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.

References in corpus (17)

• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• Determining stellar atmospheric parameters and chemical abundances of FGK stars with iSpec
• Modern stellar spectroscopy caveats
• Cross-Correlation and Maximum Likelihood Analysis: A New Approach to Combine Cross-Correlation Functions
• The Magnetic Fields at the Surface of Active Single G-K Giants
• A catalog of chromospherically active binary stars (third edition)
• Discovery of ubiquitous lithium production in low-mass stars
• Lithium in red giant stars: Constraining non-standard mixing with large surveys in the Gaia era
• Survey of Li-rich giants among Kepler and LAMOST fields: Determination of Li-rich giants Evolutionary Phase
• Study of Lithium Rich Giants with the GALAH Spectroscopic Survey
• Radial Velocity Prospects Current and Future: A White Paper Report prepared by the Study Analysis Group 8 for the Exoplanet Program Analysis Group (ExoPAG)
• Velocities from Cross-Correlation: A Guide for Self-Improvement
• Photospheric diagnostics of core helium burning in giant stars
• On the observational characteristics of lithium-enhanced giant stars in comparison with normal red giants
• Antisolar differential rotation with surface lithium enrichment on the single K-giant V1192 Orionis
• Time-series Doppler images and surface differential rotation of the effectively-single rapidly-rotating K-giant KU Pegasi
• Magnetic field structure in single late-type giants: The weak G-band giant 37 Comae from 2008 to 2011

Cited by in corpus (5)

• Light Elements in the Universe
• The Active Chromospheres of Lithium-Rich Red Giant Stars
• Evidence of extra-mixing in field giants as traced by lithium and carbon isotope ratio
• The enigma of Li-rich giants and its relation with temporal variations observed in radial velocity and stellar activity signals
• A Near-Infrared and Optical Study of NGC 5822: An Open Cluster Hosting Barium-stars and Lithium-Enriched Giant Stars