Repositorio Institucional Académico. Universidad Andrés Bello. Chile

Examinando por Autor "Monaco, L."

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A spectroscopic study of the globular cluster M28 (NGC 6626)
(Monthly Notices of the Royal Astronomical Society, 2017-01) Villanova, S.; Moni Bidin, C.; Mauro, F.; Munoz, C.; Monaco, L.
We present the abundance analysis for a sample of 17 red giant branch stars in the metal-poor globular cluster M28 based on high-resolution spectra. This is the first extensive spectroscopic study of this cluster. We derive abundances of O, Na, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Ba, La, Ce, and Eu. We find a metallicity of [Fe/H]=-1.29 ± 0.01 and an a-enhancement of +0.34 ± 0.01 (errors on the mean), typical of halo globular clusters in this metallicity regime. A large spread is observed in the abundances of light elements O, Na, and Al. Mg also shows an anti-correlation with Al with a significance of 3σ. The cluster shows a Na-O anti-correlation and a Na-Al correlation. This correlation is not linear but 'segmented' and that the stars are not distributed continuously, but form at least three well-separated subpopulations. In this aspect, M28 resembles NGC 2808 that was found to host at least five sub-populations. The presence of a Mg-Al anti-correlation favour massive AGB stars as the main polluters responsible for the multiple-population phenomenon. © 2016 The Authors.
A spectroscopic study of the globular Cluster NGC 4147
(OXFORD UNIV PRESS, 2016-08) Villanova, S.; Monaco, L.; Moni Bidin, C.; Assmann, P.
We present the abundance analysis for a sample of 18 red giant branch stars in the metal-poor globular cluster NGC 4147 based on medium- and high-resolution spectra. This is the first extensive spectroscopic study of this cluster. We derive abundances of C, N, O, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni, Y, Ba, and Eu. We find a metallicity of [Fe/H] = -1.84 +/- 0.02 and an alpha-enhancement of +0.38 +/- 0.05 (errors on the mean), typical of halo globular clusters in this metallicity regime. A significant spread is observed in the abundances of light elements C, N, O, Na, and Al. In particular, we found an Na-O anticorrelation and Na-Al correlation. The cluster contains only similar to 15 per cent of stars that belong to the first generation (Na-poor and O-rich). This implies that it suffered a severe mass-loss during its lifetime. Its [Ca/Fe] and [Ti/Fe] mean values agree better with the Galactic halo trend than with the trend of extragalactic environments at the cluster metallicity. This possibly suggests that NGC 4147 is a genuine Galactic object at odd with what claimed by some author that proposed the cluster to be member of the Sagittarius dwarf galaxy. An antirelation between the light s-process element Y and Na may also be present.
A Study of the Blue Straggler Population of the Old Open Cluster Collinder 261
(Institute of Physics Publishing, 2020-02) Rain, M. J.; Carraro, G.; Ahumada, J. A.; Villanova, S.; Boffin, H.; Monaco, L.; Beccar, G.
Blue stragglers (BSs) are stars located in an unexpected region of the color–magnitude diagram (CMD) of a stellar population, as they appear bluer and more luminous than the stars in the turn-off region. They are ubiquitous, since they have been found among Milky Way field stars, in open and globular clusters, and also in other galaxies of the Local Group. Here we present a study on the BS population of the old and metal-rich open cluster Collinder 261, based on Gaia DR2 data and on a multi-epoch radial velocity survey conducted with Fibre Large Array Multi Element Spectrograph (FLAMES) at the Very Large Telescope (VLT). We also analyze the radial distribution of the BS population to probe the dynamical status of the cluster. BS candidates were identified first with Gaia DR2, according to their position on the CMD, proper motions, and parallaxes. Their radial distribution was compared with those of main sequence, red giant, and red clump stars, to evaluate mass segregation. Additionally, their radial velocities (and the associated uncertainties) were compared with the mean radial velocity and velocity dispersion of the cluster. When possible, close binaries and long-period binaries were also identified, based on the radial velocity variations for the different epochs. We also looked for yellow stragglers, i.e., possible evolved BSs. We found 53 BS members of Collinder 261, six of them were already identified in previous catalogs. Among the BS candidates with radial velocity measurements, we found one long-period binary, five close-binary systems, three nonvariable stars; we also identified one yellow straggler
Abundance ratios of red giants in low-mass ultra-faint dwarf spheroidal galaxies
(EDP SCIENCES, 2016-04) François, P.; Monaco, L.; Bonifacio, P.; Moni Bidin, C.; Geisler, D.
