A recent study by Hon et al. reported that a close-in planet around the red clump star, 8 UMi, should have been engulfed during the expansion phase of its parent star’s evolution. They explained the survival of this exoplanet through a binary-merger channel for 8 UMi. The key to testing this formation scenario is to derive the true age of this star: is it an old “imposter” resulting from a binary merger, or a genuinely young red clump giant? To accomplish this, we derive kinematic and chemical properties for 8 UMi using astrometric data from Gaia DR3 and the element-abundance pattern measured from a high-resolution (R ∼ 75,000) spectrum taken by SOPHIE. Our analysis shows that 8 UMi is a normal thin-disk star with orbital rotation speed of V _ϕ = 244.96 km s⁻¹, and possesses a solar metallicity ([Fe/H] = −0.05 ± 0.07) and α-element-abundance ratio ([α/Fe] = +0.01 ± 0.03). By adopting well-established relationships between age and space velocities/elemental abundances, we estimate a kinematic age of 3.50−2.00+3.00 Gyr, and a chemical age of 3.25−1.50+2.50 Gyr from [C/N] and 3.47 ± 1.96 Gyr from [Y/Mg] for 8 UMi, respectively. These estimates are consistent with the isochrone-fitting age ( 1.90−0.30+1.15 Gyr) of 8 UMi, but are all much younger than the timescale required in a binary-merger scenario. This result challenges the binary-merger model; the existence of such a closely orbiting exoplanet around a giant star remains a mystery yet to be resolved.

中文翻译：

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近地行星主星 8 UMi 的运动学和化学性质

Hon 等人最近的一项研究。报道称，红丛星 8 UMi 周围的一颗近距离行星应该在其母星演化的膨胀阶段被吞没。他们通过 8 UMi 的二元合并通道解释了这颗系外行星的生存。测试这种形成场景的关键是推导出这颗恒星的真实年龄：它是双星合并产生的古老“冒名顶替者”，还是真正年轻的红丛巨星？为了实现这一目标，我们使用来自 Gaia DR3 的天体测量数据以及从高分辨率 (右∼ 75,000) 光谱由 SOPHIE 拍摄。我们的分析表明 8 UMi 是一颗正常的薄盘恒星，轨道旋转速度为V _φ = 244.96 km s ⁻¹，并且具有太阳金属丰度 ([Fe/H] = −0.05 ± 0.07) 和α-元素丰度比（[α/Fe] = +0.01±0.03）。通过采用年龄和空间速度/元素丰度之间既定的关系，我们估计运动年龄为 3.50-2.00+3.00 吉尔，化学年龄为 3.25-1.50+2.50 对于 8 UMi，分别为 [C/N] 的 Gyr 和 [Y/Mg] 的 3.47 ± 1.96 Gyr。这些估计与等时线拟合年龄一致（ 1.90-0.30+1.15 Gyr）为 8 UMi，但都比二元合并场景中所需的时间尺度要年轻得多。这一结果挑战了二元合并模型；围绕巨星运行的如此紧密的系外行星的存在仍然是一个尚未解决的谜团。