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Search Results: 1 - 10 of 144370 matches for " B. Barbuy "
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The Galactic Bulge
B. Barbuy
Revista mexicana de astronomía y astrofísica , 2002,
Abstract: Se describen y analizan los datos del Bulge y de c umulos globulares teniendo en cuenta las teor as actuales acerca de la formaci on del Bulge
Heavy elements in old very metal-rich stars
M. Trevisan,B. Barbuy
Physics , 2014, DOI: 10.1051/0004-6361/201322967
Abstract: We studied a sample of high proper motion, old and metal-rich dwarf stars, selected from the NLTT catalogue. The low pericentric distances and eccentric orbits of these solar neighbourhood stars indicate that they might have originated in the inner parts of the Galaxy. Chemical tagging can probe the formation history of stellar populations. To identify the origin of a sample of 71 very metal-rich dwarf stars, we derive the abundances of the neutron-capture elements Y, Ba, La, and Eu. The spectroscopic analysis is based on optical high-resolution echelle spectra obtained with the FEROS spectrograph at the ESO 1.52-m Telescope at La Silla, Chile. The abundances of Y, Ba, La, and Eu were derived through LTE analysis, employing the MARCS model atmospheres. The abundances of Y, Ba, La, and Eu vs. Fe and Mg as the reference elements indicate similarities between our sample of old metal-rich dwarf stars and the thin disk. On the other hand, the abundance ratios using O as the reference element, as well as their kinematics, suggest that our sample is clearly distinct from the thin-disk stars. They could be old inner thin-disk stars, as suggested previously, or bulge stars. In either cases they would have migrated from the inner parts of the Galaxy to the solar neighbourhood.
Determination of Atmospheric Parameters of T Tauri Stars
R. Piorno Schiavon,C. Batalha,B. Barbuy
Physics , 1995,
Abstract: The inferred effective temperatures (T$_{\rm eff}$) and surface gravities of T Tauri stars (TTS) are usually contaminated by the presence of a non stellar continuum emission (veiling) and the strong chromospheric activity characteristic of these objects. In this work, we develop a method to determine T$_{\rm eff}$'s and surface gravities (log$\,g$) of a group of TTS. This method is based on the comparison between observed and theoretical molecular and atomic line depth ratios being therefore insensitive to the influence of veiling. We show the strong dependence of our line depth ratios upon gravity and temperature. The resulting gravities, as expected for TTS, average between the values of dwarf and giant stars. Previously published gravities for each of our stars vary widely due in part to the differences in the adopted visual extinction, veiling (if ever considered) and methods of assessing the stellar luminosity. Our values of T$_{\rm eff}$ and log$\,g$ have the uniqueness of being entirely derived from high resolution data and are not affected by circumstellar extinction or veiling when line ratios are used. They therefore serve as more reliable input parameters for future spectral synthesis analyses of T Tauri Stars requiring model atmospheres. We provide a table relating theoretical line depth ratio with T$_{\rm eff}$ and log $\,g$ for easy assessment of TTS fundamental parameters.
A Catalogue of infrared star clusters and stellar groups
E. Bica,C. M. Dutra,B. Barbuy
Physics , 2002, DOI: 10.1051/0004-6361:20021479
Abstract: We compiled a catalogue of infrared star clusters in the Galaxy, which are most of them embedded. It condenses the growing literature information. We also include in the sample infrared stellar groups which are less dense than star clusters, such as those embedded in the dark clouds Taurus-Auriga and Chamaleon I. We provide galactic and equatorial coordinates, angular dimensions, different designations and related objects such as nebulae. A total of 189 infrared clusters and 87 embedded stellar groups are included. A fraction of 25 % of the embedded clusters are projected close to each other in pair or triplet systems, indicating that multiplicity plays an important role in star cluster formation.
Globular clusters in the Galactic bulge
E. Bica,S. Ortolani,B. Barbuy
Physics , 2015,
Abstract: A view of the Galactic bulge by means of their globular clusters is necessary for a deep understanding of its formation and evolution. Connections between the globular cluster and field star properties in terms of kinematics, orbits, chemical abundances and ages should shed light on different stellar population components. Based on spatial distribution and metallicity, we define a probable best list of bulge clusters, containing 43 entries. Future work on newly discovered objects, mostly from the VVV survey, is suggested. These candidates might alleviate the issue of missing clusters on the far side of the bulge. We discuss the reddening law affecting the cluster distances towards the center of the Galaxy, and conclude that the most suitable total-to-selective absorption value appears to be R$_{\rm V}$=3.2, in agreement with recent analyses. An update of elemental abundances for bulge clusters is provided.
