Kudritzki, R.-P., Urbaneja, M. A., Gazak, Z., Bresolin, F., Przybilla, N., Gieren, W., & Pietrzyński, G. (2012). Quantitative spectroscopy of blue supergiant stars in the disk of M81: metallicity, metallicity gradient, and distance. The Astrophysical Journal, 747(1):, pp. 1-19. doi:10.1088/0004-637X/747/1/15.