Imaging the surface of Mercury using ground-based telescopes     

Michael Mendillo  Johan Warell  Sanjay S. Limaye  Jeffrey Baumgardner  Ann Sprague  Jody K. Wilson 《Planetary and Space Science》2001,49(14-15)

We describe and compare two methods of short-exposure, high-definition ground-based imaging of the planet Mercury. Two teams have recorded images of Mercury on different dates, from different locations, and with different observational and data reduction techniques. Both groups have achieved spatial resolutions of <250 km, and the same albedo features and contrast levels appear where the two datasets overlap (longitudes 270–360°). Dark albedo regions appear as mare and correlate well with smooth terrain radar signatures. Bright albedo features agree optically, but less well with radar data. Such confirmations of state-of-the-art optical techniques introduce a new era of ground-based exploration of Mercury's surface and its atmosphere. They offer opportunities for synergistic, cooperative observations before and during the upcoming Messenger and BepiColombo missions to Mercury.  相似文献   

Rotational broadening and Doppler tomography of the quiescent X-ray nova Centaurus X-4     

M. A. P. Torres  J. Casares  I. G. Martínez-Pais  P. A. Charles 《Monthly notices of the Royal Astronomical Society》2002,334(1):233-240

We present a library of 47 open-cluster integrated spectra, mostly obtained at CASLEO (San Juan, Argentina) in the range  3600 < λ < 7400 Å  , which are made available at CDS. The data are combined with previous spectra to obtain 10 high signal-to-noise ratio basic templates in the young and intermediate-age domains, which are also provided in the library. These Galactic disc templates represent the increased time resolution spectral evolution of a stellar population unit around the Solar metallicity level. The improved signal-to-noise ratio of the present templates with respect to previous template lists, together with their increased time resolution, allowed us to improve the fundamental parameters of some open clusters. The present spectral library will be useful for several astrophysical applications, particularly for population syntheses of star-forming giant galaxies.  相似文献   

Chemo-spectrophotometric evolution of spiral galaxies – IV. Star formation efficiency and effective ages of spirals     

S. Boissier  A. Boselli  N. Prantzos  G. Gavazzi 《Monthly notices of the Royal Astronomical Society》2001,321(4):733-742

We study the star formation history of normal spirals by using a large and homogeneous data sample of local galaxies. For our analysis we utilize detailed models of chemical and spectrophotometric galactic evolution, calibrated on the Milky Way disc. We find that star formation efficiency is independent of galactic mass, while massive discs have, on average, lower gas fractions and are redder than their low-mass counterparts; put together, these findings convincingly suggest that massive spirals are older than low-mass ones. We evaluate the effective ages of the galaxies of our sample and we find that massive spirals must be several Gyr older than low-mass ones. We also show that these galaxies (having rotational velocities in the 80–400 km s⁻¹ range) cannot have suffered extensive mass losses, i.e. they cannot have lost during their lifetime an amount of mass much larger than their current content of gas+stars.  相似文献   

Shape Analysis of Isoseismals Based on Empirical and Synthetic Data   总被引：1，自引：0，他引：1  

G. Molchan  T. Kronrod  G. F. Panza 《Pure and Applied Geophysics》2002,159(6):1229-1251

—?We present an attempt to compare modeled ground-motion acceleration fields with macroseismic observations. Two techniques for the representation of the observed intensities by isoseismals, a smoothing technique and one which visualizes the local uncertainty of an isoseismal, are tested with synthetic and observed data. We show how noise in the data and irregularities in the distribution of observation sites affect the resolution of the isoseismal's shape. In addition to “standard” elongated shapes, we identify cross-like patterns in the macroseismic observations for two Italian earthquakes of strike-slip type; similar patterns are displayed by the theoretical peak acceleration fields calculated assuming the point source models given in the literature.  相似文献   

Trace-element contents and cathodoluminescence of “trapiche” rubies from Mong Hsu, Myanmar (Burma): geological significance     

