Spectral Characterization and Compositional Investigation of Eos Family

A. Doressoundiram, M. A. Barucci (Obs. de Paris), M Fulchignoni (Univ. Paris VII), M. Florczak (ON/CNPq)

Near the beginning of the century, Hirayama was the first to detect significant clusterings of asteroids orbits, that he called families. The Eos family is one of the most populous families, located around 3.0 AU from the Sun. It is the result of a total breakup of a parent body where 221 EOS is the largest fragment. Eos objects have traditionaly posed a difficult problem for asteroid classification. Their spectra ressemble the ones of S asteroids, which is particular in a region of the Main Belt dominated by C objects.

To investigate the composition and the level of homogeneity (or heterogeneity) of the members of this family, we started a spectroscopic survey at the European Southern Observatory (ESO) with wavelength coverage ranging from 0.48 to 0.92 tex2html_wrap_inline11 m. We observed 45 Eos asteroids, which constitute the first large survey of this family. Our results reveal the Eos objects have spectral signature characterizing the whole family : a maximum at tex2html_wrap_inline13 = 0.85-0.87 tex2html_wrap_inline11 m and a reflectivity gradient spanning over a continuous but limited range. Only two of the 45 investigated objects seem to be interlopers. While the lower range of the spectral distribution has been easily connected with CO-CV chondrites, we have found no satisfactory meteorite counterpart to the upper range. It seems that the spread out of Eos spectra could be interpreted by space weathering processes.