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Unrolling PALM for sparse semi-blind source separation: Sparse Blind Source Separation (BSS) has become a well established tool for a
wide range of applications - for instance, in astrophysics and remote sensing.
Classical sparse BSS methods, such as the Proximal Alternating Linearized
Minimization (PALM) algorithm, nevertheless often suffer from a difficult
hyperparameter choice, which undermines their results. To bypass this pitfall,
we propose in this work to build on the thriving field of algorithm
unfolding/unrolling. Unrolling PALM enables to leverage the data-driven
knowledge stemming from realistic simulations or ground-truth data by learning
both PALM hyperparameters and variables. In contrast to most existing unrolled
algorithms, which assume a fixed known dictionary during the training and
testing phases, this article further emphasizes on the ability to deal with
variable mixing matrices (a.k.a. dictionaries). The proposed Learned PALM
(LPALM) algorithm thus enables to perform semi-blind source separation, which
is key to increase the generalization of the learnt model in real-world
applications. We illustrate the relevance of LPALM in astrophysical
multispectral imaging: the algorithm not only needs up to $10^4-10^5$ times
fewer iterations than PALM, but also improves the separation quality, while
avoiding the cumbersome hyperparameter and initialization choice of PALM. We
further show that LPALM outperforms other unrolled source separation methods in
the semi-blind setting. | astro-ph_IM |
ATLAS Probe: Breakthrough Science of Galaxy Evolution, Cosmology, Milky
Way, and the Solar System: ATLAS (Astrophysics Telescope for Large Area Spectroscopy) is a concept for a
NASA probe-class space mission. It is the spectroscopic follow-up mission to
WFIRST, boosting its scientific return by obtaining deep NIR & MIR slit
spectroscopy for most of the galaxies imaged by the WFIRST High Latitude Survey
at z>0.5. ATLAS will measure accurate and precise redshifts for ~200M galaxies
out to z=7 and beyond, and deliver spectra that enable a wide range of
diagnostic studies of the physical properties of galaxies over most of cosmic
history. ATLAS and WFIRST together will produce a definitive 3D map of the
Universe over 2000 sq deg. ATLAS Science Goals are: (1) Discover how galaxies
have evolved in the cosmic web of dark matter from cosmic dawn through the peak
era of galaxy assembly. (2) Discover the nature of cosmic acceleration. (3)
Probe the Milky Way's dust-enshrouded regions, reaching the far side of our
Galaxy. (4) Discover the bulk compositional building blocks of planetesimals
formed in the outer Solar System. These flow down to the ATLAS Scientific
Objectives: (1A) Trace the relation between galaxies and dark matter with less
than 10% shot noise on relevant scales at 1<z<7. (1B) Probe the physics of
galaxy evolution at 1<z<7. (2) Obtain definitive measurements of dark energy
and tests of General Relativity. (3) Measure the 3D structure and stellar
content of the inner Milky Way to a distance of 25 kpc. (4) Detect and quantify
the composition of 3,000 planetesimals in the outer Solar System. ATLAS is a
1.5m telescope with a FoV of 0.4 sq deg, and uses Digital Micro-mirror Devices
(DMDs) as slit selectors. It has a spectroscopic resolution of R = 1000, and a
wavelength range of 1-4 microns. ATLAS has an unprecedented spectroscopic
capability based on DMDs, with a spectroscopic multiplex factor ~6,000. ATLAS
is designed to fit within the NASA probe-class space mission cost envelope. | astro-ph_IM |
Speckle Suppression Through Dual Imaging Polarimetry, and a Ground-Based
Image of the HR 4796A Circumstellar Disk: We demonstrate the versatility of a dual imaging polarimeter working in
tandem with a Lyot coronagraph and Adaptive Optics to suppress the highly
static speckle noise pattern--the greatest hindrance to ground-based direct
imaging of planets and disks around nearby stars. Using a double difference
technique with the polarimetric data, we quantify the level of speckle
suppression, and hence improved sensitivity, by placing an ensemble of
artificial faint companions into real data, with given total brightness and
polarization. For highly polarized sources within 0.5 arcsec, we show that we
achieve 3 to 4 magnitudes greater sensitivity through polarimetric speckle
suppression than simply using a coronagraph coupled to a high-order Adaptive
Optics system. Using such a polarimeter with a classical Lyot coronagraph at
the 3.63m AEOS telescope, we have obtained a 6.5 sigma detection in the H-band
of the 76 AU diameter circumstellar debris disk around the star HR 4796A. Our
data represent the first definitive, ground-based, near-IR polarimetric image
of the HR 4796A debris disk and clearly show the two outer ansae of the disk,
evident in Hubble Space Telescope NICMOS/STIS imaging. We derive a lower limit
to the fractional linear polarization of 29% caused by dust grains in the disk.
In addition, we fit simple morphological models of optically thin disks to our
data allowing us to constrain the dust disk scale height to 2.5{+5.0}_{-1.3} AU
and scattering asymmetry parameter (g=0.20^{+.07}_{-.10}). These values are
consistent with several lines of evidence suggesting that the HR 4796A disk is
dominated by a micron-sized dust population, and are indeed typical of disks in
transition between those surrounding the Herbig Ae stars to those associated
with Vega-like stars. | astro-ph_IM |
Characterization of the seismic field at Virgo and improved estimates of
Newtonian-noise suppression by recesses: Fluctuations of gravitational forces cause so-called Newtonian noise (NN) in
gravitational-wave (GW) detectors which is expected to limit their
low-frequency sensitivity in upcoming observing runs. Seismic NN is produced by
seismic waves passing near a detector's suspended test masses. It is predicted
to be the strongest contribution to NN. Modeling this contribution accurately
is a major challenge. Arrays of seismometers were deployed at the Virgo site to
characterize the seismic field near the four test masses. In this paper, we
present results of a spectral analysis of the array data from one of Virgo's
end buildings to identify dominant modes of the seismic field. Some of the
modes can be associated with known seismic sources. Analyzing the modes over a
range of frequencies, we provide a dispersion curve of Rayleigh waves. We find
that the Rayleigh speed in the NN frequency band 10 Hz - 20 Hz is very low
($\lesssim$100\,m/s), which has important consequences for Virgo's seismic NN.
Using the new speed estimate, we find that the recess formed under the
suspended test masses by a basement level at the end buildings leads to a 10
fold reduction of seismic NN. | astro-ph_IM |
An Updated Ultraviolet Calibration for the Swift/UVOT: We present an updated calibration of the Swift/UVOT broadband ultraviolet
(uvw1, uvm2, and uvw2) filters. The new calibration accounts for the ~1% per
year decline in the UVOT sensitivity observed in all filters, and makes use of
additional calibration sources with a wider range of colours and with HST
spectrophotometry. In this paper we present the new effective area curves and
instrumental photometric zeropoints and compare with the previous calibration. | astro-ph_IM |
Influence of the Earth on the background and the sensitivity of the GRM
and ECLAIRs instruments aboard the Chinese-French mission SVOM: SVOM (Space-based multi-band astronomical Variable Object Monitor) is a
future Chinese-French satellite mission which is dedicated to Gamma-Ray Burst
(GRB) studies. Its anti-solar pointing strategy makes the Earth cross the field
of view of its payload every orbit. In this paper, we present the variations of
the gamma-ray background of the two high energy instruments aboard SVOM, the
Gamma-Ray Monitor (GRM) and ECLAIRs, as a function of the Earth position. We
conclude with an estimate of the Earth influence on their sensitivity and their
GRB detection capability. | astro-ph_IM |
Background studies for acoustic neutrino detection at the South Pole: The detection of acoustic signals from ultra-high energy neutrino
interactions is a promising method to measure the tiny flux of cosmogenic
neutrinos expected on Earth. The energy threshold for this process depends
strongly on the absolute noise level in the target material. The South Pole
Acoustic Test Setup (SPATS), deployed in the upper part of four boreholes of
the IceCube Neutrino Observatory, has monitored the noise in Antarctic ice at
the geographic South Pole for more than two years down to 500 m depth. The
noise is very stable and Gaussian distributed. Lacking an in-situ calibration
up to now, laboratory measurements have been used to estimate the absolute
noise level in the 10 to 50 kHz frequency range to be smaller than 20 mPa.
Using a threshold trigger, sensors of the South Pole Acoustic Test Setup
registered acoustic pulse-like events in the IceCube detector volume and its
vicinity. Acoustic signals from refreezing IceCube holes and from anthropogenic
sources have been used to localize acoustic events. Monte Carlo simulations of
sound propagating from the established sources to the SPATS sensors have
allowed to check corresponding model expectations. An upper limit on the
neutrino flux at energies $E_\nu > 10^{11}$ GeV is derived from acoustic data
taken over eight months. | astro-ph_IM |
Data downloaded via parachute from a NASA super-pressure balloon: In April to May 2023, the superBIT telescope was lifted to the Earth's
stratosphere by a helium-filled super-pressure balloon, to acquire astronomical
imaging from above (99.5% of) the Earth's atmosphere. It was launched from New
Zealand then, for 40 days, circumnavigated the globe five times at a latitude
40 to 50 degrees South. Attached to the telescope were four 'DRS' (Data
Recovery System) capsules containing 5 TB solid state data storage, plus a GNSS
receiver, Iridium transmitter, and parachute. Data from the telescope were
copied to these, and two were dropped over Argentina. They drifted 61 km
horizontally while they descended 32 km, but we predicted their descent vectors
within 2.4 km: in this location, the discrepancy appears irreducible below 2 km
because of high speed, gusty winds and local topography. The capsules then
reported their own locations to within a few metres. We recovered the capsules
and successfully retrieved all of superBIT's data - despite the telescope
itself being later destroyed on landing. | astro-ph_IM |
21 cm observations: calibration, strategies, observables: This chapter aims to provide a review of the basics of 21 cm interferometric
observations and its methodologies. A summary of the main concepts of radio
interferometry and their connection with the 21 cm observables - power spectra
and images - is presented. I then provide a review of interferometric
calibration and its interplay with foreground separation, including the current
open challenges in calibration of 21 cm observations. Finally, a review of 21
cm instrument designs in the light of calibration choices and observing
strategies follows. | astro-ph_IM |
On-sky closed loop correction of atmospheric dispersion for
high-contrast coronagraphy and astrometry: Adaptive optic (AO) systems delivering high levels of wavefront correction
are now common at observatories. One of the main limitations to image quality
after wavefront correction comes from atmospheric refraction. An Atmospheric
dispersion compensator (ADC) is employed to correct for atmospheric refraction.
The correction is applied based on a look-up table consisting of dispersion
values as a function of telescope elevation angle. The look-up table based
correction of atmospheric dispersion results in imperfect compensation leading
to the presence of residual dispersion in the point-spread function (PSF) and
is insufficient when sub-milliarcsecond precision is required. The presence of
residual dispersion can limit the achievable contrast while employing
high-performance coronagraphs or can compromise high-precision astrometric
measurements. In this paper, we present the first on-sky closed-loop correction
of atmospheric dispersion by directly using science path images. The concept
behind the measurement of dispersion utilizes the chromatic scaling of focal
plane speckles. An adaptive speckle grid generated with a deformable mirror
(DM) that has a sufficiently large number of actuators is used to accurately
measure the residual dispersion and subsequently correct it by driving the ADC.
We have demonstrated with the Subaru Coronagraphic Extreme AO (SCExAO) system
on-sky closed-loop correction of residual dispersion to < 1 mas across H-band.
