This paper describes a novel homotopy method to compute fuel-optimal trajectories starting from a time-optimal solution. The time-optimal problem is proposed to serve as a gateway for solving the minimum thrust problem. Homotopy is used to link the original low-thrust fuel-optimal problem with the minimum thrust problem. Two new variables are introduced in the dynamic model. The first is a logarithm

We study the transient modulation of galactic cosmic rays (GCRs) due to coronal mass ejections (CMEs) and their associated structures detected during most part of solar cycle 24. The interplanetary counterpart of CMEs (ICMEs), while propagating in the interplanetary space, may be associated with the shock/sheath region. An ICME may (or may not) be the so-called magnetic cloud. Using the method of superposed-epoch

We consider the nonlinear ion acoustic wave induced by orbiting charged space debris objects in the plasma environment generated at the Low Earth Orbital (LEO) region. The generated nonlinear ion acoustic wave is shown to be governed by a forced Korteweg-de Vries (fKdV) equation with the forcing function dependent on the charged space debris function. For a specific relationship between the forcing

We study the effect of the Bumblebee deviation parameter \(l\) on galactic scale by means of Relative Time Delay (RTD) caused by frame dragging effect. While weak field solar system tests have been fairly accurately measured leading to an exceedingly tiny upper limit \(l\leq10^{-13}\), measurements on the large astrophysical scale are yet unavailable, so we decided to keep \(l\) neither too tiny nor

The gravitational-wave signal GW190814 involves a compact object with mass \((2.50-2.67)~{\mathrm{M}}_{\odot }\) within the so-called low mass gap. As yet, a general consensus on its nature, being a black hole, a neutron star or an exotic star, has not been achieved. We investigate the possibility this compact object to be an anisotropic neutron star. Anisotropies in a neutron star core arise naturally

This study aims to examine the dynamics of flat Friedmann-Lemaitre-Robertson-Walker (FLRW) model of universe with time varying cosmological constant \(\Lambda (t)\) in Brans-Dicke theory of gravity. The authors find a solution of the field equations using simple parametrization of scale factor \(a(t)\) i.e. \(a(t)=\exp \{(\alpha t+\beta )^{p}\}\), and power law relation between \(a(t)\) and Brans-Dicke

By expanding the perturbation function of tesseral harmonic \(J_{22}\) term of the earth’s non spherical gravitation, it is found that there is a term \(\cos 2\Omega _{e}\) related to the rotation of the earth. The period of the term is half a day, and the coefficient includes the factor \(\sin ^{2}i\) related to the orbital inclination angle. For the low polar orbit satellite with orbit inclination

We employ a perturbative analysis to study the evolution of large-scale peculiar velocity fields within the framework of Newtonian gravity and then compare our results to those of the corresponding relativistic treatment. In so doing, we use the same mathematical formalism and apply the same physical approach. This facilitates a direct and transparent comparison between the two treatments. Our study

In this paper, the prediction model for ionospheric total electron content (TEC) based on Long Short-Term Memory (LSTM) deep learning network and its performance are discussed. The input parameters of the model are previous values of daily TEC, solar radio flux at 10.7 cm parameter of 81 day moving average (\(\overline{F107\_81}\)), sunspot number (SSN), geomagnetic Kp index, and disturbance storm

This paper presents a statistical analysis of soft X-ray flares during the period January 1986 to June 2017 covering the last three solar cycles (SCs) 22, 23, and 24. We have analyzed the distribution of flare number, the relationship between the occurrence rate of soft X-ray flares and solar activity, and the duration of different intensity class (B, C, M, and X) solar flares during the period of

We present new observations of the reconnection outflow jet obtained from the crossing of a solar wind reconnection exhaust by the Wind spacecraft on 5 March 2001. The outflow jet is characterized by a bifurcated configuration, which is different from typical reconnection exhausts. The two outflow jets are mainly distributed in the region close to the exhaust boundaries. Between the two jets, the bulging

The Mücket-Treder-type potential was initially introduced to explain the discrepancy between Mercury’s observed perihelion advance and the computed value based on Newton’s law, but it can also be used for many astronomical situations as, for instance, the study of the very eccentric cometary orbits in the neighborhood of the Sun. In this paper we tackle the two-body problem in the Mücket-Treder post-Newtonian

