A new determination of the primordial helium abundance based on the HII region NGC 346.

To understand the Universe a highly accurate ($\sim$1%) primordial helium abundance (Yp) determination plays an important role; it is extremely important to constrain: Big Bang Nucleosynthesis models, elementary particle physics, and the study of galactic chemical evolution. Low-metallicity HII regions have been used to estimate it since their statistical uncertainties are relatively small. We present a new determination of the primordial helium abundance, based on long-slit spectra of the HII region NGC 346 in the small Magellanic cloud. We found that for NGC 346: X=0.7465, Y=0.2505, and Z=0.0030. By assuming $\Delta$Y/$\Delta$O = 3.3$\pm$0.7 we found that the primordial helium abundance is Yp= 0.2451$\pm$.0026 (1$\sigma$).