- 标题
- 摘要
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- 实验方案
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An image reconstruction method (IRBis) for optical/infrared interferometry
摘要： Aims.We present an image reconstruction method for optical/infrared long-baseline interferometry called IRBis (image reconstruction software using the bispectrum). We describe the theory and present applications to computer-simulated interferograms. Methods. The IRBis method can reconstruct an image from measured visibilities and closure phases. The applied optimization routine ASA_CG is based on conjugate gradients. The method allows the user to implement different regularizers, apply residual ratios as an additional metric for goodness-of-fit, and use previous iteration results as a prior to force convergence. Results. We present the theory of the IRBis method and several applications of the method to computer-simulated interferograms. The image reconstruction results show the dependence of the reconstructed image on the noise in the interferograms (e.g., for ten electron read-out noise and 139 to 1219 detected photons per interferogram), the regularization method, the angular resolution, and the reconstruction parameters applied. Furthermore, we present the IRBis reconstructions submitted to the interferometric imaging beauty contest 2012 initiated by the IAU Working Group on Optical/IR Interferometry and describe the performed data processing steps.
关键词： techniques: high angular resolution,methods: data analysis,instrumentation: interferometers,techniques: interferometric,methods: numerical,techniques: image processing
更新于2025-09-23 15:23:52
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Denoising, deconvolving, and decomposing multi-domain photon observations
摘要： Astronomical imaging based on photon count data is a non-trivial task. In this context we show how to denoise, deconvolve, and decompose multi-domain photon observations. The primary objective is to incorporate accurate and well motivated likelihood and prior models in order to give reliable estimates about morphologically different but superimposed photon flux components present in the data set. Thereby we denoise and deconvolve photon counts, while simultaneously decomposing them into diffuse, point-like and uninteresting background radiation fluxes. The decomposition is based on a probabilistic hierarchical Bayesian parameter model within the framework of information field theory (IFT). In contrast to its predecessor D3PO, D4PO reconstructs multi-domain components. Thereby each component is defined over its own direct product of multiple independent domains, for example location and energy. D4PO has the capability to reconstruct correlation structures over each of the sub-domains of a component separately. Thereby the inferred correlations implicitly define the morphologically different source components, except for the spatial correlations of the point-like flux. Point-like source fluxes are spatially uncorrelated by definition. The capabilities of the algorithm are demonstrated by means of a synthetic, but realistic, mock data set, providing spectral and spatial information about each detected photon. D4PO successfully denoised, deconvolved, and decomposed a photon count image into diffuse, point-like and background flux, each being functions of location as well as energy. Moreover, uncertainty estimates of the reconstructed fields as well as of their correlation structure are provided employing their posterior density function and accounting for the manifolds the domains reside on.
关键词： gamma rays: general,methods: data analysis,methods: statistical,X-rays: general,methods: numerical,techniques: image processing
更新于2025-09-23 15:23:52
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Detection of Faint Asteroids Based on Image Shifting and Stacking Method
摘要： In order to improve the ability to find the faint and small celestial bodies in the solar system, a method of shifting and stacking images which improves the detection efficiency of faint moving objects is applied to process the sequential optical images. This method determines the existence of moving objects by using the method of false position to pre-estimate the apparent velocities of moving objects, then determines iteratively the accurate positions of moving objects based on the SNR (Signal-to-Noise Ratio) and elongation of stellar image. Using the sequential images of the China Near Earth Object Survey Telescope (CNEOST), we carry out an experiment and succeed in detecting asteroids fainter than 21 magnitude which are invisible on a single image. Thus, the feasibility of this method is verified.
关键词： techniques: image processing,astrometry,instrumentation,methods: data analysis,telescope,methods: observational
更新于2025-09-23 15:23:52
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cuFFS: A GPU-accelerated code for Fast Faraday rotation measure Synthesis
摘要： Rotation measure (RM) synthesis is a widely used polarization processing algorithm for reconstructing polarized structures along the line of sight. Performing RM synthesis on large datasets produced by telescopes like LOFAR can be computationally intensive as the computational cost is proportional to the product of the number of input frequency channels, the number of output Faraday depth values to be evaluated and the number of lines of sight present in the data cube. The required computational cost is likely to get worse due to the planned large area sky surveys with telescopes like the Low Frequency Array (LOFAR), the Murchison Widefield Array (MWA), and eventually the Square Kilometre Array (SKA). The massively parallel General Purpose Graphical Processing Units (GPGPUs) can be used to execute some of the computationally intensive astronomical image processing algorithms including RM synthesis. In this paper, we present a GPU-accelerated code, called cuFFS or CUDA-accelerated Fast Faraday Synthesis, to perform Faraday rotation measure synthesis. Compared to a fast single-threaded and vectorized CPU implementation, depending on the structure and format of the data cubes, our code achieves an increase in speed of up to two orders of magnitude. During testing, we noticed that the disk I/O when using the Flexible Image Transport System (FITS) data format is a major bottleneck and to reduce the time spent on disk I/O, our code supports the faster HDFITS format in addition to the standard FITS format. The code is written in C with GPU-acceleration achieved using Nvidia’s CUDA parallel computing platform. The code is available at https://github.com/sarrvesh/cuFFS.
