共查询到20条相似文献，搜索用时 15 毫秒
1.
Richard S Ellis Roberto G Abraham Jarle Brinchmann Felipe Menanteau 《Astronomy& Geophysics》2000,41(2):2.10-2.16
A Holy Grail of modern astronomy is understanding the origin of Edwin Hubble's morphological sequence of galaxy types. What made some collapsing gas clouds turn into elegant spiral systems like our own Milky Way, whereas others became smooth, featureless ellipticals? More fundamentally, does the taxonomic scheme introduced by Hubble in the 1920s have any physical relevance? The Space Telescope that bears Hubble's name is providing answers to these and other questions in the context of modern theories of structure formation.
Richard S Ellis, Roberto G Abraham, Jarle Brinchmann and Felipe Menanteau show how modern telescopes producing colourful images are pointing the way to understanding galaxy evolution. 相似文献
Richard S Ellis, Roberto G Abraham, Jarle Brinchmann and Felipe Menanteau show how modern telescopes producing colourful images are pointing the way to understanding galaxy evolution. 相似文献
2.
《Journal of Atmospheric and Solar》2003,65(1):105-112
Stars with the same temperature, luminosity, chemical composition, and activity as the Sun may be designated “sunlike stars.” The variability of several dozen reasonably sunlike stars has been monitored regularly since 1966 in chromospheric Ca II HK emission, and since 1984 in the visual continuum; larger stellar samples have been observed less comprehensively. Similar solar time series exist. A comparison of solar variability with its stellar analogs indicates that the Sun's current behavior is not unusual among sunlike stars, although the amplitude of the Sun's cyclic variation, measured photometrically, may be smaller than that of its stellar analogs. If the ensemble characteristics of a sample of sunlike stars are representative of the Sun's possible behavior, then such samples may provide insight about states of solar activity, such as Maunder Minima, which have not been observed on the Sun during the contemporary era of space-based measurements. Future progress in solar–stellar research will likely require studies of (1) rigorously selected samples of sunlike field stars, and (2) larger samples from stellar clusters, observed using 4-m class telescopes equipped with multi-object spectrographs and CCD photometers. 相似文献
3.
Gravitational microlensing data combined with statistical analysis suggests that stars with solar systems like our own make up just 15% of the stars in our galaxy. 相似文献
4.
E.M. Drobyshevski 《Earth and Planetary Science Letters》1975,25(3):368-378
If surface anomalies in the composition of the metallic-line A stars (Am stars) are due to a precipitation of planet-like bodies (planetoids) on them, then one should expect a correlation to exist between the overabundance of heavier-than-iron elements on these stars and their “standard” abundances in the solar system (since chondrites provide the “standard” level for these elements). However, an anticorrelation was revealed.Nevertheless, this fact supports the original suggestion on the origin of the metallicism of A stars, and can easily be explained within the author's hypothesis on the formation of the Sun from matter escaping from the proto-Jupiter. During the terminal stages of mass transfer, the matter was strongly depleted in refractories (forming the rocky core of Jupiter). Therefore the composition of the meteorites formed should not coincide with the primary composition of the matter. Thus the Sun's outer layers may also have a distorted composition. The author concludes that it is desirable to revise the “standard” abundances of elements heavier than iron.From a comparison of the surface composition of Am stars with the composition of lunar anorthosites and that of rocks in the upper zones of the Skaergaard intrusion (Greenland), the Am phenomenon may be seen to result from a precipitation of large geochemically differentiated planetoids onto a star. Such planetoids (including the Moon) condense in the cooled envelope of the primary component of a close binary stellar system. 相似文献
5.
Pierre Maxted 《Astronomy& Geophysics》2004,45(5):5.24-5.25
Astronomers met at Keele University, Staffordshire, in June to discuss how observations of extended horizontal branch stars have changed our view of hot star atmospheres, stellar winds, single and binary star evolution, stellar pulsations and the age estimates for elliptical galaxies. Pierre Maxted reports. 相似文献
6.
