Showing papers in "Astrophysics and Space Science in 2016"

Chemical abundances in high-redshift galaxies: a powerful new emission line diagnostic

Abstract: This Letter presents a new, remarkably simple diagnostic specifically designed to derive chemical abundances for high redshift galaxies. It uses only the $\mathrm{H}\alpha$ , [N ii] and [S ii] emission lines, which can usually be observed in a single grating setting, and is almost linear up to an abundance of $12+\log (\mathrm{O}/\mathrm{H}) = 9.05$ . It can be used over the full abundance range encountered in high redshift galaxies. By its use of emission lines located close together in wavelength, it is also independent of reddening. Our diagnostic depends critically on the calibration of the N/O ratio. However, by using realistic stellar atmospheres combined with the N/O vs. O/H abundance calibration derived locally from stars and H ii regions, and allowing for the fact that high-redshift H ii regions have both high ionisation parameters and high gas pressures, we find that the observations of high-redshift galaxies can be simply explained by the models without having to invoke arbitrary changes in N/O ratio, or the presence of unusual quantities of Wolf-Rayet stars in these galaxies.

Shadow of rotating wormhole in plasma environment

Abstract: The massless particle motion around rotating wormhole in the presence of plasma environment has been studied. It has been shown that the presence of the plasma decreases the inner radius of the circular orbits of photons around rotating wormhole. The shadow cast by rotating wormhole surrounded by inhomogeneous plasma with the radial power-law density has been explored. It has been shown that the shape and size of the wormhole shadow is distorted and changed depending on i) plasma parameters, ii) wormhole rotation and iii) inclination angle between observer plane and axis of rotation of wormhole. As an example we have considered an inverse radial distribution of the plasma density and different types of the wormhole solution.

LZIFU: an emission-line fitting toolkit for integral field spectroscopy data

Abstract: We present lzifu (LaZy-IFU), an idl toolkit for fitting multiple emission lines simultaneously in integral field spectroscopy (IFS) data. lzifu is useful for the investigation of the dynamical, physical and chemical properties of gas in galaxies. lzifu has already been applied to many world-class IFS instruments and large IFS surveys, including the Wide Field Spectrograph, the new Multi Unit Spectroscopic Explorer (MUSE), the Calar Alto Legacy Integral Field Area (CALIFA) survey, the Sydney-Australian-astronomical-observatory Multi-object Integral-field spectrograph (SAMI) Galaxy Survey. Here we describe in detail the structure of the toolkit, and how the line fluxes and flux uncertainties are determined, including the possibility of having multiple distinct kinematic components. We quantify the performance of lzifu, demonstrating its accuracy and robustness. We also show examples of applying lzifu to CALIFA and SAMI data to construct emission line and kinematic maps, and investigate complex, skewed line profiles presented in IFS data. The code is made available to the astronomy community through github. lzifu will be further developed over time to other IFS instruments, and to provide even more accurate line and uncertainty estimates.

Fractal basins of attraction in the planar circular restricted three-body problem with oblateness and radiation pressure

Abstract: In this paper we use the planar circular restricted three-body problem where one of the primary bodies is an oblate spheroid or an emitter of radiation in order to determine the basins of attraction associated with the equilibrium points. The evolution of the position of the five Lagrange points is monitored when the values of the mass ratio $\mu $ , the oblateness coefficient $A_{1}$ , and the radiation pressure factor $q$ vary in predefined intervals. The regions on the configuration $(x,y)$ plane occupied by the basins of attraction are revealed using the multivariate version of the Newton-Raphson method. The correlations between the basins of convergence of the equilibrium points and the corresponding number of iterations needed in order to obtain the desired accuracy are also illustrated. We conduct a thorough and systematic numerical investigation demonstrating how the dynamical quantities $\mu $ , $A_{1}$ , and $q$ influence the basins of attractions. Our results suggest that the mass ratio and the radiation pressure factor are the most influential parameters, while on the other hand the structure of the basins of convergence are much less affected by the oblateness coefficient.

