X-ray luminosity (in 0.5−10.0 keV energy band) as a function of bolometric luminosity for massive stars in HM1 (red points) and IC 2944/2948 (blue points). The associated XID is quoted next to each point, with the prefix HM for sources in HM1 and IC for sources in IC 2944/2948: except for WR89 (XID 1 in HM1), all stars in HM1 display lower L_X/L_BOL than those of IC 2944/2948. Filled symbols correspond to bright objects whose X-ray luminosities were derived from a spectral fit (Table 2); open symbols correspond to fainter objects whose count rates were converted into X-ray luminosities; triangles indicate the known binary systems. Approximate error bars were calculated using the relative errors on the total count rates (Tables 1 and 2), except for faint objects in HM1, where they indicate the range in X-ray luminosity (see text).