# Chemical evolution models for the Galactic disk based on H II region abundances derived from a direct method and a temperature independent method

## TL;DR

This paper compares two chemical evolution models of the Galactic disk based on different methods of deriving oxygen abundances from H II regions, finding that the temperature independent method yields a model that better fits observational data and explains the O/H gradient flattening.

## Contribution

It introduces and compares two models using different abundance derivation methods, highlighting the effectiveness of the temperature independent method in fitting stellar constraints.

## Key findings

- The TIM-based model fits stellar constraints well.
- The DM-based model fails to reproduce stellar observations.
- The TIM model explains the O/H gradient flattening in the inner disk.

## Abstract

We present two chemical evolution models of our galaxy, both models are built to fit the O/H ratios derived from H II regions, using two different methods. One model is based on abundances obtained from the [O III] 4363/5007 temperatures (direct method, DM) and the other on abundances obtained from the recombination line ratios of [O II/H I] (temperature independent method, TIM). The differences between the O/H values obtained from these two methods are about 0.25 dex. We find that the model based on the TIM values produces an excellent fit to the observational stellar constraints (B-stars, Cepheids, and the Sun), while the model based on the DM fails to reproduce each of them. Moreover, the TIM model can explain the flattening of the O/H gradient observed in the inner disk due to the assumption of an inside-out star formation quenching, in the 3 - 6 kpc galactocentric range, starting ~ 9 Gyr ago.