RELATIONSHIP BETWEEN OPTICAL AND X-RAY-PROPERTIES OF O-TYPE STARS SURVEYED WITH THE EINSTEIN-OBSERVATORY

From the catalog of 289 Galactic O stars surveyed with the Einstein Observatory, we select a volume-limited sample, demonstrate that this sample is representative of the O-star population within 2.5 kpc of the Sun, and derive an X-ray luminosity function for O-type stars. With this sample, which is ∼ 10 times larger than any previously analyzed, we show that to the limits of our experimental results, there is no variation of X-ray luminosity level with either distance from the Sun, with galactocentric distance, or association membership. We confirm the previous result that X-ray and bolometric luminosity are indeed correlated: log Lx = α log Lbol, with α = 1.08 [-0.22, +0.06] and correlation coefficient r = 0.75 [-0.09, +0.03]. The large observed scatter about the above regression is inconsistent with either Lx or Lbol determination uncertainties, and leads us to conclude that the scatter is most likely dominated by intrinsic variations in X-ray emission levels. We find no strong correlation of Lx with wind terminal velocity (V∞), with the rotation rate (V sin i), or with mass-loss rate (M), but we do find a strong correlation with wind momentum flux (MV∞), as well as with the wind kinetic energy flux or "kinetic luminsoity" (1/2MV∞2). We discuss the implication of these correlations for models of X-ray luminosity generation in O-type stars.