Stage-dependent Superhump Waveform Evolution and Nonstationary Positive-superhump Timing in the Near-period-gap Dwarf Nova YZ Cancri
- 1Chinese Academy of Sciences
- 2International Centre of Supernovae (ICESUN)
- 3Key Laboratory for the Structure and Evolution of Celestial Objects
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.
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BibTeX
@article{dai2026stagedependent,
title = {{Stage-dependent Superhump Waveform Evolution and Nonstationary Positive-superhump Timing in the Near-period-gap Dwarf Nova YZ Cancri}},
author = {Zhibin Dai and Xuefei Chen and Zhanwen Han},
journal = {The Astrophysical Journal},
year = {2026},
month = oct,
doi = {10.3847/1538-4357/aea297},
url = {https://iopscience.iop.org/article/10.3847/1538-4357/aea297},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Stage-dependent Superhump Waveform Evolution and Nonstationary Positive-superhump Timing in the Near-period-gap Dwarf Nova YZ Cancri
AU - Zhibin Dai
AU - Xuefei Chen
AU - Zhanwen Han
PY - 2026
DA - 2026/10/13
JO - The Astrophysical Journal
DO - 10.3847/1538-4357/aea297
UR - https://iopscience.iop.org/article/10.3847/1538-4357/aea297
AB - 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.
SN - 0004-637X
SN - 1538-4357
ER -