HD 144941 is an extreme He (EHe) star, a rare class of subdwarf OB star formed from the merger of two white dwarf (WD) stars. Uniquely amongst EHe stars, its light curve has been reported to be modulated entirely by rotation, suggesting the presence of a magnetic field. Here, we report the first high-resolution spectropolarimetric observations of HD 144941, in which we detect an extremely strong magnetic field both in circular polarization (with a line-of-sight magnetic field averaged over the stellar disc 〈Bz〉 ∼−8 kG) and in Zeeman splitting of spectral lines (yielding a magnetic modulus of 〈B〉 ∼17 kG). We also report for the first time weak H α emission consistent with an origin and a centrifugal magnetosphere. HD 144941’s atmospheric parameters could be consistent with either a subdwarf or a main-sequence (MS) star, and its surface abundances are neither similar to other EHe stars nor to He-strong magnetic stars. However, its H α emission properties can only be reproduced if its mass is around 1 M⊙, indicating that it must be a post-MS object. Since there is no indication of binarity, it is unlikely to be a stripped star, and was therefore most likely produced in a WD merger. HD 144941 is therefore further evidence that mergers are a viable pathway for the generation of fossil magnetic fields.

中文翻译：

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双简并二元合并产物 HD 144941 中极强磁场的检测

HD 144941 是一颗极端 He (EHe) 星，是由两颗白矮星 (WD) 合并而成的一种罕见的亚矮星 OB 星。据报道，在 EHe 恒星中独一无二的是，它的光变曲线完全被旋转调制，这表明存在磁场。在这里，我们报告了 HD 144941 的第一次高分辨率光谱极化观测，其中我们检测到了一个极强的圆极化磁场（在恒星盘上平均的视线磁场 <Bz> ∼-8 kG ）和光谱线的塞曼分裂（产生<B>~17 kG的磁模量）。我们还首次报告了与起源和离心磁层一致的弱 H α 发射。HD 144941 的大气参数可能与亚矮星或主序 (MS) 星一致，它的表面丰度既不类似于其他 EHe 星，也不类似于 He 强磁星。然而，它的 H α 发射特性只有在其质量为 1 M⊙ 左右时才能再现，这表明它必须是一个后质谱物体。由于没有二元性的迹象，它不太可能是剥离的恒星，因此很可能是在 WD 合并中产生的。因此，HD 144941 进一步证明了合并是产生化石磁场的可行途径。