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NASA NTRS1979

Cosmic far-ultraviolet background radiation - Probe of a dense hot intergalactic medium

Line and continuum radiation fluxes have been computed for a wide range of enriched intergalactic medium (IGM) models. Observations of the diffuse extragalactic light at optical and far-ultraviolet wavelengths are found to provide a potentially important probe of a dense hot intergalactic medium. If the diffuse X-ray background is produced by this gas, the models constrain the cosmological density parameter (Omega) to be less than 0.4. The associated Compton distortions of the cosmic blackbody background radiation and the optical depths to distant quasars at X-ray wavelengths are also evaluated.

Sherman, R. D.↗

NASA NTRS1979

Fourier emission infrared microspectrophotometer for surface analysis. I - Application to lubrication problems

A far-infrared interferometer was converted into an emission microspectrophotometer for surface analysis. To cover the mid-infrared as well as the far-infrared the Mylar beamsplitter was made replaceable by a germanium-coated salt plate, and the Moire fringe counting system used to locate the moveable Michelson mirror was improved to read 0.5 micron of mirror displacement. Digital electronics and a dedicated minicomputer were installed for data collection and processing. The most critical element for the recording of weak emission spectra from small areas was, however, a reflecting microscope objective and phase-locked signal detection with simultaneous referencing to a blackbody source. An application of the technique to lubrication problems is shown.

Lauer, J. L.↗

NASA NTRS1979

Emissivity correction for interpreting thermal radiation from a terrestrial surface

A general method of accounting for emissivity in making temperature determinations of graybody surfaces from radiometric data is presented. The method differs from previous treatments in that a simple blackbody calibration and graphical approach is used rather than numerical integrations which require detailed knowledge of an instrument's spectral characteristics. Also, errors caused by approximating instrumental response with the Stephan-Boltzman law rather than with an appropriately weighted Planck integral are examined. In the 8-14 micron wavelength interval, it is shown that errors are at most on the order of 3 C for the extremes of the earth's temperature and emissivity. For more practical limits, however, errors are less than 0.5 C.

Sutherland, R. A.↗

NASA NTRS1980

Infrared heterodyne radiometer for airborne atmospheric transmittance measurements

An infrared heterodyne radiometer (IHR) was used to measure atmospheric transmittance at selected hydrogen fluoride (2.7 micrometer) and deuterium fluoride (3.8 micrometer) laser transitions. The IHR was installed aboard a KC-135 aircraft for an airborne atmospheric measurements program that used the sun as a backlighting source for the transmission measurements. The critical components are: a wideband indium antimonide (1nSb) photomixer, a CW HF/DF laser L0, a radiometric processor, and a 1900 K blackbody reference source. The measured heterodyne receiver sensitivity (NEP) is 1.3 x 10 to the -19th power W/Hz, which yields a calculated IHR temperature resolution accuracy of delta I sub S/-3 sub S = 0.005 for a source temperature of 1000 K and a total transmittance of 0.5. Measured atmospheric transmittance at several wavelengths and aircraft altitudes from 9.14 km (30,000 ft) to 13.72 km (45,000 ft) were obtained during the measurements program and have been compared with values predicted by the AFGL Atmospheric Line Parameter Compilation.

Wolczok, J. M.↗

NASA NTRS1980

Development and performance of a laser heterodyne spectrometer using tunable semiconductor lasers as local oscillators

A diode laser based IR heterodyne spectrometer for laboratory and field use was developed for high efficiency operation between 7.5 and 8.5 microns. The local oscillator is a PbSSe tunable diode laser kept continuously at operating temperatures of 12-60 K using a closed cycle cooler. The laser output frequency is controlled and stabilized using a high precision diode current supply, constant temperature controller, and a shock isolator mounted between the refrigerator cold tip and the diode mount. Single laser modes are selected by a grating placed in the local oscillator beam. The system employs reflecting optics throughout to minimize losses from internal reflection and absorption, and to eliminate chromatic effects. Spectral analysis of the diode laser output between 0 and 1 GHz reveals excess noise at many diode current settings, which limits the infrared spectral regions over which useful heterodyne operation can be achieved. System performance has been studied by making heterodyne measurements of etalon fringes and several Freon 13 (CF3Cl) absorption lines against a laboratory blackbody source. Preliminary field tests have also been performed using the Sun as a source.

Glenar, D.↗

NASA NTRS1979

Optically pumped carbon dioxide laser mixtures

This work explores the concept of blackbody radiation pumping of CO2 gas as a step toward utilization of solar radiation as a pumping source for laser action. To demonstrate this concept, an experiment was performed in which laser gas mixtures were exposed to 1500 K thermal radiation for brief periods of time. A gain of 2.8 x 10 to the -3rd reciprocal centimeters has been measured at 10.6 microns in a CO2-He gas mixture of 1 Torr pressure. A simple analytical model is used to describe the rate of change of energy of the vibrational modes of CO2 and to predict the gain. Agreement between the prediction and experiment is good.