G. H. A. Cole 《Surveys in Geophysics》2006,27(3):365-382
If intelligent life were common in the Universe, should we not be aware of it on Earth through contact with advanced space ships and automatic probes? Would we not at least expect to intercept communication signals between space travellers? That this is not found has led to much speculation in the past. Recent discoveries of planets around other stars (called here exoplanets) and, separately, recent discoveries in the evolution of life on Earth, including Homo sapiens, allow this question to be considered again but now with more information than before. This is the subject of the present paper. The study involves aspects of physics and chemistry in combination with biological studies. It is concluded here that the places where technologically capable intelligent life might be expected to be found in our Galaxy are so few that any such “centres of civilisation” must be separated by large distances, probably in excess of 50 light years. If true, this would make the different centres essentially isolated and would suggest that each manifestation of advanced intelligent life is a purely local development. This would agree with our experience of aloneness. Nevertheless, the number of centres throughout the Universe would still be astronomically large, even if each galaxy had only one centre. An hypothesis is proposed which could account for the existence of such centres in this form. 相似文献
7.
Phil Charles and Andy Fabian review the changes brought to X-ray astronomy by the two orbiting observatories, XMM-Newton and Chandra.
We describe here the changes to X-ray astronomy that are being brought about by the two new orbiting X-ray observatories, NASA's Chandra and ESA's XMM-Newton. Between them they bring a dramatic gain in sensitivity, spatial resolution (now comparable to ground-based optical and infrared telescopes) and spectral resolution. The superb Chandra mirrors rapidly resolved the diffuse X-ray background and have produced stunning detailed images of a wide variety of cosmic objects. Large gains have been made by both missions in spectroscopic performance, with individual X-ray emission lines now detectable in hot stellar coronae, supernova remnants, X-ray binaries, active galactic nuclei and galaxy clusters. 相似文献
We describe here the changes to X-ray astronomy that are being brought about by the two new orbiting X-ray observatories, NASA's Chandra and ESA's XMM-Newton. Between them they bring a dramatic gain in sensitivity, spatial resolution (now comparable to ground-based optical and infrared telescopes) and spectral resolution. The superb Chandra mirrors rapidly resolved the diffuse X-ray background and have produced stunning detailed images of a wide variety of cosmic objects. Large gains have been made by both missions in spectroscopic performance, with individual X-ray emission lines now detectable in hot stellar coronae, supernova remnants, X-ray binaries, active galactic nuclei and galaxy clusters. 相似文献
8.
Exoplanets 总被引：1，自引：0，他引：1
George Cole reviews the properties and significance of the planetary systems discovered around stars other than our Sun.
There has been speculation for centuries that planets might exist around stars other than our Sun. Might they form planetary systems like our solar system? Will life be found elsewhere one day? Planets were, in fact, discovered orbiting a pulsar in 1991 but, more interestingly, companions were found to stars like our Sun four years later. More stars with companions are continually being discovered and some 50 systems are known at the present time. Can some of these orbiting bodies be planets and what might they be made of? Is there a pattern in the systems being found? How do they compare with the solar system? Can they sustain living material? This article attempts to throw light on these questions. 相似文献
There has been speculation for centuries that planets might exist around stars other than our Sun. Might they form planetary systems like our solar system? Will life be found elsewhere one day? Planets were, in fact, discovered orbiting a pulsar in 1991 but, more interestingly, companions were found to stars like our Sun four years later. More stars with companions are continually being discovered and some 50 systems are known at the present time. Can some of these orbiting bodies be planets and what might they be made of? Is there a pattern in the systems being found? How do they compare with the solar system? Can they sustain living material? This article attempts to throw light on these questions. 相似文献
9.
Wilford D. Gardner Lawrence G. Sullivan Edward M. Thorndike 《Earth and Planetary Science Letters》1984,70(1):95-109
Long-term measurements on and near the seafloor were made at five locations in the Pacific as part of the Manganese Nodule Project (MANOP). Bottom Ocean Monitor (BOM) tripods deployed at each site contained a time-lapse camera, nephelometer, and current meter. From nearly three years of photographs of the seafloor, there was no evidence that benthic organisms turned over, rotated, or moved nodules. There were indications, however, that benthic organims cleaned sediment from the tops of nodules and in some cases deposited sediment underneath nodules. Currents never exceeded the expected threshold for sediment resuspension of nodule movement. Particle concentrations in the water remained uniformly low throughout the deployments. Degredation of fecal pellets and organic matter proceeded more rapidly than expected. All changes of the seafloor morphology were attributable to the activity of organisms as opposed to currents. The occurrence in one photo sequence of dark, fluffy globs may be related to phytoplankton blooms in the region of equatorial upwelling. 相似文献
10.
