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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 127 records · Page 7
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NASA NTRS1977

Ultraviolet observations of 3C 273 by the ANS

Five-band spectrophotometry between rest wavelengths of 1340 A and 2850 A is presented. The 2200-A absorption feature seems to be present in 3C 273 with a depth appropriate for an internal reddening of E(B-V) = 0.13. The dereddened ultraviolet flux distribution can be described by a power law of spectral index 1.21. This power law can account for the observed flux in X-rays. It provides more photons than needed to excite the observed H-beta by photoionization and Fe II lines by resonance fluorescence. The emission-line flux ratios, Ly-alpha/C IV/ semiforbidden C III/H-beta are 100/80/60/10.

Wu, C.-C.↗
NASA NTRS1976

X-ray spectra of the Puppis A and the Vela supernova remnants

Low-energy X-ray spectra are presented for the entire Vela supernova remnant (SNR), the two most intense subregions of the Vela SNR, and the Puppis A SNR. Acceptable chi-squared fits are obtained from the model of a high-temperature low-density plasma with Allen cosmic abundances when thermal bremsstrahlung, radiative recombination, line emission, and interstellar absorption are included. A suggested increase of 45-fold in the Si abundance for the entire Vela SNR is found unacceptable by chi-squared tests of the present spectra. The two enhanced regions of Vela are found to have different temperatures. A deficiency of at least a factor of 3 is seen in the O VII and O VIII emission from the entire Vela SNR. Because ultraviolet observations indicate a normal abundance of oxygen, this is interpreted as evidence for the existence of nonequilibrium conditions in the emitting plasma.

Moore, W. E.↗
NASA NTRS1961

A Satellite Borne Cadmium Sulfide Total Corpuscular Energy Detector

The properties of single crystals of cadmium sulfide as radiation detectors are described. It has been found possible to select crystals such that: (a) The ratio of increase of conductivity under irradiation to the rate of absorption of energy in the crystal is substantially independent of particle energy (over the examined ranges of 500 ev to 80 kev for electrons and 5 kev to 180 kev for protons) and of the magnitude of energy flux (over the range from.005 to 10 ergs/cm(sup 2 -sec); and (b) The above ration is substantially the same for protons, electrons, alpha particles, x-rays, and gamma-rays. For a driving voltage of 100 volts, typical crystal yield currents of 10(sup -7) to 10(sup- 6) amperes for each erg/cm(sup 2-sec) of energy absorbed by the crystal. The threshold of such crystal detectors (resulting from dark currents of the order of 10(sup 10 amp) is typically 10(sup -3) ergs/cm(sup 2- sec). For the selected crystals a response-temperature coefficient of -0.25% per degree centigrade is found for the temperature range -50 deg C to + 50 deg C. A description is given of a complete CdS total corpuscular energy detector for the study of geomagnetically trapped radiation by means of a satellite. The detector described has a dynamic range great than 10(sup 4), a solid angle of 10(exp -3) steradian, and a detection threshold of approximately 1 erg/cm(sup 2-sec-sterad). A similar detector employing a small magnet for the selective exclusion of electrons is also described. Noteworthy practical features of these detectors for satellite and space probe experiments are: (a) Use of bare crystals, without covering foils, in order to detect charged particles having energies as low as hundreds of electron volts. (b) Simplicity of electronic auxiliaries. (c) Compactness, lightweight and nechanical ruggedness. (d) Low electrical power requirements; and (e) Conversion of conduction current to the rate of a twostate relaxation oscillator in order to facilitate telemetric transmission of data. A pair of such detectors was flown as part of the s-46 satellite payload on March 23, 1960, but due to vehicular failure an orbit was not achieved and the operation of the CdS detectors was observed for only, six minutes of flight.

