64 pc and 100 Myr, respectively. Nearly all the stars have masses between 0.70 and 1.50 M⊙, with a median value of 1.01 M⊙. The typical metallicity is close to solar with a dispersion that is smaller than that of samples usually observed in radial velocity surveys. Several stars are confirmed or proposed here to be members of close young moving groups. Eight spectroscopic binaries are identified [ABSTRACT FROM AUTHOR]

Context. Young, nearby stars are ideal targets for direct imaging searches for giant planets and brown dwarf companions. After the first-imaged planet discoveries, vast efforts have been devoted to the statistical analysis of the occurence and orbital distributions of giant planets and brown dwarf companions at wide (≥5-6 AU) orbits. Aims. In anticipation of the VLT/SPHERE planet-imager, guaranteed-time programs, we have conducted a preparatory survey of 86 stars between 2009 and 2013 to identify new faint comoving companions to ultimately analyze the occurence of giant planets and brown dwarf companions at wide (10-2000 AU) orbits around young, solar-type stars. Methods. We used NaCo at VLT to explore the occurrence rate of giant planets and brown dwarfs between typically 0.1 and 8". Diffraction-limited observations in H-band combined with angular differential imaging enabled us to reach primary star-companion brightness ratios as small as 10-6 at 1.5". Repeated observations at several epochs enabled us to discriminate comoving companions from background objects. Results. During our survey, twelve systems were resolved as new binaries, including the discovery of a new white dwarf companion to the star HD?8049. Around 34 stars, at least one companion candidate was detected in the observed field of view. More than 400 faint sources were detected; 90% of them were in four crowded fields. With the exception of HD?8049?B, we did not identify any new comoving companions. The survey also led to spatially resolved images of the thin debris disk around HD?61005 that have been published earlier. Finally, considering the survey detection limits, we derive a preliminary upper limit on the frequency of giant planets for the semi-major axes of [10, 2000] AU: typically less than 15% between 100 and 500 AU and less than 10% between 50 and 500 AU for exoplanets that are more massive than 5 MJup and 10 MJup respectively, if we consider a uniform input distribution and a confidence level of 95%. Conclusions. The results from this survey agree with earlier programs emphasizing that massive, gas giant companions on wide orbits around solar-type stars are rare. These results will be part of a broader analysis of a total of ~210 young, solar-type stars to bring further statistical constraints for theoretical models of planetary formation and evolution. [ABSTRACT FROM AUTHOR]

We present the results of FLAMES/UVES and FLAMES/GIRAFFE spectroscopic observations of 23 low-mass stars in the L1615/L1616 cometary cloud, complemented with FORS2 and VIMOS spectroscopy of 31 additional stars in the same cloud. L1615/L1616 is a cometary cloud in which the star formation was triggered by the impact of massive stars in the Orion OB association. From the measurements of the lithium abundance and radial velocity, we confirm the membership of our sample to the cloud. We use the equivalent widths of the Hα, Hβ, and the Hei λ5876, λ6678, λ7065 Å emission lines to calculate the accretion luminosities, Lacc, and the mass accretion rates, Macc. We find in L1615/L1616 a fraction of accreting objects (∼30%), which is consistent with the typical fraction of accretors in T associations of similar age (∼3 Myr). The mass accretion rate for these stars shows a trend with the mass of the central object similar to that found for other star-forming regions, with a spread at a given mass that depends on the evolutionary model used to derive the stellar mass. Moreover, the behavior of the 2MASS/WISE colors with Macc indicates that strong accretors with log Macc ≳ -8.5 dex show large excesses in the JHKs bands, as in previous studies. We also conclude that the accretion properties of the L1615/L1616 members are similar to those of young stellar objects in T associations, like Lupus. [ABSTRACT FROM AUTHOR]

