DW Cancri : a magnetic VY Scl star with an orbital period of 86 minutes

We present the first time-resolved spectroscopic study of the cataclysmic variable DWCancri. We have determined an orbital period of 86.10 ± 0.05min, which places the system very close to the observed minimum period of hydrogen-rich cataclysmic variables. This invalidates previous speculations of DW Cnc being either a permanent superhumper below the period minimum or a nova-like variable with an orbital period longer than 3 hours showing quasi-periodic oscillations. The Balmer and He i lines have double-peaked profiles and exhibit an intense S-wave component moving with the orbital period. Remarkably, the Balmer and He i radial velocity curves are modulated at two periods: 86.10± 0.05min (orbital) and 38.58± 0.02min. The same short period is found in the equivalent width variations of the single-peaked He ii λ4686 line. We also present time-resolved photometry of the system which shows a highlycoherent variation at 38.51 min, consistent with the short spectroscopic period. The large number of similarities with the short-period intermediate polar V1025Cen lead us to suggest that DWCnc is another intermediate polar below the period gap, and we tentatively identify the photometric and spectroscopic 38min signals with the white dwarf spin period. DWCnc has never been observed to undergo an outburst, but it occasionally exhibits low states ∼ 2 mag fainter than its typical brightness level of V ≃ 14.5, resembling the behaviour of the high mass-transfer VYScl stars.