Left: Bulk of ACIS‐I image of RCW 38 at low resolution. Right: Matching field in a 2MASS K‐band image. The FOV in these figures is ﹩16^{\prime }\times 16^{\prime }﹩. Regions of interest are identified. The ellipses near the core are the "common background regions" used for sources in the core as discussed in § 2.2. At 1.7 kpc, ﹩121^{\prime \prime }=1\ \mathrm{pc}\,﹩.