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NASA NTRS1992

Optical design for the ATLAS multispectral scanner

The Airborne Terrestrial Applications Sensor (ATLAS) system is a 15-channel imager for remote sensing applications currently under development at the NASA Stennis Space Center. This paper describes the optical design of the scan head optics, which include the linescan mirror, Dall-Kirkham telescope, collimator, and three spectrometers. The sensor package has a 7.5-inch entrance aperture with a 2.0 mrad ifov, total field of view of 73 degrees, and scan rates adjustable in the range 6-50 rev/sec. The three spectrometers have a modular design for future applications growth. Design and specifications for the telescope, special dichroics, gratings, imaging lenses, and other components for the spectrometers are described. Detector arrays for the three spectrometers, and built-in sources for radiometric calibration, will also be discussed. Finally, results of overall ATLAS systems performance analysis on optical throughput, SNR and NETD are presented.

Damommio, T.↗

NASA NTRS1992

The parsec-scale jets in 3C 273 and 3C 345

We present recent centimeter-wavelength 'global-array' VLBI images of the quasars 3C 273 and 3C 345 with dynamic ranges in excess of 3000:1. They trace the jet emission on scales from r about 5 parsecs out to about 200 parsecs. The maps of 3C273 at 18 cm wavelength show a well-collimated one-sided jet with a wavy ridge line; these wiggles exist on size scales ranging from about 1 pc to over 10 kpc. We show that the well-known superluminal flow extends to r about 120 pc. Images of 3C 345 at 6 cm wavelength from data taken in 1989 and 1990 show surprising features not seen in lower dynamic-range maps of this otherwise well-studied quasar: the inner part of the jet shows edge-brightening, which is important for modeling of jet confinement. The jet fades out very abruptly at r about 40 pc, then reappears at about 70 pc; beyond 70 pc, the resumed jet flares and is more diffuse than an extrapolation of the inner jet would predict. This morphology is reminiscent of M 87, and is suggestive of a shock wave.

Unwin, Stephen C.↗

NASA NTRS1993

Evidence for the interaction of the IRS 16 wind with the ionized and molecular gas at the Galactic center

We present a number of high-resolution radio images showing evidence for the dynamical interaction of the outflow arising from the IRS 16 complex with the ionized gas associated with the Northern Arm of Sgr A West, and with the northwestern segment of the circumnuclear molecular disk which engulfs the inner few parsecs of the Galactic center. We suggest that the wind disturbs the dynamics of the Northern Arm within 0.1 pc of the center, is responsible for the waviness of the arm at larger distances, and is collimated by Sgr A West and the circumnuclear disk. The waviness is discussed in terms of the Rayleigh-Taylor instability induced by the ram pressure of the wind incident on the surface of the Northern Arm. Another consequence of this interaction is the strong mid-IR polarization of the Northern Arm in the vicinity of the IRS 16 complex which is explained as a result of the ram pressure of the wind compressing the gas and the magnetic field.

Yusef-Zadeh, Farhad↗

NASA NTRS1993

Discovery of Jovian dust streams and interstellar grains by the Ulysses spacecraft

Within 1 AU from Jupiter, the dust detector aboard the Ulysses spacecraft during the flyby on February 8, 1992 recorded periodic bursts of submicron dust particles with durations ranging from several hours to two days and occurring at about monthly intervals. These particles arrived at Ulysses in collimate streams radiating from close to the line-of-sight direction to Jupiter, suggesting a Jovian origin for the periodic bursts. Ulysses also detected a flux of micron-sized dust particles moving in high-velocity retrograde orbits. These grains are identified here as being of interstellar origin.

Gruen, E.↗

NASA NTRS1993

Circumstellar molecular gas of the HH 34 and HH 111 exciting stars

The HH 34 and HH 111 exciting stars, two pre-main-sequence objects which are the sources of highly collimated optical jets, have been observed in the J = 1-0 transition of (C-13)O and in the 2.7 mm continuum using the Owens Valley Radio Observatory Millimeter Interferometer. The high-resolution aperture synthesis maps reveal dense molecular gas concentrations at the positions of both stars. The morphology and kinematics of the bright emission-line cores suggest that the molecular gas is distributed in circumstellar disks, each about 2000 AU in diameter, elongated perpendicular to each system's outflow axis. A fainter component of (C-13)O emission extends along each source's outflow axis. Independent mass determinations based on the dust continuum and molecular line fluxes indicate for HH 34, a disk mass of 0.2 solar mass; and for HH 111, a disk mass of 0.3 solar mass. The inferred circumstellar disks of these two jet sources are significantly more massive than those found associated with T Tauri stars and are therefore among the most massive disks known in association with low-mass pre-main-sequence stars.

