Publisher: Springer-Verlag (Total: 2626 journals)

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 Astrophysics and Space ScienceJournal Prestige (SJR): 0.616 Citation Impact (citeScore): 1Number of Followers: 44      Hybrid journal (It can contain Open Access articles) ISSN (Print) 1572-946X - ISSN (Online) 0004-640X Published by Springer-Verlag  [2626 journals]
• Posing constraints on the free parameters of a new model of dark energy
EoS: responses through cosmological behaviours
• Abstract: Abstract Since the late 1990’s observations of type Ia Supernova, our universe is predicted to experience a late time cosmic acceleration. Theoretical support to this observation were intended to be built via proposition of a hypothetical fluid which staying inside the universe exerts negative pressure. Cosmologists have prescribed many candidates for this exotic fluid so far. In this alley, a popular method is to choose time dependent equation of state parameter $$\omega = \frac{p}{\rho }$$ and to parametrize it as a function of redshift. Again some common families of such parametrizations are constructed among which different members justify different properties of observed universe. Mainly, these were model dependent studies which comprise free parameters to be constrained by different observations. In this present article, a new expression for redshift parametrization is considered and we have constrain its free parameters for two Hubble parameter vs redshift data sets. These data sets are obtained depending on two basic methodologies known as different ages method and baryonic acoustic oscillation method. Different confidence contours for our model are located under the constraints of said data sets. Besides, different thermodynamic parameters related to the evolution of our universe are analysed. It is notified that our model indicates towards a delayed dark matter model which mimics EoS = $$-1(\Lambda )$$ phenomena at the present epoch. Deceleration parameters behaviour’s are studied. It is noticed that a possibility of future deceleration may occur for this new model. Outcomes for both the data sets are compared with each other.
PubDate: 2020-07-13

• WALLABY – an SKA Pathfinder H  i survey
• Abstract: Abstract The Widefield ASKAP L-band Legacy All-sky Blind surveY (wallaby) is a next-generation survey of neutral hydrogen (H i) in the Local Universe. It uses the widefield, high-resolution capability of the Australian Square Kilometer Array Pathfinder (ASKAP), a radio interferometer consisting of $$36 \times12$$ -m dishes equipped with Phased-Array Feeds (PAFs), located in an extremely radio-quiet zone in Western Australia. wallaby aims to survey three-quarters of the sky ( $$-90^{\circ} < \delta< +30^{\circ}$$ ) to a redshift of $$z \lesssim0.26$$ , and generate spectral line image cubes at ∼30 arcsec resolution and ∼1.6 mJy beam−1 per 4 km s−1 channel sensitivity. ASKAP’s instantaneous field of view at 1.4 GHz, delivered by the PAF’s 36 beams, is about 30 sq deg. At an integrated signal-to-noise ratio of five, wallaby is expected to detect around half a million galaxies with a mean redshift of $$z \sim0.05$$ (∼200 Mpc). The scientific goals of wallaby include: (a) a census of gas-rich galaxies in the vicinity of the Local Group; (b) a study of the H i properties of galaxies, groups and clusters, in particular the influence of the environment on galaxy evolution; and (c) the refinement of cosmological parameters using the spatial and redshift distribution of low-bias gas-rich galaxies. For context we provide an overview of recent and planned large-scale H i surveys. Combined with existing and new multi-wavelength sky surveys, wallaby will enable an exciting new generation of panchromatic studies of the Local Universe. — First results from the wallaby pilot survey are revealed, with initial data products publicly available in the CSIRO ASKAP Science Data Archive (CASDA).
PubDate: 2020-07-13

• Bulk viscous Bianchi type I cosmological model in Lyra geometry and in the
general theory of relativity
• Abstract: Abstract In the framework of the gravitational theory based on Lyra geometry and the general theory of relativity, we study Bianchi type I cosmological model in the presence of viscous fluid. A discussion about the suitability of the Sen equations as field equations in Lyra geometry is given. A clear physical meaning for the time component of the displacement vector, introduced in the Sen field equations used in the framework of Lyra geometry, is given by identifying it as a part of the energy momentum tensor (viscosity term). Exact solution of the Einstein field equations is given by assuming the model has a constant deceleration parameter. Moreover, we study the effect of the viscosity term on the entropy of the universe. A formula for calculating the entropy in the presence of viscosity is given by a combination between the second law of thermodynamics and the energy momentum tensor in a conservative manner. We calculate and study the thermodynamic functions (Enthalpy, Gibbs energy and Helmholtz energy) of the universe in the presence of viscosity in Lyra geometry and in the general theory of relativity. The physical and geometrical properties of the obtained models are discussed.
PubDate: 2020-07-13

