text
stringlengths 89
2.49k
| category
stringclasses 19
values |
|---|---|
Human Contrast Threshold and Astronomical Visibility: The standard visibility model in light pollution studies is the formula of
Hecht (1947), as used e.g. by Schaefer (1990). However it is applicable only to
point sources and is shown to be of limited accuracy. A new visibility model is
presented for uniform achromatic targets of any size against background
luminances ranging from zero to full daylight, produced by a systematic
procedure applicable to any appropriate data set (e.g Blackwell (1946)), and
based on a simple but previously unrecognized empirical relation between
contrast threshold and adaptation luminance. The scotopic luminance correction
for variable spectral radiance (colour index) is calculated. For point sources
the model is more accurate than Hecht's formula and is verified using
telescopic data collected at Mount Wilson by Bowen (1947), enabling the sky
brightness at that time to be determined. The result is darker than the
calculation by Garstang (2004), implying that light pollution grew more rapidly
in subsequent decades than has been supposed. The model is applied to the
nebular observations of William Herschel, enabling his visual performance to be
quantified. Proposals are made regarding sky quality indicators for public use. | astro-ph_IM |
Design and Implementation of the wvrgcal Program: This memo describes the software engineering and technical details of the
design and implementation of the wvrgcal program and associated libraries. This
program performs off-line correction of atmospheric phase fluctuations in ALMA
observations, using the 183 GHz Water Vapour Radiometers (WVRs) installed on
the ALMA 12 m dishes. The memo can be used as a guide for detailed study of the
source code of the program for purposes of further development or maintenance. | astro-ph_IM |
Upgrade of the VERITAS Cherenkov Telescope Array: The VERITAS Cherenkov telescope array has been fully operational since Fall
2007 and has fulfilled or outperformed its design specifications. We are
preparing an upgrade program with the goal to lower the energy threshold and
improve the sensitivity of VERITAS at all accessible energies. In the baseline
program of the upgrade we will relocate one of the four telescopes, replace the
photo-sensors by higher efficiency photomultipliers and install a new trigger
system. In the enhanced program of the upgrade we foresee, in addition, the
construction of a fifth telescope and installation of an active mirror
alignment system. | astro-ph_IM |
Laboratory gas-phase infrared spectra of two astronomically relevant PAH
cations: diindenoperylene, C$_{32}$H$_{16}$$^+$ and dicoronylene,
C$_{48}$H$_{20}$$^+$: The first gas-phase infrared spectra of two isolated astronomically relevant
and large PAH cations - diindenoperylene (DIP) and dicoronylene (DC) - in the
530$-$1800 cm$^{-1}$ (18.9$-$5.6 $\mu$m) range - are presented. Vibrational
band positions are determined for comparison to the aromatic infrared bands
(AIBs). The spectra are obtained via infrared multiphoton dissociation (IRMPD)
spectroscopy of ions stored in a quadrupole ion trap (QIT) using the intense
and tunable radiation of the free electron laser for infrared experiments
(FELIX). DIP$^{+}$ shows its main absorption peaks at 737 (13.57), 800 (12.50),
1001 (9.99), 1070 (9.35), 1115 (8.97), 1152 (8.68), 1278 (7.83), 1420 (7.04)
and 1550 (6.45) cm$^{-1}$($\mu$m), in good agreement with DFT calculations that
are uniformly scaled to take anharmonicities into account. DC$^+$ has its main
absorption peaks at 853 (11.72), 876 (11.42), 1032 (9.69), 1168 (8.56), 1300
(7.69), 1427 (7.01) and 1566 (6.39) cm$^{-1}$($\mu$m), that also agree well
with the scaled DFT results presented here.
The DIP$^+$ and DC$^+$ spectra are compared with the prominent infrared
features observed towards NGC 7023. This results both in matches and clear
deviations. Moreover, in the 11.0$-$14.0 $\mu$m region, specific bands can be
linked to CH out-of-plane (oop) bending modes of different CH edge structures
in large PAHs. The molecular origin of these findings and their astronomical
relevance are discussed. | astro-ph_IM |
Temperature dependence of radiation damage annealing of Silicon
Photomultipliers: The last decade has increasingly seen the use of silicon photomultipliers
(SiPMs) instead of photomultiplier tubes (PMTs). This is due to various
advantages of the former on the latter like its smaller size, lower operating
voltage, higher detection efficiency, insensitivity to magnetic fields and
mechanical robustness to launch vibrations. All these features make SiPMs ideal
for use on space based experiments where the detectors require to be compact,
lightweight and capable of surviving launch conditions. A downside with the use
of this novel type of detector in space conditions is its susceptibility to
radiation damage. In order to understand the lifetime of SiPMs in space, both
the damage sustained due to radiation as well as the subsequent recovery, or
annealing, from this damage have to be studied. Here we present these studies
for three different types of SiPMs from the Hamamatsu S13360 series. Both their
behaviour after sustaining radiation equivalent to 2 years in low earth orbit
in a typical mission is presented, as well as the recovery of these detectors
while stored in different conditions. The storage conditions varied in
temperature as well as in operating voltage. The study found that the annealing
depends significantly on the temperature of the detectors with those stored at
high temperatures recovering significantly faster and at recovering closer to
the original performance. Additionally, no significant effect from a reasonable
bias voltage on the annealing was observed. Finally the annealing rate as a
function of temperature is presented along with various operating strategies
for the future SiPM based astrophysical detector POLAR-2 as well as for future
SiPM based space borne missions. | astro-ph_IM |
Stratospheric Imaging of Polar Mesospheric Clouds: A New Window on
Small-Scale Atmospheric Dynamics: Instabilities and turbulence extending to the smallest dynamical scales play
important roles in the deposition of energy and momentum by gravity waves
throughout the atmosphere. However, these dynamics and their effects have been
impossible to quantify to date due to lack of observational guidance.
Serendipitous optical images of polar mesospheric clouds at ~82 km obtained by
star cameras aboard a cosmology experiment deployed on a stratospheric balloon
provide a new observational tool, revealing instability and turbulence
structures extending to spatial scales < 20 m. At 82 km, this resolution
provides sensitivity extending to the smallest turbulence scale not strongly
influenced by viscosity: the "inner scale" of turbulence,
$l_0\sim$10($\nu^3$/$\epsilon$)$^{1/4}$. Such images represent a new window
into small-scale dynamics that occur throughout the atmosphere but are
impossible to observe in such detail at any other altitude. We present a sample
of images revealing a range of dynamics features, and employ numerical
simulations that resolve these dynamics to guide our interpretation of several
observed events. | astro-ph_IM |
Cosmological surveys with multi-object spectrographs: Multi-object spectroscopy has been a key technique contributing to the
current era of 'precision cosmology'. From the first exploratory surveys of the
large-scale structure and evolution of the universe to the current generation
of superbly detailed maps spanning a wide range of redshifts, multi-object
spectroscopy has been a fundamentally important tool for mapping the rich
structure of the cosmic web and extracting cosmological information of
increasing variety and precision. This will continue to be true for the
foreseeable future, as we seek to map the evolving geometry and structure of
the universe over the full extent of cosmic history in order to obtain the most
precise and comprehensive measurements of cosmological parameters. Here I
briefly summarize the contributions that multi-object spectroscopy has made to
cosmology so far, then review the major surveys and instruments currently in
play and their prospects for pushing back the cosmological frontier. Finally, I
examine some of the next generation of instruments and surveys to explore how
the field will develop in coming years, with a particular focus on specialised
multi-object spectrographs for cosmology and the capabilities of multi-object
spectrographs on the new generation of extremely large telescopes. | astro-ph_IM |
Processing Images from Multiple IACTs in the TAIGA Experiment with
Convolutional Neural Networks: Extensive air showers created by high-energy particles interacting with the
Earth atmosphere can be detected using imaging atmospheric Cherenkov telescopes
(IACTs). The IACT images can be analyzed to distinguish between the events
caused by gamma rays and by hadrons and to infer the parameters of the event
such as the energy of the primary particle. We use convolutional neural
networks (CNNs) to analyze Monte Carlo-simulated images from the telescopes of
the TAIGA experiment. The analysis includes selection of the images
corresponding to the showers caused by gamma rays and estimating the energy of
the gamma rays. We compare performance of the CNNs using images from a single
telescope and the CNNs using images from two telescopes as inputs. | astro-ph_IM |
Equalizing the Pixel Response of the Imaging Photoelectric Polarimeter
On-Board the IXPE Mission: The Gas Pixel Detector is a gas detector, sensitive to the polarization of
X-rays, currently flying on-board IXPE - the first observatory dedicated to
X-ray polarimetry. It detects X-rays and their polarization by imaging the
ionization tracks generated by photoelectrons absorbed in the sensitive volume,
and then reconstructing the initial direction of the photoelectrons. The
primary ionization charge is multiplied and ultimately collected on a
finely-pixellated ASIC specifically developed for X-ray polarimetry. The signal
of individual pixels is processed independently and gain variations can be
substantial, of the order of 20%. Such variations need to be equalized to
correctly reconstruct the track shape, and therefore its polarization
direction. The method to do such equalization is presented here and is based on
the comparison between the mean charge of a pixel with respect to the other
pixels for equivalent events. The method is shown to finely equalize the
response of the detectors on board IXPE, allowing a better track reconstruction
and energy resolution, and can in principle be applied to any imaging detector
based on tracks. | astro-ph_IM |
An Advanced Atmospheric Dispersion Corrector: The Magellan Visible AO
Camera: In addition to the BLINC/MIRAC IR science instruments, the Magellan adaptive
secondary AO system will have an EEV CCD47 that can be used both for visible AO
science and as a wide-field acquisition camera. The effects of atmospheric
dispersion on the elongation of the diffraction limited Magellan adaptive
optics system point spread function (PSF) are significant in the near IR. This
elongation becomes particularly egregious at visible wavelengths, culminating
in a PSF that is 2000\{mu}m long in one direction and diffraction limited
(30-60 \{mu}m) in the other over the wavelength band 0.5-1.0\{mu}m for a source
at 45\pm zenith angle. The planned Magellan AO system consists of a deformable
secondary mirror with 585 actuators. This number of actuators should be
sufficient to nyquist sample the atmospheric turbulence and correct images to
the diffraction limit at wavelengths as short as 0.7\{mu}m, with useful science
being possible as low as 0.5\{mu}m. In order to achieve diffraction limited
performance over this broad band, 2000\{mu}m of lateral color must be corrected
to better than 10\{mu}m. The traditional atmospheric dispersion corrector (ADC)
consists of two identical counter-rotating cemented doublet prisms that correct
the primary chromatic aberration. We propose two new ADC designs: the first
consisting of two identical counter-rotating prism triplets, and the second
consisting of two pairs of cemented counter-rotating prism doublets that use
both normal dispersion and anomalous dispersion glass in order to correct both
primary and secondary chromatic aberration. The two designs perform 58% and
68%, respectively, better than the traditional two-doublet design. We also
present our design for a custom removable wide-field lens that will allow our
CCD47 to switch back and forth between an 8.6" FOV for AO science and a 28.5"
FOV for acquisition. | astro-ph_IM |
Design and Initial Performance of the Prototype for the BEACON
Instrument for Detection of Ultrahigh Energy Particles: The Beamforming Elevated Array for COsmic Neutrinos (BEACON) is a planned
neutrino telescope designed to detect radio emission from upgoing air showers
generated by ultrahigh energy tau neutrino interactions in the Earth. This
detection mechanism provides a measurement of the tau flux of cosmic neutrinos.
We have installed an 8-channel prototype instrument at high elevation at
Barcroft Field Station, which has been running since 2018, and consists of 4
dual-polarized antennas sensitive between 30-80 MHz, whose signals are
filtered, amplified, digitized, and saved to disk using a custom data
acquisition system (DAQ). The BEACON prototype is at high elevation to maximize
effective volume and uses a directional beamforming trigger to improve
rejection of anthropogenic background noise at the trigger level. Here we
discuss the design, construction, and calibration of the BEACON prototype
instrument. We also discuss the radio frequency environment observed by the
instrument, and categorize the types of events seen by the instrument,
including a likely cosmic ray candidate event. | astro-ph_IM |
Detecting and analysing the topology of the cosmic web with spatial
clustering algorithms I: Methods: In this paper we explore the use of spatial clustering algorithms as a new
computational approach for modeling the cosmic web. We demonstrate that such
algorithms are efficient in terms of computing time needed. We explore three
distinct spatial methods which we suitably adjust for (i) detecting the
topology of the cosmic web and (ii) categorizing various cosmic structures as
voids, walls, clusters and superclusters based on a variety of topological and
physical criteria such as the physical distance between objects, their masses
and local densities. The methods explored are (1) a new spatial method called
Gravity Lattice ; (2) a modified version of another spatial clustering
algorithm, the ABACUS; and (3) the well known spatial clustering algorithm
HDBSCAN. We utilize HDBSCAN in order to detect cosmic structures and categorize
them using their overdensity. We demonstrate that the ABACUS method can be
combined with the classic DTFE method to obtain similar results in terms of the
achieved accuracy with about an order of magnitude less computation time. To
further solidify our claims, we draw insights from the computer science domain
and compare the quality of the results with and without the application of our
method. Finally, we further extend our experiments and verify their
effectiveness by showing their ability to scale well with different cosmic web
structures that formed at different redshifts. | astro-ph_IM |
Seeing Science: The ability to represent scientific data and concepts visually is becoming
increasingly important due to the unprecedented exponential growth of
computational power during the present digital age. The data sets and
simulations scientists in all fields can now create are literally thousands of
times as large as those created just 20 years ago. Historically successful
methods for data visualization can, and should, be applied to today's huge data
sets, but new approaches, also enabled by technology, are needed as well.
