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E.F. Tedesco (TerraSystems, Inc.), F.-X. Desert (Observatoire de Grenoble)
A total of six deep exposures (using AOT CAM01 with a 6” PFOV) through the ISOAM LW10 filter (IRAS Band 1, i.e., 12 microns) were obtained on an approximately 12 arcminute square field centered on the ecliptic plane. Point sources were extracted using the technique described by Desert et al. (1999, A&A 342, 363). No previously known asteroids appear in these frames but a number of sources moving with velocities appropriate for main belt asteroids are present. Most of the asteroids detected have flux densities of 1 mJy or less, i.e., more than 150 times fainter than any of the asteroids observed in the IRAS Minor Planet Survey. These data provide the first direct measurement of the 12-micron sky-plane density for small asteroids on the ecliptic equator. Unfortunately, in spite of the high quality of the ISO data, little can be said regarding the diameters (and nothing regarding the albedos) of the asteroids detected. This is because their orbits, and hence distances and phase angles, are unknown and cannot be computed from the ISO positions alone. Reliable diameter determinations for these ISO asteroids will have to await their discovery. And, with V mags probably fainter than 25 for most, this is unlikely to happen in the near future.
In order to fully exploit such space-based infrared data, orbital elements of the asteroids must be known. If albedos are to be obtained, then visual wavelength photometry is required as well. Thus, the minimum requirement for obtaining asteroid diameters in the absence of supporting ground-based observations is that the space-based data must be taken at appropriate intervals and with astrometric accuracies sufficient to allow computation of an approximate orbit.
NASA’s Astrophysics Data Program supported EFT’s portion of the work reported herein.
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The author(s) of this abstract have provided an email address for comments about the abstract: etedesco@terrasys.com