The Arches cluster revisited. III. An addendum to the stellar census

Abstract

The Arches is one of the youngest, densest and most massive clusters in the Galaxy. As such it provides a unique insight into the lifecycle of the most massive stars known and the formation and survival of such stellar aggregates in the extreme conditions of the Galactic Centre. In a previous study we presented an initial stellar census for the Arches and in this work we expand upon this, providing new and revised classifications for ∼ 30% of the 105 spectroscopically identified cluster members as well as distinguishing potential massive runaways. The results of this survey emphasise the homogeneity and co-evality of the Arches and confirm the absence of H-free Wolf-Rayets of WC sub-type and predicted luminosities. The increased depth of our complete dataset also provides significantly better constraints on the main sequence population; with the identification of O9.5 V stars for the first time we now spectroscopically sample stars with initial masses ranging from ∼ 16M ⊙ to ≥ 120M ⊙ . Indeed, following from our expanded stellar census we might expect 50 stars within the Arches to have been born with masses 60M ⊙ , while all 105 spectroscopically confirmed cluster members are massive enough to leave relativistic remnants upon their demise. Moreover the well defined observational properties of the main sequence cohort will be critical to the construction of an extinction law appropriate for the Galactic Centre and consequently the quantitative analysis of the Arches population and subsequent determination of the cluster initial mass function.

X-ray Searches for Axions from Super Star Clusters

“…Arches hosts even younger and more extreme (e.g., hotter and more massive) stars than the nearby Quintuplet cluster. Indeed, it is estimated that all ∼105 spectroscopically classified stars within Arches may become core-collapse supernovae within the next ∼10 Myr [78]. A priori, the Arches and Quintuplet clusters should have similar sensitivities to axions, though as we discuss below the axion prediction from Arches is less robust to uncertainties in the initial metallicity than the Quintuplet prediction.…”