AKARI OBSERVATIONS OF BROWN DWARFS. II. CO_2 AS PROBEOF CARBON AND OXYGEN ABUNDANCE IN BROWN/ DWARFS.
AKARI OBSERVATIONS OF BROWN DWARFS. II. CO_2 AS PROBEOF CARBON AND OXYGEN ABUNDANCE IN BROWN/ DWARFS.
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AKARI 对褐矮星的观测。
DOI：
10.1088/0004-637x/734/2/73
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发表时间：
2011
期刊：
影响因子：
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通讯作者：
S. Sorahana
中科院分区：
文献类型：
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作者：
T. Tsuji;I. Yamamura;S. Sorahana
红外天文卫星AKARI最近的观测表明，三颗褐矮星4.2 μm处的CO2谱带比基于最近太阳C & O丰度的统一云模型（UCM）所预期的要强得多。这一结果一直是个谜，但我们现在发现这仅仅是由于碳氧丰度的影响。我们发现，这些强大的CO2带可以解释与UCM的基础上的经典的C & O丰度（log A C和log A O），这是约0.2德克斯相比，最近的值。由于其他三个棕矮星可以解释得相当好，最近的太阳C & O丰度，我们需要至少两个模型序列的基础上不同的化学成分来解释所有的AKARI光谱。这是因为CO2谱带对C & O丰度特别敏感，因为CO2丰度近似取决于C & O丰度的立方ACA2O。由于这个原因，即使是低分辨率的光谱非常冷的矮星，特别是二氧化碳，不能理解，除非一个模型与适当的丰度。出于同样的原因，二氧化碳是碳氧丰度的一个很好的指标，我们现在可以估计褐矮星的碳氧丰度，如下所示：AKARI观测到的六颗褐矮星中有三颗应该具有类似于经典太阳值的高C & O丰度（如log A C= 8.60和log A O= 8.92），但其他三个可能具有类似于最近太阳值的低C & O丰度（如log A C= 8.39和log A O= 8.69）。这一结果意味着，如果最近的太阳碳氧丰度是正确的，那么六颗棕矮星中的三颗相对于太阳来说是高度富金属的。
Recent observations with the infrared astronomical satellite AKARI have shown that the CO 2 bands at 4.2 μm in three brown dwarfs are much stronger than expected from the unified cloudy model (UCM) based on recent solar C & O abundances. This result has been a puzzle, but we now find it is simply due to the effect of C & O abundances. We show that these strong CO 2 bands can be explained with the UCMs based on the classical C & O abundances (log A C and log A O), which are about 0.2 dex larger compared to the recent values. Since three other brown dwarfs could be interpreted fairly well with the recent solar C & O abundances, we require at least two model sequences based on the different chemical compositions to interpret all the AKARI spectra. The reason is that the CO 2 band is especially sensitive to C & O abundances, since the CO 2 abundance depends approximately on A C A 2 O—the cube of C & O abundances. For this reason, even low-resolution spectra of very cool dwarfs, especially of CO 2, cannot be understood unless a model with proper abundances is applied. For the same reason, CO 2 is an excellent indicator of C & O abundances, and we can now estimate C & O abundances of brown dwarfs as follows: Three of the six brown dwarfs observed with AKARI should have high C & O abundances similar to the classical solar values (eg, log A C= 8.60 and log A O= 8.92), but the other three may have low C & O abundances similar to the recent solar values (eg, log A C= 8.39 and log A O= 8.69). This result implies that three of the six brown dwarfs are highly metal-rich relative to the Sun, if the recent solar C & O abundances are correct.