The Active Chromospheres of Lithium-rich Red Giant Stars
Dupree, Andrea K.; Mahadevan, Suvrath; Terrien, Ryan; Janowiecki, Steven; Lind, Karin; Hawkins, Keith; Bowler, Brendan P.; Mace, Gregory N.; Ninan, Joe P.; Bender, Chad F.; Ramsey, Lawrence W.; Afşar, Melike; Froning, Cynthia S.; Reddy, Bacham E.; Sneden, Christopher; Bozkurt, Zeynep; Topcu, Gamze Böcek; Mallick, Anohita; Nagarajan, Neel; Adamów, Monika
United States, Turkey, India, Sweden
Abstract
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. * Based on observations obtained with the Hobby-Eberly Telescope, which is a joint project of the University of Texas at Austin, the Pennsylvania State University, Ludwig-Maximilians-Universität München, and Georg-August-Universität Göttingen.