2021ApJ...908..119M

We present a spectroscopic analysis of 7774 Å O I triplet abundances, 8498-8662 Å Ca II triplet chromospheric activity, and rotation in the Pleiades open cluster, with the objective of thoroughly examining the O triplet overabundance trends observed in cool open cluster dwarfs, and to thereby make clear the cause of that trend. High-dispersion, contemporaneous spectra of the O I triplet, Ca II triplet, and Hα spectral regions in 41 Pleiades dwarfs were acquired using Hydra on the WIYN 3.5 m telescope. Our Ca II emission equivalent-width data exhibit a strong positive correlation with decreasing T_eff, with the rapidly rotating stars enhanced by up to 50% above the slowly rotating stars. Our triplet [O/H] values exhibit a statistically significant positive correlation with total Ca II triplet emission, and similarly, significant correlations have been found by every study to date that used contemporaneous O triplet abundance and chromospheric activity data, which is strong evidence that chromospheric activity is the cause of the observed overabundance trends. Based on the slowly rotating, low Ca II emission stars in the near-solar range 5450 K < T_eff < 6100 K, we find a cluster mean [O/H] = + 0.143 ± 0.061, consistent with the substantial super-solar [O/H] values exhibited by most young ( < 1 Gyr) open clusters. We also find a cluster mean [Fe/H] = + 0.029 ± 0.034, in excellent agreement with previous studies.