This paper commences a series of investigations into the stellar populations of local elliptical galaxies as determined from their integrated spectra .
The goal of the series is to determine the star formation and chemical evolution histories of present-day elliptical galaxies .
The primary galaxy sample analyzed is that of González ( 1993 , G93 ) , which consists of 39 ellipticals drawn primarily from the local field and nearby groups , plus the bulge of Messier 31 .
Single-stellar-population ( SSP ) equivalent ages , metallicities , and abundance ratios are derived from \mathrm { H } \beta , \mathrm { Mg } b , and \langle \mathrm { Fe } \rangle line strengths using an extension of the Worthey ( 1994 ) models that incorporates non-solar line-strength “ response functions ” by Tripicco & Bell ( 1995 ) .
These functions account for changes in the Lick/IDS indices caused by non-solar abundance ratios , allowing us to correct the Worthey ( 1994 ) models for the enhancements of Mg and other \alpha -like elements relative to the Fe-peak elements .

SSP-equivalent ages of the G93 ellipticals are found to vary widely , 1.5 \lesssim t \lesssim 18 Gyr , while metallicities \mathrm { [ Z / H ] } and enhancement ratios , \mathrm { [ E / Fe ] } are strongly peaked around \langle \mathrm { [ Z / H ] } \rangle = +0.26 and \langle \mathrm { [ E / Fe ] } \rangle = +0.20 ( in an aperture of radius r _ { e } / 8 ) .
The enhancement ratios \mathrm { [ E / Fe ] } are milder than previous estimates , owing to the application of non-solar abundance corrections to both \mathrm { Mg } b and \langle \mathrm { Fe } \rangle for the first time .
While \mathrm { [ E / Fe ] } is usually > 0 , it is not the “ E ” elements that are actually enhanced but rather the Fe-peak elements that are depressed ; this serves not only to weaken \langle \mathrm { Fe } \rangle but also to strengthen \mathrm { Mg } b , accounting for the overall generally mild enhancements .
Based on index strengths from the Lick/IDS galaxy library ( ( ( Trager et al .
1998 ) ) ) , C is not depressed with Fe but rather seems to be on a par with other elements such as Mg in the “ E ” group .
Gradients in stellar populations within galaxies are found to be mild , with SSP-equivalent age decreasing by 25 % , metallicity decreasing by \langle \mathrm { [ Z / H ] } \rangle = 0.20 dex , and \mathrm { [ E / Fe ] } remaining nearly constant out to an aperture of radius r _ { e } / 2 for nearly all systems .

Our ages have an overall zeropoint uncertainty of at least \sim 25 \% due to uncertainties in the stellar evolution prescription , the oxygen abundance , the effect of \mathrm { [ E / Fe ] } \neq 0 on the isochrones , and other unknowns .
However , the relative age rankings of stellar populations should be largely unaffected by these errors .
In particular , the large spread in ages appears to be real and can not be explained by contamination of \mathrm { H } \beta by blue stragglers or hot horizontal branch stars , or by fill-in of \mathrm { H } \beta by emission . Correlations between these derived SSP-equivalent parameters and other galaxy observables will be discussed in future papers .