• Modeling of ionospheric TEC corrections based on modified mapping function
and Gram–Schmidt orthogonalization at low latitude region
• Abstract: Abstract The ionospheric medium is the primary source of error for signals from the Global Positioning System (GPS) satellites. Modeling ionospheric effects is one of the main challenges in developing accurate and reliable services for Space-Based Augmentation Systems. The Mapping Function (MF) and the estimation of the model coefficients are an essential parameter in the aspects of ionospheric modeling. In the present study, a Planar Fit (PF) model is considered to model the ionospheric Total Electron Content (TEC). The Ionosphere observations (GPS-TEC) obtained directly from the GPS receiver at Koneru Lakshmaiah Education Foundation (KLEF)-Guntur (16.44° N, 80.62° E) station and are used as reference values for comparison during the period 2015. The PF model is two-fold: first, the ionospheric line-of-sight TEC is converted into vertical TEC (vTEC) based on the Modified Mapping Function (MMF), and secondly, the PF coefficients are estimated based on the Gram–Schmidt Orthogonalization (GSO). The performance of the model is tested under quiet and disturbed ionosphere conditions and for different months of the year. The PF model values are in good agreement with the GPS-TEC values for the scenarios considered. The Average Absolute Error (AAE) and Root Mean Square Error (RMSE) values are maximum in equinoxes (March and October) and moderate in winter (January and December) and minimum in summer months (July and August). The PF model is adequate for characterizing the low-latitude ionospheric characteristics in different space weather conditions. The results would support towards the development of regional ionosphere models for navigation users under the GAGAN/NavIC system in India.
PubDate: 2020-07-13

• Ionospheric electron density characteristics over Africa from
• Abstract: Abstract With the widespread availability of ground and space-based global navigation satellite system (GNSS) observables, continuous and long-term explorations of ionospheric variations have been made possible worldwide or on regional basis with improved accuracy. The Formosa Satellite Mission#3/Constellation Observing System for Meteorology, Ionosphere, and Climate (FORMOSAT-3/COSMIC) mission has a huge database of radio occultation (RO) soundings at regional and global scales with a high vertical resolution. Comparative studies between radio occultation, incoherent scatter radar and ionosonde observations indicate that COSMIC profiles agree well with ground measurements. The present paper investigates the ionospheric profiles over Africa using COSMIC data for the period from 2006 to 2017, representing almost a solar cycle year of study. The spatiotemporal variation of electron density confirms a hemispheric asymmetry among the equinoctial seasons and the solstice seasons during both low and moderate solar activity. Seasonal/winter anomaly manifestation is also clearly noticed in our observations with relatively high electron density during the winter solstice than the summer solstice. Moreover, the electron density over the region show apparent spatial and temporal variations identical to earlier ground-based ionospheric monitoring results over the African region. The outcomes from this study would strengthen the understanding of the ionospheric alterations and modelling activities in Africa, especially the areas with inadequate ground-based measuring instruments, hence, our results may complement the progress in global ionospheric modelling.
PubDate: 2020-07-13

• Microglitches in radio pulsars: the role of strange nuggets
• Abstract: Abstract Strange Nuggets are believed to be among the relics of the early universe. They appear as dark matter due to their low charge-to-mass ratio. Their distribution is believed to be the same as that of dark matter. As such, they could be accreted by high magnetic field objects and their collisions with pulsars are inevitable. Pulsar glitches are commonly seen as sudden spin-ups in pulsar frequency. It is still an open debate with regard to mechanisms giving rise to such a phenomenon. However, there is a class of sudden changes in pulsar spin frequency known as microglitches. These event are characterized by sudden small change in pulsar spin frequency ( $$\delta \nu/\nu \approx \pm 10^{-9}$$ ). Clearly, the negative signature seen in some of the events is inconsistent with the known glitch mechanisms. In this analysis, we suggest that accretion of strange nuggets with pulsars could readily give rise to microglitch events. The signature of the events depends on the energy of the strange nuggets and line of interaction.
PubDate: 2020-07-13