Context. Low-mass dwarf spheroidal galaxies are key objects for our understanding of the chemical evolution of the pristine Universe and the Local Group of galaxies. Abundance ratios in stars of these objects can be used to better understand their star formation and chemical evolution. Aims. We report on the analysis of a sample of 11 stars belonging to five different ultra-faint dwarf spheroidal galaxies (UfDSph) that is based on X-Shooter spectra obtained at the VLT. Methods. Medium-resolution spectra have been used to determine the detailed chemical composition of their atmosphere. We performed a standard 1D LTE analysis to compute the abundances. Results. Considering all the stars as representative of the same population of low-mass galaxies, we found that the [α/Fe] ratios vs.s [Fe/H] decreases as the metallicity of the star increases in a way similar to that which is found for the population of stars that belong to dwarf spheroidal galaxies. The main difference is that the solar [α/Fe] is reached at a much lower metallicity for the UfDSph than for the dwarf spheroidal galaxies. We report for the first time the abundance of strontium in CVn II. The star we analyzed in this galaxy has a very high [Sr/Fe] and a very low upper limit of barium which makes it a star with an exceptionally high [Sr/Ba] ratio.
Abundances in a sample of turnoff and subgiant stars in NGC 6121 (M 4)
(EDP Sciences, 2016-10) Spite, M.; Spite, F.; Gallagher, A.J.; Monaco, L.; Bonifacio, P.; Caffau, E.; Villanova, S.
Context. The stellar abundances observed in globular clusters show complex structures, currently not yet understood. Aims. The aim of this work is to investigate the relations between the abundances of different elements in the globular cluster M 4, selected for its uniform deficiency of iron, to explore the best models explaining the pattern of these observed abundances. Moreover, in turnoff stars, the abundances of the elements are not suspected to be affected by internal mixing. Methods. In M 4, using low and moderate resolution spectra obtained for 91 turnoff (and subgiant) stars with the ESO FLAMES Giraffe spectrograph, we have extended previous measurements of abundances (of Li, C and Na) to other elements (C, Si, Ca, Sr and Ba), using model atmosphere analysis. We have also studied the influence of the choice of the microturbulent velocity. Results. Firstly, the peculiar turnoff star found to be very Li-rich in a previous paper does not show any other abundance anomalies relative to the other turnoff stars in M 4. Secondly, an anti-correlation between C and Na has been detected, the slope being significative at more than 3σ. This relation between C and Na is in perfect agreement with the relation found in giant stars selected below the RGB bump. Thirdly, the strong enrichment of Si and of the neutron-capture elements Sr and Ba, already observed in the giants in M 4, is confirmed. Finally, the relations between Li, C, Na, Sr and Ba constrain the enrichment processes of the observed stars. Conclusions. The abundances of the elements in the turnoff stars appear to be compatible with production processes by massive AGBs, but are also compatible with the production of second generation elements (like Na) and low Li produced by, for example, fast rotating massive stars.
Ages and Heavy Element Abundances from Very Metal-poor Stars in the Sagittarius Dwarf Galaxy
(Institute of Physics Publishing, 2018-03) Hansen, C.J.; El-Souri, M.; Monaco, L.; Villanova, S.; Bonifacio, P.; Caffau, E.; Sbordone, L.
Sagittarius (Sgr) is a massive disrupted dwarf spheroidal galaxy in the Milky Way halo that has undergone several stripping events. Previous chemical studies were restricted mainly to a few, metal-rich ([Fe/H] ) stars that suggested a top-light initial mass function (IMF). Here we present the first high-resolution, very metal-poor ([Fe/H] =-1 to -3) sample of 13 giant stars in the main body of Sgr. We derive abundances of 13 elements, namely C, Ca, Co, Fe, Sr, Ba, La, Ce, Nd, Eu, Dy, Pb, and Th, that challenge the interpretation based on previous studies. Our abundances from Sgr mimic those of the metal-poor halo, and our most metal-poor star ([Fe/H] ) indicates a pure r-process pollution. Abundances of Sr, Pb, and Th are presented for the first time in Sgr, allowing for age determination using nuclear cosmochronology. We calculate ages of . Most of the sample stars have been enriched by a range of asymptotic giant branch (AGB) stars with masses between 1.3 and 5 M o. Sgr J190651.47-320147.23 shows a large overabundance of Pb (2.05 dex) and a peculiar abundance pattern best fit by a 3 M o AGB star. Based on star-to-star scatter and observed abundance patterns, a mixture of low- and high-mass AGB stars and supernovae (15-25 M o) is necessary to explain these patterns. The high level (0.29 0.05 dex) of Ca indicates that massive supernovae must have existed and polluted the early ISM of Sgr before it lost its gas. This result is in contrast with a top-light IMF with no massive stars polluting Sgr. © 2018. The American Astronomical Society. All rights reserved..
