The Quintuplet cluster

II. Analysis of the WN stars^⋆

¹ Universität Potsdam, Institut für Physik und Astronomie, 14476 Potsdam, Germany
e-mail: liermann@mpifr-bonn.mpg.de
² Universitäts-Sternwarte München, 81679 München, Germany

Received: 1 June 2009
Accepted: 30 July 2010

Abstract

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 (WR 102d, WR 102i, WR 102hb, and WR 102ea) are of spectral subtype WN9h. One further star, LHO 110, 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 Potsdam Wolf-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/L_⊙) > 6.0, with relatively low stellar temperatures, T^∗  ≈  25−35 kK. Their stellar winds contain a significant fraction of hydrogen, up to X_H ~ 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 M_⊙. 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 A_K = 3.1  ±  0.5 mag (A_V = 27  ±  4 mag) towards the Quintuplet cluster.