text
stringlengths 89
2.49k
| category
stringclasses 19
values |
|---|---|
Safeguarding Old and New Journal Tables for the VO: Status for
Extragalactic and Radio Data: Independent of established data centers, and partly for my own research,
since 1989 I have been collecting the tabular data from over 2600 articles
concerned with radio sources and extragalactic objects in general. Optical
character recognition (OCR) was used to recover tables from 740 papers. Tables
from only 41 percent of the 2600 articles are available in the CDS or CATS
catalog collections, and only slightly better coverage is estimated for the NED
database. This fraction is not better for articles published electronically
since 2001. Both object databases (NED, SIMBAD, LEDA) as well as catalog
browsers (VizieR, CATS) need to be consulted to obtain the most complete
information on astronomical objects. More human resources at the data centers
and better collaboration between authors, referees, editors, publishers, and
data centers are required to improve data coverage and accessibility. The
current efforts within the Virtual Observatory (VO) project, to provide
retrieval and analysis tools for different types of published and archival data
stored at various sites, should be balanced by an equal effort to recover and
include large amounts of published data not currently available in this way. | astro-ph_IM |
Wavelet transforms of microlensing data: Denoising, extracting intrinsic
pulsations, and planetary signals: Wavelets are waveform functions that describe transient and unstable
variations, such as noises. In this work, we study the advantages of discrete
and continuous wavelet transforms (DWT and CWT) of microlensing data to denoise
them and extract their planetary signals and intrinsic pulsations hidden by
noises. We first generate synthetic microlensing data and apply wavelet
denoising to them. For these simulated microlensing data with ideally Gaussian
nosies based on the OGLE photometric accuracy, denoising with DWT reduces
standard deviations of data from real models by $0.044$-$0.048$ mag. The
efficiency to regenerate real models and planetary signals with denoised data
strongly depends on the observing cadence and decreases from $37\%$ to $0.01\%$
by worsening cadence from $15$ min to $6$ hrs. We then apply denoising on $100$
microlensing events discovered by the OGLE group. On average, wavelet denoising
for these data improves standard deviations and $\chi^{2}_{\rm n}$ of data with
respect to the best-fitted models by $0.023$ mag, and $1.16$, respectively. The
best-performing wavelets (based on either the highest signal-to-noise ratio's
peak ($\rm{SNR}_{\rm{max}}$), or the highest Pearson's correlation, or the
lowest Root Mean Squared Error (RMSE) for denoised data) are from 'Symlet', and
'Biorthogonal' wavelets families in simulated, and OGLE data, respectively. In
some denoised data, intrinsic stellar pulsations or small planetary-like
deviations appear which were covered with noises in raw data. However, through
DWT denoising rather flattened and wide planetary signals could be
reconstructed than sharp signals. CWT and 3D frequency-power-time maps could
advise about the existence of sharp signals. | astro-ph_IM |
The DESI Experiment Part II: Instrument Design: DESI (Dark Energy Spectropic Instrument) is a Stage IV ground-based dark
energy experiment that will study baryon acoustic oscillations and the growth
of structure through redshift-space distortions with a wide-area galaxy and
quasar redshift survey. The DESI instrument is a robotically-actuated,
fiber-fed spectrograph capable of taking up to 5,000 simultaneous spectra over
a wavelength range from 360 nm to 980 nm. The fibers feed ten three-arm
spectrographs with resolution $R= \lambda/\Delta\lambda$ between 2000 and 5500,
depending on wavelength. The DESI instrument will be used to conduct a
five-year survey designed to cover 14,000 deg$^2$. This powerful instrument
will be installed at prime focus on the 4-m Mayall telescope in Kitt Peak,
Arizona, along with a new optical corrector, which will provide a three-degree
diameter field of view. The DESI collaboration will also deliver a
spectroscopic pipeline and data management system to reduce and archive all
data for eventual public use. | astro-ph_IM |
$\texttt{GWFAST}$: a Fisher information matrix Python code for
third-generation gravitational-wave detectors: We introduce $\texttt{GWFAST}$, a Fisher information matrix $\texttt{Python}$
code that allows easy and efficient estimation of signal-to-noise ratios and
parameter measurement errors for large catalogs of resolved sources observed by
networks of gravitational-wave detectors. In particular, $\texttt{GWFAST}$
includes the effects of the Earth's motion during the evolution of the signal,
supports parallel computation, and relies on automatic differentiation rather
than on finite differences techniques, which allows the computation of
derivatives with accuracy close to machine precision. We also release the
library $\texttt{WF4Py}$ implementing state-of-the-art gravitational-wave
waveforms in $\texttt{Python}$. In this paper we provide a documentation of
$\texttt{GWFAST}$ and $\texttt{WF4Py}$ with practical examples and tests of
performance and reliability. In a companion paper we present forecasts for the
detection capabilities of the second and third generation of ground-based
gravitational-wave detectors, obtained with $\texttt{GWFAST}$. | astro-ph_IM |
A fast new catadioptric design for fiber-fed spectrographs: The next generation of massively multiplexed multi-object spectrographs
(DESpec, SUMIRE, BigBOSS, 4MOST, HECTOR) demand fast, efficient and affordable
spectrographs, with higher resolutions (R = 3000-5000) than current designs.
Beam-size is a (relatively) free parameter in the design, but the properties of
VPH gratings are such that, for fixed resolution and wavelength coverage, the
effect on beam-size on overall VPH efficiency is very small. For
alltransmissive cameras, this suggests modest beam-sizes (say 80-150mm) to
minimize costs; while for catadioptric (Schmidt-type) cameras, much larger
beam-sizes (say 250mm+) are preferred to improve image quality and to minimize
obstruction losses. Schmidt designs have benefits in terms of image quality,
camera speed and scattered light performance, and recent advances such as MRF
technology mean that the required aspherics are no longer a prohibitive cost or
risk. A new Schmidt/Maksutov-derived design is presented, which differs from
previous designs in having the detector package outside the camera, and
adjacent to the spectrograph pupil. The telescope pupil already contains a hole
at its center, because of the obstruction from the telescope top-end. With a
250mm beam, it is possible to largely hide a 6cm \times 6cm detector package
and its dewar within this hole. This means that the design achieves a very high
efficiency, competitive with transmissive designs. The optics are excellent, as
least as good as classic Schmidt designs, allowing F/1.25 or even faster
cameras. The principal hardware has been costed at $300K per arm, making the
design affordable. | astro-ph_IM |
Three-dimensional extinction mapping using Gaussian random fields: We present a scheme for using stellar catalogues to map the three-dimensional
distributions of extinction and dust within our Galaxy. Extinction is modelled
as a Gaussian random field, whose covariance function is set by a simple
physical model of the ISM that assumes a Kolmogorov-like power spectrum of
turbulent fluctuations. As extinction is modelled as a random field, the
spatial resolution of the resulting maps is set naturally by the data
available; there is no need to impose any spatial binning. We verify the
validity of our scheme by testing it on simulated extinction fields and show
that its precision is significantly improved over previous dust-mapping
efforts. The approach we describe here can make use of any photometric,
spectroscopic or astrometric data; it is not limited to any particular survey.
Consequently, it can be applied to a wide range of data from both existing and
future surveys. | astro-ph_IM |
INTEGRAL/IBIS nine-year Galactic Hard X-Ray Survey: Context. The INTEGRAL observatory operating in a hard X-ray/gamma domain has
gathered a large observational data set over nine years starting in 2003. Most
of the observing time was dedicated to the Galactic source population study,
making possible the deepest Galactic survey in hard X-rays ever compiled. Aims.
We aim to perform a Galactic survey that can be used as the basis of Galactic
source population studies, and perform mapping of the Milky Way in hard X-rays
over the maximum exposure available at |b|<17.5 deg. Methods. We used sky
reconstruction algorithms especially developed for the high quality imaging of
INTEGRAL/IBIS data. Results. We present sky images, sensitivity maps, and
catalogs of detected sources in the three energy bands 17-60, 17-35, and 35-80
keV in the Galactic plane at |b|<17.5 deg. The total number of sources in the
reference 17-60 keV band includes 402 objects exceeding a 4.7 sigma detection
threshold on the nine-year time-averaged map. Among the identified sources with
known and tentatively identified natures, 253 are Galactic objects (108
low-mass X-ray binaries, 82 high-mass X-ray binaries, 36 cataclysmic variables,
and 27 are of other types), and 115 are extragalactic objects, including 112
active galactic nuclei (AGNs) and 3 galaxy clusters. The sample of Galactic
sources with S/N>4.7 sigma has an identification completeness of ~92%, which is
valuable for population studies. Since the survey is based on the nine-year sky
maps, it is optimized for persistent sources and may be biased against finding
transients. | astro-ph_IM |
gSeaGen: a GENIE-based code for neutrino telescopes: The gSeaGen code is a GENIE based application to generate neutrino-induced
events in an underwater neutrino detector. The gSeaGen code is able to generate
events induced by all neutrino flavours, taking into account topological
differences between track-type and shower-like events. The neutrino interaction
is simulated taking into account the density and the composition of the media
surrounding the detector. The main features of gSeaGen will be presented
together with some examples of its application within ANTARES and KM3NeT. | astro-ph_IM |
Spectro-photometric distances to stars: a general-purpose Bayesian
approach: We developed a code that estimates distances to stars using measured
spectroscopic and photometric quantities. We employ a Bayesian approach to
build the probability distribution function over stellar evolutionary models
given these data, delivering estimates of model parameters for each star
individually. The code was first tested on simulations, successfully recovering
input distances to mock stars with <1% bias.The method-intrinsic random
distance uncertainties for typical spectroscopic survey measurements amount to
around 10% for dwarf stars and 20\% for giants, and are most sensitive to the
quality of $\log g$ measurements. The code was validated by comparing our
distance estimates to parallax measurements from the Hipparcos mission for
nearby stars (< 300 pc), to asteroseismic distances of CoRoT red giant stars,
and to known distances of well-studied open and globular clusters. The external
comparisons confirm that our distances are subject to very small systematic
biases with respect to the fundamental Hipparcos scale (+0.4 % for dwarfs, and
+1.6% for giants). The typical random distance scatter is 18% for dwarfs, and
26% for giants. For the CoRoT-APOGEE sample, the typical random distance
scatter is ~15%, both for the nearby and farther data. Our distances are
systematically larger than the CoRoT ones by about +9%, which can mostly be
attributed to the different choice of priors. The comparison to known distances
of star clusters from SEGUE and APOGEE has led to significant systematic
differences for many cluster stars, but with opposite signs, and with
substantial scatter. Finally, we tested our distances against those previously
determined for a high-quality sample of giant stars from the RAVE survey, again
finding a small systematic trend of +5% and an rms scatter of 30%. | astro-ph_IM |
Smoothed Particle Radiation Hydrodynamics: Two-Moment method with Local
Eddington Tensor Closure: We present a new radiative transfer method (SPH-M1RT) that is coupled
dynamically with smoothed particle hydrodynamics (SPH). We implement it in the
(task-based parallel) SWIFT galaxy simulation code but it can be
straightforwardly implemented in other SPH codes. Our moment-based method
simultaneously solves the radiation energy and flux equations in SPH, making it
adaptive in space and time. We modify the M1 closure relation to stabilize
radiation fronts in the optically thin limit. We also introduce anisotropic
artificial viscosity and high-order artificial diffusion schemes, which allow
the code to handle radiation transport accurately in both the optically thin
and optically thick regimes. Non-equilibrium thermo-chemistry is solved using a
semi-implicit sub-cycling technique. The computational cost of our method is
independent of the number of sources and can be lowered further by using the
reduced speed of light approximation. We demonstrate the robustness of our
method by applying it to a set of standard tests from the cosmological
radiative transfer comparison project of Iliev et al. The SPH-M1RT scheme is
well-suited for modelling situations in which numerous sources emit ionising
radiation, such as cosmological simulations of galaxy formation or simulations
of the interstellar medium. | astro-ph_IM |
Dealing with missing data in the MICROSCOPE space mission: An adaptation
of inpainting to handle colored-noise data: The MICROSCOPE space mission, launched on April 25, 2016, aims to test the
weak equivalence principle (WEP) with a 10^-15 precision. To reach this
performance requires an accurate and robust data analysis method, especially
since the possible WEP violation signal will be dominated by a strongly colored
noise. An important complication is brought by the fact that some values will
be missing -therefore, the measured time series will not be strictly regularly
sampled. Those missing values induce a spectral leakage that significantly
increases the noise in Fourier space, where the WEP violation signal is looked
for, thereby complicating scientific returns. Recently, we developed an
inpainting algorithm to correct the MICROSCOPE data for missing values. This
code has been integrated in the official MICROSCOPE data processing pipeline
because it enables us to significantly measure an equivalence principle
violation (EPV) signal in a model-independent way, in the inertial satellite
configuration. In this work, we present several improvements to the method that
may allow us now to reach the MICROSCOPE requirements for both inertial and
spin satellite configurations. The main improvement has been obtained using a
prior on the power spectrum of the colored-noise that can be directly derived
from the incomplete data. We show that after reconstructing missing values with
this new algorithm, a least-squares fit may allow us to significantly measure
an EPV signal with a 0.96x10^-15 precision in the inertial mode and 1.2x10^-15
precision in the spin mode. Although, the inpainting method presented in this
paper has been optimized to the MICROSCOPE data, it remains sufficiently
general to be used in the general context of missing data in time series
dominated by an unknown colored-noise. The improved inpainting software, called
ICON, is freely available at http://www.cosmostat.org/software/icon. | astro-ph_IM |
Data Release 2 of S-PLUS: accurate template-fitting based photometry
covering $\sim$1000 square degrees in 12 optical filters: The Southern Photometric Local Universe Survey (S-PLUS) is an ongoing survey
of $\sim$9300 deg$^2$ in the southern sky in a 12-band photometric system. This
paper presents the second data release (DR2) of S-PLUS, consisting of 514 tiles
