36th DPS Meeting, 8-12 November 2004
Session 32 Asteroids
Poster II, Thursday, November 11, 2004, 4:15-7:00pm, Exhibition Hall 1A

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[32.13] Improved 3 micron Band Determination in the Spectra of Aqueously Altered Asteroid Regoliths

E.L. Volquardsen (University of Hawaii), A.S. Rivkin (Massachusetts Institute of Technology), S.J. Bus (University of Hawaii)

Regolithic hydration has been found to produce a broad absorption band in asteroidal reflectance spectra at 3 microns (e.g. Lebofsky et al. 1981, Icarus 48, 453 and Rivkin et al. 1995, Icarus 117, 90). The depth and area of this absorption band is related to the amount of hydrated material present and the thermal history of the asteroid regolith (Rivkin et al. 2002, Asteroids III, 237). Since these band depths can be quite small, the limiting factor for detection is S/N.

To increase the S/N obtained and potentially allow for band detection in fainter objects, we endeavored to more accurately remove telluric absorption features and decrease observational uncertainties. This was accomplished by using the HITRAN database as implemented in the ATRAN software (Lord 1992, NASA TM103957). This produces atmospheric transmission models for a range of atmospheric water amounts. A best-fit atmospheric water amount is calculated for the asteroid and standard star. Comparisons can then be made to predicted Mauna Kea water amounts and the recorded value of tau. This method has been used on low resolution 0.8 to 2.5 micron spectra and has now been extended to the 2 to 4 micron region. We obtained these high S/N observations of asteroids using the LDX mode of SpeX at the NASA IRTF (Rayner et al. 2003, PASP 115, 362). We will discuss the depth and shape of the 3 micron absorption band in the reflectance spectra of 41-Daphne as a test case for this technique.

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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.