ORCID Profile
0000-0002-0474-0896
Current Organisations
Università degli Studi di Catania
,
INAF - Osservatorio Astrofisico di Catania
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Publisher: EDP Sciences
Date: 10-2014
Publisher: EDP Sciences
Date: 2012
Publisher: EDP Sciences
Date: 24-01-2017
Publisher: Oxford University Press (OUP)
Date: 11-09-2017
Publisher: Springer Science and Business Media LLC
Date: 09-2011
DOI: 10.1038/NATURE10389
Abstract: Delta Scuti (δSct) stars are opacity-driven pulsators with masses of 1.5-2.5 M⊙, their pulsations resulting from the varying ionization of helium. In less massive stars such as the Sun, convection transports mass and energy through the outer 30 per cent of the star and excites a rich spectrum of resonant acoustic modes. Based on the solar ex le, with no firm theoretical basis, models predict that the convective envelope in δSct stars extends only about 1 per cent of the radius, but with sufficient energy to excite solar-like oscillations. This was not observed before the Kepler mission, so the presence of a convective envelope in the models has been questioned. Here we report the detection of solar-like oscillations in the δSct star HD187547, implying that surface convection operates efficiently in stars about twice as massive as the Sun, as the ad hoc models predicted.
Publisher: Oxford University Press (OUP)
Date: 27-09-2016
Publisher: EDP Sciences
Date: 13-06-2016
Publisher: EDP Sciences
Date: 05-2017
Publisher: EDP Sciences
Date: 09-2019
DOI: 10.1051/0004-6361/201935282
Abstract: Context . In the era of large high-resolution spectroscopic surveys such as Gaia -ESO and APOGEE, high-quality spectra can contribute to our understanding of the Galactic chemical evolution by providing abundances of elements that belong to the different nucleosynthesis channels, and also by providing constraints to one of the most elusive astrophysical quantities: stellar age. Aims . Some abundance ratios, such as [C/N], have been proven to be excellent indicators of stellar ages. We aim at providing an empirical relationship between stellar ages and [C/N] using open star clusters, observed by the Gaia -ESO and APOGEE surveys, as calibrators. Methods . We used stellar parameters and abundances from the Gaia -ESO Survey and APOGEE Survey of the Galactic field and open cluster stars. Ages of star clusters were retrieved from the literature sources and validated using a common set of isochrones. We used the same isochrones to determine for each age and metallicity the surface gravity at which the first dredge-up and red giant branch bump occur. We studied the effect of extra-mixing processes in our s le of giant stars, and we derived the mean [C/N] in evolved stars, including only stars without evidence of extra mixing. By combining the Gaia -ESO and APOGEE s les of open clusters, we derived a linear relationship between [C/N] and (logarithmic) cluster ages. Results . We apply our relationship to selected giant field stars in the Gaia -ESO and APOGEE surveys. We find an age separation between thin- and thick-disc stars and age trends within their populations, with an increasing age towards lower metallicity populations. Conclusions . With this empirical relationship, we are able to provide an age estimate for giant stars in which C and N abundances are measured. For giant stars, the isochrone fitting method is indeed less sensitive than for dwarf stars at the turn-off. Our method can therefore be considered as an additional tool to give an independent estimate of the age of giant stars. The uncertainties in their ages is similar to those obtained using isochrone fitting for dwarf stars.
Publisher: Oxford University Press (OUP)
Date: 29-04-2023
Abstract: We present an empirical model of age-dependent photospheric lithium depletion, calibrated using a large homogeneously analysed s le of 6200 stars in 52 open clusters, with ages from 2 to 6000 Myr and −0.3 & [Fe/H] & 0.2, observed in the Gaia-ESO spectroscopic survey. The model is used to obtain age estimates and posterior age probability distributions from measurements of the Li i 6708 Å equivalent width for in idual (pre) main-sequence stars with 3000 & Teff/K & 6500, a domain where age determination from the HR diagram is either insensitive or highly model-dependent. In the best cases, precisions of 0.1 dex in log age are achievable even higher precision can be obtained for coeval groups and associations where the in idual age probabilities of their members can be combined. The method is validated on a s le of exoplanet-hosting young stars, finding agreement with claimed young ages for some, but not others. We obtain better than 10 per cent precision in age, and excellent agreement with published ages, for seven well-studied young moving groups. The derived ages for young clusters (& Gyr) in our s le are also in good agreement with their training ages, and consistent with several published model-insensitive lithium depletion boundary ages. For older clusters, there remain systematic age errors that could be as large as a factor of 2. There is no evidence to link these errors to any strong systematic metallicity dependence of (pre) main-sequence lithium depletion, at least in the range −0.29 & [Fe/H] & 0.18. Our methods and model are provided as software – ‘Empirical AGes from Lithium Equivalent widthS’ (eagles).
