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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

Starlight Nulling Technology at the Jet Propulsion Laboratory

The current interests in extra-solar planet detection and space-based and ground-based interferometry for astronomical observations has led to the development of a number of nulling instrument designs at the Jet Propulsion Laboratory (JPL) and elsewhere. This paper summarizes briefly JPL's efforts in nulling interferometry to date and consists of illustrations of some key nulling activities. Basic layouts of nulling testbeds are described and key applications discussed.

Terrestrial Planet Finder↗
NASA NTRS1991

Observations of lightning processes using VHF radio interferometry

A single station, multiple baseline radio interferometer was used to locate the direction of VHF radiation from lightning discharges with microsec time resolution. Radiation source directions and electric field waveforms were analyzed for various types of breakdown events. These include initial breakdown and K type events of in-cloud activity, and the leaders of initial and subsequent strokes to ground and activity during and following return strokes. Radiation during the initial breakdown of a flash and in the early stages of initial leaders to ground is found to be similar. In both instances, the activity consists of localized bursts of radiation that are intense and slow moving. Motion within a given burst is unresolved by the interferometer. Radiation from in-cloud K type events is essentially the same as that from dart leaders; in both cases it is produced at the leading edge of a fast moving streamer that propagates along a well defined, often extensive path. K type events are sometimes terminated by fast field changes that are similar to the return stroke initiated by dart leaders; such K type events are the in-cloud analog of the dart leader return stroke process.

Rhodes, C. T.↗
NASA NTRS2003

Measuring Diffusion of Liquids by Common-Path Interferometry

A method of observing the interdiffusion of a pair of miscible liquids is based on the use of a common-path interferometer (CPI) to measure the spatially varying gradient of the index refraction in the interfacial region in which the interdiffusion takes place. Assuming that the indices of refraction of the two liquids are different and that the gradient of the index of refraction of the liquid is proportional to the gradient in the relative concentrations of either liquid, the diffusivity of the pair of liquids can be calculated from the temporal variation of the spatial variation of the index of refraction. This method yields robust measurements and does not require precise knowledge of the indices of refraction of the pure liquids. Moreover, the CPI instrumentation is compact and is optomechanically robust by virtue of its common- path design. The two liquids are placed in a transparent rectangular parallelepiped test cell. Initially, the interface between the liquids is a horizontal plane, above which lies pure liquid 2 (the less-dense liquid) and below which lies pure liquid 1 (the denser liquid). The subsequent interdiffusion of the liquids gives rise to a gradient of concentration and a corresponding gradient of the index of refraction in a mixing layer. For the purpose of observing the interdiffusion, the test cell is placed in the test section of the CPI, in which a collimated, polarized beam of light from a low-power laser is projected horizontally through a region that contains the mixing layer.

Rashidnia, Nasser↗
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 NTRS1972

Precision geodesy via radio interferometry.

Very-long-baseline interferometry experiments, involving observations of extragalactic radio sources, were performed in 1969 to determine the vector separations between antenna sites in Massachusetts and West Virginia. The 845.130-kilometer baseline was estimated from two separate experiments. The results agreed with each other to within 2 meters in all three components and with a special geodetic survey to within 2 meters in length; the differences in baseline direction as determined by the survey and by interferometry corresponded to discrepancies of about 5 meters. The experiments also yielded positions for nine extragalactic radio sources and allowed the hydrogen maser clocks at the two sites to be synchronized.

Hinteregger, H. F.↗
NASA NTRS1992

Solar observations with a millimeter-wavelength array

An introduction to the field of solar millimeter interferometry is given. Solar observations using the BIMA at Hat Creek since 1989 are reviewed along with other solar millimeter observations. The radiation mechanisms relevant to solar millimeter astronomy are discussed, and observations in the millimeter and microwave ranges are compared. The use of closure phases in arrays containing a small number of elements is examined.

White, S. M.↗
NASA NTRS1980

Phase versus delay in geodetic VLBI

The conditions for the applicability of the phase observable in very long baseline interferometry are discussed and examples of adequate observation programs are given. These considerations apply in particular to the Mark 2 system, which is already in operation at many observatories.

