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WTF? Discovering the Unexpected in next-generation radio continuum
surveys: Most major discoveries in astronomy have come from unplanned discoveries made
by surveying the Universe in a new way, rather than by testing a hypothesis or
conducting an investigation with planned outcomes. Next generation radio
continuum surveys such as the Evolutionary Map of the Universe (EMU: the radio
continuum survey on the new Australian SKA Pathfinder telescope), will
significantly expand the volume of observational phase space, so we can be
reasonably confident that we will stumble across unexpected new phenomena or
new types of object. However, the complexity of the instrument and the large
data volumes mean that it may be non-trivial to identify them. On the other
hand, if we don't, then we may be missing out on the most exciting science
results from EMU. We have therefore started a project called "WTF", which
explicitly aims to mine EMU data to discover unexpected science that is not
part of our primary science goals, using a variety of machine-learning
techniques and algorithms. Although targeted specifically at EMU, we expect
this approach will have broad applicability to astronomical survey data. | 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 |
Calibration of force actuators on an adaptive secondary prototype: In the context of the Large Binocular Telescope project, we present the
results of force actuator calibrations performed on an adaptive secondary
prototype called P45, a thin deformable glass with magnets glued onto its back.
Electromagnetic actuators, controlled in a closed loop with a system of
internal metrology based on capacitive sensors, continuously deform its shape
to correct the distortions of the wavefront. Calibrations of the force
actuators are needed because of the differences between driven forces and
measured forces. We describe the calibration procedures and the results,
obtained with errors of less than 1.5%. | astro-ph_IM |
Starbugs: all-singing, all-dancing fibre positioning robots: Starbugs are miniature piezoelectric 'walking' robots with the ability to
simultaneously position many optical fibres across a telescope's focal plane.
Their simple design incorporates two piezoceramic tubes to form a pair of
concentric 'legs' capable of taking individual steps of a few microns, yet with
the capacity to move a payload several millimetres per second. The Australian
Astronomical Observatory has developed this technology to enable fast and
accurate field reconfigurations without the inherent limitations of more
traditional positioning techniques, such as the 'pick and place' robotic arm.
We report on our recent successes in demonstrating Starbug technology, driven
principally by R&D efforts for the planned MANIFEST (many instrument
fibre-system) facility for the Giant Magellan Telescope. Significant
performance gains have resulted from improvements to the Starbug system,
including i) the use of a vacuum to attach Starbugs to the underside of a
transparent field plate, ii) optimisation of the control electronics, iii) a
simplified mechanical design with high sensitivity piezo actuators, and iv) the
construction of a dedicated laboratory 'test rig'. A method of reliably
rotating Starbugs in steps of several arcminutes has also been devised, which
integrates with the pre-existing x-y movement directions and offers greater
flexibility while positioning. We present measured performance data from a
prototype system of 10 Starbugs under full (closed-loop control), at field
plate angles of 0-90 degrees. | astro-ph_IM |
Discovering Strongly-lensed QSOs From Unresolved Light Curves: We present a new method of discovering galaxy-scale, strongly-lensed QSO
systems from unresolved light curves using the autocorrelation function. The
method is tested on five rungs of simulated light curves from the Time Delay
Challenge 1 that were designed to match the light-curve qualities from
existing, ongoing, and forthcoming time-domain surveys such as the Medium Deep
Survey of the Panoramic Survey Telescope And Rapid Response System 1, the
Zwicky Transient Facility, and the Rubin Observatory Legacy Survey of Space and
Time. Among simulated lens systems for which time delays can be successfully
measured by current best algorithms, our method achieves an overall true
positive rate of 28--58% for doubly-imaged QSOs (doubles) and 36--60% for
quadruply-imaged QSOs (quads) while maintains $\lesssim$10% false positive
rates. We also apply the method to observed light curves of 22 known
strongly-lensed QSOs, and recover 20% of doubles and 25% of quads. The tests
demonstrate the capability of our method for discovering strongly-lensed QSOs
from major time domain surveys. The performance of our method can be further
improved by analysing multi-filter light curves and supplementing with
morphological, colour, and/or astrometric constraints. More importantly, our
method is particularly useful for discovering small-separation strongly-lensed
QSOs, complementary to traditional imaging-based methods. | astro-ph_IM |
Matched filtering for gravitational wave detection without template bank
driven by deep learning template prediction model bank: The existing matched filtering method for gravitational wave (GW) search
relies on a template bank. The computational efficiency of this method scales
with the size of the templates within the bank. Higher-order modes and
eccentricity will play an important role when third-generation detectors
operate in the future. In this case, traditional GW search methods will hit
computational limits. To speed up the computational efficiency of GW search, we
propose the utilization of a deep learning (DL) model bank as a substitute for
the template bank. This model bank predicts the latent templates embedded in
the strain data. Combining an envelope extraction network and an astrophysical
origin discrimination network, we realize a novel GW search framework. The
framework can predict the GW signal's matched filtering signal-to-noise ratio
(SNR). Unlike the end-to-end DL-based GW search method, our statistical SNR
holds greater physical interpretability than the $p_{score}$ metric. Moreover,
the intermediate results generated by our approach, including the predicted
template, offer valuable assistance in subsequent GW data processing tasks such
as parameter estimation and source localization. Compared to the traditional
matched filtering method, the proposed method can realize real-time analysis.
The minor improvements in the future, the proposed method may expand to other
scopes of GW search, such as GW emitted by the supernova explosion. | astro-ph_IM |
Camera Calibration for the IceCube Upgrade and Gen2: An upgrade to the IceCube Neutrino Telescope is currently under construction.
For this IceCube Upgrade, seven new strings will be deployed in the central
region of the 86 string IceCube detector to enhance the capability to detect
neutrinos in the GeV range. One of the main science objectives of the IceCube
Upgrade is an improved calibration of the IceCube detector to reduce systematic
uncertainties related to the optical properties of the ice. We have developed a
novel optical camera and illumination system that will be part of 700 newly
developed optical modules to be deployed with the IceCube Upgrade. A
combination of transmission and reflection photographic measurements will be
used to measure the optical properties of bulk ice between strings and refrozen
ice in the drill hole, to determine module positions, and to survey the local
ice environments surrounding the sensor module. In this contribution we present
the production design, acceptance testing, and plan for post-deployment
calibration measurements with the camera system. | astro-ph_IM |
Asymptotic Orbits in Barred Spiral Galaxies: We study the formation of the spiral structure of barred spiral galaxies,
using an $N$-body model. The evolution of this $N$-body model in the adiabatic
approximation maintains a strong spiral pattern for more than 10 bar rotations.
We find that this longevity of the spiral arms is mainly due to the phenomenon
of stickiness of chaotic orbits close to the unstable asymptotic manifolds
originated from the main unstable periodic orbits, both inside and outside
corotation. The stickiness along the manifolds corresponding to different
energy levels supports parts of the spiral structure. The loci of the disc
velocity minima (where the particles spend most of their time, in the
configuration space) reveal the density maxima and therefore the main
morphological structures of the system. We study the relation of these loci
with those of the apocentres and pericentres at different energy levels. The
diffusion of the sticky chaotic orbits outwards is slow and depends on the
initial conditions and the corresponding Jacobi constant. | astro-ph_IM |
Photostability of gas- and solid-phase biomolecules within dense
molecular clouds due to soft X-rays: An experimental photochemistry study involving gas- and solid-phase amino
acids (glycine, DL-valine, DL-proline) and nucleobases (adenine and uracil)
under soft X-rays was performed. The aim was to test the molecular stabilities
of essential biomolecules against ionizing photon fields inside dense molecular
clouds and protostellar disks analogs. In these environments, the main energy
sources are the cosmic rays and soft X-rays. The measurements were taken at the
Brazilian Synchrotron Light Laboratory (LNLS), employing 150 eV photons.
In-situ sample analysis was performed by Time-of-flight mass spectrometer
(TOF-MS) and Fourier transform infrared (FTIR) spectrometer, for gas- and
solid- phase analysis, respectively. The half-life of solid phase amino acids,
assumed to be present at grain mantles, is at least 3E5 years and 3E8 years
inside dense molecular clouds and protoplanetary disks, respectively. We
estimate that for gas-phase compounds these values increase one order of
magnitude since the dissociation cross section of glycine is lower at gas-phase
than at solid phase for the same photon energy. The half-life of solid phase
nucleobases is about 2-3 orders of magnitude higher than found for amino acids.
The results indicate that nucleobases are much more resistant to ionizing
radiation than amino acids. We consider these implications for the survival and
transfer of biomolecules in space environments. | astro-ph_IM |
Time-division SQUID multiplexers with reduced sensitivity to external
magnetic fields: Time-division SQUID multiplexers are used in many applications that require
exquisite control of systematic error. One potential source of systematic error
is the pickup of external magnetic fields in the multiplexer. We present
measurements of the field sensitivity figure of merit, effective area, for both
the first stage and second stage SQUID amplifiers in three NIST SQUID
multiplexer designs. These designs include a new variety with improved
gradiometry that significantly reduces the effective area of both the first and
second stage SQUID amplifiers. | astro-ph_IM |
eROSITA on SRG: a X-ray all-sky survey mission: eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is the
core instrument on the Russian Spektrum-Roentgen-Gamma (SRG) mission which is
scheduled for launch in late 2012. eROSITA is fully approved and funded by the
German Space Agency DLR and the Max-Planck-Society. The design driving science
is the detection of 50 - 100 thousands Clusters of Galaxies up to redshift z ~
1.3 in order to study the large scale structure in the Universe and test
cosmological models, especially Dark Energy. This will be accomplished by an
all-sky survey lasting for four years plus a phase of pointed observations.
eROSITA consists of seven Wolter-I telescope modules, each equipped with 54
Wolter-I shells having an outer diameter of 360 mm. This would provide and
effective area at 1.5 keV of ~ 1500 cm2 and an on axis PSF HEW of 15" which
would provide an effective angular resolution of 25"-30". In the focus of each
mirror module, a fast frame-store pn-CCD will provide a field of view of 1 deg
in diameter for an active FOV of ~ 0.83 deg^2. At the time of writing the
instrument development is currently in phase C/D. | astro-ph_IM |
Gaia reference frame amid quasar variability and proper motion patterns
in the data: Gaia's very accurate astrometric measurements will allow the International
Celestial Reference Frame (ICRF) to be improved by a few orders of magnitude in
the optical. Several sets of quasars are used to define a kinematically stable
non-rotating reference frame with the barycentre of the Solar System as its
origin. Gaia will also observe a large number of galaxies which could obtain
accurate positions and proper motions although they are not point-like. The
optical stability of the quasars is critical and we investigate how accurately
the reference frame can be recovered. Various proper motion patterns are also
present in the data, the best known is caused by the acceleration of the Solar
System Barycentre, presumably, towards the Galactic centre. We review some
other less-well-known effects that are not part of standard astrometric models.
We model quasars and galaxies using realistic sky distributions, magnitudes and
redshifts. Position variability is introduced using a Markov chain model. The
reference frame is determined using the algorithm developed for the Gaia
mission which also determines the acceleration of the Solar System. We also
test a method to measure the velocity of the Solar System barycentre in a
cosmological frame. We simulate the recovery of the reference frame and the
acceleration of the Solar System and conclude that they are not significantly
disturbed in the presence of quasar variability which is statistically
averaged. However, the effect of a non-uniform sky distribution of the quasars
can result in a correlation between the reference frame and acceleration which
degrades the solution. Our results suggest that an attempt should be made to
astrometrically determine the redshift dependent apparent drift of galaxies due
to our velocity relative to the CMB, which in principle could allow the
determination of the Hubble parameter. | astro-ph_IM |
MAORY AO performances: The Multi-conjugate Adaptive Optics RelaY (MAORY) should provide 30% SR in K
band (50% goal) on half of the sky at the South Galactic Pole. Assessing its
performance and the sensitivity to parameter variations during the design phase
is a fundamental step for the engineering of such a complex system. This step,
centered on numerical simulations, is the connection between the performance
requirements and the Adaptive Optics system configuration. In this work we
present MAORY configuration and performance and we justify theAdaptive Optics
system design choices. | astro-ph_IM |
A way to deal with the fringe-like pattern in VIMOS-IFU data: The use of integral field units is now commonplace at all major observatories
offering efficient means of obtaining spectral as well as imaging information
at the same time. IFU instrument designs are complex and spectral images have
typically highly condensed formats, therefore presenting challenges for the IFU
data reduction pipelines. In the case of the VLT VIMOS-IFU, a fringe-like
pattern affecting the spectra well into the optical and blue wavelength regime
as well as artificial intensity variations, require additional reduction steps
beyond standard pipeline processing. In this research note we propose an
empirical method for the removal of the fringe-like pattern in the spectral
domain and the intensity variations in the imaging domain. We also demonstrate
the potential consequences for data analysis if the effects are not corrected.
