The Intermediate Polars

Recently discovered intermediate polars extend the limits of known behaviour. They now ll the range between, and overlap with, non-magnetic CVs and AM Hers. They have a wide range of asynchronism, a full range of eld strengths, and several diierent accretion modes and pulsation mechanisms. I highlight (i) a puzzle over the symmetry between magnetic poles, (ii) the X-ray spectra, (iii) the similarity with polars, and (iv) the mass of EX Hya. 1. The known intermediate polars Patterson (1994) provided a comprehensive review of intermediate polars (IPs or DQ Her stars), while my Capetown review (Hellier 1995) focussed on the accretion geometry. Here I do not try to be comprehensive, but instead highlight issues which need updating or further attention. The signiicant change since Patterson's parade of thècast list' has been the addition of new IPs discovered by ROSAT., with further identiications likely. With these additions I present the known IPs in Table 1. The list is conservative, including only certain or almost certain members, placing most weight on a convincing X-ray periodicity, since this is the hardest IP signature to fake. It has become traditional to plot IPs on a spin-orbit diagram (Fig. 1) and then draw conclusions from it (e.g. King & Lasota 1991 and references therein). The previously touted P spin =0.1P orb relation is not apparent in up-to-date IP lists | indeed least-square ts produce a roughly orthogonal line. The safest interpretation is as a scatter diagram with three outliers.