The Absolute Magnitude Distribution of Near Earth Objects (NEOs)

Wednesday, 17 October 2018 12:15 p.m. — 1:15 p.m. MST

AURA Lecture Hall

NOIRLab South Colloquia
FRANCISCO (FRANK) VALDES (NOAO North and NOAO South Visiting Astronomer)

The distribution of asteroid absolute magnitudes (H) for the near earth objects (NEOs) observable near opposition -- i.e. Armors, Apollos, and Atens (A^3) -- is derived from the set of ALL currently known NEOs.  The result is based only on common sense assumptions of uniformly random distributions and that the orbital phase space and H-magnitude distribution of known NEOs is representative of the total population.  There is no population or other modeling and no assumption on albedo except in interpreting the result as a size-frequency distribution (SFD).  The analysis is based on the 18355 A^3 NEOs cataloged by the MPC as of June 2018.  The observations from 9 of the top programs, in terms of distinct NEOs observed, and the smaller but deeper DECam NEO Survey are used comprising 74464 measurements of 13430 NEOs observed within 30 deg of opposition.  The only parameter in the analysis is an estimate of the detection magnitude limits for each program.

A single power-law slope for the cumulative distribution, log(N)=0.50(+-0.02)H, for H < 27 is found with no evidence for additional structure.  A turn-over fainter than 27th magnitude may occur, but the population of known NEOs is dropping off rapidly because they are difficult to detect and so is likely to be a completeness effect.  Connecting to the nearly complete census of the brightest/biggest NEOs (diameter > ~2Km) provides a normalization that estimates ~10^8 A^3 NEOs with H < ~27 corresponding to NEOs greater than ~10m in diameter for reasonable typical albedos.