XMP gas-rich dwarfs in Nearby Voids: results of SALT spectroscopy
  In the framework of an ongoing project aimed at searching for and studying
eXtremely Metal-Poor (XMP) very gas-rich blue dwarfs in nearby voids, we
conducted spectroscopy with the 11-m Southern African Large Telescope (SALT) of
26 candidates, preselected in the first paper of this series (PEPK19). For 23
of them, we detected Oxygen lines, allowing us to estimate the gas O/H ratio.
For ten of them, the oxygen abundance is found to be very low, in the range of
12+log(O/H)=6.95-7.30 dex. Of those, four void dwarfs have 12+log(O/H) < 7.19,
or Z < Zo/30. For the majority of observed galaxies, the faint line [OIII]4363A
used to estimate O/H with the direct T_e method appeared either too noisy or
was not detected. We therefore use the semi-empirical method of Izotov, Thuan
(2007) for these spectra, or, when applicable, the new 'Strong line' method of
Izotov et al. (2019b). We present and discuss the results for all void dwarfs
observed in this work. We also compare their O/H values with O/H values of ~140
void galaxies available from our recent papers. We address the properties of
the newly found unusual void XMP dwarfs and compare them with those for ten
known prototype void XMP objects. The latter small group is outstanding based
on their very small mass fraction of stars (only 0.01--0.02 of the baryonic
mass), the blue colours of stars in the outer body (indicating a
non-cosmological age for the main star-forming episode), and the low gas
metallicity (several times lower than expected for their luminosity).
