SIMBAD references

2023A&A...670A..73A - Astronomy and Astrophysics, volume 670A, 73 (2023/2-1)

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


Abstract (from CDS):

Context. Although not predicted by standard stellar evolution, the surface abundance of light elements, such as lithium (Li), carbon, and nitrogen, changes during the red giant branch (RGB) as a result of extra mixing. This is usually associated with thermohaline mixing acting after the RGB bump. Peculiar Li-enriched RGB stars might also be related to either enhanced mixing or pollution from external sources.
Aims. We measure the Li abundance and carbon isotopic ratio 12C/13C 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 measured the abundances with spectral synthesis using high-quality spectra. Multiple-epoch observations needed for exoplanet detection were used to decrease the effects of telluric contamination in 12C/13C measurements.
Results. Due to the prevalence of upper limits, the Li abundance pattern is complicated to interpret, but the comparison between RGB and core He-burning giants shows effects of mixing consistent with thermohaline. The most Li-enriched giant in the sample, classified as a RGB star close to the RGB bump, has low 12C/13C. Given that the 12C/13C should not be affected by planet engulfment, this does not seem to be the source of the high Li. There is a decreasing correlation between mass and 12C/13C in the RGB and an increasing correlation in the horizontal branch, which, once again, is consistent with thermohaline mixing. Our data also show a correlation between 12C/13C and [Fe/H]. There is no evident impact of binarity either on Li or on 12C/13C.
Conclusions. Our sample shows behavior consistent with additional mixing acting after the RGB bump. The 12C/13C adds new clues which can be used to describe extra mixing, and it could well be the best tool to study mixing in giants. Additional measurements of 12C/13C in field stars would greatly improve our ability to compare data with models and understand mixing mechanisms.

Abstract Copyright: © The Authors 2023

Journal keyword(s): stars: evolution - stars: abundances

VizieR on-line data: <Available at CDS (J/A+A/670/A73): table2.dat>

Status at CDS : Tables of objects will be appraised for possible ingestion in SIMBAD.

Simbad objects: 28

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