Showing papers in "Astrophysics and Space Science in 2017"

Recent advances in the determination of some Galactic constants in the Milky Way

Abstract: Here we statistically evaluate recent advances in determining the Sun-Galactic Center distance ( $R_{\mathit{sun}}$ ) as well as recent measures of the orbital velocity around the Galactic Center ( $V_{\mathit{lsr}}$ ), and the angular rotation parameters of various objects. Recent statistical results point to $R_{\mathit{sun}} = 8.0 \pm 0.2~\mbox{kpc}$ , $V_{\mathit{lsr}}= 230 \pm 3~\mbox{km}/\mbox{s}$ , and angular rotation at the Sun ( $\omega$ ) near $29 \pm 1~\mbox{km}/\mbox{s}/\mbox{kpc}$ for the gas and stars at the Local Standard of Rest, and near $23 \pm 2~\mbox{km}/\mbox{s}/\mbox{kpc}$ for the spiral pattern itself. This angular difference is similar to what had been predicted by density wave models, along with the observation that the galactic longitude of each spiral arm tracer (dust, cold CO) for each spiral arm becomes reversed across the Galactic Meridian (Vallee in Astrophys. J. 821:53, 2016b).

Revealing the basins of convergence in the planar equilateral restricted four-body problem

Abstract: The planar equilateral restricted four-body problem where two of the primaries have equal masses is used in order to determine the Newton-Raphson basins of convergence associated with the equilibrium points. The parametric variation of the position of the libration points is monitored when the value of the mass parameter $m_{3}$ varies 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 iterative scheme. The correlations between the attracting domains of the equilibrium points and the corresponding number of iterations needed for obtaining the desired accuracy are also illustrated. We perform a thorough and systematic numerical investigation by demonstrating how the dynamical parameter $m_{3}$ influences the shape, the geometry and the degree of fractality of the converging regions. Our numerical outcomes strongly indicate that the mass parameter is indeed one of the most influential factors in this dynamical system.

Optical spectroscopic observations of gamma-ray blazar candidates. VII. Follow-up campaign in the southern hemisphere

Abstract: Searching for low energy counterparts of $\gamma $ -rays sources is one of the major challenges in modern $\gamma $ -ray astronomy. In the third Fermi source catalog about 30% of detected sources are unidentified/unassociated Gamma-ray Sources (UGSs). We recently started an optical spectroscopic follow up campaign to confirm the blazar-like nature of candidates counterparts of UGSs. Here we report the spectra of 61 targets collected with the Southern Astrophysical Research Telescope (SOAR) between 2014 and the 2017. Our sample includes 33 potential counterparts of UGSs, selected on the basis of WISE colors, and 27 blazar candidates of uncertain type associated with gamma-ray sources of the last release of the Fermi catalog. We confirm the BZB nature of 20 sources lying within the positional uncertainty region of the UGSs. All the observed BCUs show blazar-like spectra, classified as 2 BZQs and 25 BZBs, for which we obtained 6 redshift estimates. Within the BCUs observations we report the redshift estimate for the BZB associated with, 3FGL J1106.4-3643 that is the second most distant BL Lac known to date, at $z \geq 1.084$ .

On the restricted four-body problem with the effect of small perturbations in the Coriolis and centrifugal forces

Abstract: We have studied the restricted four-body problem (R4BP) with the effect of the small perturbation in the Coriolis and centrifugal forces on the libration points and zero velocity curves (ZVCs). Further, we have supposed that all the primaries are set in an equilateral triangle configuration, moving in the circular orbits around their common centre of mass. We have observed that the effect of the small perturbation in centrifugal force has a substantial effect on the location of libration points but a small perturbation in the Coriolis force has no impact on the location of libration points. But the stability of the libration points is highly influenced by the effect of the small perturbation in the Coriolis force. It is observed that as the Coriolis parameter increases, the libration points become stable. Further, it is found that the effect of the small perturbation in the centrifugal force has a substantial influence on the regions of possible motion. Also, when the effect of small perturbation in the centrifugal force increases the forbidden region decreases; here the motion is not possible for the infinitesimal mass. It is observed when the value of the Jacobian constant decreases, the regions of possible motion increase. In addition, we have also discussed how small perturbations in the Coriolis and centrifugal forces influence the Newton–Raphson basins of convergence.

