The GTC exoplanet transit spectroscopy survey VIII. Flat transmission spectrum for the warm gas giant WASP-80b
The GTC exoplanet transit spectroscopy survey VIII. Flat transmission spectrum for the warm gas giant WASP-80b
复制标题
GTC 系外行星凌日光谱调查 VIII。
DOI：
10.1051/0004-6361/201731113
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发表时间：
2018
影响因子：
6.5
通讯作者：
Iro N.
中科院分区：
文献类型：
--
作者：
Parviainen H.;Palle E.;Chen G.;Nortmann L.;Murgas F.;Nowak G.;Aigrain S.;Booth A.;Abazorius M.;Iro N.
WASP-80 b是一个平衡温度约为800 K的温暖膨胀气体巨星，我们开始使用地面透射光谱技术研究其大气层，光谱范围从520到910 nm。观测使我们能够探测WASP-80 b大气中K和Na的存在和丰度，高空云的存在，以及光谱蓝端的瑞利散射。MethodsWe观察了两个光谱时间序列的WASP-80 b过境与OSIRIS光谱仪安装在大加那利望远镜（GTC），并利用这些观测结果来估计该行星在520 nm和910 nm之间的20 nm宽通带的透射光谱，以及在6 nm宽通带的KI和Na I共振双峰周围的透射光谱。我们联合建模三个先前公布的宽带数据集组成的27光变曲线，之前的透射光谱分析，以获得改进的估计行星的轨道参数，平均半径比，和恒星密度。来自宽带分析的参数后验用于设置透射光谱分析的信息先验。最后的透射光谱分析进行联合使用的两个晚上除以白色的方法，以消除共模systematics. ResultsWe模型剩余的波长依赖systematics.ResultsWe恢复一个平坦的透射光谱没有证据的瑞利散射或K I或Na I吸收，并获得一个改进的系统特性作为一个副产品的宽带和GTC数据集建模。从两个观测运行分别估计的透射谱是相互一致的，因为是使用参数或非参数系统学模型估计的透射谱。平坦的透射光谱有利于大气模型与高海拔云无云模型与恒星或亚恒星metallicity.ConclusionsOur结果不同意最近发表的发现强K I吸收WASP-80 b的大气基于地面的透射光谱与FORS 2在VLT。
AimsWe set out to study the atmosphere of WASP-80b, a warm inflated gas giant with an equilibrium temperature of ~800 K, using ground-based transmission spectroscopy covering the spectral range from 520 to 910 nm. The observations allow us to probe the existence and abundance of K and Na in WASP-80b’s atmosphere, existence of high-altitude clouds, and Rayleigh-scattering in the blue end of the spectrum.MethodsWe observed two spectroscopic time series of WASP-80b transits with the OSIRIS spectrograph installed in the Gran Telescopio Canarias (GTC), and use the observations to estimate the planet’s transmission spectrum between 520 nm and 910 nm in 20 nm-wide passbands, and around the K I and Na I resonance doublets in 6 nm-wide passbands. We jointly model three previously published broadband datasets consisting of 27 light curves, prior to a transmission spectroscopy analysis in order to obtain improved estimates of the planet’s orbital parameters, average radius ratio, and stellar density. The parameter posteriors from the broadband analysis are used to set informative priors on the transmission spectroscopy analysis. The final transmission spectroscopy analyses are carried out jointly for the two nights using a divide-by-white approach to remove the common-mode systematics, and Gaussian processes to model the residual wavelength-dependent systematics.ResultsWe recover a flat transmission spectrum with no evidence of Rayleigh scattering or K I or Na I absorption, and obtain an improved system characterisation as a by-product of the broadband- and GTC-dataset modelling. The transmission spectra estimated separately from the two observing runs are consistent with each other, as are the transmission spectra estimated using either a parametric or nonparametric systematics model. The flat transmission spectrum favours an atmosphere model with high-altitude clouds over cloud-free models with stellar or sub-stellar metallicities.ConclusionsOur results disagree with the recently published discovery of strong K I absorption in WASP-80b’s atmosphere based on ground-based transmission spectroscopy with FORS2 at VLT.