Sco OB2 census by de Zeeuw et al. (1999) in Galactic coordinates. The white triangles mark the 521 identified HIPPARCOS members. The boundaries of the three subgroups are indicated by the dashed white lines: from left to right, Upper Sco (US), Upper Centaurus Lupus (UCL), and Lower Centaurus Crux (LCC) appear, respectively. The “new” subgroup Lower Sco is indicated by a dashed white circle; the position of the open cluster IC 2602 is displayed by a white diamond. The Ophiuchus star forming region is centered at the small white circle (l = 354°, b = 17°). The background image is taken from the H_α map of Finkbeiner (2003).