Asteroid Phase Curves: Two- And Three-parameter Fits

Details Asteroid Phase Curves: Two- And Three-parameter Fits Asteroid Phase Curves: Two- And Three-parameter Fits

Oct 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010dps....42.3932o&link_type=abstract

American Astronomical Society, DPS meeting #42, #39.32

Astronomy and Astrophysics

Astronomy

Scientific paper

We apply the two-parameter H, G12 and the three-parameter H, G1, G2 magnitude phase functions (Muinonen et al., Icarus, in press) to photometric data from the Minor Planet Center, as modified in observational data files at Lowell Observatory, to derive improved absolute magnitudes (H) and slope parameters for individual asteroids (G12) and for groups of asteroids: e.g., main-belt zones, families (G1, G2). The Lowell Observatory orbital data file comprises about 535,000 records. Most of the photometric data are of low precision (generally rounded to 0.1 mag) and low accuracy (rms magnitude uncertainties of ± 0.5 mag are typical). To offset the low accuracy, the photometric data are very numerous: about 73,000,000 individual, largely independent magnitude estimates exist.
Here we present our preliminary estimates of absolute magnitudes using the H, G1, G2 magnitude phase functions and compare them with the values derived using the H, G12 two-parameter phase functions. A java applet version of the fitting procedures will soon be available on the web.
In future, we plan to combine the derived absolute magnitudes with thermal data from the "Spitzer Asteroid Catalog". The Spitzer catalog includes observations of several hundred near-Earth asteroids and about 100,000 main-belt asteroids most of them observed at 24 micrometer wavelength. The catalog contains fluxes, derived albedos, and diameters. By far the biggest source of error in the catalog stems from inaccurate visible magnitudes. Improved asteroid absolute magnitudes will also lead to better visible magnitude prediction and hence better calibrated asteroid albedos derived from thermal-models. Further, we plan to explore correlations among taxa, color indices, albedos, and phase curves. A significant data product will be a frequently updated list of asteroid photometric parameters and their uncertainties.
Research supported, by Magnus Ehrnrooth Foundation, Spitzer Science Center and Lowell Observatory.

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