paper

The Ch-class asteroids: Connecting a visible taxonomic class to a 3-μm band shape

arXiv:1511.01196 · doi:10.1088/0004-6256/150/6/198

Abstract

Asteroids belonging to the Ch spectral taxonomic class are defined by the presence of an absorption near 0.7 μm, which is interpreted as due to Fe-bearing phyllosilicates. Phyllosilicates also cause strong absorptions in the 3-μm region, as do other hydrated and hydroxylated minerals and H2O ice. Over the past decade, spectral observations have revealed different 3-μm band shapes the asteroid population. Although a formal taxonomy is yet to be fully established, the "Pallas-type" spectral group is most consistent with the presence of phyllosilicates. If Ch class and Pallas type are both indicative of phyllosilicates, then all Ch-class asteroids should also be Pallas-type. In order to test this hypothesis, we obtained 42 observations of 36 Ch-class asteroids in the 2- to 4-μm spectral region. We found that 88% of the spectra have 3-μm band shapes most consistent with the Pallas-type group. This is the first asteroid class for which such a strong correlation has been found. Because the Ch class is defined by the presence of an absorption near 0.7 μm, this demonstrates that the 0.7-μm band serves not only as a proxy for the presence of a band in the 3-μm region, but specifically for the presence of Pallas-type bands. There is some evidence for a correlation between band depth at 2.95 μm and absolute magnitude and/or albedo. However, we find only weak correlations between 2.95-μm band depth and semi-major axis. The connection between band depths in the 0.7- and 3-μm regions is complex and in need of further investigation.

Accepted for publication in Astronomical Journal 5 November: Replaced 4 November version since it accidentally omitted figures!

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