The 71 Second Oscillation in the Light Curve of the Old Nova DQ Herculis

Details The 71 Second Oscillation in the Light Curve of the Old Nova DQ Herculis The 71 Second Oscillation in the Light Curve of the Old Nova DQ Herculis

Nov 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...454..447z&link_type=abstract

Astrophysical Journal v.454, p.447

Astronomy and Astrophysics

Astronomy

33

Stars: Binaries: Eclipsing, Stars: Novae, Cataclysmic Variables, Stars: Individual Constellation Name: Dq Herculis, Stars: Oscillations, Stars: Rotation, Stars: White Dwarfs

Scientific paper

DQ Her is an old nova (N1934), an eclipsing binary with an orbital period of 0.1936 days, and a prototype for cataclysmic variables containing rapidly rotating, accreting, magnetic white dwarfs. We have obtained high-speed, simultaneous U, B, V, and R photometry of DQ Her and have used the photometry to update and improve the ephemerides for the eclipse and for the 71 s periodicity induced by the rotation of the white dwarf. We use the ephemerides to show that the present rate of mass transfer in DQ Her must be less than, but not much less than 3.4 × 10-9 MMsun yr-1 and that the magnetic moment of the white dwarf is near 2.7 × 1032 G cm3.
The mean fractional semiamplitudes of the 71 s oscillation just before eclipse are AU/U = 0.010±0001 ΔB/B = 0.012±0.001, ΔV/V = 0.011±0.001, and ΔR/R = 0.009±0.001. The large change in oscillation amplitude with orbital phase seen in earlier data is no longer present. The 71 s oscillation undergoes a phase shift during eclipse, and we give a much improved measurement of the shift. The phase increases smoothly by at least 100° during eclipse ingress, then jumps by 120° at mid-eclipse, and finally climbs smoothly by another 140° during eclipse egress to end at +360°. The morphology of the phase shift is not measurably different in the four passbands. The beamed radiation from the white dwarf in DQ Her irradiates its accretion disk, setting up a pattern of bright and dark regions that rotates with the white dwarf. We show that the pattern has two nearly equal bright regions in opposite directions on the disk and that the pattern rotates with a period of 142 s. The rotation period of the white dwarf is, thus, 142 s.

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