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Next: 4.3 Follow-up vs. negative Up: 4. Conclusions Previous: 4.1 Coordination and Validation

4.2 Photographic Archives

The use of photographic archives to look for VIs is an interesting field of investigation, although special care is required. Because of the less reliability of photographic magnitudes, an extra magnitude of cushion is needed. This approach has two other disadvantages. First, we will rarely find opportunities to detect the small objects which will generally be the subject of VI searches, and second, even though we may find some very deep plates, the trailing loss remains a serious problem. The great advantage is that this search can be done at any time, does not require any telescope resources, and the reliability of these results is easy to verify. Close approaches of VIs, as we described in the January 2001 and February 2003 cases, represent the best examples in which the more deep and consistent surveys can give a precious contribution. By using the elements given in Table 1 one can compute ephemerides for previous VI close encounters and use them to search plate archives for promising opportunities.

Andrea Milani