Analysis of a Century's Worth of AR Scorpii Photometry from DASCH and ASAS-SN

Abstract

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.

arXiv commentPublished in AJ on September 2, 2019; Accepted for publication on June 17, 2019, 10 pages, 7 figures

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Cited by in corpus (4)

• Long-term photometric monitoring and spectroscopy of the white dwarf pulsar AR Scorpii
• An Improved Spin-Down Rate for the Proposed White-Dwarf Pulsar AR Scorpii
• Constraining the Emission Geometry and Mass of the White Dwarf Pulsar AR Sco using the Rotating Vector Model
• An X-ray study for white dwarf binary AR Scorpii