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1.
FRW universe in RS II braneworld model filled with a combination of dark matter and dark energy in the form of modified Chaplygin gas (MCG) is considered. It is known that the equation of state (EoS) for MCG is a three-variable equation determined by A, α and B. The permitted values of these parameters are determined by the recent astrophysical and cosmological observational data. Here we present the Hubble parameter in terms of the observable parameters Ω m0, Ω x0, H 0, redshift z and other parameters like A, B, C and α. From Stern data set (12 points), we have obtained the bounds of the arbitrary parameters by minimizing the χ 2 test. The best-fit values of the parameters are obtained by 66 %, 90 % and 99 % confidence levels. Next due to joint analysis with BAO and CMB observations, we have also obtained the bounds of the parameters (B,C) by fixing some other parameters α and A. The best fit value of distance modulus μ(z) is obtained for the MCG model in RS II brane, and it is concluded that our model is perfectly consistent with the union2 sample data.  相似文献   

2.
In this paper, we study a cosmological model with the sign-changeable interaction between agegraphic dark energy (ADE) and dark matter. For the accelerated expansion of the universe, the model parameters n and β should satisfy the condition n>1 and $-\frac{2}{3}<\beta<0$ . We also investigate the effect of the parameters n and β on the evolutive behavior of our universe. Furthermore, by analysis it is shown that the equation of state of ADE with the sign-changeable interaction can cross the phantom divide from w d >?1 to w d <?1 for the appropriate n and β. This is different from that of ADE with usual interaction, whose equation of state changes from w d <?1 to w d >?1.  相似文献   

3.
We study pilgrim dark energy model by taking IR cut-offs as particle and event horizons as well as conformal age of the universe. We derive evolution equations for fractional energy density and equation of state parameters for pilgrim dark energy. The phantom cosmic evolution is established in these scenarios which is well supported by the cosmological parameters such as deceleration parameter, statefinder parameters and phase space of ω ? and \(\omega'_{\vartheta}\) . We conclude that the consistent value of parameter μ is μ<0 in accordance with the current Planck and WMAP9 results.  相似文献   

4.
We investigate the interacting NADE model in non-flat universe. The effects of spatial curvature Ω k , interaction coefficient α and the main parameter of NADE, n, on EoS parameter w d and deceleration parameter q are studied. We obtain a minimum value for n in both early and present time, in order to that our DE model crosses the phantom divide. Also in a closed universe, changing the sign of q is strongly dependent on α. It has been shown that the quantities w d and q have a different treatment for various spatial curvature. At last, we calculate the statefinder diagnostic and w−w ′ analysis in non flat universe. In non flat universe, the statefinder trajectories are discriminated by both n and α.  相似文献   

5.
In this work, we studied the Logarithmic Entropy-Corrected Holographic Dark Energy (LECHDE) model in a spatially non-flat universe and in the framework of Ho?ava-Lifshitz cosmology. As infrared cutoff of the system we considered the cut-off recently proposed by Granda and Oliveros which contains two terms, one proportional to H 2 and one to $\dot{H}$ . For the two cases containing non-interacting and interacting Dark Energy (DE) and Dark Matter (DM), we obtained the exact differential equation that determines the evolution of the density parameter. Moreover, we derived the expressions of the deceleration parameter q and, using a parametrization of the equation of state (EoS) parameter ω D of our model as ω D (z)=ω 0+ω 1 z, we derived both the expressions of ω 0 and ω 1 for both non-interacting and interacting cases. All derivations made in this work are done in small redshift approximation and for low redshift expansion of the equation of state (EoS) parameter.  相似文献   

6.
We study Bianchi type I cosmological model in the presence of magnetized anisotropic dark energy. The energy-momentum tensor consists of anisotropic fluid with anisotropic EoS p=ω ρ and a uniform magnetic field of energy density ρ B . We obtain exact solutions to the field equations using the condition that expansion is proportional to the shear scalar. The physical behavior of the model is discussed with and without magnetic field. We conclude that universe model as well as anisotropic fluid do not approach isotropy through the evolution of the universe.  相似文献   

7.
The shadow of rotating Ho?ava-Lifshitz black hole has been studied and it was shown that in addition to the specific angular momentum a, parameters of Ho?ava-Lifshitz spacetime essentially deform the shape of the black hole shadow. For a given value of the black hole spin parameter a, the presence of a parameter Λ W and KS parameter ω enlarges the shadow and reduces its deformation with respect to the one in the Kerr spacetime. We have found a dependence of radius of the shadow R s and distortion parameter δ s from parameter Λ W and KS parameter ω both. Optical features of the rotating Ho?ava-Lifshitz black hole solutions are treated as emphasizing the rotation of the polarization vector along null congruences. A comparison of the obtained theoretical results on polarization angle with the observational data on Faraday rotation measurements provides the upper limit for the δ parameter as δ≤2.1?10?3.  相似文献   

