Article ID 59 Research Article
We present a modified inertia formulation of Modified Newtonian dynamics (MOND) without retaining Galilean invariance. Assuming that the existence of a universal upper bound, predicted by MOND, to the acceleration produced by a dark halo is equivalent to a violation of the hypothesis of locality (which states that an accelerated observer is pointwise inertial), we demonstrate that Milgrom’s law is invariant under a new space–time coordinate transformation. In light of the new coordinate symmetry, we address the deficiency of MOND in resolving the mass discrepancy problem in clusters of galaxies.
Article ID 60 Editorial
Article ID 61 Research Article
We study the near photospheric Fe I 6302 Å (V-component) and chromospheric Ca II H 3968 Å radiance oscillations in the lower solar atmosphere above the four brightened and magnetically active regions of the quiet-Sun as observed by the solar optical telescope onboard Hinode. At the chosen locations (L1, L3, L4), we obtain the statistically significant periods of 5.0 min both in Ca II H and Fe I fluxes, which is interpreted as the likely signature of the presence of 5.0 min magnetoacoustic oscillations. It is also found that the higher period (7.0 min) of magnetoacoustic waves, as observed at another location (L2), may be generated locally in the quiet-Sun tube and leak to higher heights. We suggest that 5.0 min global acoustic oscillations are converted into magnetoacoustic one in the strongly magnetized quiet-Sun fluxtubes. Noting that the magnetoacoustic waves in strongly magnetized regions can transfer energy twice compared to the acoustic waves in the non-magnetized regions, the directly observed these 5.0 min magnetoacoustic oscillations at photospheric and chromospheric heights above the strongly magnetized regions reveal the transfer of significant amount of energy to partially balance the localized energy losses.
Article ID 62 Research Article
Highly magnetized neutron stars known as magnetars are some of the most interesting objects in the Universe. Non-baryonic dark matter candidate axions are produced in the highly magnetized neutron star via Bremsstrahlung process in the highly dense medium. These axions thus produced are then converted into photons in the strong magnetic field via Primakoff effect giving rise to the observed X-ray luminosity level of these objects. Our results are found within observational limit of SGRs(1806-20, 1900+14,0526-66 and 1627-41) and AXPs(4U0142+61,1E1048-5937,RXS1708-4009 and 1E1841-045).
Article ID 63 Research Article
The origin of the abundance pattern and also the (anti)correlation present among the elements found in stars of globular clusters (GCs) remains unimproved until date. The proton-capture reactions are presently recognised in concert of the necessary candidates for that sort of observed behaviour in the second generation stars. We tend to propose a reaction network of a nuclear cycle namely carbon–nitrogen–oxygen–fluorine (CNOF) at evolved stellar condition since fluorine (19F) is one such element which gets plagued by proton capture reactions. The stellar temperature thought about here ranges from 2×107 to 10×107 K and there has been an accretion occuring, with material density being 102 g/cm3 and 103 g/cm3. Such kind of temperature density conditions are probably going to be prevailing within the H-burning shell of evolved stars. The estimated abundances of 19F are then matched with the info that has been determined for a few some metal-poor giants of GC M4, M22,47 Tuc as well as NGC 6397. As far as the comparison between the observed and calculated abundances is concerned, it is found that the abundance of 19F have shown an excellent agreement with the observed abundances with a correlation coefficent above 0.9, supporting the incidence of that nuclear cycle at the adopted temperature density conditions.
Article ID 64 Research Article
The effects of nonuniform rotation and magnetic field on the instability of a self gravitating infinitely extending axisymmetric cylinder of viscoelastic ferromagnetic medium have been studied using the Generalised Hydrodynamic (GH) model. The non-uniform magnetic field and rotation are acting along the axial direction of the cylinder and the propagation of the wave is considered along the radial direction, while the ferrofluid magnetization is taken collinear with the magnetic field. A general dispersion relation representing magnetization, magnetic permeability and viscoelastic relaxation time parameters is obtained using the normal mode analysis method in the linearized perturbation equation system. Jeans criteria which represent the onset of instability of self gravitating medium are obtained under the limits; when the medium behaves like a viscous liquid (strongly coupled limit) and a Newtonian liquid (weakly coupled limit). The effects of various parameters on the Jeans instability criteria and on the growth rate of self gravitating viscoelastic ferromagnetic medium have been discussed. It is found that the magnetic polarizability due to ferromagnetization of medium marginalizes the effect of non-uniform magnetic field on the Jeans instability, whereas the viscoelasticity of the medium has the usual stabilizing effect on the instability of the system. Further, it is found that the cylindrical geometry is more stable than the Cartesian one. The variation of growth rate against the wave number and radial distance has been depicted graphically.
