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Pode ω Centauri induzir formação estelar no disco galáctico?

Salerno, Gustavo Malta
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Dissertação Formato: application/pdf
POR
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Neste trabalho investigamos um dos processos que pode levar a formação de aglomerados abertos, focando-nos nas interações ocorridas durante a passagem de um aglomerado globular através do disco Galáctico, cujos efeitos podem resultar no surgimentos daqueles. Tais interações podem ser uma alternativa aos cenários convencionais de formação estelar. Há diversos trabalhos explorando os efeitos, em nossa Galáxia, de impactos de nuvens HI, explosões de supernovas, galáxias canibalizadas ou aglomerados globulares, estes podendo inclusive ser núcleos de galáxias anãs capturadas pela Via Láctea, como parece ser o caso de ω Centauri. Trabalhos sobre interações de aglomerados globulares com o disco Galáctico invariavelmente tratam dos efeitos da Galáxia sobre o aglomerado globular, mas pouco tem sido feito com relação a análise de como os impactos de aglomerados globulares podem gerar o nascimento de aglomerados no disco Galáctico. O presente trabalho investiga o caso envolvendo o aglomerado globular ω Centauri como projétil e os aglomerados abertos massivos BDSB122 e Stephenson 2 como alvos resultantes do impacto de ω Centauri no disco Galáctico. ω Centauri é bem estudado na literatura, além de ser um dos mais massivos aglomerados globulares...

A Deep Wide-Field Variable Star Catalog of ω Centauri

Weldrake, David; Sackett, Penny; Bridges, Terry C
Fonte: University of Chicago Press Publicador: University of Chicago Press
Tipo: Artigo de Revista Científica
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We present a variable star catalog of an extensive ground-based wide-field variability survey in the globular cluster ω Centauri. Using the Australian National University 40 inch (1 m) telescope at Siding Spring Observatory, the cluster was observed with

The Age and Metallicity Relation of Omega Centauri

Stanford, Laura; Da Costa, Gary; Norris, John; Cannon, Russell
Fonte: IOP Publishing Publicador: IOP Publishing
Tipo: Artigo de Revista Científica
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We present a metallicity distribution based on photometry and spectra for 442 ω Centauri cluster members that lie at the main-sequence turnoff region of the color-magnitude diagram. This distribution is similar to that found for the red giant branch. The

A Sr-Rich Star on the Main Sequence of omega Centauri

Stanford, Laura; Da Costa, Gary; Norris, John; Cannon, Russell
Fonte: IOP Publishing Publicador: IOP Publishing
Tipo: Artigo de Revista Científica
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Abundance ratios relative to iron for carbon, nitrogen, strontium, and barium are presented for a metal-rich main-sequence star ([Fe/H] = -0.74) in the globular cluster ω Centauri. This star, designated 2015448, shows depleted carbon and solar nitrogen b

The Frequency of Large-Radius Hot and Very Hot Jupiters in ω Centauri

Weldrake, David; Sackett, Penny; Bridges, Terry C
Fonte: IOP Publishing Publicador: IOP Publishing
Tipo: Artigo de Revista Científica
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We present the results of a deep, wide-field search for transiting hot Jupiter (HJ) planets in the globular cluster ω Centauri. As a result of a 25 night observing run with the ANU 40 inch (1 m) telescope at Siding Spring Observatory, a total of 109,726

CANGAROO III Search for Gamma Rays from Centaurus A and the ω Centauri Region

Kabuki, S; Enomoto, R; Bicknell, Geoffrey; Clay, Roger W; Edwards, P G; Gunji, S; Hara, S; Hattori, T; Hayashi, S; Higashi, Y; Inoue, R; Itoh, Chie; Kajino, F; Katagiri, H; Kawachi, A; Kawasaki, S; Kifune, T; Kiuchi, R; Konno, K.; Kubo, H; Kushida, J; Mat
Fonte: IOP Publishing Publicador: IOP Publishing
Tipo: Artigo de Revista Científica
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We have observed the giant radio galaxy Centauras A and the globular cluster ω Centauri in the TeV energy region using the CANGAROO 111 stereoscopic system. The system has been in operation since 2004 with an array of four Imaging Atmospheric Cerenkov Te