Here we use the example of deriving stellar velocity, velocity dispersion and
absorption line-strength maps for early-type galaxies. We derive for each
spectrum, reduced by the ESO standard VIMOS pipeline, a correction-spectrum by
using the median of the eight surrounding spectra as a proxy for the
unaffected, underlying spectrum. This method relies on the fact that our
science targets (nearby ETGs) cover the complete FoV of the VIMOS-IFU with
slowly varying spectral properties and that the exact shape of the fringe-like
pattern is nearly independent and highly variable between neighboring spatial
positions. We find that the proposed correction methods for the removal of the
fringe-like pattern and the intensity variations in VIMOS-IFU data-cubes are
suitable to allow for meaningful data analysis in our sample of nearby
early-type galaxies. Since the method relies on the scientific target
properties it is not suitable for general implementation in the pipeline
software for VIMOS. | astro-ph_IM |
A Near Infrared Laser Frequency Comb for High Precision Doppler Planet
Surveys: We discuss the laser frequency comb as a near infrared astronomical
wavelength reference, and describe progress towards a near infrared laser
frequency comb at the National Institute of Standards and Technology and at the
University of Colorado where we are operating a laser frequency comb suitable
for use with a high resolution H band astronomical spectrograph. | astro-ph_IM |
An Inexpensive Liquid Crystal Spectropolarimeter for the Dominion
Astrophysical Observatory Plaskett Telescope: A new, inexpensive polarimetric unit has been constructed for the Dominion
Astrophysical Observatory (DAO) 1.8-m Plaskett telescope. It is implemented as
a plug-in module for the telescope's existing Cassegrain spectrograph, and
enables medium resolution (R~10,000) circular spectropolarimetry of point
sources. A dual-beam design together with fast switching of the wave plate at
rates up to 100Hz, and synchronized with charge shuffling on the CCD, is used
to significantly reduce instrumental effects and achieve high-precision
spectropolarimetric measurements for a very low cost. The instrument is
optimized to work in the wavelength range 4700 - 5300A to simultaneously detect
polarization signals in the H beta line as well as nearby metallic lines. In
this paper we describe the technical details of the instrument, our observing
strategy and data reduction techniques, and present tests of its scientific
performance. | astro-ph_IM |
Astronomical seeing and ground-layer turbulence in the Canadian High
Arctic: We report results of a two-year campaign of measurements, during arctic
winter darkness, of optical turbulence in the atmospheric boundary-layer above
the Polar Environment Atmospheric Laboratory in northern Ellesmere Island
(latitude +80 deg N). The data reveal that the ground-layer turbulence in the
Arctic is often quite weak, even at the comparatively-low 610 m altitude of
this site. The median and 25th percentile ground-layer seeing, at a height of
20 m, are found to be 0.57 and 0.25 arcsec, respectively. When combined with a
free-atmosphere component of 0.30 arcsec, the median and 25th percentile total
seeing for this height is 0.68 and 0.42 arcsec respectively. The median total
seeing from a height of 7 m is estimated to be 0.81 arcsec. These values are
comparable to those found at the best high-altitude astronomical sites. | astro-ph_IM |
pyCallisto: A Python Library To Process The CALLISTO Spectrometer Data: CALLISTO is a radio spectrometer designed to monitor the transient radio
emissions/bursts originated from the solar corona in the frequency range
$45-870$ MHz. At present, there are $\gtrsim 150$ stations (together forms an
e-CALLISTO network) around the globe continuously monitoring the Sun 24 hours a
day. We have developed a pyCallisto, a python library to process the CALLISTO
data observed by all stations of the e-CALLISTO network. In this article, we
demonstrate various useful functions that are routinely used to process the
CALLISTO data with suitable examples. This library is not only efficient in
processing the data but plays a significant role in developing automatic
classification algorithms of different types of solar radio bursts. | astro-ph_IM |
Correcting Bandwidth Depolarization by Extreme Faraday Rotation: Measurements of the polarization of radio emission are subject to a number of
depolarization effects such as bandwidth depolarization, which is caused by the
averaging effect of a finite channel bandwidth combined with the
frequency-dependent polarization caused by Faraday rotation. There have been
very few mathematical treatments of bandwidth depolarization, especially in the
context of the rotation measure (RM) synthesis method for analyzing radio
polarization data. We have found a simple equation for predicting if bandwidth
depolarization is significant for a given observational configuration. We have
derived and tested three methods of modifying RM synthesis to correct for
bandwidth depolarization. From these tests we have developed a new algorithm
that can detect bandwidth-depolarized signals with higher signal-to-noise than
conventional RM synthesis and recover the correct source polarization
properties (RM and polarized intensity). We have verified that this algorithm
works as expected with real data from the LOFAR Two-metre Sky Survey. To make
this algorithm available to the community, we have added it as a new tool in
the RM-Tools polarization analysis package. | astro-ph_IM |
The Multi-slit Approach to Coronal Spectroscopy with the Multi-slit
Solar Explorer (MUSE): The Multi-slit Solar Explorer (MUSE) is a proposed mission aimed at
understanding the physical mechanisms driving the heating of the solar corona
and the eruptions that are at the foundation of space weather. MUSE contains
two instruments, a multi-slit EUV spectrograph and a context imager. It will
simultaneously obtain EUV spectra (along 37 slits) and context images with the
highest resolution in space (0.33-0.4 arcsec) and time (1-4 s) ever achieved
for the transition region and corona. The MUSE science investigation will
exploit major advances in numerical modeling, and observe at the spatial and
temporal scales on which competing models make testable and distinguishable
predictions, thereby leading to a breakthrough in our understanding of coronal
heating and the drivers of space weather. By obtaining spectra in 4 bright EUV
lines (Fe IX 171A, Fe XV 284A, Fe XIX-XXI 108A) covering a wide range of
transition region and coronal temperatures along 37 slits simultaneously, MUSE
will be able to "freeze" the evolution of the dynamic coronal plasma. We
describe MUSE's multi-slit approach and show that the optimization of the
design minimizes the impact of spectral lines from neighboring slits, generally
allowing line parameters to be accurately determined. We also describe a
Spectral Disambiguation Code to resolve multi-slit ambiguity in locations where
secondary lines are bright. We use simulations of the corona and eruptions to
perform validation tests and show that the multi-slit disambiguation approach
allows accurate determination of MUSE observables in locations where
significant multi-slit contamination occurs. | astro-ph_IM |
The Road to Quasars: Although the extragalactic nature of 3C 48 and other quasi stellar radio
sources was discussed as early as 1960 by John Bolton and others, it was
rejected largely because of preconceived ideas about what appeared to be
unrealistically high radio and optical luminosities. Not until the 1962
occultations of the strong radio source 3C 273 at Parkes, which led Maarten
Schmidt to identify 3C 273 with an apparent stellar object at a redshift of
0.16, was the true nature understood. Successive radio and optical measurements
quickly led to the identification of other quasars with increasingly large
redshifts and the general, although for some decades not universal, acceptance
of quasars as the very luminous nuclei of galaxies. Curiously, 3C 273, which is
one of the strongest extragalactic sources in the sky, was first cataloged in
1959 and the magnitude 13 optical counterpart was observed at least as early as
1887. Since 1960, much fainter optical counterparts were being routinely
identified using accurate radio interferometer positions which were measured
primarily at the Caltech Owens Valley Radio Observatory. However, 3C 273 eluded
identification until the series of lunar occultation observations led by Cyril
Hazard. Although an accurate radio position had been obtained earlier with the
OVRO interferometer, inexplicably 3C 273 was initially misidentified with a
faint galaxy located about an arc minute away from the true quasar position. | astro-ph_IM |
Pulsar Candidate Identification Using Semi-Supervised Generative
Adversarial Networks: Machine learning methods are increasingly helping astronomers identify new
radio pulsars. However, they require a large amount of labelled data, which is
time consuming to produce and biased. Here we describe a Semi-Supervised
Generative Adversarial Network (SGAN) which achieves better classification
performance than the standard supervised algorithms using majority unlabelled
datasets. We achieved an accuracy and mean F-Score of 94.9% trained on only 100
labelled candidates and 5000 unlabelled candidates compared to our standard
supervised baseline which scored at 81.1% and 82.7% respectively. Our final
model trained on a much larger labelled dataset achieved an accuracy and mean
F-score value of 99.2% and a recall rate of 99.7%. This technique allows for
high quality classification during the early stages of pulsar surveys on new
instruments when limited labelled data is available. We open-source our work
along with a new pulsar-candidate dataset produced from the High Time
Resolution Universe - South Low Latitude Survey. This dataset has the largest
number of pulsar detections of any public dataset and we hope it will be a
valuable tool for benchmarking future machine learning models. | astro-ph_IM |
Geometric calibration of Colour and Stereo Surface Imaging System of
ESA's Trace Gas Orbiter: There are many geometric calibration methods for "standard" cameras. These
methods, however, cannot be used for the calibration of telescopes with large
focal lengths and complex off-axis optics. Moreover, specialized calibration
methods for the telescopes are scarce in literature. We describe the
calibration method that we developed for the Colour and Stereo Surface Imaging
System (CaSSIS) telescope, on board of the ExoMars Trace Gas Orbiter (TGO).
Although our method is described in the context of CaSSIS, with camera-specific
experiments, it is general and can be applied to other telescopes. We further
encourage re-use of the proposed method by making our calibration code and data
available on-line. | astro-ph_IM |
Fundamental limits to high-contrast wavefront control: The current generation of ground-based coronagraphic instruments uses
deformable mirrors to correct for phase errors and to improve contrast levels
at small angular separations. Improving these techniques, several space and
ground based instruments are currently developed using two deformable mirrors
to correct for both phase and amplitude errors. However, as wavefront control
techniques improve, more complex telescope pupil geome- tries (support
structures, segmentation) will soon be a limiting factor for these next
generation coronagraphic instruments. In this paper we discuss fundamental
limits associated with wavefront control with deformable mirrors in high
contrast coronagraph. We start with an analytic prescription of wavefront
errors, along with their wave- length dependence, and propagate them through
coronagraph models. We then consider a few wavefront control architectures,
number of deformable mirrors and their placement in the optical train of the
instrument, and algorithms that can be used to cancel the starlight scattered
by these wavefront errors over a finite bandpass. For each configuration we
derive the residual contrast as a function of bandwidth and of the properties
of the incoming wavefront. This result has consequences when setting the
wavefront requirements, along with the wavefront control architecture of future
high contrast instrument both from the ground and from space. In particular we
show that these limits can severely affect the effective Outer Working Angle
that can be achieved by a given coronagraph instrument. | astro-ph_IM |
Short Spacing Synthesis from a Primary Beam Scanned Interferometer: Aperture synthesis instruments providing a generally highly uniform sampling
of the visibility function often leave an unsampled hole near the origin of the
(u,v)-plane. In this paper, originally published in 1979, we first describe the
common solution of retrieving the information from scans made with a large
single-dish telescope. However, this is not the only means by which short
spacing visibility data can be obtained. We propose an alternative technique
that employs a short-baseline interferometer to scan the entire primary beam
area. The obvious advantage is that a short-baseline pair from the synthesis
instrument can be used, ensuring uniformity in instrumental characteristics.
