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Low solar elongation searches for NEO: a deep sky test and its implications for survey strategies

Published online by Cambridge University Press:  01 August 2006

Andrea Boattini ,
A. Milani ,
G. F. Gronchi ,
T. Spahr  and
G. B. Valsecchi
Andrea Boattini
Affiliation:
Department of Physics, University of Tor Vergata, and OAR-INAF, Via Frascati 33, 00040 Monteporzio Catone (Roma), Italy, email: [email protected]
A. Milani
Affiliation:
Department of Mathematics, University of Pisa, Piazza Pontecorvo 5, 56127 Pisa, Italy email: [email protected]
G. F. Gronchi
Affiliation:
Department of Mathematics, University of Pisa, Piazza Pontecorvo 5, 56127 Pisa, Italy email: [email protected]
T. Spahr
Affiliation:
Minor Planet Center, Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138, USA
G. B. Valsecchi
Affiliation:
IASF-INAF, Via Fosso del Cavaliere 100, 00133 Roma, Italy
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Abstract

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A survey for NEO aiming at 90% completeness for a given size range cannot ignore that a significant fraction of the population is observable essentially only at low solar elongation, in the so called “sweet spots” There are several penalties for such low elongation: poorer observing conditions imply a lower limiting magnitude, shorter available time in each night and a more difficult orbit determination. Our aim is to show that these difficulties can be overcome. We have tested the observation procedures and the mathematical methods of orbit determination on two sweet spot test runs. One was performed at ESO La Silla in Jan–Feb 2005, the other at Mauna Kea in Sept–Dec 2005. The results of the tests are presented in this paper; the observed area was not large enough (especially at Mauna Kea) to discover a significant number of new NEO, the purpose was rather to identify the problems. These tests have allowed us to identify all the key elements to be accounted for in the strategy for a successful sweet spot NEO survey. When very short arc observations from different nights have to be identified, a specific difficulty occurs at the sweet spots: the same set of observations from three nights can be fitted to two incompatible orbits, in most cases including one NEO and one MBA. This can lead to two different failures (false positive, false negative) in deciding whether a NEO has been discovered. The classical theory of preliminary orbits shows that three observations at an elongation less than 116.5° can be compatible with two different orbits. From this theory we have derived an algorithm to find the alternate solution, if it exists, when only one is available. In this way we have generated a set of examples of possible discoveries with two well determined but incompatible solutions. Most of the MBA-NEO alternatives have been solved by finding a known MBA which could be identified; in two cases the MBA solution has been confirmed by a later observation.

Keywords

surveysorbit determinationidentification
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 2 , Symposium S236: Near Earth Objects, our Celestial Neighbors: Opportunity and Risk , August 2006 , pp. 291 - 300
Copyright
Copyright © International Astronomical Union 2007

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