Chemical abundance analysis of red giant branch stars in the globular cluster E3
(EDP Sciences, 2018-08) Monaco, L.; Villanova, S.; Carraro, G.; Mucciarelli, A.; Moni Bidin, C.
Context. Globular clusters are known to host multiple stellar populations, which are a signature of their formation process. The globular cluster E3 is one of the few low-mass globulars that is thought not to host multiple populations. Aims. We investigate red giant branch stars in E3 with the aim of providing a first detailed chemical inventory for this cluster, we determine its radial velocity, and we provide additional insights into the possible presence of multiple populations in this cluster. Methods. We obtained high-resolution FLAMES-UVES/VLT spectra of four red giant branch stars likely members of E3. We performed a local thermodynamic equilibrium abundance analysis based on one-dimensional plane parallel ATLAS9 model atmospheres. Abundances were derived from line equivalent widths or spectrum synthesis. Results. We measured abundances of Na and of iron peak (Fe, V, Cr, Ni, Mn), α(Mg, Si, Ca, Ti), and neutron capture elements (Y, Ba, Eu). The mean cluster heliocentric radial velocity, metallicity, and sodium abundance ratio are ν helio = 12.6 ± 0.4 km s -1 (σ = 0.6 ± 0.2 km s -1 ), [Fe/H] = -0.89 ± 0.08 dex, and [Na/Fe] = 0.18 ± 0.07 dex, respectively. The low Na abundance with no appreciable spread is suggestive of a cluster dominated by first-generation stars in agreement with results based on lower resolution spectroscopy. The low number of stars observed does not allow us to rule out a minor population of second-generation stars. The observed chemical abundances are compatible with the trends observed in Milky Way stars. © ESO 2018.
Chemical abundances of giant stars in NGC 5053 and NGC 5634, two globular clusters associated with the Sagittarius dwarf spheroidal galaxy?
(EDP SCIENCES, 2015-07) Sbordone, L.; Monaco, L.; Moni Bidin, C.; Bonifacio, P.; Villanova, S.; Bellazzini, M.; Ibata, R.; Chiba, M.; Geisler, D.; Caffau, E.; Duffau, S.
Context. The tidal disruption of the Sagittarius dwarf spheroidal galaxy (Sgr dSph) is producing the most prominent substructure in the Milky Way (MW) halo, the Sagittarius Stream. Aside from field stars, it is suspected that the Sgr dSph has lost a number of globular clusters (GC). Many Galactic GC are thought to have originated in the Sgr dSph. While for some candidates an origin in the Sgr dSph has been confirmed owing to chemical similarities, others exist whose chemical composition has never been investigated. Aims. NGC 5053 and NGC 5634 are two of these scarcely studied Sgr dSph candidate-member clusters. To characterize their composition we analyzed one giant star in NGC 5053, and two in NGC 5634. Methods. We analyze high-resolution and signal-to-noise spectra by means of the MyGIsFOS code, determining atmospheric parameters and abundances for up to 21 species between O and Eu. The abundances are compared with those of MW halo field stars, of unassociated MW halo globulars, and of the metal-poor Sgr dSph main body population. Results. We derive a metallicity of [Fe II/H] = 2.26 +/- 0.10 for NGC 5053, and of [Fe I/H] = 1.99 +/- 0.075 and 1.97 +/- 0.076 for the two stars in NGC 5634. This makes NGC 5053 one of the most metal-poor globular clusters in the MW. Both clusters display an alpha enhancement similar to the one of the halo at comparable metallicity. The two stars in NGC 5634 clearly display the Na-O anticorrelation widespread among MW globulars. Most other abundances are in good agreement with standard MW halo trends. Conclusions. The chemistry of the Sgr dSph main body populations is similar to that of the halo at low metallicity. It is thus difficult to discriminate between an origin of NGC 5053 and NGC 5634 in the Sgr dSph, and one in the MW. However, the abundances of these clusters do appear closer to that of Sgr dSph than of the halo, favoring an origin in the Sgr dSph system.
