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Broadband photometry of 267494 (2002 VB9): A near-Earth asteroid with remarkable solar phase behavior.

ATel #3460; M. Hicks (JPL/Caltech), J. Somers (Moorpark), H. Rhoades (JPL/Caltech), M. McCormack (LACC), C. Gerhart (LAVC), J. Bauer (JPL/Caltech), A. Mainzer (JPL/Caltech), J. Masiero (JPL/Caltech), T. Grav (JHU)
on 30 Jun 2011; 00:51 UT
Credential Certification: Michael D. Hicks (Michael.Hicks@jpl.nasa.gov)

Subjects: Optical, Asteroid, Planet (minor), Solar System Object, Near-Earth Object, Potentially Hazardous Asteroid

Referred to by ATel #: 3461

The Near-Earth Object (NEO) 267494 (2002 JB9) was discovered by the LINEAR NEO Survey on May 6 2002 (MPEC 2002-J23). With an absolute magnitude H=15.7 and Minimum Orbit Intersection Distance MOID=0.034 AU, the object has been identified as a Potentially Hazardous Asteroid (PHA) by the Minor Planet center. 2002 JB9 has orbital elements similar to Jupiter-family comets (a,e,i,T=2.72,0.79,47,2.53).

We obtained 2 nights of rotationally resolved Bessel BVRI photometry and 2 nights of Bessel R photometry at the JPL 0.6-m Table Mountain Observatory, with observational circumstances listed in Table 1. The BVI data points illustrated in Figure 1 are plotted offset relative to R by the nightly colors listed in Table 2. The object's mean colors (B-R=1.114+/-0.010 mag; V-R=0.392+/-0.008 mag; R-I=0.374+/-0.006 mag) are most compatible with an X-type spectral classification (Bus Taxonomy), as shown in Figure 2 and Table 3. The X-spectral complex includes the E (high albedo), M (medium albedo), and P (low albedo) sub-classes (Tholen Taxonomy).

The extremely shallow solar phase curve generated from our photometry (Figure 3) was best fit with a phase parameter g=0.91, consistent with a high albedo and E-type spectral classification. Barring extreme shape/illumination geometries, the phase parameter of 2002 JB9 exceeds the highest tabulated in the JPL HORIZONS and Lowell ASTORB databases (1627 Ivar; g=0.60). For comparison, 44 Nysa (the archetypal E-type asteroid) has a measured g=0.46 and albedo rho=0.55. Our four nights of photometry yielded a synodic period P_syn = 2.415+/-0.001 hr (Figure 4), . The phase/albedo relationship discussed by Belskaya and Shevchenko (Icarus 147, 2000) suggests that the albedo of 2002 JB9 may be as high as 0.8-0.9. Fourteen archived WISE/NEOWISE infrared fields obtained January 16-17 2010 were expected to contain 2002 JB9. These frames were stacked, coadded, and examined carefully but no moving object was detected. The large heliocentric distance (r=4.5 AU) precluded meaningful albedo constraints from the WISE/NEOWISE flux upper limits. Additional thermal/polarimetric observations are encouraged.

Copyright 2011. 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. The student participation was supported by the National Science Foundation under REU grant 0852088 to Cal State LA.

Table 1:   Observational circumstances. 
                            Solar  Exp.   Num. Filters 
   UT DATE      r    delta  Phase   V     Exp.  Used    Observers 
               [AU]   [AU]  [deg]  [mag] 
2011 05 27.23 1.319  0.326   17.3  14.8    32   BVRI   Somers, Hicks 
2011 06 08.23 1.164  0.192   36.1  13.9    73   BVRI   Hicks, Rhoades 
2011 06 10.21 1.138  0.185   44.8  14.0    78     R    Hicks 
2011 06 14.17 1.086  0.189   63.4  14.5    10     R    Gerhart, McCormack 
Table 2:  Relative Colors. 
UT Date          B-R            V-R            R-I 
                [mag]          [mag]          [mag] 
2011 05 27  1.118+/-0.048  0.389+/-0.011  0.370+/-0.027 
2011 06 08  1.117+/-0.015  0.394+/-0.010  0.374+/-0.009 
mean:       1.114+/-0.010  0.392+/-0.008  0.374+/-0.006 
Table 3:  Best-fit SMASS II spectral analogs. 
                         Taxonomic Class 
Misfit  Object Name      (Tholen)  (Bus) 
1.280  261 Prymno            B       X 
1.511  409 Aspasia           CX      Xc 
1.557   92 Undina            X       Xc 
1.902  507 Laodica                   X 
1.996  348 May                       X