covering an area of 950 deg$^2$. The data has been fully calibrated using a new
photometric calibration technique suitable for the new generation of wide-field
multi-filter surveys. This technique consists of a $\chi^2$ minimisation to fit
synthetic stellar templates to already calibrated data from other surveys,
eliminating the need for standard stars and reducing the survey duration by
$\sim$15\%. We compare the template-predicted and S-PLUS instrumental
magnitudes to derive the photometric zero-points (ZPs). We show that these ZPs
can be further refined by fitting the stellar templates to the 12 S-PLUS
magnitudes, which better constrain the models by adding the narrow-band
information. We use the STRIPE82 region to estimate ZP errors, which are
$\lesssim10$ mmags for filters J0410, J0430, $g$, J0515, $r$, J0660, $i$, J0861
and $z$; $\lesssim 15$ mmags for filter J0378; and $\lesssim 25$ mmags for
filters $u$ and J0395. We describe the complete data flow of the S-PLUS/DR2
from observations to the final catalogues and present a brief characterisation
of the data. We show that, for a minimum signal-to-noise threshold of 3, the
photometric depths of the DR2 range from 19.9 mag to 21.3 mag (measured in
Petrosian apertures), depending on the filter. The S-PLUS DR2 can be accessed
from the website: https://splus.cloud}{https://splus.cloud. | astro-ph_IM |
Fast and Automated Peak Bagging with DIAMONDS (FAMED): Stars of low and intermediate mass that exhibit oscillations may show tens of
detectable oscillation modes each. Oscillation modes are a powerful to
constrain the internal structure and rotational dynamics of the star, hence
tool allowing one to obtain an accurate stellar age. The tens of thousands of
solar-like oscillators that have been discovered thus far are representative of
the large diversity of fundamental stellar properties and evolutionary stages
available. Because of the wide range of oscillation features that can be
recognized in such stars, it is particularly challenging to properly
characterize the oscillation modes in detail, especially in light of large
stellar samples. Overcoming this issue requires an automated approach, which
has to be fast, reliable, and flexible at the same time. In addition, this
approach should not only be capable of extracting the oscillation mode
properties of frequency, linewidth, and amplitude from stars in different
evolutionary stages, but also able to assign a correct mode identification for
each of the modes extracted. Here we present the new freely available pipeline
FAMED (Fast and AutoMated pEak bagging with DIAMONDS), which is capable of
performing an automated and detailed asteroseismic analysis in stars ranging
from the main sequence up to the core-Helium-burning phase of stellar
evolution. This, therefore, includes subgiant stars, stars evolving along the
red giant branch (RGB), and stars likely evolving toward the early asymptotic
giant branch. In this paper, we additionally show how FAMED can detect rotation
from dipolar oscillation modes in main sequence, subgiant, low-luminosity RGB,
and core-Helium-burning stars. FAMED can be downloaded from its public GitHub
repository (https://github.com/EnricoCorsaro/FAMED). | astro-ph_IM |
Searching for changing-state AGNs in massive datasets -- I: applying
deep learning and anomaly detection techniques to find AGNs with anomalous
variability behaviours: The classic classification scheme for Active Galactic Nuclei (AGNs) was
recently challenged by the discovery of the so-called changing-state
(changing-look) AGNs (CSAGNs). The physical mechanism behind this phenomenon is
still a matter of open debate and the samples are too small and of
serendipitous nature to provide robust answers. In order to tackle this
problem, we need to design methods that are able to detect AGN right in the act
of changing-state. Here we present an anomaly detection (AD) technique designed
to identify AGN light curves with anomalous behaviors in massive datasets. The
main aim of this technique is to identify CSAGN at different stages of the
transition, but it can also be used for more general purposes, such as cleaning
massive datasets for AGN variability analyses. We used light curves from the
Zwicky Transient Facility data release 5 (ZTF DR5), containing a sample of
230,451 AGNs of different classes. The ZTF DR5 light curves were modeled with a
Variational Recurrent Autoencoder (VRAE) architecture, that allowed us to
obtain a set of attributes from the VRAE latent space that describes the
general behaviour of our sample. These attributes were then used as features
for an Isolation Forest (IF) algorithm, that is an anomaly detector for a "one
class" kind of problem. We used the VRAE reconstruction errors and the IF
anomaly score to select a sample of 8,809 anomalies. These anomalies are
dominated by bogus candidates, but we were able to identify 75 promising CSAGN
candidates. | astro-ph_IM |
Simulation of ionizing radiation in cell phone camera image sensors: The Distributed Electronic Cosmic-ray Observatory (DECO) is a cell phone app
that uses a cell phone camera image sensor to detect cosmic-ray particles and
particles from radioactive decay. Images recorded by DECO are classified by a
convolutional neural network (CNN) according to their morphology. In this
project, we develop a GEANT4-derived simulation of particle interactions inside
the CMOS sensor using the Allpix$^2$ modular framework. We simulate muons,
electrons, and photons with energy range 10 keV to 100 GeV, and their deposited
energy agrees well with expectations. Simulated events are recorded and
processed in a similar way as data images taken by DECO, and the result shows
both similar image morphology with data events and good quantitative data-Monte
Carlo agreement. | astro-ph_IM |
Design and optimization of dihedral angle offsets for the next
generation lunar retro-reflectors: Lunar laser ranging (LLR) to the Apollo retro-reflectors, which features the
most long-lasting experiment in testing General Relativity theories, has
remained operational over the past four decades. To date, with significant
improvement of ground observatory conditions, the bottleneck of LLR accuracy
lies in the retro-reflectors. A new generation of large aperture
retro-reflectors with intended dihedral angle offsets have been suggested and
implemented based on NASA's recent lunar projects to reduce its ranging
uncertainty to be less than 1.0 mm. The technique relies on the
retro-reflector's ability to offset its relative angular velocity with regard
to a ground LLR observatory (LLRO), so that the LLR accuracy can be ensured
along with the larger area of beam reflection. In deployment, solid corner-cube
reflectors (CCRs) based on empirical successes of the Apollo 11 and 15 arrays
have been selected for the next generation lunar reflectors (NGLRs) due to
their stability against heat and dust problems on the Moon. In this work, we
present the optical effects in designing the new retro-reflectors given various
sets of intended diheral angle offsets (DAOs), and support the design
principles with the measurements of of two manufactured NGLRs. | astro-ph_IM |
Atmospheric effects on extensive air showers observed with the Surface
Detector of the Pierre Auger Observatory: Atmospheric parameters, such as pressure (P), temperature (T) and density,
affect the development of extensive air showers initiated by energetic cosmic
rays. We have studied the impact of atmospheric variations on extensive air
showers by means of the surface detector of the Pierre Auger Observatory. The
rate of events shows a ~10% seasonal modulation and ~2% diurnal one. We find
that the observed behaviour is explained by a model including the effects
associated with the variations of pressure and density. The former affects the
longitudinal development of air showers while the latter influences the Moliere
radius and hence the lateral distribution of the shower particles. The model is
validated with full simulations of extensive air showers using atmospheric
profiles measured at the site of the Pierre Auger Observatory. | astro-ph_IM |
Prototype Schwarzschild-Couder Telescope for the Cherenkov Telescope
Array: Commissioning Status of the Optical System: The Cherenkov Telescope Array (CTA), with more than 100 telescopes, will be
the largest ever ground-based gamma-ray observatory and is expected to greatly
improve on both gamma-ray detection sensitivity and energy coverage compared to
current-generation detectors. The 9.7-m Schwarzschild-Couder telescope (SCT) is
one of the two candidates for the medium size telescope (MST) design for CTA.
The novel aplanatic dual-mirror SCT design offers a wide field-of-view with a
compact plate scale, allowing for a large number of camera pixels that improves
the angular resolution and reduce the night sky background noise per pixel
compared to the traditional single-mirror Davies-Cotton (DC) design of
ground-based gamma-ray telescopes. The production, installation, and the
alignment of the segmented aspherical mirrors are the main challenges for the
realization of the SCT optical system. In this contribution, we report on the
commissioning status, the alignment procedures, and initial alignment results
during the initial commissioning phase of the optical system of the prototype
SCT. | astro-ph_IM |
PulsarX: a new pulsar searching package -I. A high performance folding
program for pulsar surveys: Pulsar surveys with modern radio telescopes are becoming increasingly
computationally demanding. This is particularly true for wide field-of-view
pulsar surveys with radio interferometers, and those conducted in real or
quasi-real time. These demands result in data analysis bottlenecks that can
limit the parameter space covered by the surveys and diminish their scientific
return. In this paper, we address the computational challenge of `candidate
folding' in pulsar searching, presenting a novel, efficient approach designed
to optimise the simultaneous folding of large numbers of pulsar candidates. We
provide a complete folding pipeline appropriate for large-scale pulsar surveys
including radio frequency interference (RFI) mitigation, dedispersion, folding
and parameter optimization. By leveraging the Fast Discrete Dispersion Measure
Transform (FDMT) algorithm proposed by Zackay et al. (2017), we have developed
an optimized, and cache-friendly implementation that we term the pruned FDMT
(pFDMT). The pFDMT approach efficiently reuses intermediate processing results
and prunes the unused computation paths, resulting in a significant reduction
in arithmetic operations. In addition, we propose a novel folding algorithm
based on the Tikhonov-regularised least squares method (TLSM) that can improve
the time resolution of the pulsar profile. We present the performance of its
real-world application as an integral part of two major pulsar search projects
conducted with the MeerKAT telescope: the MPIfR-MeerKAT Galactic Plane Survey
(MMGPS) and the Transients and Pulsars with MeerKAT (TRAPUM) project. In our
processing, for approximately 500 candidates, the theoretical number of
dedispersion operations can be reduced by a factor of around 50 when compared
to brute-force dedispersion, which scales with the number of candidates. | astro-ph_IM |
A new ray-tracing scheme for 3D diffuse radiation transfer on highly
parallel architectures: We present a new numerical scheme to solve the transfer of diffuse radiation
on three-dimensional mesh grids which is efficient on processors with highly
parallel architecture such as recently popular GPUs and CPUs with multi- and
many-core architectures. The scheme is based on the ray-tracing method and the
computational cost is proportional to $N_{\rm m}^{5/3}$ where $N_{\rm m}$ is
the number of mesh grids, and is devised to compute the radiation transfer
along each light-ray completely in parallel with appropriate grouping of the
light-rays. We find that the performance of our scheme scales well with the
number of adopted CPU cores and GPUs, and also that our scheme is nicely
parallelized on a multi-node system by adopting the multiple wave front scheme,
and the performance scales well with the amount of the computational resources.
As numerical tests to validate our scheme and to give a physical criterion for
the angular resolution of our ray-tracing scheme, we perform several numerical
simulations of the photo-ionization of neutral hydrogen gas by ionizing
radiation sources without the "on-the-spot" approximation, in which the
transfer of diffuse radiation by radiative recombination is incorporated in a
self-consistent manner. | astro-ph_IM |
HAWC response to atmospheric electricity activity: The HAWC Gamma Ray observatory consists of 300 water Cherenkov detectors
(WCD) instrumented with four photo multipliers tubes (PMT) per WCD. HAWC is
located between two of the highest mountains in Mexico. The high altitude (4100
m asl), the relatively short distance to the Gulf of Mexico (~100 km), the
large detecting area (22 000 m$^2$) and its high sensitivity, make HAWC a good
instrument to explore the acceleration of particles due to the electric fields
existing inside storm clouds. In particular, the scaler system of HAWC records
the output of each one of the 1200 PMTs as well as the 2, 3, and 4-fold
multiplicities (logic AND in a time window of 30 ns) of each WCD with a
sampling rate of 40 Hz. Using the scaler data, we have identified 20
enhancements of the observed rate during periods when storm clouds were over
HAWC but without cloud-earth discharges. These enhancements can be produced by
electrons with energy of tens of MeV, accelerated by the electric fields of
tens of kV/m measured at the site during the storm periods. In this work, we
present the recorded data, the method of analysis and our preliminary
conclusions on the electron acceleration by the electric fields inside the
clouds. | astro-ph_IM |
Measurements of Charge Transfer Efficiency in a Proton-irradiated Swept
Charge Device: Charge Coupled Devices (CCDs) have been successfully used in several low
energy X-ray astronomical satellite over the past two decades. Their high
energy resolution and high spatial resolution make them an perfect tool for low
energy astronomy, such as formation of galaxy clusters and environment of black
holes. The Low Energy X-ray Telescope (LE) group is developing Swept Charge
Device (SCD) for the Hard X-ray Modulation Telescope (HXMT) satellite. SCD is a
special low energy X-ray CCD, which could be read out a thousand times faster
than traditional CCDs, simultaneously keeping excellent energy resolution. A
test method for measuring the charge transfer efficiency (CTE) of a prototype
SCD has been set up. Studies of the charge transfer inefficiency (CTI) have
been performed at a temperature range of operation, with a proton-irradiated
SCD. | astro-ph_IM |
First Impressions: Early-Time Classification of Supernovae using Host
Galaxy Information and Shallow Learning: Substantial effort has been devoted to the characterization of transient
phenomena from photometric information. Automated approaches to this problem
have taken advantage of complete phase-coverage of an event, limiting their use
for triggering rapid follow-up of ongoing phenomena. In this work, we introduce
a neural network with a single recurrent layer designed explicitly for early
photometric classification of supernovae. Our algorithm leverages transfer
learning to account for model misspecification, host galaxy photometry to solve
the data scarcity problem soon after discovery, and a custom weighted loss to
prioritize accurate early classification. We first train our algorithm using
state-of-the-art transient and host galaxy simulations, then adapt its weights
and validate it on the spectroscopically-confirmed SNe Ia, SNe II, and SNe Ib/c
from the Zwicky Transient Facility Bright Transient Survey. On observed data,
our method achieves an overall accuracy of $82 \pm 2$% within 3 days of an
event's discovery, and an accuracy of $87 \pm 5$% within 30 days of discovery.
