论文标题
通过HC $ _3 $ N
Investigating Anomalous Photochemistry in the Inner Wind of IRC+10216 Through Interferometric Observations of HC$_3$N
论文作者
论文摘要
近年来，关于进化恒星富含碳风化学产品的化学，出现了许多问题。为了解决这些问题，必须通过高角度分辨率干涉观测来限制此类物种的分布，涵盖多个旋转过渡。我们使用档案ALMA观察来绘制涉及高能氰基（HC $ _3 $ n）的旋转线，向内膜（半径<8“/1000 au），IRC+10216。观察到的线条包括J = 28-27，j = 30-29，J = 30-29，J = 30-29，和J = 38-37-38-37，$ n $ n $ nc $ hc $ hc $ hc in in。以前对这款AGB恒星的线性碳连锁链的观察，该恒星显示了15“ -20” RADII（例如C $ _4 $ H，C $ _4 $ h，c $ _6 $ h，hc $ _5 $ n）的hc $ _3 $ n线的地图，此处显示出各种高度的变形，并显示出各种距离的远距离，并与距〜3“（350 au）来自中央AGB星。我们将可见性采样的非LTE辐射转移模型与观察到的亮度分布进行了比较，并在这些线上探索的HC $ _3 $ n的H $ _2 $ $ _2 $ $ 10^{ - 8} $方面得出了分数丰度。这些结果与折线膜的温暖（约200 K）区域中发生的增强光化学一致。在为IRC+10216应用专门的化学模型后，我们发现证据表明，内风中增强的HC $ _3 $ n的丰度很可能是由于该地区的太阳能二进制二元伴侣启动光化学。
In recent years, many questions have arisen regarding the chemistry of photochemical products in the carbon-rich winds of evolved stars. To address them, it is imperative to constrain the distributions of such species through high angular resolution interferometric observations covering multiple rotational transitions. We used archival ALMA observations to map rotational lines involving high energy levels of cyanoacetylene (HC$_3$N) toward the inner envelope (radius <8"/1000 AU) of the carbon star IRC+10216. The observed lines include the J=28-27, J=30-29, and J=38-37, transitions of HC$_3$N in its ground vibrational state. In contrast to previous observations of linear carbon chains toward this AGB star which show extended, hollow emission at 15"-20" radii (e.g. C$_4$H, C$_6$H, HC$_5$N), the maps of the HC$_3$N lines here show compact morphologies comprising various arcs and density enhancements, with significant emission from gas clumps at an angular distance of ~3" (350 AU) from the central AGB star. We compared visibility sampled non-LTE radiative transfer models with the observed brightness distributions, and derive a fractional abundance with respect to H$_2$ of $10^{-8}$ for HC$_3$N at the radii probed by these lines. These results are consistent with enhanced photochemistry occurring in warm (~200 K) regions of the circumstellar envelope. After application of a specialized chemical model for IRC+10216, we find evidence that the enhanced HC$_3$N abundances in the inner wind are most likely due to a solar-type binary companion initiating photochemistry in this region.
