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NASA NTRS1978

Gamma ray spectroscopy in astrophysics: An observational overview (50 keV-20 MeV)

The observational status of gamma ray astronomy based on results reported prior to April 1978 is discussed. Specific line observations are reviewed from the Sun, the galactic plane, the Galactic Center region, the active Galaxy NGC 5128 (Cen A), the Crab Nebula region, and a transient source in the general direction of the anti-Galactic Center region. A statistical method is described which determines the relative probability that a given, reported observation is due to an external source as compared to a random fluctuation in the experimental background counting rate. Only a few of the many reported observations can be considered likely extraterrestrial observations of an extraterrestrial source made with a confidence level of 99%.

Chupp, E. L.↗

NASA NTRS1978

Gamma ray spectroscopy in astrophysics: Solar gamma ray astronomy on solar maximum mission

The SMM gamma ray experiment and the important scientific capabilities of the instrument are discussed. The flare size detectable as a function of spectrum integration time was studied. A preliminary estimate indicates that a solar gamma ray line at 4.4 MeV one-fifth the intensity of that believed to have been emitted on 4 August 1972 can be detected in approximately 1000 sec with a confidence level of 99%.

Forrest, D. J.↗

NASA NTRS1977

F-8 DFBW sensor failure identification using analytic redundancy

The structure of a sensor failure detection and identification system designed for the NASA F-8 DFBW aircraft is outlined. The system is for use in a dual-redundant environment, and it takes maximal advantage of all functional relationships among the sensed variables. The identification logic uses the quality sequential probability ratio, which provides a useful on-line measure of confidence in the various forms of analytic redundancy. Preliminary simulation results indicate good behavior of the analytic decision statistic, based on the sequential probability ratio test.

Deckert, J. C.↗

NASA NTRS1977

The cosmic-ray antiproton flux - An upper limit near that predicted for secondary production

Data gathered from a balloon flight of a superconducting-magnet spectrometer have been examined for the presence of cosmic-ray antiprotons. The ratio of antiprotons to protons, p(-)/p, in cosmic rays was found to be (0.03 + or - 3.3) ten-thousandths in the rigidity interval from 4.2 to 12.5 GV. The 95%-confidence-level upper limit for p(-)/p is thus 0.00066. This upper limit is in strong contradiction to the prediction of the closed-galaxy model of Rasmussen and Peters (1975), but is not inconsistent with the prediction of the modified closed-galaxy model of Peters and Westergaard (1977). It is nearly equal to the predictions of conventional propagation models. This result provides an independent confirmation of the absence of primary antimatter in the cosmic rays at a level of approximately a few ten-thousandths.

Badhwar, G. D.↗

NASA NTRS1977

Using Landsat data to estimate evapotranspiration of winter wheat

Results obtained from an evapotranspiration model as applied to Kansas winter wheatfields were compared with results determined by a weighing lysimeter, and the standard deviation was found to be less than 0.5 mm/day (however, the 95% confidence interval was between plus and minus 0.2 mm/day). Model inputs are solar radiation, temperature, precipitation, and leaf area index; an equation was developed to estimate the leaf area index from Landsat data. The model provides estimates of transpiration, evaporation, and soil moisture.

Kanemasu, E. T.↗

NASA NTRS1977

OSO-8 X-ray polarimeter and Bragg crystal spectrometer observations

Results are discussed for observations of the Crab Nebula, Cyg X-1, and Cyg X-2 with the focusing mosaic graphite crystal X-ray polarimeter aboard OSO-8 as well as for observations of A0620-00 with the Bragg crystal spectrometer aboard the same satellite. The observed X-ray polarization of the Crab Nebula is shown to be in agreement with a previous measurement of the optical polarization and to confirm with very high confidence the earlier conclusion that the X-ray emission occurs by the synchrotron process. No evidence is found for polarization of X-rays from Cyg X-1, but a preliminary result of 4.8% + or 1.0% polarization at an energy of 2.6 keV and a position angle of 141.7 + or - 6.6 deg is reported for Cyg X-2. It is noted that this value is within the range expected for accretion disks. The spectrometry of A0620-00 yielded a continuous spectrum that can be accurately fitted with a thermal bremsstrahlung spectrum at a temperature of 15 million K.

Novick, R.↗

NASA NTRS1977

An upper limit for the flux of interstellar dust grains in the solar system

Data from the LEAM (Lunar Ejecta and Meteorite experiment, a micrometeorite detector at the Apollo 17 landing site) have been examined for evidence of interstellar (IS) dust grains traversing the solar system. The analysis technique considers IS grains approaching the solar system from the local solar apex. A model calculates the grains' hyperbolic orbits into the solar system and predicts the impact directions on the moon. The observations are then compared with the predicted impact directions to measure the IS dust flux. No evidence has been found (at the 97.5% confidence level) for a flux greater than about 6 hundred-thousandths per sq m/sec for particles of at least 2 by 10 to the -14th power g.

