Periodicities in the K2 lightcurve of HP Librae

Abstract

We analyse Kepler/K2 lightcurve data of the AM CVn system HP Librae. We detect with confidence four photometric periodicities in the system: the orbital frequency, both positive and negative superhumps, and the positive apsidal precession frequency of the accretion disc. This is only the second time that the apsidal precession frequency has ever been directly detected in the photometry of a helium accreting system, after SDSS J135154.46-064309.0. We present phase-folded lightcurves and sliding power spectra of each of the four periodicities. We measure rates of change of the positive superhump period of $10^{-7}$ days/day. We also redetect a QPO at 300 cyc/day, a feature that has been stable over decades, and show that it is harmonically related to two other QPOs, the lowest of which is centered on the superhump/orbital frequency. The continuum power spectrum is consistent with a single power law with no evidence of any breaks within our observed frequency range.

Accepted to MNRAS. The movie of the lightcurve is available at https://www.youtube.com/watch?v=fseDT2Mr-bM

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Cited by in corpus (2)

• Discovery of Persistent Quasi-Periodic Oscillations in Accreting White Dwarfs: A New Link to X-ray Binaries
• Astrophysics with the Laser Interferometer Space Antenna