The Arches cluster revisited. III. An addendum to the stellar census
  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 apparent 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 ~16Msun to >120Msun. Indeed, following from our expanded stellar census we
might expect >50 stars within the Arches to have been born with masses >60Msun,
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.
