The Age of the R127 & R128 Clusters: Implications for the LBV

TL;DR

This study estimates the ages of the R127 and R128 clusters in the LMC using photometry and explores discrepancies in star counts, implications for LBV evolution, and the need for deeper observations.

Contribution

It highlights inconsistencies in young cluster modeling, suggests possible causes like binary evolution or data incompleteness, and emphasizes the importance of improved datasets for understanding LBV origins.

Findings

Bright blue stars appear younger than lower-mass stars in the clusters.

Excluding the five brightest stars aligns observed and expected star counts.

Data incompleteness likely affects the interpretation of stellar populations.

Abstract

We infer the age of the R127 and R128 clusters in the Large Magellanic Cloud (LMC) using Str\"omgren photometry from the literature and the age-dating algorithm, Stellar Ages. Analysis using single-star evolutionary models shows a substantial discrepancy between the relative numbers of bright blue stars and lower-mass stars as compared to expectations from a Salpeter mass function, and yields a younger age for the brightest blue stars than for the rest of the cluster. This inconsistency reflects an emerging trend among young clusters in the Local Group. In general, the resolution may be binary evolution or very rapid rotation, although in the specific case of the R127 and R128 clusters, unknown incompleteness in the data may also affect the relative numbers of low- and high-mass stars. The discrepancy grows toward fainter magnitudes, suggesting that the dataset is likely incomplete. However, when the five brightest stars are excluded, the observed and expected counts become consistent, demonstrating that the brightest stars are peculiar. These findings have direct implications for the luminous blue variable (LBV) R127, which is the only confirmed LBV in the LMC located within a young stellar cluster. LBVs have traditionally been considered products of single-star evolution, although there is growing recognition that binary interactions may play a critical role in their evolution. A more complete dataset, particularly deeper imaging with the Hubble Space Telescope, is needed to confirm whether the apparent absence of coeval stars arises solely from observational incompleteness or the broader trend of inconsistency in young cluster modeling.