Increasingly, "modular craftsmanship" will be applied, as relevant
functionality from the graphically and technically best tools for a job are
combined as-needed, without low-level programming. | astro-ph_IM |
How to Scale a Code in the Human Dimension: As scientists' needs for computational techniques and tools grow, they cease
to be supportable by software developed in isolation. In many cases, these
needs are being met by communities of practice, where software is developed by
domain scientists to reach pragmatic goals and satisfy distinct and enumerable
scientific goals. We present techniques that have been successful in growing
and engaging communities of practice, specifically in the yt and Enzo
communities. | astro-ph_IM |
Background assessment for the TREX Dark Matter experiment: TREX-DM is conceived to look for low-mass Weakly Interacting Massive
Particles (WIMPs) using a gas Time Projection Chamber equipped with micromegas
readout planes at the Canfranc Underground Laboratory. The detector can hold in
the active volume 20 l of pressurized gas up to 10 bar, corresponding to 0.30
kg of Ar or 0.16 kg of Ne. The micromegas are read with a self-triggered
acquisition, allowing for thresholds below 0.4 keV (electron equivalent). A low
background level in the lowest energy region is another essential requirement.
To assess the expected background, all the relevant sources have been
considered, including the measured fluxes of gamma radiation, muons and
neutrons at the Canfranc Laboratory, together with the activity of most of the
components used in the detector and ancillary systems, obtained in a complete
assay program. The background contributions have been simulated by means of a
dedicated application based on Geant4 and a custom-made code for the detector
response. The background model developed for the detector presently installed
in Canfranc points to levels from 1 to 10 counts keV-1 kg-1 d-1 in the region
of interest, making TREX-DM competitive in the search for low-mass WIMPs. A
roadmap to further decrease it down to 0.1 counts keV-1 kg-1 d-1 is underway. | astro-ph_IM |
Neutrino Astronomy - A Review of Future Experiments: Current generation neutrino telescopes cover an energy range from about 10
GeV to beyond $10^9$ GeV. IceCube sets the scale for future experiments to make
improvements. Strategies for future upgrades will be discussed in three energy
ranges. At the low-energy end, an infill detector to IceCube's DeepCore would
add sensitivity in the energy range from a few to a few tens of GeV with the
primary goal of measuring the neutrino mass hierarchy. In the central energy
range of classical optical neutrino telescopes, next generation detectors are
being pursued in the Mediterranean and at Lake Baikal. The KM3NeT detector in
its full scale would establish a substantial increase in sensitivity over
IceCube. At the highest energies, radio detectors in ice are among the most
promising and pursued technologies to increase exposure at $10^9$ GeV by more
than an order of magnitude compared to IceCube. | astro-ph_IM |
Towards an astronomical foundation model for stars with a
Transformer-based model: Rapid strides are currently being made in the field of artificial
intelligence using Transformer-based models like Large Language Models (LLMs).
The potential of these methods for creating a single, large, versatile model in
astronomy has not yet been explored. In this work, we propose a framework for
data-driven astronomy that uses the same core techniques and architecture as
used by LLMs. Using a variety of observations and labels of stars as an
example, we build a Transformer-based model and train it in a self-supervised
manner with cross-survey data sets to perform a variety of inference tasks. In
particular, we demonstrate that a $\textit{single}$ model can perform both
discriminative and generative tasks even if the model was not trained or
fine-tuned to do any specific task. For example, on the discriminative task of
deriving stellar parameters from Gaia XP spectra, we achieve an accuracy of 47
K in $T_\mathrm{eff}$, 0.11 dex in $\log{g}$, and 0.07 dex in $[\mathrm{M/H}]$,
outperforming an expert $\texttt{XGBoost}$ model in the same setting. But the
same model can also generate XP spectra from stellar parameters, inpaint
unobserved spectral regions, extract empirical stellar loci, and even determine
the interstellar extinction curve. Our framework demonstrates that building and
training a $\textit{single}$ foundation model without fine-tuning using data
and parameters from multiple surveys to predict unmeasured observations and
parameters is well within reach. Such "Large Astronomy Models" trained on large
quantities of observational data will play a large role in the analysis of
current and future large surveys. | astro-ph_IM |
Modelling multimodal photometric redshift regression with noisy
observations: In this work, we are trying to extent the existing photometric redshift
regression models from modeling pure photometric data back to the spectra
themselves. To that end, we developed a PCA that is capable of describing the
input uncertainty (including missing values) in a dimensionality reduction
framework. With this "spectrum generator" at hand, we are capable of treating
the redshift regression problem in a fully Bayesian framework, returning a
posterior distribution over the redshift. This approach allows therefore to
approach the multimodal regression problem in an adequate fashion. In addition,
input uncertainty on the magnitudes can be included quite naturally and lastly,
the proposed algorithm allows in principle to make predictions outside the
training values which makes it a fascinating opportunity for the detection of
high-redshifted quasars. | astro-ph_IM |
Long-baseline horizontal radio-frequency transmission through polar ice: We report on analysis of englacial radio-frequency (RF) pulser data received
over horizontal baselines of 1--5 km, based on broadcasts from two sets of
transmitters deployed to depths of up to 1500 meters at the South Pole. First,
we analyze data collected usingtwo RF bicone transmitters 1400 meters below the
ice surface, and frozen into boreholes drilled for the IceCube experiment in
2011. Additionally, in Dec., 2018, a fat-dipole antenna, fed by one of three
high-voltage (~1 kV), fast (~(1-5 ns)) signal generators was lowered into the
1700-m deep icehole drilled for the South Pole Ice Core Experiment (SPICE),
approximately 3 km from the geographic South Pole. Signals from transmitters
were recorded on the five englacial multi-receiver ARA stations, with receiver
depths between 60--200 m. We confirm the long, >1 km RF electric field
attenuation length, test our observed signal arrival timing distributions
against models, and measure birefringent asymmetries at the 0.15% level. | astro-ph_IM |
Accurate, Meshless Methods for Magneto-Hydrodynamics: Recently, we developed a pair of meshless finite-volume Lagrangian methods
for hydrodynamics: the 'meshless finite mass' (MFM) and 'meshless finite
volume' (MFV) methods. These capture advantages of both smoothed-particle
hydrodynamics (SPH) and adaptive mesh-refinement (AMR) schemes. Here, we extend
these to include ideal magneto-hydrodynamics (MHD). The MHD equations are
second-order consistent and conservative. We augment these with a
divergence-cleaning scheme, which maintains div*B~0 to high accuracy. We
implement these in the code GIZMO, together with a state-of-the-art
implementation of SPH MHD. In every one of a large suite of test problems, the
new methods are competitive with moving-mesh and AMR schemes using constrained
transport (CT) to ensure div*B=0. They are able to correctly capture the growth
and structure of the magneto-rotational instability (MRI), MHD turbulence, and
the launching of magnetic jets, in some cases converging more rapidly than AMR
codes. Compared to SPH, the MFM/MFV methods exhibit proper convergence at fixed
neighbor number, sharper shock capturing, and dramatically reduced noise, div*B
errors, and diffusion. Still, 'modern' SPH is able to handle most of our tests,
at the cost of much larger kernels and 'by hand' adjustment of artificial
diffusion parameters. Compared to AMR, the new meshless methods exhibit
enhanced 'grid noise' but reduced advection errors and numerical diffusion,
velocity-independent errors, and superior angular momentum conservation and
coupling to N-body gravity solvers. As a result they converge more slowly on
some problems (involving smooth, slowly-moving flows) but more rapidly on
others (involving advection or rotation). In all cases, divergence-control
beyond the popular Powell 8-wave approach is necessary, or else all methods we
consider will systematically converge to unphysical solutions. | astro-ph_IM |
Next-generation telescopes with curved focal surface for ultra-low
surface brightness surveys: In spite of major advances in both ground- and space-based instrumentation,
the ultra-low-surface brightness universe (ULSB) still remains a largely
unexplored volume in observational parameter space. ULSB observations provide
unique constraints on a wide variety of objects, from the Zodiacal light all
the way to the optical cosmological background radiation, through dust cirri,
mass loss shells in giant stars, LSB galaxies and the intracluster light. These
surface brightness levels (>28-29 mag arcsec^-2) are observed by maximising the
efficiency of the surveys and minimising or removing the systematics arising in
the measurement of surface brightness. Based on full-system photon Monte Carlo
simulations, we present here the performance of a ground-based telescope aimed
at carrying out ULSB observations, with a curved focal surface design. Its
off-axis optical design maximises the field of view while minimising the focal
ratio. No lenses are used, as their multiple internal scatterings increase the
wings of the point spread function (PSF), and the usual requirement of a flat
focal plane is relaxed through the use of curved CCD detectors. The telescope
has only one unavoidable single refractive surface, the cryostat window, and
yet it delivers a PSF with ultra-compact wings, which allows the detection, for
a given exposure time, of surface brightness levels nearly three orders of
magnitude fainter than any other current telescope. | astro-ph_IM |
Systematic biases in low frequency radio interferometric data due to
calibration: the LOFAR EoR case: The redshifted 21 cm line of neutral hydrogen is a promising probe of the
Epoch of Reionization (EoR). However, its detection requires a thorough
understanding and control of the systematic errors. We study two systematic
biases observed in the LOFAR EoR residual data after calibration and
subtraction of bright discrete foreground sources. The first effect is a
suppression in the diffuse foregrounds, which could potentially mean a
suppression of the 21 cm signal. The second effect is an excess of noise beyond
the thermal noise. The excess noise shows fluctuations on small frequency
scales, and hence it can not be easily removed by foreground removal or
avoidance methods. Our analysis suggests that sidelobes of residual sources due
to the chromatic point spread function and ionospheric scintillation can not be
the dominant causes of the excess noise. Rather, both the suppression of
diffuse foregrounds and the excess noise can occur due to calibration with an
incomplete sky model containing predominantly bright discrete sources. We show
that calibrating only on bright sources can cause suppression of other signals
and introduce an excess noise in the data. The levels of the suppression and
excess noise depend on the relative flux of sources which are not included in
the model with respect to the flux of modeled sources. We discuss possible
solutions such as using only long baselines to calibrate the interferometric
gain solutions as well as simultaneous multi-frequency calibration along with
their benefits and shortcomings. | astro-ph_IM |
Iris: an Extensible Application for Building and Analyzing Spectral
Energy Distributions: Iris is an extensible application that provides astronomers with a
user-friendly interface capable of ingesting broad-band data from many
different sources in order to build, explore, and model spectral energy
distributions (SEDs). Iris takes advantage of the standards defined by the
International Virtual Observatory Alliance, but hides the technicalities of
such standards by implementing different layers of abstraction on top of them.
Such intermediate layers provide hooks that users and developers can exploit in
order to extend the capabilities provided by Iris. For instance, custom Python
models can be combined in arbitrary ways with the Iris built-in models or with
other custom functions. As such, Iris offers a platform for the development and
integration of SED data, services, and applications, either from the user's
system or from the web. In this paper we describe the built-in features
provided by Iris for building and analyzing SEDs. We also explore in some
detail the Iris framework and software development kit, showing how astronomers
and software developers can plug their code into an integrated SED analysis
environment. | astro-ph_IM |
A simple and efficient solver for self-gravity in the DISPATCH
astrophysical simulation framework: We describe a simple and effective algorithm for solving Poisson's equation
in the context of self-gravity within the DISPATCH astrophysical fluid
framework. The algorithm leverages the fact that DISPATCH stores multiple time
slices and uses asynchronous time-stepping to produce a scheme that does not
require any explicit global communication or sub-cycling, only the normal,
local communication between patches and the iterative solution to Poisson's
equation. We demonstrate that the implementation is suitable for both
collections of patches of a single resolution and for hierarchies of adaptively
resolved patches. Benchmarks are presented that demonstrate the accuracy,
effectiveness and efficiency of the scheme. | astro-ph_IM |
The conceptual design of GMagAO-X: visible wavelength high contrast
imaging with GMT: We present the conceptual design of GMagAO-X, an extreme adaptive optics
system for the 25 m Giant Magellan Telescope (GMT). We are developing GMagAO-X
to be available at or shortly after first-light of the GMT, to enable early
high contrast exoplanet science in response to the Astro2020 recommendations. A
key science goal is the characterization of nearby potentially habitable
terrestrial worlds. GMagAO-Xis a woofer-tweeter system, with integrated segment
phasing control. The tweeter is a 21,000 actuator segmented deformable mirror,
composed of seven 3000 actuator segments. A multi-stage wavefront sensing
system provides for bootstrapping, phasing, and high order sensing. The entire
instrument is mounted in a rotator to provide gravity invariance. After the
main AO system, visible (g to y) and near-IR (Y to H) science channels contain
integrated coronagraphic wavefront control systems. The fully corrected and,
optionally, coronagraphically filtered beams will then be fed to a suite of
focal plane instrumentation including imagers and spectrographs. This will
include existing facility instruments at GMT via fiber feeds. To assess the
design we have developed an end-to-end frequency-domain modeling framework for
assessing the performance of GMagAO-X. The dynamics of the many closed-loop
feedback control systems are then modeled. Finally, we employ a
frequency-domain model of post-processing algorithms to analyze the final
post-processed sensitivity. The CoDR for GMagAO-X was held in September, 2021.
