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1.
In this paper, relation was developed for Hyades stars between a function of the right ascensions and the angular distances from the vertex. The precision criteria of this relation are very satisfactory and a correlation coefficient value of ? 1 was found which proves that the attributes are completely related linearly. The importance of this relation was illustrated through its usages as:
  • ?a criterion for membership of the cluster,
  • ?a generating function for evaluating some parameters of the cluster,
  • ?a generating function for the initial values of the vertex equatorial coordinates which could then be improved iteratively using the procedure of differential corrections.
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    2.
    New computations of massive stars follow the evolution up to advanced stages and include:
  • -A large and flexible nuclear network consisting of 174 nuclear species that are linked by 1742 nuclear reactions.
  • -Semiconvection, overshooting and mass loss.
  • -Modern rates for both strong and weak interaction processes as well as the latest rates for the neutrino processes.
  • -Improved grid distribution and a large number of grid points.
    • The nuclear network and the diffusion equation are solved for each time step during the whole evolution. In this way the accuracy of nuclear yields and chemical abundances are mainly limited by uncertainties in the diffusion coefficient found from the convection theories. Several instability mechanisms may affect the mass loss rates of massive stars and thereby the structure and abundances of WR stars. Due to heavy mass loss at the LBV and WR stages, the masses at the pre-SN stage may be less than 5M ⊙. Yields and abundances throughout the stars are discussed together with the amount of all elements expelled.  相似文献   

    3.
    We present anon-general relativistic cosmological model with the following features.
  • All cosmological objects appear to be receding from each other. There are two mathematically distinct types of objects.
  • Type I objects have apparent magnitudes and apparent angular diameters comparable to those for standard FLRW models. Their redshifts are bounded; this bound is at least 3.
  • Type II objects can have unlimited redshifts. They appear significantly smaller than Type I objects with the same redshift, and (for redshifts greater than 1) appear brighter (and more so for larger redshifts).
    • The model is an extension of classical de Sitter spacetime in which the location of infinity is allowed to be relative.  相似文献   

    4.
    Large number of microwave antennas of size and surface accuracy appropriate for the Square Kilometre Array (SKA) have not been manufactured previously. To minimize total cost, the design needs to be much more carefully considered and optimized than would be affordable for a small number of antennas. The required surface area requires new methods of manufacture and production-line type assembly to be considered. A blend of past antenna construction technology, creativity, and new technology is needed to provide the best possible telescope for the proposed SKA science goals. The following key concepts will be discussed with respect to reflector antennas and many supporting photographs, figures and drawings will be included.
  • Surface and supporting structure – comparison of panels with a one-piece shell as produced by hydroforming.
  • Combined reflector and mount geometry – performance/cost materially governed by this geometry which must be optimized for SKA requirements which are significantly different from typical communications antennas
  • Types of fully steerable mounts – king post, turntable bearing and wheel and track
  • Pointing accuracy – factors effecting cost, non-repeatable and repeatable errors
  • Axis drive concepts – traction devices, gears, screws, etc.
  • Life cycle costs – maintenance and power costs must be considered
  • Synergistic design – all of the above factors must be considered together with the wideband feed and receiver system to optimize the whole system
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    5.
    Based on the developed method of jointly using data on the magnetic fields and brightness of filaments and coronal holes (CHs) at various heights in the solar atmosphere as well as on the velocities in the photosphere, we have obtained the following results:
  • The upward motion of matter is typical of filament channels in the form of bright stripes that often surround the filaments when observed in the HeI 1083 nm line.
  • The filament channels observed simultaneously in Hα and HeI 1083 nm differ in size, emission characteristics, and other parameters. We conclude that by simultaneously investigating the filament channels in two spectral ranges, we can make progress in understanding the physics of their formation and evolution.
  • Most of the filaments observed in the HeI 1083 nm line consist of dark knots with different velocity distributions in them. A possible interpretation of these knots is offered.
  • The height of the small-scale magnetic field distribution near the individual dark knots of filaments in the solar atmosphere varies between 3000 and 20000 km.
  • The zero surface separating the large-scale magnetic field structures in the corona and calculated in the potential approximation changes the inclination to the solar surface with height and is displaced in one or two days.
  • The observed formation of a filament in a CH was accompanied by a significant magnetic field variation in the CH region at heights from 0 to 30000 km up to the change of the predominant field sign over the entire CH area. We assume that this occurs at the stage of CH disappearance.
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    6.
    The differential equations of rotational motion of the Moon are solved by numerical integration methods. Euler's dynamical equations transformed to a convenient form are treated by techniques analogous to ordinary orbit determination procedures. The proposed method is fully consistent with the ephemeris of the Moon and can utilize a variety of observational material for the solution of the selected parameters. The parameters are grouped into three distinct groups, namely:
  • --The physical libration angles of the Moon and their time rates at an arbitrary initial epoch.
  • --Physical constants featuring the principal moments of ineria of the Moon.
  • --Parameters associated with the particular observational material being used.
    • Examples are given of comparison between the proposed method and Eckhardt's 1970 model of the physical librations of the Moon. The merits of the new method are discussed in the light of conventional data sources like Earth-based or satellite-based photography as well as newly available data types like Laser ranging to retroreflectors on the Moon.  相似文献   