Abundances on the Main Sequence of ω Centauri

Stanford, Laura; Da Costa, Gary; Norris, John; Cannon, Russell
Fonte: IOP Publishing Publicador: IOP Publishing
Tipo: Artigo de Revista Científica
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Abundance ratios of carbon, nitrogen, and strontium relative to iron, calculated using spectrum synthesis techniques, are given for a sample of main-sequence and turnoff stars that belong to the globular cluster ω Centauri. The variations of carbon, nitr

The Origin of the Double Main Sequence in ω Centauri: Helium Enrichment Due to Gas Fueling from its Ancient Host Galaxy?

Bekki, Kenji; Norris, John
Fonte: IOP Publishing Publicador: IOP Publishing
Tipo: Artigo de Revista Científica
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Recent observational studies of ω Centauri by the Hubble Space Telescope have discovered a double main sequence in the color-magnitude diagrams (CMDs) of its stellar populations. These observations suggest that the stellar population with the blue main s

Centauri e Giganti nell'artigianato artistico di ambiente etrusco

LANDI, ALICE
Fonte: La Sapienza Universidade de Roma Publicador: La Sapienza Universidade de Roma
Tipo: Tese de Doutorado
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La presente tesi di dottorato affronta l’analisi delle iconografie di Centauri e Giganti nell’artigianato artistico in Etruria seguendone il percorso evolutivo a partire dalla loro prima comparsa (primo quarto del VII secolo a.C. per i Centauri, seconda metà del VI per i Giganti) fino alle più recenti rappresentazioni di II e I secolo a.C. Il lavoro, concentrandosi su quanto finora edito, ha innanzitutto l’obiettivo di costituire un catalogo aggiornato che, suddiviso per classi di materiali, possa costituire la base per un’indagine sistematica dei soggetti iconografici in esame. Allo spoglio della bibliografia sono stati affiancati, ove possibile, la visione diretta dei materiali e il recupero della documentazione fotografica inedita, in particolare presso il Louvre, il Musée des Monnaies, Médailles et Antiques della Bibliothèque Nationale de France e il British Museum. I documenti raccolti, che costituiscono un Catalogo di circa 470 pezzi, interessano molte classi di materiali, dalla coroplastica architettonica alle diverse produzioni ceramiche (impasto ‒ white-on-red, impasti orientalizzanti con decorazione incisa e a stampo, produzione ceretana stampigliata in impasto rosso ‒, bucchero, ceramica dipinta tardo-orientalizzante...

Are Proxima and Alpha Centauri Gravitationally Bound?

Wertheimer, Jeremy G.; Laughlin, Gregory
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 17/07/2006
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Using the most recent kinematic and radial velocity data in the literature, we calculate the binding energy of Proxima Centauri relative to the center of mass of the Alpha Centauri system. When we adopt the centroids of the observed data, we find that the three stars constitute a bound system, albeit with a semi-major axis that is on order the same size as Alpha Centauri AB's Hill radius in the galactic potential. We carry out a Monte Carlo simulation under the assumption that the errors in the observed quantities are uncorrelated. In this simulation, 44% of the trial systems are bound, and systems on the 1-3 sigma tail of the radial velocity distribution can have Proxima currently located near the apastron position of its orbit. Our analysis shows that a further, very significant improvement in the characterization of the system can be gained by obtaining a more accurate measurement of the radial velocity of Proxima Centauri.; Comment: 10 pages total, 4 pages of text, 1 page of references, 3 figures, and 2 tables This article will be published in The Astronomical Journal

Observational consequences of the hypothesized helium rich stellar population in Omega Centauri