Fractal basins of attraction in the restricted four-body problem when the primaries are triaxial rigid bodies

Abstract: The planar equilateral restricted four-body problem, formulated on the basis of Lagrange’s triangular solutions is used to determine the existence and locations of libration points and the Newton-Raphson basins of convergence associated with these libration points. We have supposed that all the three primaries situated on the vertices of an equilateral triangle are triaxial rigid bodies. This paper also deals with the effect of these triaxiality parameters on the regions of motion where the test particle is free to move. Further, the regions on the configuration plane filled by the basins of attraction are determined by using the multivariate version of the Newton-Raphson iterative system. The numerical study reveals that the triaxiality of the primaries is one of the most influential parameters in the four-body problem.

Basins of convergence of equilibrium points in the pseudo-Newtonian planar circular restricted three-body problem

Abstract: The Newton-Raphson basins of attraction, associated with the libration points (attractors), are revealed in the pseudo-Newtonian planar circular restricted three-body problem, where the primaries have equal masses. The parametric variation of the position as well as of the stability of the equilibrium points is determined, when the value of the transition parameter $\epsilon $ varies in the interval $[0,1]$ . The multivariate Newton-Raphson iterative scheme is used to determine the attracting domains on several types of two-dimensional planes. A systematic and thorough numerical investigation is performed in order to demonstrate the influence of the transition parameter on the geometry of the basins of convergence. The correlations between the basins of attraction and the corresponding required number of iterations are also illustrated and discussed. Our numerical analysis strongly indicates that the evolution of the attracting regions in this dynamical system is an extremely complicated yet very interesting issue.

An early prediction of 25th solar cycle using Hurst exponent

Abstract: The analysis of long memory processes in solar activity, space weather and other geophysical phenomena has been a major issue even after the availability of enough data. We have examined the data of various solar parameters like sunspot numbers, 10.7 cm radio flux, solar magnetic field, proton flux and Alfven Mach number observed for the year 1976–2016. We have done the statistical test for persistence of solar activity based on the value of Hurst exponent ( $H$ ) which is one of the most classical applied methods known as rescaled range analysis. We have discussed the efficiency of this methodology as well as prediction content for next solar cycle based on long term memory. In the present study, Hurst exponent analysis has been used to investigate the persistence of above mentioned (five) solar activity parameters and a simplex projection analysis has been used to predict the ascension time and the maximum number of counts for 25th solar cycle. For available dataset of the year 1976–2016, we have calculated $H = 0.86$ and 0.82 for sunspot number and 10.7 cm radio flux respectively. Further we have calculated maximum number of counts for sunspot numbers and F10.7 cm index as $102.8\pm 24.6$ and $137.25\pm 8.9$ respectively. Using the simplex projection analysis, we have forecasted that the solar cycle 25th would start in the year 2021 (January) and would last up to the year 2031 (September) with its maxima in June 2024.

New agegraphic dark energy model in Brans-Dicke theory with logarithmic form of scalar field

Abstract: In this paper, the cosmological evolution of new agegraphic dark energy (NADE) model is analyzed in Brans-Dicke theory within the framework of Friedmann-Robertson-Walker Universe. The power-law assumption on Brans-Dicke scalar field is reconsidered by assuming the logarithmic form. We derive the equation of state parameter \(w_{D}\) and deceleration parameter \(q\) of NADE model. It is observed that \(w_{D}\rightarrow -1\) when \(a\rightarrow \infty \), i.e., the NADE mimics cosmological constant in the late time evolution. Indeed, due to the assumption of logarithmic form of Brans-Dicke scalar field the NADE in Brans-Dicke theory behaves like NADE in general relativity in the late time evolution. The NADE model shows a phase transition from matter dominated phase in early time to accelerated phase in late time. We further extend NADE model by including the interaction between dark matter and NADE. In this case, \(w_{D}\) definitely crosses the phantom divide line (\(w_{D}=-1\)) in the late time evolution. The phase transition from matter dominated to NADE dominated phase may be achieved at early stage in interacting model. Further, we show that the interacting NADE model resolves the cosmic coincidence problem as the energy density ratio may evolve sufficiently slow at present.

