Stellar Pulsation and the Production of Dust and Molecules in Galactic
  Carbon Stars
  New infrared spectra of 33 Galactic carbon stars from FORCAST on SOFIA reveal
strong connections between stellar pulsations and the dust and molecular
chemistry in their circumstellar shells. A sharp boundary in overall dust
content, which predominantly measures the amount of amorphous carbon, separates
the semi-regular and Mira variables, with the semi-regulars showing little dust
in their spectra and the Miras showing more. In semi-regulars, the contribution
from SiC dust increases rapidly as the overall dust content grows, but in
Miras, the SiC dust feature grows weaker as more dust is added. A similar
dichotomy is found with the absorption band from CS at $\sim$7.3 $\mu$m, which
is generally limited to semi-regular variables. Observationally, these
differences make it straightforward to distinguish semi-regular and Mira
variables spectroscopically without the need for long-term photometric
observations or knowledge of their distances. The rapid onset of strong SiC
emission in Galactic carbon stars in semi-regulars variables points to a
different dust-condensation process before strong pulsations take over. The
break in the production of amorphous carbon between semi-regulars and Miras
seen in the Galactic sample is also evident in Magellanic carbon stars, linking
strong pulsations in carbon stars to the strong mass-loss rates which will end
their lives as stars across a wide range of metallicities.