This work will aid in the direct detection of habitable exoplanets with
upcoming extremely large telescopes (ELTs) and also provide a diagnostic tool
to test the performance of instruments which require sub-milliarcsecond
correction. | astro-ph_IM |
MKID, an energy sensitive superconducting detector for the next
generation of XAO: Selected for the next generation of adaptive optics (AO) systems, the pyramid
wavefront sensor (PWFS) is recognised for its closed AO loop performance. As
new technologies are emerging, it is necessary to explore new methods to
improve it. Microwave Kinetic Inductance Detectors (MKID) are photon-counting
devices that measure the arrival time and energy of each incident photon,
providing new capabilities over existing detectors and significant AO
performance benefits. After developing a multi-wavelength PWFS simulation, we
study the benefits of using an energy sensitive detector, analyse the PWFS
performance according to wavelength and explore the possibility of using
fainter natural guide stars by widening the bandpass of the wavefront sensor. | astro-ph_IM |
Experimental Realization of an Achromatic Magnetic Mirror based on
Metamaterials: Our work relates to the use of metamaterials engineered to realize a
meta-surface approaching the exotic properties of an ideal object not observed
in nature, a "magnetic mirror". Previous realizations were based on resonant
structures which implied narrow bandwidths and large losses. The working
principle of our device is ideally frequency-independent, it does not involve
resonances and it does not rely on a specific technology. The performance of
our prototype, working at millimetre wavelengths, has never been achieved
before and it is superior to any other device reported in the literature, both
in the microwave and optical regions. The device inherently has large bandwidth
(144%), low losses (<1 %) and is almost independent of incidence-angle and
polarization-state and thus approaches the behaviour of an ideal magnetic
mirror. Applications of magnetic mirrors range from low-profile antennas,
absorbers to optoelectronic devices. Our device can be realised using different
technologies to operate in other spectral regions. | astro-ph_IM |
Extended-Path Intensity Correlation: Microarcsecond Astrometry with an
Arcsecond Field of View: We develop in detail a recently proposed optical-path modification of
astronomical intensity interferometers. Extended-Path Intensity Correlation
(EPIC) introduces a tunable path extension, enabling differential astrometry of
multiple compact sources such as stars and quasars at separations of up to a
few arcseconds. Combined with other recent technological advances in
spectroscopy and fast single-photon detection, a ground-based intensity
interferometer array can achieve microarcsecond resolution and even better
light-centroiding accuracy on bright sources of magnitude $m \lesssim 15$. We
lay out the theory and technical requirements of EPIC, and discuss the
scientific potential. Promising applications include astrometric lensing of
stars and quasar images, binary-orbit characterization, exoplanet detection,
Galactic acceleration measurements and calibration of the cosmic distance
ladder. The introduction of the path extension thus significantly increases the
scope of intensity interferometry while reaching unprecedented levels of
relative astrometric precision. | astro-ph_IM |
Deep learning of quasar lightcurves in the LSST era: Deep learning techniques are required for the analysis of synoptic
(multi-band and multi-epoch) light curves in massive data of quasars, as
expected from the Vera C. Rubin Observatory Legacy Survey of Space and Time
(LSST). In this follow-up study, we introduced an upgraded version of a
conditional neural process (CNP) embedded in a multistep approach for analysis
of large data of quasars in the LSST Active Galactic Nuclei Scientific
Collaboration data challenge database. We present a case study of a stratified
set of the u-band light curves for 283 quasars with very low variability $\sim
0.03$. In this sample, CNP average mean square error is found to be $\sim 5\%
$($\sim 0.5$ mag). Interestingly, beside similar level of variability there are
indications that individual light curves show flare like features. According to
preliminary structure function analysis, these occurrences may be associated to
microlensing events with larger time scales $5-10$ years. | astro-ph_IM |
GAMMA-LIGHT: High-Energy Astrophysics above 10 MeV: High-energy phenomena in the cosmos, and in particular processes leading to
the emission of gamma- rays in the energy range 10 MeV - 100 GeV, play a very
special role in the understanding of our Universe. This energy range is indeed
associated with non-thermal phenomena and challenging particle acceleration
processes. The technology involved in detecting gamma-rays is challenging and
drives our ability to develop improved instruments for a large variety of
applications. GAMMA-LIGHT is a Small Mission which aims at an unprecedented
advance of our knowledge in many sectors of astrophysical and Earth studies
research. The Mission will open a new observational window in the low-energy
gamma-ray range 10-50 MeV, and is configured to make substantial advances
compared with the previous and current gamma-ray experiments (AGILE and Fermi).
The improvement is based on an exquisite angular resolution achieved by
GAMMA-LIGHT using state-of-the-art Silicon technology with innovative data
acquisition. GAMMA-LIGHT will address all astrophysics issues left open by the
current generation of instruments. In particular, the breakthrough angular
resolution in the energy range 100 MeV - 1 GeV is crucial to resolve patchy and
complex features of diffuse sources in the Galaxy as well as increasing the
point source sensitivity. This proposal addresses scientific topics of great
interest to the community, with particular emphasis on multifrequency
correlation studies involving radio, optical, IR, X-ray, soft gamma-ray and TeV
emission. At the end of this decade several new observatories will be
operational including LOFAR, SKA, ALMA, HAWK, CTA. GAMMA-LIGHT will "fill the
vacuum" in the 10 MeV-10 GeV band, and will provide invaluable data for the
understanding of cosmic and terrestrial high-energy sources. | astro-ph_IM |
A Real-time Coherent Dedispersion Pipeline for the Giant Metrewave Radio
Telescope: A fully real-time coherent dedispersion system has been developed for the
pulsar back-end at the Giant Metrewave Radio Telescope (GMRT). The dedispersion
pipeline uses the single phased array voltage beam produced by the existing
GMRT software back-end (GSB) to produce coherently dedispersed intensity output
in real time, for the currently operational bandwidths of 16 MHz and 32 MHz.
Provision has also been made to coherently dedisperse voltage beam data from
observations recorded on disk.
We discuss the design and implementation of the real-time coherent
dedispersion system, describing the steps carried out to optimise the
performance of the pipeline. Presently functioning on an Intel Xeon X5550 CPU
equipped with a NVIDIA Tesla C2075 GPU, the pipeline allows dispersion free,
high time resolution data to be obtained in real-time. We illustrate the
significant improvements over the existing incoherent dedispersion system at
the GMRT, and present some preliminary results obtained from studies of pulsars
using this system, demonstrating its potential as a useful tool for low
frequency pulsar observations.
We describe the salient features of our implementation, comparing it with
other recently developed real-time coherent dedispersion systems. This
implementation of a real-time coherent dedispersion pipeline for a large, low
frequency array instrument like the GMRT, will enable long-term observing
programs using coherent dedispersion to be carried out routinely at the
observatory. We also outline the possible improvements for such a pipeline,
including prospects for the upgraded GMRT which will have bandwidths about ten
times larger than at present. | astro-ph_IM |
A graph-based spectral classification of Type II supernovae: Given the ever-increasing number of time-domain astronomical surveys,
employing robust, interpretative, and automated data-driven classification
schemes is pivotal. Based on graph theory, we present new data-driven
classification heuristics for spectral data. A spectral classification scheme
of Type II supernovae (SNe II) is proposed based on the phase relative to the
maximum light in the $V$ band and the end of the plateau phase. We utilize a
compiled optical data set that comprises 145 SNe and 1595 optical spectra in
4000-9000 $\overset{\circ}{\mathrm {A}}$. Our classification method naturally
identifies outliers and arranges the different SNe in terms of their major
spectral features. We compare our approach to the off-the-shelf umap manifold
learning and show that both strategies are consistent with a continuous
variation of spectral types rather than discrete families. The automated
classification naturally reflects the fast evolution of Type II SNe around the
maximum light while showcasing their homogeneity close to the end of the
plateau phase. The scheme we develop could be more widely applicable to
unsupervised time series classification or characterisation of other functional
data. | astro-ph_IM |
Single-pulse classifier for the LOFAR Tied-Array All-sky Survey: Searches for millisecond-duration, dispersed single pulses have become a
standard tool used during radio pulsar surveys in the last decade. They have
enabled the discovery of two new classes of sources: rotating radio transients
and fast radio bursts. However, we are now in a regime where the sensitivity to
single pulses in radio surveys is often limited more by the strong background
of radio frequency interference (RFI, which can greatly increase the
false-positive rate) than by the sensitivity of the telescope itself. To
mitigate this problem, we introduce the Single-pulse Searcher (SpS). This is a
new machine-learning classifier designed to identify astrophysical signals in a
strong RFI environment, and optimized to process the large data volumes
produced by the new generation of aperture array telescopes. It has been
specifically developed for the LOFAR Tied-Array All-Sky Survey (LOTAAS), an
ongoing survey for pulsars and fast radio transients in the northern
hemisphere. During its development, SpS discovered 7 new pulsars and blindly
identified ~80 known sources. The modular design of the software offers the
possibility to easily adapt it to other studies with different instruments and
characteristics. Indeed, SpS has already been used in other projects, e.g. to
identify pulses from the fast radio burst source FRB 121102. The software
development is complete and SpS is now being used to re-process all LOTAAS data
collected to date. | astro-ph_IM |
Unsupervised self-organised mapping: a versatile empirical tool for
object selection, classification and redshift estimation in large surveys: We present an application of unsupervised machine learning - the
self-organised map (SOM) - as a tool for visualising, exploring and mining the
catalogues of large astronomical surveys. Self-organisation culminates in a
low-resolution representation of the 'topology' of a parameter volume, and this
can be exploited in various ways pertinent to astronomy. Using data from the
Cosmological Evolution Survey (COSMOS), we demonstrate two key astronomical
applications of the SOM: (i) object classification and selection, using the
example of galaxies with active galactic nuclei as a demonstration, and (ii)
photometric redshift estimation, illustrating how SOMs can be used as totally
empirical predictive tools. With a training set of ~3800 galaxies with
z_spec<1, we achieve photometric redshift accuracies competitive with other
(mainly template fitting) techniques that use a similar number of photometric
bands (sigma(Dz)=0.03 with a ~2% outlier rate when using u*-band to 8um
photometry). We also test the SOM as a photo-z tool using the PHoto-z Accuracy
Testing (PHAT) synthetic catalogue of Hildebrandt et al. (2010), which compares
several different photo-z codes using a common input/training set. We find that
the SOM can deliver accuracies that are competitive with many of the
established template-fitting and empirical methods. This technique is not
without clear limitations, which are discussed, but we suggest it could be a
powerful tool in the era of extremely large - 'petabyte' - databases where
efficient data-mining is a paramount concern. | astro-ph_IM |
The Burke-Gaffney Observatory: A fully roboticized remote-access
observatory with a low resolution spectrograph: We describe the current state of the Burke-Gaffney Observatory (BGO) at Saint
Mary's University - a unique fully roboticized remote-access observatory that
allows students to carry out imaging, photometry, and spectroscopy projects
remotely from anywhere in the world via a web browser or social media. Stellar
spectroscopy is available with the ALPY 600 low resolution grism spectrograph
equipped with a CCD detector. We describe our custom CCD spectroscopy reduction
procedure written in the Python programming language and demonstrate the
quality of fits of synthetic spectra computed with the ChromaStarServer (CSS)
code to BGO spectra. The facility along with the accompanying Python BGO
spectroscopy reduction package and the CSS spectrum synthesis code provide an
accessible means for students anywhere to carry our projects at the
undergraduate honours level. BGO web pages for potential observers are at the
site: observatory.smu.ca/bgo-useme. All codes are available from the OpenStars
www site: openstars.smu.ca/ | astro-ph_IM |
Towards the MICADO@ELT PSF-R with simulated and real data: Observations close to the diffraction limit, with high Strehl ratios from
Adaptive Optics (AO)-assisted instruments mounted on ground-based telescopes
are a reality and will become even more widespread with the next generation
instruments that equip 30 meter-class telescopes. This results in a growing
interest in tools and methods to accurately reconstruct the observed Point
Spread Function (PSF) of AO systems. We will discuss the performance of the PSF
reconstruction (PSF-R) software developed in the context of the MICADO
instrument of the Extremely Large Telescope. In particular, we have recently
implemented a novel algorithm for reconstructing off-axis PSFs. In every case,
the PSF is reconstructed from AO telemetry, without making use of science
exposures. We will present the results coming from end-to-end simulations and
real AO observations, covering a wide range of observing conditions.
Specifically, the spatial variation of the PSF has been studied with different
AO-reference star magnitudes. The reconstructed PSFs are observed to match the
reference ones with a relative error in Strehl ratio and full-width at half
maximum below 10% over a field of view of the order of one arcmin, making the
proposed PSF-R method an appealing tool to assist observation analysis, and
interpretation. | astro-ph_IM |
First Light for the First Station of the Long Wavelength Array: The first station of the Long Wavelength Array (LWA1) was completed in April
2011 and is currently performing observations resulting from its first call for
proposals in addition to a continuing program of commissioning and
characterization observations. The instrument consists of 258 dual-polarization
dipoles, which are digitized and combined into beams. Four
independently-steerable dual-polarization beams are available, each with two
"tunings" of 16 MHz bandwidth that can be independently tuned to any frequency
between 10 MHz and 88 MHz. The system equivalent flux density for zenith
pointing is ~3 kJy and is approximately independent of frequency; this
corresponds to a sensitivity of ~5 Jy/beam (5sigma, 1 s); making it one of the
most sensitive meter-wavelength radio telescopes. LWA1 also has two "transient
buffer" modes which allow coherent recording from all dipoles simultaneously,
providing instantaneous all-sky field of view. LWA1 provides versatile and
unique new capabilities for Galactic science, pulsar science, solar and
planetary science, space weather, cosmology, and searches for astrophysical
transients. Results from LWA1 will detect or tightly constrain the presence of
hot Jupiters within 50 parsecs of Earth. LWA1 will provide excellent resolution
in frequency and in time to examine phenomena such as solar bursts, and pulsars
over a 4:1 frequency range that includes the poorly understood turnover and
steep-spectrum regimes. Observations to date have proven LWA1's potential for
pulsar observing, and just a few seconds with the completed 256-dipole LWA1
provide the most sensitive images of the sky at 23 MHz obtained yet. We are
operating LWA1 as an open skies radio observatory, offering ~2000 beam-hours
per year to the general community. | astro-ph_IM |
Pipe3D, a pipeline to analyze Integral Field Spectroscopy data: I. New
fitting phylosophy of FIT3D: We present an improved version of FIT3D, a fitting tool for the analysis of
the spectroscopic properties of the stellar populations and the ionized gas
derived from moderate resolution spectra of galaxies. FIT3D is a tool developed
to analyze Integral Field Spectroscopy data and it is the basis of Pipe3D, a
pipeline already used in the analysis of datasets like CALIFA, MaNGA, and SAMI.