At both early and late phases, our method achieves comparable or superior
results to the leading classification algorithms with a simpler network
architecture. These results help pave the way for rapid photometric and
spectroscopic follow-up of scientifically-valuable transients discovered in
massive synoptic surveys. | astro-ph_IM |
What could KIDSpec, a new MKID spectrograph, do on the ELT?: Microwave Kinetic Inductance Detectors (MKIDs) are beginning to become more
prominent in astronomical instrumentation, due to their sensitivity, low noise,
high pixel count for superconducting detectors, and inherent energy and time
resolving capability. The Kinetic Inductance Detector Spectrometer (KIDSpec)
will take advantage of these features, KIDSpec is a medium resolution MKID
spectrograph for the optical/near infrared. KIDSpec will contribute to many
science areas particularly those involving short and/or faint observations.
When short period binary systems are found, typical CCD detectors will struggle
to characterise these systems due to the very short exposures required, causing
errors as large as the estimated parameter itself. The KIDSpec Simulator (KSIM)
has been developed to investigate how much KIDSpec could improve on this.
KIDSpec was simulated on an ELT class telescope to find the extent of its
potential, and it was found that KIDSpec could observe a $m_{V}\approx{24}$
with an SNR of 5 for a 10s exposure at 1420 spectral resolution. This would
mean that KIDSpec on an ELT class telescope could spectroscopically follow up
on any LSST photometric discoveries of LISA verification sources. | astro-ph_IM |
A Digital Broadband Beamforming Architecture for 2-PAD: We describe an hierarchical, frequency-domain beamforming architecture for
synthesising a sky beam from the wideband antenna feeds of digital aperture
arrays. The development of densely-packed, all-digital aperture arrays is an
important area of research required for the Square Kilometre Array (SKA) radio
telescope. The design of real-time signal processing systems for digital
aperture arrays is currently a central challenge in pathfinder projects
worldwide. In particular, this work describes a specific implementation of the
beamforming architecture to the 2-Polarisation All-Digital (2-PAD) aperture
array demonstrator. | astro-ph_IM |
Even simpler modeling of quadruply lensed quasars (and random quartets)
using Witt's hyperbola: Witt (1996) has shown that for an elliptical potential, the four images of a
quadruply lensed quasar lie on a rectangular hyperbola that passes through the
unlensed quasar position and the center of the potential as well. Wynne and
Schechter (2018) have shown that, for the singular isothermal elliptical
potential (SIEP), the four images also lie on an `amplitude' ellipse centered
on the quasar position with axes parallel to the hyperbola's asymptotes. Witt's
hyperbola arises from equating the directions of both sides of the lens
equation. The amplitude ellipse derives from equating the magnitudes. One can
model any four points as an SIEP in three steps. 1. Find the rectangular
hyperbola that passes through the points. 2. Find the aligned ellipse that also
passes through them. 3. Find the hyperbola with asymptotes parallel to those of
the first that passes through the center of the ellipse and the pair of images
closest to each other. The second hyperbola and the ellipse give an SIEP that
predicts the positions of the two remaining images where the curves intersect.
Pinning the model to the closest pair guarantees a four image model. Such
models permit rapid discrimination between gravitationally lensed quasars and
random quartets of stars. | astro-ph_IM |
A Cyber Infrastructure for the SKA Telescope Manager: The Square Kilometre Array Telescope Manager (SKA TM) will be responsible for
assisting the SKA Operations and Observation Management, carrying out System
diagnosis and collecting Monitoring & Control data from the SKA sub-systems and
components. To provide adequate compute resources, scalability, operation
continuity and high availability, as well as strict Quality of Service, the TM
cyber-infrastructure (embodied in the Local Infrastructure - LINFRA) consists
of COTS hardware and infrastructural software (for example: server monitoring
software, host operating system, virtualization software, device firmware),
providing a specially tailored Infrastructure as a Service (IaaS) and Platform
as a Service (PaaS) solution. The TM infrastructure provides services in the
form of computational power, software defined networking, power, storage
abstractions, and high level, state of the art IaaS and PaaS management
interfaces. This cyber platform will be tailored to each of the two SKA Phase 1
telescopes (SKA_MID in South Africa and SKA_LOW in Australia) instances, each
presenting different computational and storage infrastructures and conditioned
by location. This cyber platform will provide a compute model enabling TM to
manage the deployment and execution of its multiple components (observation
scheduler, proposal submission tools, M&C components, Forensic tools and
several Databases, etc). In this sense, the TM LINFRA is primarily focused
towards the provision of isolated instances, mostly resorting to virtualization
technologies, while defaulting to bare hardware if specifically required due to
performance, security, availability, or other requirement. | astro-ph_IM |
Mid-band gravitational wave detection with precision atomic sensors: We assess the science reach and technical feasibility of a satellite mission
based on precision atomic sensors configured to detect gravitational radiation.
Conceptual advances in the past three years indicate that a two-satellite
constellation with science payloads consisting of atomic sensors based on laser
cooled atomic Sr can achieve scientifically interesting gravitational wave
strain sensitivities in a frequency band between the LISA and LIGO detectors,
roughly 30 mHz to 10 Hz. The discovery potential of the proposed instrument
ranges from from observation of new astrophysical sources (e.g. black hole and
neutron star binaries) to searches for cosmological sources of stochastic
gravitational radiation and searches for dark matter. | astro-ph_IM |
Focus Demo: CANFAR+Skytree: A Cloud Computing and Data Mining System for
Astronomy: This is a companion Focus Demonstration article to the CANFAR+Skytree poster
(Ball 2012), demonstrating the usage of the Skytree machine learning software
on the Canadian Advanced Network for Astronomical Research (CANFAR) cloud
computing system. CANFAR+Skytree is the world's first cloud computing system
for data mining in astronomy. | astro-ph_IM |
Study of hadron and gamma-ray acceptance of the MAGIC telescopes:
towards an improved background estimation: The MAGIC telescopes are an array of two imaging atmospheric Cherenkov
telescopes (IACTs) studying the gamma ray sky at very high-energies (VHE; E>100
GeV). The observations are performed in stereoscopic mode, with both telescopes
pointing at the same position in the sky. The MAGIC field of view (FoV)
acceptance for hadrons and gamma rays has a complex shape, which depends on
several parameters such as the azimuth and zenith angle of the observations. In
the standard MAGIC analysis, the strategy adopted for estimating this
acceptance is not optimal in the case of complex FoVs.
In this contribution we present the results of systematic studies intended to
characterise the acceptance for the entire FoV. These studies open the
possibility to apply improved background estimation methods to the MAGIC data,
useful to investigate the morphology of extended or multiple sources. | astro-ph_IM |
Demonstrating the Concept of Parallax with James Webb Space Telescope: We measured the parallax of the James Webb Space Telescope based on near
simultaneous observations using the Lulin One-meter Telescope and the GROWTH
India Telescope, separated at a distance of ~4214 km. This serves a great
demonstration for the concept of parallax commonly taught in introductory
astronomy courses. | astro-ph_IM |
High Cadence Optical Transient Searches using Drift Scan Imaging III:
Development of an Inexpensive Drive Control System and Characterisation and
Correction of Drive System Periodic Errors: In order to further develop and implement novel drift scan imaging
experiments to undertake wide field, high time resolution surveys for
millisecond optical transients, an appropriate telescope drive system is
required. This paper describes the development of a simple and inexpensive
hardware and software system to monitor, characterise, and correct the primary
category of telescope drive errors, periodic errors due to imperfections in the
drive and gear chain. A model for the periodic errors is generated from direct
measurements of the telescope drive shaft rotation, verified by comparison to
astronomical measurements of the periodic errors. The predictive model is
generated and applied in real-time in the form of corrections to the drive
rate. A demonstration of the system shows that that inherent periodic errors of
peak-to-peak amplitude ~100'' are reduced to below the seeing limit of ~3''.
This demonstration allowed an estimate of the uncertainties on the transient
sensitivity timescales of the prototype survey of Tingay & Joubert (2021), with
the nominal timescale sensitivity of 21 ms revised to be in the range of 20 -
22 ms, which does not significantly affect the results of the experiment. The
correction system will be adopted into the final version of high cadence
imaging experiment, which is currently under construction. The correction
system is inexpensive (<$A100) and composed of readily available hardware, and
is readily adaptable to other applications. Design details and codes are
therefore made publicly available. | astro-ph_IM |
Electric sail control mode for amplified transverse thrust: The electric solar wind sail produces thrust by centrifugally spanned high
voltage tethers interacting with the solar wind protons. The sail attitude can
be controlled and attitude maneuvers are possible by tether voltage modulation
synchronous with the sail rotation. Especially, the sail can be inclined with
respect to the solar wind direction to obtain transverse thrust to change the
osculating orbit angular momentum. Such an inclination has to be maintained by
a continual control voltage modulation. Consequently, the tether voltage
available for the thrust is less than the maximum voltage provided by the power
system. Using a spherical pendulum as a model for a single rotating tether, we
derive analytical estimations for the control efficiency for two separate sail
control modes. One is a continuous control modulation that corresponds to
strictly planar tether tip motion. The other is an on-off modulation with the
tether tip moving along a closed loop on a saddle surface. The novel on-off
mode is introduced here to both amplify the transverse thrust and reduce the
power consumption. During the rotation cycle, the maximum voltage is applied to
the tether only over two thrusting arcs when most of the transverse thrust is
produced. In addition to the transverse thrust, we obtain the thrusting angle
and electric power consumption for the two control modes. It is concluded that
while the thrusting angle is about half of the sail inclination for the
continuous modulation it approximately equals to the inclination angle for the
on-off modulation. The efficiency of the on-off mode is emphasized when power
consumption is considered, and the on-off mode can be used to improve the
propulsive acceleration through the reduced power system mass. | astro-ph_IM |
Current status of Shanghai VLBI correlator: Shanghai Astronomical Observatory has upgraded its DiFX cluster to 420 CPU
cores and a 432-TB storage system at the end of 2014. An international network
connection for the raw data transfer has also been established. The routine
operations for IVS sessions including CRF, AOV, and APSG series began in early
2015. In addition to the IVS observations, the correlator is dedicated to
astrophysical and astrometric programs with the Chinese VLBI Network and
international joint VLBI observations. It also worked with the new-built Tianma
65-m radio telescope and successfully found fringes as high as at X/Ka and Q
bands in late 2015. A more powerful platform is planned for the high data rate
and massive data correlation tasks in the future. | astro-ph_IM |
The SFXC software correlator for Very Long Baseline Interferometry:
Algorithms and Implementation: In this paper a description is given of the SFXC software correlator,
developed and maintained at the Joint Institute for VLBI in Europe (JIVE). The
software is designed to run on generic Linux-based computing clusters. The
correlation algorithm is explained in detail, as are some of the novel modes
that software correlation has enabled, such as wide-field VLBI imaging through
the use of multiple phase centres and pulsar gating and binning. This is
followed by an overview of the software architecture. Finally, the performance
of the correlator as a function of number of CPU cores, telescopes and spectral
channels is shown. | astro-ph_IM |
An optical test bench for the precision characterization of absolute
quantum efficiency for the TESS CCD detectors: The Transiting Exoplanet Survey Satellite (TESS) will search for planets
transiting bright stars with Ic<13. TESS has been selected by NASA for launch
in 2018 as an Astrophysics Explorer mission, and is expected to discover a
thousand or more planets that are smaller in size than Neptune. TESS will
employ four wide-field optical charge-coupled device (CCD) cameras with a
band-pass of 650 nm-1050 nm to detect temporary drops in brightness of stars
due to planetary transits. The 1050 nm limit is set by the quantum efficiency
(QE) of the CCDs. The detector assembly consists of four back-illuminated MIT
Lincoln Laboratory CCID-80 devices. Each CCID-80 device consists of 2048x2048
imaging array and 2048x2048 frame store regions. Very precise on-ground
calibration and characterization of CCD detectors will significantly assist in
the analysis of the science data obtained in space. The characterization of the
absolute QE of the CCD detectors is a crucial part of the characterization
process because QE affects the performance of the CCD significantly over the
redder wavelengths at which TESS will be operating. An optical test bench with
significantly high photometric stability has been developed to perform precise
QE measurements. The design of the test setup along with key hardware,
methodology, and results from the test campaign are presented. | astro-ph_IM |
Summary of the 3rd BINA Workshop: BINA-3 has been the third workshop of this series involving scientists from
India and Belgium aimed at fostering future joint research in the view of
cutting-edge observatories and advances in theory. BINA-3 was held at the
Graphic Era Hill University, 22-24 March 2023 at Bhimtal (near Nainital),
Uttarakhand, India. A major event was the inauguration of the International
Liquid-Mirror Telescope (ILMT), the first liquid mirror telescope devoted
exclusively to astronomy. BINA-3 provided impressive highlights encompassing
topics of both general astrophysics and solar physics. Research results and
future projects have been featured through invited and contributed talks, and
poster presentations. | astro-ph_IM |
Simulation of ultra-high energy photon propagation with PRESHOWER 2.0: In this paper we describe a new release of the PRESHOWER program, a tool for
Monte Carlo simulation of propagation of ultra-high energy photons in the
magnetic field of the Earth. The PRESHOWER program is designed to calculate
magnetic pair production and bremsstrahlung and should be used together with
other programs to simulate extensive air showers induced by photons. The main
new features of the PRESHOWER code include a much faster algorithm applied in
the procedures of simulating the processes of gamma conversion and
bremsstrahlung, update of the geomagnetic field model, and a minor correction.