Freeman, John W.↗
NASA NTRS1974

Line absorption studies of the interstellar gas near 1 million GHz

The Copernicus satellite now opens up the ultraviolet region for inspection, and the number of resonance lines which may be studied has increased from 6, seen in the visible, to more than 30. The distribution and properties of an important constituent of the interstellar gas, molecular hydrogen, can be studied in detail using this instrument. A more comprehensive picture may now be developed for element depletion factors, electron densities, and sources of ionization (UV photons, low energy cosmic and X-rays).

Jenkins, E. B.↗
NASA NTRS1975

On the nature of the intercloud medium

Previous analyses of Copernicus observations of interstellar absorption in the spectra of unreddened stars are reviewed in the framework of steady-state ionization models for the intercloud (low-density) component of the interstellar medium. A simple homogeneous model is described which accounts for the H, C, N, S, and Si interstellar lines in the spectrum of lambda Sco in terms of an extensive low-density medium photoionized by Lyman continuum radiation from the II Sco OB association. Quantitative constraints are placed on the maximum permissible flux of diffuse soft X-rays, and the model is generalized to interpret the observed ion, electron, and hydrogen column densities in the low-density medium. Severe constraints are found to be imposed on ionization models by the ratios Si III/Si, Si IV/Si, and S IV/S. It is concluded that the observations may be explained if 10 to 30% of a representative line of sight passes through a photoionized medium of density 0.1 to 0.2/cu cm, if H I constitutes the bulk of the gas along the line of site, and if the gas is at a similar density or is in the form of shielded clumps or clouds.

Hill, J. K.↗
NASA NTRS1975

Interstellar absorption lines toward gamma Arae

The available data on interstellar absorption lines in the spectrum of gamma Ara observed from the ground and with the Copernicus telescope have been analyzed to give column densities of various ion stages of H, C, N, O, Na, Mg, Si, P, S, Ar, Ca, Mn, and Fe. The element abundances with respect to H nuclei in H I regions are similar to the values for zeta Oph, with depletions relative to the sun tending to increase with increasing condensation temperature. For example, toward gamma Ara, Fe is depleted by a factor of 50; Mg, Si, and Mn by about 10; and S, P, and N little or none. Interstellar Si IV and probably S IV appear stronger than in most other stars, but still their low ratios to Si III and S III suggest that soft X-rays and low-energy cosmic rays are not important sources of ionization. The width of the O VI lines and the absence of N V have been interpreted as evidence for a collisionally ionized region with a temperature between 300,000 and 700,000 K containing at least 0.0004 of the total interstellar column density.

Morton, D. C.↗
NASA NTRS1972

Soft X-rays from Cygnus X-2 and from Cygnus X-1 /in eclipse/.

Observations of Cygnus X-1 (probably in eclipse) and Cygnus X-2 on Oct. 23, 1971, show quite low absorption in their spectrum, and yet they are thought to be in a double or multiple star system from the optical data. The lack of intrinsic absorption in their spectra may be taken to mean that they lie sufficiently far from their primaries for a reduction to virtually zero of their interaction with the atmosphere of the primaries.

Stevens, J. C.↗
NASA NTRS1973

Spectroscopic observations of HZ Herculis. II

Preliminary results from an extensive series of spectroscopic observations of the HZ Her optical counterpart of the eclipsing, pulsating X-ray binary Her X-1. Spectrograms with a dispersion of 30 A/mm reveal a spectral type as late as F5 near minimum in the light curve with the G-band and metallic lines present. Narrow Fe lines show that HZ Her is not a rapid rotator. Low-dispersion (115 A/mm) spectra, obtained with 10-minute time resolution, reveal rapid (10-min) variations in the 4640 N III emission and in the 4471 He I absorbtion features. The H-beta absorption is variable in equivalent width, and shows evidence of being partially filled with emission.

Bopp, B. W.↗
NASA NTRS1974

International Cosmic Ray Conference, 13th, University of Denver, Denver, Colo., August 17-30, 1973, Proceedings. Volume 5

An X-ray observation of the Norma-Lupus region, charge and isotope measurements of heavy cosmic ray nuclei and their role in the determination of cosmic ray age, and the possibility of a contribution to primary cosmic ray spectra from pulsars are among the topics covered in papers concerned with some of the results of recent cosmic ray research. Other topics covered include multiple scattering of charged particles in magnetic fields, absorption of primary cosmic rays in the atmosphere, and phase lag effects on cosmic ray modulation during a recent solar cycle. Individual items are announced in this issue.

