Images Of Astronomical Objects Research Articles

Golden spiral interferometry for radio astronomy. A proposal

Radio interferometry is a powerful technique that allows astronomers to create high-resolution images of astronomical objects. The distribution of radio telescopes in an interferometer is a critical factor that determines the resolution and sensitivity of the instrument. Traditionally, radio telescopes are distributed in a linear or circular array. However, recent work has shown that using a golden spiral distribution can improve the resolution and sensitivity of an interferometer. In this paper, the author proposes the use of a golden spiral distribution for radio interferometry, showing that a golden spiral distribution can provide a significant improvement in resolution, up to a factor of eight, compared to a linear or circular distribution. The author also proposes that a golden spiral distribution can improve the sensitivity of an interferometer; it may provide a more uniform distribution of radio telescopes than a linear or circular distribution (a known propety of spiral distributions).

Elimination of distortions of weak images of astronomical objects on the example of Saturn, Jupiter and their satellites

Elimination of distortions of weak images of astronomical objects on the example of Saturn, Jupiter and their satellites

Pixel Centroid Characterization with Laser Speckle and Application to the Nancy Grace Roman Space Telescope Detector Arrays

The Nancy Grace Roman Space Telescope will use its wide-field instrument to carry out a suite of sky surveys in the near-infrared. Several of the science objectives of these surveys, such as the measurement of the growth of cosmic structure using weak gravitational lensing, require exquisite control of instrument-related distortions of the images of astronomical objects. Roman will fly new large-format (4 × 4 k) Teledyne H4RG-10 infrared detector arrays. This paper investigates whether the pixel centroids are located on a regular grid by projecting laser speckle patterns through a double slit aperture onto a non-flight detector array. We develop a method to reconstruct the pixel centroid offsets from the stochastic speckle pattern. Due to the orientation of the test setup, only x-offsets are measured here. We test the method both on simulations, and by injecting artificial offsets into the real images. We use cross-correlations of the reconstructions from different speckle realizations to determine how much of the variance in the pixel offset maps is signal (fixed to the detector) and how much is noise. After performing this reconstruction on 64 × 64 pixel patches, and fitting out the best-fit linear mapping from pixel index to position, we find that there are residual centroid offsets in the x (column) direction from a regular grid of 0.0107 pixels rms (excluding shifts of an entire row relative to another, which our speckle patterns cannot constrain). This decreases to 0.0097 pix rms if we consider residuals from a quadratic rather than linear mapping. These rms offsets include both the physical pixel offsets, as well as any apparent offsets due to crosstalk and remaining systematic errors in the reconstruction. We comment on the advantages and disadvantages of speckle scene measurements as a tool for characterizing the pixel-level behavior in astronomical detectors.

Processing Analytical Queries over Polystore System for a Large Astronomy Data Repository

There are extremely large heterogeneous databases in the astronomical data domain, which keep increasing in size. The data types vary from images of astronomical objects to unstructured texts, relations, and key-values. Many astronomical data repositories manage such kinds of data. The Zwicky Transient Facility (ZTF) is one such data repository with a large amount of data with different varieties. Handling different types of data in a single database may have performance and efficiency issues. In this study, we propose a web-based query system built around the Polystore database architecture, and attempt to provide a solution for the growing size of data in the astronomical domain. The proposed system will unify querying over multiple datasets directly, thereby eliminating the effort to translate complex queries and simplify the work for the users in the astronomical domain. In this proposal, we study the models of data integration, analyze them, and incorporate them into a system to manage linked open data provided by astronomical domain. The proposed system is scalable, and its model can be used for various other systems to efficiently manage heterogeneous data.

Towards 3D-photonic, multi-telescope beam combiners for mid-infrared astrointerferometry.

In the past two decades high precision optical astronomical interferometry has benefited from the use of photonic technologies. Today, near-infrared interferometric instruments deliver high-resolution, hyperspectral images of astronomical objects and combine up to 4 independent telescopes at a time thanks to integrated optics (IO). Following the success of IO interferometry, several initiatives aim at developing components which could combine simultaneously more telescopes and extend their operation beyond the near-infrared bands. Here we report on the development of multi-telescope IO beam combiners for mid-infrared interferometry exploiting the three-dimensional (3D) structuring capabilities of ultrafast laser inscription. We characterise the capability of a 2-telescope and a 4-telescope beam combiner to retrieve the visibility amplitude and phase of monochromatic light fields at a wavelength of 3.39 µm. The combiner prototypes exploit different 3D architectures and are written with a femtosecond laser on substrates of Gallium Lanthanum Sulfide. Supporting numerical simulations of the performance of the beam combiners show that there is still room for improvement and indicate a roadmap for the development of future prototypes.

