Instrumentation problems in the vacuum ultraviolet below 1000 angstroms
Improved techniques for solving inherent instrumentation problems in vacuum ultraviolet below 1000 Angstroms
VACUUM ULTRAVIOLET↗
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Infrared astronomy
IR astronomy, considering basic principles, instrumentation energy production and radiation, spectroscopy, detectors and atmospheric absorption and emission
Woolf, N. J.↗
Advances in solar and cosmic X-ray astronomy - A survey of experimental techniques and observational results.
The current status of X-ray astronomy is surveyed by reviewing observational results and theoretical conclusions gained within the past two years in areas dealing with the quiet-sun, slowly-varying, and burst components of solar X-radiation and with the features of cosmic X-ray sources. Thermal and nonthermal processes responsible for a wide variety of X-ray emission mechanisms in nature are explained, and characteristics of X radiation from specific solar structures are described. Attention is given to the effects of interstellar and intergalactic matter on cosmic X-rays; the properties of galactic and extragalactic X-ray sources; and the specifications of such instruments as gas-filled ionization detectors, proportional counters, Geiger counters, scintillation detectors, photoelectric detectors, polarimeters, collimators, spectrometers, and imaging systems.
Hoover, R. B.↗
Further results on cooling mechanisms for soft X-ray flares
Analysis of data from the soft X-ray proportional counter spectrometer on OSO-4 has been continued along the lines of earlier work. It was noticed that the time profiles of X-ray counts from the OSO-4 instrument's 1 to 3 Angstrom detectors for two events showed a very rapid initial decay after maximum, followed by a much more slowly falling section. At least in the case of the larger of the two events, the change of slope seems quite definitely to be discontinuous. Temperatures and emission measures for both flares have been derived, by fitting an emission function to eight-channel count histograms which form the output of the 1 to 3 Angstrom detectors, analyzed into eight energy intervals by pulse-height analysis. The computer program is described. It employs temperature and continuum emission measures in the Culhane-Acton formula and the flux in the 6.7 KeV iron-line feature as free parameters, adjusting them by small amounts in successive iterations until the original historgram is approximately reproduced. A chi-squared is used to examine the agreement between histograms and terminates the iteration accordingly. Account is taken of the proportional counters' energy resolution in the fitting process.
Craig, I. J. D.↗
Computer simulation of an aircraft-based differential absorption and scattering system for retrieval of SO2 vertical profiles
The feasibility of using the differential absorption and scattering technique from aircraft altitudes for remotely measuring the vertical distribution of SO2 was studied via a computer simulation. Particular care was taken in this simulation to use system parameters (i.e., laser energy, telescope size, etc.) which can be accommodated on an aircraft and can be realized with commercially available technology. The vertical molecular and aerosol profiles were chosen to simulate the types of profiles which might be experienced over a large city. Results are presented on the retrieval of the assumed SO2 profile which show the effects of systematic errors due to interfering gases and aerosols, as well as random errors due to shot noise in the return signal, detector and background noise, and instrument-generated noise.
Hoell, J. M., Jr.↗
An infrared foreoptics adaptor for the Learjet Telescope
A foreoptics adapter has been built for the Learjet telescope which permits simultaneous viewing of the visible star field in the image plane and acquisition of astronomical data at infrared wavelengths (less than 1 micrometer). The device uses an adjustable dichroic beamsplitter to transmit visible wavelengths to an eyepiece (or television camera), and to reflect infrared wavelengths to a port where an infrared detector system can be mounted. The instrument is intended as a multiple user facility for the Learjet telescope. This report describes the adapter and its use.
Erickson, E. F.↗
Mariner-Jupiter-Saturn Low Energy Charged Particle Experiment
The Low Energy Charged Particle Experiment will be launched on the Mariner-Jupiter-Saturn spacecraft in August 1977. The experiment has been designed to perform particle measurements in the intense radiation belts of the Jovian and Saturnian environments, and to provide detailed spectral analysis of both solar and galactic particles in interplanetary space. A single instrument uses 23 solid-state detectors configured in two distinct detector subsystems: one optimized for interplanetary and interstellar measurements, the other for specific particle species, energies, and intensities expected near the planets.
