Near Infrared Spectra of 12 Near Earth Objects

Abstract

We present a number of spectra of Near Earth Objects taken in the period 1998-2003 with two different instruments (CGS4 and UIST) on the UKIRT telescope. Since observations with CGS4 require multiple spectral fragments to be observed sequentially and then spliced together we assess the reliability of this technique using comparisons between multiple observations of the same object, between observations of the same object with both instruments and with independent spectra of common objects. We conclude that while problems in the spectral splicing can occur, they are usually intuitively obvious and that overall our dataset is sound. The objects for which we present new spectral data are: 1627 Ivar, 4179 Toutatis, 5381 Sekhmet, (5587) 1990 SB, 6489 Golevka, (11405) 1999 CV3, (14402) 1991 DB, 25143 Itokawa, (25330) 1999 KV4, (52760) 1998 ML14, (66391) 1999 KW4, and (101955) 1999 RQ46. Our results, together with albedo data from the literature, suggest carbonaceous compositions for 25330 and 101955. The available data for 14402 suggest it may belong to the relatively rare M class. Our analysis suggests an S or Sq classification for 52760 and a V classification for 5381 Sekhmet. For all remaining objects the UKIRT data are consistent with published spectral classifications. We find that only 3 of the 12 objects are not S/Q/V-class, which is roughly consistent with the results of Binzel et al (2004, Icarus, 170, 259-294). Four spectra of Toutatis taken over a range of solar phase angles between 0.7–81 degrees and at intervals of several weeks are indistinguishable within the uncertainties and therefore do not reveal any evidence for phase reddening or surface variegation.