We have studied Friedmann–Robertson–Walker (FRW) cosmological models within the presence of General Relativistic Hydrodynamics (GRH) in General Relativity. Exact solutions of the field equations are deduced by considering the special form of the average scale factor considered by Abdussattar and Prajapati (Astrophys. Space Sci. 331:657, 2011), constraining the deceleration parameter and a special form

In this study, the ionization rate in the atmosphere induced by solar and galactic cosmic rays is calculated for the region of Athens (Greece) during the time period from 1996 to 2019 covering the last two solar cycles 23 and 24. In order to compute the cosmic ray induced ionization, the corresponding model of the University of Oulu was used along with its new version which is extended to the upper

The Fokker-Planck equation describing the diffusion of energetic particles interacting with turbulence is difficult to solve analytically. Numerical solutions are of course possible but they are not useful for applications. In the past a subspace approximation was proposed which allows to compute important quantities such as the characteristic function as well as certain expectation values. This previous

There exists a number of astronomical spectral phenomena that have remained unidentified after decades of extensive observations. The diffuse interstellar bands, the 220 nm feature, unidentified infrared emission bands, extended red emissions, and 21 and 30 μm emission features are seen in a wide variety of astrophysical environments. The strengths of these features suggest that they originate from

We analysed the open clusters Czernik 2 and NGC 7654 using CCD UBV photometric and Gaia Early Data Release 3 (EDR3) photometric and astrometric data. Structural parameters of the two clusters were derived, including the physical sizes of Czernik 2 being \(r=5^{\prime}\) and NGC 7654 as \(8^{\prime}\). We calculated membership probabilities of stars based on their proper motion components as released

Uncertainties in the satellite world lines lead to dominant positioning errors. In the present work, using the approach presented in Puchades and Sáez (Astrophys. Space Sci. 352, 307–320, 2014), a new analysis of these errors is developed inside a great region surrounding Earth. This analysis is performed in the framework of the so-called Relativistic Positioning Systems (RPS). Schwarzschild metric

In light of its auroral appearances, explosive magneto-tail behavior has long been known. Several magnetospheric processes have been interpreted and understood using global magnetohydrodynamic (MHD) models. The global MHD modelling was unable to access the temporal and spatial scales of certain magnetic structure, creating a breach between observational and theoretical studies of these electromagnetic

The temporal and spatial variations of solar magnetic activity indices in the various atmospheric layers are important for understanding and revealing the dynamic processes of magnetic field of the Sun. In this paper, the midrange periodicities (located at 50-500 days) of the solar H\(\alpha \) flare index during Solar Cycles 21–24 were studied by the Lomb–Scarge periodogram technique and the Monte

In 2016–17, the Galactic transient black hole candidate GRS 1716-249 exhibited an outburst event after a long quiescence period of almost 23 years. The source remained in the outbursting phase for almost 9 months. We study the spectral and temporal properties of the source during this outburst using archival data from four astronomy satellites, namely MAXI, Swift, NuSTAR and AstroSat. Initial spectral

We study the recovery characteristics of large-amplitude cosmic-ray decreases by utilizing the ground based neutron monitor observations. We divide large-amplitude cosmic-ray transient decreases (called Forbush decreases) in the galactic cosmic-ray intensity into different groups based on their decrease time and recovery time. We apply an exponential fit to the recovery profile of Forbush decreases

We present a statistical analysis of recurrent Forbush decreases (RFDs) in Galactic cosmic ray intensity in associated with corotating solar wind streams during low solar activity conditions. Selected RFDs recorded at the ground-based neutron monitors with low to high cutoff rigidities (\(P_{c}\)) have been separately investigated for the periods 2008-2011 (\(A < 0\), 70 events) and 2015-2016 (\(A

The time evolution of the beam-plasma instability and the ensuing emission of transverse waves is studied using a set of self-consistent equations of weak turbulence theory, considering that the electron beam is along a direction with a finite pitch angle relative to the direction of the ambient magnetic field, therefore characterizing a ring-beam electron velocity distribution. The results obtained