GUP assisted Hawking radiation of rotating acoustic black holes

Abstract: Recent studies (Steinhauer in Nat. Phys. 10:864, 2014, Phys. Rev. D 92:024043, 2015) provide compelling evidences that Hawking radiation could be experimentally proven by using an analogue black hole. In this paper, taking this situation into account we study the quantum gravitational effects on the Hawking radiation of rotating acoustic black holes. For this purpose, we consider the generalized uncertainty principle (GUP) in the phenomenon of quantum tunneling. We firstly take the modified commutation relations into account to compute the GUP modified Hawking temperature when the massive scalar particles tunnel from this black hole. Then, we find a remarkably instructive expression for the GUP entropy to derive the quantum gravity corrected Hawking temperature of the rotating acoustic black hole.

Some analytical models of anisotropic strange stars

Abstract: Over the years of the concept of local isotropy has become a too stringent condition in modeling relativistic self-gravitating objects. Taking local anisotropy into consideration, in this work, some analytical models of relativistic anisotropic charged strange stars have been developed. The Einstein–Maxwell gravitational field equations have been solved with a particular form of one of the metric potentials. The radial pressure and the energy density have been assumed to follow the usual linear equation of state of strange quark matter, the MIT bag model.

Possible formation of compact stars in $f(R,T)$ gravity

Abstract: This paper reports on the investigations regarding the possible formation of compact stars in $f(R,T)$ theory of gravity, where $R$ is the Ricci scalar and $T$ is the trace of the energy–momentum tensor. In this connection, we use the analytic solution of the Krori and Barua metric (Krori and Barua in J. Phys. A., Math. Gen. 8:508, 1975) for a spherically symmetric anisotropic star in the context of $f(R,T)$ gravity. The masses and radii of compact star models, namely Model 1, Model 2, and Model 3, are employed to incorporate the unknown constants in the Krori and Barua metric. The physical features such as regularity at the center, the anisotropy measure, causality, and the well-behaved condition of the above-mentioned class of compact starts are analyzed. Moreover, we also discuss the energy conditions, stability, and surface redshift in $f(R,T)$ gravity.

A new analytic solution representing anisotropic stellar objects in embedding class I

Abstract: A new type of embedding class-I representing anisotropic fluid distribution is presented. The new solution is free from singularity and also satisfies all physical criteria. It also satisfies all energy conditions such as SEC, WEC, NEC and DEC. The solution so obtained is used to optimize mass and radius of some well compact stars candidates like, Her X-1, SAX J1808.4-3658, RX J1856.5-3754, PSR J1614-2230 and PSR J0348+0432.

Charged anisotropic Buchdahl solution as an embedding class I spacetime

Abstract: We present a new solution of embedding class I describing the interior of a spherically symmetric charged anisotropic stellar configuration. The exact analytic solution has been explored by considering Buchdahl type metric potential $g_{rr}$ . Using this analytic solution, we have discussed various physical aspects of a compact star. The solution is free from central singularities. The solution also satisfies WEC, SEC, NEC and DEC. The compactness parameter $2M/r_{b}$ as obtained from the solution satisfies the Buchdahl-Andreasson condition. Finally we have compared the calculated masses and radii of well-known compact star candidates like RX J1856.5-3754, XTE J1739-285, PSR B0943+10 and SAX J1808.4-3658 with their observational values.

Exact Teleparallel Gravity of Binary Black Holes

Abstract: An exact solution of two singularities in the teleparallel equivalent to general relativity theory has been obtained. A holographic visualization of the binary black holes (BBHs) space-time, due to the non vanishing torsion scalar field, has been given. The acceleration tensor of BBHs space-time has been calculated. The results identify the repulsive gravity zones of the BBHs field. The total conserved quantities of the BBHs has been evaluated. Possible gravitational radiation emission by the system has been calculated without assuming a weak field initial data.

Anisotropic stars with non-static conformal symmetry

Abstract: We propose a model for relativistic compact star with anisotropy and analytically obtain exact spherically symmetric solutions which describe interior of the dense star admitting non-static conformal symmetry. Several features of the solutions, including drawbacks of the model, have been explored and discussed. For this purpose we have provided the energy conditions, TOV equation and other physical requirements and thus thoroughly have investigated stability, mass-radius relation and surface redshift of the model. It is observed that most of the features are well matched with the compact strange stars.