Here we present an overview of the science cases, instrument design, expected
performance, and concept of operations for GMagAO-X. | astro-ph_IM |
REXPACO: an algorithm for high contrast reconstruction of the
circumstellar environment by angular differential imaging: Aims. The purpose of this paper is to describe a new post-processing
algorithm dedicated to the reconstruction of the spatial distribution of light
received from off-axis sources, in particular from circumstellar disks.
Methods. Built on the recent PACO algorithm dedicated to the detection of
point-like sources, the proposed method is based on the local learning of patch
covariances capturing the spatial fluctuations of the stellar leakages. From
this statistical modeling, we develop a regularized image reconstruction
algorithm (REXPACO) following an inverse problem approach based on a forward
image formation model of the off-axis sources in the ADI sequences.
Results. Injections of fake circumstellar disks in ADI sequences from the
VLT/SPHERE-IRDIS instrument show that both the morphology and the photometry of
the disks are better preserved by REXPACO compared to standard postprocessing
methods like cADI. In particular, the modeling of the spatial covariances
proves usefull in reducing typical ADI artifacts and in better disentangling
the signal of these sources from the residual stellar contamination. The
application to stars hosting circumstellar disks with various morphologies
confirms the ability of REXPACO to produce images of the light distribution
with reduced artifacts. Finally, we show how REXPACO can be combined with PACO
to disentangle the signal of circumstellar disks from the signal of candidate
point-like sources.
Conclusions. REXPACO is a novel post-processing algorithm producing
numerically deblurred images of the circumstellar environment. It exploits the
spatial covariances of the stellar leakages and of the noise to efficiently
eliminate this nuisance term. | astro-ph_IM |
MegaPipe astrometry for the New Horizons spacecraft: The New Horizons spacecraft, launched by NASA in 2006, will arrive in the
Pluto-Charon system on July 14, 2015. There, it will spend a few hours imaging
Pluto and its moons. It will then have a small amount of reserve propellant
which will be used to direct the probe on to a second, yet to be discovered
object in the Kuiper Belt. Data from the MegaPrime camera on CFHT was used to
build a precise, high density astrometric reference frame for both the final
approach into the Pluto system and the search for the secondary target. Pluto
currently lies in the galactic plane. This is a hindrance in that there are
potential problems with confusion. However, it is also a benefit, since it
allows the use of the UCAC4 astrometric reference catalog, which is normally
too sparse for use with MegaCam images. The astrometric accuracy of the final
catalogs, as measured by the residuals, is 0.02 arcseconds. | astro-ph_IM |
Machine learning techniques to distinguish near-field interference and
far-field astrophysical signals in radio telescopes: The CHIME radio telescope operates in the frequency bandwidth of 400 to 800
MHz. The CHIME/FRB collaboration has a data pipeline that analyzes the data in
real time, suppresses radio frequency interferences (RFI) and searches for
FRBs. However, the RFI removal techniques work best for broadband and narrow
FRBs.We wish to create a RFI removal technique that works without making
assumptions about the characteristics of the FRB signal. In this thesis we
first explore the data of intensity generated by CHIME/FRB backend. After
becoming familiar with the structure and organisation of data we present a new
novel method for RFI removal using unsupervised machine learning clustering
techniques by using multiple beams on CHIME telescope. We are trying to use the
analogy of theory of interference for RFI removal by distinguishing near field
RFI and far field astrophysical signals in the data. We explored many
clustering techniques like K-means,DBSCAN etc but one technique called as
HDBSCAN looks particularly promising. Using HDBSCAN clustering technique we
have developed the new method for RFI removal. The removal technique upto this
point has been developed by us using 3 beams of CHIME telescope. The new novel
idea is still in it's incubatory phase and soon we will try to include more
beams for our new RFI removal method. We have visually observed that RFI has
been been considerably removed from our data. In future we are going to do more
calculations to further measure the signal to noise ratio (SNR) of the FRB
signal after RFI removal and we will use this technique to compare the SNR
measured by current RFI removal technique at CHIME/FRB data pipeline. | astro-ph_IM |
An iterative wave-front sensing algorithm for high-contrast imaging
systems: Wave-front sensing from focal plane multiple images is a promising technique
for high-contrast imaging systems. However, the wave-front error of an optics
system can be properly reconstructed only when it is very small. This paper
presents an iterative optimization algorithm for the measurement of large
static wave-front errors directly from only one focal plane image. We firstly
measure the intensity of the pupil image to get the pupil function of the
system and acquire the aberrated image on the focal plane with a phase error
that is to be measured. Then we induce a dynamic phase to the tested pupil
function and calculate the associated intensity of the reconstructed image on
the focal plane. The algorithm is to minimize the intensity difference between
the reconstructed image and the tested aberrated image on the focal plane,
where the induced phase is as the variable of the optimization algorithm. The
simulation shows that the wave-front of an optics system can be theoretically
reconstructed with a high precision, which indicates that such an iterative
algorithm may be an effective way for the wave-front sensing for high-contrast
imaging systems. | astro-ph_IM |
Analysis Framework for Multi-messenger Astronomy with IceCube: Combining observational data from multiple instruments for multi-messenger
astronomy can be challenging due to the complexity of the instrument response
functions and likelihood calculation. We introduce a python-based
unbinned-likelihood analysis package called i3mla (IceCube Maximum Likelihood
Analysis). i3mla is designed to be compatible with the Multi-Mission Maximum
Likelihood (3ML) framework, which enables multi-messenger astronomy analyses by
combining the likelihood across different instruments. By making it possible to
use IceCube data in the 3ML framework, we aim to facilitate the use of neutrino
data in multi-messenger astronomy. In this work we illustrate how to use the
i3mla package with 3ML and present preliminary sensitivities using the i3mla
package and 3ML through a joint-fit with HAWC Public dataset. | astro-ph_IM |
A partially dimensionally-split approach to numerical MHD: We modify an existing magnetohydrodynamics algorithm to make it more
compatible with a dimensionally-split (DS) framework. It is based on the
standard reconstruct-solve-average strategy (using a Riemann solver), and
relies on constrained transport to ensure that the magnetic field remains
divergence-free (div B = 0). The DS approach, combined with the use of a
single, cell-centred grid (for both the fluid quantities and the magnetic
field), means that the algorithm can be easily added to existing DS
hydrodynamics codes. This makes it particularly useful for mature astrophysical
codes, which often model more complicated physical effects on top of an
underlying DS hydrodynamics engine, and therefore cannot be restructured
easily. Several test problems have been included to demonstrate the accuracy of
the algorithm, and illustrative source code has been made freely available
online. | astro-ph_IM |
Advanced Architectures for Astrophysical Supercomputing: Astronomers have come to rely on the increasing performance of computers to
reduce, analyze, simulate and visualize their data. In this environment, faster
computation can mean more science outcomes or the opening up of new parameter
spaces for investigation. If we are to avoid major issues when implementing
codes on advanced architectures, it is important that we have a solid
understanding of our algorithms. A recent addition to the high-performance
computing scene that highlights this point is the graphics processing unit
(GPU). The hardware originally designed for speeding-up graphics rendering in
video games is now achieving speed-ups of $O(100\times)$ in general-purpose
computation -- performance that cannot be ignored. We are using a generalized
approach, based on the analysis of astronomy algorithms, to identify the
optimal problem-types and techniques for taking advantage of both current GPU
hardware and future developments in computing architectures. | astro-ph_IM |
KSIM: simulating KIDSpec, a Microwave Kinetic Inductance Detector
spectrograph for the optical/NIR: KIDSpec, the Kinetic Inductance Detector Spectrometer, is a proposed optical
to near IR Microwave Kinetic Inductance Detector (MKID) spectrograph. MKIDs are
superconducting photon counting detectors which are able to resolve the energy
of incoming photons and their time of arrival. KIDSpec will use these detectors
to separate incoming spectral orders from a grating, thereby not requiring a
cross-disperser. In this paper we present a simulation tool for KIDSpec's
potential performance upon construction to optimise a given design. This
simulation tool is the KIDSpec Simulator (KSIM), a Python package designed to
simulate a variety of KIDSpec and observation parameters. A range of
astrophysical objects are simulated: stellar objects, an SDSS observed galaxy,
a Seyfert galaxy, and a mock galaxy spectrum from the JAGUAR catalogue.
Multiple medium spectral resolution designs for KIDSpec are simulated. The
possible impact of MKID energy resolution variance and dead pixels were
simulated, with impacts to KIDSpec performance observed using the Reduced
Chi-Squared (RCS) value. Using dead pixel percentages from current instruments,
the RCS result was found to only increase to 1.21 at worst for one of the
designs simulated. SNR comparisons of object simulations between KSIM and
X-Shooter's ETC were also simulated. KIDSpec offers a particular improvement
over X-Shooter for short and faint observations. For a Seyfert galaxy
($m_{R}=21$) simulation with a 180s exposure, KIDSpec had an average SNR of
4.8, in contrast to 1.5 for X-Shooter. Using KSIM the design of KIDSpec can be
optimised to improve the instrument further. | astro-ph_IM |
A New Method for Band-limited Imaging with Undersampled Detectors: Since its original use on the Hubble Deep Field, "Drizzle" has become a de
facto standard for the combination of images taken by the Hubble Space Tele-
scope. However, the drizzle algorithm was developed with small, faint,
partially resolved sources in mind, and is not the best possible algorithm for
high signal-to-noise unresolved objects. Here, a new method for creating
band-limited images from undersampled data is presented. The method uses a
drizzled image as a first order approximation and then rapidly converges toward
a band-limited image which fits the data given the statistical weighting
provided by the drizzled image. The method, named iDrizzle, for iterative
Drizzle, effectively eliminates both the small high-frequency artifacts and
convolution with an interpolant kernel that can be introduced by drizzling. The
method works well in the presence of geometric distortion, and can easily
handle cosmic rays, bad pixels, or other missing data. It can combine images
taken with random dithers, though the number of dithers required to obtain a
good final image depends in part on the quality of the dither placements.
iDrizzle may prove most beneficial for producing high-fidelity point spread
functions from undersampled images, and could be particularly valuable for
future Dark Energy missions such as WFIRST and EUCLID, which will likely
attempt to do high precision supernova photometry and lensing experiments with
undersampled detectors. | astro-ph_IM |
Partially Coherent Optical Modelling of the Ultra-Low-Noise Far-Infrared
Imaging Arrays on the SPICA Mission: We have developed a range of theoretical and numerical techniques for
modeling the multi-mode, 210-34 micron, ultra-low-noise Transition Edge Sensors
that will be used on the SAFARI instrument on the ESA/JAXA cooled-aperture FIR
space telescope SPICA. The models include a detailed analysis of the resistive
and reactive properties of thin superconducting absorbing films, and a
partially coherent mode-matching analysis of patterned films in multi-mode
waveguide. The technique allows the natural optical modes, modal
responsivities, and Stokes maps of complicated structures comprising patterned
films in profiled waveguides and cavities to be determined. | astro-ph_IM |
Fully Automated Approaches to Analyze Large-Scale Astronomy Survey Data: Observational astronomy has changed drastically in the last decade: manually
driven target-by-target instruments have been replaced by fully automated
robotic telescopes. Data acquisition methods have advanced to the point that
terabytes of data are flowing in and being stored on a daily basis. At the same
time, the vast majority of analysis tools in stellar astrophysics still rely on
manual expert interaction. To bridge this gap, we foresee that the next decade
will witness a fundamental shift in the approaches to data analysis:
case-by-case methods will be replaced by fully automated pipelines that will
process the data from their reduction stage, through analysis, to storage.