We describe the philosophy behind the fitting procedure, and in detail each of
the different steps in the analysis. We present an extensive set of simulations
in order to estimate the precision and accuracy of the derived parameters for
the stellar populations. In summary, we find that using different stellar
population templates we reproduce the mean properties of the stellar population
(age, metallicity, and dust attenuation) within ~0.1 dex. A similar approach is
adopted for the ionized gas, where a set of simulated emission- line systems
was created. Finally, we compare the results of the analysis using FIT3D with
those provided by other widely used packages for the analysis of the stellar
population (Starlight, Steckmap, and analysis based on stellar indices) using
real high S/N data. In general we find that the parameters for the stellar
populations derived by FIT3D are fully compatible with those derived using
these other tools. | astro-ph_IM |
The Ecological Impact of High-performance Computing in Astrophysics: The importance of computing in astronomy continues to increase, and so is its
impact on the environment. When analyzing data or performing simulations, most
researchers raise concerns about the time to reach a solution rather than its
impact on the environment. Luckily, a reduced time-to-solution due to faster
hardware or optimizations in the software generally also leads to a smaller
carbon footprint. This is not the case when the reduced wall-clock time is
achieved by overclocking the processor, or when using supercomputers.
The increase in the popularity of interpreted scripting languages, and the
general availability of high-performance workstations form a considerable
threat to the environment. A similar concern can be raised about the trend of
running single-core instead of adopting efficient many-core programming
paradigms.
In astronomy, computing is among the top producers of green-house gasses,
surpassing telescope operations. Here I hope to raise the awareness of the
environmental impact of running non-optimized code on overpowered computer
hardware. | astro-ph_IM |
emcee: The MCMC Hammer: We introduce a stable, well tested Python implementation of the
affine-invariant ensemble sampler for Markov chain Monte Carlo (MCMC) proposed
by Goodman & Weare (2010). The code is open source and has already been used in
several published projects in the astrophysics literature. The algorithm behind
emcee has several advantages over traditional MCMC sampling methods and it has
excellent performance as measured by the autocorrelation time (or function
calls per independent sample). One major advantage of the algorithm is that it
requires hand-tuning of only 1 or 2 parameters compared to $\sim N^2$ for a
traditional algorithm in an N-dimensional parameter space. In this document, we
describe the algorithm and the details of our implementation and API.
Exploiting the parallelism of the ensemble method, emcee permits any user to
take advantage of multiple CPU cores without extra effort. The code is
available online at http://dan.iel.fm/emcee under the MIT License. | astro-ph_IM |
Analysis of Galactic molecular cloud polarization maps: a review of the
methods: The Davis-Chandrasekhar-Fermi (DCF) method using the Angular Dispersion
Function (ADF), the Histogram of Relative Orientations (HROs) and the
Polarization-Intensity Gradient Relation (P-IGR) are the most common tools used
to analyse maps of linearly polarized emission by thermal dust grains at
submilliter wavelengths in molecular clouds and star-forming regions. A short
review of these methods is given. The combination of these methods will provide
valuable tools to shed light on the impact of the magnetic fields on the
formation and evolution of subparsec scale hub-filaments that will be mapped
with the NIKA2 camera and future experiments. | astro-ph_IM |
ASTRO2020 White Paper: JWST: Probing the Epoch of Reionization with a
Wide Field Time-Domain Survey: A major scientific goal of JWST is to probe the epoch of re-ionization of the
Universe at z above 6, and up to 20 and beyond. At these redshifts, galaxies
are just beginning to form and the observable objects are early black holes,
supernovae, and cosmic infrared background. The JWST has the necessary
sensitivity to observe these targets individually, but a public deep and wide
science enabling survey in the wavelength range from 2-5 $\mu$m is needed to
discover these black holes and supernovae and to cover the area large enough
for cosmic infrared background to be reliably studied. This enabling survey
will also discover a large number of other transients and enable sciences such
as supernova cosmology up to z $\sim$ 5, star formation history at high
redshift through supernova explosions, faint stellar objects in the Milky Way,
and galaxy evolution up to z approaching 10. The results of this survey will
also serve as an invaluable target feeder for the upcoming era of ELT and SKA. | astro-ph_IM |
Testing the variation of fundamental constants by astrophysical methods:
overview and prospects: By measuring the fundamental constants in astrophysical objects one can test
basic physical principles as space-time invariance of physical laws along with
probing the applicability limits of the standard model of particle physics. The
latest constraints on the fine structure constant alpha and the
electron-to-proton mass ratio mu obtained from observations at high redshifts
and in the Milky Way disk are reviewed. In optical range, the most accurate
measurements have already reached the sensitivity limit of available
instruments, and further improvements will be possible only with next
generation of telescopes and receivers. New methods of the wavelength
calibration should be realized to control systematic errors at the sub-pixel
level. In radio sector, the main tasks are the search for galactic and
extragalactic objects suitable for precise molecular spectroscopy as well as
high resolution laboratory measurements of molecular lines to provide accurate
frequency standards. The expected progress in the optical and radio
astrophysical observations is quantified. | astro-ph_IM |
On the measurements of numerical viscosity and resistivity in Eulerian
MHD codes: We propose a simple ansatz for estimating the value of the numerical
resistivity and the numerical viscosity of any Eulerian MHD code. We test this
ansatz with the help of simulations of the propagation of (magneto)sonic waves,
Alfven waves, and the tearing mode instability using the MHD code Aenus. By
comparing the simu- lation results with analytical solutions of the
resistive-viscous MHD equations and an empirical ansatz for the growth rate of
tearing modes we measure the numerical viscosity and resistivity of Aenus. The
comparison shows that the fast-magnetosonic speed and wavelength are the
characteristic velocity and length, respectively, of the aforementioned
(relatively simple) systems. We also determine the dependance of the numerical
viscosity and resistivity on the time integration method, the spatial
reconstruction scheme and (to a lesser extent) the Riemann solver employed in
the simulations. From the measured results we infer the numerical resolution
(as a function of the spatial reconstruction method) required to properly
resolve the growth and saturation level of the magnetic field amplified by the
magnetorotational instability in the post-collapsed core of massive stars. Our
results show that it is to the best advantage to resort to ultra-high order
methods (e.g., 9th-order Monotonicity Preserving method) to tackle this problem
properly, in particular in three dimensional simulations. | astro-ph_IM |
The Pierre Auger Observatory Upgrade - Preliminary Design Report: The Pierre Auger Observatory has begun a major Upgrade of its already
impressive capabilities, with an emphasis on improved mass composition
determination using the surface detectors of the Observatory. Known as
AugerPrime, the upgrade will include new 4 m$^2$ plastic scintillator detectors
on top of all 1660 water-Cherenkov detectors, updated and more flexible surface
detector electronics, a large array of buried muon detectors, and an extended
duty cycle for operations of the fluorescence detectors. This Preliminary
Design Report was produced by the Collaboration in April 2015 as an internal
document and information for funding agencies. It outlines the scientific and
technical case for AugerPrime. We now release it to the public via the arXiv
server. We invite you to review the large number of fundamental results already
achieved by the Observatory and our plans for the future. | astro-ph_IM |
Possibility of Terahertz Observations at the ALMA site: Observational rates under terahertz (THz) opacities less than 3.0 and 2.0 at
the Atacama Large Millimeter/submillimeter Array (ALMA) site have been
calculated using the 225 GHz tipping radiometer monitoring data and the opacity
correlation between 225 GHz and THz opacities. The observational rate with THz
opacity condition less than 3.0 is 12.4% in a year, and in winter (November -
April) it is about twice higher than in summer (May - October). This
observational rate shows a large sinusoidal annual variation, and it seems to
have relation with the El Ni\~no and La Ni\~na phenomena; the La Ni\~na years
tend to have high observational rates, but the El Ni\~no years show low rates.
On the other hand, the observational rate with the THz opacity condition less
than 2.0 is only 1.9%, and no obvious annual and seasonal variations are
observed. This indicates that THz observations under low opacity condition of
less than 2.0 at the ALMA site are very difficult to be performed. | astro-ph_IM |
Detecting Dispersed Radio Transients in Real Time Using Convolutional
Neural Networks: We present a methodology for automated real-time analysis of a radio image
data stream with the goal to find transient sources. Contrary to previous
works, the transients we are interested in occur on a time-scale where
dispersion starts to play a role, so we must search a higher-dimensional data
space and yet work fast enough to keep up with the data stream in real time.
The approach consists of five main steps: quality control, source detection,
association, flux measurement, and physical parameter inference. We present
parallelized methods based on convolutions and filters that can be accelerated
on a GPU, allowing the pipeline to run in real-time. In the parameter inference
step, we apply a convolutional neural network to dynamic spectra that were
obtained from the preceding steps. It infers physical parameters, among which
the dispersion measure of the transient candidate. Based on critical values of
these parameters, an alert can be sent out and data will be saved for further
investigation. Experimentally, the pipeline is applied to simulated data and
images from AARTFAAC (Amsterdam Astron Radio Transients Facility And Analysis
Centre), a transients facility based on the Low-Frequency Array (LOFAR).
Results on simulated data show the efficacy of the pipeline, and from real data
it discovered dispersed pulses. The current work targets transients on time
scales that are longer than the fast transients of beam-formed search, but
shorter than slow transients in which dispersion matters less. This fills a
methodological gap that is relevant for the upcoming Square-Kilometer Array
(SKA). Additionally, since real-time analysis can be performed, only data with
promising detections can be saved to disk, providing a solution to the big-data
problem that modern astronomy is dealing with. | astro-ph_IM |
The Compton-Pair telescope: A prototype for a next-generation MeV
$γ$-ray observatory: The Compton Pair (ComPair) telescope is a prototype that aims to develop the
necessary technologies for future medium energy gamma-ray missions and to
design, build, and test the prototype in a gamma-ray beam and balloon flight.
The ComPair team has built an instrument that consists of 4 detector
subsystems: a double-sided silicon strip detector Tracker, a novel
high-resolution virtual Frisch-grid cadmium zinc telluride Calorimeter, and a
high-energy hodoscopic cesium iodide Calorimeter, all of which are surrounded
by a plastic scintillator anti-coincidence detector. These subsystems together
detect and characterize photons via Compton scattering and pair production,
enable a veto of cosmic rays, and are a proof-of-concept for a space telescope
with the same architecture. A future medium-energy gamma-ray mission enabled
through ComPair will address many questions posed in the Astro2020 Decadal
survey in both the New Messengers and New Physics and the Cosmic Ecosystems
themes. In this contribution, we will give an overview of the ComPair project
and steps forward to the balloon flight. | astro-ph_IM |
Effects of the Number of Active Receiver Channels on the Sensitivity of
a Reflector Antenna System with a Multi-Beam Wideband Phased Array Feed: A method for modeling a reflector antenna system with a wideband phased array
feed is presented and used to study the effects of the number of active antenna
elements and associated receiving channels on the sensitivity of the system.
Numerical results are shown for a practical system named APERTIF that is
currently under developed at The Netherlands Institute for Radio Astronomy
(ASTRON) | astro-ph_IM |
Optical amplification for astronomical imaging at higher resolution: Heisenberg's uncertainty principle tells us that it is impossible to
determine simultaneously the position of a photon crossing a telescope's
aperture and its momentum. Super-resolution imaging techniques rely on
modification of the observed sample, or on entangling photons. In astronomy we
have no access to the object, but resolution may be improved by optical
amplification. Unfortunately, spontaneous emission contributes noise and
negates the possible gain from stimulated emissions. We show that it is
possible to increase the weight of the stimulated photons by considering photon
statistics, and observe an improvement in resolution. Most importantly, we
demonstrate a method which can apply for all imaging purposes. | astro-ph_IM |
MCAO for the European Solar Telescope: first results: We analise the efficiency of wavefront reconstruction in the MultiConjugate
Adaptive Optics system for the European Solar Telescope (EST). We present
preliminary results derived from numerical simulations. We study a 4 meter
class telescope with multiple deformable mirrors conjugated at variable
heights. Along with common issues, difficulties peculiar to the solar case have
to be considered, such as the low contrast and extended nature of the natural
guide features. Our findings identify basic requirements for the EST Adaptive
Optics system and show some of its capabilities. | astro-ph_IM |
Simulation of Stray Light Contamination on CHEOPS Detector: The aim of this work is to quantify the amount of Earth stray light that
reaches the CHEOPS (CHaracterising ExOPlanets Satellite) detector. It will
carry out follow-up measurements on transiting planets. This requires exquisite
data that can be acquired only by a space-borne observatory and by well
understood and mitigated sources of noise. Earth stray light is one of them
which becomes the most prominent noise for faint stars.
A software suite was developed to evaluate the contamination by the stray
light. As the satellite will be launched in late 2017, the year 2018 is
analysed for three different altitudes. Given an visible region at any time,
the stray light contamination is simulated at the entrance of the telescope.
The amount that reaches the detector is, however, much lower, as it is reduced
by the point source transmittance function.
Information about the faintest star visible in any direction in the sky is
therefore available and is compared to a potential list of targets. The
influence of both the visibility region and the unavoidable South Atlantic
Anomaly are also studied as well as the effect of a changing optical assembly.
A methodology to compute the visible region of the sky and the stray light flux
is described. Techniques to prepare the scheduling of the observation and a
possible way of calibrating the dark current and the map of hot pixels are
presented.
