Li-rich giant stars under scrutiny: binarity, magnetic activity, and the evolutionary status after Gaia DR2

Abstract

We present a study of the evolutionary state of a few lithium-rich giant stars based on the Gaia DR2 parallaxes and photometry. We also investigate the chromospheric activity, the presence of a surface magnetic field, and the radial velocity for our sample stars. We analysed both archive and new data. We gathered archive spectra from several instruments, mainly ELODIE and NARVAL, and we added new data acquired with the spectrograph MUSICOS†. We applied the Least-Squares Deconvolution technique to obtain Stokes V and Stokes I mean profiles to compute longitudinal magnetic field for a subset. Moreover, for the same subset, we analysed the Ca II H and K emission lines to calculate the S-index. We also derived atmospheric parameters and Li abundances for all eighteen stars of our sample. We found that stars previously classified as RGB may actually be at a different evolutionary state. Furthermore, we identified that most stars in our sample with detection of surface magnetic field show at least moderate rotation velocities, but nonetheless, we could not detect a magnetic field in two fast rotators. Due to our small sample of magnetic giants, it is difficult to determine if the presence of surface magnetic field and the Li-rich giant phenomena could be somehow linked. The large variation of the radial velocity of part of our sample indicates that some of them might have a binary companion, which may change the way we look at the Li problem in giant stars.

Light Elements in the Universe

“…We have selected a number of key topics, while we remind to the recent literature for several issues that we will not cover. The latter include the multiple populations of globular clusters (e.g., Gratton et al, 2004Renzini 2008;D'Orazi et al, 2015;Milone et al, 2017;D'Antona et al, 2019;Milone et al, 2020a, Milone et al, 2020b; the abundances of C, N, and O from emission-line spectra of H II regions and planetary nebulae (e.g., Toribio San Cipriano et al, 2016;Toribio San Cipriano et al, 2017;, Esteban et al, 2019Stanghellini and Haywood, 2018); post-main sequence Li evolution (e.g., Charbonnel et al, 2020;Deepak and Reddy, 2020;; and references therein), Li-rich giant stars and their nature (e.g., Casey et al, 2016, Casey et al, 2019Gao et al, 2019;Gonçalves et al, 2020;Jorissen et al, 2020;Martell et al, 2020;Sanna et al, 2020;Wheeler et al, 2020;Yan et al, 2020); boron abundances in massive stars (e.g., Proffitt et al, 2016, and references therein); light elements in the context of exoplanet hosting stars (e.g., Delgado Mena et al, 2012;Delgado Mena et al, 2014); the lithium depletion boundary (see, e.g., Stauffer, 2000;Lodieu, 2020;Martín et al, 2020; an references therein); 6 Li/ 7 Li isotopic ratio and its implications for Li nucleosynthesis (e.g., González Hernández et al, 2019, and references therein).…”

The Gaia-ESO survey: Mixing processes in low-mass stars traced by lithium abundance in cluster and field stars

“…Sackmann & Boothroyd 1999;Palacios et al 2001;Cassisi et al 2016). The Li enrichment has been also attributed to possible external pollution, such as planet engulfment or pollution by a binary companion (see, for instance, the case of Li-rich K giant Holanda et al 2020) or to magnetic activity (Gonçalves et al 2020). The ingestion of a planet or a companion brown dwarf can indeed contribute to increase the angular momentum of the system, producing additional Li (see, e.g.…”

Medindo a atividade cromosférica a partir dos espectros estelares

“…Particularmente, neste trabalho foi realizado um breve detalhamento das características físicas da cromosfera de estrelas do tipo solar. Os trabalhos publicados por Ferreira et al 2020 [67] e Gonçalves, B. F. O. et al 2020 [68] também utilizam a formulação para o cálculo do S-index baseado no que foi apresentado neste trabalho e podem servir como fonte para um aprofundamento posterior.…”