This study examines Kaniadakis holographic dark energy in the anisotropic and spatially homogeneous Bianchi type-II spacetime, framed within the Brans-Dicke-Rastall theory of gravity. The dark energy model is established by analyzing the correlation between the metric potentials to resolve the model's field equations. This results in a variable deceleration parameter that signifies a shift in the cosmic acceleration rate from deceleration to acceleration. This scenario involves the formulation of numerous cosmological parameters, including the scalar field, equation of state, deceleration, skewness, squared speed of sound, and statefinder parameters. The examination of these characteristics is presented through graphical representation. The examination of the evolution parameter substantiates the notion of holographic dark energy. Furthermore, the statefinder cosmic plane is linked to the lambda RasCDM framework and other recognized dark energy hypotheses.
This paper presents the technical setup and observational results of a solar imaging system deployed at the Astronomical Observatory Belogradchik (AO-Belogradchik). A Celestron C11 Schmidt-Cassegrain telescope, equipped with a DayStar Energy Rejection Filter (ERF) and a Hydrogen Alpha (H-alpha) Quantum filter, was used to capture high-resolution images of solar prominences and sunspots. The optical configuration of the system, including the optimization of the focal ratio (f/31.1) and thermal stabilization, enabled precise H alpha imaging. Angular-resolution calculations (1.83") and linear-resolution (24.9 mu m) confirmed the capability of the system to resolve fine solar features. The results demonstrate the effectiveness of off-axis ERF mounting and pixel binning for CMOS sensor optimization.
We present observations of the H beta emission line of the recurrent nova T CrB, conducted over four nights between August 2023 and July 2024 using the 2.0m RCC telescope at the Rozhen National Astronomical Observatory. By subtracting the red giant contribution from each spectrum, we isolate the double-peaked H beta emission associated with the accretion disc. We measure the peak separation, which varies between 131 and 179 km s(-1). From this, we estimate the average size of the H beta-emitting region within the disc to be R-beta = 45 +/- 11 R-circle dot, corresponding to approximately 55% of the white dwarf's Roche lobe. Comparing with the H alpha emission, we find that the H beta emission originates from a region around the white dwarf that is about half the size of the H alpha-emitting disc.
Gravitational lensing of quasars is a powerful tool for probing cosmological parameters and the internal structure of quasars. In particular, time delays between multiple lensed images provide key constraints on the Hubble constant (H0), contributing to ongoing efforts to resolve the Hubble tension. Using simulated observations from the upcoming Roman Space Telescope, we investigate the impact of flare-induced perturbations on the light curves and time delays of lensed quasar images. Through Monte Carlo simulations, we construct quasar-galaxy systems based on observed redshift distributions and galaxy mass-luminosity functions. Modeling the lensing effect with the Singular Isothermal Ellipsoid (SIE) profile, we examine double, triple, and quadruple quasar configurations. For each case, we compute angular separations, time delays, and time delay differences. Our analysis reveals that within a flare distance range of 10 to 1000 pc, intrinsic quasar variability caused by flares can disrupt correlations between lensed images. Specifically, 22.41% of double quasars and 9.52% of quadruple quasars exhibit no correlation between their light curves due to flare activity. These multiple time delays introduce uncertainties that may impact the precision of cosmological parameter measurements, particularly the determination of H0. These findings underscore the necessity of accounting for quasar variability when applying time-delay cosmography.
We search for periods in a compiled two centuries historical light curve (1823-2023) of eta Carinae in BV band, applying four periodogram methods. The Structure Eminence Function (SEF) marks the positions of the significant repetitive structures (humps in the function), responsible for quasi-periods. Its "derivative"- the Periodograph Function (PGF) makes the humps manifest more clearly, since it is a normalized SEF with subtracted background, which yields a spectrum of the quasi-periods and periods, analogues to the power spectrum of the other methods. The periodogram methods CLEAN and Lomb-Scargle are also used in a comparative framework. Our analysis yields two prominent periods in the selected three data sets-"earlier" included V-band photometry from 1866 to 1926 and "recent" which includes B and V-band photometry from 1963-2023. One of the periods that can be linked to the well established orbital period of the system is conspicuous in all data sets and has value of P-1 = 5.6 +/- 0.1 yr in the "earlier" data and P-1 = 5.7 +/- 0.1 yr in the "recent" data. Since the difference of 0.1 yr between these periods does not depend on the methods we use, it may hint at a period increase over one century. A less prominent period of P-2 = 4.9 +/- 0.1 yr is also detected in the three data sets. This period is well pronounced in all V-band data and less prominent in "recent" B-band data. CLEAN and Lomb-Scargle methods applied on the same three data sets yield results that coincide with the SEF and PGF results. This shorter period may be explained by a geometric effect manifesting in the light curve of eta Car.
