A COMPARATIVE-STUDY OF THE OPTICAL PULSATIONS IN THE INTERMEDIATE POLARS

An attempt is made to assemble all known published measurements of the optical spectrum of the pulsations in the intermediate polar stars, a nd to convert these measurements to an absolute flux scale for the pur pose of examining similarities and correlations among this class of ca taclysmic variables. By using only absolute amplitudes (not relative o r fractional amplitudes), we may investigate the intrinsic nature of t he pulsations. For all systems studied, a power law is able to provide a good fit to the pulse spectrum. With the exception of DQ Her itself , all the pulses are intrinsically blue, generally declining monotonic ally with wavelength. We find no universal features common to all syst ems, nor do we find any strong correlations. For some systems a blackb ody can adequately fit the data, and from these fits we derive estimat es for the temperatures and areas of the pulse-emitting region. For th e two cases where data are available, the sideband pulse spectra are f latter in their energy distribution than the spin pulse spectra, lendi ng credibility to the belief that they are the result of reprocessing. Although not a sideband pulse, the pulse in DQ Her itself does come f rom reprocessing, and from our blackbody fit we estimate that between 6 and 23 per cent of the disc area is involved in the reprocessing. We speculate that in many of the intermediate polars, optically thin emi ssion should be able to provide a good fit to the pulse spectrum; inde ed, for those spectra whose slope is bluer than the Rayleigh-Jeans slo pe, this is the only simple and plausible emission mechanism.