Deimos: A reddish, D-type asteroid spectrum

Abstract

We have obtained high quality CCD spectra of Deimos from 0.5 to 1.0 microns at a spectral resolution of 15 A. The spectra are remarkably red, similar to the spectra of D type asteroids rather than those of carbonaceous chondrites or C type asteroids. During the 1988 opposition of Mars, we obtained new CCD spectra of its outer satellite, Deimos. The data were obtained over a 2 1/2 hour period on the night of 9 Oct., using the 1.54 meter Catalina telescope and the LPL long-slit CCD spectrometer. From 0.5 to 1.1 microns, the spectrum is dispersed across an 800 x 800 Texas Instruments CCD chip at a scale of 7.21 A per pixel for an effective lambda/delta(lambda) approximately equals 500. The primary observational difficulty in ground based spectroscopy of Deimos was its proximity to Mars. To minimize scattered light from Mars, Deimos was observed near greatest elongation. The spectrograph slit was narrowed to 2.5 arcseconds, slightly larger than the seeing disk. An apodizing mask at the re-imaged telescope primary, to remove the diffraction cross of Mars light caused by the telescope's secondary mirror mount. Residual scattered light was modeled and removed in data reduction. Solar analog stars BS560, BS2007, and BS8931 were observed to allow removal of telluric absorptions. The resulting spectrum is plotted with other data.