Tomandl, D. A.↗

NASA NTRS1977

Solar-generated quasi-biennial geomagnetic variation

The existence of highly correlated quasi-biennial variations in the geomagnetic field and in solar activity is demonstrated. The analysis uses a numerical filter technique applied to monthly averages of the geomagnetic horizontal component and of the Zurich relative sunspot number. Striking correlations are found between the quasi-biennial geomagnetic variations determined from several magnetic observatories located at widely different longitudes, indicating the worldwide nature of the obtained variation. The correlation coefficient between the filtered Dst index and the filtered relative sunspot number is found to be -0.79 at confidence level greater than 99% with a time lag of 4 months, solar activity preceding the Dst variation. The correlation between the unfiltered data of Dst and those of the sunspot number is also high with a similar time lag. Such a time lag has not been discussed in the literature, and a further study is required to establish the mode of sun-earth relationship that gives this time delay.

Sugiura, M.↗

NASA NTRS1977

Comparison of numerical and experimental 'conical' flow fields in supersonic corners with compression and/or expansion

The flow field produced by the intersection of two plane solid surfaces in a supersonic stream is a complex interference flow. These flows can be fully compressive, fully expansive, or of mixed compression-expansion nature. This paper presents a comparison of the experimentally obtained flow-field structure in an axial corner with that predicted numerically by using a shock-capturing finite-difference method. The effect of sweep and surface deflection are evaluated, and the general influence of each is presented for the three classes of corner flow. The results show that the numerical method is a valuable aid in understanding the flow structure for simple configurations. In addition, confidence in the numerical method is gained for use in solving more general three-dimensional configurations where the flow is nonconical and several wave interaction may be presented.

Anderson, D. A.↗

NASA NTRS1978

Positions of galactic X-ray sources - l/II/ between 320 and 340 deg

The precise (20-40 sec) positions of seven X-ray sources in the celestial region corresponding to the galactic longitude range from 320 to 340 deg are reported. The sources include a recurrent transient X-ray source (MX1608-52) and a source 2S1553-542 coincident with a gamma-ray source within the given errors of position. The positions reported reduce the previously reported areas of the error region for six of the sources by factors ranging from 10 to 100. The presented results add confidence to the proposed radio candidates for 4U1624-49 and 4U1642-45 considered by Sanduleak and Dolan (1974) and Seaquist (1977).

Apparao, K. M. V.↗

NASA NTRS1978

Positions of galactic X-ray sources with l/II/ between -20 deg and +6 deg

The precise positions of nine X-ray sources in the vicinity of the galactic center are reported. The data were obtained as part of the comprehensive survey of the galactic plane performed with the rotating modulation collimator detectors on the SAS-3 X-ray observatory. The sources include the binary X-ray source 4U 1700-37 which has a well established optical counterpart that lies 7 sec from the reported position. The other sources GX 349+2, 4U 1702-42, 4U 1705-44, MX 1716-31, A 1742-294, 4U 1755-33, GX 5-1, and 2S 1803-245 lack established counterparts in other wavelengths. The obtained position for GX 5-1 adds confidence to the radio counterpart proposed by Braes et al. (1972). The reported position for 4U 1755-33 excludes the optical counterpart proposed by Jones et al. (1974).

Jernigan, J. G.↗

NASA NTRS1977

Use of Landsat multispectral imagery in estimating snow areal extent and snow water content cost-effectively

Landsat color composites are used in conjunction with a limited amount of aerial survey data and ground-truth measurements in order to estimate snow areal extent and snow water content. The snow water content estimations are based on the inexpensive Landsat data and the much more expensively obtained information on ground snow courses. A cost-effectiveness analysis of the procedures showed the expenses involved in obtaining confidence intervals of 80, 90, 95 and 99% for the estimates.

Khorram, S.↗

NASA NTRS1978

Free collapse of a rotating sphere of stars

The free-fall collapse of a system of 115,000 stars was studied by means of a three-dimensional simulation on the ILLIAC IV computer. The system started from a spherical shape with uniform density and rigid rotation which balanced the gravitational force in the equatorial plane. The system settled down into a 'hot' prolate 'bar' in about two initial rotation periods. This bar rotates about a short axis and is a long-lived form. Detailed discussion of the development of this system leads to several important dynamical inferences: (1) the first collapse does not become triaxial, and the prolate form follows much later; (2) forms seen in projection along the rotation axis are strikingly similar to forms seen in disk galaxy simulations, notwithstanding an unusual thickness along the rotation axis (this strengthens confidence in disk galaxy simulations); (3) many elliptical galaxies must be prolate objects rotating about a short axis and seen in projection; and (4) collapse models of galaxy formation lead to strongly anisotropic velocity dispersions, which are not in agreement with observation.

