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At least 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Preliminary design analysis for the solar optical telescope main mirror actuator

The resolution of the SOT Gregorian telescope was maintained if the conic foci of the elliptical secondary and parabolic primary were made to coincide within plus or minus 38 microns across the prime focus plane and to within 5 microns in focus. An error in coincidence across the focal plane caused all point images to show additional coma with all the comatic tails pointing in the same direction. An error in focus became magnified by the square of the magnification of the secondary and simply increased the diameter of the point source. Offsetting or rastering the sun may be accomplished by swinging the primary in an arc about the point of coincidence of the conic foci so long as the coincidence is kept to within the tolerance stated.

Dunn, R. B.↗
NASA NTRS1978

Compton scattering of microwave background radiation by gas in galaxy clusters

Based on data on the X-ray spectrum of the Coma cluster, interpreted as thermal bremsstrahlung, the expected brightness depletion from Compton scattering of the microwave background in the direction of the cluster is computed. The calculated depletion is about one-third that recently observed by Gull and Northover, and the discrepancy is discussed. In comparing the observed microwave depletion in the direction of other clusters which are X-ray sources it is found that there is no correlation with the cluster X-ray luminosity. Consequently, the microwave depletion observations cannot yet be taken as good evidence for a thermal bremsstrahlung origin for the X-ray emission. The perturbation from Compton scattering of photons on the high-frequency (Wien) tail of the blackbody distribution is computed and found to be much larger than predicted in previous calculations. In the Wien tail the effect is a relative increase in the blackbody intensity that is appreciably greater in magnitude than the depletion in the Rayleigh-Jeans domain.

Gould, R. J.↗
NASA NTRS1978

The light curve of the nucleus of comet d'Arrest

This paper reports new photoelectric photometry of the nucleus of P/d'Arrest (1976e) during August 4, 5, and 6, 1976 (UT), just before perihelion passage. The comet appeared as a bright stellar nucleus with a faint surrounding coma. The average visual magnitude from the nuclear region (16-arcsec diaphragm) was 11.60. The visual brightness varies with an amplitude of 0.15 plus or minus 0.02 mag. There is evidence for a period of 5.17 plus or minus 0.01 hr. We interpret such a periodic variation as due to the rotation of the nucleus. The colors of the nuclear region are very similar to those of a solar-type star, and they do not vary significantly with aspect angle.

Fay, T. D., Jr.↗
NASA NTRS1978

A cometary ionosphere model for Io

A source for the ionosphere of Io is proposed based on the assumption that the satellite is rather moonlike but continuously bombarded by intense fluxes of energetic particles, which makes its surface electrically conducting so that a significant Birkeland current is drawn up along magnetic field lines from Jupiter's ionosphere. It is suggested that the ion current is neutralized upon contact with Io's surface and that subsequent sputtering of this material from the surface supplies the satellite's neutral atmosphere. A model for the generation and maintenance of Io's ionosphere is outlined, according to which the structure of the ionosphere is determined by the impact of energetic trapped electrons from the Jovian magnetosphere and the ram pressure of the corotational magnetospheric wind. The first of these two processes provides the main ionization mechanism, while the second compresses the upstream (or 'nighttime') ionosphere via Alfven's critical-velocity phenomenon. It is concluded that Io's ionosphere is more nearly analogous to the coma and tail of a comet in the solar wind than to the earthlike case of a permanent gravitationally bound ionosphere.

Cloutier, P. A.↗
NASA NTRS1977

The comet-solar wind interaction

The important roles of comets as natural probes of the solar wind, particularly at high heliographic latitudes and small heliocentric distances, unattained thus far by artificial space probes, is stressed. It is becoming clear the solar wind is not merely responsible for shaping and maintaining the cometary plasma tail, but is also indirectly responsible for the rapid ionization processes in the coma. Despite this, however, the detailed interaction of the solar wind with comets, which is underlined by the complex and time-varying morphology observed in the cometary head and the tail, constitutes a formidable problem, and is only very imperfectly understood at present. The current views are critically reviewed and an attempt is made to identify the dominant physical mechanisms that are involved.

