The Dust Budget of the SMC: Are AGB Stars the Primary Dust Source at Low
  Metallicity?
  We estimate the total dust input from the cool evolved stars in the Small
Magellanic Cloud (SMC), using the 8 micron excess emission as a proxy for the
dust-production rate. We find that Asymptotic Giant Branch (AGB) and red
supergiant (RSG) stars produce (8.6-9.5) x 10^7 solar masses per year of dust,
depending on the fraction of far-infrared sources that belong to the evolved
star population (with 10%-50% uncertainty in individual dust-production rates).
RSGs contribute the least (<4%), while carbon-rich AGB stars (especially the
so-called "extreme" AGB stars) account for 87%-89% of the total dust input from
cool evolved stars. We also estimate the dust input from hot stars and
supernovae (SNe), and find that if SNe produce 10^-3 solar masses of dust each,
then the total SN dust input and AGB input are roughly equivalent. We consider
several scenarios of SNe dust production and destruction and find that the
interstellar medium (ISM) dust can be accounted for solely by stellar sources
if all SNe produce dust in the quantities seen around the dustiest examples and
if most SNe explode in dense regions where much of the ISM dust is shielded
from the shocks. We find that AGB stars contribute only 2.1% of the ISM dust.
Without a net positive contribution from SNe to the dust budget, this suggests
that dust must grow in the ISM or be formed by another unknown mechanism.
