We present the first direct determination of a stellar metallicity in the spiral galaxy NGC 4258 (D = 7.6 Mpc) based on the quantitative analysis of a low-resolution (∼ 5Å) Keck LRIS spectrum of a blue supergiant star located in its disk. A determination of stellar metallicity in this galaxy is important for the absolute calibration of the Cepheid Period-Luminosity relation as an anchor for the extragalactic distance scale and for a better characterization of its dependence as a function of abundance. We find a value 0.2 dex lower than solar metallicity at a galactocentric distance of 8.7 kpc, in agreement with recent H II region studies using the weak forbidden auroral oxygen line at 4363Å. We determine the effective stellar temperature, gravity, luminosity and line-of-sight extinction of the blue supergiant being studied. We show that it fits well on the flux-weighted gravity-luminosity relation (FGLR), strengthening the potential of this method as a new extragalactic distance indicator.
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