Searching for chemical inhomogeneities in open clusters

Carrera, R.; Martı́nez-Vázquez, C. E.

doi:10.1051/0004-6361/201322048

Cited by 17 publications

(12 citation statements)

References 105 publications

(126 reference statements)

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“…NGC 2420 was earlier regarded to be a transition system between solar-metallicity open clusters and more metal-poor globular clusters. However, for this cluster more recent analyses with high-resolution spectroscopy suggest a metallicity ranging from [Fe/H] = -0.05 to -0.20 (see Carrera & Martínez-Vázquez (2013)), i.e. rather close to solar ([Fe/H]≡ 0.0).…”

Section: Introductionmentioning

confidence: 75%

“…rather close to solar ([Fe/H]≡ 0.0). Age estimates vary between 1 and 3 Gyrs (see references in Table 1) and in Carrera & Martínez-Vázquez (2013)). The highly interesting and quite old cluster NGC 6791 (Brogaard et al (2012)) seems to be unique in showing different abundances for different stars, with an Na/O anti-correlation similar to that found in globular clusters, suggesting that several generations of stars have formed while the cluster was massive enough to retain the material expelled by AGB stars within the cluster.…”

Section: Introductionmentioning

confidence: 99%

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Gravitational scattering of stars and clusters and the heating of the Galactic disk

Gustafsson

Church²,

Davies³

et al. 2016

A&A

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Context. Could the velocity spread, increasing with time, in the Galactic disk be explained as a result of gravitational interactions of stars with giant molecular clouds (GMCs) and spiral arms? Do the old open clusters high above the Galactic plane provide clues to this question? Aims. We explore the effects on stellar orbits of scattering by inhomogeneities in the Galactic potential due to GMCs, spiral arms and the Galactic bar, and whether high-altitude clusters could have formed in orbits closer to the Galactic plane and later been scattered. Methods. Simulations of test-particle motions are performed in a realistic Galactic potential. The effects of the internal structure of GMCs are explored. The destruction of clusters in GMC collisions is treated in detail with N-body simulations of the clusters. Results. The observed velocity dispersions of stars as a function of time are well reproduced. The GMC structure is found to be significant, but adequate models produce considerable scattering effects. The fraction of simulated massive old open clusters, scattered into orbits with |z| > 400 pc, is typically 0.5%, in agreement with the observed number of high-altitude clusters and consistent with the present formation rate of massive open clusters. Conclusions. The heating of the thin Galactic disk is well explained by gravitational scattering by GMCs and spiral arms, if the local correlation between the GMC mass and the corresponding voids in the gas is not very strong. Our results suggest that the high-altitude metal-rich clusters were formed in orbits close to the Galactic plane and later scattered to higher orbits. It is possible, though not very probable, that the Sun formed in such a cluster before scattering occurred.

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Section: Introductionmentioning

confidence: 75%

Section: Introductionmentioning

confidence: 99%

Gravitational scattering of stars and clusters and the heating of the Galactic disk

Gustafsson

Church²,

Davies³

et al. 2016

A&A

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“…As noted in Section 3, point (9) above, unlike the secondgeneration products invoked in GCs, we expect this process to occur identically in sufficiently massive open clusters. Measuring abundance spreads in open cluster stars is challenging and very few open clusters (especially very massive ones) have strong constraints (see Martell & Smith 2009;Pancino et al 2010;Bragaglia et al 2012;Carrera & Martinez-Vazquez 2013). In the (limited) compilations above, every OC for which significant abundance spreads can be definitively ruled out lies significantly below the threshold size/mass (1) we predict.…”

Section: Open Clustersmentioning

confidence: 80%

Some Stars Are Totally Metal: A New Mechanism Driving Dust Across Star-Forming Clouds, and Consequences for Planets, Stars, and Galaxies

