We have studied alpha attractor cosmology with exponential harmonic fields and reheating phase after inflation. The results show that, for large limit of alpha, the inflationary parameters of the used model confirm the observational data. For exponential harmonic fields, we have obtained constraints on reheating parameters. It arises that for these fields, reheating can last longer than canonical and

A one-step hybrid block method which is applied for solving Lane-Emden second-order singular differential equations arising in astrophysics is developed. The present technique is obtained by considering three intra-step nodal points, which are chosen appropriately in order to get optimized errors of the main formulas approximating the solution and the first derivative at the final position of the block

Recent studies showed that observations of line emission from shocks in YSO jets require a substantial amount of ionization of the pre-shock matter. Photoionization from X-ray emitted close to the central source may be responsible for the initial ionization fraction. The aim of our work is to study the effect of X-ray photoionization, coming from the vicinity of the central star, on the ionization

Under the premise that the current observations of the cosmic microwave background radiation set a very stringent limit to the anisotropy of the universe, we consider an anisotropic model in the presence of a barotropic perfect fluid and a homogeneous scalar field, which transits to a flat FRW cosmology for late times in a dust epoch, presenting an accelerated volume expansion. Furthermore, the scalar

Samples of red giant branch (RGB) stars have been compiled from the literature for seven moving groups, and searches made for both GALEX FUV and Johnson \(\mathit{BV}\) photometry. It has been possible to derive a colour index \((\mathit{FUV}-B)\) for many giants, which has been combined with \(B-V\) to give a two-colour diagram for each kinematic group. In addition, analogous data have been gleaned

In this paper we deal with the Tsallis holographic dark energy from a dynamical system approach. Here we assume the Hubble horizon as an infra red cutoff. We consider the cosmic evolution of the model in noninteracting, linearly, sign changeable and nonlinearly interacting cases. The analysis includes an autonomous system of equations and then we analyze the related phase spaces. We find that for a

This article is devoted to the study of the dynamical aspects of the perfect fluid cosmological model in the presence of an attractive massive scalar field in an axially symmetric Bianchi type-I space time in Lyra (Math. Z. 54:52, 1951) geometry. An exact cosmological model is presented by solving Einstein field equations using physically valid conditions. We have evaluated all the dynamical and geometrical

The ESA-Gaia satellite is regularly producing Alerts on objects where photometric variability has been detected after several passages over the same region of the sky. The physical nature of these objects has often to be determined with the help of complementary observations from ground-based facilities. We have compared the list of Gaia Alerts (from the beginning in 2014 to Nov. 1st, 2018) with archival

A theoretical and numerical study on amplitude modulated positron-acoustic waves (PAWs) in a magnetized four-component space plasma (containing immobile positive ions, inertial cold positrons, and inertia-less hot electrons and positrons following Cairn’s non-thermal distribution function) has been carried out. The reductive perturbation method have been applied to derive the corresponding nonlinear

We review the observational properties and possible carriers of the 21 and 30 μm features seen in the spectra of evolved carbon-rich objects. The 30 μm feature is generally taken to be due to MgS, possibly in combination with other sulfides. It is commonly assumed that the sulfides coat grains of SiC or amorphous carbon, but it remains unclear if coated grains can produce the observed feature given

Ion-scale magnetic flux ropes have been observed in the reconnection diffusion region. In this paper, we show a typical ion-scale flux rope observed by the Magnetospheric Multiscale spacecraft at the subsolar magnetopause. The most intriguing feature of this flux rope is that the rapid variations of electron density are correlated with the changes of electron temperature and pitch angle distribution

This study aims to investigate the effects of the solar activity phases on the magnetospheric processes in relation to daily relativistic electron (\(E>2\) MeV) dynamics at geosynchronous orbit (GEO) during Solar Cycles 23–24. GOES observations indicate that in the descending phase the electron fluxes are seasonally dependent with largest flux in equinoctial periods, relatively high, and 27-day recurrent

