Global change,the water cycle,and our search for Mauna Loa     

Charles J. Vrsmarty 《水文研究》2002,16(1):135-139

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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   

Radar observations of Itokawa in 2004 and improved shape estimation     

Steven J. Ostro  Lance A. M. Benner  Christopher Magri  Jon D. Giorgini  Randy Rose  Raymond F. Jurgens  Donald K. Yeomans  Alice A. Hine  Michael C. Nolan  Daniel J. Scheeres  Stephen B. Broschart  Mikko Kaasalainen  Jean‐Luc Margot 《Meteoritics & planetary science》2005,40(11):1563-1574

Abstract— We present June 2004 radar images of asteroid 25143 Itokawa (1998 SF36) that improve upon the longitude‐latitude coverage of images obtained in 2001 by Ostro et al. (2004) and use the 2001–2004 data to refine that paper's constraints on Itokawa's shape. The 2004 images, the first of the asteroid's southern side, look distinctly different from the 2001 images, revealing leading edges that are much more curved and rugged than the nearly convex leading edges seen at northern latitudes in 2001. Itokawa is shaped like a slightly asymmetrical, bent, lumpy ellipsoid with dimensions along the principal axes within 10% of 594 times 320 times 288 m. To illustrate the uncertainty space associated with shape reconstruction from images with suboptimal orientational coverage, we present two alternative three‐dimensional models of the object.  相似文献   

International Association For Landscape Ecology Seminar     

Steven A. Carlson 《The Professional geographer》1985,37(2):222-222

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Optical and near-infrared observations of the microquasar V4641 Sgr during the 1999 September outburst     

S. Chaty  P. A. Charles  J. Martí  I. F. Mirabel  L. F. Rodríguez  T. Shahbaz 《Monthly notices of the Royal Astronomical Society》2003,343(1):169-174

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Spectroscopic identification of the infrared counterpart to GX5-1     

R. M. Bandyopadhyay  T. Shahbaz  P. A. Charles 《Monthly notices of the Royal Astronomical Society》2003,340(3):L13-L16

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Chandra and RXTE spectroscopy of the Galactic microquasar XTE J1550−564 in outburst     

J. M. Miller  H. L. Marshall  R. Wijnands †  T. Di Matteo  D. W. Fox  J. Kommers  D. Pooley  T. Belloni  J. Casares  P. A. Charles  A. C. Fabian  M. van der Klis  W. H. G. Lewin 《Monthly notices of the Royal Astronomical Society》2003,338(1):7-13

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Measurements of the north polar cap of Mars and the Earth's northern hemisphere ice and snow cover     

J. Foster  M. Owe  Charles Capen 《Earth, Moon, and Planets》1986,35(3):223-235

The boundaries of the polar caps of Mars have been measured on more than 3000 photographs since 1905 from the plate collection at the Lowell Observatory. For the Earth, the polar caps have been accurately mapped only since the mid 1960's when satellites were first available to synoptically view the polar regions. The polar caps of both planets wax and wane in response to changes in the seasons, and interannual differences in polar cap behavior on Mars as well as Earth are intimately linked to global energy balance. Data on the year to year variations in the extent of the north polar caps of Mars and Earth have been assembled and compared, although only 6 years of concurrent data were available for comparison.  相似文献   

Monitoring selective availability dither frequencies and their effect on GPS data   总被引：1，自引：1，他引：0  

Christian Rocken  Charles Meertens 《Journal of Geodesy》1991,65(3):162-169

Summary The signals transmitted by Block II satellites of the Global Positioning System (GPS) can be degraded to limit the highest accuracy of the system (10 m or better point positioning) to authorized users. This mode of degraded operation is called Selective Availability (S/A). S/A involves the degradation in the quality of broadcast orbits and satellite clock dithering. We monitored the dithered satellite oscillator and investigated the effect of this clock dithering on high accuracy relative positioning. The effect was studied over short 3-meter and zero-baselines with two GPS receivers. The equivalent S/A effects for baselines ranging from 0 to >10,000 km can be examined with short test baselines if the receiver clocks are deliberately mis-synchronized by a known and varying amount. Our results show that the maximum effect of satellite clock dithering on GPS double difference phase residuals grows as a function of the clock synchronization error according to: S/A _effect =0.04 cm/msec, and it increases as a function of baseline length like: S/A _effect =0.014 cm/100 km. These are equations for maximum observed values of post-fit residuals due to S/A. The effect on GPS baselines is likely to be smaller than the 0.14 mm for a baseline separation of 100 km. We therefore conclude, for our limited data set, and for the level of S/A during our tests, that S/A clock dithering has negligible effect on all terrestrial GPS baselines if double difference processing techniques are employed and if the GPS receivers remain synchronized to better than 10 msec. S/A may constitute a problem, however, if accurate point processing is required, or if GPS receivers are not synchronized. We suggest and test two different methods to monitor satellite frequency offsets due to S/A. S/A modulates GPS carrier frequencies in the range of-2 Hz to +2 Hz over time periods of several minutes. The methods used in this paper to measure the satellite clock dither could be applied by the civilian GPS community to continuously monitor S/A clock dithering. The monitored frequencies may aid high accuracy point positioning applications in a postprocessing mode (Malys and Ortiz 1989), and differential GPS with poorly synchronized receivers (Feigl et al. 1991).  相似文献   

V792 Her=HD 155638: A totally eclipsing RS CVn binary     

Charles H. Nelson  Douglas S. Hall  Francis C. Fekel  Robert E. Fried  Richard E. Lines  Helen C. Lines 《Astrophysics and Space Science》1991,182(1):1-17

Photometry of HD 155638=V792 Her has been analyzed to determine the elements of this totally eclipsing RS CVn binary. The light variation outside eclipse was found to have a period of 27^d.07±0^d.07, which is slightly different from the 27^d.5384±0^d.0045 orbital period. Analysis of the eclipses was achieved by a modification of the Russell-Merrill technique. With the aid of radial velocity measures, absolute elements were obtained for the hot and cool stars, respectively;R _h=2.58R ,R _c=12.28R ,M _h=1.40M ,M _c=1.46M ,i=80^o.61 and velocity semi-amplitudesK _c=48.36 km s^–1±0.79 km s^–1, andK _h=50.50 km s^–1±0.33 km s^–1. The apparent magnitudes areV _h=9 ^m .73 andV _c=8 ^m .48. The distance to HD 155638 was estimated to be 310 parsecs.  相似文献