Constant light element abundances suggest that the extended P1 in NGC 2808 is not a consequence of CNO-cycle nucleosynthesis

Cabrera-Ziri, I.; Lardo, C.; Mucciarelli, A.

doi:10.1093/mnras/stz707

Cited by 21 publications

(27 citation statements)

References 38 publications

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“…Milone et al (2017) presented the chromosome maps of the 57 clusters included in their HST UV Legacy Survey of Galactic GCs (HUGS; Piotto et al 2015) and showed that, for the majority of their clusters, the RGB stars can be easily divided into two main groups, which they refer to as first (1G) and second (2G) generations. Indeed, some overlap between stars in the Milone et al (2017) sample and previous spectroscopic studies indicate that stars belonging to the 1G have a primordial chemical composition, while the abundances of the 2G stars show traces of processed material, for example Na enrichment and O depletion O'Malley & Chaboyer 2018;Cabrera-Ziri et al 2019). More recently, Marino et al (2019) retrieved spectroscopic abundances from literature studies for stars in the chromosome maps of 29 GCs, confirming that stars belonging to the primordial population (or 1G) have light-element abundances similar to those of field stars, while the 2G stars are enhanced in N, Na, and depleted in O.…”

Section: Introductionmentioning

confidence: 82%

A stellar census in globular clusters with MUSE: multiple populations chemistry in NGC 2808

Latour

Husser

Giesers

et al. 2019

A&A

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Context. Galactic globular clusters (GCs) are now known to host multiple populations displaying particular abundance variations. The different populations within a GC can be well distinguished following their position in the pseudo two-colors diagrams, also referred to as "chromosome maps." These maps are constructed using optical and near-UV photometry available from the Hubble Space Telescope (HST) UV survey of GCs. However, the chemical tagging of the various populations in the chromosome maps is hampered by the fact that HST photometry and elemental abundances are both only available for a limited number of stars. Aims. The spectra collected as part of the MUSE survey of globular clusters provide a spectroscopic counterpart to the HST photometric catalogs covering the central regions of GCs. In this paper, we use the MUSE spectra of 1115 red giant branch (RGB) stars in NGC 2808 to characterize the abundance variations seen in the multiple populations of this cluster. Methods. We used the chromosome map of NGC 2808 to divide the RGB stars into their respective populations. We then combined the spectra of all stars belonging to a given population, resulting in one high signal-to-noise ratio spectrum representative of each population. Results. Variations in the spectral lines of O, Na, Mg, and Al are clearly detected among four of the populations. In order to quantify these variations, we measured equivalent width differences and created synthetic populations spectra that were used to determine abundance variations with respect to the primordial population of the cluster. Our results are in good agreement with the values expected from previous studies based on high-resolution spectroscopy. We do not see any significant variations in the spectral lines of Ca, K, and Ba. We also do not detect abundance variations among the stars belonging to the primordial population of NGC 2808. Conclusions. We demonstrate that in spite of their low resolution, the MUSE spectra can be used to investigate abundance variations in the context of multiple populations.

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Section: Introductionmentioning

confidence: 82%

A stellar census in globular clusters with MUSE: multiple populations chemistry in NGC 2808

Latour

Husser

Giesers

et al. 2019

A&A

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“…Furthermore, there is no evidence that a significant variation of [C+N+O/Fe] has been directly observed within the 1G, see Marino et al (2019) and Cabrera-Ziri et al (2019, for the case of NGC 2808). Thus as aforementioned, we then need to reject this simulation as unsatisfactory.…”

Section: Sim 4: Starting the Simulation From The Variable Stars Distmentioning

confidence: 99%

Is helium the key parameter in the extended colour spread of the first generation stars in M3?

