The X-ray Sun in Time: XMM Observations of the Solar Twin 18 Scorpii

We propose to complete an indepth study of the evolution of the corona of asolarmass star over its mainsequence lifetime by observing with XMM a star (18Sco) with nearly identical physical properties to the Sun. One of the few starsremaining in the Sun in Time program that does not have Xray measures is 18Sco, which has been identified as the Closest Ever Solar Twin (Porto de Mello& da Silva 1997). This nearby G2 V star has M_V, T_eff, Fe/H, R/R_0, inferredage and mass that are closely matched to the Sun. Also, it.smagneticallyrelated chromospheric activity is very similar to the Sun. 18 Scoprovides an important check on the behavior of our present Sun. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]