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Continuing the observational programme, which was started in 1976 at the European Southern Observatory (ESO), La Silla, by Debehogne a lot of new photographic plates was obtained during February-March in 1989. These plates are used for the determination of positions of asteroids selected by „Ephemerides of Minor Planets for 1989”︁, edited by the Institute of Theoretical Astronomy of Leningrad (ITA) in 1988. They permit also discoveries of new celestial bodies as well as reidentifications of lost or badly observed asteroids during the last years. For the part treated here, the examination of the plates has revealed nine asteroids not mentioned in the Russian Ephemerides or in the disquettes as fournished by the Minor Planet Centre (MPC) of SAO. Seven were present in the ITA source. 相似文献
34.
We present the results of spectral modeling of 17 Trojan asteroids. The surface composition of this group of objects (located just beyond the main belt, trapped in Jupiter's stable Lagrange points) remains uncertain due to an absence of diagnostic absorption features in their spectra. We quantitatively analyze spectra of these objects covering the range 0.3-4.0 μm using the formulation for scattering in a particulate medium developed by Hapke. Since the widest spectral range possible is desired to provide the most robust results, recently measured near-IR spectra are combined with previously published visible and near-IR data. These composite spectra are converted to and modeled in terms of geometric albedo to provide the additional constraint of the absolute brightness of the asteroids. It is important that this modeling is performed for a large number of objects, and results are derived based on trends among best-fit models. Under this rigorous examination, we find that it is unlikely that the red spectral slope is a result of organics on the surfaces, due mainly to the lack of absorptions in the L-band. Instead, anhydrous silicates adequately describe the spectral characteristics of this group of objects. A significant fraction of carbonaceous material is also likely present, but is not responsible for the red spectral slope in these models. Also, using these models, we estimate that these surfaces contain at most a few wt% of H2O ice and no more than 10-30 wt% of hydrated silicates. 相似文献
35.
We present the results of a visible spectroscopic survey of 820 asteroids carried on between November 1996 and September 2001 at the 1.52 m telescope at ESO (La Silla). The instrumental set-up allowed an useful spectral range of about 4900 Å<λ<9200 Å. The global spatial distribution of the observed asteroids covers quite well all the region between 2.2 and 3.3 AU though some concentrations are apparent. These are due to the fact that several sub-sets of asteroids, such as families and groups, have been selected and studied during the development of the survey. The observed asteroids have been classified using the Tholen and the Bus taxonomies which, in general, agree quite well. 相似文献
36.
37.
Ricardo Génova-Santos José Alberto Rubiño-Martín Rafael Rebolo † Kieran Cleary ‡ Rod D. Davies Richard J. Davis Clive Dickinson § Nelson Falcón ‡‡ Keith Grainge Carlos M. Gutiérrez Michael P. Hobson Michael E. Jones ¶ Rüdiger Kneissl Katy Lancaster Carmen P. Padilla-Torres Richard D. E. Saunders Paul F. Scott Angela C. Taylor ¶ Robert A. Watson †† 《Monthly notices of the Royal Astronomical Society》2005,363(1):79-92
38.
Yu. A. Chernetenko 《Astronomy Letters》2007,33(12):848-851
The Sun-to-Mercury mass ratio adopted by the International Astronomical Union (6023600 ± 250) was obtained in 1987 by analyzing Mariner 10 observations (Anderson et al. 1987) and since then has not been improved. The large number of asteroids in Mercury-approaching orbits and the ever-increasing accuracy of their observations allow the mass of Mercury to be estimated by a different method. We have improved the orbital parameters of 43 asteroids and obtained 6023440 ± 530 for the Sun-to-Mercury mass ratio through a simultaneous solution based on their optical and radar observations. A further improvement in this estimate is possible in the immediate future owing to the rapid increase in the number of known asteroids whose observations can be used to solve this problem. 相似文献
39.
Manabu Yuasa 《Celestial Mechanics and Dynamical Astronomy》1992,54(1-3):291-293
The asteroids whose perihelion distances (q) are smaller than 0.983 AU and aphelion distances (% MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXafv3ySLgzGmvETj2BSbqefm0B1jxALjhiov2D% aebbfv3ySLgzGueE0jxyaibaiGc9yrFr0xXdbba91rFfpec8Eeeu0x% Xdbba9frFj0-OqFfea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs% 0dXdbPYxe9vr0-vr0-vqpWqaaeaabiGaciaacaqabeaadaqaaqGaaO% qaaiqadgfagaqeaaaa!3D1C!\[\bar Q\]) are larger than 1.017 AU are called Apollo type objects. Similarly Amor type objects are defined by the conditions: 0.987 AU < % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXafv3ySLgzGmvETj2BSbqefm0B1jxALjhiov2D% aebbfv3ySLgzGueE0jxyaibaiGc9yrFr0xXdbba91rFfpec8Eeeu0x% Xdbba9frFj0-OqFfea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs% 0dXdbPYxe9vr0-vr0-vqpWqaaeaabiGaciaacaqabeaadaqaaqGaaO% qaaiqadghagaqeaaaa!3D3C!\[\bar q\] < 1.382 AU and % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXafv3ySLgzGmvETj2BSbqefm0B1jxALjhiov2D% aebbfv3ySLgzGueE0jxyaibaiGc9yrFr0xXdbba91rFfpec8Eeeu0x% Xdbba9frFj0-OqFfea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs% 0dXdbPYxe9vr0-vr0-vqpWqaaeaabiGaciaacaqabeaadaqaaqGaaO% qaaiqadgfagaqeaaaa!3D1C!\[\bar Q\] > 1.666 AU. Both types are peculiar asteroids and have common dynamical behaviors. So, we regard these two type asteroids as one group and try to search for families among them. 相似文献
40.
We present thermal emission spectra (5.2-38 μm) of the Trojan asteroids 624 Hektor, 911 Agamemnon, and 1172 Aneas. The observations used the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope. Emissivity spectra are created by dividing the measured Spectral Energy Distribution (SED) by a model of the thermal continuum. We employ the Standard Thermal Model (STM), allowing physical parameters (e.g., radius and albedo) to vary in order to find the best thermal continuum fit to the SED. The best-fit effective radius (R) and visible geometric albedo (pv) for Hektor (R=110.0±7.3, ) and Aneas (R=69.1±5.1, ) agree very well with previous estimates, and for Agamemnon (R=71.5±5.2, ) we find slightly a smaller size and higher albedo than previously derived. Other thermal models (e.g., thermophysical) result in estimates of R and pv that vary a few percent from the STM, but the resulting emissivity spectra are identical. The emissivity spectra of all three asteroids display an emissivity plateau near 10-μm and another broader rise from ∼18 to 28 μm. We interpret these as indications of fine-grained silicates on the surfaces of these asteroids. The emissivity spectra more closely resemble emission spectra from cometary comae than those from solid surfaces and measured in the laboratory for powdered meteorites and regolith analogs. We hypothesize that the coma-like emission from the solid surfaces of trojans may be due to small silicate grains being imbedded in a relatively transparent matrix, or to a very under-dense (fairy-castle) surface structure. These hypotheses need to be tested by further laboratory and theoretical scattering work as well as continued thermal emission observations of asteroids. 相似文献