Quantitative Spectroscopy of Supergiants in the Local Group Dwarf Galaxy IC 1613: Metallicity and Distance

Abstract

We present a spectral analysis of 21 blue supergiant stars of spectral types late B to early A within the Local Group dwarf galaxy IC 1613, based on VLT Focal Reducer and Low Dispersion Spectrograph 2 low-resolution spectra. Combining our results with studies of early B-type blue supergiants, we report a wide bimodal distribution of metallicities with two peaks around [ Z ] ∼ −0.50 dex and [ Z ] ∼ −0.85 dex. The bimodal distribution correlates with spatial location, when compared with column densities of neutral hydrogen in IC 1613. While the low [ Z ] objects appear in regions of relatively high ISM H i column densities or close to them, the high [ Z ] supergiants are found in the central H i hole that is almost devoid of hydrogen. This suggests there are varied chemical evolution histories for the young stellar populations in IC 1613. Utilizing the flux-weighted gravity–luminosity relation, we determine IC 1613's distance modulus as m  −  M  = 24.39 ± 0.11 mag. This value is in agreement within previous distance measurements using the near-infrared period–luminosity relationship of Cepheids and the tip of the red giant branch.