The new simulation procedure increases the flexibility of the code so that it
can also be applied to other magnetic field configurations such as, for
example, encountered in the vicinity of the sun or neutron stars. | astro-ph_IM |
Gaia astrometry for stars with too few observations - a Bayesian
approach: Gaia's astrometric solution aims to determine at least five parameters for
each star, together with appropriate estimates of their uncertainties and
correlations. This requires at least five distinct observations per star. In
the early data reductions the number of observations may be insufficient for a
five-parameter solution, and even after the full mission many stars will remain
under-observed, including faint stars at the detection limit and transient
objects. In such cases it is reasonable to determine only the two position
parameters. Their formal uncertainties would however grossly underestimate the
actual errors, due to the neglected parallax and proper motion. We aim to
develop a recipe to calculate sensible formal uncertainties that can be used in
all cases of under-observed stars. Prior information about the typical ranges
of stellar parallaxes and proper motions is incorporated in the astrometric
solution by means of Bayes' rule. Numerical simulations based on the Gaia
Universe Model Snapshot (GUMS) are used to investigate how the prior influences
the actual errors and formal uncertainties when different amounts of Gaia
observations are available. We develop a criterion for the optimum choice of
priors, apply it to a wide range of cases, and derive a global approximation of
the optimum prior as a function of magnitude and galactic coordinates. The
feasibility of the Bayesian approach is demonstrated through global astrometric
solutions of simulated Gaia observations. With an appropriate prior it is
possible to derive sensible positions with realistic error estimates for any
number of available observations. Even though this recipe works also for
well-observed stars it should not be used where a good five-parameter
astrometric solution can be obtained without a prior. Parallaxes and proper
motions from a solution using priors are always biased and should not be used. | astro-ph_IM |
Visible astro-comb filtered by a passively-stabilized Fabry-Perot cavity: We demonstrate a compact 29.3 GHz visible astro-comb covering the spectrum
from 560nm to 700nm. A 837 MHz Yb:fiber laser frequency comb phase locked to a
Rb clock served as the seed comb to ensure the frequency stability and high
side mode suppression ratio. After the visible super-continuum generation, a
cavity-length-fixed Fabry-Perot cavity made by ultra-low expansion glass was
utilized to filter the comb teeth for eliminating the rapid active dithering.
The mirrors were home-made complementary chirped mirrors pair with zero
dispersion and high reflection to guarantee no mode skipping. These filtered
comb teeth were clearly resolved in an astronomical spectrograph of 49,000
resolution, exhibiting sharp linetype, zero noise floor, and uniform exposure
amplitude. | astro-ph_IM |
Characterization Of Inpaint Residuals In Interferometric Measurements of
the Epoch Of Reionization: Radio Frequency Interference (RFI) is one of the systematic challenges
preventing 21cm interferometric instruments from detecting the Epoch of
Reionization. To mitigate the effects of RFI on data analysis pipelines,
numerous inpaint techniques have been developed to restore RFI corrupted data.
We examine the qualitative and quantitative errors introduced into the
visibilities and power spectrum due to inpainting. We perform our analysis on
simulated data as well as real data from the Hydrogen Epoch of Reionization
Array (HERA) Phase 1 upper limits. We also introduce a convolutional neural
network that capable of inpainting RFI corrupted data in interferometric
instruments. We train our network on simulated data and show that our network
is capable at inpainting real data without requiring to be retrained. We find
that techniques that incorporate high wavenumbers in delay space in their
modeling are best suited for inpainting over narrowband RFI. We also show that
with our fiducial parameters Discrete Prolate Spheroidal Sequences (DPSS) and
CLEAN provide the best performance for intermittent ``narrowband'' RFI while
Gaussian Progress Regression (GPR) and Least Squares Spectral Analysis (LSSA)
provide the best performance for larger RFI gaps. However we caution that these
qualitative conclusions are sensitive to the chosen hyperparameters of each
inpainting technique. We find these results to be consistent in both simulated
and real visibilities. We show that all inpainting techniques reliably
reproduce foreground dominated modes in the power spectrum. Since the
inpainting techniques should not be capable of reproducing noise realizations,
we find that the largest errors occur in the noise dominated delay modes. We
show that in the future, as the noise level of the data comes down, CLEAN and
DPSS are most capable of reproducing the fine frequency structure in the
visibilities of HERA data. | astro-ph_IM |
Simultaneous analysis of large INTEGRAL/SPI datasets: optimizing the
computation of the solution and its variance using sparse matrix algorithms: Nowadays, analyzing and reducing the ever larger astronomical datasets is
becoming a crucial challenge, especially for long cumulated observation times.
The INTEGRAL/SPI X-gamma-ray spectrometer is an instrument for which it is
essential to process many exposures at the same time in order to increase the
low signal-to-noise ratio of the weakest sources. In this context, the
conventional methods for data reduction are inefficient and sometimes not
feasible at all. Processing several years of data simultaneously requires
computing not only the solution of a large system of equations, but also the
associated uncertainties. We aim at reducing the computation time and the
memory usage. Since the SPI transfer function is sparse, we have used some
popular methods for the solution of large sparse linear systems; we briefly
review these methods. We use the Multifrontal Massively Parallel Solver (MUMPS)
to compute the solution of the system of equations. We also need to compute the
variance of the solution, which amounts to computing selected entries of the
inverse of the sparse matrix corresponding to our linear system. This can be
achieved through one of the latest features of the MUMPS software that has been
partly motivated by this work. In this paper we provide a brief presentation of
this feature and evaluate its effectiveness on astrophysical problems requiring
the processing of large datasets simultaneously, such as the study of the
entire emission of the Galaxy. We used these algorithms to solve the large
sparse systems arising from SPI data processing and to obtain both their
solutions and the associated variances. In conclusion, thanks to these newly
developed tools, processing large datasets arising from SPI is now feasible
with both a reasonable execution time and a low memory usage. | astro-ph_IM |
Why should we keep measuring zenital dependence of muon flux? Results
obtained at Campinas (SP) BR: The zenital dependence of muon flux which reaches the earth's surface is well
known as proportional to cos^n(\theta). Generally, for practical purposes and
simplicity in calculations, n is taken as 2. However, compilations of
measurements show dependence on the geographical location of the experiments as
well as the muons energy range. Since analytical solutions appear to be
increasingly less necessary because of the higher accessibility to low cost
computational power, accurate and precise determination of the value of the
exponent n, under different conditions, can be useful in the necessary
calculations to estimate signals and backgrounds, either for terrestrial and
underground experiments. In this work we discuss a method for measuring n using
a simple muon telescope and the results obtained for measurements taken at
Campinas (SP), Brazil. After validation of the method, we intend to extend the
measurements for different geographic locations due to the simplicity of the
method, and thus collect more values of n that currently exist in compilations
of general data on cosmic rays. | astro-ph_IM |
Optical calibration of large format adaptive mirrors: Adaptive (or deformable) mirrors are widely used as wavefront correctors in
adaptive optics systems. The optical calibration of an adaptive mirror is a
fundamental step during its life-cycle: the process is in facts required to
compute a set of known commands to operate the adaptive optics system, to
compensate alignment and non common-path aberrations, to run chopped or
field-stabilized acquisitions. In this work we present the sequence of
operations for the optical calibration of adaptive mirrors, with a specific
focus on large aperture systems such as the adaptive secondaries. Such systems
will be one of the core components of the extremely large telescopes.
Beyond presenting the optical procedures, we discuss in detail the actors,
their functional requirements and the mutual interactions. A specific emphasys
is put on automation, through a clear identification of inputs, outputs and
quality indicators for each step: due to a high degrees-of-freedom count
(thousands of actuators), an automated approach is preferable to constraint the
cost and schedule. In the end we present some algorithms for the evaluation of
the measurement noise; this point is particularly important since the
calibration setup is typically a large facility in an industrial environment,
where the noise level may be a major show-stopper. | astro-ph_IM |
Numerical Strategies of Computing the Luminosity Distance: We propose two efficient numerical methods of evaluating the luminosity
distance in the spatially flat {\Lambda}CDM universe. The first method is based
on the Carlson symmetric form of elliptic integrals, which is highly accurate
and can replace numerical quadratures. The second method, using a modified
version of Hermite interpolation, is less accurate but involves only basic
numerical operations and can be easily implemented. We compare our methods with
other numerical approximation schemes and explore their respective features and
limitations. Possible extensions of these methods to other cosmological models
are also discussed. | astro-ph_IM |
Investigation of Residual Blaze Functions in Slit-Based Echelle
Spectrograph: We have studied the Residual Blaze Functions (RBF) resulting from division of
individual echelle orders by extracted flat-field in spectra obtained by
slit-fed OES spectrograph of 2m telescope of Ond\v{r}ejov observatory, Czech
Republic. We have eliminated the dependence on target and observation
conditions by semiautomatic fitting of global response function, thus getting
the instrument-only dependent part, which may be easily incorporated into data
reduction pipeline. The improvement of reliability of estimation of continuum
on spectra of targets with wide and shallow lines is noticeable and the merging
of all orders into the one long spectrum gives much more reliable results. | astro-ph_IM |
FACT - The First G-APD Cherenkov Telescope: Status and Results: The First G-APD Cherenkov telescope (FACT) is the first telescope using
silicon photon detectors (G-APD aka. SiPM). It is built on the mount of the
HEGRA CT3 telescope, still located at the Observatorio del Roque de los
Muchachos, and it is successfully in operation since Oct. 2011. The use of
Silicon devices promises a higher photon detection efficiency, more robustness
and higher precision than photo-multiplier tubes. The FACT collaboration is
investigating with which precision these devices can be operated on the
long-term. Currently, the telescope is successfully operated from remote and
robotic operation is under development. During the past months of operation,
the foreseen monitoring program of the brightest known TeV blazars has been
carried out, and first physics results have been obtained including a strong
flare of Mrk501. An instantaneous flare alert system is already in a testing
phase. This presentation will give an overview of the project and summarize its
goals, status and first results. | astro-ph_IM |
Dishing up the Data: A Decade of Space Missions: The past decade has seen Parkes once again involved in a wide range of space
tracking activities that have added to its illustrious legacy. This
contribution is a personal recollection of those tracking efforts - both real
and celluloid. We begin in a light-hearted vein with some behind-the-scenes
views of the popular film, "The DISH", and then turn to more serious
contributions; discussing the vital role of the telescope in alleviating the
great "traffic jam" at Mars in 2003/04 and salvaging the Doppler Wind
Experiment as the Huygens probe descended though the atmosphere of Saturn's
largest moon, Titan, in mid-decade. We cap off the decade with a discussion of
the search for the missing Apollo 11 slow-scan TV tapes. | astro-ph_IM |
High Contrast and High Angular Imaging at Subaru Telescope: Adaptive Optics projects at Subaru Telescope span a wide field of
capabilities ranging from ground-layer adaptive optics (GLAO) providing partial
correction over a 20 arcmin FOV to extreme adaptive optics (ExAO) for exoplanet
imaging. We describe in this paper current and upcoming narrow field-of-view
capabilities provided by the Subaru Extreme Adaptive Optics Adaptive Optics
(SCExAO) system and its instrument modules, as well as the upcoming
3000-actuator upgrade of the Nasmyth AO system. | astro-ph_IM |
POLARIX: a pathfinder mission of X-ray polarimetry: Since the birth of X-ray astronomy, spectral, spatial and timing observation
improved dramatically, procuring a wealth of information on the majority of the
classes of the celestial sources. Polarimetry, instead, remained basically
unprobed. X-ray polarimetry promises to provide additional information
procuring two new observable quantities, the degree and the angle of
polarization. POLARIX is a mission dedicated to X-ray polarimetry. It exploits
the polarimetric response of a Gas Pixel Detector, combined with position
sensitivity, that, at the focus of a telescope, results in a huge increase of
sensitivity. Three Gas Pixel Detectors are coupled with three X-ray optics
which are the heritage of JET-X mission. POLARIX will measure time resolved
X-ray polarization with an angular resolution of about 20 arcsec in a field of
view of 15 arcmin $\times$ 15 arcmin and with an energy resolution of 20 % at 6
keV. The Minimum Detectable Polarization is 12 % for a source having a flux of
1 mCrab and 10^5 s of observing time. The satellite will be placed in an
equatorial orbit of 505 km of altitude by a Vega launcher.The telemetry
down-link station will be Malindi. The pointing of POLARIX satellite will be
gyroless and it will perform a double pointing during the earth occultation of
one source, so maximizing the scientific return. POLARIX data are for 75 % open
to the community while 25 % + SVP (Science Verification Phase, 1 month of
operation) is dedicated to a core program activity open to the contribution of
associated scientists. The planned duration of the mission is one year plus
three months of commissioning and SVP, suitable to perform most of the basic
science within the reach of this instrument. | astro-ph_IM |
S-ACF: A selective estimator for the autocorrelation function of
irregularly sampled time series: We present a generalised estimator for the autocorrelation function, S-ACF,
which is an extended version of the standard estimator of the autocorrelation
function (ACF). S-ACF is a versatile definition that can robustly and
efficiently extract periodicity and signal shape information from a time
series, independent of the time sampling and with minimal assumptions about the
underlying process. Calculating the autocorrelation of irregularly sampled time
series becomes possible by generalising the lag of the standard estimator of
the ACF to a real parameter and introducing the notion of selection and weight
functions. We show that the S-ACF reduces to the standard ACF estimator for
regularly sampled time series. Using a large number of synthetic time series we
demonstrate that the performance of the S-ACF is as good or better than