This technique is the basis for the mosaicing algorithms now commonly used in
aperture synthesis radio astronomy imaging. | astro-ph_IM |
Trend Filtering -- II. Denoising Astronomical Signals with Varying
Degrees of Smoothness: Trend filtering---first introduced into the astronomical literature in Paper
I of this series---is a state-of-the-art statistical tool for denoising
one-dimensional signals that possess varying degrees of smoothness. In this
work, we demonstrate the broad utility of trend filtering to observational
astronomy by discussing how it can contribute to a variety of spectroscopic and
time-domain studies. The observations we discuss are (1) the Lyman-$\alpha$
forest of quasar spectra; (2) more general spectroscopy of quasars, galaxies,
and stars; (3) stellar light curves with planetary transits; (4) eclipsing
binary light curves; and (5) supernova light curves. We study the
Lyman-$\alpha$ forest in the greatest detail---using trend filtering to map the
large-scale structure of the intergalactic medium along quasar-observer lines
of sight. The remaining studies share broad themes of: (1) estimating
observable parameters of light curves and spectra; and (2) constructing
observational spectral/light-curve templates. We also briefly discuss the
utility of trend filtering as a tool for one-dimensional data reduction and
compression. | astro-ph_IM |
Processing System for Coherent Dedispersion of Pulsar Radio Emission: The work describes a system for converting VLBI observation data using the
algorithms of coherent dedispersion and compensation of two-bit signal
sampling. Coherent dedispersion is important for processing pulsar observations
to obtain the best temporal resolution, while correction for signal sampling
makes it possible to get rid of a number of parasitic effects that interfere
with the analysis of the diffraction pattern of pulsars. A pipeline has been
established that uses the developed converter and the ASC Software Correlator,
which will allow reprocessing all archived data of Radioastron pulsar
observations and to conduct a search for giant pulses, which requires the best
temporal resolution. | astro-ph_IM |
Dual Purpose Lyot Coronagraph Masks for Simultaneous High-Contrast
Imaging and High-Resolution Wavefront Sensing: Directly imaging Earth-sized exoplanets with a visible-light coronagraph
instrument on a space telescope will require a system that can achieve
$\sim10^{-10}$ raw contrast and maintain it for the duration of observations
(on the order of hours or more). We are designing, manufacturing, and testing
Dual Purpose Lyot coronagraph (DPLC) masks that allow for simultaneous
wavefront sensing and control using out-of-band light to maintain high contrast
in the science focal plane. Our initial design uses a tiered metallic focal
plane occulter to suppress starlight in the transmitted coronagraph channel and
a dichroic-coated substrate to reflect out-of-band light to a wavefront sensing
camera. The occulter design introduces a phase shift such that the reflected
channel is a Zernike wavefront sensor. The dichroic coating allows higher-order
wavefront errors to be detected which is especially critical for compensating
for residual drifts from an actively-controlled segmented primary mirror. A
second-generation design concept includes a metasurface to create
polarization-dependent phase shifts in the reflected beam, which has several
advantages including an extended dynamic range. We will present the focal plane
mask designs, characterization, and initial testing at NASA's High Contrast
Imaging Testbed (HCIT) facility. | astro-ph_IM |
Updated Inflight Calibration of Hayabusa2's Optical Navigation Camera
(ONC) for Scientific Observations during the Cruise Phase: The Optical Navigation Camera (ONC-T, ONC-W1, ONC-W2) onboard Hayabusa2 are
also being used for scientific observations of the mission target, C-complex
asteroid 162173 Ryugu. Science observations and analyses require rigorous
instrument calibration. In order to meet this requirement, we have conducted
extensive inflight observations during the 3.5 years of cruise after the launch
of Hayabusa2 on 3 December 2014. In addition to the first inflight calibrations
by Suzuki et al. (2018), we conducted an additional series of calibrations,
including read-out smear, electronic-interference noise, bias, dark current,
hot pixels, sensitivity, linearity, flat-field, and stray light measurements
for the ONC. Moreover, the calibrations, especially flat-fields and
sensitivities, of ONC-W1 and -W2 are updated for the analysis of the
low-altitude (i.e., high-resolution) observations, such as the gravity
measurement, touchdowns, and the descents for MASCOT and MINERVA-II payload
releases. The radiometric calibration for ONC-T is also updated in this study
based on star and Moon observations. Our updated inflight sensitivity
measurements suggest the accuracy of the absolute radiometric calibration
contains less than 1.8% error for the ul-, b-, v-, Na-, w-, and x-bands based
on star calibration observations and ~5% for the p-band based on lunar
calibration observations. The radiance spectra of the Moon, Jupiter, and Saturn
from the ONC-T show good agreement with the spacecraft-based observations of
the Moon from SP/SELENE and WAC/LROC and with ground-based telescopic
observations for Jupiter and Saturn. | astro-ph_IM |
Optical NEP in Hot-Electron Nanobolometers: For the first time, we have measured the optical noise equivalent power (NEP)
in titanium (Ti) superconducting hot-electron nanobolometers (nano-HEBs). The
bolometers were 2{\mu}mx1{\mu}mx20nm and 1{\mu}mx1{\mu}mx20nm planar
antenna-coupled devices. The measurements were done at {\lambda} = 460 {\mu}m
using a cryogenic black body radiation source delivering optical power from a
fraction of a femtowatt to a few 100s of femtowatts. A record low NEP =
3x10^{-19} W/Hz^{1/2} at 50 mK has been achieved. This sensitivity meets the
requirements for SAFARI instrument on the SPICA telescope. The ways for further
improvement of the nano-HEB detector sensitivity are discussed. | astro-ph_IM |
Scintillation Pulse Shape Discrimination in a Two-Phase Xenon Time
Projection Chamber: The energy and electric field dependence of pulse shape discrimination in
liquid xenon have been measured in a 10 gm two-phase xenon time projection
chamber. We have demonstrated the use of the pulse shape and charge-to-light
ratio simultaneously to obtain a leakage below that achievable by either
discriminant alone. A Monte Carlo is used to show that the dominant fluctuation
in the pulse shape quantity is statistical in nature, and project the
performance of these techniques in larger detectors. Although the performance
is generally weak at low energies relevant to elastic WIMP recoil searches, the
pulse shape can be used in probing for higher energy inelastic WIMP recoils. | astro-ph_IM |
Ultra-sensitive Super-THz Microwave Kinetic Inductance Detectors for
future space telescopes: Future actively cooled space-borne observatories for the far-infrared,
loosely defined as a 1--10 THz band, can potentially reach a sensitivity
limited only by background radiation from the Universe. This will result in an
increase in observing speed of many orders of magnitude. A spectroscopic
instrument on such an observatory requires large arrays of detectors with a
sensitivity expressed as a noise equivalent power NEP = 3 $\times 10^{-20}$
$W\surd{Hz}$. We present the design, fabrication, and characterisation of
microwave kinetic inductance detectors (MKIDs) for this frequency range
reaching the required sensitivity. The devices are based on thin-film NbTiN
resonators which use lens-antenna coupling to a submicron-width aluminium
transmission line at the shorted end of the resonator where the radiation is
absorbed. We optimised the MKID geometry for a low NEP by using a small
aluminium volume of $\approx$ 1$\mu m^3$ and fabricating the aluminium section
on a very thin (100 nm) SiN membrane. Both methods of optimisation also reduce
the effect of excess noise by increasing the responsivity of the device, which
is further increased by reducing the parasitic geometrical inductance of the
resonator. We measure the sensitivity of eight MKIDs with respect to the power
absorbed in the detector using a thermal calibration source filtered in a
narrow band around 1.55 THz. We obtain a
NEP$_{exp}(P_{abs})\:=\:3.1\pm0.9\times10^{-20}\:W\surd{Hz}$ at a modulation
frequency of 200 Hz averaged over all measured MKIDs. The NEP is limited by
quasiparticle trapping. The measured sensitivity is sufficient for
spectroscopic observations from future, actively cooled space-based
observatories. Moreover, the presented device design and assembly can be
adapted for frequencies up to $\approx$ 10 THz and can be readily implemented
in kilopixel arrays. | astro-ph_IM |
New Periodograms Separating Orbital Radial Velocities and Spectral Shape
Variation: We present new periodograms that are effective in distinguishing Doppler
shift from spectral shape variability in astronomical spectra. These
periodograms, building upon the concept of partial distance correlation,
separate the periodic radial velocity modulation induced by orbital motion from
that induced by stellar activity. These tools can be used to explore large
spectroscopic databases in search of targets in which spectral shape variations
obscure the orbital motion; such systems include active planet-hosting stars or
binary systems with an intrinsically variable component. We provide a detailed
prescription for calculating the periodograms, demonstrate their performance
via simulations and real-life case studies, and provide a public Python
implementation. | astro-ph_IM |
A new method of testing the gravitational redshift effect with radio
interferometers: We propose a new method to measure gravitational redshift effect using
simultaneous interferometric observations of a distant radio source to
synchronize clocks. The first order by $v/c$ contribution to the signal (the
classical Doppler effect) is automatically canceled in our setup. When other
contributions from the velocities of the clocks, clock imperfection and
atmosphere are properly taken into account, the residual gravitational redshift
can be measured with the relative precision of $\sim 10^{-3}$ for RadioAstron
space-to-ground interferometer or with precision up to few $10^{-5}$ with the
next generation of space radio interferometers. | astro-ph_IM |
The performance of SiPM-based gamma-ray detector (GRD) of GECAM-C: As a new member of GECAM mission, the GECAM-C (also called High Energy Burst
Searcher, HEBS) is a gamma-ray all-sky monitor onboard SATech-01 satellite,
which was launched on July 27th, 2022 to detect gamma-ray transients from 6 keV
to 6 MeV, such as Gamma-Ray Bursts (GRBs), high energy counterpart of
Gravitational Waves (GWs) and Fast Radio Bursts (FRBs), and Soft Gamma-ray
Repeaters (SGRs). Together with GECAM-A and GECAM-B launched in December 2020,
GECAM-C will greatly improve the monitoring coverage, localization, as well as
temporal and spectral measurements of gamma-ray transients. GECAM-C employs 12
SiPM-based Gamma-Ray Detectors (GRDs) to detect gamma-ray transients . In this
paper, we firstly give a brief description of the design of GECAM-C GRDs, and
then focus on the on-ground tests and in-flight performance of GRDs. We also
did the comparison study of the SiPM in-flight performance between GECAM-C and
GECAM-B. The results show GECAM-C GRD works as expected and is ready to make
scientific observations. | astro-ph_IM |
PhotoNs-GPU:A GPU accelerated cosmological simulation code: We present a GPU-accelerated cosmological simulation code, PhotoNs-GPU, based
on algorithm of Particle Mesh Fast Multipole Method (PM-FMM), and focus on the
GPU utilization and optimization. A proper interpolated method for truncated
gravity is introduced to speed up the special functions in kernels. We verify
the GPU code in mixed precision and different levels of interpolated method on
GPU. A run with single precision is roughly two times faster that double
precision for current practical cosmological simulations. But it could induce a
unbiased small noise in power spectrum. Comparing with the CPU version of
PhotoNs and Gadget-2, the efficiency of new code is significantly improved.
Activated all the optimizations on the memory access, kernel functions and
concurrency management, the peak performance of our test runs achieves 48% of
the theoretical speed and the average performance approaches to 35% on GPU. | astro-ph_IM |
Optical Characterization & Testbed Development for μ-Spec Integrated
Spectrometers: This paper describes a cryogenic optical testbed developed to characterize
u-Spec spectrometers in a dedicated dilution refrigerator (DR) system. u-Spec
is a far-infrared integrated spectrometer that is an analog to a Rowland-type
grating spectrometer. It employs a single-crystal silicon substrate with
niobium microstrip lines and aluminum kinetic inductance detectors (KIDs).
Current designs with a resolution of 512 are in fabrication for the EXCLAIM
(Experiment for Cryogenic Large Aperture Intensity Mapping) balloon mission.
The primary spectrometer performance and design parameters are efficiency, NEP,
inter-channel isolation, spectral resolution, and frequency response for each
channel. Here we present the development and design of an optical
characterization facility and preliminary validation of that facility with
earlier prototype R=64 devices. We have conducted and describe initial optical
measurements of R = 64 devices using a swept photomixer line source. We also
discuss the test plan for optical characterization of the EXCLAIM R = 512
u-Spec devices in this new testbed. | astro-ph_IM |
Measurement of turbulence profile from defocused ring images: A defocused image of a bright single star in a small telescope contains rich
information on the optical turbulence, i.e. the seeing. The concept of a novel
turbulence monitor based on recording sequences of ring-like intrafocal images
and their analysis is presented. It can be implemented using standard
inexpensive telescopes and cameras. Statistics of intensity fluctuations in the
rings and their radial motion allow measurement of the low-resolution
turbulence profile, the total seeing, and the atmospheric time constant. The
algorithm of processing the images and extracting the turbulence parameters is
developed and extensively tested by numerical simulation. Prescriptions to
correct for finite exposure time and partially saturated scintillation are
given. A prototype instrument with a 0.13-m aperture was tested on the sky. The
RINGSS (Ring-Image Next Generation Scintillation Sensor) can be used as a
portable turbulence monitor for site testing and as an upgrade of existing
seeing monitors. | astro-ph_IM |
Thermal architecture for the QUBIC cryogenic receiver: QUBIC, the QU Bolometric Interferometer for Cosmology, is a novel forthcoming
instrument to measure the B-mode polarization anisotropy of the Cosmic
Microwave Background. The detection of the B-mode signal will be extremely
challenging; QUBIC has been designed to address this with a novel approach,
namely bolometric interferometry. The receiver cryostat is exceptionally large
and cools complex optical and detector stages to 40 K, 4 K, 1 K and 350 mK
using two pulse tube coolers, a novel 4He sorption cooler and a double-stage
3He/4He sorption cooler. We discuss the thermal and mechanical design of the
cryostat, modelling and thermal analysis, and laboratory cryogenic testing. | astro-ph_IM |
Cryogenic cooling with cryocooler on a rotating system: We developed a system that continuously maintains a cryocooler for long
periods on a rotating table. A cryostat that holds the cryocooler is set on the
table. A compressor is located on the ground and supplies high-purity (>
99.999%) and high-pressure (1.7 MPa) helium gas and electricity to the
cryocooler. The operation of the cryocooler and other instruments requires the
development of interface components between the ground and rotating table. A
combination of access holes at the center of the table and two rotary joints
allows simultaneous circulation of electricity and helium gas. The developed
system provides two innovative functions under the rotating condition; cooling
from room temperature and the maintenance of a cold condition for long periods.
We have confirmed these abilities as well as temperature stability under a
condition of continuous rotation at 20 revolutions per minute. The developed
system can be applied in various fields; e.g., in tests of Lorentz invariance,
searches for axion, radio astronomy and cosmology, and application of radar
systems. In particular, there is a plan to use this system for a radio
telescope observing cosmic microwave background radiation. | astro-ph_IM |
A dual-mask coronagraph for observing faint companions to binary stars: Observations of binary stars for faint companions with conventional
coronagraphic methods are challenging, as both targets will be bright enough to
obscure any nearby faint companions if their scattered light is not suppressed.
