Opposition polarimetry and photometry of S- and E-type asteroids     

Irina N Belskaya  Vasilij G Shevchenko  Yurij N Krugly  Yurij S Efimov  Alberto Cellino 《Icarus》2003,166(2):276-284

The first results of the observational program devoted to simultaneous investigation of asteroid polarimetric and photometric opposition phenomena are presented. UBVRI polarimetric and V-band photometric observations of the S-type Asteroid 20 Massalia and the E-type Asteroids 214 Aschera and 620 Drakonia were carried out in 1996-1999 down to phase angles of 0.08°, 0.7°, and 1.2°, correspondingly. The S-type Asteroid 20 Massalia is characterized by the pronounced brightness opposition surge with an amplitude larger than that observed for the E-type asteroids. A sharp peak of negative polarization at small phase angles was not observed for this asteroid. The value of polarization degree at phase angle α<1° is less than 0.5% for both S and E types. The negative polarization branches of S and especially E-asteroids have an asymmetrical shape. The phase angle at which the polarization minimum occurs is close to the angle at which non-linear increase begins in the asteroid magnitude phase curves. A relation of the observed effects to the mechanism of coherent backscattering is discussed.  相似文献   

Parameters of the intense X-ray and gamma-ray radiation from the solar flare of May 20, 2002, as observed from the Coronas-F spacecraft     

A. V. Bogomolov  A. P. Ignat’ev  K. Kudela  S. N. Kuznetsov  Yu. I. Logachev  O. V. Morozov  I. N. Myagkova  S. N. Oparin  A. A. Pertsov  S. I. Svertilov  B. Yu. Yushkov 《Astronomy Letters》2003,29(3):199-204

We consider temporal, spectral, and polarization parameters of the hard X-ray and gamma-ray radiation observed during the solar flare of May 20, 2002, in the course of experiments with the SONG and SPR-N instruments onboard the Coronas-F spacecraft. This flare is one of the most intense gamma-ray events among all of the bursts of solar hard electromagnetic radiation detected since the beginning of the Coronas-F operation (since July 31, 2001) and one of the few gamma-ray events observed during solar cycle 23. A simultaneous analysis of the Coronas-F and GOES data on solar thermal X-ray radiation suggests that, apart from heating due to currents of matter in the the flare region, impulsive heating due to the injection of energetic electrons took place during the near-limb flare S21E65 of May 20, 2002. These electrons produced intense hard X-ray and gamma-ray radiation. The spectrum of this radiation extends up to energies ≥7 MeV. Intense gamma-ray lines are virtually unobservable against the background of the nonthermal continuum. The polarization of the hard X-ray (20–100 keV) radiation was estimated to be ≤15–20%. No significant increase in the flux of energetic protons from the flare under consideration was found. At the same time, according to ACE data, the fluxes of energetic electrons in interplanetary space increased shortly (～25 min) after the flare.  相似文献   

Jets in AGN as seen with an ultimate angular resolution     

L.I. Gurvits 《Astrophysics and Space Science》2003,287(1-4):235-240

Jets and cores in Active Galactic Nuclei (AGN) constitute the dominant radio structural pattern in a broad range of angular scales from hundreds of arc seconds down to sub-milliarcseconds. This brief review desribes some recent results in studying the most compact `core-jet' morphologies in AGN using Very Long Baseline Interferometry (VLBI) technique. They include measurements of the cross-section brightness distribution in pc-scale radio jets and attempts to investigate the most compact cores with brightness temperatures in excess of 10¹³ K.  相似文献   

Asteroseismological studies of three β Cephei stars: IL Vel, V433 Car and KZ Mus     

G. Handler  R. R. Shobbrook  F. F. Vuthela  L. A. Balona  F. Rodler  T. Tshenye 《Monthly notices of the Royal Astronomical Society》2003,341(3):1005-1019

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The D-CIXS X-ray mapping spectrometer on SMART-1     

M Grande  R BrowningN Waltham  D ParkerS.K Dunkin  B KentB Kellett  C.H PerryB Swinyard  A PerryJ Feraday  C HoweG McBride  K PhillipsJ Huovelin  P MuhliP.J Hakala  O VilhuJ Laukkanen  N ThomasD Hughes  H AlleyneM Grady  R LundinS Barabash  D BakerP.E Clark  C.D MurrayJ Guest  I CasanovaL.C d'Uston  S MauriceB Foing  D.J Heather  V FernandesK Muinonen  S.S RussellA Christou  C OwenP Charles  H KoskinenM Kato  K SipilaS Nenonen  M HolmstromN Bhandari  R ElphicD Lawrence 《Planetary and Space Science》2003,51(6):427-433

The D-CIXS Compact X-ray Spectrometer will provide high quality spectroscopic mapping of the Moon, the primary science target of the ESA SMART-1 mission. D-CIXS consists of a high throughput spectrometer, which will perform spatially localised X-ray fluorescence spectroscopy. It will also carry a solar monitor, to provide the direct calibration needed to produce a global map of absolute lunar elemental abundances, the first time this has been done. Thus it will achieve ground breaking science within a resource envelope far smaller than previously thought possible for this type of instrument, by exploiting two new technologies, swept charge devices and micro-structure collimators. The new technology does not require cold running, with its associated overheads to the spacecraft. At the same time it will demonstrate a radically novel approach to building a type of instrument essential for the BepiColombo mission and potential future planetary science targets.  相似文献   

