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1.
For the case of closed Friedmann models with the cosmological constant, an N - dependence is plotted, whereN is the conformal time of existence of the Universe, and is the ratio of the cosmological constant to its Einstein's value. The observational properties of the asymptotic model of the first kind (the so-called Al model) corresponding to the maximum of this dependence are analyzed. For the matter-dominated models, the maximum is achieved at the point = 1. Formulae for the calculation of the age of the Universe and for that of the photometric distance in the Al model are deduced. The observational properties of the A1 model are compared to the corresponding properties of the standard cosmological model ( = 0) which does not occupy any special distinguished position on the N - diagram. It is shown that from the standpoint of the modern observational cosmology these two models cannot be told one from another. However, the A1 model has better standing from the viewpoint of the strong wordings of the anthropic cosmological principle.  相似文献   

2.
The angular size-redshift test for quasars was compared with various cosmological models including non standard models. The possible effects of radio source orientation and relativistic beaming were taken into account in the analysis.It was found that orientation effects alone were not sufficient to explain the observed-z relation in terms of Friedmann models. In addition, linear size evolution of the formD ~ (1 +z)–n , with 0.75 n 1.2 would be required for 0 1.0, or possibly an inverse correlation between luminosity and linear size. The non-standard cosmological models all gave better fits to the deprojected data than the Friedmann models in the absence of evolutionary effects, with the tired light effect providing the best fit.  相似文献   

3.
Exact Bianchi-type VIII and IX models in the presence of zero-mass scalar fields are presented, when the source of the gravitational field is a perfect fluid withP=. Some physical and geometrical properties of the models are also discussed.  相似文献   

4.
A new series of neutron star models has been computed. The equation of state used included the effects of nuclear dissolution, nuclear forces, and the presence of hyperons. The nuclear forces were introduced through use of a generalized form of the Levinger-SimmonsV andV potentials. The maximum stable masses obtained were 2.28 and 2.37M , respectively. Details are given of the structure of the outer layers which are expected to be crystalline. Expressions are given for the angular momentum and rotational energy of a neutron star and the relevant moment of inertia is tabulated for the models.  相似文献   

5.
Light curves have been constructed for a number of model astroids as represented by three series of triaxial ellipsoids (one almost prolate, one almost oblate and one in between). The light curves have maximumpossible amplitudes (m) ranging from 0m.1 to 1.0. The case m=0m.7 is illustrated in some detail. Quite complicated patterns of motion are shown at times to lead to simplelooking light curves for the prolate models. It is argued that models of this latter type are likely to be over-represented in any sampling of asteroidal light curves because of simple selection effects.  相似文献   

6.
The dependence of the Li-abundance on the equivalent width of the Li-resonance doublet at 6708 Å is calculated for different umbral models. The choice of the model strongly influences the deduced Li-abundance (up to a factor 8 or log Li = 0.9) even when using recent umbral models. Detailed discussion of the observations and reduction with the most suitable umbral model (Stellmacher and Wiehr, 1970) leads to an abundance of log Li = 1.1±0.05 (in the log H = 12.0 scale).  相似文献   

7.
Existing models of the quiet chromosphere-corona transition region predict a distribution of emission measure over temperature that agrees with observation for T 105 K. These network models assume that all magnetic field lines that emerge from the photosphere extend into and are in thermal contact with the corona. We show that the observed fine-scale structure of the photospheric magnetic network instead suggests a two-component picture in which magnetic funnels that open into the corona emerge from only a fraction of the network. The gas that makes up the hotter transition region is mostly contained within these funnels, as in standard models, but, because the funnels are more constricted in our picture, the heat flowing into the cooler transition region from the corona is reduced by up to an order of magnitude. The remainder of the network is occupied by a population of low-lying loops with lengths 104 km. We propose that the cooler transition region is mainly located within such loops, which are magnetically insulated from the corona and must, therefore, be heated internally. The fine-scale structure of ultraviolet spectroheliograms is consistent with this proposal, and theoretical models of internally heated loops can explain the behavior of the emission measure below T 105 K.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.  相似文献   

8.
The excitation rate P of solar p-modes is computed with a model of stochastic excitation which involves constraints on the averaged properties of the solar turbulence. These constraints are obtained from a 3D simulation. Resulting values for P are found 4.5 times larger than when the calculation assumes properties of turbulent convection which are derived from an 1D solar model based on Gough (1977)'s formulation of the mixing-length theory (GMLT). This difference is mainly due to the assumed values for the mean anisotropy of the velocity field in each case.Calculations based on 3D constraints bring the P maximum closer to the observational one.We also compute P for several models of intermediate mass stars (1 M 2 M).Differences in the values of P max between models computed with the classical mixing-length theory and GMLT models are found large enough for main sequence stars to suggest that measurements of P in this mass range will be able to discriminate between different models of turbulent convection.  相似文献   

