Na-O anticorrelation and horizontal branches

Gratton, R.; Lucatello, S.; Bragaglia, A.; Carretta, E.; Cassisi, S.; Momany, Y.; Pancino, E.; Valenti, E.; Caloi, V.; Claudi, R.; D’Antona, Francesca; Desidera, S.; François, P.; James, G.; Moehler, S.; Ortolani, S.; Pasquini, L.; Piotto, G.; Recio–Blanco, A.

doi:10.1051/0004-6361:20066061

Cited by 85 publications

(80 citation statements)

References 55 publications

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“…The data analysis has already been described in detail elsewhere (Carretta et al 2006(Carretta et al , 2007aGratton et al 2006Gratton et al , 2007Carretta et al 2009a,b) and will not be repeated here. Only a few procedures will be briefly summarised here.…”

Section: The Dataset and Analysismentioning

confidence: 99%

Intrinsic iron spread and a new metallicity scale for globular clusters

Carretta¹,

Bragaglia²,

Gratton

et al. 2009

A&A

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665

773

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We have collected spectra of about 2000 red giant branch (RGB) stars in 19 Galactic globular clusters (GC) using FLAMES@VLT (about 100 stars with GIRAFFE and about 10 with UVES, respectively, in each GC). These observations provide an unprecedented, precise, and homogeneous data-set of Fe abundances in GCs. We use it to study the cosmic scatter of iron and find that, as far as Fe is concerned, most GCs can still be considered mono-metallic, since the upper limit to the scatter of iron is less than 0.05 dex, meaning that the degree of homogeneity is better than 12%. The scatter in Fe we find seems to have a dependence on luminosity, possibly due to the well-known inadequacies of stellar atmospheres for upper-RGB stars and/or to intrinsic variability. It also seems to be correlated with cluster properties, like the mass, indicating a larger scatter in more massive GCs which is likely a (small) true intrinsic scatter. The 19 GCs, covering the metallicity range of the bulk of Galactic GCs, define an accurate and updated metallicity scale. We provide transformation equations for a few existing scales. We also provide new values of [Fe/H], on our scale, for all GCs in the Harris catalogue.

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Section: The Dataset and Analysismentioning

confidence: 99%

Intrinsic iron spread and a new metallicity scale for globular clusters

Carretta¹,

Bragaglia²,

Gratton

et al. 2009

A&A

Self Cite

665

773

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show abstract

“…The first evidence rests on the chemical analysis that reveals large star-to-star abundance variations in light elements in all individual clusters studied so far, while the iron abundance stays constant (for a review see Gratton et al 2004). This includes the well-documented anticorrelations between C-N, O-Na, Mg-Al, Li-Na, and F-Na (Kraft 1994;Carretta et al 2006Carretta et al , 2007Carretta et al , 2009Gratton et al 2007;Pasquini et al 2007;Bonifacio et al 2007;Lind et al 2009). This global chemical pattern requires H-burning at high temperatures around 75 ×10 6 K (Arnould et al 1999;Prantzos et al 2007).…”

Section: Introductionmentioning

confidence: 97%

Evolution of two stellar populations in globular clusters

Decressin¹,

Baumgardt²,

Charbonnel

et al. 2010

A&A

128

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Aims. We investigate the early evolution of two distinct populations of low-mass stars in globular clusters under the influence of primordial gas expulsion driven by supernovae and study whether this process can increase the fraction of second generation stars at the level required by observations. Methods. We analyse N-body models that take the effect of primordial gas expulsion into account. We divide the stars into two populations that mimic the chemical and dynamical properties of stars in globular clusters so that second-generation stars start with a more centrally concentrated distribution. Results. The main effect of gas expulsion is to eject mostly first-generation stars while second-generation stars remain bound to the cluster. In the most favourable cases, second-generation stars can account for 60% of the bound stars we see today. We also find that, at the end of the gas expulsion phase, the radial distribution of the two populations is still different, so that long-term evolution will further increase the fraction of second generation stars. Conclusions. The large fraction of chemically anomalous stars is readily explainable as a second generation of stars formed out of the slow winds of rapidly rotating massive stars if globular clusters suffer explosive residual gas expulsion for a star formation efficiency of about 0.33.

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“…In Carretta et al (2007a, Paper II) we analysed NGC 6752, a cluster with a long blue HB and a relatively modest extension of the Na-O anticorrelation. Three papers (Gratton et al , 2007Carretta et al 2007b -Papers III, V, and VI, respectively), focused on the two peculiar bulge clusters NGC 6441 and NGC 6388. Paper IV (Carretta et al 2007c) dealt with the analysis of the Na-O anticorrelation in NGC 6218 and the first detection of a He-poor/Herich stellar population among giant stars in GCs.…”

Section: Introductionmentioning

confidence: 99%

Na-O anticorrelation and HB

Carretta¹,

Bragaglia²,

Gratton

et al. 2009

A&A

Self Cite

724

851

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We present abundances of Fe, Na, and O for 1409 red giant stars in 15 galactic globular clusters (GCs), derived from the homogeneous analysis of high-resolution FLAMES/GIRAFFE spectra. Combining the present data with results from our FLAMES/UVES spectra and from previous studies within the project, we obtained a total sample of 1958 stars in 19 clusters, the largest and most homogeneous database of this kind to date. The programme clusters cover a range in metallicity from [Fe/H] = −2.4 dex to [Fe/H] = −0.4 dex, with a wide variety of global parameters (morphology of the horizontal branch, mass, concentration, etc.). For all clusters we find the Na-O anticorrelation, the classical signature of the operation of proton-capture reactions in H-burning at high temperature in a previous generation of more massive stars that are now extinct. Using quantitative criteria (from the morphology and extension of the Na-O anticorrelation), we can define three different components of the stellar population in GCs. We separate a primordial component (P) of first-generation stars, and two components of second-generation stars, that we name intermediate (I) and extreme (E) populations from their different chemical composition. The P component is present in all clusters, and its fraction is almost constant at about one third. The I component represents the bulk of the cluster population. On the other hand, E component is not present in all clusters, and it is more conspicuous in some (but not in all) of the most massive clusters. We discuss the fractions and spatial distributions of these components in our sample and in two additional clusters (M 3 = NGC 5272 and M 13 = NGC6205) with large sets of stars analysed in the literature. We also find that the slope of the anti-correlation (defined by the minimum O and maximum Na abundances) changes from cluster-to-cluster, a change that is represented well by a bilinear relation on cluster metallicity and luminosity. This second dependence suggests a correlation between average mass of polluters and cluster mass.

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Na-O anticorrelation and horizontal branches

Cited by 85 publications

References 55 publications

Intrinsic iron spread and a new metallicity scale for globular clusters

Intrinsic iron spread and a new metallicity scale for globular clusters

Evolution of two stellar populations in globular clusters

Na-O anticorrelation and HB

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