THE X-RAY SELECTED CATACLYSMIC VARIABLES H0459-242(246 AND H0857)

We report the discovery of two cataclysmic variables located with the assistance of X-ray positions from the HEAO 1 Modulation Collimator an d the Large-Area Sky Survey. Each case is distinguished by evidence of two periodic modulations that appear to represent the orbital period and the spin period of the white dwarf, respectively. The first case, H0459 + 246, has been observed optically during faint states (V approx imately 16), in which there are spectral features of both an accretion disk and a K star. The light curves in the V and I bands are consiste nt with ellipsoidal variations in the secondary stars with a binary pe riod of 9.952 hr. X-ray observations with EXOSAT reveal a strong pulsa tion with a period approximations 62 minutes. This result confirms an ''intermediate polar'' classification for H0459 + 246. The pulsation i s observed at 63.2 minutes in the optical I band. The long orbital per iod opens the possibility that H0459 + 246 is a relatively young inter mediate polar that might evolve into a polar. The second case, H0857 - 242, shows radial velocity modulations at 1.78 hr along with photomet ric variations at a period approximately 49 minutes. The latter are ob served only during the decay phase of dwarf nova outbursts (13 < V < 1 7), which apparently recur frequently. Given the lack of X-ray monitor ing observations and the absence of proof that the 49 minute periodici ty is coherent over long time-scales, we regard H0857 - 242 as a candi date intermediate polar. Photographic records from the Harvard Observa tory Plate Library further reveal superoutbursts for H0857 - 242 (V ap proximately 11). A bright X-ray source that is both an intermediate po lar and a continually cycling dwarf nova may provide an effective mean s of measuring the time delay for the arrival of accreting matter at t he white dwarf surface, relative to the onset of optical brightening.