Chemical abundances of giant stars in NGC 5053 and NGC 5634, two globular clusters associated with the Sagittarius dwarf spheroidal galaxy?
(EDP Sciences, 2015-07) Sbordone, L.; Monaco, L.; Moni, Bidin C.; Bonifacio, P.; Villanova, S.; Bellazzini, M.; Ibata, R.; Chiba, M.; Geisler, D.; Caffau, E.; Duffau, S.
Context. The tidal disruption of the Sagittarius dwarf spheroidal galaxy (Sgr dSph) is producing the most prominent substructure in the Milky Way (MW) halo, the Sagittarius Stream. Aside from field stars, it is suspected that the Sgr dSph has lost a number of globular clusters (GC). Many Galactic GC are thought to have originated in the Sgr dSph. While for some candidates an origin in the Sgr dSph has been confirmed owing to chemical similarities, others exist whose chemical composition has never been investigated. Aims. NGC 5053 and NGC 5634 are two of these scarcely studied Sgr dSph candidate-member clusters. To characterize their composition we analyzed one giant star in NGC 5053, and two in NGC 5634. Methods. We analyze high-resolution and signal-to-noise spectra by means of the MyGIsFOS code, determining atmospheric parameters and abundances for up to 21 species between O and Eu. The abundances are compared with those of MW halo field stars, of unassociated MW halo globulars, and of the metal-poor Sgr dSph main body population. Results. We derive a metallicity of [Feii/H] = -2.26 ± 0.10 for NGC 5053, and of [Fe? i/H] = -1.99 ± 0.075 and -1.97 ± 0.076 for the two stars in NGC 5634. This makes NGC 5053 one of the most metal-poor globular clusters in the MW. Both clusters display an α enhancement similar to the one of the halo at comparable metallicity. The two stars in NGC 5634 clearly display the Na-O anticorrelation widespread among MW globulars. Most other abundances are in good agreement with standard MW halo trends. Conclusions. The chemistry of the Sgr dSph main body populations is similar to that of the halo at low metallicity. It is thus difficult to discriminate between an origin of NGC 5053 and NGC 5634 in the Sgr dSph, and one in the MW. However, the abundances of these clusters do appear closer to that of Sgr dSph than of the halo, favoring an origin in the Sgr dSph system. © ESO, 2015.
Chemical composition of the stellar cluster Gaia1: No surprise behind Sirius
(EDP Sciences, 2017-07) Mucciarelli, A.; Monaco, L.; Bonifacio, P.; Saviane, I.
We observed six He-clump stars of the intermediate-Age stellar cluster Gaia1 with the MIKE/Magellan spectrograph. A possible extra-galactic origin of this cluster, recently discovered thanks to the first data release of the ESA Gaia mission, has been suggested, based on its orbital parameters. Abundances for Fe, α, proton-And neutron-capture elements have been obtained. We find no evidence of intrinsic abundance spreads. The iron abundance is solar ([FeI/H] = + 0.00 ± 0.01; σ = 0.03 dex). All the other abundance ratios are generally solar-scaled, similar to the Galactic thin disk and open cluster stars of similar metallicity. The chemical composition of Gaia1 does not support an extra-galactic origin for this stellar cluster, which can be considered as a standard Galactic open cluster.
Discovery of a thin lithium plateau among metal-poor red giant branch stars
(EDP Sciences, 2022-05-01) Mucciarelli, A.; Monaco, L.; Bonifacio, P.; Salaris, M.; Deal, M.; Spite, M.; Richard, O.A.; Lallement, R.
