标题： 彗星中NH_3射电谱线的近期探测 显示英文标题

标题： Recent Searches for the Radio Lines of NH_3 in Comets

摘要： 对四颗彗星C/2001 A2（LINEAR）、153P/Ikeya-Zhang、C/2001 Q4（NEAT）和C/2002 T7（LINEAR）的氨分子反转线进行了观测，这些观测是在它们各自接近地球时使用Effelsberg 100米射电望远镜完成的。 在这几颗彗星中未能检测到氨的四个最低能级亚稳态线（J,K=J），J=1–4。 我们得出以下NH_3生成率的3σ上限，并与相应的水生成率比较，得到NH_3相对于H_2O的百分比丰度： Q(NH_3) < 1.9×10^26 s^-1 (0.63%) 对于C/2001 A2（LINEAR）， Q(NH_3) < 2.7×10^26 s^-1 (0.13%) 对于C/2001 Q4（NEAT）， Q(NH_3) < 2.3×10^27 s^-1 (0.74%) 对于C/2002 T7（LINEAR）和Q(NH_3) ≤ 6.3×10^26 s^-1 (0.63%) 对于彗星153P/Ikeya-Zhang。 在0.74%或更低时，氨与水的比例值比C/1995 O1（Hale-Bopp）和1P/Halley的值低一个因数2，这表明彗星之间存在化学多样性。 在2004年观测的两颗彗星中清楚地检测到了OH的18厘米谱线，从而验证了彗星的星历表。 显示英文摘要

摘要： Radio observations in the ammonia inversion lines of four comets, C/2001 A2 (LINEAR), 153P/Ikeya-Zhang, C/2001 Q4 (NEAT) and C/2002 T7 (LINEAR), were performed at the Effelsberg 100-m Radio Telescope during their respective close approaches to Earth. None of the four lowest energy metastable lines (J,K=J),J=1--4, could be detected in these comets. We derive the following 3 sigma upper bounds on the NH_3 production rate, and c omparing to the corresponding water production rates, percentage NH_3 abundances relative to H_2O: Q(NH_3) < 1.9x10^26 s^-1 (0.63%) for C/2001 A2 (LINEAR), Q(NH_3) < 2.7x10^26 s^-1 (0.13%) for C/2001 Q4 (NEAT), Q(NH_3) < 2.3x10^27 s^-1 (0.74%) for C/2002 T7 (LINEAR) and Q(NH_3) <= 6.3x10^26 s^-1 (0.63%) for Comet 153P/Ikeya-Zhang. At 0.74% or less, the ammonia-to-water ratios are factors of 2 below the value for C/1995 O1 (Hale-Bopp) and 1P/Halley, suggesting chemical diversity between comets. The 18-cm lines of OH were clearly detected in the two comets observed during the 2004 campaign, thereby validating the cometary ephemerides.