AI 中文总结
研究通过TESS观测发现VY Scl型类新星MASTER OT J072703.91-631952.8的热稳定吸积盘发生动力学坍缩，提出该系统存在此前未被识别的动力学驱动循环，无法用质量转移变化范式解释。
AI 中文摘要
标准盘不稳定性理论预测，类新星变星因质量转移率高，应存在热稳定、无爆发的吸积盘；但解释这些系统观测到的偶发耀发/衰减现象，却普遍需要借助质量转移变化。本文报告热稳定吸积盘动力学坍缩的观测证据：在VY Scl型类新星系统MASTER OT J072703.91-631952.8的一次衰减事件中，TESS偶然捕捉到该坍缩，且由向轨道频率演化的异常负超周的出现所追踪。同时，该系统经历了一次异常爆发事件，其光变曲线呈显著对称的45天轮廓，表明能量释放机制与激变变星中已记录的爆发事件根本不同。值得注意的是，爆发与盘坍缩的同时发生难以与质量转移变化范式调和：爆发意味着质量转移增强，而盘坍缩则指示质量转移下降。约700天内的形态演化（兼具负超周与正超周）显示，该系统从圆盘过渡到偏心盘，再到倾斜态，最终形成极小盘构型。该演化序列为VY Scl型类新星的热稳定吸积盘中存在此前未被识别的动力学驱动循环提供了证据。
英文摘要
While standard disk instability theory predicts thermal-steady, outburst-free disks in nova-like variables due to their high mass transfer rates, mass transfer variations are prevailingly invoked to explain the occasional flaring/fading phenomena observed in these systems. Here we report the observational evidence for a dynamical collapse of a thermally stable accretion disk, captured serendipitously by TESS during a fading episode of the VY Scl-type nova-like system MASTER OT J072703.91-631952.8, and traced by the emergence of an unusual negative superhump that evolves toward its orbital frequency. Simultaneously, the system underwent an anomalous eruptive event featuring a remarkably symmetric 45-day light-curve profile, indicative of a mild energy-release mechanism fundamentally distinct from documented eruptive events in cataclysmic variables. Notably, the concurrence of the eruption and the disk collapse is difficult to reconcile with the paradigm of mass transfer variations: the eruption implies enhanced mass transfer, whereas the disk collapse indicates a decline. The morphological disk evolution over $\sim 700$ days, characterized by both negative and positive superhumps, indicates a transition from a circular disk to an eccentric disk, followed by a tilted state and ultimately a minimal disk configuration. This evolutionary sequence provides evidence for a previously unrecognized dynamics-driven cycle operating in the thermally stable accretion disk of a VY Scl-type nova-like star.