We propose coronagraphic examination of binary stars using an apodized pupil
Lyot coronagraph and a pair of actively-controlled image plane masks to
suppress both stars simultaneously. The performance is compared to imaging with
a band-limited mask, a dual-mask Lyot coronagraph and with no coronagraph at
all. An imaging procedure and control system for the masks are also described. | astro-ph_IM |
PRAXIS: low thermal emission high efficiency OH suppressed fibre
spectrograph: PRAXIS is a second generation instrument that follows on from GNOSIS, which
was the first instrument using fibre Bragg gratings for OH background
suppression. The Bragg gratings reflect the NIR OH lines while being
transparent to light between the lines. This gives a much higher signal-noise
ratio at low resolution but also at higher resolutions by removing the
scattered wings of the OH lines. The specifications call for high throughput
and very low thermal and detector noise so that PRAXIS will remain sky noise
limited. The optical train is made of fore-optics, an IFU, a fibre bundle, the
Bragg grating unit, a second fibre bundle and a spectrograph. GNOSIS used the
pre-existing IRIS2 spectrograph while PRAXIS will use a new spectrograph
specifically designed for the fibre Bragg grating OH suppression and optimised
for 1470 nm to 1700 nm (it can also be used in the 1090 nm to 1260 nm band by
changing the grating and refocussing). This results in a significantly higher
transmission due to high efficiency coatings, a VPH grating at low incident
angle and low absorption glasses. The detector noise will also be lower.
Throughout the PRAXIS design special care was taken at every step along the
optical path to reduce thermal emission or stop it leaking into the system.
This made the spectrograph design challenging because practical constraints
required that the detector and the spectrograph enclosures be physically
separate by air at ambient temperature. At present, the instrument uses the
GNOSIS fibre Bragg grating OH suppression unit. We intend to soon use a new OH
suppression unit based on multicore fibre Bragg gratings which will allow
increased field of view per fibre. Theoretical calculations show that the gain
in interline sky background signal-noise ratio over GNOSIS may very well be as
high as 9 with the GNOSIS OH suppression unit and 17 with the multicore fibre
OH suppression unit. | astro-ph_IM |
Deep Generative Models of Gravitational Waveforms via Conditional
Autoencoder: We construct few deep generative models of gravitational waveforms based on
the semi-supervising scheme of conditional autoencoders and their variational
extensions. Once the training is done, we find that our best waveform model can
generate the inspiral-merger waveforms of binary black hole coalescence with
more than $97\%$ average overlap matched filtering accuracy for the mass ratio
between $1$ and $10$. Besides, the generation time of a single waveform takes
about one millisecond, which is about $10$ to $100$ times faster than the EOBNR
algorithm running on the same computing facility. Moreover, these models can
also help to explore the space of waveforms. That is, with mainly the
low-mass-ratio training set, the resultant trained model is capable of
generating large amount of accurate high-mass-ratio waveforms. This result
implies that our generative model can speed up the waveform generation for the
low latency search of gravitational wave events. With the improvement of the
accuracy in future work, the generative waveform model may also help to speed
up the parameter estimation and can assist the numerical relativity in
generating the waveforms of higher mass ratio by progressively self-training. | astro-ph_IM |
Ultra-Low-Frequency Radio Astronomy Observations from a Selenocentric
Orbit: first results of the Longjiang-2 experiment: This paper introduces the first results of observations with the
Ultra-Long-Wavelength (ULW) -- Low Frequency Interferometer and Spectrometer
(LFIS) on board the selenocentric satellite Longjiang-2. We present a brief
description of the satellite and focus on the LFIS payload. The in-orbit
commissioning confirmed a reliable operational status of the instrumentation.
We also present results of a transition observation, which offers unique
measurements on several novel aspects. We estimate the RFI suppression required
for such a radio astronomy instrumentation at the Moon distances from Earth to
be of the order of 80 dB. We analyse a method of separating Earth- and
satellite-originated radio frequency interference (RFI). It is found that the
RFI level at frequencies lower than a few MHz is smaller than the receiver
noise floor. | astro-ph_IM |
Geopolitical Implications of a Successful SETI Program: We discuss the recent "realpolitik" analysis of Wisian & Traphagan (2020,
W&T) of the potential geopolitical fallout of the success of SETI. They
conclude that "passive" SETI involves an underexplored yet significant risk
that, in the event of a successful, passive detection of extraterrestrial
technology, state-level actors could seek to gain an information monopoly on
communications with an ETI. These attempts could lead to international conflict
and potentially disastrous consequences. In response to this possibility, they
argue that scientists and facilities engaged in SETI should preemptively engage
in significant security protocols to forestall this risk.
We find several flaws in their analysis. While we do not dispute that a
realpolitik response is possible, we uncover concerns with W&T's presentation
of the realpolitik paradigm, and we argue that sufficient reason is not given
to justify treating this potential scenario as action-guiding over other
candidate geopolitical responses. Furthermore, even if one assumes that a
realpolitik response is the most relevant geopolitical response, we show that
it is highly unlikely that a nation could successfully monopolize communication
with ETI. Instead, the real threat that the authors identify is based on the
perception by state actors that an information monopoly is likely. However, as
we show, this perception is based on an overly narrow contact scenario.
Overall, we critique W&T's argument and resulting recommendations on
technical, political, and ethical grounds. Ultimately, we find that not only
are W&T's recommendations unlikely to work, they may also precipitate the very
ills that they foresee. As an alternative, we recommend transparency and data
sharing (which are consistent with currently accepted best practices), further
development of post-detection protocols, and better education of policymakers
in this space. | astro-ph_IM |
Multi-Band Feeds: A Design Study: Broadband antenna feeds are of particular interest to existing and future
radio telescopes for multi-frequency studies of astronomical sources. Although
a 1:15 range in frequency is difficult to achieve, the well-known Eleven feed
design offers a relatively uniform response over such a range, and reasonably
well-matched responses in E & H planes. However, given the severe Radio
Frequency Interference in several bands over such wide spectral range, one
desires to selectively reject the corresponding bands. With this view, we have
explored the possibilities of having a multi-band feed antenna spanning a wide
frequency range, but which would have good response only in a number of
pre-selected (relatively) RFI-free windows (for a particular telescope-site).
The designs we have investigated use the basic configuration of pairs of
dipoles as in the Eleven feed, but use simple wire dipoles instead of folded
dipoles used in the latter. From our study of the two designs we have
investigated, we find that the design with feed-lines constructed using
co-axial lines shows good rejection in the unwanted parts of the spectrum and
control over the locations of resonant bands. | astro-ph_IM |
Potential for Observing Methane on Mars Using Earth-based Extremely
Large Telescopes: The Red Planet has fascinated humans for millennia, especially for the last
few centuries, and particularly during the Space Age. The nagging suspicion of
extant Martian life is both fed by, and drives the many space missions to Mars
and recent detections of large, seasonal volumes of atmospheric methane have
re-fuelled the discussion. Methane's strongest vibrational frequency (around
3.3 micron) occurs in the lower half of astronomers' L Band in the near infra
red, and is readily detectable in the Martian atmosphere from ground based
spectroscopes at high, dry locations such as Hawaii and Chile. However,
resolution of specific spectral absorption lines that categorically identify
methane are disputed in the literature, as are their origins. With the proposed
construction of extremely large telescopes operating in the optical/NIR, the
question became: could these ELTs supplement, or even replace space-based
instruments trained on Martian methane? A 2012 review of immediate-past,
present and future NIR spectrometers on Earth, in the air, in Earth orbit, in
solar orbit, in L2 orbit, in Mars orbit, and on Mars, revealed a wide range of
capabilities and limitations. Spatial, spectral, radiometric and temporal
resolutions were all considered and found to be complex, inter-related and
highly instrument-specific. The Giant Magellan Telescope, the Thirty Meter
Telescope and the European Extremely Large Telescope will each have at least
one L Band spectrometer supported by state-of-the-art adaptive optics and be
capable of extreme spatial, spectral and radiometric resolution. Replicating
observations over time will provide a critical constraint to theoretical
considerations about the biotic or abiotic origins of any detected methane and
it is recommended that existing datasets be mined, science cases for the ELTs
include Martian methane and collaboration between science teams be enhanced. | astro-ph_IM |
A Bayesian approach to high fidelity interferometric calibration II:
demonstration with simulated data: In a companion paper, we presented BayesCal, a mathematical formalism for
mitigating sky-model incompleteness in interferometric calibration. In this
paper, we demonstrate the use of BayesCal to calibrate the degenerate gain
parameters of full-Stokes simulated observations with a HERA-like hexagonal
close-packed redundant array, for three assumed levels of completeness of the a
priori known component of the calibration sky model. We compare the BayesCal
calibration solutions to those recovered by calibrating the degenerate gain
parameters with only the a priori known component of the calibration sky model
both with and without imposing physically motivated priors on the gain
amplitude solutions and for two choices of baseline length range over which to
calibrate. We find that BayesCal provides calibration solutions with up to four
orders of magnitude lower power in spurious gain amplitude fluctuations than
the calibration solutions derived for the same data set with the alternate
approaches, and between $\sim10^7$ and $\sim10^{10}$ times smaller than in the
mean degenerate gain amplitude on the full range of spectral scales accessible
in the data. Additionally, we find that in the scenarios modelled only BayesCal
has sufficiently high fidelity calibration solutions for unbiased recovery of
the 21 cm power spectrum on large spectral scales ($k_\parallel \lesssim
0.15~h\mathrm{Mpc}^{-1}$). In all other cases, in the completeness regimes
studied, those scales are contaminated. | astro-ph_IM |
Combine User's Manual: {\sc Combine} is an add-on to {\sc SigSpec} and {\sc Cinderella}. A {\sc
SigSpec} result file or a file generated by {\sc Cinderella} contains the
significant sinusoidal signal components in a time series. In this file, {\sc
Combine} checks one frequency after the other for being a linear combination of
previously examined frequencies. If this attempt fails, the corresponding
frequency is considered ``genuine''. Only genuine frequencies are used to form
linear combinations subsequently. A purely heuristic model is employed to
assign a reliability to each linear combination and to justify whether to
consider a frequency genuine or a linear combination. | astro-ph_IM |
VAST: An ASKAP Survey for Variables and Slow Transients: The Australian Square Kilometre Array Pathfinder (ASKAP) will give us an
unprecedented opportunity to investigate the transient sky at radio
wavelengths. In this paper we present VAST, an ASKAP survey for Variables and
Slow Transients. VAST will exploit the wide-field survey capabilities of ASKAP
to enable the discovery and investigation of variable and transient phenomena
from the local to the cosmological, including flare stars, intermittent
pulsars, X-ray binaries, magnetars, extreme scattering events, interstellar
scintillation, radio supernovae and orphan afterglows of gamma ray bursts. In
addition, it will allow us to probe unexplored regions of parameter space where
new classes of transient sources may be detected. In this paper we review the
known radio transient and variable populations and the current results from
blind radio surveys. We outline a comprehensive program based on a multi-tiered
survey strategy to characterise the radio transient sky through detection and
monitoring of transient and variable sources on the ASKAP imaging timescales of
five seconds and greater. We also present an analysis of the expected source
populations that we will be able to detect with VAST. | astro-ph_IM |
A Novel Hybrid Algorithm for Lucky Imaging: Lucky imaging is a high-resolution astronomical image recovery technique with
two classic implementation algorithms, i.e. image selecting, shifting and
adding in image space and data selecting and image synthesizing in Fourier
space. This paper proposes a novel lucky imaging algorithm where with
space-domain and frequency-domain selection rates as a link, the two classic
algorithms are combined successfully, making each algorithm a proper subset of
the novel hybrid algorithm. Experimental results show that with the same
experiment dataset and platform, the high-resolution image obtained by the
proposed algorithm is superior to that obtained by the two classic algorithms.
