8,374 research outputs found
NGC 3105: a young open cluster with low metallicity
NGC 3105 is a young open cluster hosting blue, yellow and red supergiants.
This rare combination makes it an excellent laboratory to constrain
evolutionary models of high-mass stars. It is poorly studied and fundamental
parameters such as its age or distance are not well defined. We intend to
characterize in an accurate way the cluster as well as its evolved stars, for
which we derive for the first time atmospheric parameters and chemical
abundances. We identify 126 B-type likely members within a radius of
2.70.6 arcmin, which implies an initial mass, 4100
M. We find a distance of 7.20.7 kpc for NGC 3105, placing it at
=10.01.2 kpc. Isochrone fitting supports an age of 286 Ma,
implying masses around 9.5 M for the supergiants. A high fraction of
Be stars (25 %) is found at the top of the main sequence down to
spectral type b3. From the spectral analysis we estimate for the cluster a
=+46.90.9 km s and a low metallicity,
[Fe/H]=-0.290.22. We also have determined, for the first time, chemical
abundances for Li, O, Na, Mg, Si, Ca, Ti, Ni, Rb, Y, and Ba for the evolved
stars. The chemical composition of the cluster is consistent with that of the
Galactic thin disc. An overabundance of Ba is found, supporting the enhanced
-process. NGC 3105 has a low metallicity for its Galactocentric distance,
comparable to typical LMC stars. It is a valuable spiral tracer in a very
distant region of the Carina-Sagittarius spiral arm, a poorly known part of the
Galaxy. As one of the few Galactic clusters containing blue, yellow and red
supergiants, it is massive enough to serve as a testbed for theoretical
evolutionary models close to the boundary between intermediate and high-mass
stars.Comment: 18 pages, 13 figures. Accepted for publication in A&
Community experiences of organised crime in Scotland
The research explored community experiences of serious organised crime in Scotland (SOC). The report provides information on the nature and extent of the impact of SOC on everyday life in the community, as well as offering suggestions for policy development. The study sought to answer the following questions: 1)What are the relationships that exist between SOC and communities in Scotland? 2)What are the experiences and perceptions of residents, stakeholders and organisations of the scope and nature of SOC within their local area? and 3)How does SOC impact on community wellbeing, and to what extent can the harms associated with SOC be mitigated
Recommended from our members
GEO debris and interplanetary dust: fluxes and charging behaviour
GEO debris and interplanetary dust: fluxes and charging behavior
In September 1996, a dust/debris detector: GORID was launched into the
geostationary (GEO) region as a piggyback instrument on the Russian Express-2
telecommunications spacecraft. The instrument began its normal operation in
April 1997 and ended its mission in July 2002. The goal of this work was to use
GORID's particle data to identify and separate the space debris to
interplanetary dust particles (IDPs) in GEO, to more finely determine the
instrument's measurement characteristics and to derive impact fluxes. While the
physical characteristics of the GORID impacts alone are insufficient for a
reliable distinction between debris and interplanetary dust, the temporal
behavior of the impacts are strong enough indicators to separate the
populations based on clustering. Non-cluster events are predominantly
interplanetary, while cluster events are debris. The GORID mean flux
distributions (at mass thresholds which are impact speed dependent) for IDPs,
corrected for dead time, are 1.35x10^{-4} m^{-2} s^{-1} using a mean detection
rate: 0.54 d^{-1}, and for space debris are 6.1x10^{-4} m^{-2} s^{-1} using a
mean detection rate: 2.5 d^{-1}. Beta-meteoroids were not detected. Clusters
could be a closely-packed debris cloud or a particle breaking up due to
electrostatic fragmentation after high charging.Comment: * Comments: 6 pages, 4 postscript figures, in Dust in Planetary
Systems 2005, Krueger, H. and Graps, A. eds., ESA Publications, SP in press
(2006). For high resolution version, see:
http://www.mpi-hd.mpg.de/dustgroup/~graps/dips2005/GrapsetalDIPS2005.pd
Nano dust impacts on spacecraft and boom antenna charging
High rate sampling detectors measuring the potential difference between the
