WISE composite-color image of the CMa R1 region. Red shows band 4, 22.2 μm. Green showsband 3, 12.1 μm. Blue shows band 1, 3.4 μm. The yellow circles delimit the area of the YSO groups identified by Fischer et al. (2016). The circles in cyan show the position of XMM-Newton fields observed by Santos-Silva et al. (2018); 387 young stars are found in these fields. The majority have counterparts in the X-ray sources previously detected with ROSAT by Gregorio-Hetem et al. (2009), although they indicate an extended distribution of young stars west of the nebula. The white contours trace the ¹³CO emission. The dashed thin line shows the galactic longitude at b = 0°, and the white dashed ellipse represents the CMa shell (see Fig. 1).