V. Garnier  D. Ohnenstetter  G. Giuliani  P. Blanc  D. Schwarz 《Mineralogy and Petrology》2002,76(3-4):179-193

Summary ?Mong Hsu rubies of the “trapiche” type are sporadically seen in the gem market. However, they have never been described in the field. The study of the nature of solid inclusions, the variation of trace-element contents, as well as the cathodoluminescence behaviour of six “trapiche” rubies permit the conclusion that these rubies crystallised in the same geological environment (marble-type deposit) as the normal rubies from Mong Hsu: (1) Cr and V are the main chromophorous elements in both ruby types; they act, together with Ti, as activators or quenchers for cathodoluminescence; (2) calcite, dolomite, rutile, mica, diaspore, apatite, chlorite, and feldspar are solid inclusions found in both ruby types; (3) the presence of bastn?site in trapiche ruby and fluorite in non-trapiche ruby indicates the circulation of F-bearing fluids during ruby deposition; (4) the distribution of trace-element contents in the crystal is similar for both ruby types. In the Cr₂O₃ vs. Fe₂O₃ and Cr₂O₃ vs. Fe₂O₃/TiO₂ diagrams, the population fields of Mong Hsu “trapiche” and non-“trapiche” rubies overlap. They are distinct from those of rubies and sapphires hosted in basalts from South-east Asia. Received October 30, 2001; revised version accepted March 25, 2002  相似文献   

Some New Observed Properties of Elliptical Galaxies     

D. Gerbal  H.V. Capelato  F. Durret  G.B. Lima Neto  I. Márquez 《Astrophysics and Space Science》2001,276(2-4):861-868

We suggest that elliptical galaxies, as stellar systems in a stage of quasi-equilibrium, may have a specific entropy. We use the Sérsic law to describe the light profile. The specific entropy (the Boltzmann–Gibbs definition) is then calculated assuming that the galaxy behaves as a spherical, isotropic, one-component system. We predict a relation between the three parameters of the Sérsic law linked to the specific entropy, defining a surface in the parameter space, an ‘entropic plane’. We have analysed a sample of simulated merging elliptical galaxies (virtual) and a sample of galaxies belonging to the Coma Cluster (real). Both virtual and realgalaxies are: 1) located in their own ‘entropic plane‘ and 2) in this plane, they are located on a straight line, indicating constant entropy: another physical property A careful examination of the value of the specific entropy indicates a very small increase in the specific entropy with the generation after merging (virtual sample). Although one cannot distinguish between various generations for real galaxies, the distribution of specific entropy in this sample is very similar to that in the virtual sample. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

First results from the Isaac Newton Telescope Wide Angle Survey: the     quasar survey     

R.G. Sharp  R.G. McMahon  M.J. Irwin  S.T. Hodgkin 《Monthly notices of the Royal Astronomical Society》2001,326(4):L45-L49

We report the first results of an observational programme designed to determine the luminosity density of high-redshift quasars     quasars) using deep multicolour CCD data. We report the discovery and spectra of three     high-redshift     quasars, including one with     . At     , this is the fourth highest redshift quasar currently published. Using these preliminary results we derive an estimate of the         quasar space density in the redshift range     of     . When completed, the survey will provide a firm constraint on the contribution to the ionizing UV background in the redshift range     from quasars by determining the faint-end slope of the quasar luminosity function. The survey uses imaging data taken with the 2.5-m Isaac Newton Telescope as part of the Public Isaac Newton Group Wide Field Survey (WFS). This initial sample of objects is taken from two fields of effective area ∼12.5 deg² from the final ∼100 deg².  相似文献   

The scaling of the redshift power spectrum: observations from the Las Campanas redshift survey     

Y.P. Jing  G. Börner 《Monthly notices of the Royal Astronomical Society》2001,325(4):1389-1396

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2001 Leonard Medal Citation for Harry Y. McSween,Jr.     

Michael J. Drake 《Meteoritics & planetary science》2002,37(1):5-6

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The EVN-MarkIV VLBI Data Processor     

R. T. Schilizzi  W. Aldrich  B. Anderson  A. Bos  R. M. Campbell  J. Canaris  R. Cappallo  J. L. Casse  A. Cattani  J. Goodman  H. J. van Langevelde  A. Maccafferri  R. Millenaar  R. G. Noble  F. Olnon  S. M. Parsley  C. Phillips  S. V. Pogrebenko  D. Smythe  A. Szomoru  H. Verkouter  A. R. Whitney 《Experimental Astronomy》2001,12(1):49-67

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