According to infrared measurements of the James Webb Space Telescope, there exist very luminous galaxies at distances z similar to 13 that should not exist according to the standard Lambda CDM cosmological model for the flat universe with normalized curvature index k = 0. In this paper, we introduce a spacetime-lens principle that could explain why these very distant galaxies shine so much. We present 10 specific examples showing that the observed large flux luminosities may be mere optical effects due to the positive curvature index k = 1 of an expanding 3-sphere modeling our physical universe in time. For Euclidean or hyperbolic geometries such large flux luminosities seem implausible. This suggests that the right model of a homogeneous and isotropic physical universe for each fixed time instant is a 3-sphere. The angular size of the most frequent fluctuations in the power spectrum of the CMB radiation is about 1(degrees). This enables us to exclude flat and hyperbolic geometries and also indicates that the correct curvature index is k = 1.
In this work, we investigate the mass density - size scaling law in molecular clouds (MCs). This relation reflects the fractal nature of MCs and plays a key role for understanding the physics, structure and evolution of these objects. We make use of the notion "ensemble of MCs", introduced in our previous work (Donkov, Veltchev & Klessen, 2017), in which all MCs with the same probability density function (PDF) of mass density and effective size are represented by an abstract spherical cloud with the same PDF and size. In this spirit, the model is built on the base of abstract scales of the clouds' substructures (which are simply the radii of the spherical object). We consider two forms of the mass density - size scaling law: differential and integral, which in turn reveal the local and the global fractal clouds' structure. Both scaling functions are characterized by their scaling exponents, which can be explicitly expressed by the PDF of mass density, in the general case. Moreover, we derive a first order linear differential equation connecting the two scaling exponents and obtain its exact solution. As examples, we apply this abstract construction to two PDFs: the so called power-law tail and the log-normal. Both have great importance for MC structure and evolution, as the latter corresponds to the earlier stages of clouds' evolution, when supersonic turbulence dominates the physical processes, while the former describes the latest stages of evolution, when star-formation takes place. The obtained results for the scaling exponents in both examples are qualitatively and numerically consistent with respective observations and simulations of MCs.
Asteroid 2020 CD3 is one of the Earth's Temporary Captured Orbiters. This study aims to investigate the dynamical evolution of the asteroid, notably its pre-capture and post-capture phases. The dynamics was analyzed through the framework of Circular Restricted Three-Body Problem with the Sun and the Earth-Moon system as primaries. We investigated the role of invariant manifold from Lyapunov and Halo orbits to the asteroid motion. It shows that the invariant manifold of Lyapunov orbit may play a significant role for guiding the asteroid to enter the Hill region of Earth through the Lagrange point L-1. We also discovered that the invariant manifold of Lyapunov orbit guides the asteroid after the escape process from L-2. In contrast, we found that the asteroid differs from Halo orbit's invariant manifold, both for pre-and post-captured periods.
This report presents a quantitative comparison between confined, eruptive and all (2177) M-class solar flares (SFs) over the last two solar cycles (SC) and separately in SC 23 and 24. The properties of the SFs, related radio bursts and the parent sunspots (Hale type and total area) are examined. The differences are presented and discussed in the framework of space weather.
This paper presents a fully automated data reduction software for the highresolution echelle spectrograph ESpeRo that operates on the 2m-telescope of the Rozhen National Astronomical Observatory, Bulgarian Academy of Sciences. The pipeline applies the standard preprocessing corrections to the observational data, including cosmic ray removal, bias subtraction, and flat-field correction. It further identifies and extracts the echelle orders and calibrates the extracted spectra for wavelength. In addition, it provides the option to normalize the obtained spectra of the individual echelle orders by intensity and to merge them into a continuous one-dimensional spectrum spanning the full spectral range of the instrument.
