Stromgren Photometry of Galactic Globular Clusters. I. New Calibrations of the Metallicity Index

Calamida, A.; Bono, G.; Stetson, P. B.; Freyhammer, L. M.; Cassisi, S.; Grundahl, F.; Pietrinferni, A.; Hilker, M.; Primas, F.; Richtler, T.; Romaniello, M.; Buonanno, R.; Caputo, F.; Castellani, M.; Corsi, C. E.; Ferraro, I.; Iannicola, G.; Pulone, L.

doi:10.1086/521424

Cited by 66 publications

(143 citation statements)

References 77 publications

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“…These GCs also behave differently for what concerns Ba abundances. To show this, we used the Johnson UBVI photometry by Momany (unpublished photometry, reduced as in Momany et al 2003) for 47 Tuc and the Strömgren photometry by Grundahl for NGC 6752 (Calamida et al 2007) to reproduce the clear splits shown by Milone et al (2012Milone et al ( , 2013. We took the Ba abundances from D 'Orazi et al (2010), cross-identified the stars, and plotted the ones in common in Fig.…”

Section: Discussionmentioning

confidence: 99%

NGC 362: another globular cluster with a split red giant branch

Carretta

Bragaglia

Gratton

et al. 2013

A&A

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We obtained FLAMES GIRAFFE+UVES spectra for both first-and second-generation red giant branch (RGB) stars in the globular cluster (GC) NGC 362 and used them to derive abundances of 21 atomic species for a sample of 92 stars. The surveyed elements include proton-capture (O, Na, Mg, Al, Si), α-capture (Ca, Ti), Fe-peak (Sc, V, Mn, Co, Ni, Cu), and neutron-capture elements (Y, Zr, Ba, La, Ce, Nd, Eu, Dy). The analysis is fully consistent with that presented for twenty GCs in previous papers of this series. Stars in NGC 362 seem to be clustered into two discrete groups along the Na-O anti-correlation with a gap at [O/Na] ∼ 0 dex. Na-rich, second generation stars show a trend to be more centrally concentrated, although the level of confidence is not very high. When compared to the classical second-parameter twin NGC 288 with similar metallicity but different horizontal branch type and a much lower total mass, the proton-capture processing in stars of NGC 362 seems to be more extreme, confirming previous analysis. We discovered the presence of a secondary RGB sequence, which is redder than the bulk of the RGB. A preliminary estimate shows that this sequence comprises about 6% of RGB stars. Our spectroscopic data and literature photometry indicate that this sequence is populated almost exclusively by giants rich in Ba and is probably rich in all s-process elements, as found in other clusters. In this regard, NGC 362 joins previously studied GCs like NGC 1851, NGC 6656 (M 22), and NGC 7089 (M 2).

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Section: Discussionmentioning

confidence: 99%

NGC 362: another globular cluster with a split red giant branch

Carretta

Bragaglia

Gratton

et al. 2013

A&A

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“…7). -We used literature photometry in u, b, v, and y Strömgren bands (Grundahl et al 1999;Calamida et al 2007) to define a new color index ((u − y) + (v − b)). We found that the u versus (u − y) + (v − b) diagram is a powerful tool to identify the double RGB and SGB of NGC 1851 and showed that the faint-SGB is clearly connected with the red-RGB, while blue-RGB stars are linked to the bright-SGB (Fig.…”

Section: Summary and Discussionmentioning

confidence: 99%

“…The resulting photometry was calibrated using stars in common with the V, I Bellazzini et al (2001) catalog, covering an 8 × 8 field centered on the cluster. We also used publicly available Strömgren u, v, b, y photometry 1 of NGC 1851 from Grundahl et al (1999) and Calamida et al (2007). We refer the reader to that paper for details about observations and data reduction of Ströemgren photometry.…”