The surface lithium abundance, A(Li), of warm metal-poor dwarf stars exhibits a narrow plateau down to [Fe/H] ~-2.8 dex, while at lower metallicities the average value drops by 0.3 dex with a significant star-by-star scatter (called 'lithium meltdown'). This behaviour is in conflict with predictions of standard stellar evolution models calculated with the initial A(Li) provided by the standard Big Bang nucleosynthesis. The lower red giant branch (LRGB) stars provide a complementary tool to understand the initial A(Li) distribution in metal-poor stars. We have collected a sample of high-resolution spectra of 58 LRGB stars spanning a range of [Fe/H] between ~-7.0 dex and ~-1.3 dex. The LRGB stars display an A(Li) distribution that is clearly different from that of the dwarfs, without signatures of a meltdown and with two distinct components: (a) a thin A(Li) plateau with an average A(Li) = 1.09 ± 0.01 dex (σ = 0.07 dex) and (b) a small fraction of Li-poor stars with A(Li) lower than ~0.7 dex. The A(Li) distribution observed in LRGB stars can be reconciled with an initial abundance close to the cosmological value by including an additional chemical element transport in stellar evolution models. The required efficiency of this transport allows us to also match the Spite plateau lithium abundance measured in the dwarfs. The emerging scenario is that all metal-poor stars formed with the same initial A(Li), but those that are likely the product of coalescence or that experienced binary mass transfer show lower A(Li). We conclude that the A(Li) in LRGB stars is qualitatively compatible with the cosmological A(Li) value and that the meltdown observed in dwarf stars does not reflect a real drop in the abundance at birth. © 2022 BMJ Publishing Group. All rights reserved.
ESPRESSO highlights the binary nature of the ultra-metal-poor giant HE 0107-5240
(EDP Sciences, 2020) Bonifacio, P.; Molaro, P.; Adibekyan, V.; Aguado, D.; Alibert, Y.; Allende Prieto, C.; Caffau, E.; Cristiani, S.; Cupani, G.; Marcantonio, P.; D'Odorico, D.; Ehrenreich, D.; Figueira, P.; Genova, R.; González Hernández, J.; Lo Curto, G.; Lovis, C.; Martins, C.; Mehner, A.; Micela, G.; Monaco, L.; Nunes, N.; Pepe, F.; Poretti, E.; Rebolo, R.; Santos, N.; Saviane, I.; Sousa, S.; Sozzetti, A.; Suarez-Mascareño, A.; Udry, S.; Zapatero-Osorio, M.
Context. The vast majority of the known stars of ultra low metallicity ([Fe=H] >-4:5) are known to be enhanced in carbon, and belong to the 'low-carbon band' (A(C) = log(C=H) + 12 7:6). It is generally, although not universally, accepted that this peculiar chemical composition reflects the chemical composition of the gas cloud out of which these stars were formed. The first ultra-metalpoor star discovered, HE 0107-5240, is also enhanced in carbon and belongs to the 'low-carbon band'. It has recently been claimed to be a long-period binary, based on radial velocity measurements. It has also been claimed that this binarity may explain its peculiar composition as being due to mass transfer from a former AGB companion. Theoretically, low-mass ratios in binary systems are much more favoured amongst Pop III stars than they are amongst solar-metallicity stars. Any constraint on the mass ratio of a system of such low metallicity would shed light on the star formation mechanisms in this metallicity regime. Aims.We acquired one high precision spectrum withESPRESSO in order to check the reality of the radial velocity variations. In addition we analysed all the spectra of this star in the ESO archive obtained with UVES to have a set of homogenously measured radial velocities. Methods. The radial velocities were measured using cross correlation against a synthetic spectrum template. Due to the weakness of metallic lines in this star, the signal comes only from the CH molecular lines of the G-band. Results. The measurement obtained in 2018 from an ESPRESSO spectrum demonstrates unambiguously that the radial velocity of HE 0107-5240 has increased from 2001 to 2018. Closer inspection of the measurements based on UVES spectra in the interval 2001-2006 show that there is a 96% probability that the radial velocity correlates with time, hence the radial velocity variations can already be suspected from the UVES spectra alone. Conclusions.We confirm the earlier claims of radial velocity variations in HE0107-5240. The simplest explanation of such variations is that the star is indeed in a binary system with a long period. The nature of the companion is unconstrained and we consider it is equally probable that it is an unevolved companion or a white dwarf. Continued monitoring of the radial velocities of this star is strongly encouraged.
Gaia-ESO Survey: Gas dynamics in the Carina nebula through optical emission lines
(EDP SCIENCES, 2016-06) Damiani, F.; Bonito, R.; Magrini, L.; Prisinzano, L.; Mapelli, M.; Micela, G.; Kalari, V.; Maíz Apellániz, J.; Gilmore, G.; Randich, S.; Alfaro, E.; Flaccomio, E.; Koposov, S.; Klutsch, A.; Lanzafame, A. C.; Pancino, E.; Sacco, G. G.; Bayo, A.; Carraro, G.; Casey, A. R.; Costado, M. T.; Franciosini, E.; Hourihane, A.; Lardo, C.; Lewis, J.; Monaco, L.; Morbidelli, L.; Worley, C.; Zaggia, S.; Zwitter, T.; Dorda, R.