Source record↗
NASA NTRS1974

On ionization in H I regions

A comparison is made of the K I, Na I, Ca II, and H I interstellar absorption lines formed in relatively low-density interstellar clouds in H I regions. The data indicate that the fractional ionization (ratio of electron density to hydrogen density) is nearly constant for a range in hydrogen densities covering a factor of 15. If ionization balance exists in the clouds, then ionization of hydrogen by either low-energy cosmic rays or soft X-rays cannot be the principal source of the observed free electrons, and the hydrogen ionization rate is less than 10 to the -16th power per sec for these processes.

Hobbs, L. M.↗
NASA NTRS1975

ANS results on X-ray binaries

A short description is given of the Astronomical Netherlands Satellite ANS and the X-ray instruments of the Space Research Laboratory in Utrecht. ANS observed in February 1975 a soft _ KeV) X-ray flux in Her-x-I during the 'off'-state with an intensity of a factor I0 lower than observed previously in the 'on'-state. The measured uncorrected intensity is (1.1 ± 0.2)10^(-11) ergs/sq.cm sec in 0.2 - 0.28 keV at earth. The ANS observations on Cyg-X-I are summarized. Duping the May 75 flaring state a very high intensity at 0.5 keV is measured consistent with a power-law Ph0ton-spectrum with index 3.5 and an interstellar absorption of 7.10^(21) atoms/sq.cm, but not consistent with spectra that show an additional cut-off below 1KeV and an absorption of 7 10^(21) atoms/sq.cm. Intensity changes on a time scale of minutes, as observed in Cyg-X-1 lowstate, are not observed during the flaring state.

J. Heise↗
NASA NTRS1976

Stellar crystal X-ray spectroscopy on OSO-8

The large-area graphite crystal X-ray spectrometer on the OSO-8 satellite is described, and its response to stellar line and continuum radiation is discussed. A high resolution X-ray spectrum of Sco X-1 obtained from a preliminary analysis of quick look data shows a strong, smooth continuum with an absence of emission or absorption features over the energy range 2.2 to 8 keV. Upper limits are set on narrow line emission from highly ionized states of S, Ca, and Fe.

Kestenbaum, H. L.↗
NASA NTRS1976

The X-ray variability of Vela X-1 (3U 0900-40)

From observations of Vela X-1 with the MSSL 2.5-7.5 keV detector onboard Copernicus, the behavior of the source can be characterized by three phases: (1) high intensity, (2) low intensity, and (3) eclipse. Combining data from the 1972 Uhuru observations with eclipse observation yields a binary period of 8.963 + or - 0.001 days with zero phase on 1975 Feb. 6.97 + or - 0.04 UT. The low intensity phase is interpreted as being due to increased absorption in an accretion wake traveling across the line of sight (the spectral slope remains relatively constant throughout the cycle). Another period of enhanced absorption immediately after exit from eclipse may be due to a bow shock. Comparison of the two observations suggests that these structures vary from cycle to cycle and, since the orbital period is long, probably during each cycle.

Charles, P. A.↗
NASA NTRS1977

Backscatter of hard X-rays in the solar atmosphere

The solar photosphere backscatters a substantial fraction of the hard X rays from solar flares incident upon it. This reflection was studied using a Monte Carlo simulation which takes into account Compton scattering and photo-electric absorption. Both isotropic and anisotropic X ray sources are considered. The bremsstrahlung from an anisotropic distribution of electrons are evaluated. By taking the reflection into account, the inconsistency is removed between recent observational data regarding the center-to-limb variation of solar X ray emission and the predictions of models in which accelerated electrons are moving down toward the photosphere.

Bai, T.↗