4 X-RAY-SELECTED CATACLYSMIC VARIABLES IN THE GALACTIC PLANE

We have identified four X-ray sources from the Einstein Galactic Plane Survey with faint cataclysmic variables. The optical counterparts to 1E 0830.9 - 2238, 1E 1449.7 - 6804, 1E 1516.6 - 6826, and 1E 1719.1 - 1946 were selected because of their blue excesses, and confirmed through spectroscopic observations. One source, 1E 0830.9 - 2238, may be an AM Her type magnetic variable based on the presence of a strong He II λ4686 emission line. The other three sources all have low X-ray luminosities (Lx < 1031 ergs s-1) and two of them, 1E 1449.7 - 6804 and 1E 1719.1 - 1946, are also optically faint (Mv > 11.5) and nearby (d < 200 pc). The latter two sources are inferred to have mass accretion rates among the lowest observed for active cataclysmic variables (Ṁ < 2 x 10-12 M⊙ yr-1). The existence of a population of intrinsically faint cataclysmic variables, which are difficult to discover through traditional means but can be identified through their X-ray emission or very blue colors, implies that the observed local space density of active cataclysmic variables is at least as high as a few x 10-5 pc-3.