The Age of Westerlund 1 Revisited
Emma R. Beasor, Ben Davies, Nathan Smith, Robert D. Gehrz, Donald, F. Figer

TL;DR
This study revisits the age of Westerlund 1, finding evidence that challenges the previously assumed 4-5 million years, and suggests the cluster is significantly older, around 10 million years, based on bolometric luminosity measurements.
Contribution
The paper provides new bolometric luminosity estimates for Westerlund 1's cool supergiants, revealing an older age than previously thought and questioning the single-age stellar evolution model for the cluster.
Findings
Cool supergiants are 0.4 dex fainter than 5 Myr models predict.
Estimated cluster age is approximately 10.4 Myr, older than prior estimates.
Discrepancy persists despite accounting for extinction and variability.
Abstract
The cluster Westerlund~1 (Wd1) is host to a large variety of post main-sequence (MS) massive stars. The simultaneous presence of these stars can only be explained by stellar models if the cluster has a finely-tuned age of 4-5Myr, with several published studies independently claiming ages within this range. At this age, stellar models predict that the cool supergiants (CSGs) should have luminosities of , close to the empirical luminosity limit. Here, we test that prediction using archival data and new photometry from SOFIA to estimate bolometric luminosities for the CSGs. We find that these stars are on average 0.4dex too faint to be 5Myr old, regardless of which stellar evolution model is used, and instead are indicative of a much older age of Myr. We argue that neither systematic uncertainties in the extinction law nor stellar…
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