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Harris, A. W.

Publications and source records attributed to Harris, A. W..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Asteroid lightcurve observations from 1979-1981

An account is given of the results of photometric light curve observations in the V band for asteroids, yielding estimates of the mean and maximum reduced magnitudes for each object. On the basis of fits of the H-G magnitude relation for 33 objects, the mean values of the slope parameter are examined for different taxonomic classes; these values are then applied to the analysis of less complete data sets. While in the case of the moderate albedo S and M class asteroids the H-G relation appears to fit the available data, the relation for dark asteroids appears to predict more of an opposition than is characteristically present.

Harris, A. W.↗
NASA NTRS1989

Phase relations of high albedo asteroids - The unusual opposition brightening of 44 Nysa and 64 Angelina

The present photoelectric lightcurve observations of 44 Nysa at one aspect, and 64 Angelina at both polar aspects, indicate the presence of an opposition spike or brightening of approximately 0.25 mag within several deg of zero-phase angle. Since the three curves are identical within the bounds of observational scatter, the opposition spike cannot be judged anomalous within the asteroid taxonomic class E. The general similarity of the observed phase curves to those of the Uranian satellites and the rings of Saturn supports the status of the spike as an ordinary property of moderate-to-high albedo atmosphereless surfaces.

Harris, A. W.↗
NASA NTRS1989

The diameter, shape, albedo, and rotation of 47 Aglaja

Observations of the September 16, 1984 occultation of SAO 146599 by the C-type asteroid 47 Aglaja from 13 sites in the continental U.S. have yielded a diameter of 136.4 + or - 1.2 km, leading to the calculation of a rotational period of 13.2 + or - 0.01 hr. At the time of the occultation, the zero-phase-angle visual geometric albedo of the asteroid's phase was 0.071 + or - 0.002. It is suggested that a substantial portion of the object's mean brightness variation with ecliptic longitude is ascribable to albedo differences over its surface.

Millis, R. L.↗
NASA NTRS1989

The puzzling case of asteroid 8 Flora solved

This paper reports the results obtained in an international campaign devoted to the observations of the asteroid 8 Flora, a possible target of the Vesta mission. Using the lightcurves obtained during three oppositions (1980, 1983, 1984), a synodic rotational period of 12.87 hours was determined. This period, applied to the lightcurves of 8 Flora already published, satisfactorily explains these observations. Applying the AM-method described by Zappala et al. (1983), the pole position was calculated. The slope parameter G, determined during the 1969 and 1983 apparitions, differs by about 0.10. Considering that in those years the ecliptic longitudes of the asteroid were about 115 degrees apart, this fact probably indicates the presence of variations in the structure and chemical compositions of the surface.

Di Martino, M.↗
NASA NTRS1989

Physical studies of Apollo-Amor asteroids - UBVRI photometry of 1036 Ganymed and 1627 Ivar

The 1036 Ganymed and 1627 Ivar photoelectric lightcurves presently discussed indicate in the former case a drastic lightcurve shape change, in conjunction with a significant increase of the synodic rotation period; a substantial change in viewing conditions during the apparition, and a complex interaction between these changes and the asteroid's irregular shape, are indicated by the change. In the latter asteroid's case, a prograde rotation rate is apparent in the observed decrease in synodic period. Both asteroids' phase curves exhibit deviations from the H-G magnitude system phase function at large phase angles.

Hahn, G.↗
NASA NTRS1989

Photoelectric observations of asteroids 3, 24, 60, 261, and 863

Observations of the five asteroids designated 3 Juno, 24 Themis, 60 Echo, 261 Prymo, and 863 Benkoela over the 1978-1984 period have been subjected to Fourier analysis to obtain composite lightcurves. The method yields a rotation-period value, mean absolute magnitudes for each night of observation, and Fourier coefficients that define composite-lightcurve shape, with formal error estimates for all quantities. The first three of the asteroids listed exhibit significant variation in surface albedo.

