The chemistry of extragalactic carbon stars
  Prompted by the ongoing interest in Spitzer Infrared Spectrometer spectra of
carbon stars in the Large Magellanic Cloud, we have investigated the
circumstellar chemistry of carbon stars in low-metallicity environments.
Consistent with observations, our models show that acetylene is particularly
abundant in the inner regions of low metallicity carbon-rich AGB stars -- more
abundant than carbon monoxide. As a consequence, larger hydrocarbons have
higher abundances at the metallicities of the Magellanic Clouds than in stars
with solar metallicity. We also find the oxygen and nitrogen chemistry is
suppressed at lower metallicity, as expected. Finally, we calculate molecular
line emission from carbon stars in the Large and Small Magellanic Cloud and
find that several molecules should be readily detectable with the Atacama Large
Millimeter Array at Full Science operations.
