Laura Murphy

In this poster we explain key ways in which rotation affects the evolution of the first stars. Fig 1 is a HR diagram where the x-axis shows surface temperature and the y-axis shows luminosity. On this HR diagram we show the stellar evolutionary tracks of our models of masses 9, 12, 15, 20, 30, 40, 60, 85 and 120 solar masses, with and without rotation. From this we can tell the main differences between the rotating and non-rotating tracks. We notice two main effects, firstly that rotating models show a steeper increase in luminosity during H-burning, and secondly that rotating models vary a lot in surface temperature during He-burning compared to non-rotating models of the same initial mass. This is because rotational mixing increases the core size which increases luminosity, and helps transport heavy elements to the H-shell which boosts energy production in the envelope and changes the surface temperature. Fig 2 is a plot of the final nitrogen abundance of each of our 18 models, of masses 9-120 solar masses both rotating and non-rotating. We find that rotating models don't always have higher nitrogen abundance than non-rotating models. This is surprising since rotational mixing helps transport heavy elements to the H-shell where nitrogen production occurs. Through studying the evolution of the interior structure and energy generation of our models in detail we have found that rotational mixing can cause the CNO boost (where significant nitrogen production occurs) to occur earlier in He-burning. When this happens it causes the core to retract which limits further transport of heavy elements to the H-shell and subsequently hinders enrichment. These results improve our understanding of the evolution of the first stars and how they are impacted by rotation.