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[en] The external accuracy of photometric parameters of asteroids is investigated by a comparison of published lists. Absolute magnitudes are consistent at the ±0.1 mag level but phase coefficients are still rather uncertain. (author). 1 fig., 1 tab., 5 refs
[en] The data on 37 asteroids obtained with the Calsberg Automatic Meridian Circle at La Palma have been used to obtain the photometric parameters G and H and to draw phase diagrams. This supplements data on 51 asteroids and on 31 asteroids using the same techniques. Synodic periods were obtained for 6 asteroids and composite lightcurves drawn. For 10 Hygiea our value of 17.5 hours is different from that of Vesely and Taylor (1985) but in agreement with the result reported by Harris and Young (1983). 24 asteroids were of type S and the mean value of 0.19 agrees very well with that of Lagerkvist and Williams (1987) and Lagerkvist et al. (1988). For the 6 asteroids of type C we get a mean G value of 0.04 agreeing well with earlier results
[en] Preliminary results are presented of an attempt to define threshold values of eccentricity and inclination for which a second order - fourth degree analytical theory of asteroid motion still provides mean semimajor axes of acceptable accuracy. (author). 2 figs., 1 tab., 6 refs
[en] The distribution of asteroid taxonomic classes and, presumably, actual composition varies systematically with heliocentric distance and is seen qualitatively in the results of a variety of taxonomy methods. In general, the distribution of taxonomic classes is characterized by moderate-albedo asteroids dominant in the inner belt with low-albedo asteroids prevalent in the outer belt and beyond. If the differences in taxonomic classes are assumed to be due to differences in composition, then the asteroid belt can be divided into many compositionally distinct regions defined by peaks and troughs in the distributions of the various classes. Unfortunately, differences in the class definitions used by different classification methods are manifested in the bias-corrected distribution of the classes, which makes detailed interpretation of these trends difficult. UBV color differences among members of the moderate-albedo S class show a distribution in semimajor axis which indicates subgroups in the S class. Explanations of the causes of the overall trends range from primarily dynamical to primarily in situ arrangements of igneous, metamorphic and unaltered primitive material, but a combination of several of these factors may be more likely
[en] Synchronous binary asteroids may exist in a long-term stable equilibrium, where the opposing torques from mutual body tides and the binary YORP (BYORP) effect cancel. Interior of this equilibrium, mutual body tides are stronger than the BYORP effect and the mutual orbit semimajor axis expands to the equilibrium; outside of the equilibrium, the BYORP effect dominates the evolution and the system semimajor axis will contract to the equilibrium. If the observed population of small (0.1-10 km diameter) synchronous binaries are in static configurations that are no longer evolving, then this would be confirmed by a null result in the observational tests for the BYORP effect. The confirmed existence of this equilibrium combined with a shape model of the secondary of the system enables the direct study of asteroid geophysics through the tidal theory. The observed synchronous asteroid population cannot exist in this equilibrium if described by the canonical 'monolithic' geophysical model. The 'rubble pile' geophysical model proposed by Goldreich and Sari is sufficient, however it predicts a tidal Love number directly proportional to the radius of the asteroid, while the best fit to the data predicts a tidal Love number inversely proportional to the radius. This deviation from the canonical and Goldreich and Sari models motivates future study of asteroid geophysics. Ongoing BYORP detection campaigns will determine whether these systems are in an equilibrium, and future determination of secondary shapes will allow direct determination of asteroid geophysical parameters.
[en] We present the optical observations of the Near Earth Object 107P/(4015) Wilson-Harrington during the 2009/2010 apparition taken in search of low-level comet activity. Our photometric and spectroscopic data were collected 28-86 days after the perihelion passage on 2009 October 22 in a wide range of solar phase angles of 39 deg. - 68 deg. A disk-integrated phase function was constructed, giving a geometric albedo of 0.055 ± 0.012, phase integral of q = 0.34, and Bond albedo of AB = 0.019. The photometric property shows a profile similar to low albedo asteroids and comet nuclei. No emission lines were found in our spectrum, giving a flat reflectance similar to low albedo asteroids. Although we could not find any evidence for cometary activity in our photometric and spectroscopic data, we found an upper limit of 0.001% on the fractional active area. We derived the upper limit of the optical depth of the dust trail and tail, 7 x 10-10. We conclude that 107P/(4015) Wilson-Harrington was completely dormant or inactive in the 2009/2010 return.
[en] A substantial body of indirect evidence suggests that some asteroids have satelities, although none has been detected unambiguously. Collisions between asteroids provide physically plausible mechanisms for the production of binaries, but these operate with low probability; only a small minority of asteroids are likely to have satellites. The abundance of binary asteroids can constrain the collisional history of the entire belt population. The allowed angular momentum of binaries and their rate of tidal evolution limit separations to no more than a few tens of the primary's radii. Their expected properties are consistent with failure to detect them by current imaging techniques
[en] The outcomes of asteroidal catastrophic collisions are strongly affected by the target asteroid's gravity, since only the fragments escaping with initial velocities higher than the target's escape velocity are not reaccumulated into 'rubble pile' remnants. This idea can be compared with the observational evidence on the properties of family asteroids in several ways: (1) the shape and spin period of the 'reaccumulated' family asteroids will roughly fit the relationships valid for self-gravitating fluid bodies; (2) the relative velocities of the few escaping fragments arising from a breakup event marginally overcoming self-gravity will often have an anisotropic distribution, affecting the final distribution of orbital elements; (3) the amount of mass which in a given family escaped to 'infinity' will be correlated with the target's size, since only for objects larger than approx. 100 km self-gravity plays an important role. These predictions are discussed and compared with the available data. (Auth.)
[en] Observations with the adaptive optics system on the Very Large Telescope reveal that the outer main belt asteroid (702) Alauda has a small satellite with primary to secondary diameter ratio of ∼56. The secondary revolves around the primary in 4.9143 ± 0.007 days at a distance of 1227 ± 24 km, yielding a total system mass of (6.057 ± 0.36) x 1018 kg. Combined with an IRAS size measurement, our data yield a bulk density of 1570 ± 500 kg m-3 for this B-type asteroid.