  The quantitative spectral analysis of low resolution Keck LRIS spectra of
blue supergiants in the disk of the giant spiral galaxy M81 is used to
determine stellar effective temperatures, gravities, metallicities,
luminosites, interstellar reddening and a new distance using the Flux-weighted
Gravity--Luminosity Relationship (FGLR). Substantial reddening and extinction
is found with E(B-V) ranging between 0.13 to 0.38 mag and an average value of
0.26 mag. The distance modulus obtained after individual reddening corrections
is 27.7+/-0.1 mag. The result is discussed with regard to recently measured
TRGB and Cepheid distances. The metallicities (based on elements such as iron,
titanium, magnesium) are supersolar (~0.2 dex) in the inner disk (R<=5kpc) and
slightly subsolar (~ -0.05 dex) in the outer disk (R>10 kpc) with a shallow
metallicity gradient of 0.034 dex/kpc. The comparison with published oxygen
abundances of planetary nebulae and metallicities determined through fits of
HST color-magnitude diagrams indicates a late metal enrichment and a flattening
of the abundance gradient over the last 5 Gyrs. This might be the result of gas
infall from metal rich satellite galaxies. Combining these M81 metallicities
with published blue supergiant abundance studies in the Local Group and the
Sculptor Group a galaxy mass metallicity-relationship based solely on stellar
spectroscopic studies is presented and compared with recent studies of SDSS
star forming galaxies.
