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

Clark, J. S., Lohr, M. E., Patrick, L. R., Najarro, F. 2019. The Arches cluster revisited III. An addendum to the stellar census. Astronomy and Astrophysics 623, DOI: 10.1051/0004-6361/201834529

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 similar to 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 similar to 16 M-circle dot to >= 120 M-circle dot. Indeed, following from our expanded stellar census we might expect greater than or similar to 50 stars within the Arches to have been born with masses greater than or similar to 60 M-circle dot, 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.

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