Haenecour Pierre, Floss Christine, José Jordi, Amari Sachiko, Lodders Katharina, Jadhav Manavi, Wang Alian, Gyngard Frank
Laboratory for Space Sciences, Washington University in St. Louis, One Brookings Drive, St. Louis, MO 63130-4899, USA.
Department of Earth and Planetary Sciences, Washington University in St. Louis, One Brookings Drive, St. Louis, MO 63130-4899, USA.
Astrophys J. 2016;825. doi: 10.3847/0004-637X/825/2/88. Epub 2016 Jul 6.
Presolar grains constitute the remnants of stars that existed before the formation of the solar system. In addition to providing direct information on the materials from which the solar system formed, these grains provide ground-truth information for models of stellar evolution and nucleosynthesis. Here we report the in situ identification of two unique presolar graphite grains from the primitive meteorite LaPaz Icefield 031117. Based on these two graphite grains, we estimate a bulk presolar graphite abundance of ppm in this meteorite. One of the grains (LAP-141) is characterized by an enrichment in C and depletions in S, and contains a small iron sulfide subgrain, representing the first unambiguous identification of presolar iron sulfide. The other grain (LAP-149) is extremely C-rich and N-poor, with one of the lowest C/C ratios observed among presolar grains. Comparison of its isotopic compositions with new stellar nucleosynthesis and dust condensation models indicates an origin in the ejecta of a low-mass CO nova. Grain LAP-149 is the first putative nova grain that quantitatively best matches nova model predictions, providing the first strong evidence for graphite condensation in nova ejecta. Our discovery confirms that CO nova graphite and presolar iron sulfide contributed to the original building blocks of the solar system.
前太阳颗粒是太阳系形成之前存在的恒星的残余物。这些颗粒除了提供有关太阳系形成物质的直接信息外，还为恒星演化和核合成模型提供了真实信息。在此，我们报告了从原始陨石拉巴斯冰原031117中对两颗独特的前太阳石墨颗粒的原位鉴定。基于这两颗石墨颗粒，我们估计该陨石中前太阳石墨的总体丰度为百万分之一。其中一颗颗粒（LAP-141）的特征是碳富集、硫贫化，并且包含一个小的硫化铁亚颗粒，这是前太阳硫化铁的首次明确鉴定。另一颗颗粒（LAP-149）极度富碳且贫氮，是在前太阳颗粒中观测到的碳/碳比最低的之一。将其同位素组成与新的恒星核合成和尘埃凝聚模型进行比较表明，它起源于低质量碳氧新星的抛射物。颗粒LAP-149是第一个在数量上与新星模型预测最佳匹配的假定新星颗粒，为新星抛射物中的石墨凝聚提供了首个有力证据。我们的发现证实，碳氧新星石墨和前太阳硫化铁是太阳系原始组成部分。