The simulations show that there are seasonal variations on the amount of flux
received and on the altitude. However, the South Atlantic Anomaly impacts more
direly higher orbits. This high radiation region demand the interruption of the
science operations. Even if the viewing zone at low altitude is smaller, the
availability of instrument is greater. There exist two favoured regions for the
observations. The field of view is the widest then as the plane of the orbit
and of the terminator merge. | astro-ph_IM |
The Gaia mission: Gaia is a cornerstone mission in the science programme of the European Space
Agency (ESA). The spacecraft construction was approved in 2006, following a
study in which the original interferometric concept was changed to a
direct-imaging approach. Both the spacecraft and the payload were built by
European industry. The involvement of the scientific community focusses on data
processing for which the international Gaia Data Processing and Analysis
Consortium (DPAC) was selected in 2007. Gaia was launched on 19 December 2013
and arrived at its operating point, the second Lagrange point of the
Sun-Earth-Moon system, a few weeks later. The commissioning of the spacecraft
and payload was completed on 19 July 2014. The nominal five-year mission
started with four weeks of special, ecliptic-pole scanning and subsequently
transferred into full-sky scanning mode. We recall the scientific goals of Gaia
and give a description of the as-built spacecraft that is currently (mid-2016)
being operated to achieve these goals. We pay special attention to the payload
module, the performance of which is closely related to the scientific
performance of the mission. We provide a summary of the commissioning
activities and findings, followed by a description of the routine operational
mode. We summarise scientific performance estimates on the basis of in-orbit
operations. Several intermediate Gaia data releases are planned and the data
can be retrieved from the Gaia Archive, which is available through the Gaia
home page at http://www.cosmos.esa.int/gaia. | astro-ph_IM |
Conditions for Coronal Observation at the Lijiang Observatory in 2011: The sky brightness is a critical parameter for estimating the coronal
observation conditions for solar observatory. As part of a site-survey project
in Western China, we measured the sky brightness continuously at the Lijiang
Observatory in Yunnan province in 2011. A sky brightness monitor (SBM) was
adopted to measure the sky brightness in a region extending from 4.5 to 7.0
apparent solar radii based on the experience of the Daniel K. Inouye Solar
Tele- scope (DKIST) site survey. Every month, the data were collected manually
for at least one week. We collected statistics of the sky brightness at four
bandpasses located at 450, 530, 890, and 940 nm. The results indicate that
aerosol scattering is of great importance for the diurnal variation of the sky
brightness. For most of the year, the sky brightness remains under 20
millionths per airmass before local Noon. On average, the sky brightness is
less than 20 millionths accounts for 40.41 % of the total observing time in a
clear day. The best observation time is from 9:00 to 13:00 (Beijing time).
Lijiang Observatory is therefore suitable for coronagraphs investigating the
structures and dynamics of the corona. | astro-ph_IM |
Deep reinforcement learning for smart calibration of radio telescopes: Modern radio telescopes produce unprecedented amounts of data, which are
passed through many processing pipelines before the delivery of scientific
results. Hyperparameters of these pipelines need to be tuned by hand to produce
optimal results. Because many thousands of observations are taken during a
lifetime of a telescope and because each observation will have its unique
settings, the fine tuning of pipelines is a tedious task. In order to automate
this process of hyperparameter selection in data calibration pipelines, we
introduce the use of reinforcement learning. We test two reinforcement learning
techniques, twin delayed deep deterministic policy gradient (TD3) and soft
actor-critic (SAC), to train an autonomous agent to perform this fine tuning.
For the sake of generalization, we consider the pipeline to be a black-box
system where the summarized state of the performance of the pipeline is used by
the autonomous agent. The autonomous agent trained in this manner is able to
determine optimal settings for diverse observations and is therefore able to
perform 'smart' calibration, minimizing the need for human intervention. | astro-ph_IM |
Optimal Filtration and a Pulsar Time Scale: An algorithm is proposed for constructing a group (ensemble) pulsar time
based on the application of optimal Wiener filters. This algorithm makes it
possible to separate the contributions of variations of the atomic time scale
and of the pulsar rotation to barycentric residual deviations of the pulse
arrival times. The method is applied to observations of the pulsars PSR
B1855+09 and PSR B1937+21, and is used to obtain corrections to UTC relative to
the group pulsar time PT$_{\rm ens}$. Direct comparison of the terrestrial time
TT(BIPM06) and the group pulsar time PT$_{\rm ens}$ shows that they disagree by
no more than $0.4\pm 0.17\; \mu$s. Based on the fractional instability of the
time difference TT(BIPM06) -- PT$_{\rm ens}$, a new limit for the energy
density of the gravitational-wave background is established at the level
$\Omega_g {h}^2\sim 10^{-9}$. | astro-ph_IM |
On-sky demonstration of optical polaroastrometry: A method for measuring the difference between centroids of polarized flux and
total flux of an astronomical object - {\it polaroastrometry} - is proposed.
The deviation of the centroid of flux corresponding to Stokes parameter $Q$ or
$U$ from the centroid of total flux multiplied by dimensionless Stokes
parameter $q$ or $u$ respectively, was used as a signal. The efficiency of the
method is demonstrated on the basis of observations made in the $V$ band by
using an instrument combining features of a two-beam polarimeter with a
rotating half-wave plate and a speckle interferometer. The polaroastrometric
signal noise is 60-70 $\mu$as rms for a total number of accumulated
photoelectrons $N_e$ of $10^9$ from a 70-cm telescope; this corresponds to a
total integration time of 500 sec and an object magnitude $V=6$ mag. At smaller
$N_e$ the noise increases as $\approx 1.7^{\prime\prime}/\sqrt{N_e}$, while at
larger $N_e$ it remains the same owing to imperfection of the half-wave plate.
For main sequence stars that are unpolarized and polarized by interstellar dust
and the Mira type variable R Tri the signal was undetectable. For the Mira type
variable $\chi$ Cyg the polaroastrometric signal is found to be $310\pm70$ and
$300\pm70$ $\mu$as for Stokes $Q$ and $U$ respectively; for $o$ Cet these
values are $490\pm100$ and $1160\pm100$ $\mu$as. The significant value of the
polaroastrometric signal provides evidence of the asymmetry of the polarized
flux distribution. | astro-ph_IM |
Correlated magnetic noise in global networks of gravitational-wave
interferometers: observations and implications: One of the most ambitious goals of gravitational-wave astronomy is to observe
the stochastic gravitational-wave background. Correlated noise in two or more
detectors can introduce a systematic error, which limits the sensitivity of
stochastic searches. We report on measurements of correlated magnetic noise
from Schumann resonances at the widely separated LIGO and Virgo detectors. We
investigate the effect of this noise on a global network of interferometers and
derive a constraint on the allowable coupling of environmental magnetic fields
to test mass motion in gravitational-wave detectors. We find that while
correlated noise from global electromagnetic fields could be safely ignored for
initial LIGO stochastic searches, it could severely impact Advanced LIGO and
third-generation detectors. | astro-ph_IM |
High-resolution Solar Image Reconstruction Based on Non-rigid Alignment: Suppressing the interference of atmospheric turbulence and obtaining
observation data with a high spatial resolution is an issue to be solved
urgently for ground observations. One way to solve this problem is to perform a
statistical reconstruction of short-exposure speckle images. Combining the
rapidity of Shift-Add and the accuracy of speckle masking, this paper proposes
a novel reconstruction algorithm-NASIR (Non-rigid Alignment based Solar Image
Reconstruction). NASIR reconstructs the phase of the object image at each
frequency by building a computational model between geometric distortion and
intensity distribution and reconstructs the modulus of the object image on the
aligned speckle images by speckle interferometry. We analyzed the performance
of NASIR by using the correlation coefficient, power spectrum, and coefficient
of variation of intensity profile (CVoIP) in processing data obtained by the
NVST (1m New Vacuum Solar Telescope). The reconstruction experiments and
analysis results show that the quality of images reconstructed by NASIR is
close to speckle masking when the seeing is good, while NASIR has excellent
robustness when the seeing condition becomes worse. Furthermore, NASIR
reconstructs the entire field of view in parallel in one go, without phase
recursion and block-by-block reconstruction, so its computation time is less
than half that of speckle masking. Therefore, we consider NASIR is a robust and
high-quality fast reconstruction method that can serve as an effective tool for
data filtering and quick look. | astro-ph_IM |
Astro2020 Project White Paper: PolyOculus -- Low-cost Spectroscopy for
the Community: As astronomy moves into the era of large-scale time-domain surveys, we are
seeing a flood of new transient and variable sources which will reach biblical
proportions with the advent of LSST. A key strategic challenge for astronomy in
this era is the lack of suitable spectroscopic followup facilities. In response
to this need, we have developed the PolyOculus approach for producing
large-area-equivalent telescopes by using fiber optics to link modules of
multiple semi-autonomous, small, inexpensive, commercial-off-the-shelf
telescopes. Crucially, this scalable design has construction costs which are
$>10x$ lower than equivalent traditional large-area telescopes. In addition,
PolyOculus is inherently highly automated and well-suited for remote
operations. Development of this technology will enable the expansion of major
research efforts in the LSST era to a host of smaller universities and
colleges, including primarily-undergraduate institutions, for budgets
consistent with their educational expenditures on similar facilities. We
propose to develop and deploy a 1.6-m prototype demonstrator at the Mt. Laguna
Observatory in California, followed by a full-scale 5-meter-class PolyOculus
facility for linkage to existing and upcoming time-domain surveys. | astro-ph_IM |
Towards a cosmic-ray mass-composition study at Tunka Radio Extension
(ARENA 2016): The Tunka Radio Extension (Tunka-Rex) is a radio detector at the TAIGA
facility located in Siberia nearby the southern tip of Lake Baikal. Tunka-Rex
measures air-showers induced by high-energy cosmic rays, in particular, the
lateral distribution of the radio pulses. The depth of the air-shower maximum,
which statistically depends on the mass of the primary particle, is determined
from the slope of the lateral distribution function (LDF). Using a
model-independent approach, we have studied possible features of the
one-dimensional slope method and tried to find improvements for the
reconstruction of primary mass. To study the systematic uncertainties given by
different primary particles, we have performed simulations using the CONEX and
CoREAS software packages of the recently released CORSIKA v7.5 including the
modern high-energy hadronic models QGSJet-II.04 and EPOS-LHC. The simulations
have shown that the largest systematic uncertainty in the energy deposit is due
to the unknown primary particle. Finally, we studied the relation between the
polarization and the asymmetry of the LDF. | astro-ph_IM |
The advantages of using a Lucky Imaging camera for observations of
microlensing events: In this work, we study the advantages of using a Lucky Imaging camera for the
observations of potential planetary microlensing events. Our aim is to reduce
the blending effect and enhance exoplanet signals in binary lensing systems
composed of an exoplanet and the corresponding parent star. We simulate
planetary microlensing light curves based on present microlensing surveys and
follow-up telescopes where one of them is equipped with a Lucky imaging camera.
This camera is used at the Danish $1.54$-m follow-up telescope. Using a
specific observational strategy, For an Earth-mass planet in the resonance
regime, where the detection probability in crowded-fields is smaller, lucky
imaging observations improve the detection efficiency which reaches 2 per cent.
Given the difficulty of detecting the signal of an Earth-mass planet in
crowded-field imaging even in the resonance regime with conventional cameras,
we show that Lucky Imaging can substantially improve the detection efficiency. | astro-ph_IM |
Hunting electromagnetic counterparts of gravitational-wave events using
the Zwicky Transient Facility: Detections of coalescing binary black holes by LIGO have opened a new window
of transient astronomy. With increasing sensitivity of LIGO and participation
of the Virgo detector in Cascina, Italy, we expect to soon detect coalescence
of compact binary systems with one or more neutron stars. These are the prime
targets for electromagnetic follow-up of gravitational wave triggers, which
holds enormous promise of rich science. However, hunting for electromagnetic
counterparts of gravitational wave events is a non-trivial task due to the
sheer size of the error regions, which could span hundreds of square degrees.
The Zwicky Transient facility (ZTF), scheduled to begin operation in 2017, is
designed to cover such large sky-localization areas. In this work, we present
the strategies of efficiently tiling the sky to facilitate the observation of
the gravitational wave error regions using ZTF. To do this we used simulations
consisting of 475 binary neutron star coalescences detected using a mix of two-
and three-detector networks. Our studies reveal that, using two overlapping
sets of ZTF tiles and a (modified) ranked-tiling algorithm, we can cover the
gravitational-wave sky-localization regions with half as many pointings as a
simple contour-covering algorithm. We then incorporated the ranked-tiling
strategy to study our ability to observe the counterparts. This requires
optimization of observation depth and localization area coverage. Our results
show that observation in r-band with ~600 seconds of integration time per
pointing seems to be optimum for typical assumed brightnesses of
electromagnetic counterparts, if we plan to spend equal amount of time per
pointing. However, our results also reveal that we can gain by as much as 50%
in detection efficiency if we linearly scale our integration time per pointing
based on the tile probability. | astro-ph_IM |
Monte-Carlo Imaging for Optical Interferometry: We present a flexible code created for imaging from the bispectrum and
visibility-squared. By using a simulated annealing method, we limit the
probability of converging to local chi-squared minima as can occur when
traditional imaging methods are used on data sets with limited phase
information. We present the results of our code used on a simulated data set
utilizing a number of regularization schemes including maximum entropy. Using
the statistical properties from Monte-Carlo Markov chains of images, we show
how this code can place statistical limits on image features such as unseen
binary companions. | astro-ph_IM |
r-Java 2.0: the astrophysics: [Context:] This article is the second in a two part series introducing r-Java
2.0, a nucleosynthesis code for open use that performs r-process calculations
and provides a suite of other analysis tools. [Aims:] The first paper discussed
the nuclear physics inherent to r-Java 2.0 and in this article the astrophysics
incorporated into the software will be detailed. [Methods:] R-Java 2.0 allows
the user to specify the density and temperature evolution for an r-process
simulation. Defining how the physical parameters (temperature and density)
evolve can effectively simulate the astrophysical conditions for the r-process.