Publisher: American Astronomical Society
Date: 21-10-2016
Publisher: Wiley
Date: 22-11-2010
Abstract: We report on the ground‐based follow‐up program of spectroscopic and photometric observations of solar‐like asteroseismic targets for the Kepler space mission. These stars constitute a large group of more than a thousand objects which are the subject of an intensive study by the Kepler Asteroseismic Science Consortium Working Group 1 (KASC WG‐1). In the current work we will discuss the methods we use to determine the fundamental stellar atmospheric parameters using high‐quality stellar spectra. These provide essential constraints for the asteroseismic modelling and make it possible to verify the parameters in the Kepler Input Catalogue (KIC) (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Publisher: EDP Sciences
Date: 2020
DOI: 10.1051/0004-6361/201936651
Abstract: Context. Open clusters exquisitely track the Galactic disc chemical properties and its time evolution a substantial number of studies and large spectroscopic surveys focus mostly on the chemical content of relatively old clusters (age ≳ 1 Gyr). Interestingly, the less studied young counterpart populating the solar surrounding has been found to be solar (at most), with a notable surprising lack of young metal-rich objects. While there is wide consensus about the moderately above-solar composition of the Hyades cluster, the metallicity of Praesepe is still controversial. Recent studies suggest that these two clusters share identical chemical composition and age, but this conclusion is disputed. Aims. With the aim of reassessing the metallicity of Praesepe, and its difference (if any) with the Hyades cluster, we present in this paper a spectroscopic investigation of ten solar-type dwarf members. Methods. We exploited GIARPS at the TNG to acquire high-resolution, high-quality optical and near-IR spectra and derived stellar parameters, metallicity ([Fe/H]), light elements, α - and iron-peak elements, by using a strictly differential (line-by-line) approach. We also analysed in the very same way the solar spectrum and the Hyades solar analogue HD 28099. Results. Our findings suggest that Praesepe is more metal-rich than the Hyades, at the level of Δ[Fe/H] = +0.05 ± 0.01 dex, with a mean value of [Fe/H] = +0.21 ± 0.01 dex. All the other elements scale with iron, as expected. This result seems to reject the hypothesis of a common origin for these two open clusters. Most importantly, Praesepe is currently the most metal-rich, young open cluster living in the solar neighbourhood.
Publisher: EDP Sciences
Date: 09-2018
DOI: 10.1051/0004-6361/201832841
Abstract: Context . Several works have found an increase of the abundances of the s -process neutron-capture elements in the youngest Galactic stellar populations. These trends provide important constraints on stellar and Galactic evolution and they need to be confirmed with large and statistically significant s les of stars spanning wide age and distance intervals. Aims . We aim to trace the abundance patterns and the time evolution of five s -process elements – two belonging to the first peak, Y and Zr, and three belonging to the second peak, Ba, La, and Ce – using the Gaia -ESO IDR 5 results for open clusters and disc stars. Methods . From the UVES spectra of cluster member stars, we determined the average composition of clusters with ages .1 Gyr. We derived statistical ages and distances of field stars, and we separated them into thin and thick disc populations. We studied the time-evolution and dependence on metallicity of abundance ratios using open clusters and field stars whose parameters and abundances were derived in a homogeneous way. Results . Using our large and homogeneous s le of open clusters, thin and thick disc stars, spanning an age range larger than 10 Gyr, we confirm an increase towards young ages of s -process abundances in the solar neighbourhood. These trends are well defined for open clusters and stars located nearby the solar position and they may be explained by a late enrichment due to significant contribution to the production of these elements from long-living low-mass stars. At the same time, we find a strong dependence of the s -process abundance ratios on the Galactocentric distance and on the metallicity of the clusters and field stars. Conclusions . Our results, derived from the largest and most homogeneous s le of s -process abundances in the literature, confirm the growth with decreasing stellar ages of the s -process abundances in both field and open cluster stars. At the same time, taking advantage of the abundances of open clusters located in a wide Galactocentric range, these results offer a new perspective on the dependence of the s -process evolution on the metallicity and star formation history, pointing to different behaviours at various Galactocentric distances.
