arXiv subjects

Beatriz Barbuy

Publications and source records attributed to Beatriz Barbuy.

At least 73 records · Page 4Linked to original sources

arXiv2012

Homogeneous Metallicities and Radial Velocities for Galactic Globular Clusters

Well determined radial velocities and abundances are essential for analyzing the properties of the Globular Cluster system of the Milky Way. However more than 50% of these clusters have no spectroscopic measure of their metallicity. In this context, this work provides new radial velocities and abundances for twenty Milky Way globular clusters which lack or have poorly known values for these quantities. The radial velocities and abundances are derived from spectra obtained at the Ca II triplet using the FORS2 imager and spectrograph at the VLT, calibrated with spectra of red giants in a number of clusters with well determined abundances. For about half of the clusters in our sample we present significant revisions of the existing velocities or abundances, or both. We also confirm the existence of a sizable abundance spread in the globular cluster M54, which lies at the center of the Sagittarius dwarf galaxy. In addition evidence is provided for the existence of a small intrinsic internal abundance spread (sigma [Fe/H](int) ~ 0.11-0.14 dex, similar to that of M54) in the luminous distant globular cluster NGC 5824. This cluster thus joins the small number of Galactic globular clusters known to possess internal metallicity ([Fe/H]) spreads.

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arXiv2011

A Fossil Bulge Globular Cluster revealed by VLT Multi-Conjugate Adaptive Optics

The globular cluster HP1 is projected on the bulge, very close to the Galactic center. The Multi-Conjugate Adaptive Optics (MCAO) Demonstrator (MAD) at the Very Large Telescope (VLT) allowed to acquire high resolution deep images that, combined with first epoch New Technology Telescope (NTT) data, enabled to derive accurate proper motions. The cluster and bulge field stellar contents were disentangled by means of this process, and produced unprecedented definition in the color-magnitude diagrams for this cluster. The metallicity of [Fe/H] ~ -1.0 from previous spectroscopic analysis is confirmed, which together with an extended blue horizontal branch, imply an age older than the halo average. Orbit reconstruction results suggest that HP1 is spatially confined within the bulge.

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arXiv2011

Age and metallicity of star clusters in the Small Magellanic Cloud from integrated spectroscopy

Context: Analysis of ages and metallicities of star clusters in the Magellanic Clouds provide information for studies on the chemical evolution of the Clouds and other dwarf irregular galaxies. Aims: The aim is to derive ages and metallicities from integrated spectra of 14 star clusters in the Small Magellanic Cloud, including a few intermediate/old age star clusters. Methods: Making use of a full-spectrum fitting technique, we compared the integrated spectra of the sample clusters to three different sets of single stellar population models, using two fitting codes available in the literature. Results: We derive the ages and metallicities of 9 intermediate/old age clusters, some of them previously unstudied, and 5 young clusters. Conclusions: We point out the interest of the newly identified as intermediate/old age clusters HW1, NGC 152, Lindsay 3, Lindsay 11, and Lindsay 113. We also confirm the old ages of NGC 361, NGC 419, Kron 3, and of the very well-known oldest SMC cluster, NGC 121.

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arXiv2009

Open cluster survival within the solar circle: Teutsch145 and Teutsch146

Teutsch145 and Teutsch146 are shown to be open clusters (OCs) orbiting well inside the Solar circle, a region where several dynamical processes combine to disrupt most OCs on a time-scale of a few 10^8yrs. BVI photometry from the GALILEO telescope is used to investigate the nature and derive the fundamental and structural parameters of the optically faint and poorly-known OCs Teutsch145 and 146. These parameters are computed by means of field-star decontaminated colour-magnitude diagrams (CMDs) and stellar radial density profiles (RDPs). Cluster mass estimates are made based on the intrinsic mass functions (MFs). We derive the ages 200+100-50Myr and 400+/-100Myr, and the distances from the Sun 2.7+/-0.3kpc and 3.8+/-0.2kpc, respectively for Teutsch145 and 146. Their integrated apparent and absolute magnitudes are m_V ~ 12.4, m_V ~ 13.3, M_V ~- 5.6 and M_V ~- 5.3. The MFs (detected for stars with m>1Msun) have slopes similar to Salpeter's IMF. Extrapolated to the H-burning limit, the MFs would produce total stellar masses of ~1400Msun, typical of relatively massive OCs. Both OCs are located deep into the inner Galaxy and close to the Crux-Scutum arm. Since cluster-disruption processes are important, their primordial masses must have been higher than the present-day values. The conspicuous stellar density excess observed in the innermost bin of both RDPs might reflect the dynamical effects induced by a few 10^8yrs of external tidal stress.

