Thermal infrared and optical observations of four near-Earth asteroids

Abstract

We present thermal infrared photometry and spectrophotometry of four near-Earth asteroids (NEAs), namely (433) Eros, (66063) 1998 RO 1, (137032) 1998 UO 1, and (138258) 2000 GD 2, using the United Kingdom Infrared Telescope (UKIRT) in 2002. For two objects, i.e. (433) Eros and (137032) 1998 UO 1, quasi-simultaneous optical observations were also obtained, using the Jacobus Kapteyn Telescope (JKT). For (127032) 1998 UO 1, we obtain a rotation period P = 3.0 ± 0.1 h and an absolute visual magnitude H V = 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 D eff , geometric albedos p v , and beaming parameters η. The derived values are (433) Eros: D eff = 23.3 ± 3.5 km (at lightcurve maximum), p v = 0.24 ± 0.07 , η = 0.95 ± 0.19 ; (66063) 1998 RO 1: D eff = 0.62 −0.09 +0.25 km , p v = 0.30 −0.17 +0.09 ; (137032) 1998 UO 1: D eff < 1.13 km , p v > 0.29 ; (138258) 2000 GD 2: D eff = 0.27 ± 0.04 km , p v = 0.56 −0.22 +0.32 , η = 0.74 ± 0.15 . (66063) 1998 RO 1 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 ( D p ) and secondary ( D s ) components: D p = 0.56 −0.09 +0.23 km and D s = 0.27 −0.05 +0.13 km . The diameter and albedo of (138258) 2000 GD 2 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.