We present a CCD photometric survey for the search of variable stars in four open clusters namely Berkeley 69, King 5, King 7 and Berkeley 20. The time series observations were carried out for 1 and/or 2 nights for each of the clusters in the year 1998, which have led to identify nineteen variable stars in these clusters. Out of these 19 variable stars, five stars show \(\delta \) Scuti-like variability

The work is the study of Bianchi type-I models with holographic dark energy in the framework of \( f(R) \) theory of gravitation. The exact solutions of the field equations are deduced by considering the exponential and power-law volumetric expansion. Various physical and kinematical properties of the models are discussed. In addition to make our interpretation more clear for that we have taken the

We studied dust acoustic solitary waves (DASW) in a five component cometary plasma by deriving the Kadomstev–Petiashvili (KP) equation. The five components consist of two components of electrons described by kappa distributions with different temperatures and spectral indices, a lighter (hydrogen) and a heavier (oxygen) ion component, both ion components are described by Maxwellian distributions. Dust

Analysis of spectropolarimetric observations of two circular sunspots located close to disk centre in H\({\alpha }\) (6562.8 Å) and Fe i (6569.22 Å) is presented in this paper. The corresponding active region numbers are NOAA 10940 and NOAA 10941 referred to as AR1 and AR2, respectively. The vector magnetic field at the photosphere is derived through inversion of Stokes profiles of Fe i under Milne–Eddington

Ongoing research on pulsar timing array (PTA) to detect gravitational radiation is reviewed. Here, we discuss the use of millisecond pulsars as a gravitational wave detector, the sources of gravitational radiation detectable by PTAs and the current status of PTA experiments pointing out the future possibilities.

We study the distributions of \(\gamma \)-ray properties of a sample of \(\gamma \)-ray loud blazars taken from the third catalogue of blazars detected by Fermi-Large Area Telescope (Fermi-LAT). We compute the \(\gamma \)-ray dominance (\(D_{\mathrm {g}}\)) of the sample which includes 415 flat spectrum radio quasars (FSRQs) and 535 BL Lacertae objects (BL Lacs). We find that BL Lacs and FSRQs are

The study of the solar energetic particle events (SEPs) and their association with solar flares and other activities are very crucial to understand the space weather. Keeping this in view, here we present the study of SEPs (intensity \(\ge 10\) pfu) during the solar cycles 21–24 (1976–2017) in \(> 10\) MeV energy channels associated with solar flares. For our analysis, we have used the data from different

Archival Vilnius CCD photometric observations are presented for the heavily reddened star cluster Melotte 105, resulting in colour-magnitude diagrams and spectral class estimates. There is considerable lack of agreement between studies for reddening, age and distance for this cluster explaining why the archival data are being made available by this paper. The derived reddening \(E(B-V)=0.34\pm 0.04\)

In view of the negative results from various dark matter detection experiments, we propose alternate models by postulating a minimal field strength (minimal curvature) and also a minimal acceleration. These postulates lead to modified Newtonian dynamics, modified Newtonian gravity, and modified relativistic gravity. Through these postulates, we show that the observed flat rotation curves of galaxies

A simulation of the radiation field inside a habitable module (a diameter of 6 m and length of 12 m) of a spacecraft generated by isotropic Galactic Cosmic Radiation (GCR) in deep interplanetary space is carried out for minimum and maximum solar activity using the FLUKA code. Protons, alpha-particles, deuterons, \(^{\mathrm {3}}\)He, and nuclei with \({Z} > 2\) are considered as primary GCR irradiating

Solar flare activity is characterized by different classification systems, both in optical and X-ray ranges. The most generally accepted classifications of solar flares describe important parameters of flares such as the maximum of brightness of the flare in the optical range – \(H_{\alpha }\) flare class (change from F to B), area of the flare in \(H_{\alpha }\) (change from S for areas less than

