C60+与星际弥散带的交叉证认

Abstract: The so-called “diffuse interstellar bands” (DIBs) are a large number of absorption bands superimposed on the interstellar extinction curve in the optical and near-infrared wavelength range. Since their first detection over 90 years ago, not even a single DIB has been identified. Very recently, the gas-phase absorption spectrum of C60 cation has been experimentally obtained and found to agree with five DIBs at 9348.4、9365.2、9427.8、9577.0、9632.1Å both in peak wavelengths and relative intensities, suggesting that C60 cation may be a promising DIB carrier candidate. We propose to examine the hypothesis of C60 cation as a DIB carrier based on a cross-correlation study of the infrared emission bands of C60 cation at 6.4, 7.1, 8.2 and 10.5μm with the five DIBs at 9348.4、9365.2、9427.8、9577.0、9632.1Å. Our rationale is that, if C60 cation is indeed responsible for the 9348.4、9365.2、9427.8、9577.0、9632.1Å DIBs, for those lines of sight toward which these five DIBs have been detected, one expects to see the 6.4, 7.1, 8.2 and 10.5μm emission bands of C60 cation, while for those lines of sight toward which the 6.4, 7.1, 8.2 and 10.5μm emission bands of C60 cation have been detected, one expects to see the five DIBs at 9348.4、9365.2、9427.8、9577.0、9632.1Å. This will allow us to constrain the hypothesis of C60 cation as a DIB carrier.

星际弥散带(DIBs)是叠加在星际消光曲线上的数百条吸收光谱带,其载体至今仍未获得证认。最近有研究发现,C60+的电子吸收光谱与5条DIBs（9348.4、9365.2、9427.8、9577、9632.1Å）很类似,从而C60+作为DIBs的可能载体受到了极大关注。本项目以检验C60+作为DIBs载体之假说为目的,研究星际空间C60+与DIBs的关系:(1)对具有上述DIBs的星际视线,搜寻Spitzer和ISO红外数据,看是否有对应丰度的波长为6.4、7.1、8.2、10.5μm的C60+辐射谱;(2)对具有C60+这些红外辐射谱的星际视线,从国内外望远镜光谱库中搜寻可见、近红外吸收谱,看是否有对应强度的上述DIBs；(3)考察各天区的上述DIBs数据,看这些DIBs是否相关。如果C60+确实是DIBs的载体,那么上述5条DIBs与C60+红外辐射谱应互相对应,且各DIBs之间应相关。

星际弥散带(DIBs)是叠加在星际消光曲线上的数百条吸收光谱带,其载体至今仍未获得证认。2015年, 瑞士巴塞尔大学Campbell 等人通过实验首次得以测量C60+的气相谱，发现C60+ 的气相谱与9348.4、9365.2、9427.8、9577.0、9632.1Å五条DIBs的中心波长以及相对强度很一致，从而C60+作为DIBs的可能载体受到了极大关注。为揭示 C60+与DIB的关系，我们对DIBs和C60+ 开展了一系列研究。(1)观测收集了1000多个目标星的光谱数据,通过拟合得到了9365.2Å，9427.8Å，9577.0Å，9632.1Å 4条DIBs的等值宽度,研究发现这4条DIBs(9365.2Å，9427.8Å，9577.0Å，9632.1Å)的等值宽度之间具有很强的正相关性,表明它们可能起源于同一载体。(2)搜寻了Spitzer和ISO红外数据, 在大质量恒星形成区Sgr B2 发现了C60和C24红外特征谱。(3) 用“消光分解”(decomposition) 定量分析方法对大量消光曲线进行了分析,得到了可见光、2175Å消光驼峰、远紫外三部分消光的积分总量；研究了星际中气态C与星际消光2175Å消光驼峰、远紫外强度之间的关系; 结果发现它们没有明显的相关性;这一结果表明星际2175Å 消光驼峰可能不是来自于星际空间单一C元素的贡献。