This paper also proposes a new lucky image selection and storage scheme, which
can greatly save computer memory and enable lucky imaging algorithm to be
implemented in a common desktop or laptop with small memory and to process
astronomical images with more frames and larger size. Besides, through
simulation analysis, this paper discusses the binary star detection limits of
the novel lucky imaging algorithm and traditional ones under different
atmospheric conditions. | astro-ph_IM |
A Statistical Framework for the Utilization of Simultaneous Pupil Plane
and Focal Plane Telemetry for Exoplanet Imaging, Part I: Accounting for
Aberrations in Multiple Planes: A new generation of telescopes with mirror diameters of 20 m or more, called
extremely large telescopes (ELTs) has the potential to provide unprecedented
imaging and spectroscopy of exo-planetary systems, if the difficulties in
achieving the extremely high dynamic range required to differentiate the
planetary signal from the star can be overcome to a sufficient degree. Fully
utilizing the potential of ELTs for exoplanet imaging will likely require
simultaneous and self-consistent determination of both the planetary image and
the unknown aberrations in multiple planes of the optical system, using
statistical inference based on the wavefront sensor and science camera data
streams. This approach promises to overcome the most important systematic
errors inherent in the various schemes based on differential imaging, such as
ADI and SDI. This paper is the first in a series on this subject, in which a
formalism is established for the exoplanet imaging problem, setting the stage
for the statistical inference methods to follow in the future. Every effort has
been made to be rigorous and complete, so that validity of approximations to be
made later can be assessed. Here, the polarimetric image is expressed in terms
of aberrations in the various planes of a polarizing telescope with an adaptive
optics system. Further, it is shown that current methods that utilize focal
plane sensing to correct the speckle field, e.g., electric field conjugation,
rely on the tacit assumption that aberrations on multiple optical surfaces can
be represented as aberration on a single optical surface, ultimately limiting
their potential effectiveness for ground-based astronomy. | astro-ph_IM |
The GAMMA-400 gamma-ray telescope characteristics. Angular resolution
and electrons/protons separation: The measurements of gamma-ray fluxes and cosmic-ray electrons and positrons
in the energy range from 100 MeV to several TeV, which will be implemented by
the specially designed GAMMA-400 gamma-ray telescope, concern with the
following broad range of science topics. Searching for signatures of dark
matter, surveying the celestial sphere in order to study gamma-ray point and
extended sources, measuring the energy spectra of Galactic and extragalactic
diffuse gamma-ray emission, studying gamma-ray bursts and gamma-ray emission
from the Sun, as well as high precision measuring spectra of high-energy
electrons and positrons, protons and nuclei up to the knee. To clarify these
scientific problems with the new experimental data the GAMMA-400 gamma-ray
telescope possesses unique physical characteristics comparing with previous and
present experiments. For gamma-ray energies more than 100 GeV GAMMA-400
provides the energy resolution of ~1% and angular resolution better than 0.02
deg. The methods developed to reconstruct the direction of incident gamma
photon are presented in this paper, as well as, the capability of the GAMMA-400
gamma-ray telescope to distinguish electrons and positrons from protons in
cosmic rays is investigated. | astro-ph_IM |
Two phase mixtures in SPH - A new approach: We present a new approach to simulating mixtures of gas and dust in smoothed
particle hydrodynamics (SPH). We show how the two-fluid equations can be
rewritten to describe a single-fluid 'mixture' moving with the barycentric
velocity, with each particle carrying a dust fraction. We show how this
formulation can be implemented in SPH while preserving the conservation
properties (i.e. conservation of mass of each phase, momentum and energy). We
also show that the method solves two key issues with the two fluid approach: it
avoids over-damping of the mixture when the drag is strong and prevents a
problem with dust particles becoming trapped below the resolution of the gas.
We also show how the general one-fluid formulation can be simplified in the
limit of strong drag (i.e. small grains) to the usual SPH equations plus a
diffusion equation for the evolution of the dust fraction that can be evolved
explicitly and does not require any implicit timestepping. We present tests of
the simplified formulation showing that it is accurate in the small
grain/strong drag limit. We discuss some of the issues we have had to solve
while developing this method and finally present a preliminary application to
dust settling in protoplanetary discs. | astro-ph_IM |
GAPS: A New Cosmic Ray Anti-matter Experiment: The General AntiParticle Spectrometer (GAPS) is a balloon-borne instrument
designed to detect cosmic-ray antimatter using the novel exotic atom technique,
obviating the strong magnetic fields required by experiments like AMS, PAMELA,
or BESS. It will be sensitive to primary antideuterons with kinetic energies of
$\approx0.05-0.2$ GeV/nucleon, providing some overlap with the previously
mentioned experiments at the highest energies. For $3\times35$ day balloon
flights, and standard classes of primary antideuteron propagation models, GAPS
will be sensitive to $m_{\mathrm{DM}}\approx10-100$ GeV c$^{-2}$ WIMPs with a
dark-matter flux to astrophysical flux ratio approaching 100. This clean
primary channel is a key feature of GAPS and is crucial for a rare event
search. Additionally, the antiproton spectrum will be extended with high
statistics measurements to cover the $0.07 \leq E \leq 0.25 $ GeV domain. For
$E>0.2$ GeV GAPS data will be complementary to existing experiments, while
$E<0.2$ GeV explores a new regime. The first flight is scheduled for late 2020
in Antarctica. These proceedings will describe the astrophysical processes and
backgrounds relevant to the dark matter search, a brief discussion of detector
operation, and construction progress made to date. | astro-ph_IM |
Earth-Moon VLBI project. Modeling of scientific outcome: Modern radio astrometry has reached the limit of the resolution that is
determined by the size of the Earth. The only way to overcome that limit is to
create the radio telescopes outside our planet. It is proposed to build an
autonomous remote-controlled radio observatory on the Moon. Working together
with the existing radio telescopes on Earth in the VLBI mode, the new
observatory will form an interferometer baseline up to 410000 km, enhancing the
present astrometric and geodetic capabilities of VLBI. We perform numerical
simulations of Earth-Moon VLBI observations operating simultaneously with the
international VLBI network. It is shown that these observations will
significantly improve the precision of determination of Moon's orbital motion,
libration angles, ICRF, and relativistic parameters. | astro-ph_IM |
Uploading User-Defined Functions onto the AMIDAS Website: The AMIDAS website has been established as an online interactive tool for
running simulations and analyzing data in direct Dark Matter detection
experiments. At the first phase of the website building, only some commonly
used WIMP velocity distribution functions and elastic nuclear form factors have
been involved in the AMIDAS code. In order to let the options for velocity
distribution as well as for nuclear form factors be more flexible, we have
extended the AMIDAS code to be able to include user-uploaded files with their
own functions. In this article, I describe the preparation of files of
user-defined functions onto the AMIDAS website. Some examples will also be
given. | astro-ph_IM |
Minimum-variance multitaper spectral estimation on the sphere: We develop a method to estimate the power spectrum of a stochastic process on
the sphere from data of limited geographical coverage. Our approach can be
interpreted either as estimating the global power spectrum of a stationary
process when only a portion of the data are available for analysis, or
estimating the power spectrum from local data under the assumption that the
data are locally stationary in a specified region. Restricting a global
function to a spatial subdomain -- whether by necessity or by design -- is a
windowing operation, and an equation like a convolution in the spectral domain
relates the expected value of the windowed power spectrum to the underlying
global power spectrum and the known power spectrum of the localization window.
The best windows for the purpose of localized spectral analysis have their
energy concentrated in the region of interest while possessing the smallest
effective bandwidth as possible. Solving an optimization problem in the sense
of Slepian (1960) yields a family of orthogonal windows of diminishing
spatiospectral localization, the best concentrated of which we propose to use
to form a weighted multitaper spectrum estimate in the sense of Thomson (1982).
Such an estimate is both more representative of the target region and reduces
the estimation variance when compared to estimates formed by any single
bandlimited window. We describe how the weights applied to the individual
spectral estimates in forming the multitaper estimate can be chosen such that
the variance of the estimate is minimized. | astro-ph_IM |
Noise reduction on single-shot images using an autoencoder: We present an application of autoencoders to the problem of noise reduction
in single-shot astronomical images and explore its suitability for upcoming
large-scale surveys. Autoencoders are a machine learning model that summarises
an input to identify its key features, then from this knowledge predicts a
representation of a different input. The broad aim of our autoencoder model is
to retain morphological information (e.g., non-parametric morphological
information) from the survey data whilst simultaneously reducing the noise
contained in the image. We implement an autoencoder with convolutional and
maxpooling layers. We test our implementation on images from the Panoramic
Survey Telescope and Rapid Response System (Pan-STARRS) that contain varying
levels of noise and report how successful our autoencoder is by considering
Mean Squared Error (MSE), Structural Similarity Index (SSIM), the second-order
moment of the brightest 20 percent of the galaxy's flux M20, and the Gini
coefficient, whilst noting how the results vary between the original images,
stacked images, and noise reduced images. We show that we are able to reduce
noice, over many different targets of observations, whilst retaining the
galaxy's morphology, with metric evaluation on a target by target analysis. We
establish that this process manages to achieve a positive result in a matter of
minutes, and by only using one single shot image compared to multiple survey
images found in other noise reduction techniques. | astro-ph_IM |
Numerical Error in Interplanetary Orbit Determination Software: The core of every orbit determination process is the comparison between the
measured observables and their predicted values, computed using the adopted
mathematical models, and the minimization, in a least square sense, of their
differences, known as residuals. In interplanetary orbit determination, Doppler
observables, obtained by measuring the average frequency shift of the received
carrier signal over a certain count time, are compared against their predicted
values, usually computed by differencing two round-trip light-times. This
formulation is known to be sensitive to round-off errors, caused by the use of
finite arithmetic in the computation, giving rise to an additional noise in the
residuals, called numerical noise, that degrades the accuracy of the orbit
determination solution. This paper presents a mathematical model for the
expected numerical errors in two-way and three-way Doppler observables,
computed using the differenced light-time formulation. The model was validated
by comparing its prediction to the actual noise in the computed observables,
obtained by NASA/Jet Propulsion Laboratory's Orbit Determination Program. The
model proved to be accurate within $3 \times 10^{-3} \,\text{mm/s}$ at $60
\,\text{s}$ integration time. Then it was applied to the case studies of
Cassini's and Juno's nominal trajectories, proving that numerical errors can
assume values up to $6 \times 10^{-2} \,\text{mm/s}$ at $60 \,\text{s}$
integration time, and consequently that they are an important noise source in
the Doppler-based orbit determination processes. Three alternative strategies
are proposed and discussed in the paper to mitigate the effects of numerical
noise. | astro-ph_IM |
Efficient modeling of correlated noise II. A flexible noise model with
fast and scalable methods: Correlated noise affects most astronomical datasets and to neglect accounting
for it can lead to spurious signal detections, especially in low
signal-to-noise conditions, which is often the context in which new discoveries
are pursued. For instance, in the realm of exoplanet detection with radial
velocity time series, stellar variability can induce false detections. However,
a white noise approximation is often used because accounting for correlated
noise when analyzing data implies a more complex analysis. Moreover, the
computational cost can be prohibitive as it typically scales as the cube of the
dataset size.
For some restricted classes of correlated noise models, there are specific
algorithms that can be used to help bring down the computational cost. This
improvement in speed is particularly useful in the context of Gaussian process
regression, however, it comes at the expense of the generality of the noise
model.
Here, we present the S+LEAF noise model, which allows us to account for a
large class of correlated noises with a linear scaling of the computational
cost with respect to the size of the dataset. The S+LEAF model includes, in
particular, mixtures of quasiperiodic kernels and calibration noise. This
efficient modeling is made possible by a sparse representation of the
covariance matrix of the noise and the use of dedicated algorithms for matrix
inversion, solving, determinant computation, etc.
We applied the S+LEAF model to reanalyze the HARPS radial velocity time
series of HD 136352. We illustrate the flexibility of the S+LEAF model in
handling various sources of noise. We demonstrate the importance of taking
correlated noise into account, and especially calibration noise, to correctly
assess the significance of detected signals.
We provide an open-source implementation of the S+LEAF model, available at
https://gitlab.unige.ch/jean-baptiste.delisle/spleaf. | astro-ph_IM |
A flexible method for estimating luminosity functions via Kernel Density
Estimation -- II. Generalization and Python implementation: We propose a generalization of our previous KDE (kernel density estimation)
method for estimating luminosity functions (LFs). This new upgrade further
extend the application scope of our KDE method, making it a very flexible
approach which is suitable to deal with most of bivariate LF calculation
problems. From the mathematical point of view, usually the LF calculation can
be abstracted as a density estimation problem in the bounded domain of
$\{Z_1<z<Z_2,~ L>f_{\mathrm{lim}}(z) \}$. We use the transformation-reflection
KDE method ($\hat{\phi}$) to solve the problem, and introduce an approximate
method ($\hat{\phi}_{\mathrm{1}}$) based on one-dimensional KDE to deal with
the small sample size case. In practical applications, the different versions
of LF estimators can be flexibly chosen according to the Kolmogorov-Smirnov
test criterion. Based on 200 simulated samples, we find that for both cases of
dividing or not dividing redshift bins, especially for the latter, our method
performs significantly better than the traditional binning method
$\hat{\phi}_{\mathrm{bin}}$. Moreover, with the increase of sample size $n$,
our LF estimator converges to the true LF remarkably faster than
$\hat{\phi}_{\mathrm{bin}}$. To implement our method, we have developed a
public, open-source Python Toolkit, called \texttt{kdeLF}. With the support of
\texttt{kdeLF}, our KDE method is expected to be a competitive alternative to
existing nonparametric estimators, due to its high accuracy and excellent
stability. \texttt{kdeLF} is available at
\url{http://github.com/yuanzunli/kdeLF} with extensive documentation available
at \url{http://kdelf.readthedocs.org/en/latest~}. | astro-ph_IM |
Cyclic Spectral Analysis of Radio Pulsars: Cyclic spectral analysis is a signal processing technique designed to deal
with stochastic signals whose statistics vary periodically with time. Pulsar
radio emission is a textbook example of this signal class, known as
cyclostationary signals. In this paper, we discuss the application of cyclic
spectral analysis methods to pulsar data, and compare the results with the
traditional filterbank approaches used for almost all pulsar observations to
date. In contrast to standard methods, the cyclic spectrum preserves phase
information of the radio signal. This feature allows us to determine the
impulse response of the interstellar medium and the intrinsic, unscattered
pulse profile directly from a single observation. We illustrate these new
analysis techniques using real data from an observation of the millisecond
pulsar B1937+21. | astro-ph_IM |
Entering into the Wide Field Adaptive Optics Era on Maunakea: As part of the National Science Foundation funded "Gemini in the Era of
MultiMessenger Astronomy" (GEMMA) program, Gemini Observatory is developing
GNAO, a widefield adaptive optics (AO) facility for Gemini-North on Maunakea,
the only 8m-class open-access telescope available to the US astronomers in the
northern hemisphere. GNAO will provide the user community with a queue-operated
Multi-Conjugate AO (MCAO) system, enabling a wide range of innovative solar
system, Galactic, and extragalactic science with a particular focus on
synergies with JWST in the area of time-domain astronomy. The GNAO effort
builds on institutional investment and experience with the more limited
block-scheduled Gemini Multi-Conjugate System (GeMS), commissioned at Gemini
South in 2013. The project involves close partnerships with the community
through the recently established Gemini AO Working Group and the GNAO Science
Team, as well as external instrument teams. The modular design of GNAO will
enable a planned upgrade to a Ground Layer AO (GLAO) mode when combined with an
Adaptive Secondary Mirror (ASM). By enhancing the natural seeing by an expected
factor of two, GLAO will vastly improve Gemini North's observing efficiency for
seeing-limited instruments and strengthen its survey capabilities for
multi-messenger astronomy. | astro-ph_IM |
Improved Image Quality Over 10' Fields with the `Imaka Ground Layer
Adaptive Optics Experiment: `Imaka is a ground layer adaptive optics (GLAO) demonstrator on the
University of Hawaii 2.2m telescope with a 24'x18' field-of-view, nearly an
order of magnitude larger than previous AO instruments. In 15 nights of
observing with natural guide star asterisms ~16' in diameter, we measure median
AO-off and AO-on empirical full-widths at half-maximum (FWHM) of 0''95 and
0''64 in R-band, 0''81 and 0''48 in I-band, and 0''76 and 0''44 at 1 micron.
