4,307 research outputs found
Red Giants in the Small Magellanic Cloud. II. Metallicity Gradient and Age-Metallicity Relation
We present results from the largest CaII triplet line metallicity study of
Small Magellanic Cloud (SMC) field red giant stars to date, involving 3037
objects spread across approximately 37.5 sq. deg., centred on this galaxy. We
find a median metallicity of [Fe/H]=-0.99+/-0.01, with clear evidence for an
abundance gradient of -0.075+/-0.011 dex / deg. over the inner 5 deg. We
interpret the abundance gradient to be the result of an increasing fraction of
young stars with decreasing galacto-centric radius, coupled with a uniform
global age-metallicity relation. We also demonstrate that the age-metallicity
relation for an intermediate age population located 10kpc in front of the NE of
the Cloud is indistinguishable from that of the main body of the galaxy,
supporting a prior conjecture that this is a stellar analogue of the Magellanic
Bridge. The metal poor and metal rich quartiles of our RGB star sample (with
complementary optical photometry from the Magellanic Clouds Photometric Survey)
are predominantly older and younger than approximately 6Gyr, respectively.
Consequently, we draw a link between a kinematical signature, tentatively
associated by us with a disk-like structure, and the upsurges in stellar
genesis imprinted on the star formation history of the central regions of the
SMC. We conclude that the increase in the star formation rate around 5-6Gyr ago
was most likely triggered by an interaction between the SMC and LMC.Comment: To appear in MNRA
Red Giants in the Small Magellanic Cloud. I. Disk and Tidal Stream Kinematics
We present results from an extensive spectroscopic survey of field stars in
the Small Magellanic Cloud (SMC). 3037 sources, predominantly first-ascent red
giants, spread across roughly 37.5 sq. deg, are analysed. The line of sight
velocity field is dominated by the projection of the orbital motion of the SMC
around the LMC/Milky Way. The residuals are inconsistent with both a
non-rotating spheroid and a nearly face on disk system. The current sample and
previous stellar and HI kinematics can be reconciled by rotating disk models
with line of nodes position angle, theta, ~ 120-130 deg., moderate inclination
(i ~ 25-70 deg.), and rotation curves rising at 20-40 km/s/kpc. The metal-poor
stars exhibit a lower velocity gradient and higher velocity dispersion than the
metal-rich stars. If our interpretation of the velocity patterns as bulk
rotation is appropriate, then some revision to simulations of the SMC orbit is
required since these are generally tuned to the SMC disk line-of-nodes lying in
a NE-SW direction. Residuals show strong spatial structure indicative of
non-circular motions that increase in importance with increasing distance from
the SMC centre. Kinematic substructure in the north-west part of our survey
area is associated with the tidal tail or Counter-Bridge predicted by
simulations. Lower line-of-sight velocities towards the Wing and the larger
velocities just beyond the SW end of the SMC Bar are probably associated with
stellar components of the Magellanic Bridge and Counter-Bridge, respectively.
Our results reinforce the notion that the intermediate-age stellar population
of the SMC is subject to substantial stripping by external forces.Comment: To appear in MNRA
Star Clusters in the Magellanic Clouds-1: Parameterisation and Classification of 1072 Clusters in the LMC
We have introduced a semi-automated quantitative method to estimate the age
and reddening of 1072 star clusters in the Large Magellanic Cloud (LMC) using
the Optical Gravitational Lensing Experiment (OGLE) III survey data. This study
brings out 308 newly parameterised clusters. In a first of its kind, the LMC
clusters are classified into groups based on richness/mass as very poor, poor,
moderate and rich clusters, similar to the classification scheme of open
clusters in the Galaxy. A major cluster formation episode is found to happen at
125 +- 25 Myr in the inner LMC. The bar region of the LMC appears prominently
in the age range 60 - 250 Myr and is found to have a relatively higher
concentration of poor and moderate clusters. The eastern and the western ends
of the bar are found to form clusters initially, which later propagates to the
central part. We demonstrate that there is a significant difference in the
distribution of clusters as a function of mass, using a movie based on the
propagation (in space and time) of cluster formation in various groups. The
importance of including the low mass clusters in the cluster formation history
is demonstrated. The catalog with parameters, classification, and cleaned and
isochrone fitted CMDs of 1072 clusters, which are available as online material,
can be further used to understand the hierarchical formation of clusters in
selected regions of the LMC.Comment: 19 pages, 19figures, published in MNRAS on August 16, 2016
Supplementary material is available in the MNRAS websit
Optical/IR studies of Be stars in NGC 6834 with emphasis on two specific stars
We present optical and infrared photometric and spectroscopic studies of two
Be stars in the 70--80-Myr-old open cluster NGC 6834. NGC 6834(1) has been
reported as a binary from speckle interferometric studies whereas NGC 6834(2)
may possibly be a gamma Cas-like variable. Infrared photometry and spectroscopy
from the United Kingdom Infrared Telescope (UKIRT), and optical data from
