Mixed Populations in Globular Clusters: Et Tu, 47 Tuc?

Anderson, Jay; Piotto, G.; King, I. R.; Bedin, L. R.; Guhathakurta, Puragra

doi:10.1088/0004-637x/697/1/l58

Cited by 141 publications

(206 citation statements)

References 16 publications

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“…Finally, if the observed broadening of the MS in 47 Tuc is interpreted in terms of helium variation, homology relations reproduce the measured Δ log T eff = 0.003 with ΔY = 0.023, again close to the conclusion based on isochrones (Anderson et al 2009). …”

Section: Application To Globular Clusterssupporting

confidence: 85%

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Revisiting the helium abundance in globular clusters with multiple main sequences

2009

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Abstract. For nearby K dwarfs, the broadening of the observed Main Sequence at low metallicities is much narrower than expected from isochrones with the standard helium-to-metal enrichment ratio ΔY /ΔZ ∼ 2. A much higher value, of order 10, is formally needed to reproduce the observed broadening, but it returns helium abundances in awkward contrast with Big Bang Nucleosynthesis. This steep enrichment ratio resembles, on a milder scale, the very high ΔY /ΔZ estimated from the multiple Main Sequences observed in some metal-poor Globular Clusters. We argue that a revision of low Main Sequence stellar models, suggested from nearby stars, could help to reduce the overwhelmingly high ΔY /ΔZ deduced so far for those clusters. Under the most favourable assumptions, the estimated helium content for the enriched populations may decrease from Y 0.4 to as low as Y 0.3, with intermediate values being plausible.

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Section: Application To Globular Clusterssupporting

confidence: 85%

“…Recent observations also seem to support a MS broadening in 47 Tuc (Anderson et al 2009 Casagrande et al (2006) to translate the dereddened maximum observed colour split between the bMS and rMS returns Δ log T eff = 0.0185 implying ΔY = 0.144 and Y bMS = 0.39 (Fig. 2).…”

Section: Application To Globular Clustersmentioning

confidence: 78%

Revisiting the helium abundance in globular clusters with multiple main sequences

2009

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“…The studies by Milone and collaborators include: NGC 1851 (Milone et al 2008), 47 Tuc (Anderson et al 2009;Milone et al 2012), NGC 6388 and (maybe) NGC 6441 (Bellini et al 2013), NGC 362, NGC 5286, NGC 6656, NGC 6715, andNGC 7089 (Piotto et al 2012).…”

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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“…We are aware that very high quality photometric data for 47 Tuc show the possible presence of multipopulation from the analysis of the subgiant branch (see e.g. Anderson et al 2009), however, a discussion of this problem is beyond the scope of the present paper.…”

Section: Comparison With Observational Datamentioning

confidence: 94%

The Pisa Stellar Evolution Data Base for low-mass stars

Dell’Omodarme

Valle

Degl’Innocenti

et al. 2012

A&A

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Context. The last decade showed an impressive observational effort from the photometric and spectroscopic point of view for ancient stellar clusters in our Galaxy and beyond, leading to important and sometimes surprising results. Aims. The theoretical interpretation of these new observational results requires updated evolutionary models and isochrones spanning a wide range of chemical composition so that the possibility of multipopulations inside a stellar cluster is also taken also into account. Methods. With this aim we built the new "Pisa Stellar Evolution Database" of stellar models and isochrones by adopting a welltested evolutionary code (FRANEC) implemented with updated physical and chemical inputs. In particular, our code adopts realistic atmosphere models and an updated equation of state, nuclear reaction rates and opacities calculated with recent solar elements mixture. Results. A total of 32 646 models have been computed in the range of initial masses 0.30 ÷ 1.10 M for a grid of 216 chemical compositions with the fractional metal abundance in mass, Z, ranging from 0.0001 to 0.01, and the original helium content, Y, from 0.25 to 0.42. Models were computed for both solar-scaled and α-enhanced abundances with different external convection efficiencies. Correspondingly, 9720 isochrones were computed in the age range 8÷15 Gyr, in time steps of 0.5 Gyr. The whole database is available to the scientific community on the web. Models and isochrones were compared with recent calculations available in the literature and with the color-magnitude diagram of selected Galactic globular clusters. The dependence of relevant evolutionary quantities, namely turn-off and horizontal branch luminosities, on the chemical composition and convection efficiency were analyzed in a quantitative statistical way and analytical formulations were made available for reader's convenience. These relations can be useful in several fields of stellar evolution, e.g. evolutionary properties of binary systems, synthetic models for simple stellar populations and for star counts in galaxies, and chemical evolution models of galaxies.

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Mixed Populations in Globular Clusters: Et Tu, 47 Tuc?

Cited by 141 publications

References 16 publications

Revisiting the helium abundance in globular clusters with multiple main sequences

Revisiting the helium abundance in globular clusters with multiple main sequences

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

The Pisa Stellar Evolution Data Base for low-mass stars

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