A LARGE STELLAR EVOLUTION DATABASE FOR POPULATION SYNTHESIS STUDIES. V. STELLAR MODELS AND ISOCHRONES WITH CNONa ABUNDANCE ANTICORRELATIONS

Pietrinferni, A.; Cassisi, S.; Salaris, Maurizio; Percival, S. M.; Ferguson, Jason W.

doi:10.1088/0004-637x/697/1/275

Cited by 138 publications

(165 citation statements)

References 47 publications

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“…5). Although the influence of initial helium abundance on the stellar properties has already been extensively described in the literature (e.g., Iben & Faulkner 1968;Iben & Rood 1969;Demarque et al 1971;Sweigart 1978;D'Antona et al 2005;Caloi & D'Antona 2007;Salaris & Cassisi 2005;Maeder 2009;Pietrinferni et al 2009;Sbordone et al 2011;Valcarce et al 2012;Cassisi et al 2013;Kippenhahn et al 2013), to our knowledge this is the first investigation of the impact of helium content higher than ∼0.42 on the whole evolution (from the pre-main sequence to the end of the AGB phase) at low [Fe/H], and for such a broad mass range 4 .…”

Section: Objectives Of the Present Series Of Papersmentioning

confidence: 91%

Evolution of long-lived globular cluster stars

Chantereau

Charbonnel

Decressin

2015

A&A

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Context. Our understanding of the formation and early evolution of globular clusters (GCs) has been totally overthrown with the discovery of the peculiar chemical properties of their long-lived host stars. Aims. As a consequence, the interpretation of the observed color-magnitude diagrams and of the properties of the GC stellar populations requires the use of stellar models computed with relevant chemical compositions.Methods. We present a grid of 224 stellar evolution models for low-mass stars with initial masses between 0.3 and 1.0 M and initial helium mass fraction between 0.248 and 0.8 computed for [Fe/H] = -1.75 with the stellar evolution code STAREVOL. This grid is made available to the community. Results. We explore the implications of the assumed initial chemical distribution for the main properties of the stellar models: evolution paths in the Hertzsprung-Russel diagram (HRD), duration and characteristics of the main evolutionary phases, and the chemical nature of the white dwarf remnants. We also provide the ranges in initial stellar mass and helium content of the stars that populate the different regions of the HRD at the ages of 10 and 13.4 Gyr, which are typical for Galactic GCs.

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Section: Objectives Of the Present Series Of Papersmentioning

confidence: 91%

Evolution of long-lived globular cluster stars

Chantereau

Charbonnel

Decressin

2015

A&A

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“…The constraints arise because mass loss affects the efficiency of atomic diffusion and radiative levitation, and excessive mass loss rates would produce surface abundances inconsistent with observations. Michaud et al (2011) considered a HB model with T eff ≈ 30 000 K and determined that mass loss rates compatible 2 Although SG stars appear to be O-depleted compared to the FG counterpart, as long as the C + N + O sum is kept constant, the evolutionary and structural properties of HB stars are barely affected (Pietrinferni et al 2009). Given that SG stars in NGC 6752 do not show any evidence of CNO enhancement (Carretta et al 2005;Yong et al 2013), our assumption of adopting the same α−enhanced mixture for stellar models representing both FG and SG stars is justified.…”

