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4.1 Coordination and Validation Issues

The organizational efforts needed for a VI campaign depend greatly on the circumstances of the apparition. In particular, the predicted brightness of the VI will be decisive in determining whether dedicated time on large telescopes will be necessary, or whether smaller instruments can be used. A comparatively large community of professional and non-professional asteroid observers has been successful in the follow-up of NEAs that are generally brighter than V=20. So, when a VI is brighter than V=18, this community can perform the necessary observations, but issues of validation and coordination will be more challenging than if a few experienced professionals with very large instruments are involved, as would be necessary if the VI is fainter than V=18.

Given the special responsibility in the validation of a negative observation, we suggest a few general guidelines for any VI search:

At least two independent observing teams using two different facilities should be involved in the search for each VI around the same time. The allocation of observing time should be sufficient to take into account bad weather conditions. It may be advisable to get confirmation of the negative observations on a second night from one of the two teams.

The observation epoch should be chosen carefully to consider factors such as the expected galactic latitude, solar elongation, and brightness, as well as the lunar phase. Observers must be very careful if the VI is expected to move rather slowly (5-10 arcmin/day or less) to ensure that it does not remain hidden by any star glare throughout the whole or most of the exposure time. Confusion with field stars is less of an issue if multiple exposures with the same instrument are available.

The observers must be able to detect objects two magnitudes fainter than the nominal one expected for the VI, taking into account trailing losses due to the asteroid's apparent motion, as discussed in Sec. 3.3. This ``safety cushion" should be adjusted on a case by case basis, depending on the photometric accuracy of the observers in the discovery apparition and on the magnitude consistency observed. The limiting magnitude needs to be calibrated for objects with a specific motion rate. For some long-lost objects discovered photographically it may be advisable to extend the factor of safety to three magnitudes. To validate the capability to detect at the level needed, the observer could be required to measure the position, taken at a short time interval, of a known asteroid near the VI which is somewhat fainter than the predicted VI magnitude.

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Next: 4.2 Photographic Archives Up: 4. Conclusions Previous: 4. Conclusions
Andrea Milani