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High resolution dynamic spectra of solar emissions in the range 80 to 20 MHz are discussed. The major features of observations described are (1) decametric storms, (2) type 3 bursts, and (3) time profile of type 3 bursts.
The bright visual-wavelength emission lines in spectra of filaments in the Crab Nebula cannot be used to derive unique values for the relative abundances of elements there, even under a simplifying assumption that heating is due entirely to photoionization by the Crab's nonthermal continuum. However, a range of possibilities may be estimated. By mass, helium is more abundant than hydrogen; but the mass fraction of heavier elements may be surprisingly small. Such conclusions are subject to modification if a noticeable fraction of the energy density involves fast particles around 1 MeV.
The observational techniques and results of IR measurements of the minor and trace molecular composition of the lower stratosphere are reviewed. Emphasis is given to those theoretical aspects of the formation of emission and absorption spectra which affect the quantitative interpretation of observational data in terms of the vertical distribution of observed molecular species. The principal experimental techniques currently being used are briefly reviewed, followed by a detailed summary of current knowledge of the abundances and spatial variability of the known minor constituents. The question of the determination of the minimum detectable concentration of a constituent molecule and its relationship to the instrumental parameters, the molecular transition intensities, and observation geometry is discussed; upper limit concentrations are given for some additional species of importance in current stratospheric studies.
A combined analytic and phenomenological approach, utilizing Maxwell's equations in the Born approximation with radiative transfer theory, is used to describe the propagation of microwave intensity in a scattering medium characterized by three-dimensional random fluctuations in refractive index, as well as nonrandom variations in permittivity, temperature, and loss. This approach yields microwave intensities as a function of polarization, direction, and position. Numerical techniques are presented to solve the transport equations, which include cases of spatially varying coefficients, and highly peaked phase functions. Some computed results illustrating the behavior of microwave intensity in various media are presented. Included are the angular and frequency spectra of thermal emission from semi-infinite media, and the diffuse transmission and reflection response of a scattering layer. The effects of scatterer geometry and scale sizes; correlation function; and gradients in temperature, loss, and scattering parameters are also demonstrated. This model should be particularly useful in interpreting active and passive remote sensing data.
Data for the stability of thin conductive indium tin oxide films on 0.003 inch thick Kapton substrates during exposure of the surface to electron beams are reported. The electron beam energy was 3 keV and the diameter was about 0.8 mm. Thermal effects and surface modifications are considered. For primary current greater than 0.6 microamperes, an obvious dark discoloration with diameter approximately that of the beam was produced. The structure of the discolored region was studied with the scanning electron microscope, and the findings are stated. Surface modifications were explored by AES, obtaining spectra and secondary emission coefficient as a function of time for different beam intensities. In all cases beam exposure results in a decrease of the secondary yield but because of thermal effects this change, as well as composition changes, cannot be directly interpreted in terms of electron beam dosage.
The thermal synchrotron (TS) interpretation of gamma-ray burst continuum spectra requires an emission region which is hot, optically thin, and possessed of a super-Eddington flux of 10 to the 30 ergs/sq cm per sec for a 10-km neutron star. In order to maintain a pair population close to the Maxwellian, the collision excitation rate into higher Landau levels must exceed the cyclotron decay rates. Even if collective processes whose rates are close to the electron plasma frequency, or scattering by heavy ions, are invoked, a particle density of 10 to the 25th/cu cm is still needed. Both hypotheses point in the direction of a dense but thin emitting sheet, to whose structure attention is presently given together with the generation, propagation and coupling of the electromagnetic energy fluxes. A flare-like model can account for most of gamma ray bursts' general features.
The chemical composition, emission and line spectra, and structure of comet nuclei, cometary atmospheres, and comet tails are discussed. The role of ultraviolet and infrared astronomy in defining comets is examined.
Two X-ray emitting cataclysmic variables were discovered as a result of a program to identify faint X-ray sources located by the HEAO-A3 modulation collimator experiment. The objects, H0534-581 and 1H0542-407, have similar high excitation spectra with intense emission lines showing broad and narrow components. Photometry shows that H0534-581 and 1H0542-407 have average magnitudes of V=14.9 and 15.7 respectively, leading to Lx/Lopt ratios of 1.5 (typical of dwarf novae in quiescence). While pronounced variability of delta B or = 1.5 mag is observed from both systems, there is no clear evidence for repeatable orbital periods between 1 and 4 hr.
A field portable spectrometer suitable for collecting data relevant to remote sensing applications in the 8 to 12 micrometer atmospheric window has been built at the Jet Propulsion Laboratory. The instrument employs a single cooled HgCdTe detector and a continuously variable filter wheel analyzer. The spectral range covered is 5 to 14.5 micrometers and the resolution is approximately 1.5 percent of the wavelength. A description of the hardware is followed by a discussion of the analysis of the spectral data leading to finished emissivity and radiance spectra. A section is devoted to the evaluation of the instrument performance with respect to spectral resolution, radiometric precision, and accuracy. Several examples of spectra acquired in the field are included.
