Microstructural and Chemical Investigations of Presolar Silicates from Diverse Stellar Environments

• Published in: The Astrophysical journal 2022-02, Vol.925 (2), p.110
• Main Authors: Sanghani, Manish N., Lajaunie, Luc, Marhas, Kuljeet Kaur, Rickard, William D. A., Hsiao, Silver Sung-Yun, Peeters, Zan, Shang, Hsien, Lee, Der-Chuen, Calvino, José. J., Bizzarro, Martin
• Format: Article
• Language: English
• Subjects: Aluminum; Amorphization; Astrophysics; Asymptotic giant branch stars; Calcium; Chemical composition; Circumstellar grains; Core-collapse supernovae; Crystal structure; Crystallinity; Electron microscopy; Enstatite; Forsterite; Interstellar dust; Interstellar matter; Interstellar medium; Iron; Magnesium; Meteorites; Nonequilibrium conditions; Olivine; Outflow; Presolar grains; Silica; Silicate grains; Silicates; Silicon; Spectroscopy; Supernova; Supernovae; Type II supernovae
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ac3332

We report the structural and chemical investigation of nine presolar silicate grains from the CH3/CB b 3 chondrite Isheyevo and CR2 chondrite Northwest Africa (NWA) 801. Five of these grains belong to group 1, likely condensed in low- to intermediate-mass asymptotic giant branch (AGB) stars, super-AGB stars, or core-collapse supernovae, while the remaining four grains belong to group 4 and have a supernova origin. The advanced transmission electron microscopy and associated electron spectroscopy analyses show a diverse range of chemical and structural compositions for presolar silicates. Two GEMS (glass with embedded metal and sulfide)-like silicates, each from different groups, condensed under nonequilibrium conditions in stellar outflows. Two nonstoichiometric silicates from group 1 have dissimilar formation and alteration histories. An amorphous silicate from group 1 with olivine-like [(Mg,Fe) 2 SiO 4 ] composition likely formed as a crystalline olivine that subsequently amorphized in the interstellar medium. An oldhamite (CaS) grain within a stoichiometric enstatite (MgSiO 3 ) from group 1 probably formed by heterogeneous condensation in circumstellar outflows. Of the two crystalline grains from group 4, one is an antigorite [(Mg,Fe) 3 Si 2 O 5 (OH) 4 ], while the other is a nontronite [Na,Fe 2 (Si,Al) 4 O 10 (OH) 2 .nH 2 O], both formed as a crystalline forsterite and later altered to have hydrated silicate composition. A group-4 silicate has a chemical composition similar to a low Ca-pyroxene [(Ca,Mg)(Si,Al) 2 O 6 ]. Our data imply that presolar grains from different groups can have a similar range of grain-formation conditions.