<i>Gaia</i>-ESO survey: Lithium abundances in open cluster Red Clump stars

Magrini, L.; Smiljanić, R.; Franciosini, E.; Pasquini, L.; Randich, S.; Casali, G.; Vázquez, C. Viscasillas; Bragaglia, A.; Spina, L.; Biazzo, K.; Tautvaišienė, G.; Masseron, T.; Swaelmen, M. Van der; Pancino, E.; Jiménez-Esteban, F.; Guiglion, G.; Martell, Sarah L.; Bensby, T.; D’Orazi, V.; Baratella, M.; Korn, A. J.; Jofré, P.; Gilmore, G.; Worley, C. C.; Hourihane, A.; Gonneau, A.; Sacco, G. G.; Morbidelli, L.

doi:10.1051/0004-6361/202141275

Cited by 21 publications

(19 citation statements)

References 30 publications

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“…The Li equivalent width can include other nearby weak lines, and a nonzero value does not require a detectable Li abundance. Finally, open cluster samples of evolved giants have numerous true upper limits (see Magrini et al 2021 for a recent analysis based on data from the Gaia-ESO survey), and such stars must also exist in a field sample.…”

Section: Standard Model Prediction For the LI Content Of Field Clump ...mentioning

confidence: 99%

“…When comparing field populations, it is therefore of paramount importance to ensure that differences in the underlying mass distributions are accounted for. This complication is avoided if looking at stellar clusters, and indeed a recent analysis of cluster data from the Gaia-ESO survey cannot confirm any universal Li production event between the upper RGB and the RC (Magrini et al 2021).…”

Section: Introductionmentioning

confidence: 99%

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Mass Matters: No Evidence for Ubiquitous Lithium Production in Low-mass Clump Giants

Chanamé

Pinsonneault

Aguilera-Gómez

et al. 2022

ApJ

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Known sources of lithium (Li) in the universe include the Big Bang, novae, asymptotic giant branch stars, and cosmic-ray spallation. During their longer-lived evolutionary phases, stars are not expected to add to the Li budget of the Galaxy, but to largely deplete it. In this context, recent analyses of Li data from GALAH and LAMOST for field red clump (RC) stars have concluded that there is the need for a new production channel of Li, ubiquitous among low-mass stars, and that would be triggered on the upper red giant branch (RGB) or at helium ignition. This is distinct from the Li-rich giant problem and reflects bulk RC star properties. We provide an analysis of the GALAH Li data that accounts for the distribution of progenitor masses of field RC stars observed today. Such progenitors are different than today’s field RGB stars. Using standard post-main-sequence stellar evolution, we show that the distribution of Li among field RC giants as observed by GALAH is consistent with standard model predictions, and does not require new Li production mechanisms. Our model predicts a large fraction of very low Li abundances from low-mass progenitors, with higher abundances from higher mass ones. Moreover, there should be a large number of upper limits for RC giants, and higher abundances should correspond to higher masses. The most recent GALAH data indeed confirm the presence of large numbers of upper limits, and a much lower mean Li abundance in RC stars, in concordance with our interpretation.

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Section: Standard Model Prediction For the LI Content Of Field Clump ...mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Mass Matters: No Evidence for Ubiquitous Lithium Production in Low-mass Clump Giants

Chanamé

Pinsonneault

Aguilera-Gómez

et al. 2022

ApJ

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“…Gratton et al 2000). Large samples of stars that can be used to trace this mixing are now available from a variety of spectroscopic surveys, including GALAH (Buder et al 2019), APOGEE (Abdurro'uf et al 2022), and GAIA-ESO (Magrini et al 2021a). However, observed surface abundance trends are in tension with standard theoretical stellar evolution models, which predict that the surface chemistry should not evolve in this regime.…”

Section: Introductionmentioning

confidence: 99%

Characterizing Observed Extra Mixing Trends in Red Giants using the Reduced Density Ratio from Thermohaline Models

