Near-infrared observations of MUSES-C mission target

We present near-infrared photometric and spectroscopic observations of the MUSES-C Japanese asteroid sample return mission target (25143) 1998 SF36, which were obtained with the 8-m SUBARU telescope. The near-infrared colors were found to be J - H = 0.49+/-0.04 and H - K = 0.02+/-0.04, where J, H, and K are the magnitudes at the center wavelength of 1.25, 1.63, and 2.12 mum, respectively. Comparing these colors to those of known taxonomic type asteroids, we find this asteroid to be S-type. We combined our M'-band (4.68 mum) photometric data with N-band photometric data obtained at the mid-IR wavelength. Using the free beaming parameter thermal model (FBM), the derived size of 1998 SF36, assuming the shape of an ellipsoid, are a = 620+/-140 m, b = 280+/-60 m, and c = 160+/-30 m, and geometric albedo in the V-band (0.55 mum) is 0.35+/-0.11. The beaming parameter from FBM is found to be 1.1. Our results show that the albedo of 1998 SF36 is high among S-type asteroids, and that the thermal inertia seems to be higher than that of average asteroids. From this we can say that the regolith thickness of this small asteroid is thin, and/or the surface is covered with bare rocks. We also obtained photometric and spectroscopic data in the L-band (3.77 mum). Since there is no clear absorption band seen around 3 mum, we estimate that the water abundance of the surface material is less than 1% in weight.