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1.
Thomas Schildknecht 《Astronomy and Astrophysics Review》2007,14(1):41-111
Space debris—man-made non-functional objects of all sizes in near-Earth space—has been recognized as an increasing threat
for current and future space operations. The debris population in near-Earth space has therefore been extensively studied
during the last decade. Information on objects at altitudes higher than about 2,000 km is, however, still comparatively sparse.
Debris in this region is best detected by surveys utilizing optical telescopes. Moreover, the instruments and the applied
observation techniques, as well as the processing methods, have many similarities with those used in optical surveys for ‘astronomical’
objects like near-Earth objects (NEOs).
The present article gives a general introduction to the problem of space debris, presents the used observation and processing
techniques emphasizing the similarities and differences compared to optical surveys for NEOs, and reviews the results from
optical surveys for space debris in high-altitude Earth orbits. Predictions on the influence of space debris on the future
of space research and space astronomy in particular are reported as well. 相似文献
2.
G. Hasinger J.-U. Fischer A. D. Schwope T. Boller J. Trümper W. Voges 《Astronomische Nachrichten》1997,318(6):329-334
We have selected a complete, flux-limited sample of bright point-like sources with absorbed X-ray spectra from the ROSAT All-Sky survey, the ROSAT Hard Survey (RHS). The sample is drawn from the high-galactic latitude sky, |bII| > ±30°, and avoids the general direction of the Magellanic Clouds and the Virgo Cluster. It comprises a total of 182 objects of which 118 were previosly catalogued objects and 64 were new AGN candidates. Through optical follow-up studies at La Silla, Calar Alto and the 6m Zelentchuk telescope we could identify 56 of the new objects, thus achieving a spectrscopic completeness of 96% of the sample. The selection strategy turned out to be extremely useful. Out of the new identifications, 84% are indeed active galaxies or emission line galaxies. While 14 objects are new BL Lac candidates 33 of the new AGN are Seyfert galaxies with a redshift distribution in the range 0.021–0.63, peaking at around 0.06, i.e. relatively local. Surprisingly, about 40% of the X-ray selected Seyfert galaxies seem to reside in interacting systems. With smaller selection uncertainties this fraction exceeds the number of paired galaxies in optically selected samples and therefore gives strong support to the idea that AGN activity is triggered by interaction. 相似文献
3.
Mark Clampin Marco Sirianni George F. Hartig Holland C. Ford Garth D. Illingworth Bill Burmester William Koldewynd Andre R. Martel Adam Riess Ronald J. Schrein Pamela C. Sullivan 《Experimental Astronomy》2002,14(2):107-115
The Advanced Camera for Surveys (ACS), installed in the Hubble Space telescope in March 2002, will significantly extend HST's
deep, survey imaging capabilities. ACS has met, or exceeded, all of its key performance specifications. In this paper we briefly
review the in-flight performance of the instrument's CCD detectors and preview early ACS science observations.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
地震作用下宝成铁路地质灾害调查分析 总被引：1，自引：0，他引：1
2008年5月12日四川汶川发生8.0级特大地震,受此影响宝成铁路成都局管段沿线产生严重的次生地质灾害。通过对铁路沿线震后地质灾害的现场调查,总结了地震作用下产生的灾害类型,分析了地震的致灾作用和地震次生灾害的影响因素,在此基础上结合实际提出防灾工程建议。 相似文献
6.
Nelson D. Padilla Michael A. Strauss 《Monthly notices of the Royal Astronomical Society》2008,388(3):1321-1334
We determine the underlying shapes of spiral and elliptical galaxies in the Sloan Digital Sky Survey Data Release 6 (SDSS DR6) from the observed distribution of projected galaxy shapes, taking into account the effects of dust extinction and reddening. We assume that the underlying shapes of spirals and ellipticals are well approximated by triaxial ellipsoids. The elliptical galaxy data are consistent with oblate spheroids, with a correlation between luminosity and ellipticity: the mean values of minor to middle axis ratios are 0.41 ± 0.03 for M r ≈−18 ellipticals and 0.76 ± 0.04 for M r ≈−22.5 ellipticals. Ellipticals show almost no dependence of axial ratio on galaxy colour, implying a negligible dust optical depth.