While major effort has been invested in data reduction automation, automated
data analysis has mostly been neglected despite the urgent need. Scientific
data mining will face serious challenges to identify, understand and eliminate
the sources of systematic errors that will arise from this automation. As a
special case, we present an artificial intelligence (AI) driven pipeline that
is prototyped in the domain of stellar astrophysics (eclipsing binaries in
particular), current results and the challenges still ahead. | astro-ph_IM |
Automatic morphological classification of galaxy images: We describe an image analysis supervised learning algorithm that can
automatically classify galaxy images. The algorithm is first trained using a
manually classified images of elliptical, spiral, and edge-on galaxies. A large
set of image features is extracted from each image, and the most informative
features are selected using Fisher scores. Test images can then be classified
using a simple Weighted Nearest Neighbor rule such that the Fisher scores are
used as the feature weights. Experimental results show that galaxy images from
Galaxy Zoo can be classified automatically to spiral, elliptical and edge-on
galaxies with accuracy of ~90% compared to classifications carried out by the
author. Full compilable source code of the algorithm is available for free
download, and its general-purpose nature makes it suitable for other uses that
involve automatic image analysis of celestial objects. | astro-ph_IM |
Study of cosmogenic activation above ground of Ar for DarkSide-20k: The production of long-lived radioactive isotopes due to the exposure to
cosmic rays on the Earth's surface is an hazard for experiments searching for
rare events like the direct detection of galactic dark matter particles. The
use of large amounts of liquid Argon is foreseen in different projects, like
the DarkSide-20k experiment, intended to look for Weakly Interacting Massive
Particles at the Laboratori Nazionali del Gran Sasso. Here, results from the
study of the cosmogenic activation of Argon carried out in the context of
DarkSide-20k are presented. The induced activity of several isotopes, including
39Ar, and the expected counting rates in the detector have been deduced,
considering exposure conditions as realistic as possible. | astro-ph_IM |
The analysis of effective galaxies number count for Chinese Space
Station Optical Survey(CSS-OS) by image simulation: The Chinese Space Station Optical Survey (CSS-OS) is a mission to explore the
vast universe. This mission will equip a 2-meter space telescope to perform a
multi-band NUV-optical large area survey (over 40% of the sky) and deep survey
(~1% of the sky) for the cosmological and astronomical goals. Galaxy detection
is one of the most important methods to achieve scientific goals. In this
paper, we evaluate the galaxy number density for CSS-OS in i band (depth, i ~26
for large area survey and ~27 for the deep survey, point source, 5-sigma by the
method of image simulation. We also compare galaxies detected by CSS-OS with
that of LSST (i~27, point source, 5-sigma. In our simulation, the HUDF galaxy
catalogs are used to create mock images due to long enough integration time
which meets the completeness requirements of the galaxy analysis for CSS-OS and
LSST. The galaxy surface profile and spectrum are produced by the morphological
information, photometric redshift and SEDs from the catalogs. The instrumental
features and the environmental condition are also considered to produce the
mock galaxy images. The galaxies of CSS-OS and LSST are both extracted by
SExtractor from the mock i band image and matched with the original catalog.
Through the analysis of the extracted galaxies, we find that the effective
galaxy number count is ~13 arcmin^-2, ~40 arcmin^-2 and ~42 arcmin^-2 for
CSS-OS large area survey, CSS-OS deep survey and LSST, respectively. Moreover,
CSS-OS shows the advantage in small galaxy detection with high spatial
resolution, especially for the deep survey: about 20% of the galaxies detected
by CSS-OS deep survey are not detected by LSST, and they have a small effective
radius of re < 0.3". | astro-ph_IM |
Matched filter in the low-number count Poisson noise regime: an
efficient and effective implementation: The matched filter (MF) is widely used to detect signals hidden within the
noise. If the noise is Gaussian, its performances are well-known and
describable in an elegant analytical form. The treatment of non-Gaussian noises
is often cumbersome as in most cases there is no analytical framework. This is
true also for Poisson noise which, especially in the low-number count regime,
presents the additional difficulty to be discrete. For this reason in the past
methods have been proposed based on heuristic or semi-heuristic arguments.
Recently, an analytical form of the MF has been introduced but the computation
of the probability of false detection or false alarm (PFA) is based on
numerical simulations. To overcome this inefficient and time consuming approach
we propose here an effective method to compute the PFA based on the saddle
point approximation (SA). We provide the theoretical framework and support our
findings by means of numerical simulations. We discuss also the limitations of
the MF in practical applications. | astro-ph_IM |
Investigating the In-Flight Performance of the UVIT Payload on ASTROSAT: We have studied the performance of the Ultraviolet Imaging Telescope payload
on AstroSat and derived a calibration of the FUV and NUV instruments on board.
We find that the sensitivity of both the FUV and NUV channels is as expected
from ground calibrations, with the FUV effective area about 35% and the NUV
effective area about the same as that of GALEX. The point spread function of
the instrument is on the order of 1.2-1.6 arcsec. We have found that
pixel-to-pixel variations in the sensitivity are less than 10% with spacecraft
motion compensating for most of the flat-field variations. We derived a
distortion correction but recommend that it be applied post-processing as part
of an astrometric solution. | astro-ph_IM |
The Importance of Telescope Training in Data Interpretation: In this State of the Profession Consideration, we will discuss the state of
hands-on observing within the profession, including: information about
professional observing trends; student telescope training, beginning at the
undergraduate and graduate levels, as a key to ensuring a base level of
technical understanding among astronomers; the role that amateurs can take
moving forward; the impact of telescope training on using survey data
effectively; and the need for modest investments in new, standard
instrumentation at mid-size aperture telescope facilities to ensure their
usefulness for the next decade. | astro-ph_IM |
Fully-Automated Reduction of Longslit Spectroscopy with the Low
Resolution Imaging Spectrometer at Keck Observatory: I present and summarize a software package ("LPipe") for completely
automated, end-to-end reduction of both bright and faint sources with the
Low-Resolution Imaging Spectrometer (LRIS) at Keck Observatory. It supports all
gratings, grisms, and dichroics, and also reduces imaging observations,
although it does not include multislit or polarimetric reduction capabilities
at present. It is suitable for on-the-fly quicklook reductions at the
telescope, for large-scale reductions of archival data-sets, and (in many
cases) for science-quality post-run reductions of PI data. To demonstrate its
capabilities the pipeline is run in fully-automated mode on all LRIS longslit
data in the Keck Observatory Archive acquired during the 12-month period
between August 2016 and July 2017. The reduced spectra (of 675 single-object
targets, totaling ~200 hours of on-source integration time in each camera), and
the pipeline itself, are made publicly available to the community. | astro-ph_IM |
Pulsar scattering in space and time: We report on a recent global VLBI experiment in which we study the scatter
broadening of pulsars in the spatial and time domain simultaneously. Depending
on the distribution of scattering screen(s), geometry predicts that the less
spatially broadened parts of the signal arrive earlier than the more broadened
parts. This means that over one pulse period the size of the scattering disk
should grow from pointlike to the maximum size. An equivalent description is
that the pulse profile shows less temporal broadening on the longer baselines.
This contribution presents first results that are consistent with the expected
expanding rings. We also briefly discuss how the autocorrelations can be used
for amplitude calibration. This requires a thorough investigation of the
digitisation and the sampler statistics and is not fully solved yet. | astro-ph_IM |
Antenna characterization for the HIRAX experiment: The Hydrogen Intensity and Real-time Analysis eXperiment (HIRAX) aims to
improve constraints on the dark energy equation of state through measurements
of large-scale structure at high redshift ($0.8<z<2.5$), while serving as a
state-of-the-art fast radio burst detector. Bright galactic foregrounds
contaminate the 400--800~MHz HIRAX frequency band, so meeting the science goals
will require precise instrument characterization. In this paper we describe
characterization of the HIRAX antenna, focusing on measurements of the antenna
beam and antenna noise temperature.
Beam measurements of the current HIRAX antenna design were performed in an
anechoic chamber and compared to simulations. We report measurement techniques
and results, which find a broad and symmetric antenna beam for $\nu <$650MHz,
and elevated cross-polarization levels and beam asymmetries for $\nu >$700MHz.
Noise temperature measurements of the HIRAX feeds were performed in a custom
apparatus built at Yale. In this system, identical loads, one cryogenic and the
other at room temperature, are used to take a differential (Y-factor)
measurement from which the noise of the system is inferred. Several measurement
sets have been conducted using the system, involving CHIME feeds as well as
four of the HIRAX active feeds. These measurements give the first noise
temperature measurements of the HIRAX feed, revealing a $\sim$60K noise
temperature (relative to 30K target) with 40K peak- to-peak frequency-dependent
features, and provide the first demonstration of feed repeatability. Both
findings inform current and future feed designs. | astro-ph_IM |
Exploring the Capabilities of Gibbs Sampling in Pulsar Timing Arrays: We explore the use of Gibbs sampling in estimating the noise properties of
individual pulsars and illustrate its effectiveness using the NANOGrav 11-year
data set. We find that Gibbs sampling noise modeling (GM) is more efficient
than the current standard Bayesian techniques (SM) for single pulsar analyses
by yielding model parameter posteriors with average effective-sample-size ratio
(GM/SM) of 6 across all parameters and pulsars. Furthermore, the output of GM
contains posteriors for the Fourier coefficients that can be used to
characterize the underlying red noise process of any pulsar's timing residuals,
which are absent in current implementations of SM. Through simulations, we
demonstrate the potential for such coefficients to measure the spatial
cross-correlations between pulsar pairs produced by a gravitational wave
background. | astro-ph_IM |
EMC design for the actuators of FAST reflector: The active reflector is one of the three main innovations of the
Five-hundred-meter Aperture Spherical radio Telescope (FAST). The deformation
of such a huge spherically shaped reflector into different transient parabolic
shapes is achieved by using 2225 hydraulic actuators which change the position
of the 2225 nodes through the connected down tied cables. For each different
tracking process of the telescope, more than 1/3 of these 2225 actuators must
be in operation to tune the parabolic aperture accurately to meet the surface
error restriction. It means that some of these actuators are inevitably located
within the main beam of the receiver, and the Electromagnetic Interference
(EMI) from the actuators must be mitigated to ensure the scientific output of
the telescope. Based on the threshold level of interference detrimental to
radio astronomy presented in ITU-R Recommendation RA.769 and EMI measurements,
the shielding efficiency (SE) requirement of each actuator is set to be 80dB in
the frequency range from 70MHz to 3GHz. Therefore, Electromagnetic
Compatibility (EMC) was taken into account in the actuator design by measures
such as power line filters, optical fibers, shielding enclosures and other
structural measures. In 2015, all the actuators had been installed at the FAST
site. Till now, no apparent EMI from the actuators has been detected by the
receiver, which proves the effectiveness of these EMC measures. | astro-ph_IM |
Rethinking the modeling of the instrumental response of telescopes with
a differentiable optical model: We propose a paradigm shift in the data-driven modeling of the instrumental
response field of telescopes. By adding a differentiable optical forward model
into the modeling framework, we change the data-driven modeling space from the
pixels to the wavefront. This allows to transfer a great deal of complexity
from the instrumental response into the forward model while being able to adapt
to the observations, remaining data-driven. Our framework allows a way forward
to building powerful models that are physically motivated, interpretable, and
that do not require special calibration data. We show that for a simplified
setting of a space telescope, this framework represents a real performance
breakthrough compared to existing data-driven approaches with reconstruction
errors decreasing 5 fold at observation resolution and more than 10 fold for a
3x super-resolution. We successfully model chromatic variations of the
instrument's response only using noisy broad-band in-focus observations. | astro-ph_IM |
Radiative transfer and molecular data for astrochemistry (Review): The estimation of molecular abundances in interstellar clouds from
spectroscopic observations requires radiative transfer calculations, which
depend on basic molecular input data. This paper reviews recent developments in
the fields of molecular data and radiative transfer. The first part is an
overview of radiative transfer techniques, along with a "road map" showing
which technique should be used in which situation. The second part is a review
of measurements and calculations of molecular spectroscopic and collisional
data, with a summary of recent collisional calculations and suggested modeling
strategies if collision data are unavailable. The paper concludes with an
overview of future developments and needs in the areas of radiative transfer
and molecular data. | astro-ph_IM |
Performance results of HESP physical model: As a continuation to the published work on model based calibration technique
with HESP(Hanle Echelle Spectrograph) as a case study, in this paper we present
the performance results of the technique. We also describe how the open
parameters were chosen in the model for optimization, the glass data accuracy
and handling the discrepancies. It is observed through simulations that the
discrepancies in glass data can be identified but not quantifiable. So having
an accurate glass data is important which is possible to obtain from the glass
manufacturers. The model's performance in various aspects is presented using
the ThAr calibration frames from HESP during its pre-shipment tests. Accuracy
of model predictions and its wave length calibration comparison with
conventional empirical fitting, the behaviour of open parameters in
optimization, model's ability to track instrumental drifts in the spectrum and
the double fibres performance were discussed. It is observed that the optimized
model is able to predict to a high accuracy the drifts in the spectrum from
environmental fluctuations. It is also observed that the pattern in the
spectral drifts across the 2D spectrum which vary from image to image is
predictable with the optimized model. We will also discuss the possible science
cases where the model can contribute. | astro-ph_IM |
Estimating effective wind speed from Gemini Planet Imager's adaptive
optics data using covariance maps: The Earth's turbulent atmosphere results in speckled and blurred images of
astronomical objects when observed by ground based visible and near-infrared
telescopes. Adaptive optics (AO) systems are employed to reduce these
atmospheric effects by using wavefront sensors (WFS) and deformable mirrors.
