原恒星包层和激波中的氮氧化物：ASAI巡天
Nitrogen oxide in protostellar envelopes and shocks: the ASAI survey
摘要：
IRAM 30-m ASAI无偏光谱测量在毫米窗口的高灵敏度使我们能够检测到NO排放对I类对象SVS 13-A和原恒星流出冲击L1157-B1。我们检测到的超精细成分的$^2Π_{\rm 1/2}$ $J$ = 3/2 $\to$ 1/2（在151 GHz）和$^2Π_{\rm 1/2}$ $J$ = 5/2 $\to$ 3/2（250 GHz）的光谱模式。这两个对象显示出不同的NO配置文件：（i）SVS 13-A发射通过窄（1.5公里秒$^{-1}$）线在系统速度，而（ii）L1157-B1显示宽（$\sim$ 5公里秒$^{-1}$）蓝移发射。对于SVS 13-A，分析得出$T_{\rm ex}$ $\geq$ 4 K，$N(\rm NO)$ $\leq$ 3 $\times$ 10 $^{15}$ cm $^{-2}$，并表明NO与原恒星包层有关。在L1157-B1中，NO正在追踪延长的流出腔：$T_{\rm ex}$ $\simeq$ 4--5 K，和$N(\rm NO)$ = 5.5 $\pm$ 1.5 $\times$ 10 $^{15}$ cm $^{-2}$。使用C $^{18}$ O，$^{13}$ C $^{18}$ O，C $^{17}$ O，和$^{13}$ C $^{17}$ O ASAI观测，我们得到一个NO分数丰度小于$\sim$ 10 $^{-7}$的SVS 13-A信封，与以前的测量对扩展PDR和星前天体。相反，对L1157-B1，$\sim$ 6 $\times$ 10 $^{-6}$测量到明确的$X(NO)$增强，表明NO产生在电击中增加。使用公共代码UCLCHEM解释NO观测结果，证实在SVS 13-A中观察到的丰度可以在气体密度为10 $^5$ cm $^{-3}$和动力学温度为40 K的包层中获得。在L1157-B1中的NO丰度是用10 $^5$ cm $^{-3}$的冲击前密度进行$\sim$ 45 km s $^{-1}$冲击再现的。
英文摘要：
The high-sensitivity of the IRAM 30-m ASAI unbiased spectral survey in the mm-window allows us to detect NO emission towards both the Class I object SVS13-A and the protostellar outflow shock L1157-B1. We detect the hyperfine components of the $^2Π_{\rm 1/2}$ $J$ = 3/2 $\to$ 1/2 (at 151 GHz) and the $^2Π_{\rm 1/2}$ $J$ = 5/2 $\to$ 3/2 (250 GHz) spectral pattern. The two objects show different NO profiles: (i) SVS13-A emits through narrow (1.5 km s$^{-1}$) lines at the systemic velocity, while (ii) L1157-B1 shows broad ($\sim$ 5 km s$^{-1}$) blue-shifted emission. For SVS13-A the analysis leads to $T_{\rm ex}$ $\geq$ 4 K, $N(\rm NO)$ $\leq$ 3 $\times$ 10$^{15}$ cm$^{-2}$, and indicates the association of NO with the protostellar envelope. In L1157-B1, NO is tracing the extended outflow cavity: $T_{\rm ex}$ $\simeq$ 4--5 K, and $N(\rm NO)$ = 5.5$\pm$1.5 $\times$ 10$^{15}$ cm$^{-2}$. Using C$^{18}$O, $^{13}$C$^{18}$O, C$^{17}$O, and $^{13}$C$^{17}$O ASAI observations we derive an NO fractional abundance less than $\sim$ 10$^{-7}$ for the SVS13-A envelope, in agreement with previous measurements towards extended PDRs and prestellar objects. Conversely, a definite $X(NO)$ enhancement is measured towards L1157-B1, $\sim$ 6 $\times$ 10$^{-6}$, showing that the NO production increases in shocks. The public code UCLCHEM was used to interpret the NO observations, confirming that the abundance observed in SVS13-A can be attained in an envelope with a gas density of 10$^5$ cm$^{-3}$ and a kinetic temperature of 40 K. The NO abundance in L1157-B1 is reproduced with pre-shock densities of 10$^5$ cm$^{-3}$ subjected to a $\sim$ 45 km s$^{-1}$ shock.
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