X-ray luminosity vs. stellar mass for the sources in CMa R1 (black triangles) compared with T Tauri stars in other star-forming regions: Orion nebula cluster (ONC), Taurus molecular cloud (TMC), and Collinder 69 (Coll69). The dashed line indicates the limit of mass adopted to define our “best sample”. The gap at 0.4–0.5 M_⊙ is not real, but due to difficulties in interpolating models on this mass range.