Stage-dependent Superhump Waveform Evolution and Nonstationary Positive-superhump Timing in the Near-period-gap Dwarf Nova YZ Cancri
Year: 2026
Type: article
Abstract: We present a photometric and timing study of the near-period-gap SU UMa-type dwarf nova YZ Cancri, based on nearly continuous Transiting Exoplanet Survey Satellite (TESS) photometry and long-baseline ground-based observations. Our main observational result is that the positive-superhump (SH) waveform follows a repeatable, stage-dependent sequence during superoutbursts (SOs). In the two well-covered TESS SOs, and consistently in the long-baseline ground-based SO sample, the plateau waveform evolves from an early sawtooth profile (ST), through a double-humped profile with unequal maxima (DHd), to a more symmetric double-humped profile with nearly similar maxima (DHs). The global and time-resolved Lomb–Scargle periodograms show that power near the positive-SH timescale and its harmonics is concentrated during SOs, whereas quiescent and normal-outburst intervals lack a comparably persistent SH-band signal. The dense TESS maxima–minima timing sequence shows different clock stability in different waveform stages: precursor modulations have slightly longer local periods, the middle-to-late DHs plateau is the most regular timing interval, and the postplateau evolution is affected by phase switching and possible secondary/late-SH contamination. The TESS data also reveal profile-clock coupling, with SH amplitude and rise/decay durations evolving together with the timing residuals. As a secondary timing constraint, we obtain a common TESS-timing-based mean positive-SH period of P sh ′ = 0.09043 ( 27 ) day, corresponding to an SH excess of 4.03(31)% and an approximate mass ratio of q = 0.175(11). The repeatable ST–DHd–DHs sequence makes YZ Cnc a useful system near the lower edge of the period gap and may trace the growth, redistribution, stabilization, and decay of the light source associated with an eccentric, precessing accretion disk during SOs.
Source: The Astrophysical Journal
Authors: Zhibin Dai, Xuefei Chen, Zhanwen Han
Institution: Chinese Academy of Sciences
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $4,499
OpenAlex ID: W7212016773