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Broad-band photometry of NHATS target 387733 (2003 GS)

ATel #6090; M. Hicks (JPL/Caltech), J. Frederick (PCC), I. Harley (PCC)
on 23 Apr 2014; 17:57 UT
Credential Certification: Michael D. Hicks (Michael.Hicks@jpl.nasa.gov)

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

The near-Earth asteroid (2003 GS) was discovered by the LONEOS Sky Survey on April 12, 2003 (MPEC 2003-G25). The object passed within 0.0875 AU on April 12, 2014 and is scheduled to be observed at radar wavelength at Arecibo on April 18-20 (E. Howell, personal communication). 2003 GS has been flagged by NASA's Near-Earth Object Human Space Flight Accessible Targets Study (NHATS) as a potentially attractive mission target. Though close to full moon, we took advantage of the object's 2014 apparition to obtain three partial nights of time-resolved photometry (April 12-14 2014 UT) at the JPL Table Mountain Observatory 0.6-m telescope, as summarized in Table 1 and Figures 1-3 [1] [2] [3].

The rotationally averaged colors of the asteroid (B-R=1.233+/-0.012 mag; V-R=0.466+/-0.012 mag; R-I=0.361+/-0.034 mag) were found most compatible with an S-type spectral classification, an association obtained through a comparison of our colors with the 1341 asteroid spectra in the SMASS II database (Bus & Binzel 2002) [Figure 4 and Table 2]. As shown in Figure 5 , our solar phase coverage allow the determination of absolute magnitude (H_R=18.50 mag) and solar phase parameter g=0.17, consistent with an S-Family taxonomic classification. Using our V-R color, we measured an absolute magnitude in the V band H_V=18.97+/-0.02 mag.

After converting our observed flux to normalized flux, we performed a rotational period search using standard Fourier techniques. Figure 6 plots chi-squared 2nd and 3rd order Fourier model misfit as a function of assumed rotation period, with a clear minimum near 2.5 hr. Assuming a double-peaked lightcurve, we found a best-fit synodic period P_syn = 2.469+/-0.001 hr, as shown in Figure 7 . The rapid rotation and low lightcurve amplitude suggests a potential binary NEO system; there was no clear evidence of a two-period system in our data.

Copyright 2014. 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 AST-1156756 to Los Angeles City College.

Table 1: Observational summary. 
                       Solar        Lunar    . 
UT Date     r   delta  Phase  V     Elong.  Filters   Observers 
           [AU]  [AU]  [deg] [mag]  [deg] 
Apr 12.40 1.087 0.087  15.0  14.7    41.6    BVRI     Hicks 
Apr 13.31 1.086 0.088  16.7  14.8    31.1      R      Harley, Frederick, Hicks 
Apr 14.26 1.086 0.088  18.7  14.9    23.6      R      Hicks 
Table 2:  Best-fit SMASS II spectral analogs. 
                           TAXONOMIC CLASS 
1.983     39 Laetitia         S       S 
2.988   3198 Wallonia                 S 
3.037   1351 Uzbekistania             Xk 
3.218   6704 1988 CJ                  K 
3.449     56 Melete           P       Xk