Observations required

Most of the NEOs detected by search programs are never observed again!  Follow up observations are required in the following disciplines:

  • Astrometry – precise positional measurements as early as possible after detection, in order to refine the orbit of the object and prevent it being lost.
  • Photometry – determining rotational light-curves (typically 4-12 hour periods) when near periapse. From this can be derived some idea of the size and shape, spin rate, pole orientation, and duplicity or the presence of satellite objects.
  • Spectroscopy – measurement of reflection spectra to assist in determining composition, type and family membership, generally referred to as taxonomy.

ASTROMETRY – regular follow up is required of objects in the region of Vmag 20-21.  Pixel scale of the CCD should be half of FWHM.  So if best seeing is 2” the pixel scale should be 1”/pixel.  Good guiding accuracy will improve reliability in measurements.  Since objects will be fast moving, exposures should preferably be as short as possible to avoid capturing motion, hence favouring larger aperture telescopes.  The Minor Planet Centre requires timing accurate to 0.00001 day, Right Ascension to 0s.01, the Declination to 0″.1, and derived magnitudes to 0.1 mag.

PHOTOMETRY – Useful work can also be done with smaller apertures on objects in the region of Vmag 16-18.  Good guiding accuracy is required, especially for longer exposures on fainter objects as a S/N ratio of at least 20 is necessary.  Periods with an accuracy of within about 1% can be generated in a single night’s photometry, and to within about 0.1% if photometry on the same object is conducted over several nights.

SPECTROSCOPY – Useful work is only really possible with large apertures.  About 4 magnitudes will be lost in the optical system, and spectroscopy can only be conducted on brighter objects unless the aperture is large.  Good guiding accuracy is required to enable long exposures for fainter objects and to ensure acceptable S/N ratio.