Analysis of ionospheric TEC from GNSS observables over the Turkish region and predictability of IRI and SPIM models

Abstract: The present study investigates the ionospheric Total Electron Content (TEC) variations in the lower mid-latitude Turkish region from the Turkish Permanent GNSS Network (TPGN) and International GNSS Services (IGS) observations during the period from January 2015 to December 2015. The corresponding TEC predicted by the International Reference Ionosphere (IRI 2012) and Standard Plasmasphere-Ionosphere Model (SPIM), and interpolated from Global Ionosphere Maps (GIMs) are evaluated to realize their reliability over the region. We studied the diurnal and monthly behavior of TEC and the relative TEC deviations along with the upper and lower quartiles to represent its spatio-temporal variability. The diurnal variation of GNSS-derived TEC indicates its maximum peak value around 10.00 UT which decreases gradually to attain minimum value after midnight. The monthly maximum value of TEC is observed in March followed by May and August, and the lowest value is seen during September. Studies show that the monthly relative deviation of TEC variability lies in the range of −1 to 4 units for all stations with the maximum difference between positive and negative variability remaining around 5. The studies also cover seasonal variation, grand-mean of ionospheric TEC and TEC intensity from the TPGN. The seasonal ionospheric VTEC pattern over all stations depicts slight increment in VTEC distribution during March equinox compared to September equinox. The December solstice perceived relatively higher VTEC than June solstice. The overall of VTEC values enhanced at all stations towards end of the year 2015 compare to mid of year due the high solar activity. The maximum grand-mean of VTEC is registered in March equinox while the lowest value is seen in September irrespective of all stations. The measured grand-mean intensity variations of VTEC values are in ascending phase during March, May, August and November months, but in descending phase during February, April, June and September months. The latitudinal study shows daytime TEC slowly decreasing with latitudes with a latitudinal gradient range of 0.1–0.2 TECU/degree. Additionally, the TEC analysis during the strong geomagnetic storm period (07–11 September 2015; SYM-H −120 nT) infers relatively better predictability of the SPIM model compared to the IRI 2012 model. The outputs of this study would complement towards a complete understanding of the lower mid-latitude ionospheric dynamics and its effects on radio propagations, particularly over the Turkish region.

Existence of relativistic structures in f ( R , T ) $f(R,T)$ gravity

Abstract: In this paper, we study the impact of three different $f(R,T)$ models in the modeling of anisotropic relativistic stellar structures, where $R$ is the Ricci scalar and $T$ is the trace of the energy-momentum tensor. For this purpose, we assume static geometry of spherically symmetric self-gravitating object and after choosing appropriate vacuum solution, we evaluated some constraints for the smooth matching of exterior and interior geometries at the boundary surface. We considered observational values of three well-known stellar structures and checked the viability of energy conditions in the presence of quadratic, exponential and cubic $f(R,T)$ models. The distributions of energy density, behavior of anisotropic pressure, role of fundamental gravitational forces as well as stability investigation have been performed through plots in the realistic modeling of compact stars. We infer that modified gravitational theories could be treated as viable tool to study the existence of compact stellar structures at both theoretical and cosmological scales.