Mezen Bay—a key area for understanding Weichselian glaciations in northern Russia     

Kurt H. Kjr  Igor N. Demidov  Eiliv Larsen  Andrew Murray  Jan K. Nielsen 《第四纪科学杂志》2003,18(1):73-93

Sediment successions in coastal cliffs around Mezen Bay, southeastern White Sea, record an unusually detailed history of former glaciations, interstadial marine and fluvial events from the Weichselian. A regional glaciation model for the Weichselian is based on new data from the Mezen Bay area and previously published data from adjacent areas. Following the Mikulinian (Eemian) interglacial a shelf‐centred glaciation in the Kara Sea is reflected in proglacial conditions at 100–90 ka. A local ice‐cap over the Timan ridge existed between 75 and 65 ka. Renewed glaciation in the Kara Sea spread southwestwards around 60 ka only, interrupted by a marine inundation, before it advanced to its maximum position at about 55–50 ka. After a prolonged ice‐free period, the Scandinavian ice‐sheet invaded the area from the west and terminated east of Mezen Bay about 17 ka. The previously published evidence of a large ice‐dammed lake in the central Arkhangelsk region, Lake Komi, finds no support in this study. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Ion Irradiation of Asphaltite: Optical Effects and Implications for Trans-Neptunian Objects and Centaurs     

Moroz  L. V.  Baratta  G.  Distefano  E.  Strazzulla  G.  Starukhina  L. V.  Dotto  E.  Barucci  M. A. 《Earth, Moon, and Planets》2003,92(1-4):279-289

Trans-Neptunian Objects (TNOs) and Centaurs show remarkable colour variationsin the visual and near-infrared spectral regions. Surface alteration processes such asspace weathering (e.g., bombardment with ions) and impact resurfacingmay play an important role in the colour diversity of such bodies. Ion irradiation ofhydrocarbon ices and their mixtures with water ice transforms neutral (grey) surfacecolours of ices to red and further to grey. Along with the ices, TNOs and Centaursprobably contain complex carbonaceous compounds, in particular, complexhydrocarbons. Unlike ices, such refractory organic materials have originally lowvisual albedos and red colours in the visible and near-infrared ranges. Here wepresent the first results of ion irradiation experiments on asphaltite. Asphaltite isa natural complex hydrocarbon material. The reflectance spectra of asphaltite inthe 0.4–0.8 μm range have been recorded before irradiation and after eachirradiation step. We demonstrate that irradiation of this red dark material with30 keV H⁺ and 15 keV N⁺ ions gradually transforms its colour from redto grey as a result of carbonization. A moderate increase in the visual albedo hasbeen observed. These results may imply that the surfaces of primitive red objectsoptically dominated by complex refractory organics may show a similar spaceweathering trend. Our laboratory results were compared with published coloursof TNOs and Centaurs. A broad variety of spectral colours observed for TNOs andCentaurs may be reproduced by various spectra of irradiated organics correspondingto different ion fluences. However, such objects probably also contain ices and silicatecomponents which show different space weathering trends. This fact, together with alack of information about albedos, may explain difficulties to reveal correlations between surface colours within TNO and Centaur populations and their other properties, such as absolute magnitudes and orbital parameters.  相似文献   

Microtextures and crystal chemistry in P21/c pigeonites     

M. Tribaudino  D. Pasqual  G. Molin  L. Secco 《Mineralogy and Petrology》2003,77(3-4):161-176

Summary ?A single-crystal X-ray investigation was performed on crystals of P2₁/c natural pigeonite with varying Ca and Fe^* ( = Fe²⁺ + Mn²⁺) contents, in order to verify the effect of microtextural disorder on structure refinements and to constrain the crystal chemistry of pigeonite. Antiphase domains and exsolution lamellae affect differently the refinement results. In a crystal free of exsolution the structure obtained after refinement with all reflections is an average of that of the antiphase domains and of their boundaries, whereas in an exsolved crystal it represents only the structure of the prevailing pigeonite lamellae. The refinement using only h + k odd reflections seems to give the structure of the Ca-free pigeonite characteristic of the antiphase domains rather than that of Ca-rich domain walls. The ratio of the scale factors in refinements with all reflections and with only h + k odd reflections allows the ratios of the exsolved augite and pigeonite phases to be estimated. The crystal chemistry of the investigated samples follows the trends outlined by data on Ca-free and Fe-free synthetic samples. In particular, it is shown that Ca and Fe^* substitution for Mg induce similar changes in the average structure, i.e. both induce an expansion in the M1 polyhedron and decrease the difference between the M2–O3 distances. Received October 18, 2001; revised version accepted February 15, 2002  相似文献   

The discovery of two distant, massive clusters of galaxies in the ROSAT All-Sky Survey     

A. C. Edge  H. Ebeling  †  M. Bremer  H. Röttgering  M. P. van Haarlem  R. Rengelink  N. J. D. Courtney 《Monthly notices of the Royal Astronomical Society》2003,339(4):913-924

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The 2dF QSO Redshift Survey – X. Lensing of background QSOs by galaxy groups     

A. D. Myers  P. J. Outram  T. Shanks  B. J. Boyle  S. M. Croom  N. S. Loaring  L. Miller  R. J. Smith 《Monthly notices of the Royal Astronomical Society》2003,342(2):467-482

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