Aims. We present observations from the Gaia-ESO Survey in the lines of Hα, [N II], [S II], and He I of nebular emission in the central part of the Carina nebula. Methods. We investigate the properties of the two already known kinematic components (approaching and receding), which account for the bulk of emission. Moreover, we investigate the features of the much less known low-intensity high-velocity (absolute RV >50 km s-1) gas emission. Results. We show that gas giving rise to Hα and He I emission is dynamically well correlated with but not identical to gas seen through forbidden-line emission. Gas temperatures are derived from line-width ratios, and densities from [S II] doublet ratios. The spatial variation of N ionization is also studied, and found to differ between the approaching and receding components. The main result is that the bulk of the emission lines in the central part of Carina arise from several distinct shell-like expanding regions, the most evident found around η Car, the Trumpler 14 core, and the star WR25. These “shells” are non-spherical and show distortions probably caused by collisions with other shells or colder, higher-density gas. Some of them are also partially obscured by foreground dust lanes, while very little dust is found in their interior. Preferential directions, parallel to the dark dust lanes, are found in the shell geometries and physical properties, probably related to strong density gradients in the studied region. We also find evidence that the ionizing flux emerging from η Car and the surrounding Homunculus nebula varies with polar angle. The high-velocity components in the wings of Hα are found to arise from expanding dust reflecting the η Car spectrum.
High-speed stars: Galactic hitchhikers
(EDP Sciences, 2020-06) Caffau, E.; Monaco, L.; Bonifacio, P.; Sbordone, L.; Haywood, M.; Spite, M.; Di Matteo, P.; Spite, F.; Mucciarelli, A.; François, P.; Matas Pinto, A.M.
Context. The search for stars born in the very early stages of the Milky Way star formation history is of paramount importance in the study of the early Universe since their chemistry carries irreplaceable information on the conditions in which early star formation and galaxy buildup took place. The search for these objects has generally taken the form of expensive surveys for faint extremely metal-poor stars, the most obvious but not the only candidates to a very early formation. Aims. Thanks to Gaia DR2 radial velocities and proper motions, we identified 72 bright cool stars displaying heliocentric transverse velocities in excess of 500 km s-1. These objects are most likely members of extreme outer-halo populations, either formed in the early Milky Way build-up or accreted from since-destroyed self-gravitating stellar systems. Methods. We analysed low-resolution FORS spectra of the 72 stars in the sample and derived the abundances of a few elements. Despite the large uncertainties on the radial velocity determination, we derived reliable orbital parameters for these objects. Results. The stars analysed are mainly slightly metal poor, with a few very metal-poor stars. Their chemical composition is much more homogeneous than expected. All the stars have very eccentric halo orbits, some extending well beyond the expected dimension of the Milky Way. Conclusions. These stars can be the result of a disrupted small galaxy or they could have been globular cluster members. Age estimates suggest that some of them are evolved blue stragglers, now on the subgiant or asymptotic giant branches. © E. Caffau et al. 2020.
Investigating a predicted metallicity [Fe/H] variation in the Type II Globular Cluster NGC 362
(Oxford University Press, 2022-09-01) Vargas, C.; Villanova, S.; Geisler, D.; Muñoz, C.; Monaco, L.; O'Connell, J.; Sarajedini, Ata
NGC 362 is a non-common Type II Galactic globular cluster, showing a complex pseudo two-colour diagram or 'chromosome map'. The clear separation of its stellar populations in the colour-magnitude diagram and the distribution of the giant stars in the chromosome map strongly suggests that NGC 362 could host stars with both cluster-nominal, as well as enhanced heavy-element abundances, and one of them could be iron. However, despite previous spectroscopic observations of NGC 362, no such iron variation has been detected. Our main goal is to confirm or disprove this result by searching for any internal variation of [Fe/H], which would give us insight into the formation and evolution of this interesting globular cluster. In this paper, we present the abundance analysis for a sample of 11 red giant branch members based on high-resolution and high S/N spectra obtained with the MIKE echelle spectrograph mounted at the Magellan-Clay telescope. HST and GAIA photometry and astrometry has been used to determine atmospheric parameters and membership. We obtained Teff, log(g), and vt for our target stars and measured the mean iron content of the sample and its dispersion with three different methods, which lead to [Fe/H]1 =-1.10±0.02, [Fe/H]2 =-1.09 ±0.01, and [Fe/H]3 =-1.10 ±0.01, while the internal dispersion turned out to be σ[ Fe/H ]1 = 0.06 ±0.01, σ[Fe/H ]2 = 0.03 ±0.01, and σ[ Fe/H ]3 = 0.05 ±0.01, respectively. The error analysis gives an internal dispersion due to observational error of 0.05 dex. Comparing the observed dispersion with the internal errors, we conclude that NGC 362 does not show any trace of an internal iron spread. © 2022 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.