Section: Source Catalogs and Sample Selectionmentioning

confidence: 99%

C and N abundances of main sequence and subgiant branch stars in NGC 1851

Lardo

Milone

Marino

et al. 2012

A&A

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We present the first chemical analysis of stars on the double subgiant branch (SGB) of the globular cluster NGC 1851. We obtained 48 Magellan IMACS spectra of subgiants and fainter stars covering the spectral region between 3650-6750 Å to derive C and N abundances from the spectral features at 4300 Å (G-band) and at ∼3883 Å (CN). We added to our sample ∼45 unvevolved stars previously observed with FORS2 at the VLT. These two datasets were homogeneously reduced and analyzed. We derived abundances of C and N for a total of 64 stars and found considerable star-to-star variations in both [C/H] and [N/H] at all luminosities extending to the red giant branch (RGB) base (V ∼ 18.9). These abundances appear to be strongly anticorrelated, as would be expected from the CN-cycle enrichment, but we did not detect any bimodality in the C or N content. We used Hubble space telescope (HST) and ground-based photometry to select two groups of faint-and bright-SGB stars from the visual and Strömgren color-magnitude diagrams. Significant variations in the carbon and nitrogen abundances are present among stars of each group, which indicates that each SGB hosts multiple subgenerations of stars. Bright-and faint-SGB stars differ in the total C+N content, where the fainter SGB have about 2.5 times the C+N content of the brighter ones. Coupling our results with literature photometric data and abundance determinations from highresolution studies, we identify the fainter SGB with the red-RGB population, which also should be richer on average in Ba and other s-process elements, as well as in Na and N, when compared to brighter SGB and the blue-RGB population.

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“…To supplement this evidence, we used the Strömgren photometry by Grundahl (available through the database used by Calamida et al 2007) to plot the stars of the P, I, and E components in NGC 1851. The definition of the primordial (P), intermediate (I), and extreme (E) population in a cluster, based on 8 Note that the analysis considered here for ω Cen (Johnson & Pilachowski 2010) is not strictly consistent with the other determinations shown in the plot, which come from our FLAMES survey.…”

Section: The Complex Nucleosynthesis In Ngc 1851mentioning

confidence: 99%

Multiple stellar populations in the globular cluster NGC 1851

Carretta

Lucatello

Gratton

et al. 2011

A&A

163

278

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We present a detailed chemical tagging of individual stellar populations in the Galactic globular cluster (GC) NGC 1851. Abundances are derived from FLAMES spectra for the largest sample of giants (124) and the most extensive number of elements ever analysed in this peculiar GC. The chemistry is characterised using homogeneous abundances of proton-capture (O, Na, Mg, Al, Si), α-capture (Ca, Ti), Fe-peak (Sc, V, Mn, Co, Ni, Cu), and neutron-capture elements (Y, Zr, Ba, La, Ce, Nd, Eu, Dy). We confirm the presence of an [Fe/H] spread larger than the observational errors in this cluster, but too small to clearly separate different sub-populations. We instead propose a classification scheme using a combination of Fe and Ba (which is much more abundant in the more metal-rich group) by means of a cluster analysis. With this approach, we separated stars into two components of a metal-rich (MR) and a metal-poor (MP) population. Each component displays a Na-O anticorrelation, which is a signature of a genuine GC, but has different ratios of primordial (FG) to polluted (SG) stars. Moreover, clear (anti)correlations of Mg and Si with Na and O are found for each component. The level of [α/H] tracks iron and is higher in the MR population, which might therefore have received an additional contribution from core-collapse supernovae. When considering all s-process elements, the MR population shows a larger enrichment than the MP one. This is probably due to the contribution of intermediate-low mass stars, because we find that the level of heavy s-process elements is higher than that of light s-process nuclei in the MR stars; however, a large contribution from low mass stars is unlikely, because it would likely cancel the O-Na anticorrelation. Finally, we confirm the presence of correlations between the amount of proton-capture elements and the level of s-process elements previously found by other investigations, at least for the MR population. This finding apparently requires a quite long delay for the second generation of the MR component. Scenarios for the formation of NGC 1851 appear complex, and are not yet well understood. A merger of two distinct GCs in a parent dwarf galaxy, each cluster with a different Ba level and an age difference of ∼1 Gyr, might explain (i) the double subgiant branch; (ii) a possible difference in C content between the two original GCs; and (iii) the Strömgren photometry of this peculiar cluster. However, the correlation existing between p-capture and n-capture elements within the MR population requires the additional assumption of a long delay for its second generation. More observations are required to fully understand the formation of this GC.

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Stromgren Photometry of Galactic Globular Clusters. I. New Calibrations of the Metallicity Index

Cited by 66 publications

References 77 publications

NGC 362: another globular cluster with a split red giant branch

NGC 362: another globular cluster with a split red giant branch

C and N abundances of main sequence and subgiant branch stars in NGC 1851

Multiple stellar populations in the globular cluster NGC 1851

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