Disks around T Tauri stars are known to lose mass, as best shown by the profiles of the forbidden emission lines of low-ionization species. At least two separate kinematic components have been identified, one characterized by velocity shifts of tens to hundreds of km s-1 (HVC) and one with a much lower velocity of a few km s-1 (LVC). The HVC are convincingly associated to the emission of jets, but the origin of the LVC is still unknown. In this paper we analyze the forbidden line spectrum of a sample of 44 mostly lowmass young stars in Lupus and σ Ori observed with the X-shooter ESO spectrometer. We detect forbidden line emission of Oi, Oii, S ii, Ni, and Nii, and characterize the line profiles as LVC, blueshifted HVC, and redshifted HVC. We focus our study on the LVC. We show that there is a good correlation between line luminosity and both Lstar and the accretion luminosity (or the mass accretion rate) over a large interval of values (Lstar ∼ 10-2-1 L☉ ; Lacc ∼ 10-5-10-1 L☉; Macc ∼ 10-11-10-7 M☉/yr). The lines show the presence of a slow wind (Vpeak < 20 km s-1) that is dense (nH > 108 cm-3), warm (T ∼ 5000-10 000 K), mostly neutral. We estimate the mass of the emitting gas and provide a value for the maximum volume it occupies. Both quantities increase steeply with the stellar mass, from ∼10-12 M☉ and ∼0.01 AU3 for Mstar ∼ 0:1 M☉, to ∼3 x 10-10 M☉ and ∼1 AU3 for Mstar ∼ 1 M☉, respectively. These results provide quite stringent constraints to wind models in low-mass young stars, that need to be explored further. [ABSTRACT FROM AUTHOR]

The measurement of the Rossiter-McLaughlin effect for transiting exoplanets places constraints on the orientation of the orbital axis with respect to the stellar spin axis, which can shed light on the mechanisms shaping the orbital configuration of planetary systems. Here we present the interesting case of the Saturn-mass planet HAT-P-18b, which orbits one of the coolest stars for which the Rossiter- McLaughlin effect has been measured so far. We acquired a spectroscopic time-series, spanning a full transit, with the HARPS-N spectrograph mounted at the TNG telescope. The very precise radial velocity measurements delivered by the HARPS-N pipeline were used to measure the Rossiter-McLaughlin effect. Complementary new photometric observations of another full transit were also analysed to obtain an independent determination of the star and planet parameters. We find that HAT-P-18b lies on a counter-rotating orbit, the sky-projected angle between the stellar spin axis and the planet orbital axis being λ = 132 ± 15 deg. By joint modelling of the radial velocity and photometric data we obtain new determinations of the star (M⋆ = 0.770 ± 0.027 M☉; R⋆ = 0.717 ± 0.026 R☉; ; V sin I⋆ = 1.58 ± 0.18 km s-1) and planet (Mp = 0.196 ± 0.008 MJ; Rp = 0.947 ± 0.044 RJ) parameters. Our spectra provide for the host star an effective temperature Teff = 4870 ± 50 K, a surface gravity of log g⋆ = 4.57 ± 0.07 cm s-2, and an iron abundance of [Fe/H] = 0.10 ± 0.06. HAT-P-18b is one of the few planets known to transit a star with Teff ≲ 6250 K on a retrograde orbit. Objects such as HAT-P-18b (low planet mass and/or relatively long orbital period) most likely have a weak tidal coupling with their parent stars, therefore their orbits preserve any original misalignment. As such, they are ideal targets to study the causes of orbital evolution in cool main-sequence stars. [ABSTRACT FROM AUTHOR]

We present VLT/X-shooter observations of a sample of 36 accreting low-mass stellar and substellar objects (YSOs) in the Lupus star-forming region, spanning a range in mass from ~0.03 to ~1.2 M, but mostly with 0.1 M☉ < M⋆ < 0.5 M☉. Our aim is twofold: firstly, to analyse the relationship between excess-continuum and line emission accretion diagnostics, and, secondly, to investigate the accretion properties in terms of the physical properties of the central object. The accretion luminosity (Lacc), and in turn the accretion rate ( Ṁacc), was derived by modelling the excess emission from the UV to the near-infrared as the continuum emission of a slab of hydrogen. We computed the flux and luminosity (Lline) of many emission lines of H, He, and Ca II, observed simultaneously in the range from ~330 nm to 2500 nm. The luminosity of all the lines is well correlated with Lacc. We provide empirical relationships between Lacc and the luminosity of 39 emission lines, which have a lower dispersion than relationships previously reported in the literature. Our measurements extend the Paβ and Brγ relationships to Lacc values about two orders of magnitude lower than those reported in previous studies. We confirm that different methodologies of measuring Lacc and Ṁacc yield significantly different results: Hα line profile modelling may underestimate Ṁacc by 0.6 to 0.8 dex with respect to Ṁacc derived from continuum-excess measures. These differences may explain the probably spurious bi-modal relationships between Ṁacc and other YSOs properties reported in the literature. We derived Ṁacc in the range 2 × 10-12-4 × 10-8 M☉ yr-1 and conclude that Ṁacc ∝ M⋆ 1.8(±0.2), with a dispersion lower by a factor of about 2 than in previous studies. A number of properties indicate that the physical conditions of the accreting gas are similar over more than 5 orders of magnitude in Ṁacc, confirming previous suggestions that the geometry of the accretion flow controls the rate at which the disc material accretes onto the central star. [ABSTRACT FROM AUTHOR]