To determine the precise positions of stars in CCD frames, various centering algorithms have been proposed for astrometry. The effective point spread function (ePSF) and the Gaussian centering algorithms are two representative centering algorithms. This paper compares in detail and investigates these two centering algorithms in performing data reduction. Specifically, synthetic star images in different

We review recent progress in elucidating the relationship between high-energy radiation and the interstellar medium (ISM) in young supernova remnants (SNRs) with ages of ∼2000 yr, focusing in particular on RX J1713.7−3946 and RCW 86. Both SNRs emit strong nonthermal X-rays and TeV \(\gamma \)-rays, and they contain clumpy distributions of interstellar gas that includes both atomic and molecular hydrogen

The Main Belt Comet 133P/Elst-Pizarro is one of the targets in China’s asteroid exploration mission. To support this goal, gravity field estimation for this celestial object was simulated and analyzed using two-way and four-way range rate observations. A circular terminator orbit was designed for the spacecraft, and the forces acting on it were modeled to estimate the related dynamic values. Various

An analytical method is developed for finding the coefficients of zonal spherical harmonics of the azimuthally averaged potential of a rotating stratified inhomogeneous triaxial ellipsoid. Two models are considered: i) an ellipsoid of discrete layers of finite thickness, including the two-component Core – Shell model; ii) an inhomogeneous ellipsoid consisting of infinitely thin equidensity layers with

In this paper we analyze the frequency shifts of the light emitted by particles describing stable circular geodesics around a static black hole immersed in an external magnetic field of arbitrary strength. This system is represented by the Ernst solution of the Einstein-Maxwell equations. The presence of the magnetic field and its magnitude affects both the geodesics and the red-blueshifts of the light

This paper aims to analyzing the characteristics of a spherically symmetric relativistic star in the context of massive Brans-Dicke gravity. The system of field equations is derived for specific forms of coupling and potential functions by employing the MIT bag model. The unknown metric tensors are evaluated through a well-behaved function along with Karmarkar condition for class-one embedding. The

The redshift (\(z\)) evolution of the Extragalactic Background Light (EBL) photon density is very important to understand the history of cosmological structure formation of galaxies and stars since the epoch of recombination. The EBL photons with the characteristic spectral energy distribution ranging from ultraviolet/optical to far-infrared provide a major source of opacity of the Universe to the

In the context of scaling relations between Supermassive Black Holes and host-galaxy properties, we aim to enhance the comparison between \(M_{\bullet } - M_{G}\sigma ^{2}\) and \(M_{\bullet } - \sigma \) relations from a statistical point of view. First, it is suggested to take into account the predictive accuracy of the scaling relation, in addition to the classical measures of goodness of fit. Here

Many exoplanets are discovered in binary star systems in internal or in circumbinary orbits. Whether the planet can be habitable or not depends on the possibility to maintain liquid water on its surface, and therefore on the luminosity of its host stars and on the dynamical properties of the planetary orbit. The trajectory of a planet in a double star system can be determined, approximating stars and

The kappa distribution has been used for decades as a numerical fitting function to represent the energetic particle distributions measured with satellite instruments. The distributions are generally either a three dimensional distribution in the particle velocity or the one dimensional distribution in a velocity component in a particular direction. The theoretical basis for the origin of the kappa

The distant retrograde orbits (DROs) can serve as the parking orbits for a long-term cis-lunar space station. This paper gives a comprehensive study on the transfer problem from DROs to Earth orbits, including low Earth orbits (LEOs), medium Earth orbits (MEOs), and geosynchronous orbits (GSOs), in the bicircular restricted four-body problem (BR4BP) via optimizations within a large solution space.