ASTRONIRCAM—the infrared camera-spectrograph for the 2.5-m telescope of SAI Caucasian observatory

ASTRONIRCAM is a cryogenic-cooled slit spectrograph for the spectral range 1-2.5 mkm installed at the Nasmyth focus of the 2.5-meter telescope of the Caucasian observatory of Sternberg Astronomical Institute of Lomonosov Moscow State University. The instrument is equipped with the HAWAII-2RG 2048x2048 HgCdTe array. Grisms are used as dispersive elements. In the photometric mode ASTRONIRCAM allows for extended astronomical object imaging in the field of view of 4.6x4.6 arc minutes with the 0.269 arcsec/pixel scale in standard photometric bands J, H, K and Ks as well as in narrow-band filters CH_4, [Fe II], H_2 v=1-0 S(1), Br_gamma and CO. In the spectroscopic mode, ASTRONIRCAM takes spectra of extended or point-like sources with spectral resolution R=lambda/Delta lambda <= 1200. The general design, optical system, detector electronics and readout, amplification and digitization scheme are considered. The conversion factor GAIN measurement results are described as well as its dependence on the accumulated signal (non-linearity). The full transmission of the atmosphere-to-detector train ranges from 40 to 50\% in the wide-band photometry mode. The ASTRONIRCAM sensitivity at the 2.5-m telescope is characterized by the limiting J=20, K=19 star magnitudes measured with the 10% precision and 15 minutes integration at the 1 arcsec atmospheric seeing conditions. The references to first results published on the base of ASTRONIRCAM observations are given.

3D Printing Technology: A Unique Way of Making Hubble Space Telescope Images Accessible to Non-Visual Learners

Astronomy traditionally is a visual science by which sighted people have contemplated the night sky. Astronomy has also spurred the development of sophisticated telescopes and instruments, featuring capabilities that extend to wavelengths beyond the visible, to record images of celestial objects. While the scientific data from telescopes is somewhat specialized and technical, astronomers routinely process their data to produce visually appealing formats for the public at large and also widely contribute to education and outreach efforts. Astronomical data is treated through image processing techniques including color and intensity choices that result in imagery that best represents the science being investigated in its greatest aesthetic appeal. Making such astronomical imagery accessible to those who are visually impaired has been a long-standing challenge. Yet, it is recognized that such individuals should have an opportunity to explore, discover, learn about, and contribute to astronomy and science in general. Considerable work has been done by educators, scientists, and artists to make science in general and astronomy in particular more accessible through the use of various technologies, including low resolution tactile images on thermoform and swell-touch pages based on the visual materials. Recently, 3D printers have emerged as a new tool for making reproductions of objects so that they can be useable and understood by a broader community of learners, including the visually impaired. This article outlines an innovative study that is aimed at taking images of astronomical objects and translating them into a 3D tactile representation of the object’s structure and composition for engagement and discovery by a range of users and learning styles. Using the star cluster NGC 602 as observed by the Hubble Space Telescope as the initial test case, we investigated processes for creating appropriate digital file structures, tested tactile approaches, and utilized focus groups to determine usability of the products.

Research on the High-resolution Imaging of Astronomical Objects Based on the Phase Difference Method

High resolution imaging of astronomical objects based on the phase difference method consists in estimating the object and the wave front phase distribution introduced by atmospheric turbulence from one or more pairs of shortexposure images collected simultaneously in focus and out of focus. On the basis of computer simulations of the telescopic imaging system and the image acquisition process of the phase difference method, we used the signal estimates and the optimization theory to determine the objective function under a Gaussian noise model, and carried out numerical solution of the image restoration problem with the finite inner memory quasi-Newtonian method suitable for large scale unconstrained optimization. The restored results show that the present technique based on the phase difference method can effectively eliminate the influence of atmospheric turbulence and solve the problem of restoring extended astronomical objects.

