Chemical Evolution Of Globular Clusters Research Articles

A Study of the λ10830 He I Line Among Red Giants in Messier 13 1 1The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial

Two properties of Messier 13 are pertinent to the study of mass loss among metal-poor stars and the chemical evolution of globular clusters: (1) an extended blue horizontal branch, which seems to demand mass loss from red giant progenitor stars and possibly an enhanced helium abundance, and (2) the presence of internal abundance inhomogeneities of elements in the mass range from C to Al. A popular explanation for this second phenomenon is that M13 was self-enriched by intermediate-mass asymptotic giant branch (IM-AGB) stars of a type that may also have been able to instigate helium enrichment. Spectra of the λ10830 absorption feature produced by He I have been obtained by using the NIRSPEC spectrometer on the Keck 2 telescope for seven red giants in M13 chosen to have a range in λ3883 CN band strengths, oxygen, and sodium abundances. Whereas these spectra do reveal the presence of fast winds among some M13 red giants, they provide little support for helium abundance differences of the type that might have been generated by a burst of IM-AGB star activity within the M13 protocluster.

The effect of intermediate-mass close binaries on the chemical evolution of globular clusters

Context. The chemical processes during the Asymptotic Giant Branch (AGB) evolution of intermediate mass single stars predict most of the observations of the different populations in globular clusters although some important issues still need to be further clarified. In particular, to reproduce the observed anticorrelations of Na-O and Al-Mg, chemically enriched gas lost during the AGB phase of intermediate mass single stars must be mixed with matter with a pristine chemical composition. The source of this matter is still a matter of debate. Furthermore, observations reveal that a significant fraction of the intermediate mass and massive stars are born as components of close binaries. Aims. We will investigate the effects of binaries on the chemical evolution of Globular Clusters and on the origin of matter with a pristine chemical composition that is needed for the single star AGB scenario to work Methods. We use a population synthesis code that accounts for binary physics in order to estimate the amount and the composition of the matter returned to the interstellar medium of a population of binaries. Results. We demonstrate in the present paper that the mass lost by a significant population of intermediate mass close binaries in combination with the single star AGB pollution scenario may help to explain the chemical properties of the different populations of stars in Globular Clusters.

The chemical evolution of globular clusters - II. Metals and fluorine

In the first paper of this series, we proposed a new framework in which to model the chemical evolution of globular clusters. This model is predicated upon the assumption that clusters form within an interstellar medium enriched locally by the ejecta of a single Type Ia supernova and varying numbers of asymptotic giant branch stars, superimposed on an ambient medium pre-enriched by low-metallicity Type II supernovae. Paper I was concerned with the application of this model to the observed abundances of several reactive elements and so-called non-metals for three classical intermediate-metallicity clusters, with the hallmark of the work being the successful recovery of many of their well-known elemental and isotopic abundance anomalies. Here, we expand upon our initial analysis by (i) applying the model to a much broader range of metallicities (from the factor of 3 explored in Paper I, to now a factor of ∼50; i.e. essentially, the full range of Galactic globular cluster abundances; and (ii) incorporating a broader suite of chemical species, including a number of iron-peak isotopes, heavier α-elements and fluorine. While allowing for an appropriate fine-tuning of the model input parameters, most empirical globular cluster abundance trends are reproduced; our model would suggest the need for a higher production of calcium, silicon and copper in low-metallicity (or so-called ‘prompt’) Type Ia supernovae than predicted in current stellar models in order to reproduce the observed trends in NGC 6752, and a factor of 2 reduction in carbon production from asymptotic giant branch stars to explain the observed trends between carbon and nitrogen. Observations of heavy-element isotopes produced primarily by Type Ia supernovae, including those of titanium, iron and nickel, could support/refute unequivocally our proposed framework, although currently the feasibility of the proposed observations is well beyond current instrumental capabilities. Hydrodynamical simulations would be necessary to study its viability from a dynamical point of view.

Mining SDSS in search of multiple populations in globular clusters

Several recent studies have reported the detection of an anomalous color spread along the red giant branch (RGB) of some globular clusters (GC) that appears only when color indices including a near ultraviolet band (such as Johnson U or Stromgren u) are considered. This anomalous spread in color indexes such as U-B or c_{y} has been shown to correlate with variations in the abundances of light elements such as C, N, O, Na, etc., which, in turn, are generally believed to be associated with subsequent star formation episodes that occurred in the earliest few 10^{8} yr of the cluster's life. Here we use publicly available u, g, r Sloan Digital Sky Survey photometry to search for anomalous u-g spreads in the RGBs of nine Galactic GCs. In seven of them (M 2, M 3, M 5, M 13, M 15, M 92 and M 53), we find evidence of a statistically significant spread in the u-g color, not seen in g-r and not accounted for by observational effects. In the case of M 5, we demonstrate that the observed u-g color spread correlates with the observed abundances of Na, the redder stars being richer in Na than the bluer ones. In all the seven clusters displaying a significant u-g color spread, we find that the stars on the red and blue sides of the RGB, in (g, u-g) color magnitude diagrams, have significantly different radial distributions. In particular, the red stars (generally identified with the second generation of cluster stars, in the current scenario) are always more centrally concentrated than blue stars (generally identified with the first generation) over the range sampled by the data (0.5r_{h} < r < 5r_{h}), in qualitative agreement with the predictions of some recent models of the formation and chemical evolution of GCs. Our results suggest that the difference in the radial distribution between first and second generation stars may be a general characteristic of GCs.

