标题： 暗影中的秘密：通过凌日光谱法获得快速旋转A型系外行星宿主恒星的高精度恒星丰度 显示英文标题

标题： Secrets in the shadow: High precision stellar abundances of fast-rotating A-type exoplanet host stars through transit spectroscopy

摘要： 上下文。 快速旋转的A型恒星的光谱具有强烈展宽的吸收线。 这种效应导致吸收线的混合，阻碍了对恒星光球层中元素丰度的测量。 目标。 当系外行星穿过其宿主恒星时，它会遮挡直接位于行星背后的恒星光谱。 我们旨在提取这个被遮挡的光谱，因为它受旋转展宽的影响较小，能够解决原本难以获取的弱线的混合问题。 这使我们能够更精确地测量超热木星系统中的金属丰度，其中许多系统的宿主恒星旋转速度很快。 方法。 我们开发了一种新方法，在光谱时间序列中隔离行星背后的恒星光谱，并重建宿主恒星的盘积分非展宽光谱。 我们系统地使用WASP-189 b穿越其快速旋转的A型宿主恒星的模型生成光谱对该方法进行了测试，评估了边缘暗化、吸收线选择、信噪比范围的影响；并展示了对光球参数（$T_{\text{eff}}$，$\log g$）和元素丰度的敏感性。 我们将该方法应用于HARPS高分辨率光谱仪的观测数据。 结果。 对于WASP-189，我们获得了之前文献中未报道的几种元素（Mg、Ca和Ti）的金属丰度和光球层丰度，与普通展宽的恒星光谱相比，准确度显著提高。 该方法可以普遍应用于其他凌日系统，这些系统的丰度测定由于严重的线混合而通过光谱合成不精确。 准确确定系外行星宿主恒星的光球特性非常重要，因为它可以为行星的形成和演化提供进一步的见解。 显示英文摘要

摘要： Context. The spectra of fast-rotating A-type stars have strongly broadened absorption lines. This effect causes blending of the absorption lines, hindering the measurement of the abundances of the elements that are in the stellar photosphere. Aims. As the exoplanet transits across its host star, it obscures the stellar spectrum that is emitted from directly behind the planet. We aim to extract this obscured spectrum because it is less affected by rotational broadening, resolving the blending of weak lines of elements that would otherwise remain inaccessible. This allows us to more precisely measure the metal abundances in ultra-hot Jupiter systems, many of which have fast rotating host stars. Methods. We develop a novel method that isolates the stellar spectra behind the planet during a spectral time-series, and reconstructs the disc-integrated non-broadened spectrum of the host star. We have systematically tested this method with model-generated spectra of the transit of WASP-189 b across its fast-rotating A-type host star, assessing the effects of limb darkening, choice of absorption lines, signal to noise regime; and demonstrating the sensitivity to photospheric parameters ($T_{\text{eff}}$, $\log g$) and elemental abundances. We apply the method to observations by the HARPS high-resolution spectrograph. Results. For WASP-189, we obtain the metallicity and photospheric abundances for several species previously not reported in literature, Mg, Ca and Ti, with significantly improved accuracy compared to the ordinary broadened stellar spectrum. This method can be generally applied to other transiting systems in which abundance determinations via spectral synthesis are imprecise due to severe line blending. It is important to accurately determine the photospheric properties of exoplanet host stars, as it can provide further insight into the formation and evolution of the planets.