Campbell, J.↗
NASA NTRS1989

Effect of temperature gradient on the optical quality of mercurous chloride crystals

Single crystals of mercurous chloride were grown at temperature gradients of 8, 11 and 17 K/cm by the physical vapor transport method. The optical quality of these crystals was evaluated by measuring bulk scattering and inhomogeneity of refractive index by birefringence interferometry. It was observed that a high temperature gradient at the solid-vapor interface induced thermal stresses and crystals showed higher scattering and irregular fringes.

Singh, N. B.↗
NASA NTRS1994

Centaurus A, the core of the problem

The bright, peculiar elliptical galaxy Centaurus A (NGC 5128, PKS 1322-427) was one of the first extragalactic radio sources to be optically identified (Bolton et al. 1949). At a distance of 4 Mpc, Centaurus A is the closest active radio galaxy and affords the highest linear imaging resolution (1 mas approximately equal to 0.02 pc) and hence the best prospects for studying an active nucleus close to the central radio source. We present the results of multi-epoch, 8.4-GHz, very long baseline interferometry (VLBI), imaging observations of the nucleus made over the past three years. The nucleus possesses a core-jet structure where the inner portion of the jet shows apparent linear motion with a velocity substantially less than the speed of light.

Tingay, S. J.↗
NASA NTRS1990

Bibliography of spatial interferometry in optical astronomy

The Bibliography of Spatial Interferometry in Optical Astronomy is a guide to the published literature in applications of spatial interferometry techniques to astronomical observations, theory and instrumentation at visible and infrared wavelengths. The key words spatial and optical define the scope of this discipline, distinguishing it from spatial interferometry at radio wavelengths, interferometry in the frequency domain applied to spectroscopy, or more general electro-optics theoretical and laboratory research. The main bibliography is a listing of all technical articles published in the international scientific literature and presented at the major international meetings and workshops attended by the spatial interferometry community. Section B summarizes publications dealing with the basic theoretical concepts and algorithms proposed and applied to optical spatial interferometry and imaging through a turbulent atmosphere. The section on experimental techniques is divided into twelve categories, representing the most clearly identified major areas of experimental research work. Section D, Observations, identifies publications dealing specifically with observations of astronomical sources, in which optical spatial interferometry techniques have been applied.

Gezari, Daniel Y.↗
NASA NTRS2015

The Structure of Pre-Transitional Protoplanetary Disks. II Azimuthal Asymmetries, Different Radial Distributions of Large and Small Dust Grains in PDS 70

The formation scenario of a gapped disk, i.e., transitional disk, and its asymmetry is still under debate. Proposed scenarios such as disk-planet interaction, photoevaporation, grain growth, anticyclonic vortex, eccentricity, and their combinations would result in different radial distributions of the gas and the small (sub-micron size) and large (millimeter size) dust grains as well as asymmetric structures in a disk. Optical/near-infrared (NIR) imaging observations and (sub-)millimeter interferometry can trace small and large dust grains, respectively; therefore multi-wavelength observations could help elucidate the origin of complicated structures of a disk. Here we report Submillimeter Array observations of the dust continuum at 1.3 mm and CO-12 J = 2 yields 1 line emission of the pre-transitional protoplanetary disk around the solar-mass star PDS 70. PDS 70, a weak-lined T Tauri star, exhibits a gap in the scattered light from its disk with a radius of approx. 65 AU at NIR wavelengths. However, we found a larger gap in the disk with a radius of approx. 80 AU at 1.3 mm. Emission from all three disk components (the gas and the small and large dust grains) in images exhibits a deficit in brightness in the central region of the disk, in particular, the dust disk in small and large dust grains has asymmetric brightness. The contrast ratio of the flux density in the dust continuum between the peak position to the opposite side of the disk reaches 1.4. We suggest the asymmetries and different gap radii of the disk around PDS 70 are potentially formed by several (unseen) accreting planets inducing dust filtration.

Submillimeter Array observations↗