CRYSTALLINE SILICATES IN EVOLVED STARS. I. SPITZER/INFRARED SPECTROGRAPH SPECTROSCOPY OF IRAS?16456–3542, 18354–0638, AND 23239+5754

摘要

We report the Spitzer Infrared Spectrograph (IRS) observations of three evolved stars: IRAS?16456–3542, 18354–0638, and 23239+5754. The 9.9-37.2 μm Spitzer/IRS high-resolution spectra of these three sources exhibit rich sets of enstatite-dominated crystalline silicate emission features. IRAS?16456–3542 is extremely rich in crystalline silicates, with 90% of its silicate mass in crystalline form, the highest to date ever reported for crystalline silicate sources.