A transition from a decelerated to an accelerated phase of the universe expansion from the simplest non-trivial polynomial function of T in the f(R,T) formalism

Abstract: In this work we present cosmological solutions from the simplest non-trivial polynomial function of \(T\) in \(f(R,T)\) theory of gravity, with \(R\) and \(T\) standing for the Ricci scalar and trace of the energy-momentum tensor, respectively. Although such an approach yields a highly non-linear differential equation for the scale factor, we show that it is possible to obtain analytical solutions for the cosmological parameters. For some values of the free parameters, the model is able to predict a transition from a decelerated to an accelerated expansion of the universe and the values of the deceleration parameter agree with observation.

The gamma-ray blazar quest: new optical spectra, state of art and future perspectives

Abstract: We recently developed a procedure to recognize \(\gamma\)-ray blazar candidates within the positional uncertainty regions of the unidentified/unassociated \(\gamma\)-ray sources (UGSs). Such procedure was based on the discovery that Fermi blazars show peculiar infrared colors. However, to confirm the real nature of the selected candidates, optical spectroscopic data are necessary. Thus, we performed an extensive archival search for spectra available in the literature in parallel with an optical spectroscopic campaign aimed to reveal and confirm the nature of the selected \(\gamma\)-ray blazar candidates. Here, we first search for optical spectra of a selected sample of \(\gamma\)-ray blazar candidates that can be potential counterparts of UGSs using the Sloan Digital Sky Survey (SDSS DR12). This search enables us to update the archival search carried out to date. We also describe the state-of-art and the future perspectives of our campaign to discover previously unknown \(\gamma\)-ray blazars.

Solutions of the Einstein’s field equations with anisotropic pressure compatible with cold star model

Abstract: In this paper we obtain a new static and spherically symmetric model of compact star whose spacetime satisfies Karmarkar’s condition (1948). The Einstein’s field equations are solved by employing a physically reasonable choice of the metric coefficient $g_{rr}$ so that the obtained solution is free from central singularities. Our model satisfies all the energy conditions as well as the causality condition. By assigning some particular values mass and radius of the compact stars PSR J0347+0432, Cen X-3 and Vela X-1 have been obtained which are very close to the observational data proposed by Antoniadis et al. (Science 340:1233232, 2013), Abubekerov et al. (Astron. Rep. 48:89, 2004) and Ash et al. (Mon. Not. R. Astron. Soc. 307:357, 1999). For the neutron star candidate PSR J0348+0432, we expect a very stiff equation of state to support its massive mass which corresponds to a large value of the adiabatic index of 6.66 at the center.

Influence of the electric induction drag on the orbit of a charged satellite moving in the ionosphere (solution by the method of the average value)

Abstract: The secular effects of the electric induction drag on the orbit of a charged satellite moving in the ionosphere are examined by the method of average values. The first solutions are obtained under the assumption of non-rotation of the Earth; the second solutions are obtained assuming rotation of the Earth. In the first case the semi-major axis exhibits secular variation, but the other orbital elements exhibit no secular variation. In the second case both semi-major axis and eccentricity exhibit secular variation, but the other orbital elements exhibit no secular variation. It can be shown that the semi-major axis is contracted due to the action of the electric induction drag if the satellite has enough charge in the ionosphere. The eccentricity is decreased gradually with time, but its variation is very small for the case of a rotating Earth. An example is presented in which the secular effects of the electric induction drag on the orbits of a charged satellite are calculated. The numerical results are given in Table 1 and a discussion of them is presented in Table 2.

Generalized second law of thermodynamics in f (R, T) theory of gravity

Abstract: We present a study of the generalized second law of thermodynamics in the scope of the \(f(R,T)\) theory of gravity, with \(R\) and \(T\) representing the Ricci scalar and trace of the energy-momentum tensor, respectively. From the energy-momentum tensor equation for the \(f(R,T)=R+f(T)\) case, we calculate the form of the geometric entropy in such a theory. Then, the generalized second law of thermodynamics is quantified and some relations for its obedience in \(f(R,T)\) gravity are presented. Those relations depend on some cosmological quantities, as the Hubble and deceleration parameters, and also on the form of \(f(T)\).

