Abstract
Abstract We identify member stars of more than 90 open clusters in the LAMOST survey. With the method of Fang et al., the chromospheric activity (CA) indices, for 1091 member stars in 82 open clusters and for 1118 member stars in 83 open clusters, are calculated. The relations between the average , in each open cluster and its age are investigated in different T eff and [Fe/H] ranges. We find that CA starts to decrease slowly from log t = 6.70 to log t = 8.50, and then decreases rapidly until log t = 9.53. The trend becomes clearer for cooler stars. The quadratic functions between log R′ and log t with 4000 K < T eff < 5500 K are constructed, which can be used to roughly estimate ages of field stars with accuracy about 40% for and 60% for .
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