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Title:
Low solar elongation searches for NEO: a deep sky test and its implications for survey strategies
Authors:
Boattini, Andrea; Milani, A.; Gronchi, G. F.; Spahr, T.; Valsecchi, G. B.
Publication:
Near Earth Objects, our Celestial Neighbors: Opportunity and Risk, Proceedings if IAU Symposium 236. Edited by G.B. Valsecchi and D. Vokrouhlický, and A. Milani. Cambridge: Cambridge University Press, 2007., pp.291-300
Publication Date:
00/2007
Origin:
CUP
DOI:
10.1017/S1743921307003353
Bibliographic Code:
2007IAUS..236..291B

Abstract

A survey for NEOs aiming at 90% completeness for a given size range cannot ignore that a significant fraction of the population passes in the neighborhood of opposition either never or very rarely or only in very poor observing conditions. Thus, a fraction of the available telescope time needs to be used at low solar elongations in the so called "sweet spots". However, there are several penalties for such sweet spot observations: i) poorer observing conditions, implying a lower limiting magnitude; ii) shorter available observing time for each night; iii) more difficult orbit determination. Other classes of objects are poorly observed either because of higher apparent magnitude (especially Main Belt Asteroids, MBAs) or because of too slow motion (distant objects); however, this makes easier to find the NEOs. We have tested the observations and the mathematical methods of identification/orbit determination on two sweet spot test runs conducted in 2005. One performed at La Silla (ESO) with the 2.2-m and 3.5-m NTT and the other one conducted at Mauna Kea with 3.6-m CFHT and 8.3-m Subaru. Also, when short arc observations from different observing 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 (often Aten) and one MBA. This can lead to two different failures in deciding wether a NEO has been discovered: a false positive leads to the waste of resources (follow-up, computations) for a MBA which would be more easily discovered at opposition, a false negative leads to the loss of the NEO which may not be reobservable soon. In this way we generated a large number of examples of possible discoveries with two well determined but incompatible solutions. Most of the MBA-NEO alternatives resulted in a known MBA or in a new designated one as soon as it was confirmed by a later observations. Of the 9 real NEOs detected, 1 has been confirmed by follow-up, 5 by identification with previously known NEA, 2 were precoveries; 1 has been lost due to telescope unavailability. These results served to define an efficient observing protocol.
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