The Cusp/Core problem: supernovae feedback versus the baryonic clumps and dynamical friction model

Abstract: In the present paper, we compare the predictions of two well known mechanisms considered able to solve the cusp/core problem (a. supernova feedback; b. baryonic clumps-DM interaction) by comparing their theoretical predictions to recent observations of the inner slopes of galaxies with masses ranging from dSphs to normal spirals. We compare the $\alpha$ - $V_{\mathrm{rot}}$ and the $\alpha$ - $M_{\ast}$ relationships, predicted by the two models with high resolution data coming from Adams et al. (Astrophys. J. 789, 63, 2014), Simon et al. (Astrophys. J. 621, 757, 2005), LITTLE THINGS (Oh et al. in Astron. J. 149, 180, 2015), THINGS dwarves (Oh et al. in Astron. J. 141, 193, 2011a; Oh et al. in Astron. J. 142, 224, 2011b), THINGS spirals (Oh et al. in Astron. J. 149, 180, 2015), Sculptor, Fornax and the Milky Way. The comparison of the theoretical predictions with the complete set of data shows that the two models perform similarly, while when we restrict the analysis to a smaller subsample of higher quality, we show that the method presented in this paper (baryonic clumps-DM interaction) performs better than the one based on supernova feedback. We also show that, contrarily to the first model prediction, dSphs of small mass could have cored profiles. This means that observations of cored inner profiles in dSphs having a stellar mass $<10^{6}~M_{\odot}$ not necessarily imply problems for the $\varLambda$ CDM model.

New local interstellar spectra for protons, helium and carbon derived from PAMELA and Voyager 1 observations

Abstract: With the cosmic ray observations made by the Voyager 1 spacecraft outside the dominant modulating influence of the heliosphere, the comparison of computed galactic spectra with experimental data at lower energies is finally possible. Spectra for specifically protons, helium and carbon nuclei, computed by galactic propagation models, can now be compared with observations at low energies from Voyager 1 and at high energies from the PAMELA space detector at Earth. We set out to reproduce the Voyager 1 observations in the energy range of 6 MeV/nuc to 60 MeV/nuc, and the PAMELA spectrum above 50 GeV/nuc, using the GALPROP code, similarly to our previous study for Voyager 1 electrons. By varying the galactic diffusion parameters in the GALPROP plain diffusion model, specifically the rigidity dependence of spatial diffusion, and then including reacceleration, we compute spectra simultaneously for galactic protons, helium and carbon. We present new local interstellar spectra, with expressions for the energy range of 3 MeV/nuc to 100 GeV/nuc, which should be of value for solar modulation modeling.

Some interior models of compact stars in $f(R)$ gravity

Abstract: This paper deals with the interior models of compact stars in the framework of modified $f(R)$ theory of gravity, which is the generalization of the Einstein’s gravity. In order to complete the study, we have involved solution of Krori and Barua to the static spacetime with fluid source in modified $f(R)$ theory of gravity. Further, we have matched the interior solution with the exterior solution to determine the constants of Krori and Barua solution. Finally, the constants have been formulated by using the observational data of various compact stars like 4U1820-30, Her X-1, SAX J1808-3658. Using the evaluated form of the solutions, we have discussed the regularity of matter components at the center as well as on the boundary, energy conditions, anisotropy, stability analysis and mass-radius relation of the compact stars 4U1820-30, Her X-1, SAX J1808-3658.

Gravitational lensing by Reissner-Nordström black holes with topological defects

Abstract: Using a new geometrical approach introduced by Gibbons and Werner we study the deflection angle by Reissner-Nordstrom black holes in the background spacetimes with a global monopole and a cosmic string. By calculating the corresponding optical Gaussian curvature and applying the Gauss-Bonnet theorem to the optical metric we find the leading terms of the deflection angle in the weak limit approximation. We find that the deflection angle increases due to the presence of topological defects.