various facilities are combined with archival data to understand the nature of
these candidates. High signal-to-noise near-IR spectra obtained from UKIRT have
enabled us to study the optical depth effects in the hydrogen emission lines of
these stars. We have explored the spectral classification scheme based on the
intensity of emission lines in the and bands and contrasted it with the
conventional classification based on the intensity of hydrogen and helium
absorption lines. This work also presents hitherto unavailable UBV CCD
photometry of NGC 6834, from which the evolutionary state of the Be stars is
identified.Comment: Published in Research in Astronomy and Astrophysics, RAA 14 (2014)
1173-1192, 20 pages, 10 figure
Nurses' knowledge, attitude, practice and barriers towards the use of evidence based nursing practice (EBNP) at government Hospital in Malaysia
In the nursing profession, EBNP makes a positive contribution to healthcare outcomes,
care delivery, clinical teaching and research. The research objective was to determine
the nurses’ knowledge, attitude, practice of EBNP and barriers to adopt EBNP in four
hospitals in Malaysia, Hospital Universiti Sains Malaysia (Hospital USM), Hospital
Pulau Pinang (HPP), Hospital Sultan Abdul Halim (HSAH) and Hospital Seberang Jaya
(HSJ). A cross-sectional study was conducted from January until December 2012
among nurses working in all disciplines, on shift or day time duties in four selected
hospitals. The questionnaire was adapted from a Singapore study. The data were
analysed with SPSS version 21.0, using descriptive statistics, Independent T-Test, One-
Way ANOVA and Multi-Factorial ANOVA. Results showed that among the nurses
working in four different Malaysian hospitals, nearly 50% knew what the evidence
based practice meant. The items assessing the attitude showed a large number nurses
responding that they did neither agree nor disagree with statements provided. The
majority of the remaining nurses tended to show a rather positive attitude except when
asked about how the workload interfered with their EBP practice. Most nurses
recognized there were many barriers to EBP in their working place. The significant
mean differences of practice on EBNP between senior and junior nurses were observed for the statements 1, 2, and 3 (p=<0.001), (p=0.005) and (p=0.028) respectively. Multifactorial
ANOVA analysis used to determine the effect of academic qualification,
working place, working experience and training on nurses’ knowledge towards EBNP.
In conclusion, this study may have helped to increase understanding of knowledge,
attitudes, practice and barriers to adopt EBNP to the utilization of research by nurses
through an exploration of perceived barriers and facilitators on the part of nurses
Evidence of a counterrotating core in the Large Magellanic Cloud
Stellar radial velocity in the central region of the Large Magellanic Cloud
(LMC) is used to estimate the radial velocity curve along various position
angles (PA) including the line of nodes (LON). The central part of the radial
velocity profile, along the LON, shows a V-shaped profile - a clear indication
of counterrotation. The counterrotating region and the secondary bar have
similar location and PA. The origin of the counter-rotating core could be
internal(secondary bar) or external(accretion). To explain the observed
velocity profile, we propose the existence of two disks in the inner LMC, with
one counterrotating. This two disk model is found to match the HI velocities as
well. Two disks with different LON and velocity profiles can create regions
which are kinematically and spatially separated. Predicted such locations are
found to match the observed locations where the HI clouds are found to have two
velocities.Comment: 12 pages including 3 figures, to appear in ApJ Letter
Entanglement entropy and multifractality at localization transitions
The von Neumann entanglement entropy is a useful measure to characterize a
quantum phase transition. We investigate the non-analyticity of this entropy at
disorder-dominated quantum phase transitions in non-interacting electronic
systems. At these critical points, the von Neumann entropy is determined by the
single particle wave function intensity which exhibits complex scale invariant
fluctuations. We find that the concept of multifractality is naturally suited
for studying von Neumann entropy of the critical wave functions. Our numerical
simulations of the three dimensional Anderson localization transition and the
integer quantum Hall plateau transition show that the entanglement at these
transitions is well described using multifractal analysis.Comment: v3, 5 pages, published versio
Issues in Physics Practicals in an Open and Distance Learning Environment
This paper reviews the objectives of physics practicals in physics education in relation to the
hilosophy of open and distance learning programme. The various issues that arise in the
implementation of physics experiment based on an existing practical model are presented. Two
major concerns are the effectiveness of the practical sessions and sustaining the fundamentals
of the open and distance learning programme. A new practical physics model is then proposed,
which enables students to experience physics experiments without violating the open and
distance learning programme fundamentals. (Authors' abstract
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