Ionospheric TEC from the Turkish Permanent GNSS Network (TPGN) and comparison with ARMA and IRI models

Abstract: The present study investigates the ionospheric Total Electron Content (TEC) variations in the lower mid-latitude Turkish region from the Turkish Permanent GNSS Network (TPGN) and International GNSS Services (IGS) observations during the year 2016. The corresponding vertical TEC (VTEC) predicted by Auto Regressive Moving Average (ARMA) and International Reference Ionosphere 2016 (IRI-2016) models are evaluated to realize their effectiveness over the region. The spatial, diurnal and seasonal behavior of VTEC and the relative VTEC variations are modeled with Ordinary Least Square Estimator (OLSE). The spatial behavior of modeled result during March equinox and June solstice indicates an inverse relationship of VTEC with the longitude across the region. On the other hand, the VTEC variation during September equinox and December solstice including March equinox and June solstice are decreasing with increase in latitude. The GNSS observed and modeled diurnal variation of the VTEC show that the VTEC slowly increases with dawn, attains a broader duration of peak around 09.00 to 12.00 UT, and thereafter decreases gradually reaching minimum around 21.00 UT. The seasonal variation of VTEC shows an annual mode, maxima in equinox and minima in solstice. The average value of VTEC during the June solstice is with slightly higher value than the March equinox though variations during the latter season is more. Moreover, the study shows minimum average value during December solstice compared to June solstice at all stations. The comparative analysis demonstrates the prediction errors by OLSE, ARMA and IRI remaining between 0.23 to 1.17%, 2.40 to 4.03% and 24.82 to 25.79% respectively. Also, the observed VTEC seasonal variation has good agreement with OLSE and ARMA models whereas IRI-VTEC often underestimated the observed value at each location. Hence, the deviations of IRI estimated VTEC compared to ARMA and OLSE models claim further improvements in IRI model over the Turkish region. Although IRI estimations are well accepted over the mid-latitudes but the performance over the lower mid-latitudes is not satisfactory and needs further improvement. The long-term TEC data from the TPGN network can be incorporated in the IRI under laying database with appropriate calibration for further improvement of estimation accuracy over the region.

Classification of gamma-ray burst durations using robust model-comparison techniques

Abstract: Gamma-Ray Bursts (GRBs) have been conventionally bifurcated into two distinct categories dubbed “short” and “long”, depending on whether their durations are less than or greater than two seconds respectively. However, many authors have pointed to the existence of a third class of GRBs with mean durations intermediate between the short and long GRBs. Here, we apply multiple model comparison techniques to verify these claims. For each category, we obtain the best-fit parameters by maximizing a likelihood function based on a weighted superposition of two (or three) lognormal distributions. We then do model-comparison between each of these hypotheses by comparing the chi-square probabilities, Akaike Information Criterion (AIC), and Bayesian Information Criterion (BIC). We uniformly apply these techniques to GRBs from Swift (both observer and intrinsic frame), BATSE, BeppoSAX, and Fermi-GBM. We find that the Swift GRB distributions (in the observer frame) for the entire dataset favor three categories at about $2.4\sigma$ from difference in chi-squares, and show decisive evidence in favor of three components using both AIC and BIC. However, when the same analysis is done for the subset of Swift GRBs with measured redshifts, two components are favored with marginal significance. For all the other datasets, evidence for three components is either very marginal or disfavored.

Homotopy method for optimization of variable-specific-impulse low-thrust trajectories

Abstract: The homotopy method has been used as a useful tool in solving fuel-optimal trajectories with constant-specific-impulse low thrust. However, the specific impulse is often variable for many practical solar electric power-limited thrusters. This paper investigates the application of the homotopy method for optimization of variable-specific-impulse low-thrust trajectories. Difficulties arise when the two commonly-used homotopy functions are employed for trajectory optimization. The optimal power throttle level and the optimal specific impulse are coupled with the commonly-used quadratic and logarithmic homotopy functions. To overcome these difficulties, a modified logarithmic homotopy function is proposed to serve as a gateway for trajectory optimization, leading to decoupled expressions of both the optimal power throttle level and the optimal specific impulse. The homotopy method based on this homotopy function is proposed. Numerical simulations validate the feasibility and high efficiency of the proposed method.

