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We present the results of a comprehensive statistical survey of dwarf novae and nova-like variables with detectable wind outflow or a documented lack thereof. After careful consideration of selection effects on wind detectability, we find that systems exhibiting wind outflow have (1) a white dwarf mass larger than 0.8 $M_\odot$, (2) observed X-ray emission and (3) inclinations between $35^\circ$ to $65^\circ$. This result strongly supports a radiative driving wind mechanism originating at the heated, metal-enriched, differentially rotating equatorial region of the accreting white dwarf and provides new constraints on the model. The first condition stems from the greater efficiency of the wind driving process the deeper the potential well of the white dwarf. The second condition (X-ray emission) is strongly correlated with the existence of sub-Keplerian rotational velocity and hence strong inward-directed accretion luminosity from shear. If the winds are well-collimated along the rotational axis of the systems, then they should be easily observed in the low inclination systems. Thus, if the absence of winds from low inclination systems is real, then it may indicate that the winds have more complicated geometric configurations. If the wind driving region is an equatorial belt on the white dwarf surface heated up by compression and accretion luminosity, then the outflow in the polar direction direction is smaller. Disks in CV's may block the winds emitted in inclination angles larger than $\approx 80^\circ$. If the result that winds are absent in the systems with inclination angles larger than $65^\circ$ is not a coincidence due to our small number of sampling, it may indicate that the disks have a rather strong interaction with the winds. Motivated by the result of this survey, we are investigating the dynamical and evolutionary characteristics of this wind-driving model with a two dimensional, fully-implicit, hydrodynamic code now being developed to follow evolution through the outburst phase of high accretion.
This work is supported by NASA grant NAGW-3158 and in part by NSF grant AST90-16283, both to Villanova University.
