On the Incorporation of Metallicity Data into Star Formation History
  Measurements from Resolved Stellar Populations
  The combination of spectroscopic stellar metallicities and resolved star
color-magnitude diagrams (CMDs) has the potential to constrain the entire star
formation and chemical enrichment history (SFH) of a galaxy better than fitting
CMDs alone (as is most common in SFH studies using resolved stellar
populations). In this paper, two approaches for incorporating external
metallicity information into color-magnitude diagram fitting techniques are
presented. Overall, the joint fitting of metallicity and CMD information can
increase the precision on measured age-metallicity relationships and star
formation rates by ~10% over CMD fitting alone. However, systematics in stellar
isochrones and mismatches between spectroscopic and photometric metallicity
determinations can reduce the accuracy of the recovered SFHs. I present a
simple mitigation of these systematics that can reduce the amplitude of these
systematics to the level obtained from CMD fitting alone, while ensuring the
age-metallicity relationship is consistent with spectroscopic metallicities. As
is the case in CMD-fitting analysis, improved stellar models and calibrations
between spectroscopic and photometric metallicities are currently the primary
impediment to gains in SFH precision from jointly fitting stellar metallicities
and CMDs.
