Hierarchical Observing Protocol (HOP) for Asteroids

E. Bowell, B. W. Koehn, L. H. Wasserman (Lowell Obs.), K. Muinonen (U. Helsinki)

From the standpoint of orbit improvement, we seek to answer two questions: (1) When is it best or necessary to make astrometric observations of a given asteroid? (2) Which are the best asteroids to observe at a given time? Answering these questions allows one to address a third: (3) How should we best marshal and optimize the use of limited resources in making astrometric observations of asteroids? Such issues are increasing in importance as the number of observers and astrometric data mushroom.

We have developed two tools necessary for implementing HOP: (1) Observability of a chosen asteroid over a chosen time interval (consult the WWW at http://asteroid.lowell.edu/cgi-bin/koehn/obs), and (2) Observing strategy required to achieve the numbering of a chosen asteroid (http://asteroid.lowell.edu/cgi-bin/koehn/obsstrat). We find that four ``rules of thumb" can be used as precepts for HOP: The first concerns the numberability of asteroids, the second the rate of increase of ephemeris uncertainty of newly discovered asteroids, the third adduces that the improvement in an asteroid's orbit is proportional to the improvement in its ephemeris uncertainty that results from making an accurate observation, and the fourth states that peaks in ephemeris uncertainty generally occur near opposition.

We give examples of the use of .../obs and .../obstrat, which indicate that, during the discovery apparition, observations are needed at time intervals that increase geometrically (generally, by a factor of 3 to 5), and subsequently that one or two nights' observation per apparition suffice for an asteroid to be numbered after two or three apparitions (NEAs), three or four apparitions (MBAs), or six or more apparitions (transneptunians). We plan to create a web site for observers to make ranked lists of astrometric targets for their own locations/instrumentation, and we show how observations can be coordinated so as to assure that important targets are observed in a timely manner and wasteful duplication of effort is reduced.