Some AO systems are not fast enough to correct for strong, fast, high
turbulence wind layers leading to the wind butterfly effect, or wind-driven
halo, reducing contrast capabilities in coronagraphic images. Estimating the
effective wind speed of the atmosphere allows us to calculate the atmospheric
coherence time. This is not only an important parameter to understand for site
characterization but could be used to help remove the wind butterfly in post
processing. Here we present a method for estimating the atmospheric effective
wind speed from spatio-temporal covariance maps generated from pseudo open-loop
(POL) WFS data. POL WFS data is used as it aims to reconstruct the full
wavefront information when operating in closed-loop. The covariance maps show
how different atmospheric turbulent layers traverse the telescope. Our method
successfully recovered the effective wind speed from simulated WFS data
generated with the soapy python library. The simulated atmospheric turbulence
profiles consist of two turbulent layers of ranging strengths and velocities.
The method has also been applied to Gemini Planet Imager (GPI) AO WFS data.
This gives insight into how the effective wind speed can affect the wind-driven
halo seen in the AO image point spread function. In this paper, we will present
results from simulated and GPI WFS data. | astro-ph_IM |
The Scaling of the RMS with Dwell Time in NANOGrav Pulsars: Pulsar Timing Arrays (PTAs) are collections of well-timed millisecond pulsars
that are being used as detectors of gravitational waves (GWs). Given current
sensitivity, projected improvements in PTAs and the predicted strength of the
GW signals, the detection of GWs with PTAs could occur within the next decade.
One way we can improve a PTA is to reduce the measurement noise present in the
pulsar timing residuals. If the pulsars included in the array display
uncorrelated noise, the root mean square (RMS) of the timing residuals is
predicted to scale as $\mathrm{T}^{-1/2}$, where T is the dwell time per
observation. In this case, the sensitivity of the array can be increased by
increasing T. We studied the 17 pulsars in the five year North American
Nanohertz Observatory for Gravitational Waves (NANOGrav) data set to determine
if the noise in the timing residuals of the pulsars observed was consistent
with this property. For comparison, we performed the same analysis on PSR
B1937+21, a pulsar that is known to display red noise. With this method, we
find that 15 of the 17 NANOGrav pulsars have timing residuals consistent with
the inverse square law. The data also suggest that these 15 pulsars can be
observed for up to eight times as long while still exhibiting an RMS that
scales as root T. | astro-ph_IM |
Citizen Science Astronomy with a Network of Small Telescope: The Launch
and Deployment of JWST: We present a coordinated campaign of observations to monitor the brightness
of the James Webb Space Telescope (JWST) as it travels toward the second
Earth-Sun Lagrange point and unfolds using the network ofUnistellar digital
telescopes. Those observations collected by citizen astronomers across the
world allowed us to detect specific phases such as the separation from the
booster, glare due to a change of orientation after a maneuver, the unfurling
of the sunshield, and deployment of the primary mirror. After deployment of the
sunshield on January 6 2022, the 6-h lightcurve has a significant amplitude and
shows small variations due to the artificial rotation of the space telescope
during commissionning. These variations could be due to the deployment of the
primary mirror or some changes in orientation of the space telescope. This work
illustrates the power of a worldwide array of small telescopes, operated by
citizen astronomers, to conduct large scientific campaigns over a long
timeframe. In the future, our network and others will continue to monitor JWST
to detect potential degradations to the space environment by comparing the
evolution of the lightcurve. | astro-ph_IM |
A convergent blind deconvolution method for post-adaptive-optics
astronomical imaging: In this paper we propose a blind deconvolution method which applies to data
perturbed by Poisson noise. The objective function is a generalized
Kullback-Leibler divergence, depending on both the unknown object and unknown
point spread function (PSF), without the addition of regularization terms;
constrained minimization, with suitable convex constraints on both unknowns, is
considered. The problem is nonconvex and we propose to solve it by means of an
inexact alternating minimization method, whose global convergence to stationary
points of the objective function has been recently proved in a general setting.
The method is iterative and each iteration, also called outer iteration,
consists of alternating an update of the object and the PSF by means of fixed
numbers of iterations, also called inner iterations, of the scaled gradient
projection (SGP) method. The use of SGP has two advantages: first, it allows to
prove global convergence of the blind method; secondly, it allows the
introduction of different constraints on the object and the PSF. The specific
constraint on the PSF, besides non-negativity and normalization, is an upper
bound derived from the so-called Strehl ratio, which is the ratio between the
peak value of an aberrated versus a perfect wavefront. Therefore a typical
application is the imaging of modern telescopes equipped with adaptive optics
systems for partial correction of the aberrations due to atmospheric
turbulence. In the paper we describe the algorithm and we recall the results
leading to its convergence. Moreover we illustrate its effectiveness by means
of numerical experiments whose results indicate that the method, pushed to
convergence, is very promising in the reconstruction of non-dense stellar
clusters. The case of more complex astronomical targets is also considered, but
in this case regularization by early stopping of the outer iterations is
required. | astro-ph_IM |
The Near-Infrared Spectrograph (NIRSpec) on the James Webb Space
Telescope IV. Capabilities and predicted performance for exoplanet
characterization: The Near-Inrared Spectrograph (NIRSpec) on the James Webb Space Telescope
(JWST) is a very versatile instrument, offering multiobject and integral field
spectroscopy with varying spectral resolution ($\sim$30 to $\sim$3000) over a
wide wavelength range from 0.6 to 5.3 micron, enabling scientists to study many
science themes ranging from the first galaxies to bodies in our own Solar
System. In addition to its integral field unit and support for multiobject
spectroscopy, NIRSpec features several fixed slits and a wide aperture
specifically designed to enable high precision time-series and transit as well
as eclipse observations of exoplanets. In this paper we present its
capabilities regarding time-series observations, in general, and transit and
eclipse spectroscopy of exoplanets in particular. Due to JWST's large
collecting area and NIRSpec's excellent throughput, spectral coverage, and
detector performance, this mode will allow scientists to characterize the
atmosphere of exoplanets with unprecedented sensitivity. | astro-ph_IM |
DQSEGDB: A time-interval database for storing gravitational wave
observatory metadata: The Data Quality Segment Database (DQSEGDB) software is a database service,
backend API, frontend graphical web interface, and client package used by the
Laser Interferometer Gravitational-Wave Observatory (LIGO), Virgo, GEO600 and
the Kamioka Gravitational wave detector for storing and accessing metadata
describing the status of their detectors. The DQSEGDB has been used in the
analysis of all published detections of gravitational waves in the advanced
detector era. The DQSEGDB currently stores roughly 600 million metadata entries
and responds to roughly 600,000 queries per day with an average response time
of 0.223 ms. | astro-ph_IM |
A Case Study in Astronomical 3-D Printing: The Mysterious Eta Carinae: 3-D printing moves beyond interactive 3-D graphics and provides an excellent
tool for both visual and tactile learners, since 3-D printing can now easily
communicate complex geometries and full color information. Some limitations of
interactive 3-D graphics are also alleviated by 3-D printable models, including
issues of limited software support, portability, accessibility, and
sustainability. We describe the motivations, methods, and results of our work
on using 3-D printing (1) to visualize and understand the Eta Car Homunculus
nebula and central binary system and (2) for astronomy outreach and education,
specifically, with visually impaired students. One new result we present is the
ability to 3-D print full-color models of Eta Car's colliding stellar winds. We
also demonstrate how 3-D printing has helped us communicate our improved
understanding of the detailed structure of Eta Car's Homunculus nebula and
central binary colliding stellar winds, and their links to each other. Attached
to this article are full-color 3-D printable files of both a red-blue
Homunculus model and the Eta Car colliding stellar winds at orbital phase
1.045. 3-D printing could prove to be vital to how astronomer's reach out and
share their work with each other, the public, and new audiences. | astro-ph_IM |
A Fourier optics approach to evaluate the astrometric performance of
MICADO: We present our investigation into the impact of wavefront errors on high
accuracy astrometry using Fourier Optics. MICADO, the upcoming near-IR imaging
instrument for the Extremely Large Telescope, will offer capabilities for
relative astrometry with an accuracy of 50 micro arcseconds ({\mu}as). Due to
the large size of the point spread function (PSF) compared to the astrometric
requirement, the detailed shape and position of the PSF on the detector must be
well understood. Furthermore, because the atmospheric dispersion corrector of
MICADO is a moving component within an otherwise mostly static instrument, it
might not be sufficient to perform a simple pre-observation calibration.
Therefore, we have built a Fourier Optics framework, allowing us to evaluate
the small changes in the centroid position of the PSF as a function of
wavefront error. For a complete evaluation, we model both the low order surface
form errors, using Zernike polynomials, and the mid- and high-spatial
frequencies, using Power Spectral Density analysis. The described work will
then make it possible, performing full diffractive beam propagation, to assess
the expected astrometric performance of MICADO. | astro-ph_IM |
Status of the Medium-Sized Telescope for the Cherenkov Telescope Array: The Cherenkov Telescope Array (CTA), is an international project for the next
generation ground- based observatory for gamma-ray astronomy in the energy
range from 20 GeV to 300 TeV. The sensitivity in the core energy range will be
dominated by up to 40 Medium-Sized Telescopes (MSTs). The MSTs, of
Davies-Cotton type with a 12 m diameter reflector are currently in the
prototype phase. A full-size mechanical telescope structure has been assembled
in Berlin. The telescope is partially equipped with different mirror
prototypes, which are currently being tested and evaluated for performances
characteristics. A report concentrating on the details of the tele- scope
structure, the drive assemblies and the optics of the MST prototype will be
given. | astro-ph_IM |
The antinucleus annihilation reconstruction algorithm of the GAPS
experiment: The General AntiParticle Spectrometer (GAPS) is an Antarctic balloon-borne
detector designed to measure low-energy cosmic antinuclei (< 0.25 GeV/n), with
a specific focus on antideuterons, as a distinctive signal from dark matter
annihilation or decay in the Galactic halo. The instrument consists of a
tracker, made up of ten planes of lithium-drifted Silicon Si(Li) detectors,
surrounded by a plastic scintillator Time-of-Flight system. GAPS uses a novel
particle identification method based on exotic atom capture and decay with the
emission of pions, protons, and atomic X-rays from a common annihilation
vertex.
An important ingredient for the antinuclei identification is the
reconstruction of the "annihilation star" topology. A custom antinucleus
annihilation reconstruction algorithm, called the "star-finding" algorithm, was
developed to reconstruct the annihilation star fully, determining the
annihilation vertex position and reconstructing the tracks of the primary and
secondary charged particles. The reconstruction algorithm and its performances
were studied on simulated data obtained with the Geant4-based GAPS simulation
software, which fully reproduced the detector geometry. This custom algorithm
was found to have better performance in the vertex resolution and
reconstruction efficiency compared with a standard Hough-3D algorithm. | astro-ph_IM |
Adaptive Kernel Density Estimation proposal in gravitational wave data
analysis: Markov Chain Monte Carlo approach is frequently used within Bayesian
framework to sample the target posterior distribution. Its efficiency strongly
depends on the proposal used to build the chain. The best jump proposal is the
one that closely resembles the unknown target distribution, therefore we
suggest an adaptive proposal based on Kernel Density Estimation (KDE). We group
parameters of the model according to their correlation and build KDE based on
the already accepted points for each group. We adapt the KDE-based proposal
until it stabilizes. We argue that such a proposal could be helpful in
applications where the data volume is increasing and in the hyper-model
sampling. We tested it on several astrophysical datasets (IPTA and LISA) and
have shown that in some cases KDE-based proposal also helps to reduce the
autocorrelation length of the chains. The efficiency of this proposal is
reduces in case of the strong correlations between a large group of parameters. | astro-ph_IM |
The LAUE project for broadband gamma-ray focusing lenses: We present the LAUE project devoted to develop an advanced technology for
building a high focal length Laue lens for soft gamma--ray astronomy (80-600
keV). The final goal is to develop a focusing optics that can improve the
current sensitivity in the above energy band by 2 orders of magnitude. | astro-ph_IM |
All-sky Radio SETI: Over the last decade, Aperture Arrays (AA) have successfully replaced
parabolic dishes as the technology of choice at low radio frequencies - good
examples are the MWA, LWA and LOFAR. Aperture Array based telescopes present
several advantages, including sensitivity to the sky over a very wide
field-of-view. As digital and data processing systems continue to advance, an
all-sky capability is set to emerge, even at GHz frequencies. We argue that
assuming SETI events are both rare and transitory in nature, an instrument with
a large field-of-view, operating around the so-called water-hole (1-2 GHz),
might offer several advantages over contemporary searches. Sir Arthur C. Clarke
was the first to recognise the potential importance of an all-sky radio SETI
capability, as presented in his book, Imperial Earth. As part of the global SKA
(Square Kilometre Array) project, a Mid-Frequency Aperture Array (MFAA)
prototype known as MANTIS (Mid- Frequency Aperture Array Transient and
Intensity-Mapping System) is now being considered as a precursor for SKA-2.