关键词： Computing methodologies: graphics processors,Techniques: image processing,Techniques: polarimetric,GPGPU,Methods: data analysis
更新于2025-09-23 15:22:29
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Precision Light Curves from <i>TESS</i> Full-frame Images: A Different Imaging Approach
摘要： The Transiting Exoplanet Survey Satellite (TESS) will observe ～150 million stars brighter than T mag ? , with 16 photometric precision from 60 ppm to 3%, enabling an array of exoplanet and stellar astrophysics investigations. While light curves will be provided for ～400,000 targets observed at 2 minute cadence, observations of most stars will only be provided as full-frame images (FFIs) at 30 minute cadence. The TESS image scale of ～21″/pix is highly susceptible to crowding, blending, and source confusion, and the highly spatially variable point-spread function (PSF) will challenge traditional techniques, such as aperture and Gaussian-kernel PSF photometry. We use official “End-to-End 6” TESS simulated FFIs to demonstrate a difference image analysis pipeline, using a δ-function kernel, that achieves the mission specification noise floor of 60 ppm hr?1/2. We show that the pipeline performance does not depend on position across the field, and only ～2% of stars appear to exhibit residual systematics at the level of ～5 ppt. We also demonstrate recoverability of planet transits, eclipsing binaries, and other variables. We provide the pipeline as an open-source tool at https://github.com/ryanoelkers/DIA in both IDL and PYTHON. We intend to extract light curves for all point sources in the TESS FFIs as soon as they become publicly available, and will provide the light curves through the Filtergraph data visualization service. An example data portal based on the simulated FFIs is available for inspection at https://filtergraph.com/tess_ffi.
关键词： techniques: image processing,catalogs,methods: data analysis
更新于2025-09-23 15:22:29
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Characterization of the White-light Brightness of the F-corona between 5° and 24° Elongation
摘要： The white-light F-corona arises from light scattered by circumsolar dust. Using weekly models of the eastern side of the F-corona between 5° and 24° elongation, we analyzed the elongation and time dependence of the brightness of its photometric axis. The models were constructed from STEREO-A SECCHI/HI-1 images taken between 2007 December and 2014 March. We found that the brightness profiles can be approximated by power laws, with the coefficients of the models depending upon the observer’s ecliptic longitude. Their variation is not symmetric with respect to the orbital nodes of the dust plane, nor is the behavior similar in the two halves of the spacecraft orbit delimited by the line of nodes. The exponents range between ?2.31 and ?2.35, the former occurring when the observer is at the nodes. The asymmetry observed in the behavior of the proportionality constant is indicative of the projected center of the dust cloud being offset from the Sun’s center by ～0.4 Re. The coefficients exhibit a secular variation correlated with the location of the barycenter of the solar system. We also used the HI-1 frames obtained during STEREO-A calibration rolls to model the 360° F-corona. We found that (1) its flattening index (f = 1 - Rpol/Req) decreases from ～0.66 to ～0.46 with decreasing elongation and (2) the isophotes’ shape can be approximated by a series of superellipses, with the superellipse index n increasing (nonlinearly) with brightness (n ~ 1.65). Cubic extrapolation of the results below 5° elongation points to a circular F-corona below ～1° elongation.
关键词： scattering,zodiacal dust,methods: data analysis,Sun: corona,techniques: image processing
更新于2025-09-23 15:22:29
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The optical morphologies of galaxies in the IllustrisTNG simulation: a comparison to Pan-STARRS observations
摘要： We have generated synthetic images of ～27 000 galaxies from the IllustrisTNG and the original Illustris hydrodynamic cosmological simulations, designed to match Pan-STARRS observations of log10(M?/M(cid:4)) ≈ 9.8–11.3 galaxies at z ≈ 0.05. Most of our synthetic images were created with the SKIRT radiative transfer code, including the effects of dust attenuation and scattering, and performing the radiative transfer directly on the Voronoi mesh used by the simulations themselves. We have analysed both our synthetic and real Pan-STARRS images with the newly developed statmorph code, which calculates non-parametric morphological diagnostics – including the Gini–M20 and concentration–asymmetry–smoothness statistics – and performs 2D S′ersic ?ts. Overall, we ?nd that the optical morphologies of IllustrisTNG galaxies are in good agreement with observations, and represent a substantial improvement compared to the original Illustris simulation. In particular, the locus of the Gini–M20 diagram is consistent with that inferred from observations, while the median trends with stellar mass of all the morphological, size and shape parameters considered in this work lie within the ～1σ scatter of the observational trends. However, the IllustrisTNG model has some dif?culty with more stringent tests, such as producing a strong morphology–colour relation. This results in a somewhat higher fraction of red discs and blue spheroids compared to observations. Similarly, the morphology–size relation is problematic: while observations show that discs tend to be larger than spheroids at a ?xed stellar mass, such a trend is not present in IllustrisTNG.