9.
We present a minimum-gradient model to complement a maximum-gradient model (Zwaan, 1974). Both models are compatible with published continuum intensities and within constraints on the temperature gradient; both are adjusted to T eff=4000K. In order to explain the visual intensities the minimum-gradient model requires an additional line-haze opacity which is only slightly smaller than in the maximum-gradient model.We show that various published models are not compatible with plausible constraints on the temperature gradient.  相似文献   

10.
Double-lined spectra have been obtained at 2 Å/mm for the Mn star 112 Herculis AB. The components are shown to be a B6.5V star and A2V star. Hydrogen-line-blanketed models are used to calculate atmospheric abundances. The best models appear to beT e=13500 K, logg=4.0, T =2.5 km/sec for the primary; andT e=10000K, logg=4.2, T =6 km/sec for the secondary. Both stars appear to have the same abundances. Helium, carbon, magnesium, aluminum, silicon, calcium, vanadium, and nickel appear to be considerably underabundant; phosphorus, scandium, titanium, manganese, iron, gallium, and mercury considerably overabundant; and chromium, strontium, and zirconium normal in abundance.  相似文献   

11.
In this paper, we try to insert into a single evolutionary scheme — in dealing with chemical evolution of galaxies — two different viewpoints that (at least in not too much complicated models) have been treated separately: namely, theS models, allowing mass conservation; andI models, allowing initial zero masses and no mass conservation due to gas inflow. The true evolution of a real proto-galaxy (after reaching the state of maximum expansion) is simulated as follows: A spheroidal gas mass continued to collapse and form stars until a flat configuration is reached after a timeT c has elapsed, while a given amount of gas flows in on a time-scale . According to this scheme, the basic equations of chemical evolution are derived and models which simulate the history of solar neighborhood, other regions and Galactic spheroid component are built up, in the whole range between theS-limit (mass conservation) and theI-limit (zero initial mass and subsequent accretion due to inflowing gas). Concerning the solar neighbourhood, we find that neither the occurrence of gas inflow nor inflow on time-scales 2–3 109 yr are necessary in order to reproduce the temporal behaviour and the empirical distribution of metal content, as pointed out by some authors. On the contrary, the constraint on the lower mass limit for stars formed,m mf0.01, allows only models with T c (i.e. inflow time-scale of the order of the contraction time), while the constraint on the disk mass fraction,R D(T a)0.75, rules out the cases near theI-limit forT c0.55 but permits all cases forT c2.75. Concerning other regions, models are built up which roughly simulate elliptical, spiral and irregular galaxies, and all less extended regions resembling such systems.If the stellar birthrate function is assumed to be an universal law, the chemical evolution of the Galactic disk may be understood in terms of different zones (that might be thought as concentric and coaxial rings) the total density of which decreases monotonically, owing to a corresponding decrease in total mass and/or increase in volume, when passing from the center to the border of the disk. The constraintsm mf0.01 andR D(T a)0.75 for different regions of the Galactic disk would also rule out all models well beyond theS-limit, but further results are required in order to confirm this conclusion. Finally, concerning the Galactic spheroid component, it is found that onlyS models with massive halos (R D(T a)0.01) are able to reproduce in an acceptable way the empirical metal abundance distribution. In order to obtain a complete fit, a spheroid component has to be assumed, with a steeper mass spectrum exponent in the stellar birthrate function, and a lower yield of metallicity, in respect to the disk component. According to this last model, a mean value of disk metal content (with respect to spatial distribution) of the order of the solar value also results.  相似文献   

12.
Cold plus hot (neutrino) dark matter models are studied and compared with the tilted cold dark matter models (which have a non-Zel'dovich initial density perturbation spectrum). For the hybrid dark matter models, a simpler treatment for the relativistic neutrinos is presented. The numerical results of this treatment are shown to be in good agreement with those given by other authors. Comparing the theoretical and the observational results of the quadrupole fluctuations of the cosmic background radiation and the large-scale velocity field of galaxies, the hybrid dark matter models require a fraction of neutrino density 0.3, a fraction of cold dark matter c 0.7 and a number of massive neutrino speciesN = 1 for the case of Hubble's constantH 0 = 50 km s–1 Mpc–1. The distribution of comoving number density of quasars at high redshifts is studied using the Press-Schechter theory. The calculations show that the hybrid dark matter model ( c 0.7, 0.3) and the tilted CDM model withn = 0.7 0.8 both account for the observed quasar abundance at high redshift.  相似文献   

