Resolve the white-dwarf spin-period ambiguity

Determine whether the white dwarf in the intermediate polar V844 Herculis has a spin period of 29.3 minutes, corresponding to the observed spectroscopic and photometric modulation, or 58.6 minutes, corresponding to twice that modulation period.

Background

The paper identifies V844 Herculis as an intermediate polar because its quiescent emission-line wings vary with the same approximately 29-minute period detected photometrically during superoutbursts. In most intermediate polars, such high-velocity emission is associated with magnetically channeled accretion curtains that corotate with the white dwarf, making the modulation a tracer of the white-dwarf spin.

Some intermediate polars exhibit a dominant photometric signal at twice the spin frequency when both accretion curtains are similarly visible. Because the available V844 Herculis data do not establish whether the emission wings are sufficiently asymmetric or symmetric, the authors cannot distinguish the 29.3-minute spin interpretation from the 58.6-minute alternative.

References

A few IPs show a dominant periodicity at double the spin frequency, meaning the true spin period may be twice as long as the observed modulation. Given the limited data for this system, we cannot rule out a WD spin period of 58-minutes.

— V844 Herculis: An Exceptional Intermediate Polar Hiding in an Ordinary Dwarf Nova  (2609.26530 - Greiveldinger et al., 22 Sep 2026) in Section 4.1, “Emission Line Variability in Quiescence”