Bibcode
Clark, J. S.; Lohr, M. E.; Patrick, L. R.; Najarro, F.; Dong, H.; Figer, D. F.
Referencia bibliográfica
Astronomy and Astrophysics, Volume 618, id.A2, 25 pp.
Fecha de publicación:
10
2018
Revista
Número de citas
34
Número de citas referidas
30
Descripción
Context. Found within the central molecular zone, the Quintuplet is one
of the most massive young clusters in the Galaxy. As a consequence it
offers the prospect of constraining stellar formation and evolution in
extreme environments. However, current observations suggest that it
comprises a remarkably diverse stellar population that is difficult to
reconcile with an instantaneous formation event. Aims: To better
understand the nature of the cluster our aim is to improve observational
constraints on the constituent stars. Methods: In order to
accomplish this goal we present Hubble Space Telescope/NICMOS+WFC3
photometry and Very Large Telescope/SINFONI+KMOS spectroscopy for
˜100 and 71 cluster members, respectively. Results:
Spectroscopy of the cluster members reveals the Quintuplet to be far
more homogeneous than previously expected. All supergiants are
classified as either O7-8 Ia or O9-B0 Ia, with only one object of
earlier (O5 I-III) spectral type. These stars form a smooth
morphological sequence with a cohort of seven early-B hypergiants and
six luminous blue variables and WN9-11h stars, which comprise the
richest population of such stars of any stellar aggregate known. In
parallel, we identify a smaller population of late-O hypergiants and
spectroscopically similar WN8-9ha stars. No further H-free Wolf-Rayet
(WR) stars are identified, leaving an unexpectedly extreme ratio of 13:1
for WC/WN stars. A subset of the O9-B0 supergiants are unexpectedly
faint, suggesting they are both less massive and older than the greater
cluster population. Finally, no main sequence objects were identifiable.
Conclusions: Due to uncertainties over which extinction law to
apply, it was not possible to quantitatively determine a cluster age via
isochrone fitting. Nevertheless, we find an impressive coincidence
between the properties of cluster members preceding the H-free WR phase
and the evolutionary predictions for a single, non-rotating 60
M⊙ star; in turn this implies an age of ˜3.0-3.6
Myr for the Quintuplet. Neither the late O-hypergiants nor the low
luminosity supergiants are predicted by such a path; 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 evolve from stars with an initial mass in excess of 60
M⊙ but it appears difficult to reconcile their
observational properties with theoretical expectations. This is
important since one would expect the most massive stars within the
Quintuplet to be undergoing core-collapse/SNe at this time; since the
WRs represent an evolutionary phase directly preceding this event,their
physical properties are crucial to understanding both this process and
the nature of the resultant relativistic remnant. As such, the
Quintuplet provides unique observational constraints on the evolution
and death of the most massive stars forming in the local, high
metallicity Universe.
Based on observations made at the European Southern Observatory,
Paranal, Chile under programme ESO 093.D-0306.
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