关键词： galaxies: statistics,galaxies: formation,galaxies: structure,methods: numerical,techniques: image processing
更新于2025-09-23 15:22:29
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KMTNet Nearby Galaxy Survey. I. Optimal Strategy for Low Surface Brightness Imaging with KMTNet
摘要： In hierarchical galaxy formation models, galaxies evolve through mergers and accretions. Tidally disrupted debris from these processes can remain as diffuse, faint structures, which can provide useful insight into the assembly history of galaxies. To investigate the properties of the faint structures in outskirts of nearby galaxies, we conduct deep and wide-field imaging survey with Korea Microlensing Telescope Network (KMTNet). We present our observing strategy and optimal data reduction process to recover the faint extended features in the imaging data of NGC 1291 taken with KMTNet. Through the dark sky flat-fielding and optimal sky subtraction, we can effectively remove inhomogeneous patterns. In the combined images, the peak-to-peak global sky gradients were reduced to less than ～0.5% and ～0.3% of the original B- and R-band sky levels, respectively. However, we find local spatial fluctuations in the background sky that can affect the precise measurement of the sky value. Consequently, we can reach the surface brightness of mB,1σ～29.5 and mR,1σ～28.5 mag arcsec?2 in azimuthally averaged one-dimensional surface brightness profiles, which is mainly limited by the uncertainty in the sky determination. These results suggest that the deep imaging data produced by KMTNet are suitable to study the faint features of nearby galaxies such as outer disks and dwarf companions, but unideal (not impossible) to detect stellar halos. The one-dimensional profile revealed that NGC 1291 appeared to have a Type I disk out to R ～30 kpc with no obvious color gradient, and excess light due to a stellar halo was undetected.
关键词： galaxies: structure,galaxies: individual (NGC 1291),galaxies: stellar content,techniques: image processing
更新于2025-09-23 15:21:21
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Searching for Subsecond Stellar Variability with Wide-field Star Trails and Deep Learning
摘要： We present a method that enables wide-field ground-based telescopes to scan the sky for subsecond stellar variability. The method has operational and image processing components. The operational component takes star trail images. Each trail serves as a light curve for its corresponding source and facilitates subexposure photometry. We train a deep neural network to identify stellar variability in wide-field star trail images. We use the Large Synoptic Survey Telescope Photon Simulator to generate simulated star trail images and include transient bursts as a proxy for variability. The network identifies transient bursts on timescales down to 10 ms. We argue that there are multiple fields of astrophysics that can be advanced by the unique combination of time resolution and observing throughput that our method offers.
关键词： techniques: image processing,methods: observational,techniques: photometric
更新于2025-09-23 15:21:01
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Solar hard X-ray imaging by means of compressed sensing and finite isotropic wavelet transform
摘要： Aims. Compressed sensing realized by means of regularized deconvolution and the finite isotropic wavelet transform is effective and reliable in hard X-ray solar imaging. Methods. The method uses the finite isotropic wavelet transform with the Meyer function as the mother wavelet. Furthermore, compressed sensing is realized by optimizing a sparsity-promoting regularized objective function by means of the fast iterative shrinkage-thresholding algorithm. Eventually, the regularization parameter is selected by means of the Miller criterion. Results. The method is applied against both synthetic data mimicking measurements made with the Spectrometer/Telescope Imaging X-rays (STIX) and experimental observations provided by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). The performances of the method are qualitatively validated by comparing some morphological properties of the reconstructed sources with those of the corresponding synthetic configurations. Furthermore, the results concerning experimental data are compared with those obtained by applying other visibility-based reconstruction methods. Conclusions. The results show that when the new method is applied to synthetic STIX visibility sets, it provides reconstructions with a spatial accuracy comparable to the accuracy provided by the most popular method in hard X-ray solar imaging and with a higher spatial resolution. Furthermore, when it is applied to experimental RHESSI data, the reconstructions are characterized by reliable photometry and by a notable reduction of the ringing effects caused by the instrument point spread function.
关键词： techniques: image processing,Sun: X-rays, gamma rays,Sun: flares
更新于2025-09-23 15:21:01