Context. Near-Earth asteroid 162173 (1999 JU3) is a potential flyby and rendezvous target for interplanetary missions because of its easy-to-reach orbit. The physical and thermal properties of the asteroid are relevant for establishing the scientific mission goals and also important in the context of near-Earth object studies in general. Aims. Our goal was to derive key physical parameters such as shape, spin-vector, size, geometric albedo, and surface properties of 162173 (1999 JU3). Methods. With three sets of published thermal observations (ground-based N-band, Akari IRC, Spitzer IRS), we applied a thermophysical model to derive the radiometric properties of the asteroid. The calculations were performed for the full range of possible shape and spin-vector solutions derived from the available sample of visual lightcurve observations. Results. The near-Earth asteroid 162173 (1999 JU3) has an effective diameter of 0.87 ± 0.03 km and a geometric albedo of 0.070 ± 0.006. The χ 2 -test reveals a strong preference for a retrograde sense of rotation with a spin-axis orientation of λ ecl = 73 • , β ecl = −62 • and P sid = 7.63 ± 0.01 h. The most likely thermal inertia ranges between 200 and 600 J m −2 s −0.5 K −1 , about a factor of 2 lower than the value for 25143 Itokawa. This indicates that the surface lies somewhere between a thick-dust regolith and a rock/boulder/cm-sized, gravel-dominated surface like that of 25143 Itokawa. Our analysis represents the first time that shape and spin-vector information has been derived from a combined data set of visual lightcurves (reflected light) and mid-infrared photometry and spectroscopy (thermal emission).

Context. The recently discovered Apollo-type near-Earth asteroid 2005 UD has been suggested to be a fragment of (3200) Phaethon. Aims. To test this hypothesis, we carried out photometric observations of 2005 UD using the 1-m telescope at Lulin Observatory. Methods. Multi-color photometry was used to compare the surface properties of (3200) Phaethon and 2005 UD. Surface-color variation due to the rotation was also examined. Conclusions. The similarity of surface colors between (3200) Phaethon and 2005 UD observationally supports the hypothesis that 2005 UD is likely to be a fragment of (3200) Phaethon. A simple explanation for the inhomogeneity of the surface is that we see the surface and subsurface of the precursor object. Another explanation is the topographical structure that such as a large crater causes on this heterogeneous surface.

[1] The D type asteroids are among the darkest objects known in our solar system. Here, we present infrared spectra of one of the main-belt D type asteroids, 773 Irmintraud. In contrast to previous observations of D type asteroids, we found a gap of reflectance around 3 mm in wavelength. The 3 mm gap is one of the spectral signatures of OH or H 2 O as water ice or in hydrous minerals, which had formed in the processes of aqueous alteration in the early solar system. We suggest that D type asteroids, which are all the while considered as unaltered primitive material, could be aqueously altered. Our data do support the presence of water on a compositionally primitive D type asteroid.

We observed the optical afterglow of the bright gamma-ray burst GRB030329 on the nights of 2003 March 29, using the Kiso observatory (the University of Tokyo) 1.05 m Schmidt telescope. Data were taken from March 29 13:21:26 UT to 17:43:16 (0.072 to 0.253 days after the burst), using an Rc-band filter. The obtained Rc-band light curve has been fitted successfully by a single power law function with decay index of 0.891±0.004. These results remain unchanged when incorporating two early photometric data points at 0.065 and 0.073 days, reported by Price et al.(2003) using the SSO 40 inch telescope, and further including -2 -RTT150 data (Burenin et al. 2003) covering at about 0.3 days. Over the period of 0.065-0.285 days after the burst, any deviation from the power-law decay is smaller than ±0.007 mag. The temporal structure reported by Uemura et al. (2003) does not show up in our R-band light curve.

We present the results of photometric observations carried out with four small telescopes of the asteroid 4 Vesta in the B, R C , and z ′ bands at a minimum phase angle of 0.1 • . The magnitudes, reduced to unit distance and zero phase angle, were M B (1,1,0) = 3.83 ± 0.01,M R C (1,1,0) = 2.67 ± 0.01, and M z ′ (1,1,0) = 3.03 ± 0.01 mag. The absolute magnitude obtained from the IAU H-G function is ∼0.1 mag darker than the magnitude at a phase angle of 0 • determined from the Shevchenko function and Hapke models with the coherent backscattering effect term. Our photometric measurements allowed us to derive geometric albedos of 0.35 in the B band, 0.41 in the R C band, and 0.31 in the z ′ bands by using the Hapke model with the coherent backscattering effect term. Using the Hapke model, the porosity of the optically active regolith on Vesta was estimated to be ρ = 0.4-0.7, yielding the bluk density of 0.9-2.0 × 10 3 kg m −3 . It is evident that the opposition effect for Vesta makes a contribution to not only the shadow-hiding effect, but also the coherent backscattering effect that 1 appears from ca. 1 • . The amplitude of the coherent backscatter opposition effect for Vesta increases with a brightening of reflectance. By comparison with other solar system bodies, we suggest that multiple-scattering on an optically active scale may contribute to the amplitude of the coherent backscatter opposition effect (B C0 ).