13,277 research outputs found
A Package for the Automated Classification of Periodic Variable Stars
We present a machine learning package for the classification of periodic
variable stars. Our package is intended to be general: it can classify any
single band optical light curve comprising at least a few tens of observations
covering durations from weeks to years, with arbitrary time sampling. We use
light curves of periodic variable stars taken from OGLE and EROS-2 to train the
model. To make our classifier relatively survey-independent, it is trained on
16 features extracted from the light curves (e.g. period, skewness, Fourier
amplitude ratio). The model classifies light curves into one of seven
superclasses - Delta Scuti, RR Lyrae, Cepheid, Type II Cepheid, eclipsing
binary, long-period variable, non-variable - as well as subclasses of these,
such as ab, c, d, and e types for RR Lyraes. When trained to give only
superclasses, our model achieves 0.98 for both recall and precision as measured
on an independent validation dataset (on a scale of 0 to 1). When trained to
give subclasses, it achieves 0.81 for both recall and precision. In order to
assess classification performance of the subclass model, we applied it to the
MACHO, LINEAR, and ASAS periodic variables, which gave recall/precision of
0.92/0.98, 0.89/0.96, and 0.84/0.88, respectively. We also applied the subclass
model to Hipparcos periodic variable stars of many other variability types that
do not exist in our training set, in order to examine how much those types
degrade the classification performance of our target classes. In addition, we
investigate how the performance varies with the number of data points and
duration of observations. We find that recall and precision do not vary
significantly if the number of data points is larger than 80 and the duration
is more than a few weeks. The classifier software of the subclass model is
available from the GitHub repository (https://goo.gl/xmFO6Q).Comment: 16 pages, 11 figures, accepted for publication in A&
Automated Classification of Periodic Variable Stars detected by the Wide-field Infrared Survey Explorer
We describe a methodology to classify periodic variable stars identified
using photometric time-series measurements constructed from the Wide-field
Infrared Survey Explorer (WISE) full-mission single-exposure Source Databases.
This will assist in the future construction of a WISE Variable Source Database
that assigns variables to specific science classes as constrained by the WISE
observing cadence with statistically meaningful classification probabilities.
We have analyzed the WISE light curves of 8273 variable stars identified in
previous optical variability surveys (MACHO, GCVS, and ASAS) and show that
Fourier decomposition techniques can be extended into the mid-IR to assist with
their classification. Combined with other periodic light-curve features, this
sample is then used to train a machine-learned classifier based on the random
forest (RF) method. Consistent with previous classification studies of variable
stars in general, the RF machine-learned classifier is superior to other
methods in terms of accuracy, robustness against outliers, and relative
immunity to features that carry little or redundant class information. For the
three most common classes identified by WISE: Algols, RR Lyrae, and W Ursae
Majoris type variables, we obtain classification efficiencies of 80.7%, 82.7%,
and 84.5% respectively using cross-validation analyses, with 95% confidence
intervals of approximately +/-2%. These accuracies are achieved at purity (or
reliability) levels of 88.5%, 96.2%, and 87.8% respectively, similar to that
achieved in previous automated classification studies of periodic variable
stars.Comment: 48 pages, 17 figures, 1 table, accepted by A
Near-Ultraviolet Properties of a Large Sample of Type Ia Supernovae as Observed with the Swift UVOT
We present ultraviolet (UV) and optical photometry of 26 Type Ia supernovae
(SNe~Ia) observed from March 2005 to March 2008 with the NASA {\it Swift}
Ultraviolet and Optical Telescope (UVOT). The dataset consists of 2133
individual observations, making it by far the most complete study of the UV
emission from SNe~Ia to date. Grouping the SNe into three subclasses as derived
from optical observations, we investigate the evolution of the colors of these
SNe, finding a high degree of homogeneity within the normal subclass, but
dramatic differences between that group and the subluminous and SN 2002cx-like
groups. For the normal events, the redder UV filters on UVOT (, ) show
more homogeneity than do the bluer UV filters (, ). Searching for
purely UV characteristics to determine existing optically based groupings, we
find the peak width to be a poor discriminant, but we do see a variation in the
time delay between peak emission and the late, flat phase of the light curves.
The UV light curves peak a few days before the band for most subclasses (as
was previously reported by Jha et al. 2006a), although the SN 2002cx-like
objects peak at a very early epoch in the UV. That group also features the
bluest emission observed among SNe~Ia. As the observational campaign is
ongoing, we discuss the critical times to observe, as determined by this study,
in order to maximize the scientific output of future observations.Comment: Accepted to Astrophysical Journa
XTE J1701-462 and its Implications for the Nature of Subclasses in Low-Magnetic-Field Neutron Star Low-Mass X-Ray Binaries
We report on an analysis of RXTE data of the transient neutron star low-mass
X-ray binary (NS-LMXB) XTE J1701-462, obtained during its 2006-2007 outburst.
The X-ray properties of the source changed between those of various types of
NS-LMXB subclasses. At high luminosities the source switched between two types
of Z source behavior and at low luminosities we observed a transition from Z
source to atoll source behavior. These transitions between subclasses primarily
manifest themselves as changes in the shapes of the tracks in X-ray color-color
and hardness-intensity diagrams, but they are accompanied by changes in the kHz
quasi-periodic oscillations, broad-band variability, burst behavior, and/or
X-ray spectra. We find that the low-energy X-ray flux is a good parameter to
track the gradual evolution of the tracks in color-color and hardness-intensity
diagrams, allowing us to resolve the evolution of the source in greater detail
than before and relate the observed properties to other NS-LMXBs. We further
find that during the transition from Z to atoll, characteristic behavior known
as the atoll upper banana can equivalently be described as the final stage of a
weakening Z source flaring branch, thereby blurring the line between the two
subclasses. Our findings strongly suggest that the wide variety in behavior
observed in NS-LXMBs with different luminosities can be linked through changes
in a single variable parameter, namely the mass accretion rate, without the
need for additional differences in the neutron star parameters or viewing
angle. We briefly discuss the implications of our findings for the spectral
changes observed in NS LMXBs and suggest that, contrary to what is often
assumed, the position along the color-color tracks of Z sources is not
determined by the instantaneous mass accretion rate.Comment: Submitted to ApJ, comments are welcome. 13 pages, 8 figure
Interpretable detection of unstable smart TV usage from power state logs
Power state logs from smart TVs are collected in order to construct a time-series representation of their usage. Time-series that belong to a TV exhibiting instability problems are classified accordingly. To do so, an automated feature extraction approach is used, together with linear classification methods in order to realise interpretable classification decisions. A normalized true positive rate of 0.84 ± 0.10 is obtained for the classification. The normalized true negative rate equals 0.80 ± 0.03. The final model returns a regularity statistic called the Approximate Entropy as its most important feature
Anisotropic selection in cellular genetic algorithms
In this paper we introduce a new selection scheme in cellular genetic
algorithms (cGAs). Anisotropic Selection (AS) promotes diversity and allows
accurate control of the selective pressure. First we compare this new scheme
with the classical rectangular grid shapes solution according to the selective
pressure: we can obtain the same takeover time with the two techniques although
the spreading of the best individual is different. We then give experimental
results that show to what extent AS promotes the emergence of niches that
support low coupling and high cohesion. Finally, using a cGA with anisotropic
selection on a Quadratic Assignment Problem we show the existence of an
anisotropic optimal value for which the best average performance is observed.
Further work will focus on the selective pressure self-adjustment ability
provided by this new selection scheme
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