• Local dark energy in the Sculptor Filament of galaxies
• Abstract: Abstract Two dozens of different mass galaxies observed at distances less than 10 Mpc from the Local Group are organized in the elongated structure known as the Sculptor Filament. We use recent Hubble Space Telescope data on local galaxies to study the dynamical structure and evolutionary trends of the filament. An N-body computer model, which reproduces its observed kinematics, is constructed under the assumption that the filament is embedded in the universal dark energy background. In the model, the motions of the filament members are controlled by their mutual gravity attraction force and the anti-gravity repulsion force produced by the local dark energy. It is found that the dark energy repulsion dominates the force field of the outer parts of the filament. Because of this, the filament expands and its expansion proceeds with acceleration. The dark energy domination increases with cosmic time and introduces to the filament the linear velocity–distance relation with the universal time-rate (“the Hubble constant”) that depends asymptotically on the dark energy density only.
PubDate: 2020-07-13

• Non-integrability, stability and periodic solutions for a quartic galactic
potential in a rotating reference frame
• Abstract: Abstract This work aims to study the influence of the rotation of the galaxy which it is modelled as a bi-symmetrical potential consists of a two-dimensional harmonic oscillator with quartic perturbing terms on some dynamics aspects for the problem of the motion of stars. We prove analytically the non-integrability of the motion (i.e., the motion is chaotic) when the parameters meet certain conditions. Poincaré surface of section is introduced as a numerical method that is employed to confirm the obtained analytical results. We present the equilibrium points and examine their stability. We also clarify the force resulting from the rotating frame serves as a stabilizer for the maximum equilibrium points. We illustrate graphically the size of stability zones depends on the value of the angular velocity for the frame. Based on the Lyapunov theorem, the periodic solutions are constructed near the equilibrium point. Additionally, we prove the existence of one or two families of periodic solutions according to the equilibrium point is either saddle or stable, respectively. The permitted zones of possible motion are delimited and they are graphically explained for different values of the parameters.
PubDate: 2020-07-09

• Resonant magnetohydrodynamic oscillations in flowing high beta plasmas
• Abstract: Abstract The plasma motion in the dissipative layer of a flowing high beta plasma is studied. The linearized magnetohydrodynamic (MHD) equations are used to study the plasma motion. Using the perturbation method presented by Ruderman (2009) the solution of equations of motion are determined. The effect of the plasma flow is to change the distance between the slow and Alfvénic resonant points as well as the thickness of the mixed dissipative layer.
PubDate: 2020-07-08

• A formula for the start of a new sunspot cycle
• Abstract: Abstract It is known that the solar radio flux is strongly correlated to the sunspot cycle and that the flux is nearly the same at every minimum. If 64 sfu is taken as the baseline for all cycles, then we can calculate the proxy sunspot number from the flux, and vice versa. Furthermore, we find that the fitted adjusted flux divided by the fitted sunspot number gives a strong marker for the start of Solar Cycle 25 in October 2019. The high resolution 2K (based on 2048×2048 pixels SDO images) sunspot number currently indicates a start in June 2019.
PubDate: 2020-07-08

• Distance scale for high-luminosity stars in OB associations and in field
with Gaia DR2. Spurious systematic motions
• Abstract: Abstract We calculated the median parallaxes for 47 OB associations including at least 10 stars with known Gaia DR2 parallaxes. A comparison between trigonometric and photometric parallaxes of OB associations reveals a zero-point offset of $$\Delta \varpi=-0.11\pm0.04$$ mas indicating that Gaia DR2 parallaxes are, on average, underestimated and the distances derived from them are overestimated. The correction of $$\Delta \varpi=-0.11$$ mas is consistent with the estimate that Arenou et al. (2018) obtained for bright stars. An analysis of parallaxes of OB associations and high-luminosity field stars confirms our previous conclusion (Dambis et al. 2001) that the distance scale for OB stars established by Blaha and Humphreys (1989) must be reduced by 10–20%. Spurious systematic motions of 10–20 km s−1 at the distances of 2–3 kpc from the Sun are found to arise from the use of the uncorrected Gaia DR2 parallaxes.
PubDate: 2020-07-07

• New H  i observations of KK 69. Is KK 69 a dwarf galaxy
in transition'
• Abstract: Abstract We present new H i data of the dwarf galaxy KK 69, obtained with the Giant Metrewave Radio Telescope (GMRT) with a signal-to-noise ratio almost double previous observations. We carried out a Gaussian spectral decomposition and stacking methods to identify the cold neutral medium (CNM) and the warm neutral medium (WNM) of the H i gas. We found that 30% of the total H i gas, which corresponds to a mass of ∼107 M⊙, is in the CNM phase. The distribution of the H i in KK 69 is not symmetric. Our GMRT H i intensity map of KK 69 overlaid onto a Hubble Space Telescope image reveals an offset of ∼4 kpc between the H i high-density region and the stellar body, indicating it may be a dwarf transitional galaxy. The offset, along with the potential truncation of the H i body, are evidence of interaction with the central group spiral galaxy NGC 2683, indicating the H i gas is being stripped from KK 69. Additionally, we detected extended H i emission of a dwarf galaxy member of the group as well as a possible new galaxy located near the north-eastern part of the NGC 2683 H i disk.
PubDate: 2020-07-07

