Abstract
Absolute magnitude (H) of an asteroid is a fundamental parameter
describing the size and the apparent brightness of the body. Because of
its surface shape, properties and changing illumination, the brightness
changes with the geometry and is described by the phase function
governed by the slope parameter (G). Although many years have been spent
on detailed observations of individual asteroids to provide H and G,
vast majority of minor planets have H based on assumed G and due to the
input photometry from multiple sources the errors of these values are
unknown. We compute H of ~ 180 000 and G of few thousands asteroids
observed with the Pan-STARRS PS1 telescope in well defined photometric
systems. The mean photometric error is 0.04 mag. Because on average
there are only 7 detections per asteroid in our sample, we employed a
Monte Carlo (MC) technique to generate clones simulating all possible
rotation periods, amplitudes and colors of detected asteroids. Known
asteroid colors were taken from the SDSS database. We used debiased spin
and amplitude distributions dependent on size, spectral class
distributions of asteroids dependent on semi-major axis and starting
values of G from previous works. H and G (G12 respectively) were derived
by phase functions by Bowell et al. (1989) and Muinonen et al. (2010).
We confirmed that there is a positive systematic offset between H based
on PS1 asteroids and Minor Planet Center database up to -0.3 mag peaking
at 14. Similar offset was first mentioned in the analysis of SDSS
asteroids and was believed to be solved by weighting and normalizing
magnitudes by observatory codes. MC shows that there is only a
negligible difference between Bowell's and Muinonen's solution of H.
However, Muinonen's phase function provides smaller errors on H. We also
derived G and G12 for thousands of asteroids. For known spectral
classes, slope parameters agree with the previous work in general,
however, the standard deviation of G in our sample is twice as larger,
most likely due to sparse phase curve sampling. In the near future we
plan to complete the H and G determination for all PS1 asteroids
(500,000) and publish H and G values online. This work was supported by
NASA grant No. NNX12AR65G.
Original language | English |
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Article number | 208.22 |
Pages (from-to) | 80 |
Number of pages | 1 |
Journal | Bulletin of the American Astronomical Society |
Volume | 45 |
Publication status | Published - 01 Oct 2013 |