Investigation of a sample of carbon-enhanced metal-poor stars observed with FORS and GMOS
(EDP Sciences, 2018-06) Caffau, E.; Gallagher, A.J.; Bonifacio, P.; Spite, M.; Duffau, S.; Spite, F.; Monaco, L.; Sbordone, L.
Aims. Carbon-enhanced metal-poor (CEMP) stars represent a sizeable fraction of all known metal-poor stars in the Galaxy. Their formation and composition remains a significant topic of investigation within the stellar astrophysics community. Methods. We analysed a sample of low-resolution spectra of 30 dwarf stars, obtained using the visual and near UV FOcal Reducer and low dispersion Spectrograph for the Very Large Telescope (FORS/VLT) of the European Southern Observatory (ESO) and the Gemini Multi-Object Spectrographs (GMOS) at the GEMINI telescope, to derive their metallicity and carbon abundance. Results. We derived C and Ca from all spectra, and Fe and Ba from the majority of the stars. Conclusions. We have extended the population statistics of CEMP stars and have confirmed that in general, stars with a high C abundance belonging to the high C band show a high Ba-content (CEMP-s or -r/s), while stars with a normal C abundance or that are C-rich, but belong to the low C band, are normal in Ba (CEMP-no). © ESO 2018.
Kinematics and chemistry of recently discovered reticulum 2 and horologium 1 dwarf galaxies
(Institute of Physics Publishing, 2015-09) Koposov, Sergey E.; Casey, Andrew R.; Belokurov, Vasily; Lewis, James R.; Gilmore, Gerard; Worley, Clare; Hourihane, Anna; Randich, S.; Bensby, T.; Bragaglia, A.; Bergemann, M.; Carraro, G.; Costado, M.T.; Flaccomio, E.; Francois, P.; Heiter, U.; Hill, V.; Jofre, P.; Lando, C.; Lanzafame, A.C.; Laverny, P.; Monaco, L.; Morbidelli, L.; Sbordone, L.; Mikolaitis, Š.; Ryde, N.
We report on VLT/GIRAFFE spectra of stars in two recently discovered ultra-faint satellites, Reticulum 2 and Horologium 1, obtained as part of the Gaia-ESO Survey. We identify 18 members in Reticulum 2 and five in Horologium 1. We find Reticulum 2 to have a velocity dispersion of , implying a mass-to-light ratio (M/L) of ∼500. The mean metallicity of Reticulum 2 is , with an intrinsic dispersion of ∼0.3 dex and α-enhancement of ∼0.4 dex. We conclude that Reticulum 2 is a dwarf galaxy. We also report on the serendipitous discovery of four stars in a previously unknown stellar substructure near Reticulum 2 with and , far from the systemic velocity of Reticulum 2. For Horologium 1 we infer a velocity dispersion of and a M/L ratio of ∼600, leading us to conclude that Horologium 1 is also a dwarf galaxy. Horologium 1 is slightly more metal-poor than Reticulum 2 () and is similarly α-enhanced: with a significant spread of metallicities of 0.17 dex. The line-of-sight velocity of Reticulum 2 is offset by 100 km s-1 from the prediction of the orbital velocity of the Large Magellanic Cloud (LMC), thus making its association with the Cloud uncertain. However, at the location of Horologium 1, both the backward-integrated orbit of the LMC and its halo are predicted to have radial velocities similar to that of the dwarf. Therefore, it is possible that Horologium 1 is or once was a member of the Magellanic family. © 2015. The American Astronomical Society. All rights reserved..
Lithium abundance in lower red giant branch stars of Omega Centauri
(EDP Sciences, 2018-10) Mucciarelli, A.; Salaris, M.; Monaco, L.; Bonifacio, P.; Fu, X.; Villanova, S.
