8,706 research outputs found
Subtraction of Newtonian Noise Using Optimized Sensor Arrays
Fluctuations in the local Newtonian gravitational field present a limit to
high precision measurements, including searches for gravitational waves using
laser interferometers. In this work, we present a model of this perturbing
gravitational field and evaluate schemes to mitigate the effect by estimating
and subtracting it from the interferometer data stream. Information about the
Newtonian noise is obtained from simulated seismic data. The method is tested
on causal as well as acausal implementations of noise subtraction. In both
cases it is demonstrated that broadband mitigation factors close to 10 can be
achieved removing Newtonian noise as a dominant noise contribution. The
resulting improvement in the detector sensitivity will substantially enhance
the detection rate of gravitational radiation from cosmological sources.Comment: 29 pages, 11 figure
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
Towards Space-like Photometric Precision from the Ground with Beam-Shaping Diffusers
We demonstrate a path to hitherto unachievable differential photometric
precisions from the ground, both in the optical and near-infrared (NIR), using
custom-fabricated beam-shaping diffusers produced using specialized
nanofabrication techniques. Such diffusers mold the focal plane image of a star
into a broad and stable top-hat shape, minimizing photometric errors due to
non-uniform pixel response, atmospheric seeing effects, imperfect guiding, and
telescope-induced variable aberrations seen in defocusing. This PSF reshaping
significantly increases the achievable dynamic range of our observations,
increasing our observing efficiency and thus better averages over
scintillation. Diffusers work in both collimated and converging beams. We
present diffuser-assisted optical observations demonstrating
ppm precision in 30 minute bins on a nearby bright star
16-Cygni A (V=5.95) using the ARC 3.5m telescope---within a factor of 2
of Kepler's photometric precision on the same star. We also show a transit of
WASP-85-Ab (V=11.2) and TRES-3b (V=12.4), where the residuals bin down to
ppm in 30 minute bins for WASP-85-Ab---a factor of 4 of
the precision achieved by the K2 mission on this target---and to 101ppm for
TRES-3b. In the NIR, where diffusers may provide even more significant
improvements over the current state of the art, our preliminary tests have
demonstrated ppm precision for a star on the 200"
Hale Telescope. These photometric precisions match or surpass the expected
photometric precisions of TESS for the same magnitude range. This technology is
inexpensive, scalable, easily adaptable, and can have an important and
immediate impact on the observations of transits and secondary eclipses of
exoplanets.Comment: Accepted for publication in ApJ. 30 pages, 20 figure
New Techniques for High-Contrast Imaging with ADI: the ACORNS-ADI SEEDS Data Reduction Pipeline
We describe Algorithms for Calibration, Optimized Registration, and Nulling
the Star in Angular Differential Imaging (ACORNS-ADI), a new, parallelized
software package to reduce high-contrast imaging data, and its application to
data from the SEEDS survey. We implement several new algorithms, including a
method to register saturated images, a trimmed mean for combining an image
sequence that reduces noise by up to ~20%, and a robust and computationally
fast method to compute the sensitivity of a high-contrast observation
everywhere on the field-of-view without introducing artificial sources. We also
include a description of image processing steps to remove electronic artifacts
specific to Hawaii2-RG detectors like the one used for SEEDS, and a detailed
analysis of the Locally Optimized Combination of Images (LOCI) algorithm
commonly used to reduce high-contrast imaging data. ACORNS-ADI is written in
python. It is efficient and open-source, and includes several optional features
which may improve performance on data from other instruments. ACORNS-ADI
requires minimal modification to reduce data from instruments other than
HiCIAO. It is freely available for download at
www.github.com/t-brandt/acorns-adi under a BSD license.Comment: 15 pages, 9 figures, accepted to ApJ. Replaced with accepted version;
mostly minor changes. Software update
SARAS 2: A Spectral Radiometer for probing Cosmic Dawn and the Epoch of Reionization through detection of the global 21 cm signal
The global 21 cm signal from Cosmic Dawn (CD) and the Epoch of Reionization