Peletier, D. P.↗
A measurement of the absolute flux of cosmic-ray electrons
A balloon-borne superconducting magnet spectrometer was used to measure the absolute flux of cosmic-ray electrons. The instrument consisted of a gas Cerenkov detector, a momentum spectrometer, and a lead-scintillator shower counter. In order to determine electron flux in the interstellar medium, observed fluxes for energy loss in the atmosphere and the payload were corrected, taking into account solar modulation effects and bremsstrahlung energy losses. Fluxes were measured at an average atmospheric depth of 5.8 g/sq cm, and the solar modulation was 300 MeV. A cosmic-ray electron flux of 367 E to the exp(3.15 + or -0.2) per sq m/sr s GeV was obtained in the energy range 4.5-63.5 GeV. The uncertainty of the absolute (electron-positron) flux was 10 percent. A summary of the electron data is given in a table.
Golden, R. L.↗
Interstellar Medium Absorption Profile Spectrograph (IMAPS)
The design and fabrication of an objective-grating echelle spectrograph to fly on sounding rockets and record spectra of stars from approximately 920 to 1120A with a resolving power lambda/delta lambda = 200,000 is discussed. The scientific purpose of the program is to observe, with ten times better velocity resolution than before, the plentiful absorption lines in this spectral region produced by atoms, ions and molecules in the interstellar medium. In addition, an important technical goal is to develop and flight-quality a new ultraviolet, photon-counting image sensor which has a windowless, opaque photocathode and a CCD bombarded directly by the accelerated photoelectrons. Except for some initial difficulties with the performance of CCDs, the development of the payload instrument is relatively straightforward and our overall design goals are satisfied. The first flight occurred in late 1984, but no data were obtained because of an inrush of air degraded the instrument's vacuum and caused the detector's high voltage to arc. A second flight in early 1985 was a complete success and obtained a spectrum of pi Sco. Data from this mission are currently being reduced; quick-look versions of the spectra indicate that excellent results will be obtained. Currently, the payload is being reconfigured to fly on a Spartan mission in 1988.
Jenkins, E. B.↗
Performance characteristics of multi-anode microchannel array detector systems
The multi-anode microchannel arrays (MAMAs) are state-of-the-art, pulse-counting, photoelectric array detectors designed specifically for use in space astrophysics instruments. The present paper provides a description of recent progress related to the development of ultraviolet and visible-light versions of the MAMA detectors, taking into account a comparison of the operating characteristics of these devices with those of photoconductive array detectors, such as the CCDs. Attention is given to MAMA detector system design parameters, the operating characteristics of MAMAs and CCDs, MAMA performance characteristics, and future developments.
Timothy, J. G.↗
The dynamics of charged dust in the tail of Comet Giacobini-Zinner
A numerical simulation has been performed to calculate the distributions of dust particles of various sizes down the tail of comet P/Giacobini-Zinner. When the electrostatic charging of the grains in the plasma and radiative environment of the comet is taken into account, it is found that the distribution of the grains (particularly at the lowest end of the mass spectrum) in a plane normal to the orbital plane is entirely different from what is expected had the grains been uncharged. Although the NASA-ICE spacecraft, which will fly through the tail of this comet almost normal to its orbital plane on September 11, 1985, has no dedicated dust experiments, it is expected that the plasma wave instrument will serve as an indirect detector, even of the smallest grains, via the plasma clouds created by the high-velocity dust impacts. Knowledge of the spatial variation of the grain sizes encountered along the flight path of the spacecraft will provide us with the information necessary to calculate the electrostatic potential of the grains, which in turn will lead to an estimation of the role of the electromagnetic forces on the dynamics of such grains.
Horanyi, M.↗
Particle acceleration
Data is compiled from Solar Maximum Mission and Hinothori satellites, particle detectors in several satellites, ground based instruments, and balloon flights in order to answer fundamental questions relating to: (1) the requirements for the coronal magnetic field structure in the vicinity of the energization source; (2) the height (above the photosphere) of the energization source; (3) the time of energization; (4) transistion between coronal heating and flares; (5) evidence for purely thermal, purely nonthermal and hybrid type flares; (6) the time characteristics of the energization source; (7) whether every flare accelerates protons; (8) the location of the interaction site of the ions and relativistic electrons; (9) the energy spectra for ions and relativistic electrons; (10) the relationship between particles at the Sun and interplanetary space; (11) evidence for more than one acceleration mechanism; (12) whether there is single mechanism that will accelerate particles to all energies and also heat the plasma; and (13) how fast the existing mechanisms accelerate electrons up to several MeV and ions to 1 GeV.
