The Quintuplet cluster II. Analysis of the WN stars
A. Liermann1, W.-R. Hamann1, L. M. Oskinova1, H. Todt1, and K. Butler2
2 Universitäts-Sternwarte München, 81679 München, Germany
Based on K-band integral-field spectroscopy, we analyze four Wolf-Rayet
stars of the nitrogen sequence (WN) found in the inner part of the
Quintuplet cluster. All WN stars (WR102d, WR102i, WR102hb, and WR102ea)
are of spectral subtype WN9h. One further star, LHO110, is included in
the analysis which has been classified as Of/WN? previously but turns
out to be most likely a WN9h star as well. The PotsdamWolf-Rayet (PoWR)
models for expanding atmospheres are used to derive the fundamental
stellar and wind parameters. The stars turn out to be very luminous, log
(L/Lsun) > 6.0, with relatively low stellar temperatures,
T* ~ 25 - 35 kK. Their
stellar winds contain a significant fraction of hydrogen, up to
XH ~ 0.45 (by mass). We discuss the position of
the Galactic center WN stars in the Hertzsprung-Russell diagram and find
that they form a distinct group. In this respect, the Quintuplet WN
stars are similar to late-type WN stars found in the Arches cluster and
elsewhere in the Galaxy. Comparison with stellar evolutionary models
reveals that the Quintuplet WN stars should have been initially more
massive than 60 Msun. They are about 2.4 - 3.6 million years
old, and might still be central hydrogen burning objects. The analysis
of the spectral energy distributions of the program stars results in a
mean extinction of AK = 3.1 ± 0.5 mag (AV =
27 ± 4 mag) towards the Quintuplet cluster.
Published in Astronomy & Astrophysics
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