The enigma of Li-rich giants and its relation with temporal variations observed in radial velocity and stellar activity signals

Abstract

Despite the large number of studies focused on the characterisation of Li-rich stars and understanding the mechanisms leading to such enrichment, their origin remains a mystery. Magnetic activity, particularly the phenomena usually associated with it, and the Li abundance (A(Li)) of stars, are in general thought to be connected. As of today, however, just how they are connected is unclear. In this work, we study a sample of young but evolved intermediate-mass red giants that are inhabitants of open clusters where planets have been searched for. Our aim is to use radial velocity (RV) and stellar activity indicator signals to look for relations between Li abundances and stellar activity or variability. We explored how the standard deviation (STD), peak-to-peak amplitude (PTP), mean, and median of typical stellar activity indicators (BIS, FWHM, $T_{\text{eff}}$, and H$\alpha$ index) change as a function of the Li content of 82 red giants. Furthermore, we computed weighted Pearson correlation coefficients (${\rho }_w$) between time series of RV measurements and the stellar activity indicators for the stars in our sample. To aid our results, we also studied generalized Lomb-Scargle periodograms (GLSP) to capture possible significant periodic temporal variations in our data. Our analysis indicates that the STD and PTP of BIS and FWHM, the mean and median of the H$\alpha$ index, and $v\sin (i)$ increase exponentially with A(Li) in our sample of red giants. Significant temporal variations and correlations between RVs and activity indicators also tend to be found preferentially for stars where high A(Li) is observed. Most of the Li-rich stars in our sample either show strong correlations of RV with at least one of the stellar activity indicators or reveal significant periodic temporal variations in their GLSPs of stellar activity indicators that are consistent with those found for RV.

Published in A&A

References in corpus (27)

• The generalised Lomb-Scargle periodogram. A new formalism for the floating-mean and Keplerian periodograms
• Planets around evolved intermediate-mass stars. I. Two substellar companions in the open clusters NGC 2423 and NGC 4349
• Stellar chromospheric activity of 1,674 FGK stars from the AMBRE-HARPS sample I. A catalogue of homogeneous chromospheric activity
• The HARPS search for southern extra-solar planets XXXV. The interesting case of HD41248: stellar activity, no planets?
• Observable Signatures of Planet Accretion in Red Giant Stars I: Rapid Rotation and Light Element Replenishment
• Open Clusters as Galactic Disk Tracers: I. Project Motivation, Cluster Membership and Bulk Three-Dimensional Kinematics
• Expanding bubbles in Orion A: [CII] observations of M42, M43, and NGC 1977
• Rapid Rotation of Low-Mass Red Giants Using APOKASC: A Measure of Interaction Rates on the Post-main-sequence
• Discovery of ubiquitous lithium production in low-mass stars
• The lithium abundances for a large sample of red giants
• Lithium-rich Giants in LAMOST Survey. I. The Catalog
• The Gaia-ESO Survey: Galactic evolution of lithium from iDR6
• The effect of stellar activity on the spectroscopic stellar parameters of the young solar twin HIP 36515
• Survey of Li-rich giants among Kepler and LAMOST fields: Determination of Li-rich giants Evolutionary Phase
• The Penn State - Torun Centre for Astronomy Planet Search stars. II. Lithium abundance analysis of the Red Giant Clump sample
• The Gaia-ESO Survey: Galactic evolution of lithium at high metallicity
• Atmospheric stellar parameters for large surveys using FASMA, a new spectral synthesis package
• Lithium in stellar atmospheres: observations and theory
• Search for lithium-rich giants in 32 open clusters with high-resolution spectroscopy
• WIYN Open Cluster Study: The Old Open Cluster, NGC 188, and a Re-evaluation of Lithium-Richness Among Red Giants
• Optimising the H$\alpha$ index for the identification of activity signals in FGK stars. Improvement of the correlation between H$\alpha$ and CaII H&K
• Many Roads Lead to Lithium: Formation Pathways For Lithium-Rich Red Giants
• The Active Chromospheres of Lithium-Rich Red Giant Stars
• Evidence of extra-mixing in field giants as traced by lithium and carbon isotope ratio
• Li-rich K giants, dust excess, and binarity
• Planets around evolved intermediate-mass stars III. Planet candidates and long-term activity signals in six open clusters
• Li-rich giant stars under scrutiny: Binarity, magnetic activity and the evolutionary status after Gaia DR2

Cited by in corpus (2)

• Precise radial velocities of giant stars -- XVII. Distinguishing planets from intrinsically induced radial velocity signals in evolved stars
• A Near-Infrared and Optical Study of NGC 5822: An Open Cluster Hosting Barium-stars and Lithium-Enriched Giant Stars