Optical and thermal infrared observations of six near-Earth asteroids in 2002

We present thermal infrared photometry and spectrophotometry of six Near-Earth Asteroids (NEAs) using the 3.8 m United Kingdom Infrared Telescope (UKIRT) together with quasi-simultaneous optical observations of five NEAs taken at the 1.0 m Jacobus Kapteyn Telescope (JKT). For Asteroid (6455) 1992 HE we derive a rotational period P=2.736±0.002h, and an absolute visual magnitude H=14.32±0.24. For Asteroid 2002 HK12 we derive H=18.22(+0.37,−0.30). The Standard Thermal Model (STM), the Fast Rotating Model (FRM) and the Near-Earth Asteroid Thermal Model (NEATM) have been fitted to the measured fluxes to derive albedos and effective diameters. The derived geometric albedos and effective diameters are (6455) 1992 HE: pv=0.26±0.08, Deff=3.55±0.5km; 1999 HF1: pv=0.18±0.07, Deff=3.73(+1.0,−0.5)km; 2000 ED104: pv=0.18±0.05, Deff=1.21±0.2km; 2002 HK12: pv=0.24(+0.25,−0.11), Deff=0.62±0.2km; 2002 NX18: pv=0.031±0.009, Deff=2.24±0.3km; 2002 QE15: pv=0.15(+0.08,−0.06), Deff=1.94±0.4km. The limitations of using the NEATM to observe NEAs at high phase angles are discussed.