Exploring stable models in $f(R,T, R_{\mu\nu}T^{\mu\nu})$ gravity

Abstract: We examine in this paper the stability analysis in $f(R,T, R_{\mu u }T^{\mu u})$ modified gravity, where $R$ and $T$ are the Ricci scalar and the trace of the energy-momentum tensor, respectively. By considering the flat Friedmann universe, we obtain the corresponding generalized Friedmann equations and we evaluate the geometrical and matter perturbation functions. The stability is developed using the de Sitter and power-law solutions. We search for application the stability of two particular cases of $f(R,T, R_{\mu u}T^{\mu u})$ model by solving numerically the perturbation functions obtained.

Some Bianchi type generalized ghost piligrim dark energy models in general relativity

Abstract: In this paper, we consider Bianchi type- $\mathit{III}$ , $V$ and $\mathit{VI}_{0}$ space-times filled with generalized ghost pilgrim dark energy (GGPDE) in general relativity. Here we assume the anisotropic distribution of GGPDE by introducing skewness parameters. To get deterministic solutions, we consider the scale factor $a(t)=(t^{n}e^{t})^{ \frac{1}{k}}$ , so called hybrid expansion, which yields a time dependent deceleration parameter, and exhibits a transition of the Universe from early decelerated phase to the recent accelerating phase. To describe the behavior of the obtained models we construct equation of state ( $\omega_{\varLambda }$ ), squared sound speed ( $v_{s}^{2}$ ) parameters and $\omega_{\varLambda }$ – $\dot{\omega }_{\varLambda }$ , $r$ – $s$ planes. It is worth mentioning here that the analysis of evolution parameters supports the concept of pilgrim dark energy (PDE). Also, these models remain stable for PDE parameter $\beta =-0.5$ . Moreover, the cosmological planes correspond to $\varLambda \mathit{CDM}$ limit as well as different well-known dark energy models.

Magnetized particle motion around non-Schwarzschild black hole immersed in an external uniform magnetic field

Abstract: The motion of a magnetized particle orbiting around non-Schwarzschild black hole immersed in an external uniform magnetic field is considered. The influence of deformation parameter $h$ to effective potential of the radial motion of the magnetized particle around non-Schwarzschild black hole using Hamilton-Jacobi formalism is studied. We have obtained numerical values of area $\Delta \rho $ where magnetized particles can move which is expanding (narrowing) due to the effect of the negative (positive) deformation. Finally, we have studied the collision of two particles (magnetized-neutral, magnetized-magnetized, magnetized-charged) in non-Schwarzschild spacetime and got the center-of-mass energy $(E_{c.m})$ for the particles. Moreover, we have found the capture radius ( $r_{cap}$ ) – the distance from the central object to the point where particles collide and fall down to the central compact object. It is shown that non-Schwarzschild black holes could also act as particle accelerators with arbitrarily high center-of-mass energy.

Gravitational lensing by a non-Schwarzschild black hole in a plasma

Abstract: We study gravitational lensing in the vicinity of a massive object described by non-Schwarzschild geometry surrounded by a homogeneous plasma. The expression for the deflection angle in a non-Schwarzschild space-time in the weak field regime in the presence of plasma have been derived. It has been shown that the obtained deflection angle depends on (i) the frequency of the electromagnetic wave, due to the dispersion properties of the plasma; (ii) the gravitational mass $M$ ; and (iii) deformation parameter $\epsilon$ of the gravitational lens. Moreover, the influence of deformation parameter of the gravitational lens and plasma frequency on the magnification of brightness of the source star has been studied in the case of microlensing.

Unimodular Mimetic $F(R)$ Inflation

Abstract: We propose the unimodular-mimetic $F(R)$ gravity theory, to resolve cosmological constant problem and dark matter problem in a unified geometric manner. We demonstrate that such a theory naturally admits accelerating universe evolution. Furthermore, we construct unimodular-mimetic $F(R)$ inflationary cosmological scenarios compatible with the Planck and BICEP2/Keck-Array observational data. We also address the graceful exit issue, which is guaranteed by the existence of unstable de Sitter vacua.

