Evolution of Negative Superhumps, Quasiperiodic Oscillations, and Outbursts in the Z Cam-type Dwarf Nova AH Her

Abstract

AH Her is a Z Cam-type dwarf nova with an orbital period of ∼0.258 days. Dwarf nova oscillations and long-period dwarf nova oscillations have been detected, but no quasiperiodic oscillations (QPOs) and negative superhumps (NSHs) have been found. We investigated the association between NSHs, QPOs, and outbursts of AH Her based on Transiting Exoplanet Survey Satellite photometry. We find for the first time NSHs with a period of 0.24497(1) days in AH Her, and trace the variation in the amplitude and period of NSHs with the outburst. The amplitude of the NSHs is the most significant at quiescence, weakening as the outburst rises, becoming undetectable at the top, rebounding and weakening at the plateau, and strengthening again as the outburst declines. The variation in the accretion disk radius can explain the NSH amplitude variation except for the plateau, so we suggest that the relationship between the NSH amplitude and outburst can be used as a window to study the accretion disk instability and the origin of NSHs. In addition, we find periodic variations in the amplitude, maxima, and shape of the NSHs ranging from 2.33(2) to 2.68(5) days, which may be related to the precession of the tilted disk. Finally, we find QPOs at the top of AH Her’s long outburst with ∼2800 s similar to those of HS 2325+8205, suggesting that the presence of QPOs at the top of Z Cam’s long outburst may be a general phenomenon.