An Infrared Census of DUST in Nearby Galaxies with Spitzer (DUSTiNGS). V. the Period-Luminosity Relation for Dusty Metal-poor AGB Stars

The survey for DUST in Nearby Galaxies with Spitzer (DUSTiNGS) has identified hundreds of candidate dust-producing asymptotic giant branch (AGB) stars in several nearby metal-poor galaxies. We have obtained multi-epoch follow-up observations for these candidates with the Spitzer Space Telescope and measured their infrared (IR) light curves. This has allowed us to confirm their AGB nature and investigate pulsation behavior at very low metallicity. We have obtained high-confidence pulsation periods for 88 sources in seven galaxies. We have confirmed DUSTiNGS variable star candidates with a 20% success rate and determined the pulsation properties of 19 sources already identified as thermally pulsing AGB stars. We find that the AGB pulsation properties are similar in all galaxies surveyed here, with no discernible difference between the DUSTiNGS galaxies (down to 1.4% solar metallicity; [Fe/H] = -1.85) and the far more metal-rich Magellanic Clouds (up to 50% solar metallicity; [Fe/H] = -0.38). These results strengthen the link between dust production and pulsation in AGB stars and establish the IR period-luminosity relation as a reliable tool (±4%) for determining distances to galaxies, regardless of metallicity.