David Moss 《地球物理与天体物理流体动力学》2013,107(5):497-505
We argue that global magnetic field reversals similar to those observed in the Milky Way occur quite frequently in mean-field galactic dynamo models that have relatively strong, random, seed magnetic fields that are localized in discrete regions. The number of reversals decreases to zero with reduction of the seed strength, efficiency of the galactic dynamo and size of the spots of the seed field. A systematic observational search for magnetic field reversals in a representative sample of spiral galaxies promises to give valuable information concerning seed magnetic fields and, in this way, to clarify the initial stages of galactic magnetic field evolution. 相似文献
11.
Geomagnetism and Aeronomy - We analyze physical characteristics of late-type stars wherein the Kepler mission registered superflares. We use the revised stellar fundamental parameters, i.e.... 相似文献
12.
Summary Indirect phase reflection height measurements have been performed at the Panská Ves Observatory, Czechoslovakia, for 30 years to monitor solar flare effects (SFA). Only after introducing the new receiver in May 1985, could the indirect phase height analysis (IPHA) method be applied to measurements along the Allouis — Panská Ves 162 kHJ measuring path. The IPHA method allows the electron density and pressure variability in the lower ionosphere to be studied, particularly near the 80 km altitude. This paper describes the theoretical background of the IPHA method, the measuring equipment used at Panská Ves, the method of evaluating records and checking of data, and the program package developed by us both for graphic and numerical processing, as well as our efforts to develop a homogeneous East European IPHA network. The IPHA method has been introduced succesfully at the Panská Ves Observatory. 相似文献
13.
When galaxies collide, stars are born. But many such close encounters also result in the formation of clusters with many of the characteristics of ancient globular clusters. Richard de Grijs argues the case that this process represents continuing formation of globular clusters in a hierarchical scheme of galaxy formation. 相似文献
14.
P. Vysko
il 《Journal of Geodynamics》1991,14(1-4)
After the November 1981 earthquake in the Aswan area along the Kalabsha fault, Nubian Desert, studies on its origin were initiated in the Helwan Institute of Astronomy and Geophysics [now National Research Institute of Astronomy and Geophysics (NRIAG) in Helwan]. As a first step an array of seismic stations were established in cooperation with the Lamont-Doherty Geological Observatory and the correlation between the number of seismic events and the water level in Lake Nasser was investigated. In order to understand the eartqquake mechanism, additional information on the crustal deformation due to water load was required, and the International Center on Recent Crustal Movements (ICRCM) was invited to consult in the necessary procedures aimed at recent crustal movement studies around part of the western bank of Lake Nasser. The first local network of horizontal and vertical geodetic measurements was established and measured in 1984. Simultaneously, with respect to the extreme meteorological conditions in the desert, additional investigations as refraction studies, stability of bench marks etc. were initiated. The extension of the network and an increase of repeated measurements first brought results during the last few years. The results of these studies will be reported in the following papers in detail as a homogenous block of scientific communication. 相似文献
15.
The accuracy of the Winkler technique for measuring dissolved oxygen was increased to 0.002–0.005 mg O2/l with a photometric endpoint detection method. This precision is valuable for accurate measurements of primary production
only if an oxygen release on illuminating dark adapted samples and the instability of the oxygen concentration of undersaturated
water are taken into account.
This work was supported by the ‘Swiss National Science Foundation’. 相似文献
16.
J. B. Rundle P. B. Rundle W. Klein J. de sa Martins K. F. Tiampo A. Donnellan L. H. Kellogg 《Pure and Applied Geophysics》2002,159(10):2357-2381
17.
