Searching for multiple stellar populations in the massive, old open cluster Berkeley 39

Bragaglia, A.; Gratton, R.; Carretta, E.; D’Orazi, V.; Sneden, C.; Lucatello, S.

doi:10.1051/0004-6361/201220366

Cited by 89 publications

(75 citation statements)

References 39 publications

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“…These properties have to be combined with the fact that, starting at R GC = 9−10 kpc, the disk mean metallicity drops below [Fe/H] ≈ −0.3 dex, with an apparent flat distribution beyond this distance. In particular, this is observed for open clusters, which exhibit a (possibly) steeper drop in metallicity for older clusters (ages > 4 Gyr; see Bragaglia et al 2012, Fig. 7), while field giants have mean metallicities of −0.48 dex and [α/Fe] = +0.12 (Bensby et al 2011), in good agreement with Adibekyan et al (2012) for similar stars.…”

Section: The Status Of Metal-poor Thin Disk Stars and The Outer Thin supporting

confidence: 58%

The age structure of stellar populations in the solar vicinity

Haywood

Matteo

Lehnert

et al. 2013

A&A

535

175

868

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We analyze a sample of solar neighborhood stars that have high-quality abundance determinations and show that there are two distinct regimes of [α/Fe] versus age, which we identify as the epochs of the thick and thin disk formation. A tight correlation between metallicity and [α/Fe] versus age is clearly identifiable for thick disk stars, implying that this population formed from a well mixed interstellar medium, probably initially in starburst and then more quiescently, over a time scale of 4−5 Gyr. Thick disk stars have vertical velocity dispersions which correlate with age, with the youngest objects of this population having small scale heights similar to those of thin disk stars. A natural consequence of these two results is that a vertical metallicity gradient is expected in this population. We suggest that the youngest thick disk set the initial conditions from which the inner thin disk started to form about 8 Gyr ago, at [Fe/H] in the range of (−0.1, +0.1) dex and [α/Fe] ∼ 0.1 dex. This also provides an explanation for the apparent coincidence between the existence of a step in metallicity at 7−10 kpc in the thin disk and the confinement of the thick disk within R < 10 kpc. We suggest that the outer thin disk developed outside the influence of the thick disk, giving rise to a separate structure, but also that the high alphaenrichment of those regions may originate from a primordial pollution of the outer regions by the gas expelled from the forming thick disk. Metal-poor thin disk stars ([Fe/H] < −0.4 dex) in the solar vicinity, whose properties are best explained by them originating in the outer disk, are shown to be as old as the youngest thick disk (9−10 Gyr). This implies that the outer thin disk started to form while the thick disk was still forming stars in the inner parts of the Galaxy. Hence, while the overall inner (thick+thin) disk is comprised of two structures with different scale lengths and whose combination may give the impression of an inside-out formation process, the thin disk itself probably formed its first stars in its outskirts. Moreover, we point out that, given the tight age−metallicity and age-[α/Fe] relations that exist in the thick disk, an inside-out process would give rise to a radial gradient in metallicity and α-elements in this population, which is not observed. Finally, we argue that our results leave little room for radial migration (in the sense of churning) either to have contaminated the solar vicinity, or, on a larger scale, to have redistributed stars in significant proportion across the solar annulus.

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Section: The Status Of Metal-poor Thin Disk Stars and The Outer Thin supporting

confidence: 58%

The age structure of stellar populations in the solar vicinity

Haywood

Matteo

Lehnert

et al. 2013

A&A

535

175

868

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“…NGC 6475, NGC 7789, and Trumpler 20) were taken from a variety of references. These include some values of turn-off masses that we adopted in this work (e.g., for the Hyades and Trumpler 20) and those quoted in the original sources of the abundances (Tautvaišienė et al 2000(Tautvaišienė et al , 2005Friel et al 2003;Carretta et al 2005;Schuler et al 2009;Villanova et al 2009;Mikolaitis et al 2010Mikolaitis et al , 2011Bragaglia et al 2012;Santrich et al 2013;Carraro et al 2014). Apart from one cluster, Collinder 261 at 1.06 M and [Na/Fe] = +0.37, Fig.…”

