Redetermination of the Space Weathering Rate Using Spectra of Iannini Asteroid Family Members

Details Redetermination of the Space Weathering Rate Using Spectra of Iannini Asteroid Family Members Redetermination of the Space Weathering Rate Using Spectra of Iannini Asteroid Family Members

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007dps....39.2009w&link_type=abstract

American Astronomical Society, DPS meeting #39, #20.09; Bulletin of the American Astronomical Society, Vol. 39, p.448

Astronomy and Astrophysics

Astronomy

Scientific paper

We have obtained moderate S/N ( 85) spectra at a realized resolution of R 100 for 11 members of the Iannini family, until recently the youngest known family at under 5 million years of age. The spectra were acquired using ESI in its low-resolution prism mode on the Keck II telescope. The family members belong to the S class of asteroids with perhaps some K class members. The Iannini family members's average spectral slope, the slope of the best-fit line constrained to pivot about 1 at 550 nm, is (0.30±0.04)/μm, matching that previously reported using SDSS color photometry. Using our spectra for this family as well as new observations of Karin family members and new classifications of some older families we revised the space weathering rate of S class asteroids. We parameterize the space weathering rate of the principal component color of the spectrum (PC1), which is correlated with the spectral slope, as PC1(t) = PC1(0) + Δ PC1[1 - \exp^{-(t/κ)α}]. Our revised rate suggests that the characteristic time scale for space weathering is τ = 570 ± 220 Myr and that new S class clusters will have an initial color of PC1(0) = 0.31 ± 0.04. This rate is in better agreement with lab measurements, supporting the use of space weathering as a dating method. Under the assumption that all the spectra should be identical, since the members all derive from the same parent body and are presumably covered with similar regolith, we combined them to obtain a high-S/N composite spectrum for the family. While the combined spectrum is clearly within the S/K class we note the appearance of a 'green feature' near 550 nm that has not previously been identified in asteroid spectra. We tentatively identify it as a feature in the pyroxene spectra as observed in the lab.

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