Synchronous Photometry of DQ Herculis

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Abstract
We have made photometric measurements of DQ Her, synchronized with the 71.1 s pulsation of the white dwarf component. Synchronous averaging reduces noise due to the rapid light fluctuations in the system and due to seeing variations. This has enabled us to derive an accurate mean light curve for the 71.1 s pulsation. The light curve is sinusoidal to better than 10 per cent. Observations made during eclipses in the system demonstrate that the binary period is increasing linearly with time. This is interpreted as mass loss at a rate |$\geqslant\,1.0\,\times\,{10}^{-7}\,{M}_{\,\circ}\,\text{yr}^{-1}$| . Detailed observations of the 71.1 s pulsations at the time of eclipse of the white dwarf component demonstrate that the white dwarf itself does not contribute more than 2 or 3 per cent of the total light in the system. Thus the true amplitude of the pulsations is probably in excess of 1 magnitude. Similarly we are able to show that shoulders in the light curve immediately preceding and following eclipse cannot be due to a bright spot on the white dwarf. We suggest that the nebula surrounding the white dwarf is optically thick, and the resulting eclipse of a bright area in the nebulosity itself is responsible for the shoulders. This suggestion also explains the general variation in amplitude of the 71.1 s pulsations.

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