8.
We consider the planar restricted three-body problem and the collinear equilibrium point L 3, as an example of a center × saddle equilibrium point in a Hamiltonian with two degrees of freedom. We explore numerically the existence of symmetric and non-symmetric homoclinic orbits to L 3, when varying the mass parameter μ. Concerning the symmetric homoclinic orbits (SHO), we study the multi-round, m-round, SHO for m ≥ 2. More precisely, given a transversal value of μ for which there is a 1-round SHO, say μ 1, we show that for any m ≥ 2, there are countable sets of values of μ, tending to μ 1, corresponding to m-round SHO. Some comments on related analytical results are also made.  相似文献   

9.
This study set out to examine the effect of anisotropy on the various dark energy models by using the observational data, including the Sandage-Loeb test, Strongly gravitationally lensing, observational Hubble data, and Baryon Acoustic Oscillations data. In particular, we consider three cases of dark energy models: the cosmological constant model, which is most favored by current observations, the wCDM model where dark energy is introduced with constant w equation of state parameter and in Chevalier-Polarski-Linder parametrization where ω is allowed to evolve with redshift. With an anisotropy framework, a maximum likelihood method to constrain the cosmological parameters was implemented. With an anisotropic universe, we also study the behavior of different cosmological parameters such as Hubble parameter, EoS parameter, and deceleration parameter of dark energy models mentioned. The results indicate that the Bianchi type I model for the dark energy models are consistent with the combined observational data.  相似文献   

10.
In this paper, we investigate a cosmological model with the sign-changeable interaction between new agegraphic dark energy (NADE) and dark matter. By analysis it is shown that the equation of state (EoS) of NADE can cross the phantom divide under the condition of the model parameter β<0. In addition, we plot the trajectories of the interacting NADE model for different values of the parameters n and β in the statefinder plane. It is found that the statefinder trajectories can be distinguished by both n and β. Furthermore, we study the interacting NADE model by means of the w?w′ analysis.  相似文献   

11.
In this paper, we study the new holographic dark energy model in the framework of modified f(R) Horava-Lifshitz Gravity. We apply correspondence scheme to construct model the in underlying scenario using power-law form of scale factor. To explore accelerated expansion of the universe, some well-known cosmological parameters (equation of state parameter and squared speed of sound) and cosmological planes (ω Λ – \(\omega'_{\varLambda}\) and statefinder) are discussed for reconstructed model. It is interesting to conclude that these parameters represent phantom behavior of the universe with stable configuration. also, the cosmological planes show compatible results with recent observations for accelerated expansion of the universe.  相似文献   

12.
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13.
Observations by the Mars Color Imager (MARCI) on board the Mars Reconnaissance Orbiter (MRO) in two ultraviolet (UV, Bands 6 and 7; 258 nm, and 320 nm, respectively) and one visible (Band 1, 436 nm) channels of the 2007 planet encircling dust storm are combined with those made by the two Mars Exploration Rovers (MERs) to better characterize the single scattering albedo (ω0) of martian dust aerosols. Exploiting the low contrast of the surface in the UV (and blue) as well as the reduced importance of surface reflectance under very dusty conditions, we utilize the sampling of photometric angles by the MARCI cross-track geometry to synthesize an analog of the classical Emergence Phase Function (EPF). This so-called “pseudo-EPF”, used in conjunction with the “ground-truth” measurements provided by the MERs, is able to effectively isolate the effects of the dust ω0. The motivation for this approach is the elimination of a significant portion of the type of uncertainty involved in many previous radiative transfer analyses. Furthermore, we produce a self-consistent set of complex refractive indices (m=n+ik) through our use of an explicit microphysical representation of the aerosol scattering properties. Because of uncertainty in the exact size of the dust particles during the epoch of the observations, we consider two effective particle radii (reff) to cover the range anticipated from the literature: 1.6 and 1.8 μm. The resulting set of model-data comparisons, ω0, and m are presented along with an assessment of potential sources of error and uncertainty. Analysis of the Band 1 results is limited to ω0 as a “proof-of-concept” for our approach through a comparison to contemporaneous CRISM EPF results at 440 nm. The derived ω0 are: assuming , and 0.765, for Bands 6, 7, and 1, respectively; for , for the same band order. For either reff case, the total estimated error is 0.022, 0.019, and 0.010, again for Bands 6, 7, and 1. We briefly discuss our retrievals, including the asymmetry parameter (g) associated with our model phase functions, within the context of previous efforts, with an emphasis on the improved precision of our results compared to those in the literature. We also suggest several applications of our results, including an extension of the dust climatological record using MARCI Band 7 pseudo-EPFs outside of 2007 global dust event. Initial work on this particular application using a sample of 135 pseudo-EPFs near the MERs suggests that optical depth retrievals with a precision in the range 0.2-0.4 may be possible under moderate loading conditions (i.e., τ < 1.5).  相似文献   

