Broadband Colors and Rotation Lightcurves of the Potentially Hazardous Asteroid 2009 UN3.
ATel #2449; M. Hicks (JPL/Caltech), T. Barajas (LACC), J. Shitanishi (CSULA)
on 18 Feb 2010; 19:57 UT
Credential Certification: Michael D. Hicks (Michael.Hicks@jpl.nasa.gov)
Subjects: Optical, Asteroid, Planet (minor), Solar System Object
The Near-Earth Asteroid (NEA) 2009 UN3 was discovered by the Siding Springs
Survey on October 19 2009 (MPEC 2009-U52). With an expected diameter
800 m < D < 1700 m, and with a Minimum Orbit Intersection Distance
MOID = 0.024 AU, the NEA has been designated as a Potentially Hazardous
Asteroid (PHA) by the Minor Planet Center. We took advantage of the object's
2010 apparition to obtain Bessel BVRI colors and rotational lightcurves
over the course of three nights at the JPL Table
Mountain 0.6-m telescope (TMO), as illustrated in Figures 1-3
and summarized in Table 1. This object was scheduled for radar observation
with the Goldstone and Arecibo Facilities near the NEA's closest Earth approach
February 9 2010.
Our data constrains 2009 UN3's size, composition, shape, and rotational
state. The colors obtained February 14 UT (B-R=1.269+/-0.010;
V-R=0.462+/-0.009; R-I=0.274+/-0.011) are most compatible with an S-type
taxonomy. This association was obtained through a comparison of our
colors with the 1341 asteroid spectra in the SMASS II database as archived
on the PDS node (Bus & Binzel 2002)
[Figure 4 and Table 2].
Light-time corrected photometry was converted to reduced magnitude assuming
a phase parameter G=0.15, consistent with an S-type classification. The
February 14 BVI data were registered to R using our measured colors. We performed a
rotational period search using standard Fourier techniques.
plots 4th and 5th-order Fourier model misfit as a function of assumed
rotation period. We found a best-fit synodic period P_syn = 4.123+/-0.010 hr,
as shown in
Figure 6 .
Two additional minima, P_syn =2.08 hr and P_syn = 6.19 hr,
require single-peaked and triple-peaked lightcurves and are not compatible
with a simple triaxial ellipsoid asteroid shape. Our photometry yields H_v=18.63+/-0.01 mag, significantly fainter than the
H_v=17.702 mag listed in the JPL HORIZONS database, and implies an effective
diameter D=575+/-75 m for an albedo rho=0.20+/-0.05.
2009 UN3 remains at high declination and brighter than V=19 through March
13 2010. We welcome collaborations with other minor planet observers:
Additional R-band photometry should allow a direct measurement of the
object's solar phase behavior in order to better constrain albedo and
Copyright 2010. 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.
UT DATE r delta phase Vexp Num. FILTER OBSERVER
[AU] [AU] [deg] [mag] Exp.
2010 02 14.48 1.028 0.076 56.7 14.3 109 BVRI Barajas, Shitanishi
2010 02 15.37 1.031 0.088 58.2 14.6 86 R Hicks
2010 02 16.41 1.035 0.101 59.4 14.9 151 R Hicks
Table 2: Best-fit SMASS II spectral analogs.
MISFIT OBJECT NAME (THOLEN) (BUS)
1.86 3873 Roddy S
2.40 2905 Plaskett S
3.03 264 Libussa S S
3.08 4702 Berounka S
3.20 226 Weringia S