Systematic uncertainties in the analysis of star cluster parameters based on broad-band imaging observations     

R. de Grijs  P. Anders  H. J. G. L. M. Lamers  N. Bastian  U. Fritze-v. Alvensleben  G. Parmentier †  M. E. Sharina  S. Yi 《Monthly notices of the Royal Astronomical Society》2005,359(3):874-894

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Microwave observations of Saturn's rings: anisotropy in directly transmitted and scattered saturnian thermal emission     

David E. Dunn  Lawrence A. Molnar  Imke de Pater 《Icarus》2004,171(1):183-198

We present a new Very Large Array (VLA) image of Saturn, made from data taken in October 1998 at a wavelength of λ3.6 cm. The moderate ring opening angle (B≈15°) allows us to explore direct transmission of microwave photons through the A and C rings. We find a strong asymmetry of photons transmitted through the A ring, but not in the C ring, a new diagnostic of wake structure in the ring particles. We also find a weak asymmetry between east and west for the far side of the ansae. To facilitate quantitative comparison between dynamic models of the A ring and radio observations, we extend our Monte Carlo radiative transfer code (described in Dunn et al., 2002, Icarus 160, 132-160) to include idealized wakes. We show the idealized model can reproduce the properties of dynamic simulations in directly transmitted light. We examine the model behavior in directly transmitted and scattered light over a range of physical and geometric wake parameters. Finally, we present a wake model with a plausible set of physical parameters that quantitatively reproduces the observed intensity and asymmetry of the A ring both across the planet and in the ansae.  相似文献   

Simultaneous operation of the Sea Beam multibeam echo-sounder andthe SeaMARC II bathymetric sidescan sonar system     

de Moustier  C. Lonsdale  P.F. Shor  A.N. 《Oceanic Engineering, IEEE Journal of》1990,15(2):84-94

An experiment aboard the Scripps Institution of Oceanography's RV Thomas Washington has demonstrated the seafloor mapping advantages to be derived from combining the high-resolution bathymetry of a multibeam echo-sounder with the sidescan acoustic imaging plus wide-swath bathymetry of a shallow-towed bathymetric sidescan sonar. To a void acoustic interference between the ship's 12-kHz Sea Beam multibeam echo-sounder and the 11-12-kHz SeaMARC II bathymetric sidescan sonar system during simultaneous operations, Sea Beam transmit cycles were scheduled around SeaMARC II timing events with a sound source synchronization unit originally developed for concurrent single-channel seismic, Sea Beam, and 3.5-kHz profile operations. The scheduling algorithm implemented for Sea Beam plus SeaMARC II operations is discussed, and the initial results showing their combined seafloor mapping capabilities are presented  相似文献   

Dynamical and compositional assessment of near‐Earth object mission targets     

Richard P. BINZEL  Ettore PEROZZI  Andrew S. RIVKIN  Alessandro ROSSI  Alan W. HARRIS  Schelte J. BUS  Giovanni B. VALSECCHI  Stephen M. SLIVAN 《Meteoritics & planetary science》2004,39(3):351-366

Abstract— Using an H‐plot analysis, we identify 234 currently known near‐Earth objects that are accessible for rendezvous with a “best case” delta‐V of less than 7 km/s. We provide a preliminary compositional interpretation and assessment of these potential targets by summarizing the taxonomic properties for 44 objects. Results for one‐half (22) of this sample are based on new spectroscopic measurements presented here. Our approach provides an easy‐to‐update method for giving guidelines to both observers and mission analysts for focusing on objects for which actual mission opportunities are most likely to be found. Observing prospects are presented for categorizing the taxonomic properties of the most accessible targets that are not yet measured.  相似文献   

A 20 cm2 CCD mosaic camera for a dark matter search part I : Mechanics,optics and cryogeny     

Arnaud  M.  Aubourg  E.  Bareyre  P.  Br';ehin  S.  Caridroit  R.  de Kat  J.  Dispau  G.  Djidi  K.  Gros  M.  Lachièze-Rey  M.  Laigneau  Y.  Laurent  B.  Lesquoy  E.  Lavocat  Ph.  Magneville  C.  Mazeau  B.  Milsztajn  A.  Moscoso  L.  Pasquaud  J.  Paul  B.  Perrin  P.  Petibon  J.  Piret  Y.  Queinnec  F.  Rich  J.  Spiro  M.  de Trogoff  J.  Vigroux  L.  Zylberajch  S.  Ansari  R.  Cavalier  F.  Moniez  M.  Beaulieu  J. P.  Ferlet  R.  Grison  Ph.  Vidal-Madjar  A.  Adrianzyk  G.  Berger  J. P.  Burnage  R.  Delclite  J. C.  Kohler  D.  Magnan  R.  Richaud  A.  Guibert  J.  Moreau  O.  Tajahmady  F.  Baranne  A.  Maurice  E.  Prévôt  L.  Gry  C. 《Experimental Astronomy》1994,4(3-4):265-278

A 20cm ² CCD mosaic camera has been especially built to search for dark galactic halo objects by the gravitational microlensing effect. The sensitive area is made of 16 edge-buttable CCDs developped by Thomson-CTS, with 23×23 µm ² pixels. The 35 kg camera housing and mechanical equipment is presented. The associated electronics and data acquisition system are described in a separate paper. The camera resides at the focal plane of a 40 cm, f/10, Ferson reflector. The instrument has been in operation since December 1991 at the La Silla Observatory (ESO).  相似文献   

Star cluster ecology – V. Dissection of an open star cluster: spectroscopy     

Simon F. Portegies Zwart †  Piet Hut  Stephen L. W. McMillan  Junichiro Makino 《Monthly notices of the Royal Astronomical Society》2004,351(2):473-486

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B0850+054: a new gravitational lens system from CLASS     

A. D. Biggs  D. Rusin  I. W. A. Browne  A. G. de Bruyn  N. J. Jackson  L. V. E. Koopmans  J. P. McKean  S. T. Myers  R. D. Blandford  K.-H. Chae  C. D. Fassnacht  M. A. Norbury  T. J. Pearson  P. M. Phillips  A. C. S. Readhead  P. N. Wilkinson 《Monthly notices of the Royal Astronomical Society》2003,338(4):1084-1088

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A high-resolution rotation curve of NGC 6822: a test-case for cold dark matter     

D. T. F. Weldrake  W. J. G. de Blok †  F. Walter 《Monthly notices of the Royal Astronomical Society》2003,340(1):12-28

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Stellar populations in local star-forming galaxies – II. Recent star formation properties and stellar masses     

P. G. Pérez-González  A. Gil de Paz †  J. Zamorano  J. Gallego  A. Alonso-Herrero  A. Aragón-Salamanca 《Monthly notices of the Royal Astronomical Society》2003,338(2):525-543

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Thermal effects in the ultrarelativistic two-stream instability     

Stephen M. White 《Astrophysics and Space Science》1985,116(1):173-187

The dispersion relation for longitudinal waves in a one-dimensional ultrarelativistic plasma is calculated. Analytical and numerical results for the growth rate and frequency of the two-stream instability are presented as a function of the energy spread in the denser stream when the dilute stream is cold. The case of energy spreads in both beams is investigated numerically: it is found that relatively small energy spreads in both streams can lead to suppression of the instability.  相似文献