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  Genevieve J. Graves: EZ_Ages IDL Code  
       
       
  EZ_Ages is an IDL code package that computes the mean, light-weighted stellar population age, [Fe/H], and abundance enhancements [Mg/Fe], [C/Fe], [N/Fe], and [Ca/Fe] for unresolved stellar populations. This is accomplished by comparing Lick index line strengths between the data and the stellar population models of Schiavon (2007), using a methoed described in Graves & Schiavon (2008). The algorithm uses the inversion of index-index model grids to determine ages and abundances, and exploits the sensitivities of the various Lick indices to measure Mg, C, N, and Ca enhancements over their solar abundances with respect to Fe.  
       
       
  The input you need: (1) The fully reduced data spectrum  
    (2) The measured velocity dispersion for the stellar system  
    (3) The resolution of the instrument set-up used  
    (4) Optional: an error spectrum for calculating Lick index and stellar population parameter statistical errors  
  Or alternatively: (1) Lick index absorption line strengths & errors, measured at the Lick/IDS resolution  
       
  The output you'll get: (1) The best-fitting single burst age and [Fe/H] for the stellar system  
    (2) Measured abundances for [Mg/Fe], [C/Fe], [N/Fe], and [Ca/Fe]  
    (3) Statistical error estimates for all stellar population parameters listed above (if an error spectrum is available)  
    (4) Investigate the effects of assuming an α-enhanced isochrone, or using different Lick indices to do the population fitting  
       
       
  Conditions of use:  
  Send your email address to graves@astro.berkeley.edu so that I can keep you updated on any significant changes to the code, and cite the following two papers: Graves & Schiavon 2008, astro-ph/0803.1483 (presents EZ_Ages and describes the model-fitting process) and Schiavon 2007, ApJS, 171, 146 (presents the stellar population model used by EZ_Ages).  
       
     
   
  Note that the EZ_Ages code requires the IDL Astronomy Users Library, which can be downloaded here.  
       
       
  Instructions for Installation and Usage:  
       
   
       
  Using Lick_EW to measure Lick indices and errors (needed as input for EZ_Ages)  
       
   
  It is strongly recommended that all users read Graves & Schiavon (2008) to understand how the modelling process works, as well as its applicability, limitations, systematic uncertainties, and correlated observational errors.  
       
       
  This work is supported by the National Science Foundation through grants AST 00-71198 and AST 05-07483.  
       
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