An updated stellar census of the Quintuplet cluster
  The Quintuplet is one of the most massive galactic clusters known, but
appears to host a diverse stellar population that is difficult to reconcile
with an instantaneous formation event. We present HST photometry and VLT
spectroscopy in order to improve observational constraints, finding the
Quintuplet to be far more homogeneous than previously thought. O7-8 Ia and
O9-B0 Ia supergiants form a smooth morphological sequence with a cohort of
seven early-B hypergiants and six luminous blue variables and WN9-11h stars,
which together comprise the richest population of such stars of any known
stellar aggregate. No further H-free Wolf-Rayets were found, resulting in a
13:1 ratio for WC/WN stars. However a small population of late-O hypergiants
and WN8-9ha stars was identified, while a subset of the supergiants are
unexpectedly faint, suggesting they are both less massive and older than the
greater cluster population. We find an impressive coincidence between cluster
members preceding the H-free WR phase and the evolutionary predictions for a
60Msun star, suggesting an age of ~3.0-3.6Myr for the Quintuplet. Neither the
late-O hypergiants nor the low luminosity supergiants are predicted; we suggest
that the former either result from rapid rotators or are the products of binary
driven mass-stripping, while the latter may be interlopers. The H-free WRs must
have had initial masses >60Msun, but it is difficult to reconcile their
observational properties with theoretical expectations. Since the WRs represent
an evolutionary phase directly preceding core-collapse, they are are crucial to
understanding both this process and the nature of the resultant relativistic
remnants, providing unique constraints on the evolution and death of the most
massive stars forming in the local, high metallicity Universe (Abridged).