There is a strong variation of spiral galaxy shapes with colour indicating the presence of dust. The intrinsic shapes of spiral galaxies in the SDSS DR6 are consistent with flat discs with a mean and dispersion of thickness to diameter ratio of (21 ± 2) per cent, and a face-on ellipticity, e , of ln( e ) =−2.33 ± 0.79 . Not including the effects of dust in the model leads to discs that are systematically rounder by up to 60 per cent. More luminous spiral galaxies tend to have thicker and rounder discs than lower luminosity spirals. Both elliptical and spiral galaxies tend to be rounder for larger galaxies.
The marginalized value of the edge-on r -band dust extinction E0 in spiral galaxies is E 0 ≃ 0.45 mag for galaxies of median colours, increasing to E 0 = 1 mag for g − r > 0.9 and E 0 = 1.9 for the luminous and most compact galaxies, with half-light radii <2 h −1 kpc . 相似文献
There is a strong variation of spiral galaxy shapes with colour indicating the presence of dust. The intrinsic shapes of spiral galaxies in the SDSS DR6 are consistent with flat discs with a mean and dispersion of thickness to diameter ratio of (21 ± 2) per cent, and a face-on ellipticity, e , of ln( e ) =−2.33 ± 0.79 . Not including the effects of dust in the model leads to discs that are systematically rounder by up to 60 per cent. More luminous spiral galaxies tend to have thicker and rounder discs than lower luminosity spirals. Both elliptical and spiral galaxies tend to be rounder for larger galaxies.
The marginalized value of the edge-on r -band dust extinction E
7.
Nick Scoville 《Astrophysics and Space Science》2008,313(1-3):287-291
ALMA will be the premier instrument for the study of galaxy evolution in the early universe—enabling studies of the gas content,
dynamics and dynamical masses, and star formation with unparalleled resolution and sensitivity. Galaxy evolution and AGN growth
in the early universe are believed to be strongly driven by merging and dynamical interactions. Thus, a full exploration of
the environmental influence is absolutely essential. The Cosmic Evolution Survey (COSMOS) is specifically designed to probe
the correlated coevolution of galaxies, star formation, active galactic nuclei (AGN) and dark matter (DM) large-scale structure
(LSS) over the redshift range z>0.5 to 3. In this contribution I review the characteristics of the COSMOS survey and very exciting initial results on mapping
large scale structure in galaxies and dark matter. The survey includes multi-wavelength imaging and spectroscopy from X-ray
to radio wavelengths covering a 2 square degree equatorial field. Given the very high sensitivity and resolution of these
datasets, COSMOS will provide unprecedented samples of objects at z>3 for followup studies wit ALMA. 相似文献
8.
An important research area in oceanographic surveying and mapping is to obtain submarine topography by remote sensing technique, especially by SAR imagery. In this article, problems related to SAR imagery are analyzed to provide references for the further research. 相似文献
9.
Sloan Digital Sky Survey 总被引：1，自引：0，他引：1
Stephen M. Kent 《Astrophysics and Space Science》1994,217(1-2):27-30
The Sloan Digital Sky Survey is a project which will produce a detailed digital phometric map of half the northern sky to about 23 magnitude using a special purpose wide field telescope of 2.5 meter aperture. This map will be used to select about a million galaxies and 100,000 quasars, for which high resolution spectra will be obtained using the same telescope. A catalog will be produced of all the detected objects, about 100 million galaxies and a similar number of stars, and a million quasar candidates. 相似文献
10.
The Edinburgh-Cape Blue Object Survey is a major survey to discover blue stellar objects brighter than B 18 in the southern sky. It is covering an area of sky of 10,000 square degrees with |b| > 30° and < 0°. The blue stellar objects are selected by automatic techniques from U and B pairs of UK Schmidt Telescope plates scanned with the COSMOS measuring machine. Follow-up photometry and spectroscopy are being obtained with the SAAO telescopes to classify objects brighter than B = 16.5. This paper describes the survey, the techniques used to extract the blue stellar objects, the photometric accuracy, the spectroscopic classification, and the completeness of the survey. 相似文献