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NASA NTRS2011

Measuring the Optical Properties of Astrophysical Dust Analogues: Instrumentation and Methods

Dust is found throughout the universe and plays an important role for a wide range of astrophysical phenomena. In recent years, new infrared facilities have provided powerful new data for understanding these phenomena. However, interpretation of these data is often complicated by a lack of complementary information about the optical properties of astronomically relevant materials. The Optical Properties of Astronomical Silicates with Infrared Techniques (OPASI-T) program at NASA's Goddard Space Flight Center is designed to provide new high-quality laboratory data from which we can derive the optical properties of astrophysical dust analogues. This program makes use of multiple instruments, including new equipment designed and built specifically for this purpose. The suite of instruments allows us to derive optical properties over a wide wavelength range, from the near-infrared through the millimeter, also providing the capability for exploring how these properties depend upon the temperature of the sample. In this paper, we discuss the overall structure of the research program, describe the new instruments that have been developed to meet the science goals, and demonstrate the efficacy of these tools.

Rinehart, S. A.↗

NASA NTRS2013

Optical Properties of Iron Silicates in the Infrared to Millimeter as a Function of Wavelength and Temperature

The Optical Properties of Astronomical Silicates with Infrared Techniques (OPASI-T) program utilizes multiple instruments to provide spectral data over a wide range of temperature and wavelengths. Experimental methods include Vector Network Analyzer (VNA) and Fourier Transform Spectroscopy (FTS) transmission, and reflection/scattering measurements. From this data, we can determine the optical parameters for the index of refraction, n, and the absorption coefficient, k. The analysis of the laboratory transmittance data for each sample type is based upon different mathematical models, which are applied to each data set according to their degree of coherence. Presented here are results from iron silicate dust grain analogs, in several sample preparations and at temperatures ranging from 5-300 K, across the infrared and millimeter portion of the spectrum (from 2.5-10,000 μm or 4,000-1 cm(exp −1).

Optical↗

NASA NTRS2013

Optical Properties of Iron Silicates in the Infrared to Millimeter as a Function of Wavelength and Temperature

The Optical Properties of Astronomical Silicates with Infrared Techniques program utilizes multiple instruments to provide spectral data over a wide range of temperatures and wavelengths. Experimental methods include Vector Network Analyzer and Fourier transform spectroscopy transmission, and reflection/scattering measurements. From this data, we can determine the optical parameters for the index of refraction, n, and the absorption coefficient, k. The analysis of the laboratory transmittance data for each sample type is based upon different mathematical models, which are applied to each data set according to their degree of coherence. Presented here are results from iron silicate dust grain analogs, in several sample preparations and at temperatures ranging from 5 to 300 K, across the infrared and millimeter portion of the spectrum (from 2.5 to 10,000/micron or 4000 to 1/cm).

Dust↗

NASA NTRS1990

Amplitude and intensity spatial interferometry; Proceedings of the Meeting, Tucson, AZ, Feb. 14-16, 1990

Attention is given to such topics as ground interferometers, space interferometers, speckle-based and interferometry-based astronomical observations, adaptive and atmospheric optics, speckle techniques, and instrumentation. Particular papers are presented concerning recent progress on the IR Michelson array; the IOTA interferometer project; a space interferometer concept for the detection of extrasolar earth-like planets; IR speckle imaging at Palomar; optical diameters of stars measured with the Mt. Wilson Mark III interferometer; the IR array camera for interferometry with the cophased Multiple Mirror Telescope; optimization techniques appliesd to the bispectrum of one-dimensional IR astronomical speckle data; and adaptive optical iamging for extended objects.

Breckinridge, Jim B.↗

NASA NTRS1994

Planning and scheduling the Hubble Space Telescope: Practical application of advanced techniques

NASA's Hubble Space Telescope (HST) is a major astronomical facility that was launched in April, 1990. In late 1993, the first of several planned servicing missions refurbished the telescope, including corrections for a manufacturing flaw in the primary mirror. Orbiting above the distorting effects of the Earth's atmosphere, the HST provides an unrivaled combination of sensitivity, spectral coverage and angular resolution. The HST is arguably the most complex scientific observatory ever constructed and effective use of this valuable resource required novel approaches to astronomical observation and the development of advanced software systems including techniques to represent scheduling preferences and constraints, a constraint satisfaction problem (CSP) based scheduler and a rule based planning system. This paper presents a discussion of these systems and the lessons learned from operational experience.