Metallicities of the Milky Way globular cluster (GC) system are interpreted within the framework of a closed box model of chemical evolution. Model age-metallicity relations normalised to the Sun are compared with an observed age-metallicity relation constructed from literature data for the Galactic globular clusters and solar neighbourhood dwarf stars. One branch of the GC age-metallicity relation

This paper presents different families of transfers from Low Lunar Orbit to Distant Retrograde Orbits in the Earth-Moon system and analyzes their characteristics from the perspective of velocity increment requirement, transfer time, and sensitivity to small perturbations. Initially, families of transfer trajectories in the Circular Restricted Three-Body Problem are found by the predictor-corrector

Two parameters such as magnetic fields near the light cylinder \(B_{lc} \) and rates of rotational energy losses \(\frac{dE}{dt} \) for 1795 radio pulsars without high energy emission (R), 52 radio loud gamma-ray pulsars (\(\gamma\)+R), 33 radio quiet gamma-ray pulsars (\(\gamma\)) and 61 radio loud X-ray pulsars (X+R) are compared with each other in this work. Pulsars with registered X-ray and gamma-ray

In this paper, we present the multi-wavelength study of a high level of solar activity during which a single active region produced multiple flares/CMEs. According to the sunspot observations, the current solar cycle 24 manifest to be less intense in comparison with the previous recent sunspot cycles. In the course of the current sunspot cycle 24, several small and large sunspot groups have produced

This work presents an analytical approach for studying the cosmological 21cm background signal from the Dark Ages (DA) and subsequent Epoch of Reionization (EoR). We simulate differential observations of a galaxy cluster to demonstrate how these epochs can be studied with a specific form of the Sunyaev-Zel’dovich Effect called the SZE-21cm. This work produces simulated maps of the SZE-21cm and shows

The coincidental detection of the gravitational wave event GW 170817 and the gamma-ray burst GRB 170817A marked the advent of multi-messenger astronomy and represented a milestone in the study of GRBs. Significant progress in this field is expected in the coming years with the increased sensitivity of gravitational waves detectors and the launch of new facilities for the high-energy survey of the sky

The regional ionospheric models are successful in capturing the variability of ionosphere with the inclusion of local ground-based GPS observations and location dependent ionospheric dynamics. In this context, there is a need to develop regional ionospheric maps that aids in improving the consistency of global models. In this paper, an attempt is made to understand the potentiality of multi-instrument

We investigate whether certain extra-solar multi-planet systems simultaneously follow the scaling and spacing rules of the angular-momentum-deficit model. The masses and semi-major axes of exoplanets in ten multi-planet systems are considered. It is found that GJ 667C, HD 215152, HD 40307, and Kepler-79 systems are currently close to configurations of the angular-momentum-deficit model. In a gas-poor

Impacts of solar flare vary at different parts of the lower ionosphere depending on it’s proximity to the direct exposure of incoming solar radiation. The quantitative analysis of this phenomena can be attributed to ‘solar zenith angle (\(\chi (t)\))’ profile over ionosphere. We numerically solve the ‘electron continuity equation’ to obtain the lower ionospheric electron density profile (\(N_{e}(t)\))

Despite that the tricarbon monosulfide (C3S) is among the first sulfur-containing carbon-chain molecules to be detected in the interstellar medium, no studies focused on the determination of its collisional rates. These rate coefficients are essential to estimate the abundance of C3S in the interstellar medium. Computations of the C3S(\(^{1}\Sigma^{+}\)) downward rate coefficients, induced by collision

The global features of the modulation of galactic cosmic ray protons and helium nuclei in a very quiet heliosphere are studied with a comprehensive, three-dimensional, drift model and compared to proton and helium observations measured by PAMELA from 2006 to 2009. Combined with accurate very local interstellar spectra (VLIS) for protons and helium nuclei, this provides the opportunity to study in detail

