Engineering topics

Tholen, D. J.

Publications and source records attributed to Tholen, D. J..

29 records · Page 2

NASA NTRS1985

Results from observations of the 15 June 1983 occultation by the Neptune system

Observations of eight Neptune occultations from six sites in the southwestern Pacific on June 15, 1983. The data were used to search for evidence of rings around Neptune down to a distance of 0.03 Neptune radii from the planetary surface, but the results were negative. An astrometric analysis of the timings yielded solution for the equatorial radius a(0) of Neptune at 1 microbar pressure and the oblatness e at this level. The results are: a(0) = 25,295 + or - 50 km; e = 0.022 + or - 0.004, from which a value for a(1) (equatorial radius at 1 bar pressure) of 24,830 + or - 100 km; and a rotation period of P = 15 h (+3, -2 h) is derived. These results are based on a recent determination of Neptune's pole position and mass quadruple moment, and are consistent with the hypothesis that Neptune and Uranus have homologous mass distributions, although the constraint on interior structure is a weak one. If the probable uncertainty of the pole position is taken into account, error bars on e and derived quantities should be increased by about 50 percent. The present determinations of Neptune atmospheric temperatures at 1 microbar are consistent with earlier results and when combined with all previous data give an average value of 156 + or - 10 K. There is only slight evidence for any latitude dependence in the temperatures. Profiles with a high signal-to-noise ratio suggest the possible presence of an absorbing layer at altitudes higher than the 1-microbar level.

Hubbard, W. B.↗

NASA NTRS1985

The eight-color asteroid survey - Results for 589 minor planets

Results are presented from reflection spectrophotometry of 589 minor planets in a photometric system using eight filter passbands ranging from 0.34- to 1.04-micron wavelength. The sampling completeness approaches or exceeds 50 percent of the numbered asteroids for the near-earth objects, the Hungarias, the Nysa family, the Cybeles, the Hildas, and the Trojans. The general evolution of predominant compositional type from S to C to D with increasing heliocentric distance is evident, as is the spectral homogeneity of the Eos, Koronis, Nysa, and Themis families.

Zellner, B.↗

NASA NTRS1985

Outer solar system materials - Ices and color systematics

Our program of VJHK colorimetric observations and spectrophotometry is reviewed and updated. Attention is given to the probable connections between VJHK colors and the ratios of bright ices and dark soils on many outer solar system small bodies' surfaces. VJHK color systematics may clarify ice/soil behaviors in bodies too faint for high resolution spectra. Comets appear colored by soils most closely resembling D-class Trojan asteroid soils. Our recent model of comet surface properties, involving weakly-bonded ice/soil regoliths, helps explain comet eruptive phenomena. The work suggests the importance of considering ices in the context of their intimate mixture with non-volatile soils.

Hartmann, W. K.↗

NASA NTRS1984

2060 Chiron - Visual and thermal infrared observations

Five-color (wavelength = 0.36-0.85 microns) and thermal infrared (wavelength = 22.5 microns) photometric observations of the unusual asteroid 2060 Chiron were made. Between 0.36 and 0.85 microns, Chiron's reflectance spectrum is similar to those of C-class asteroids as well as Saturn's satellite Phoebe. However, the thermal IR measurements imply an albedo greater than 0.05 (i.e., a diameter of less than 250 km at the 2-sigma level) that is probably higher than those of C-class asteroids or Phoebe.

Lebofsky, L. A.↗

NASA NTRS1984

Multicolor photometry of outer Jovian satellites

Multicolor photometry was obtained of satellites J6 Himalia, J7 Elara, and J10 Lysithea in the prograde cloud of outer Jovian satellites, and of J8 Pasiphae, J9 Sinope, and J11 Carme in the retrograde cloud. The data for J9 are fragmentary; otherwise, the satellites all look like C-class asteroids, except J11, which shows a remarkable brightness in the ultraviolet. The absence of D-class spectra among the outer Jovian satellites suggests that they were not derived from the same population as the outer-belt and Trojan asteroid populations.

