Mid‐infrared spectroscopy of refractory inclusions (CAIs) in CV and CO chondrites

We present laboratory mid-infrared absorption spectra (2.5 μm to 16.0 μm) of powdered calcium-aluminum-rich inclusions (CAIs) and matrix separated from the carbonaceous chondrites Allende (CV3.2), Vigarano (CV3.3), and Ornans (CO3.3). Two groups of spectra with different features were found for the CAI: in the first group spectra are dominated by spinel, pyroxene, and sodalite nepheline, where main features occur at 9.3 μm, 10.3 μm, and 11.3 μm. In the second group, characteristic minerals are spinel and melilite with typical band maxima at 11.0 μm and 12.3 μm, and a broad feature between 14.0 μm and 15.0 μm. The position of the broad spinel feature probably depends on its iron content. Comparison of band positions in spectra from the CAI components to observed circumstellar emission spectra indicates the potential occurrence of CAI-like material. Pyroxene- and spinel-rich features could occur in spectra of dust around the Herbig Ae star HD104237, the T Tauri star Hen3-600 and the post-AGB star R Sge. Melilite- and spinel-rich components possibly appear in the spectrum of HD104237, Hen3-600, 04187_1927, R Sge, and the planetary nebula Hb 12. There is also indication for a spinel component in dust from the Herbig Ae/Be star HD179218. The spectra of the AGB stars R Cas and θ Aps show no features of CAI-type spinel.