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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[32.02] Major-Element Ratios of 433 Eros: New Calibration of the NEAR-Shoemaker X-ray Spectrometer Data

L.F. Lim (NASA/GSFC and Cornell University), L.R. Nittler (Carnegie Institution of Washington), R.D. Starr (Catholic University), T.P. McClanahan (NASA/GSFC)

Elemental abundance ratios for six elements (Mg, Al, Si, S, Ca, Fe) in the surface layer of 433 Eros were derived [1,2] from solar-induced fluorescence measured by the NEAR-Shoemaker X-ray spectrometer (XRS). Calibration of these data depended critically on knowledge of the incident solar spectrum.

Unfortunately, the gas solar monitor carried by NEAR was inadequately calibrated prior to launch. Previously published XRS results were based partly on broadband measurements by the Earth-orbiting GOES-8 (Geostationary Operational Environmental Satellites) X-ray detectors and partly on a preliminary solar monitor calibration carried out by the present authors. The new solar monitor calibration is based on a more recent set of physical models of the solar spectrum at various temperatures [3,4], an improved fitting procedure, analysis of a large number of flight spectra, and comparison with concurrent data from the GOES and YOHKOH BCS X-ray detectors. The elemental composition of the surface of 433 Eros will be discussed together with the new estimates of systematic uncertainties.

[1] Trombka, J.I., et al. (2000) Science 289, 2101-2105. [2] Nittler, L.R., et al. (2001) Meteorit. Planet. Sci. 36, 1673-1695. [3] Dere, K.P., et al. (1997) A&AS 125, 149-173. [4] Young, P.R., et al. (2003) ApJS 144, 135-152.

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