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The Canis Major OB1 Association has an intriguing scenario of star formation,especially in the Canis Major R1 (CMa R1) region traditionally assigned to areflection nebula, but in reality an ionized region. This work is focused onthe young stellar population associated to CMa R1, for which our previousresults from ROSAT, optical and near-infrared data had revealed two stellargroups with different ages, suggesting a possible mixing of populationsoriginated from distinct star-formation episodes. The X-ray data allow thedetected sources to be characterized according to hardness ratios, light curvesand spectra. Estimates of mass and age were obtained from the 2MASS catalogue,and used to define a complete subsample of stellar counterparts, forstatistical purposes. A catalogue of 387 XMM-Newton sources is provided, 78%being confirmed as members or probable members of the CMa R1 association.Flares were observed for 13 sources, and the spectra of 21 bright sources couldbe fitted by a thermal plasma model. Mean values of fits parameters were usedto estimate X-ray luminosities. We found a minimum value of log(L$_X$[erg/s]) =29.43, indicating that our sample of low-mass stars (M$_\star$ $\leq$ 0.5M$_\odot$), being faint X-ray emitters, is incomplete. Among the 250 objectsselected as our complete subsample (defining our best sample), 171 are found tothe East of the cloud, near Z CMa and dense molecular gas, 50% of them beingyoung (< 5 Myr) and 30% being older (> 10 Myr). The opposite happens to theWest, near GU CMa, in areas lacking molecular gas: among 79 objects, 30% areyoung and 50% are older. These findings confirm that a first episode ofdistributed star formation occurred in the whole studied region ~10 Myr ago anddispersed the molecular gas, while a second, localized episode (< 5 Myr) tookplace in the regions where molecular gas is still present.

Star formation history of Canis Major OB1 - II. A bimodal X-ray population revealed by XMM-Newton