  The survey for DUST in Nearby Galaxies with Spitzer (DUSTiNGS) identified
several candidate Asymptotic Giant Branch (AGB) stars in nearby dwarf galaxies
and showed that dust can form even in very metal-poor systems (Z ~ 0.008
$Z_\odot$). Here, we present a follow-up survey with WFC3/IR on the Hubble
Space Telescope (HST), using filters that are capable of distinguishing
carbon-rich (C-type) stars from oxygen-rich (M-type) stars: F127M, F139M, and
F153M. We include six star-forming DUSTiNGS galaxies (NGC 147, IC 10, Pegasus
dIrr, Sextans B, Sextans A, and Sag DIG), all more metal-poor than the
Magellanic Clouds and spanning 1 dex in metallicity. We double the number of
dusty AGB stars known in these galaxies and find that most are carbon rich. We
also find 26 dusty M-type stars, mostly in IC 10. Given the large dust excess
and tight spatial distribution of these M-type stars, they are most likely on
the upper end of the AGB mass range (stars undergoing Hot Bottom Burning).
Theoretical models do not predict significant dust production in metal-poor
M-type stars, but we see evidence for dust excess around M-type stars even in
the most metal-poor galaxies in our sample (12+log(O/H) = 7.26-7.50). The low
metallicities and inferred high stellar masses (up to ~10 $M_\odot$) suggest
that AGB stars can produce dust very early in the evolution of galaxies (~30
Myr after they form), and may contribute significantly to the dust reservoirs
seen in high-redshift galaxies.
