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At least 1,117 records · Page 62
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NASA NTRS1992

Time series observations of O stars. I - IUE observations of variability in the stellar wind of Zeta Puppis

Stellar wind variability in Zeta Pup (O4 I(n)f) is described based on 31 high-resolution IUE observations secured over 5 1/2 days in 1989 April. Extensive changes are evident in the absorption regions of Si IV 1393.76, 1402.77A and N IV 1718.55A P Cygni profiles. Both lines exhibit similar patterns of variability, which are characterized by the development and subsequent blueward migration, of discrete absorption components. The formation of four discrete features is identified over about 2.2 days of intensive observations, with a recurrence time of about 15 hr. The time scales, velocities, and accelerations of the progressive absorption enhancements are determined. These changes are accompanied by fluctuations of up to about 200 km/s in the maximum observed blue edge velocities in saturated C IV and N V P Cygni profiles.

Prinja, R. K.↗
NASA NTRS1992

Rapid oscillations in cataclysmic variables. VIII - YY Draconis (=3A 1148 + 719)

A 16th magnitude cataclysmic variable presumably a dwarf nova, was detected near one of the positions permitted for the hard (2-10 keV) X-ray source 3A 1148 + 719. The optical and UV spectra of YY Dra are fairly typical of cataclysmic variables, except that the TiO absorption bands of an M dwarf can be seen for greater than 5000 A. This shows that the accretion disk is intrinsically faint in quiescence, suggesting a very low accretion rate. Yet the fairly blue continuum slope in the vacuum UV indicates the presence of a small hot object, presumably the white dwarf. The radial velocities at H-alpha indicate a 4.0-hr orbital period, and the IR light curve appears to show the expected 'double-humped' waveform from the distorted secondary. High-speed photometry in the U band reveals a stable periodicity of about 1-percent semiamplitude at a period of 275 s, with some power also in the subharmonic at about 550 s.

Patterson, J.↗
NASA NTRS1992

Estimates of solar variability using the solar backscatter ultraviolet (SBUV) 2 Mg II index from the NOAA 9 satellite

The Mg II core to wing index was first developed for the Nimbus 7 solar backscatter ultraviolet (SBUV) instrument as an indicator of solar variability on both solar 27-day rotational and solar cycle time scales. This work extends the Mg II index to the NOAA 9 SBUV 2 instrument and shows that the variations in absolute value between Mg II index data sets caused by interinstrument differences do not affect the ability to track temporal variations. The NOAA 9 Mg II index accurately represents solar rotational modulation but contains more day-to-day noise than the Nimbus 7 Mg II index. Solar variability at other UV wavelengths is estimated by deriving scale factors between the Mg II index rotational variations and at those selected wavelengths. Based on the 27-day average of the NOAA 9 Mg II index and the NOAA 9 scale factors, the solar irradiance change from solar minimum in September 1986 to the beginning of the maximum of solar cycle 22 in 1989 is estimated to be 8.6 percent at 205 nm, 3.5 percent at 250 nm, and less than 1 percent beyond 300 nm.

Cebula, Richard P.↗
NASA NTRS1992

The upper layer circulation of the Black Sea - Its variability as inferred from hydrographic and satellite observations

Quasi-synoptic hydrographic data and satellite imagery are used to describe the circulation and the structural variability of the Black Sea with particular emphasis on the Turkish coast. The circulation is indicated to involve a variable cyclonic circulation with no apparent central locus and a well-defined cyclonic 'Rim Current' containing meanders and interacting eddy fields confined to the shelf slope. Interspersed between the coastal eddies are filaments and intense jets, often with dipole eddies at their termina. The extension of these features across the shelf-slope into the central basin offshore waters implies important dynamical processes related to the shell-deep basin exchanges. These features are often steered by the topography and evolve continuously through the mixed baroclinic-barotropic instability of the Rim Current.

Oguz, Temel↗
NASA NTRS1992

EC 19314 - 5915 - A bright, eclipsing cataclysmic variable from the Edinburgh-Cape Blue Object Survey

A deeply eclipsing cataclysmic variable, with an orbital period of 4.75 hr, has been discovered in the southern Edinburgh-Cape Blue Object Survey. The star, EC 19314 - 5915, lies close to the positional constraints of a previously unidentified HEAO-1 hard X-ray source, 1H1930 - 5989. Its optical spectrum is unusual in that it shows, apart from the emission lines characteristic of a novalike, or dwarf nova cataclysmic variable (Balmer, He I and He II), metallic absorption lines typical of a late-G star. The individual time-resolved spectra, with the tertiary absorption lines removed, show absorption reversals in the Balmer emission lines, increasing in strength for the higher series. The Balmer emission radial velocities are therefore severely distorted in comparison to the He II 4686-A emission and He I 4471-A absorption radial velocity curves. An independent distance estimate of about 600 pc is derived for EC19314 - 5915, from the spectroscopic parallax of the third star.

