Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “photometric”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Photometric analysis of a space shuttle water venting

Presented here is a preliminary interpretation of a recent experiment conducted on Space Shuttle Discovery (Mission STS 29) in which a stream of liquid supply water was vented into space at twilight. The data consist of video images of the sunlight-scattering water/ice particle cloud that formed, taken by visible light-sensitive intensified cameras both onboard the spacecraft and at the AMOS ground station near the trajectory's nadir. This experiment was undertaken to study the phenomenology of water columns injected into the low-Earth orbital environment, and to provide information about the lifetime of ice particles that may recontact Space Shuttle orbits later. The findings about the composition of the cloud have relevance to ionospheric plasma depletion experiments and to the dynamics of the interaction of orbiting spacecraft with the environment.

Viereck, R. A.↗
NASA NTRS1991

Photometric geodesy of main-belt asteroids. IV - An updated analysis of lightcurves for poles, periods, and shapes

The Drummond et al. (1988) analysis of main-belt asteroids is presently extended, using three independent methods to derive poles, periods, phase functions, and triaxial ellipsoid shapes from lightcurve maxima and minima. This group of 26 asteroids is also reinvestigated with a view to the distributions of triaxial shapes and obliquity distributions. Poles weakly tend to avoid asteroid orbital planes; a rough-smooth dichotomization appears to be justified by the persistence of two solar phase angle-amplitude relations. Seven of the objects may be Jacobi ellipsoids if axial ratios are slightly exaggerated by a systematic effect of the analytical method employed.

Drummond, J. D.↗
NASA NTRS1991

The photometric roughness of Ariel is not unusual

Voyager 2 images of the Uranian satellite Ariel are reanalyzed, with a focus on the large-scale roughness parameter theta-bar. The techniques used to reduce the data and fit the Hapke parameters are described, and the results are presented in tables and graphs. Using the whole-disk phase curve, theta-bar of 27 + or - 1 deg is obtained, somewhat higher than but in good general agreement with the values for the other Uranian satellites. The anomalously high value (42 deg) found by Helfenstein et al. (1988) is attributed to miscalibration of the clear-filter image for phase angle 144.7 deg.

Skypeck, A.↗
NASA NTRS1991

Photometric binary stars in Praesepe and the search for globular cluster binaries

A radial velocity study of the stars which are located on a second sequence above the single-star zero-age main sequence at a given color in the color-magnitude diagram of the open cluster Praesepe, (NGC 2632) shows that 10, and possibly 11, of 17 are binary systems. Of the binary systems, five have full amplitudes for their velocity variations that are greater than 50 km/s. To the extent that they can be applied to globular clusters, these results suggests that (1) observations of 'second-sequence' stars in globular clusters would be an efficient way of finding main-sequence binary systems in globulars, and (2) current instrumentation on large telescopes is sufficient for establishing unambiguously the existence of main-sequence binary systems in nearby globular clusters.

Bolte, Michael↗
NASA NTRS1991

Ganymede and Callisto - Surface textural dichotomies and photometric analysis

Complete solar phase curves of the Ganymede and Callisto leading and trailing hemispheres, which have been obtained by reducing Voyager imaging observations and combining them with ground-based telescopic data, are presently fit to scattering models in order to derive hemispherical values of the single scattering albedo, the single particle phase function (SPPF), the compaction state (CS) of the optically active portion of the regolith, and the mean slope angle of macroscopic features. While Callisto's leading side is composed of particles that are more strongly backscattering than the trailing side, no hemispheric differences are found in the CS, surface roughness, or SPPF.

Buratti, Bonnie J.↗
NASA NTRS1991

Comet Levy (1990c) - Groundbased photometric results

Emission bands of OH, NH, CN, C3, and C2 have been isolated, together with continuum points at 3650 and 4845 A, by narrowband filter photometry of Comet Levy; all species are noted to exhibit strong asymmetry near perihelion, in association with production rates for most species that are about twice as large before perihelion as after it in the 1-3 AU distance range. The asymmetry of the OH production rate was almost double that of the other species, and exhibited maximum production over a month before other species.

