AR Scorpii ( AR Sco ) is a binary star system containing the only known white dwarf ( WD ) pulsar .
Previously reported photometric datasets only provide coverage back to 2005 , but we extend the observational baseline for AR Sco back to the beginning of the 20th century by analyzing observations from the Digital Access to a Sky Century at Harvard project ( DASCH ) .
We find that the orbital waveform of AR Sco remained constant across that baseline with no significant deviations from its average brightness .
This result strongly suggests that the absence of accretion in modern observations is a long-term feature of AR Sco .
Additionally , the DASCH light curve provides an opportunity to test an earlier prediction that an obliquity of the WD would result in a precessional period observable in long-term studies of the orbital light curve .
The DASCH observations do not indicate the presence of such a period , and we show that previous , inconclusive tests of this hypothesis were insensitive to the existence of a precessional period .
Furthermore , the long DASCH baseline enables us to constrain the rate of change of the orbital frequency to \dot { \nu } \lesssim 3.8 \times 10 ^ { -20 } Hz s ^ { -1 } , constraining the efficacy of magnetic braking as a mechanism of angular-momentum loss in this system .
Finally , we discuss how the combination of the orbital waveform ’ s stability , high amplitude , and short period should make it possible to identify additional WD pulsars in all-sky survey data .