A new determination of the primordial helium abundance using the
  analyses of HII region spectra from SDSS
  The precision measurement of the primordial helium abundance $Y_p$ is a
powerful probe of the early Universe. The most common way to determine $Y_p$ is
analyses of observations of metal-poor \HII regions found in blue compact dwarf
galaxies. We present the spectroscopic sample of 100 \HII regions collected
from the Sloan Digital Sky Survey. The final analysed sample consists of our
sample and HeBCD database from Izotov et al. 2007. We use a self-consistent
procedure to determine physical conditions, current helium abundances, and
metallicities of the \HII regions. From a regression to zero metallicity, we
have obtained $Y_p = 0.2462 \pm 0.0022$ which is one of the most stringent
constraints obtained with such methods up to date and is in a good agreement
with the Planck result $Y_{\rm p}^{\it {Planck}} = 0.2471 \pm 0.0003$. Using
the determined value of $Y_p$ and the primordial deuterium abundance taken from
Particle Data Group (Zyla et al. 2020) we put a constraint on the effective
number of neutrino species $N_{\rm eff} = 2.95 \pm 0.16$ which is consistent
with the Planck one $N_{\rm eff} = 2.99 \pm 0.17$. Further increase of
statistics potentially allows us to achieve Planck accuracy, which in turn will
become a powerful tool for studying the self-consistency of the Standard
Cosmological Model and/or physics beyond.
