Thermal infrared and optical observations of four near-Earth asteroids

We present thermal infrared photometry and spectrophotometry of four near-Earth asteroids (NEAs), namely (433) Eros, (66063) 1998 RO1, (137032) 1998 UO1, and (138258) 2000 GD2, using the United Kingdom Infrared Telescope (UKIRT) in 2002. For two objects, i.e. (433) Eros and (137032) 1998 UO1, quasi-simultaneous optical observations were also obtained, using the Jacobus Kapteyn Telescope (JKT). For (127032) 1998 UO1, we obtain a rotation period P=3.0±0.1 hP=3.0±0.1 h and an absolute visual magnitude HV=16.7±0.4HV=16.7±0.4. The Standard Thermal Model (STM), Fast Rotating Model (FRM) and near-Earth asteroid Thermal Model (NEATM) have been fitted to the IR fluxes to determine effective diameters DeffDeff, geometric albedos pvpv, and beaming parameters η  . The derived values are (433) Eros: Deff=23.3±3.5 kmDeff=23.3±3.5 km (at lightcurve maximum), pv=0.24±0.07pv=0.24±0.07, η=0.95±0.19η=0.95±0.19; (66063) 1998 RO1: Deff=0.62−0.09+0.25 km, pv=0.30−0.17+0.09; (137032) 1998 UO1: Deff<1.13 kmDeff<1.13 km, pv>0.29pv>0.29; (138258) 2000 GD2: Deff=0.27±0.04 kmDeff=0.27±0.04 km, pv=0.56−0.22+0.32, η=0.74±0.15η=0.74±0.15. (66063) 1998 RO1 is a binary asteroid from lightcurve characteristics [Pravec, P., and 56 colleagues, 2006. Icarus 181, 63–93] and we estimate the effective diameter of the primary (DpDp) and secondary (DsDs) components: Dp=0.56−0.09+0.23 km and Ds=0.27−0.05+0.13 km. The diameter and albedo of (138258) 2000 GD2 are consistent with the trend of decreasing diameter for S- and Q-type asteroids found by Delbó et al. [Delbó, M., Harris, A.W., Binzel, R.P., Pravec, P., Davies, J.K., 2003. Icarus 166, 116–130]. A possible trend of increasing beaming parameter with diameter for small (less than about 3 km) S- and Q-type asteroids is found.