Mendis, D. A.↗
NASA NTRS1978

Human Neurological Development: Past, Present and Future

Neurological development is considered as the major human potential. Vision, vestibular function, intelligence, and nutrition are discussed as well as the treatment of neurological disfunctions, coma, and convulsive seizures.

Pelligra, R.↗
NASA NTRS1979

A study of the feasibility of ultraviolet spectrometry for cometary missions

Ultraviolet spectra fo the comet West obtained by sounding rocket experiments in 1976 are reproduced and interpreted in order to estimate the expected brightness of the emission features and determine the spatial extent of these features for the proposed Halley Flyby/Tempel 2 rendezvous and the possible Halley or Encke flybys close to perihelion. A coma model was constructed and evaluated for the physical condition of candidate targets such as heliocentric distance, gas production, and composition. In addition to brightness profiles, the neutral and ion densities of the principal species are also dervied. The brightness profiles can be used to determine the feasibility of utilizing the space telescope to provide supporting observations during the mission. Basic parameters identified are spectral range, wavelength resolution, spatial resolution, sensitivity and dynamic range, rejection of scattered light, and integration or accumulation time.

Feldman, P. D.↗
NASA NTRS1979

Report of the Comet Science Working Group

Scientific objectives and mission strategies for a flyby of Halley's comet and rendezvous with Tempel-2 are discussed. Instrumentation to be carried by both the rendezvous spacecraft and the coma probe payload are listed. Known characteristics of both comets are summarized.

Source record↗
NASA NTRS1978

The design of a multi-detector spectrometer for the infrared

A modified Ebert-Fastie spectrometer has been developed for atmospheric temperature sounding applications. The device is described with reference to its resolution, grating, focal-length mirror, mirror, equivalent f-number, and projected area of grating. The images of the entrance slit appear tilted backwards away from the concave mirror. Astigmatism and spherical aberration are reduced by asperizing the mirror. The resolution and f-number of the instrument are limited by the sagittal coma. The orientation and size of the exit slit are functions of wavelength.

Koch, D. G.↗
NASA NTRS1979

Photometric studies of composite stellar systems. III - UBVR and JHK observations of E and S0 galaxies

Infrared (JHK) photometry is presented for a sample of E and S0 galaxies. The sample comprises 80 field galaxies, 35 galaxies in the Virgo cluster, and 22 in the Coma cluster. The galaxies span a range of 6 mag in absolute magnitude. Multiaperture UBVR photometry for 107 field galaxies is also presented. The infrared data are combined with these optical data or with published optical data to give V-K colors. This paper describes the observational techniques and lists the data.

Persson, S. E.↗
NASA NTRS1981

Acoustically-tuned optical spectrometer

Lens arrangement corrects for aberrations and gives resolution of 0.7 seconds of arc. In spectrometer, light from telescope is relayed by doublet lens to acoustically tuned optical filter. Selected wavelengths are relayed by triplet lens to charge coupled device camera. Intervening cylindrical lens, tilted at 12 degree angle, corrects for astigmatism and coma introduced by two element birefringent crystal in filter.

Sklar, E.↗
NASA NTRS1980

Interference filter photometry of periodic comet Ashbrook-Jackson

P/Ashbrook-Jackson has a period of 7.43 years and comes to perihelion at 2.284 AU. It is a low inclination object (12.5 deg) of moderate eccentricity (0.400). In 1963, it made the best possible apparition, coming to perihelion and opposition virtually simultaneously, but no one made physical observations of faint periodic comets in 1963. In 1978 Ashbrook-Jackson came to opposition on Sept. 28, just 40 days after perihelion. It will be just over 100 years before an equally favorable apparition recurs. P/Ashbrook-Jackson was recovered by Pereyra at Cordoba Observatory on April 28, 1977, more than a year and a quarter before perilhelion and already showing a diffuse coma with central condensation. Its helio-centric distance was then 3.7 AU. An extensive program was planned, but equipment problems and weather ultimately limited it to the two nights of data reported here.

