265 research outputs found
Muon Background Reduction in CLIC
We report on a study concerning the reduction of muon backgrounds in CLIC
using magnetised iron.Comment: Proceedings of the International Workshop on future Linear Colliders
2011 (LCWS11), Granada, Spain. 4 pages, 4 figure
A Micron-Scale Laser-Based Beam Profile Monitor for the International Linear Collider
A micron-scale laser-wire system was constructed and tested at the Accelerator Test Facility (ATF) extraction line at the High Energy Accelerator Research Organisation (KEK) in Japan. The system was evaluated through collision tests, electron beam tests, laser beam measurements and simulations. Beam halo measurements were carried out in order to compare the beam halo to a theory of its production through gas scattering and towards evaluating it as a source of background for diagnostic instruments at ATF2 and the International Linear Collider (ILC). Simulations were carried out to test the signal extraction of the system at the future ATF2 and of a similar system in the proposed ILC beam delivery system, with implications for sharing the signal extraction region with the polarimeter
Mangrove or mudflat: Prioritising fish habitat for conservation in a turbid tropical estuary
Mangrove habitats are typically the focus of conservation efforts in tropical estuaries because their structural complexity is thought to support greater biodiversity and nursery function than unvegetated habitats. However, evidence for this paradigm has been equivocal in turbid tropical estuaries where unvegetated mudflats are also highly productive. The present study compared the community composition, biodiversity, nursery-role and commercial fish biomass in two mangrove habitats and one mudflat habitat in the Gulf of Paria, Trinidad. A total of 12 705 fishes, comprising 63 species from 26 families, were sampled in mangrove creeks, seaward mangrove fringe and the subtidal margin of an intertidal mudflat from June 2014 to June 2015. The composition of the creek and mudflat communities were distinct, while the community of the mangrove fringe more closely resembled the mudflat than the mangrove creeks. Mean species richness (MSR), total species richness (TSR) extrapolated from species accumulation curves, and juvenile species richness (JSR) were significantly greater in the mudflat (MSR = 11.4 ± 1.0; TSR = 75 ± 14; JSR = 9.1 ± 0.8) than mangrove creeks (MSR = 9.0 ± 0.5; TSR = 49 ± 3; JSR = 6.1 ± 0.4) and the seaward mangrove fringe (MSR = 6.4 ± 0.7; TSR = 58 ± 14; JSR = 5.2 ± 0.4). Meanwhile, Shannon Weiner diversity, juvenile fish abundance and commercial fish biomass were comparable between habitats. These findings caution against the generalisation that mangroves are the most important habitat for fishes in turbid tropical estuaries. There is now a growing body of evidence that mudflats warrant consideration as important repositories of biodiversity and nursery function for juvenile fishes
Maximum Reduced Proper Motion Method: Detection of New Nearby Ultracool Dwarfs
In this paper, we describe how to use the Maximum Reduced Proper Motion
method (Phan-Bao et al. 2003) to detect 57 nearby L and late-M dwarfs (d_phot
<= 30 pc): 36 of them are newly discovered. Spectroscopic observations of 43 of
the 57 ultracool dwarfs were previously reported in Martin et al. (2010). These
ultracool dwarfs were identified by color criteria in ~5,000 square degrees of
the DENIS database and then further selected by the method for spectroscopic
follow-up to determine their spectral types and spectroscopic distances. We
also report here our newly measured proper motions of these ultracool dwarfs
from multi-epoch images found in public archives (ALADIN, DSS, 2MASS, DENIS),
with at least three distinct epochs and time baselines of 2 to 46 years.Comment: 9 pages, 5 figures, 3 tables, accepted for publication in
Astronomische Nachrichte
Spectral classification of Pleiades brown dwarf candidates
We report on the results of the spectroscopy of 10 objects previously
classified as brown dwarf candidates via RIJHK colors by Eisenbeiss et al.