    7.
    We report the results of the application of our approach to study the behavior of solar activity in the past, where:
  • When reconstructing the variations of solar activity, geomagnetic parameters, and the interplanetary magnetic field in the past we select a sequence of increasing time scales, which can be naturally represented by the potentials of available observational data. We select a total of four time scales: 150–200 years, 400 years, 1000 years, and 10000 years.
  • When constructing the series of each successive (in terms of length) time scale we use the data of the previous time scale as reference data.
  • We abandon, where possible, the series of traditional statistical parameters in favor of the series of physical parameters.
  • When deriving the relations between any parameters of solar activity, geomagnetic disturbance, and the interplanetary magnetic field, we take into account the differential nature of relations on different time scales. To this end, we use the earlier proposed MSR and DPS methods.
  • To verify the resulting reconstructions, we use the “principle of witnesses”, which uses independent (in some cases, indirect) information as initial data.
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    8.
    Four consecutive years of a quasi-continuous survey of the solar Lα line are presented. Absolute calibration and aging correction are evaluated producing higher quality measurements which are:
  • -the total Lα flux,
  • -the central Lα flux,
  • -the blue wing flux at 0.33 Å from the center,
  • -the slope of the blue wing at the same location.
    • Empirical laws are deduced from this large amount of data giving a relation between these different parameters and the flux integrated over the whole line. Furthermore, other empirical laws are obtained between the total Lα flux and two solar activity indices. These relations give a possibility of evaluating the solar Lα flux even when no observation is available and, as previously found by Prinz (1974), show that to a first approximation the solar Lα flux is composed of a quiet and of an active component. The active component changes with the 27 days period; the quiet one with the 11 yr solar cycle.  相似文献   

    9.
    The absolute temperature of the cosmic microwave background (CMB) has been measured at a frequency of 1280 MHz. The observation was made with a modified version of the L-band receiver used in the Giant Metre wavelength Radio Telescope (GMRT): the feed horn was replaced by a corrugated plate and the receiver was placed on the ground, directed at zenith, and shielded from ground radiation by an aluminium screen with corrugated edges. Novel techniques have been adopted for
  • ?reducing and cancelling unwanted contributions to the system temperature of the receiver and
  • ?calibrating the contributions from the feed assembly and receiver.
    • The thermodynamic temperature of the CMB is estimated to be 3.45 ± 0.78 K.  相似文献   

    10.
    The majority of flare activity arises in active regions which contain sunspots, while Coronal Mass Ejection (CME) activity can also originate from decaying active regions and even so-called quiet solar regions which contain a filament. Two classes of CME, namely flare-related CME events and CMEs associated with filament eruption are well reflected in the evolution of active regions. The presence of significant magnetic stresses in the source region is a necessary condition for CME. In young active regions magnetic stresses are increased mainly by twisted magnetic flux emergence and the resulting magnetic footpoint motions. In old, decayed active regions twist can be redistributed through cancellation events. All the CMEs are, nevertheless, caused by loss of equilibrium of the magnetic structure. With observational examples we show that the association of CME, flare and filament eruption depends on the characteristics of the source regions:
  • ?the strength of the magnetic field, the amount of possible free energy storage,
  • ?the small- and large-scale magnetic topology of the source region as well as its evolution (new flux emergence, photospheric motions, cancelling flux), and
  • ?the mass loading of the configuration (effect of gravity). These examples are discussed in the framework of theoretical models.
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    11.
    The observational data permit us to establish clear statistical correlations between different parameters of stellar flare activity and the characteristics of quiet stars. These relations are:
    1. between energies and frequencies of flares on stars of different luminosities;
    2. between total radiation energies of flares and quiet stars both in X-ray and Balmer emission lines;
    3. between flare decay rates just after the maxima and flare luminosities at maxima.
      相似文献   

