Red Variable Stars in Three M81 Group Dwarf Galaxies

Abstract Archival [3.6] and [4.5] images are used to identify characterize variable stars in the Magellanic-type galaxies Holmberg II, NGC 2366, IC 2574. Using parametric nonparametric detection methods, 74 confirmed or suspected long-period variables (LPVs) found. The period distributions of LPVs 2366 2574 similar. While distribution Ho II is uncertain due small number statistics, there appears be a deficiency with periods between 550 650 days when compared diffusely distributed on sky, do not follow underlying light from unresolved stars, as expected if episodes star formation within past few hundred megayears have occurred throughout galaxies, including their outer regions. Distances computed for period–luminosity relations (PLRs) agree ∼0.1 mag those based tip red giant branch (RGB). Efforts estimate an LPV-based distance modulus complicated by presence first overtone pulsators among <600 days, although PLR at end consistent estimated RGB-tip. In addition LPVs, 10 candidate sgB[e] luminous blue two supergiant also identified. Nine that show evidence variability identified locations color–magnitude diagram.