Title: A magnetic white dwarf formed through a binary merger within 35 million years Show Chinese title

Title: 通过双星合并在3500万年内形成的磁性白矮星

Abstract: White dwarfs (WDs) represent the final evolutionary stage of most stars, typically originating from progenitor stars with masses below approximately 8 $M_{\odot}$ to 10 $M_{\odot}$. Formation through single-star evolution generally requires at least 25 Myr, with the youngest WDs often near the Chandrasekhar limit of 1.4 $M_{\odot}$. In contrast, WDs formed via binary channels, such as mergers or mass transfer, can develop smaller masses in a shorter timescale and may exhibit unique characteristics, including strong surface magnetic fields and rapid rotation. Accurately determining the ages of these WDs is essential for understanding their formation. A valuable method involves studying WDs in star clusters, where member stars share the same age and chemical composition, allowing for precise constraints on the formation times and metallicities of the WDs' progenitors. Here we report a WD found in the open cluster RSG 5, which is only 35 Myr old. The WD's mass is lower than 1.05 $M_{\odot}$, indicating it may not have formed through single-star evolution. The WD possesses an exceptionally strong surface magnetic field ($\ge 200$ MG), a short rotational period ($\sim 6.5$ min), and, most notably, a co-rotating half-ring of ionized circumstellar debris. This distinctive feature provides evidence for a binary merger origin, a scenario further substantiated by our stellar evolution models. Show Chinese abstract

Abstract: 白矮星（WDs）代表了大多数恒星的最终演化阶段，通常起源于质量低于约8$M_{\odot}$到10$M_{\odot}$的前身恒星。 通过单星演化形成通常需要至少25 Myr，最年轻的WDs通常接近1.4$M_{\odot}$的钱德拉塞卡极限。 相反，通过双星渠道形成的WDs，如合并或质量转移，可以在更短的时间尺度内形成较小的质量，并可能表现出独特的特征，包括强表面磁场和快速旋转。 准确确定这些WDs的年龄对于理解它们的形成至关重要。 一种有价值的方法是研究星团中的WDs，其中成员恒星具有相同的年龄和化学组成，这使得能够对WDs前身的形成时间和金属丰度进行精确约束。 在此，我们报告在开放星团RSG 5中发现的一个WD，该星团仅有35 Myr的年龄。 该WD的质量低于1.05$M_{\odot}$，表明它可能不是通过单星演化形成的。 该WD具有异常强的表面磁场（$\ge 200$MG），短的自转周期（$\sim 6.5$分钟），并且最显著的是，有一个与自转同步的电离周围碎片半环。 这一显著特征提供了双星合并起源的证据，这一情景进一步得到了我们的恒星演化模型的支持。