Are Lithium-Rich Giants Binaries?: A Radial Velocity Variability Analysis of 1,400 Giants

Low-mass giants with large amounts of lithium (Li) have challenged stellarevolution for decades. One of the possibilities usually discussed to explainthem involves the interaction with a close binary companion. This predicts thatwhen compared against their non-enriched counterparts, Li-rich giants shouldpreferentially be found as part of binary systems. In order to test thisscenario, we assemble a sample of 1418 giants with radial velocities (RVs) fromRAVE, GALAH, and Gaia, as well as stellar parameters and Li abundances fromGALAH. Evolutionary states can be determined for 1030 of these giants. Wedevelop a method that quantifies the degree of RV variability, which we use asa proxy for close binary companions. The method is tested and calibratedagainst samples of known RV standard stars and known spectroscopic binaries. Wealso compare the results of our RV variability analysis with binarityindicators from Gaia. We find that the accuracy of the classification iscontrolled by the precision of the RVs, which for the set of RVs available forthe giants is 80-85giants contains a fraction of Li-rich objects in the red clump (RC) that istwice as large as that for first-ascent giants (RGB). Among RC giants, thefractions of Li-rich objects with high RV variability and with no RVvariability are the same as those for Li-normal objects, which argues against abinary interaction scenario for the genesis of the bulk of Li-rich giants atthat evolutionary stage. On the other hand, Li-rich giants in the RGB appear tohave a small but detectable preference for higher RV variability, and thuspossibly a larger close binary fraction, than the Li-normal giants at thatstage. Additional measurements of the RVs of these giants at higher RVprecision would greatly help confirm and more robustly quantify these results.