Harris, A. W.↗
NASA NTRS1989

Photometric lightcurve observations and reduction techniques

Photoelectric light curves were used to determine the period of rotation, obtain the estimates of shape and pole orientation, and define the phase relation, or brightness as a function of solar phase angle, of asteroids. Methods for taking and reducing observations are described, with particular consideration given to the correction for atmospheric extinction, the use of Fourier analysis in constructing composite light curves, and the analysis of errors. Also discussed are computer programs that solve two principal problems: the determination of the time-variable extinction function for a night and the constuction of composite light curves.

Harris, A. W.↗
NASA NTRS1989

Asteroid lightcurve parameters

A light curve data file is presented. Each citation includes the year, all authors, journal or book name, volume, and first and last page numbers. The asteroid list is ordered by asteroid number, followed by asteroid name, the period in hours, amplitude of variation or range of amplitude observed, and a reliability code.

Lagerkvist, C.-I.↗
NASA NTRS1987

Photoelectric lightcurves of the asteroid 1862 Apollo

A period of rotation of 3.0655 + or - 0.0008 hr is presently established for the 1862 Apollo asteroid on the basis of photoelectric light curves obtained during December 1980 and April-May 1982. The slope of the phase curve is typical for a moderate albedo asteroid. A pole position has been calculated using the observed deviation of the light curve from constant periodicity. While the formal uncertainty of the solution for the pole position is less than 10 deg, it may be several times that figure or even entirely wrong.

Harris, A. W.↗
NASA NTRS1986

The abundance of interstellar sulphur and zinc in high density sight-lines

On the basis of early absorption line studies of individual lines of sight with the Copernicus satellite, chlorine, sulphur and zinc were classed together as elements which showed little or no depletion, relative to hydrogen, in the interstellar medium. The abundances of other less volatile elements, such as Fe and Mg were found to vary widely from one sight-line to another with gas-phase abundances in some cases being orders of magnitude below their solar counterparts. Detailed studies are reported of the depletion/density behavior of two other volatile elements which were previously considered to be virtually undepleted, S and Zn, using equivalent width data from both Copernicus and IUE observations. The results provide further evidence that the established dependence of depletion on n bar (H) extends to volatile elements and show that their use as tracers of metallicity, or for estimating hydrogen column densities, may lead to large errors in sight-lines through dense regions. It now appears that such elements may take part in the surface chemistry of grains and be important constituents of grain mantle material, although they probably do not contribute significantly to the bulk mass of grains. Due to the very similar atomic masses and ionization potentials of sulphur and phosphorous, the thermal velocity distributions of the singly ionized species of these elements in interstellar clouds should be very similar. However, a comparison of Doppler widths (b-values) derived for SIT and PIT in the same sight-lines from the Bohlin et al Copernicus equivalent width measurements has revealed an unexpected systematic discrepancy of a factor of approx. 1.7. This Discrepancy indicates that the normally adopted oscillators strengths of the PII lambda lambda 1153 and 1302 A lines may require revision.

Harris, A. W.↗
NASA NTRS1986

Asteroid lightcurve studies

The use of light curves to characterize the dynamics of asteroids is discussed in a review of recent statistical and theoretical investigations. The summary, detailed, and bibliographic lists comprising the IAU light-curve data set are briefly characterized, and studies of rotation rates, shapes and pole positions, and phase relations are surveyed. Rotation-rate differences among the taxonomic classes and with asteroid size are noted, along with a wide dispersion of rotation rates in objects smaller than about 100 km.

Harris, A. W.↗
NASA NTRS1986

Origins of satellites

Solar system origin and planetary formation are discussed with emphasis placed on accretion disk dynamics, disk instabilities, giant gaseous protoplanets, condensation, sedimentation, coagulation, planetesimal swarm evolution, giant planet formation, and implications for satellites. Disk formation and the dynamics of a protosatellite disk are considered as well as satellite accretion, impact disruption and ablation, and satellite capture. Possible explanations for each of the satellite systems are offered. It is concluded that satellite formation involves a variety of processes.

