标题： 使用CARMENES近红外通道探测HD 209458 b传输光谱中的水汽 显示英文标题

标题： Water vapor detection in the transmission spectra of HD 209458 b with the CARMENES NIR channel

摘要： 目标：我们旨在探测热木星HD 209458 b大气中的H$_2$O，并利用CARMENES在近红外波段进行多波段研究。 方法：由于行星凌日期间径向速度的大幅变化，来自该行星大气的H$_2$O吸收线会发生多普勒位移，这一位移约为几十公里每秒（km s$^{-1}$），而地球的地面吸收线和恒星线可以视为准静态的。我们利用这一点，使用主成分分析算法SYSREM去除地面和恒星光谱线。残余光谱包含了数千条行星分子线的信号，这些信号远低于噪声水平。我们通过将光谱与大气吸收模型进行交叉相关来提取这些信息。 结果：我们在HD 209458 b中发现了H$_2$O存在的证据，信噪比（S/N）为6.4。信号蓝移了--5.2 $^{+2.6}_{-1.3}$ km s$^{-1}$，尽管存在误差范围，这仍然是该热木星昼夜边界处存在从白天到夜晚风的有力证据。此外，我们还针对CARMENES覆盖的三个近红外波段分别进行了多波段研究以单独检测H$_2$O。 我们利用信噪比(S/N)为5.8的1.0$\mu$m波段检测到来自HD 209458 b的H$_2$O，并且在信噪比为2.8的1.15$\mu$m波段也发现了迹象。 在1.4$\mu$m波段没有发现明确的行星信号。 结论：我们在HD 209458 b的1.0$\mu$m波段上检测到的显著信号代表了迄今为止从该波段（最蓝的一个）首次检测到H$_2$O。不利的观测条件可能是导致1.15和1.4$\mu$m波段未能得出明确结果的原因。 在HD 209458 b的1.0$\mu$米波段检测到H$_2$O，但在HD 189733 b中几乎检测不到，这支持了后者有更强的气溶胶消光作用。 显示英文摘要

摘要： Aims: We aim at detecting H$_2$O in the atmosphere of the hot Jupiter HD 209458 b and perform a multi-band study in the near infrared with CARMENES. Methods: The H$_2$O absorption lines from the planet's atmosphere are Doppler-shifted due to the large change in its radial velocity during transit. This shift is of the order of tens of km s$^{-1}$, whilst the Earth's telluric and the stellar lines can be considered quasi-static. We took advantage of this to remove the telluric and stellar lines using SYSREM, a principal component analysis algorithm. The residual spectra contain the signal from thousands of planetary molecular lines well below the noise level. We retrieve this information by cross-correlating the spectra with models of the atmospheric absorption. Results: We find evidence of H$_2$O in HD 209458 b with a signal-to-noise ratio (S/N) of 6.4. The signal is blueshifted by --5.2 $^{+2.6}_{-1.3}$ km s$^{-1}$, which, despite the error bars, is a firm indication of day-to-night winds at the terminator of this hot Jupiter. Additionally, we performed a multi-band study for the detection of H$_2$O individually from the three NIR bands covered by CARMENES. We detect H$_2$O from its 1.0 $\mu$m band with a S/N of 5.8, and also find hints from the 1.15 $\mu$m band, with a low S/N of 2.8. No clear planetary signal is found from the 1.4 $\mu$m band. Conclusions: Our significant signal from the 1.0 $\mu$m band in HD 209458 b represents the first detection of H$_2$O from this band, the bluest one to date. The unfavorable observational conditions might be the reason for the inconclusive detection from the stronger 1.15 and 1.4 $\mu$m bands. H$_2$O is detected from the 1.0 $\mu$m band in HD 209458 b, but hardly in HD 189733 b, which supports a stronger aerosol extinction in the latter.