The earthquake magnitude was introduced into seismology nearly 40 yr ago, as a purely empirical concept. After an unparalleled success in scientific and practical applications the magnitude is developing into a concept with a clearer physical meaning and a more solid theoretical foundation. The magnitude determined from the maximum particle amplitude or velocity reflects the maximum radiation power of the seismic source in the frequency band recorded on a particular seismograph. Recently developed models for seismic sources assist in classifying earthquakes according to size and spectral character. From corresponding scaling laws the relations between various magnitude scales can be established. The magnitude aims at enabling one to compare the sizes of seismic sources ranging in character from nearly aseismic events to explosions. While the former are characterized by a relatively long-peroidic radiation maximum, the latter radiate primarily short-periodic seismic energy. Tectonic earthquakes are likely to range in character between the two extreme spectral cases. A comparison of earthquake magnitude with stellar magnitude leads to analogies in spectral character between earthquakes and stars, whereby seismic sources seem to follow a distribution similar to the Hertzsprung-Russell diagram for stars. Before seismological practice can catch up with the new cognitions, improvements in the definition of the earthquake magnitude are in need. 相似文献
18.
Robert E. Dickinson 《Pure and Applied Geophysics》1964,59(1):155-171
Summary We continue the theoretical investigation of geostrophically balanced motions of a star gas in a rotating galaxy. The method of small perturbations is employed to derive a quasi geostrophic vorticity equation suitable for solving initial value problems for slow galactic eddying motions. The results derived for this simple theoretical model are then generalized to obtain approximate geostrophic forecast equations suitable for study of nonlinear galactic motions over a whole disk galaxy. A simple discussion of the stability of our approximate vorticity equation is presented. It is expected that in the absence of rapid gravitational instabilities, actual eddy motions observed in spiral galaxies will be at least approximately of the type of motion discussed in this paper. The Rossby adjustment problem is investigated in this context. 相似文献
19.
为推进地震数据共享,构建了蒙城地球物理国家野外科学观测站地震数据共享服务平台,目的是为安徽省防震减灾和国民经济建设提供数据服务,增强地震部门社会服务功能。平台提供的多元化的地震数据共享服务,将进一步提升野外站整体科研水平。 相似文献
20.
I. S. Veselovsky 《Geomagnetism and Aeronomy》2009,49(8):1148-1153
At what evolutionary stage of the Sun as a star the accumulation of its matter from the interstellar medium ended and the
dominant outflow of solar wind (SW) streams started is one of the main outstanding questions in the astrophysical aspect of
the problem of SW origin. It is unknown when and how this happened in detail, although the onset of thermonuclear reactions
in the solar interior undoubtedly played a crucial role in the energetics and dynamics of the star, which could lead to such
a change of the regimes. Therefore, it is hypothesized that the accretion or plasma outflow from the star was determined by
the preceding evolution, i.e., by the “memory“ and not just by the distribution of instantaneous density, temperature, magnetic
field, and other macroscopic parameters of the system that consists of this star, its nearest stellar environment, and interstellar
gas. Depending on this, neighboring stars can serve as donors or acceptors of interstellar gas. Some of them can simultaneously
or alternately play both roles. The polytropic solution for centrally symmetric flows obtained by Bondi is degenerate in the
sign of the radial velocity. It is suitable for describing the quasi-stationary regimes of both types. However, the theory
of transient processes has not been developed. Hence, the question of whether there exist stars similar in their internal
structure and parameters to the present-day Sun but without stellar wind emission or even with interstellar gas accretion
can be answered only observationally. The possibility that such stars exist is not ruled out; it does not contradict any laws
of nature. The plasma-physical aspect of the problem of SW origin concerns much shorter time intervals than the main evolutionary
time scale measured in billions of years. Hence, this aspect of the problem has been studied much better, although it is also
fairly complex and has not yet been solved in much detail due to the multi-scale character of the flow formation processes.
The SW as a permanent supermagnetosonic plasma outflow in the radial direction appears against the background of much more
powerful nonequilibrium and unsteady motions, which are ordered only partially in the upper solar atmosphere and corona (turbosphere).
The instantaneous SW state is controlled by the fluxes of free energy, matter, and momentum that enter the corona from the
convection zone and underlying solar atmospheric layers. Although the main physical mechanisms of the transport of free energy
of the electromagnetic field and plasma are generally well known, they need a quantitative analysis as applied to specific
realizations in frequent and rare particle collisions in the solar corona to ascertain the nonlocal processes of the formation
of fields and plasma flows, including the SW. 相似文献