Stapelfeldt, Karl R.↗

NASA NTRS1993

A flattened cloud core in NGC 2024

The (J, K) (1, 1) and (2, 2) NH3 lines were mapped toward a molecular cloud core in NGC 2024 using the VLA in its C/D-configuration. This region is associated with one of the most highly collimated molecular outflows. We find that the molecular condensations associated with the far-infrared sources FIR 5, FIR 6, and FIR 7 have kinetic temperatures of about 40 K. We also find line broadening toward FIR 6 and FIR 7. This suggests that these condensations may not be protostars heated by gravitational energy released during collapse but that they have an internal heating source. A flattened structure of ammonia emission is found extending parallel to the unipolar CO outflow structure, but displaced systematically to the east. If the NH3 emission traces the denser gas environment, there is no evidence that a dense gas structure is confining the molecular outflow. Instead, the location of the high-velocity outflow along the surface of the NH3 structure suggests that a wind is sweeping material from the surface of this elongated cloud core.

Ho, Paul T. P.↗

NASA NTRS1993

A study of an expanding interplanatary magnetic cloud and its interaction with the earth's magnetosphere - The interplanetary aspect

High time resolution interplanetary magnetic field and plasma measurements of an interplanetary magnetic cloud and its interaction with the earth's magnetosphere on January 14/15, 1988 are interpreted and discussed. It is argued that the data are consistent with the theoretical model of magnetic clouds as flux ropes of local straight cylindrical geometry. The data also suggest that this cloud is aligned with its axis in the ecliptic plane and pointing in the east-west direction. Evidence consisting of the intensity and directional distribution of energetic particle in the magnetic cloud argues in favor of the connectedness of the magnetic field lines to the sun's surface. The intensities of about 0.5 MeV ions is rapidly enhanced and the particles stream in a collimated beam along the magnetic field preferentially from the west of the sun. The particles travel form a flare site along the cloud magnetic field lines, which are thus presumably still attached to the sun.

Farrugia, C. J.↗

NASA NTRS1993

High-resolution mid-infrared imaging and astrometry of the nucleus of the Seyfert galaxy NGC 1068

The Goddard Infrared Array Camera was used to obtain a high resolution image of the nucleus of NGC 1068 at 12.4 microns. In addition, the peak emission at 12.4 microns relative to the peak of the optical continuum was determined. The distribution of the 12.4 micron emission relates to both the forbidden O III 5007A 'ionization cone' and the optical continuum emission imaged by HST. This distribution is also found to have an alignment perpendicular to the plane of a putative molecular torus. It is suggested that the extended mid-infrared emission is thermal radiation from dust in circumnuclear clouds heated by the collimated optical/UV AGN source. A portion of the unresolved 12.4 micron emission possibly originates from the torus. The infrared emission peak is found to coincide with the apex of the ionization cone, which is presumed to be the location of the torus.

Braatz, J. A.↗

NASA NTRS1993

The Oriented Scintillation Spectrometer Experiment - Instrument description

The Oriented Scintillation Spectrometer Experiment on the Arthur Holly Compton Gamma Ray Observatory satellite uses four actively shielded NaI (Tl)-CsI(Na) phoswich detectors to provide gamma-ray line and continuum detection capability in the 0.05-10 MeV energy range. The instrument includes secondary capabilities for gamma-ray and neutron detection between 10 and 250 MeV. The detectors have 3.8 deg x 11.04 deg (FWHM) fields of view defined by tungsten collimators. Each detector has an independent, single-axis orientation system which permits offset pointing from the spacecraft Z-axis for background measurements and multitarget observations. The instrument, and its calibration and performance, are described.

Johnson, W. N.↗

NASA NTRS1993

Correcting X-ray spectra obtained from the AXAF VETA-I mirror calibration for pileup, continuum, background and deadtime

The VETA-I mirror was calibrated with the use of a collimated soft X-ray source produced by electron bombardment of various anode materials. The FWHM, effective area and encircled energy were measured with the use of proportional counters that were scanned with a set of circular apertures. The pulsers from the proportional counters were sent through a multichannel analyzer that produced a pulse height spectrum. In order to characterize the properties of the mirror at different discrete photon energies one desires to extract from the pulse height distribution only those photons that originated from the characteristic line emission of the X-ray target source. We have developed a code that fits a modeled spectrum to the observed X-ray data, extracts the counts that originated from the line emission, and estimates the error in these counts. The function that is fitted to the X-ray spectra includes a Prescott function for the resolution of the detector a second Prescott function for a pileup peak and a X-ray continuum function. The continuum component is determined by calculating the absorption of the target Bremsstrahlung through various filters, correcting for the reflectivity of the mirror and convolving with the detector response.

Chartas, G.↗

NASA NTRS1992

Cosmic rays and shock waves in active galaxies

Studies of nonthermal radio emission in the inner regions of active galaxies reveal clear morphological evidence for shock waves. It is argued that the shocks are driven by collimated outflow of plasma from the AGN. I describe a model in which the synchrotron radio emission arises from ambient relativistic electrons and magnetic fields which have been compressed in a radiative shock wave. No active particle acceleration at the shock front is required in this picture. The prospects for diagnosing active acceleration from radio continuum and optical emission line observations are briefly discussed.