This factor of 1.5-1.7 reduction in the size of the point spread function (PSF)
results from correcting both the atmosphere and telescope tracking errors. The
AO-on PSF is uniform out to field positions ~5' off-axis, with a typical
standard deviation in the FWHM of 0''018. Images exhibit variation in FWMM by
4.5% across the field, which has been applied as a correction to the
aforementioned quantities. The AO-on PSF is also 10x more stable in time
compared to the AO-off PSF. In comparing the delivered image quality to proxy
measurements, we find that in both AO-off and AO-on data, delivered image
quality is correlated with `imaka's telemetry, with R-band correlation
coefficients of 0.68 and 0.70, respectively. At the same wavelength, the data
are correlated to DIMM and MASS seeing with coefficients of 0.45 and 0.55. Our
results are an essential first step to implementing facility-class, wide-field
GLAO on Maunakea telescopes, enabling new opportunities to study extended
astronomical sources, such as deep galaxy fields, nearby galaxies or star
clusters, at high angular resolution. | astro-ph_IM |
Collisionless Stellar Hydrodynamics as an Efficient Alternative to
N-body Methods: For simulations that deal only with dark matter or stellar systems, the
conventional N-body technique is fast, memory efficient, and relatively simple
to implement. However when including the effects of gas physics, mesh codes are
at a distinct disadvantage compared to SPH. Whilst implementing the N-body
approach into SPH codes is fairly trivial, the particle-mesh technique used in
mesh codes to couple collisionless stars and dark matter to the gas on the
mesh, has a series of significant scientific and technical limitations. These
include spurious entropy generation resulting from discreteness effects, poor
load balancing and increased communication overhead which spoil the excellent
scaling in massively parallel grid codes.
We propose the use of the collisionless Boltzmann moment equations as a means
to model collisionless material as a fluid on the mesh, implementing it into
the massively parallel FLASH AMR code. This approach, which we term
"collisionless stellar hydrodynamics" enables us to do away with the
particle-mesh approach. Since the parallelisation scheme is identical to that
used for the hydrodynamics, it preserves the excellent scaling of the FLASH
code already demonstrated on peta-flop machines.
We find the classic hydrodynamic equations and Boltzmann moment equations can
be reconciled under specific conditions, allowing us to generate analytic
solutions for collisionless systems using conventional test problems. We
confirm the validity of our approach using a suite of demanding test problems,
including the use of a modified Sod shock test. We conclude by demonstrating
the ability of our code to model complex phenomena by simulating the evolution
of a spiral galaxy whose properties agree with those predicted by swing
amplification theory. (Abridged) | astro-ph_IM |
Preliminary Astrometric Results from Kepler: Although not designed as an astrometric instrument, Kepler is expected to
produce astrometric results of a quality appropriate to support many of the
astrophysical investigations enabled by its photometric results. On the basis
of data collected during the first few months of operation, the astrometric
precision for a single 30 minute measure appears to be better than 4
milliarcseconds (0.001 pixel). Solutions for stellar parallax and proper
motions await more observations, but the analysis of the astrometric residuals
from a local solution in the vicinity of a star have already proved to be an
important tool in the process of confirming the hypothesis of a planetary
transit. | astro-ph_IM |
Provenance of astronomical data: In the context of Open Science, provenance has become a decisive piece of
information to provide along with astronomical data. Provenance is explicitly
cited in the FAIR principles, that aims to make research data Findable,
Accessible, Interoperable and Reusable. The IVOA Provenance Data Model,
published in 2020, puts in place the foundations for structuring and managing
detailed provenance information, from the acquisition of raw data, to the
dissemination of final products. The ambition is to provide for each
astronomical dataset a sufficiently fine grained and detailed provenance
information so that end-users understand the quality, reliability and
trustworthiness of the data. This would ensure that the Reusable principle is
respected. | astro-ph_IM |
First Generation Heterodyne Instrumentation Concepts for the Atacama
Large Aperture Submillimeter Telescope: (abridged) The Atacama Large Aperture Submillimeter Telescope (AtLAST)
project aims to build a 50-m-class submm telescope with $>1^\circ$ field of
view, high in the Atacama Desert, providing fast and detailed mapping of the
mm/submm sky. It will thus serve as a strong complement to existing facilities
such as ALMA. ALMA's small field of view ($<15^{\prime\prime}$ at 350 GHz)
limits its mapping speed for large surveys. Instead, a single dish with a large
field of view such as the AtLAST concept can host large multi-element
instruments that can more efficiently map large portions of the sky. Small
aperture survey instruments (typically much smaller than $<3\times$ the size of
an interferometric array element) can mitigate this somewhat but lack the
resolution for accurate recovery of source location and have small collecting
areas. Furthermore, small aperture survey instruments do not provide sufficient
overlap in the spatial scales they sample to provide a complete reconstruction
of extended sources (i.e.\ the zero-spacing information is incomplete in
$u,v$-space.) The heterodyne instrumentation for the AtLAST telescope that we
consider here will take advantage of extensive developments in the past decade
improving the performance and pixel count of heterodyne focal plane arrays.
Such instrumentation, with higher pixel counts, has alredy begun to take
advantage of integration in the focal planes to increase packaging efficiency
over simply stacking modular mixer blocks in the focal plane. We extrapolate
from the current state-of-the-art to present concept first-generation
heterodyne designs for AtLAST. | astro-ph_IM |
Improving Planet-Finding Spectrometers: Like the miniaturization of modern computers, next-generation radial velocity
instruments will be significantly smaller and more powerful than their
predecessors. | astro-ph_IM |
An in-depth exploration of LAMOST Unknown spectra based on density
clustering: LAMOST (Large Sky Area Multi-Object Fiber Spectroscopic Telescope) has
completed the observation of nearly 20 million celestial objects, including a
class of spectra labeled `Unknown'. Besides low signal-to-noise ratio, these
spectra often show some anomalous features that do not work well with current
templates. In this paper, a total of 638,000 `Unknown' spectra from LAMOST DR5
are selected, and an unsupervised-based analytical framework of `Unknown'
spectra named SA-Frame (Spectra Analysis-Frame) is provided to explore their
origins from different perspectives. The SA-Frame is composed of three parts:
NAPC-Spec clustering, characterization and origin analysis. First,
NAPC-Spec(Nonparametric density clustering algorithm for spectra) characterizes
different features in the "unknown" spectrum by adjusting the influence space
and divergence distance to minimize the effects of noise and high
dimensionality, resulting in 13 types. Second, characteristic extraction and
representation of clustering results are carried out based on spectral lines
and continuum, where these 13 types are characterized as regular spectra with
low S/Ns, splicing problems, suspected galactic emission signals, contamination
from city light and un-gregarious type respectively. Third, a preliminary
analysis of their origins is made from the characteristics of the observational
targets, contamination from the sky, and the working status of the instruments.
These results would be valuable for improving the overall data quality of
large-scale spectral surveys. | astro-ph_IM |
Expectation Maximization for Hard X-ray Count Modulation Profiles: This paper is concerned with the image reconstruction problem when the
measured data are solar hard X-ray modulation profiles obtained from the Reuven
Ramaty High Energy Solar Spectroscopic Imager (RHESSI)} instrument. Our goal is
to demonstrate that a statistical iterative method classically applied to the
image deconvolution problem is very effective when utilized for the analysis of
count modulation profiles in solar hard X-ray imaging based on Rotating
Modulation Collimators. The algorithm described in this paper solves the
maximum likelihood problem iteratively and encoding a positivity constraint
into the iterative optimization scheme. The result is therefore a classical
Expectation Maximization method this time applied not to an image deconvolution
problem but to image reconstruction from count modulation profiles. The
technical reason that makes our implementation particularly effective in this
application is the use of a very reliable stopping rule which is able to
regularize the solution providing, at the same time, a very satisfactory
Cash-statistic (C-statistic). The method is applied to both reproduce synthetic
flaring configurations and reconstruct images from experimental data
corresponding to three real events. In this second case, the performance of
Expectation Maximization, when compared to Pixon image reconstruction, shows a
comparable accuracy and a notably reduced computational burden; when compared
to CLEAN, shows a better fidelity with respect to the measurements with a
comparable computational effectiveness. If optimally stopped, Expectation
Maximization represents a very reliable method for image reconstruction in the
RHESSI context when count modulation profiles are used as input data. | astro-ph_IM |
LUCI: A Python package for SITELLE spectral analysis: High-resolution optical integral field units (IFUs) are rapidly expanding our
knowledge of extragalactic emission nebulae in galaxies and galaxy clusters. By
studying the spectra of these objects -- which include classic HII regions,
supernova remnants, planetary nebulae, and cluster filaments -- we are able to
constrain their kinematics (velocity and velocity dispersion). In conjunction
with additional tools, such as the BPT diagram, we can further classify
emission regions based on strong emission-line flux ratios. LUCI is a
simple-to-use python module intended to facilitate the rapid analysis of IFU
spectra. LUCI does this by integrating well-developed pre-existing python tools
such as astropy and scipy with new machine learning tools for spectral analysis
(Rhea et al. 2020). Furthermore, LUCI provides several easy-to-use tools to
access and fit SITELLE data cubes. | astro-ph_IM |
Automatic Classification of Variable Stars in Catalogs with missing data: We present an automatic classification method for astronomical catalogs with
missing data. We use Bayesian networks, a probabilistic graphical model, that
allows us to perform inference to pre- dict missing values given observed data
and dependency relationships between variables. To learn a Bayesian network
from incomplete data, we use an iterative algorithm that utilises sampling
methods and expectation maximization to estimate the distributions and
probabilistic dependencies of variables from data with missing values. To test
our model we use three catalogs with missing data (SAGE, 2MASS and UBVI) and
one complete catalog (MACHO). We examine how classification accuracy changes
when information from missing data catalogs is included, how our method
compares to traditional missing data approaches and at what computational cost.
Integrating these catalogs with missing data we find that classification of
variable objects improves by few percent and by 15% for quasar detection while
keeping the computational cost the same. | astro-ph_IM |
Apodized Lyot Coronagraph for VLT-SPHERE: Laboratory tests and
performances of a first prototype in the visible: We present some of the High Dynamic Range Imaging activities developed around
the coronagraphic test-bench of the Laboratoire A. H. Fizeau (Nice). They
concern research and development of an Apodized Lyot Coronagraph (ALC) for the
VLT-SPHERE instrument and experimental results from our testbed working in the
visible domain. We determined by numerical simulations the specifications of
the apodizing filter and searched the best technological process to manufacture
it. We present the results of the experimental tests on the first apodizer
prototype in the visible and the resulting ALC nulling performances. The tests
concern particularly the apodizer characterization (average transmission radial
profile, global reflectivity and transmittivity in the visible), ALC nulling
performances compared with expectations, sensitivity of the ALC performances to
misalignments of its components. | astro-ph_IM |
Automated Adaptive Optics: Large area surveys will dominate the forthcoming decades of astronomy and
their success requires characterizing thousands of discoveries through
additional observations at higher spatial or spectral resolution, and at
complementary cadences or periods. Only the full automation of adaptive optics
systems will enable high-acuity, high-sensitivity follow-up observations of
several tens of thousands of these objects per year, maximizing on-sky time.