Interference filters centered at 0.365, 0.387, 0.406, 0.484, and 0.514 microns have been selected to represent UV continuum, CN emission, C3 emission, blue continuum, and C2 emission in cometary spectra, respectively. Adopted magnitudes and colors of this filter system are presented for 50 standard stars, ranging in bue magnitude from 4 to 12, in spectral type from O to K, and distributed primarily around equatorial regins of the sky. The tabulated uncertainties are generally of the order of 0.02 mag or smaller; the zero points of the photometric system are chosen so that blue continuum magnitudes are approximately equivalent to Johnson B, and so that color indices average zero for solar analog stars.
A search for white dwarf companions of MS-type stars was conducted, using IUE. The overendowments of these stars in typical S-process nuclides suggest that they, like the Ba II stars, may owe their peculiar compositions to earlier mass transfer. Short-wavelength IUE spectra show striking emission line variability in HD35155, HD61913, and 4 Ori; HD35155 and 4 Ori show evidence of white dwarf companions.
A field portable spectrometer has been built at the Jet Propulsion Laboratory which is suitable for collecting data relevant to remote sensing applications in the 4.7- to 5.6- and 8- to 12-micrometer atmospheric windows. The instrument employs a single cooled HgCdTe detector and a continuously variable filter wheel analyzer. The spectral range covered is 5- to 14.5-micrometers and the resolution is approximately 1.5 percent of the wavelength. A description of the hardware is followed by a discussion of the data processing steps leading to emissivity and radiance spectra. A section is devoted to the evaluation of the instrument performance with respect to spectral resolution, radiometric precision, and accuracy. Several examples of spectra acquired in the field are included.
The first phase-resolved IUE observations of the AM Herculis system E1405-451 is reported. The spectra show bright emission lines from N V, C IV, and He II, whose centroids vary drastically during the 101.5 minute period. The radial velocities measured from the line centroids show a sinusoidal variation with a semiamplitude of 300 km/s. An explanation for the observed emission line velocities is considered using a model for the system having inclination i = 60 deg and magnetic colatitude Delta = 20 deg.
Simultaneous observations of the AM Her type variable H0538+608 made with IUE, EXOSAT, and a 1.3 m ground based telescope, and subsequent optical spectrophotometry at high and low resolution are discussed. The X-ray and optical data show clear evidence of a 3.30 + or - 0.03 hr period. Three SWP spectra were taken outside of eclipse and during overlapping phase intervals. The UV spectra contain strong emission lines characteristic of this class of objects and a flat continuum which appears to be deficient, given the brightness of source at optical and X-ray wavelengths. There is evidence for intensity variations in emission lines, particularly C IV. The X-ray light curves for H0538+608 reveal behavior which may be related to irregularities in its accretion flow.
A large sample of type II events is the basis of the present study of the properties of interplanetary type II bursts' radio-emission properties. Type II spectra seem to be composed of fundamental and harmonic components of plasma emission, where the intensity of the fundamental component increases relative to the harmonic as the burst evolves with heliocentric distance; burst average flux density increases as a power of the associated shock's average velocity. Solar wind density structures may have a significant influence on type II bandwidths.
Determinations have been made of concentration profiles of HOCl in the earth's stratosphere, including the diurnal variation. Measurements of the rotational Q2 branch at 99.5/cm and of five RR(J3) transitions between 143 and 159/cm were made using far-infrared thermal emission spectroscopy. The spectra were obtained during a balloon flight of the FIRS 2 far-infrared Fourier-transform spectrometer and telescope from Palestine, Texas on May 12-13, 1988. From these measurements, altitude profiles of HOCl from 23 to 42 km are obtained. Daytime and nighttime average profiles of HOCl, as well as measurements on a 30-min time scale through the sunset transition at a single (35 km) altitude are presented. The measured profiles are lower than the current predictions from several modeling groups by a factor of approximately 0.6.
The Arecibo 305 m telescope has been used to observe radio bursts from flare stars at 430 and 1415 MHz. Dynamic spectra of the emission with bandwidths of 10 MHz in the former case and 40 MHz in the latter are recorded. For AD Leo, the microwave burst emission was 100 percent right circularly polarized, achieved brightness temperatures near 10 to the 16th K, was generally broadband in character, but was superposed with finite structures in both frequency and time. Quasi-periodic pulsations were clearly present as well as a sudden reduction feature. For YZ CMi, the emission was 100 percent left circularly polarized and was relatively broadband with fine structures. Instabilities driven by anisotropies in the electron distribution, particularly the loss-cone distribution, are considered to account for the coherent radiation.
The results of observations of 22 bright Galactic X-ray point sources are presented, and the most reliable measurements to date of X-ray column densities to these sources are derived. The results are consistent with the idea that some of the objects have a component of column density intrinsic to the source in addition to an interstellar component. The K-edge absorption due to oxygen is clearly detected in 10 of the sources and the Fe L and Ne K edges are detected in a few. The spectra probably reflect emission originating in a collisionally excited region combined with emission from a photoionized region excited directly by the central source.