Spectroscopy of blue supergiants in the spiral galaxy NGC 300

We have obtained VLT low-resolution (similar to5 Angstrom) multiobject spectroscopy in the 4000-5000 Angstrom spectral range of about 70 blue supergiant candidates in the Sculptor Group spiral galaxy NGC 300, selected from previous wide-field photometry. Of the 62 spectroscopically confirmed blue supergiants, with spectral types ranging from late O to F, 57 have types between early B and mid-A. We present a detailed spectral catalog containing identification, magnitudes, colors, and spectral types. We employ synthetic spectra calculated from blue supergiant model atmospheres for different metallicities to determine metal abundances for two A0 supergiants of the sample. In agreement with the expectations, the star closer to the galactic center is found to be more metal-rich than the object at a larger galactocentric distance. We will employ this technique on the whole supergiant sample to determine the stellar abundance gradient in the disk of NGC 300, together with the internal reddening from a comparison of the observed versus synthetic colors. This will allow, among other things, an accurate calibration of the effect of metallicity on the Cepheid period-luminosity relation. Using the Balmer Hbeta line profile, we have estimated the mass-loss rate for one of the brightest A2 supergiants in the sample. Under additional reasonable assumptions, we determined the wind momentum of the star and compared it with the value expected from the empirical wind momentum-luminosity relationship (WLR) for A-type supergiants of Kudritzki et al. Good agreement is obtained. We will derive mass-loss rates and wind momenta for all stars in our sample from the Halpha line profiles in forthcoming work, and we will then thoroughly test the usefulness of the WLR for distance measurement out to about 15 Mpc.