Revista Mexicana de Astronomia y Astrofisica, Vol. 21, p. 223 - 227
Edmunds, M. G.; Vílchez, J. M.; Terlevich, E.; Pagel, B. E. J.; Díaz, A. I.
Spectrophotometric data of giant H II regions covering the spectral range from λ3600 to 9700 Å in the spiral galaxies M101 and M51 have been analyzed in order to determine reliable chemical abundances and radial gradients. The behaviour of the S/O ratio with metallicity is also explored. The data are consistent, within the errors, with a constant S/O abundance although uncertainties are large.