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217807 (2000 XK44): Broad-band photometry of a slowly rotating near-Earth asteroid.

ATel #2371; M. Hicks (JPL/Caltech), T. Barajas (LACC), J. Somers (Moorpark College), J. Shitanishi (CSULA), D. Mayes (JPL/Caltech)
on 5 Jan 2010; 22:25 UT
Credential Certification: Michael D. Hicks (Michael.Hicks@jpl.nasa.gov)

Subjects: Optical, Asteroid, Planet (minor), Solar System Object

The Near-Earth Asteroid (NEA) 217807 (2000 XK44) was discovered Dec 5 2000 by the LINEAR moving-object survey (MPEC 2000-X28) and experienced a close-approach to the Earth (delta=0.074 AU) on Nov 04 2000, at which time the object was scheduled for radar observation at the Arecibo facility. We obtained nine nights of CCD photometry [Table 1] at the JPL Table Mountain 0.6-mm telescope, equipped with Bessel BVRI filters, to help constrain the asteroid's rotational state and surface composition.

BVRI color cycles were collected Oct 31 and Nov 01, as illustrated in Figure 1, and were averaged to determine disk-integrated colors (B-R=1.328+/-0.015; V-R=0.490+/-0.010; R-I=0.366+/-0.010). The broad-band colors agree well with the optical spectroscopy obtained Nov 09 at the P200 by Hicks & Lawrence (ATEL#2323). A comparison of the 2000 XK44 colors with the 1341 asteroid spectra in the SMASS II database (Bus & Binzel 2002) [Figure 2 and Table 2] suggest strongly an S-type taxonomic classification.

All R-band data were corrected to reduced magnitude R(1,1,0) by assuming a phase parameter G=0.15, allowing for a rotational period search using standard Fourier techniques. Figure 3 plots chi-squared 2nd and 3rd-order Fourier model misfits as a function of assumed rotation period. Our analysis found two possible period solutions (P1=25.7 hr, P2=66.8 hr). Both models suffer from a sudden data-model discontinuity near 0 deg rotational phase, as shown in Figure 4 and Figure 5 . This suggests that 2000 XK44 may be in a slightly excited or tumbling rotational state, however our data is insufficient to explore this possibility further.

2000 XK44 will not have another similarly well-placed apparition until Oct 28 2046 (delta=0.085 AU). Minor planet observers are encouraged to collect additional R-band photometry of this NEA during the remainder of its current apparition to help us resolve the ambiguity in period and rotational state.

Copyright 2009. All rights reserved. The research described in this telegram was carried out at the Jet Propulsion Laboratory, under a contract with the National Aeronautics and Space Administration.

 

Table 1:  Observational Circumstances.  
  
   UT DATE       r     delta   phase   V      Num.  FILTER  OBSERVER  
                [AU]    [AU]   [deg]  [mag]   Exp.  
2009 10 31.36  1.060   0.076   26.9   13.8     79    BVRI   Hicks  
2009 11 01.41  1.060   0.075   24.5   13.6    124    BVRI   Barajas  
2009 11 14.26  1.073   0.087   15.0   13.7     43     R     Somers, Hicks  
2009 11 15.25  1.075   0.090   16.4   13.8    268     R     Barajas, Shitanishi  
2009 11 19.25  1.082   0.102   21.2   14.3    205     R     Barajas, Shitanishi  
2009 11 25.21  1.096   0.123   26.1   14.9    144     R     Hicks  
2009 12 03.19  1.120   0.157   29.4   15.5    181     R     Mayes   
2009 12 04.21  1.125   0.164   29.7   15.6    147     R     Mayes  
2009 12 17.19  1.152   0.200   30.6   16.2    116     R     Hicks  

 

Table 2:  Best-fit SMASS II spectral analogs.           
                             TAXONOMIC CLASS  
MISFIT      OBJECT NAME      (THOLEN)  (BUS)  
 3.40   443 Photographica       S       Sl  
 3.55    18 Melpomene           S       S  
 3.91   124 Alkeste             S       S  
 4.01   673 Edda                S       S  
 4.16   782 Montefiore          S       Sl  
 4.29  3576 Galina                      Sl