Star formation history of early-type galaxies in low density environments III. The isophote shape parameter and nuclear line-strength indices

Using two line-strength indices, H+K(CaII) and Delta 4000, sensible to the age of the stellar population, we analyze the correlations between the shap e and the 'galaxy age' suggested by de Jong & Davies (1997) on the basis th at discy galaxies have higher H beta indices. By enlarging their sample with the present one, we find that the significan ce of the correlation a(4)/a vs. line- strength indices disappears. We conclude that the 'age of the stellar population of early-type galaxies' is not correlated to the isophote shape parameter.