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      Volume 35, Issue 1

      March 2014,   pages  1-106

    • Changed Relation between Solar 10.7-cm Radio Flux and some Activity Indices which describe the Radiation at Different Altitudes of Atmosphere during Cycles 21–23

      E. A. Bruevich V. V. Bruevich G. V. Yakunina

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      The correlation coefficients of the linear regression of six solar indices versus 10.7 cm radio flux 𝐹10.7 were analysed in solar cycles 21, 22 and 23. We also analysed the interconnection between these indices and 𝐹10.7 with help of approximation by polynomials of second order. The indices we have studied in this paper are: the relative sunspot numbers – SSN, 530.3 nm coronal line flux – 𝐹530 , the total solar irradiance – TSI, Mg II 280 nm core-to-wing ratio UV-index, the Flare Index – FI and the counts of flares. In most cases the regressions of these solar indices vs. 𝐹10.7 are close to the linear regression except the moments of time near the minimums and maximums of the 11-year activity. For the linear regressions, we found that correlation coefficients 𝐾corr(𝑡) for the solar indices vs. 𝐹10.7 and SSN dropped to their minimum values twice during each 11-year cycle.

    • Orbital Mechanics near a Rotating Asteroid

      Yu Jiang Hexi Baoyin

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      This study investigates the different novel forms of the dynamical equations of a particle orbiting a rotating asteroid and the effective potential, the Jacobi integral, etc. on different manifolds. Nine new forms of the dynamical equations of a particle orbiting a rotating asteroid are presented, and the classical form of the dynamical equations has also been found. The dynamical equations with the potential and the effective potential in scalar form in the arbitrary body-fixed frame and the special body-fixed frame are presented and discussed. Moreover, the simplified forms of the effective potential and the Jacobi integral have been derived. The dynamical equation in coefficient-matrix form has been derived. Other forms of the dynamical equations near the asteroid are presented and discussed, including the Lagrange form, the Hamilton form, the symplectic form, the Poisson form, the Poisson-bracket form, the cohomology form, and the dynamical equations on Kähler manifold and another complex manifold. Novel forms of the effective potential and the Jacobi integral are also presented. The dynamical equations in scalar form and coefficient-matrix form can aid in the study of the dynamical system, the bifurcation, and the chaotic motion of the orbital dynamics of a particle near a rotating asteroid. The dynamical equations of a particle near a rotating asteroid are presented on several manifolds, including the symplectic manifold, the Poisson manifold, and complex manifolds, which may lead to novel methods of studying the motion of a particle in the potential field of a rotating asteroid.

    • X-ray Flares Observed from Six Young Stars Located in the Region of Star Clusters NGC 869 and IC 2602

      Himali Bhatt J. C. Pandey K. P. Singh Ram Sagar Brijesh Kumar

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      We present, for the first time, an analysis of seven intense X-ray flares observed from six stars (LAV 796, LAV 1174, SHM2002 3734, 2MASS 02191082+5707324, V553 Car, V557 Car). These stars are located in the region of young open star clusters NGC 869 and IC 2602. These flares detected in the XMM-Newton data show a rapid rise (10–40 min) and a slow decay (20–90 min). The X-ray luminosities during the flares in the energy band 0.3–7.5 keV are in the range of 1029.9 to 1031.7 erg s-1. The strongest flare was observed with the ratio ∼ 13 for count rates at peak of the flare to the quiescent intensity. The maximum temperature during the flares has been found to be ∼ 100 MK. The semi-loop lengths for the flaring loops are estimated to be of the order of 1010 cm. The physical parameters of the flaring structure, the peak density, pressure and minimum magnetic field required to confine the plasma have been derived and found to be consistent with flares from pre-main sequence stars in the Orion and the Taurus-Auriga-Perseus region.

    • Comparative Studies of Population Synthesis Models in the Framework of Modified Strömgren Filters

      Yuvraj Harsha Sreedhar Karl Rakos Gerhard Hensler

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      Evolutionary models form a vital part of stellar population research in understanding their evolution, but despite their long history of development, they are often misrepresented and the properties of stellar population observed through broadband and spectroscopic measurements are also misinterpreted. With growing numbers of these synthesis models, model comparison becomes an important analysis to choose a suitable model for understanding stellar populations and model up-gradation. Along with model comparison, we reinvestigate the technique ofmodified Strömgren photometry to measure reliable parameter-sensitive colours and estimate precise model ages and metallicities. The assessment of Rakos/Schulz models with GALEV and Worthey’s Lick/IDS model find smaller colour variation: 𝛥 (𝑢𝑧 - 𝑣𝑧) ≤ 0.056, 𝛥 (𝑏𝑧 - 𝑦𝑧) ≤ -0.05 and 𝛥 (𝑣𝑧 − 𝑦𝑧) ≤ 0.061. The study conveys a good agreement of GALEV models with modified Strömgren colours but with poor UV model predictions and observed globular cluster data, while the spectroscopic models perform badly because of outdated isochrone and stellar spectral libraries with inaccurate/insufficient knowledge of various stellar phases and their treatment. Overall, the assessment finds modified Strömgren photometry well suited to study different types stellar populations by mitigating the effects of age-metallicity degeneracy.

    • Interacting Winds in Eclipsing Symbiotic Systems – The Case Study of EG Andromedae

      Emanuele Calabrò

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      We report the mathematical representation of the so called eccentric eclipse model, whose numerical solutions can be used to obtain the physical parameters of a quiescent eclipsing symbiotic system. Indeed the nebular region produced by the collision of the stellar winds should be shifted to the orbital axis because of the orbital motion of the system. This mechanism is not negligible, and it led us to modify the classical concept of an eclipse. The orbital elements obtained from spectroscopy and photometry of the symbiotic EG Andromedae were used to test the eccentric eclipse model. Consistent values for the unknown orbital elements of this symbiotic were obtained. The physical parameters are in agreement with those obtained by means of other simulations for this system.

    • Analysis of Optical Variations of BL Lac Object AO 0235+164

      Wang Hong-tao

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      Historical optical BVRI band data are combined on the BL Lac object AO 0235 + 164. In order to examine the possible existence of lags and correlations between variations in different optical bands from this source, a statistical analysis is performed through the Discrete Correlation Function (DCF) method. Monte Carlo simulations called Flux Redistribution/Random Subset Selection (FR/RSS) are performed to obtain statistically meaningful values for the cross-correlation time lags and their related uncertainties. The analysis confirms that the variations in different optical light curves are strongly correlated, with no or very weak lag within the errors. Long term variability of color indices are also analysed. No color variabilities are found.

    • Evolution of Primordial Black Holes in Loop Quantum Cosmology

      D. Dwivedee B. Nayak M. Jamil L. P. Singh R. Myrzakulov

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      In this work, we study the evolution of primordial black holes within the context of loop quantum cosmology. First we calculate the scale factor and energy density of the Universe for different cosmic era and then taking these as inputs, we study evolution of primordial black holes. From our estimation it is found that accretion of radiation does not affect evolution of primordial black holes in loop quantum cosmology. We also conclude that due to slow variation of scale factor, the upper bound on initial mass fraction of presently evaporating PBHs are much greater in loop quantum cosmology than the standard case.

  • 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.

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