A classification of HII regions based on Oxygen and Helium lines: The cases of TOL2146-391 and TOL0357-3915

TL;DR

This study analyzes the physical conditions of two HII regions using spectrophotometry, introducing a new method to estimate temperature inhomogeneities and classifying HII regions based on oxygen and helium line diagnostics.

Contribution

It presents a novel approach using the HELIO10 program to estimate temperature inhomogeneities in HII regions, and offers a classification scheme based on oxygen ionization and t^2 values.

Findings

HELIO10 is effective for estimating t^2 without heavy element recombination lines.

HII regions occupy distinct areas in the oxygen ionization versus t^2 diagram.

Average t^2 values can be assigned to regions with similar physical characteristics.

Abstract

We present long slit spectrophotometry of two HII regions: TOL2146-391 and TOL0357-3915. We performed a detailed analysis that involves abundance determinations relaxing the assumption of homogeneous temperature. The temperature inhomogeneities values, t^2, were obtained through two methods: (i) comparing abundances from oxygen recombination lines to abundances from collisionally excited lines and (ii) by using the line intensity ratios of a set of HeI lines together with the HELIO10 program. We find that the HELIO10 program is a good alternative to obtain a t^2 value in photoionized regions where recombination lines of heavy elements are not available. We have plotted 27 high and low metallicity HII regions in an oxygen degree of ionization versus t^2 diagram; we find areas populated by HII regions and areas void of them; the physical characteristics of each area are discussed. In addition, an average t^2 value can be determined for the objects in each area. We propose to use this <t^2> value for the cases where a direct measurement of t^2 cannot be determined