Context. Traditionally, the chromospheres of late-type stars are studied through their strongest emission lines, Hα and Ca iiHK emission. Our knowledge on the whole emission line spectrum is more elusive as a result of the limited spectral range and sensitivity of most available spectrographs. Aims. We intend to reduce this gap with a comprehensive spectroscopic study of the chromospheric emission line spectrum of a sample of non-accreting pre-main sequence stars (Class III sources). Methods. We analyzed X-shooter/VLT spectra of 24 Class III sources from three nearby star-forming regions (σOrionis, Lupus III, and TWHya). We determined the effective temperature, surface gravity, rotational velocity, and radial velocity by comparing the observed spectra with synthetic BT-Settl model spectra. We investigated in detail the emission lines emerging from the stellar chromospheres and combined these data with archival X-ray data to allow for a comparison between chromospheric and coronal emissions. Results. For some objects in the sample the atmospheric and kinematic parameters are presented here for the first time. The effective temperatures are consistent with those derived for the same stars from an empirical calibration with spectral types. Small differences in the surface gravity found between the stars can be attributed to differences in the average age of the three star-forming regions. The strength of lithium absorption and radial velocities confirm the young age of all but one object in the sample (Sz 94). Both X-ray and Hα luminosity as measured in terms of the bolometric luminosity are independent of the effective temperature for early-M stars but decline toward the end of the spectral M sequence. For the saturated early-M stars the average emission level is almost one dex higher for X-rays than for Hα: log(LLx/Lbol) = -2.85 ± 0.36 vs. log (LHα/Lbol) = -3.72 ± 0.21. When all chromospheric emission lines (including the Balmer series up to H11, Ca ii HK, the Ca ii infrared triplet, and several He i lines) are summed up the coronal flux still dominates that of the chromosphere, typically by a factor 2-5. Flux-flux relations between activity diagnostics that probe different atmospheric layers (from the lower chromosphere to the corona) separate our sample of active pre-main sequence stars from the bulk of field M dwarfs studied in the literature. Flux ratios between individual optical emission lines show a smooth dependence on the effective temperature. The Balmer decrements can roughly be reproduced by an NLTE radiative transfer model devised for another young star of similar age. Future, more complete chromospheric model grids can be tested against this data set. [ABSTRACT FROM AUTHOR]

Over the past decade, a growing number of deep imaging surveys have started to provide meaningful constraints on the population of extrasolar giant planets at large orbital separation. Primary targets for these surveys have been carefully selected based on their age, distance and spectral type, and often on their membership to young nearby associations where all stars share common kinematics, photometric and spectroscopic properties. The next step is a wider statistical analysis of the frequency and properties of low mass companions as a function of stellar mass and orbital separation. In late 2009, we initiated a coordinated European Large Program using angular differential imaging in the H band (1.66 μm) with NaCo at the VLT. Our aim is to provide a comprehensive and statistically significant study of the occurrence of extrasolar giant planets and brown dwarfs at large (5-500 AU) orbital separation around ~150 young, nearby stars, a large fraction of which have never been observed at very deep contrast. The survey has now been completed and we present the data analysis and detection limits for the observed sample, for which we reach the planetary-mass domain at separations of ≳50 AU on average. We also present the results of the statistical analysis that has been performed over the 75 targets newly observed at high-contrast. We discuss the details of the statistical analysis and the physical constraints that our survey provides for the frequency and formation scenario of planetary mass companions at large separation. [ABSTRACT FROM PUBLISHER]

