Optical detection of the rapidly spinning white dwarf in V1460 Her

TL;DR

This study uses optical photometry to monitor the 39-second spin pulses of the white dwarf in V1460 Her, aiming to understand its spin evolution and compare it with other similar systems.

Contribution

It provides the first precise ephemeris for the white dwarf's spin in V1460 Her and sets constraints on its spin evolution over a four-year baseline.

Findings

Spin pulses detected with 0.4% amplitude in g-band.

No evidence of spin-up or spin-down detected.

Lower limit on spin period change timescale is >4×10^7 years.

Abstract

Accreting magnetic white dwarfs offer an opportunity to understand the interplay between spin-up and spin-down torques in binary systems. Monitoring of the white dwarf spin may reveal whether the white dwarf spin is currently in a state of near-equilibrium, or of uni-directional evolution towards longer or shorter periods, reflecting the recent history of the system and providing constraints for evolutionary models. This makes the monitoring of the spin history of magnetic white dwarfs of high interest. In this paper we report the results of a campaign of follow-up optical photometry to detect and track the 39 sec white dwarf spin pulses recently discovered in Hubble Space Telescope data of the cataclysmic variable V1460 Her. We find the spin pulsations to be present in g-band photometry at a typical amplitude of 0.4%. Under favourable observing conditions, the spin signal is detectable using 2-meter class telescopes. We measured pulse-arrival times for all our observations, which allowed us to derive a precise ephemeris for the white dwarf spin. We have also derived an orbital modulation correction that can be applied to the measurements. With our limited baseline of just over four years, we detect no evidence yet for spin-up or spin-down of the white dwarf, obtaining a lower limit of |P/Pdot|> 4e7 years, which is already 4 to 8 times longer than the timescales measured in two other cataclysmic variable systems containing rapidly rotating white dwarfs, AE Aqr and AR Sco.