ASASSN-24hd; 连接 WZ Sge 型和 SU UMa 型超级外翻的矮小星云

WZ Sge 型矮小星云(DNe)在类星体可变星中形成一个子类,其特征是在外翻期间出现短期变化称为超级峰值。本文我们报告了 ASASSN-24hd 在 2024-2025 年外翻期间的光学地面观测和 TESS 观测。ASASSN-24hd 是首个被 TESS 完全覆盖的 WZ Sge 型 DN 外翻,为研究超级峰值的演化提供了绝佳机会。我们的观测确立了其早期和 stage-A 普通超级峰值为 0.05711(4) 和 0.05919(5) d,分别导致其质量比为 0.098(4)。TESS 观测确认,在普通超级峰出现后,其超级峰周期、幅度和 profile 的演化通常与 Kepler 和 TESS 观测到的 SU UMa 型 DNe 的行为一致。Furthermore, we find that ASASSN-24hd in outburst shares a great similarity to the 2010 superoutburst of an SU UMa-type DN V585 Lyr, observed by Kepler, particularly including the superhump evolution and the long waiting time ($\gtrsimeq$ 5 d) before the stage A--B transition of ordinary superhumps。The shorter superoutburst cycles and smaller outburst amplitude in V585 Lyr than those of ASASSN-24hd disfavor the interpretation that V585 Lyr is, in fact, a face-on WZ Sge-type DN where early superhumps are undetectable。Instead, one possibility of their critical differences is either low quiescence viscosity or inner disk truncation, which has been invoked to explain the extreme nature of WZ Sge-type DNe, but future observations in quiescence are vital to conclude. These findings emphasize the borderline between SU UMa-type and WZ Sge-type DNe.