Hopkins

2014

ApJ

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Dust grains in neutral gas behave as aerodynamic particles, so they can develop large local density fluctuations entirely independent of gas density fluctuations. Specifically, gas turbulence can drive order-of-magnitude "resonant" fluctuations in the dust density on scales where the gas stopping/drag timescale is comparable to the turbulent eddy turnover time. Here we show that for large grains (size 0.1 μm, containing most grain mass) in sufficiently large molecular clouds (radii 1-10 pc, masses 10 4 M), this scale becomes larger than the characteristic sizes of prestellar cores (the sonic length), so large fluctuations in the dust-togas ratio are imprinted on cores. As a result, star clusters and protostellar disks formed in large clouds should exhibit significant abundance spreads in the elements preferentially found in large grains (C, O). This naturally predicts populations of carbonenhanced stars, certain highly unusual stellar populations observed in nearby open clusters, and may explain the "UV upturn" in early-type galaxies. It will also dramatically change planet formation in the resulting protostellar disks, by preferentially "seeding" disks with an enhancement in large carbonaceous or silicate grains. The relevant threshold for this behavior scales simply with cloud densities and temperatures, making straightforward predictions for clusters in starbursts and high-redshift galaxies. Because of the selective sorting by size, this process is not necessarily visible in extinction mapping. We also predict the shape of the abundance distribution-when these fluctuations occur, a small fraction of the cores may actually be seeded with abundances Z ∼ 100 Z such that they are almost "totally metal" (Z ∼ 1)! Assuming the cores collapse, these totally metal stars would be rare (1 in ∼10 4 in clusters where this occurs), but represent a fundamentally new stellar evolution channel.

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“…Moreover, highresolution spectra provide a detailed chemical composition for the cluster, which has usually a high level of homogeneity (see, e.g. De Silva et al 2006;Carrera & Martínez-Vázquez 2013;Bovy 2016;Liu et al 2016).…”

Section: Evolution In Open Clustersmentioning

confidence: 99%

The Gaia-ESO survey: Mixing processes in low-mass stars traced by lithium abundance in cluster and field stars

Magrini

Lagarde²,

Charbonnel³

et al. 2021

A&A

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Aims. We aim to constrain the mixing processes in low-mass stars by investigating the behaviour of the Li surface abundance after the main sequence. We take advantage of the data from the sixth internal data release of Gaia-ESO, IDR6, and from the Gaia Early Data Release 3, EDR3s. Methods. We selected a sample of main-sequence, sub-giant, and giant stars in which the Li abundance is measured by the Gaia-ESO survey. These stars belong to 57 open clusters with ages from 130 Myr to about 7 Gyr and to Milky Way fields, covering a range in [Fe/H] between ∼ − 1.0 and ∼ + 0.5 dex, with few stars between ∼ − 1.0 and ∼ − 2.5 dex. We studied the behaviour of the Li abundances as a function of stellar parameters. We inferred the masses of giant stars in clusters from the main-sequence turn-off masses, and for field stars through comparison with stellar evolution models using a maximum likelihood technique. We compared the observed Li behaviour in field giant stars and in giant stars belonging to individual clusters with the predictions of a set of classical models and of models with mixing induced by rotation and thermohaline instability. Results. The comparison with stellar evolution models confirms that classical models cannot reproduce the observed lithium abundances in the metallicity and mass regimes covered by the data. The models that include the effects of both rotation-induced mixing and thermohaline instability account for the Li abundance trends observed in our sample in all metallicity and mass ranges. The differences between the results of the classical models and of the rotation models largely differ (up to 2 dex), making lithium the best element with which to constrain stellar mixing processes in low-mass stars. We discuss the nature of a sample of Li-rich stars. Conclusions. We demonstrate that the evolution of the surface abundance of Li in giant stars is a powerful tool for constraining theoretical stellar evolution models, allowing us to distinguish the effect of different mixing processes. For stars with well-determined masses, we find a better agreement of observed surface abundances and models with rotation-induced and thermohaline mixing. Rotation effects dominate during the main sequence and the first phases of the post-main-sequence evolution, and the thermohaline induced mixing after the bump in the luminosity function.

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Searching for chemical inhomogeneities in open clusters

Cited by 17 publications

References 105 publications

Gravitational scattering of stars and clusters and the heating of the Galactic disk

Gravitational scattering of stars and clusters and the heating of the Galactic disk

Some Stars Are Totally Metal: A New Mechanism Driving Dust Across Star-Forming Clouds, and Consequences for Planets, Stars, and Galaxies

The Gaia-ESO survey: Mixing processes in low-mass stars traced by lithium abundance in cluster and field stars

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