MANTIS can be seen as a first step towards an all-sky radio SETI capability at
GHz frequencies. This development has the potential to transform the field of
SETI research, in addition to several other scientific programmes. | astro-ph_IM |
Scattering efficiencies measurements of soft protons at grazing
incidence from an Athena Silicon Pore Optics sample: Soft protons are a potential threat for X-ray missions using grazing
incidence optics, as once focused onto the detectors they can contribute to
increase the background and possibly induce radiation damage as well. The
assessment of these undesired effects is especially relevant for the future ESA
X-ray mission Athena, due to its large collecting area. To prevent degradation
of the instrumental performance, which ultimately could compromise some of the
scientific goals of the mission, the adoption of ad-hoc magnetic diverters is
envisaged. Dedicated laboratory measurements are fundamental to understand the
mechanisms of proton forward scattering, validate the application of the
existing physical models to the Athena case and support the design of the
diverters. In this paper we report on scattering efficiency measurements of
soft protons impinging at grazing incidence onto a Silicon Pore Optics sample,
conducted in the framework of the EXACRAD project. Measurements were taken at
two different energies, ~470 keV and ~170 keV, and at four different scattering
angles between 0.6 deg and 1.2 deg. The results are generally consistent with
previous measurements conducted on eROSITA mirror samples, and as expected the
peak of the scattering efficiency is found around the angle of specular
reflection. | astro-ph_IM |
Mining for Strong Gravitational Lenses with Self-supervised Learning: We employ self-supervised representation learning to distill information from
76 million galaxy images from the Dark Energy Spectroscopic Instrument Legacy
Imaging Surveys' Data Release 9. Targeting the identification of new strong
gravitational lens candidates, we first create a rapid similarity search tool
to discover new strong lenses given only a single labelled example. We then
show how training a simple linear classifier on the self-supervised
representations, requiring only a few minutes on a CPU, can automatically
classify strong lenses with great efficiency. We present 1192 new strong lens
candidates that we identified through a brief visual identification campaign,
and release an interactive web-based similarity search tool and the top network
predictions to facilitate crowd-sourcing rapid discovery of additional strong
gravitational lenses and other rare objects:
https://github.com/georgestein/ssl-legacysurvey. | astro-ph_IM |
The Radar Echo Telescope for Cosmic Rays: Pathfinder Experiment for a
Next-Generation Neutrino Observatory: The Radar Echo Telescope for Cosmic Rays (RET-CR) is a recently initiated
experiment designed to detect the englacial cascade of a cosmic-ray initiated
air shower via in-ice radar, toward the goal of a full-scale, next-generation
experiment to detect ultra high energy neutrinos in polar ice. For cosmic rays
with a primary energy greater than 10 PeV, roughly 10% of an air-shower's
energy reaches the surface of a high elevation ice-sheet ($\gtrsim$2 km)
concentrated into a radius of roughly 10 cm. This penetrating shower core
creates an in-ice cascade many orders of magnitude more dense than the
preceding in-air cascade. This dense cascade can be detected via the radar echo
technique, where transmitted radio is reflected from the ionization deposit
left in the wake of the cascade. RET-CR will test the radar echo method in
nature, with the in-ice cascade of a cosmic-ray initiated air-shower serving as
a test beam. We present the projected event rate and sensitivity based upon a
three part simulation using CORSIKA, GEANT4, and RadioScatter. RET-CR expects
$\sim$1 radar echo event per day. | astro-ph_IM |
AstroCloud: A Distributed Cloud Computing and Application Platform for
Astronomy: Virtual Observatory (VO) is a data-intensively online astronomical research
and education environment, which takes advantages of advanced information
technologies to achieve seamless and global access to astronomical information.
AstroCloud is a cyber-infrastructure for astronomy research initiated by
Chinese Virtual Observatory (China-VO) project, and also a kind of physical
distributed platform which integrates lots of tasks such as telescope access
proposal management, data archiving, data quality control, data release and
open access, cloud based data processing and analysis. It consists of five
application channels, i.e. observation, data, tools, cloud and public and is
acting as a full lifecycle management system and gateway for astronomical data
and telescopes. Physically, the platform is hosted in six cities currently,
i.e. Beijing, Nanjing, Shanghai, Kunming, Lijiang and Urumqi, and serving more
than 17 thousand users. Achievements from international Virtual Observatories
and Cloud Computing are adopted heavily. In the paper, backgrounds of the
project, architecture, Cloud Computing environment, key features of the system,
current status and future plans are introduced. | astro-ph_IM |
Portable Adaptive Optics for Exoplanet Imaging: The Portable Adaptive Optics (PAO) is a low-cost and compact system, designed
for 4-meter class telescopes that have no Adaptive Optics (AO), because of the
physical space limitation at the Nasmyth or Cassegrain focus and the
historically high cost of the conventional AO. The initial scientific
observations of the PAO are focused on the direct imaging of exoplanets and
sub-stellar companions. This paper discusses the PAO concept and the associated
high-contrast imaging performance in our recent observational runs. PAO is
delivering a Strehl ratio better than 0.6 in H band under median seeing
conditions of 1 arcsec. Combined with our dedicated image rotation and
subtraction (IRS) technique and the optimized IRS (O-IRS) algorithm, the
averaged contrast ratio for a Vmag (5-9) primary star is 1.3E10-5 and 3.3E10-6
at angular distance of 0.36 arcsec under exposure time of 7 minutes and 2
hours, respectively. PAO has successfully recovered the known exoplanet of
\k{appa} And b, in our recent observation at 3.5-meter ARC telescope at Apache
Point Observatory. We have performed the associated astrometry and photometry
analysis of the recovered kappa And b planet, which gives a projected
separation of 0.984 +/- 0.05 arcsec, a position angle of 51.1 +/- 0.5 degrees,
and a mass of 10.15 (-1.255) (+2.19) MJup. These results demonstrate that PAO
can be used for direct imaging of exoplanets with medium-sized telescopes. | astro-ph_IM |
Finding the UV-Visible Path Forward: Proceedings of the Community
Workshop to Plan the Future of UV/Visible Space Astrophysics: We present the science cases and technological discussions that came from the
workshop entitled "Finding the UV-Visible Path Forward" held at NASA GSFC June
25-26, 2015. The material presented outlines the compelling science that can be
enabled by a next generation space-based observatory dedicated for UV-visible
science, the technologies that are available to include in that observatory
design, and the range of possible alternative launch approaches that could also
enable some of the science. The recommendations to the Cosmic Origins Program
Analysis Group from the workshop attendees on possible future development
directions are outlined. | astro-ph_IM |
The possibility of determining open-cluster parameters from BVRI
photometry: In the last decades we witnessed an increase in studies of open clusters of
the Galaxy, especially because of the good determination for a wide range of
values of parameters such as age, distance, reddening, and proper motion. The
reliable determination of the parameters strongly depends on the photometry
available and especially on the U filter, which is used to obtain the color
excess E(B-V) through the color-color diagram (U-B) by (B-V) by fitting a zero
age main-sequence. Owing to the difficulty of performing photometry in the U
band, many authors have tried to obtain E(B-V) without the filter. But because
of the near linearity of the color-color diagrams that use the other bands,
combined with the fact that most fitting procedures are highly subjective (many
done "by eye") the reliability of those results has always been questioned. Our
group has recently developed, a tool that performs isochrone fitting in
open-cluster photometric data with a global optimization algorithm, which
removes the need to visually perform the fits and thus removes most of the
related subjectivity. Here we apply our method to a set of synthetic clusters
and two observed open clusters (Trumpler 1 and Melotte 105) using only
photometry for the BVRI bands. Our results show that, considering the cluster
structural variance caused only by photometric and Poisson sampling errors, our
method is able to recover the synthetic cluster parameters with errors of less
than 10% for a wide range of ages, distances, and reddening, which clearly
demonstrates its potential. The results obtained for Trumpler 1 and Melotte 105
also agree well with previous literature values. | astro-ph_IM |
A Simple Proposal for Radial 3D Needlets: We present here a simple construction of a wavelet system for the
three-dimensional ball, which we label \emph{Radial 3D Needlets}. The
construction envisages a data collection environment where an observer located
at the centre of the ball is surrounded by concentric spheres with the same
pixelization at different radial distances, for any given resolution. The
system is then obtained by weighting the projector operator built on the
corresponding set of eigenfunctions, and performing a discretization step which
turns out to be computationally very convenient. The resulting wavelets can be
shown to have very good localization properties in the real and harmonic
domain; their implementation is computationally very convenient, and they allow
for exact reconstruction as they form a tight frame systems. Our theoretical
results are supported by an extensive numerical analysis. | astro-ph_IM |
The upcoming spectroscopic powerhouses at the Isaac Newton Group of
Telescopes: The Isaac Newton Group of Telescopes is completing a strategic change for the
scientific use of its two telescopes, the 4.2-m William Herschel Telescope
(WHT) and the 2.5-m Isaac Newton Telescope (INT). After more than 30 years
operating as multi-purpose telescopes, the telescopes will soon complete their
shift to nearly-single instrument operation dominated by large surveys.
At the WHT, the WEAVE multi-fibre spectrograph is being commissioned in late
2022. Science surveys are expected to launch in 2023. 30% of the available time
will be offered in open time. For the INT, construction of HARPS-3, a
high-resolution ultra-stable spectrograph for extra-solar planet studies, is
underway, with deployment planned for late 2024. The INT itself is being
modernised and will operate as a robotic telescope. An average of 40% of the
time will be offered as open time.
The ING will maintain its student programme. Plans call for moving student
work from the INT to the WHT once the INT starts operating robotically. | astro-ph_IM |
Audible universe: A multi-disciplinary team recently came together online to discuss the
application of sonification in astronomy, focussing on the effective use of
sound for scientific discovery and for improving accessibility to astronomy
research and education. Here we provide a meeting report. | astro-ph_IM |
Hierarchical approach to matched filtering using a reduced basis: Searching for gravitational waves from compact binary coalescence (CBC) is
performed by matched filtering the observed strain data from gravitational-wave
observatories against a discrete set of waveform templates designed to
accurately approximate the expected gravitational-wave signal, and are chosen
to efficiently cover a target search region. The computational cost of matched
filtering scales with both the number of templates required to cover a
parameter space and the in-band duration of the waveform. Both of these factors
increase in difficulty as the current observatories improve in sensitivity,
especially at low frequencies, and may pose challenges for third-generation
observatories. Reducing the cost of matched filtering would make searches of
future detector data more tractable. In addition, it would be easier to conduct
searches that incorporate the effects of eccentricity, precession or target
light sources (e.g. subsolar). We present a hierarchical scheme based on a
reduced basis method to decrease the computational cost of conducting a
matched-filter based search. Compared to the current methods, we estimate
without any loss in sensitivity, a speedup by a factor of ~ 10 for sources with
signal-to-noise ratio (SNR) of at least =6.0, and a factor of ~ 6 for SNR of at
least 5. Our method is dominated by linear operations which are highly
parallelizable. Therefore, we implement our algorithm using graphical
processing units (GPUs) and evaluate commercially motivated metrics to
demonstrate the efficiency of GPUs in CBC searches. Our scheme can be extended
to generic CBC searches and allows for efficient matched filtering using GPUs. | astro-ph_IM |
The Influence of Satellite Trails on H.E.S.S. Gamma-Ray Astronomical
Observations: The number of satellites launched into low earth orbit has almost tripled (to
over 4000) in the last three years due to the increasing commercialisation of
space. Satellite constellations with a total of over 400,000 satellites are
proposed to be launched in the near future. Many of these satellites are highly
reflective, resulting in a high optical brightness that affects ground-based
astronomical observations across the electromagnetic spectrum. Despite this,
the potential effect of these satellites on Imaging Atmospheric Cherenkov
Telescopes (IACTs) has so far been assumed to be negligible due to their
nanosecond integration times. This has, however, never been verified. We aim to
identify satellite trails in data taken by the High Energy Stereoscopic System
(H.E.S.S.) IACT array in Namibia, using Night Sky Background (NSB) data from
the CT5 camera installed in 2019. We determine which observation times and
pointing directions are affected the most, and evaluate the impact on Hillas
parameters used for classification and reconstruction of high-energy Extensive
Air Shower events. Finally, we predict how future planned satellite launches
will affect gamma-ray observations with IACTs. | astro-ph_IM |
A new photopolymer based VPHG for astronomy: The case of SN 2013fj: The spectroscopic studies of near infrared emission arising from supernovae
allow to derive crucial quantities that could better characterise physical
conditions of the expanding gas, such as the CaII IR HVF spectral feature. For
this reason is mandatory to have Diffractive Optical Elements (DOEs) with a
spectral coverage in the range 8000 - 10000 Angstroms (for low z sources)
combined with a reasonable Signal to Noise Ratio (S/N) and medium-low
resolution. In order to cope with all of those requirements we developed a
Volume Phase Holographic Grating (VPHG) based on an innovative photosensitive
material, developed by Bayer MaterialScience. We demonstrated the capabilities
of this new DOE through observation of SN 2013fj as case study at Asiago
Copernico Telescope where AFOSC spectrograph is available. | astro-ph_IM |
The fiber-fed preslit of GIANO at T.N.G: Giano is a Cryogenic Spectrograph located in T.N.G. (Spain) and commisioned
in 2013. It works in the range 950-2500 nm with a resolving power of 50000.
