€Joy (1940) found that RU Peg (Dwarf Nova) had a G3 absorption spectrum, as well as an emission
spectrum, suggesting it was double
€Joy (1956) found that SS Cyg had composite spectrum,
and that radial velocity
variations occurred on a timescale
of 6h 38m again suggesting
it was double
€Walker (1954) found DQ Her to be an eclipsing binary
€Kraft (1962) suggested all CVs might be binaries
€Crawford & Kraft (1956) found that the secondary of AE Aqr occupied
its ³zero velocity surface²
(Roche Lobe) so that some gas might be lost at the L1 point
€Kuiper (1941) had suggested for other binaries that turbulent gas would have angular momentum and
swirl around the primary
€Greenstein & Kraft (1959) found line profile changes through eclipse
of DQ Her which result from the
eclipse first of one side of the disk then the other Þ confirmed this was the eclipse of a prograde rotating
disk
€Kraft (1961) found a spectroscopic variation on the orbital period
resulting from impact region of the
stream on the disk
€Large survey by Kraft (1962) on Palomar 200² telescope found orbital motion in almost all CVs,
indicating they are close binaries with a white dwarf primary and a low
mass main sequence secondary