This article presents the results of our research on a multifaceted Centennial problem of the apparent inability of Newton's gravity to treat observations of galaxies and their hierarchical structure by Kepler's laws. The suspected cause is "Dark Matter" (further, Galactic Dark Matter - GDM), which is invisible but interacts with ordinary matter through Newton's gravity. However, misapplying Newton's theory is not excluded: there are cases demonstrating galactic observations in terms of GDM-free Keplerian orbits. We revisited this problem in all aspects and scrutiny. As a result, we found hidden roots of compromised conceptions of Kepler's orbits and mass-to-light ratio Upsilon. Then we developed an approximate algorithm for treating galactic observations in the Newtonian gravitation framework and demonstrated its success in examples of the Milky Way and other galaxies. Now astronomers believing in the deficiency of Newton's gravity theory can verify its asserted ability to treat galactic observations free of the GDM. We also considered observations on a cosmic scale for a possible interplay of GDM with Cold Dark Matter (CDM) and other parameters of the Lambda-CDM Cosmology. The conclusion is made that GDM and CDM were introduced for different reasons and our results do not necessarily affect the Cosmological Model.
The present paper studies the dynamics of the Friedmann-Lemaitre -Robertson-Walker (FLRW) cosmological model with a decaying vacuum energy density A in the presence of an arbitrary spatial curvature k. Here, we consider three models: Model I-G constant, P boolean AND = constant, Model II: G not equal 0, P Lambda = constant, Model III-G not equal 0, p boolean AND not equal 0. We take A as a function of Hubble parameter H. In Model II since matter is not conserved here, we propose an empirical expression of rho m=f(t)rho oa(3)o /a(3) pm to be Also in Model III, since G not equal 0, G does not remain constant here. So, we varies with time through H through the following relation: G = G.H(-1/m), where Go,m is an element of R and m > 0 The use of these expressions benefit us in expressing various cosmological parameters terms of redshift value z. In the recent years, analysing cosmological parameters graphically with respect to change in redshift 2 has become a vital matter in studying dynamics of the Universe in modern cosmology. Here, we set up the dynamical system out of the field equations by introducing new set of variables for each of the models and analyze the stability of the developed system in each of the models. We find out the fixed points of the system in finite phase plane as well as analysis of stability of fixed points at infinity using Poincare sphere. The perturbation plots for each of the axes are presented and the values of cosmological parameters have been estimated for each of the models. In Cosmological parameters such as the equation of state parameter for dark energy sector w(de), total density parameter rotal, the Hubble parameter H and the deceleration parameter q are obtained as functions of redshift 2 and their plots over redshifts are also provided. From the plot of q with respect to O, we find the value of transition redshift 2. The present values of the above parameters are estimated and they are in agreement with the observational data. For each of the models, we present the testing of the model's parameter space for the present values of H, q, the transition redshift 24 and w(de) for testing the significance of the discrepancy between the theoretically calculated value and the observational data. It is found that all the cosmological models developed in spacetimes of arbitrary spacial curvature support the accelerated expansion phenomena of the evolving Universe.
We have constructed a surrogate model to predict neutron star mass and radius from a three-segment parameterized piecewise polytropic equation of state using an artificial neural network. We have trained the network with the generated data from the fourth-order Runge-Kutta-based solver of the Tolman-Oppenheimer-Volkoff equation. It shows that the neural network predicts the mass-radius with no less than 99% accuracy and significantly reduces the computation time compared to the traditional Runge-Kutta method. However, caution is advised when predicting outside the training data parameter ranges, as the model exhibits poor accuracy in extrapolating data and tends to generate false output values where no stellar solution exists. We have argued that this situation may also occur in other similar neural network-based surrogate models.
We analyse high resolution optical spectra of MWC148 (optical counterpart of the gamma-ray source HESS J0632+057) obtained at Observatoire de Haute Provence and Rozhen Observatory. We measure equivalent widths of 7 diffuse interstellar bands and estimate the interstellar extinction E_{B-V}=0.85 +/- 0.08.
During the last decade and a half, the new generation spectropolarimeter Narval at Pic du Midi, France allowed the study of weak magnetic fields in cool giant stars that are fairly evolved after main sequence. We present a short summary on the recent knowledge on the magnetic fields and activity in giants situated in the upper right part of the Hertzsprung-Russel (H-R) diagram and discuss on the possible mechanisms for magnetic field generation in the asymptotic giants branch (AGB) and post-AGB stars.
T CrB is a symbiotic star that experiences nova outbursts every similar to 80 yr. The next, long-anticipated nova outburst should occur during the 2024-2026 period. Here, we present results of high-resolution optical spectroscopy of T CrB in the period 2016-2023. In these spectra, we measured the equivalent widths of the H alpha, H beta, HeI and HeII emission lines. The maximum equivalent width (EW) was recorded on May 2021, when the EW of H alpha reached-44.6 angstrom and H beta = -21.5 angstrom. At the other extreme, the minimum of EW(H alpha) = -2.9 angstrom was recorded in October 2023. After October 2023, the B-band emission brightened, suggesting a re-appearance of the orbital modulation. In addition to the optical data, we study the X-ray behaviour in the same period. We find a strong correlation between EW(H alpha) and X-ray flux with a correlation coefficient -0.78 and a significance of 2.6 x 10(-5).
