Table 15: Comparison of mean and median X-ray luminosities for NGC 2451 A and B and other clusters of similar age, i.e., $\alpha $ Per and Pleiades (Prosser et al. 1996) and NGC 6475 (Prosser et al. 1995). The log $L_{\rm x}$ values are given separately for F-type stars ( $0.31\le (B-V)_0<0.59$), G-type stars ( $0.59\le (B-V)_0<0.82$), K-type stars ( $0.82\le (B-V)_0<1.41$), and M-type stars ( (B-V)0>1.41). The values in parentheses indicate the number of stars used. Note that in the case of NGC 6475 the colour intervals are slightly different and that the K-type stars are divided into early types (upper values) and late types (lower values).
  F stars G stars K stars M stars
Cluster mean median mean median mean median mean median
NGC 2451 A 29.62$~\pm~$0.28 29.23 (8) 29.91$~\pm~$0.14 29.83 (6) 29.49$~\pm~$0.18 29.02 (10) 29.29$~\pm~$0.08 29.29 (8)
(incl. upp.lim.)   29.23 (8)   29.46 (9)   <28.99 (15)   29.29 (8)
NGC 2451 B 29.97$~\pm~$0.11 29.81 (14) 29.95$~\pm~$0.08 29.82 (16) 29.77$~\pm~$0.06 29.71 (11) - -
$\alpha $ Per 29.67$~\pm~$0.11 29.59 29.70$~\pm~$0.10 29.68 29.59$~\pm~$0.07 29.62 29.05$~\pm~$0.04 28.98
Pleiades 29.34$~\pm~$0.08 29.33 29.37$~\pm~$0.11 29.21 29.33$~\pm~$0.06 29.38 28.98$~\pm~$0.04 28.99
          29.57$~\pm~$0.08 29.64    
NGC 6475 29.32$~\pm~$0.07 29.25 29.45$~\pm~$0.05 29.44 29.39$~\pm~$0.06 29.33 - -


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