Yesil, O.↗

NASA NTRS1980

The 16- to 38-micron spectrum of Callisto

The emission spectrum of Callisto was measured between 16 and 38 microns with a spectral resolution of 1/30 of a wavelength, using the NASA Kuiper Airborne Observatory on the night of October 30-31, 1975. Within the errors, the observed spectrum is like that of a 155 K blackbody, in both shape and absolute intensity. The infrared emission and diameter of Callisto indicate a bolometric Bond albedo of 0.05 + or - 0.14, which is consistent with heating of the surface by absorbed sunlight.

Forrest, W. J.↗

NASA NTRS1980

IUE observations of circumstellar emission from the late type variable R Aquarii /M7 + pec/

IUE observations of R Aquarii (M7 + pec) have been obtained in low dispersion in order to study its circumstellar emission. Strong permitted, semiforbidden, and forbidden emission lines are identified that are superposed on a bright ultraviolet continuum. From the analysis it is deduced that the strong emission-line spectrum that involves semiforbidden C III, C IV, semiforbidden Si III, forbidden O II, and forbidden O III probably arises from a dense compact nebula the size of which is comparable to the binary system of which R Aqr is the primary star. Low-excitation emission lines of Fe II, Mg II, O I, and Si II suggest the presence of a warm chromosphere (T less than about 10,000 K) in the primary M7 late type giant. The secondary is identified as a white dwarf, comparable to or somewhat brighter than the sun, since such a star can produce enough ionizing photons to excite the continuum and emission-line spectrum and yet be sufficiently faint to escape detection by direct observation. The UV continuum observed is attributed to Balmer recombination and not to blackbody emission from the hot companion. The general spectral properties of R Aqr between 1200 A and 3200 A are discussed in the context of the model for the circumstellar nebula, the companion, and the mass-loss rate of the primary star.

Michalitsianos, A. G.↗

NASA NTRS1980

Flux distributions and colors of accretion disks

The disk model of Shakura and Sunyaev (1973) and Novikov and Thorne (1973) is used to calculate temperature distributions and integrated spectral fluxes for disks around a typical white dwarf and a typical neutron star, under the assumption that each element of the disk locally radiates as a blackbody. In addition, the disks' integrated UBV colors are calculated using the grid colors for real model atmospheres calculated by Buser and Kurucz (1978) and the observed colors given by Allen (1973). In all the calculations the effect of radiation from one part of the disk on all the other parts is included.

Pacharintanakul, P.↗

NASA NTRS1980

Coaxial radiative and convective heat transfer in gray and nongray gases

Coupled radiative and convective heat transfer is investigated for an absorbing gas flowing in a finite length channel and heated by blackbody radiation directed along the flow axis. The problem is formulated in one dimension and numerical solutions are obtained for the temperature profile of the gas and for the radiation escaping the channel entrance, assuming both gray and nongray absorption spectra. Due to radiation trapping, the flowing gas is found to have substantially smaller radiation losses for a given peak gas temperature than a solid surface that is radiatively heated to this temperature. A greenhouse effect is also evident whereby radiation losses are minimized for a gas having stronger absorption at long wavelengths.

Mattick, A. T.↗

NASA NTRS1980

Radiometric observations of the 752.033-GHz rotational absorption line of H2O from a laboratory jet

With the aid of a high-resolution two-stage heterodyne radiometer, spectral absorption measurements of the 752.033 GHz line of water vapor were carried out, using a blackbody continuum as a background radiation source for investigating the absorptive properties of the H2O content of high altitude rocket plumes. To simulate this physical situation in a laboratory environment, a small steam jet was operated within a large high-vacuum chamber, with the H2O jet plume traversing the radiometer line of sight. The experiments verified that this rotational line is optically thick, with excitation temperatures below 100 K, in the downstream part of the plume, as predicted by theoretical modelling.

Dionne, G. F.↗

NASA NTRS1980

Discovery of a compact X-ray source at the center of the supernova remnant RCW 103

A point source of X-ray emission has been detected at the center of the supernova remnant RCW 103 using the Einstein Observatory. The 10 arcsec radius error circle is centered at alpha 16h13m47.8s, delta = -50 deg 55 arcmin 05 arcsec (1950) and contains two candidate stars of approximately 20th magnitude. No coincident point source of radio emission is known, but it is pointed out that the X-ray object lies 1.2 deg away from the centroid position of a gamma-ray source, CG 333 + 0. The observed flux from the object at the earth is approximately 7 x 10 to the -13th ergs/sq cm s in the 0.6-2 keV band. It is likely that the object is either a hot neutron star or an X-ray emitting pulsar. In contrast to the Crab and Vela pulsars, however, no extended X-ray emission associated with the point source is discernible. If the object is a hot neutron star, it has a blackbody temperature of 2 x 10 to the 6th K, and would represent the first detection of surface radiation from a neutron star.