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arXiv2009

Pfleiderer2: identification of a new globular cluster in the Galaxy

We provide evidence that indicate the star cluster Pfleiderer 2, which is projected in a rich field, as a newly identified Galactic globular cluster. Since it is located in a crowded field, core extraction and decontamination tools were applied to reveal the cluster sequences in B, V and I Color-Magnitude Diagrams (CMDs). The main CMD features of Pfleiderer 2 are a tilted Red Giant Branch, and a red Horizontal Branch, indicating a high metallicity around solar. The reddening is E(B-V)=1.01. The globular cluster is located at a distance from the Sun d$_{\odot}$ = 16$\pm$2 kpc. The cluster is located at 2.7 kpc above the Galactic plane and at a distance from the Galactic center of R$_{\rm GC}$=9.7 kpc, which is unusual for a metal-rich globular cluster.

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arXiv2009

Both accurate and precise gf-values for FeII lines

We present a new set of oscillator strengths for 142 FeII lines in the wavelength range 4000-8000 A. Our gf-values are both accurate and precise, because each multiplet was globally normalized using laboratory data (accuracy), while the relative gf-values of individual lines within a given multiplet were obtained from theoretical calculations (precision). Our line list was tested with the Sun and high-resolution (R ~ 10^5), high-S/N (~700-900) Keck+HIRES spectra of the metal-poor stars HD 148816 and HD 140283, for which line-to-line scatter (sigma) in the iron abundances from FeII lines as low as 0.03, 0.04, and 0.05 dex are found, respectively. For these three stars the standard error in the mean iron abundance from FeII lines is negligible (sigma_mean <= 0.01 dex). The mean solar iron abundance obtained using our gf-values and different model atmospheres is A_Fe = 7.45 (sigma = 0.02).

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arXiv2008

Self-consistent physical parameters for MC clusters from CMD modelling: application to SMC clusters observed with the SOAR telescope

The Magellanic Clouds (MCs) present a rich system of stellar clusters that can be used to probe the dynamical and chemical evolution of these neighboring and interacting irregular galaxies. In particular, these stellar clusters (SCs) present combinations of age and metallicity that are not found for this class of objects in the Milky Way, being therefore very useful templates to test and to calibrate integrated light simple stellar population (SSP) models applied to unresolved distance galaxies. On its turn, the age and metallicity for a cluster can be determined spatially resolving its stars, by means of analysis of its colour-magnitude diagrams (CMDs). In this work we present our method to determine self-consistent physical parameters (age, metallicity, distance modulus and reddening) for a stellar cluster, from CMDs modelling of relatively unstudied SCs in the Small Magellanic Cloud (SMC) imaged in the BVI filters with the 4.1 m SOAR telescope. Our preliminary results confirm our expectations that come from a previous integrated spectra and colour analysis: at least one of them (Lindsay 2) is an intermediate-age stellar cluster with ~ 2.6 Gyr and [Fe/H] ~ -1.3, being therefore a new interesting witness regarding the reactivation of the star formation in the MCs in the last 4 Gyr.

