On the cause of the discrepancy between groundbased and spaceborne lightcurves of Ganymede and Callisto in the <Emphasis Type="Italic">V</Emphasis> band

Properties of the surfaces of Jupiter’s satellites—Ganymede and Callisto—are shortly described. Their images acquired in space missions are shown. Causes of the discrepancy between orbital lightcurves of the satellites obtained from the earth and spaceborne maps of the satellites are considered. The groundbased observations were carried out under phase angles of solar illumination ranging from 0° to 12°, and the maps were built from images acquired from spacecraft in a wide interval of solar phase angles. We suggest that the main cause of the discrepancies between the lightcurves is the coherent backscattering effect observed only at small phase angles of the sun.     

Evidence of the complex structure of asteroid 21 Lutetia

We discuss the results of the analysis of three sets of observations of asteroid 21 Lutetia—spectrophotometry, simultaneous BVR photometry, and spectrometry—which show that the asteroid is not a monolithic body. The frequency analysis of the B-V and V-R color indices and the V values, which were obtained from simultaneous BVR measurements in 2004 and calculated from the spectrophotometric observations performed in 2000 (the synthetic values and the color indices), allowed us to demonstrate that the known rotation period of 8.^h172 of the asteroid does not exist at all. At a rather high confidence level, six new periods were found: 2.^h0, 2.^h93, 16.^h8, 1.^d25, 3.^d25, and 60^d. During spectral observations with a 1.25-m telescope at the southern laboratory of the Sternberg Astronomical Institute in Nauchnyi (Crimea) in 2004, the spectra of two components spaced 2.8″ apart were registered. In the short-wavelength spectral range, quick variations of the reflectance of the components were observed. They show the changes in their spectral types from S to C. The analysis of the synthetic values of the color indices determined from the spectrophotometric observations in 2000 confirmed the presence of quick spectral variations. We conclude that asteroid 21 Lutetia is a complex satellite system. This statement is confirmed by the analysis of data published in different sources.     

On the Family of the Binary Asteroid 423 Diotima

We identified the family of the binary asteroid 423 Diotima consisting of 411 members in the phase space of orbital elements—semimajor axes a (or mean motions n), eccentricities e, and inclinations i—by using an electronic version of the ephemerides of minor planets EMP-2003 containing osculating orbital elements for 34992 asteroids of the main belt. The 9/4 resonance with Jupiter clearly separates the family of 423 Diotima from the family of Eos, which, according to EMP for 2003, contains 1204 asteroids.     

Photometric and Colorimetric Observations of Asteroid 423 Diotima and Their Analysis

Series of photometric and colorimetric observations of the Main-Belt asteroid 423 Diotima during its five oppositions were obtained at the Crimean Astrophysical Observatory. It was concluded, based on the results of a frequency analysis of the V-band photometry obtained in 1990, that the asteroid is a binary system: the rotation period of the primary component is equal to 4_. ^h56, and the period of rotation and the orbital period of the satellite are equal to 14_. ^h90. An analysis of simultaneous BV and BVR observations made in 1993 and 1998–1999 yielded a rotation period of 4_. ^h54 ± 0_. ^h01 for the primary component. An analysis of the sets of V-band observations of the asteroid made from 1982 through 2000 allowed us to find the period of forced precession, which was equal to 113^d (or 226^d). It was suggested that the axis of the primary component of the binary asteroid precesses and the large amplitude of brightness variations (about 1 ^m ) is due to its lenticular shape.     

On possible binarity of Leatitia asteroid 39

The 39 Laetitia asteroid was observed by the digital television complex at the Crimean Astrophysical Observatory in 2000 in three spectral bands close to B, V and R simultaneously. An analysis of the variations in the absolute magnitude shows that there is a known period of rotation P = 0.^d214093. In variations of color indices B-V and V-R, this period is absent. Frequency analysis of color indices B-V and V-R makes it possible to reveal the true periods of rotation for components as follows: P ₁ = 0.^d237 and P ₂ = 0.^d177. The theoretical and observed period of librations agrees in value. Based on the two detected periods of rotation for asteroid components according to color indices B-V and V-R, a period of the libration of the satellite according to integral magnitude, we conclude that this asteroid is a binary one.     

Photometry of Io and Europa at the Crimean Astrophysical Observatory and reasons for differences between ground-based and space observations

Photometric observations of Jupiter’s moons Io and Europa in the spectral band V have been made at the Crimean Astrophysical Observatory for four years in order to construct their light curves reduced to a Solar phase angle of 6°. Comparison of these data with other ground-based observations shows good agreement. This study confirms why the moons that are close to Jupiter have a brighter leading hemisphere. The trailing hemispheres of Io and Europa, which are located in the rapidly rotating magnetic field of Jupiter, are exposed to bombardment by charged particles of the magnetic field. Leaving out of consideration the differences in brightness between the two hemispheres results in serious discrepancies between the space and ground-based photometry data.