New calibrations of spectrophotometric indices of elliptical galaxies as functions of spectrophotometric indices are presented , permitting estimates of mean stellar population ages and metallicities .
These calibrations are based on evolutionary models including a two-phase interstellar medium , infall and a galactic wind .
Free parameters were fixed by requiring that models reproduce the mean trend of data in the color-magnitude diagram as well as in the plane of indices H \beta - Mg _ { 2 } and Mg _ { 2 } - < Fe > .
To improve the location of faint ellipticals ( M _ { B } > -20 ) in the H \beta - Mg _ { 2 } diagram , down-sizing was introduced .
An application of our calibrations to a sample of ellipticals and a comparison with results derived from single stellar population models is given .
Our models indicate that mean population ages span an interval of 7-12 Gyr and are correlated with metallicities , which range from \sim half up to three times solar .