EOS Family: A Spectroscopic Study

Abstract The Eos family detected by Hirayama in 1918 has been always considered to be compositionally homogeneous. To investigate the composition and the homogeneity of the members of this family, we started a spectroscopic survey at the European Southern Observatory (ESO) with wavelength coverage ranging from 4800 to 9200 A. We observed 45 Eos asteroid members, which constitutes the first large survey of this family. Our results reveal the Eos objects have spectral signature characterizing the whole family: a maximum at λ ∼ 8000–8500 A and a reflectivity gradient spanning a continuous range. Only two of the 45 investigated objects seem to be interlopers. While the lower range of this spectral distribution has been easily connected with CO–CV chondrites, we have found no satisfactory meteorite counterpart to the upper range. We have interpreted the spread out of Eos spectra to be the results of compositional variation among the Eos members, implying that the Eos parent body was partially differentiated. Moreover, a space weathering effect has been proven to be present, but with a minor role played in the diversity of Eos family, the major role being the compositional variation.

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