The planar restricted three-body problem when both primaries are triaxial rigid bodies: Equilibrium points and periodic orbits

Abstract: The restricted three-body problem when the primaries are triaxial rigid bodies is considered and its basic dynamical features are studied. In particular, the equilibrium points are identified as well as their stability is determined in the special case when the Euler angles of rotational motion are accordingly $\theta_{i} = \psi_{i} = \pi/2$ and $\varphi_{i} = \pi/2$ , $i = 1, 2$ . It is found that three unstable collinear equilibrium points exist and two triangular such points which may be stable. Special attention has also been paid to the study of simple symmetric periodic orbits and 31 families consisting of such orbits have been determined. It has been found that only one of these families consists entirely of unstable members while the remaining families contain stable parts indicating that other families bifurcate from them. Finally, using the grid-search technique a global solution in the space of initial conditions is obtained which comprises simple and of higher multiplicities symmetric periodic orbits as well as escape and collision orbits.

Spectral study of GX 339-4 with TCAF using Swift and NuSTAR observation

Abstract: We fit spectra of galactic transient source GX 339-4 during its 2013 outburst using Two Component Advective Flow (TCAF) solution. For the first time, we are fitting combined NuSTAR and Swift observation with TCAF. We use TCAF to fit 0.8–9.0 keV Swift and 4–79 keV NuSTAR spectra along with the LAOR model. To fit the data we use disk accretion rate, halo accretion rate, size of the Compton cloud and the density jump of advective flows at this cloud boundary as model parameters. From TCAF fitted flow parameters, and energy spectral index we conclude that the source was in the hard state throughout this particular outburst. The present analysis also gives some idea about the broadening of Fe $K_{\alpha }$ with the accretion rate. Since TCAF does not include Fe line yet, we make use of the ‘LAOR model’ as a phenomenological model and find an estimate of the Kerr parameter to be ${\sim} 0.99$ for this candidate.

Rogue waves in electronegative space plasmas: The link between the family of the KdV equations and the nonlinear Schrödinger equation

Abstract: We examine the likelihood of the ion-acoustic rogue waves propagation in a non-Maxwellian electronegative plasma in the framework of the family of the Korteweg–de Vries (KdV) equations (KdV/modified KdV/Extended KdV equation). For this purpose, we use the reductive perturbation technique to carry out this study. It is known that the family of the KdV equations have solutions of distinct structures such as solitons, shocks, kinks, cnoidal waves, etc. However, the dynamics of the nonlinear rogue waves is governed by the nonlinear Schrodinger equation (NLSE). Thus, the family of the KdV equations is transformed to their corresponding NLSE developing a weakly nonlinear wave packets. We show the possible region for the existence of the rogue waves and define it precisely for typical parameters of space plasmas. We investigate numerically the effects of relevant physical parameters, namely, the negative ion relative concentration, the nonthermal parameter, and the mass ratio on the propagation of the rogue waves profile. The present study should be helpful in understanding the salient features of the nonlinear structures such as, ion-acoustic solitary waves, shock waves, and rogue waves in space and in laboratory plasma where two distinct groups of ions, i.e. positive and negative ions, and non-Maxwellian (nonthermal) electrons are present.

Anisotropic charged core envelope star

Abstract: We study a charged compact object with anisotropic pressures in a core envelope setting. The equation of state is quadratic in the core and linear in the envelope. There is smooth matching between the three regions: the core, envelope and the Reissner-Nordstrom exterior. We show that the presence of the electric field affects the masses, radii and compactification factors of stellar objects with values which are in agreement with previous studies. We investigate in particular the effect of electric field on the physical features of the pulsar PSR J1614-2230 in the core envelope model. The gravitational potentials and the matter variables are well behaved within the stellar object. We demonstrate that the radius of the core and the envelope can vary by changing the parameters in the speed of sound.

Relativistic compact anisotropic charged stellar models with Chaplygin equation of state

Abstract: This paper presents a new model of static spherically symmetric relativistic charged stellar objects with locally anisotropic matter distribution together with the Chaplygin equation of state. The interior spacetime has been matched continuously to the exterior Reissner–Nordstrom geometry. Different physical properties of the stellar model have been investigated, analyzed, and presented graphically.