Newsham, G.; Terndrup, D. M.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 19/04/2007
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In response to the proposed high helium content stars as an explanation for the double main sequence observed in Omega Centauri, we investigated the consequences of such stars elsewhere on the color-magnitude diagram. We concentrated on the horizontal branch where the effects of high helium are expected to show themselves more clearly. In the process, we developed a procedure for comparing the mass loss suffered by differing stellar populations in a physically motivated manner. High helium stars in the numbers proposed seem absent from the horizontal branch of Omega Centauri unless their mass loss history is very different from that of the majority metal-poor stars. It is possible to generate a double main sequence with existing Omega Centauri stars via accretion of helium rich pollution consistent with the latest AGB ejecta theoretical yields, and such polluted stars are consistent with the observed HB morphology of Omega Centauri. Polluted models are consistent with observed merging of the main sequences as opposed to our models of helium rich stars. Using the (B-R)/(B+V+R) statistic, we find that the high helium bMS stars require an age difference compared to the rMS stars that is too great, whereas the pollution scenario stars have no such conflict for inferred Omega Centauri mass losses.; Comment: 37 pages...

The Kapteyn moving group is not tidal debris from $\omega$ Centauri

Navarrete, Camila; Chanamé, Julio; Ramírez, Iván; Meza, Andrés; Anglada-Escudé, Guillem; Shkolnik, Evgenya
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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The Kapteyn moving group has been postulated as tidal debris from $\omega$ Centauri. If true, members of the group should show some of the chemical abundance patterns known for stars in the cluster. We present an optical and near-infrared high-resolution, high-S/N spectroscopic study of 14 stars of the Kapteyn group, plus 10 additional stars (the $\omega$ Cen-group) that, while not listed as members of the Kapteyn group as originally defined, have been nevertheless associated dynamically with $\omega$ Centauri. Abundances for Na, O, Mg, Al, Ca and Ba were derived from the optical spectra, while the strength of the chromospheric He I 10830 {\AA} line is studied as a possible helium abundance indicator. The resulting Na-O and Mg-Al patterns for stars of the combined Kapteyn and $\omega$ Cen-group samples do not resemble those of $\omega$ Centauri, and are not different from those of field stars of the Galactic halo. The distribution of equivalent widths of the He I 10830 {\AA} line is consistent with that found among non-active field stars. Therefore, no evidence is found for second-generation stars within our samples, which most likely rules out a globular-cluster origin. Moreover, no hint of the unique Ba-overabundance at the metal-rich end...

Magnesium Isotope Ratios in omega Centauri Red Giants

Da Costa, G S; Norris, John E; Yong, David
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 01/04/2013
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We have used high resolution observations obtained at the AAT with UHRF (R ~ 100,000) and at Gemini-S with b-HROS (R ~ 150,000) to determine magnesium isotope ratios for seven omega Centauri red giants that cover a range in iron abundance from [Fe/H] = --1.78 to --0.78 dex, and for two red giants in M4 (NGC 6121). The omega Centauri stars sample both the "primordial" (i.e., O-rich, Na and Al-poor) and the "extreme" (O-depleted, Na and Al-rich) populations in the cluster. The primordial population stars in both omega Centauri and M4 show (25Mg, 26Mg)/24 Mg isotopic ratios that are consistent with those found for the primordial population in other globular clusters with similar [Fe/H] values. The isotopic ratios for the omega Centauri extreme stars are also consistent with those for extreme population stars in other clusters. The results for the extreme population stars studied indicate that the 26Mg/24Mg ratio is highest at intermediate metallicities ([Fe/H] < --1.4 dex), and for the highest [Al/Fe] values. Further, the relative abundance of 26Mg in the extreme population stars is notably higher than that of 25Mg, in contrast to model predictions. The 25Mg/24Mg isotopic ratio in fact does not show any obvious dependence on either [Fe/H] or [Al/Fe] nor...