We demonstrate a technique to generate new class of exact solutions to the Einstein-Maxwell system describing a static spherically symmetric relativistic star with anisotropic matter distribution. An interesting feature of the new class of solutions is that one can easily switch off the electric and/or anisotropic effects in this formulation. Consequently, we show that a plethora of well known stellar

This paper explores and analyzes a set of solutions describing the interior structure of relativistic compact stellar structures with variable cosmological constant \(\Lambda (r)\). We consider the solution of Krori–Barua space-time to a static spherical symmetric metric. Furthermore, we match our interior stellar structure with the exterior Schwarzschild geometry to determine the values of the constants

This paper presents the performance of the latest version of the International Reference Ionosphere (IRI-2016) model for estimating the Total Electron Content (TEC) variations in the mid-latitudinal Turkish regions during low solar activity years (2015–2018). Moreover, TEC is estimated from dual-frequency Global Navigation Satellite System (GNSS) receivers operating in different regions of Turkey:

We study the luminosity function of long gamma-ray bursts (LGRBs) using the peak flux obtained from three LGRB samples with known redshifts: (a) a sample of 251 LGRBs from the Swift/BAT satellite/instrument; (b) a sample of 37 LGRBs from the Fermi/GBM telescope; (c) a sample of 152 GRBs from the Konus-Wind instrument. For the Swift/BAT and Fermi/GBM samples, we use data available on the Swift Burst

High magnetic field (high-B) pulsars are key sources to bridge magnetars and conventional rotation powered pulsars, and thus to understand the origin of magnetar activities. We have estimated a tight upper limit on the X-ray flux of one of the youngest high-B pulsars PSR J1208−6238 for the first time; a Chandra 10 ks observation shows no significant source. Depending on the emission models, we have

Quasar projected pairs (QPPs) can be used for investigating the circumgalactic medium of quasars through the study of intervening absorption lines in the spectrum of the background quasar (QSOB) that are at the same redshift of the foreground quasar (QSOF). Here we report on optical spectroscopy, gathered at Gran Telescopio Canarias, of 14 QPPs. In 7 cases we find MgII absorption lines associated with

We have shown the generation/amplification of fast macro-scale plasma flows in the degenerate two-fluid astrophysical systems with initial turbulent (micro-scale) magnetic/velocity fields due to the Unified Reverse Dynamo/Dynamo mechanism. This process is simultaneous with and complementary to the micro-scale unified dynamo. It is found that the generation of macro-scale flows is an essential consequence

The ionospheric response over the low and mid-latitudes along the \(78^{\circ}\pm 3^{\circ}\)E longitude sector is studied for the 20th December 2015 geomagnetic storm. The global positioning system (GPS) derived total electron content (TEC) over mid & low-latitude stations and also an ionosonde observation of the F2 layer critical frequency over a mid-latitude station are analyzed. On the day of storm

Lepton (electron and positron) capture rates on iron-regime nuclei are an essential element for modeling the late stages of progression of massive stars that become core collapse and thermonuclear supernova. As per previous simulation studies, lepton capture (LC) rates on isotopes of vanadium are believed to have a substantial effect in regulating the Ye (lepton to baryon fraction) during the final

We present the results from the measurement of secondary cosmic gamma-ray flux using a NaI(Tl) scintillator detector during a total solar eclipse. The unique feature of this experiment is that it was carried out at a place where the solar eclipse was not observable. The total solar eclipse of August 21, 2017, was visible in most of the regions of North America during the day, whereas India, falling

We study the motion of a secondary celestial body under the influence of a corrected gravitational potential in a modified Newtonian dynamics scenario. Furthermore we look within the Milky-way where the first correction to the potential results from a modified Poisson equation, and includes two mew terms one of which is of the form \(\ln(r/r_{\max})\) and the other is associated with the cosmological

Stellar flybys in star clusters may perturb the evolution of young planetary systems in terms of disk truncation, planetary migration and planetary mass accretion. We investigate the feedback of a young planetary system during a single close stellar encounter in a typical open young stellar cluster. We consider 5 masses for the stellar perturbers: 0.5, 0.8, 1, 3 and \(8~\mbox{M}_{\odot }\), in coplanar

