We present medium-resolution VLT/FORS2 spectroscopy of six cataclysmic variables (CVs)
discovered by the Sloan Digital Sky Survey (SDSS). We determine orbital periods for
SDSS J023322.61+005059.5 (96.08 ± 0.09 min), SDSS J091127.36+084140.7 (295.74 ±
0.22 min), SDSS J103533.02+055158.3 (82.10 ± 0.09 min) and SDSS J121607.03+052013.9
(most likely 98.82 ± 0.16 min, but the one-day aliases at 92 and 107 min are also possible)
using radial velocities measured from their Hα and Hβ emission lines. Three of the four orbital periods measured here are close to the observed 75–80 min minimum period for CVs,
indicating that the properties of the population of these objects discovered by the SDSS are
substantially different to those of the CVs found by other means. Additional photometry of
SDSS J023322.61+005059.5 reveals a periodicity of approximately 60 min which we interpret as the spin period of the white dwarf, suggesting that this system is an intermediate polar
with a low accretion rate. SDSS J103533.02+055158.3 has a period right at the observed minimum value, a spectrum dominated by the cool white dwarf primary star and exhibits deep
eclipses, so is an excellent candidate for an accurate determination of the parameters of the
system. The spectroscopic orbit of SDSS J121607.03+052013.9 has a velocity amplitude of
only 13.8 ± 1.6 km s−1, implying that this system has an extreme mass ratio. From several
physical constraints we find that this object must contain either a high-mass white dwarf or a
brown-dwarf-mass secondary component or both.
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