This paper analyzes the Three events of Solar Parameters and Interplanetary Coronal Mass Ejections in the maximum phase of Solar Cycle 24 and focuses on the magnetic activity of interplanetary coronal mass ejection during the solar cycle 24. We investigate the magnetic field magnitude (B), Proton temperature (Tp), Proton density (Np). From this study, we find the highest peak of IP (Interplanetary) shocks on disk center MC (Magnetic cloud) events during the solar cycle 24 and also we investigate the magnetic activity of the solar cycle. In this study, we find that the ACE spacecraft shows the fastest coronal mass ejection and highest interplanetary shock wave on solar cycle 24. It is important to note that extreme events can happen at any time during a cycle. In solar cycle 24, from July 13, 2012 to July 15, 2012 largest storm occurred because the magnetic field was -52nT and linear speed was 1500 kms(-1) observed.
In the background of the Saez-Ballester (Saez and Ballester 1986) theory of gravitation, the manuscript presents the study of Renyi holographic dark energy deter-mined through interaction and non-interaction in the anisotropic and spatially homogeneous Bianchi type-Ispace-time. We determine both non-interacting and interacting dark energy models by considering a correlation between the metric potentials to solve the field equations of the model. This results in a dynamical deceleration parameter which demonstrates a shift in the cosmic rate of acceleration from deceleration to acceleration, with a redshift z change that is compatible with observations. Despite assuming several values to parameters w(de) close to -1 at z= 0 (the present epoch) and being in agreement with the most recent observations, the equation of state parameter w(de )for the two Renyi holographic dark en-ergy models displays substantially different dynamic behaviour. Next, we discovered that the squared sound speed, v(s)(2), is negative, implying instability against perturbations. The w(de)-w(de)' plane is constructed to investigate the evolution of the models' EoS parameter turned out to be in a zone of freezing. As should be the case in an expanding universe, the strong energy conditions of the models are violated. Our models include the Chaplygin gas, Lambda CDM limit, and are inclined towards the steady-state model. Statefinders (r, s), and r - q planes were also examined.
This paper investigates a mathematical model of a star formation system, including in-fall of gas from the local environment and out-flow of gas due to supernovae explosions and perturbations. In particular, the objective is to study how the variable density of interstellar components of the system namely atomic, molecular, and stellar components, interact in the star formation cycle. Under special parametric conditions, both limit cycle and stationary state behavior are observed. This indicates a stable star formation cycle in discrete episodes and an unstable star formation cycle converging to a stationary state. Observations of duty cycles under various parameters with varying intensity of supernovae shockwaves for dwarf galaxies, showed that the system adopts a self-regulatory oscillation state beyond a particular value. Analysis of giant galaxies showed decreased oscillatory periods for higher values. This is implied by the low production rate of supernovae in dwarf galaxies, increased production of cold gas, continuation of the cyclic behavior for a longer time. Stronger shockwaves increase the rate of dissipation of gases, resulting in shredding of mass, to get transferred into a precipitous lower mass. Star-forming rate (SFR) of high-mass star systems was found to vary against higher-order perturbations of supernovae shockwave but remained the same in the case of low-mass star systems.
In this paper we have undertaken the study of systems with two radiating primaries in the framework of an elliptic restricted three-body problem, where the orbits of the two massive bodies about each other are assumed to be elliptic and the mass of the third body is negligible. We have made a comparative study of analytical and numerical results for the position of equilibrium points in the case of two binary systems, Eta Cassiopeiae and Gliese 65. We have further studied the Hill's curves and observed the pulsation of the curves with the true anomaly and change in size of the forbidden regions (the size of the interior forbidden region decreases but the region enclosed by the larger boundary enclosing all primaries and equilibrium points increases in size) of motion with change in radiation pressure of the two primaries. We did a study of Basin of Attraction for the planar equilibrium points and found that the size of basins changes (decreases for L (2)- L (5) and increases for L- 1 ) with the value of radiation pressure q (1) of the first primary, whereas the symmetry of the basin of attraction of L (1) was observed to be distorted with decrease in radiation pressure q (2) of the second primary.