The collinear libration point of the Sun-Earth Circular Restricted Three-Body Problem (CR3BP), \(L_{3}\) is located opposite to the Earth with respect to the Sun. Whereas several space missions have been launched to the other two collinear equilibrium points, i.e., \(L_{1}\) and \(L_{2}\), the region around \(L_{3}\) is so far unexploited essentially because of the severe communication limitations

In this paper, we consider a holographic dark energy model driven by the gravitationally induced adiabatic matter creation with constant creation rate. It is assumed that the present accelerating stage is a consequence of the negative pressure describing the irreversible process of gravitational matter creation. Exact solutions are obtained to discuss the evolution of the universe. We obtain the best-fit

Many space agencies are working on solutions for manned operations on the Moon, both on its surface and in cislunar space. In such a scenario, with stable human presence, a launch facility would be needed and launch vehicles could take advantage of the benefits of the lunar environment. In the present paper missions to Earth (to a geostationary orbit) and to Mars (to an areostationary orbit), from

We consider the 3-dimensional space with \(t_{1} = \mbox{constant}\) in a super dense star which is spheroidal. We report a class of static spherically symmetric physically viable models based on a particular actual solution of Einsteins field equations. The models of the class admit densities of the order of \(2 \times 10^{14}~\mbox{gm}\,\mbox{cm}^{-3}\), radii of the order of a few kilometers and

The effect of rotation, porosity and finite ion Larmor radius (FLR) corrections on the gravitational instability and radiative instability of infinite homogeneous plasma has been explored, accounting for the consequences of radiative heat-loss function and thermal conductivity. The general dispersion relation is obtained by means of the normal mode analysis method with the help of appropriate linearized

The petroleum and coal models of the unidentified infrared emissions (UIE), sometimes referred also as unidentified infrared bands (UIBs) has been reviewed mainly based on the work of the authors with the inclusion of unpublished results. It is shown that the petroleum and coal model of the UIE converges and merges quite well with the MAON (Mixed Aromatic Aliphatic Organic Nanoparticles) model of the

A methodology is proposed to design optimal time-fixed impulsive transfers in the vicinity of the L2 libration point of the Earth-Moon system, taking the construction of a space station around the collinear libration points as the background. The approximate analytical expression of motions around the L2 point in the CRTBP is given, and the expression in the ERTBP is derived by linearizing the dynamical

This work investigates the basic features of Nonlinear Ion Acoustic Solitary waves (NIASWs) and their dynamical behaviours in an unmagnetized relativistic collisionless plasma system via the Schamel Korteweg-de Vries (SKdV) equation. Such plasma is composed by the generalized distributed electrons, Boltzmann distributed positrons and relativistic warm ions. The influences of plasma parameters on NIASWs

We have carried out an intensive study of photometric (Kepler Mission) and spectroscopic data on the system Kepler-2 (HAT-P-7A) using the dedicated software WinFitter 6.4. The mean individual data-point error of the normalized flux values for this system is 0.00015, leading to the model’s specification for the mean reference flux to an accuracy of ∼0.5 ppm. This testifies to the remarkably high accuracy

The basic purpose of this communication, is to investigate the dynamical nature of Bianchi type-I universe with perfect fluid content in Sáez-Ballester (SB) theory (Phys. Lett. A 113:467–470, 1986). We got the solution of modified Einstein’s field equations (EFEs) by considering the bilinearly varying deceleration parameter (BVDP) and the gravitational constant \((G)\) as a power function of average

In this paper, a very first use of the \(\kappa \)-deformed Kaniadakis distribution is made in the context of arbitrary amplitude ion-acoustic solitary waves (IASWs) in a magnetized plasma composed of cold fluid ions and non-Maxwellian electrons. The basic equations governing the dynamics of nonlinear structures are reduced to an evolution equation in the form of an energy-balance like equation through