Shaping the solar wind temperature anisotropy by the interplay of electron and proton instabilities

Abstract: A variety of nonthermal characteristics like kinetic, e.g., temperature, anisotropies and suprathermal populations (enhancing the high energy tails of the velocity distributions) are revealed by the in-situ observations in the solar wind indicating quasistationary states of plasma particles out of thermal equilibrium. Large deviations from isotropy generate kinetic instabilities and growing fluctuating fields which should be more efficient than collisions in limiting the anisotropy (below the instability threshold) and explain the anisotropy limits reported by the observations. The present paper aims to decode the principal instabilities driven by the temperature anisotropy of electrons and protons in the solar wind, and contrast the instability thresholds with the bounds observed at 1 AU for the temperature anisotropy. The instabilities are characterized using linear kinetic theory to identify the appropriate (fastest) instability in the relaxation of temperature anisotropies $A_{e,p} = T_{e,p,\perp}/ T _{e,p,\parallel} e1$ . The analysis focuses on the electromagnetic instabilities driven by the anisotropic protons ( $A_{p} \lessgtr1$ ) and invokes for the first time a dynamical model to capture the interplay with the anisotropic electrons by correlating the effects of these two species of plasma particles, dominant in the solar wind.

Shock waves in dusty plasma with two temperature superthermal ions

Abstract: An investigation of dust acoustic shock waves in dusty plasma containing two temperature ions is presented. The present investigation is motivated by the observations of Geotail spacecraft that report the occurrence of two temperature ion populations in Earth’s magnetotail. We have derived Burgers equation to study dust acoustic shock structures in an unmagnetized plasma with two temperature superthermal ions. We have also derived the modified Burgers equation at critical values of physical parameters for which nonlinear coefficient ( $A$ ) of Burgers equation vanishes. The numerical analysis is performed in context with observations in Earth’s magnetotail and the influence of various plasma parameters viz. ions temperature ratio, superthermality of hot and cold ions, kinematic viscosity etc. has been observed on characteristics of DA shocks. It is observed that the amplitude of positive shocks via Burgers equation decreases whereas that of modified shocks with higher order nonlinearity increases with increase in superthermality of cold ions.

Comparing the fractal basins of attraction in the Hill problem with oblateness and radiation

Abstract: The basins of convergence, associated with the roots (attractors) of a complex equation, are revealed in the Hill problem with oblateness and radiation, using a large variety of numerical methods. Three cases are investigated, regarding the values of the oblateness and radiation. In all cases, a systematic and thorough scan of the complex plane is performed in order to determine the basins of attraction of the several iterative schemes. The correlations between the attracting domains and the corresponding required number of iterations are also illustrated and discussed. Our numerical analysis strongly suggests that the basins of convergence, with the highly fractal basin boundaries, produce extraordinary and beautiful formations on the complex plane.

Anisotropic extension of Finch and Skea stellar model

Abstract: In this paper, the spacetime geometry of Finch and Skea [Class. Quantum Gravity 6:467, 1989] has been utilized to obtain closed-form solutions for a spherically symmetric anisotropic matter distribution. By examining its physical admissibility, we have shown that the class of solutions can be used as viable models for observed pulsars. In particular, a specific class of solutions can be used as an ‘anisotropic switch’ to examine the impact of anisotropy on the gross physical properties of a stellar configuration. Accordingly, the mass–radius relationship has been analyzed.

Time varying \(G\) and \(\varLambda\) cosmology in \(f(R,T)\) gravity theory

Abstract: We have studied the time dependence of the gravitational constant $G$ and cosmological constant $\varLambda$ by taking into account an anisotropic and homogeneous Bianchi type-I space-time in the framework of the modified $f(R,T)$ theory of gravity proposed by Harko et al. (Phys. Rev. D 84:024020, 2011). For a specific choice of $f(R,T)=R+2f(T)$ where $f(T)=-\lambda T$ , two solutions of the modified gravity field equations have been generated with the help of a variation law between the expansion anisotropy ( ${\sigma}/{\theta}$ ) and the scale factor ( $S$ ), together with a general non-linear equation of state. The solution for $m eq3$ corresponds to singular model of the universe whereas the solution for $m=3$ represents a non-singular model. We infer that the models entail a constant value of the deceleration parameter. A careful analysis of all the physical parameters of the models has also been carried out.

