Deuterium and 15N fractionation in N2H+ during the formation of a Sun-like star
Deuterium and 15N fractionation in N2H+ during the formation of a Sun-like star
复制标题
类太阳恒星形成过程中 N2H 中的氘和 15N 分馏
DOI：
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发表时间：
2018
期刊：
影响因子：
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通讯作者：
J. Soldateschi
中科院分区：
文献类型：
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作者：
M. D. Simone;F. Fontani;C. Codella;C. Ceccarelli;B. Lefloch;R. Bachiller;A. López;E. Caux;E. Caux;C. Vastel;C. Vastel;J. Soldateschi
虽然化学模型预测N$_2$H$^+$中的氘分馏是恒星形成过程中一个很好的进化示踪剂，但氮的分馏仍然是一个知之甚少的过程。最近的模型对N$_2$H$^+$两种分馏机制的相似演化趋势提出了质疑，该模型基于一个经典情景，即在冷气体中发生的离子中性反应应该会导致N$_2$D$^+$、$^{15}$NNH$^+$和N$^{15}$NH$^+$丰度的增强。在ASAI IRAM-30m大型项目的框架下，我们研究了N$_2$H$^+$中氘和$^{15}$N的分异，这是类太阳恒星形成过程中最著名的不同演化阶段的代表。目标是最终确认（或否认）经典的“离子中性反应”情景，该情景预测了D和$^{15}$N分馏的类似趋势。从$^{15}$NNH$^+$和N$^{15}$NH$^+$同位素中均未发现$^{14}$N/$^{15}$N比值的演化趋势。因此，我们的发现证实，在类太阳恒星的形成过程中，核心的演化与$^{15}$N的分值无关。$^{14}$N/$^{15}$N随时间的独立性也在高质量恒星形成核心中发现，这表明在彗星和原行星盘中发现的$^{15}$N的富集不太可能发生在核心尺度上。然而，我们已经确定了预期的H/D比值的演化趋势，即N$_2$H$^+$/N$_2$D$^+$比值在前恒星核心阶段减小，在原恒星阶段单调增大。我们也清楚地证实，这两种分馏机制是不相关的。
Although chemical models predict that the deuterium fractionation in N$_2$H$^+$ is a good evolutionary tracer in the star formation process, the fractionation of nitrogen is still a poorly understood process. Recent models have questioned the similar evolutionary trend expected for the two fractionation mechanisms in N$_2$H$^+$, based on a classical scenario in which ion-neutral reactions occurring in cold gas should have caused an enhancement of the abundance of N$_2$D$^+$, $^{15}$NNH$^+$, and N$^{15}$NH$^+$. In the framework of the ASAI IRAM-30m large program, we have investigated the fractionation of deuterium and $^{15}$N in N$_2$H$^+$ in the best known representatives of the different evolutionary stages of the Sun-like star formation process. The goal is to ultimately confirm (or deny) the classical "ion-neutral reactions" scenario that predicts a similar trend for D and $^{15}$N fractionation. We do not find any evolutionary trend of the $^{14}$N/$^{15}$N ratio from both the $^{15}$NNH$^+$ and N$^{15}$NH$^+$ isotopologues. Therefore, our findings confirm that, during the formation of a Sun-like star, the core evolution is irrelevant in the fractionation of $^{15}$N. The independence of the $^{14}$N/$^{15}$N ratio with time, found also in high-mass star-forming cores, indicates that the enrichment in $^{15}$N revealed in comets and protoplanetary disks is unlikely to happen at core scales. Nevertheless, we have firmly confirmed the evolutionary trend expected for the H/D ratio, with the N$_2$H$^+$/N$_2$D$^+$ ratio decreasing before the pre-stellar core phase, and increasing monotonically during the protostellar phase. We have also confirmed clearly that the two fractionation mechanisms are not related.
影响因子：
3.2
作者：
V. Mannings;A. Boss;S. Russell
通讯作者：
V. Mannings;A. Boss;S. Russell