Publisher: EDP Sciences
Date: 26-01-2015
Publisher: EDP Sciences
Date: 08-2014
Publisher: EDP Sciences
Date: 02-2018
DOI: 10.1051/0004-6361/201731677
Abstract: Lithium abundance in most of the warm metal-poor main sequence stars shows a constarnt plateau ( A (Li) ~ 2.2 dex) and then the upper envelope of the lithium vs. metallicity distribution increases as we approach solar metallicity. Meteorites, which carry information about the chemical composition of the interstellar medium (ISM) at the solar system formation time, show a lithium abundance A (Li) ~ 3.26 dex. This pattern reflects the Li enrichment history of the ISM during the Galaxy lifetime. After the initial Li production in big bang nucleosynthesis, the sources of the enrichment include asymptotic giant branch (AGB) stars, low-mass red giants, novae, type II supernovae, and Galactic cosmic rays. The total amount of enriched Li is sensitive to the relative contribution of these sources. Thus different Li enrichment histories are expected in the Galactic thick and thin disc. We investigate the main sequence stars observed with UVES in Gaia -ESO Survey iDR4 catalogue and find a Li- [ α /Fe] anticorrelation independent of [Fe/H], T eff , and log ( g ). Since in stellar evolution different α enhancements at the same metallicity do not lead to a measurable Li abundance change, the anticorrelation indicates that more Li is produced during the Galactic thin disc phase than during the Galactic thick disc phase. We also find a correlation between the abundance of Li and s-process elements Ba and Y, and they both decrease above the solar metallicity, which can be explained in the framework of the adopted Galactic chemical evolution models.
Publisher: EDP Sciences
Date: 12-2020
DOI: 10.1051/0004-6361/202039031
Abstract: Discovering wide companions of stellar systems allows us to constrain the dynamical environment and age of the latter. We studied four probable wide companions of four different stellar systems. The candidates were selected mainly based on their similar kinematic properties to the central star using Gaia DR2. The central stars are V4046 Sgr, HIP 74865, HIP 65426, and HIP 73145, and their probable wide companions are 2MASS J18152222-3249329, 2MASS J15174874-3028484, 2MASS J13242119-5129503, and 2MASS J14571503-3543505 respectively. V4046 Sgr is a member of β -Pictoris Moving Group while the rest of the stellar systems are acknowledged as members of the Scorpius-Centaurus association. The selected stellar systems are particularly interesting because all of them are already known to possess a low-mass companion and/or a spatially resolved disk. Identifying wider companions of these stars can improve their eligibility as benchmarks for understanding the formation channels of various triple systems, and can help us to determine the orbits of their possibly undiscovered inner, wider companions in case of higher multiplicity. By analyzing the X-shooter spectra of the wide companion candidates of these stars, we obtained their stellar parameters and determined their ages. We find that 2MASS J15174874-3028484 (0.11 M ⊙ , 7.4 ± 0.5 Myr), an already recognized pre-main sequence (PMS) member of Scorpius-Centaurus association, is a highly probable wide companion of HIP 74865. 2MASS J13242119-5129503 (0.04 M ⊙ , 16 ± 2.2 Myr) is ruled out as a plausible wide companion of HIP 65426, but confirmed to be a new sub-stellar member of the Scorpius-Centaurus association. 2MASS J14571503-3543505 (0.02 M ⊙ , 17.75 ± 4.15 Myr) is a probable sub-stellar member of the same association, but we cannot confirm whether or not it is gravitationally bound to HIP 73145. 2MASS J18152222-3249329 (0.3 M ⊙ , older than 150 Myr) is determined to be a mildly active main sequence star, much older than members of β -Pictoris Moving Group, and unbound to V4046 Sgr despite their similar kinematic features. PMS wide companions such as 2MASS J15174874-3028484 might have formed through cascade fragmentation of their natal molecular core, hinting at high multiplicity in shorter separations which can be confirmed with future observations.
Publisher: EDP Sciences
Date: 09-2023
Publisher: EDP Sciences
Date: 28-02-2020
DOI: 10.1051/0004-6361/201937309
Abstract: 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 ∼16″.0, or 2400 AU, and position angle 114.61°) companion of the GQ Lup A-B system, most likely gravitationally bound to it. A VLT/X-shooter 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 GQ Lup A-B system. A possible scenario for the formation of the triple system is that GQ Lup A and 2MASS J15491331-3539118 formed by fragmentation of a turbulent core in the Lup I filament, while GQ Lup B, the BD companion of GQ Lup A at 0″.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 GQ Lup A and 2MASS J15491331-3539118.