Wilson, Andrew S.↗

NASA NTRS1992

The Germanium GAlactic Plane Patrol mission

The goal of the Germanium GAlactic Plane Patrol mission (GGAPP) is to provide a continuous monitor of the Galactic Plane (GP) for variable sources of gamma-ray lines. Potentially interesting sources include black hole candidates, X-ray binary systems, pulsars, gamma-ray bursts, and solar flares. The GGAPP instrument is an array of Ge detectors cooled by a mechanical refrigerator to achieve a spectral resolution of 2 keV at 1 MeV (1/500). A bismuth germanate (BGO) shield will restrict the field-of-view (FOV) to within 20 deg of the GP, and a modulation collimator system will locate strong sources to less than 0.3 deg in galactic longitude, provide a direct means of subtracting background, and mapping the diffuse emission from the GP. The spacecraft will be rotationally stabilized with the spin axis perpendicular to the GP such that the modulator scans in galactic longitude. A HEO or L1 orbit will keep GGAPP far away from the strong background produced by the Earth. GGAPP will provide a natural bridge between GRO and future missions such as INTEGRAL/NAE.

Tueller, Jack↗

NASA NTRS1993

The collapse of clouds and the formation and evolution of stars and disks

We consider the interrelationships among the structure of molecular clouds; the collapse of rotating cloud cores; the formation of stars and disks; the origin of molecular outflows, protostellar winds, and highly collimated jets; the birth of planetary and binary systems; and the dynamics of star/disk/satellite interactions. Our discussion interweaves theory with the results of observations that span from millimeter wavelengths to X-rays.

Shu, Frank↗

NASA NTRS1992

Flight-qualification of a wideband laser diode transmitter module

A diffraction-limited laser diode transmitter module suitable for wideband direct detection laser communication is described. The transmitter module incorporates a high power semiconductor diode laser, collimating lens, thermal control, and driver circuit in a hermetic enclosure. The module has undergone environmental testing which demonstrates its suitability for space application, and accelerated lifetesting of the laser diode suggests an operational lifetime of nearly ten years.

Holcomb, Terry L.↗

NASA NTRS1992

High power master oscillator power amplifier (MOPA) AlGaAs laser for intersatellite communications

A master oscillator power amplifier (MOPA) configuration has been developed using an anti-reflection-coated AlGaAs semiconductor broad area laser in a reflective amplifier mode. For CW injection, the MOPA produced 340 mW of diffraction-limited power. The semiconductor MOPA configuration also produced peak diffraction-limited powers of 360 mW and 320 mW for quaternary pulse position Q-PPM modulation rates of 50 Mbps and 325 Mbps, respectively, for a peak injected power of 100 mW. Angular beamsteering during modulation was minimized by collimating the injected beam. The diffraction-limited peak power was limited by the frequency chirp of the master oscillator and also by the coupling losses of the injected beam.

Cornwell, Donald M., Jr.↗

NASA NTRS1993

Spectral measurements of shock layer radiation in an arc-jet wind tunnel

Measurements were made of the radiating gas cap of a blunt body in an NASA Ames 20 MW arcjet wind tunnel. The test gas was air. Spectra of the flux incident on a small aperture centered at the stagnation region were obtained. A helium-cooled MgF window transmitted flux into an evacuated collimating system that focused the aperture onto the entrance slit of a spectrometer. Data were obtained with films and by photomultipliers. The range covered was 120 nm to 1000 nm and the resolution was 0.05 nm to 0.5 nm. This paper presents preliminary results from the experiment. Representative spectral records from 200 nm to 1000 nm are shown. The spectra show the atomic lines from oxygen and nitrogen in the IR, as well as the molecular systems of NO, N2, N2(+), and CN. Copper, as a contaminant, and carbon are tentatively identified.

Palumbo, Giuseppe↗

NASA NTRS1993

Electromagnetically driven relativistic jets - A class of self-consistent numerical solutions

We explore the generalized Grad-Shafranov (GS) equation (Lovelace et al. 1986), which describes the cross-field balance of the magnetic flux surfaces in a stationary, axisymmetric, cold relativistic MHD wind. We construct a family of self-consistent, jet-type, non-self-similar solutions in which flux surfaces thread the equatorial plane vertically and are eventually collimated into nested cylinders. These solutions conserve the total energy and angular momentum along each flux surface and satisfy the relativistic GS equation in the cross-field direction. We find that the total specific energy in the flow depends primarily on a dimensionless combination of the poloidal magnetic flux, the rotation, and the mass loading rate, which reduces to Michel's (1969) magnetization parameter for radial winds. The final width of the flow and its ratio of kinetic energy flux to Poynting flux depend sensitively on the pressure distribution of the ambient medium, which is required to contain the jet at its outer edge when no jet-confirming external toroidal magnetic field is present. Furthermore, we show that the magnetic pressure in the flow can be much higher near the axis than close to the edge, reflecting the 'pinching' effect of the toroidal magnetic field.

Li, Zhi-Yun↗

NASA NTRS1994

Optical Correlator Performs Novelty Filtering

Experimental real-time optical correlator performs correlation and novelty filtering in photorefractive crystal. Crystal oriented enabling cross-polarization diffraction: together with polarizing beam splitter, increases signal-to-noise ratio. Laser and optical components expand, collimate, and divide laser beam.

Liu, Duncan Tsuen-Hsi↗