Title:

Probing the formation and processing of silicates with ISO and Spitzer
Spectroscopy


Francisca Kemper
University of California, Los Angeles

Abstract:

Silicates are formed by evolved stars, in particular around asymptotic
giant branch stars and red supergiants. ISO spectroscopy has revealed
that in many cases silicates in circumstellar environments are found
to have a high degree of crystallinity.  Evolved stars eject their
circumstellar material into the interstellar medium.  The composition
of interstellar silicates are studied by means of infrared absorption
features, also observed with ISO, and it is found that the
interstellar silicates are almost completely amorphous. I will discuss
time scales and processes for the amorphization of crystalline
silicates ejected by post-main-sequence stars.  The formation process
of silicates in the outflows of evolved stars is not understood. I
will (hopefully) present Spitzer IRS spectroscopy of AGB stars in the
LMC, of which the low metallicity can give us new insights in the
processes involved in the formation of interstellar dust.