  The well-known age-metallicity-attenuation degeneracy does not permit unique
and good estimates of basic parameters of stars and stellar populations. The
effects of dust can be avoided using spectral line indices, but current methods
have not been able to break the age-metallicity degeneracy. Here we show that
using at least two new spectral line indices defined and measured on
high-resolution (R= 6000) spectra of a signal-to-noise ratio (S/N) > 10 one
gets unambiguous estimates of the age and metallicity of intermediate to old
stellar populations. Spectroscopic data retrieved with new astronomical
facilities, e.g., X-shooter, MEGARA, and MOSAIC, can be employed to infer the
physical parameters of the emitting source by means of spectral line index and
index--index diagram analysis.