Over the last three solar cycles, the precursor method has proven to be a very reliable technique for forecasting ensuing solar cycles. In the present work, we have used the geomagnetic activity indices: \(aa\) and \(Ap\) measured during the last 4 years of the descending phase of solar activity cycles as precursors for predicting the strength of the next solar cycle 25. From the indices \(aa\) and

The present study is outcome of investigation of Bianchi type-I cosmological model in Sáez-Ballester theory of gravity with variable deceleration parameter. Here, we have also considered variable cosmological constant \(\Lambda\) which may be a probable candidate to discuss dark energy. The solution of the field equations has been found using variable deceleration parameter i.e. \(q=-1+\beta H\) (with

In this study the statistics of ionospheric total electron content (TEC), derived from a GSV4004B dual-frequency Global Positioning System (GPS) receiver at Agartala station (23.450°N, 91.150°E) located in northern equatorial ionization anomaly (EIA) crest region of the Indian subcontinent, is reported with a performance analysis of IRI-2016 and IRI-2012 models during the ascending, maxima, declining

In this work, we present a method for absolute measurement of air fluorescence yield based on high resolution optical emission spectroscopy. The absolute measurement of the air fluorescence yield is feasible using the Cherenkov light, emitted by an electron beam simultaneously with the fluorescence light, as a “standard candle”. The separation of these two radiations can be accomplished exploiting

We are considering the spacetime described by the metric proposed by Mannheim and Kazanas. The effective potential and the circular orbits are discussed. The rotational velocity derived from the geodesics equation agrees with the observed flat galactic rotation curves. Finally, solutions to the Gordon equation for massless bosons evolving in this spacetime are obtained in terms of Heun general functions

In this paper Robe-finite straight segment model is analyzed under the effects of viscosity and perturbations in the Coriolis and centrifugal forces. We have taken the first primary \(P_{1}\) as a rigid spherical shell \(m_{1}\) filled with viscous, homogeneous incompressible fluid of density \(\rho _{1}\), and the second primary \(P_{2}\) as a finite straight segment of length \(2l\). A third body

The comparative analysis of measured and modelled Vertical Total Electron Content (VTEC) in low, mid and high latitude assists in the correction of Global Positioning System (GPS) measurements. In this study, we compare VTEC from GPS and International Reference Ionosphere (IRI) models (2007, 2012 and 2016) over mid latitude Sukkur (Lat \(27.7^{\circ}~\text{N}\), Long \(68.8^{\circ}~\text{E}\)) region

It is shown that the solar wind interaction with dusty plasma in planetary magnetospheres gives rise to electrostatic instabilities and solitary structures. Non-Maxwellian electrons increase the growth rate of shear flow instability and reduce the amplitude of solitary pulses formed by the modified dust ion acoustic wave (mDIAW) in nonlinear regime. Dust number density plays the similar role. The kappa

In this paper, we use the distributions of two-component radio emissions to investigate the consequences of relativistic beaming on the unified scheme of blazar populations and radio galaxies. Our results show remarkable continuity in the distributions of source luminosities (radio core and extended luminosities, \(L_{C}\) and \(L_{E}\) respectively as well as \(\gamma \)-ray luminosity \(L_{\gamma

We present for the first time the X-ray luminosity function of short gamma-ray bursts (sGRBs) estimated from 22 Fermi sGRBs. We find that the cumulative distribution of X-ray emission at rest frame 200 s is well described by a broken power law function, which is \(\phi (L_{\mathrm{X,0}})\propto L_{\mathrm{X,0}}^{-0.20\pm 0.04}\) for dim bursts and \(\phi (L_{\mathrm{X,0}})\propto L_{\mathrm{X,0}}^{-1

With outer space being speculated as the source of handedness in molecules of biological importance, there is a great need to explore the gas-phase stereoinversion in molecules under the conditions akin to interstellar medium. In this work, quantum-mechanical computations are performed to trace the pathways for gas-phase stereoinversion in isoleucine, an amino acid with two chiral centres. Contrary

We examined the behaviour of blazar OJ 287 based on 12 year observation data in optic, UV, X-ray, and gamma ray. The optical, UV, and X-ray data of OJ 287 were obtained from Swift archive, which provide more or less simultaneous optical–X-ray observations, while gamma ray data were obtained from Fermi archive. The occurrence of outburst episode in 2007 can be confirmed in Swift/UVOT data. In addition

Extreme high-energy peaked BL Lac objects (EHBLs) are an emerging class of blazars with exceptional spectral properties, e.g., enhanced emission in the hard X-ray region and a hard spectrum at very high \(\gamma \)-ray energies. Currently, no suitable model exists to explain the high-energy radiation mechanism of EHBLs. Here we apply a new model of the emission process to describe the Spectral Energy