Phase transition of charged-AdS black holes and quasinormal modes: A time domain analysis

Abstract: In this work, we investigate the time evolution of a massless scalar perturbation around small and large $\text{RN-AdS}_{4}$ black holes for the purpose of probing the thermodynamic phase transition. We show that below the critical point the scalar perturbation decays faster with increasing of the black hole size, both for small and large black hole phases. Our analysis of the time profile of quasinormal mode reveals a sharp distinction between the behaviors of both phases, providing a reliable tool to probe the black hole phase transition. However at the critical point $P=P_{c}$ , as the black hole size extends, we note that the damping time increases and the perturbation decays faster, the oscillation frequencies raise either in small and large black hole phase. In this case the time evolution approach fails to track the $\text{AdS}_{4}$ black hole phase.

Electromagnetic effects on the evolution of LTB geometry in modified gravity

Abstract: We study the influence of Palatini $f(R)$ gravity and tilted observer on the dynamics of Lemaitre–Tolman–Bondi space-time in the presence of electromagnetic field. The imperfect charged fluid seen by tilted observer is considered in comparison with charged dust fluid seen by nontilted observer. We develop the relations between tilted and nontilted variables by including electric charge in Palatini $f(R)$ gravity. In this framework, we explore the evolution of energy density inhomogeneities for tilted and nontilted observers by calculating the energy conservation laws for charged fluid. Finally, we evaluate a constraint on the electric charge in the collapse of stellar objects, which leads to the instability of nontilted congruence.

New classes of polytropic models

Abstract: The gravitational behaviour of a dense compact object is studied in isotropic coordinates. We obtain new classes of static, spherically symmetric classes of solutions to the Einstein–Maxwell field equations by assuming an anisotropic pressures and a barotropic equation of state which is polytropic. Four new classes of exact solutions are found with different polytropic indices. We can regain masses of several observed astronomical objects. A physical analysis indicates that the models are well behaved.

Indexing of exoplanets in search for potential habitability: application to Mars-like worlds

Abstract: Study of exoplanets is one of the main goals of present research in planetary sciences and astrobiology. Analysis of huge planetary data from space missions such as CoRoT and Kepler is directed ultimately at finding a planet similar to Earth—the Earth’s twin, and answering the question of potential exo-habitability. The Earth Similarity Index (ESI) is a first step in this quest, ranging from 1 (Earth) to 0 (totally dissimilar to Earth). It was defined for the four physical parameters of a planet: radius, density, escape velocity and surface temperature. The ESI is further sub-divided into interior ESI (geometrical mean of radius and density) and surface ESI (geometrical mean of escape velocity and surface temperature). The challenge here is to determine which exoplanet parameter(s) is important in finding this similarity; how exactly the individual parameters entering the interior ESI and surface ESI are contributing to the global ESI. Since the surface temperature entering surface ESI is a non-observable quantity, it is difficult to determine its value. Using the known data for the Solar System objects, we established the calibration relation between surface and equilibrium temperatures to devise an effective way to estimate the value of the surface temperature of exoplanets. ESI is a first step in determining potential exo-habitability that may not be very similar to a terrestrial life. A new approach, called Mars Similarity Index (MSI), is introduced to identify planets that may be habitable to the extreme forms of life. MSI is defined in the range between 1 (present Mars) and 0 (dissimilar to present Mars) and uses the same physical parameters as ESI. We are interested in Mars-like planets to search for planets that may host the extreme life forms, such as the ones living in extreme environments on Earth; for example, methane on Mars may be a product of the methane-specific extremophile life form metabolism.

