Astronomy and Astrophysics – Astronomy
Scientific paper
May 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...180.0803h&link_type=abstract
American Astronomical Society, 180th AAS Meeting, #08.03; Bulletin of the American Astronomical Society, Vol. 24, p.739
Astronomy and Astrophysics
Astronomy
Scientific paper
The largest of the minor planets, 1 Ceres, has an apparent angular diameter of only 84 mas at perigee. Since the limit for angular resolution of ground-based observations is 100 mas, direct measurements of diameters are possible only for the very largest of the asteroids and then only under exceptional seeing conditions. In response to this limitation, several alternate methods have been explored. Polarimetry, radar, occultations, speckle interferometry, and radiometry have all been applied to the problem. This list both points up the ingenuity of minor planet observers and the inhomogeneity of the resulting measurements. It has been estimated that errors as high as 40% might result from inadequate modeling of parameters such as the texture of regoliths and rotation. To reduce such errors and find an optimal calibration for the Standard Thermal Model, accurate diameters are needed for a large number of asteroids. Furthermore, in order to discover and eliminate correlations between the errors and the various parameters of the Standard Thermal Model, these diameters should cover as wide a range of the asteroid population as possible. A Long-Term HST GO program is proposed which would use the FGSs to generate a uniquely homogeneous sample of accurate apparent diameters for approximately 100 asteroids. The improved diameter estimates could be used to re-calibrate and extend the photometric/radiometric method of albedo and linear diameter determination. The target minor planets have been carefully chosen to represent the widest possible cross-section of the asteroid population with regard to sizes, taxonomic types, light-curve periods and amplitudes. The list consists of approximately 100 asteroids including 32 reference objects whose diameters are known from occultation measurements or speckle interferometry with uncertainties typically less than 10 belt asteroids. The targets' apparent angular diameters at perigee range from 8 mas to 84 mas and their absolute magnitudes vary from 3.2 to 11.9. The light-curve periods vary from 3 to 60 hours while the amplitudes range from 0.01 to 1.50.
Holfeltz Sherie T.
Taff Laurence G.
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