时间分辨的哈勃空间望远镜宽视场相机3分光光度测量揭示高辐照褐矮星SDSS 1557B的昼夜热量再分布效率低下
Time-resolved Hubble Space Telescope Wide Field Camera 3 Spectrophotometry Reveals Inefficient Day-to-Night Heat Redistribution in the Highly Irradiated Brown Dwarf SDSS 1557B
AI总结：
本研究利用哈勃望远镜的观测数据分析白矮星-褐矮星双星SDSS 1557的相位分辨光谱，发现该高辐照褐矮星昼夜热量再分布效率弱，夜侧以云层为主、昼侧受H⁻不透明度和温度反转主导。
摘要：
围绕白矮星运行的超短周期褐矮星为研究潮汐锁定、快速自转（1-3小时）且受高辐照的大气特性提供了独特契机。本文呈现了白矮星-褐矮星（WD-BD）双星系统SDSS 1557的相位分辨分光光度测量结果，该系统是我们6个天体样本中的第5个WD-BD双星系统。利用哈勃空间望远镜宽视场相机3近红外G141仪器，1.1至1.7μm的相位曲线显示出自转调制信号，其半振幅为10.5±0.1%。我们观测到振幅存在波长依赖性，波长越长振幅越大，但未发现波长相关的相位偏移。经相位分辨提取的褐矮星光谱呈现陡峭斜率且几乎无特征。一个简单的辐射能量再分布大气模型复现了三个不同相位的半球积分亮温，并发现了再分布效率较弱的证据。我们的模型还预测出比已发表结果更高的轨道倾角。研究发现，作为样本中辐照强度第二高的褐矮星，SDSS 1557B的夜侧可能以云层为主，而无特征的昼侧光谱可能主要由H⁻不透明度和温度反转主导，这与另一颗高辐照褐矮星EPIC2122B的情况非常相似。
英文摘要：
Brown dwarfs in ultra-short period orbits around white dwarfs offer a unique opportunity to study the properties of tidally-locked, fast rotating (1-3 hr), and highly-irradiated atmospheres. Here, we present phase-resolved spectrophotometry of the white dwarf-brown dwarf (WD-BD) binary SDSS 1557, which is the fifth WD-BD binary in our six-object sample. Using the Hubble Space Telescope Wide Field Camera 3 Near-infrared G141 instrument, the 1.1 to 1.7 $μ$m phase curves show rotational modulations with semi-amplitudes of 10.5$\pm$0.1%. We observe a wavelength dependent amplitude, with longer wavelengths producing larger amplitudes, while no wavelength dependent phase shifts were identified. The phase-resolved extracted BD spectra exhibit steep slopes and are nearly featureless. A simple radiative energy redistribution atmospheric model recreates the hemisphere integrated brightness temperatures at three distinct phases and finds evidence for weak redistribution efficiency. Our model also predicts a higher inclination than previously published. We find that SDSS 1557B, the second most irradiated BD in our sample, is likely dominated by clouds on the night side, whereas the featureless day side spectrum is likely dominated by H$^-$ opacity and a temperature inversion, much like the other highly-irradiated BD EPIC2122B.
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