2,184 research outputs found
Optimized Principal Component Analysis on Coronagraphic Images of the Fomalhaut System
We present the results of a study to optimize the principal component
analysis (PCA) algorithm for planet detection, a new algorithm complementing
ADI and LOCI for increasing the contrast achievable next to a bright star. The
stellar PSF is constructed by removing linear combinations of principal
components, allowing the flux from an extrasolar planet to shine through. The
number of principal components used determines how well the stellar PSF is
globally modelled. Using more principal components may decrease the number of
speckles in the final image, but also increases the background noise. We apply
PCA to Fomalhaut VLT NaCo images acquired at 4.05 micron with an apodized phase
plate. We do not detect any companions, with a model dependent upper mass limit
of 13-18 M_Jup from 4-10 AU. PCA achieves greater sensitivity than the LOCI
algorithm for the Fomalhaut coronagraphic data by up to 1 magnitude. We make
several adaptations to the PCA code and determine which of these prove the most
effective at maximizing the signal-to-noise from a planet very close to its
parent star. We demonstrate that optimizing the number of principal components
used in PCA proves most effective for pulling out a planet signal.Comment: Accepted for publication in ApJ, 7 pages, 9 figure
A PCA-based approach for subtracting thermal background emission in high-contrast imaging data
Ground-based observations at thermal infrared wavelengths suffer from large
background radiation due to the sky, telescope and warm surfaces in the
instrument. This significantly limits the sensitivity of ground-based
observations at wavelengths longer than 3 microns. We analyzed this background
emission in infrared high contrast imaging data, show how it can be modelled
and subtracted and demonstrate that it can improve the detection of faint
sources, such as exoplanets. We applied principal component analysis to model
and subtract the thermal background emission in three archival high contrast
angular differential imaging datasets in the M and L filter. We describe how
the algorithm works and explain how it can be applied. The results of the
background subtraction are compared to the results from a conventional mean
background subtraction scheme. Finally, both methods for background subtraction
are also compared by performing complete data reductions. We analyze the
results from the M dataset of HD100546 qualitatively. For the M band dataset of
beta Pic and the L band dataset of HD169142, which was obtained with an annular
groove phase mask vortex vector coronagraph, we also calculate and analyze the
achieved signal to noise (S/N). We show that applying PCA is an effective way
to remove spatially and temporarily varying thermal background emission down to
close to the background limit. The procedure also proves to be very successful
at reconstructing the background that is hidden behind the PSF. In the complete
data reductions, we find at least qualitative improvements for HD100546 and
HD169142, however, we fail to find a significant increase in S/N of beta Pic b.
We discuss these findings and argue that in particular datasets with strongly
varying observing conditions or infrequently sampled sky background will
benefit from the new approach.Comment: 12 pages, 17 figures, 1 table, Accepted for publication in A&
Simulations of Strong Gravitational Lensing with Substructure
Galactic sized gravitational lenses are simulated by combining a cosmological
N-body simulation and models for the baryonic component of the galaxy. The lens
caustics, critical curves, image locations and magnification ratios are
calculated by ray-shooting on an adaptive grid. When the source is near a cusp
in a smooth lens' caustic the sum of the magnifications of the three closest
images should be close to zero. It is found that in the observed cases this sum
is generally too large to be consistent with the simulations implying that
there is not enough substructure in the simulations. This suggests that other
factors play an important role. These may include limited numerical resolution,
lensing by structure outside the halo, selection bias and the possibility that
a randomly selected galaxy halo may be more irregular, for example due to
recent mergers, than the isolated halo used in this study. It is also shown
that, with the level of substructure computed from the N-body simulations, the
image magnifications of the Einstein cross type lenses are very weak functions
of source size up to \sim 1\kpc. This is also true for the magnification
ratios of widely separated images in the fold and cusp caustic lenses. This
means that selected magnification ratios for different the emission regions of
a lensed quasar should agree with each other, barring microlensing by stars.