Automation will also enable rapid response to target-of-opportunity events
within minutes, minimizing the time between discovery and characterization.
In June 2012, we demonstrated the first fully automated operation of an
astronomical adaptive optics system by observing 125 objects in succession with
the Robo-AO system. Efficiency has increased ever since, with a typical night
comprising 200-250 automated observations at the visible diffraction limit. By
observing tens of thousands of targets in the largest-ever adaptive-optics
surveys, Robo-AO has demonstrated the ability to address the follow-up needs of
current and future large astronomical surveys. | astro-ph_IM |
CREDO project: The Cosmic-Ray Extremely Distributed Observatory (CREDO) is a project created
a few years ago in the Institute of Nuclear Physics PAS in Krak\'ow and
dedicated is to global studies of extremely extended cosmic-ray phenomena. The
main reason for creating such a project was that the cosmic-ray ensembles (CRE)
are beyond the capabilities of existing detectors and observatories. Until now,
cosmic ray studies, even in major observatories, have been limited to the
recording and analysis of individual air showers therefore ensembles of
cosmic-rays, which may spread over a significant fraction of the Earth were
neither recorded nor analyzed. In this paper the status and perspectives of the
CREDO project are presented. | astro-ph_IM |
Speckle Space-Time Covariance in High-Contrast Imaging: We introduce a new framework for point-spread function (PSF) subtraction
based on the spatio-temporal variation of speckle noise in high-contrast
imaging data where the sampling timescale is faster than the speckle evolution
timescale. One way that space-time covariance arises in the pupil is as
atmospheric layers translate across the telescope aperture and create small,
time-varying perturbations in the phase of the incoming wavefront. The
propagation of this field to the focal plane preserves some of that space-time
covariance. To utilize this covariance, our new approach uses a
Karhunen-Lo\'eve transform on an image sequence, as opposed to a set of single
reference images as in previous applications of Karhunen-Lo\'eve Image
Processing (KLIP) for high-contrast imaging. With the recent development of
photon-counting detectors, such as microwave kinetic inductance detectors
(MKIDs), this technique now has the potential to improve contrast when used as
a post-processing step. Preliminary testing on simulated data shows this
technique can improve contrast by at least 10-20% from the original image, with
significant potential for further improvement. For certain choices of
parameters, this algorithm may provide larger contrast gains than spatial-only
KLIP. | astro-ph_IM |
Finding faint HI structure in and around galaxies: scraping the barrel: Soon to be operational HI survey instruments such as APERTIF and ASKAP will
produce large datasets. These surveys will provide information about the HI in
and around hundreds of galaxies with a typical signal-to-noise ratio of $\sim$
10 in the inner regions and $\sim$ 1 in the outer regions. In addition, such
surveys will make it possible to probe faint HI structures, typically located
in the vicinity of galaxies, such as extra-planar-gas, tails and filaments.
These structures are crucial for understanding galaxy evolution, particularly
when they are studied in relation to the local environment. Our aim is to find
optimized kernels for the discovery of faint and morphologically complex HI
structures. Therefore, using HI data from a variety of galaxies, we explore
state-of-the-art filtering algorithms. We show that the intensity-driven
gradient filter, due to its adaptive characteristics, is the optimal choice. In
fact, this filter requires only minimal tuning of the input parameters to
enhance the signal-to-noise ratio of faint components. In addition, it does not
degrade the resolution of the high signal-to-noise component of a source. The
filtering process must be fast and be embedded in an interactive visualization
tool in order to support fast inspection of a large number of sources. To
achieve such interactive exploration, we implemented a multi-core CPU (OpenMP)
and a GPU (OpenGL) version of this filter in a 3D visualization environment
($\tt{SlicerAstro}$). | astro-ph_IM |
The NRL Program in X-ray Navigation: This chapter describes the development of X-ray Navigation at the Naval
Research Laboratory (NRL) within its astrophysics research programs. The
prospects for applications emerged from early discoveries of X-ray source
classes and their properties. Starting around 1988 some NRL X-ray astronomy
programs included navigation as one of the motivations. The USA experiment
(1999) was the first flight payload with an explicit X-ray navigation theme.
Subsequently, NRL has continued to work in this area through participation in
DARPA and NASA programs. Throughout, the general concept of X-ray navigation
(XRNAV) has been broad enough to encompass many different uses of X-ray source
observations for attitude determination, position determination, and
timekeeping. Pulsar-based X-ray navigation (XNAV) is a special case. | astro-ph_IM |
The nature of the near-infrared interline sky background using fibre
Bragg grating OH suppression: We analyse the near-infrared interline sky background, OH and O2 emission in
19 hours of H band observations with the GNOSIS OH suppression unit and the
IRIS2 spectrograph at the 3.9-m AAT. We find that the temporal behaviour of OH
emission is best described by a gradual decrease during the first half of the
night followed by a gradual increase during the second half of the night
following the behaviour of the solar elevation angle. We measure the interline
background at 1.520 microns where the instrumental thermal background is very
low and study its variation with zenith distance, time after sunset, ecliptic
latitude, lunar zenith angle and lunar distance to determine the presence of
non-thermal atmospheric emission, zodiacal scattered light and scattered
moonlight. Zodiacal scattered light is too faint to be detected in the summed
observations. Scattered moonlight due to Mie scattering by atmospheric aerosols
is seen at small lunar distances (< 11 deg), but is otherwise too faint to
detect. Except at very small lunar distances the interline background at a
resolving power of R~2400 when using OH suppression fibres is dominated by a
non-thermal atmospheric source with a temporal behaviour that resembles
atmospheric OH emission suggesting that the interline background contains
instrumentally-scattered OH. However, the interline background dims more
rapidly than OH early in the night suggesting contributions from rapid dimming
molecules. The absolute interline background is 560 +/- 120 photons s^-1 m^-2
micron^-1 arcsec^-2 under dark conditions. This value is similar to previous
measurements without OH suppression suggesting that non-suppressed atmospheric
emission is responsible for the interline background. Future OH suppression
fibre designs may address this by the suppression of more sky lines using more
accurate sky line measurements taken from high resolution spectra. | astro-ph_IM |
A Gaussian process cross-correlation approach to time delay estimation
in active galactic nuclei: We present a probabilistic cross-correlation approach to estimate time delays
in the context of reverberation mapping (RM) of Active Galactic Nuclei (AGN).
We reformulate the traditional interpolated cross-correlation method as a
statistically principled model that delivers a posterior distribution for the
delay. The method employs Gaussian processes as a model for observed AGN light
curves. We describe the mathematical formalism and demonstrate the new approach
using both simulated light curves and available RM observations. The proposed
method delivers a posterior distribution for the delay that accounts for
observational noise and the non-uniform sampling of the light curves. This
feature allow us to fully quantify its uncertainty and propagate it to
subsequent calculations of dependent physical quantities, e.g., black hole
masses. It delivers out-of-sample predictions, which enables us to subject it
to model selection and it can calculate the joint posterior delay for more than
two light curves. Because of the numerous advantages of our reformulation and
the simplicity of its application, we anticipate that our method will find
favour not only in the specialised community of RM, but in all fields where
cross-correlation analysis is performed. We provide the algorithms and examples
of their application as part of our Julia GPCC package. | astro-ph_IM |
Near-UV Spectroscopy with the VLT: The 39-meter European Extremely Large Telescope (E-ELT) is expected to have
very low throughput in the blue part of the visible spectrum. Because of that,
a blue-optimised spectrograph at the 8-meter Very Large Telescope could
potentially be competitive against the E-ELT at wavelengths shorter than 400
nm. A concept study for such an instrument was concluded in 2012. This would be
a high-throughput, medium resolution (R $\sim$ 20\,000) spectrograph, operating
between 300 and 400 nm. It is currently expected that construction of this
instrument will start in the next few years. In this contribution, I present a
summary of the instrument concept and of some of the possible Galactic and
extragalactic science cases that motivate such a spectrograph. | astro-ph_IM |
Sub-kilometre scale ionospheric studies at the SKA-Low site, using MWA
extended baselines: The ambitious scientific goals of SKA require a matching capability for
calibration of instrumental and atmospheric propagation contributions as
functions of time, frequency and position. The development of novel calibration
algorithms to meet these requirements is an active field of research. In this
work {we aim to characterize} these, focusing on the spatial and temporal
structure scales of the ionospheric effects; ultimately, these provide the
guidelines for designing the optimum calibration strategy. We used empirical
ionospheric measurements at the site where the SKA-Low will be built, using MWA
Phase-2 Extended baseline observations and the station-based Low-frequency
Excision of Atmosphere in Parallel (LEAP) calibration algorithm. We have done
this via direct regression analysis of the ionospheric screens and by forming
the full and detrended structure functions. We found that 50% of the screens
show significant non-linear structures at scales >0.6km that dominate at >2km,
and 1% show significant sub-minute temporal changes, providing that there is
sufficient sensitivity. Even at the moderate sensitivity and baseline lengths
of MWA, non-linear corrections are required at 88 MHz during moderate-weather
and at 154 MHz during poor weather, or for high SNR measurements. Therefore we
predict that improvements will come from correcting for higher-order defocusing
effects in observations with MWA Phase-2, and further with new developments in
MWA Phase-3. Because of the giant leap in sensitivity, the correction for
complex ionospheric structures will be mandatory on SKA-Low, for both imaging
and tied-array beam formation. | astro-ph_IM |
Direct Imaging in the Habitable Zone and the Problem of Orbital Motion: High contrast imaging searches for exoplanets have been conducted on 2.4-10 m
telescopes, typically at H band (1.6 microns) and used exposure times of ~1 hr
to search for planets with semi-major axes of > ~10 AU. We are beginning to
plan for surveys using extreme-AO systems on the next generation of 30-meter
class telescopes, where we hope to begin probing the habitable zones (HZs) of
nearby stars. Here we highlight a heretofore ignorable problem in direct
imaging: planets orbit their stars. Under the parameters of current surveys,
orbital motion is negligible over the duration of a typical observation.
However, this motion is not negligible when using large diameter telescopes to
observe at relatively close stellar distances (1-10pc), over the long exposure
times (10-20 hrs) necessary for direct detection of older planets in the HZ. We
show that this motion will limit our achievable signal-to-noise ratio and
degrade observational completeness. Even on current 8m class telescopes,
orbital motion will need to be accounted for in an attempt to detect HZ planets
around the nearest sun-like stars alpha Cen A & B, a binary system now known to
harbor at least one planet. Here we derive some basic tools for analyzing this
problem, and ultimately show that the prospects are good for de-orbiting a
series of shorter exposures to correct for orbital motion. | astro-ph_IM |
Neutrino direction and energy resolution of Askaryan detectors: Detection of high-energy neutrinos via the radio technique allows for an
exploration of the neutrino energy range from $\sim10^{16}$\~eV to
$\sim10^{20}$\~eV with unprecedented precision. These Askaryan detectors have
matured in two pilot arrays (ARA and ARIANNA) and the construction of a
large-scale detector is actively discussed in the community. In this
contribution, we present reconstruction techniques to determine the neutrino
direction and energy from the observed few-nanoseconds short radio flashes and
quantify the resolution of one of such detectors. The reconstruction of the
neutrino direction requires a precise measurement of both the signal direction
as well as the signal polarization. The reconstruction of the neutrino energy
requires, in addition, the measurement of the vertex distance, obtainable from
the time difference of two signal paths through the ice, and the viewing angle
of the in-ice shower via the frequency spectrum. We discuss the required
algorithms and quantify the resolution using a detailed Monte Carlo simulation
study. | astro-ph_IM |
Radon backgrounds in the DEAP-1 liquid-argon-based Dark Matter detector: The DEAP-1 \SI{7}{kg} single phase liquid argon scintillation detector was
operated underground at SNOLAB in order to test the techniques and measure the
backgrounds inherent to single phase detection, in support of the
\mbox{DEAP-3600} Dark Matter detector. Backgrounds in DEAP are controlled
through material selection, construction techniques, pulse shape discrimination
and event reconstruction. This report details the analysis of background events
observed in three iterations of the DEAP-1 detector, and the measures taken to
reduce them.
