26 research outputs found
The Quintuplet Cluster III. Hertzsprung-Russell diagram and cluster age
The Quintuplet, one of three massive stellar clusters in the Galactic center,
is located about 30pc in projection from Sagittarius A*. Based on near-infrared
K-band spectra we determine temperatures and luminosities for all stars in our
sample and construct the Herztsprung-Russell diagram. We find two distinct
groups: early-type OB stars and late-type KM stars, well separated from each
other. By comparison with Geneva stellar evolution models we derive initial
masses exceeding 8 solar masses for the OB stars, that are located along an
isochrone corresponding to a cluster age of about 4 million years. In addition,
we derive number ratios (e. g. N_WR/N_O) and compare them with predictions of
population synthesis models. We find that an instantaneous burst of star
formation at about 3.3 to 3.6\,Myr ago is the most likely scenario to form the
Quintuplet cluster. The late-type stars in the sample are red giant branch
(RGB) stars or red supergiants (RSGs) according to their spectral signatures.
It is discussed if they could physically belong to the Quintuplet cluster.
Furthermore, we apply a mass-luminosity relation to construct the initial mass
function (IMF) of the cluster. We find indications for a slightly top-heavy
IMF.Comment: 10 pages, 9 figures, 2 tables, accepted for publication in A&
New Wolf-Rayet star and its circumstellar nebula in Aquila
We report the discovery of a new Wolf-Rayet star in Aquila via detection of
its circumstellar nebula (reminiscent of ring nebulae associated with late WN
stars) using the Spitzer Space Telescope archival data. Our spectroscopic
follow-up of the central point source associated with the nebula showed that it
is a WN7h star (we named it WR121b). We analyzed the spectrum of WR121b by
using the Potsdam Wolf-Rayet (PoWR) model atmospheres, obtaining a stellar
temperature of ~ 50 kK. The stellar wind composition is dominated by helium
with ~ 20 per cent of hydrogen. The stellar spectrum is highly reddened
(E_{B-V} = 2.85 mag). Adopting an absolute magnitude of M_v = -5.7, the star
has a luminosity of log L/Lsun = 5.75 and a mass-loss rate of 10^{-4.7}
Msun/yr, and resides in a distance of 6.3 kpc. We searched for a possible
parent cluster of WR121b and found that this star is located at ~ 1 degree from
the young star cluster embedded in the giant HII region W43 (containing a
WN7+a/OB? star -- WR121a). We also discovered a bow shock around the O9.5III
star ALS9956, located at ~ 0.5 degree from the cluster. We discuss the
possibility that WR121b and ALS9956 are runaway stars ejected from the cluster
in W43.Comment: 9 pages, 7 figures, accepted to MNRA
Two extremely luminous WN stars in the Galactic center with circumstellar emission from dust and gas
We study relatively isolated massive WN-type stars in the Galactic center.
The K-band spectra of WR102ka and WR102c are exploited to infer the stellar
parameters and to compute synthetic stellar spectra using the Potsdam
Wolf-Rayet (PoWR) model atmosphere code. These models are combined with
dust-shell models for analyzing the Spitzer IRS spectra of these objects.
Archival IR images complement the interpretation. We report that WR102ka and
WR102c are among the most luminous stars in the Milky Way. The mid-IR continua
for both objects are dominated by dust emission. For the first time we report
the presence of dust in the close vicinity of WN stars. Also for the first
time, we have detected lines of pure-rotational transitions of molecular
hydrogen in a massive-star nebula. A peony-shaped nebula around 102ka is
resolved by the Spitzer MIPS camera. We attribute the formation of this nebula
to the recent evolutionary history of WR102ka.Comment: accepted to A&A, see NASA/Spitzer Press Release at
http://www.spitzer.caltech.edu/Media/releases/ssc2008-1
Two extremely luminous WN stars in the Galactic center with circumstellar emission from dust and gas
Waste Incineration-an Important Element of the Integrated Waste Management System in Germany
Neue Verfahren der thermischen Abfallbehandlung Dokumentation. Stand: Anfang 1980
TIB: AC 5701 (1980) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman