Helium abundances in HII regions
Abstract
The formation of elements is a key problem in order to understand the evolution of the Universe. Particularly, the formation of ^{4}He has been fundamental for the study of cosmology and the chemical evolution of galaxies. The primordial abundance of ^{4}He (Y_{P}) has allowed us to verify the details of the SBBN theory. The value of Y_{P} can be determined from observations of the helium and hydrogen emission lines from low metallicity galaxies, where the small star formation rate has enriched the gas with a few helium and heavy elements. It is commonly known that the total abundance of an element relative to the hydrogen is given by all its ion abundances. In practice, not all the ionization stages are observed. Therefore, we must correct for unobserved stages using ICFs. As a particular case ICF(He) has been ignored due to the fact that, for high ionization HII regions, its correction is 1-2% (which can be positive or negative depending on the exact nature of the particular HII region). Nevertheless, if we want to have a high determination of helium abundance in order to determine a better value of Y_{P}, the ICF(He) becomes important.
- Publication:
-
Cosmic Feast of the Elements
- Pub Date:
- November 2017
- Bibcode:
- 2017cfe..confE..41V
- Keywords:
-
- galaxies;
- nebulae;
- stars;
- abundances;
- models;
- observations