Spatial distribution of all detected X-ray sources (crosses), and of stars from the SSB optical catalogue (dots) within 15′ of cluster center. The two tilted blue squares are the two ACIS-I FOVs. The dashed line running almost diagonally throughout the figure is the cluster symmetry axis obtained from our principal-component analysis. The Galactic Plane direction is here approximately towards South-East. The big red arrow at top right indicates galactic North. Color codes for X-ray detected sources (crosses) are: blue for OB stars, cyan for A−F (including some B-type) stars, red for low-mass pre-main-sequence stars, purple for field MS stars, magenta for foreground stars, and green for optically unidentified sources.