Our present study involves the strange stars model in the framework of \(f(R,T)\) theory of gravitation. We have taken a linear function of the Ricci scalar \(R\) and the trace \(T\) of the stress-energy tensor \(T_{\mu\nu}\) for the expression of \(f(R,T)\), i.e., \(f(R,T)=R+ 2 \gamma T \) to obtain the proposed model, where \(\gamma \) is a coupling constant. Moreover, to solve the hydrostatic equilibrium

Artificial Light pollution (AL) in Turkey and in Turkish observatories between 2012–2020 have been studied using the archival data of Visible Infrared Imaging Radiometer Suite (VIIRS) instrument. The astroGIS database has been used in processing the data (astrogis.org) Aksaker et al. (2020a). The total energy released to space from Turkey increased by 80% in 2019 with respect to 2012. In the span of

In this work, we establish a model of holographic dark energy interacting with dark matter in flat Friedmann-Lemaitre-Robertson-Walker (FLRW) universe and test this model with observational data of Type-Ia supernovae (SNeIa), baryon acoustic oscillation (BAO), cosmic microwave background (CMB) anisotropy and Hubble parameter \(H(z)\). Next we obtain the deceleration parameter and the coincidence parameter

It is now well established that Coronal Mass Ejections (CMEs) may produce shocks in near Sun and interplanetary medium. A Type-II radio burst is characterized by shock and associated emission with very slow frequency drift rate (∼0.1 MHz/sec). A CME driven shock and their velocity, acceleration/deceleration signature can be observed by a Type-II solar radio burst which drifts with the shock speed and

We present the cosmological model of a bouncing universe with causal fluid in the universe. The dissipative effects of the causal cosmic fluid is probed with both truncated Israel–Stewart theory and full Israel–Stewart theory. The following classes of non-vanishing scale factors of bouncing cosmology are considered with a viscous fluid: (i) the power-law bouncing model, (ii) the exponential bouncing

We study the solar flare of July 19, 2000 of M6.4/3N class, which occurred in the active region NOAA 9087. Echelle Zeeman spectrograms of this flare were obtained with the horizontal solar telescope of the Astronomical Observatory of Taras Shevchenko National University of Kyiv. Physical conditions were compared for two times corresponding to the pre-peak and peak phases of the flare in area of a small

The nonlinear dynamics of an elliptic restricted three-body system with perturbations such as radiation and albedo are studied in this paper. The effects of different perturbation parameters on the nonlinear dynamic behavior of the third-body are analyzed through the system’s bifurcation diagram. The second- and third-order approximate periodic solutions near the collinear libration points in the plane

We investigate the problem of determining the shape of a rotating celestial object – e.g., a comet or an asteroid – under its own gravitational field. More specifically, we consider an object symmetric with respect to one axis – such as a dumbbell – that rotates around a second axis perpendicular to the symmetry axis. We assume that the object can be modeled as an incompressible fluid of constant mass

In order to support the analysis of potential long-term trends in the Sun’s variability and trace the WRR ground calibration ratio to the measurement on the satellite. We established the total solar irradiance (TSI) calibration model in orbit for the new generation of solar radiation monitor on the FY-3E satellite. First, we measured the non-equivalence of the instrument, and the air to vacuum ratio

In this work, we examine a spherically symmetric compact body with isotropic pressure profile. In this context we obtain a new class of exact solutions of Einstein-Maxwell field equation for compact stars with uniform charged distributions on the basis of Pseudo-spheroidal space-time with a particular form of electric field intensity and the metric potential \(g_{11}\). Taking these two parameters

We remind that the “ring down” features observed in the LIGO gravitational waves (GW) resulted from trembling of “photon spheres” (\(R_{\mathit{photon}}=3M\), by using units \(G=c=1\)) of newly formed compact objects and not from the trembling of their event horizons (EH) \(R=2M\) (Cardoso et al. 2016). Further, the tentative evidence for late time “echoes” in GWs might be signatures of horizonless

Coronal mass ejections (CMEs) largely influence the space weather and cause geomagnetic perturbations. Hence, the statistical studies pertaining to the occurrence of CMEs over the solar cycles and their consequence at the near-Earth region are extremely important. For an in-depth understanding, such studies need to be carried out considering various observational aspects of CMEs. With this motivation