Stability of a rhomboidal configuration with a central body

Abstract: We consider a planar system of five bodies respectively located at $\mathbf{r}_{0}$ , $\mathbf{r}_{1}$ , $\mathbf{r}_{2}$ , $\mathbf{r}_{3}$ and $\mathbf{r}_{4}$ with masses $m_{0} \geq 0$ , $m_{1}= m_{2}= m$ and $m_{3}= m_{4}= \tilde{m}$ moving on a plane. The body of mass $m_{0}$ is considered to be at the center of the configuration which is assumed to be the origin of the coordinate system. The other four bodies, called the primaries, form a rhombus configuration at all time. We assume that the mutual attraction among all the bodies is of the Newtonian type.

Gaugessence: a dark energy model with early time radiation-like equation of state

Abstract: In this work, we study a new quintessence model associated with non-Abelian gauge fields, minimally coupled to Einstein gravity. This gauge theory has been recently introduced and studied as an inflationary model, called gauge-flation. Here, however, we are interested in the late time cosmology of the model in the presence of matter and radiation to explain the present time accelerating Universe. During the radiation and matter eras, the gauge field tracks radiation and basically acts like a dark radiation sector. As we approach lower redshifts, the dark component takes the form of a dark energy source which eventually becomes the dominate part of the energy budget of the Universe. Due to the tracking feature of our model, solutions with different initial values are attracted to a common trajectory. The existence of early dark radiation is a robust prediction of our model which contributes to the effective number of relativistic species, $N_{eff}$ and has its own interesting observational features.

The Norma spiral arm: large-scale pitch angle

Abstract: In the inner Galaxy, we statistically find the mean pitch angle of the recently mapped Norma arm in two galactic quadrants (observed tangentially at galactic longitudes near $l=328^{\circ}$ and near $l=20^{\circ}$ ), using the twin-tangent method, and obtain $-13.7^{\circ}\pm 1.4^{\circ}$ . We compared with other measurements in the literature. Also, using the latest published data on pitch angle and the latest published data on the radial starting point of the four arms ( $R_{\mathrm{Gal}} = 2.2~\mbox{kpc}$ ) in each galactic quadrant, a revised velocity plot of the Norma spiral arm is made, along with other spiral arms in the Milky Way, in each Galactic quadrant.

On the conservation of the Jacobi integral in the post-Newtonian circular restricted three-body problem

Abstract: In the present paper, using the first-order approximation of the $n$ -body Lagrangian (derived on the basis of the post-Newtonian gravitational theory of Einstein, Infeld, and Hoffman), we explicitly write down the equations of motion for the planar circular restricted three-body problem in the Solar system. Additionally, with some simplified assumptions, we obtain two formulas for estimating the values of the mass-distance and velocity-speed of light ratios appropriate for a given post-Newtonian approximation. We show that the formulas derived in the present study, lead to good numerical accuracy in the conservation of the Jacobi constant and almost allow for an equivalence between the Lagrangian and Hamiltonian approaches at the same post-Newtonian order. Accordingly, the dynamics of the system is analyzed in terms of the Poincare sections method and Lyapunov exponents, finding that for specific values of the Jacobi constant the dynamics can be either chaotic or regular. Our results suggest that the chaoticity of the post-Newtonian system is slightly increased in comparison with its Newtonian counterpart.

Anisotropic compact star models in Karmarkar space time continuum

Abstract: In the present article, we have explored some new anisotropic compact star models by using embedded class one space time metric. We proceed our calculations by assuming a particular form of $g_{rr}$ metric potential and solved for the other metric $g_{tt}$ using Karmarkar condition. The matter density, radial pressure, tangential pressure, mass function, surface red-shift, anisotropy are all well behaved inside the fluid sphere. The solution satisfies all energy conditions i.e. strong energy condition, null energy condition, dominant energy condition and weak energy condition. The solution also satisfies the causality condition and can represent stable stellar fluid system as the adiabatic index $\varGamma > 4/3$ and the stability factor $-1\leq v_{t}^{2}-v_{r}^{2}\leq 0$ holds good inside the fluid sphere. We have framed our solution for two compact stars PSR J1614-2230 and SAX J1808.4-3658, which are well-behaved in all respects. The mass and radius of the compact stars PSR J1614-2230 and SAXJ1808.4-3658, obtained from the models are very close to the observational data proposed by Gangopadhyay et al. (Mon. Not. R. Astron. Soc. 431:3216, 2013) and Bhattacharya (2001) respectively.