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arXiv2007

FSR1767 - a new globular cluster in the Galaxy

The globular cluster (GC) nature of the recently catalogued candidate FSR 1767 is established in the present work. It results as the closest GC so far detected in the Galaxy. The nature of this object is investigated by means of 2MASS colour-magnitude diagrams (CMDs), the stellar radial density profile (RDP) and proper-motions (PM). The properties are consistent with an intermediate metallicity ($\feh\approx-1.2$) GC with a well-defined turnoff (TO), red-giant branch (RGB) and blue horizontal-branch (HB). The distance of FSR 1767 from the Sun is $\ds\approx1.5$ kpc, and it is located at the Galactocentric distance $\rgc\approx5.7$ kpc. With the space velocity components $(V,W)=(184\pm14,-43\pm14)\rm km s^{-1}$, FSR 1767 appears to be a Palomar-like GC with $\mv\approx-4.7$, that currently lies $\approx57$ pc below the Galactic plane. The RDP is well represented by a King profile with the core and tidal radii $\rc=0.24\pm0.08$ pc and $\rt=3.1\pm1.0$ pc, respectively, with a small half-light radius $\rh=0.60\pm0.15$ pc. The optical absorption is moderate for an infrared GC, $A_V=6.2\pm0.3$, which together with its central direction and enhanced contamination explains why it has so far been overlooked.

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arXiv2006

Analysis of 26 Barium Stars II. Contributions of s-, r- and p-processes in the production of heavy elements

Barium stars show enhanced abundances of the slow neutron capture (s-process) heavy elements, and for this reason they are suitable objects for the study of s-process elements. The aim of this work is to quantify the contributions of the s-, r- and p-processes for the total abundance of heavy elements from abundances derived for a sample of 26 barium stars. The abundance ratios between these processes and neutron exposures were studied. The abundances of the sample stars were compared to those of normal stars thus identifying the fraction relative to the s-process main component. The fittings of the sigmaN curves (neutron capture cross section times abundance, plotted against atomic mass number) for the sample stars suggest that the material from the companion asymptotic giant branch star had approximately the solar isotopic composition as concerns fractions of abundances relative to the s-process main component. The abundance ratios of heavy elements, hs, ls and s and the computed neutron exposure are similar to those of post-AGB stars. For some sample stars, an exponential neutron exposure fits well the observed data, whereas for others, a single neutron exposure provides a better fit. The comparison between barium and AGB stars supports the hypothesis of binarity for the barium star formation. Abundances of r-elements that are part of the s-process path in barium stars are usually higher than those in normal stars,and for this reason, barium stars seemed to be also enriched in r-elements, although in a lower degree than s-elements. No dependence on luminosity classes was found in the abundance ratios behaviour among the dwarfs and giants of the sample barium stars.

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arXiv2006

Analysis of 26 Barium Stars I. Abundances

We present a detailed analysis of 26 barium stars, including dwarf barium stars, providing their atmospheric parameters (Teff, log g, [Fe/H], vt) and elemental abundances. We aim at deriving gravities and luminosity classes of the sample stars, in particular to confirm the existence of dwarf barium stars. Accurate abundances of chemical elements were derived. Abundance ratios between nucleosynthetic processes, by using Eu and Ba as representatives of the r- and s-processes are presented. High-resolution spectra with the FEROS spectrograph at the ESO-1.5m Telescope, and photometric data with Fotrap at the Zeiss telescope at the LNA were obtained. The atmospheric parameters were derived in an iterative way, with temperatures obtained from colour-temperature calibrations. The abundances were derived using spectrum synthesis for Li, Na, Al, alpha-, iron peak, s- and r-elements atomic lines, and C and N molecular lines. Atmospheric parameters in the range 4300 < Teff < 6500, -1.2 < [Fe/H] < 0.0 and 1.4 < log g < 4.6 were derived, confirming that our sample contains giants, subgiants and dwarfs. The abundance results obtained for Li, Al, Na, alpha- and iron peak elements for the sample stars show that they are compatible with the values found in the literature for normal disk stars in the same range of metallicities. Enhancements of C, N and heavy elements relative to Fe, that characterise barium stars, were derived and showed that [X/Ba] vs. [Ba/H] and [X/Ba] vs. [Fe/H] present different behaviour as compared to [X/Eu] vs. [Eu/H] and [X/Eu] vs. [Fe/H], reflecting the different nucleosynthetic sites for the s- and r-processes.

