FORWARD AND INVERSE MODELING OF THE EMISSION AND TRANSMISSION SPECTRUM OF GJ 436B: INVESTIGATING METAL ENRICHMENT, TIDAL HEATING, AND CLOUDS
FORWARD AND INVERSE MODELING OF THE EMISSION AND TRANSMISSION SPECTRUM OF GJ 436B: INVESTIGATING METAL ENRICHMENT, TIDAL HEATING, AND CLOUDS
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GJ 436B 发射和传输频谱的正向和逆向建模：研究金属富集、潮汐加热和云
DOI：
10.3847/1538-3881/153/2/86
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发表时间：
2016
期刊：
影响因子：
--
通讯作者：
R. Lupu
中科院分区：
文献类型：
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作者：
C. Morley;H. Knutson;M. Line;J. Fortney;D. Thorngren;M. Marley;D. Teal;R. Lupu
海王星质量的GJ 436b是研究最多的凌日系外行星之一，它的热发射和透射谱被反复测量。我们在之前的研究的基础上回答了关于这颗行星的悬而未决的问题，包括它潜在的高金属丰度和其内部的潮汐加热。我们对GJ 436b在3.6和4.5μm的热辐射进行了新的观测，减少了GJ 436b在这些波长的通量估计的不确定性，并证明了跨越7年以上的斯皮策观测之间的一致性。分析了斯皮策热发射光度法和哈勃WFC3透射谱。我们使用了自洽模型和检索模型的双管齐下的建模方法。我们通过潮汐加热、不平衡化学和热再分配来改变金属丰度和本征光度。我们还研究了云和光化学烟雾，但没有找到有力的证据来证明这两种现象。自洽模型和反演模型相结合表明，GJ436b具有较高的大气金属丰度，最适合太阳金属丰度的数百倍或更高，潮汐加热使其内部升温，最佳本征有效温度在300-350K左右，以及不平衡化学。较高的金属丰度(>；600×太阳)来自岩石而不是冰冷物质的吸积。假定内部温度为Tint∼300K-350K，我们得到一个耗散因子Q‘∼2×10~5-10~6，比海王星的Q’大，这意味着轨道的潮汐环化时间尺度较长。我们认为，海王星质量的行星可能比想象的更加多样化，金属增强跨越几个数量级，可能超过1000倍的太阳金属丰度。利用詹姆斯·韦伯太空望远镜等仪器进行的高保真观测将是描述这种多样性的关键。
The Neptune-mass GJ 436b is one of the most studied transiting exoplanets with repeated measurements of its thermal emission and transmission spectra. We build on previous studies to answer outstanding questions about this planet, including its potentially high metallicity and tidal heating of its interior. We present new observations of GJ 436b’s thermal emission at 3.6 and 4.5 μm, which reduce uncertainties in estimates of GJ 436b’s flux at those wavelengths and demonstrate consistency between Spitzer observations spanning more than 7 yr. We analyze the Spitzer thermal emission photometry and Hubble WFC3 transmission spectrum. We use a dual-pronged modeling approach of both self-consistent and retrieval models. We vary the metallicity, intrinsic luminosity from tidal heating, disequilibrium chemistry, and heat redistribution. We also study clouds and photochemical hazes, but do not find strong evidence for either. The self-consistent and retrieval models combine to suggest that GJ 436b has a high atmospheric metallicity, with best fits at or above several hundred times solar metallicity, tidal heating warming its interior with best-fit intrinsic effective temperatures around 300–350 K, and disequilibrium chemistry. High metal enrichments (>600× solar) occur from the accretion of rocky, rather than icy, material. Assuming the interior temperature Tint ∼ 300–350 K, we find a dissipation factor Q′ ∼ 2 × 105–106, larger than Neptune’s Q′, implying a long tidal circularization timescale for the orbit. We suggest that Neptune-mass planets may be more diverse than imagined, with metal enhancements spanning several orders of magnitude, to perhaps over 1000× solar metallicity. High-fidelity observations with instruments like the James Webb Space Telescope will be critical for characterizing this diversity.