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Brown, L. W.

Publications and source records attributed to Brown, L. W..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Imaging and data processing with the Low Frequency Space Array

The Low Frequency Space Array (LFSA) is being designed to image the entire sky at extremely low radio frequencies with arcmin to subarcmin resolution. To accomplish this goal, data from LFSA will be continuously integrated for many months and then be used with aperture synthesis techniques to produce images. The three dimensional nature of LFSA and the effects of orbital geometry make LFSA a continuously evolving array which has an excellent synthesized point-response function. After transforming the data to produce an initial image, it is possible to remove low-level sidelobe responses remaining in the image and thereby produce a high dynamic-range image. Interference (both man-made and from solar-system objects) is a potential problem for LFSA, but appropriate data handling techniques are available which should eliminate any of its effects.

Simon, R. S.↗
NASA NTRS1986

Composition of faint comets

The study uses an emission line, differential imaging camera built by the Science Operations Branch. This instrument allows photometric data to be obtained over a large area of a comet in a large number of resolution elements. The detector is a 100x100 Reticon array which with interchangeable optics can give resolutions from 2" to 30" over a field of 1' to 15'. The camera through its controlling computer can simultaneously take images in on-line and continuum filters and through computer subtraction and calibration present a photometric image of the comet produced by only the emission of the molecule under study. Initial work has shown two significant problems. First the auxiliary equipment of the telescope has not allowed the unambiguous location of faint comets so that systematic observations could be made, and secondly initial data has not shown much molecular emission from the faint comets which were located. Work last year on a software and hardware display system and this year on additional guide motors on the 36-inch telescope has allowed the differential camera to act as its own finder and guide scope. Comet IRAS was observed in C2 and CO+, as well as an occultation by the comet of SAO029103. The perodic comet Giacobini-Zinner was also observed in C2.

Brown, L. W.↗
NASA NTRS1985

C2 imagery of the inner coma of Comet IRAS-Araki-Alcock

May 10, 1983 observations of the comet IRAS-Araki-Alcock are analyzed to determine the spatial molecular abundance of C2 in the inner coma, via the Delta-v = +1 Swan band sequence near 4690 A. The observations indicate a deficiency of C2 emission across a projected diameter of about 2000 km that is centered on the peak of continuum emission. Comet imagery indicates a sunward-pointing coma that suggests an outburst of subsurface volatile ices through a nonvolatile surface crust, as predicted for periodic comets. These results are discussed in the framework of instrumental and observational constraints.

Oliversen, R. J.↗
NASA NTRS1984

Space Shuttle separate-surface control-system study

A control system concept is presented that produces proportional control of yaw moment for the space shuttle from early entry to Mach 2 with only software modifications of the vehicle. It uses separate deflections of the inboard and outboard elevon surfaces and is evaluated, by determining the maximum static yawing moment available by considering the deflection limits of the elevon surfaces. A proportional moment slightly in excess of that produced by the most effective reaction control system (RCS) jet for yaw control can be obtained. In addition to the static moment study, a control law is designed which is intended to produce desired flying qualities.

Brown, L. W.↗
NASA NTRS1983

An extensive galactic search for conformer II glycine

The most extensive galactic search reported to date for conformer II glycine, a higher energy form of the simplest amino acid has been conducted. The search utilized four glycine transitions at centimeter wavelengths and 21 at millimeter wavelengths to observe 18 galactic molecular sources and one comet. No conformer II glycine lines were detected, and measurements of representative sources were used to compute upper limits on total column densities. Several unidentified lines were detected and are reported here with some suggested possible identifications.

Snyder, L. E.↗
NASA NTRS1981

OH emission in the direction of TV Gem and BI Cyg

The NRAO-Green Bank 43-m telescope and 18-cm receiver have detected OH maser main-line emission at 1665 MHz, in the direction of the two late-type supergiants TV Gem and BI Cyg. The detection of the two new OH maser sources is noteworthy in view of the small number of late-type supergiants known to be molecular radio sources, or associated in close proximity with OH emission clouds. The IR, UV and radio properties of the two stars are discussed.

