The seven sisters DANCe II. Proper motions and the lithium rotation-activity connection for G and K Pleiades

Abstract

Context. Stellar clusters open the window to understanding stellar evolution and, in particular, the change with time and the dependence on mass of different stellar properties. As such, stellar clusters act as laboratories where different theories can be tested. Aims. We try to understand the origin of the connection between lithium depletion in F, G, and K stars, rotation and activity in the Pleiades open cluster. Methods. We have collected all the relevant data in the literature, including information regarding rotation period, binarity, and activity, and cross-matched this data with proper motions, multiwavelength photometry, and membership probability from the DANCe database. To avoid biases, we only included single members of the Pleiades with probabilities larger than 75% in the discussion. Results. The analysis confirms that there is a strong link between activity, rotation, and the lithium equivalent width excess, especially for the range Lum(bol) = 0.5–0.2L_⊙ (about K2–K7 spectral types or 0.75–0.95 M_⊙). Conclusions. It is not possible to disentangle these effects, but we cannot exclude that the observed lithium overabundance is partially an observational effect from enhanced activity owing to a large coverage by stellar spots induced by high rotation rates. Since a bona fide lithium enhancement is present in young, fast rotators, both activity and rotation should play a role in the lithium problem.

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