Structure of DQ Herculis

The old nova (1934) DQ Her is a short-period eclipsing binary which also has a regular 71 s oscillation. A reexamination of the data shows no evidence for change in the orbital period. The 71 sec period is extraordinarily stable, with vertical-bar1/Pvertical-barapprox. =1012. In analogy with pulsars, this stability indicates that rigid-body rotation is the timing mechanism. A white dwarf with a crystalline core, coupled to the surface by a magnetic field, explains both the timing and the luminosity modulation. The dominant source of optical light is reradiated ultraviolet from the white dwarf. The combination of reradiation by structures rotating with the binary orbit and by matter with a constant configuration gives rise to two terms at differing frequencies whose interference leads to the observed phase shift at eclipse