The DUSTiNGS survey ( DUST in Nearby Galaxies with Spitzer ) is a 3.6 and 4.5 µm imaging survey of 50 nearby dwarf galaxies designed to identify dust-producing Asymptotic Giant Branch ( AGB ) stars and massive stars .
Using 2 epochs , spaced approximately 6 months apart , we identify a total of 526 dusty variable AGB stars ( sometimes called “ extreme ” or x-AGB stars ; [ 3.6 ] - [ 4.5 ] > 0.1 mag ) .
Of these , 111 are in galaxies with { [ Fe / H ] } < -1.5 and 12 are in galaxies with { [ Fe / H ] } < -2.0 , making them the most metal-poor dust-producing AGB stars known .
We compare these identifications to those in the literature and find that most are newly discovered large-amplitude variables , with the exception of \approx 30 stars in NGC 185 and NGC 147 , 1 star in IC 1613 , and 1 star in Phoenix .
The chemical abundances of the x-AGB variables are unknown , but the low metallicities suggest that they are more likely to be carbon-rich than oxygen-rich and comparisons with existing optical and near-IR photometry confirms that 70 of the x-AGB variables are confirmed or likely carbon stars .
We see an increase in the pulsation amplitude with increased dust production , supporting previous studies suggesting that dust production and pulsation are linked .
We find no strong evidence linking dust production with metallicity , indicating that dust can form in very metal-poor environments .