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arXiv 0901.2134astro-ph.SR
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两颗晚型T矮星中一氧化碳的光谱探测

Spectroscopic Detection of Carbon Monoxide in Two Late-type T Dwarfs

T. R. Geballe, D. Saumon, D. A. Golimowski, S. K. Leggett, M. S. Marley, K. S. Noll

摘要:

两颗晚型T矮星2 MASS J 09373487 +2931409和Gliese 570 D的M波段光谱证实了光度学的证据,即光球层CO的丰度水平远远超过化学平衡预测的水平。这些新的和明确的检测CO,再加上更早的光谱检测到的一氧化碳在格利泽229 B和现有的M波段测光的一个大的选择T矮星,表明垂直混合在光球驱动器的CO丰度的化学平衡,是一个共同的,可能是普遍的特征中晚期型T矮星。M波段光谱允许确定每个物体大气中垂直混合的时间尺度,这是晚T矮星中首次测量这一重要参数。对2 MASS J 09373487 +2931409的光谱能量分布的详细分析得出以下金属丰度、温度、表面重力和光度值:[M/H]~-0.3,T_eff=925- 975 K,log g=5.20-5.47,log L/L_sun=-5.308 +/- 0.027。年龄为3-10 Gyr,质量范围为45-69 M_Jup。

英文摘要:

M band spectra of two late-type T dwarfs, 2MASS J09373487+2931409, and Gliese 570D, confirm evidence from photometry that photospheric CO is present at abundance levels far in excess of those predicted from chemical equilibrium. These new and unambiguous detections of CO, together with an earlier spectroscopic detection of CO in Gliese 229B and existing M band photometry of a large selection of T dwarfs, suggest that vertical mixing in the photosphere drives the CO abundance out of chemical equilibrium and is a common, and likely universal feature of mid-to-late type T dwarfs. The M band spectra allow determinations of the time scale of vertical mixing in the atmosphere of each object, the first such measurements of this important parameter in late T dwarfs. A detailed analysis of the spectral energy distribution of 2MASS J09373487+2931409 results in the following values for metallicity, temperature, surface gravity, and luminosity: [M/H]~-0.3, T_eff=925-975K, log g=5.20-5.47, log L/L_sun=-5.308 +/- 0.027. The age is 3-10 Gyr and the mass is in the range 45-69 M_Jup.

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