A dynamical model has been developed to envisage the star formation scenario in filamentary molecular clouds. In the present work a double well potential has been considered to find the number of stable stationary points as the origin of field star, binary stars or stellar associations. It is found that low density structure can lead to the formation of field stars while an intermediate density structure

The formation of a temporary third radiation belt in the slot region of Earth’s magnetosphere was reported (Baker et al. in Science 340:186-190, 2013a) from the early data of the radiation belt storm probes (RBSP) mission. The cumulative flux of relativistic electrons in L = 3-3.5 for the third radiation belt of that study is calculated here and defined as threshold flux (TF) (105 cm−2 s−1 sr−1 MeV−1)

We study the geo-effectiveness of high-speed streams (HSS) detected during the consecutive eight years (2009 - 2016) period of solar cycle 24. These HSS are of different speeds and durations. During their passage, solar wind plasma and magnetic field parameters are also not similar. We utilize solar wind plasma and magnetic field parameters during the HSS passage in addition to two geomagnetic indices

In the present paper, the relation between the CMEs and their linked solar flares is examined during the entire solar cycle 23. During this solar cycle and under certain temporal and spatial conditions, 521 CMEs linked with solar flares are selected. These selected CMEs are separated into two groups according to their time of detection, 254 Before Flare-ECME events (BF-CMEs) and 267 After Flare–ECME

Low-energy bi-impulsive Earth-Moon transfers are investigated by using periodic orbits. Two Earth-Moon transfer design strategies in the CR3BP are proposed, termed direct and indirect design strategy. In the direct design strategy, periodic orbits which approach both vicinities of the Earth and Moon are selected as candidate periodic orbits, which can provide an initial guess of bi-impulsive Earth-Moon

We present the star formation rates (SFRs) of galaxies with redshifts of 0 < \(z\) < 6 and cosmic star formation rate densities as a function of redshift. The SFRs for the galaxies at infrared emission have been investigated for 1752 sources from the Spitzer 70 μm observations of the Spitzer COSMOS Legacy survey and the various surveys in the literature. Analyzing the SFRs of these objects provides

Open clusters (OCs) are important objects in exploring the structure and history of the Milky Way. Large amount of sky survey data can be used to detect OCs. However, analyzing these data manually has become a bottleneck of OC identification. This study proposes a multi-scale density feature learning (MSDFL), which includes the open cluster kernel density map to visualize the features of OCs; and open

There exists a small but statistically significant north–south asymmetry in most of the solar activity indices and it has important implications on the solar dynamo mechanism. Here we analyzed the daily sunspot-group data reported by the Greenwich Photoheliographic Results (GPR) during the period 1874 – 1976, Debrecen Photoheligraphic Data (DPD) during the period 1977 – 2017, and the revised Version-2

In this article, we examine the solution for expanding cosmology, which imitates properties similar to an interplay of dark matter and dark energy. The effective fluid of this toy model may behaves like dust matter at early epoch and as a cosmological constant at later epoch. Also, for this solution, the cosmological parameters are calculated and the model is able to explain dynamical universe evolution

Binary systems of Population III can evolve to microquasars when one of the stars collapses into a black hole. When the compact object accretes matter at a rate greater than the Eddington rate, powerful jets and winds driven by strong radiation pressure should form. We investigate the structure of the jet-wind system for a model of Population III microquasar on scales beyond the jet-wind formation

The supermassive black hole at the Galactic Centre is surrounded by the so-called Circumnuclear Disc (CND) with a sharp inner edge at 1.5 pc. Both its outer extent and the total mass contained within it are somewhat unknown making it difficult to conclude on its long term stability. In this work we report the results of our simulations for the orbital evolution of the CND taking into account its warped

In this work, we compiled a sample of 1172 4FGL blazars with available spectral information and broadband intensities to the study the spectral indices. Based on this sample, we studied the correlations of spectral indices, and further studied BCU classification by using multi-band spectral indices. Among these sources, there are 196 BCUs, we manage to classify these sources into either FSRQs or BL