Research Byte

Published in the RSAA Lunations
Vol1 Issue9 1–31 October 2020

 Stellar evolutionary tracks trace how a star of a given mass evolves on the Hertzsprung-Russell diagram and are computed from stellar evolution theory. Stellar tracks require a set of elemental abundance ratios as an input parameter and have usually been calculated by scaling the relative abundance ratios of the Sun. Unfortunately, Solar relative abundance ratios do not match observed abundance ratios in nearby HII regions. As a result, stellar population synthesis and photoionization models are unable to derive reliable, high-resolution metallicity diagnostics for HII regions and star forming galaxies.

We have created the Stromlo Stellar Tracks, a set of stellar evolutionary models for massive stars at abundance ratios scaled to nearby HII regions. The Stromlo models are computed self-consistently with the stellar opacity and allows for consistent abundance ratios to be used in stellar population synthesis for the first time. This will revolutionize stellar evolution synthesis models as theoretical prediction of emission lines depends on the ionizing potential and the shape of the ionizing radiation field, produced solely by the stellar evolution synthesis models.

We show that the models produce remarkably different ionizing photon luminosities depending on the input physics. The effect of the elemental abundance ratios on the hardness of the stellar ionizing radiation field has important consequences in the context of interpreting observations of high-redshift star-forming galaxies and their importance during the epoch of reionization. 

The Stromlo Stellar Track paper is soon to be submitted to ApJ. 

 

Katie Grasha