Miller, Glenn E.↗

NASA NTRS1982

Differential imaging using charge-coupled device (CCD) imagers with on-chip charge storage

A CCD technique is described which allows long integration periods between readouts together with moderate chopping rates. During each phase of a differential chopping cycle, one set of charge images is shifted to the center of the chip, which is light sensitive. At the same time, the other set of charge images is shifted under one of two masked areas which serve as charge-storage sites. Since the vertical shifting between phases can be accomplished in much less time than the typical exposure per phase, there is negligible image smearing. For a given light level and chopping rate the performance of this technique is limited primarily by the readout noise and the vertical charge transfer inefficiency. If many transfer cycles are required between readouts, the charge transfer inefficiency will diffuse the accumulated charge images along the vertical columns. Laboratory and astronomical data obtained with this technique using a CCD camera and the 2.3 m telescope on Kitt Peak are presented.

Stockman, H. S.↗

NASA NTRS2016

Application of Compressive Sensing to Gravitational Microlensing Data and Implications for Miniaturized Space Observatories

Compressive Sensing is a technique for simultaneous acquisition and compression of data that is sparse or can be made sparse in some domain. It is currently under intense development and has been profitably employed for industrial and medical applications. We here describe the use of this technique for the processing of astronomical data. We outline the procedure as applied to exoplanet gravitational microlensing and analyze measurement results and uncertainty values. We describe implications for on-spacecraft data processing for space observatories. Our findings suggest that application of these techniques may yield significant, enabling benefits especially for power and volume-limited space applications such as miniaturized or micro-constellation satellites.

Gravitational Microlensing↗

NASA NTRS2016

Application of Compressive Sensing to Gravitational Microlensing Data and Implications for Miniaturized Space Observatories

Compressive Sensing↗

NASA NTRS1980

Conference on Applications of Digital Image Processing to Astronomy, Pasadena, Calif., August 20-22, 1980, Proceedings

The astronomic applications of non-military digital image processing are covered in this conference volume. Systems like CCD's, interactive data analysis facilities, stellar speckle interferometry, sky flux subsystems, guide star systems and various image processing systems are described. Techniques in photometry including filtering, automatic photometry, and image restoration are examined. Digital spectral analyses of galaxies, supernova remnants, stars and other celestial bodies are discussed together with algorithms developed to calibrate, clean up, enhance, and quantitatively analyze data. The techniques of image processing permit astronomers to make much more efficient use of their data for both subjective and quantitative analyses. Future missions, such as the Space Telescope, representing a vast data base are briefly covered.

Elliott, D. A.↗

NASA NTRS1980

Infrared heterodyne spectroscopy in astronomy

A heterodyne spectrometer was constructed and applied to problems in infrared astronomical spectroscopy. The instrument offers distinct observational advantages for the detection and analysis of individual spectral lines at Doppler-limited resolution. Observations of carbon dioxide in planetary atmospheres and ammonia in circumstellar environments demonstrate the substantial role that infrared heterodyne techniques will play in the astronomical spectroscopy of the future.

Betz, A.↗

NASA NTRS1989

A Bayesian classification of the IRAS LRS Atlas

The availability of a reclassification of the IRAS LRS Atlas of spectra using a new Bayesian classification procedure (AutoClass) is announced. The classes of objects which result from the application of the AutoClass algorithm include many of the previously known LRS classes. New classes which have interesting astronomical and astrophysical interpretations were also found. Techniques, such as the AutoClass algorithm, have a bright future in the arena of astronomical classification problems.

Goebel, J.↗

NASA NTRS1980

X-ray astronomical spectroscopy

The elementary spectral signatures of fundamental physical processes that might be operable in galactic and extragalactic X-ray sources are reviewed. Some of the instrument limitations of experimental techniques used in X-ray astronomical spectroscopy are described. X-ray spectroscopic measurements are examined for various types of X-ray-emitting objects, including degenerate and nondegenerate stellar systems, supernova remnants, clusters of galaxies, active galactic nuclei, and quasars.