Newburn, R. L., Jr.↗
NASA NTRS1980

Cometary collisions on the moon and Mercury

Unusual swirl patterns of bright and dark material on the moon and Mercury are proposed to be remnants of collisions with gas/dust-rich regions within a cometary coma. This interpretation provides important new clues for understanding cometary fine structure, impact effects of low-density material, and the origin of certain pronounced magnetic anomalies.

Schultz, P. H.↗
NASA NTRS1980

Rotation and outbursts of comet P/Schwassmann-Wachmann 1

The paper examines rotation and outbursts of comet P/Schwassmann-Wachmann 1. The observations of the P/Schwassmann-Wachmann 1 show this comet to flare above its quiescent level from before perihelion q=5.5 AU, to after aphelion Q of about 7AU. Cometary 'afternoon' activity suggests counterclockwise rotation of aphelion pole as seen near lambda=100 deg; outburst dates were derived from observed coma diameters, and the rotation was found to be direct with pole near lambda=280 deg. Usually one large area of the comet is active during one opposition, although two were observed concurrently in four very active oppositions; old active areas persist near the East limb of the comet and new areas resist development toward the West limb.

Whipple, F. L.↗
NASA NTRS1980

Radio observation of comet Meier /1978f/ in 18-cm OH lines

Observations of 18-cm OH spectral lines in comet Meier (1978f) with the 1000-ft. Arecibo telescope show spatial resolution of the OH coma by the 2.9 arcmin beam (=3.7 x 10 to the 5th km). The data agree with predictions of the solar Fraunhofer spectrum-pumping theory of comet OH excitation. On the assumption that the OH parent molecule (e.g., H2O) has a Haser-model scale length of about 1.0 x 10 to the 5th km at heliocentric distance 1 AU, an OH scale length of less than 10 to the 6th km, and probably near 1.0 x 10 to the 5th km is derived. Assuming a recently calculated value of the OH lifetime and the solar radiative pumping model, the results indicate an OH production rate of 10 to the 29th Kayser at heliocentric distance 2 AU.

Giguere, P. T.↗
NASA NTRS1980

The heating of gas in clusters of galaxies by relativistic electrons - Collective effects

We show that the rate at which gas is heated in X-ray clusters of galaxies by streaming relativistic electrons can be much greater than the Coulomb heating rate because of the stimulated growth of a high level of electrostatic turbulence and its subsequent collapse to shorter wavelengths. This enhanced heating (and, hence, energy loss) rate allows the X-ray emitting gas to be heated by those particles which are observable through their synchrotron emission at low radio frequencies and yields a radio source size consistent with the observed radio halo sizes in the Coma cluster. The heating of gas in clusters of galaxies by relativistic electrons will significantly affect the cluster gas dynamics.

Scott, J. S.↗
NASA NTRS1981

The Comet Halley handbook: An observer's guide

The orbit of Comet Halley is described as well as its expected physical behavior (brightness, tail lengths, coma diameters) in 1985-1986 during which time its preperihelion positon will allow better conditions for Northern Hemisphere observers. Southern Hemisphere observers will prefer post perihelion observation. Ephemeris data for 1981-1987 are presented in tables.

Yeomans, D. K.↗
NASA NTRS1980

Comet Science Working Group report on the Halley Intercept Mission

The Halley Intercept Mission is described and the scientific benefits expected from the program are defined. One characteristic of the mission is the optical navigation and resulting accurate delivery of the spacecraft to a desired point near the nucleus. This accuracy of delivery has two important implications: (1) high probability that the mass spectrometers and other in situ measurement devices will reach the cometary ionosphere and the zone of parent molecules next to the nucleus; (2) high probability that sunlit, high resolution images of Halley's nucleus will be obtained under proper lighting conditions. In addition an observatory phase is included during which high quality images of the tail and coma structure will be obtained at progressively higher spatial resolutions as the spacecraft approaches the comet. Complete measurements of the comet/solar wind interaction can be made around the time of encounter. Specific recommendations are made concerning project implementation and spacecraft requirements.

Source record↗