    12.
      相似文献   

    13.
    The recent observation of the absorption of radiation belts in the vicinity of Saturn's bright rings and historical observations of the ring system make the following related results apparent:
  • - The gaps in the rings are caused by the presence of at least 6 small, extremely dense and probably electrically charged ‘sweeper’ moons which effectively sweep the ring matter clean from the gaps. This is known due to the fading of the inner ring edges whereas the outer edges are well defined. Their orbital periods will differ from the expected Keplerian periods if the moons and Saturn do possess electric fields.
  • - Absorption of radiation belts near the rings (of Jupiter also) implies that the ring particles themselves are not absorbing the radiation but the small moons are. This is consistent with the observed radiation belt absorption near the outer Saturnian moons.
  • - If electric fields of the sweeper moons cause the ring edge fading as observed (and not simply gravitational), then Saturn itself must maintain an electric field in its vicinity by way of a sizeable proton wind to affect the uneven ring edge fading and will be surrounded by an H+ cloud at least to approximately the A-ring. this is consistent with the detection of an H+ cloud surrounding Saturn (Weiseret al., 1977, p. 755). The other possibility is that these moons are extremely dense and have very large internal magnetic fields.
  • - Because of their location, these moons must be captured and if very dense as believed, may be core remnants of a nova.
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    14.
    Starbursts are systems with very high star formation rate per unit area. They are the preferred place where massive stars form; the main source of thermal and mechanical heating in the interstellar medium, and the factory where the heavy elements form. Thus, starbursts play an important role in the origin and evolution of galaxies. The similarities between the physical properties of local starbursts and high-z star-forming galaxies, highlight the cosmological relevance of starbursts. On the other hand, nearby starbursts are laboratories where to study violent star formation processes and their interaction with the interstellar and intergalactic media, in detail and deeply. Starbursts are bright at ultraviolet (UV) wavelengths, as they are in the far-infrared, due to the ‘picket-fence’ interstellar dust distribution. After the pioneering IUE program, high spatial and spectral resolution UV observations of local starburst galaxies, mainly taken with HST and FUSE, have made relevant contributions to the following issues:
  • The determination of the initial mass function (IMF) in violent star forming systems in low and high metallicity environments, and in dense (e.g. in stellar clusters) and diffuse environments: A Salpeter IMF with high-mass stars constrains well the UV properties.
  • The modes of star formation: Starburst clusters are an important mode of star formation. Super-stellar clusters have properties similar to globular clusters.
  • The role of starbursts in AGN: Nuclear starbursts can dominate the UV light in Seyfert 2 galaxies, having bolometric luminosities similar to the estimated bolometric luminosities of the obscured AGN.
  • The interaction between massive stars and the interstellar and intergalactic media: Outflows in cold, warm and coronal phases leave their imprints on the UV interstellar lines. Outflows of a few hundred km s?1 are ubiquitous phenomena in starbursts. These metal-rich outflows and the ionizing radiation can travel to the halo of galaxies and reach the intergalactic medium.
  • The contribution of starbursts to the reionization of the universe: In the local universe, the fraction of ionizing photons that escape from galaxies and reach the intergalactic medium is of a few percent. However, in high-z star-forming galaxies, the results are more controversial.
    • Despite the very significant progress over the past two decades in our understanding of the starburst phenomenon through the study of the physical processes revealed at satellite UV wavelengths, there are important problems that still need to be solved. High-spatial resolution UV observations of nearby starbursts are crucial to further progress in understanding the violent star formation processes in galaxies, the interaction between the stellar clusters and the interstellar medium, and the variation of the IMF. High-spatial resolution spectra are also needed to isolate the light from the center to the disk in UV luminous galaxies at z = 0.1–0.3 found by GALEX. Thus, a new UV mission furnished with an intermediate spectral resolution long-slit spectrograph with high spatial resolution and high UV sensitivity is required to further progress in the study of starburst galaxies and their impact on the evolution of galaxies.  相似文献   