The $^{222}$Rn decay rate in the liquid argon was measured to be between 16
and \SI{26}{\micro\becquerel\per\kilogram}. We found that the background
spectrum near the region of interest for Dark Matter detection in the DEAP-1
detector can be described considering events from three sources: radon
daughters decaying on the surface of the active volume, the expected rate of
electromagnetic events misidentified as nuclear recoils due to inefficiencies
in the pulse shape discrimination, and leakage of events from outside the
fiducial volume due to imperfect position reconstruction. These backgrounds
statistically account for all observed events, and they will be strongly
reduced in the DEAP-3600 detector due to its higher light yield and simpler
geometry. | astro-ph_IM |
AtmoHEAD 2013 workshop / Atmospheric Monitoring for High-Energy
Astroparticle Detectors: A 3-day international workshop on atmospheric monitoring and calibration for
high-energy astroparticle detectors, with a view towards next-generation
facilities. The atmosphere is an integral component of many high-energy
astroparticle detectors. Imaging atmospheric Cherenkov telescopes and
cosmic-ray extensive air shower detectors are the two instruments driving the
rapidly evolving fields of very-high- and ultra-high-energy astrophysics. In
these instruments, the atmosphere is used as a giant calorimeter where cosmic
rays and gamma rays deposit their energy and initiate EASs; it is also the
medium through which the resulting Cherenkov light propagates. Uncertainties in
real-time atmospheric conditions and in the fixed atmospheric models typically
dominate all other systematic errors. With the improved sensitivity of upgraded
IACTs such as H.E.S.S.-II and MAGIC-II and future facilities like the Cherenkov
Telescope Array (CTA) and JEM-EUSO, statistical uncertainties are expected to
be significantly reduced, leaving the atmosphere as the limiting factor in the
determination of astroparticle spectra. Varying weather conditions necessitate
the development of suitable atmospheric monitoring to be integrated in the
overall instrument calibration, including Monte Carlo simulations. With
expertise distributed across multiple collaborations and scientific domains, an
interdisciplinary workshop is being convened to advance progress on this
critical and timely topic. | astro-ph_IM |
Dark Ages Radio Explorer Mission: Probing the Cosmic Dawn: The period between the creation of the cosmic microwave background at a
redshift of ~1000 and the formation of the first stars and black holes that
re-ionize the intergalactic medium at redshifts of 10-20 is currently
unobservable. The baryonic component of the universe during this period is
almost entirely neutral hydrogen, which falls into local regions of higher dark
matter density. This seeds the formation of large-scale structures including
the cosmic web that we see today in the filamentary distribution of galaxies
and clusters of galaxies. The only detectable signal from these dark ages is
the 21-cm spectral line of hydrogen, redshifted down to frequencies of
approximately 10-100 MHz. Space-based observations of this signal will allow us
to determine the formation epoch and physics of the first sources of ionizing
radiation, and potentially detect evidence for the decay of dark matter
particles. JPL is developing deployable low frequency antenna and receiver
prototypes to enable both all-sky spectral measurements of neutral hydrogen and
ultimately to map the spatial distribution of the signal as a function of
redshift. Such observations must be done from space because of Earth's
ionosphere and ubiquitous radio interference. A specific application of these
technologies is the Dark Ages Radio Explorer (DARE) mission. This small
Explorer class mission is designed to measure the sky-averaged hydrogen signal
from the shielded region above the far side of the Moon. These data will
complement ground-based radio observations of the final stages of intergalactic
re-ionization at higher frequencies. DARE will also serve as a scientific
percursor for space-based interferometry missions to image the distribution of
hydrogen during the cosmic dark ages. | astro-ph_IM |
A method to develop mission critical data processing systems for
satellite based instruments. The spinning mode case: Modern satellite based experiments are often very complex real-time systems,
composed by flight and ground segments, that have challenging resource related
constraints, in terms of size, weight, power, requirements for real-time
response, fault tolerance, and specialized input/output hardware-software, and
they must be certified to high levels of assurance. Hardware-software data
processing systems have to be responsive to system degradation and to changes
in the data acquisition modes, and actions have to be taken to change the
organization of the mission operations. A big research & develop effort in a
team composed by scientists and technologists can lead to produce software
systems able to optimize the hardware to reach very high levels of performance
or to pull degraded hardware to maintain satisfactory features. We'll show
real-life examples describing a system, processing the data of a X-Ray detector
on satellite-based mission in spinning mode. | astro-ph_IM |
Bayesian modelling of scattered light in the LIGO interferometers: Excess noise from scattered light poses a persistent challenge in the
analysis of data from gravitational wave detectors such as LIGO. We integrate a
physically motivated model for the behavior of these "glitches" into a standard
Bayesian analysis pipeline used in gravitational wave science. This allows for
the inference of the free parameters in this model, and subtraction of these
models to produce glitch-free versions of the data. We show that this inference
is an effective discriminator of the presence of the features of these
glitches, even when those features may not be discernible in standard
visualizations of the data. | astro-ph_IM |
Trigonometric Extension of the Geometric Correction Factor: Prototype
for adding precision to adaptive ray tracing in ENZO: In this paper, we describe a method designed to add precision to radiation
simulations in the adaptive mesh refinement cosmological hydrodynamics code
ENZO. We build upon the geometric correction factor described in
\textit{ENZO+MORAY: radiation hydrodynamics adaptive mesh refinement
simulations with adaptive ray tracing} (Wise and Abel 2011) which accounts for
partial coverage of a ray's solid angle with a cube. Because of this geometric
mismatch in the methods to approximate this, there are artifacts in the
radiation field. Here, we address the two-dimensional extension, which acts as
a sufficient estimate of the three-dimensional case and, in practice, the
Hierarchical Equal Area isoLatitude Pixelization of the sphere (HEALPix)
(Gorski 2005). We will demonstrate the value of an extension to the geometric
correction factor and lay the groundwork for a future implementation to ENZO to
improve simulations of radiation from point sources. | astro-ph_IM |
An Analysis of DES Cluster Simulations through the IMCAT and Shapelets
Weak Lensing Pipelines: We have run two completely independent weak lensing analysis pipelines on a
set of realistic simulated images of a massive galaxy cluster with a singular
isothermal sphere profile (galaxy velocity dispersion sigma_v=1250 km/ sec).
The suite of images was constructed using the simulation tools developed by the
Dark Energy Survey. We find that both weak lensing pipelines can accurately
recover the velocity dispersion of our simulated clusters, suggesting that
current weak lensing tools are accurate enough for measuring the shear profile
of massive clusters in upcoming large photometric surveys. We also demonstrate
how choices of some cuts influence the final shear profile and sigma_v
measurement. Analogously to the STEP program, we make all of these cluster
simulation images publically available for other groups to analyze through
their own weak lensing pipelines. | astro-ph_IM |
Noise statistics in a fast digital radio receiver: the Bedlam backend
for the Parkes Radio Telescope: The digital record of the voltage in a radio telescope receiver, after
frequency conversion and sampling at a finite rate, is not a perfect
representation of the original analog signal. To detect and characterise a
transient event with a duration comparable to the inverse bandwidth it is
necessary to compensate for these effects, which modifies the statistics of the
signal, making it difficult to determine the significance of a potential
detection. We present an analysis of these modified statistics and demonstrate
them with experimental results from Bedlam, a new digital backend for the
Parkes radio telescope. | astro-ph_IM |
A 50 mK test bench for demonstration of the readout chain of
Athena/X-IFU: The X-IFU (X-ray Integral Field Unit) onboard the large ESA mission Athena
(Advanced Telescope for High ENergy Astrophysics), planned to be launched in
the mid 2030s, will be a cryogenic X-ray imaging spectrometer operating at 55
mK. It will provide unprecedented spatially resolved high-resolution
spectroscopy (2.5 eV FWHM up to 7 keV) in the 0.2-12 keV energy range thanks to
its array of TES (Transition Edge Sensors) microcalorimeters of more than 2k
pixel. The detection chain of the instrument is developed by an international
collaboration: the detector array by NASA/GSFC, the cold electronics by NIST,
the cold amplifier by VTT, the WFEE (Warm Front-End Electronics) by APC, the
DRE (Digital Readout Electronics) by IRAP and a focal plane assembly by SRON.
To assess the operation of the complete readout chain of the X-IFU, a 50 mK
test bench based on a kilo-pixel array of microcalorimeters from NASA/GSFC has
been developed at IRAP in collaboration with CNES. Validation of the test bench
has been performed with an intermediate detection chain entirely from NIST and
Goddard. Next planned activities include the integration of DRE and WFEE
prototypes in order to perform an end-to-end demonstration of a complete X-IFU
detection chain. | astro-ph_IM |
An update to the EVEREST K2 pipeline: Short cadence, saturated stars,
and Kepler-like photometry down to Kp = 15: We present an update to the EVEREST K2 pipeline that addresses various
limitations in the previous version and improves the photometric precision of
the de-trended light curves. We develop a fast regularization scheme for third
order pixel level decorrelation (PLD) and adapt the algorithm to include the
PLD vectors of neighboring stars to enhance the predictive power of the model
and minimize overfitting, particularly for faint stars. We also modify PLD to
work for saturated stars and improve its performance on extremely variable
stars. On average, EVEREST 2.0 light curves have 10-20% higher photometric
precision than those in the previous version, yielding the highest precision
light curves at all Kp magnitudes of any publicly available K2 catalog. For
most K2 campaigns, we recover the original Kepler precision to at least Kp =
14, and to at least Kp = 15 for campaigns 1, 5, and 6. We also de-trend all
short cadence targets observed by K2, obtaining even higher photometric
precision for these stars. All light curves for campaigns 0-8 are available
online in the EVEREST catalog, which will be continuously updated with future
campaigns. EVEREST 2.0 is open source and is coded in a general framework that
can be applied to other photometric surveys, including Kepler and the upcoming
TESS mission. | astro-ph_IM |
Characterization of a multi-etalon array for ultra-high resolution
spectroscopy: The upcoming Extremely Large Telescopes (ELTs) are expected to have the
collecting area required to detect potential biosignature gases in the
atmosphere of rocky planets around nearby low-mass stars. Some efforts are
currently focusing on searching for molecular oxygen (O2), since O2 is a known
biosignature on Earth. One of the most promising methods to search for O2 is
transmission spectroscopy in which high-resolution spectroscopy is combined
with cross-correlation techniques. In this method, high spectral resolution is
required both to resolve the exoplanet's O2 lines and to separate them from
foreground telluric absorption. While current astronomical spectrographs
typically achieve a spectral resolution of 100,000, recent studies show that
resolutions of 300,000 -- 400,000 are optimal to detect O2 in the atmosphere of
earth analogs with the ELTs. Fabry Perot Interferometer (FPI) arrays have been
proposed as a relatively low-cost way to reach these resolutions. In this
paper, we present performance results for our 2-FPI array lab prototype, which
reaches a resolving power of 600,000. We further discuss the use of
multi-cavity etalons (dualons) to be resolution boosters for existing
spectrographs. | astro-ph_IM |
Optimal detuning for quantum filter cavities: Vacuum quantum fluctuations impose a fundamental limit on the sensitivity of
gravitational-wave interferometers, which rank among the most sensitive
precision measurement devices ever built. The injection of conventional
squeezed vacuum reduces quantum noise in one quadrature at the expense of
increasing noise in the other. While this approach improved the sensitivity of
the Advanced LIGO and Advanced Virgo interferometers during their third
observing run (O3), future improvements in arm power and squeezing levels will
bring radiation pressure noise to the forefront. Installation of a filter
cavity for frequency-dependent squeezing provides broadband reduction of
quantum noise through the mitigation of this radiation pressure noise, and it
is the baseline approach planned for all of the future gravitational-wave
detectors currently conceived. The design and operation of a filter cavity
requires careful consideration of interferometer optomechanics as well as
squeezing degradation processes. In this paper, we perform an in-depth analysis
to determine the optimal operating point of a filter cavity. We use our model
alongside numerical tools to study the implications for filter cavities to be
installed in the upcoming "A+" upgrade of the Advanced LIGO detectors. | astro-ph_IM |
The Power Board of the KM3NeT Digital Optical Module: design, upgrade,
and production: The KM3NeT Collaboration is building an underwater neutrino observatory at
the bottom of the Mediterranean Sea consisting of two neutrino telescopes, both
composed of a three-dimensional array of light detectors, known as digital
optical modules. Each digital optical module contains a set of 31 three inch
photomultiplier tubes distributed over the surface of a 0.44 m diameter
pressure-resistant glass sphere. The module includes also calibration
instruments and electronics for power, readout and data acquisition. The power
board was developed to supply power to all the elements of the digital optical
module. The design of the power board began in 2013, and several prototypes
were produced and tested. After an exhaustive validation process in various
laboratories within the KM3NeT Collaboration, a mass production batch began,
resulting in the construction of over 1200 power boards so far. These boards
were integrated in the digital optical modules that have already been produced
and deployed, 828 until October 2023. In 2017, an upgrade of the power board,
to increase reliability and efficiency, was initiated. After the validation of
a pre-production series, a production batch of 800 upgraded boards is currently
underway. This paper describes the design, architecture, upgrade, validation,
and production of the power board, including the reliability studies and tests
conducted to ensure the safe operation at the bottom of the Mediterranean Sea
throughout the observatory's lifespan | astro-ph_IM |
Reduction of CCD observations made with a scanning Fabry--Perot
interferometer. III. Wavelength scale refinement: We describe the recent modifications to the data reduction technique for
observations acquired with the scanning Fabry-Perot interferometer (FPI)
mounted on the 6-m telescope of the Special Astrophysical Observatory that
allow the wavelength scale to be correctly computed in the case of large mutual
offsets of studied objects in interferograms. Also the parameters of the
scanning FPIs used in the SCORPIO-2 multimode focal reducer are considered. | astro-ph_IM |
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