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We have determined the correlation between observed stellar X-ray luminosities, bolometric luminosities, and projected rotational velocities v sin / for stars of various spectral types and luminosity classes observed by the Einstein Observatory. There are two clearly defined patterns of behavior observed. Early type stars (03-A5) have X-ray luminosities which are proportional to bolometric luminosity. The proportionality constant is (1.4±0.3)X10~7 and is independent of luminosity class. In contrast, late type stars (G to M) have X-ray luminosities strongly dependent on rotation rate [L x~(v sin /) 1-9±0 ' 5 ] and independent of bolometric luminosity; this relation for late type stars is again found to be independent of luminosity class. This dependence is equivalent to a relation/^ ~Q 2 between the X-ray surface flux and the stellar angular velocity. F stars as a class are intermediate, having X-ray luminosities substantially higher than would be predicted on the basis of the early type star L x-L bol relation, but substantially lower than expected from the late type velocity dependence. The location of RS CVn stars as a class is discussed with respect to the dependence of X-ray luminosity on rotation.

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