Tholen, D. J.↗

NASA NTRS1983

The rotation, color, phase coefficient, and diameter of 1915 Quetzalcoatl

Photoelectric observations of 1915 Quetzalcoatl on March 2, 1981 show that this asteroid has a rotational period of 4.9 + or - 0.3 hr and a lightcurve amplitude of 0.26 magnitudes. B-V and U-B colors are found to be 0.83 + or - 0.04 and 0.43 + or - 0.03, respectively, consistent with Quetzalcoatl being an S-type asteroid. Additional observations from March 31, 1981, give a linear phase coefficient of 0.033 mag/deg and a mean B(1,0) magnitude of 20.10. The resulting estimated mean diameter for Quetzalcoatl is only 0.37 km, making it one of the smallest asteroids for which physical observations have yet been made.

Binzel, R. P.↗

NASA NTRS1983

Lightcurves and phase function of asteroid 44 Nysa during its 1979 apparition

Lightcurves of asteroid 44 Nysa obtained during 20 nights in 1979 as part of a global compaign are presented. The synodic period was 6 hours and 25.3 minutes. The phase coefficient of the primary maximum was 0.026 mag/deg and the absolute V magnitude 7.05. The phase function is linear from 2 to 25 deg, no opposition effect is present.

Birch, P. V.↗

NASA NTRS1983

Eight-color photometry of Hyperion, Iapetus, and Phoebe

The Phoebe, Hyperion and Iapetus Saturn satellites are discussed in light of eight-color spectrophotometry, which together with observed V magnitudes and Voyager spacecraft-derived diameters yields geometric albedos of 0.07 for Iapetus, 0.06 for Phoebe, and maximum- and minimum-dimension based limits of 0.19 and 0.25 respectively for Hyperion. While both Hyperion and Iapetus have similar, very reddish spectra, it is noted that Hyperion has a much higher albedo than the dark side of Iapetus. The mean spectrum of Phoebe is much flatter, with a broad absorption feature near 1 micron. The determination of these optical differences between the surface materials of Phoebe and the dark side of Iapetus constrains the possible interaction modes between Phoebe and the other two satellites.

Tholen, D. J.↗

NASA NTRS1982

The eight-color asteroid survey - Standard stars

Compositionally diagnostic information regarding the spectral reflectance of faint asteroids and planetary satellites, obtained using a photometric system, is presented. Standard UBV and range in effective wavelength from 0.34 to 1.04 microns are among the eight broadband filters relative to the study. An InGaAsP photomultiplier of high quantum efficiencies employed for longer wavelengths, allows work to magnitude 17 and fainter when used in conjunction with a 2 m telescope. Magnitudes and color indices with mean uncertainty + or - 0.006 mag for 50 standard stars are presented, and by setting the mean colors of four of these stars to zero, the zero point of the system is established. Sun color implications resulting from the study are U-B = 0.20 + or - 0.02, and B-V = 0.67 + or - 0.02.

Tedesco, E. F.↗

NASA NTRS1982

Occultation by a possible third satellite of Neptune

The 24 May 1981 close approach of Neptune to an uncataloged star was photoelectrically monitored from two observatories separated by 6 kilometers parallel to the occultation track. An 8.1-second drop in signal, recorded simultaneously at both sites, is interpreted as resulting from the passage of a third satellite of Neptune in front of the star. From the duration of the event, the derived minimum diameter for an object sharing Neptune's motion is 180 kilometers. If the object was in Neptune's equatorial plane and there are no significant errors in the prediction ephemeris, the object was located at a distance of 3 Neptune radii from Neptune's center.

Reitsema, H. J.↗

NASA NTRS1981

The diameter and albedo of 1943 Anteros

The results of broadband visual and infrared photometry of the Apollo-Amor asteroid 1943 Anteros during its 1980 apparition are reported. By means of a radiometric model, a diameter of 2.3 + or - 0.2 km and a visual geometric albedo of 0.13 + or - 0.03 is calculated. The albedo and reflectance spectrum of Anteros imply that it is a type S asteroid. Thus, Anteros may have a silicate surface similar to other Apollo-Amor asteroids as well as some stony-iron meteorites.

Veeder, G. J.↗