# Combined Effects of Rotation and Age Spreads on Extended Main Sequence Turn Offs

## TL;DR

This study investigates how stellar rotation and age spreads influence the extended main sequence turn offs in star clusters, using synthetic models to compare with observational data from Hubble and Gaia.

## Contribution

It introduces a flexible modeling approach that combines rotation and age effects to explain eMSTOs, providing new insights into their origins.

## Key findings

- Rotation alone can qualitatively reproduce eMSTO structures.
- Age spreads are favored in some clusters but not conclusively.
- Models suggest both rotation and age spreads contribute to eMSTOs.

## Abstract

The extended main sequence turn offs (eMSTOs) of several young to intermediate age clusters are examined in the Magellanic Clouds and the Milky Way. We explore the effects of extended star formation (eSF) and a range of stellar rotation rates on the behavior of the color-magnitude diagram (CMD), paying particular attention to the MSTO. We create synthetic stellar populations based on MESA stellar models to simulate observed Hubble Space Telescope and Gaia star cluster data. We model the effect of rotation as a non-parametric distribution, allowing for maximum flexibility. In our models the slow rotators comprise the blueward, and fast rotators the redward portion of the eMSTO. We simulate data under three scenarios: non-rotating eSF, a range of rotation rates with a single age, and a combination of age and rotation effects. We find that two of the five clusters (the youngest and oldest) favor an age spread, but these also achieve the overall worst fits of all clusters. The other three clusters show comparable statistical evidence between rotation and an age spread. In all five cases, a rotation rate distribution alone is capable of qualitatively matching the observed eMSTO structure. In future work, we aim to compare our predicted Vsin(i) with observations in order to better constrain the physics related to stellar rotation.