论文标题
CN在TW hya中的激发条件
The Excitation Conditions of CN in TW Hya
论文作者
论文摘要
我们报告了两种圆盘中氰化物阴离子CN的观察结果，涵盖了$ n = 1-0 $，$ n = 2-1 $和$ n = 3-2 $ transitions。使用线堆叠技术，在观察到的频率范围内检测到30个超细转变。从线堆积方法中利用超光谱分辨率的揭示了先前未通过实验室光谱解决的超精细分量的分裂。 All transitions display a similar emission morphology, characterized by an azimuthally symmetric ring, peaking at $\approx 45$~au (0.75"), and a diffuse outer tail extending out to the disk edge at $\approx 200$~au. Excitation analyses assuming local thermodynamic equilibrium (LTE) yield excitation temperatures in excess of the derived kinetic temperatures based on the local line所有精细的结构组的宽度，建议使用0D辐射转移代码radex的LTE假设，我们证明，当局部H $ _2 $密度下降到$ 10^{7}〜{\ rm cm cm^{ - 3}} $ shode时，可能会出现这种非LTE效果。 $ z \， / \，r \ gtrsim 0.2 $，与模型预测一致，这些预测是通过振动激发的h $ _2 $在磁盘大气层中形成的，其中紫外线照射降低了。
We report observations of the cyanide anion, CN, in the disk around TW~Hya covering the $N=1-0$, $N=2-1$ and $N=3-2$ transitions. Using line stacking techniques, 24 hyperfine transitions are detected out of the 30 within the observed frequency ranges. Exploiting the super-spectral resolution from the line stacking method reveals the splitting of hyperfine components previously unresolved by laboratory spectroscopy. All transitions display a similar emission morphology, characterized by an azimuthally symmetric ring, peaking at $\approx 45$~au (0.75"), and a diffuse outer tail extending out to the disk edge at $\approx 200$~au. Excitation analyses assuming local thermodynamic equilibrium (LTE) yield excitation temperatures in excess of the derived kinetic temperatures based on the local line widths for all fine structure groups, suggesting assumptions of LTE are invalid. Using the 0D radiative transfer code RADEX, we demonstrate that such non-LTE effects may be present when the local H$_2$ density drops to $10^{7}~{\rm cm^{-3}}$ and below. Comparison with models of TW~Hya find similar densities at elevated regions in the disk, typically $z \, / \, r \gtrsim 0.2$, consistent with model predictions where CN is formed via vibrationally excited H$_2$ in the disk atmospheric layers where UV irradiation is less attenuated.
