The seven sisters DANCe

Abstract

Context. Stellar clusters are open windows to understand stellar evolution. Specifically, the change with time and the dependence on mass of different stellar properties. As such, they are our 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 particular 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 with proper motions, multi-wavelength photometry and membership probability from the DANCe database. In order to avoid biases, only Pleiades single members with probabilities larger than 75% have been included in the discussion. Results. The analysis confirms that there is a strong link between activity, rotation and the lithium equivalent width excess, specially for the range Lum(bol) = 0.5 − 0.2 L ⊙ (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 due to enhanced activity, due 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.

The lithium-rotation connection in the 125 Myr-old Pleiades cluster

“…This quantity involves a geometric projection factor which limits its applicability, in particular for low v sin i which may correspond to truly slow rotators or moderate/fast rotators seen at a low inclination. Prior to the recent studies of Gondoin (2014), Barrado et al (2016), and Somers & Stassun (2017), only King et al (2000) had previously used preliminary estimates of rotational periods derived from the photometric modulation of the stellar luminosity by surface spots. Even though these were much fewer and not nearly as accurate as the Kepler K2 periods used here, King et al (2000) claimed that a few Pleiades K dwarfs with long rotational periods, that is, true slow rotators, were exhibiting Li-excess.…”

“…31881corr that among cluster members less massive than about 0.9M , those with the highest projected rotational velocities were systematically lithium-rich compared to their similar-mass, lowvelocity siblings. Subsequent studies confirmed these early results and showed that the lithium spread affects mostly earlyto mid-K stars in the Pleiades cluster (e.g., Russell 1996;King et al 2000; Barrado et al 2016), while late-K and M dwarfs are heavily lithium depleted (e.g., Garcia Lopez et al 1994;Oppenheimer et al 1997) down to near the hydrogen burning mass limit where lithium starts to reappear Rebolo et al 1996;Stauffer et al 1998). Since then, additional examples of a lithium-rotation connection among low-mass dwarfs have been reported for young open clusters (e.g., M34 andNGC 2516, Jones et al 1997;Jeffries et al 1998, respectively), young moving groups (e.g., β Pic, Messina et al 2016), and even for star forming regions as young as 5 Myr (e.g., NGC 2264.…”

“…Crosses are objects without a lithium equivalent width measurement available in the literature, which encompasses mostly late-K-and M-type stars. Circles pertain to LiI 670.8 nm equivalent width measurements gathered from the literature (see Barrado et al 2016) while triangles indicate new lithium equivalent width measurements reported in this study. The color of the symbol scales with lithium equivalent width (in mÅ), as shown on the right side of the plot.…”

“…We refrain from considering additional periods available from the latter however, as some may be affected by aliases or harmonics. The periodic sample of Rebull et al (2016) was cross-matched with the compilation of 210 lithium equivalent width measurements published by Barrado et al (2016). This led to an initial sample of 131 Pleiades members with both a known rotational period and a lithium measurement.…”

Low-mass eclipsing binaries in the WFCAM Transit Survey: the persistence of the M-dwarf radius inflation problem

“…Moreover, the chromospheric activity can also be corre-lated with rotation (Bouvier 1990), thus, fast rotators may have inflated radii. In fact, fast rotators during the early pre-MS phase may have their radii enlarged by strong magnetic fields (Somers & Pinsonneault 2014;Barrado et al 2016, and references therein).…”