Holt, S. S.↗

NASA NTRS1980

Acousto-optic spectrometer for radio astronomy

Recent developments in acousto-optic techniques and in photodetector arrays have made feasible a new type of RF spectrometer, offering the advantages of wide bandwidth, high resolution, large number of channels in compact, lightweight, energy efficient, and relatively low cost systems. Such a system employs an acousto-optic diffraction cell which serves the key role of converting RF signals to ultrasonic traveling-waves modulating the optical index of the cell. The cell is illuminated across its aperture by a monochromatic laser beam. A fraction of the light is diffracted by the acoustic waves. A focusing lens follows the cell and essentially performs a Fourier transform of the RF signal into a far-field intensity pattern. CSIRO in Australia and the Tokyo Astronomical Observatory in Japan have taken the lead in using acousto-optic techniques in astronomical applications. The first practical device was successfully made at CSIRO for obtaining dynamical spectrographs of solar radio emission.

Chin, G.↗

NASA NTRS2004

Transitsearch Workshop

The discovery of more than 100 planets around nearby solar-like stars that surpass Jupiter in size yet orbit their stars more quickly than Mercury has heralded a new era in astronomy. These enigmatic 'Hot-Jupiters' are large enough and close enough to their parent stars that their 'transits' can be captured by astronomers equipped with a small computer controlled telescope and a quality electronic CCD camera. The planet reveals its presence through the periodic decrease in brightness as it passes (or transits) in front of the star as seen from Earth. The first known transiting extrasolar planet HD 209458b, in the constellation Pegasus, has been the subject of hundreds of scientific papers since its discovery in 1999. The transit of 8th magnitude HD 209458 has been observed by at least a dozen non-professional astronomers using telescopes as small as 4 inches in aperture. Using equipment already in hand, and armed with target lists, transit time predictions, observing techniques and software procedures developed by astronomers at NASA's Ames Research Center and the University of California at Santa Cruz, non-professional astronomers can contribute significantly to the study of extrasolar planets by carefully measuring the brightness of stars with known Hot-Jupiters. In this way, we may resume (after a two century interruption!) the tradition of planetary discoveries by amateur astronomers begun with William Herschel's 1787 discovery of the 'solar' planet Uranus. In the few years transitsearch has been in existence, investigators Tim Castellano (NASA Ames) and Greg Laughlin (UCSC) have written articles for Sky and Telescope and Astronomy magazines, have been featured in stories by the Reuters News Service, Nature magazine, Science magazine, Space.com, the American Institute of Physics and others and received several hundred thousand total hits on their website www.transitsearch,org.

Castellano, T.↗

NASA NTRS1970

Figure sensing techniques

Figure sensing interferometry for control of astronomical mirror optics

Crane, R., Jr.↗

NASA NTRS1977

Infrared upconversion for astronomy

The basic theory of upconversion is presented, along with a brief historical summary of upconversion techniques. Upconverters were used in astronomical studies, but have met with only modest success. Upconversion will become a useful detection method for astronomy only if substantial but perhaps forseeable, improvements can be realized.

Boyd, R. W.↗

NASA NTRS1984

Two-dimensional infrared detector arrays

An introduction to overall IR array concepts and particular array designs is presented, and examples of laboratory and observational data obtained with IR arrays are given. Hybrid array designs, extrinsic silicon accumulation-mode charge injection devices, and switched-FET or switched-sample photoconductor techniques are summarized. Three recent astronomical observation projects which used IR arrays are examined.

Mccreight, C. R.↗

NASA NTRS1990

Spatial interferometry in optical astronomy

A bibliographic guide is presented to publications of spatial interferometry techniques applied to optical astronomy. Listings appear in alphabetical order, by first author, as well as in specific subject categories listed in chronological order, including imaging theory and speckle interferometry, experimental techniques, and observational results of astronomical studies of stars, the Sun, and the solar system.

Gezari, Daniel Y.↗