Publisher: EDP Sciences
Date: 05-2017
Publisher: American Astronomical Society
Date: 23-09-2015
Publisher: EDP Sciences
Date: 10-2023
Publisher: American Astronomical Society
Date: 31-10-2012
Publisher: EDP Sciences
Date: 07-2017
Publisher: Oxford University Press (OUP)
Date: 04-07-2016
Publisher: Oxford University Press (OUP)
Date: 20-05-2016
Publisher: American Astronomical Society
Date: 25-10-2010
Publisher: EDP Sciences
Date: 09-2021
DOI: 10.1051/0004-6361/202141069
Abstract: Context. Young open clusters (ages of less than 200 Myr) have been observed to exhibit several peculiarities in their chemical compositions. These anomalies include a slightly sub-solar iron content, super-solar abundances of some atomic species (e.g. ionised chromium), and atypical enhancements of [Ba/Fe], with values up to ~0.7 dex. Regarding the behaviour of the other s -process elements like yttrium, zirconium, lanthanum, and cerium, there is general disagreement in the literature: some authors claim that they follow the same trend as barium, while others find solar abundances at all ages. Aims. In this work we expand upon our previous analysis of a s le of five young open clusters (IC 2391, IC 2602, IC 4665, NGC 2516, and NGC 2547) and one star-forming region (NGC 2264), with the aim of determining abundances of different neutron-capture elements, mainly Cu I , Sr I , Sr II , Y II , Zr II , Ba II , La II , and Ce II . For NGC 2264 and NGC 2547 we present the measurements of these elements for the first time. Methods. We analysed high-resolution, high signal-to-noise spectra of 23 solar-type stars observed within the Gaia -ESO survey. After a careful selection, we derived abundances of isolated and clean lines via spectral synthesis computations and in a strictly differential way with respect to the Sun. Results. We find that our clusters have solar [Cu/Fe] within the uncertainties, while we confirm that [Ba/Fe] is super-solar, with values ranging from +0.22 to +0.64 dex. Our analysis also points to a mild enhancement of Y, with [Y/Fe] ratios covering values between 0 and +0.3 dex. For the other s -process elements we find that [X/Fe] ratios are solar at all ages. Conclusions. It is not possible to reconcile the anomalous behaviour of Ba and Y at young ages with standard stellar yields and Galactic chemical evolution model predictions. We explore different possible scenarios related to the behaviour of spectral lines, from the dependence on the different ionisation stages and the sensitivity to the presence of magnetic fields (through the Landé factor) to the first ionisation potential effect. We also investigate the possibility that they may arise from alterations of the structure of the stellar photosphere due to the increased levels of stellar activity that affect the spectral line formation, and consequently the derived abundances. These effects seem to be stronger in stars at ages of less than ~ 100 Myr. However, we are still unable to explain these enhancements, and the Ba puzzle remains unsolved. With the present study we suggest that other elements, for ex le Sr, Zr, La, and Ce, might be more reliable tracer of the s -process at young ages, and we strongly encourage further critical observations.
Publisher: EDP Sciences
Date: 07-2018
DOI: 10.1051/0004-6361/201832645
Abstract: Context. The origin and dynamical evolution of star clusters is an important topic in stellar astrophysics. Several models have been proposed in order to understand the formation of bound and unbound clusters and their evolution, and they can be tested by examining the kinematical and dynamical properties of clusters over a wide range of ages and masses. Aims. We use the Gaia -ESO Survey products to study four open clusters (IC 2602, IC 2391, IC 4665, and NGC 2547) that lie in the age range between 20 and 50 Myr. Methods. We employ the gravity index γ and the equivalent width of the lithium line at 6708 Å together with effective temperature T eff and the metallicity of the stars in order to discard observed contaminant stars. Then we derive the cluster radial velocity dispersions σ c , the total cluster mass M tot , and the half mass radius r hm . Using the Gaia -DR1 TGAS catalogue, we independently derive the intrinsic velocity dispersion of the clusters from the astrometric parameters of cluster members. Results. The intrinsic radial velocity dispersions derived by the spectroscopic data are higher than those derived from the TGAS data, possibly due to the different masses of the considered stars. Using M tot and r hm we derive the virial velocity dispersion σ vir and we find that three out of four clusters are supervirial. This result is in agreement with the hypothesis that these clusters are dispersing, as predicted by the “residual gas expulsion” scenario. However, recent simulations show that the virial ratio of young star clustersmay be overestimated if it is determined using the global velocity dispersion, since the clusters are not fully relaxed.
