The Active Chromospheres of Lithium-Rich Red Giant Stars

Christopher Sneden, Melike Afsar, Zeynep Bozkurt, Monika Adamow, Anohita Mallick, Bacham E. Reddy, Steven Janowiecki, Suvrath Mahadevan, Brendan P. Bowler, Keith Hawkins, Karin Lind, Andrea K. Dupree, Joe P. Ninan, Neel Nagarajan, Gamze Bocek Topcu, Cynthia S. Froning, Chad F. Bender, Ryan Terrien, Lawrence W. Ramsey, Gregory N. Mace

Submitted on 13 September 2022


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 \species{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 VJ,MV color-magnitude diagram and their Gaia \teff, \logg\ values. Most of our target stars are Li-poor in the sense of having normally low Li abundances, defined here as \eps{Li}~<~1.25. Over 90\% of these Li-poor stars have weak λ10830 features. But more than half of the 83 Li-rich stars (\eps{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 also may have a higher binary fraction than do 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.


Comment: Astrophysical Journal, in press

Subjects: Astrophysics - Solar and Stellar Astrophysics; Astrophysics - Astrophysics of Galaxies