Within r-Java 2.0 the user has the option to select astrophysical environments
which have unique sets of input parameters available for the user to adjust. In
this work we study three proposed r-process sites; neutrino-driven winds around
a proto-neutron star, ejecta from a neutron star merger and ejecta from a quark
nova. The underlying physics that define the temperature and density evolution
for each site is described in this work. [Results:] In this paper a survey of
the available parameters for each astrophysical site is undertaken and the
effect on final r-process abundance is compared. The resulting abundances for
each site are also compared to solar observations both independently and in
concert. R-Java 2.0 is available for download from the website of the
Quark-Nova Project: http://quarknova.ucalgary.ca/ | astro-ph_IM |
Radio Detection of High Energy Neutrinos in Ice: Radio-based detection of high-energy particles is growing in maturity. In
this chapter, we focus on the detection of neutrinos with energies in excess of
10 PeV that interact in the thick, radio-transparent ice found in the polar
regions. High-energy neutrinos interacting in the ice generate short duration,
radio-frequency flashes through the Askaryan effect that can be measured with
antennas installed at shallow depths. The abundant target material and the long
attenuation lengths of around 1 km allow cost-effective instrumentation of huge
volumes with a sparse array of radio detector stations. This detector
architecture provides sufficient sensitivity to the low flux of
ultra-high-energy neutrinos to probe the production of ultra-high-energy cosmic
rays whose origin is one of the longest-standing riddles in astroparticle
physics. We describe the signal characteristics, propagation effects, detector
setup, suitable detection sites, and background processes. We give an overview
of the current experimental landscape and an outlook into the future where
almost the entire sky can be viewed by a judicious choice of detector
locations. | astro-ph_IM |
STATCONT: A statistical continuum level determination method for
line-rich sources: STATCONT is a python-based tool designed to determine the continuum emission
level in spectral data, in particular for sources with a line-rich spectrum.
The tool inspects the intensity distribution of a given spectrum and
automatically determines the continuum level by using different statistical
approaches. The different methods included in STATCONT are tested against
synthetic data. We conclude that the sigma-clipping algorithm provides the most
accurate continuum level determination, together with information on the
uncertainty in its determination. This uncertainty can be used to correct the
final continuum emission level, resulting in the here called `corrected
sigma-clipping method' or c-SCM. The c-SCM has been tested against more than
750 different synthetic spectra reproducing typical conditions found towards
astronomical sources. The continuum level is determined with a discrepancy of
less than 1% in 50% of the cases, and less than 5% in 90% of the cases,
provided at least 10% of the channels are line free. The main products of
STATCONT are the continuum emission level, together with a conservative value
of its uncertainty, and datacubes containing only spectral line emission, i.e.,
continuum-subtracted datacubes. STATCONT also includes the option to estimate
the spectral index, when different files covering different frequency ranges
are provided. | astro-ph_IM |
Measurement of the cosmic-ray energy spectrum above $10^{16}$ eV with
the LOFAR Radboud Air Shower Array: The energy reconstruction of extensive air showers measured with the LOFAR
Radboud Air Shower Array (LORA) is presented in detail. LORA is a particle
detector array located in the center of the LOFAR radio telescope in the
Netherlands. The aim of this work is to provide an accurate and independent
energy measurement for the air showers measured through their radio signal with
the LOFAR antennas. The energy reconstruction is performed using a
parameterized relation between the measured shower size and the cosmic-ray
energy obtained from air shower simulations. In order to illustrate the
capabilities of LORA, the all-particle cosmic-ray energy spectrum has been
reconstructed, assuming that cosmic rays are composed only of protons or iron
nuclei in the energy range between $\sim2\times10^{16}$ and $2\times10^{18}$
eV. The results are compatible with literature values and a changing mass
composition in the transition region from a galactic to an extragalactic origin
of cosmic rays. | astro-ph_IM |
The Faulkes Telescope Project: Not Just Pretty Pictures: The Faulkes Telescope (FT) Project is an educational and research arm of the
Las Cumbres Observatory Global Telescope Network (LCOGTN). As well as producing
spectacular images of galaxies, nebulae, supernovae remnants, star clusters,
etc., the FT team is involved in several projects pursuing scientific goals.
Many of these projects also incorporate data collected and analysed by schools
and amateur astronomers. | astro-ph_IM |
Bokeh Mirror Alignment for Cherenkov Telescopes: Imaging Atmospheric Cherenkov Telescopes (IACTs) need imaging optics with
large apertures and high image intensities to map the faint Cherenkov light
emitted from cosmic ray air showers onto their image sensors. Segmented
reflectors fulfill these needs, and composed from mass production mirror facets
they are inexpensive and lightweight. However, as the overall image is a
superposition of the individual facet images, alignment remains a challenge.
Here we present a simple, yet extendable method, to align a segmented reflector
using its Bokeh. Bokeh alignment does not need a star or good weather nights
but can be done even during daytime. Bokeh alignment optimizes the facet
orientations by comparing the segmented reflectors Bokeh to a predefined
template. The optimal Bokeh template is highly constricted by the reflector's
aperture and is easy accessible. The Bokeh is observed using the out of focus
image of a near by point like light source in a distance of about 10 focal
lengths. We introduce Bokeh alignment on segmented reflectors and demonstrate
it on the First Geiger-mode Avalanche Cherenkov Telescope (FACT) on La Palma,
Spain. | astro-ph_IM |
Reconstruction methods for acoustic particle detection in the deep sea
using clusters of hydrophones: This article focuses on techniques for acoustic noise reduction, signal
filters and source reconstruction. For noise reduction, bandpass filters and
cross correlations are found to be efficient and fast ways to improve the
signal to noise ratio and identify a possible neutrino-induced acoustic signal.
The reconstruction of the position of an acoustic point source in the sea is
performed by using small-volume clusters of hydrophones (about 1 cubic meter)
for direction reconstruction by a beamforming algorithm. The directional
information from a number of such clusters allows for position reconstruction.
The algorithms for data filtering, direction and position reconstruction are
explained and demonstrated using simulated data. | astro-ph_IM |
Overview of the Advanced X-ray Imaging Satellite (AXIS): The Advanced X-ray Imaging Satellite (AXIS) is a Probe-class concept that
will build on the legacy of the Chandra X-ray Observatory by providing
low-background, arcsecond-resolution imaging in the 0.3-10 keV band across a
450 arcminute$^2$ field of view, with an order of magnitude improvement in
sensitivity. AXIS utilizes breakthroughs in the construction of lightweight
segmented X-ray optics using single-crystal silicon, and developments in the
fabrication of large-format, small-pixel, high readout rate CCD detectors with
good spectral resolution, allowing a robust and cost-effective design. Further,
AXIS will be responsive to target-of-opportunity alerts and, with onboard
transient detection, will be a powerful facility for studying the time-varying
X-ray universe, following on from the legacy of the Neil Gehrels (Swift) X-ray
observatory that revolutionized studies of the transient X-ray Universe. In
this paper, we present an overview of AXIS, highlighting the prime science
objectives driving the AXIS concept and how the observatory design will achieve
these objectives. | astro-ph_IM |
Spectrally resolved imaging with the solar gravitational lens: We consider the optical properties of the solar gravitational lens (SGL)
treating the Sun as a massive compact body. Using our previously developed
wave-optical treatment of the SGL, we convolve it with a thin-lens representing
an optical telescope, and estimate the power spectral density and associated
photon flux at individual pixel locations on the image sensor at the focal
plane of the telescope. We also consider the solar corona, which is the
dominant noise source when imaging faint objects with the SGL. We evaluate the
signal-to-noise ratio at individual pixels as a function of wavelength. To
block out the solar light, we contrast the use of a conventional internal
coronagraph with a Lyot-stop to an external occulter (i.e., starshade). An
external occulter, not being a subject to the diffraction limit of the
observing telescope, makes it possible to use small telescopes (e.g., $\sim
40$~cm) for spatially and spectrally resolved imaging with the SGL in a broad
range of wavelengths from optical to mid-infrared (IR) and without the
substantial loss of optical throughput that is characteristic to internal
devices. Mid-IR observations are especially interesting as planets are
self-luminous at these wavelengths, producing a strong signal, while there is
significantly less noise from the solar corona. This part of the spectrum
contains numerous features of interest for exobiology and biosignature
detection. We develop tools that may be used to estimate instrument
requirements and devise optimal observing strategies to use the SGL for
high-resolution, spectrally resolved imaging, ultimately improving our ability
to confirm and study the presence of life on a distant world. | astro-ph_IM |
The Maunakea Spectroscopic Explorer: Thousands of Fibers, Infinite
Possibilities: The Maunakea Spectroscopic Explorer (MSE) is a massively multiplexed
spectroscopic survey facility that will replace the Canada-France-Hawaii
Telescope over the next two decades. This 12.5-meter telescope, with its 1.5
square degree field-of-view, will observe 18,000-20,000 astronomical targets in
every pointing from 0.36-1.80 microns at low/moderate resolution (R~3,000,
6,000) and from 0.36-0.90 microns at high resolution (R~30,000). Parallel
positioning of all fibers in the field will occur, providing simultaneous
full-field coverage for both resolution modes. Unveiling the composition and
dynamics of the faint Universe, MSE will impact nearly every field of
astrophysics across all spatial scales, from individual stars to the largest
scale structures in the Universe, including (i) the ultimate Gaia follow-up
facility for understanding the chemistry and dynamics of the distant Milky Way,
including the distant halo at high spectral resolution, (ii) the unparalleled
study of galaxy formation and evolution at cosmic noon, (iii) the determination
of the neutrino mass, and (iv) the generation of insights into inflationary
physics through a cosmological redshift survey that probes a large volume of
the Universe with a high galaxy density. Initially, CFHT will build a
Pathfinder instrument to fast-track the development of MSE technology while
providing multi-object and IFU spectroscopic capability. | astro-ph_IM |
Effects of the Number of Active Receiver Channels on the Sensitivity of
a Reflector Antenna System with a Multi-Beam Wideband Phased Array Feed: A method for modeling a reflector antenna system with a wideband phased array
feed is presented and used to study the effects of the number of active antenna
elements and associated receiving channels on the sensitivity of the system.
