HST HOT-JUPITER TRANSMISSION SPECTRAL SURVEY: CLEAR SKIES FOR COOL SATURN WASP-39b
HST HOT-JUPITER TRANSMISSION SPECTRAL SURVEY: CLEAR SKIES FOR COOL SATURN WASP-39b
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DOI：
10.3847/0004-637x/827/1/19
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发表时间：
2016-08-10
影响因子：
4.9
通讯作者：
Vidal-Madjar, Alfred
中科院分区：
文献类型：
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作者：
Fischer, Patrick D.;Knutson, Heather A.;Vidal-Madjar, Alfred
我们呈现。哈勃太空望远镜（HST）太空望远镜成像光谱仪（STIS）的低温土星质量系外行星WASP-39b在0.29-1.025 μ m范围内的透射光谱，以及斯皮策IRAC在3.6和4.5 μ m范围内的补充凌日观测数据。WASP-39b的低密度和大大气压尺度高度使其特别适合使用该技术进行大气表征。我们检测了瑞利散射斜率以及钠和钾的吸收特征；这是第一颗系外行星，通过无云大气模型预测的扩展翼，可以清楚地探测到这两种碱特征。完整的透射光谱与一个以h -2为主的清晰大气或一个含有霾的微弱贡献的大气很好地匹配，这与Sing等人提出的这些数据的初步还原很好地一致。据预测，WASP-39b的压力-温度分布与HD 189733b和WASP-6b相当，这使它成为我们在HST STIS调查中观测到的最冷的凌日气体巨星之一。尽管如此相似，WASP-39b似乎大部分是无云的，而HD 189733b和WASP-6b的透射光谱都表明存在高空云或雾霾。这些观测结果进一步强调了短周期轨道上多云和无云气体巨行星的惊人多样性，以及为这些大气开发预测云模型所面临的相应挑战。
We present the. Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) optical transmission spectroscopy of the cool Saturn-mass exoplanet WASP-39b from 0.29-1.025 mu m, along with complementary transit observations from Spitzer IRAC at 3.6 and 4.5 mu m. The low density and large atmospheric pressure scale height of WASP-39b make it particularly amenable to atmospheric characterization using this technique. We detect a Rayleigh scattering slope as well as sodium and potassium absorption features; this is the first exoplanet in which both alkali features are clearly detected with the extended wings predicted by cloud-free atmosphere models. The full transmission spectrum is well matched by a clear H-2-dominated atmosphere, or one containing a weak contribution from haze, in good agreement with the preliminary reduction of these data presented in Sing et al.. WASP-39b is predicted to have a pressure-temperature profile comparable to that of HD 189733b and WASP-6b, making it one of the coolest transiting gas giants observed in our HST STIS survey. Despite this similarity, WASP-39b appears to be largely cloud-free, while the transmission spectra of HD 189733b and WASP-6b both indicate the presence of high altitude clouds or hazes. These observations further emphasize the surprising diversity of cloudy and cloud-free gas giant planets in short-period orbits and the corresponding challenges associated with developing predictive cloud models for these atmospheres.