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At least 145 records · Page 8

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NASA NTRS1981

Accretion disk coronae

Recent observations of partial X-ray eclipses from 4U1822-37 have shown that the central X-ray source in this system is diffused by a large Compton-thick accretion disk corona (ADC). Another binary, 4U2129-47, also displays a partial eclipse and contains an ADC. The possible origin of an ADC is discussed and a simple hydrostatic evaporated ADC model is developed which, when applied to 4U1822-37, 4U2129+47 and Cyg X-3, can explain their temporal and spectral properties. The quasi-sinusoidal modulation of all three sources can be reconciled with the partial occultation of the ADC by a bulge at the edge of the accretion disk which is caused by the inflowing material. The height of this bulge is an order of magnitude larger than the hydrostatic disk height and is the result of turbulence in the outer region of the disk. The spectral properties of all three sources can be understood in terms of Compton scattering of the original source spectrum by the ADC. Spectral variations with epoch in Cyg X-3 are probably caused by changes in the optical depth of the corona. A consequence of our model is that any accreting neutron star X-ray source in a semi-detached binary system which is close to its Eddington limit most likely contains an optically thick ADC.

White, N. E.↗

NASA NTRS1982

Radar investigation of asteroids

The dual polarization CW radar system which permits simultaneous reception in the same rotational sense of circular polarization as transmitted (i.e., the "SC" sense) and in the opposite ("OC") sense, was used to observe five previously unobserved asteroids: 2 Pallas, 8 Flora, 22 Kalliope, 132 Aethra, and 471 Papagena. Echoes from Pallas and Flora were easily detected in the OC sense on each of several nights. Weighted mean echo power spectra also show marginally significant responses in the SC sense. An approximately 4.5 standard deviation signal was obtained for Aethra. The Doppler shift of the peak is about 10 Hz higher than that predicted from the a priori trial ephemeris. Calculations are performed to determine whether this frequency offset can be reconciled dynamically with optical positions reported for Aethra.

Ostro, S. J.↗

NASA NTRS1982

The absence of rapid X-ray variability in active galaxies

Variations on time scales ranging from minutes to several hours in the X-ray flux from 54 observations of 38 active galaxies are identified. The sample is composed mostly of Seyfert I galaxies but also includes radio galaxies, NELG's BL Lacs and 3C 273. Only NGC 6814 varied on time scales as short as 100 sec. No other source was observed to vary with a time scale of less than 12 hours. Large amplitude short term variations are not a characteristic of the X-ray emission from active galaxies. Upper limits on sigma sub I/I ranged from 2% for Cen A, 5% for NGC 4151, to approximately 20% for sources giving 1 ct/sec in the detector. Three objects NGC 3227, NGC 4151 and MCG 5-23-16 show variability consistent with a time scale of approximately 1 day. Ways to reconcile the rapid variability seen for NGC 6814 (and NGC 4051) with the general stability observed for the other objects are considered.

Tennant, A. F.↗

NASA NTRS1982

Microwave and hard X-ray observations of a solar flare with a time resolution of better than 100 MS

Simultaneous microwave and X-ray observations are presented for a solar flare detected on 1980 May 8 starting at 1937 UT. The X-ray observations were made with the Hard X-Ray Burst Spectrometer on the Solar Maximum Mission and covered the energy range from 28-490 keV with a time resolution of 10 ms. The microwave observations were made with the 5 and 45 foot antennas at the Itapetinga Radio Observatory at frequencies of 7 and 22 GHz, with time resolutions of 100 ms and 1 ms respectively. Detailed correlation analysis of the different time profiles of the event show that the major impulsive in the X-ray flux preceded the corresponding microwave peaks at 22 GHz by about 240ms. For this particular burst the 22 GHz peaks preceded the 7 GHz by about 1.5s. Observed delays of the microwave peaks are too large for a simple electron beam model but they can be reconciled with the speeds of shock waves in a thermal model.

Kaufmann, P.↗

NASA NTRS1982

The relevance of the IUE results on young stars for Earth's paleoatmosphere

Using the latest IUE results for seven T Tauri stars, which are believed to represent the young Sun and a detailed photochemical chemical model of the paleoatmosphere, the vertical distribution of Oxygen and Ozone in the early atmosphere was calculated. The calculations indicate that the surface Oxygen mixing ratio is as much as six orders of magnitude larger than previously estimated, but appears low enough for the formation of amino acids via the Urey-Miller type of experiments. It is believed that the quantification of the oxygen level in the Earth's paleoatmosphere presented can reconcile the demands of both biological and geological considerations.

Canuto, V. M.↗

NASA NTRS1980

Flow behavior of droplet chondrules in the Manych /L-3/ chondrite

The Manych (L-3) chondrite contains chondrules that have radically different thermal histories. The high-SiO2 composition cooled at about 1 K/min to a glassy state or more slowly to form a variety of fractions of crystals. The low-SiO2 composition cooled at about 3000 K/min to form a glassy coating or much more slowly to form microporphyry. The extreme range of cooling rates displayed by objects in the Manych chondrite is difficult to reconcile with a model involving droplet condensation at low pressure which provides a uniform temperature, a uniform cooling rate, and an ambient that is not necessarily cold. The experimental results presented here are interpreted to mean that the origin of the chondrules is likely a result of impact melting because of the range of cooling histories represented in the chondrite.

