Dust at sub-solar metallicity: the case of post-AGB stars in the Large
  Magellanic Cloud
  Low- and intermediate-mass stars are one of the important dust sources in the
interstellar medium (ISM) of galaxies. The compositions of dust ejected from
these stars are likely to affect those in the ISM. We investigate dust in
post-Asymptotic Giant Branch (AGB) stars, which are in a late evolutionary
phase for low- and intermediate-mass stars, and which produce a wide variety of
dust grains. We are particularly targeting post-AGB stars in the Large
Magellanic Cloud (LMC), which has about half of the solar metallicity, to
investigate the effects of sub-solar metallicity on dust compositions. Using
the Spitzer Space Telescope, we obtained 5-30 micron spectra of 24 post-AGB
candidates in the LMC. Five are C-rich post-AGB stars, and this presentation
focuses on spectra of these stars. We found that rare dust features in the
Milky Way, such as a 21 micron unidentified feature are commonly found in LMC
post-AGB stars. The 6-8 micron spectra are compared with those of Galactic
objects. Four spectra match the Galactic templates of polycyclic aromatic
hydrocarbon (PAH) features. However, we found the three objects show 7.85
micron feature which have not found in Galactic post-AGB stars. Low metallicity
conditions definitely affect the dust formation process and compositions.
