若い惑星の星雲K4-47における極度のC,N,O同位素濃縮
D R Schmidt1, N J Woolf1, T J Zega2
1Department of Astronomy, Steward Observatory, University of Arizona, Tucson, AZ, USA.
Nature
|December 21, 2018
まとめ
惑星の星雲K4-47は,希少な同位体の高濃度を示し,窒素-15と酸素-17の新しい源を示唆しています. この発見は現在の恒星核合成モデルと 恒星間物質の進化に挑戦しています
科学分野:
- 天文学と天体物理学
- 宇宙化学
- 核天体物理学
背景:
- 炭素,窒素,酸素は 恒星で形成された重要な元素で 銀河の化学的進化を理解するために 極めて重要です
- 同位体比 (例えば,12C/13C,14N/15N,16O/17O) は,初期の太陽系における核合成と化学プロセスのトレーサとして機能する.
- 15Nと17Oのような稀な同位体の起源は完全に理解されていませんが,以前は新星と超新星が主要な源と考えられていました.
研究 の 目的:
- 双極惑星星雲K4-47の 同位体組成を調べるため
- 稀な同位体15Nと17Oの生産のための潜在的な新しい源を特定する.
- 恒星核合成と化学進化のモデルを比較し,精錬する.
主な方法:
- 惑星の星雲K4-47のミリメートル波長観測
- K4-47内の炭素含有分子の識別
- 同位体比の測定: 12C/13C,14N/15N,そして16O/17O
主要な成果:
- K4-47は炭素が豊富であることが確認されています.
- 12C/13C = 2.2 ± 0.8,16O/17O = 21.4 ± 10.3,そして14N/15N = 13.6 ± 6.5という珍しい同位体の異常な濃度が検出されました.
- これらの比率は太陽系値と大きく異なっており,独特の核合成過程を示しています.
結論:
- 観測されたK4-47の同位体異常は,ヘリウムシェルフラッシュを経験したJ型アシンプトティック巨大分岐星から発生した可能性があることを示唆している.
- 別の説明としては,K4-47が二進星系であるか,白矮星が合併した結果である.
- この発見は,炭素,窒素,酸素の核合成に関する現在の理解が不完全であり,星塵の粒子の分類の再評価が必要であることを示唆している.
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