We present results of our study of the long-period eclipsing binary star NN Delphini (hereafter NN Del). The results are based on spectral data obtained with the HRS échelle spectrograph of the Southern African Large Telescope (SALT). Our constructed velocity curve is based on 19 spectra obtained between 2017 and 2019 years and covers all phases of the binary’s orbit. The orbital period, \(P=99.252\) days

The study aims to take an advantage of the systematic combination of statistical procedures namely Principal Component analysis (PCA), Linear Model to develop a local climatological model for ionospheric Total Electron Content (TEC) irregularities. Further, Auto Regressive Moving Average (ARMA) model, Neural Network (NN) model are used to forecast the ionospheric irregularities over Bengaluru region

Several kinds of instabilities are often observed in the solar wind. We studied the linear theory of the current-driven electrostatic ion acoustic instability at frequencies near the ion cyclotron frequency at distances from the Sun over 0.3 to 1 AU. The properties of current driven electrostatic ion-acoustic instability are investigated. The instability parameters, such as angular wave frequency,

The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a Chinese-French satellite dedicated to the observation and study of Gamma-Ray Bursts (GRBs) and other variable sources. Among the four scientific payloads onboard SVOM, the Gamma-Ray Monitor (GRM) is designed to detect GRBs in the 15 keV to 5 MeV energy range. The final performance of GRM can be affected by the space environment

In this paper, we investigate the dynamics of the exterior retrograde \(1/n\) resonances within the framework of the planar circular restricted three-body problem (PCRTBP), taking the \(1/{-2}\) and \(1/{-3}\) resonances as examples. We prove that there is no asymmetric libration in retrograde \(1/n\) resonances using analytical, numerical integrations, and semi-analytical methods, by mutual authenticating

Using the AV18 equation of state, we numerically calculate the structure of a neutron star in Rastall gravity. The results show that the parameter \(\lambda \) originated from Rastall gravity has a great effect on the mass and the radius of a neutron star. When \(\lambda =1\), the Rastall equations of motion can be reduced to those in the general relativity. In terms of the stability condition for

We study compact stars formed by dark and ordinary matter, with attributes of both neutron star matter and quark star matter. We assume an equation of state for dark matter which is consistent with the rotational curves of galaxies and for color-flavor-locked (CFL) distributions for ordinary matter. This is done in the curved Krori-Barua spacetime geometry in general relativity. We find new exact solutions

We consider the planar circular restricted three body problem with oblate primaries. Using a suitable symplectic scaling and the Poincaré continuation method, we prove that in the proximity of any of the primaries there exist unstable periodic orbits.

In this paper, we construct dark halo models which are merely supported by geometry of space time. We concentrate on the inhomogeneous space time around some spiral galaxies whose have dark matter. After characterizing the dark halo models, the possibility of the energy density of such a field which could justify the rotation curves of stars in the dark halo is explored.

We have studied, in a series of papers, the properties of the \(M_{\bullet}\) versus \(M_{G}\sigma^{2}\) relation and we have found that it is useful to describe the evolution of galaxies in the same way as the HR diagram does for stars and to predict the masses of Supermassive Black Holes that are difficult to be guessed using other scaling relations. In this paper, analyzing five samples of galaxies

This article has been retracted. Please see the retraction notice for more detail: https://doi.org/10.1007/s10509-019-3678-x

In the present work, a significant rotational lines of the \(B^{4}\Sigma ^{-} \mbox{--} X^{4}\Sigma ^{ -} \) (\(0,0\)) band system of the AlC molecule were identified in high resolution FTS sunspot umbral spectra in the region from 22,450 to 22,600 cm−1. Among the well-resolved identified lines, the rotational temperatures have been estimated to be 4018 K for photosphere and 3722 K for a hot umbra

Insight-HXMT, the first X-ray astronomical satellite in China, aims to reveal new sources in the Galaxy and to study fundamental physics of X-ray binaries from 1 to 250 keV. It has three collimated telescopes, the High Energy X-ray telescope (HE), the Medium Energy X-ray telescope (ME), and the Low Energy X-ray telescope (LE). Before the launch, in-orbit backgrounds of these three telescopes had been

