A grid of synthetic spectra and indices Fe5270, Fe5335, Mgb and Mg₂ as a function of stellar parameters and [ α/Fe]

We have computed a grid of synthetic spectra in the wavelength range 4600–5600 Å using revised model atmospheres, for a range of atmospheric parameters and values of [ and +0.4. The Lick indices Fe5270, Fe5335, Mgb and Mg 2 are measured on the grid spectra for to 8.3 Å. Relations between the indices Fe5270, Fe5335 and Mg 2 and the stellar parameters effective temperature , [Fe/H] and [ α /Fe] , valid in the range K, are presented. These fitting functions are given for and 8.3 Å. The indices were also measured for a list of 97 reference stars with well-known stellar parameters observed at ESO and OHP, and these are compared to the computed indices. Finally, a comparison of the indices measured on the observed spectra and those derived from the fitting functions based on synthetic spectra is presented.