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A. S. Rivkin (MIT), L. A. McFadden (U. of Maryland), M. Sykes (PSI), R. P. Binzel (MIT)
Observations of 4 Vesta using SpeX, a medium resolution,0.8-5.4 micron spectrograph at the IRTF are reported. We observed in the 2.0-4.2 micron cross-dispersed mode (LXD mode) with the 0.8 arcsec-wide slit on 8, 9, and 11 August 2004 UT, with data smoothed with a Gaussian to a final resolution of 250. On 2004 10 August we observed between 0.8-2.5 microns using single prism mode with R=250, also with the 0.8 arcsec slit. The seeing ranged from roughly 0.3-1.5 arcseconds.
We measured the 3-micron region looking for variations with respect to longitude, with 55 LXD spectra over the three nights completely sampling the portion of Vesta's surface visible from Earth. These show no band depths greater than observational uncertainties (roughly 0.5%) at any phase, and no variation in the 2.95/2.5 micron reflectance ratio larger than 1%. Larger variations are present at other wavelengths. In particular, variation is seen at different longitudes beyond 3.4 microns and is interpreted in terms of thermal emission and may arise due to albedo variation across the surface. We cannot confirm the findings of Hasegawa et al. 2003, although we note that their observations were made at a significantly different aspect.
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.