Brown, L. W.↗
NASA NTRS1981

The effects of lateral aerodynamic uncertainties on the handling qualities of the space shuttle orbiter at Mach numbers of 1.5 and .6

The effects of aerodynamic uncertainties on the handling qualities of the space shuttle orbiter were investigated with the use of six-degree-of-freedom, nonlinear equations of motion on the hybrid computer system. Flight condition characteristics for Mach numbers of 1.5 and .6 for the nominal and off nominal angle of attack conditions were selected for this investigation. Results revealed that at the low Mach number condition (.6), only a few problems existed for the angle of attack range considered and the many combinations of large aerodynamic variations considered. Moreover, none of these problems were considered to be related to poor handling qualities. For the angle of attack conditions considered at the high Mach number (1.5) problems existed with reduction of roll rate which can result in roll reversal conditions. In many cases, sideslip became proverse and increased rudder deflections and yaw jets were required.

Brown, L. W.↗
NASA NTRS1980

150 GHz observations of three radio galaxies

Radio galaxies were observed for the first time at 150 GHz. The central sources in Cyg A and 3C 111 were detected, as were the two radio lobes of Cyg A. No emission was found from the central source in 3C 236. The millimeter-wavelength emission from the central sources in Cyg A and 3C 111 is probably due in each case to a compact component that is optically thin to synchrotron radiation above about 35 GHz. These components are similar, although the compact component in 3C 111 is more luminous at both radio and X-ray wavelengths than the one in Cyg A. The 3C 111 central source was much weaker than anticipated on the basis of prior observations at 90 GHz, perhaps due to variability. Even at 150 GHz, there is no evidence of a high-frequency cutoff in the spectrum of the central source in Cyg A, and variability of this source also is expected. The flux densities of the Cyg A lobes are consistent with the power laws derived at lower frequencies, indicating that no steepening occurs in their spectra out to at least 150 GHz. There is no evidence for a compact, optically thick component in 3C 236.

Kafatos, M.↗
NASA NTRS1979

Reversal of the /O III/lambda 4363/H sub gamma lambda 4340 ratio in the planetary nebula IC 4997

Five image-tube spectrograms of the planetary nebula IC 4997 obtained during August 1977 show that the intensity forbidden ratio O III 4363 A/H-gamma 4340 A was equal to unity, but a sixth one obtained in April 1978 showed the ratio to be 0.91. These results represent a significant increase in the intensity ratio, which had been declining from 1895 to 1962 (when it was considerably less than unity), and is interpreted as resulting from a gradual increase in temperature of the nebula's central star accompanied by a transient event which led to a temporarily high value for the ratio in mid-1977.

Feibelman, W. A.↗
NASA NTRS1979

Preliminary study of pilot lateral control of two light airplanes near the stall

For two representative light, single-engine airplanes the single-axis piloting task of controlling bank angle with combined aileron and rudder, and a two-axis task of controlling bank angle with aileron and sideslip with rudder have been studied. For these tasks existing divergence criteria have been applied to determine conditions for closed-loop stability for selected flight conditions near the stall; in addition closed-loop stability characteristics and airplane response to bank angle command were calculated. Results obtained from applying the divergence criterion and from calculations of airplane responses to bank angle command indicate that aileron-alone bank angle control is marginally acceptable at high angle of attack. Of the two rudder control techniques considered, rudder used with the aileron in controlling bank angle increasd stability and produced satisfactory responses; the combined bank angle and sideslip control task does not warrant further consideration because of the task difficulty and the small improvement indicated in airplane closed-loop response with this technique.

Moul, M. T.↗
NASA NTRS1978

Merged infrared catalogue

A compilation of equatorial coordinates, spectral types, magnitudes, and fluxes from five catalogues of infrared observations is presented. This first edition of the Merged Infrared Catalogue contains 11,201 oservations from the Two-Micron Sky Survey, Observations of Infrared Radiation from Cool Stars, the Air Force Geophysics Laboratory four Color Infrared Sky Survey and its Supplemental Catalog, and from Catalog of 10 micron Celestial Objects (HALL). This compilation is a by-product of a computerized infrared data base under development at Goddard Space Flight Center; the objective is to maintain a complete and current record of all infrared observations from 1 micron m to 1000 micron m of nonsolar system objects. These observations are being placed into a standardized system.