Buckley, D. A. H.↗
NASA NTRS1993

Tropical Pacific moisture variability

The research objectives are the following: (1) to describe synoptic scale variability of moisture over the tropical Pacific Ocean and the systems leading to this variability; (2) to implement satellite analysis procedures to accomplish (1); (3) to incorporate additional satellite information into operational analysis/forecast systems at NMC; and (4) to synthesize knowledge gained from satellite observations through diagnosis and numerical models. Significant accomplishments in FY 91/92 are presented and include the following: (1) satellite forecast applications; (2) satellite data analysis; and (3) tropical plume mechanisms.

Mcguirk, James P.↗
NASA NTRS1992

Effect of Personal and Situational Variables on Noise Annoyance: with Special Reference to Implications for En Route Noise

Over 680 publications from 282 social surveys of residents' reactions to environmental noise have been examined to locate 495 published findings on 26 topics concerning non-noise explanations for residents' reactions to environmental noise. This report (1) tabulates the evidence on the 26 response topics, (2) identifies the 495 findings, and (3) discusses the implications for en route noise assessment. After controlling for noise level, over half of the social survey evidence indicates that noise annoyance is not strongly affected by any of the nine demographic variables examined (age, sex, social status, income, education, homeownership, type of dwelling, length of residence, or receipt of benefits from the noise source), but is positively associated with each of the five attitudinal variables examined (a fear of danger from the noise source, a sensitivity towards noise generally, the belief that the authorities can control the noise, the awareness of non-noise impacts of the source, and the belief that the noise source is not important).

Fields, James M.↗
NASA NTRS1993

The SU(2) action-angle variables

Operator angle-action variables are studied in the frame of the SU(2) algebra, and their eigenstates and coherent states are discussed. The quantum mechanical addition of action-angle variables is shown to lead to a noncommutative Hopf algebra. The group contraction is used to make the connection with the harmonic oscillator.

Ellinas, Demosthenes↗
NASA NTRS1992

Pervasive variability in the quiet solar transition region

Extreme UV spectroheliograms from an experimental time series are employed to investigate the nature of the quiet solar transition region with respect to temporal variability. A statistical treatment is developed to analyze the fraction of spatial elements that yield intensity variations significantly higher than the signal noise. The EUV intensity in every spatial resolution varies on a time scale of minutes by about 10-30 percent, and the fractional amplitude of the temporal variations is found to be nearly independent of mean intensity. The paper concludes that the quiet solar transition region is probably generated and modulated by small-scale magnetic activity, since the temporal variability in the transition region is spatially uniform and rather pervasive.

Rabin, Douglas↗
NASA NTRS1992

Analyst variability in labeling of unsupervised classifications

Analyst variability in the labeling of unsupervised classifications is tested for Landsat 5 Thematic Mapper image products covering two test sites in southern California. The accuracy of results are tested using samples from a photo interpreted base map of the area. The significance of differences between analysts is indicated by comparing Kappa statistics derived from error matrices. Analyst variability is found to be statistically significant in most cases. Certain analysts provided consistently better results for a given study area or degree of training. This work demonstrates the potential influence of analyst bias on what would otherwise seem to be a fairly objective method and suggests that controls for this subjectivity should be factored into experimental designs.

Mcgwire, Kenneth C.↗
NASA NTRS1992

Temperature and size variabilities of the Western Pacific Warm Pool

Variabilities in sea-surface temperature and size of the Western Pacific Warm Pool were tracked with 10 years of satellite multichannel sea-surface temperature observations from 1982 to 1991. The results show that both annual mean sea-surface temperature and the size of the warm pool increased from 1983 to 1987 and fluctuated after 1987. Possible causes of these variations include solar irradiance variabilities, El Nino-Southern Oscillaton events, volcanic activities, and global warming.

Yan, Xiao-Hai↗
NASA NTRS1992

Modeling the seasonal variability of a coupled Arctic ice-ocean system

The seasonal variability of the ice-ocean system in the Arctic Basin and the Norwegian, Greenland, and Barents Seas was modeled using a three-dimensional coupled ice-ocean model developed at Princeton University. The snow-ice model uses a three-level thermodynamic scheme similar to Semtner's (1976), but is extended to include the effect of leads. It is shown that simulations using the climatological monthly forcing fields produce a realistic seasonal variability of the ice cover. The ice thickness had a considerable sensitivity to the choice of the long-wave back radiation scheme, but these effects can be reduced through dynamical factors.

