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

Status Report From: arXiv.org e-Print archive
Posted: Monday, November 9, 2015

Andrew S. Rivkin, Cristina A. Thomas, Ellen S. Howell, Joshua P. Emery
(Submitted on 4 Nov 2015)

Asteroids belonging to the Ch spectral taxonomic class are defined by the presence of an absorption near 0.7 {\mu}m, which is interpreted as due to Fe-bearing phyllosilicates. Phyllosilicates also cause strong absorptions in the 3-{\mu}m region, as do other hydrated and hydroxylated minerals and H2O ice. Over the past decade, spectral observations have revealed different 3-{\mu}m 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-{\mu}m spectral region. We found that 88% of the spectra have 3-{\mu}m 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 {\mu}m, this demonstrates that the 0.7-{\mu}m band serves not only as a proxy for the presence of a band in the 3-{\mu}m region, but specifically for the presence of Pallas-type bands. There is some evidence for a correlation between band depth at 2.95 {\mu}m and absolute magnitude and/or albedo. However, we find only weak correlations between 2.95-{\mu}m band depth and semi-major axis. The connection between band depths in the 0.7- and 3-{\mu}m regions is complex and in need of further investigation.

Comments: Accepted for publication in Astronomical Journal
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:1511.01196 [astro-ph.EP](or arXiv:1511.01196v1 [astro-ph.EP] for this version)
Submission history
From: Andrew Rivkin
[v1] Wed, 4 Nov 2015 03:10:20 GMT (280kb)
http://arxiv.org/abs/1511.01196

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