This instrument was designed and built for direct feeding from the telescope
[2]. However, due to constraints imposed on the telescope interfacing during
the pre-commissioning phase, it had to be positioned on the rotating building,
far from the telescope focus. Therefore, a new interface to the telescope,
based on IR-transmitting ZBLAN fibers with 85\mu m core, was
developed.Originally designed to work directly at the $f/11$ nasmyth focus of
the telescope, in 2011 it has decided to use a fiber to feed it. The beam from
the telescope is focused on a double fiber boundle by a Preslit Optical Bench
attached to the Nasmith A interface of the telescope. This Optical Bench
contains the fiber feeding system and other important features as a guiding
system, a fiber viewer, a fiber feed calibration lamp and a nodding facility
between the two fibers. The use of two fibers allow us to have in the
echellogram two spectrograms side by side in the same acquisition: one of the
star and the other of the sky or simultaneously to have the star and a
calibration lamp. Before entering the cryostat the light from the fiber is
collectd by a second Preslit Optical Bench attached directly to the Giano
cryostat: on this bench the correct f-number to illuminate the cold stop is
generated and on the same bench is placed an image slicer to increase the
efficiency of the system. | astro-ph_IM |
Standard FITS template for simulated astrophysical scenes with the
WFIRST coronagraph: The science investigation teams (SITs) for the WFIRST coronagraphic
instrument have begun studying the capabilities of the instrument to directly
image reflected light off from exoplanets at contrasts down to contrasts of
~10^-9 with respect to the stellar flux. Detection of point sources at these
high contrasts requires yield estimates and detailed modeling of the image of
the planetary system as it propagates through the telescope optics. While the
SITs might generate custom astrophysical scenes, the integrated model,
propagated through the internal speckle field, is typically done at JPL. In
this white paper, we present a standard file format to ensure a single
distribution system between those who produce the raw astrophysical scenes, and
JPL modelers who incorporate those scenes into their optical modeling. At its
core, our custom file format uses FITS files, and incorporates standards on
packaging astrophysical scenes. This includes spectral and astrometric
information for planetary and stellar point sources, zodiacal light and
extragalactic sources that may appear as contaminants. Adhering to such a
uniform data distribution format is necessary, as it ensures seamless work flow
between the SITs and modelers at JPL for the goals of understanding limits of
the WFIRST coronagraphic instrument. | astro-ph_IM |
The performance of the MAGIC telescopes using deep convolutional neural
networks with CTLearn: The Major Atmospheric Gamma Imaging Cherenkov (MAGIC) telescope system is
located on the Canary Island of La Palma and inspects the very high-energy
(VHE, few tens of GeV and above) gamma-ray sky. MAGIC consists of two imaging
atmospheric Cherenkov telescopes (IACTs), which capture images of the air
showers originating from the absorption of gamma rays and cosmic rays by the
atmosphere, through the detection of Cherenkov photons emitted in the shower.
The sensitivity of IACTs to gamma-ray sources is mainly determined by the
ability to reconstruct the properties (type, energy, and arrival direction) of
the primary particle generating the air shower. The state-of-the-art IACT
pipeline for shower reconstruction is based on the parameterization of the
shower images by extracting geometric and stereoscopic features and machine
learning algorithms like random forest or boosted decision trees. In this
contribution, we explore deep convolutional neural networks applied directly to
the pixelized images of the camera as a promising method for IACT full-event
reconstruction and present the performance of the method on observational data
using CTLearn, a package for IACT event reconstruction that exploits deep
learning. | astro-ph_IM |
Polarization loss in reflecting coating: In laser gravitational waves detectors optical loss restricts sensitivity. We
discuss polarization scattering as one more possible mechanism of optical
losses. Circulated inside interferometer light is polarized and after
reflection its plane of polarization can turn a little due to reflecting
coating of mirror can have slightly different refraction index along axes $x,\,
y$ in plane of mirror surface (optical anisotropy). This anisotropy can be
produced during manufacture of coating (elasto-optic effect). This orthogonal
polarized light, enhanced in cavity, produces polarization optical loss.
Polarization map of mirrors is very important and we propose to measure it.
Polarization loss can be important in different precision optical experiments
based on usage of polarized light, for example, in quantum speed meter. | astro-ph_IM |
LSST Target of Opportunity proposal for locating a core collapse
supernova in our galaxy triggered by a neutrino supernova alert: A few times a century, a core collapse supernova (CCSN) occurs in our galaxy.
When such galactic CCSNe happen, over 99\% of its gravitational binding energy
is released in the form of neutrinos. Over a period of tens of seconds, a
powerful neutrino flux is emitted from the collapsing star. When the exploding
shock wave finally reaches the surface of the star, optical photons escaping
the expanding stellar envelope leave the star and eventually arrive at Earth as
a visible brightening. Crucially, although the neutrino signal is prompt, the
time to the shock wave breakout can be minutes to many hours later. This means
that the neutrino signal will serve as an alert, warning the optical astronomy
community the light from the explosion is coming. Quickly identifying the
location of the supernova on the sky and disseminating it to the all available
ground and spaced-based instruments will be critical to learn as much as
possible about the event. Some neutrino experiments can report pointing
information for these galactic CCSNe. In particular, the Super-Kamiokande
experiment can point to a few degrees for CCSNe near the center of our galaxy.
A CCSN located 10 kpc from Earth is expected to result in a pointing resolution
on the order of 3 degrees. LSST's field of view (FOV) is well matched to this
initial search box. LSSTs depth is also uniquely suited for identifying CCSNe
even if they fail or are obscured by the dust of the galactic plane. This is a
proposal to, upon receipt of such an alert, prioritize the use of LSST for a
full day of observing to continuously monitor a pre-identified region of sky
and, by using difference imaging, identify and announce the location of the
supernova. | astro-ph_IM |
Measuring the Evolution of the NuSTAR Detector Gains: The memo describes the methods used to track the long-term gain variations in
the NuSTAR detectors. It builds on the analysis presented in Madsen et al.
(2015) using the deployable calibration source to measure the gain drift in the
NuSTAR CdZnTe detectors. This is intended to be a live document that is
periodically updated as new entries are required in the NuSTAR gain CALDB
files. This document covers analysis up through early-2022 and the gain v011
CALDB file released in version 20240226. | astro-ph_IM |
Versatile Directional Searches for Gravitational Waves with Pulsar
Timing Arrays: By regularly monitoring the most stable millisecond pulsars over many years,
pulsar timing arrays (PTAs) are positioned to detect and study correlations in
the timing behaviour of those pulsars. Gravitational waves (GWs) from
supermassive black hole binaries (SMBHBs) are an exciting potentially
detectable source of such correlations. We describe a straight-forward
technique by which a PTA can be "phased-up" to form time series of the two
polarisation modes of GWs coming from a particular direction of the sky. Our
technique requires no assumptions regarding the time-domain behaviour of a GW
signal. This method has already been used to place stringent bounds on GWs from
individual SMBHBs in circular orbits. Here, we describe the methodology and
demonstrate the versatility of the technique in searches for a wide variety of
GW signals including bursts with unmodeled waveforms. Using the first six years
of data from the Parkes Pulsar Timing Array, we conduct an all-sky search for a
detectable excess of GW power from any direction. For the lines of sight to
several nearby massive galaxy clusters, we carry out a more detailed search for
GW bursts with memory, which are distinct signatures of SMBHB mergers. In all
cases, we find that the data are consistent with noise. | astro-ph_IM |
The ATLAS All-Sky Stellar Reference Catalog: The Asteroid Terrestrial-impact Last Alert System (ATLAS) observes most of
the sky every night in search of dangerous asteroids. Its data are also used to
search for photometric variability, where sensitivity to variability is limited
by photometric accuracy. Since each exposure spans 7.6 deg corner to corner,
variations in atmospheric transparency in excess of 0.01 mag are common, and
0.01 mag photometry cannot be achieved by using a constant flat field
calibration image. We therefore have assembled an all-sky reference catalog of
approximately one billion stars to m~19 from a variety of sources to calibrate
each exposure's astrometry and photometry. Gaia DR2 is the source of astrometry
for this ATLAS Refcat2. The sources of g, r, i, z photometry include Pan-STARRS
DR1, the ATLAS Pathfinder photometry project, ATLAS re-flattened APASS data,
SkyMapper DR1, APASS DR9, the Tycho-2 catalog, and the Yale Bright Star
Catalog. We have attempted to make this catalog at least 99% complete to m<19,
including the brightest stars in the sky. We believe that the systematic errors
are no larger than 5 millimag RMS, although errors are as large as 20 millimag
in small patches near the galactic plane. | astro-ph_IM |
Data Multiplexing in Radio Interferometric Calibration: New and upcoming radio interferometers will produce unprecedented amounts of
data that demand extremely powerful computers for processing. This is a
limiting factor due to the large computational power and energy costs involved.
Such limitations restrict several key data processing steps in radio
interferometry. One such step is calibration where systematic errors in the
data are determined and corrected. Accurate calibration is an essential
component in reaching many scientific goals in radio astronomy and the use of
consensus optimization that exploits the continuity of systematic errors across
frequency significantly improves calibration accuracy. In order to reach full
consensus, data at all frequencies need to be calibrated simultaneously. In the
SKA regime, this can become intractable if the available compute agents do not
have the resources to process data from all frequency channels simultaneously.
In this paper, we propose a multiplexing scheme that is based on the
alternating direction method of multipliers (ADMM) with cyclic updates. With
this scheme, it is possible to simultaneously calibrate the full dataset using
far fewer compute agents than the number of frequencies at which data are
available. We give simulation results to show the feasibility of the proposed
multiplexing scheme in simultaneously calibrating a full dataset when a limited
number of compute agents are available. | astro-ph_IM |
A distributed data warehouse system for astroparticle physics: A distributed data warehouse system is one of the actual issues in the field
of astroparticle physics. Famous experiments, such as TAIGA, KASCADE-Grande,
produce tens of terabytes of data measured by their instruments. It is critical
to have a smart data warehouse system on-site to store the collected data for
further distribution effectively. It is also vital to provide scientists with a
handy and user-friendly interface to access the collected data with proper
permissions not only on-site but also online. The latter case is handy when
scientists need to combine data from different experiments for analysis. In
this work, we describe an approach to implementing a distributed data warehouse
system that allows scientists to acquire just the necessary data from different
experiments via the Internet on demand. The implementation is based on
CernVM-FS with additional components developed by us to search through the
whole available data sets and deliver their subsets to users' computers. | astro-ph_IM |
Swift publication statistics: a comparison with other major
observatories: Swift is a satellite equipped with gamma-ray, X-ray, and optical-UV
instruments aimed at discovering, localizing and collecting data from gamma-ray
bursts (GRBs). Launched at the end of 2004, this small-size mission finds about
a hundred GRBs per year, totaling more than 700 events as of 2012. In addition
to GRBs, Swift observes other energetic events, such as AGNs, novae, and
supernovae. Here we look at its success using bibliometric tools; that is the
number of papers using Swift data and their impact (i.e., number of citations
to those papers). We derived these for the publication years 2005 to 2011, and
compared them with the same numbers for other major observatories. Swift
provided data for 1101 papers in the interval 2005-2011, with 24 in the first
year, to 287 in the last year. In 2011, Swift had more than double the number
of publications as Subaru, it overcame Gemini by a large fraction, and reached
Keck. It is getting closer to the ~400 publications of the successful
high-energy missions XMM-Newton and Chandra, but is still far from the most
productive telescopes VLT (over 500) and HST (almost 800). The overall average
number of citations per paper, as of November 2012, is 28.3, which is
comparable to the others, but lower than Keck (41.8). The science topics
covered by Swift publications have changed from the first year, when over 80%
of the papers were about GRBs, while in 2011 it was less than 30%. | astro-ph_IM |
Status of predictive wavefront control on Keck II adaptive optics bench:
on-sky coronagraphic results: The behavior of an adaptive optics (AO) system for ground-based high contrast
imaging (HCI) dictates the achievable contrast of the instrument. In conditions
where the coherence time of the atmosphere is short compared to the speed of
the AO system, the servo-lag error becomes the dominate error term of the AO
system. While the AO system measures the wavefront error and subsequently
applies a correction (taking a total of 1 to 2 milli-seconds), the atmospheric
turbulence above the telescope has changed. In addition to reducing the Strehl
ratio, the servo-lag error causes a build-up of speckles along the direction of
the dominant wind vector in the coronagraphic image, severely limiting the
contrast at small angular separations. One strategy to mitigate this problem is
to predict the evolution of the turbulence over the delay. Our predictive
wavefront control algorithm minimizes the delay in a mean square sense and has
been implemented on the Keck II AO bench. In this paper we report on the latest
results of our algorithm and discuss updates to the algorithm itself. We
explore how to tune various filter parameters on the basis of both daytime
laboratory tests and on-sky tests. We show a reduction in residual-mean-square
wavefront error for the predictor compare to the leaky integrator implemented
on Keck. Finally, we present contrast improvements for both day time and on-sky
tests. Using the L-band vortex coronagraph for Keck's NIRC2 instrument, we find
a contrast gain of 2.03 at separation of 3~$\lambda/D$ and up to 3 for larger
separations (4-6~$\lambda/D$). | astro-ph_IM |
hammurabi X: Simulating Galactic Synchrotron Emission with Random
Magnetic Fields: We present version X of the hammurabi package, the HEALPix-based numeric
simulator for Galactic polarized emission. Improving on its earlier design, we
have fully renewed the framework with modern C++ standards and features.