Section: Open Clustersmentioning

confidence: 99%

TheGaia-ESO Survey: Sodium and aluminium abundances in giants and dwarfs

Smiljanić

Romano

Bragaglia

et al. 2016

A&A

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Context. Stellar evolution models predict that internal mixing should cause some sodium overabundance at the surface of red giants more massive than ∼1.5-2.0 M . The surface aluminium abundance should not be affected. Nevertheless, observational results disagree about the presence and/or the degree of Na and Al overabundances. In addition, Galactic chemical evolution models adopting different stellar yields lead to very different predictions for the behavior of [Na/Fe] and [Al/Fe] versus [Fe/H]. Overall, the observed trends of these abundances with metallicity are not well reproduced. Aims. We readdress both issues, using new Na and Al abundances determined within the Gaia-ESO Survey. Our aim is to obtain better observational constraints on the behavior of these elements using two samples: i) more than 600 dwarfs of the solar neighborhood and of open clusters and ii) low-and intermediate-mass clump giants in six open clusters. Methods. Abundances were determined using high-resolution UVES spectra. The individual Na abundances were corrected for nonlocal thermodynamic equilibrium effects. For the Al abundances, the order of magnitude of the corrections was estimated for a few representative cases. For giants, the abundance trends with stellar mass are compared to stellar evolution models. For dwarfs, the abundance trends with metallicity and age are compared to detailed chemical evolution models. Results. Abundances of Na in stars with mass below ∼2.0 M , and of Al in stars below ∼3.0 M , seem to be unaffected by internal mixing processes. For more massive stars, the Na overabundance increases with stellar mass. This trend agrees well with predictions of stellar evolutionary models. For Al, our only cluster with giants more massive than 3.0 M , NGC 6705, is Al enriched. However, this might be related to the environment where the cluster was formed. Chemical evolution models that well fit the observed [Na/Fe] vs. [Fe/H] trend in solar neighborhood dwarfs cannot simultaneously explain the run of [Al/Fe] with [Fe/H], and vice versa. The comparison with stellar ages is hampered by severe uncertainties. Indeed, reliable age estimates are available for only a half of the stars of the sample. We conclude that Al is underproduced by the models, except for stellar ages younger than about 7 Gyr. In addition, some significant source of late Na production seems to be missing in the models. Either current Na and Al yields are affected by large uncertainties, and/or some important Galactic source(s) of these elements has as yet not been taken into account.

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“…To increase the sample studied with high-resolution spectroscopy, we obtained data for a few old and massive open clusters (OCs; i.e. Berkeley 39, NGC 6791: Bragaglia et al 2012Bragaglia et al , 2014 and low-mass GCs, which are also connected with the Sgr dSph (Terzan 8, NGC 6139, and NGC 5634;Carretta et al 2014a;Bragaglia et al 2015;Carretta et al 2017).…”

Section: Introductionmentioning

confidence: 99%

NGC 6535: the lowest mass Milky Way globular cluster with a Na-O anti-correlation?

Bragaglia

Carretta

D’Orazi

et al. 2017

A&A

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To understand globular clusters (GCs) we need to comprehend how their formation process was able to produce their abundance distribution of light elements. In particular, we seek to figure out which stars imprinted the peculiar chemical signature of GCs. One of the best ways is to study the light-element anti-correlations in a large sample of GCs that are analysed homogeneously. As part of our spectroscopic survey of GCs with FLAMES, we present here the results of our study of about 30 red giant member stars in the low-mass, low-metallicity Milky Way cluster NGC 6535. We measured the metallicity (finding [Fe/H]=−1.95, rms=0.04 dex in our homogeneous scale) and other elements of the cluster and, in particular, we concentrate here on O and Na abundances. These elements define the normal Na-O anti-correlation of classical GCs, making NGC 6535 perhaps the lowest mass cluster with a confirmed presence of multiple populations. We updated the census of Galactic and extragalactic GCs for which a statement on the presence or absence of multiple populations can be made on the basis of high-resolution spectroscopy preferentially, or photometry and low-resolution spectroscopy otherwise; we also discuss the importance of mass and age of the clusters as factors for multiple populations.

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Searching for multiple stellar populations in the massive, old open cluster Berkeley 39

Cited by 89 publications

References 39 publications

The age structure of stellar populations in the solar vicinity

The age structure of stellar populations in the solar vicinity

TheGaia-ESO Survey: Sodium and aluminium abundances in giants and dwarfs

NGC 6535: the lowest mass Milky Way globular cluster with a Na-O anti-correlation?

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