Klein, L. C.↗

NASA NTRS1982

On the three-dimensional magnetic structure of the plasmoid created in the magnetotail at substorm onset

The magnetic field in the plasmoid which is created by the reconnection of magnetic field lines at a neutral line formed in the near-earth region of the plasma sheet at substorm onset, and which flows out of the magnetotail into the magnetosphere's wake, displays a strong positive or negative Y(SM) component that has been difficult to reconcile with the standard, two-dimensional reconnection geometry. It is shown that this deviation of the magnetic field is a manifestation of the newly-reconnected field line loop's draping toward the tail's central or midnight meridian, and that the draping is a consequence of the three-dimensional plasma flow associated with the reconnection process.

Hones, E. W., Jr.↗

NASA NTRS1982

Ultraviolet continuum absorption /less than about 1000 A/ above the quiet sun transition region

Lyman continuum absorption shortward of 912 A in the quiet sun solar transition region is investigated by combining spectra obtained from the Apollo Telescope Mount experiments on Skylab. The most recent atomic data are used to compute line intensities for lines that fall on both sides of the Lyman limit. Lines of O III, O IV, O V, and S IV are considered. The computed intensity ratios of most lines from O IV, O V, and S IV agree with the experimental ratios to within a factor of 2. However, the discrepancies show no apparent wavelength dependence. From this fact, it is concluded that at least part of the discrepancy between theory and observation for lines of these ions can be accounted for by uncertainties in instrumental calibration and atomic data. However, difficulties remain in reconciling observation and theory, particularly for lines of O III, and one line of S IV. The other recent results of Schmahl and Orrall (1979) are also discussed in terms of newer atomic data.

Doschek, G. A.↗

NASA NTRS1982

The coronal field lines of an evolving bipolar magnetic region

A simple potential field model is presented to illustrate that loops of magnetic flux rise upward through the corona during the relatively short growth phase of a bipolar magnetic region but contract back to the sun's surface during the much longer decay phase of the photospheric region. To reconcile this behavior with the unidirectional, solar-wind-driven convection of flux outward from the sun, one must postulate the existence of an X-type neutral line in the middle corona where open field lines can be converted back to closed ones.

Sheeley, N. R., Jr.↗

NASA NTRS1982

UV radiation from the young sun and oxygen and ozone levels in the prebiological palaeoatmosphere

UV measurements of young T-Tauri stars, resembling the sun at an age of a few million years, have recently been made with the International Ultraviolet Explorer. They indicate that young stars emit up to 10,000 times more UV than the present sun. The implications for the origin and evolution of O2 and O3 in the prebiological palaeoatmosphere are presented here. The results of photochemical calculations indicate that the O2 surface mixing ratio was a factor 10,000-1,000,000 times greater than the standard value of 10 to the -15. This new value reconciles the simultaneous existence of oxidized iron and reduced uranium.

Canuto, V. M.↗

NASA NTRS1982

The polar ionosphere

Self-consistent concepts which in many cases demonstrate the required relationships between electric currents, conductivity and electric fields are emerging from International Magnetospheric Study period research on the polar ionosphere and its role in the coupling between the ionosphere and the magnetopause. Observed phenomena may now be explained in terms of realistic variations in the electric current, conductivity and electric field parameters, and the distribution and composition of plasma can be reconciled with large scale plasma motion and ion production regions. Gaps remain, however, in the current understanding of the polar ionosphere's electrodynamic and plasma properties.

Heelis, R. A.↗

NASA NTRS1982

Chronic central vascular expansion induces hypokalemia in conscious primates

Central vascular expansion maintained for four days in conscious squirrel monkeys reconciles the apparently conflicting short-term fluid and electrolyte responses to water immersion and atrial balloon distension, with those described for prolonged weightlessness during space flight. The monkeys are subjected to an increased lower body positive air pressure (LBPP) of 20 torr which produces a 3 cm water increase in the central venous pressure. Results show a marked increase in the urinary excretion of sodium, potassium, and water during the firxt six hours of LBPP, and the diuresis is maintained throughout the period of LBPP, although the levels of sodium and potassium excretion decline after 24 hours of exposure. Plasma aldosterone transiently drops within the first three hours of LBPP, and then regains normal levels within 24 hours, after which time these levels are maintained despite the continued LBPP stimulus. It is suggested that the normal plasma aldosterone levels observed in the experiments, as well as during space flight, might, epresent a relative hyposecretion in terms of volume homeostasis and a relative hypersecretion with respect to plasma potassium regulation. Thus, kaliuresis and marked natriuresis is confined primarly to the first 24 hours of central volume expansion, a period for which comparable data from space flights are lacking.