commonly used Gaussian and rectangular kernel estimators, and is comparable to
a combination of interpolation and the standard estimator. We apply the S-ACF
to astrophysical data by extracting rotation periods for the spotted star KIC
5110407, and compare our results to Gaussian process (GP) regression and
Lomb-Scargle (LS) periodograms. We find that the S-ACF periods typically agree
better with those from GP regression than from LS periodograms, especially in
cases where there is evolution in the signal shape. The S-ACF has a wide range
of potential applications and should be useful in quantitative science
disciplines where irregularly sampled time series occur. A Python
implementation of the S-ACF is available under the MIT license. | astro-ph_IM |
Optimising LSST Observing Strategy for Weak Lensing Systematics: The LSST survey will provide unprecedented statistical power for measurements
of dark energy. Consequently, controlling systematic uncertainties is becoming
more important than ever. The LSST observing strategy will affect the
statistical uncertainty and systematics control for many science cases; here,
we focus on weak lensing systematics. The fact that the LSST observing strategy
involves hundreds of visits to the same sky area provides new opportunities for
systematics mitigation. We explore these opportunities by testing how different
dithering strategies (pointing offsets and rotational angle of the camera in
different exposures) affect additive weak lensing shear systematics on a
baseline operational simulation, using the $\rho-$statistics formalism. Some
dithering strategies improve systematics control at the end of the survey by a
factor of up to $\sim 3-4$ better than others. We find that a random
translational dithering strategy, applied with random rotational dithering at
every filter change, is the most effective of those strategies tested in this
work at averaging down systematics. Adopting this dithering algorithm, we
explore the effect of varying the area of the survey footprint, exposure time,
number of exposures in a visit, and exposure to the Galactic plane. We find
that any change that increases the average number of exposures (in filters
relevant to weak lensing) reduces the additive shear systematics. Some ways to
achieve this increase may not be favorable for the weak lensing statistical
constraining power or for other probes, and we explore the relative trade-offs
between these options given constraints on the overall survey parameters. | astro-ph_IM |
Astronomy and the new SI: In 2019 the International System of units (SI) conceptually re-invented
itself. This was necessary because quantum-electronic devices had become so
precise that the old SI could no longer calibrate them. The new system defines
values of fundamental constants (including $c,h,k,e$ but not $G$) and allows
units to be realized from the defined constants through any applicable equation
of physics. In this new and more abstract SI, units can take on new guises ---
for example, the kilogram is at present best implemented as a derived
electrical unit. Relevant to astronomy, however, is that several formerly
non-SI units, such as electron-volts, light-seconds, and what we may call
"gravity seconds" $GM/c^3$, can now be interpreted not as themselves units, but
as shorthand for volts and seconds being used with particular equations of
physics. Moreover, the classical astronomical units have exact and rather
convenient equivalents in the new SI: zero AB magnitude amounts to
$\simeq5\times10^{10}$ photons $\rm m^{-2}\,s^{-1}$ per logarithmic frequency
or wavelength interval, $\rm 1\,au\simeq 500$ light-seconds, $\rm 1\,pc\simeq
10^8$ light-seconds, while a solar mass $\simeq5$ gravity-seconds. As a result,
the unit conversions ubiquitous in astrophysics can now be eliminated, without
introducing other problems, as the old-style SI would have done. We review a
variety of astrophysical processes illustrating the simplifications possible
with the new-style SI, with special attention to gravitational dynamics, where
care is needed to avoid propagating the uncertainty in $G$. Well-known systems
(GPS satellites, GW170817, and the M87 black hole) are used as examples
wherever possible. | astro-ph_IM |
Astro2020 Science White Paper: Science Platforms for Resolved Stellar
Populations in the Next Decade: Over the past decade, research in resolved stellar populations has made great
strides in exploring the nature of dark matter, in unraveling the star
formation, chemical enrichment, and dynamical histories of the Milky Way and
nearby galaxies, and in probing fundamental physics from general relativity to
the structure of stars. Large surveys have been particularly important to the
biggest of these discoveries. In the coming decade, current and planned surveys
will push these research areas still further through a large variety of
discovery spaces, giving us unprecedented views into the low surface brightness
Universe, the high surface brightness Universe, the 3D motions of stars, the
time domain, and the chemical abundances of stellar populations. These
discovery spaces will be opened by a diverse range of facilities, including the
continuing Gaia mission, imaging machines like LSST and WFIRST, massively
multiplexed spectroscopic platforms like DESI, Subaru-PFS, and MSE, and
telescopes with high sensitivity and spatial resolution like JWST, the ELTs,
and LUVOIR. We do not know which of these facilities will prove most critical
for resolved stellar populations research in the next decade. We can predict,
however, that their chance of success will be maximized by granting use of the
data to broad communities, that many scientific discoveries will draw on a
combination of data from them, and that advances in computing will enable
increasingly sophisticated analyses of the large and complex datasets that they
will produce. We recommend that Astro2020 1) acknowledge the critical role that
data archives will play for stellar populations and other science in the next
decade, 2) recognize the opportunity that advances in computing will bring for
survey data analysis, and 3) consider investments in Science Platform
technology to bring these opportunities to fruition. | astro-ph_IM |
The Zwicky Transient Facility: The Zwicky Transient Facility (ZTF) is a next-generation optical synoptic
survey that builds on the experience and infrastructure of the Palomar
Transient Factory (PTF). Using a new 47 deg$^2$ survey camera, ZTF will survey
more than an order of magnitude faster than PTF to discover rare transients and
variables. I describe the survey and the camera design. Searches for young
supernovae, fast transients, counterparts to gravitational-wave detections, and
rare variables will benefit from ZTF's high cadence, wide area survey. | astro-ph_IM |
Reconstructing inclined extensive air showers from radio measurements: We present a reconstruction algorithm for extensive air showers with zenith
angles between 65$^\circ$ and 85$^\circ$ measured with radio antennas in the
30-80 MHz band. Our algorithm is based on a signal model derived from CoREAS
simulations which explicitly takes into account the asymmetries introduced by
the superposition of charge-excess and geomagnetic radiation as well as by
early-late effects. We exploit correlations among fit parameters to reduce the
dimensionality and thus ensure stability of the fit procedure. Our approach
reaches a reconstruction efficiency near 100% with an intrinsic resolution for
the reconstruction of the electromagnetic energy of well below 5\%. It can be
employed in upcoming large-scale radio detection arrays using the 30-80 MHz
band, in particular the AugerPrime Radio detector of the Pierre Auger
Observatory, and can likely be adapted to experiments such as GRAND operating
at higher frequencies. | astro-ph_IM |
PolarLight: a CubeSat X-ray Polarimeter based on the Gas Pixel Detector: The gas pixel detector (GPD) is designed and developed for high-sensitivity
astronomical X-ray polarimetry, which is a new window about to open in a few
years. Due to the small mass, low power, and compact geometry of the GPD, we
propose a CubeSat mission Polarimeter Light (PolarLight) to demonstrate and
test the technology directly in space. There is no optics but a collimator to
constrain the field of view to 2.3 degrees. Filled with pure dimethyl ether
(DME) at 0.8 atm and sealed by a beryllium window of 100 micron thick, with a
sensitive area of about 1.4 mm by 1.4 mm, PolarLight allows us to observe the
brightest X-ray sources on the sky, with a count rate of, e.g., ~0.2 counts/s
from the Crab nebula. The PolarLight is 1U in size and mounted in a 6U CubeSat,
which was launched into a low Earth Sun-synchronous orbit on October 29, 2018,
and is currently under test. More launches with improved designs are planned in
2019. These tests will help increase the technology readiness for future
missions such as the enhanced X-ray Timing and Polarimetry (eXTP), better
understand the orbital background, and may help constrain the physics with
observations of the brightest objects. | astro-ph_IM |
The Jiao Tong University Spectroscopic Telescope Project: The Jiao Tong University Spectroscopic Telescope (JUST) is a 4.4-meter f/6.0
segmentedmirror telescope dedicated to spectroscopic observations. The JUST
primary mirror is composed of 18 hexagonal segments, each with a diameter of
1.1 m. JUST provides two Nasmyth platforms for placing science instruments. One
Nasmyth focus fits a field of view of 10 arcmin and the other has an extended
field of view of 1.2 deg with correction optics. A tertiary mirror is used to
switch between the two Nasmyth foci. JUST will be installed at a site at Lenghu
in Qinghai Province, China, and will conduct spectroscopic observations with
three types of instruments to explore the dark universe, trace the dynamic
universe, and search for exoplanets: (1) a multi-fiber (2000 fibers)
medium-resolution spectrometer (R=4000-5000) to spectroscopically map galaxies
and large-scale structure; (2) an integral field unit (IFU) array of 500
optical fibers and/or a long-slit spectrograph dedicated to fast follow-ups of
transient sources for multimessenger astronomy; (3) a high-resolution
spectrometer (R~100000) designed to identify Jupiter analogs and Earth-like
planets, with the capability to characterize the atmospheres of hot exoplanets. | astro-ph_IM |
Towards a data-driven model of the sky from low Earth orbit as observed
by the Hubble Space Telescope: The sky observed by space telescopes in Low Earth Orbit (LEO) can be
dominated by stray light from multiple sources including the Earth, Sun and
Moon. This stray light presents a significant challenge to missions that aim to
make a secure measurement of the Extragalactic Background Light (EBL). In this
work we quantify the impact of stray light on sky observations made by the
Hubble Space Telescope (HST) Advanced Camera for Surveys. By selecting on
orbital parameters we successfully isolate images with sky that contain minimal
and high levels of Earthshine. In addition, we find weather observations from
CERES satellites correlates with the observed HST sky surface brightness
indicating the value of incorporating such data to characterise the sky.
Finally we present a machine learning model of the sky trained on the data used
in this work to predict the total observed sky surface brightness. We
demonstrate that our initial model is able to predict the total sky brightness
under a range of conditions to within 3.9% of the true measured sky. Moreover,
we find that the model matches the stray light-free observations better than
current physical Zodiacal light models. | astro-ph_IM |
Lattice Boltzmann Method for Electromagnetic Wave Propagation: We present a new Lattice Boltzmann (LB) formulation to solve the Maxwell
equations for electromagnetic (EM) waves propagating in a heterogeneous medium.
By using a pseudo-vector discrete Boltzmann distribution, the scheme is shown
to reproduce the continuum Maxwell equations. The technique compares well with
a pseudo-spectral method at solving for two-dimensional wave propagation in a
heterogeneous medium, which by design contains substantial contrasts in the
refractive index. The extension to three dimensions follows naturally and,
owing to the recognized efficiency of LB schemes for parallel computation in
irregular geometries, it gives a powerful method to numerically simulate a wide
range of problems involving EM wave propagation in complex media. | astro-ph_IM |
Characterizing Variable Stars in a Single Night with LSST: Stars exhibit a bewildering variety of variable behaviors ranging from
explosive magnetic flares to stochastically changing accretion to periodic
pulsations or rotations. The principal LSST surveys will have cadences too
sparse and irregular to capture most of these phenomena. A novel idea is
proposed here to observe a single Galactic field, rich in unobscured stars, in
a continuous sequence of $\sim 15$ second exposures for one long winter night
in a single photometric band. The result will be a unique dataset of $\sim 1$
million regularly spaced stellar lightcurves. The lightcurves will gives a
particularly comprehensive collection of dM star variability. A powerful array
of statistical procedures can be applied to the ensemble of lightcurves from
the long-standing fields of time series analysis, signal processing and
econometrics. Dozens of `features' describing the variability can be extracted
and subject to machine learning classification, giving a unique authoritative
objective classification of rapidly variable stars. The most effective features
can then inform the wider LSST community on the best approaches to variable
star identification and classification from the sparse, irregular cadences that
dominate the LSST project. | astro-ph_IM |
Tails: Chasing Comets with the Zwicky Transient Facility and Deep
Learning: We present Tails, an open-source deep-learning framework for the
identification and localization of comets in the image data of the Zwicky
Transient Facility (ZTF), a robotic optical time-domain survey currently in
operation at the Palomar Observatory in California, USA. Tails employs a custom
EfficientDet-based architecture and is capable of finding comets in single
images in near real time, rather than requiring multiple epochs as with
traditional methods. The system achieves state-of-the-art performance with 99%
recall, 0.01% false positive rate, and 1-2 pixel root mean square error in the
predicted position. We report the initial results of the Tails efficiency
evaluation in a production setting on the data of the ZTF Twilight survey,
including the first AI-assisted discovery of a comet (C/2020 T2) and the
recovery of a comet (P/2016 J3 = P/2021 A3). | astro-ph_IM |
Extreme-value modelling for the significance assessment of periodogram
peaks: I propose a new procedure to estimate the False Alarm Probability, the
measure of significance for peaks of periodograms. The key element of the new
procedure is the use of generalized extreme-value distributions, the limiting
distribution for maxima of variables from most continuous distributions. This
technique allows reliable extrapolation to the very high probability levels
required by multiple hypothesis testing, and enables the derivation of
confidence intervals of the estimated levels. The estimates are stable against
deviations from distributional assumptions, which are otherwise usually made
either about the observations themselves or about the theoretical univariate
distribution of the periodogram. The quality and the performance of the
procedure is demonstrated on simulations and on two multimode variable stars
from Sloan Digital Sky Survey Stripe 82. | astro-ph_IM |
HCF (HREXI Calibration Facility): Mapping out sub-pixel level responses
from high resolution Cadmium Zinc Telluride (CZT) imaging X-ray detectors: The High Resolution Energetic X-Ray Imager (HREXI) CZT detector development
program at Harvard is aimed at developing tiled arrays of finely pixelated CZT
detectors for use in wide-field coded aperture 3-200 keV X-ray telescopes. A
pixel size of $\simeq$ 600 $\mu m$ has already been achieved in the ProtoEXIST2
(P2) detector plane with CZT read out by the NuSTAR ASIC. This paves the way
for even smaller 300 $\mu m$ pixels in the next generation HREXI detectors.
