Broadband Photometry of the Near-Earth Asteroid 136993 (1998 ST49).
ATel #4588; M. Hicks (JPL/Caltech), M. Brewer (VCC), J. Somers (Moorpark College)
on 20 Nov 2012; 00:22 UT
Credential Certification: Michael D. Hicks (Michael.Hicks@jpl.nasa.gov)
Subjects: Optical, Asteroid, Solar System Object, Near-Earth Object
The near-Earth asteroid 136993 (1998 ST49) was discovered on 1998 October 29 by the LINEAR NEO survey (MPEC 1998-T05). We obtained two nights of Bessel BVRI and two nights of Bessel R observations at the JPL Table Mountain Observatory (TMO) 0.6-m telescope. The observational circumstances summarized in Table 1.
The object's rotationally averaged colors (B-R=1.192+/-0.022 mag; V-R=0.439+/-0.0011 mag; R-I=0.367+/-0.024 mag) were found most compatible with an Xe-type spectral classification (Bus Taxonomy) [
and Table 2]. This classification differs significantly from the Q-type taxonomy reported by Binzel et al. (2001, Icarus 151, 139-149). An Xe classification would imply a high albedo, however the solar phase curve generated from our data yields a solar phase parameter g=0.18, consistent with the moderate albedos typical for S-type asteroids
The asteroid's colors and phase behavior suggests strongly that 1998 ST49 is an S-type asteroid. Our measured absolute magnitude H_V=17.81+/-0.02 mag implies an effective diameter D~0.9 km, assuming a geometric albedo rho=0.15.
Assuming a solar phase parameter g=0.18, we performed a period search using standard Fourier techniques
and found a best-fit rotational period P_syn=2.3027+/-0.0002 hr, near the rotational break-up speed
and in agreement with the period reported by A. Galad (2007, Earth, Moon and Planets, 100, 77-82).
Copyright 2012. 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 V Filters OBSERVERS
[AU] [AU] [deg] [mag]
2012 10 17.18 1.051 0.074 41.6 13.7 BVRI Brewer, Hicks
2012 10 28.17 0.994 0.120 86.1 16.1 BVRI Somers, Hicks
2012 10 30.14 0.986 0.134 89.0 16.4 R Hicks
2012 10 31.12 0.982 0.142 90.1 16.6 R Hicks
Table 2: Best-fit SMASS II spectral analogs.
MISFIT OBJECT NAME (THOLEN) (BUS)
1.279 815 Coppelia Xe
1.291 556 Phyllis S S
1.328 6249 Jennifer Xe
1.521 1730 Marceline Xe
1.766 1351 Uzbekistania Xk