Schleicher, David G.↗
NASA NTRS1992

Photometric variability of Charon at 2.2 microns

Pluto-Charon images obtained on each of four nights at 2.2, 1.2, and 1.7 microns are presently fitted by a two-source image model in which the position of Charon and the ratio of its signal to that of Pluto are free parameters. At 2.2 microns, Charon is fainter than Pluto by magnitudes which, when combined with Pluto-Charon system photometry, yield apparent magnitudes of 15.01 + or - 0.08 for Charon at 0.06 lightcurve phase and 15.46 + or - 0.05 at lightcurve phase 0.42. In view of these results, Charon is variable in this filter bypass due to geometric albedo changes as a function of longitude.

Bosh, A. S.↗
NASA NTRS1992

A photometric survey of outer belt asteroids

Since 1989, we have been conducting a research program devoted to the study of the Trojans and outer belt asteroids (Hilda and Cybele groups), in order to characterize their rotational properties and shapes. As an outcome of several observational campaigns, we determined rotational periods and lightcurve amplitudes for 23 distant asteroids, using both CCD and photoelectric photometry. In this paper, we compare the rotational properties of main belt asteroids and Trojans, based on the preliminary results of this survey.

Dimartino, M.↗
NASA NTRS1992

0.7- to 23-micron photometric observations of P/Halley 2986 III and six recent bright comets

Infrared photometry over 0.7-23 micron range is presented for P/Halley 1986 III and six other recent bright comets. It is concluded that comets can be classified by their thermal infrared energy distributions. IR Type I comets have low continuum superheat and the 10-micron silicate emission is muted or absent. IR Type II comets have large continuum superheat and strong silicate emission features. Simultaneous measurements of P/Halley and Bradfield 1980 XV are generally consistent with the steady-state model for nuclear ablation. P/Halley's dust coma had an average albedo of 0.20 at a scattering angle of 130 deg. The correlation between superheat and 20-micron silicate excess, the flattened forward-scattering peak of the albedo curve, and the relatively low backscattering albedo are all consistent with laboratory and theoretical results for nonspherical and fluffy grains. The results appear to be especially consistent with core-mantle grain models such as those proposed by Greenberg and Hage (1989).

Gehrz, R. D.↗
NASA NTRS1992

Periodic photometric variability of the black hole binary V404 Cygni

Periodic variations of V404 Cyg having a period of 6.474 +/- 0.005 d with a full amplitude of 0.2 mag were discovered with CCD photometry, in the I band, of the compact star. The light curve consists of two maxima and two minima per cycle, and the shape suggests that it is due to ellipsoidal variations of the secondary star which is tidally distorted by the presence of the massive compact object. It is proposed that the secondary is a 1 solar mass K0 IV star with MV of about 2.5 mag at a distance of about 3.5 kpc. It is suggested that if the secondary star is nearly filling its Roche lobe, then the orbital inclination must be about 60 deg. If the inclination is as high as 80 deg, then the secondary star fills about 90 percent of the Roche lobe. These limits imply a compact star mass of 8-12 solar masses and thus strengthen the evidence that the compact star is extremely massive and possibly a black hole.

Wagner, R. M.↗
NASA NTRS1993

A spectroscopic and photometric study of FK Comae in 1989

Results of an observational campaign, coordinated between visual photometry, optical spectroscopy, and UV spectroscopy, to elucidate the characteristics of FK Comae are presented. The photometry showed complicated but systematic behavior. Photospheric absorption lines were distorted by a Doppler-shifted bump caused by dark starspots resulting in small apparent radial velocity variations. No radial velocity variations characteristic of orbital motion were seen to a level of 3 km/s. Broad emission in H-alpha was modulated at the photospheric rotational amplitude, implying an origin no farther from the rotational axis than 1 stellar radius. The strengths of Ca II lines are modulated in phase with H-alpha but do not have velocity-modulated wings like H-alpha.

