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K. Muinonen, J. Virtanen, J. Torppa, M. Granvik (Univ. Helsinki Observatory), J. Näränen (Nordic Optical Telescope, La Palma), K. Aksnes, T. Grav (Univ. Oslo Institute for Theoretical Astrophysics), G. Hahn (DLR Institute for Planetary Exploration), C.-I. Lagerkvist, H. Rickman (Uppsala Univ. Astronomical Observatory), R. Michelsen (Univ. Copenhagen Astronomical Observatory)
In order to accrue knowledge on the physical and dynamical properties of near-Earth objects (NEOs), the recently established Nordic Near-Earth-Object Network (NEON) carries out a long-term photometric and astrometric NEO observing program at the 2.56-m Nordic Optical Telescope on La Palma (http://www.astro.helsinki.fi/~psr/NEO/not_obs.html). The spin vector, shape, and surface properties of an individual NEO are estimated from photometric observations at varying observation and illumination geometries. Improved orbits---including potential collision orbits with the Earth---can be derived from sky-plane positions available from the dedicated astrometry or the photometric observations.
We have developed novel algorithms for statistical inversion of an object's shape from lightcurves and/or sparsely distributed photometric observations. The algorithms allow the computation of shapes starting from a single observed lightcurve and yield a complete error analysis of the spins and shapes obtained. Note that when only small numbers of observations are available the spectrum of potential spins and shapes is wide.
As to the astrometric component of the program, we concentrate on potentially hazardous NEOs in need of a few additional observations to secure their recovery in the subsequent apparition. As one goal of the astrometric component, we aim at obtaining R-band photometry for each observed object. In the long run, this will provide us information of the true NEO absolute magnitude and size distributions greatly improving the impact risk estimation.
As of 2004 Sept. 1, NEON has made photometric observations of seven NEOs: (1917) Cuyo, (2061) Anza, 2001 US16, (68950) 2002 GF15, 2003 RX7, 2004 LJ1, and 2004 HW. Making use of the new observations, we show up-to-date models for the spins and shapes of these objects. NEON has made astrometric observations of more than 30 NEOs in urgent need of additional positions---these observations have culminated in the recovery of 1998 VN (MPEC 2004-M30).
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.