Vlahos, L.↗
Profiles of nitric oxide in the upper stratosphere
Results are presented from NO measurements obtained with a chemiluminescent NO detector and an in situ ozone instrument aboard high altitude balloons launched at Air sur L'Adour and Gap, France. NO profiles were obtained between 35 and 40 km in the late morning of September 17, 1987 and the early afternoon of June 18, 1988. The average NO concentration was 9 ppbv at 35 km, increasing with altitude to 11.5 ppbv at 40 km. The difference in the temperature profile significantly contributes to the observed change in the NO concentration.
Kondo, Y.↗
Strategy for contamination control to improve Wide-Field/Planetary Camera far-ultraviolet performance
A multifaceted contamination control strategy has been developed for the second generated Wide-Field and Planetary Camera (WFPC-2) to improve the FUV stability by several orders of magnitude, compared to the first camera (WFPC-1). The strategy involves: improved on-orbit boil-off capability of the detector optics, added internal shielding and instrument venting, in-process subassembly vacuum bakeout at elevated temperatures, material substitution, sample testing in ultraclean vacuum facility, and internal instrument contamination-transport modeling. A science performance goal of 1 percent photometric accuracy at 1470 A over an extended time (of at least 30 days) has been established as a contamination control target for WFPC-2. The WFPC-2 is currently planned to be launched by the Shuttle in mid-1993 and replace the WFPC-1 which was recently launched with the HST.
Leschly, Kim↗
Data analysis of the COMPTEL instrument on the NASA gamma ray observatory
The Compton imaging telescope (COMPTEL) on the Gamma Ray Observatory (GRO) is a wide field of view instrument. The coincidence measurement technique in two scintillation detector layers requires specific analysis methods. Straightforward event projection into the sky is impossible. Therefore, detector events are analyzed in a multi-dimensional dataspace using a gamma ray sky hypothesis convolved with the point spread function of the instrument in this dataspace. Background suppression and analysis techniques have important implications on the gamma ray source results for this background limited telescope. The COMPTEL collaboration applies a software system of analysis utilities, organized around a database management system. The use of this system for the assistance of guest investigators at the various collaboration sites and external sites is foreseen and allows different detail levels of cooperation with the COMPTEL institutes, dependent on the type of data to be studied.
Diehl, R.↗
Assessment of a prototype sunphotometer for network applications, phase 1
Data taken in Tucson, AZ, for comparing the CE sunphotometer's results against the Univ. of Arizona's no. 3 solar radiometer are in very good agreement. The spectral voltage intercepts obtained on 15 different days taken with the CE instrument during a seven week period are stable and follow the same daily trends as the voltage intercepts for similar wavelengths contained in the Univ. of Arizona's no. 3 radiometer. The spectral optical depths obtained from both instruments are also in very good agreement and follow the same trends. The only problem that exists in the CE instrument does not have a heater to stabilize the detector temperature which is important around 1000 nm. Zenith sky radiance scans are in good agreement, but both instruments are biased by direct solar rays entering the instrument's respective entrance apertures. All diffuse light data shown were, therefore, taken with the instruments shielded from the direct sun. The CE sunphotometer results pertaining to the water vapor wavelength's are also in good agreement with the Univ. of Arizona's no. 3 and should prove useful for water vapor retrieval.
Reagan, J. A.↗
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↗
X-Ray Emission from a Simulated Cluster of Galaxies
Using the 1993 cluster simulation of Katz & White, we analyze the intracluster medium and investigate the accuracy of the standard hydrostatic method for determining cluster masses. We show that the simulated cluster gas is in hydrostatic equilibrium with a subsonic flow toward the center. Inside a radius of (approx.) 100 kpc, this flow is in a steady state. The cooling time is shorter than a Hubble time within the central 50 kpc. The flow rate is regulated by the gas sink in the middle of the cluster and the PdV work done as the gas flows in, verifying the standard cooling flow scenario. We simulate observations of the cluster using the instrument parameters of the EXOSAT ME detector and the Einstein IPC detector. Even though the intracluster gas is not isothermal, isothermal models of the cluster, excluding regions within 100 kpc of galaxies, fit the EXOSAT X-ray spectra as well as they fit real clusters. The X- ray surface brightness distribution is similar to that of real clusters, again excluding the galaxies. We simulate the procedure used to determine the masses of real clusters. We use the equation of hydrostatic equilibrium together with the temperature derived from an isothermal fit to the simulated EXOSAT spectrum and the density profile derived from a fit to the simulated IPC surface brightness profile to determine the mass. A comparison of the derived mass profile to the actual mass profile shows that errors of a factor of 2 are possible. If the actual temperature profile is used, the cluster mass is found to an accuracy of better than 25% within the virial radius.
Tsai, John C.↗