We study the mode conversion and damping of MHD waves in a gravitationally stratified low-\(\beta \) to high-\(\beta \) isothermal atmosphere of the Sun permeated by a uniform vertical magnetic field. We solve the MHD equations by MacCormack method to examine the effect of viscosity on amplitudes of physical quantities such as velocity, mass density, gas pressure and magnetic field before and after

Radiative capture reaction \(d(\alpha ,\gamma )^{6}Li \) is the only process in the Big-Bang model that produces \({}^{6}Li \). We develop the formalism based on pionless Effective Field Theory (EFT) for deuteron-alpha scattering to derive the cross-section of deuteron-alpha radiative capture. Based on this model, nucleons and alpha particle interact through separable two-body forces. The alpha particle

Starting from one dimensional Kappa distribution for electrons, we have systematically developed the combined Kappa-Cairns distribution. We have found the effective bounds of both nonthermal parameters \(\kappa \) and \(\beta _{e}\) for the combined Kappa-Cairns distribution. This distribution can generate more highly energetic particles in comparison with both Kappa and Cairns distributions. We have

The \(VRI\) passbands light curves of V344 Lac were presented and analyzed by using the latest version of the W-D code. The observed spectrum reveals that V344 Lac is not an A3 type but would be a later F type star according to the yielded temperature. The results of solution show that V344 Lac is an A-subtype contact binary, with a moderate photometric mass ratio of \(0.387\pm 0.003\) and a moderate

Using the archival data of the Neutron star Interior Composition Explorer, we study the evolution of two-peak phase separations of the Crab pulsar’s X-ray pulse profiles, and present a possible method to predict the next glitch epochs of the Crab pulsar. The phase separations increased with time in a form of quasi-periodic fluctuation. We fit the evolution of the phase separations by using a magic

This manuscript explores the dynamics of an inflationary model using two known exact solutions, i.e., logamediate and exponential expansion. To achieve this, the framework of generalized induced gravity non-minimally coupled to Ricci scalar is taken under consideration. Using slow-roll approximation and a generalized form of coupling function, we find the possible forms of potential needed to produce

Within the scope of a FRW cosmological model we have studied the role of spinor field in the evolution of the Universe when it is non-minimally coupled to the gravitational one. We considered a few types of nonlinearity. It was found that if the spinor field nonlinearity describes an ordinary matter such as radiation, the presence of non-minimality becomes essential and leads to the rapid expansion

Abstract Since the first laboratory synthesis of C60 in 1985, fullerene-related species have been proposed to interpret various astronomical features. After more than 25 years’ efforts, several circumstellar and interstellar features have been convincingly assigned to C60, C70, and C\(_{60}^{+}\). These successes resulted from the recent advancements in observational, experimental, as well as computational

Abstract In this paper, we present the timing and spectral results for the seven distant and poorly investigated BL Lacertae sources with redshifts \(z\gtrsim 0.5\), using the archival data obtained with the Swift and other multifrequency instruments during 2006 August–2015 July. Our timing study has revealed a number of the 0.3–10 keV flux changes from the fluctuations observed within one day to the

Abstract This paper aims to examine different star identification algorithms in star sensors and compare the previous algorithms with the newly proposed algorithms. The star identification algorithms in this paper include three geometric methods, which require a minimum of five stars in the sensor field of view. These algorithms are compared with the angle, combined triangle, and pyramid algorithms

Abstract The theory of gravitational anti-screening, which has previously been applied to various astronomical observations as an alternative to dark matter, is now applied to the solar system. The effect that gravitational anti-screening has on the precession rate of the planets will be determined and compared to current observations. In addition, the effect that gravitational anti-screening will

Abstract For a finite-sized classical electron, energy conservation requires that the Born self-energy \(U_{e}^{\mathit{Born}}\), due to the electric field which surrounds the electron, be added to the electron’s rest mass energy \(m_{e}c^{2}\). \(U_{e}^{\mathit{Born}}\), which scales inversely with the electron radius \(R_{e}\), is very large and, in fact, would dominate all other energy contributions