Schmitz, M.↗
NASA NTRS1978

Detection of a weak maser emission pedestal associated with the SiO maser

Results are reported for high-spectral-resolution observations of the v = 1, J = 1-0 SiO maser sources at 43,122.027 MHz (6.95 mm wavelength) associated with the variable stars Omega Cet, NML Tau, VY CMa, R Leo, W Hya, VX Sgr, NML Cyg, and R Cas. A weak underlying maser emission pedestal is clearly observed in the spectra of all but NML Cyg and R Cas. The data indicate that the underlying pedestal of SiO emission appears to originate in a shell-like region around the star, has a thermal appearance even though it must be due to weak maser emission, and appears to be part of the spectral signature of SiO maser emission from late-type stars. It is found that the center velocities of the pedestals may be used to determine stellar radial velocities. Observations of large-scale time variations in the intensity of the Ori A SiO maser and the detection of weak maser pedestals associated with each of the two strong emission-feature groups in Orion are also discussed. It is suggested that the Orion molecular cloud might contain two late-type long-period variable stars that may be semiregular variables.

Snyder, L. E.↗
NASA NTRS1978

Preliminary results of linear polarization measurements at 99 GHz

The results of the first linear polarization measurements of extrasolar radio sources at a frequency above 35 GHz are presented. For the quasars 3C 273 and 3C 345, the observed position angles are in accord with the predictions of Inoue, and the measurements are consistent with the suggestion that the compact components responsible for the high-frequency emission are affected by high degrees of internal Faraday depolarization. For the radio galaxy 3C 274 (Virgo A) the observed position angle and degree of polarization are consistent with the model of Hobbs and Waak.

Hobbs, R. W.↗
NASA NTRS1978

Stratospheric ozone measurement with an infrared heterodyne spectrometer

Measurements of a stratospheric ozone concentration profile are made by detecting infrared absorption lines with a heterodyne spectrometer. The infrared spectrometer is based on a line-by-line tunable CO2 lasers, a liquid-nitrogen cooled HgCdTe photomixer, and a 64-channel spectral line receiver. The infrared radiation from the source is mixed with local-oscillator radiation. The difference frequency signal in a bandwidth above and below the local-oscillator frequency is detected. The intensity in each sideband is found by subtracting sideband contributions. It is found that absolute total column density is 0.32 plus or minus 0.02 cm-atm with a peak mixing ratio at about 24 km. The (7,1,6)-(7,1,7) O3 line center frequency is identified as 1043.1772/cm. Future work will involve a number of ozone absorption lines and measurements of diurnal variation. Completely resolved stratospheric lines may be inverted to yield concentration profiles of trace constituents and stratospheric gases.

Abbas, M. M.↗
NASA NTRS1978

Cygnus A at 99 GHz - Observations of the three principal components and interpretation of the central source

The three principal emission components of Cygnus A have been observed at 99 GHz, the highest frequency at which radio measurements of this source have been accomplished. The observations show no definite indication of a high-frequency cutoff in the spectrum of the compact central component, which perhaps may be attributed to an optically thin synchrotron source that peaks at a frequency of several hundred GHz.

Hobbs, R. W.↗
NASA NTRS1978

Stratospheric ozone measurement with an infrared heterodyne spectrometer

A stratospheric ozone absorption line in the 10 microns band was measured and resolved completely, using an infrared heterodyne spectrometer with spectral resolution of 5 MHz (0.000167 cm to -1 power). The vertical concentration profile of stratospheric ozone was obtained through an analytical inversion of the measured spectral line profile. The absolute total column density was 0.34 cm atm with a peak mixing ratio occurring at approximately 24 km. The (7,1,6) to (7,1,7) O3 line center frequency was found to be 1043.1775 + or - 0.00033 cm to toe -1 power, or 430 + or - 10 MHz higher than the P(24) CO2 laser line frequency.

Abbas, M. M.↗
NASA NTRS1978

New silicon monoxide masers

Seven Mira variable stars with silicon monoxide maser emission have been found. All are later than M4 and heavily reddened. Two were observed near maximum light. One, Y Cas, seems to bear out the correlation of 43-GHz SiO maser luminosity and mean spectral type at maximum light. RT Aql, however, falls about 1 mag below the expected brightness. A catalog of SiO maser stars is given.

Dickinson, D. F.↗