TAKING THE PULSE OF DQ HERCULIS

We discuss high-speed spectrophotometric observations of DQ Herculis a cquired with the Double Spectrograph and ''2D-FRUTTI'' detector on the Hale 5 m telescope. Trailed spectrograms and Doppler tomograms of the steady (unpulsed) light of Bahner, He I and He II lines reveals disk emission, while disk absorption components appear in He I and Ca II li nes. Balmer and Ca II emission also originate in the Roche lobe of the secondary star; in neither case can we be certain whether the emissio n is intrinsic or is due to irradiation of the secondary star. We dete ct 71 s pulsations in both the continuum and in the He II lambda 4686 emission line. Our pulse-phased trailed spectrograms exhibit He II lam bda 4686 emission moving from red to blue across the line profile but not from blue to red, verifying with improved sensitivity and waveleng th resolution the basic results of Chanan, Nelson, and Margon (1978). We also find some evidence for pulsation on the red side of the Balmer lines. For pulses arising from reprocessing of rotating X-ray beams i rradiating an accretion disk, we are evidently seeing the reprocessing sites on the far side but not on the near side, owing to a less favor able viewing angle. In the context of this model, our data are largely consistent with a single beam sweeping the disk with period 71 s, alt hough we cannot rule out the possibility that two beams (originating a t the two poles of a magnetic dipole) excite the pulsed optical emissi on. The latter circumstance would imply a white dwarf spin period of 1 42 s. The pulsed component of the He II lambda 4686 light is totally e clipsed, and the center of the source of pulsed He II lambda 4686 ligh t is likely to be displaced or extended From the white dwarf. The He I I lambda 4686 pulsation amplitude is strongest at +500 km s(-1) implyi ng that the reprocessed emission is anisotropic, enhanced in the inwar d (toward the white dwarf) add backward (opposite to the local Kepleri an flow) directions. This anisotropy could arise through enhanced emis sivity of the saturated He II line in the direction of acceleration, i nward and backward in the corotating frame, as disk gas becomes thread ed onto held lines of the more slowly rotating magnetosphere inside th e corotation radius.