Abstract In this paper we study the generation of high energy emission from normal pulsars. For this purpose we consider the particles accelerated in the outer magnetosphere sliding along the closed magnetic field lines. It has been shown that in due course of motion the initial small pitch angle increases and at a certain distance from the neutron star the synchrotron emission becomes significant

Abstract The interaction of interplanetary coronal mass ejections (ICME) with each other and with co-rotating interaction regions (CIR) changes their configuration, dynamics, magnetic field and plasma characteristics and can make space weather forecasting difficult. During the period of March 20–25, 2011, the Solar Terrestrial Relation Observatory (STEREO B) encountered a compound stream containing

Abstract In this paper, we have investigated some features of anisotropic accelerating Bianchi type-I cosmological model in the presence of two non-interacting fluids, i.e. one usual string and other dark energy fluid towards the gravitational field equations for the linear form of \(f(T)\) gravity, where \(T\) be the torsion. To achieve a physically realistic solution of the field equations, we have

Abstract We investigate the effects of anisotropy on ghost dark energy model from the latest observational data. We have fitted our model with the present observational data including Supernovae type Ia (SNIa) and the Hubble expansion history H(z) datasets, and compare the results with the \(\Lambda \)CDM model. We test the possible dipole anisotropy of the ghost dark energy model, by using the Pantheon

In the Discussion section of the initial online publication an incorrect percentage was specified for the observed contribution of the hard X-ray tail in the middle and upper flaring branch to the total flux of 3.0–80.0 keV. The original article has been corrected.

Equation 7 was included in error. It is irrelevant to the calculation of the correlation entropy and should be ignored.

Abstract Extended Red Emission (ERE) is a widely observed optical emission process, present in a wide range of circumstellar and interstellar environments in the Milky Way galaxy as well as other galaxies. Definitive identifications of the ERE carriers and the ERE process are still a matter of debate. Numerous models have been proposed in recent decades, often developed without consideration of the

Abstract Light propagating through Dark Matter suffers gravitational frequency shifts. We derive the differential equation and its solution for spherical Dark Matter. This is then applied to condensed neutrino objects (CNO) which are a candidate for Dark Matter. The Local Group of Galaxies seems to be embedded within a CNO (Morley and Buettner in MDPI Universe 3(4):81, 2017), and we derive the gravitational

Abstract A flat Friedmann-Robertson-Walker (FRW) cosmological model with perfect fluid has been investigated within the framework of the particle creation mechanism. Perfect fluid isentropic particle creation rate as a function of Hubble parameter has been incorporated. By considering a simple parametrization of Hubble parameter, we discuss the cosmological scenarios through time evolution of the cosmological

Abstract Searching for as yet undetected \(\gamma \)-ray sources is one of the main stated goals of the Fermi Large Area Telescope Collaboration. In this paper, we explore the capability of a filtering method based on a finite mixture of von Mises–Fisher distributions. The proposed procedure is specifically designed to handle data with support on the unit sphere. The assumption of a parametric model

Abstract Linear and nonlinear propagation characteristics of drift ion acoustic waves are analyzed in an inhomogeneous plasma comprising of warm ions having shear flow parallel to the magnetic field and electrons that are followed by a distribution which is dictated by spectral indices, \(r\) and \(q\) in low and high phase density regions. In the linear regime, the dispersion relation of the drift-ion

Abstract We searched for a resolution of the flat galactic rotation curve problem from geometry instead of assuming the existence of dark matter. We observed that the scale independence of the rotational velocity in the outer region of galaxies could point out to a possible existence of local scale symmetry and therefore the gravitational phenomena inside such regions should be described by the unique