Tailo

D’Antona

Caloi

et al. 2019

Monthly Notices of the Royal Astronomical Society

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The study of the "chromosome maps" of Galactic Globular Clusters has shown that the stars identified as 'first generation' often define an extended sequence in the m F275W − m F814W colour, whose straightforward interpretation, by comparison with synthetic spectra, is that they are inhomogeneous in helium content. The cluster M 3 (NGC 5272) is one of the most prominent example of this phenomenon, since its first generation is distributed on an extended colour range, formally corresponding to a large helium enhancement (∼ 0.1). It is necessary to ask whether the bulk of photometric observations available for this cluster supports or falsifies this interpretation. For this purpose, we examine the horizontal branch morphology, the period and magnitude distributions of the RR Lyrae variables, and the main sequence colour distribution. Simulating the first generation stars with such internal variation of helium content we can not meet all the observational constraints at the same time, concluding that the origin of the first generation colour spread is still without a straightforward explanation.

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“…However, these scenarios have a number of significant drawbacks that call into question their feasibility, the most important ones being: (i) the mass budget problem (e.g., Prantzos & Charbonnel 2006;Larsen et al 2012), (ii) the positive correlation between MPs and cluster mass (abundance spread and fraction of P2 stars - Carretta et al 2010;Schiavon et al 2013;Bastian & Lardo 2015;Milone et al 2017), (iii) the inability to reproduce some of the detailed observed chemical patterns (e.g., Lardo et al 2018;Cabrera-Ziri et al 2019), (iv) the lack of observational evidence for multiple episodes of star-formation within young massive clusters (e.g., Cabrera-Ziri et al 2014;Martocchia et al 2018b;Saracino et al 2020a) and (v) the observed trends of MP properties with cluster age (Martocchia et al 2019;Li & de Grijs 2019).…”

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confidence: 99%

Leveraging HST with MUSE: II. Na-abundance variations in intermediate age star clusters

Martocchia

Kamann

Saracino

et al. 2020

Monthly Notices of the Royal Astronomical Society

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Ancient (>10 Gyr) globular clusters (GCs) show chemical abundance variations in the form of patterns among certain elements, e.g. N correlates with Na and anti-correlates with O. Recently, N abundance spreads have also been observed in massive star clusters that are significantly younger than old GCs, down to an age of ∼2 Gyr. However, so far N has been the only element found to vary in such young objects. We report here the presence of Na abundance variations in the intermediate age massive star clusters NGC 416 (∼6.5 Gyr old) and Lindsay 1 (∼7.5 Gyr old) in the Small Magellanic Cloud, by combining HST and ESO-VLT MUSE observations. Using HST photometry we were able to construct “chromosome maps” and separate sub-populations with different N content, in the red giant branch of each cluster. MUSE spectra of individual stars belonging to each population were combined, resulting in high signal-to-noise spectra representative of each population, which were compared to search for mean differences in Na. We find a mean abundance variation of Δ[Na/Fe]=0.18 ± 0.04 dex for NGC 416 and Δ[Na/Fe]=0.24 ± 0.05 dex for Lindsay 1. In both clusters we find that the population that is enhanced in N is also enhanced in Na, which is the same pattern to the one observed in ancient GCs. Furthermore, we detect a bimodal distribution of core-helium burning Red Clump (RC) giants in the UV colour magnitude diagram of NGC 416. A comparison of the stacked MUSE spectra of the two RCs shows the same mean Na abundance difference between the two populations. The results reported in this work are a crucial hint that star clusters of a large age range share the same origin: they are the same types of objects, but only separated in age.

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Constant light element abundances suggest that the extended P1 in NGC 2808 is not a consequence of CNO-cycle nucleosynthesis

Cited by 21 publications

References 38 publications

A stellar census in globular clusters with MUSE: multiple populations chemistry in NGC 2808

A stellar census in globular clusters with MUSE: multiple populations chemistry in NGC 2808

Is helium the key parameter in the extended colour spread of the first generation stars in M3?

Leveraging HST with MUSE: II. Na-abundance variations in intermediate age star clusters

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