An AKARI Search for Intracluster Dust of Globular Clusters

Abstract We report on observations of 12 globular clusters with the Far-Infrared Surveyor (FIS) aboard the AKARI satellite. Our goal is to search for emission from cold dust within clusters. We detected diffuse emissions toward NGC6402 and 2808, but the IRAS 100$\mu$m maps show the presence of strong background radiation. They are likely to have been emitted from the Galactic cirrus. We also detected 28 point-like sources mainly in WIDE-S images (90$\micron$). At least several of them are not associated with clusters, but background galaxies identified in external catalogs. We present the spectral energy distributions (SEDs) by combining near-and-mid infrared data obtained with the Infrared Camera (IRC), if possible. Those SEDs suggest that most of the point sources are background galaxies. For most of the other clusters, we have confirmed a lack of intracluster dust. We evaluated the upper limits of the intracluster dust mass to be between 10$^{-5}$ and 10$^{-3}\MO$, depending on the dust temperature. The inferred lifetime of the intracluster dust is shorter than 5Myr ($T_{\mathrm{d}}$$=$ 70K) or 50Myr (35K). Such a short lifetime indicates some mechanism(s) are at work to remove the intracluster dust. We also discuss its impact on the chemical evolution of globular clusters.

Formation of Massive Black Holes in Globular Clusters

The hydrodynamic formation of massive black holes (BHs) in globular clusters is considered. In particular, we examine the possibility of BH formation induced by the radiation drag that is exerted on the interstellar matter by stellar radiation in globular clusters. The radiation drag extracts angular momentum from interstellar gas and thus allows the gas to accrete onto the cluster center. By incorporating the realistic chemical evolution of globular clusters, we scrutinize the efficiency of the radiation drag to assess the total accreted mass. As a result, we find that if a globular cluster is more massive than ≈6 × 106 M☉ in the present-day stellar component, a massive BH with >260 M☉ can form within it. But the BH-to-cluster mass ratio is considerably smaller than the BH-to-bulge mass ratio (≈10-3) found in galactic bulges. The results are not sensitive to the assumed stellar initial mass function and star formation rate in the cluster, as long as the resulting color-magnitude relation, metallicity, and mass-to-luminosity ratio satisfy those observed in globular clusters. Hence, the putative linear relation between BH mass and bulge mass (MBH-Mbulge relation) cannot be extrapolated to globular cluster systems. In the present regime, we discuss the BH formation in M15, G1, ω Cen, the M33 nucleus, and the compact X-ray sources in M82. Finally, we discuss observational indications of the formation process of massive BHs in globular clusters. We find that the final phase of BH growth due to the radiation drag can be observed as ultraluminous X-ray sources (ULXs) with ~1041 ergs s-1.

Formation of Massive Black Holes in Globular Clusters

The hydrodynamic formation of massive black holes (BHs) in globular clusters is considered. In particular, we examine the possibility of BH formation induced by the radiation drag that is exerted on the interstellar matter by stellar radiation in globular clusters. The radiation drag extracts angular momentum from interstellar gas and thus allows the gas to accrete onto the cluster center. By incorporating the realistic chemical evolution of globular clusters, we scrutinize the efficiency of the radiation drag to assess the total accreted mass. As a result, we find that if a ½�

On the evolution of lithium 7 in globular clusters

view Abstract Citations (7) References (35) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the Evolution of Lithium 7 in Globular Clusters Vangioni-Flam, Elisabeth ; Casse, Michel ; Oberto, Yvette Abstract The inhomogeneous big-bang models flourishing presently in the literature predict that the primordial mass fraction of Li-7 could reach 10 to the -7th, whereas the observed value in unevolved halo stars is about 6 x 10 to the -10th, in marked contrast. Using a simple model of chemical evolution of globular clusters, it is shown that these results cannot be reconciled: Li-7 is unsignificantly depleted in the cluster gas during the limited time of star formation, whereas the abundance of Fe, originating from relatively massive and short-lived stars increases by two orders of magnitude. The observed constancy of log (Li/H) versus (Fe/H) is thus reproduced. Publication: The Astrophysical Journal Pub Date: February 1990 DOI: 10.1086/168337 Bibcode: 1990ApJ...349..510V Keywords: Globular Clusters; Lithium; Metallicity; Stellar Evolution; Nuclear Fusion; Stellar Composition; Stellar Luminosity; Astrophysics; CLUSTERS: GLOBULAR; LUMINOSITY FUNCTION; NUCLEOSYNTHESIS; STARS: ABUNDANCES; STARS: EVOLUTION full text sources ADS | data products SIMBAD (1)