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arXiv2005

Globular cluster system and Milky Way properties revisited

Updated data of the 153 Galactic globular clusters are used to readdress fundamental parameters of the Milky Way. We build a reduced sample, decontaminated of the clusters younger than 10Gyr, those with retrograde orbits and/or evidence of relation to dwarf galaxies. The 33 metal-rich globular clusters of the reduced sample extend basically to the Solar circle and distribute over a region with projected axial-ratios typical of an oblate spheroidal, $\rmΔx:Δy:Δz\approx1.0:0.9:0.4$. The 81 metal-poor globular clusters span a nearly spherical region of axial-ratios $\approx1.0:1.0:0.8$ extending from the central parts to the outer halo. A new estimate of the Sun's distance to the Galactic center is provided, $\rm R_O=7.2\pm0.3 kpc$. The metal-rich and metal-poor radial-density distributions flatten for $\rm R_{GC}\leq2 kpc$ and are well represented both by a power-law with a core-like term and Sérsic's law; at large distances they fall off as $\rm\sim R^{-3.9}$. Both metallicity components appear to have a common origin, which is different from that of the dark matter halo. Structural similarities of the metal-rich and metal-poor radial distributions with the stellar halo are consistent with a scenario where part of the reduced sample was formed in the primordial collapse, and part was accreted in an early period of merging. This applies to the bulge as well, suggesting an early merger affecting the central parts of the Galaxy. We estimate that the present globular cluster population corresponds to $\rm\leq23\pm6%$ of the original one. The fact that the volume-density radial distributions of the metal-rich and metal-poor globular clusters of the reduced sample follow both a core-like power-law and Sérsic's law indicates that we are dealing with spheroidal subsystems in all scales.

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arXiv2003

Detailed Analysis of Nearby Bulgelike Dwarf Stars III. Alpha and Heavy-element abundances

The present sample of nearby bulgelike dwarf stars has kinematics and metallicities characteristic of a probable inner disk or bulge origin. Ages derived by using isochrones give 10-11 Gyr for these stars and metallicities are in the range -0.80< [Fe/H]< +0.40. We calculate stellar parameters from spectroscopic data, and chemical abundances of Mg, Si, Ca, Ti, La, Ba, Y, Zr and Eu are derived by using spectrum synthesis. We found that [alpha-elements/Fe] show different patterns depending on the element. Si, Ca and Ti-to-iron ratios decline smoothly for increasing metallicities, and follow essentially the disk pattern. O and Mg, products of massive supernovae, and also the r-process element Eu, are overabundant relative to disk stars, showing a steeper decline for metallicities [Fe/H] > -0.3 dex. [s-elements/Fe] roughly track the solar values with no apparent trend with metallicity for [Fe/H] < 0, showing subsolar values for the metal rich stars. Both kinematical and chemical properties of the bulgelike stars indicate a distinct identity of this population when compared to disk stars.

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arXiv2002

Keck-Nirspec Infrared OH Lines: Oxygen Abundances in Metal-Poor Stars Down to [Fe/H] = -2.9

Infrared OH lines at 1.5 - 1.7 um in the H band were obtained with the NIRSPEC high-resolution spectrograph at the 10m Keck Telescope for a sample of seven metal-poor stars. Detailed analyses have been carried out, based on optical high-resolution data obtained with the FEROS spectrograph at ESO. Stellar parameters were derived by adopting infrared flux method effective temperatures, trigonometric and/or evolutionary gravities and metallicities from FeII lines. We obtain that the sample stars with metallicities [Fe/H] < -2.2 show a mean oxygen abundance [O/Fe] ~ 0.54, for a solar oxygen abundance of epsilon(O) = 8.87, or [O/Fe] ~ 0.64 if epsilon(O) = 8.77 is assumed.

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arXiv2002

Detailed Analysis of Nearby Bulgelike Dwarf Stars II. Lithium Abundances

Li abundances are derived for a sample of bulgelike stars with isochronal ages of 10-11 Gyr. These stars have orbits with pericentric distances, Rp, as small as 2-3 kpc and Zmax < 1 kpc. The sample comprises G and K dwarf stars in the metallicity range -0.80<[Fe/H]< +0.40. Few data of Li abundances in old turn-off stars (> 4.5 Gyr) within the present metallicity range are available. M67 (4.7 Gyr) and NGC 188 (6 Gyr) are the oldest studied metal-rich open clusters with late-type stars. Li abundances have also been studied for few samples of old metal-rich field stars. In the present work a high dispersion in Li abundances is found for bulgelike stars for all the metallicity range, comparable with values in M67. The role of metallicity and age on a Li depletion pattern is discussed. The possible connection between Li depletion and oxygen abundance due to atmospheric opacity effects is investigated.

