We have gathered near-infrared zyJ-band high-resolution spectra of nearly 300 field red giant stars with known lithium abundances in order to survey their He i λ10830 absorption strengths. This transition is an indicator of chromospheric activity and/or mass loss in red giants. The majority of stars in our sample reside in the red clump or red horizontal branch based on their V − J, M V color–magnitude diagram, and Gaia T eff and log(g) values. Most of our target stars are Li-poor in the sense of having normally low Li abundances, defined here as log ϵ(Li) < 1.25. Over 90% of these Li-poor stars have weak λ10830 features. However, more than half of the 83 Li-rich stars (log ϵ(Li) > 1.25) have strong λ10830 absorptions. These large λ10830 lines signal excess chromospheric activity in Li-rich stars; there is almost no indication of significant mass loss. The Li-rich giants may also have a higher binary fraction than Li-poor stars, based on their astrometric data. It appears likely that both residence on the horizontal branch and present or past binary interaction play roles in the significant Li–He connection established in this survey.
We have gathered optical-region spectra, derived model atmosphere parameters, and computed elemental abundances for 15 red giant stars in the open cluster NGC 7789. We focus on the light element group CNOLi that provides clues to evolutionary changes associated with internal fusion events and chemical mixing. We confirm and extend an early report that NGC 7789 stars 193 and 301 have anomalously large Li abundances, and that these values are apparently unconnected to any other elements’ abundances in these stars. A companion study of He i λ10830 lines in both field stars and cluster members shows that star 301 has a strong He feature while star 193 does not. Possible explanations for the large Li abundances of these stars include helium flash-induced mixing events and binary interactions at some past or present times. In either case an internal eruption of energy could cause fresh synthesis of lithium via the Cameron-Fowler Berillyum transport mechanism. Rapid transport of lithium to the outer layers may have created significant chromospheric transient disturbances, producing enough helium ionization to allow for the strong λ10830 absorption in star 301.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.