Studying the characteristics of terdiurnal tides in the ionosphere provides an important pathway to understand the dynamic coupling between the low atmosphere and the ionosphere. Based on the TEC data from the Madrigal database at the Massachusetts Institute of Technology Haystack Observatory, a decomposition and nonlinear fitting method is used to derive ionospheric terdiurnal tides. Statistical analysis

WISE observations of visual carbon stars (VCSs), infrared carbon stars (IRCSs), extreme carbon stars (ECSs), J-type carbon stars JCSs), and silicate carbon stars (SCSs) are presented in this paper. We found that in the WISE observational region carbon stars still form a sequence of VCSs → IRCSs → ECSs with the color gradually increasing. We also found that in the WISE two-color diagrams the JCS distribution

The size and availability of Sun-Jupiter and Sun-Neptune saddle regions are determined. Within these regions the net gravitational field is \(\leq 10^{-10}\text{ ms}^{-2}\). These regions are therefore suitable for experiments which can provide evidence for the alternative gravitational theories of MOND and gravitational anti-screening. A particular experiment is outlined where the relative separation

In this study, we investigate the effects of light pollution in France using GIS data which was first used in Aksaker et al. (Mon. Not. R. Astron. Soc. 493:1204, 2020) (so called astroGIS database - astrogis.org). A subset of Artificial Light layer of astroGIS database has been adapted for years between January 2012 and December 2019. During 2019, half a million of lumen has been released into space

Total Electron Content (TEC) is used for calculation of Ionospheric delay. The Precise forecast of TEC is useful to correct the range measurements. TEC depends on the time of measurement, solar radiation (SSN & F10.7), geomagnetic index (AP & KP), season and geographic location of the user. In this paper, Cokriging geostatistical method is applied to build the Surrogate Model (COKSM) to estimate the

Electrons are accelerated at the shock wave diffuse and advect outward, and subsequently drift away into the emitting region of the jet that is located in the downstream flow from the plane shock. The current work considers the acceleration of the electrons in the shock front. Assuming a proper boundary condition at the interface between the shock and the downstream zones, a novel particle distribution

This study examines the influence of space weather conditions on ionospheric TEC variations at different latitudes around the world. According to the space weather condition indices (geomagnetic storm-activity indices, solar activity indices, magnetic field change indices, plasma density and proton flux indices) different time periods were chosen. GPS observations were used to obtain TEC data derived

Using a semi-phenomenological model of the imbalanced Alfvénic turbulence, we study the turbulence transition from magnetohydrodynamic to sub-ion kinetic scales in the conditions typical for the fast solar wind. We show that the transition takes place in a wide wave number interval where the energy spectrum does not follow any power law. For larger turbulence imbalances, both boundaries of the transition

Gravitational wave (GW) has become one of the most active fields in physics and astronomy since the first direct detection of GW event in 2015. As is well known, multiple images of GW events are possible through the gravitational lenses. Here, we propose a novel mirror imaging mechanism for GW events different from the gravitational lens. In the literature, the superconductor was predicted to be highly

The purpose of present work is to provide a new mathematical model for hybrid compact stars composed of strange quark matter (\(\mathit{SQM}\)) and normal baryonic matter distribution in the modified Rastall theory of gravitation. The simplest form of phenomenological \(\mathit{MIT}\) bag model equation of state (\(P_{q}=\frac{1}{3}(\rho _{q}-4B_{g})\)) has been used to correlate the density and pressure

We use the Iocco et al. (2015) compilation of 2,780 circular velocity measurements as a baseline sample to analyze the Milky Way rotation curve. We focus on techniques that adequately capture the small-scale structure (structure on the order of ∼0.5 kpc) present in the Milky Way rotation curve and that can be used to show the azimuthal anisotropy of the Milky Way rotation curve. We fit the data with

We investigate the existence of high dense compact objects in the light of Rastall gravity theory. The material content is driven by an imperfect fluid distribution and the inner geometry is described by the Tolman–Kuchowicz space–time. The validity of the obtained model is checked by studying the main salient features such as energy–density, radial and tangential pressures and anisotropy factor. Since