32,817 research outputs found
Kernel-phases for high-contrast detection beyond the resolution limit
The detection of high contrast companions at small angular separation appears
feasible in conventional direct images using the self-calibration properties of
interferometric observable quantities. In the high-Strehl regime, available
from space borne observatories and using AO in the mid-infrared, quantities
comparable to the closure-phase that are used with great success in
non-redundant masking inteferometry, can be extracted from direct images, even
taken with a redundant aperture. These new phase-noise immune observable
quantities, called Kernel-phases, are determined a-priori from the knowledge of
the geometry of the pupil only. Re-analysis of HST/NICMOS archive and other
ground based AO images, using this new Kernel-phase algorithm, demonstrates the
power of the method, and its ability to detect companions at the resolution
limit and beyond.Comment: 7 pages, 4 figures, 2011 SPIE conference proceeding
Sub-Classifier Construction for Error Correcting Output Code Using Minimum Weight Perfect Matching
Multi-class classification is mandatory for real world problems and one of
promising techniques for multi-class classification is Error Correcting Output
Code. We propose a method for constructing the Error Correcting Output Code to
obtain the suitable combination of positive and negative classes encoded to
represent binary classifiers. The minimum weight perfect matching algorithm is
applied to find the optimal pairs of subset of classes by using the
generalization performance as a weighting criterion. Based on our method, each
subset of classes with positive and negative labels is appropriately combined
for learning the binary classifiers. Experimental results show that our
technique gives significantly higher performance compared to traditional
methods including the dense random code and the sparse random code both in
terms of accuracy and classification times. Moreover, our method requires
significantly smaller number of binary classifiers while maintaining accuracy
compared to the One-Versus-One.Comment: 7 pages, 3 figure
Investigating Light Curve Modulation via Kernel Smoothing. I. Application to 53 fundamental mode and first-overtone Cepheids in the LMC
Recent studies have revealed a hitherto unknown complexity of Cepheid
pulsation. We implement local kernel regression to search for both period and
amplitude modulations simultaneously in continuous time and to investigate
their detectability, and test this new method on 53 classical Cepheids from the
OGLE-III catalog. We determine confidence intervals using parametric and
non-parametric bootstrap sampling to estimate significance and investigate
multi-periodicity using a modified pre-whitening approach that relies on
time-dependent light curve parameters. We find a wide variety of period and
amplitude modulations and confirm that first overtone pulsators are less stable
than fundamental mode Cepheids. Significant temporal variations in period are
more frequently detected than those in amplitude. We find a range of modulation
intensities, suggesting that both amplitude and period modulations are
ubiquitous among Cepheids. Over the 12-year baseline offered by OGLE-III, we
find that period changes are often non-linear, sometimes cyclic, suggesting
physical origins beyond secular evolution. Our method more efficiently detects
modulations (period and amplitude) than conventional methods reliant on
pre-whitening with constant light curve parameters and more accurately
pre-whitens time series, removing spurious secondary peaks effectively.Comment: Re-submitted including revisions to Astronomy and Astrophysic
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