We have revisited the calibration of the visual binary system Zeta Herculis
with the goal to give the seismological properties of the G0 IV sub-giant Zeta
Her A. We have used the most recent physical and observational data. For the
age we have obtained 3387 Myr, for the masses respectively 1.45 and 0.98 solar
mass, for the initial helium mass fraction 0.243, for the initial mass ratio of
heavy elements to hydrogen 0.0269 and for the mixing-length parameters
respectively 0.92 and 0.90 using the Canuto & Mazitelli (1991, 1992) convection
theory. Our results do not exclude that Zeta Her A is itself a binary
sub-system; the mass of the hypothetical unseen companion would be smaller than
0.05 solar mass. The adiabatic oscillation spectrum of Zeta Her A is found to
be a complicated superposition of acoustic and gravity modes; some of them have
a dual character. This greatly complicates the classification of the non-radial
modes. The echelle diagram used by the observers to extract the frequencies
will work for ell=0, 2, 3. The large difference is found to be of the order of
42 mu Hz, in agreement with the Martic et al. (2001) seismic observations.Comment: 12 pages, A&A in pres