New photometric observations of the hierarchical eclipsing TY CrA system were taken in the optical with Variable Young Stellar Object Survey 6 (VYSOS6) and in the near-infrared (IR) with Son of ISAAC (SOFI) and Rapid Eye Mount Infra Red (REMIR). They are the first observations showing the deep eclipse minimum of the pre-main-sequence secondary in the near-IR. For the first time, the secondary minimum can be reliably used in the calculation of the O−C diagram of TY CrA. By now, the O−C diagram can be studied on a time basis of about two decades. We confirm, that the O−C diagram cannot be explained by the spectroscopic tertiary. For the first time, the light curve of the inner eclipsing binary is analysed in both optical and near-IR bands simultaneously. In combination with already published spectroscopic elements, precise absolute dimensions and masses of the primary and the secondary component are obtained using the roche code. The inclusion of the near-IR data puts strong constraints on the third light which is composed of the reflection nebula, the spectroscopic tertiary and a visual fourth component. The absolute parameters of the inner eclipsing binary agree very well with previous work except of the primary radius (1.46 ± 0.15 R⊙) and luminosity (40 ± 10 L⊙) which are clearly smaller. While the parameters of the secondary are well understood when assuming an age of about 3–5 Myr, the primary seems considerably undersized. Low metallicity cannot explain the parameters of the primary. [ABSTRACT FROM AUTHOR]

Context. The lack of knowledge of photospheric parameters and the level of chromospheric activity in young low-mass pre-main sequence stars introduces uncertainties when measuring mass accretion rates in accreting (Class II) young stellar objects. A detailed investigation of the effect of chromospheric emission on the estimates of mass accretion rate in young low-mass stars is still missing. This can be undertaken using samples of young diskless (Class III) K and M-type stars. Aims. Our goal is to measure the chromospheric activity of Class III pre main sequence stars to determine its effect on the estimates of the accretion luminosity (Lacc) and mass accretion rate ( Macc) in young stellar objects with disks. Methods. Using VLT/X-shooter spectra, we analyzed a sample of 24 nonaccreting young stellar objects of spectral type between K5 and M9.5. We identified the main emission lines normally used as tracers of accretion in Class II objects, and we determined their fluxes in order to estimate the contribution of the chromospheric activity to the line luminosity. Results. We have used the relationships between line luminosity and accretion luminosity derived in the literature for Class II objects to evaluate the impact of chromospheric activity on the accretion rate measurements. We find that the typical chromospheric activity would bias the derived accretion luminosity by Lacc,noise < 10-3 L☉, with a strong dependence on the Teff of the objects. The noise on M acc depends on stellar mass and age, and the typical values of log( Macc,noise) range between ∼-9.2 to -11.6 M☉/yr. Conclusions. Values of Lacc ≲ 10-3 L☉ obtained in accreting low-mass pre main sequence stars through line luminosity should be treated with caution because the line emission may be dominated by the contribution of chromospheric activity. [ABSTRACT FROM AUTHOR]

We have analyzed a broad-band optical and near-infrared spectrum of FUTauA, which is a presumed young brown dwarf in the Taurus star forming region that has intrigued both theorists and observers by its overluminosity in the Hertzsprung-Russell (HR) diagram with respect to standard pre-main sequence evolutionary models. FUTauA is brighter than any other Taurus member of the same or similar spectral type, and various phenomena (accretion, activity, binarity) have been put forth as possible explanations. The new data, obtained with the X-shooter spectrograph at the Very Large Telescope, include an unprecedented wealth of information on stellar parameters and simultaneously observed accretion and outflow indicators for FUTauA. We present the first measurements of gravity (log g = 3.5 ± 0.5), radial velocity (RV = 22.5 ± 2.9 kms-1), rotational velocity (v sin i = 20 ±5 kms-1), and lithium equivalent width (EWLi = 430 ± 20mÅ) for FUTauA. From the rotational velocity and the published period we infer a disk inclination of i ≳ 50°. The lithium content is much lower than theoretically expected for such a young very low-mass object, adding another puzzling feature to this object's properties. We determine the mass accretion rate of FUTauA from comparison of the luminosities of 20 emission lines to empirical calibrations from the literature and find a mean of log Macc [M☉/yr] = -9.9 with standard deviation σ = 0.2. The accretion rate determined independently from modeling of the excess emission in the Balmer and Paschen continua is consistent with this value. The corresponding accretion luminosity is too low to make a significant contribution to the bolometric luminosity. Strong magnetic activity affecting the stellar parameters or binarity of FUTauA, both combined with extreme youth, may be responsible for its position in the HR diagram. The existence of an outflow in FUTauA is demonstrated through the first detection of forbidden emission lines from which we obtain an estimate for the mass loss rate, log Mout [M☉/yr] < -10.4. The mass outflow and inflow rates can be combined to yield Mout/ Macc ~ 0.3, a value that is in agreement with jet-launching models. [ABSTRACT FROM AUTHOR]