Numerical results are shown for a practical system named APERTIF that is
currently under developed at The Netherlands Institute for Radio Astronomy
(ASTRON) | astro-ph_IM |
How proper are Bayesian models in the astronomical literature?: The well-known Bayes theorem assumes that a posterior distribution is a
probability distribution. However, the posterior distribution may no longer be
a probability distribution if an improper prior distribution (non-probability
measure) such as an unbounded uniform prior is used. Improper priors are often
used in the astronomical literature to reflect a lack of prior knowledge, but
checking whether the resulting posterior is a probability distribution is
sometimes neglected. It turns out that 23 articles out of 75 articles (30.7%)
published online in two renowned astronomy journals (ApJ and MNRAS) between Jan
1, 2017 and Oct 15, 2017 make use of Bayesian analyses without rigorously
establishing posterior propriety. A disturbing aspect is that a Gibbs-type
Markov chain Monte Carlo (MCMC) method can produce a seemingly reasonable
posterior sample even when the posterior is not a probability distribution
(Hobert and Casella, 1996). In such cases, researchers may erroneously make
probabilistic inferences without noticing that the MCMC sample is from a
non-existing probability distribution. We review why checking posterior
propriety is fundamental in Bayesian analyses, and discuss how to set up
scientifically motivated proper priors. | astro-ph_IM |
Direct measurement of the intra-pixel response function of Kepler Space
Telescope's CCDs: Space missions designed for high precision photometric monitoring of stars
often under-sample the point-spread function, with much of the light landing
within a single pixel. Missions like MOST, Kepler, BRITE, and TESS, do this to
avoid uncertainties due to pixel-to-pixel response nonuniformity. This approach
has worked remarkably well. However, individual pixels also exhibit response
nonuniformity. Typically, pixels are most sensitive near their centers and less
sensitive near the edges, with a difference in response of as much as 50%. The
exact shape of this fall-off, and its dependence on the wavelength of light, is
the intra-pixel response function (IPRF). A direct measurement of the IPRF can
be used to improve the photometric uncertainties, leading to improved
photometry and astrometry of under-sampled systems. Using the spot-scan
technique, we measured the IPRF of a flight spare e2v CCD90 imaging sensor,
which is used in the Kepler focal plane. Our spot scanner generates spots with
a full-width at half-maximum of $\lesssim$5 microns across the range of 400 nm
- 900 nm. We find that Kepler's CCD shows similar IPRF behavior to other
back-illuminated devices, with a decrease in responsivity near the edges of a
pixel by $\sim$50%. The IPRF also depends on wavelength, exhibiting a large
amount of diffusion at shorter wavelengths and becoming much more defined by
the gate structure in the near-IR. This method can also be used to measure the
IPRF of the CCDs used for TESS, which borrows much from the Kepler mission. | astro-ph_IM |
The wavefront sensing making-of for THEMIS solar telescope: An adaptive optics system with a single deformable mirror is being
implemented on the THEMIS 90cm solar telescope. This system is designed to
operate in the visible and is required to be as robust as possible in order to
deliver the best possible correction in any atmospheric conditions, even if
wavefronts are sensed on some low-contrast solar granulation. In extreme
conditions, the images given by the subapertures of the Shack-Hartmann
wavefront sensor get randomly blurred in space, in the set of subapertures, and
the distribution of blurred images is rapidly changing in time, some of them
possibly fading away. The algorithms we have developed for such harsh
conditions rely on inverse problem approach. As an example, with the gradients
of the wavefronts, the wavefront sensor also estimates their errors, including
their covariance. This information allows the control loop to promptly optimize
itself to the fast varying conditions, both in space (wavefront reconstruction)
and in time. A major constraint is to fit the calculations in a low-cost
multi-core CPU. An overview of the algorithms in charge of implementing this
strategy is presented, focusing on wavefront sensing. | astro-ph_IM |
HCGrid: A Convolution-based Gridding Framework for RadioAstronomy in
Hybrid Computing Environments: Gridding operation, which is to map non-uniform data samples onto a uniformly
distributedgrid, is one of the key steps in radio astronomical data reduction
process. One of the mainbottlenecks of gridding is the poor computing
performance, and a typical solution for suchperformance issue is the
implementation of multi-core CPU platforms. Although such amethod could usually
achieve good results, in many cases, the performance of gridding is
stillrestricted to an extent due to the limitations of CPU, since the main
workload of gridding isa combination of a large number of single instruction,
multi-data-stream operations, which ismore suitable for GPU, rather than CPU
implementations. To meet the challenge of massivedata gridding for the modern
large single-dish radio telescopes, e.g., the Five-hundred-meterAperture
Spherical radio Telescope (FAST), inspired by existing multi-core CPU
griddingalgorithms such as Cygrid, here we present an easy-to-install,
high-performance, and open-source convolutional gridding framework, HCGrid,in
CPU-GPU heterogeneous platforms. Itoptimises data search by employing
multi-threading on CPU, and accelerates the convolutionprocess by utilising
massive parallelisation of GPU. In order to make HCGrid a more
adaptivesolution, we also propose the strategies of thread organisation and
coarsening, as well as optimalparameter settings under various GPU
architectures. A thorough analysis of computing timeand performance gain with
several GPU parallel optimisation strategies show that it can leadto excellent
performance in hybrid computing environments. | astro-ph_IM |
The Locus Algorithm III: A Grid Computing system to generate catalogues
of optimised pointings for Differential Photometry: This paper discusses the hardware and software components of the Grid
Computing system used to implement the Locus Algorithm to identify optimum
pointings for differential photometry of 61,662,376 stars and 23,799 quasars.
The scale of the data, together with initial operational assessments demanded a
High Performance Computing (HPC) system to complete the data analysis. Grid
computing was chosen as the HPC solution as the optimum choice available within
this project. The physical and logical structure of the National Grid computing
Infrastructure informed the approach that was taken. That approach was one of
layered separation of the different project components to enable maximum
flexibility and extensibility. | astro-ph_IM |
Effects of transients in LIGO suspensions on searches for gravitational
waves: This paper presents an analysis of the transient behavior of the Advanced
LIGO suspensions used to seismically isolate the optics. We have characterized
the transients in the longitudinal motion of the quadruple suspensions during
Advanced LIGO's first observing run. Propagation of transients between stages
is consistent with modelled transfer functions, such that transient motion
originating at the top of the suspension chain is significantly reduced in
amplitude at the test mass. We find that there are transients seen by the
longitudinal motion monitors of quadruple suspensions, but they are not
significantly correlated with transient motion above the noise floor in the
gravitational wave strain data, and therefore do not present a dominant source
of background noise in the searches for transient gravitational wave signals. | astro-ph_IM |
Investigation of the radio wavefront of air showers with LOPES
measurements and CoREAS simulations (ARENA 2014): We investigated the radio wavefront of cosmic-ray air showers with LOPES
measurements and CoREAS simulations: the wavefront is of approximately
hyperbolic shape and its steepness is sensitive to the shower maximum. For this
study we used 316 events with an energy above 0.1 EeV and zenith angles below
$45^\circ$ measured by the LOPES experiment. LOPES was a digital radio
interferometer consisting of up to 30 antennas on an area of approximately 200
m x 200 m at an altitude of 110 m above sea level. Triggered by KASCADE-Grande,
LOPES measured the radio emission between 43 and 74 MHz, and our analysis might
strictly hold only for such conditions. Moreover, we used CoREAS simulations
made for each event, which show much clearer results than the measurements
suffering from high background. A detailed description of our result is
available in our recent paper published in JCAP09(2014)025. The present
proceeding contains a summary and focuses on some additional aspects, e.g., the
asymmetry of the wavefront: According to the CoREAS simulations the wavefront
is slightly asymmetric, but on a much weaker level than the lateral
distribution of the radio amplitude. | astro-ph_IM |
Scaling of collision strengths for highly-excited states of ions of the
H- and He-like sequences: Emission lines from highly-excited states (n >= 5) of H- and He-like ions
have been detected in astrophysical sources and fusion plasmas. For such
excited states, R-matrix or distorted wave calculations for electron-impact
excitation are very limited, due to the large size of the atomic basis set
needed to describe them. Calculations for n >= 6 are also not generally
available. We study the behaviour of the electron-impact excitation collision
strengths and effective collision strengths for the most important transitions
used to model electron collision dominated astrophysical plasmas, solar, for
example. We investigate the dependence on the relevant parameters: the
principal quantum number n or the nuclear charge Z. We also estimate the
importance of coupling to highly-excited states and the continuum by comparing
the results of different sized calculations. We provide analytic formulae to
calculate the electron-impact excitation collision strengths and effective
collision strengths to highly-excited states (n >= 8) of H- and He-like ions.
These extrapolated effective collision strengths can be used to interpret
astrophysical and fusion plasma via collisional-radiative modelling. | astro-ph_IM |
Gaia: unraveling the chemical and dinamical history of our Galaxy: The Gaia astrometric mission - the Hipparcos successor - is described in some
detail, with its three instruments: the two (spectro)photometers (BP and RP)
covering the range 330-1050 nm, the white light (G-band) imager dedicated to
astrometry, and the radial velocity spectrometer (RVS) covering the range
847-874 nm at a resolution R \simeq 11500. The whole sky will be scanned
repeatedly providing data for ~10^9 point-like objects, down to a magnitude of
V \simeq 20, aiming to the full 6D reconstruction of the Milky Way kinematical
and dinamical structure with unprecendented precision. The horizon of
scientific questions that can find an answer with such a set of data is vast,
including besides the Galaxy: Solar system studies, stellar astrophysics,
exoplanets, supernovae, Local group physics, unresolved galaxies, Quasars, and
fundamental physics. The Italian involvement in the mission preparation is
briefly outlined. | astro-ph_IM |
Inequalities faced by women in access to permanent positions in
astronomy in France: We investigate inequalities in access to permanent positions in professional
astronomy in France, focusing on the hiring stage. We use results from a
national survey conducted on behalf of the French society of astronomy and
astrophysics (SF2A) aimed at young astronomers holding a PhD obtained in
France, and answered by over 300 researchers. We find that women are nearly two
times less likely than men to be selected by the (national or local) committees
attributing permanent positions ($p=0.06$). We also find that applicants who
did their undergraduate studies in an elite school ("Grande \'Ecole"), where
women are largely under-represented, rather than in a university, are nearly
three times more likely to succeed in obtaining a position ($p=0.0026$). Our
analysis suggests the existence of two biases in committees attributing
permanent positions in astronomy in France: a gender bias, and a form of
elitism. These biases against women in their professional life impacts their
personal life as our survey shows that a larger fraction of them declare that
having children can have a negative effect on their careers. They are half as
many as men having children in the sample. National committees (such as the
CNRS) have acknowledged this issue for several years now, hence one can hope
that changes will be seen in the next decade. | astro-ph_IM |
New Gapless COS G140L Mode Proposed for Background-Limited Far-UV
Observations: Here we describe the observation and calibration procedure for a new G140L
observing mode for the Cosmic Origins Spectrograph (COS) aboard the Hubble
Space Telescope (HST). This mode, CENWAV = 800, is designed to move the far-UV
band fully onto the Segment A detector, allowing for more e cient ob- servation
and analysis by simplifying calibration management between the two channels,
and reducing the astigmatism in this wavelength region. We also de- scribe some
of the areas of scientific interest for which this new mode will be especially
suited. | astro-ph_IM |
First low frequency all-sky search for continuous gravitational wave
signals: In this paper we present the results of the first low frequency all-sky
search of continuous gravitational wave signals conducted on Virgo VSR2 and
VSR4 data. The search covered the full sky, a frequency range between 20 Hz and
128 Hz with a range of spin-down between $-1.0 \times 10^{-10}$ Hz/s and $+1.5
\times 10^{-11}$ Hz/s, and was based on a hierarchical approach. The starting
point was a set of short Fast Fourier Transforms (FFT), of length 8192 seconds,
built from the calibrated strain data. Aggressive data cleaning, both in the
time and frequency domains, has been done in order to remove, as much as
possible, the effect of disturbances of instrumental origin. On each dataset a
number of candidates has been selected, using the FrequencyHough transform in
an incoherent step. Only coincident candidates among VSR2 and VSR4 have been
examined in order to strongly reduce the false alarm probability, and the most
significant candidates have been selected. Selected candidates have been
subject to a follow-up by constructing a new set of longer FFTs followed by a
further incoherent analysis, still based on the FrequencyHough transform. No
evidence for continuous gravitational wave signals was found, therefore we have
set a population-based joint VSR2-VSR4 90$\%$ confidence level upper limit on
the dimensionless gravitational wave strain in the frequency range between 20
Hz and 128 Hz. This is the first all-sky search for continuous gravitational
waves conducted, on data of ground-based interferometric detectors, at
frequencies below 50 Hz. We set upper limits in the range between about
$10^{-24}$ and $2\times 10^{-23}$ at most frequencies. Our upper limits on
signal strain show an improvement of up to a factor of $\sim$2 with respect to
the results of previous all-sky searches at frequencies below $80~\mathrm{Hz}$. | astro-ph_IM |
Modeling the Optical Cherenkov Signals by Cosmic Ray Extensive Air
Showers Directly Observed from Sub-Orbital and Orbital Altitudes: Future experiments based on the observation of Earth's atmosphere from
sub-orbital and orbital altitudes plan to include optical Cherenkov cameras to
observe extensive air showers produced by high-energy cosmic radiation via its
interaction with both the Earth and its atmosphere. As discussed elsewhere,
particularly relevant is the case of upward-moving showers initiated by
astrophysical neutrinos skimming and interacting in the Earth. The Cherenkov
cameras, by looking above Earth's limb, can also detect cosmic rays with
energies starting from less than a PeV up to the highest energies (tens of
EeV). Using a customized computation scheme to determine the expected optical
Cherenkov signal from these high-energy cosmic rays, we estimate the
sensitivity and event rate for balloon-borne and satellite-based instruments,
focusing our analysis on the Extreme Universe Space Observatory aboard a Super
Pressure Balloon 2 (EUSO-SPB2) and the Probe of Extreme Multi-Messenger
Astrophysics (POEMMA) experiments. We find the expected event rates to be
larger than hundreds of events per hour of experimental live time, enabling a
promising overall test of the Cherenkov detection technique from sub-orbital
and orbital altitudes as well as a guaranteed signal that can be used for
understanding the response of the instrument. | astro-ph_IM |
PRAXIS: low thermal emission high efficiency OH suppressed fibre
spectrograph: PRAXIS is a second generation instrument that follows on from GNOSIS, which
was the first instrument using fibre Bragg gratings for OH background
suppression. The Bragg gratings reflect the NIR OH lines while being
transparent to light between the lines. This gives a much higher signal-noise
ratio at low resolution but also at higher resolutions by removing the
scattered wings of the OH lines. The specifications call for high throughput
and very low thermal and detector noise so that PRAXIS will remain sky noise
limited. The optical train is made of fore-optics, an IFU, a fibre bundle, the
Bragg grating unit, a second fibre bundle and a spectrograph. GNOSIS used the
pre-existing IRIS2 spectrograph while PRAXIS will use a new spectrograph
specifically designed for the fibre Bragg grating OH suppression and optimised
for 1470 nm to 1700 nm (it can also be used in the 1090 nm to 1260 nm band by
changing the grating and refocussing). This results in a significantly higher
transmission due to high efficiency coatings, a VPH grating at low incident
angle and low absorption glasses. The detector noise will also be lower.
Throughout the PRAXIS design special care was taken at every step along the
optical path to reduce thermal emission or stop it leaking into the system.
