1,133 research outputs found
Dynamics of the solar chromosphere. V. High-frequency modulation in ultraviolet image sequences from TRACE
We search for signatures of high-frequency oscillations in the upper solar
photosphere and low chromosphere in the context of acoustic heating of outer
stellar atmospheres. We use ultraviolet image sequences of a quiet center-disk
area from the Transition Region and Coronal Explorer (TRACE) mission which were
taken with strict cadence regularity. The latter permits more reliable
high-frequency diagnosis than in earlier work. Spatial Fourier power maps,
spatially averaged coherence and phase-difference spectra, and spatio-temporal
k-f decompositions all contain high-frequency features that at first sight seem
of considerable intrinsic interest but actually are more likely to represent
artifacts of different nature. Spatially averaged phase difference measurement
provides the most sensitive diagnostic and indicates the presence of acoustic
modulation up to f=20 mHz (periods down to 50 seconds) in internetwork areas.Comment: 9 pages, 8 figure
ARCHI: pipeline for light curve extraction of CHEOPS background star
High precision time series photometry from space is being used for a number
of scientific cases. In this context, the recently launched CHEOPS (ESA)
mission promises to bring 20 ppm precision over an exposure time of 6 hours,
when targeting nearby bright stars, having in mind the detailed
characterization of exoplanetary systems through transit measurements. However,
the official CHEOPS (ESA) mission pipeline only provides photometry for the
main target (the central star in the field). In order to explore the potential
of CHEOPS photometry for all stars in the field, in this paper we present
archi, an additional open-source pipeline module{\dag}to analyse the background
stars present in the image. As archi uses the official Data Reduction Pipeline
data as input, it is not meant to be used as independent tool to process raw
CHEOPS data but, instead, to be used as an add-on to the official pipeline. We
test archi using CHEOPS simulated images, and show that photometry of
background stars in CHEOPS images is only slightly degraded (by a factor of 2
to 3) with respect to the main target. This opens a potential for the use of
CHEOPS to produce photometric time series of several close-by targets at once,
as well as to use different stars in the image to calibrate systematic errors.
We also show one clear scientific application where the study of the companion
light curve can be important for the understanding of the contamination on the
main target.Comment: 14 pages, 13 figures, accepted for publication in MNRAS, all code
available at https://github.com/Kamuish/arch
Vision Algorithm for the Solar Aspect System of the HEROES Mission
This work covers the design and test of a machine vision algorithm for generating high-accuracy pitch and yaw pointing solutions relative to the sun for the High Energy Replicated Optics to Explore the Sun (HEROES) mission. It describes how images were constructed by focusing an image of the sun onto a plate printed with a pattern of small fiducial markers. Images of this plate were processed in real time to determine relative position of the balloon payload to the sun. The algorithm is broken into four problems: circle detection, fiducial detection, fiducial identification, and image registration. Circle detection is handled by an "Average Intersection" method, fiducial detection by a matched filter approach, identification with an ad-hoc method based on the spacing between fiducials, and image registration with a simple least squares fit. Performance is verified on a combination of artificially generated images, test data recorded on the ground, and images from the 2013 fligh
New ATCA, ALMA and VISIR observations of the candidate LBV SK-67266 (S61): the nebular mass from modelling 3D density distributions
We present new observations of the nebula around the Magellanic candidate
Luminous Blue Variable S61. These comprise high-resolution data acquired with
the Australia Telescope Compact Array (ATCA), the Atacama Large
Millimetre/Submillimetre Array (ALMA), and VISIR at the Very Large Telescope
(VLT). The nebula was detected only in the radio, up to 17 GHz. The 17 GHz ATCA
map, with 0.8 arcsec resolution, allowed a morphological comparison with the
H Hubble Space Telescope image. The radio nebula resembles a spherical
shell, as in the optical. The spectral index map indicates that the radio
emission is due to free-free transitions in the ionised, optically thin gas,
but there are hints of inhomogeneities. We present our new public code RHOCUBE
to model 3D density distributions, and determine via Bayesian inference the
nebula's geometric parameters. We applied the code to model the electron
density distribution in the S61 nebula. We found that different distributions
fit the data, but all of them converge to the same ionised mass, ~0.1 , which is an order of magnitude smaller than previous estimates. We
show how the nebula models can be used to derive the mass-loss history with
high-temporal resolution. The nebula was probably formed through stellar winds,
rather than eruptions. From the ALMA and VISIR non-detections, plus the derived
extinction map, we deduce that the infrared emission observed by space
telescopes must arise from extended, diffuse dust within the ionised region.Comment: 17 pages, 9 figures. Authors list corrected. In press in MNRAS.
RHOCUBE code available online ( https://github.com/rnikutta/rhocube
Roadmap for PCS, the Planetary Camera and Spectrograph for the E-ELT
Presently, dedicated instruments at large telescopes (SPHERE for the VLT, GPI for Gemini) are
about to discover and explore self-luminous giant planets by direct imaging and spectroscopy. The next
generation of 30m-40m ground-based telescopes, the Extremely Large Telescopes, have the potential to
dramatically enlarge the discovery space towards older giant planets seen in reflected light and ultimately even a
small number of rocky planets. The E-ELT Planetary Camera and Spectrograph (PCS) serves this purpose.
Building on the heritage of the EPICS phase-A study, this paper presents revised requirements, a possible
concept, and the R&D necessary to realize the instrument
Image Quality Modeling and Characterization of Nyquist Sampled Framing Systems with Operational Considerations for Remote Sensing
The trade between detector and optics performance is often conveyed through the Q metric, which is defined as the ratio of detector sampling frequency and optical cutoff frequency. Historically sensors have operated at Q~1, which introduces aliasing but increases the system modulation transfer function (MTF) and signal-to-noise ratio (SNR). Though mathematically suboptimal, such designs have been operationally ideal when considering system parameters such as pointing stability and detector performance. Substantial advances in read noise and quantum efficiency of modern detectors may compensate for the negative aspects associated with balancing detector/optics performance, presenting an opportunity to revisit the potential for implementing Nyquist-sampled (Q~2) sensors. A digital image chain simulation is developed and validated against a laboratory testbed using objective and subjective assessments. Objective assessments are accomplished by comparison of the modeled MTF and measurements from slant-edge photographs. Subjective assessments are carried out by performing a psychophysical study where subjects are asked to rate simulation and testbed imagery against a Delta-NIIRS scale with the aid of a marker set. Using the validated model, additional test cases are simulated to study the effects of increased detector sampling on image quality with operational considerations. First, a factorial experiment using Q-sampling, pointing stability, integration time, and detector performance is conducted to measure the main effects and interactions of each on the response variable, Delta-NIIRS. To assess the fidelity of current models, variants of the General Image Quality Equation (GIQE) are evaluated against subject-provided ratings and two modied GIQE versions are proposed. Finally, using the validated simulation and modified IQE, trades are conducted to ascertain the feasibility of implementing Q~2 designs in future systems
Models and Analysis of Vocal Emissions for Biomedical Applications
The MAVEBA Workshop proceedings, held on a biannual basis, collect the scientific papers presented both as oral and poster contributions, during the conference. The main subjects are: development of theoretical and mechanical models as an aid to the study of main phonatory dysfunctions, as well as the biomedical engineering methods for the analysis of voice signals and images, as a support to clinical diagnosis and classification of vocal pathologies
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