VW Hydra的深前导- dip-主超爆发序列的深度观测：TESS的高密度观测对热-潮汐不稳定性模型的约束
A Deep Precursor-Dip-Main Superoutburst Sequence in VW Hydri Observed with TESS: High-Cadence Constraints on the Thermal-Tidal Instability Model
AI总结：
TESS观测揭示VW Hydra超爆发序列的深前导-dip特征，推断质量比并排除棕矮星供体，为低q矮新星潮汐不稳定性模型提供基准。
摘要：
我们展示了TESS对SU UMa型矮新星VW Hydra三次超爆发的120秒采样观测。其中两个事件（SO2在第87+88扇区和SO3在第93扇区）表现出明显的前导- dip后迅速上升到主超爆发平台的形态。这种形态，此前在开普勒光曲线中观察到V1504 Cyg和V344 Lyr，是热-潮汐不稳定性（TTI）模型的关键预测，当正常（前导）爆发使盘仅略微扩展到3:1共振半径时，允许潮汐不稳定性缓慢增长，产生接近宁静的深dip，然后快速放大驱动主超爆发。滑动窗口时间-频率分析揭示了超脉动功率在衰减和接近最小光度期间已存在，随着dip期间的平滑周期演变，在系统返回热状态后稳定，与3:1共振处盘偏心率的增长和饱和一致。从稳定阶段A超脉动周期，我们推断出代表性的质量比q=0.131±0.002。结合典型的SU UMa白矮星质量先验或在轨道周期为107分钟的半经验供体序列，推断出的组件质量为M1≈0.6-1.0M⊙和M2≈0.08-0.14M⊙，排除了棕矮星供体的可能性，并确立VW Hydra作为低q矮新星中测试潮汐不稳定性模型的基准系统。
英文摘要：
We present 120s cadence TESS observations of three superoutbursts of the SU UMa-type dwarf nova VW Hydri. Two events (SO2 in Sectors 87+88 and SO3 in Sector 93) exhibit a pronounced, temporally pronounced precursor-dip followed by a rapid rise into the main superoutburst plateau. This morphology, previously seen in Kepler light curves of V1504 Cyg and V344 Lyr, is a key prediction of the thermal-tidal instability (TTI) model when a normal (precursor) outburst expands the disk only marginally beyond the 3:1 resonance radius, allowing the tidal instability to grow slowly and produce a deep dip approaching quiescence before rapid amplification drives the main superoutburst. A sliding-window time-frequency analysis reveals superhump power already during the decline and near minimum light, with a smooth period evolution across the dip and stabilization after the system returns to the hot state, consistent with the growth and saturation of disk eccentricity at the 3:1 resonance. From the stabilized Stage A superhump periods, we infer a representative mass ratio $q = 0.131 \pm 0.002$. Combined with either a typical SU UMa white-dwarf mass prior or the semi-empirical donor sequence at an orbital period of 107~min, the implied component masses are $M_1 \simeq 0.6$--$1.0\,M_\odot$ and $M_2 \simeq 0.08$--$0.14\,M_\odot$, ruling out a brown-dwarf donor and establishing VW~Hyi as a benchmark system for testing tidal-instability models in low-$q$ dwarf novae.
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