3,537 research outputs found
A downward revision to the distance of the 1806-20 cluster and associated magnetar from Gemini near-Infrared spectroscopy
We present H- and K-band spectroscopy of OB and Wolf-Rayet (WR) members of
the Milky Way cluster 1806-20 (G10.0-0.3), to obtain a revised cluster distance
of relevance to the 2004 giant flare from the SGR 1806-20 magnetar. From GNIRS
spectroscopy obtained with Gemini South, four candidate OB stars are confirmed
as late O/early B supergiants, while we support previous mid WN and late WC
classifications for two WR stars. Based upon an absolute Ks-band magnitude
calibration for B supergiants and WR stars, and near-IR photometry from NIRI at
Gemini North plus archival VLT/ISAAC datasets, we obtain a cluster distance
modulus of 14.7+/-0.35 mag. The known stellar content of the 1806-20 cluster
suggests an age of 3-5 Myr, from which theoretical isochrone fits infer a
distance modulus of 14.7+/-0.7 mag. Together, our results favour a distance
modulus of 14.7+/-0.4 mag (8.7^+1.8_-1.5 kpc) to the 1806-20 cluster, which is
significantly lower than the nominal 15 kpc distance to the magnetar. For our
preferred distance, the peak luminosity of the December 2004 giant flare is
reduced by a factor of three to 7 X 10^46 erg/s, such that the contamination of
BATSE short gamma ray bursts (GRB's) from giant flares of extragalactic
magnetars is reduced to a few percent. We infer a magnetar progenitor mass of
~48^+20_-8 Msun, in close agreement with that obtained recently for the
magnetar in Westerlund 1.Comment: 6 pages, 4 figures, accepted for MNRAS Letter
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The Wolf-Rayet population of Westerlund 1
New NTT/SOFI near-IR narrow-band imaging and spectroscopy reveals an additional four Wolf-Rayet (WR) stars in the massive cluster Westerlund 1, bringing the total WR population to 24. Sixteen of the WR stars in Wd1 have been classified WN5â11, while eight are WC8â9. An observed WR to RSG/YHG ratio of âŒ3 suggests an age of 4.5â5.0 Myr, with WR stars descended from 40â55MSolar progenitors. On the basis of dust and hard X-ray emission, we estimate that 40â65% are probable members of massive star binary systems
Cluster and nebular properties of the central star-forming region of NGC 1140
We present new high spatial resolution HST/ACS imaging of NGC 1140 and high
spectral resolution VLT/UVES spectroscopy of its central star-forming region.
The central region contains several clusters, the two brightest of which are
clusters 1 and 6 from Hunter, O'Connell & Gallagher, located within
star-forming knots A and B, respectively. Nebular analysis indicates that the
knots have an LMC-like metallicity of 12 + log(O/H) = 8.29 +/- 0.09. According
to continuum subtracted H alpha ACS imaging, cluster 1 dominates the nebular
emission of the brighter knot A. Conversely, negligible nebular emission in
knot B originates from cluster 6. Evolutionary synthesis modelling implies an
age of 5 +/- 1 Myr for cluster 1, from which a photometric mass of (1.1 +/-
0.3) x 10^6 Msun is obtained. For this age and photometric mass, the modelling
predicts the presence of ~5900 late O stars within cluster 1. Wolf-Rayet
features are observed in knot A, suggesting 550 late-type WN and 200 early-type
WC stars. Therefore, N(WR)/N(O) ~ 0.1, assuming that all the WR stars are
located within cluster 1. The velocity dispersions of the clusters were
measured from constituent red supergiants as sigma ~ 23 +/- 1 km/s for cluster
1 and sigma ~ 26 +/- 1 km/s for cluster 6. Combining sigma with half-light
radii of 8 +/- 2 pc and 6.0 +/- 0.2 pc measured from the F625W ACS image
implies virial masses of (10 +/- 3) x 10^6 Msun and (9.1 +/- 0.8) x 10^6 Msun
for clusters 1 and 6, respectively. The most likely reason for the difference
between the dynamical and photometric masses of cluster 1 is that the velocity
dispersion of knot A is not due solely to cluster 1, as assumed, but has an
additional component associated with cluster 2.Comment: 13 pages, 7 figure
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Stimulation of bone growth with thrombin peptide derivatives
Disclosed is a method of stimulating bone growth at a site in a subject in need of osteoinduction. The method comprises the step of administering a therapeutically effective amount of an agonist of the non-proteolytically activated thrombin receptor to the site.Board of Regents, University of Texas Syste
Properties of Hot Stars in the Wolf-Rayet galaxy NGC5253 from ISO Spectroscopy
ISO-SWS spectroscopy of the WR galaxy NGC5253 is presented, and analysed to
provide estimates of its hot young star population. Our approach differs from
previous investigations in that we are able to distinguish between the regions
in which different infrared fine-structure lines form, using complementary
ground-based observations. The high excitation nebular [SIV] emission is formed
in a very compact region, which we attribute to the central super-star-nucleus,
and lower excitation [NeII] nebular emission originates in the galactic core.
We use photo-ionization modelling coupled with the latest theoretical O-star
flux distributions to derive effective stellar temperatures and ionization
parameters of Teff>38kK, logQ=8.25 for the compact nucleus, with Teff=35kK,
logQ<8 for the larger core. Results are supported by more sophisticated
calculations using evolutionary synthesis models. We assess the contribution
that Wolf-Rayet stars may make to highly ionized nebular lines (e.g. [OIV]).
From our Br(alpha) flux, the 2" nucleus contains the equivalent of
approximately 1000 O7V star equivalents and the starburst there is 2-3Myr old;
the 20" core contains about 2500 O7V star equivalents, with a representative
age of 5Myr. The Lyman ionizing flux of the nucleus is equivalent to the 30
Doradus region. These quantities are in good agreement with the observed mid-IR
dust luminosity of 7.8x10^8 L(sun) Since this structure of hot clusters
embedded in cooler emission may be common in dwarf starbursts, observing a
galaxy solely with a large aperture may result in confusion. Neglecting the
spatial distribution of nebular emission in NGC5253, implies `global' stellar
temperatures (or ages) of 36kK (4.8Myr) and 39kK (2.9 or 4.4Myr) from the
observed [NeIII/II] and [SIV/III] line ratios, assuming logQ=8.Comment: 16 pages, 7 figures, uses mn.sty, to appear in MNRA
The Arches cluster revisited: II. A massive eclipsing spectroscopic binary in the Arches cluster
We have carried out a spectroscopic variability survey of some of the most massive stars in the Arches cluster, using K-band observations obtained with SINFONI on the VLT. One target, F2, exhibits substantial changes in radial velocity; in combination with new KMOS and archival SINFONI spectra, its primary component is found to undergo radial velocity variation with a period of 10.483+/-0.002 d and an amplitude of ~350 km/s-1. A secondary radial velocity curve is also marginally detectable. We reanalyse archival NAOS-CONICA photometric survey data in combination with our radial velocity results to confirm this object as an eclipsing SB2 system, and the first binary identified in the Arches. We model it as consisting of an 82+/-12 Mâ WN8-9h primary and a 60+/-8 Mâ O5-6 Ia+ secondary, and as having a slightly eccentric orbit, implying an evolutionary stage prior to strong binary interaction. As one of four X-ray bright Arches sources previously proposed as colliding-wind massive binaries, it may be only the first of several binaries to be discovered in this cluster, presenting potential challenges to recent models for the Arches' age and composition. It also appears to be one of the most massive binaries detected to date; the primary's calculated initial mass of >~120 Mâ would arguably make this the most massive binary known in the Galaxy
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