宇宙结晶性难题：来自IRAS 17495-2534的线索
The Cosmic Crystallinity Conundrum: Clues from IRAS 17495-2534
摘要：
自发现以来，宇宙结晶硅酸盐对理解尘埃的形成和演化提出了几个挑战。IRAS 17495 $-$ 2534的中红外光谱，是一颗高度模糊的富氧渐近巨星分支（AGB）恒星，是迄今为止观测到的唯一一个显示出清晰的结晶硅酸盐吸收特征的光谱源。这提供了一个前所未有的机会来测试尘埃形成的竞争假设。观测到的光谱特征表明，无论是非晶态尘埃还是晶态尘埃，其主要成分都是镁橄榄石（Mg 2 SiO 4），而不是顽火辉石（MgSiO 3）或其他硅酸盐成分。我们证实，高质量损失率应产生更多的结晶材料，并显示为什么这应该是由镁橄榄石为主。Mg 2 SiO 4玻璃的存在表明另一个因素（可能是C/O）在确定天体矿物学中是关键的。结晶度，质量损失率和初始恒星质量之间的相关性表明，只有质量最大的AGB恒星贡献了大量的晶体物质的星际介质，解决了其低结晶度的难题。
英文摘要：
Since their discovery, cosmic crystalline silicates have presented several challenges to understanding dust formation and evolution. The mid-infrared spectrum of IRAS 17495$-$2534, a highly obscured oxygen-rich asymptotic giant branch (AGB) star, is the only source observed to date which exhibits a clear crystalline silicate absorption feature. This provides an unprecedented opportunity to test competing hypotheses for dust formation. Observed spectral features suggest that both amorphous and crystalline dust is dominated by forsterite (Mg\_2 SiO\_4) rather than enstatite (MgSiO\_3) or other silicate compositions. We confirm that high mass-loss rates should produce more crystalline material, and show why this should be dominated by forsterite. The presence of Mg\_2 SiO\_4 glass suggests that another factor (possibly C/O) is critical in determining astromineralogy. Correlation between crystallinity, mass-loss rate and initial stellar mass suggests that only the most massive AGB stars contribute significant quantities of crystalline material to the interstellar medium, resolving the conundrum of its low crystallinity.
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