The Liverpool Telescope Spectrograph: FRODOSpec

We describe in some detail one of the instruments that will be available in 2004 to the research community. FRODOSpec is an integral field unit spectrograph that will be available for use with the 2 m robotic Liverpool Telescope on the island of La Palma. We anticipate that this instrument will open up major areas of research that cannot be carried out with conventionally operated telescopes. Some of these research areas relate to indirect imaging of astronomical objects like Doppler tomography and eclipse mapping.

Astrometric and photometric precision of measurements at digital processing of tv wide-angle images of astronomical objects

Astrometric and photometric precision of measurements at digital processing of tv wide-angle images of astronomical objects

Experimental measurements of estimator bias and the signal-to-noise ratio for deconvolution from wave-front sensing

Deconvolution from wave-front sensing (DWFS) has been proposed as a method for achieving high-resolution images of astronomical objects from ground-based telescopes. The technique consists of the simultaneous measurement of a short-exposure focal-plane speckled image, as well as the wave front, by use of a Shack-Hartmann sensor placed at the pupil plane. In early studies it was suspected that some problems would occur in poor seeing conditions; however, it was usually assumed that the technique would work well as long as the wave-front sensor subaperture spacing was less than r(0) (L/r(0) < 1). Atmosphere-induced phase errors in the pupil of a telescope imaging system produce both phase errors and magnitude errors in the effective short-exposure optical transfer function (OTF) of the system. Recently it has been shown that the commonly used estimator for this technique produces biased estimates of the magnitude errors. The significance of this bias problem is that one cannot properly estimate or correct for the frame-to-frame fluctuations in the magnitude of the OTF but can do so only for fluctuations in the phase. An auxiliary estimate must also be used to correct for the mean value of the magnitude error. The inability to compensate for the magnitude fluctuations results in a signal-to-noise ratio (SNR) that is less favorable for the technique than was previously thought. In some situations simpler techniques, such as the Knox-Thompson and bispectrum methods, which require only speckle gram data from the focal plane of the imaging system, can produce better results. We present experimental measurements based on observations of bright stars and the Jovian moon Ganymede that confirm previous theoretical predictions.

A balloon flight test of a coded-mask telescope with a multi-element germanium detector

The use of a small array of germanium detectors to obtain high spectral resolution X-ray and γ-ray images of astronomical objects has been demonstrated with a coded mask telescope flown as a piggy-back instrument on the NASA GRIS balloon payload. The design of the experimental telescope is discussed and images of the Crab nebula and of Cygnus X-1 obtained during the flight are presented. The quality of the images is shown to be very close to that expected from simulations.

Bidimensional Spectroscopy with the 6-meter Telescope in Time Resolving Mode

Degradation of images of astronomical objects during observations with large optical telescope may be described as combination of atmosphere turbulence on a time scale shorter than some tenths of a second and random fluctuation of object’s position due to telescope and observer’s guiding errors, bending of construction under external factors (wind, etc.). Special investigations on the 6-meter telescope (Balega, 1989) showed, that the peak frequency of such low-frequency fluctuations is located near 1 Hz.The method of Time Resolving Image Mode, developed by J.-L.Nieto et al (1987) for post-detection improvement of angular resolution at CFHT, showed that, even in places with excellent quality of atmosphere, the resolution of large telescope may be increased by 20-30% only, although powerful methods of image recentering and frames selection were performed. Moreover, such method of data processing may be applied to relatively bright objects only. For 6-meter telescope, resolution improvement would be useless at all due to smaller Fried parameter and larger main mirror.

Redesigning a Baker-Nunn Camera for CCD Imaging

AbstractThe University of NSW’s Automated Patrol Telescope is a modified Baker-Nunn satellite tracking camera, now used for CCD imaging of astronomical objects. The f/1 Baker-Nunn optical design gives a 30° field of view with an approximately spherical focal surface of radius ≈500 mm. While the focal plane curvature is tolerable across the 1.4° × 1.0° field of the present CCD, it becomes unacceptable when a larger CCD is used. In addition, the use of glass filters in the highly convergent beam produces intolerable spherical aberration. We present a design modification to the original Baker-Nunn which enables a 5° diameter flat field to be produced when using B, V, R or I filters. By making this modification, we plan to perform multicolour imaging, using a new large-format CCD with a 2.9° × 1.9° field of view.