    15.
    Some aspects of the perturbative influence of radiation reflected by the Earth's surface on the motion of an artificial satellite are discussed. We concentrate on consequences of the extreme models with anisotropic reflection on the Earth's surface (specular reflection, clouds with anisotropic phase function). The possible effects of Lála's modification of the Earth's albedo nominal value are investigated. The role of the satellite surface optical properties is pointed out in the context of the albedo effect. All mentioned models are purely numerical. The whole message of the paper can be summarized in the following items
  • -It is very doubtful that the 10?8 ÷ 10?9 m s?2 level is reached when determining the perturbing accelerations caused by the albedo effect in the case of the ERS-1 satellite due to poorly defined optical characteristics of the Earth's atmosphere, the Earth and the satellite's surface.
  • -In the general case this albedo effect uncertainty level is about 50% with respect to the averaged values, and probably as high as 100% with respect to the instantaneous values of the perturbing accelerations.
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    16.
    Information about space distribution is collected for selected classes of evolving stars in the globular cluster M13. After a rigorous elimination of field stars, three samples are examined, corresponding to the red giant stage (G), the blue (B) and the yellow (YG) parts of the horizontal branch. It is shown that results are easy to understand in terms of:
    1. A substantial mass loss in the H-shell burning stage;
    2. Evolution along the horizontal branch from the blue side to the red one;
    3. A mixing in the observed giant branch of two populations with sensible differences in masses.
    Theoretical interpretations are briefly discussed with reference to the reliability and usefulness of this type of investigation.  相似文献   

    17.
    Dwarf elliptical (dE) galaxies, with blue absolute magnitudes typically fainter than MB =?16, are the most numerous type of galaxy in the nearby universe. Tremendous advances have been made over the past several years in delineating the properties of both Local Group satellite dE's and the large dE populations of nearby clusters. We review some of these advances, with particular attention to how well currently available data can constrain
    1. models for the formation of dE's
    2. the physical and evolutionary connections between different types of galaxies (nucleated and nonnucleated dE's, compact E's, irregulars, and blue compact dwarfs) that overlap in the same portion of the mass-spectrum of galaxies
    3. the contribution of dE's to the galaxy luminosity functions in clusters and the field
    4. the star-forming histories of dE's and their possible contribution to faint galaxy counts, and
    5. the clustering properties of dE's.
    In addressing these issues, we highlight the extent to which selection effects temper these constraints, and outline areas where new data would be particularly valuable.  相似文献   

    18.
    After a short summary of the results expected from the HIPPARCOS mission, the author gives several examples illustrating the needs that will arise afterwards in order to maintain the level of precision achieved and to extend it to many more objects. Three domains are particularly dealt with in this paper:
    1. The maintenance of the HIPPARCOS reference system that will degrade at the rate of 2 mas per year. The instruments intended to contribute to this task should concentrate on observing a few stars as accurately as possible. The best candidates are astrolabes and optical interferometers.
    2. The extension of the HIPPARCOS catalogue to more stars using astrographs, Schmidt telescopes, and photoelectric meridian circles. A particularly important objective would be to reduce the GSE catalogue to this system and determine its proper motions with second epoch plates.
    3. The determination of new parallaxes and double star parameters in particular with CCD astrometry, astrometric photometry and various interferometric techniques.
      相似文献   

    19.
    This paper is primarily concerned with the questions of models and the mechanisms of radio emission for pulsars, the polarization of this radiation and related topic. For convenience and to provide a more complete picture of the problems involved, a short summary of the data on pulsars is also given. Besides the introduction, the paper contains the following sections:
    1. Some Facts about Pulsars.
    2. The Astrophysical Nature of Pulsars.
    3. Coherent Mechanisms of Radio Emission from Pulsars.
    4. Models of Pulsars: Magnetic, Pulsating White Dwarfs and Neutron Stars.
    5. The Polarization of the Radio Emission from Pulsars.
    6. A Synthesized Model of Pulsars — Magnetic, Pulsating and Rotating Neutron Stars.
    7. Concluding Remarks.
      相似文献   

    20.
    An analysis of the data concerning high-velocity stars from Eggen's catalogue aimed at a determination of the approximate slope of the mass function for the spherical component of our Galaxy, and at estimating the local circular velocity, as well as the local rotation velocity, as by-products, has been performed. Our conclusions are that:
    1. A linear dependence of the mass on the radius is very likely;
    2. the value of the limiting radius is most likely equal to (40±10) kpc;
    3. the two local velocities are approximately equal to each other, being both equal to (230±30) km s?1;
    4. the local escape velocity appears to be most likely equal to (520±30) km s?1;
    5. the total mass of a corona, obtained in this way, is (5±1)×1011 M ⊙.
      相似文献   

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