ABSTRACT We present stellar parameters and abundances of 11 elements (Li, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni and Zn) of 13 F6-K2 main-sequence stars in the young groups AB Doradus, Carina Near and Ursa Major. The exoplanet-host star ι Horologii is also analysed. The three young associations have lithium abundance consistent with their age. All other elements show solar abundances. The three groups are characterized by a small scatter in all abundances, with mean [Fe/H] values of 0.10 (σ = 0.03), 0.08 (σ = 0.05) and 0.01 (σ = 0.03) dex for AB Doradus, Carina Near and Ursa Major, respectively. The distribution of elemental abundances appears congruent with the chemical pattern of the Galactic thin disc in the solar vicinity, as found for other young groups. This means that the metallicity distribution of nearby young stars, targets of direct-imaging planet-search surveys, is different from that of old, field solar-type stars, i.e. the typical targets of radial velocity surveys. The young planet-host star ι Horologii shows a lithium abundance lower than that found for the young association members. It is found to have a slightly super-solar iron abundance ([Fe/H] = 0.16 ± 0.09), while all [X/Fe] ratios are similar to the solar values. Its elemental abundances are close to those of the Hyades cluster derived from the literature, which seems to reinforce the idea of a possible common origin with the primordial cluster. [ABSTRACT FROM AUTHOR]

We present high-quality, medium-resolution X-shooter/VLT spectra in the range 300-2500 nm for a sample of 12 very low mass stars in the σ Orionis cluster. The sample includes eight stars with evidence of disks from Spitzer and four without disks, with masses ranging from 0.08 to 0.3 Mʘ. The aim of this first paper is to investigate the reliability of the many accretion tracers currently used to measure the mass accretion rate in low-mass young stars and the accuracy of the correlations between these secondary tracers (mainly accretion line luminosities) found in the literature. We use our spectra to measure the accretion luminosity from the continuum excess emission in the UV and visual; the derived mass accretion rates range from 10-9 Mʘ yr-1 down to 5 × 10-11 Mʘ yr-1, allowing us to investigate the behavior of the accretion-driven emission lines in very low mass accretion rate regimes. We compute the luminosity of ten accretion-driven emission lines from the UV to the near-IR, which are all obtained simultaneously. In general, most of the secondary tracers correlate well with the accretion luminosity derived from the continuum excess emission. We recompute the relationships between the accretion luminosities and the line luminosities, and we confirm the validity of the correlations given in the literature, with the possible exception of Hα. Metallic lines, such as the CaII IR triplet or the Na I line at 589.3 nm, show a larger dispersion. When looking at individual objects, we find that the hydrogen recombination lines, from the UV to the near-IR, give good and consistent measurements of Lacc that often better agree than the uncertainties introduced by the adopted correlations. The average Lacc derived from several hydrogen lines, measured simultaneously, have a much reduced error. This suggests that some of the spread in the literature correlations may be due to the use of nonsimultaneous observations of lines and continuum. Three stars in our sample deviate from this behavior, and we discuss them individually. [ABSTRACT FROM AUTHOR]

We present a new observational campaign, Dwarf, aimed at detection of circumbinary extrasolar planets using the timing of the minima of low-mass eclipsing binaries. The observations will be performed within an extensive network of relatively small to medium-size telescopes with apertures of ∼20-200 cm. The starting sample of the objects to be monitored contains (i) low-mass eclipsing binaries with M and K components, (ii) short-period binaries with a sdB or sdO component, and (iii) post-common-envelope systems containing a WD, which enable to determine minima with high precision. Since the amplitude of the timing signal increases with the orbital period of an invisible third component, the timescale of the project is long, at least 5-10 years. The paper gives simple formulas to estimate the suitability of individual eclipsing binaries for the circumbinary planet detection. Intrinsic variability of the binaries (photospheric spots, flares, pulsation etc.) limiting the accuracy of the minima timing is also discussed. The manuscript also describes the best observing strategy and methods to detect cyclic timing variability in the minima times indicating the presence of circumbinary planets. First test observations of the selected targets are presented (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