Multi-threading support has been built in to meet the growing computational
workload in future research. For the first time, we present precision profiles
of hammurabi line-of-sight integral kernel with multi-layer HEALPix shells. In
addition to fundamental improvements, this report focuses on simulating
polarized synchrotron emission with Gaussian random magnetic fields. Two fast
methods are proposed for realizing divergence-free random magnetic fields
either on the Galactic scale where a field alignment and strength modulation
are imposed, or on a local scale where more physically motivated models like a
parameterized magneto-hydrodynamic (MHD) turbulence can be applied. As an
example application, we discuss the phenomenological implications of Gaussian
random magnetic fields for high Galactic latitude synchrotron foregrounds. In
this, we numerically find B/E polarization mode ratios lower than unity based
on Gaussian realizations of either MHD turbulent spectra or in spatially
aligned magnetic fields. | astro-ph_IM |
Modelling astronomical adaptive optics performance with
temporally-filtered Wiener reconstruction of slope data: We build on a long-standing tradition in astronomical adaptive optics (AO) of
specifying performance metrics and error budgets using linear systems modeling
in the spatial-frequency domain. Our goal is to provide a comprehensive tool
for the calculation of error budgets in terms of residual temporally filtered
phase power spectral densities and variances. In addition, the fast simulation
of AO-corrected point spread functions (PSFs) provided by this method can be
used as inputs for simulations of science observations with next-generation
instruments and telescopes, in particular to predict post-coronagraphic
contrast improvements for planet finder systems. We extend the previous results
and propose the synthesis of a distributed Kalman filter to mitigate both
aniso-servo-lag and aliasing errors whilst minimizing the overall residual
variance. We discuss applications to (i) analytic AO-corrected PSF modeling in
the spatial-frequency domain, (ii) post-coronagraphic contrast enhancement,
(iii) filter optimization for real-time wavefront reconstruction, and (iv) PSF
reconstruction from system telemetry. Under perfect knowledge of wind
velocities, we show that $\sim$60 nm rms error reduction can be achieved with
the distributed Kalman filter embodying anti- aliasing reconstructors on 10 m
class high-order AO systems, leading to contrast improvement factors of up to
three orders of magnitude at few ${\lambda}/D$ separations
($\sim1-5{\lambda}/D$) for a 0 magnitude star and reaching close to one order
of magnitude for a 12 magnitude star. | astro-ph_IM |
A Bayesian approach to high fidelity interferometric calibration II:
demonstration with simulated data: In a companion paper, we presented BayesCal, a mathematical formalism for
mitigating sky-model incompleteness in interferometric calibration. In this
paper, we demonstrate the use of BayesCal to calibrate the degenerate gain
parameters of full-Stokes simulated observations with a HERA-like hexagonal
close-packed redundant array, for three assumed levels of completeness of the a
priori known component of the calibration sky model. We compare the BayesCal
calibration solutions to those recovered by calibrating the degenerate gain
parameters with only the a priori known component of the calibration sky model
both with and without imposing physically motivated priors on the gain
amplitude solutions and for two choices of baseline length range over which to
calibrate. We find that BayesCal provides calibration solutions with up to four
orders of magnitude lower power in spurious gain amplitude fluctuations than
the calibration solutions derived for the same data set with the alternate
approaches, and between $\sim10^7$ and $\sim10^{10}$ times smaller than in the
mean degenerate gain amplitude on the full range of spectral scales accessible
in the data. Additionally, we find that in the scenarios modelled only BayesCal
has sufficiently high fidelity calibration solutions for unbiased recovery of
the 21 cm power spectrum on large spectral scales ($k_\parallel \lesssim
0.15~h\mathrm{Mpc}^{-1}$). In all other cases, in the completeness regimes
studied, those scales are contaminated. | astro-ph_IM |
Point Source Detection and Flux Determination with PGWave: One of the largest uncertainties in the Point Source (PS) studies, at
Fermi-LAT energies, is the uncertainty in the diffuse background. In general
there are two approaches for PS analysis: background-dependent methods, that
include modeling of the diffuse background, and background-independent methods.
In this work we study PGWave, which is one of the background-independent
methods, based on wavelet filtering to find significant clusters of gamma rays.
PGWave is already used in the Fermi-LAT catalog pipeline for finding candidate
sources. We test PGWave, not only for source detection, but especially to
estimate the flux without the need of a background model. We use Monte Carlo
(MC) simulation to study the accuracy of PS detection and estimation of the
flux. We present preliminary results of these MC studies. | astro-ph_IM |
Is HDF5 a good format to replace UVFITS?: The FITS (Flexible Image Transport System) data format was developed in the
late 1970s for storage and exchange of astronomy-related image data. Since
then, it has become a standard file format not only for images, but also for
radio interferometer data (e.g. UVFITS, FITS-IDI). But is FITS the right format
for next-generation telescopes to adopt? The newer Hierarchical Data Format
(HDF5) file format offers considerable advantages over FITS, but has yet to
gain widespread adoption within radio astronomy. One of the major holdbacks is
that HDF5 is not well supported by data reduction software packages. Here, we
present a comparison of FITS, HDF5, and the MeasurementSet (MS) format for
storage of interferometric data. In addition, we present a tool for converting
between formats. We show that the underlying data model of FITS can be ported
to HDF5, a first step toward achieving wider HDF5 support. | astro-ph_IM |
2HOT: An Improved Parallel Hashed Oct-Tree N-Body Algorithm for
Cosmological Simulation: We report on improvements made over the past two decades to our adaptive
treecode N-body method (HOT). A mathematical and computational approach to the
cosmological N-body problem is described, with performance and scalability
measured up to 256k ($2^{18}$) processors. We present error analysis and
scientific application results from a series of more than ten 69 billion
($4096^3$) particle cosmological simulations, accounting for $4 \times 10^{20}$
floating point operations. These results include the first simulations using
the new constraints on the standard model of cosmology from the Planck
satellite. Our simulations set a new standard for accuracy and scientific
throughput, while meeting or exceeding the computational efficiency of the
latest generation of hybrid TreePM N-body methods. | astro-ph_IM |
Apertif, Phased Array Feeds for the Westerbork Synthesis Radio Telescope: We describe the APERture Tile In Focus (Apertif) system, a phased array feed
(PAF) upgrade of the Westerbork Synthesis Radio Telescope which has transformed
this telescope into a high-sensitivity, wide field-of-view L-band imaging and
transient survey instrument. Using novel PAF technology, up to 40 partially
overlapping beams can be formed on the sky simultaneously, significantly
increasing the survey speed of the telescope. With this upgraded instrument, an
imaging survey covering an area of 2300 deg2 is being performed which will
deliver both continuum and spectral line data sets, of which the first data has
been publicly released. In addition, a time domain transient and pulsar survey
covering 15,000 deg2 is in progress. An overview of the Apertif science
drivers, hardware and software of the upgraded telescope is presented, along
with its key performance characteristics. | astro-ph_IM |
On Point Spread Function modelling: towards optimal interpolation: Point Spread Function (PSF) modeling is a central part of any astronomy data
analysis relying on measuring the shapes of objects. It is especially crucial
for weak gravitational lensing, in order to beat down systematics and allow one
to reach the full potential of weak lensing in measuring dark energy. A PSF
modeling pipeline is made of two main steps: the first one is to assess its
shape on stars, and the second is to interpolate it at any desired position
(usually galaxies). We focus on the second part, and compare different
interpolation schemes, including polynomial interpolation, radial basis
functions, Delaunay triangulation and Kriging. For that purpose, we develop
simulations of PSF fields, in which stars are built from a set of basis
functions defined from a Principal Components Analysis of a real ground-based
image. We find that Kriging gives the most reliable interpolation,
significantly better than the traditionally used polynomial interpolation. We
also note that although a Kriging interpolation on individual images is enough
to control systematics at the level necessary for current weak lensing surveys,
more elaborate techniques will have to be developed to reach future ambitious
surveys' requirements. | astro-ph_IM |
Two modified ILC methods to detect point sources in Cosmic Microwave
Background maps: We propose two detection techniques that take advantage of a small sky area
approximation and are based on modifications of the "internal linear
combination" (ILC) method, an approach widely used in Cosmology for the
separation of the various components that contribute to the microwave
background. The main advantage of the proposed approach, especially in handling
multi-frequency maps of the same region, is that it does not require the "a
priori" knowledge of the spatial power-spectrum of either the CMB and/or the
Galactic foreground. Hence, it is more robust, easier and more intuitive to
use. The performance of the proposed algorithms is tested with numerical
experiments that mimic the physical scenario expected for high Galactic
latitude observations with the Atacama Large Millimeter/submillimeter Array
(ALMA). | astro-ph_IM |
Three recipes for improving the image quality with optical long-baseline
interferometers: BFMC, LFF, \& DPSC: We present here three recipes for getting better images with optical
interferometers. Two of them, Low- Frequencies Filling and Brute-Force Monte
Carlo were used in our participation to the Interferometry Beauty Contest this
year and can be applied to classical imaging using V 2 and closure phases.
These two addition to image reconstruction provide a way of having more
reliable images. The last recipe is similar in its principle as the
self-calibration technique used in radio-interferometry. We call it also
self-calibration, but it uses the wavelength-differential phase as a proxy of
the object phase to build-up a full-featured complex visibility set of the
observed object. This technique needs a first image-reconstruction run with an
available software, using closure-phases and squared visibilities only. We used
it for two scientific papers with great success. We discuss here the pros and
cons of such imaging technique. | astro-ph_IM |
NEBULAR: A simple synthesis code for the hydrogen and helium nebular
spectrum: NEBULAR is a lightweight code to synthesize the spectrum of an ideal, mixed
hydrogen and helium gas in ionization equilibrium, over a useful range of
densities, temperatures and wavelengths. Free-free, free-bound and two-photon
continua are included as well as parts of the HI, HeI and HeII line series.
NEBULAR interpolates over publicly available data tables; it can be used to
easily extract information from these tables without prior knowledge about
their data structure. The resulting spectra can be used to e.g. determine
equivalent line widths, constrain the contribution of the nebular continuum to
a bandpass, and for educational purposes. NEBULAR can resample the spectrum on
a user-defined wavelength grid for direct comparison with an observed spectrum;
however, it can not be used to fit an observed spectrum. | astro-ph_IM |
Prospects for a radio air-shower detector at South Pole: IceCube is currently not only the largest neutrino telescope but also one of
the world's most competitive instruments for studying cosmic rays in the PeV to
EeV regime where the transition from galactic to extra-galactic sources should
occur. Further augmenting this observatory with an array of radio sensors in
the 10-100 MHz regime will additionally permit observation of the geomagnetic
radio emission from the air shower. Yielding complementary information on the
shower development a triple-technology array consisting of radio sensors, the
ground sampling stations of IceTop and the in-ice optical modules of IceCube,
should significantly improve the understanding of cosmic rays, as well as
enhance many aspects of the physics reach of the observatory. Here we present
first results from two exploratory setups deployed at the South Pole. Noise
measurements from data taken in two consecutive seasons show a very good
agreement of the predicted and observed response of the antennas designed
specifically for this purpose. The radio background is found to be highly
dominated by galactic noise with a striking absence of anthropogenic radio
emitters in the frequency band from 25-300 MHz. Motivated by the excellent
suitability of the location, we present first performance studies of a proposed
Radio Air-Shower Test Array (RASTA) using detailed MonteCarlo simulation and
discuss the prospects for its installation. | astro-ph_IM |
Subsets and Splits
No saved queries yet
Save your SQL queries to embed, download, and access them later. Queries will appear here once saved.