Section: Mass Loss On the Hot Hbmentioning

confidence: 99%

On the missing second generation AGB stars in NGC 6752

Cassisi

Salaris

Pietrinferni

et al. 2014

A&A

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In recent years the view of Galactic globular clusters as simple stellar populations has changed dramatically, it is now thought that basically all globular clusters host multiple stellar populations, each with its own chemical abundance pattern and colour-magnitude diagram sequence. Recent spectroscopic observations of asymptotic giant branch stars in the globular cluster NGC 6752 have disclosed a low [Na/Fe] abundance for the whole sample, suggesting that they are all first generation stars, and that all second generation stars fail to reach the AGB in this cluster. A scenario proposed to explain these observations invokes strong mass loss in second generation horizontal branch stars -all located at the hot side of the blue and extended horizontal branch of this cluster -possibly induced by the metal enhancement associated to radiative levitation. This enhanced mass loss would prevent second generation stars from reaching the asymptotic giant branch phase, thus explaining at the same time the low value of the ratio between horizontal branch and asymptotic giant branch stars (the R 2 parameter) observed in NGC 6752. We have critically discussed this mass-loss scenario, finding that the required mass-loss rates are of the order of 10 −9 M yr −1 , significantly higher than current theoretical and empirical constraints. By making use of synthetic horizontal branch simulations, we demonstrate that our modelling correctly predicts the R 2 parameter for NGC 6752, without the need to invoke very efficient mass loss during the core He-burning stage. As a test of our stellar models we show that we can reproduce the observed value of R 2 for both M 3, a cluster of approximately the same metallicity and with a redder horizontal branch morphology, and M 13, a cluster with a horizontal branch very similar to NGC 6752. However, our simulations for the NGC 6752 horizontal branch predict however the presence of a significant fraction of second generation stars (about 50%) along the cluster asymptotic giant branch. We conclude that there is no simple explanation for the lack of second generation stars in the spectroscopically surveyed sample, although the interplay between mass loss (with low rates) and radiative levitation may play a role in explaining this puzzle.

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“…For this reason we will use the same metallicity value for each set of Y values in our analysis. Even though variations of other elements can be associated to He-enrichment and also produce some changes in the theoretical evolutionary tracks and ZAHB loci (C+N+O and/or other heavier elements; Milone et al 2008;Cassisi et al 2008;Pietrinferni et al 2009;Ventura et al 2009;Marín-Franch et al 2009;Alves-Brito et al 2012;VandenBerg et al 2012), in this paper we focus exclusively on He. We leave the calculations with non-standard metal ratios for future papers, where we also plan to increase the ranges of masses, metallicities, and [α/Fe] ratios covered.…”

Section: Evolutionary Tracksmentioning

confidence: 99%

Effects of helium enrichment in globular clusters

Valcarce

Catelan

Sweigart

2012

A&A

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Aims. Recently, the study of globular cluster (GC) color−magnitude diagrams (CMDs) has shown that some of them harbor multiple populations with different chemical compositions and/or ages. In the first case, the most common candidate is a spread in the initial helium abundance, but this quantity is difficult to determine spectroscopically due to the fact that helium absorption lines are not present in cooler stars, whereas for hotter GC stars gravitational settling of helium becomes important. As a consequence, indirect methods to determine the initial helium abundance among populations are necessary. For that reason, in this series of papers, we investigate the effects of a helium enrichment in populations covering the range of GC metallicities. Methods. In this first paper, we present the theoretical evolutionary tracks, isochrones, and zero-age horizontal branch (ZAHB) loci calculated with the Princeton-Goddard-PUC (PGPUC) stellar evolutionary code, which has been updated with the most recent input physics and compared with other theoretical databases. The chemical composition grid covers 9 metallicities ranging from Z = 1.60 × 10 −4 to 1.57 × 10 −2 (−2.25 < ∼ [Fe/H] < ∼ −0.25), 7 helium abundances from Y = 0.230 to 0.370, and an alpha-element enhancement of [α/Fe] = 0.3. Results. The effects of different helium abundances that can be observed in isochrones are: splits in the main sequence (MS), differences in the luminosity (L) and effective temperature (T eff ) of the turn off point, splits in the sub giant branch being more prominent for lower ages or higher metallicities, splits in the lower red giant branch (RGB) being more prominent for higher ages or higher metallicities, differences in L of the RGB bump (with small changes in T eff ), and differences in L at the RGB tip. At the ZAHB, when Y is increased there is an increase of L for low T eff , which is affected in different degrees depending on the age of the GC being studied. Finally, the ZAHB morphology distribution depending on the age explains how for higher GC metallicities a population with higher helium abundance could be hidden at the red ZAHB locus.

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A LARGE STELLAR EVOLUTION DATABASE FOR POPULATION SYNTHESIS STUDIES. V. STELLAR MODELS AND ISOCHRONES WITH CNONa ABUNDANCE ANTICORRELATIONS

Cited by 138 publications

References 47 publications

Evolution of long-lived globular cluster stars

Evolution of long-lived globular cluster stars

On the missing second generation AGB stars in NGC 6752

Effects of helium enrichment in globular clusters

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