Moore-Ede, M. C.↗

NASA NTRS1982

Sulfuric acid vapor and other cloud-related gases in the Venus atmosphere - Abundances inferred from observed radio opacity

It is suggested that the absorbing characteristics of sulfuric acid vapor appear to reconcile what had been thought to be an inconsistency among measurements and deductions regarding the constituents of the Venus atmosphere and radio occultation, radar reflection, and radio emission measurements of its opacity. Laboratory measurements of sulfuric acid, sulfur dioxide, water vapor, and carbon dioxide are used to model relative contributions to opacity as a function of height in a way that is consistent with observations of the constituents and absorbing properties of the atmosphere. It is concluded that sulfuric acid vapor is likely to be the principal microwave absorber in the 30-50 km altitude range of the middle atmosphere of Venus.

Steffes, P. G.↗

NASA NTRS1982

Adsorption and excess fission Xe - Adsorption of Xe on vacuum crushed minerals

It is hypothesized that adsorption is not likely to provide a sufficiently precise mechanism for the concentration of excess fission Xe in the entire lunar regolith, in view of laboratory analogs of the lunar soil and calculations of the residence times of noble gases in the present day regolith. Lunar cold trap and episodic degassing models are difficult to reconcile, however, with the generality of excess fission Xe in all gas-rich highland breccias. It is concluded that the high Xe concentration in such highland breccias is not the result of Xe adsorption prior to the trapping of this component.

Bernatowicz, T. J.↗

NASA NTRS1982

The atmospheres of Io and other satellites

Voyager measurements of gaseous SO2 in a hot spot region and of ions of sulfur, oxygen, and SO2(+) in the plasma torus, combined with the groundbased measurements of SO2 frost on the surface, indicate that SO2 is perhaps the dominant constituent of Io's atmosphere. Indeed the ionosphere of Io can be sustained by a pure SO2 atmosphere in thermal equilibrium with the surface. Upper limits on common volatiles H2O, CO2, NH3, and CH4 and exceedingly small, although S2 and Ar may still be present. Photochemistry of SO2 could lead to O2 as the major gas on the night side. Reasonable processes for loss to the torus include thermal escape, sputtering, and sweep-up of ions. The symmetry of the sodium cloud between eastern and western elongation is difficult to reconcile with any substantial, diurnally varying atmosphere. Europa, Ganymede, and Callisto may have oxygen atmospheres resulting from photolysis of water vapor. A pressure of approximately 10 to the -6th microbar is predicted, consistent with the Voyager upper limit for Ganymede. A much higher pressure might be present if the water vapor pressure is increased by a low albedo (Callisto) or sputtering (Europa).

Kumar, S.↗

NASA NTRS1983

Infrared photometry of O stars

The results of a survey of 50 O stars in the J, H, K, L, and M bands are described. The observations are described, and the fitting of reddening relations to them is discussed. The zero points in the reddening relations are related to the intrinsic colors of the samples of normal stars, and these are compared with theoretical colors. The comparison reveals anomalies at L and M, which are discussed. The residuals for an individual star from the reddening relations are a measure of its infrared excesses, if indeed it has any. How the excesses can be fitted to a stellar wind model to derive a parameter that involves the rate of mass loss in the wind, the stellar radius and temperature, and wind terminal velocity is considered. The results for a number of individual stars are discussed and compared with other mass loss measurements, and it is concluded that no single model is capable of reconciling the IR, UV, radio, and H-alpha observations for the stars.

Castor, J. I.↗

NASA NTRS1983

Thermal infrared constraints on ammonia ice particles as candidates for clouds in the atmosphere of Saturn

Saturn atmosphere thermal IR emission observations have uncovered two phenomena that may be accounted for by large ammonia ice particles: the depression of thermal brightness near the equator, and inconsistent IR and radio occultation results. Ammonia ice particles yield the opacity that can account for the contrast between the equatorial region and a brighter area near 15 deg S, and may also reconcile the 45-micron brightness of these two regions with the mean temperature structure of Voyager 2 radio occultation results. A cloud model whose ice particles are distributed in an equal ratio with gas particles up to the 100 mbar pressure level is found to fit the equatorial data, while a thinner cloud, or one that does not extend higher than the 400 mbar limit of the convective region matches the 15 deg S data.

Orton, G. S.↗

NASA NTRS1983

A second-order effect of stratospheric vertical motions

A byproduct of stratospheric motion distinct from the normal downgradient transport represented by vertical eddy diffusion is studied. It is suggested that an air parcel executes a random walk over a range that could be several kilometers, and similar amplitudes could be present in wavelike oscillations. The photochemical loss rate should therefore be averaged over this range, which give an effect that is proportional to the curvature of the profile of loss rate, and is particularly large for fluorocarbon-11, CFCl3. Test computations are presented which indicate that the known discrepancy between observations and predictions for this compound can be at least partly reconciled for plausible values of the amplitude.

Hunten, D. M.↗