1,159 research outputs found
Characterizing AGB stars in Wide-field Infrared Survey Explorer (WISE) bands
Since asymptotic giant branch (AGB) stars are bright and extended infrared
objects, most Galactic AGB stars saturate the Wide-field Infrared Survey
Explorer (WISE) detectors and therefore the WISE magnitudes that are restored
by applying point-spread-function fitting need to be verified. Statistical
properties of circumstellar envelopes around AGB stars are discussed on the
basis of a WISE AGB catalog verified in this way. We cross-matched an AGB star
sample with the WISE All-Sky Source Catalog and the Two Mircon All Sky Survey
catalog. Infrared Space Observatory (ISO) spectra of a subsample of WISE AGB
stars were also exploited. The dust radiation transfer code DUSTY was used to
help predict the magnitudes in the W1 and W2 bands, the two WISE bands most
affected by saturation, for calibration purpose, and to provide physical
parameters of the AGB sample stars for analysis. DUSTY is verified against the
ISO spectra to be a good tool to reproduce the spectral energy distributions of
these AGB stars. Systematic magnitude-dependent offsets have been identified in
WISE W1 and W2 magnitudes of the saturated AGB stars, and empirical calibration
formulas are obtained for them on the basis of 1877 (W1) and 1558 (W2) AGB
stars that are successfully fit with DUSTY. According to the calibration
formulae, the corrections for W1 at 5 mag and W2 at 4 mag are and
0.217 mag, respectively. In total, we calibrated the W1/W2 magnitudes of
2390/2021 AGB stars. The model parameters from the DUSTY and the calibrated
WISE W1 and W2 magnitudes are used to discuss the behavior of the WISE
color-color diagrams of AGB stars. The model parameters also reveal that O-rich
AGB stars with opaque circumstellar envelopes are much rarer than opaque C-rich
AGB stars toward the anti-Galactic center direction, which we attribute to the
metallicity gradient of our Galaxy.Comment: 9 pages in two column format, 7 figures, accepted for publication in
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Inside-out growth or inside-out quenching? clues from colour gradients of local galaxies
We constrain the spatial gradient of star formation history within galaxies
using the colour gradients in NUV-u and u-i for a local spatially-resolved
galaxy sample. By splitting each galaxy into an inner and an outer part, we
find that most galaxies show negative gradients in these two colours. We first
rule out dust extinction gradient and metallicity gradient as the dominant
source for the colour gradient. Then using stellar population models, we
explore variations in star formation history to explain the colour gradients.
As shown by our earlier work, a two-phase SFH consisting of an early secular
evolution (growth) phase and a subsequent rapid evolution (quenching) phase is
necessary to explain the observed colour distributions among galaxies. We
explore two different inside-out growth models and two different inside-out
quenching models by varying parameters of the SFH between inner and outer
regions of galaxies. Two of the models can explain the observed range of colour
gradients in NUV-u and u-i colours. We further distinguish them using an
additional constraint provided by the u-i colour gradient distribution, under
the assumption of constant galaxy formation rate and a common SFH followed by
most galaxies. We find the best model is an inside-out growth model in which
the inner region has a shorter e-folding time scale in the growth phase than
the outer region. More spatially resolved ultraviolet (UV) observations are
needed to improve the significance of the result.Comment: 11 pages, 7 figures, accepted for publication in MNRA
Lost in Translation: Word Sense Disambiguation.
In natural languages, a word can take on different meanings in different contexts. Word sense disambiguation (WSD) refers to the task of determining the correct meaning or sense of a word in context
Building An Ontology-Based Multilingual Lexicon For Word Sense Disambiguation In Machine Translation.
Word sense disambiguation (WSD) requires the establishment of a list of the different meanings of words. WSD efforts in machine translation require) in addition) the equivalent translation words in target languages
The Quenching Timescale and Quenching Rate of Galaxies
The average star formation rate (SFR) in galaxies has been declining since the redshift of 2. A fraction of galaxies quench and become quiescent. We constrain two key properties of the quenching process: the quenching timescale and the quenching rate among galaxies. We achieve this by analyzing the galaxy number density profile in NUV−u color space and the distribution in NUV−u versus u − i color–color diagram with a simple toy-model framework. We focus on galaxies in three mass bins between 1010 and 1010.6 M ⊙. In the NUV−u versus u − i color–color diagram, the red u − i galaxies exhibit a different slope from the slope traced by the star-forming galaxies. This angled distribution and the number density profile of galaxies in NUV−u space strongly suggest that the decline of the SFR in galaxies has to accelerate before they turn quiescent. We model this color–color distribution with a two-phase exponential decline star formation history. The models with an e-folding time in the second phase (the quenching phase) of 0.5 Gyr best fit the data. We further use the NUV−u number density profile to constrain the quenching rate among star-forming galaxies as a function of mass. Adopting an e-folding time of 0.5 Gyr in the second phase (or the quenching phase), we found the quenching rate to be 19%/Gyr, 25%/Gyr and 33%/Gyr for the three mass bins. These are upper limits of the quenching rate as the transition zone could also be populated by rejuvenated red-sequence galaxies
Factors that Influence the Decision to Pursue Studies or Work after Graduation: A Study among Final Year Undergraduates in Universiti Sains Malaysia
Postgraduate education is becoming more and more important in developed countries such as US and Europe, as well as in developing countries. The government of Malaysia is also trying to encourage students to pursue postgraduate studies by implementing policies such as MyBrain 15. The purpose of this research is to determine the factors that influence the decision to pursue postgraduate studies among final year undergraduates in Malaysia. A sample of 434 respondents from Universiti Sains Malaysia is used in this study and a logit regression is estimated to examine the factors that influence the choice to pursue postgraduate studies versus the choice to work. The findings of this study reveal that variables such as gender, academic stream, race, family income, CGPA and expected difference in future income are significantly related to the decision to pursue postgraduate studies. Policy recommendations based on the findings of this study include encouragement for males to pursue postgraduate studies, giving sufficient and sustainable financial aid, ensuring a higher premium for postgraduates, improving the university ranking and reputation as well as offering programmes with affordable fees and creating a better environment for students to study
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