Evidence of N@d2-ice on the surface of the icy dwarf Planet 136472 (2005 FY9)

We present high signal precision optical reflectance spectra of 2005 FY9 taken with the Red Channel Spectrograph and the 6.5-m MMT telescope on 2006 March 4 UT (5000-9500 A; 6.33 A^?pixel@u-@u1) and 2007 February 12 UT (6600-8500 A; 1.93 A^?pixel@u-@u1). From cross-correlation experiments between the 2006 March 4 spectrum and a pure CH@d4-ice Hapke model, we find the CH@d4-ice bands in the MMT spectrum are blueshifted by 3 +/- 4 A relative to bands in the pure CH@d4-ice Hapke spectrum. The higher resolution MMT spectrum of 2007 February 12 UT enabled us to measure shifts of individual CH@d4-ice bands. We find the 7296, 7862, and 7993 A CH@d4-ice bands are blueshifted by 4 +/- 2, 4 +/- 4, and 6 +/- 5 A. From four measurements we report here and one of our previously published measurements, we find the CH@d4-ice bands are shifted by 4 +/- 1 A. This small shift is important because it suggest the presence of another ice component on the surface of 2005 FY9. Laboratory experiments show that CH@d4-ice bands in spectra of CH@d4 mixed with other ices are blueshifted relative to bands in spectra of pure CH@d4-ice. A likely candidate for the other component is N@d2-ice because its weak 2.15 ^km band and blueshifted CH@d4 bands are seen in spectra of Triton and Pluto. Assuming the shift is due to the presence of N@d2, spectra taken on two consecutive nights show no difference in CH@d4/N@d2. In addition, we find no measurable difference in CH@d4/N@d2 at different depths into the surface of 2005 FY9.