Advanced X-ray Astrophysics Facility

This paper describes the Advanced X-ray Astrophysics Facility (AXAF), a program of the National Aeronautics and Space Administration (NASA). AXAF is a large free-flying observatory featuring a high performance x-ray telescope. Through advances in the technology of large x-ray optics and science instrumentation, AXAF will be capable of forming images of astronomical objects in x-ray light that will go far beyond the previous highly successful HEAO-B (Einstein) Observatory. Its pictures will be 10 times sharper; it will be able to detect sources 100 times fainter; it will cover twice the energy band; and it will be 1,000 times more sensitive for observing the detailed energy profile of sources. The increased sensitivity of AXAF will permit the study of active galaxies, quasars, and clusters of galaxies at very large distances. The optical system, pointing and control system, and instrument complement are presented in sufficient detail for a good understanding of overall AXAF advancements and capabilities.

The Advanced X-Ray Astrophysics Facility

AbstractThe Advanced X-Ray Astrophysics Facility (AXAF) is a remarkable and unique scientific endeavor. It will be a space-based earth orbiting X-ray observatory, designed to address fundamental questions in astronomy and astrophysics. It is remarkable in that it represents enormous advances in observational capability. It is unique in that it will be the best means of obtaining high resolution, spectrally resolved X-ray images of astronomical objects for the rest of this century and beyond.

Diffraction-limited imaging. II - Optical aperture-synthesis imaging of two binary stars

We have used the technique of nonredundant masking at the Hale 5 m telescope and radio VLBI imaging software are used to make optical aperture-synthesis maps of two binary stars, β Corona Borealis and σ Herculis. The dynamic range of the map of β CrB is about 50:1. For σ Her, we find a separation of 70 milliarcsec. These maps demonstrate the potential of the nonredundant masking technique for diffraction-limited imaging of astronomical objects with high dynamic range. We find that the optimal integration time for measuring the closure phase is found to be longer than that for measuring the fringe amplitude. There is not a close relationship between amplitude errors and phase errors, as is found in radio astronomy, and amplitude self-calibration is less effective at optical wavelengths than at radio wavelengths. The primary beam sensitivity correlation made in radio astronomy is not necessary in optical interferometry.

The very large array: Design and performance of a modern synthesis radio telescope

Since its development in the 1960's, the technique of obtaining high-resolution radio images of astronomical objects using Fourier synthesis has advanced sufficiently so that today such images often provide better angular resolution than is obtainable with the largest optical telescopes. A synthesis array measures the Fourier transform of the observed brightness distribution by cross-correlating the signals from antennas separated by distances up to tens of kilometers. The antennas must be equipped with low-noise receiving systems and connected together by phase-stable transmission links. Wide-bandwidth digital correlators are used to perform the cross correlation. The data-reduction algorithms and computing system play a critical role in determining the quality of the images produced by the array. The Very Large Array (VLA) synthesis telescope, recently constructed in New Mexico, consists of twenty-seven 25-m-diameter antennas arranged in a Y-shaped array. Each arm of the Y is approximately 21 km long and the antetmas can be moved to various positions on the arms by a rail-mounted transporter. The antennas are equipped with cryogenically cooled receiving systems and are interconnected by low-loss, TE <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</inf> -mode, large-diameter waveguide. The cross-correlation products for each of the 351 pair combinations of antennas are measured for 4 IF signals by a 50-MHz bandwidth digital correlator. In this paper we discuss the design of synthesis arrays in general, and describe the design and performance of the VLA in particular, under the seven headings: array geometry design, sensitivity considerations, phase stability requirements, signal transmission system, delay and correlator system, control system, and data-reduction requirments. In each section, we review the underlying instrumental requirements and provide details of how the VLA was designed to meet them. Recently developed data-reduction algorithms provide effective ways of correcting synthesis images for the effects of missing Fourier components and instrumental and atmospheric amplitude and phase errors. The power of these algorithms is demonstrated using actual VLA images.

A procedure to correct the images of astronomical objects for the distortions due to atmospheric turbulence

A method is proposed to obtain diffraction limited pictures of extended astonomical objects in spite of the wavefront distortions due to atmospheric turbulence. The method does not require any prior knowledge on the brightness distribution across the object. The presence of reference details is not necessary.

Radio Astronomy with the Very Large Array

The construction of the Very Large Array of radio telescopes has been completed, and this new research instrument is now being used to make radio images of astronomical objects with a resolution comparable to or better than that of ground-based optical telescopes. The role of the Very Large Array in current and future research is discussed both in principle and in terms of a sample of observing projects.