Tuohy, I.↗

NASA NTRS1982

Radiant Heating of Ampoule contents

Ampoule charge heating system exploits spectral properties of blackbody radiation and ampoule material transparency to heat charge to high temperature. Cooling gas prevents softening of outside wall of ampoule. Use of proposed method may be limited by tendency of silica (or any other viteous material) to devitrify on prolonged exposure to temperatures near softening point.

Holland, L. R.↗

NASA NTRS1981

Measurement of HO2 and other trace gases in the stratosphere using a high resolution far infrared spectrometer at 28 Km

A progress report and data analyses from the December 1980 flight are presented. The following areas are covered: (1) computer analysis of the flight spectra to obtain phase corrected, normalized sums of spectra for retrieval of atmospheric profiles; (2) study of atmospheric HF, HCl, and H2O; (3) stratospheric H2O2 and HOCl; (4) laboratory spectroscopy of HOCl; and (5) design study of a new balloon gondola. The majority of the flight data were taken in the low background mode, i.e., one input to the spectrometer looking at the sky and the other looking at a LN2 temperature blackbody. An analysis of HF stratospheric measurements was undertaken in conjunction with the HF analysis. High quality spectra showing the HOCl q-branches under optically thin conditions were also obtained.

Traub, W. A.↗

NASA NTRS1981

IUE observations of circumstellar emission from the late-type variable R AQR (M6 + pec)

The IUE observations of R Aqr (M7 + pec) obtained in low dispersion are discussed with particular reference to circumstellar emission. Strong permitted, semiforbidden, and forbidden emission lines are seen, superimposed on a bright ultraviolet continuum. It is deduced that the strong emission line spectrum that involves C III, C IV, Si III, (0 II) and (0 III) probably arises from a dense compact nebula the size of which is comparable to the orbital radius of the binary system of which R Aqr is the primary star. The low excitation emission lines of Fe II, Mg II, 0 I, and Si II probably a white dwarf, comparable to or somewhat brighter than the Sun, since such a star can produce enough ionizing photons to excite the continuum and emission line spectrum and yet be sufficiently faint as to escape detection by direct observation. The UV continuum is attributed to Balmer recombination from the dense nebula and not to blackbody emission from the hot companion.

Hobbs, R. W.↗

NASA NTRS1981

The diffuse galactic gamma radiation: The Compton contribution and component separation by energy interval and galactic coordinates

The radiation to be expected from cosmic ray interactions with matter and photons was examined. Particular emphasis is placed on the Compton emission. Both the photon density in and near the visible region and that in the region are deduced from the estimates of the emission functions throughout the Galaxy. The blackbody radiation is also included in the estimate of the total Compton emission. The result suggests that the gamma ray Compton radiation from cosmic ray ineractions with galactic visible and infrared photons is substantially larger than previously believed.

Kniffen, D. A.↗

NASA NTRS1980

Repeatable, multiple-peaked structure in Type I X-ray bursts

A distinct, identifiable, multiple-peaked structure has been observed in Type I X-ray bursts from three sources. At energies below 6 keV, the light curves look like typical Type I bursts. At higher energies, the burst is double-peaked, with both the depth of the dip and the separation between the peaks increasing with energy. A light curve of the energy-integrated intensity shows no distinct double peak, suggesting that only a single energy release occurs. Blackbody fits to the evolving burst spectra yield changing radii and temperatures, inversely correlated, during the early part of the burst. The physical interpretation of these changes is uncertain. Burst decay spectra yield relatively constant radii with decreasing temperatures. It is proposed that Compton scattering may be responsible for the dips in the higher-energy light curves by shifting photons to lower energies.

Hoffman, J. A.↗

NASA NTRS1980

Io - Ground-based observations of hot spots

Observations of Io in eclipse demonstrate conclusively that Io emits substantial amounts of radiation at 4.8 and 3.8 micrometers and a measurable amount at 2.2 micrometers. Color temperatures derived from the observations fit blackbody emission at 560 K. The required source area to yield the observed 4.8-micrometer flux is approximately 5 x 10 to the -5th of the disk of Io and is most likely comprised of small hot spots in the vicinity of the volcanoes.

Sinton, W. M.↗