Multiple Stellar Populations in the Globular Cluster omega Centauri as Tracers of a Merger Event

Lee, Young-Wook; Joo, Jong-Myung; Sohn, Young-Jong; Rey, Soo-Chang; Lee, Hyun-chul; Walker, Alistair
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 09/11/1999
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The discovery of the Sagittarius dwarf galaxy, which is being tidally disrupted by and merging with the Milky Way, supports the view that the halo of the Galaxy has been built up at least partially by the accretion of similar dwarf systems. The Sagittarius dwarf contains several distinct populations of stars, and includes M54 as its nucleus, which is the second most massive globular cluster associated with the Milky Way. The most massive globular cluster is omega Centauri, and here we report that omega Centauri also has several distinct stellar populations, as traced by red-giant-branch stars. The most metal-rich red-giant-branch stars are about 2 Gyr younger than the dominant metal-poor component, indicating that omega Centauri was enriched over this timescale. The presence of more than one epoch of star formation in a globular cluster is quite surprising, and suggests that omega Centauri was once part of a more massive system that merged with the Milky Way, as the Sagittarius dwarf galaxy is in the process of doing now. Mergers probably were much more frequent in the early history of the Galaxy and omega Centauri appears to be a relict of this era.; Comment: 7 pages, 3 figures, Latex+nature.sty (included), To appear in November 4th issue of Nature

Formation of Omega Centauri by Tidal Stripping of a Dwarf Galaxy

Ideta, Makoto; Makino, Junichiro
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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We have investigated whether or not a tidal stripping scenario can reproduce the observed surface-brightness profile of omega Centauri using N-body simulations. Assuming that the progenitor of omega Centauri is a dwarf elliptical galaxy, we model it with a King model with a core radius being the same as that of omega Centauri. A dark matter halo of the dwarf is not taken into account. We consider two different models of the Milky Way potential: a singular isothermal sphere and a three-component model. The progenitor dwarf is expressed as an N-body system, which orbits in the fixed Galactic potential. The dwarf lost more than 90 per cent of its mass during the first few pericenter passages. Thereafter, the mass remains practically constant. The final surface-density profile is in good agreement with the observational data on omega Centauri, if the pericenter distance of the orbit of the progenitor dwarf is around 500 pc. This value is within the error bar of the current proper motion data on omega Centauri and Galactic parameters. Although our simulation is limited to a King-like progenitor dwarf without a dark matter halo, it strongly suggests that the current density profile of omega Centauri is nicely reproduced by a tidal stripping scenario...

A Determination of the Chemical Composition of Alpha Centauri A from Strong Lines

Hathi, Nimish P.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 09/08/2004
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Using the theory of collisional line broadening developed by Anstee and O'Mara (1991, 1995) and the spectrum synthesis software developed by John Ross, the abundances of Fe, Mg, Ca and Na in Alpha Centauri A are determined from strong lines. The abundances are approximately 0.2 dex higher than in the Sun. The derived abundances are independent of non-thermal motions in the atmosphere of Alpha Centauri A. The microturbulence obtained from medium-strong lines using the abundances obtained from the strong lines is 1.34 +/- 0.12 km/s, i.e., 0.20 km/s larger than in the Sun, which is fully consistent with the lower surface gravity of Alpha Centauri A. This microturbulence can then be used in determination of the abundance of other elements for which there are no strong lines in the spectrum. This thesis is the first application of this theory to determine abundances and the microturbulence of Alpha Centauri A. Recent results are published by Doyle et al.(astro-ph/0407468); Comment: Master's Thesis (UQ, Brisbane, 1997). 57 pages, 7 figures

RAVE stars tidally stripped/ejected from $\omega$ Centauri globular cluster

Fernández-Trincado, J. G.; Robin, A. C.; Vieira, K.; Moreno, E.; Bienaymé, O.; Reylé, C.; Valenzuela, O.; Pichardo, B.; Robles-Valdez, F.; Martins, A. M. M.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 12/08/2015
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Using six-dimesional phase-space information from the Fourth Data release of the Radial Velocity Experiment (RAVE) over the range of Galactic longitude 240$^{\circ}< l <$ 360$^{\circ}$ and $V_{LSR} < -239$ kms$^{-1}$, we have computed orbits for 329 RAVE stars that were originally selected as chemically and kinematically related to $\omega$ Centauri. The orbits were integrated in a Milky-Way-like axisymmetric Galactic potential, ignoring the effects of the dynamical evolution of $\omega$ Centauri due to the tidal effects of the Galaxy disk on the cluster along time. We also ignored secular changes in the Milky Way potential over time. In a Monte Carlo scheme, and under the assumption that the stars may have been ejected with velocities greater than the escape velocity ($V_{rel}>V_{esc,0}$) from the cluster, we identified 15 stars as having close encounters with $\omega$ Centauri: (\textit{i}) 8 stars with relative velocities $V_{rel}< 200 $ kms$^{-1}$ may have been ejected $\sim$ 200 Myr ago from $\omega$ Centauri; (\textit{ii}) other group of 7 stars were identified with high relative velocity $V_{rel}> 200 $ kms$^{-1}$ during close encounters, and seems unlikely that they have been ejected from $\omega$ Centauri. We also confirm the link between J131340.4-484714 as potential member of $\omega$ Centauri...