Article ID 65 Research Article
The purpose of the present study is to investigate the association of the cosmic ray intensity (CRI) and interplanetary magnetic field (IMF) with high speed solar wind streams (HSSWS) and slow speed solar wind streams (SSSWS) for solar cycle −23 and 24. We have found very interesting and adequate results where CRI provides inverse relationship with the above mentioned streams. Since the correlation coefficient in case of HSSWS is found to be high as compared to SSSWS, it implies that HSSWS are more competent parameters to produce decrease in CRI as compared to SSSWS. Overall analysis of our study shows that CRI, IMF and product of wind speed and IMF (V.B) are poorly correlated with each other for both solar cycles. The year 2016 showed remarkable behavior as there was a drastic increase in the values of interplanetary magnetic field in comparison to the previous years which caused the change in pattern of solar wind streams.
Article ID 66 Research Article
In this work, we investigate the electromagnetic perturbation around a quantum-corrected Schwarzschild black hole. The complex frequencies of the quasinormal modes are evaluated by the third-order WKB approximation. The numerical results obtained showed that the complex frequencies depend on the quantum correction parameter a of a black hole, which the real parts and the magnitudes of the imaginary parts of quasinormal modes decrease with the increase in factor a. These conclusions show that the electromagnetic perturbation around the black hole oscillate and damp more slowly owing to the presence of the quantum correction parameter.
Article ID 67 Research Article
In this study, eighty six Hα (6563 Å) emission line spectra from the central region (∼40′×40′) of the Orion Nebula (NGC1976, M42, Sh2-281) have been obtained using DEFPOS spectrometer with a circular field of view of 4′ at TUBITAK National Observatory (TUG, Antalya, Turkey). Measurements provide information about the intensities, line widths, and radial velocities of the gas surrounding the Sh2-281 HII-region. The intensities, the radial velocities and the line widths of the Hα emission line were found in the range of from 319.85 R to 6009.08 R (mean 2006 ± 400 R), from −14.91 km s−1 to +5.40 km s−1 (mean −4.51 ± 3.80 km s−1), and from 27.83 km s−1 to 49.60 km s−1 (mean 41.09 ± 7.74 km s−1), respectively. Moreover, the mean emission measure (EM) calculated from IHα values was obtained as 4513.02 cm−6 pc. The mean LSR velocity of the nebula was found to be −4.51 km s−1 and was compared with some previous works. The intensity values of DEFPOS data were also compared with the data obtained from VTSS, SkyView, and SHASSA maps using APER and SKY codes. We found that our results were approximately the similar variation with VTSS (mean 2002.04 R), SkyView (mean 2680.05 R), and SHASSA (mean 2400.06 R) maps. We believe that DEFPOS spectrometer with a 4′ diameter field of view is able to provide a powerful tool for the study of diffuse ionized gas and this new results may have significant contribution to the literature.