The source size dependence of the magnification ratio between the closest pair
of images is more sensitive to substructure.Comment: 28 pages, 2 tables and 14 figures. Accepted to MNRA
High-contrast Imaging with Spitzer: Deep Observations of Vega, Fomalhaut, and epsilon Eridani
Stars with debris disks are intriguing targets for direct imaging exoplanet
searches, both due to previous detections of wide planets in debris disk
systems, as well as commonly existing morphological features in the disks
themselves that may be indicative of a planetary influence. Here we present
observations of three of the most nearby young stars, that are also known to
host massive debris disks: Vega, Fomalhaut, and eps Eri. The Spitzer Space
Telescope is used at a range of orientation angles for each star, in order to
supply a deep contrast through angular differential imaging combined with
high-contrast algorithms. The observations provide the opportunity to probe
substantially colder bound planets (120--330 K) than is possible with any other
technique or instrument. For Vega, some apparently very red candidate point
sources detected in the 4.5 micron image remain to be tested for common proper
motion. The images are sensitive to ~2 Mjup companions at 150 AU in this
system. The observations presented here represent the first search for planets
around Vega using Spitzer. The upper 4.5 micron flux limit on Fomalhaut b could
be further constrained relative to previous data. In the case of eps Eri,
planets below both the effective temperature and the mass of Jupiter could be
probed from 80 AU and outwards, although no such planets were found. The data
sensitively probe the regions around the edges of the debris rings in the
systems where planets can be expected to reside. These observations validate
previous results showing that more than an order of magnitude improvement in
performance in the contrast-limited regime can be acquired with respect to
conventional methods by applying sophisticated high-contrast techniques to
space-based telescopes, thanks to the high degree of PSF stability provided in
this environment.Comment: 11 pages, 12 figures, accepted for publication in A&
PynPoint: a modular pipeline architecture for processing and analysis of high-contrast imaging data
The direct detection and characterization of planetary and substellar
companions at small angular separations is a rapidly advancing field. Dedicated
high-contrast imaging instruments deliver unprecedented sensitivity, enabling
detailed insights into the atmospheres of young low-mass companions. In
addition, improvements in data reduction and PSF subtraction algorithms are
equally relevant for maximizing the scientific yield, both from new and
archival data sets. We aim at developing a generic and modular data reduction
pipeline for processing and analysis of high-contrast imaging data obtained
with pupil-stabilized observations. The package should be scalable and robust
for future implementations and in particular well suitable for the 3-5 micron
wavelength range where typically (ten) thousands of frames have to be processed
and an accurate subtraction of the thermal background emission is critical.
PynPoint is written in Python 2.7 and applies various image processing
techniques, as well as statistical tools for analyzing the data, building on
open-source Python packages. The current version of PynPoint has evolved from
an earlier version that was developed as a PSF subtraction tool based on PCA.
The architecture of PynPoint has been redesigned with the core functionalities
decoupled from the pipeline modules. Modules have been implemented for
dedicated processing and analysis steps, including background subtraction,
frame registration, PSF subtraction, photometric and astrometric measurements,
and estimation of detection limits. The pipeline package enables end-to-end
data reduction of pupil-stabilized data and supports classical dithering and
coronagraphic data sets. As an example, we processed archival VLT/NACO L' and
M' data of beta Pic b and reassessed the planet's brightness and position with
an MCMC analysis, and we provide a derivation of the photometric error budget.Comment: 16 pages, 9 figures, accepted for publication in A&A, PynPoint is
available at https://github.com/PynPoint/PynPoin
Magnetic structure of antiferromagnetic NdRhIn5
The magnetic structure of antiferromagnetic NdRhIn5 has been determined using
neutron diffraction. It has a commensurate antiferromagnetic structure with a
magnetic wave vector (1/2,0,1/2) below T_N = 11K. The staggered Nd moment at
1.6K is 2.6mu_B aligned along the c-axis. We find the magnetic structure to be
closely related to that of its cubic parent compound NdIn3 below 4.6K. The
enhanced T_N and the absence of additional transitions below T_N for NdRhIn5
are interpreted in terms of an improved matching of the
crystalline-electric-field (CEF), magnetocrystalline, and exchange interaction
anisotropies. In comparison, the role of these competing anisotropies on the
magnetic properties of the structurally related compound CeRhIn5 is discussed.Comment: 4 pages, 4 figure
Testing Optimized Principal Component Analysis on Coronagraphic Images of the Fomalhaut System
We present the results of a study to optimize the principal component analysis (PCA) algorithm for planet detection, a new algorithm complementing ADI and LOCI for increasing the contrast achievable next to a bright star. We apply PCA to our Fomalhaut VLT NACO Apodizing Phase Plate NB4.05 dat
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