Unlocking the Secrets of Star Cluster UPK 220 with Gaia and TESS
Open star clusters (OCs) like UPK 220 offer a unique laboratory for understanding the life cycle of stars. These gravitationally bound groups of stars share the same age and chemical composition, making them perfect for studying stellar evolution and the dynamics of the Milky Way. Recent advancements in stellar databases like Gaia DR3 and observations from the TESS telescope have expanded our understanding of these clusters. In this study, İnci Akkaya Oralhan and her team focus on UPK 220, an intermediate-age open cluster, using combined data from Gaia DR3 and TESS to uncover new insights about its member stars, especially the intriguing variable stars.
Data and Methods
To determine which stars belong to UPK 220, the team used a membership selection algorithm called pyUPMASK, which helps distinguish cluster members from unrelated field stars. They analyzed the positions, movements, and brightness of over 280 stars using data from Gaia DR3. After narrowing down the likely cluster members, they turned to data from TESS, which observes stars over long periods to detect brightness changes caused by variability.
In the study, eight variable stars were identified within UPK 220. These stars were categorized based on the patterns in their light curves. Three were eclipsing binary systems (where two stars orbit each other and periodically block each other’s light), two were pulsating stars, two were magnetically active, and one was a rotating variable.
Analyzing the Variable Stars
The variable stars offered a wealth of information. The eclipsing binaries were modeled using specialized software to determine their orbital and physical characteristics. This modeling revealed details about their masses, temperatures, and radii. The team also noticed some interesting pulsating stars, which change brightness due to internal processes. One such star resembled a classical Cepheid, a type of star known for its regular pulsations and its usefulness in measuring distances in space.
Magnetically active stars showed brightness changes due to large star spots on their surfaces, similar to sunspots but much larger. Finally, rotating variables exhibited periodic changes in brightness due to their rotation.
Determining the Cluster's Properties
By combining the data from these variable stars with advanced stellar models, the team refined their estimates of the cluster's key properties. They determined UPK 220’s distance to be about 832 parsecs (roughly 2,700 light-years away) and its age to be around 200 million years. The metallicity—essentially the amount of elements heavier than hydrogen and helium—was found to be lower than the Sun’s, indicating that UPK 220 formed from a more metal-poor gas cloud.
Discussion
The findings suggest that variable stars can be powerful tools for improving the accuracy of cluster measurements. Comparing their results with previous studies, the authors highlighted some discrepancies, particularly in age and metallicity estimates. These differences are likely due to variations in the data sources and methods used in earlier analyses. By incorporating both Gaia and TESS data, the study offers a more precise picture of UPK 220’s characteristics.
Conclusion
The study of UPK 220 highlights the importance of combining multiple datasets to achieve a comprehensive understanding of open star clusters. Future work, including ground-based spectral observations, could further refine the cluster’s properties and provide deeper insights into its fascinating population of variable stars.
Source: Oralhan
