Article,
Nature versus nurture: distinguishing effects from stellar processing and chemical evolution on carbon and nitrogen in red giant stars
Affiliations
- [1] Ohio State University [NORA names: United States; America, North; OECD];
- [2] American Museum of Natural History [NORA names: United States; America, North; OECD];
- [3] Observatoire de la Côte d'Azur [NORA names: France; Europe, EU; OECD];
- [4] ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D) [NORA names: Australia; Oceania; OECD];
- [5] University of New South Wales [NORA names: Australia; Oceania; OECD];
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Abstract
The surface [C/N] ratios of evolved giants are strongly affected by the first dredge-up (FDU) of nuclear-processed material from stellar cores. C and N also have distinct nucleosynthetic origins and serve as diagnostics of mixing and mass-loss. We use subgiants to find strong trends in the birth [C/N] with [Fe/H], which differ between the low- αand high- αpopulations. We demonstrate that these birth trends have a strong impact on the surface abundances after the FDU. This effect is neglected in current stellar models, which use solar-scaled C and N. We map out the FDU as a function of evolutionary state, mass, and composition using a large and precisely measured asteroseismic data set in first-ascent red giant branch (RGB) and core He-burning, or red clump (RC), stars. We describe the domains where [C/N] is a useful mass diagnostic and find that the RC complements the RGB and extends the range of validity to higher mass. We find evidence for extra mixing on the RGB below [Fe/H] = -0.4, matching literature results, for high- αgiants, but there is no clear evidence of mixing in the low- αgiants. The predicted signal of mass-loss is weak and difficult to detect in our sample. We discuss implications for stellar physics and stellar population applications.