ABSTRACT Recently, several studies have shown that young, open clusters are characterized by a considerable overabundance in their barium content. In particular, D'Orazi et al. reported that in some younger clusters [Ba/Fe] can reach values as high as ∼0.6 dex. The work also identified the presence of an anticorrelation between [Ba/Fe] and cluster age. For clusters in the age range ∼4.5 Gyr -500 Myr, this is best explained by assuming a higher contribution from low-mass asymptotic giant branch stars to the Galactic chemical enrichment. The purpose of this work is to investigate the ubiquity of the barium overabundance in young stellar clusters. We analysed high-resolution spectroscopic data, focusing on the s-process elemental abundance for three nearby young associations, i.e. AB Doradus, Carina-Near and Ursa Major. The clusters have been chosen such that their age spread would complement the D'Orazi et al. study. We find that while the s-process elements Y, Zr, La and Ce exhibit solar ratios in all three associations, Ba is overabundant by ∼0.2 dex. Current theoretical models cannot reproduce this abundance pattern; thus, we investigate whether this unusually large Ba content might be related to chromospheric effects. Although no correlation between [Ba/Fe] and several activity indicators seems to be present, we conclude that different effects could be at work which may (directly or indirectly) be related to the presence of hot stellar chromospheres. [ABSTRACT FROM AUTHOR]

Recently, several studies have shown that young, open clusters are characterized by a considerable overabundance in their barium content. In particular, D’Orazi et al. reported that in some younger clusters [Ba/Fe] can reach values as high as ∼0.6 dex. The work also identified the presence of an anticorrelation between [Ba/Fe] and cluster age. For clusters in the age range ∼4.5 Gyr-500 Myr, this is best explained by assuming a higher contribution from low-mass asymptotic giant branch stars to the Galactic chemical enrichment.The purpose of this work is to investigate the ubiquity of the barium overabundance in young stellar clusters. We analysed high-resolution spectroscopic data, focusing on the s-process elemental abundance for three nearby young associations, i.e. AB Doradus, Carina-Near and Ursa Major. The clusters have been chosen such that their age spread would complement the D’Orazi et al. study.We find that while the s-process elements Y, Zr, La and Ce exhibit solar ratios in all three associations, Ba is overabundant by ∼0.2 dex. Current theoretical models cannot reproduce this abundance pattern; thus, we investigate whether this unusually large Ba content might be related to chromospheric effects. Although no correlation between [Ba/Fe] and several activity indicators seems to be present, we conclude that different effects could be at work which may (directly or indirectly) be related to the presence of hot stellar chromospheres. [ABSTRACT FROM AUTHOR]

Context. The recent star formation history in the solar vicinity is not yet well constrained, and the real nature of the so-called Gould Belt is still unclear. Aims. We present a study of the large-scale spatial distribution of 6482 ROSAT All-Sky Survey (RASS) X-ray sources in approximately 5000 deg2 in the general direction of Orion. We examine the astrophysical properties of a sub-sample of ~100 optical counterparts, using optical spectroscopy. This sub-sample is then used to investigate the space density of the RASS young star candidates by comparing X-ray number counts with Galactic model predictions. Methods. The young star candidates were selected from the RASS using X-ray criteria. We characterize the observed sub-sample in terms of spectral type, lithium content, radial and rotational velocities, and iron abundance. A population synthesis model is then applied to analyze the stellar content of the RASS in the studied area. Results. We find that stars associated with the Orion star-forming region, as expected, do show a high lithium content. As in previous RASS studies, a population of late-type stars with lithium equivalent widths larger than that of the Pleiades stars of the same spectral type (hence younger than ∼70-100 Myr) is found widely spread over the studied area. Two new young stellar aggregates, namely "X-ray Clump 0534+22" (age ∼ 2-10 Myr) and "X-ray Clump 0430-08" (age ∼ 2-20 Myr), are also identified. Conclusions. The spectroscopic follow-up and comparison with Galactic model predictions reveal that the X-ray selected stellar population in the general direction of Orion is characterized by three distinct components, namely the clustered, the young dispersed, and the widespread field populations. The clustered population is mainly associated with regions of recent or ongoing star formation and correlates spatially with molecular clouds. The dispersed young population follows a broad lane that apparently coincides spatially with the Gould Belt, while the widespread population consists primarily of active field stars older than 100 Myr. We expect the still "bi-dimensional" picture emerging from this study to grow in depth as soon as the distance and the kinematics of the studied sources will become available from the future Gaia mission. [ABSTRACT FROM AUTHOR]