Article ID 68 Research Article
Active Galactic Nuclei (AGN) feedback is regarded as an important non-gravitational process in galaxy clusters, providing useful constraints on large-scale structure formation. It modifies the structure and energetics of the intra-cluster medium (ICM) and hence its understanding is crucially needed in order to use clusters as high precision cosmological probes. In this context, particularly keeping in mind the upcoming high quality radio data expected from radio surveys like Square Kilometre Array (SKA) with its higher sensitivity, high spatial and spectral resolutions, we review our current understanding of AGN feedback, its cosmological implications and the impact that SKA can have in revolutionizing our understanding of AGN feedback in large-scale structures. Recent developments regarding the AGN outbursts and its possible contribution to excess entropy in the hot atmospheres of groups and clusters, its correlation with the feedback energy in ICM, quenching of cooling flows and the possible connection between cool core clusters and radio mini-halos, are discussed. We describe current major issues regarding modeling of AGN feedback and its impact on the surrounding medium. With regard to the future of AGN feedback studies, we examine the possible breakthroughs that can be expected from SKA observations. In the context of cluster cosmology, for example, we point out the importance of SKA observations for cluster mass calibration by noting that most of z>1 clusters discovered by eROSITA X-ray mission can be expected to be followed up through a 1000 hour SKA1-mid programme. Moreover, approximately 1000 radio mini halos and ∼2500 radio halos at z<0.6 can be potentially detected by SKA1 and SKA2 and used as tracers of galaxy clusters and determination of cluster selection function.
Article ID 69 Research Article
In this work, we investigate the propagation of three-dimensional nonlinear dust-acoustic and dust-Coulomb waves in an unmagnetized warm dusty plasma consisting of electrons, ions, and charged dust particles. The grain charge fluctuation is incorporated through the current balance equation. Using the perturbation method, a Kadomtsev–Petviashvili (KP) equation is obtained. It has been shown that the charge fluctuation would modify the wave structures, and the waves in such systems are unstable due to high-order long wave perturbations.
Article ID 70 Research Article
This paper presents a Multi-satellite Data Analysis and Simulator Tool (MDAST), developed with the original goal to support the science requirements of a Martian 3-Unit CubeSat mission profile named Bleeping Interplanetary Radiation Determination Yo-yo (BIRDY). MDAST was firstly designed and tested by taking into account the positions, attitudes, instruments field of view and energetic particles flux measurements from four spacecrafts (ACE, MSL, STEREO A, and STEREO B). Secondly, the simulated positions, attitudes and instrument field of view from the BIRDY CubeSat have been adapted for input. And finally, this tool can be used for data analysis of the measurements from the four spacecrafts mentioned above so as to simulate the instrument trajectory and observation capabilities of the BIRDY CubeSat. The onset, peak and end time of a solar particle event is specifically defined and identified with this tool. It is not only useful for the BIRDY mission but also for analyzing data from the four satellites aforementioned and can be utilized for other space weather missions with further customization.
Article ID 71 Research Article
The energy density of the universe is estimated to be composed of 68% dark energy. Dark energy is associated with the accelerated expansion of the universe. In this work, we consider the evolution of the number density $n(z)$ and light intensity $I(z)$ of galaxies with redshift $z$ for a matter-dominated Friedmann universe in the presence of dark energy and compare the results with a matter-dominated Friedmann universe without dark energy effects. Computational results of $n(z)$ and $I(z)$ are presented in a suitable form for comparison with future observed dependencies to test the fractal-homogeneous models of open, closed and flat matter-dominated universe. From our results, there was increased structure formation in the universe from z=0 to $z ≈ 1$ when the rate of growth started to slow down. Furthermore, there is reduced structure formation for a universe driven by dark energy as compared to one without dark energy.
Article ID 72 Research Article
The spatial morphological study of stellar clusters has been carried out through their identified probable members. The field stars decontamination is performed by the statistical cleaning approach (depends on the magnitude and colour of stars within the field and cluster regions). The colour magnitude ratio diagram (CMRD) approach is used to separate the stellar sequences of cluster systems. The age, distance and reddening of each cluster is estimated through the visual inspection of best fitted isochrone in colour magnitude diagrams (CMDs). The mean proper motion values of stellar clusters are obtained through the extracted data from PPMXL and UCAC4 catalogs. Moreover, these values vary according to the extracted data-set from these catalogues. This variation has occurred due to different estimation efficiency of proper motions. The two colour ratio (TCR) and two colour magnitude ratio (TCMR) values of each cluster is determined by utilizing the WISE and PPMXL catalogues, these values are found abnormal for Teutsch 106. In addition, the TCMR values are similar to TCR values at longer wavelength, whereas both values are far away from each other at shorter wavelength. The fraction of young stellar objects (YSOs) is also computed for each cluster.
Volume 38 | Issue 4
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.