This article describes a new HREXI calibration facility (HCF) which enables a
high resolution sub-pixel level (100 $\mu m$) 2D scan of a 256 $cm^2$ tiled
array of 2 $\times$ 2 cm CZT detectors illuminated by a bright X-ray AmpTek
Mini-X tube source at timescales of around a day. HCF is a significant
improvement from the previous apparatus used for scanning these detectors which
took $\simeq$ 3 weeks to complete a 1D scan of a similar detector plane.
Moreover, HCF has the capability to scan a large tiled array of CZT detectors
($32cm \times 32cm$) at 100 $\mu m$ resolution in the 10 - 50 keV energy range
which was not possible previously. This paper describes the design,
construction, and implementation of HCF for the calibration of the P2 detector
plane. | astro-ph_IM |
Disentangled Representation Learning for Astronomical Chemical Tagging: Modern astronomical surveys are observing spectral data for millions of
stars. These spectra contain chemical information that can be used to trace the
Galaxy's formation and chemical enrichment history. However, extracting the
information from spectra, and making precise and accurate chemical abundance
measurements are challenging. Here, we present a data-driven method for
isolating the chemical factors of variation in stellar spectra from those of
other parameters (i.e. \teff, \logg, \feh). This enables us to build a spectral
projection for each star with these parameters removed. We do this with no ab
initio knowledge of elemental abundances themselves, and hence bypass the
uncertainties and systematics associated with modeling that rely on synthetic
stellar spectra. To remove known non-chemical factors of variation, we develop
and implement a neural network architecture that learns a disentangled spectral
representation. We simulate our recovery of chemically identical stars using
the disentangled spectra in a synthetic APOGEE-like dataset. We show that this
recovery declines as a function of the signal to noise ratio, but that our
neural network architecture outperforms simpler modeling choices. Our work
demonstrates the feasibility of data-driven abundance-free chemical tagging. | astro-ph_IM |
Design and modeling of a moderate-resolution astronomic spectrograph
with volume-phase holographic gratings: We present an optical design of astronomic spectrograph based on a cascade of
volume-phase holographic gratings. The cascade consists of three gratings. Each
of them provides moderately high spectral resolution in a narrow range of 83
nm. Thus the spectrum image represents three lines covering region 430-680 nm.
Two versions of the scheme are described: a full-scale one with estimated
resolving power of 5300-7900 and a small-sized one intended for creation of a
lab prototype, which provides the resolving power of 1500-3000. Diffraction
efficiency modeling confirms that the system throughput can reach 75 %, while
stray light caused by the gratings crosstalk is negligible. We also propose a
design of image slicer and focal reducer allowing to couple the instrument with
the 6-m telescope. Finally, we present concept of the opto-mechanical design. | astro-ph_IM |
Using Virtual Observatory with Python: querying remote astronomical
databases: This tutorial is devoted to extending an existing catalogue with data taken
elsewhere, either from CDS Vizier or Simbad database. As an example, we used
the so-called 'Spectroscopic Survey of Stars in the Solar Neighborhood' (aka.
S4N, Allende Prieto et al. 2004) in order to retrieve all objects with
available data for the set of fundamental stellar parameters effective
temperature, surface gravity and metallicity. Then for each object in this
dataset we query Simbad database to retrieve the projected rotational velocity.
This combines Vizier and Simbad queries made using Python astroquery module.
The tutorial covers remote database access, filtering tables with arbitrary
criteria, creating and writing your own tables, and basics of plotting in
Python. | astro-ph_IM |
Synthesizing carbon nanotubes in space: Context. As the 4th most abundant element in the universe, carbon (C) is
widespread in the interstellar medium (ISM) in various allotropic forms (e.g.,
fullerenes have been identified unambiguously in many astronomical
environments, the presence of polycyclic aromatic hydrocarbon molecules in
space has been commonly admitted, and presolar graphite as well as nanodiamonds
have been identified in meteorites). As stable allotropes of these species,
whether carbon nanotubes (CNTs) and their hydrogenated counterparts are also
present in the ISM or not is unknown.
Aims. We explore the possible routes for the formation of CNTs in the ISM and
calculate their fingerprint vibrational spectral features in the infrared (IR).
Methods. We study the hydrogen-abstraction/acetylene-addition (HACA)
mechanism and investigate the synthesis of nanotubes using density functional
theory (DFT). The IR vibrational spectra of CNTs and hydrogenated nanotubes
(HNTs), as well as their cations, have also been obtained with DFT.
Results. We find that CNTs could be synthesized in space through a feasible
formation pathway. CNTs and cationic CNTs, as well as their hydrogenated
counterparts, exhibit intense vibrational transitions in the IR. Their possible
presence in the ISM could be investigated by comparing the calculated
vibrational spectra with astronomical observations made by the Infrared Space
Observatory, Spitzer Space Telescope, and particularly the upcoming James Webb
Space Telescope. | astro-ph_IM |
Statistical framework for estimating GNSS bias: We present a statistical framework for estimating global navigation satellite
system (GNSS) non-ionospheric differential time delay bias. The biases are
estimated by examining differences of measured line integrated electron
densities (TEC) that are scaled to equivalent vertical integrated densities.
The spatio-temporal variability, instrumentation dependent errors, and errors
due to inaccurate ionospheric altitude profile assumptions are modeled as
structure functions. These structure functions determine how the TEC
differences are weighted in the linear least-squares minimization procedure,
which is used to produce the bias estimates. A method for automatic detection
and removal of outlier measurements that do not fit into a model of receiver
bias is also described. The same statistical framework can be used for a single
receiver station, but it also scales to a large global network of receivers. In
addition to the Global Positioning System (GPS), the method is also applicable
to other dual frequency GNSS systems, such as GLONASS (Globalnaya
Navigazionnaya Sputnikovaya Sistema). The use of the framework is demonstrated
in practice through several examples. A specific implementation of the methods
presented here are used to compute GPS receiver biases for measurements in the
MIT Haystack Madrigal distributed database system. Results of the new algorithm
are compared with the current MIT Haystack Observatory MAPGPS bias
determination algorithm. The new method is found to produce estimates of
receiver bias that have reduced day-to-day variability and more consistent
coincident vertical TEC values. | astro-ph_IM |
Atmospheric transparency in the optical and near IR range above the
Shatdzhatmaz summit: The study of atmospheric extinction based on the MASS data has been carried
out using the classical photometric pairs method. The extinction in V band can
be estimated at 0.m 19. The water vapour content has been derived from GPS
measurements. The median value of PWV for clear nights is equal to 7.7 mm. | astro-ph_IM |
Non-LTE radiation hydrodynamics in PLUTO: Modeling the dynamics of most astrophysical structures requires an adequate
description of the radiation-matter interaction. Several numerical
(magneto)hydrodynamics codes were upgraded with a radiation module to fulfill
this request. However, those among them that use either the flux-limited
diffusion (FLD) or the M1 radiation moment approaches are restricted to the
local thermodynamic equilibrium (LTE). This assumption may be not valid in some
astrophysical cases. We present an upgraded version of the LTE
radiation-hydrodynamics module implemented in the PLUTO code, originally
developed by Kolb et al. (2013), which we have extended to handle non-LTE
regimes. Starting from the general frequency-integrated comoving-frame
equations of radiation hydrodynamics (RHD), we have justified all the
assumptions made to obtain the non-LTE equations actually implemented in the
module, under the FLD approximation. An operator-split method is employed, with
two substeps: the hydrodynamic part is solved with an explicit method by the
solvers already available in PLUTO, the non-LTE radiation diffusion and energy
exchange part is solved with an implicit method. The module is implemented in
the PLUTO environment. It uses databases of radiative quantities that can be
provided independently by the user: the radiative power loss, the Planck and
Rosseland mean opacities. Our implementation has been validated through
different tests, in particular radiative shock tests. The agreement with the
semi-analytical solutions (when available) is good, with a maximum error of 7%.
Moreover, we have proved that non-LTE approach is of paramount importance to
properly model accretion shock structures. Our radiation FLD module represents
a step toward the general non-LTE RHD modeling. The module is available, under
request, for the community. | astro-ph_IM |
Timing Calibration of the NuSTAR X-ray Telescope: The Nuclear Spectroscopic Telescope Array (NuSTAR) mission is the first
focusing X-ray telescope in the hard X-ray (3-79 keV) band. Among the phenomena
that can be studied in this energy band, some require high time resolution and
stability: rotation-powered and accreting millisecond pulsars, fast variability
from black holes and neutron stars, X-ray bursts, and more. Moreover, a good
alignment of the timestamps of X-ray photons to UTC is key for multi-instrument
studies of fast astrophysical processes. In this Paper, we describe the timing
calibration of the NuSTAR mission. In particular, we present a method to
correct the temperature-dependent frequency response of the on-board
temperature-compensated crystal oscillator. Together with measurements of the
spacecraft clock offsets obtained during downlinks passes, this allows a
precise characterization of the behavior of the oscillator. The calibrated
NuSTAR event timestamps for a typical observation are shown to be accurate to a
precision of ~65 microsec. | astro-ph_IM |
Solar diameter with 2012 Venus transit: The role of Venus and Mercury transits is crucial to know the past history of
the solar diameter. Through the W parameter, the logarithmic derivative of the
radius with respect to the luminosity, the past values of the solar luminosity
can be recovered. The black drop phenomenon affects the evaluation of the
instants of internal and external contacts between the planetary disk and the
solar limb. With these observed instants compared with the ephemerides the
value of the solar diameter is recovered. The black drop and seeing effects are
overcome with two fitting circles, to Venus and to the Sun, drawn in the
undistorted part of the image. The corrections of ephemerides due to the
atmospheric refraction will also be taken into account. The forthcoming transit
of Venus will allow an accuracy on the diameter of the Sun better than 0.01
arcsec, with good images of the ingress and of the egress taken each second.
Chinese solar observatories are in the optimal conditions to obtain valuable
data for the measurement of the solar diameter with the Venus transit of 5/6
June 2012 with an unprecedented accuracy, and with absolute calibration given
by the ephemerides. | astro-ph_IM |
Simons Observatory Large Aperture Telescope Receiver Design Overview: The Simons Observatory (SO) will make precision temperature and polarization
measurements of the cosmic microwave background (CMB) using a series of
telescopes which will cover angular scales between one arcminute and tens of
degrees and sample frequencies between 27 and 270 GHz. Here we present the
current design of the large aperture telescope receiver (LATR), a 2.4 m
diameter cryostat that will be mounted on the SO 6 m telescope and will be the
largest CMB receiver to date. The cryostat size was chosen to take advantage of
the large focal plane area having high Strehl ratios, which is inherent to the
Cross-Dragone telescope design. The LATR will be able to accommodate thirteen
optics tubes, each having a 36 cm diameter aperture and illuminating several
thousand transition-edge sensor (TES) bolometers. This set of equipment will
provide an opportunity to make measurements with unparalleled sensitivity.
However, the size and complexity of the LATR also pose numerous technical
challenges. In the following paper, we present the design of the LATR and
include how we address these challenges. The solutions we develop in the
process of designing the LATR will be informative for the general CMB
community, and for future CMB experiments like CMB-S4. | astro-ph_IM |
Digital Signal Processing in Cosmology: We address the problem of discretizing continuous cosmological signals such
as a galaxy distribution for further processing with Fast Fourier techniques.
Discretizing, in particular representing continuous signals by discrete sets of
sample points, introduces an enormous loss of information, which has to be
understood in detail if one wants to make inference from the discretely sampled
signal towards actual natural physical quantities. We therefore review the
mathematics of discretizing signals and the application of Fast Fourier
Transforms to demonstrate how the interpretation of the processed data can be
affected by these procedures. It is also a well known fact that any practical
sampling method introduces sampling artifacts and false information in the form
of aliasing. These sampling artifacts, especially aliasing, make further
processing of the sampled signal difficult. For this reason we introduce a fast
and efficient supersampling method, frequently applied in 3D computer graphics,
to cosmological applications such as matter power spectrum estimation. This
method consists of two filtering steps which allow for a much better
approximation of the ideal sampling procedure, while at the same time being
computationally very efficient.Thus, it provides discretely sampled signals
which are greately cleaned from aliasing contributions. | astro-ph_IM |
A Frequency Selective Surface based focal plane receiver for the OLIMPO
balloon-borne telescope: We describe here a focal plane array of Cold-Electron Bolometer (CEB)
detectors integrated in a Frequency Selective Surface (FSS) for the 350 GHz
detection band of the OLIMPO balloon-borne telescope. In our architecture, the
two terminal CEB has been integrated in the periodic unit cell of the FSS
structure and is impedance matched to the embedding impedance seen by it and
provides a resonant interaction with the incident sub-mm radiation. The
detector array has been designed to operate in background noise limited
condition for incident powers of 20 pW to 80 pW, making it possible to use the
same pixel in both photometric and spectrometric configurations. We present
high frequency and dc simulations of our system, together with fabrication
details. The frequency response of the FSS array, optical response measurements
with hot/cold load in front of optical window and with variable temperature
black body source inside cryostat are presented. A comparison of the optical
response to the CEB model and estimations of Noise Equivalent power (NEP) is
also presented. | astro-ph_IM |
Efficient Catalog Matching with Dropout Detection: Not only source catalogs are extracted from astronomy observations. Their sky
coverage is always carefully recorded and used in statistical analyses, such as
correlation and luminosity function studies. Here we present a novel method for
catalog matching, which inherently builds on the coverage information for
better performance and completeness. A modified version of the Zones Algorithm
is introduced for matching partially overlapping observations, where irrelevant
parts of the data are excluded up front for efficiency. Our design enables
searches to focus on specific areas on the sky to further speed up the process.
