The Near-Infrared and Optical Spectra of Methane Dwarfs and Brown Dwarfs
The Near-Infrared and Optical Spectra of Methane Dwarfs and Brown Dwarfs
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甲烷矮星和褐矮星的近红外和光谱
DOI：
10.1086/308462
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发表时间：
1999
期刊：
影响因子：
--
通讯作者：
C. M. Sharp
中科院分区：
文献类型：
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作者：
Adam Burrows;M. Marley;C. M. Sharp
我们发现，在7700 ° C处饱和钾共振线的压力加宽的红翼是Gliese 229 B近红外光谱中异常吸收的来源，并由此延伸到一般的甲烷矮星。大体上，这一结论得到了Tsuji等人1999年工作的支持。Gliese 229 B的WFPC 2 I波段测量也与这一假设一致。此外，这个K I共振双峰的蓝翼、Na D线在5890 nm的红翼，以及Li I线在6708 nm的组合，可以自然地解释观测到的格利泽229 B WFPC 2 R带通量。因此，我们得出结论，中性碱金属在甲烷矮星的近红外光谱和光学光谱中起着核心作用，它们的谱线有可能为棕矮星的性质提供重要的诊断。我们推测甲烷矮星的近红外光谱和光学光谱的系统学，对于一个给定的质量和组成，这源于逐步埋葬与减少Teff的碱金属原子更大的压力和深度。此外，我们推测，那些太阳系外的巨行星（EGP），达到800-1300 K范围内的Teff值，因为恒星的日照将显示在其反射光谱和反射光谱的中性碱金属的签名。我们估计，主要是由于Na-D线的吸收，EGP τ Boo B在λ = 0.48 μm处的几何散射度小于0.1，这与Charbonneau等人最近在1999年获得的新的（和低的）上限0.3一致。
We identify the pressure-broadened red wings of the saturated potassium resonance lines at 7700 Å as the source of anomalous absorption seen in the near-infrared spectra of Gliese 229B and, by extension, of methane dwarfs in general. In broad outline, this conclusion is supported by the 1999 work of Tsuji et al. The WFPC2 I-band measurement of Gliese 229B is also consistent with this hypothesis. Furthermore, a combination of the blue wings of this K I resonance doublet, the red wings of the Na D lines at 5890 Å, and, perhaps, the Li I line at 6708 Å can explain in a natural way the observed WFPC2 R-band flux of Gliese 229B. Hence, we conclude that the neutral alkali metals play a central role in the near-infrared and optical spectra of methane dwarfs and that their lines have the potential to provide crucial diagnostics of brown dwarf properties. We speculate on the systematics of the near-infrared and optical spectra of methane dwarfs, for a given mass and composition, that stems from the progressive burial with decreasing Teff of the alkali metal atoms to larger pressures and depths. Moreover, we surmise that those extrasolar giant planets (EGPs) that achieve Teffvalues in the 800-1300 K range because of stellar insolation will show signatures of the neutral alkali metals in their albedo and reflection spectra. We estimate that, predominantly because of absorption by Na D lines, the geometric albedo of the EGP τ Boo b at λ = 0.48 μm is less than 0.1, which is consistent with the new (and low) upper limit of 0.3 recently obtained by Charbonneau et al. in 1999.