X-ray luminosity range of M 35 sample stars (crosses) with masses between 0.8 M_⊙ and 1.2 M_⊙ compared with median luminosities of stars with similar masses in the α Per, Pleiades, M 34, and the Hyades. The vertical error bars indicate the 25% and 75% quartiles of the distributions (Micela 2002). The various lines represent X-ray luminosity evolution models (see Sect. 5) of solar mass stars with initial rotation periods on the ZAMS ranging from 0.2 to 3.4 days.