X-ray luminosity as a function of wind parameters. Only the stars with wind velocities measured from the UV spectra are shown. The mass-loss rates are uncertain within a factor of 2–3 due to systematic errors, i.e., Δlog Ṁ ≈ 0.3−0.5 (see Sect. 3.4 for a discussion on errors). From left to right columns: results for dwarfs, giants, and supergiants. First row from the top: correlations with wind terminal velocity; second row from the top: dependence on mass-loss rate calculated using the empirical SpT–Ṁ relations derived in Sect. 3.4; middle row: dependence on wind density; fourth row from the top: dependence on wind kinetic luminosity; bottom row: dependence of X-ray luminosity on modified stellar wind momentum. The color coding of different spectral subtypes is the same as in Fig. 5. Linear fits are shown with a line.