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Alkali-Activity Correlations in Open Clusters
The Astronomical Journal
  • Jeremy R King, Clemson University
  • Simon C Schuler, Clemson University
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The American Astronomical Society

We present a census of correlations between activity measures and neutral resonance lines of the alkali elements Li i and K i in open clusters and star-forming regions. The majority of very young associations and star formation regions show no evidence of Li-activity correlations, perhaps because their chromospheric activity indicators have a dominant origin in accretion processes with implied disk-clearing timescales in the range of a few times 106 to $4 ;107 yr. Alkali-alkali and/or alkali-activity correlations are newly noted within IC 2391, M34, and perhaps Blanco 1 and NGC 6475. Global X-ray luminosities are not as robust indicators as traditional optical indicators of alkali-activity correlations, nor are Li i–K i relations. Intracluster alkali-activity correlations are not global but are seen only within different intracluster subsamples, evincing rich behavior. Li- and K-activity correlations appear to go hand in hand, likely suggesting that at least some part of intracluster Li variance is not due to real differential Li depletion. Although up to $90% of the star-to-star variance in Li i and K i within such a subsample can be related to that in optical chromospheric emission, significant Li dispersion above observational scatter may remain even after accounting for this. We suggest, for example, that at least three independent mechanisms (including a possible intracluster age spread) influence the distribution in the M34 Li-Teff plane. We argue that Li-activity correlations are not illusory manifestations of a physical Li-rotation connection. Although an unexpected corre-lation between Li, chromospheric emission, and the k6455 Ca i feature in cool M34 dwarfs indicates that the role of ‘‘activity’’ is played by spots/plages, we note that the alkali-activity correlations are qualitatively opposite in sign to other abundance anomalies being rapidly delineated in active, young, cool stars.

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