The Gaia-ESO Survey: Inhibited extra mixing in two giants of the open cluster Trumpler 20?

Abstract

We report the discovery of two Li-rich giants, with A(Li) ~ 1.50, in an analysis of a sample of 40 giants of the open cluster Trumpler 20 (with turnoff mass ~ 1.8 Msun). The cluster was observed in the context of the Gaia-ESO Survey. The atmospheric parameters and Li abundances were derived using high-resolution UVES spectra. The Li abundances were corrected for nonlocal thermodynamical equilibrium (non-LTE) effects. Only upper limits of the Li abundance could be determined for the majority of the sample. Two giants with detected Li turned out to be Li rich: star MG 340 has A(Li) non-LTE = 1.54 \pm 0.21 dex and star MG 591 has A(Li) non-LTE = 1.60 \pm 0.21 dex. Star MG 340 is on average ~ 0.30 dex more rich in Li than stars of similar temperature, while for star MG 591 this difference is on average ~ 0.80 dex. Carbon and nitrogen abundances indicate that all stars in the sample have completed the first dredge-up. The Li abundances in this unique sample of 40 giants in one open cluster clearly show that extra mixing is the norm in this mass range. Giants with Li abundances in agreement with the predictions of standard models are the exception. To explain the two Li-rich giants, we suggest that all events of extra mixing have been inhibited. This includes rotation-induced mixing during the main sequence and the extra mixing at the red giant branch luminosity bump. Such inhibition has been suggested in the literature to occur because of fossil magnetic fields in red giants that are descendants of main-sequence Ap-type stars.

arXiv commentA&A accepted, 8 pages, 5 figures

References in corpus (52)

• PARSEC: stellar tracks and isochrones with the PAdova and TRieste Stellar Evolution Code
• Departures from LTE for neutral Li in late-type stars
• Thermohaline mixing: A physical mechanism governing the photospheric composition of low-mass giants
• Thermohaline instability and rotation-induced mixing. III - Grid of stellar models and asymptotic asteroseismic quantities from the pre-main sequence up to the AGB for low- and intermediate-mass stars at various metallicities
• The accretion of planets and brown dwarfs by giant stars -- II. solar mass stars on the red giant branch
• Gaia-ESO Survey: The analysis of high-resolution UVES spectra of FGK-type stars
• The Evolutionary Status of Be Stars: Results from a Photometric Study of Southern Open Clusters
• A secondary clump of red giant stars: why and where
• Rotational mixing in low-mass stars : I Effect of the mu-gradients in main sequence and subgiant Pop I stars
• A prevalence of dynamo-generated magnetic fields in the cores of intermediate-mass stars
• Origin of lithium enrichment in K giants
• Rapidly-rotating lithium-rich K giants: The new case of the giant PDS365
• Observable Signatures of Planet Accretion in Red Giant Stars I: Rapid Rotation and Light Element Replenishment
• The Magnetic Fields at the Surface of Active Single G-K Giants
• Detailed chemical composition of the open cluster IC 4651: The iron peak, alpha elements, and Li
• The Gaia-ESO Survey: processing of the FLAMES-UVES spectra
• Metal-Poor Lithium-Rich Giants in the Radial Velocity Experiment Survey
• Lithium-Rich Giants in Globular Clusters
• On the Numerical Treatment and Dependence of Thermohaline Mixing in Red Giants
• Lithium-Rich Field Giants in the Sloan Digital Sky Survey
• Old puzzle, new insights: a lithium rich giant quietly burning helium in its core
• Lithium-rich giants in the Galactic thick disk
• Beryllium Enhancement as Evidence for Accretion in a Lithium-Rich F Dwarf
• The thermohaline, Richardson, Rayleigh-Taylor, Solberg-Hoiland, and GSF criteria in rotating stars
• Inhibition of thermohaline mixing by a magnetic field in Ap star descendants: Implications for the Galactic evolution of 3He
• BD+48 740 - Li overabundant giant star with a planet. A case of recent engulfment?
• The Gaia-ESO Survey: CNO abundances in the open clusters Trumpler 20, NGC 4815, and NGC 6705
• Li-rich RGB stars in the Galactic Bulge
• The Lithium Flash - Thermal instabilities generated by lithium burning in RGB stars
• The Penn State - Torun Centre for Astronomy Planet Search stars. II. Lithium abundance analysis of the Red Giant Clump sample
• On the red-giant luminosity bump
• A super lithium-rich red-clump star in the open cluster Trumpler 5
• The Gaia-ESO Survey: Reevaluation of the parameters of the open cluster Trumpler 20 using photometry and spectroscopy
• On Infrared Excesses Associated With Li-Rich K Giants
• Discovery of Super-Li Rich Red Giants in Dwarf Spheroidal Galaxies
• Searching for Li-rich giants in a sample of 12 open clusters: Li enhancement in two stars with substellar companions
• Spectroscopic Study of IRAS 19285+0517(PDS 100): A Rapidly Rotating Li-Rich K Giant
• On the nature of Lithium-rich giant stars: constraints from Beryllium abundances
• The effects of differential reddening and stellar rotation on the appearance of multiple populations in star clusters: the case of Trumpler 20
• 2D or not 2D: the effect of dimensionality on the dynamics of fingering convection at low Prandtl number
• The Chemical Compositions and Evolutionary Status of Red Giants in the Open Cluster NGC 752
• Far-infrared study of K giants in the solar neighborhood: Connection between Li enrichment and mass-loss
• Photometric characterization of the Galactic star cluster Trumpler 20
• Lithium and magnetic fields in giants. HD 232862 : a magnetic and lithium-rich giant star
• On the serendipitous discovery of a Li-rich giant in the globular cluster NGC 362
• The Be-test in the Li-rich star \#1657 of NGC 6397: evidence for Li-flash in RGB stars?
• IRAS12556-7731: a "chamaeleonic" lithium-rich M-giant
• Lithium enrichment on the single active K1-giant DI Piscium -- Possible joint origin of differential rotation and Li enrichment
• A new stellar mixing process operating below shell convection zones following off-center ignition
• Complex Organic and Inorganic Compounds in Shells of Lithium-rich K Giant Stars
• Lithium in Open Cluster Red Giants Hosting Substellar Companions
• Polarimetry of Li-rich giants

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• The Correlation Between Mixing Length and Metallicity on the Giant Branch: Implications for Ages in the Gaia Era
• X-Shooter spectroscopy of young stellar objects in Lupus. Atmospheric parameters, membership and activity diagnostics
• Study of Lithium Rich Giants with the GALAH Spectroscopic Survey
• Lithium Enrichment Signatures of Planetary Engulfment Events in Evolved Stars
• The Gaia-ESO Survey: properties of newly discovered Li-rich giants
• The Gaia-ESO Survey: Calibrating the lithium-age relation with open clusters and associations. I. Cluster age range and initial membership selections
• On Lithium-Rich Red Giants. II. Engulfment on the Giant Branch of Trumpler 20
• Li-rich Giants in LAMOST Survey. III. The statistical analysis of Li-rich giants