We present Li, Na, Al, and Fe abundances of 199 lower red giant branch star members of the stellar system Omega Centauri, using high-resolution spectra acquired with FLAMES at the Very Large Telescope. The A(Li) distribution is peaked at A(Li) ∼ 1 dex with a prominent tail towards lower values. The peak of the distribution well agrees with the lithium abundances measured in lower red giant branch stars in globular clusters and Galactic field stars. Stars with A(Li) ∼ 1 dex are found at metallicities lower than [Fe/H] ∼ -1.3 dex but they disappear at higher metallicities. On the other hand, Li-poor stars are found at all metallicities. The most metal-poor stars exhibit a clear Li-Na anti-correlation, where about 30% of the sample have A(Li) lower than ∼0.8 dex, while these stars represent a small fraction of normal globular clusters. Most of the stars with [Fe/H] > -1.6 dex are Li poor and Na rich. The Li depletion measured in these stars is not observed in globular clusters with similar metallicities and we demonstrate that it is not caused by the proposed helium enhancements and/or young ages. Hence, these stars formed from a gas already depleted in lithium. Finally, we note that Omega Centauri includes all the populations (Li-normal/Na-normal, Li-normal/Na-rich, and Li-poor/Na-rich stars) observed, to a lesser extent, in mono-metallic GCs. © ESO 2018.
Lithium on the lower red giant branch of five Galactic globular clusters
(EDP Sciences, 2022-01-01) Aguilera-Gómez, C.; Monaco, L.; Mucciarelli, A.; Salaris, M.; Villanova, S.; Pancino, E.
Context. Lithium is one of the few elements produced during Big Bang nucleosynthesis in the early universe. Moreover, its fragility makes it useful as a proxy for stellar environmental conditions. As such, the lithium abundance in old systems is at the core of various astrophysical investigations. Aims. Stars on the lower red giant branch are key to studies of globular clusters where main sequence stars are too faint to be observed. We use these stars to analyze the initial Li content of the clusters and compare it to cosmological predictions, to measure spreads in Li between different stellar populations, and to study signs of extra depletion in these giants. Methods. We used the GIRAFFE spectra to measure the lithium and sodium abundances of lower red giant branch stars in five globular clusters. These cover an extensive range in metallicity, from [Fe/H] ∼-0.7 to [Fe/H] ∼-2.3 dex. Results. We find that the lithium abundance in these lower red giant branch stars forms a plateau, with values from A(Li)NLTE = 0.84 to 1.03 dex, showing no clear correlation with metallicity. When using stellar evolutionary models to calculate the primordial abundance of these clusters, we recover values of A(Li)NLTE = 2.1 - 2.3 dex, consistent with the constant value observed in warm metal-poor halo stars, namely the Spite plateau. Additionally, we find no difference in the lithium abundance of first and second population stars in each cluster. We also report the discovery of a Li-rich giant in the cluster NGC 3201, with A(Li)NLTE = 1.63 ± 0.18 dex, where the enrichment mechanism is probably pollution from external sources.
Long-term radial-velocity variations of the Sun as a star: The HARPS view
(EDP SCIENCES, 2016-03) Lanza, A. F.; Molaro, P.; Monaco, L.; Haywood, R. D.
Context. Stellar radial velocities play a fundamental role in the discovery of extrasolar planets and the measurement of their physical parameters as well as in the study of stellar physical properties. Aims. We investigate the impact of the solar activity on the radial velocity of the Sun using the HARPS spectrograph to obtain measurements that can be directly compared with those acquired in the extrasolar planet search programmes. Methods. We used the Moon, the Galilean satellites, and several asteroids as reflectors to measure the radial velocity of the Sun as a star and correlated this velocity with disc-integrated chromospheric and magnetic indexes of solar activity that are similar to stellar activity indexes. We discuss in detail the systematic effects that affect our measurements and the methods to account for them. Results. We find that the radial velocity of the Sun as a star is positively correlated with the level of its chromospheric activity at similar to 95 percent significance level. The amplitude of the long-term variation measured in the 2006-2014 period is 4.98 +/- 1.44 m/s, which is in good agreement with model predictions. The standard deviation of the residuals obtained by subtracting a linear best fit is 2.82 m/s and is due to the rotation of the reflecting bodies and the intrinsic variability of the Sun on timescales shorter than the activity cycle. A correlation with a lower significance is detected between the radial velocity and the mean absolute value of the line-of-sight photospheric magnetic field flux density. Conclusions. Our results confirm similar correlations found in other late-type main-sequence stars and provide support to the predictions of radial velocity variations induced by stellar activity based on current models.

Examinando por Autor "Monaco, L."

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