Miller, R. H.↗

NASA NTRS1978

Molecular hydrogen emission from T Tauri stars

Results are presented for a search for molecular hydrogen emission in the v = 1-0 S(1) line at 2.2 microns in five T Tauri stars, including T Tau itself, RY Tau, SU Aur, DK Tau, and HL Tau. Molecular hydrogen emission was detected only in T Tau; the results suggest that the emitting region is probably larger than 5 arcsec (2.5-sigma confidence level) and that the emission is probably centered on the star. Upper limits on the line strengths are given for the other four stars. Various excitation mechanisms for the H2 in T Tau are considered, and the mass-loss rate and neutral-particle density in the shocked region are estimated for the case of shock excitation.

Beckwith, S.↗

NASA NTRS1978

OSO 8 X-ray spectra of clusters of galaxies. I - Observations of twenty clusters: Physical correlations

OSO 8 X-ray spectra from 2 to 20 keV have been analyzed for 26 clusters of galaxies. For 20 clusters temperatures, emission integrals, iron abundances, and low-energy absorption measurements are presented. The data give, in general, better fits to thermal bremsstrahlung than to power-law models. Eight clusters have positive iron emission-line detections at the 90% confidence level, and all 20 cluster spectra are consistent with Fe/H = 0.000014 by number with the possible exception of Virgo. Thus it is confirmed that X-ray emission in this energy band is predominantly thermal radiation from hot intracluster gas rather than inverse Compton radiation. Physical correlations between X-ray spectral parameters and other cluster properties are examined. It is found that (1) the X-ray temperature is approximately proportional to the square of the velocity dispersion of the galaxies; (2) the emission integral is a strong function of the X-ray temperature; (3) the X-ray temperature and emission integral are better correlated with cluster central-galaxy density than with richness; and (4) the fraction of galaxies which are spirals is correlated with the observed ram pressure in the cluster core.

Mushotzky, R. F.↗

NASA NTRS1978

Space Shuttle Plume Simulation Effect on Aerodynamics

Technology for simulating plumes in wind tunnel tests was not adequate to provide the required confidence in test data where plume induced aerodynamic effects might be significant. A broad research program was undertaken to correct the deficiency. Four tasks within the program are reported. Three of these tasks involve conducting experiments, related to three different aspects of the plume simulation problem: (1) base pressures; (2) lateral jet pressures; and (3) plume parameters. The fourth task involves collecting all of the base pressure test data generated during the program. Base pressures were measured on a classic cone ogive cylinder body as affected by the coaxial, high temperature exhaust plumes of a variety of solid propellant rockets. Valid data were obtained at supersonic freestream conditions but not at transonic. Pressure data related to lateral (separation) jets at M infinity = 4.5, for multiple clustered nozzles canted to the freestream and operating at high dynamic pressure ratios. All program goals were met although the model hardware was found to be large relative to the wind tunnel size so that operation was limited for some nozzle configurations.

Hair, L. M.↗

NASA NTRS1978

On-orbit spacecraft reliability

Operational and historic data for 350 spacecraft from 52 U.S. space programs were analyzed for on-orbit reliability. Failure rates estimates are made for on-orbit operation of spacecraft subsystems, components, and piece parts, as well as estimates of failure probability for the same elements during launch. Confidence intervals for both parameters are also given. The results indicate that: (1) the success of spacecraft operation is only slightly affected by most reported incidents of anomalous behavior; (2) the occurrence of the majority of anomalous incidents could have been prevented piror to launch; (3) no detrimental effect of spacecraft dormancy is evident; (4) cycled components in general are not demonstrably less reliable than uncycled components; and (5) application of product assurance elements is conductive to spacecraft success.

Bloomquist, C.↗

NASA NTRS1978

Design and physical characteristics of the Transonic Aircraft Technology (TACT) research aircraft

The Transonic Aircraft Technology (TACT) research program provided data necessary to verify aerodynamic concepts, such as the supercritical wing, and to gain the confidence required for the application of such technology to advanced high performance aircraft. An F-111A aircraft was employed as the flight test bed to provide full scale data. The data were correlated extensively with predictions based on data obtained from wind tunnel tests. An assessment of the improvement afforded at transonic speeds in drag divergence, maneuvering performance, and airplane handling qualities by the use of the supercritical wing was included in the program. Transonic flight and wind tunnel testing techniques were investigated, and specific research technologies evaluated were also summarized.

Painter, W. D.↗