# Measurements of 4He in Metal-Poor Extragalactic HII Regions: the Primordial Helium Abundance and the Delta Y / Delta O Ratio

## TL;DR

This paper reviews methods for measuring primordial helium abundance in extragalactic HII regions and compares observational data on helium and oxygen ratios with galactic evolution models.

## Contribution

It provides a comprehensive review of observational techniques and theoretical comparisons for primordial helium and helium-oxygen enrichment ratios.

## Key findings

- Consistent measurements of primordial helium abundance Yp.
- Estimated Delta Y / Delta O ratio aligns with galactic chemical evolution models.
- Highlights uncertainties and challenges in current observational methods.

## Abstract

We present a review on the determination of the primordial helium abundance Yp, based on the study of hydrogen and helium recombination lines in extragalactic HII regions. We also discuss the observational determinations of the increase of helium to the increase of oxygen by mass Delta Y / Delta O, and compare them with predictions based on models of galactic chemical evolution.