Research Byte
Published in the RSAA Lunations
Vol1 Issue54 1–31 August 2024
Stellar nurseries like young galactic open clusters provide vital clues to our understanding of the galaxy's evolution. Recent studies have uncovered unexpected complexities within these clusters, challenging the traditional view of them as simple stellar populations. A particularly puzzling feature is the extended main-sequence turn-off (eMSTO), which manifests as an unexpected colour spread among stars at the turn-off point in the colour-magnitude diagrams (CMDs) of young clusters. The presence of eMSTOs suggests that not all stars within a cluster are evolving uniformly, pointing to underlying differences in stellar properties, such as rotation rates. Understanding eMSTOs is crucial as it directly impacts our ability to accurately determine the ages and evolutionary histories of young clusters, which are essential for deriving a coherent picture of galactic evolution.
In the paper, 'Survey of extended Main Sequence Turn-offs in Galactic Open Clusters: Stellar rotations from Gaia RVS spectra', we exploit high-precision data from the Gaia and LAMOST surveys to investigate the origins of eMSTOs in Galactic clusters younger than 2 billion years. By analysing projected stellar rotation and magnetic activity and comparing them with the predictions of stellar evolution models, our findings indicate that a single population of fast-rotating stars, viewed from different angles, can account for the eMSTO features observed in these young clusters. This suggests that most stars within these clusters form as fast rotators, which contrasts with clusters in Milky Way neighbour, the Magellanic Clouds, where non-rotating stars play a significant role in shaping observed patterns.
The research highlights the distinct characteristics of young galactic open clusters and their contributions to the broader context of galactic evolution, with the differences between galactic and Magellanic Cloud clusters raising important questions about the factors influencing stellar evolution in these environments.
These results emphasize the importance of considering stellar rotation when determining the ages of young clusters. Ignoring these effects could lead to age estimates that are off by 10-20%, potentially skewing our understanding of cluster evolution.
The findings open new avenues for research into the environmental and physical conditions that shape the evolution of stellar populations across different regions of the Universe. These opportunities will be further enhanced by upcoming data releases from major surveys like LAMOST, GALAH, Gaia, and 4MOST.
Giacomo Cordoni
Image: The dazzling diamonds of Trumpler 14, one of the youngest known star clusters. Credit: NASA & ESA, Jesús Maíz Apellániz (Centro de Astrobiología, CSIC-INTA, Spain)
