Emission Corrections for Hydrogen Features of the Graves et. al 2007
  Sloan Digital Sky Survey Averages of Early Type, Non-liner Galaxies
  For purposes of stellar population analysis, emission corrections for Balmer
series indices on the Lick index system in Sloan Digital Sky Survey (SDSS)
stacked quiescent galaxy spectra are derived, along with corrections for
continuum shape and gross stellar content, as a function of the Mg $b$ Lick
index strength. These corrections are obtained by comparing the observed Lick
index measurements of the SDSS with new observed measurements of 13 Virgo
Cluster galaxies, and checked with model grids. From the H$\alpha$ Mg $b$
diagram a linear correction for the observed measurement is constructed using
best fit trend lines. Corrections for H$\beta$, H$\gamma$ and H$\delta$ are
constructed using stellar population models to predict continuum shape changes
as a function of Mg $b$ and Balmer series emission intensities typical of H{\sc
II} regions. The corrections themselves are fairly secure, but the
interpretation for H$\delta$ and H$\gamma$ indices is complicated by the fact
that the H$\delta$ and H$\gamma$ indices are sensitive to elemental abundances
other than hydrogen.
