Oxygen Metallicity Determinations from Optical Emission Lines in
  Early-type Galaxies
  We measured the oxygen abundances of the warm (T$\sim 10^{4}K$) phase of gas
in seven early-type galaxies through long-slit observations. A template spectra
was constructed from galaxies void of warm gas and subtracted from the
emission-line galaxies, allowing for a clean measurement of the nebular lines.
The ratios of the emission lines are consistent with photoionization, which
likely originates from the UV flux of post-asymototic giant branch (PAGB)
stars. We employ H II region photoionization models to determine a mean oxygen
metallicity of $1.01\pm0.50$ solar for the warm interstellar medium (ISM) in
this sample. This warm ISM 0.5 to 1.5 solar metallicity is consistent with
modern determinations of the metallicity in the hot (T$\sim 10^{6}-10^{7}K$)
ISM and the upper range of this warm ISM metallicity is consistent with stellar
population metallicity determinations. A solar metallicity of the warm ISM
favors an internal origin for the warm ISM such as AGB mass loss within the
galaxy.
