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.