Postoperative management of sternal dehiscence requires the organised effort of a multidisciplinary medical team, including orthopaedic surgeons, plastic surgeons, microbiologists, critical care nurses and rehabilitation experts. Clinical care of this complication impacts heavily on health-care costs, length of hospital stay, and the time to full recovery and return to regular work activity. There are various surgical approaches to sternal resynthesis, but they are often unsuccessful. In this paper, we describe the case of a 67-year-old male complaining of chronic pain due to sternal dehiscence after coronary artery bypass grafting surgery. We first report a technique for sternal resynthesis, performed in the cardiac surgery setting, using a combination of autologous bone graft and autologous platelet-derived gel (APG), and describe its postoperative management and outcome. The four-month follow-up was uneventful and a CT scan confirmed full healing of the nonunion site with solid bridging bone. [ABSTRACT FROM AUTHOR]

Objectives: During extracorporeal circulation (ECC) there is a great hemodynamic stress with possible impact on the microcirculation, including cochlear one. Previous studies have evaluated the effect of ECC on inner ear with contrasting results. The aim of this study is to evaluate possible modifications of the outer hair cells (OHC) function after open heart surgery (OHS) under ECC with transient evoked (TEOAEs) and distortion product otoacoustic emissions (DPOAEs). Methods: Ten patients (5 F and 5 M), undergoing OHS with ECC, were subjected to an audiological assessment pre- and postoperatively. We compared the pre-operative and post-operative mean auditory thresholds, mean TEOAEs reproducibility and amplitude, and mean DPOAEs amplitude. Student's t-test was used to compare different values. Results: No significant differences were found between pre- and post-operative audiological assessment both in hearing level and in otoacoustic emissions. Conclusion: OHC function seems to be not affected by hemodynamic stress induced by ECC. Further studies on a larger scale will be necessary to confirm our preliminary data. [ABSTRACT FROM AUTHOR]

Located at the Galactic anticentre, Sh 2-284 is an H region that harbours several young open clusters. Dolidze 25, a rare metal-poor () young cluster, is one of these. Given its association with Sh 2-284, it is reasonable to assume a low metallicity for the whole H region. Sh 2-284 is expected to host a significant population of pre-main-sequence (PMS) stars of both low and intermediate mass (Herbig Ae stars). We aim to characterize these stars by means of a spectroscopic and photometric survey conducted with VIMOS@VLT and complemented with additional optical and infrared observations. In this survey we selected and characterized 23 PMS objects. We derived the effective temperature, the spectral energy distribution and luminosity of these objects, and, using theoretical PMS evolutionary tracks with the appropriate metallicity, we estimated the mass and the age of the studied objects. We also estimated a distance of 4 kpc for Sh 2-284, using the spectroscopic parallax of three OB stars. From the age determination we concluded that triggered star formation is occurring in this region. Our results show that a significant fraction of the young stellar objects (YSOs) may have preserved their disc/envelopes, in contrast with what is found in other recent studies of low-metallicity star-forming regions in the Galaxy. Finally, among the 23 bona fide PMS stars, we identified eight stars that are good candidates to be pulsators of the δ Scuti type. [ABSTRACT FROM AUTHOR]

In this paper, we present a thorough study of the T Tauri system MO Lup. We report on its previously unrecognized triple spectroscopic nature. Our study is mainly based on high-resolution spectroscopic monitoring. The elements of the spectroscopic orbits are derived from a detailed analysis of radial velocity data for the short-period spectroscopic binary (SB2) components, revealing the existence of a long-term variation in the systemic radial velocity due to a third body orbiting the SB2 system with a period longer than the 5.25-yr span of our data. The estimated stellar parameters, combined with the high lithium content, allow us to confirm the pre-main-sequence (PMS) status of the system. In addition, variability is observed in both the line intensities and profiles of the main emission features, in particular the Hα line, indicative of an intense chromospheric activity in the low-mass SB2 components, possibly suggesting a modulation with the orbital phase. The preliminary orbital solution for the hierarchical triple system makes this object a very suitable target for follow-up observations with the Very Large Telescope Interferometer, for the determination of precise masses of the components that will allow constraints on PMS evolutionary models. [ABSTRACT FROM AUTHOR]