B. Barbuy,B. Dias,A. Alves-Brito,M. Zoccali
Revista mexicana de astronomía y astrofísica , 2009,
Abstract: We are carrying studies on the metal-poor globular clusters of the Galactic bulge. These objects appear to be very old, and might be relics of the rst objects in the Galaxy. High resolution observations carried out with VLT-UVES, VLT-FLAMES and Gemini-PHOENIX are presented, and the abundance pattern of these globulars is studied.
Chemical abundances in the galactic bulge: evidence for a fast enrichment
M. Zoccali,D. Minniti,B. Barbuy,V. Hill
Revista mexicana de astronomía y astrofísica , 2006,
Abstract: Hemos derivado abundancias de ox geno para 42 gigantes K en cuatro campos hacia el bulbo gal actico. Aqu presentamos los resultados para ox geno, de acuerdo a las l neas prohibidas en 6300 A. El ox geno muestra una bien de nida tendencia con [Fe/H]. Siendo [O/Fe] m as alto en las estrellas del bulbo que en las del disco grueso, estas ultimas ya se encuentran m as enriquecidas por el ox geno que las estrellas del disco delgado (Bensby, Feltzing, & Lundstrom 2004). Este resultado apoya el escenario en el cual el bulbo se form o de manera m as r apida, y probablemente antes que el disco grueso.
Evidence for rotation-induced mixing in evolved intermediate mass stars
R. Smiljanic,B. Barbuy,J. R. De Medeiros,A. Maeder
Revista mexicana de astronomía y astrofísica , 2006,
Abstract: Muchos resultados observacionales parecen indicar procesos de mezclado m as e cientes en estrellas de masas intermedias (5-20 M ) que los esperados de los m etodos est andar. Por lo general se piensa que estos procesos son producidos por la rotaci on estelar. De nuestro an alisis reciente de 19 estrellas de masas intermedias evolucionadas se ha encontrado que estas presentan diferentes e ciencias de mezclado interno. La comparaci on de estos resultados y de otros de la bibliograf a , con modelos evolutivos estelares rotacionales y no rotacionales nos ha permitido encontrar, por vez primera, una importante correlaci on entre masa estelar y [N/C]; es decir, la clase de correlaci on que se espera sea producida por mezclado inducido por rotaci on.
Measuring stellar oscillations using equivalent widths of absorption lines
T. R. Bedding,H. Kjeldsen,J. Reetz,B. Barbuy
Physics , 1996, DOI: 10.1093/mnras/280.4.1155
Abstract: Kjeldsen et al. (1995, AJ 109, 1313; astro-ph/9411016) have developed a new technique for measuring stellar oscillations and claimed a detection in the G subgiant eta Boo. The technique involves monitoring temperature fluctuations in a star via their effect on the equivalent width of Balmer lines. In this paper we use synthetic stellar spectra to investigate the temperature dependence of the Balmer lines, Ca II, Fe I, the Mg b feature and the G~band. We present a list of target stars likely to show solar-like oscillations and estimate their expected amplitudes. We also show that centre-to-limb variations in Balmer-line profiles allow one to detect oscillation modes with l<=4, which accounts for the detection by Kjeldsen et al. of modes with degree l=3 in integrated sunlight.
The FeH Wing-Ford Band in Spectra of M Stars
Ricardo P. Schiavon,B. Barbuy,Patan D. Singh
Physics , 1997, DOI: 10.1086/304332
Abstract: We study the FeH Wing-Ford band at 9850 - 10200 Angstrons by means of the fit of synthetic spectra to the observations of M stars, employing recent model atmospheres. On the basis of the spectrum synthesis, we analyze the dependence of the band upon atmospheric parameters. FeH lines are a very sensitive surface gravity indicator, being stronger in dwarfs. They are also sensitive to metallicity (Allard & Hauschildt 1995). The blending with CN lines, which are stronger in giants, does not affect the response of the Wing-Ford band to surface gravity at low resolution (or high velocity dispersions) because CN lines, which are spread all along the spectrum, are smeared out at convolutions of FWHM $\simgreat$ 3 Angstrons. We conclude that the Wing-Ford band is a suitable dwarf/giant indicator for the study of composite stellar populations.
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