Fonfría J P, Hinkle K H, Cernicharo J, Richter M J, Agúndez M, Wallace L
Grupo de Astrofísica Molecular, Instituto de Ciencia de los Materiales, CSIC, C/ Sor Juana Inés de la Cruz, 3, Cantoblanco, 28049, Madrid, Spain.
National Optical Astronomy Observatory, P.O. Box 26732, Tucson, Arizona 85726, USA.
Astrophys J. 2017 Feb 1;835(2). doi: 10.3847/1538-4357/835/2/196. Epub 2017 Jan 31.
High spectral resolution mid-IR observations of ethylene (CH) towards the AGB star IRC+10216 were obtained using the Texas Echelon Cross Echelle Spectrograph (TEXES) at the NASA Infrared Telescope Facility (IRTF). Eighty ro-vibrational lines from the 10.5 m vibrational mode with ≲ 30 were detected in absorption. The observed lines are divided into two groups with rotational temperatures of 105 and 400 K (warm and hot lines). The warm lines peak at ≃ -14 km s with respect to the systemic velocity, suggesting that they are mostly formed outwards from ≃ 20. The hot lines are centered at -10 km s indicating that they come from a shell between 10 and 20. 35% of the observed lines are unblended and can be fitted with a code developed to model the emission of a spherically symmetric circumstellar envelope. The analysis of several scenarios reveal that the CH abundance relative to H in the range 5 - 20 is 6.9 × 10 in average and it could be as high as 1.1 × 10. Beyond 20, it is 8.2 × 10. The total column density is (6.5 ± 3.0) × 10 cm. CH is found to be rotationally under local thermodynamical equilibrium (LTE) and vibrationally out of LTE. One of the scenarios that best reproduce the observations suggests that up to 25% of the CH molecules at 20 could condense onto dust grains. This possible depletion would not influence significantly the gas acceleration although it could play a role in the surface chemistry on the dust grains.
利用美国国家航空航天局红外望远镜设施（IRTF）的德州阶梯交叉阶梯光谱仪（TEXES），对渐近巨星分支（AGB）恒星IRC+10216进行了高光谱分辨率的中红外乙烯（CH）观测。在吸收谱中检测到了来自10.5 m振动模式、转动量子数J≲30的80条转动-振动谱线。观测到的谱线分为两组，转动温度分别为105 K和400 K（温线和热线）。温线相对于系统速度在≃ -14 km s处达到峰值，表明它们主要形成于≃ 20处的外层。热线以-10 km s为中心，表明它们来自10至20之间的壳层。35%的观测谱线未混合，可以用一个为模拟球对称星周包层发射而开发的代码进行拟合。对几种情况的分析表明，在5 - 20范围内，CH相对于H的丰度平均为6.9×10，最高可达1.1×10。超过20时，为8.2×10。总柱密度为(6.5 ± 3.0)×10 cm。发现CH在转动上处于局部热力学平衡（LTE）之下，在振动上偏离LTE。最能重现观测结果的一种情况表明，在20处高达25%的CH分子可能会凝结在尘埃颗粒上。这种可能的消耗虽然可能在尘埃颗粒的表面化学中起作用，但不会对气体加速产生显著影响。