main body and boom antennas of interplanetary spacecraft have been shown to be
efficient means to measure the voltage pulses induced by nano dust impacts on
the spacecraft body itself (see Meyer-Vernet et al, Solar Phys. 256, 463
(2009)). However, rough estimates of the free charge liberated in post impact
expanding plasma cloud indicate that the cloud's own internal electrostatic
field is too weak to account for measured pulses as the ones from the TDS
instrument on the STEREO spacecraft frequently exceeding 0.1 V/m. In this paper
we argue that the detected pulses are not a direct measure of the potential
structure of the plasma cloud, but are rather the consequence of a transitional
interruption of the photoelectron return current towards the portion of the
antenna located within the expanding cloud
Spatial Clustering of Dark Matter Halos: Secondary Bias, Neighbor Bias, and the Influence of Massive Neighbors on Halo Properties
We explore the phenomenon commonly known as halo assembly bias, whereby dark
matter halos of the same mass are found to be more or less clustered when a
second halo property is considered, for halos in the mass range . Using the Large Suite of Dark Matter Simulations
(LasDamas) we consider nine commonly used halo properties and find that a
clustering bias exists if halos are binned by mass or by any other halo
property. This secondary bias implies that no single halo property encompasses
all the spatial clustering information of the halo population. The mean values
of some halo properties depend on their halo's distance to a more massive
neighbor. Halo samples selected by having high values of one of these
properties therefore inherit a neighbor bias such that they are much more
likely to be close to a much more massive neighbor. This neighbor bias largely
accounts for the secondary bias seen in halos binned by mass and split by
concentration or age. However, halos binned by other mass-like properties still
show a secondary bias even when the neighbor bias is removed. The secondary
bias of halos selected by their spin behaves differently than that for other
halo properties, suggesting that the origin of the spin bias is different than
of other secondary biases.Comment: 14 pages, LaTeX; minor revisions, and added references; results
unchange
Unveiling the nature of INTEGRAL objects through optical spectroscopy. VII. Identification of 20 Galactic and extragalactic hard X-ray sources
Within the framework of our program of assessment of the nature of
unidentified or poorly known INTEGRAL sources, we present here spectroscopy of
optical objects, selected through positional cross-correlation with soft X-ray
detections (afforded with satellites such as Swift, ROSAT, Chandra and/or
XMM-Newton) as putative counterparts of hard X-ray sources detected with the
IBIS instrument onboard INTEGRAL. Using 6 telescopes of various sizes and
archival data from two on-line spectroscopic surveys we are able to identify,
either for the first time or independent of other groups, the nature of 20
INTEGRAL hard X-ray sources. Our results indicate that: 11 of these objects are
active galactic nuclei (AGNs) at redshifts between 0.014 and 0.978, 7 of which
display broad emission lines, 2 show narrow emission lines only, and 2 have
unremarkable or no emission lines (thus are likely Compton thick AGNs); 5 are
cataclysmic variables (CVs), 4 of which are (possibly magnetic) dwarf novae and
one is a symbiotic star; and 4 are Galactic X-ray binaries (3 with high-mass
companions and one with a low-mass secondary). It is thus again found that the
majority of these sources are AGNs or magnetic CVs, confirming our previous
findings. When possible, the main physical parameters for these hard X-ray
sources are also computed using the multiwavelength information available in
the literature. These identifications support the importance of INTEGRAL in the
study of the hard X-ray spectrum of all classes of X-ray emitting objects, and
the effectiveness of a strategy of multi-catalogue cross-correlation plus
optical spectroscopy to securely pinpoint the actual nature of unidentified
hard X-ray sources.Comment: 16 pages, 8 figures, 5 tables. Accepted for publication on Astronomy
& Astrophysics, main journal. Slight changes made to match the
proof-corrected version; references adde
- …