This made the spectrograph design challenging because practical constraints
required that the detector and the spectrograph enclosures be physically
separate by air at ambient temperature. At present, the instrument uses the
GNOSIS fibre Bragg grating OH suppression unit. We intend to soon use a new OH
suppression unit based on multicore fibre Bragg gratings which will allow
increased field of view per fibre. Theoretical calculations show that the gain
in interline sky background signal-noise ratio over GNOSIS may very well be as
high as 9 with the GNOSIS OH suppression unit and 17 with the multicore fibre
OH suppression unit. | astro-ph_IM |
A passive FPAA based RF scatter meteor detector: In the article we present a hardware meteor detector. The detection principle
is based on the electromagnetic wave reflection from the ionized meteor trail
in the atmosphere. The detector uses the ANADIGM field programmable analogue
array (FPAA), which is an attractive alternative for a typically used detecting
equipment - a PC computer with dedicated software. We implement an analog
signal path using most of available FPAA resources to obtain precise audio
signal detection. Our new detector was verified in collaboration with the
Polish Fireball Network - the organization which monitors meteor activity in
Poland. When compared with currently used signal processing PC software
employing real radio meteor scatter signals, our low-cost detector proved to be
more precise and reliable. Due to its cost and efficiency superiority over the
current solution, the presented module is going to be implemented in the
planned distributed detectors system. | astro-ph_IM |
μ-Spec Spectrometers for the EXCLAIM Instrument: The EXperiment for Cryogenic Large-Aperture Intensity Mapping (EXCLAIM) is a
cryogenic balloon-borne instrument that will map carbon monoxide and
singly-ionized carbon emission lines across redshifts from 0 to 3.5, using an
intensity mapping approach. EXCLAIM will broaden our understanding of these
elemental and molecular gases and the role they play in star formation
processes across cosmic time scales. The focal plane of EXCLAIM's cryogenic
telescope features six {\mu}-Spec spectrometers. {\mu}-Spec is a compact,
integrated grating-analog spectrometer, which uses meandered superconducting
niobium microstrip transmission lines on a single-crystal silicon dielectric to
synthesize the grating. It features superconducting aluminum microwave kinetic
inductance detectors (MKIDs), also in a microstrip architecture. The
spectrometers for EXCLAIM couple to the telescope optics via a hybrid planar
antenna coupled to a silicon lenslet. The spectrometers operate from 420 to 540
GHz with a resolving power R={\lambda}/{\Delta}{\lambda}=512 and employ an
array of 355 MKIDs on each spectrometer. The spectrometer design targets a
noise equivalent power (NEP) of 2x10-18W/\sqrt{Hz} (defined at the input to the
main lobe of the spectrometer lenslet beam, within a 9-degree half width),
enabled by the cryogenic telescope environment, the sensitive MKID detectors,
and the low dielectric loss of single-crystal silicon. We report on these
spectrometers under development for EXCLAIM, providing an overview of the
spectrometer and component designs, the spectrometer fabrication process,
fabrication developments since previous prototype demonstrations, and the
current status of their development for the EXCLAIM mission. | astro-ph_IM |
Data model as agile basis for evolving calibration software: We design the imaging data calibration and reduction software for MICADO, the
First Light near-IR instrument on the Extremely Large Telescope. In this
process we have hit the limit of what can be achieved with a detailed software
design that is primarily captured in pdf/word documents.
Trade-offs between hardware and calibration software are required to meet
stringent science requirements. To support such trade-offs, more software needs
to be developed in the early phases of the project: simulators, archives,
prototype recipes and pipelines. This requires continuous and efficient
exchange of evolving designs between the software and hardware groups, which is
hard to achieve with manually maintained documents. This, and maintaining the
consistency between the design documents and various software components is
possible with a machine readable version of the design.
We construct a detailed design that is readable by both software and humans.
From this the design documentation, prototype pipelines and data archives are
generated automatically. We present the implementation of such an approach for
the calibration software detailed design for the ELT MICADO imager which is
based on expertise and lessons learned in earlier projects (e.g. OmegaCAM,
MUSE, Euclid). | astro-ph_IM |
Photometric Redshift Biases from Galaxy Evolution: Proposed cosmological surveys will make use of photometric redshifts of
galaxies that are significantly fainter than any complete spectroscopic
redshift surveys that exist to train the photo-z methods. We investigate the
photo-z biases that result from known differences between the faint and bright
populations: a rise in AGN activity toward higher redshift, and a metallicity
difference between intrinsically luminous and faint early-type galaxies. We
find that even very small mismatches between the mean photometric target and
the training set can induce photo-z biases large enough to corrupt derived
cosmological parameters significantly. A metallicity shift of ~0.003dex in an
old population, or contamination of any galaxy spectrum with ~0.2% AGN flux, is
sufficient to induce a 10^-3 bias in photo-z. These results highlight the
danger in extrapolating the behavior of bright galaxies to a fainter
population, and the desirability of a spectroscopic training set that spans all
of the characteristics of the photo-z targets, i.e. extending to the 25th mag
or fainter galaxies that will be used in future surveys. | astro-ph_IM |
New Generation Stellar Spectral Libraries in the Optical and
Near-Infrared I: The Recalibrated UVES-POP Library for Stellar Population
Synthesis: We present re-processed flux calibrated spectra of 406 stars from the
UVES-POP stellar library in the wavelength range 320-1025 nm, which can be used
for stellar population synthesis. The spectra are provided in the two versions
having spectral resolving power R=20,000 and R=80,000. Raw spectra from the ESO
data archive were re-reduced using the latest version of the UVES data
reduction pipeline with some additional algorithms that we developed. The most
significant improvements in comparison with the original UVES-POP release are:
(i) an updated Echelle order merging, which eliminates "ripples" present in the
published spectra, (ii) a full telluric correction, (iii) merging of
non-overlapping UVES spectral setups taking into account the global continuum
shape, (iv) a spectrophotometric correction and absolute flux calibration, and
(v) estimates of the interstellar extinction. For 364 stars from our sample, we
computed atmospheric parameters $T_\mathrm{eff}$, surface gravity log $g$,
metallicity [Fe/H], and $\alpha$-element enhancement [$\alpha$/Fe] by using a
full spectrum fitting technique based on a grid of synthetic stellar
atmospheres and a novel minimization algorithm. We also provide projected
rotational velocity $v\sin i$ and radial velocity $v_{rad}$ estimates. The
overall absolute flux uncertainty in the re-processed dataset is better than 2%
with sub-% accuracy for about half of the stars. A comparison of the
recalibrated UVES-POP spectra with other spectral libraries shows a very good
agreement in flux; at the same time, $Gaia$ DR3 BP/RP spectra are often
discrepant with our data, which we attribute to spectrophotometric calibration
issues in $Gaia$ DR3. | astro-ph_IM |
Prediction of Apophis Asteroid Flyby Optimal Trajectories and Data
Fusion of Earth-Apophis Mission Launch Windows using Deep Neural Networks: In recent years, understanding asteroids has shifted from light worlds to
geological worlds by exploring modern spacecraft and advanced radar and
telescopic surveys. However, flyby in 2029 will be an opportunity to conduct an
internal geophysical study and test the current hypothesis on the effects of
tidal forces on asteroids. The Earth-Apophis mission is driven by additional
factors and scientific goals beyond the unique opportunity for natural
experimentation. However, the internal geophysical structures remain largely
unknown. Understanding the strength and internal integrity of asteroids is not
just a matter of scientific curiosity. It is a practical imperative to advance
knowledge for planetary defense against the possibility of an asteroid impact.
This paper presents a conceptual robotics system required for efficiency at
every stage from entry to post-landing and for asteroid monitoring. In short,
asteroid surveillance missions are futuristic frontiers, with the potential for
technological growth that could revolutionize space exploration. Advanced space
technologies and robotic systems are needed to minimize risk and prepare these
technologies for future missions. A neural network model is implemented to
track and predict asteroids' orbits. Advanced algorithms are also needed to
numerically predict orbital events to minimize error | astro-ph_IM |
Dawes Review 5: Australian Aboriginal Astronomy and Navigation: The traditional cultures of Aboriginal Australians include a significant
astronomical component, perpetuated through oral tradition, ceremony, and art.
This astronomical knowledge includes a deep understanding of the motion of
objects in the sky, which was used for practical purposes such as constructing
calendars and for navigation. There is also evidence that traditional
Aboriginal Australians made careful records and measurements of cyclical
phenomena, recorded unexpected phenomena such as eclipses and meteorite
impacts, and could determine the cardinal points to an accuracy of a few
degrees. Putative explanations of celestial phenomena appear throughout the
oral record, suggesting traditional Aborig- inal Australians sought to
understand the natural world around them, in the same way as modern scientists,
but within their own cultural context. There is also a growing body of evidence
for sophisticated navigational skills, including the use of astronomically
based songlines. Songlines are effectively oral maps of the landscape, and are
an efficient way of transmitting oral navigational skills in cultures that do
not have a written language. The study of Aboriginal astronomy has had an
impact extending beyond mere academic curiosity, facilitating cross-cultural
understanding, demonstrating the intimate links between science and culture,
and helping students to engage with science. | astro-ph_IM |
Performances of an upgraded front-end-board for the NectarCAM camera: The Front-End Board (FEB) is a key component of the NectarCAM camera, which
has been developed for the Medium-Sized-Telescopes (MST) of the Cherenkov
Telescope Array Observatory (CTAO). The FEB is responsible for reading and
converting the signals from the camera's photo-multiplier tubes (PMTs) into
digital data, as well as generating module level trigger signals. This
contribution provides an overview of the design and performances of a new
version of the FEB that utilizes an improved version of the NECTAr chip. The
NECTAr chip includes a switched capacitor array for sampling signals at 1 GHz,
and a 12-bit analog-to-digital converter (ADC) for digitizing each sample when
the trigger signal is received. The integration of this advanced NECTAr chip
significantly reduces the deadtime of NectarCAM by an order of magnitude as
compared to the previous version. This contribution also presents the results
of laboratory testing of the new FEB, including measurements of timing
performance, linearity, dynamic range, and deadtime. | astro-ph_IM |
Realizing the potential of astrostatistics and astroinformatics: This Astro2020 State of the Profession Consideration White Paper highlights
the growth of astrostatistics and astroinformatics in astronomy, identifies key
issues hampering the maturation of these new subfields, and makes
recommendations for structural improvements at different levels that, if acted
upon, will make significant positive impacts across astronomy. | astro-ph_IM |
Extension of the Bayesian searches for anisotropic stochastic
gravitational-wave background with non-tensorial polarizations: The recent announcement of strong evidence for a stochastic
gravitational-wave background (SGWB) by various pulsar timing array
collaborations has highlighted this signal as a promising candidate for future
observations. Despite its non-detection by ground-based detectors such as
Advanced LIGO and Advanced Virgo, Callister \textit{et
al.}~\cite{tom_nongr_method} developed a Bayesian formalism to search for an
isotropic SGWB with non-tensorial polarizations, imposing constraints on signal
amplitude in those components that violate general relativity using LIGO's
data. Since our ultimate aim is to estimate the spatial distribution of
gravitational-wave sources, we have extended this existing method to allow for
anisotropic components in signal models. We then examined the potential
benefits from including these additional components. Using injection campaigns,
we found that introducing anisotropic components into a signal model led to
more significant identification of the signal itself and violations of general
relativity. Moreover, the results of our Bayesian parameter estimation
suggested that anisotropic components aid in breaking down degeneracies between
different polarization components, allowing us to infer model parameters more
precisely than through an isotropic analysis. In contrast, constraints on
signal amplitude remained comparable in the absence of such a signal. Although
these results might depend on the assumed source distribution on the sky, such
as the Galactic plane, the formalism presented in this work has laid a
foundation for establishing a generalized Bayesian analysis for an SGWB,
including its anisotropies and non-tensorial polarizations. | astro-ph_IM |
Photoprocessing of formamide ice: route towards prebiotic chemistry in
space: Aims. Formamide (HCONH2) is the simplest molecule containing the peptide bond
first detected in the gas phase in Orion-KL and SgrB2. In recent years, it has
been observed in high temperature regions such as hot corinos, where thermal
desorption is responsible for the sublimation of frozen mantles into the gas
phase. The interpretation of observations can benefit from information gathered
in the laboratory, where it is possible to simulate the thermal desorption
process and to study formamide under simulated space conditions such as UV
irradiation. Methods. Here, two laboratory analyses are reported: we studied
formamide photo-stability under UV irradiation when it is adsorbed by space
relevant minerals at 63 K and in the vacuum regime. We also investigated
temperature programmed desorption of pure formamide ice in the presence of TiO2
dust before and after UV irradiation. Results. Through these analyses, the
effects of UV degradation and the interaction between formamide and different
minerals are compared.We find that silicates, both hydrates and anhydrates,
offer molecules a higher level of protection from UV degradation than mineral
oxides. The desorption temperature found for pure formamide is 220 K. The
desorption temperature increases to 250 K when the formamide desorbs from the
surface of TiO2 grains. Conclusions. Through the experiments outlined here, it
is possible to follow the desorption of formamide and its fragments, simulate
the desorption process in star forming regions and hot corinos, and constrain
parameters such as the thermal desorption temperature of formamide and its
fragments and the binding energies involved. Our results offer support to
observational data and improve our understanding of the role of the grain
surface in enriching the chemistry in space. | astro-ph_IM |
Geometric calibration of Colour and Stereo Surface Imaging System of
ESA's Trace Gas Orbiter: There are many geometric calibration methods for "standard" cameras. These
methods, however, cannot be used for the calibration of telescopes with large
focal lengths and complex off-axis optics. Moreover, specialized calibration
methods for the telescopes are scarce in literature. We describe the
calibration method that we developed for the Colour and Stereo Surface Imaging
System (CaSSIS) telescope, on board of the ExoMars Trace Gas Orbiter (TGO).
