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宇宙電波観測を用いた、暗黒星雲コアにおける環状C3H2の オルト・パラ比と化学進化の相関に関する研究

Correlation between Nuclear Spin Ratio of cyclic-C3H2 and Chemical Evolution in TMC-1

森澤 勇介
Yusuke MORISAWA


 

野辺山45 m電波望遠鏡を用いて,暗黒星雲TMC-1の5つのコアにおける環状C3H2のオルト遷移4本,パラ遷移4本,計8つの純回転遷移を観測することにより,環状C3H2のオルト/パラ比の分布を求めた。その結果,オルト/パラ比はコアの化学進化の進化度と相関があることがわかった。化学モデル計算から,この相関は化学反応における核スピン保存則を使って説明できることを示した。

Ortho-to-para nuclear spin ratio of cyclopropenylidene (c-C3H2) in TMC-1 cores was investigated using the 45 m radio telescope at Nobeyama Radio Observatory. We have observed four ortho lines (JKaKc = 212-101, 312-303, 321-312, and 330-321) and four para lines (JKaKc = 202111, 211-202, 220-211, and 322-313) of c-C3H2 in six cores in TMC-1. A statistical equilibrium analysis of the observed intensities revealed clear correlation between the ortho-to-para ratio of c-C3H2 and chemical evolution of the molecular cloud; the ortho-to-para ratio in younger cores is less than 2, while that in older cores is close to the statistical ratio of 3. A simple chemical model calculation indicates that the correlation is ascribed to the conservation of nuclear spin angular moment in chemical reactions relevant to the production, destruction, and re-production of c-C3H2.


Keywords:Astronomical observation, Millimeter-wave, Chemical evolution, Interstellar molecule, Nuclear spin modification



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