  AR Scorpii (AR Sco) is the only radio-pulsing white dwarf known to date. It
shows a broad-band spectrum extending from radio to X-rays whose luminosity
cannot be explained by thermal emission from the system components alone, and
is instead explained through synchrotron emission powered by the spin-down of
the white dwarf. We analysed NTT/ULTRACAM, TNT/ULTRASPEC, and GTC/HiPERCAM
high-speed photometric data for AR Sco spanning almost seven years and obtained
a precise estimate of the spin frequency derivative, now confirmed with
50-sigma significance. Using archival photometry, we show that the spin down
rate of P/Pdot = 5.6e6 years has remained constant since 2005. As well as
employing the method of pulse-arrival time fitting used for previous estimates,
we also found a consistent value via traditional Fourier analysis for the first
time. In addition, we obtained optical time-resolved spectra with WHT/ISIS and
VLT/X-shooter. We performed modulated Doppler tomography for the first time for
the system, finding evidence of emission modulated on the orbital period. We
have also estimated the projected rotational velocity of the M-dwarf as a
function of orbital period and found that it must be close to Roche lobe
filling. Our findings provide further constraints for modelling this unique
system.