• Investigation of global ionospheric response of the severe geomagnetic
storm on June 22-23, 2015 by GNSS-based TEC observations
• Abstract: Abstract The magnetosphere and ionosphere have a crucial interaction during severe geomagnetic storms. The Global Navigation Satellite System (GNSS) provides high-quality ionospheric observations with high temporal and spatial resolution, is generally preferred to investigate the ionospheric variation. In this study, the storm-time ionospheric response of the June 2015 severe storm (Dstmin = −208 nT) was investigated by the Total Electron Content (TEC) data of the Global Ionosphere Maps (GIMs), COSMIC radio occultation (RO) and a chain of International GNSS Service (IGS) stations. GIMs were used to show the global TEC variation during the storm. COSMIC RO data were also utilized to investigate the TEC variation and electron density profiles in an anomaly area with a limited time interval. GNSS TEC data of the 16 IGS stations were utilized to investigate the ionospheric variability on different latitudes of hemispheres. The results showed that intense positive phases formed in high latitudes of the Southern Hemisphere (SH) and the western longitudes of the Northern Hemisphere (NH), especially over the North Atlantic Ocean until the main phase of the storm. Besides, negative phases were observed in high latitudes and eastern longitudes of the NH. During the recovery phase of the storm, positive phases were seen in the low latitudes of the SH and the ionospheric conditions calmed down in the entire SH after the depletion of these phases. Negative phases were also observed almost wholly covered in the NH, which denser in the European-African sector. As a particular result, the electron density profiles of COSMIC RO showed that the ionospheric phases of the June 2015 storm not only related to TEC values but also the altitude of maximum electron density.
PubDate: 2020-07-07

• Light trapping by the dark matter
• Abstract: Abstract Considering the dark matter as self-gravitating Bose-Einstein condensate in a gravito-chemical equilibrium state, we have studied the light trajectory through the halo. Found that depending on the initial direction cosine of the light ray, there are three types of trajectories: (a) the refracted light i.e. light which can refracts away from the halo to the out side, (b) the trapped light i.e. light that is trapped into the halo i.e. an observer, situated outside of the halo, can not observe it and (c) the reflected light: in this case the halo behaves as a perfect reflector to the outside light. The light trapping can introduce asymmetry in the observed spectrum and modify the apparent number of stars in a dark matter dominated galaxy.
PubDate: 2020-07-07

• Identifying Galactic sources of high-energy neutrinos
• Abstract: Abstract High-energy neutrinos present the ultimate signature for a cosmic ray accelerator. Galactic sources responsible for acceleration of cosmic ray up to the knee in cosmic ray spectrum will provide a guaranteed, albeit subdominant, contribution to the high-energy cosmic neutrino flux. In this review, we discuss the the prospects for identification of high-energy neutrinos from sources of the very high energy gamma ray emission in the Milky Way. We present the status of the search for point-like and extended emission from these sources, and describe how the results of these studies indicate that neutrino telescopes are closing in on identifying Galactic sources of high-energy neutrinos.
PubDate: 2020-06-25

• Effects of dust temperature and radiative heat-loss functions on the
magnetogravitational instability of viscoelastic dusty plasma
• Abstract: Abstract The effects of dust temperature and radiative heat-loss functions on the instability of selfgravitating homogeneous viscoelastic dusty plasma have been studied using the modified GH model. A general dispersion relation representing the dust temperature, radiative heat-loss functions, magnetic field, thermal conductivity and relaxation time parameters are obtained using the normal mode analysis method in the linearized perturbation equations system. Jeans criteria that represent the onset of instability of selfgravitating medium are obtained under the limits; when the medium behaves like a viscous liquid (strongly coupled limit) and a Newtonian liquid (weakly coupled limit) for some limiting cases. The effects of various parameters on the Jeans instability criteria and on the growth rate of selfgravitating viscoelastic dusty plasma have been discussed. It is found that the dust temperature and radiative heat-loss functions modify the instability criterion by reducing the critical wave number.
PubDate: 2020-06-22