Another important advantage of the new method over traditional techniques is
its ability to quickly detect dropouts, i.e., the missing components that are
in the observed regions of the celestial sphere but did not reach the detection
limit in some observations. These often provide invaluable insight into the
spectral energy distribution of the matched sources but rarely available in
traditional associations. | astro-ph_IM |
Reproducibility of the First Image of a Black Hole in the Galaxy M87
from the Event Horizon Telescope (EHT) Collaboration: This paper presents an interdisciplinary effort aiming to develop and share
sustainable knowledge necessary to analyze, understand, and use published
scientific results to advance reproducibility in multi-messenger astrophysics.
Specifically, we target the breakthrough work associated with the generation of
the first image of a black hole, called M87. The image was computed by the
Event Horizon Telescope Collaboration. Based on the artifacts made available by
EHT, we deliver documentation, code, and a computational environment to
reproduce the first image of a black hole. Our deliverables support new
discovery in multi-messenger astrophysics by providing all the necessary tools
for generalizing methods and findings from the EHT use case. Challenges
encountered during the reproducibility of EHT results are reported. The result
of our effort is an open-source, containerized software package that enables
the public to reproduce the first image of a black hole in the galaxy M87. | astro-ph_IM |
Rapid search for massive black hole binary coalescences using deep
learning: The coalescences of massive black hole binaries are one of the main targets
of space-based gravitational wave observatories. Such gravitational wave
sources are expected to be accompanied by electromagnetic emissions. Low
latency detection of the massive black hole mergers provides a start point for
a global-fit analysis to explore the large parameter space of signals
simultaneously being present in the data but at great computational cost. To
alleviate this issue, we present a deep learning method for rapidly searching
for signals of massive black hole binaries in gravitational wave data. Our
model is capable of processing a year of data, simulated from the LISA data
challenge, in only several seconds, while identifying all coalescences of
massive black hole binaries with no false alarms. We further demonstrate that
the model shows robust resistance to a wide range of generalization cases,
including various waveform families and updated instrumental configurations.
This method offers an effective approach that combines advances in artificial
intelligence to open a new pathway for space-based gravitational wave
observations. | astro-ph_IM |
Experimental study of clusters in dense granular gas and implications
for the particle stopping time in protoplanetary disks: In protoplanetary disks, zones of dense particle configuration promote planet
formation. Solid particles in dense clouds alter their motion through
collective effects and back reaction to the gas. The effect of particle-gas
feedback with ambient solid-to-gas ratios $\epsilon > 1$ on the stopping time
of particles is investigated. In experiments on board the International Space
Station we studied the evolution of a dense granular gas while interacting with
air. We observed diffusion of clusters released at the onset of an experiment
but also the formation of new dynamical clusters. The solid-to-gas mass ratio
outside the cluster varied in the range of about $\epsilon_{\rm avg} \sim 2.5 -
60$. We find that the concept of gas drag in a viscous medium still holds, even
if the medium is strongly dominated in mass by solids. However, a collective
factor has to be used, depending on $\epsilon_{\rm avg} $, i.e. the drag force
is reduced by a factor 18 at the highest mass ratios. Therefore, flocks of
grains in protoplanetary disks move faster and collide faster than their
constituents might suggest. | astro-ph_IM |
Performance update of an event-type based analysis for the Cherenkov
Telescope Array: The Cherenkov Telescope Array (CTA) will be the next-generation observatory
in the field of very-high-energy (20 GeV to 300 TeV) gamma-ray astroparticle
physics. The traditional approach to data analysis in this field is to apply
quality cuts, optimized using Monte Carlo simulations, on the data acquired to
maximize sensitivity. Subsequent steps of the analysis typically use the
surviving events to calculate one set of instrument response functions (IRFs)
to physically interpret the results. However, an alternative approach is the
use of event types, as implemented in experiments such as the Fermi-LAT. This
approach divides events into sub-samples based on their reconstruction quality,
and a set of IRFs is calculated for each sub-sample. The sub-samples are then
combined in a joint analysis, treating them as independent observations. In
previous works we demonstrated that event types, classified using Machine
Learning methods according to their expected angular reconstruction quality,
have the potential to significantly improve the CTA angular and energy
resolution of a point-like source analysis. Now, we validated the production of
event-type wise full-enclosure IRFs, ready to be used with science tools (such
as Gammapy and ctools). We will report on the impact of using such an
event-type classification on CTA high-level performance, compared to the
traditional procedure. | astro-ph_IM |
Polarized wavelets and curvelets on the sphere: The statistics of the temperature anisotropies in the primordial cosmic
microwave background radiation field provide a wealth of information for
cosmology and for estimating cosmological parameters. An even more acute
inference should stem from the study of maps of the polarization state of the
CMB radiation. Measuring the extremely weak CMB polarization signal requires
very sensitive instruments. The full-sky maps of both temperature and
polarization anisotropies of the CMB to be delivered by the upcoming Planck
Surveyor satellite experiment are hence being awaited with excitement.
Multiscale methods, such as isotropic wavelets, steerable wavelets, or
curvelets, have been proposed in the past to analyze the CMB temperature map.
In this paper, we contribute to enlarging the set of available transforms for
polarized data on the sphere. We describe a set of new multiscale
decompositions for polarized data on the sphere, including decimated and
undecimated Q-U or E-B wavelet transforms and Q-U or E-B curvelets. The
proposed transforms are invertible and so allow for applications in data
restoration and denoising. | astro-ph_IM |
HEIDI: An Automated Process for the Identification and Extraction of
Photometric Light Curves from Astronomical Images: The production of photometric light curves from astronomical images is a very
time-consuming task. Larger data sets improve the resolution of the light
curve, however, the time requirement scales with data volume. The data analysis
is often made more difficult by factors such as a lack of suitable calibration
sources and the need to correct for variations in observing conditions from one
image to another. Often these variations are unpredictable and corrections are
based on experience and intuition.
The High Efficiency Image Detection & Identification (HEIDI) pipeline
software rapidly processes sets of astronomical images. HEIDI automatically
selects multiple sources for calibrating the images using an algorithm that
provides a reliable means of correcting for variations between images in a time
series. The algorithm takes into account that some sources may intrinsically
vary on short time scales and excludes these from being used as calibration
sources. HEIDI processes a set of images from an entire night of observation,
analyses the variations in brightness of the target objects and produces a
light curve all in a matter of minutes.
HEIDI has been tested on three different time series of asteroid 939 Isberga
and has produced consistent high quality photometric light curves in a fraction
of the usual processing time. The software can also be used for other transient
sources, e.g. gamma-ray burst optical afterglows.
HEIDI is implemented in Python and processes time series astronomical images
with minimal user interaction. HEIDI processes up to 1000 images per run in the
standard configuration. This limit can be easily increased. HEIDI is not
telescope-dependent and will process images even in the case that no telescope
specifications are provided. HEIDI has been tested on various Linux . HEIDI is
very portable and extremely versatile with minimal hardware requirements. | astro-ph_IM |
Exploring a search for long-duration transient gravitational waves
associated with magnetar bursts: Soft gamma repeaters and anomalous X-ray pulsars are thought to be magnetars,
neutron stars with strong magnetic fields of order $\mathord{\sim}
10^{13}$--$10^{15} \, \mathrm{gauss}$. These objects emit intermittent bursts
of hard X-rays and soft gamma rays. Quasiperiodic oscillations in the X-ray
tails of giant flares imply the existence of neutron star oscillation modes
which could emit gravitational waves powered by the magnetar's magnetic energy
reservoir. We describe a method to search for transient gravitational-wave
signals associated with magnetar bursts with durations of 10s to 1000s of
seconds. The sensitivity of this method is estimated by adding simulated
waveforms to data from the sixth science run of Laser Interferometer
Gravitational-wave Observatory (LIGO). We find a search sensitivity in terms of
the root sum square strain amplitude of $h_{\mathrm{rss}} = 1.3 \times 10^{-21}
\, \mathrm{Hz}^{-1/2}$ for a half sine-Gaussian waveform with a central
frequency $f_0 = 150 \, \mathrm{Hz}$ and a characteristic time $\tau = 400 \,
\mathrm{s}$. This corresponds to a gravitational wave energy of
$E_{\mathrm{GW}} = 4.3 \times 10^{46} \, \mathrm{erg}$, the same order of
magnitude as the 2004 giant flare which had an estimated electromagnetic energy
of $E_{\mathrm{EM}} = \mathord{\sim} 1.7 \times 10^{46} (d/ 8.7 \,
\mathrm{kpc})^2 \, \mathrm{erg}$, where $d$ is the distance to SGR 1806-20. We
present an extrapolation of these results to Advanced LIGO, estimating a
sensitivity to a gravitational wave energy of $E_{\mathrm{GW}} = 3.2 \times
10^{43} \, \mathrm{erg}$ for a magnetar at a distance of $1.6 \, \mathrm{kpc}$.
These results suggest this search method can probe significantly below the
energy budgets for magnetar burst emission mechanisms such as crust cracking
and hydrodynamic deformation. | astro-ph_IM |
The EPOCH Project: I. Periodic variable stars in the EROS-2 LMC database: The EPOCH (EROS-2 periodic variable star classification using machine
learning) project aims to detect periodic variable stars in the EROS-2 light
curve database. In this paper, we present the first result of the
classification of periodic variable stars in the EROS-2 LMC database. To
classify these variables, we first built a training set by compiling known
variables in the Large Magellanic Cloud area from the OGLE and MACHO surveys.
We crossmatched these variables with the EROS-2 sources and extracted 22
variability features from 28 392 light curves of the corresponding EROS-2
sources. We then used the random forest method to classify the EROS-2 sources
in the training set. We designed the model to separate not only $\delta$ Scuti
stars, RR Lyraes, Cepheids, eclipsing binaries, and long-period variables, the
superclasses, but also their subclasses, such as RRab, RRc, RRd, and RRe for RR
Lyraes, and similarly for the other variable types. The model trained using
only the superclasses shows 99% recall and precision, while the model trained
on all subclasses shows 87% recall and precision. We applied the trained model
to the entire EROS-2 LMC database, which contains about 29 million sources, and
found 117 234 periodic variable candidates. Out of these 117 234 periodic
variables, 55 285 have not been discovered by either OGLE or MACHO variability
studies. This set comprises 1 906 $\delta$ Scuti stars, 6 607 RR Lyraes, 638
Cepheids, 178 Type II Cepheids, 34 562 eclipsing binaries, and 11 394
long-period variables. A catalog of these EROS-2 LMC periodic variable stars
will be available online at http://stardb.yonsei.ac.kr and at the CDS website
(http://vizier.u-strasbg.fr/viz-bin/VizieR). | astro-ph_IM |
Towards time symmetric N-body integration: Computational efficiency demands discretised, hierarchically organised, and
individually adaptive time-step sizes (known as the block-step scheme) for the
time integration of N-body models. However, most existing N-body codes adapt
individual step sizes in a way that violates time symmetry (and symplecticity),
resulting in artificial secular dissipation (and often secular growth of energy
errors). Using single-orbit integrations, I investigate various possibilities
to reduce or eliminate irreversibility from the time stepping scheme.
Significant improvements over the standard approach are possible at little
extra effort. However, in order to reduce irreversible step-size changes to
negligible amounts, such as suitable for long-term integrations of planetary
systems, more computational effort is needed, while exact time reversibility
appears elusive for discretised individual step sizes. | astro-ph_IM |
Search for Continuous Gravitational Wave Signals in Pulsar Timing
Residuals: A New Scalable Approach with Diffusive Nested Sampling: Detecting continuous nanohertz gravitational waves (GWs) generated by
individual close binaries of supermassive black holes (CB-SMBHs) is one of the
primary objectives of pulsar timing arrays (PTAs). The detection sensitivity is
slated to increase significantly as the number of well-timed millisecond
pulsars will increase by more than an order of magnitude with the advent of
next-generation radio telescopes. Currently, the Bayesian analysis pipeline
using parallel tempering Markov chain Monte Carlo has been applied in multiple
studies for CB-SMBH searches, but it may be challenged by the high
dimensionality of the parameter space for future large-scale PTAs. One solution
is to reduce the dimensionality by maximizing or marginalizing over
uninformative parameters semi-analytically, but it is not clear whether this
approach can be extended to more complex signal models without making overly
simplified assumptions. Recently, the method of diffusive nested (DNest)
sampling shown the capability of coping with high dimensionality and
multimodality effectively in Bayesian analysis. In this paper, we apply DNest
to search for continuous GWs in simulated pulsar timing residuals and find that
it performs well in terms of accuracy, robustness, and efficiency for a PTA
including $\mathcal{O}(10^2)$ pulsars. DNest also allows a simultaneous search
of multiple sources elegantly, which demonstrates its scalability and general
applicability. Our results show that it is convenient and also high beneficial
to include DNest in current toolboxes of PTA analysis. | astro-ph_IM |
The POLARBEAR-2 and Simons Array Focal Plane Fabrication Status: We present on the status of POLARBEAR-2 A (PB2-A) focal plane fabrication.
The PB2-A is the first of three telescopes in the Simon Array (SA), which is an
array of three cosmic microwave background (CMB) polarization sensitive
telescopes located at the POLARBEAR (PB) site in Northern Chile. As the
successor to the PB experiment, each telescope and receiver combination is
named as PB2-A, PB2-B, and PB2-C. PB2-A and -B will have nearly identical
receivers operating at 90 and 150 GHz while PB2-C will house a receiver
operating at 220 and 270 GHz. Each receiver contains a focal plane consisting
of seven close-hex packed lenslet coupled sinuous antenna transition edge
sensor bolometer arrays. Each array contains 271 di-chroic optical pixels each
of which have four TES bolometers for a total of 7588 detectors per receiver.