Stevenson, D. J.↗
NASA NTRS1984

Radar and photoelectric observations of asteroid 2100 Ra-Shalom

Asteroid Ra-Shalom was subjected to 13-cm wavelength radar and V-filter photoelectric observations during its August-September 1981 apparition; the radar data yield echoes in the same sense of circular polarization as transmitted (SC) as well as in the opposite sense (OC). SC-to-OC echo power ratio estimates indicate that most of the backscattering is due to single reflections from surface elements that are relatively smooth at decimeter scales. The photoelectric data suggest a value of 19.79 hours for the synodic rotation period.

Ostro, S. J.↗
NASA NTRS1984

The lightcurve and phase relation of the asteroid 133 Cyrene

The asteroid 133 Cyrene was observed photometrically on 17 nights during oppositions in 1979 and 1980. The synodic period of rotation was found to be 12.708 + or - 0.001 h with an amplitude of 0.30 m during both oppositions. At large phase angles, the phase relation is quite ordinary (0.025 mag/degree); however, the low phase angle observations reveal a dramatic opposition brightening, about 0.2 mag/degree near zero phase angle. The absolute magnitude, V(1,0), extrapolated with the above linear phase coefficient, is 8.40. The following color indices were also measured: B-V = 0.90, U-B = 0.51.

Harris, A. W.↗
NASA NTRS1984

Lightcurves and phase relations of the asteroids 82 Alkmene and 444 Gyptis

The asteroids 82 Alkmene and 444 Gyptis were observed photoelectrically at Table Mountain Observatory and at Torino Observatory during their 1979 opposition in order to determine their rotation periods and phase relations. The observations of 82 Alkmene yielded a rotation period of 12.999 h + or 0.002 h and an amplitude of variation of 0.55. The measured and corrected absolute magnitudes, when plotted against phase angle, is the best fit Lumme and Bowell (1981) theoretical phase function. The rotation period and amplitude of variation for 444 Gyptis are 6.214 h and 0.15, respectively. The phase relation of this asteroid is poorly fit by the Lumme and Bowell theory when only the multiple scattering parameter and the zero phase angle are treated as variables. A good fit can be obtained by adjusting some of the other parameters of their theory, but the physical interpretation is ambiguous.

Harris, A. W.↗
NASA NTRS1984

Asteroid rotation rates

A trend of increasing mean rotational frequency with increasing diameter is noted in asteroids with diameters greater than 120 km, irrespective of M-, S-, and C-type asteroid subset and family or nonfamily membership. This trend cannot be accounted for by observational selection. For asteroids with diameters smaller than 120 km mean rotational frequency increases with decreasing diameter, but within this group there is a subset with exceptionally long rotational periods. This marked change in the distribution at 120-km diameter could separate primordial asteroids from their collision products. It is also noted that, for asteroids of a given diameter, M asteroids rotate faster than S asteroids, which in turn rotate faster than C asteroids. For all types, family members rotate faster than nonfamily members.

Dermott, S. F.↗
NASA NTRS1984

The origin and evolution of planetary rings

Roche (1847) suggested that Saturn's rings may be the fragments of a disrupted satellite rather than the uncoagulated remnant of a circumplanetary disk from which the regular satellites formed. In order to address this unresolved central issue, attention is given to the dynamical processes of viscous spreading, gas drag, particulate coagulation, and the effect of further matter infall from heliocentric orbit onto the planet/disk, all of which act on a gas/solid disk in Keplerian motion. In view of these considerations, it is suggested that rings were created by the disruption of large satellites which were less sensitive to the destructive processes present during the planet's formation. This hypothesis explains the presence of shepherd satellites, such as large collision fragments, which coexist in the same orbital range as the ring particles.

Harris, A. W.↗