  We present the analysis of the coadded rest-frame UV spectrum (1200<z<2000 A)
of five K-luminous galaxies at z~2 from the K20 survey. The composite spectrum
is characterized by strong absorption lines over the UV continuum from C, N, O,
Al, Si, and Fe in various ionization stages. While some of these lines are
interstellar, several among the strongest absorptions are identified with
stellar photospheric lines. Most of the photospheric and interstellar features
are stronger in the K-luminous composite spectrum than in LBGs at z~3. This
suggests higher metallicity and possibly also larger interstellar velocity
dispersion caused by macroscopic motions. The absorption lines and the slope of
the UV continuum is well matched by the spectrum of the nearby luminous
infrared galaxy NGC 6090, which is in the process of merging. A metallicity
higher than solar is suggested by comparing the pure photospheric lines (SiIII,
CIII, FeV) with starburst models. The evidence of high metallicity, together
with the high masses, high star-formation rates, and possibly strong
clustering, well qualify these galaxies as progenitors of local massive
ellipticals.