(EoR), at redshifts , probes the nature of first sources of
radiation as well as physics of the Inter-Galactic Medium (IGM). Given that the
signal is predicted to be extremely weak, of wide fractional bandwidth, and
lies in a frequency range that is dominated by Galactic and Extragalactic
foregrounds as well as Radio Frequency Interference, detection of the signal is
a daunting task. Critical to the experiment is the manner in which the sky
signal is represented through the instrument. It is of utmost importance to
design a system whose spectral bandpass and additive spurious can be well
calibrated and any calibration residual does not mimic the signal. SARAS is an
ongoing experiment that aims to detect the global 21 cm signal. Here we present
the design philosophy of the SARAS 2 system and discuss its performance and
limitations based on laboratory and field measurements. Laboratory tests with
the antenna replaced with a variety of terminations, including a network model
for the antenna impedance, show that the gain calibration and modeling of
internal additives leave no residuals with Fourier amplitudes exceeding 2~mK,
or residual Gaussians of 25 MHz width with amplitudes exceeding 2~mK. Thus,
even accounting for reflection and radiation efficiency losses in the antenna,
the SARAS~2 system is capable of detection of complex 21-cm profiles at the
level predicted by currently favoured models for thermal baryon evolution.Comment: 44 pages, 17 figures; comments and suggestions are welcom
A Novel Rate Control Algorithm for Onboard Predictive Coding of Multispectral and Hyperspectral Images
Predictive coding is attractive for compression onboard of spacecrafts thanks
to its low computational complexity, modest memory requirements and the ability
to accurately control quality on a pixel-by-pixel basis. Traditionally,
predictive compression focused on the lossless and near-lossless modes of
operation where the maximum error can be bounded but the rate of the compressed
image is variable. Rate control is considered a challenging problem for
predictive encoders due to the dependencies between quantization and prediction
in the feedback loop, and the lack of a signal representation that packs the
signal's energy into few coefficients. In this paper, we show that it is
possible to design a rate control scheme intended for onboard implementation.
In particular, we propose a general framework to select quantizers in each
spatial and spectral region of an image so as to achieve the desired target
rate while minimizing distortion. The rate control algorithm allows to achieve
lossy, near-lossless compression, and any in-between type of compression, e.g.,
lossy compression with a near-lossless constraint. While this framework is
independent of the specific predictor used, in order to show its performance,
in this paper we tailor it to the predictor adopted by the CCSDS-123 lossless
compression standard, obtaining an extension that allows to perform lossless,
near-lossless and lossy compression in a single package. We show that the rate
controller has excellent performance in terms of accuracy in the output rate,
rate-distortion characteristics and is extremely competitive with respect to
state-of-the-art transform coding
Gemini Frontier Fields: Wide-field Adaptive Optics -band Imaging of the Galaxy Clusters MACS J0416.1-2403 and Abell 2744
We have observed two of the six Frontier Fields galaxy clusters, MACS
J0416.1-2403 and Abell 2744, using the Gemini Multi-Conjugate Adaptive Optics
System (GeMS) and the Gemini South Adaptive Optics Imager (GSAOI). With
0.08"-0.10" FWHM our data are nearly diffraction-limited over a 100"x100" wide
area. GeMS/GSAOI complements the Hubble Space Telescope (HST) redwards of
1.6microns with twice the angular resolution. We reach a 5 sigma depth of Ks =
25.6 mag (AB) for compact sources. In this paper we describe the observations,
the data processing and the initial public data release. We provide fully
calibrated, co-added images matching the native GSAOI pixel scale as well as
the larger plate scales of the HST release, adding to the legacy value of the
Frontier Fields. Our work demonstrates that even for fields at high galactic
latitude, where natural guide stars are rare, current multi-conjugated adaptive
optics technology at 8m-telescopes has opened a new window on the distant
Universe. Observations of a third Frontier Field, Abell 370, are planned.Comment: Accepted for publication in ApJS; significantly revised compared to
the first submissio
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