13.
On the basis of a a careful analysis of resonance line formation (both for singlets and doublets) in structured winds, presenttime dependent models of the line driven winds of hot stars (Owocki et al., this volume; Feldmeier, this volume) are shown to be able to explain a number of observational features with respect to variability and structure: they are (in principle) able to reproduce theblack andbroad troughs (without any artificial turbulence velocity) and the blue edge variability observed in saturated resonance lines; they might explain the long lived narrow absorption components often observed in unsaturated lines at high velocities; they predict a relation between the edge velocity of UV-lines and the radiation temperature of the observed X-ray emission.As a first example of the extent to which theoretical models can be constrained by comparisons between observations and profiles calculated by spectrum synthesis from structured winds, we show here that models with deep-seated onset of structure formation ( 1.1R * ) produce resonance lines which agreequalitatively with observational findings; in contrast, the here presented models with structure formation only well out in the wind ( 1.6R * ) fail in this respect.  相似文献   

14.
Cosmological models are investigated within the framework of the bimetric theory of gravitation with a Lagrangian that is quadratic with respect to intensities g ik|l . It is shown that the theory predicts not only singular but also nonsingular solutions.  相似文献   

15.
Because of a suspicion that a positive correlation exists between the luminosity of the first-class galaxies and the richness of the clusters, an attempt is made of taking into account the difference in richness (and presumably in total population) between the clusters withz<0.1 and the ones with 0.1<z0.2 (all being in the list of Peach, 1969) in the analysis of the redshift-magnitude relation of the brightest members.This analysis carried out with the clusters of richness 1 and 2, both present in the intervals of redshift 0.0–0.1 and 0.1–0.2 supports the steady-state model of the Universe in comparison with the category of the models with =0.This result induces another kind of selection effect, due to difference in the mean space density of the data points between the region withz<0.1 and the one with 0.1<z0.2, the mean volume occupied by the observed cluster being correlated with the luminosity of its brightest galaxy: also in this case the analysis supports the steady-state cosmology, while the tendency is clearly towards lower value ofq 0.The last result brings into consideration the models of the Universe with 0: the results obtained are compatible with those obtained by the analysis of other relations i.e. logN-logS of the 3C sources;N-z relation of the quasistellar objects;m-z for brightest quasars.  相似文献   

16.
The analysis of solar wind He++ and H+ ion distribution functions, collected over five months by the satellite Prognoz 1, shows that these are in general maxwellian but that often tails appear at higher speeds. The existing relation V-T, the observation of ratios of T/Tp 3.83 and V/Vp 1.035 give evidence of preferential He++ ion heating and acceleration. The criteria for heating by dissipation of hydromagnetic waves proposed by Barnes and Hung (1973) are tested experimentally. Finally, multifluid models are likely to predict certain observations such as dependence of the velocity ratio V/Vp on the solar wind flux.  相似文献   

17.
Along with the presentation of several new analytic solutions, the dynamics of slowly rotating perfect-fluid model universes are investigated, and their physical and geometrical properties are discussed from all angles. The rotational perturbations of such models are examined in detail in order to substantiate the possibility that the Universe is endowed with some rotation. The nature and role of the rotational velocity (r, t) which is related to the local dragging of inertial frames and that of the matter rotation (r, t) are studied for uniform and non-uniform motions. We find out the restrictions on the radii of the models for real astrophysical situations, and the periods of physical validity of them are also obtained. Rotating models which are expanding as well are obtained, in which cases the rotational velocities are found to decay with the time; and these models may be taken as examples of real astrophysical objects in this Universe.  相似文献   

18.
The mean moment-of-inertia ratio,I/MR 2, of Mars cannot be derived from its precessional constant because the exact value of the Martian axial precession is unknown presently. Using the known geodetic parameters of Mars as the constrained condition, we constructed nine Martian internal structure models (see Table II). We can then estimate the nonhydrostatic components of the principal moment-of-inertia for these models. The interplanetary comparison suggests that the reasonable range of the mean moment-of-inertia ratio,I/MR 2, of Mars is 0.350 0.360, and the range of the corresponding radius of Mars' core is 1520 1850 km. The two parameterically simple models recommended in this paper (see Table IV) can be used for reference in the future theoretical researches.  相似文献   

19.
Semi-empirical models of solar faculae, cospatial with strong photospheric magnetic fields, have been constructed from continuum observations. The center-to-limb contrast of the various models was computed taking into account their geometrical shape. The adopted model whose horizontal size was taken to be 750 km, indicates that, in field regions, the temperature begins to rise outwards at z -125 km (above 5000 = 1) and that the extrapolated temperature at z -400 km is about 1500 K above that of the undisturbed atmosphere; the electron density is higher by a factor of about 30.  相似文献   

20.
Possibilities to explain the observed 1/a-distribution are discussed in the light of improved understanding of the dynamical evolution of long-period comets. It appears that the fading problem applies both to single-injection and continuous-injection models. Although uncertainties due to nongravitational effects do not allow detailed results to be drawn from the observed 1/a-distribution at small perihelion distance q, that for q 1.5 AU shows that a constant fading probability cannot explain all the features of the observed distribution. Assuming that comets can reappear following a period of fading, values for the assumed constant fading and renewal probabilities, and the total cometary flux have been estimated for q > 1.5 AU.  相似文献   

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