MHD shock waves and discontinuities are often observed in the solar wind. We studied a strong shock wave event on 7 June 2014, during a solar maximum. The properties of forward shock are investigated and all physical parameters of interplanetary shock are analyzed. The upstream parameters, such as Alfven velocity and sound speed are calculated, and the angle (\({\theta }\)) between the upstream magnetic

The paper deals with the dynamics of particles which are on the surface of the cometary nucleus. The key point is to research the behavior of the particles as a result of local sublimation. Generally, we can describe three mechanisms related to the particles behavior. Relatively small particles (of the order of micrometers) are ejected into the atmosphere of the comet due to sublimation. Slightly larger

The propagation of cylindrical shock wave in rotational axisymmetric perfect gas under isothermal flow condition with azimuthal magnetic field is investigated. Distributions of gas dynamical quantities are discussed. The density, magnetic pressure, azimuthal fluid velocity and axial fluid velocity are assumed to be varying according to power law with distance from the axis of symmetry in the undisturbed

Indian siddhāntic texts are well known for their indigenous approach to solutions of problems in astronomy which also speaks of their expertise in mathematics. The text Sūryasiddhānta is considered as an authority and we come across a number of texts as commentaries on this text. They range from 8th Century CE to 19th century CE. The study of the stars that have been listed in the text appears relatively

We present results of the first time observations of whistlers during day time (sunrise) on 4th January 2017 at 01 UT (\(\hbox {UT} + 5.30 = \hbox {IST}\)) at Indian low latitude ground station Varanasi (geomag. lat. \(14{^{\circ }}55^\prime \hbox {N}\), geomag. long. \(153{^{\circ }}54^\prime \hbox { E}\), L.1.078). The main goal of analysis is to study the propagation characteristic of the observed

The propagation of cylindrical ionizing shock waves in a self-gravitating ideal gas with axial magnetic field is investigated. The density and magnetic pressure are assumed to be varying according to power law with distance in the undisturbed medium. Approximate analytical solutions are obtained by expanding the flow variables in power series. The zeroth order and first order approximate solutions

In this paper, the neutral particle trajectory around a rotating black hole in the four-dimensional Kerr space–time is studied. The equation of motion is derived by using the Kerr metric within the slowly rotating and weak-field limit. The stability conditions of the orbital motion of the neutral particle are deduced. For small amplitude of motion, the approximate solutions of the resulting differential

Dynamical models for dark energy are an alternative to the cosmological constant. It is important to investigate properties of perturbations in these models and go beyond the smooth FRLW cosmology. This allows us to distinguish different dark energy models with the same expansion history. For this, one often needs the potential for a particular expansion history. We study how such potentials can be

We investigate the astronomical almanacs of the Manchukuo state, which lasted for 14 years, from 1932 to 1945. We examine their contents and analyze the accuracy of the time data by using the almanacs for the years from 1933 to 1945. We find that the calendar of the Qing dynasty in China, Shixianshu, provided the name of the almanac. In addition, the reference location of the time data was Xinjing

In standard cosmologies, dark energy interacts only gravitationally with dark matter. An extension to this picture is interacting quintessence (IQ) model where scalar field coupled directly to cold dark matter. The percentage deviation is studied in IQ model with respect to \(\Lambda \)CDM for varied values of the interacting parameter W. We investigated the effect of interaction on matter, kaiser

About \(\sim \)200 radio pulsars have been observed to exhibit nulling episodes – short and long. We find that the nulling fraction of a pulsar does not have any obvious correlation with any of the intrinsic pulsar parameters. It also appears that the phenomenon of nulling may be preferentially experienced by pulsars with emission coming predominantly from the polar cap region, and also having extremely

This review summarizes recent studies of the cold neutral hydrogen gas associated with galaxies probed via the HI 21-cm absorption line. HI 21-cm absorption against background radio-loud quasars is a powerful tool to study the neutral gas distribution and kinematics in foreground galaxies from kilo-parsec to parsec scales. At low redshifts (\(z<0.4\)), it has been used to characterize the distribution