A comprehensive chemical abundance analysis of the extremely metal poor
  Leoncino Dwarf galaxy (AGC 198691)
  We re-examine the extremely metal-poor (XMP) dwarf galaxy AGC 198691 using a
high quality spectrum obtained by the LBT's MODS instrument. Previous spectral
observations obtained from KOSMOS on the Mayall 4-m and the Blue Channel
spectrograph on the MMT 6.5-m telescope did not allow for the determination of
sulfur, argon, or helium abundances. We report an updated and full chemical
abundance analysis for AGC 198691, including confirmation of the extremely low
"direct" oxygen abundance with a value of 12 + log(O/H) = 7.06 $\pm$ 0.03. AGC
198691's low metallicity potentially makes it a high value target for helping
determine the primordial helium abundance ($Y_p$). Though complicated by a Na I
night sky line partially overlaying the He I $\lambda$5876 emission line, the
LBT/MODS spectrum proved adequate for determining AGC 198691's helium
abundance. We employ the recently expanded and improved model of Aver et al.
(2021), incorporating higher Balmer and Paschen lines, augmented by the
observation of the infrared helium emission line He I $\lambda$10830 obtained
by Hsyu et al. (2020). Applying our full model produced a reliable helium
abundance determination, consistent with the expectation for its metallicity.
Although this is the lowest metallicity object with a detailed helium
abundance, unfortunately, due to its faintness (EW(H$\beta$) $<$ 100 AA) and
the compromised He I $\lambda$5876, the resultant uncertainty on the helium
abundance is too large to allow a significant improvement on the measurement of
$Y_p$.