Huenemoerder, David P.↗
NASA NTRS1993

Photometric calibration of NGS/POSS and ESO/SRC plates using the NOAO PDS measuring engine. II - Surface photometry

In this paper we present a method to calibrate surface photometry of faint sources measured from direct photographic plates, such as those of the NGS/POSS and ESO/SRC Sky Survey. This calibration procedure does not require scanning sensitometer spots on the plates, but instead uses measurements of the brightness profiles of many faint stars of known brightness to fit a linearized approximation to the characteristic curve. The approximation is valid for only low- to medium-density emulsions, so this technique is appropriate only for relatively faint emission. Comparison between measurements of representative extended sources on the NGS/POSS and CCD images indicates that surface photometry can be obtained from the Sky Survey plates accurate to 0.1-0.3 mag in the range mu(B) between 23 and 27 and mu(R) between 22 and 26 mag/sq arcsec.

Cutri, Roc M.↗
NASA NTRS1993

Photometric and spectroscopic observations of 5145 Pholus

Light curve observations carried out in January and February 1992 are presented. We find an amplitude of 0.2 magnitude and a period of 0.4157 day. Fine structures of the light curve and their variability with time are discussed in terms of the changing phase angle and deviations of the object's shape from a regular ellipsoid. The present orbital and physical properties alone for 5145 Pholus do not provide a clue for either a cometary or an asteroidal origin. It seems to have properties in common with both and thus could form a bridge between these two groups.

Hoffmann, Martin↗
NASA NTRS1992

Multiperiodicities in the photometric variability of RS CVn binaries - What we know after 15 years

An overview of the behavior of the RS CVn binaries is presented. It is argued that chromospherically active stars vary in brightness on a variety of different time scales, each involving very different physics. Some of them are literally periodic, some are quasi-periodic or cyclical, and some can be described only in terms of a time scale. Connections between some of the different periods, cycles, and time scales are explained. Attention is given to orbital period, rotation period, migration, spot lifetimes, magnetic cycles and flares.

Hall, Douglas S.↗
NASA NTRS1993

The quality of photometric information in the Hipparcos Input Catalog

Comparison with independent photoelectric photometry is used to assess the quality of magnitudes and colors in the Hipparcos Input Catalog. These magnitudes and colors will play an important role in the luminosity calibration of Hipparcos stars. We conclude that photoelectric photometry, available for about 37 percent of the catalog, is of uniformly good quality, and the error estimates in the Catalog are very accurate. On the other hand, colors determined from poor spectral classes suffer from very significant errors, also correctly estimated in the Catalog, which make them essentially unsuited for the purpose of luminosity calibration. Only stars with either photoelectric colors or good 2D spectral classes can be used in a high-accuracy luminosity calibration.

Casertano, Stefano↗
NASA NTRS1992

Photometric calibration of the International Ultraviolet Explorer (IUE) at low resolution - The LWP camera

We present and discuss the low resolution absolute calibration for the LWP camera of the International Ultraviolet Explorer (IUE). The calibration, implemented in routine processing of LWP low resolution images on December 22, 1987 at both GSFC and VILSPA IUE ground stations, is based on the last set of Intensity Transfer Function (ITF 2) obtained in September 1984 and on a substantially larger amount of IUE observations of standard stars than used for the preliminary calibration by Cassatella & Harris (1983) based on the earlier ITF (ITF 1). The new ITF and the associated calibration provide upgraded performances in flux accuracy, signal-to-noise ratio and linearity with respect to the earlier LWP ITF1 which was implemented in processing LWP data obtained in the period from October 16, 1983 until December 21, 1987.

Cassatella, A.↗
NASA NTRS1993

A study of the contrast of sunspots from photometric images

The thermal contrast alpha, and the umbra-penumbra A(u)/A(p) were calculated for 63 sunspots of various sizes and morphologies. Results show that values of alpha ranged from 0.1807 to 0.4266 and A(u)/A(p) ranged from 0.0089 to 0.4899. The values of thermal contrast and umbra-penumbra were compared with complexity ratings, magnetic field strength, and time factors and found to be independent of these parameters.

Beck, John G.↗