Fraser¹,

Joyce²,

Anders³

et al. 2022

Preprint

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Observations show an almost ubiquitous presence of extra mixing in low-mass upper giant branch stars. The most commonly invoked explanation for this is the thermohaline instability. One dimensional stellar evolution models include prescriptions for thermohaline mixing, but our ability to make direct comparisons between models and observations has thus far been limited. Here, we propose a new framework to facilitate direct comparison: Using carbon to nitrogen measurements from the SDSS-IV APOGEE survey as a probe of mixing and a fluid parameter known as the reduced density ratio from one dimensional stellar evolution programs, we compare the observed amount of extra mixing on the upper giant branch to predicted trends from three-dimensional fluid dynamics simulations. By applying this method, we are able to place empirical constraints on the efficiency of mixing across a range of masses and metallicities. We find that the observed amount of extra mixing is strongly correlated with the reduced density ratio and that trends between reduced density ratio and fundamental stellar parameters are robust across choices for modeling prescription. We show that stars with available mixing data tend to have relatively low density ratios, which should inform the regimes selected for future simulation efforts. Finally, we show that there is increased mixing at low values of the reduced density ratio, which is consistent with current hydrodynamical models of the thermohaline instability. The introduction of this framework sets a new standard for theoretical modeling efforts, as validation for not only the amount of extra mixing, but trends between the degree of extra mixing and fundamental stellar parameters is now possible.

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“…These are the super Li-rich giants (Yan et al 2018;Singh et al 2021). The Li-enriched giants are found in different parts of our Galaxy (Gonzalez et al 2009;Monaco et al 2011;Molaro et al 2020, just to name a few), open clusters (Magrini et al 2021b), and globular clusters (Kirby et al 2016;Aguilera-Gómez et al 2022). These giants seem to be particularly rare in globular clusters.…”

Section: Introductionmentioning

confidence: 95%

“…The internal transport processes affecting the surface abundances after the luminosity bump seem to be strongly metallicity-dependent (Shetrone et al 2019) also depending on stellar mass (Magrini et al 2021b). Thermohaline-mixing is currently the mechanism associated to these changes of chemical abundances after the bump (e.g.…”

Section: Introductionmentioning

confidence: 99%

Evidence of extra-mixing in field giants as traced by lithium and carbon isotope ratio

Aguilera-Gómez¹,

Jones²,

Chanamé³

2022

Preprint

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Context.Although not predicted by standard stellar evolution, it is known that the surface abundance of light elements, such as lithium, carbon, and nitrogen, changes during the red giant branch (RGB) as a result of extra-mixing. This is associated usually with thermohaline mixing acting after the RGB bump. Peculiar lithium-enriched RGB stars might also be related to either enhanced extra-mixing or pollution from external sources. Aims. We analyze the lithium (Li) abundance and carbon isotopic ratio C 12 /C 13 in a sample of 166 field red giants with −0.3 ≤[Fe/H]≤ 0.2, targeted by the EXPRESS radial velocity program to analyze the effects of extra-mixing. Methods. We measure the abundances with spectral synthesis using high-resolution and signal-to-noise spectra. Multiple-epoch observations needed for exoplanet detection are used to decrease the effects of telluric contamination in C 12 /C 13 measurements.Results. The Li abundance pattern is complicated to interpret, but the comparison between RGB and core-He burning giants shows the effects of extra-mixing consistent with thermohaline. The most Li-enriched giant in the sample was classified as a RGB star close to the luminosity function bump with low C 12 /C 13 . Given that the C 12 /C 13 should not be affected by external mechanisms, contamination by an external source, such as a planet, does not seem to be the source of the high Li. The carbon isotopic ratio presents new clues to describe the extra-mixing. There is a decreasing correlation between mass and C 12 /C 13 in the RGB and an increasing correlation in the horizontal branch, which, once again, is consistent with thermohaline mixing. Our data also shows a correlation between C 12 /C 13 and [Fe/H]. There is no evident impact of binarity either on Li or C 12 /C 13 . Conclusions. Our sample shows behavior that is consistent with additional mixing acting after the RGB bump. Lithium, which is heavily affected by rotational mixing and other processes, does not show a clear trend. Instead, the carbon isotope ratio could be the best tool to study mixing in red giants. Additional measurements of C 12 /C 13 in field stars would greatly improve our ability to compare with models and understand the mixing mechanisms.

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Gaia-ESO survey: Lithium abundances in open cluster Red Clump stars

Cited by 21 publications

References 30 publications

Mass Matters: No Evidence for Ubiquitous Lithium Production in Low-mass Clump Giants

Mass Matters: No Evidence for Ubiquitous Lithium Production in Low-mass Clump Giants

Characterizing Observed Extra Mixing Trends in Red Giants using the Reduced Density Ratio from Thermohaline Models

Evidence of extra-mixing in field giants as traced by lithium and carbon isotope ratio

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