LRG-BEASTS：使用NTT/EFOSC2在WASP-94A b大气中的钠吸收和瑞利散射
LRG-BEASTS: sodium absorption and Rayleigh scattering in the atmosphere of WASP-94A b using NTT/EFOSC2
摘要：
我们提出了WASP-94 A b的光学透射光谱，这是这个高度膨胀的热木星的第一个大气特征。这颗行星的半径为$1.72^{+0.06}_{-0.05}$ R $_{\textrm{Jup}}$，质量只有$0.456^{+0.032}_{-0.036}$ M $_{\textrm{Jup}}$，平衡温度为$1508 \pm 75$ K。我们在智利拉西拉的ESO新技术望远镜（NTT）上用EFOSC 2仪器观测了这颗行星的凌日光谱：这是NTT/EFOSC 2首次用于透射光谱。对于$\sim200$埃的面元宽度，我们实现了$128$ ppm的平均渡越深度精度。这种高精度部分是通过将所有波长箱中的高斯过程超参数联系起来实现的。由此产生的透射光谱，跨越$3800 - 7140$埃的波长范围，表现出钠吸收与$4.9σ$的意义，这表明一个相对无云的大气。钠信号可能变宽，最佳拟合宽度为$78_{-32}^{+67}$埃，而仪器分辨率为$27.2 \pm 0.2$埃。我们还检测到一个陡峭的斜率在蓝端的透射光谱，表明存在的瑞利散射在大气中的WASP-94 A b。检索模型显示的证据所观察到的斜率是超瑞利和潜在的原因进行了讨论。最后，我们在WASP-94 A的CaII H&K线中发现了狭窄的吸收核心，这表明该恒星被逃离热木星的气体所笼罩。
英文摘要：
We present an optical transmission spectrum for WASP-94A b, the first atmospheric characterisation of this highly-inflated hot Jupiter. The planet has a reported radius of $1.72^{+0.06}_{-0.05}$ R$_{\textrm{Jup}}$, a mass of only $0.456^{+0.032}_{-0.036}$ M$_{\textrm{Jup}}$, and an equilibrium temperature of $1508 \pm 75$ K. We observed the planet transit spectroscopically with the EFOSC2 instrument on the ESO New Technology Telescope (NTT) at La Silla, Chile: the first use of NTT/EFOSC2 for transmission spectroscopy. We achieved an average transit-depth precision of $128$ ppm for bin widths of $\sim200$ Angstrom. This high precision was achieved in part by linking Gaussian Process hyperparameters across all wavelength bins. The resulting transmission spectrum, spanning a wavelength range of $3800 - 7140$ Angstrom, exhibits a sodium absorption with a significance of $4.9σ$, suggesting a relatively cloud-free atmosphere. The sodium signal may be broadened, with a best fitting width of $78_{-32}^{+67}$ Angstrom in contrast to the instrumental resolution of $27.2 \pm 0.2$ Angstrom. We also detect a steep slope in the blue end of the transmission spectrum, indicating the presence of Rayleigh scattering in the atmosphere of WASP-94A b. Retrieval models show evidence for the observed slope to be super-Rayleigh and potential causes are discussed. Finally, we find narrow absorption cores in the CaII H&K lines of WASP-94A, suggesting the star is enshrouded in gas escaping the hot Jupiter.
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