3.8 μm Imaging of 400–600 K Brown Dwarfs and Orbital Constraints for WISEP J045853.90+643452.6AB
3.8 μm Imaging of 400–600 K Brown Dwarfs and Orbital Constraints for WISEP J045853.90+643452.6AB
复制标题
400–600 K 棕矮星的 3.8 μm 成像和 WISEP J045853.90+643452.6AB 的轨道约束
作者：
S. Leggett;T. Dupuy;C. Morley;M. Marley;W. Best;Michael C. Liu;D. Apai;S. Casewell;T. Geballe;J. Gizis;J. Pineda;M. Rieke;G. Wright
晚T型和Y型棕矮星发射的能量的一半出现在3.5 ≤ λ μm ≤ 5.5处。我们提出了在双子座北望远镜上获得的九颗晚T和Y矮星的新L '（3.43 ≤ λ μm ≤ 4.11）测光，并从另外两颗矮星的光谱合成了L'。这些目标包括两个以0.25英寸分辨率成像的二元系统。其中之一，WISEP J045853.90+643452.6AB，显示了显着的运动，我们提出了一个天体测量分析的二进制使用哈勃太空望远镜，凯克自适应光学，双子座图像。我们比较了λ <$4 μm的观测值和模型，发现对于温度低于700 K的褐矮星，模型的通量太低。这种差异随着温度的降低而增加，并且在Teff = 500 K时是Δ 2的因子，在Teff = 400 K时是Δ 4的因子。加热模型大气的上层，产生的光谱更接近于观测到的光谱。在辐射-对流边界之上的冷棕矮星大气的热结构可能无法用纯辐射平衡来模拟;相反，热可能是由热化学不稳定性（先前建议的L-到T-型转变）或破碎的重力波（先前建议的太阳系巨行星）引入的。一维模型可能无法捕获这些大气，这些大气可能具有水平和垂直压力/温度变化。
Half of the energy emitted by late-T- and Y-type brown dwarfs emerges at 3.5 ≤ λ μm ≤ 5.5. We present new L′ (3.43 ≤ λ μm ≤ 4.11) photometry obtained at the Gemini North telescope for nine late-T and Y dwarfs, and synthesize L′ from spectra for an additional two dwarfs. The targets include two binary systems that were imaged at a resolution of 0.″25. One of these, WISEP J045853.90+643452.6AB, shows significant motion, and we present an astrometric analysis of the binary using Hubble Space Telescope, Keck Adaptive Optics, and Gemini images. We compare λ ∼ 4 μm observations to models, and find that the model fluxes are too low for brown dwarfs cooler than ∼700 K. The discrepancy increases with decreasing temperature, and is a factor of ∼2 at Teff = 500 K and ∼4 at Teff = 400 K. Warming the upper layers of a model atmosphere generates a spectrum closer to what is observed. The thermal structure of cool brown dwarf atmospheres above the radiative-convective boundary may not be adequately modeled using pure radiative equilibrium; instead heat may be introduced by thermochemical instabilities (previously suggested for the L- to T-type transition) or by breaking gravity waves (previously suggested for the solar system giant planets). One-dimensional models may not capture these atmospheres, which likely have both horizontal and vertical pressure/temperature variations.
DOI：
10.3847/1538-4365/aaf6af
发表时间：
2018-12
期刊：
The Astrophysical Journal Supplement Series
影响因子：
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作者：
J. Kirkpatrick;E. Martin;R. Smart;Alfred J. Cayago;C. Beichman;F. Marocco;C. Gelino;J. Faherty-
通讯作者：
J. Kirkpatrick;E. Martin;R. Smart;Alfred J. Cayago;C. Beichman;F. Marocco;C. Gelino;J. Faherty-