Oscillations in the Habitable Zone around Alpha Centauri B

Forgan, Duncan
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 06/02/2012
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The Alpha Centauri AB system is an attractive one for radial velocity observations to detect potential exoplanets. The high metallicity of both Alpha Centauri A and B suggest that they could have possessed circumstellar discs capable of forming planets. As the closest star system to the Sun, with well over a century of accurate astrometric measurements (and Alpha Centauri B exhibiting low chromospheric activity) high precision surveys of Alpha Centauri B's potential exoplanetary system are possible with relatively cheap instrumentation. Authors studying habitability in this system typically adopt habitable zones (HZs) based on global radiative balance models that neglect the radiative perturbations of Alpha Centauri A. We investigate the habitability of planets around Alpha Centauri B using 1D latitudinal energy balance models (LEBMs), which fully incorporate the presence of Alpha Centauri A as a means of astronomically forcing terrestrial planet climates. We find that the extent of the HZ is relatively unchanged by the presence of Alpha Centauri A, but there are variations in fractional habitability for planets orbiting at the boundaries of the zone due to Alpha Centauri A, even in the case of zero eccentricity. Temperature oscillations of a few K can be observed at all planetary orbits...

The stellar dynamics of ω[omega] Centauri

Merritt, David; Meylan, Georges; Mayor, Michel
Fonte: Astronomical Journal Publicador: Astronomical Journal
Tipo: Artigo de Revista Científica Formato: 579432 bytes; application/pdf
EN_US
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The stellar dynamics of ω[omega] Centauri are inferred from the radial velocities of 469 stars measured with CORAVEL (Mayor et al. 1997). Rather than fit the data to a family of models, we generate estimates of all dynamical functions nonparametrically, by direct operation on the data. The cluster is assumed to be oblate and edge-on but mass is not assumed to follow light. The mean motions are consistent with axisymmetry but the rotation is not cylindrical. The peak rotational velocity is 7.9 km s−1 at ∼ 11 pc from the center. The apparent rotation of ω[omega] Centauri is attributable in part to its proper motion. We reconstruct the stellar velocity ellipsoid as a function of position, assuming isotropy in the meridional plane. We find no significant evidence for a difference between the velocity dispersions parallel and perpendicular to the meridional plane. The mass distribution inferred from the kinematics is slightly more extended than, though not strongly inconsistent with, the luminosity distribution. We also derive the two-integral distribution function f(E, Lz) implied by the velocity data. (Refer to PDF file for exact formulas).; Also archived in: arXiv:astro-ph/9612184 v1 18 Dec 1996 AND Rutgers Astrophysics Preprint Series No. 205; This work was supported by NSF grant AST 90-16515 and NASA grant NAG 5-2803 to DM.

The Evolution of Copper in the Globular Cluster Omega Centauri

Cunha, Katia; Smith, Verne V; Suntzeff, Nicholas B; Norris, John; Da Costa, Gary; Plez, Bertrand
Fonte: University of Chicago Press Publicador: University of Chicago Press
Tipo: Artigo de Revista Científica
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Copper abundances are presented for 40 red giant members of the massive Galactic globular cluster ω Centauri, as well as 15 red giant members of the globular clusters NGC 288, NGC 362, NGC 3201, NGC 6752, and M4 (NGC 6121). The spectra are of relatively