• Electromagnetic instabilities of low-beta alpha/proton beams in space
plasmas
• Abstract: Abstract Relative drifts between different species or particle populations are characteristic to solar plasma outflows, e.g., in the fast streams of the solar winds, coronal mass ejections and interplanetary shocks. This paper characterizes the dispersion and stability of the low-beta alpha/proton drifts in the absence of any intrinsic thermal anisotropies, which are usually invoked in order to stimulate various instabilities. The dispersion relations derived here describe the full spectrum of instabilities and their variations with the angle of propagation and plasma parameters. The results unveil a potential competition between instabilities of the electromagnetic proton cyclotron and alpha cyclotron modes. For conditions specific to a low-beta solar wind, e.g., at low heliocentric distances in the outer corona, the instability operates on the alpha cyclotron branch. The growth rates of the alpha cyclotron mode are systematically stimulated by the (parallel) plasma beta and/or the alpha-proton temperature ratio. One can therefore expect that this instability develops even in the absence of temperature anisotropies, with potential to contribute to a self-consistent regulation of the observed drift of alpha particles.
PubDate: 2020-06-22

• Radiative capture of proton by C13$^{13}\mbox{C}$ at low energy
• Abstract: Abstract Radiative capture $$p + {}^{13}\mathrm{C}\rightarrow {}^{14}\mathrm{N}+\gamma$$ at energies bearing astrophysical consequences is one of the important processes in the CNO cycle. We focus on the possibility of describing the main contribution to the total cross section of the radiative capture process in the framework of the single-particle potential model without separation into direct and resonant transitions. In case where the single-particle potential model fails to describe other partial components, we use the R-matrix approach. The partial components of the astrophysical S-factor are calculated for all possible electric dipole transitions. The calculated value of the total S-factor at zero energy is in good agreement with earlier reported values. Based on the value of total astrophysical S-factor depending on the collision energy, we calculate the nuclear reaction rates for $${p} + {^{13}\mathrm{C}} \rightarrow {^{14}\mathrm{{N}}}+\gamma$$.
PubDate: 2020-06-22

• The solar cycle: predicting the peak of solar cycle 25
• Abstract: Abstract Motivated by a successful prediction on the peak of solar cycle 24 (81.7, comparable to the observed 81.9, Du in Astrophys. Space Sci. 338:9, 2012), based on the logarithmic relationship between the maximum amplitude ($$R_{ \mathrm{m}}$$) of a solar cycle and the preceding minimum $$aa$$ geomagnetic index ($$aa_{\mathrm{min}}$$), we perform a prediction on the peak of the upcoming cycle 25 using the sunspot number of the new version instead. If the suggested error in $$aa$$ (3 nT) before 1957 is corrected, the correlation between $$\ln R_{\mathrm{m}}$$ and $$\ln aa_{\mathrm{min}}$$ ($$r=0.92$$) is stronger than that not corrected ($$r=0.86$$). Based on this relationship, the peak value of cycle 25 is predicted to be $$R_{\mathrm{m}}(25)\simeq 151.1\pm 16.9$$, about 30% stronger than cycle 24. Employing the ‘Waldmeier effect’ that the rise time of a cycle is well anti-correlated to its amplitude, we estimated the rise time, $$T_{\mathrm{a}}(25)=4.3\pm 0.2\pm 0.6$$, and the peak time of cycle 25, $$2024.1 \pm 0.8$$ (years), which is during April 2023 and November 2024.
PubDate: 2020-06-19

• Interacting Tsallis and Rényi holographic dark energy with hybrid
expansion law
• Abstract: Abstract The manuscript presents the dynamics of Tsallis holographic dark energy (THDE) and Rényi holographic dark energy (RHDE) prescribed by a non-linear interaction in the FRW spacetime and for a scale factor evolving with a composite power law-exponential (hybrid) form. To construct the energy densities of these holographic dark energy models, I assume the Hubble cutoff to be the IR limit. I find that the deceleration parameter undergoes a signature flipping at a redshift $$z$$ consistent with observations. The EoS parameter $$\omega _{de}$$ for both the HDE models exhibit quite contrasting dynamical behavior despite assuming values close to −1 at $$z=0$$ and therefore consistent with current observations. Next, I find the squared sound speed $$c_{s}^{2}$$ to be positive for the THDE model ensuring stability against perturbations, whereas for the RHDE model, $$c_{s}^{2}<0$$ implying instability against perturbations. Furthermore, I analyzed the evolutionary behavior of the EoS parameter of the HDE models by constructing the $$\omega _{de}-\omega _{de}^{\prime }$$ plane and find that the plane lies in the freezing region for the THDE model and in the thawing region for the RHDE model.
PubDate: 2020-06-18

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