14.
In this paper, we investigate analytically the level space of the imaginary part of quasinormal frequencies for a black hole with a deficit solid angle and quintessence-like matter by the Padmanabhan’s method (Padmanabhan in Class. Quantum Gravity 21:L1, 2004). Padmanabhan presented a method to study analytically the imaginary part of quasinormal frequencies for a class of spherically symmetric spacetimes including Schwarzschild-de Sitter black holes which has an evenly spaced structure. The results show that the level space of scalar and gravitational quasinormal frequencies for this kind of black holes only depend on the surface gravity of black-hole horizon in the range of $-1<w<-\frac{1}{3}$ , respectively. We also extend the range of w to w≤?1, the results of which are similar to that in $-1<w<-\frac{1}{3}$ case. Particularly, a black hole with a deficit solid angle in accelerating universe will be a Schwarzschild-de Sitter black hole, fixing w=?1 and ε 2=0. And a black hole with a deficit solid angle in the accelerating universe will be a Schwarzschild black hole,when ρ 0=0 and ε 2=0. In this paper, w is the parameter of state equation, ε 2 is a parameter relating to a deficit solid angle and ρ 0 is the density of static spherically symmetrical quintessence-like matter at r=1.  相似文献   

15.
The processing of the plates of the Kitab part of the FON project has been completed. In total, 1963 plates were processed. The catalog of equatorial coordinates α, δ, and B-magnitudes for 13 413268 stars and galaxies up to B ≤ 17.5 m for the epoch 1984.97 is compiled. The Epson Expression 10000XL scanner with a 1200 dpi scanning mode and a plate size of 30 × 30 cm or 13000 × 13000 pel was used to digitize astronegatives. Coordinates of stars and galaxies are obtained in the Tycho-2 catalog system and B-magnitudes are obtained in the photovoltaic system. The catalog internal accuracy for all objects is σα,δ = 0.23" and σ B = 0.15 m (for stars in the range B = 5 m …14 m , errors are σα,δ = 0.085" and σ B = 0.054 m ) for equatorial coordinates and stellar B-magnitudes, respectively. Convergence between the calculated and reference positions is σα,δ = 0.042", and convergence between photoelectric B-magnitudes is σ B = 0.16 m . Coordinate errors with respect to the UCAC-4 catalog are σα,δ = 0.26" (9892697 or 73.75% of stars and galaxies were identified).  相似文献   

16.
We present a study of the baryonic fraction in galaxy clusters aimed at constraining the cosmological parameters Ωm, ΩLgr; and the ratio between the pressure and density of the `dark' energy, w. We use results on the gravitating mass profiles of a sample of nearby galaxy clusters observed with the BeppoSAX X-ray satellite (Ettori, De Grandi and Molendi, 2002)to set constraints on the dynamical estimate of Ωm. We then analyze Chandra observations of a sample of eight distant clusters with redshift in the range 0.72 and 1.27 and evaluate the geometrical limits on the cosmological parameters Ωm, ΩΛ and w by requiring that the gas fraction remains constant with respect to the look-back time. By combining these two independent probability distributions and using a priori distributions on both Ωb and H 0 peaked around primordial nucleosynthesis and HST-Key Project results respectively, we obtain that, at 95.4 per cent level of confidence, (i) w < —0.54, (ii)Ωm = 0.34+0.11 —0.05, ΩΛ = 1.50+0.24 —1.13 for w = — 1 (corresponding to the case for a cosmological constant), and (iii) Ωm = 1 —ΩΛ = 0.33+0.06 —0.05 for a flat Universe. This paper summarizes the work in press at Astronomy & Astrophysics by Ettori, Tozzi and Rosati (astro-ph/0211335).  相似文献   