Abstract Although photometric redshift estimation using machine learning (ML) methods is gaining popularity in recent times, almost all previous work has focused on estimating the redshift, \(z\), for \(z < 1\). Few projects, employing state-of-the-art deep learning techniques have worked on a greater range of redshift values. However, the rigorous demand for a large dataset has limited the deep learning

Abstract This paper focuses on the validation of the latest version of the International Reference Ionosphere (IRI-2016) model in predicting the vertical total electron content (VTEC) variation over Ethiopian ionospheric region during a high solar activity (2012-2016) phase. The diurnal, monthly and seasonal VTEC variations were analyzed from dual-frequency global positioning system (GPS) and IRI-2016

Abstract We have analyzed time series of solar wind speed, density, temperature and interplanetary magnetic field observed by ‘Advanced Composition Explorer’ (ACE) at the Earth orbits during solar maximum and minimum using nonlinear time series tools. Evidence for deterministic nonlinearity is present in all solar wind parameters. The dimension of the attractor obtained from each solar wind parameters

We present the results of time-series photometric analysis of 15106 A-K type stars observed by the Kepler space mission. We identified 513 new rotational variables and measured their starspot rotation periods as a function of spectral type and discuss the distribution of their amplitudes. We examined the well-established period-color relationship that applies to stars of spectral types F5-K for all

The ANTARES radiation hydrodynamics code is capable of simulating the solar granulation in detail unequaled by direct observation. We introduce a state-of-the-art numerical tool to the solar physics community and demonstrate its applicability to model the solar granulation. The code is based on the weighted essentially non-oscillatory finite volume method and by its implementation of local mesh refinement

In this study, the hierarchical stability of the seven known large size ratio triple asteroids is investigated. The effect of the solar gravity and primary's J2 are considered. The force function is expanded in terms of mass ratios based on the Hill's approximation and the large size ratio property. The empirical stability parameters are used to examine the hierarchical stability of the triple asteroids

The goal of this conference is to consider whether it is possible within the next few decades to detect Earth-like planets around other stars using telescopes or interferometers on the ground or in space. Implicit in the term "Earth-like" is the idea that such planets might be habitable by Earth-like organisms, or that they might actually be inhabited. Here, I shall address two questions from the standpoint

Models of planetary formation can be tested by comparison of their ability to predict features of our Solar System in a consistent way, and then extrapolated to other hypothetical planetary systems by different choice of parameters. When this is done, it is found that the resulting systems are insensitive to direct effects of the mass of the star, but do strongly depend on the properties of the disk

High resolution interferometer and single-dish observations of young, deeply embedded stellar systems reveal a complex chemistry in the circumstellar environments of low to intermediate mass stars. Depletions of gas-phase molecules, grain mantle evaporation, and shock interactions actively drive chemical processes in different regions around young stars. We present results for two systems, IRAS 05338-0624

Recent observational studies of the chemical composition of circumstellar matter around both high- and low-mass young stellar objects are reviewed. The molecular abundances are found to be a strong function of evolutionary state, but not of system mass or luminosity. The data are discussed with reference to recent theoretical models.

The formation of the gas giant planets Jupiter and Saturn probably required the growth of massive approximately 15 Earth-mass cores on a time scale shorter than the approximately 10(7) time scale for removal of nebular gas. Relatively minor variations in nebular parameters could preclude the growth of full-size gas giants even in systems in which the terrestrial planet region is similar to our own

Studies of element abundances and values of D/H in the atmospheres of the outer planets and Titan support a two-step model for the formation of these bodies. This model suggests that the dimensions of Uranus provide a good index for the sensitivity required to detect planets around other stars. The high proportion of N2 on the surfaces of Pluto and Triton indicates that this gas was the dominant reservoir

An overview is presented of a number of astrometry and astrophysics programs based on radio sources from the Parkes 2.7 GHz catalogues. The programs cover the optical identification and spectroscopy of flat-spectrum Parkes sources and the determination of their milliarc-second radio structures and positions. Work is also in progress to tie together the radio and Hipparcos positional reference frames