Evolution of negative superhumps, quasi-periodic oscillations and outbursts in the Z Cam-type dwarf nova AH Her

TL;DR

This study reports the first detection of negative superhumps in AH Her, analyzes their variation with outbursts, and explores their relation to accretion disk dynamics and quasi-periodic oscillations in a Z Cam-type dwarf nova.

Contribution

It identifies and characterizes negative superhumps in AH Her for the first time, linking their amplitude variations to outburst phases and disk precession phenomena.

Findings

First detection of negative superhumps in AH Her

NSHs amplitude varies with outburst phases

QPOs observed at the top of long outbursts

Abstract

AH Her is a Z Cam-type dwarf nova with an orbital period of ~ 0.258 d. Dwarf nova oscillations and long-period dwarf nova oscillations have been detected, but no quasi-periodic oscillations (QPOs) and negative superhumps (NSHs) have been found. We investigated the association between NSHs, QPOs, and outbursts of AH Her based on \textit{TESS} photometry. We find for the first time the NSHs with a period of 0.24497(1) d in AH Her, and trace the variation of the amplitude and period of NSHs with the outburst. The amplitude of the NSHs is 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 of the accretion disk radius can explain the NSHs amplitude variation except for the plateau, so we suggest that the relationship between NSHs amplitude and outburst can be used as a window to study the accretion disk instability and the origin of NSHs. In addition, we find the periodic variations in the amplitude, maxima, and shape of the NSHs ranging from 2.33(2) d to 2.68(5) d, 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 HS 2325+8205, suggesting that the presence of QPOs at the top of Z Cam's long outburst may be a general phenomenon