(2009), who performed deep imaging observations on a 0.4 sq.deg. field at the
edge of the Pleiades. We describe and judge on classification techniques in the
region of M-type stars. To classify and characterise the objects, visual and
near infrared spectra have been obtained with VLT FORS and ISAAC. The spectral
classification was performed using the shape of the spectra as well as spectral
indices that are sensitive to the spectral type and luminosity class of Mtype
stars and late M-type brown dwarfs. Furthermore a spectrophotometric distance
was calculated and compared the distance of the Pleiades to investigate the
membership probability. As a second argument we analyzed the proper motion. The
brown dwarf candidates were found not to be brown dwarfs, but late-K to
mid-M-type dwarf stars. Based on the obtained distance and tabulated proper
motions we conclude that all objects are background dwarf stars.Comment: 10 pages, 5 figure
Southern Infrared Proper Motion Survey III: Constraining the mass function of low mass stars
The stellar mass function is one of the fundamental distributions of stellar
astrophysics. Its form at masses similar to the Sun was found by Salpeter
(1955) to be a power-law with a slope of . Since
then the mass function in the field, in stellar clusters and in other galaxies
has been studied to identify variation due to environment and mass range. Here
we use results from previous papers in the SIPS series to constrain the mass
function of low mass stars (0.075Mm). We use simulations
of the low mass local stellar population based on those in Deacon & Hambly
(2006) to model the results of the SIPS-II survey (Deacon & Hambly, 2007). We
then vary the input parameters of these simulations (the exponent of the mass
function and a stellar birthrate parameter ) and compare the
simulated survey results with those from the actual survey. After a correction
for binarity and taking into account potential errors in our model we find that
for the quoted mass range.Comment: Submitted to astro-p
Low Mass Stars and Brown Dwarfs in Praesepe
Presented are the results of a large and deep optical-near-infrared
multi-epoch survey of the Praesepe open star cluster using data from the UKIDSS
Galactic Clusters Survey. Multiple colour magnitude diagrams were used to
select potential members and proper motions were used to assign levels of
membership probability. From our sample, 145 objects were designated as high
probability members (p >= 0.6) with most of these having been found by previous
surveys although 14 new cluster members are also identified. Our membership
assignment is restricted to the bright sample of objects (Z < 18). From the
fainter sample, 39 candidates were found from an examination of multiple colour
magnitude plots. Of these, 2 have small but significant membership
probabilities. Finally, using theoretical models, cluster luminosity and mass
functions were plotted with the later being fitted with a power law of alpha =
1.11 +/- 0.37 for the mass range 0.6 to 0.125 Msun and an assumed cluster age
of 500 Myrs in the UKIDSS Z photometric band. Likewise taking an assumed
cluster age of 1 Gyr we find alpha = 1.10 +/- 0.37. Similar values were also
found for the J and K bands. These results compare favourably with the result
of Kraus & Hillenbrand (2007) (alpha = 1.4 +/- 0.2) but are significantly lower
than that of the more recent study conducted by Boudreault et al. (2009) (alpha
= 1.8 +/- 0.1).Comment: 21 pages, 11 figures, 3 tables and 4 appendices. Accepted for
publication in MNRAS, corrected a missing referenc
The UKIDSS-2MASS Proper Motion Survey I: Ultracool dwarfs from UKIDSS DR4
The UKIRT Infrared Deep Sky Survey (UKIDSS) is the first of a new generation
of infrared surveys. Here we combine the data from two UKIDSS components, the
Large Area Survey (LAS) and the Galactic Cluster Survey (GCS), with 2MASS data
to produce an infrared proper motion survey for low mass stars and brown
dwarfs. In total we detect 267 low mass stars and brown dwarfs with significant
proper motions. We recover all ten known single L dwarfs and the one known T
dwarf above the 2MASS detection limit in our LAS survey area and identify eight
additional new candidate L dwarfs. We also find one new candidate L dwarf in
our GCS sample. Our sample also contains objects from eleven potential common
proper motion binaries. Finally we test our proper motions and find that while
the LAS objects have proper motions consistent with absolute proper motions,
the GCS stars may have proper motions which are significantly under-estimated.
This is due possibly to the bulk motion of some of the local astrometric
reference stars used in the proper motion determination.Comment: Accepted for publication in MNRA
BDSIM: An Accelerator Tracking Code with Particle-Matter Interactions
Beam Delivery Simulation (BDSIM) is a program that simulates the passage of
particles in a particle accelerator. It uses a suite of standard high energy
physics codes (Geant4, ROOT and CLHEP) to create a computational model of a
particle accelerator that combines accurate accelerator tracking routines with
all of the physics processes of particles in Geant4. This unique combination
permits radiation and detector background simulations in accelerators where
both accurate tracking of all particles is required over long range or over
many revolutions of a circular machine, as well as interaction with the
material of the accelerator.Comment: 20 pages, 17 figures. Accepted for publication 28th Jan 202
A 1500 deg2 near infrared proper motion catalogue from the UKIDSS Large Area Survey
The United Kingdom Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS) began in 2005, with the start of the UKIDSS programme as a 7 year effort to survey roughly 4000 deg2 at high Galactic latitudes in Y, J, H and K bands. The survey also included a significant quantity of two epoch J band observations, with an epoch baseline greater than 2 years to calculate proper motions. We present a near-infrared proper motion catalogue for the 1500 deg2 of the two epoch LAS data, which includes 135â625 stellar sources and a further 88â324 with ambiguous morphological classifications, all with motions detected above the 5Ï level. We developed a custom proper motion pipeline which we describe here. Our catalogue agrees well with the proper motion data supplied for a 300 deg2 subset in the current Wide Field Camera Science Archive (WSA) 10th data release (DR10) catalogue, and in various optical catalogues, but it benefits from a larger matching radius and hence a larger upper proper motion detection limit. We provide absolute proper motions, using LAS galaxies for the relative to absolute correction. By using local second-order polynomial transformations, as opposed to linear transformations in the WSA, we correct better for any local distortions in the focal plane, not including the radial distortion that is removed by the UKIDSS pipeline. We present the results of proper motion searches for new brown dwarfs and white dwarfs. We discuss 41 sources in the WSA DR10 overlap with our catalogue with proper motions >300âmasâyrâ1, several of which are new detections. We present 15 new candidate ultracool dwarf binary systems
- âŠ