Colour asymmetry between galaxies with clockwise and counterclockwise handedness

Abstract: Recent studies have shown that SDSS galaxies with clockwise patterns are photometrically different from galaxies with anti-clockwise patterns. The purpose of this study is to identify possible differences between the colour of galaxies with clockwise handedness and the colour of galaxies with anti-clockwise handedness. A dataset of 162,514 SDSS galaxies was separated into clockwise and counterclockwise galaxies, and the colours of spiral galaxies with clockwise handedness were compared to the colour of spiral galaxies with anti-clockwise handedness. The results show that the i-r colour in clockwise galaxies in SDSS is significantly higher compared to anti-clockwise SDSS galaxies. The colour difference is strongest between the right ascension of 30° and 60°, while the RA range of 180° to 210° shows a much smaller difference. Similarly, comparing other photometric measurements in clockwise and anti-clockwise galaxies exhibit statistically significant difference, showing the SDSS pipeline is sensitive to the handedness of the galaxy.

Morphology of equatorial plasma bubbles during low and high solar activity years over Indian sector

Abstract: In the present study, slant total electron content (STEC) data computed from ground based GPS measurements over Hyderabad (Geog. Lat. 17.41° N, geog. long. 78.55° E, mag. lat. 08.81° N) and two close stations at Bangalore (Geog. Lat. 13.02°/13.03° N, geog. long. 77.57°/77.51° E, mag. lat. 04.53°/04.55° N) in Indian region during 2007–2012, have been used to study the occurrences and characteristics of equatorial plasma bubbles (EPBs). The analysis found maximum EPB occurrences during the equinoctial months and minimum during the December solstice throughout 2007–2012 except during the solar minimum years in 2007–2009. During 2007–2009, the maximum EPB occurrences were observed in June solstice which could not be predicted by the model proposed by Tsunoda (J. Geophys. Res., 90:447–456, 1985). The equinox maximum in EPB occurrences for high solar activity years could be caused by the vertical F-layer drift due to pre-reversal electric field (PRE), and expected to be maximum when day-night terminator aligns with the magnetic meridian i.e. during the equinox months whereas maximum occurrences during the solstice months of solar minimum could be caused by the seed perturbation in plasma density induced by gravity waves from tropospheric origins. Generally EPB occurrences are found to be more prominent during nighttime hours (2000–2400 hours) than the daytime hours. Peak in EPB occurrences is in early night for high solar activity years whereas same is late night for low solar activity. The day and nighttime EPB occurrences have been analyzed and found to vary in accordance with solar activity with an annual correlation coefficient ( $R$ ) of ∼0.99 with $\mathrm{F}_{10.7}~\mbox{cm}$ solar Flux. Additionally, solar activity influence on EPB occurrences is seasonal dependent with a maximum influence during the equinox season ( $R=0.88$ ) and a minimum during winter season ( $R =0.73$ ). The solar activity influences on EPB occurrences are found in agreement with the previous works reported in the Brazilian, African-Asian and Pacific longitudes sector but different than that in Atlantic sector.

Equilibrium points and zero velocity surfaces in the axisymmetric restricted five-body problem

Abstract: In this paper, we have analyzed the motion of an infinitesimal mass in axisymmetric restricted five-body problem. The four primaries are supposed to be in axisymmetric central configurations based on Erdi and Czirjak and the motion is governed by mutual gravity only. We have derived the equations of motion of the infinitesimal mass firstly and then found the number and locations of equilibrium points numerically for various angle coordinates. In addition, the zero velocity surfaces (ZVS) are drawn and regions of motion are analyzed for specific configurations. Finally the linear stability of equilibrium points are discussed preliminarily.