New candidates for extremely metal-poor emission-line galaxies in the
  SDSS/BOSS DR10
  We present a spectroscopic study of eight extremely low-metallicity candidate
emission-line galaxies with oxygen abundances possibly below 12 +log O/H =
7.35. These galaxies were selected from Data Release 10 of the Sloan Digital
Sky Survey/Baryon Oscillation Spectroscopic Survey (SDSS/BOSS DR10). We will
call these extremely metal-deficient galaxies XMD galaxies. The electron
temperature-sensitive emission line [O~{\sc iii}] $\lambda$4363 is detected in
three galaxies and marginally detected in two galaxies, allowing for abundance
determination by a "direct" method. Because of large uncertainties in the [O
{\sc iii}]$\lambda$4363\AA\ line fluxes, we also calculated oxygen abundance in
these galaxies together with the remaining three galaxies using a strong-line
semi-empirical method. This method gives oxygen abundances higher than 7.35 for
three galaxies with detected [O {\sc iii}]$\lambda$4363\AA\ line and lower than
7.35 for the remaining five objects of the sample. The newly-discovered
galaxies represent excellent targets for follow-up spectroscopic observations
with the largest telescopes to improve the oxygen abundance determination and
to increase the number of these very rare low-metallicity objects. The extreme
location of the most massive and luminous XMD galaxies and XMD candidates in
the stellar mass-metallicity diagram implies that these galaxies may be genuine
young objects.
  With stellar masses of up to $\sim$ 10$^7$ - 10$^8$$M_{\odot}$, the galaxies
are not chemically enriched and strongly deviate to lower metallicity as
compared to the relation obtained for a large sample of low-redshift,
star-forming galaxies.