We have produced a set of two types of candidate arrays for PB2-A. The first we
call Version 11 (V11) and uses a silicon oxide (SiOx) for the transmission
lines and cross-over process for orthogonal polarizations. The second we call
Version 13 (V13) and uses silicon nitride (SiNx) for the transmission lines and
cross-under process for orthogonal polarizations. We have produced enough of
each type of array to fully populate the focal plane of the PB2-A receiver. The
average wirebond yield for V11 and V13 arrays is 93.2% and 95.6% respectively.
The V11 arrays had a superconducting transition temperature (Tc) of 452 +/- 15
mK, a normal resistance (Rn) of 1.25 +/- 0.20 Ohms, and saturations powers of
5.2 +/- 1.0 pW and 13 +/- 1.2 pW for the 90 and 150 GHz bands respectively. The
V13 arrays had a superconducting transition temperature (Tc) of 456 +/-6 mK, a
normal resistance (Rn) of 1.1 +/- 0.2 Ohms, and saturations powers of 10.8 +/-
1.8 pW and 22.9 +/- 2.6 pW for the 90 and 150 GHz bands respectively. | astro-ph_IM |
A Method To Characterize the Wide-Angle Point Spread Function of
Astronomical Images: Uncertainty in the wide-angle Point Spread Function (PSF) at large angles
(tens of arcseconds and beyond) is one of the dominant sources of error in a
number of important quantities in observational astronomy. Examples include the
stellar mass and shape of galactic halos and the maximum extent of starlight in
the disks of nearby galaxies. However, modeling the wide-angle PSF has long
been a challenge in astronomical imaging. In this paper, we present a
self-consistent method to model the wide-angle PSF in images. Scattered light
from multiple bright stars is fitted simultaneously with a background model to
characterize the extended wing of the PSF using a Bayesian framework operating
on pixel-by-pixel level. The method is demonstrated using our software
elderflower and is applied to data from the Dragonfly Telephoto Array to model
its PSF out to 20-25 arcminutes. We compare the wide-angle PSF of Dragonfly to
that of a number of other telescopes, including the SDSS PSF, and show that on
scales of arcminutes the scattered light in the Dragonfly PSF is markedly lower
than that of other wide-field imaging telescopes. The energy in the wings of
the Dragonfly point-spread function is sufficiently low that optical
cleanliness plays an important role in defining the PSF. This component of the
PSF can be modelled accurately, highlighting the power of our self-contained
approach. | astro-ph_IM |
Systematic Serendipity: A Test of Unsupervised Machine Learning as a
Method for Anomaly Detection: Advances in astronomy are often driven by serendipitous discoveries. As
survey astronomy continues to grow, the size and complexity of astronomical
databases will increase, and the ability of astronomers to manually scour data
and make such discoveries decreases. In this work, we introduce a machine
learning-based method to identify anomalies in large datasets to facilitate
such discoveries, and apply this method to long cadence lightcurves from NASA's
Kepler Mission. Our method clusters data based on density, identifying
anomalies as data that lie outside of dense regions. This work serves as a
proof-of-concept case study and we test our method on four quarters of the
Kepler long cadence lightcurves. We use Kepler's most notorious anomaly,
Boyajian's Star (KIC 8462852), as a rare `ground truth' for testing outlier
identification to verify that objects of genuine scientific interest are
included among the identified anomalies. We evaluate the method's ability to
identify known anomalies by identifying unusual behavior in Boyajian's Star, we
report the full list of identified anomalies for these quarters, and present a
sample subset of identified outliers that includes unusual phenomena, objects
that are rare in the Kepler field, and data artifacts. By identifying <4% of
each quarter as outlying data, we demonstrate that this anomaly detection
method can create a more targeted approach in searching for rare and novel
phenomena. | astro-ph_IM |
The Radio Detector of the Pierre Auger Observatory -- status and
expected performance: As part of the ongoing AugerPrime upgrade of the Pierre Auger Observatory, we
are deploying short aperiodic loaded loop antennas measuring radio signals from
extensive air showers in the 30-80 MHz band on each of the 1,660 surface
detector stations. This new Radio Detector of the Observatory allows us to
measure the energy in the electromagnetic cascade of inclined air showers with
zenith angles larger than $\sim 65^\circ$. The water-Cherenkov detectors, in
turn, perform a virtually pure measurement of the muon component of inclined
air showers. The combination of both thus extends the mass-composition
sensitivity of the upgraded Observatory to high zenith angles and therefore
enlarges the sky coverage of mass-sensitive measurements at the highest
energies while at the same time allowing us to cross-check the performance of
the established detectors with an additional measurement technique. In this
contribution, we outline the concept and design of the Radio Detector, report
on its current status and initial results from the first deployed stations, and
illustrate its expected performance with a detailed, end-to-end simulation
study. | astro-ph_IM |
Radio Weak Lensing Shear Measurement in the Visibility Domain - II.
Source Extraction: This paper extends the method introduced in Rivi et al. (2016b) to measure
galaxy ellipticities in the visibility domain for radio weak lensing surveys.
In that paper we focused on the development and testing of the method for the
simple case of individual galaxies located at the phase centre, and proposed to
extend it to the realistic case of many sources in the field of view by
isolating visibilities of each source with a faceting technique. In this second
paper we present a detailed algorithm for source extraction in the visibility
domain and show its effectiveness as a function of the source number density by
running simulations of SKA1-MID observations in the band 950-1150 MHz and
comparing original and measured values of galaxies' ellipticities. Shear
measurements from a realistic population of 10^4 galaxies randomly located in a
field of view of 1 deg^2 (i.e. the source density expected for the current
radio weak lensing survey proposal with SKA1) are also performed. At SNR >= 10,
the multiplicative bias is only a factor 1.5 worse than what found when
analysing individual sources, and is still comparable to the bias values
reported for similar measurement methods at optical wavelengths. The additive
bias is unchanged from the case of individual sources, but is significantly
larger than typically found in optical surveys. This bias depends on the shape
of the uv coverage and we suggest that a uv-plane weighting scheme to produce a
more isotropic shape could reduce and control additive bias. | astro-ph_IM |
The ARCADE 2 Instrument: The second generation Absolute Radiometer for Cosmology, Astrophysics, and
Diffuse Emission (ARCADE 2) instrument is a balloon-borne experiment to measure
the radiometric temperature of the cosmic microwave background and Galactic and
extra-Galactic emission at six frequencies from 3 to 90 GHz. ARCADE 2 utilizes
a double-nulled design where emission from the sky is compared to that from an
external cryogenic full-aperture blackbody calibrator by cryogenic switching
radiometers containing internal blackbody reference loads. In order to further
minimize sources of systematic error, ARCADE 2 features a cold fully open
aperture with all radiometrically active components maintained at near 2.7 K
without windows or other warm objects, achieved through a novel thermal design.
We discuss the design and performance of the ARCADE 2 instrument in its 2005
and 2006 flights. | astro-ph_IM |
Science Platforms for Heliophysics Data Analysis: We recommend that NASA maintain and fund science platforms that enable
interactive and scalable data analysis in order to maximize the scientific
return of data collected from space-based instruments. | astro-ph_IM |
MuSCAT2: four-color Simultaneous Camera for the 1.52-m Telescopio Carlos
Sánchez: We report the development of a 4-color simultaneous camera for the 1.52~m
Telescopio Carlos S\'anchez (TCS) in the Teide Observatory, Canaries, Spain.
The new instrument, named MuSCAT2, has a capability of 4-color simultaneous
imaging in $g$ (400--550 nm), $r$ (550--700 nm), $i$ (700--820 nm), and $z_s$
(820--920 nm) bands. MuSCAT2 equips four 1024$\times$1024 pixel CCDs, having a
field of view of 7.4$\times$7.4 arcmin$^2$ with a pixel scale of 0.44 arcsec
per pixel. The principal purpose of MuSCAT2 is to perform high-precision
multi-color exoplanet transit photometry. We have demonstrated photometric
precisions of 0.057%, 0.050%, 0.060%, and 0.076% as root-mean-square residuals
of 60~s binning in $g$, $r$, $i$ and $z_s$ bands, respectively, for a G0 V star
WASP-12 ($V=11.57\pm0.16$). MuSCAT2 has started science operations since
January 2018, with over 250 telescope nights per year. MuSCAT2 is expected to
become a reference tool for exoplanet transit observations, and will
substantially contribute to the follow-up of the TESS and PLATO space missions. | astro-ph_IM |
Rejection criteria based on outliers in the KiDS photometric redshifts
and PDF distributions derived by machine learning: The Probability Density Function (PDF) provides an estimate of the
photometric redshift (zphot) prediction error. It is crucial for current and
future sky surveys, characterized by strict requirements on the zphot
precision, reliability and completeness. The present work stands on the
assumption that properly defined rejection criteria, capable of identifying and
rejecting potential outliers, can increase the precision of zphot estimates and
of their cumulative PDF, without sacrificing much in terms of completeness of
the sample. We provide a way to assess rejection through proper cuts on the
shape descriptors of a PDF, such as the width and the height of the maximum
PDF's peak. In this work we tested these rejection criteria to galaxies with
photometry extracted from the Kilo Degree Survey (KiDS) ESO Data Release 4,
proving that such approach could lead to significant improvements to the zphot
quality: e.g., for the clipped sample showing the best trade-off between
precision and completeness, we achieve a reduction in outliers fraction of
$\simeq 75\%$ and an improvement of $\simeq 6\%$ for NMAD, with respect to the
original data set, preserving the $\simeq 93\%$ of its content. | astro-ph_IM |
The Effects of Improper Lighting on Professional Astronomical
Observations: Europe and a number of countries in the world are investing significant
amounts of public money to operate and maintain large, ground-based
astronomical facilities. Even larger projects are under development to observe
the faintest and most remote astrophysical sources in the universe. As of
today, on the planet there are very few sites that satisfy all the demanding
criteria for such sensitive and expensive equipment, including a low level of
light pollution. Because of the uncontrolled growth of incorrect illumination,
even these protected and usually remote sites are at risk. Although the reasons
for intelligent lighting reside in energy saving and environmental effects, the
impact on scientific research cannot be neglected or underestimated, because of
its high cultural value for the progress of the whole mankind. After setting
the stage, in this paper I review the effects of improper lighting on
professional optical and near-UV astronomical data, and discuss the possible
solutions to both preserve the night sky natural darkness and produce an
efficient and cost-effective illumination. | astro-ph_IM |
The surface detector array of the Telescope Array experiment: The Telescope Array (TA) experiment, located in the western desert of
Utah,USA, is designed for observation of extensive air showers from extremely
high energy cosmic rays. The experiment has a surface detector array surrounded
by three fluorescence detectors to enable simultaneous detection of shower
particles at ground level and fluorescence photons along the shower track. The
TA surface detectors and fluorescence detectors started full hybrid observation
in March, 2008. In this article we describe the design and technical features
of the TA surface detector. | astro-ph_IM |
Soft proton scattering at grazing incidence from X-ray mirrors: analysis
of experimental data in the framework of the non-elastic approximation: Astronomical X-ray observatories with grazing incidence optics face the
problem of pseudo-focusing of low energy protons from the mirrors towards the
focal plane. Those protons constitute a variable, unpredictable component of
the non X-ray background that strongly affects astronomical observations and a
correct estimation of their flux at the focal plane is then essential. For this
reason, we investigate how they are scattered from the mirror surfaces when
impacting with grazing angles. We compare the non-elastic model of reflectivity
of particles at grazing incidence proposed by Remizovich et al. (1980) with the
few available experimental measurements of proton scattering from X-ray
mirrors. We develop a semi-empirical analytical model based on the fit of those
experimental data with the Remizovich solution. We conclude that the scattering
probability weakly depends on the energy of the impinging protons and that the
relative energy losses are necessary to correctly model the data. The model we
propose assumes no dependence on the incident energy and can be implemented in
particle transport simulation codes to generate, for instance, proton response
matrices for specific X-ray missions. Further laboratory measurements at lower
energies and on other mirror samples, such as ATHENA Silicon Pore Optics, will
improve the resolution of the model and will allow us to build the proper
proton response matrices for a wider sample of X-ray observatories. | astro-ph_IM |
Studying the Impact of Optical Aberrations on Diffraction-Limited Radial
Velocity Instruments: Spectrographs nominally contain a degree of quasi-static optical aberrations
resulting from the quality of manufactured component surfaces, imperfect
alignment, design residuals, thermal effects, and other other associated
phenomena involved in the design and construction process. Aberrations that
change over time can mimic the line centroid motion of a Doppler shift,
introducing radial velocity (RV) uncertainty that increases time-series
variability. Even when instrument drifts are tracked using a precise wavelength
calibration source, barycentric motion of the Earth leads to a wavelength shift
of stellar light causing a translation of the spectrum across the focal plane
array by many pixels. The wavelength shift allows absorption lines to
experience different optical propagation paths and aberrations over observing
epochs. We use physical optics propagation simulations to study the impact of
aberrations on precise Doppler measurements made by diffraction-limited,
high-resolution spectrographs. We quantify the uncertainties that
cross-correlation techniques introduce in the presence of aberrations and
barycentric RV shifts. We find that aberrations which shift the PSF
photo-center in the dispersion direction, in particular primary horizontal coma
and trefoil, are the most concerning. To maintain aberration-induced RV errors
less than 10 cm/s, phase errors for these particular aberrations must be held
well below 0.05 waves at the instrument operating wavelength. Our simulations
further show that wavelength calibration only partially compensates for
instrumental drifts, owing to a behavioral difference between how
cross-correlation techniques handle aberrations between starlight versus
calibration light. Identifying subtle physical effects that influence RV errors
will help ensure that diffraction-limited planet-finding spectrographs are able
to reach their full scientific potential. | astro-ph_IM |
Subsets and Splits
No saved queries yet
Save your SQL queries to embed, download, and access them later. Queries will appear here once saved.