Although our method is described in the context of CaSSIS, with camera-specific
experiments, it is general and can be applied to other telescopes. We further
encourage re-use of the proposed method by making our calibration code and data
available on-line. | astro-ph_IM |
T35: a small automatic telescope for long-term observing campaigns: The T35 is a small telescope (14") equipped with a large format CCD camera
installed in the Sierra Nevada Observatory (SNO) in Southern Spain. This
telescope will be a useful tool for the detecting and studying pulsating stars,
particularly, in open clusters. In this paper, we describe the automation
process of the T35 and show also some images taken with the new
instrumentation. | astro-ph_IM |
Advanced Environmentally Resistant Lithium Fluoride Mirror Coatings for
the Next-Generation of Broadband Space Observatories: Recent advances in the physical vapor deposition (PVD) of protective fluoride
films have raised the far-ultraviolet (FUV: 912-1600 {\AA}) reflectivity of
aluminum-based mirrors closer to the theoretical limit. The greatest gains, at
more than 20%, have come for lithium fluoride-protected aluminum, which has the
shortest wavelength cutoff of any conventional overcoat. Despite the success of
the NASA FUSE mission, the use of lithium fluoride (LiF)-based optics is rare,
as LiF is hygroscopic and requires handling procedures that can drive risk.
With NASA now studying two large mission concepts for astronomy, Large
UV-Optical-IR Surveyor (LUVOIR) and the Habitable Exoplanet Imaging Mission
(HabEx), which mandate throughput down to 1000 {\AA}, the development of
LiF-based coatings becomes crucial. This paper discusses steps that are being
taken to qualify these new enhanced LiF-protected aluminum (eLiF) mirror
coatings for flight. In addition to quantifying the hygroscopic degradation, we
have developed a new method of protecting eLiF with an ultrathin (10-20 {\AA})
capping layer of a non-hygroscopic material to increase durability. We report
on the performance of eLiF-based optics and assess the steps that need to be
taken to qualify such coatings for LUVOIR, HabEx, and other FUV-sensitive space
missions. | astro-ph_IM |
AstroSat - a multi-wavelength astronomy satellite: AstroSat is a multi-wavelength astronomy satellite, launched on 2015
September 28. It carries a suite of scientific instruments for multi-wavelength
observations of astronomical sources. It is a major Indian effort in space
astronomy and the context of AstroSat is examined in a historical perspective.
The Performance Verification phase of AstroSat has been completed and all
instruments are working flawlessly and as planned. Some brief highlights of the
scientific results are also given here. | astro-ph_IM |
The Zadko Telescope: A Southern Hemisphere Telescope for Optical
Transient Searches, Multi-Messenger Astronomy and Education: The new 1-m f/4 fast-slew Zadko Telescope was installed in June 2008 about 70
km north of Perth, Western Australia. It is the only metre-class optical
facility at this southern latitude between the east coast of Australia and
South Africa, and can rapidly image optical transients at a longitude not
monitored by other similar facilities. We report on first imaging tests of a
pilot program of minor planet searches, and Target of Opportunity observations
triggered by the Swift satellite. In 12 months, 6 gamma-ray burst afterglows
were detected, with estimated magnitudes; two of them, GRB 090205 (z = 4.65)
and GRB 090516 (z = 4.11), are among the most distant optical transients imaged
by an Australian telescope. Many asteroids were observed in a systematic
3-month search. In September 2009, an automatic telescope control system was
installed, which will be used to link the facility to a global robotic
telescope network; future targets will include fast optical transients
triggered by highenergy satellites, radio transient detections, and LIGO
gravitational wave candidate events. We also outline the importance of the
facility as a potential tool for education, training, and public outreach. | astro-ph_IM |
Comparative performance of some popular ANN algorithms on benchmark and
function approximation problems: We report an inter-comparison of some popular algorithms within the
artificial neural network domain (viz., Local search algorithms, global search
algorithms, higher order algorithms and the hybrid algorithms) by applying them
to the standard benchmarking problems like the IRIS data, XOR/N-Bit parity and
Two Spiral. Apart from giving a brief description of these algorithms, the
results obtained for the above benchmark problems are presented in the paper.
The results suggest that while Levenberg-Marquardt algorithm yields the lowest
RMS error for the N-bit Parity and the Two Spiral problems, Higher Order
Neurons algorithm gives the best results for the IRIS data problem. The best
results for the XOR problem are obtained with the Neuro Fuzzy algorithm. The
above algorithms were also applied for solving several regression problems such
as cos(x) and a few special functions like the Gamma function, the
complimentary Error function and the upper tail cumulative
$\chi^2$-distribution function. The results of these regression problems
indicate that, among all the ANN algorithms used in the present study,
Levenberg-Marquardt algorithm yields the best results. Keeping in view the
highly non-linear behaviour and the wide dynamic range of these functions, it
is suggested that these functions can be also considered as standard benchmark
problems for function approximation using artificial neural networks. | astro-ph_IM |
Ultra-fast model emulation with PRISM; analyzing the Meraxes galaxy
formation model: We demonstrate the potential of an emulator-based approach to analyzing
galaxy formation models in the domain where constraining data is limited. We
have applied the open-source Python package PRISM to the galaxy formation model
Meraxes. Meraxes is a semi-analytic model, purposefully built to study the
growth of galaxies during the Epoch of Reionization (EoR). Constraining such
models is however complicated by the scarcity of observational data in the EoR.
PRISM's ability to rapidly construct accurate approximations of complex
scientific models using minimal data is therefore key to performing this
analysis well.
This paper provides an overview of our analysis of Meraxes using measurements
of galaxy stellar mass densities; luminosity functions; and color-magnitude
relations. We demonstrate the power of using PRISM instead of a full Bayesian
analysis when dealing with highly correlated model parameters and a scarce set
of observational data. Our results show that the various observational data
sets constrain Meraxes differently and do not necessarily agree with each
other, signifying the importance of using multiple observational data types
when constraining such models. Furthermore, we show that PRISM can detect when
model parameters are too correlated or cannot be constrained effectively. We
conclude that a mixture of different observational data types, even when they
are scarce or inaccurate, is a priority for understanding galaxy formation and
that emulation frameworks like PRISM can guide the selection of such data. | astro-ph_IM |
Application of a Regional Model to Astronomical Site Testing in Western
Antarctica: The quality of ground based astronomical observations are significantly
affected by telluric conditions, and the search for best sites has led to the
construction of observatories at remote locations, including recent initiatives
on the high plateaus of E Antarctica where the calm, dry and cloud free
conditions during winter are recognized as amongst the best. Site selection is
an important phase of any observatory development project, and candidate sites
must be tested with specialized equipment, a process both time consuming and
costly. A potential screening of site locations before embarking on field
testing is through the use of climate models. Here, we describe the application
of the Polar version of the Weather Research and Forecast (WRF) model to the
preliminary site suitability assessment of an unstudied region in W Antarctica.
Numerical simulations with WRF were carried out for the winter of 2011 at 3 km
and 1 km spatial resolution over a region centered on the Ellsworth mountain
range. Comparison with observations of surface wind speed and direction,
temperature and specific humidity at nine automatic weather stations indicate
that the model succeed in capturing the mean and time variability of these
variables. Credible features shown by the model include zones of high winds
over the southernmost part of the Ellsworth Mntns, a deep thermal inversion
over the Ronne-Fincher Ice Shelf and strong west to east moisture gradient
across the entire study area. Comparison of simulated cloud fraction with a
spacebourne Lidar climatology indicates that the model may underestimate cloud
occurrence, a problem that has been noted in previous studies. A simple scoring
system was applied to reveal the most promising locations. The results of this
study indicate that the WRF model is capable of providing useful guidance
during the initial site selection stage of project development. | astro-ph_IM |
AMIDAS-II: Upgrade of the AMIDAS Package and Website for Direct Dark
Matter Detection Experiments and Phenomenology: In this paper, we give a detailed user's guide to the AMIDAS (A
Model-Independent Data Analysis System) package and website, which is developed
for online simulations and data analyses for direct Dark Matter detection
experiments and phenomenology. Recently, the whole AMIDAS package and website
system has been upgraded to the second phase: AMIDAS-II, for including the new
developed Bayesian analysis technique.
AMIDAS has the ability to do full Monte Carlo simulations as well as to
analyze real/pseudo data sets either generated by another event generating
programs or recorded in direct DM detection experiments. Moreover, the
AMIDAS-II package can include several "user-defined" functions into the main
code: the (fitting) one-dimensional WIMP velocity distribution function, the
nuclear form factors for spin-independent and spin-dependent cross sections,
artificial/experimental background spectrum for both of simulation and data
analysis procedures, as well as different distribution functions needed in
Bayesian analyses. | astro-ph_IM |
Monte-Carlo Imaging for Optical Interferometry: We present a flexible code created for imaging from the bispectrum and
visibility-squared. By using a simulated annealing method, we limit the
probability of converging to local chi-squared minima as can occur when
traditional imaging methods are used on data sets with limited phase
information. We present the results of our code used on a simulated data set
utilizing a number of regularization schemes including maximum entropy. Using
the statistical properties from Monte-Carlo Markov chains of images, we show
how this code can place statistical limits on image features such as unseen
binary companions. | astro-ph_IM |
Long-term stability of fibre-optic transmission for multi-object
spectroscopy: We present an analysis of the long-term stability of fibre-optic transmission
properties for fibre optics in astronomy. Data from six years of operation of
the AAOmega multi-object spectrograph at the Anglo-Australian Telescope is
presented. We find no evidence for significant degradation in the bulk
transmission properties of the 38 m optical fibre train. Significant losses
(<20% relative, 4% absolute) are identified and associated with the end
termination of the optical fibres in the focal plane. Improved monitoring and
maintenance can rectify the majority of this performance degradation. | astro-ph_IM |
Observation of axisymmetric standard magnetorotational instability in
the laboratory: We report the first direct evidence for the axisymmetric standard
magnetorotational instability (SMRI) from a combined experimental and numerical
study of a magnetized liquid-metal shear flow in a Taylor-Couette cell with
independently rotating and electrically conducting end caps. When a uniform
vertical magnetic field $B_i$ is applied along the rotation axis, the measured
radial magnetic field $B_r$ on the inner cylinder increases linearly with a
small magnetic Reynolds number $Rm$ due to the magnetization of the residue
Ekman circulation. Onset of the axisymmetric SMRI is identified from the
nonlinear increase of $B_r$ beyond a critical $Rm$ in both experiments and
nonlinear numerical simulations. The axisymmetric SMRI exists only at
sufficiently large $Rm$ and intermediate $B_i$, a feature consistent with
theoretical predictions. Our simulations further show that the axisymmetric
SMRI causes the velocity and magnetic fields to contribute an outward flux of
axial angular momentum in the bulk region, just as it should in accretion
disks. | astro-ph_IM |
Investigating the Efficiency of the Beijing Faint Object Spectrograph
and Camera (BFOSC) of the Xinglong 2.16-m Reflector: The Beijing Faint Object Spectrograph and Camera (BFOSC) is one of the most
important instruments of the 2.16-m telescope of the Xinglong Observatory.
Every year there are ~ 20 SCI-papers published based on the observational data
of this telescope. In this work, we have systemically measured the total
efficiency of the BFOSC of the 2.16-m reflector, based on the observations of
two ESO flux standard stars. We have obtained the total efficiencies of the
BFOSC instrument of different grisms with various slit widths in almost all
ranges, and analysed the factors which effect the efficiency of telescope and
spectrograph. For the astronomical observers, the result will be useful for
them to select a suitable slit width, depending on their scientific goals and
weather conditions during the observation; For the technicians, the result will
help them systemically find out the real efficiency of telescope and
spectrograph, and further to improve the total efficiency and observing
capacity of the telescope technically. | 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 |
Understanding Instrumental Stokes Leakage in Murchison Widefield Array
Polarimetry: This paper offers an electromagnetic, more specifically array theory,
perspective on understanding strong instrumental polarization effects for
planar low-frequency "aperture arrays" with the Murchison Widefield Array (MWA)
as an example. A long-standing issue that has been seen here is significant
instrumental Stokes leakage after calibration, particularly in Stokes Q at high
frequencies. A simple model that accounts for inter-element mutual coupling is
presented which explains the prominence of Q leakage seen when the array is
scanned away from zenith in the principal planes. On these planes, the model
predicts current imbalance in the X (E-W) and Y (N-S) dipoles and hence the Q
leakage. Although helpful in concept, we find that this model is inadequate to
explain the full details of the observation data. This finding motivates
further experimentation with more rigorous models that account for both mutual
coupling and embedded element patterns. Two more rigorous models are discussed:
the "full" and "average" embedded element patterns. The viability of the "full"
model is demonstrated by simulating current MWA practice of using a Hertzian
dipole model as a Jones matrix estimate. We find that these results replicate
the observed Q leakage to approximately 2 to 5%. Finally, we offer more direct
indication for the level of improvement expected from upgrading the Jones
matrix estimate with more rigorous models. Using the "average" embedded pattern
as an estimate for the "full" model, we find that Q leakage of a few percent is
achievable. | astro-ph_IM |
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