5,996 research outputs found
Photometric metallicity map of the Large Magellanic Cloud
We have estimated a metallicity map of the Large Magellanic Cloud (LMC) using
the Magellanic Cloud Photometric Survey (MCPS) and Optical Gravitational
Lensing Experiment (OGLE III) photometric data. This is a first of its kind map
of metallicity up to a radius of 4 - 5 degrees, derived using photometric data
and calibrated using spectroscopic data of Red Giant Branch (RGB) stars. We
identify the RGB in the V, (VI) colour magnitude diagrams of small
subregions of varying sizes in both data sets. We use the slope of the RGB as
an indicator of the average metallicity of a subregion, and calibrate the RGB
slope to metallicity using spectroscopic data for field and cluster red giants
in selected subregions. The average metallicity of the LMC is found to be
[Fe/H] = 0.37 dex ([Fe/H] = 0.12) from MCPS data, and [Fe/H] =
0.39 dex ([Fe/H] = 0.10) from OGLE III data. The bar is found be the
most metal-rich region of the LMC. Both the data sets suggest a shallow radial
metallicity gradient up to a radius of 4 kpc (0.0490.002 dex kpc
to 0.0660.006 dex kpc). Subregions in which the mean metallicity
differs from the surrounding areas do not appear to correlate with previously
known features; spectroscopic studies are required in order to assess their
physical significance.Comment: 28 pages, 40 figures, 7 tables, Accepted for publication in MNRAS.
arXiv admin note: text overlap with arXiv:1101.1771, arXiv:1302.6211 by other
author
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
Multifractality and Conformal Invariance at 2D Metal-Insulator Transition in the Spin-Orbit Symmetry Class
We study the multifractality (MF) of critical wave functions at boundaries
and corners at the metal-insulator transition (MIT) for noninteracting
electrons in the two-dimensional (2D) spin-orbit (symplectic) universality
class. We find that the MF exponents near a boundary are different from those
in the bulk. The exponents at a corner are found to be directly related to
those at a straight boundary through a relation arising from conformal
invariance. This provides direct numerical evidence for conformal invariance at
the 2D spin-orbit MIT. The presence of boundaries modifies the MF of the whole
sample even in the thermodynamic limit.Comment: 5 pages, 4 figure
On the determination of age and mass functions of stars in young open star clusters from the analysis of their luminosity functions
Based on the CCD observations of remote young open clusters NGC 2383, NGC
2384, NGC 4103, NGC 4755, NGC 7510 and Hogg 15, we constructed their observed
luminosity functions (LFs). The observed LFs are corrected for field star
contamination determined with the help of galactic star count model. In the
case of Hogg 15 and NGC 2383 we also considered the additional contamination
from neighbouring clusters NGC 4609 and NGC 2384 respectively. These
corrections provided the realistic pattern of cluster LF in the vicinity of the
MS turn on point and at fainter magnitudes, revealed the so called H-feature
arising due to transition of the Pre-MS phase to MS, which is dependent on the
cluster age. The theoretical LFs were constructed representing a cluster
population model with continuous star formation for a short time scale and a
power law Initial Mass Function (IMF) and these were fitted to the observed LF.
As a result we are able to determine for each cluster a set of parameters,
describing cluster population (the age, duration of star formation, IMF slope
and percentage of field star contamination). It was found that in spite of the
non-monotonic behaviour of observed LFs, cluster IMFs can be described as the
power law functions with slopes similar to Salpeter's value. The present MS
turn on cluster ages are several times lower than those derived from the
fitting of theoretical isochrones to the turn off region of the upper Main
Sequences.Comment: 17 pages, 5 figures, To appear in MNRA
Evidence of a mis-aligned secondary bar in the Large Magellanic Cloud
Evidence of a mis-aligned secondary bar, within the primary bar of the Large
Magellanic Cloud (LMC) is presented. The density distribution and the
de-reddened mean magnitudes () of the red clump stars in the bar obtained
from the OGLE II data are used for this study. The bar region which
predominantly showed wavy pattern in the line of sight in \citet{a03} was
located. These points in the X-Z plane delineate an S-shaped pattern, clearly
indicating a mis-aligned bar. This feature is statistically significant and
does not depend on the considered value of for the LMC center. The rest
of the bar region were not found to show the warp or the wavy pattern. The
secondary bar is found to be considerably elongated in the Z-direction, with an
inclination of 66.5 0.9, whereas the undisturbed part of the
primary bar is found to have an inclination of 15.1 2.7, such
that the eastern sides are closer to us with respect to the western sides of
both the bars. The PA of the secondary bar is found to be 108.4
7.3. The streaming motions found in the H I velocity map close to the
LMC center could be caused by the secondary bar. The recent star formation and
the gas distribution in LMC could be driven by the mis-aligned secondary bar.Comment: 10 pages, to appear in ApJ Letter
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
Comparison of CFD and DSMC Using Calibrated Transport Parameters
Hypersonic re-entry flows span a wide range of length scales where regions of both rarefied and continuum flow exist. Traditional computational fluid dynamics (CFD) techniques do not provide an accurate solution for the rarefied regions of such mixed flow fields. Although direct simulation Monte Carlo (DSMC) can be used to accurately capture both the continuum and rarefied features of mixed flow fields, they are computationally expensive when employed to simulate the low Knudsen number continuum regimes. Thus, a hybrid framework for seamlessly combining the two methodologies, CFD and DSMC, continues to be a topic of significant research effort. Ensuring consistency in the reaction kinetics and transport models employed within CFD and DSMC is a crucial requirement for obtaining a reliable solution from a hybrid framework for combined continuum/rarefied high speed flows. This paper represents one of the first studies to utilize the calibrated transport parameters developed to ensure consistency between CFD and DSMC solvers. The new variable soft sphere (VSS) parameters are compared to both previous standard variable hard sphere (VHS) parameters and also to solutions from the CFD transport properties that the new parameters were developed to reproduce
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