Publisher: EDP Sciences
Date: 16-05-2016
Publisher: EDP Sciences
Date: 07-2014
Publisher: EDP Sciences
Date: 09-2018
DOI: 10.1051/0004-6361/201833027
Abstract: A ims. We report 20 new lithium-rich giants discovered within the Gaia -ESO Survey, including the first Li-rich giant with an evolutionary stage confirmed by CoRoT (Convection, Rotation and planetary Transits) data. We present a detailed overview of the properties of these 20 stars. M ethods. Atmospheric parameters and abundances were derived in model atmosphere analyses using medium-resolution GIRAFFE or high-resolution UVES (Ultraviolet and Visual Echelle Spectrograph) spectra. These results are part of the fifth internal data release of the Gaia -ESO Survey. The Li abundances were corrected for non-local thermodynamical equilibrium effects. Other stellar properties were investigated for additional peculiarities (the core of strong lines for signs of magnetic activity, infrared magnitudes, rotational velocities, chemical abundances, and Galactic velocities). We used Gaia DR2 parallaxes to estimate distances and luminosities. R esults. The giants have A (Li) 2.2 dex. The majority of them (14 of 20 stars) are in the CoRoT fields. Four giants are located in the field of three open clusters, but are not members. Two giants were observed in fields towards the Galactic bulge, but likely lie in the inner disc. One of the bulge field giants is super Li-rich with A (Li) = 4.0 dex. Conclusions . We identified one giant with infrared excess at 22 μ m. Two other giants, with large v sin i , might be Li-rich because of planet engulfment. Another giant is found to be barium enhanced and thus could have accreted material from a former asymptotic giant branch companion. Otherwise, in addition to the Li enrichment, the evolutionary stages are the only other connection between these new Li-rich giants. The CoRoT data confirm that one Li-rich giant is at the core-He burning stage. The other giants are concentrated in close proximity to the red giant branch luminosity bump, the core-He burning stages, or the early-asymptotic giant branch. This is very clear from the Gaia -based luminosities of the Li-rich giants. This is also seen when the CoRoT Li-rich giants are compared to a larger s le of 2252 giants observed in the CoRoT fields by the Gaia -ESO Survey, which are distributed throughout the red giant branch in the T eff -log g diagram. These observations show that the evolutionary stage is a major factor for the Li enrichment in giants. Other processes, such as planet accretion, contribute at a smaller scale.
Publisher: American Astronomical Society
Date: 08-01-2013
Publisher: EDP Sciences
Date: 14-10-2019
Publisher: EDP Sciences
Date: 07-2018
DOI: 10.1051/0004-6361/201833383
Abstract: Extensive surveys of star-forming regions with Spitzer have revealed populations of disk-bearing young stellar objects. These have provided crucial constraints, such as the timescale of dispersal of protoplanetary disks, obtained by carefully combining infrared data with spectroscopic or X-ray data. While observations in various regions agree with the general trend of decreasing disk fraction with age, the Lupus V and VI regions appeared to have been at odds, having an extremely low disk fraction. Here we show, using the recent Gaia data release 2 (DR2), that these extremely low disk fractions are actually due to a very high contamination by background giants. Out of the 83 candidate young stellar objects (YSOs) in these clouds observed by Gaia , only five have distances of ~150 pc, similar to YSOs in the other Lupus clouds, and have similar proper motions to other members in this star-forming complex. Of these five targets, four have optically thick (Class II) disks. On the one hand, this result resolves the conundrum of the puzzling low disk fraction in these clouds, while, on the other hand, it further clarifies the need to confirm the Spitzer selected diskless population with other tracers, especially in regions at low galactic latitude like Lupus V and VI. The use of Gaia astrometry is now an independent and reliable way to further assess the membership of candidate YSOs in these, and potentially other, star-forming regions.
Publisher: EDP Sciences
Date: 03-2023
DOI: 10.1051/0004-6361/202245261
Abstract: 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 s le 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.
Location: No location found
No related grants have been discovered for Antonio Frasca.