17.
Results of the scattered solar radiation spectrum measurements made deep in the Venus atmosphere by the Venera 11 and 12 descent probes are presented. The instrument had two channels: spectrometric (to measure downward radiation in the range 0.45 < γ < 1.17 μm) and photometric (four filters and circular angle scanning in an almost vertical plane). Spectra and angular scans were made in the height range from 63 km above the planet surface. The integral flux of solar radiation is 90 ± 12 W m?2 measured on the surface at the subsolar point. The mean value of surface absorbed radiation flux per planetary unit area is 17.5 ± 2.3 W m?2. For Venera 11 and 12 landing sites the atmospheric absorbed radiation flux is ～15 W m?2 for H >; 43 km and ～45 W m?2 for H < 48 km in the range 0.45 to 1.55 μm. At the landing sites of the two probes the investigated portion of the cloud layer has almost the same structure: it consists of three parts with boundaries between them at about 51 and 57 km. The base of clouds is near 48 km above the surface. The optical depth of the cloud layer (below 63 km) in the range 0.5 to 1 μm does not depend on the wavelength and is ～29 and ～38 for the Venera 11 and 12 landing sites, respectively. The single-scattering albedo, ω0, in the clouds is very close to 1 outside the absorption bands. Below 58 km the parameter (1 ? ω0) is <10?3 for 0.49 and 0.7 μm. The parameter (1 ? ω0) obviously increases above 60 km. Below 48 km some aerosol is present. The optical depth here is a strong function of wavelength. It varies from 1.5 to 3 at λ = 0.49 μm and from 0.13 to 0.4 at 1.0 μm. The mean size of particles below the cloud deck is about 0.1 μm. Below 35 km true absorption was found at λ < 0.55 μm with the (1 ? ω0) maximum at H ≈ 15 km. The wavelength and height dependence of the absorption coefficient are compatible with the assumption that sulfur with a mixing ratio ～2 × 10?8 normalized to S2 molecules is the absorber. The upper limits of the mixing ratio for Cl2, Br2, and NO2 are 4 × 10?8, 2 × 10?11, and 4 × 10?10, respectively. The CO2 and H2O bands are confidently identified in the observed spectra. The mean value of the H2O mixing ratio is 3 × 10?5 < FH2O < 10?4 in the undercloud atmosphere. The H2O mixing ratio evidently varies with height. The most probable profile is characterized by a gradual increase from FH2O = 2 × 10?5 near the surface to a 10 to 20 times higher value in the clouds.  相似文献   

18.
This paper presents a new family of interior solutions of Einstein–Maxwell field equations in general relativity for a static spherically symmetric distribution of a charged perfect fluid with a particular form of charge distribution. This solution gives us wide range of parameter, K, for which the solution is well behaved hence, suitable for modeling of superdense star. For this solution the gravitational mass of a star is maximized with all degree of suitability by assuming the surface density equal to normal nuclear density, ρ nm=2.5×1017 kg?m?3. By this model we obtain the mass of the Crab pulsar, M Crab, 1.36M ⊙ and radius 13.21 km, constraining the moment of inertia >?1.61×1038 kg?m2 for the conservative estimate of Crab nebula mass 2M ⊙. And M Crab=1.96M ⊙ with radius R Crab=14.38 km constraining the moment of inertia >?3.04×1038 kg?m2 for the newest estimate of Crab nebula mass, 4.6M ⊙. These results are quite well in agreement with the possible values of mass and radius of Crab pulsar. Besides this, our model yields moments of inertia for PSR J0737-3039A and PSR J0737-3039B, I A =1.4285×1038 kg?m2 and I B =1.3647×1038 kg?m2 respectively. It has been observed that under well behaved conditions this class of solutions gives us the overall maximum gravitational mass of super dense object, M G(max)=4.7487M ⊙ with radius $R_{M_{\max}}=15.24~\mathrm{km}$ , surface redshift 0.9878, charge 7.47×1020 C, and central density 4.31ρ nm.  相似文献   

19.
《New Astronomy Reviews》1999,43(8-10):599-602
The position of PSR0329+54 on the International Celestial Reference Frame was measured at epochs March 1995, May 1996, and May 1998. Our observations detected the proper motion of PSR0329+54. The position and proper motion agreed well with the position determined by Bartel et al. (1985). From combined analysis with our data and that of Bartel, the proper motion of PSR0329+54 was determined: μα=+17.4±0.3 mas yr−1, μδ=−11.0±0.3 mas yr−1. These results are consistent with the value by Harrison et al. (1993)measured with the MERLIN interferometer. We also determined the coordinates of PSR0329+54 very accurately within the ICRF: α=03h32m59s.3761±0s.0002, δ=54°34′43′′.5119±0′′.0015 at 1995.  相似文献   

20.
We present some results about the continuation of doubly-symmetric horseshoe orbits in the general planar three-body problem. This is done by means of solving a boundary value problem with one free parameter which is the quotient of the masses of two bodies μ 3=m 3/m 1, keeping constant μ 2=m 2/m 1 (m 1 represents the mass of a big planet whereas m 2 and m 3 of minor bodies). For the numerical continuation of the horseshoe orbits we have considered m 2/m 1=3.5×10?4, and the variation of μ 3 from 3.5×10?4 to 9.7×10?5 or vice versa, depending on the orbit selected as “seed”. We discuss some issues related to the periodicity and symmetry of the orbits. We study the stability of some of them taking the limit μ 3→0. The numerical continuation was done using the software AUTO.  相似文献   

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