• Issue front cover thumbnail

      Volume 28, Issue 2-3

      June 2007,   pages  67-166

    • Cosmology and Cosmogony in a Cyclic Universe

      Jayant V. Narlikar Geoffrey Burbidge R. G. Vishwakarma

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      In this paper we discuss the properties of the quasi-steady state cosmological model (QSSC) developed in 1993 in its role as a cyclic model of the universe driven by a negative energy scalar field. We discuss the origin of such a scalar field in the primary creation process first described by F. Hoyle & J. V. Narlikar forty years ago. It is shown that the creation processes which take place in the nuclei of galaxies are closely linked to the high energy and explosive phenomena, which are commonly observed in galaxies at all redshifts.

      The cyclic nature of the universe provides a natural link between the places of origin of the microwave background radiation (arising in hydrogen burning in stars), and the origin of the lightest nuclei (H, D, He3 and He4). It also allows us to relate the large scale cyclic properties of the universe to events taking place in the nuclei of galaxies. Observational evidence shows that ejection of matter and energy from these centers in the form of compact objects, gas and relativistic particles is responsible for the population of quasi-stellar objects (QSOs) and gamma-ray burst sources in the universe.

      In the later parts of the paper we briefly discuss the major unsolved problems of this integrated cosmological and cosmogonical scheme – the understanding of the origin of the intrinsic redshifts, and the periodicities in the redshift distribution of the QSOs.

    • Some Doubts on the Validity of the Foreground Galactic Contribution Subtraction from Microwave Anisotropies

      Martín López-Corredoira

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      The Galactic foreground contamination in CMBR anisotropies, especially from the dust component, is not easily separable from the cosmological or extragalactic component. In this paper, some doubts will be raised concerning the validity of the methods used until now to remove Galactic dust emission and will show that none of them achieves its goal.

      First, I review the recent bibliography on the topic and discuss critically the methods of foreground subtraction: the cross-correlation with templates, analysis assuming the spectral shape of the Galactic components, the ``maximum entropy method”, ``internal linear combination”, and ``wavelet-based high resolution fitting of internal templates”. Second, I analyse the Galactic latitude dependence from WMAP data. The frequency dependence is discussed with data in the available literature. The result is that all methods of subtracting the Galactic contamination are inaccurate. The Galactic latitude dependence analysis or the frequency dependence of the anisotropies in the range 50–250 GHz put a constraint on the maximum Galactic contribution in the power spectrum to be less than ∼ 10% (68% C. L.) for an ∼ 1 degree scale, and possibly higher for larger scales.

      The origin of most of the signals in the CMBR anisotropies is not Galactic. In any case, the subtraction of the galaxy is not accurate enough to allow a ``precision Cosmology”; other sources of contamination (extragalactic, solar system) are also present.

    • Effects of the Size of Cosmological N-body Simulations on Physical Quantities – II: Halo Formation and Destruction Rate

      Jayanti Prasad

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      In this study we show how errors due to finite box size affect formation and the destruction rate for haloes in cosmological N-body simulations. In an earlier study we gave an analytic prescription of finding the corrections in the mass function. Following the same approach, in this paper we give analytical expressions for corrections in the formation rate, destruction rate and the rate of change in comoving number density, and compute their expected values for the power law (𝑛 = -2) and LCDM models.

    • On Surface Tension for Compact Stars

      R. Sharma S. D. Maharaj

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      In an earlier analysis it was demonstrated that general relativity gives higher values of surface tension in strange stars with quark matter than neutron stars. We generate the modified Tolman–Oppenheimer–Volkoff equation to incorporate anisotropic matter and use this to show that pressure anisotropy provides for a wide range of behaviour in the surface tension than is the case with isotropic pressures. In particular, it is possible that anisotropy drastically decreases the value of the surface tension.

    • Does Si Play a Role in the Formation of Extrasolar Planet Systems?

      C. Huang G. Zhao H. W. Zhang Y. Q. Chen

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      With the high signal-to-noise ratio spectra, we obtained Si abundances of 22 extrasolar planet host stars, and discussed some constraints on the planet formation. Using our silicon abundance results and other authors’ Si abundance studies about planets-harboring stars, we investigated the correlation between the dynamical properties and the silicon abundance. We propose a hypothesis that higher primordial metallicity in the host stars’ birth cloud with higher abundance of Si will make the cloud more sticky to bypass the time scale restriction in planet formation and easier to form the planets.

    • Activity Cycle of Solar Filaments

      K. J. Li Q. X. Li P. X. Gao J. Mu H. D. Chen T. W. Su

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      Long-term variation in the distribution of the solar filaments observed at the Observatorie de Paris, Section de Meudon from March 1919 to December 1989 is presented to compare with sunspot cycle and to study the periodicity in the filament activity, namely the periods of the coronal activity with the Morlet wavelet used. It is inferred that the activity cycle of solar filaments should have the same cycle length as sunspot cycle, but the cycle behavior of solar filaments is globally similar in profile with, but different in detail from, that of sunspot cycles. The amplitude of solar magnetic activity should not keep in phase with the complexity of solar magnetic activity. The possible periods in the filament activity are about 10.44 and 19.20 years. The wavelet local power spectrum of the period 10.44 years is statistically significant during the whole consideration time. The wavelet local power spectrum of the period 19.20 years is under the 95% confidence spectrum during the whole consideration time, but over the mean red-noise spectrum of 𝛼 = 0.72 before approximate Carrington rotation number 1500, and after that the filament activity does not statistically show the period. Wavelet reconstruction indicates that the early data of the filament archive (in and before cycle 16) are more noiseful than the later (in and after cycle 17).

    • Forbidden Transition Probabilities of Astrophysical Interest among Low-lying States of V III

      Andrei Irimia

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      Electric and magnetic multipole transitions among low-lying states of doubly ionized vanadium were computed using the multi-configuration Hartree–Fock (MCHF) method with Breit–Pauli (BP) corrections to a non-relativistic Hamiltonian. Energy levels were determined up to and including 3𝑑2(1𝐺)4𝑠 b 2𝐺7/2 and computed energies were found to be in good agreement with experiment and other theories. In addition to Einstein 𝐴𝑘𝑖 coefficients for some E2 and M1 transitions, lifetime data and selected weighted oscillator strengths are also reported.

  • Journal of Astrophysics and Astronomy | News

    • Continuous Article Publication

      Posted on January 27, 2016

      Since January 2016, the Journal of Astrophysics and Astronomy has moved to Continuous Article Publishing (CAP) mode. This means that each accepted article is being published immediately online with DOI and article citation ID with starting page number 1. Articles are also visible in Web of Science immediately. All these have helped shorten the publication time and have improved the visibility of the articles.

    • Editorial Note on Continuous Article Publication

      Posted on July 25, 2019

      Click here for Editorial Note on CAP Mode

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