Hakkinen, Sirpa↗
NASA NTRS1993

Nongray radiative interactions in entry region flows with variable properties

The entrance region flow between parallel plates is investigated numerically and the variation of fluid properties with temperature is considered. The effect of variable properties for both laminar and turbulent flows is presented. Laminar flows are found to be affected to a larger extent than turbulent flows, as far as the effect of variable properties are concerned.

Krishnamurthy, R.↗
NASA NTRS1993

Rapid oscillations in cataclysmic variables. IX - BG Canis Minoris (=3A 0729+103)

Results of a 10-yr photometric program on BG Canis Minoris, a novalike variable distinguished by the presence of a strictly coherent 913-s wave in its light curve, are presented. Long-term ephemerides for the orbital clock, which manifests itself through a 3.2-h light modulation, and the 913-s clock, are presented. The light curve exhibits a persistent 0.3 mag modulation at a period consistent with the 3.2-h spectroscopic period. Well-distributed timings of the orbital minima prove that the period is 0.1347486 day. It is inferred from the shape of the waveform and from the existence of X-ray dips with a sharp energy dependence that the modulation is caused by absorption. Power spectra of the nightly light curves show variable secondary features, in addition to the regular 913-s pulse. The 913-s period, presumably the first harmonic of the true white-dwarf spin period, is decreasing by 0.0022 s/yr.

Patterson, Joseph↗
NASA NTRS1992

UV variability and the nature of the continuum source in NGC5548

The short-wave UV continuum of NGC5548 varied quasi-periodically during the IUE monitoring from December 1988 to August 1989. The spectral index of this SWP continuum varied in tight correlation with it, inviting comparison with models to search for clues to the physical nature of the continuum source. The observed covariation of spectral index and continuum are consistent with the model of a black body of constant area (that of a sphere the size of Neptune's orbit) but variable temperature ( 18,000K to 25,000 K). A thin accretion disk around a black hole may also be consistent with this data if the accretion rate can be variable on time scales of 100 days while remaining uniform across the disk. There is marginal evidence for hysteresis in which spectral index changes lead changes in the SWP flux, although the CCF peaks at zero time lag.

Stoner, R. E.↗
NASA NTRS1993

A seven-year northern sky survey of Ap stars for rapid variability

A high-speed photometric survey of 120 Ap stars in the northern sky, has been conducted, between 1985 and 1991, in order to search for rapid variability. Stars of spectral types, namely from B8 to F4, have been selected for the survey. The selected pulsational variable stars occupy the hotter regions of the instability strip of the Hertzsprung-Russel diagram. Noted is the absence of pulsations in the hotter B8-A3 Ap stars; this does not, however, preclude the existence of pulsations, since HD 218495 was recently discovered to be a rapidly oscillating Ap (roAp) star. The primary result of this study is that various combinations of photometric indices, while pointing towards roAp stars having the characteristic signatures of cool, SrCrEu stars, still fail to isolate the roAp phenomenon from similar nonpulsating Ap stars. Color-magnitude and color-color diagrams are presented in order to complete this survey.

Nelson, Matthew J.↗
NASA NTRS1993

Sea surface height variability during 1986-1988 in the tropical Pacific Ocean

A description of the sea surface height variabilities during 1986-1988 in the tropical Pacific Ocean is presented on the basis of Geosat altimeter data and a tropical Pacific Ocean GCM (OGCM) forced with observed winds from Florida State University. Both data sets are validated against in situ sea-level measurements at 12 selected sea-level stations in the equatorial Pacific and were found to be in good agreement with these measurements with correlation coefficients of 0.69 for Geosat and 0.71 for OGCM. The Geosat altimeter data are capable of describing sea surface height variabilities during 1986-1988 in the tropical Pacific, in particular, the seasonal cycle, the 1987 El Nino and 1988 La Nina episodes, and the December 1986 equatorial Kelvin wave event. The OGCM-simulated surface dynamic height is found to be sensitive to different surface wind products.

Chao, YI↗
NASA NTRS1993

Prevalent properties of gamma-ray burst variability

With the aim of isolating universal characteristics of gamma-ray burst variability, we compare time histories for 20 bright bursts detected by the Burst and Transient Source Experiment (Fishman et al., 1992). Using an autocorrelation function method, we find that the durations of individual structures within a burst, as well as the burst as a whole, become shorter with increasing energy in most events. We introduce the skewness function, a measure of temporal asymmetry. We find that most bursts exhibit a net skewness, in the sense that the intensity rises more rapidly than it falls. Over short time scales, bursts exhibit no preferred asymmetry. Taken together, these properties suggest that the overall time structure of a burst is due to an explosive phenomenon in which the evolution is initially energetic and rapid and is later slower during a 'cooling' period. We cannot rule out the possibility that short time-scale variability is caused by radiation beams sweeping past the observer.

Link, Bennett↗