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arXiv2001

Detailed Analysis of Nearby Bulge-like Dwarf Stars I. Stellar Parameters, Kinematics and Oxygen Abundances

High resolution échelle spectra were obtained with the FEROS spectrograph at the 1.5m ESO telescope for 35 nearby bulge-like stars with metallicities in the range -0.8 $\leq$ [Fe/H] $\leq$ +0.4. Geneva photometry, astrometric data from Hipparcos and radial velocities from Coravel are available for these stars. From Hipparcos data it appears that the turnoff of this population indicates an age of 10-11 Gyr (Grenon 1999). Detailed analysis of the sample stars is carried out and atmospheric parameters derived from spectroscopic and photometric determinations are presented. Oxygen abundances are derived based on the forbidden [O I] $λ$ 6300.3 {\rm Å} line. The results show an oxygen overabundance pattern for most of the sample stars when compared to their disk counterparts.

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arXiv2001

Oxygen Abundances in Metal-Poor Stars (-2.2 < [Fe/H] < -1.2) from Infrared OH lines

Infrared OH lines at 1.55 - 1.56 um in the H-band were obtained with the Phoenix high-resolution spectrograph at the 2.1m telescope of the Kitt Peak National Observatory for a sample of 14 metal-poor stars. Detailed analyses of the sample stars have been carried out, deriving stellar parameters based on two methods: (a) spectroscopic parameters; (b) IRFM effective temperatures, trigonometric gravities and metallicities from Fe II lines. The Fe I lines present in the H-band region observed showed to be well fitted by the stellar parameters within $Δ$[Fe/H] < 0.15 dex. The oxygen abundances were derived from fits of spectrum synthesis calculations to the infrared OH lines. CO lines in the H- and K-bands were obtained for a subsample in order to determine their carbon abundances. Adopting the spectroscopic parameters a mean oxygen-to-iron ratio of [O/Fe] ~ +0.52 is obtained, whereas using the IRFM temperatures, Hipparcos gravities and [FeII/H], [O/Fe] ~ +0.25 is found. A mean of the two methods gives a final value of [O/Fe] ~ +0.4 for the metallicity range -2.2 < [Fe/H] < -1.2 of the sample metal-poor stars.

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arXiv1999

Near-infrared Spectral Features in Single-aged Stellar Populations

Synthetic spectra for single-aged stellar populations of metallicities [M/H] = -0.5, 0.0 and +0.5, ages = 3 to 17 Gyrs, and initial mass function exponents x = 0.1 to 2.0 were built in the wavelength range 6000-10200 Angstrons. For such we have employed the grid of synthetic spectra described in Schiavon & Barbuy (1999), computed for the stellar parameters 2500 <= Teff <= 6000 K, -0.5 <= log g <= 5.0, [M/H] = -0.5, 0.0 and +0.5, and [alpha/Fe] = 0.0, together with the isochrones by Bertelli et al. (1994) and Baraffe et al. (1998). The behavior of the features NaI8190, CaII8662, TiO6600 and FeH9900 in the integrated spectra of single stellar populations were studied in terms of metallicity, initial mass function and age variations. The main conclusions are that the NaI doublet is an IMF-sensitive feature, which is however sensitive also to metallicity and age, whereas TiO, CaII and FeH are very sensitive to metallicity and essentially insensitive to IMF and age.

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arXiv1999

Oscillator Strengths and Damping Constants for Atomic Lines in the J and H Bands

We have built a line list in the near-infrared J and H bands (1.00-1.34, 1.49-1.80 um) by gathering a series of laboratory and computed line lists. Oscillator strengths and damping constants were computed or obtained by fitting the solar spectrum. The line list presented in this paper is, to our knowledge, the most complete one now available, and supersedes previous lists.

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