HS 0943 + 1404 , a true intermediate polar ⋆

We have identified a new intermediate polar, HS 0943+1404, as part of our ongoing search for cataclysmic variables in the Hamburg Quasar Survey. The orbital and white dwarf spin periods determined from time-resolved photometry and spectroscopy are P orb ≃ 250 min and Pspin = 69.171 ± 0.001 min, respectively. The combination of a large ratio Pspin/P orb ≃ 0.3 and a long orbital period is very unusual compared to the other known intermediate polars. The magnetic moment of the white dwarf is estimated to be µ1 ∼ 10 34 G cm 3 , which is in the typical range of polars. Our extensive photometry shows that HS 0943+1404 enters into deep (∼ 3 mag) low states, which are also a characteristic feature of polars. We therefore suggest that the system is a true " intermediate " polar that will eventually synchronise, that is, a transitional object between intermediate polars and polars. The optical spectrum of HS 0943+1404 also exhibits a number of unusual emission lines, most noticeably N II λ5680, which is likely to reflect enhanced nitrogen abundances in the envelope of the secondary.