• Volume 40, Issue 3

June 2019

• First law of black hole thermodynamics for the Kerr black hole using foliation

This article follows a simpler approach (Siddiqui et al. 2011, Chin. Phys. Lett. 28, 050401) using foliation’s concept with virtual displacement of hyper-surfaces near the event horizon to derive the first law of black hole thermodynamics for the Kerr black hole spacetime.

• Impact of light pollution on the visibility of astronomical objects in medium-sized cities in Central Europe on the example of the city of Rzeszów, Poland

This paper discusses the influence of light pollution of the night sky on the conditions of visibility of astronomical objects such as planets, stars and comets. This phenomenon has a huge impact on the observability of astronomical objects, especially in cities, where the brightness of the sky makes it difficult or even impossible to conduct astronomical observations. The main purpose of this article is to measure and analyse the surface brightness of the night sky in Rzeszów and its surroundings. A device called the Sky Quality Meter was used tomeasure the brightness of the night sky. This paper presents measurement results for the years 2015 and 2018, from which it is clear that the quality of the night sky has been deteriorated in terms of the observability of celestial bodies. As an example, the numerical value of the measurement for the centre of Rzeszów has been taken. In 2015, this value was $18.70\pm 1.87$ mag/arcsec$^2$, while in 2018, it was equal to $16.73\pm 1.67$ mag/arcsec$^2$.The results obtained were used to analyse the visibility of celestial bodies. Here, particular attention was paid to the analysis of the visibility of comets (also during the outburst), in the context of increasing light pollution of the night sky. Observers in neighboring villages have also experienced a change in the sky quality from Bortle Class V to Class VII, requiring objects to be approximately one magnitude brighter in order to be visible.

• Accelerating universe with variable EoS parameter of dark energy in Brans–Dicke theory of gravitation

We have investigated the spatially homogeneous and isotropic Friedmann–Robertson–Walker (FRW) universe filled with barotropic fluid and dark energy in the framework of the Brans–Dicke theory of gravitation. Here we have discussed three models: (i) law of variation for Hubble’s parameter, which leads to a constant value of deceleration parameter, (ii) hybrid expansion law model, and (iii) special form of deceleration parameter model. We have found that among all these derived models, the most suitable standard cosmological model according to the recent cosmological observations is the model with special form of deceleration parameter.

• Shannon entropy transfer between solar magnetic modes

Based on Shannon entropy transfer estimation technique and Stanford’s solar global magnetic field harmonic coefficients, several new facts about solar magnetic modes have been found. The entropy transferring between most of the modes has been subjected to a steady modulation with a period near 72 solar rotations (5.38 years). As a rule, the amplitudes of entropy transferring modulation were less or equal to 0.1 bit/solar rotation. These modulations had no relations with intensity or configuration of the solar magnetic fields. Besides,Shannon entropy exchanges have been found between some modes—the sign of dependencies of them. Such modes had sector nature. The influence of a magnetic mode on another is strongest with the delay time between the two modes being twenty to forty solar rotations. Special properties have been revealed for zonal modes also.

• Knowledge discovery through text-based similarity searches for astronomy literature

The increase in the number of researchers coupled with the ease of publishing and distribution of scientific papers (due to technological advancements) has resulted in a dramatic increase in astronomy literature.This has likely led to the predicament that the body of the literature is too large for traditional human consumption and that related and crucial knowledge is not discovered by researchers. In addition to the increased production of astronomical literature, recent decades have also brought several advancements in computational linguistics. Especially, the machine-aided processing of literature dissemination might make it possible to convert this stream of papers into a coherent knowledge set. In this paper, we present the application of computational linguistics techniques to astronomy literature. In particular, we developed a tool that will find similar articles purely based on text content from an input paper. We find that our technique performs robustly in comparisonwith other tools recommending articles given a reference paper (known as recommender system). Our novel tool shows great power in combining computational linguistics with astronomy literature and suggests thatadditional research in this endeavor will likely produce even better tools that will help researchers cope with vast amounts of knowledge being produced.

• Thermal shaping of thin glass panels for hard X-ray telescope optics

We present a process for thermal forming of thin glass panels of borosilicate glass to produce mirror segments for X-ray telescope optics. The mirror segments are required to be shaped in a parabolic and hyperbolic shape in accordance with Wolter-I type design of X-ray telescope optics. Thermal forming of glass is a low-cost method to produce light-weight mirror segments. The process makes use of a semi-cylindrical quartz mold having surface roughness of the order of 1 nm. Flat glass sheets of 0.2 mm and 0.3 mm thickness are placedon the diametric edges of the mold. With a suitable thermal cycle, the glass sheets are thermally formed as per the shape of the mold. The shape of these formed glass sheets was measured using a non-contact optical setup.The surface quality measurements of the formed glass sheets were performed using atomic force microscope and they were found to be in the range of 0.04–0.33 nm. Once tested for acceptance, these glass sheets are coatedusing sputter deposition of multi-layers of high and low atomic number materials for hard X-ray reflection. Such mirror segments do not require polishing of the surface before being coated with multi-layers.

• Hypersurface-homogeneous modified holographic Ricci dark energy cosmological model by hybrid expansion law in Saez–Ballester theory of gravitation

The main motive of this investigation is to study the behavior of cosmological model in the presence of matter and a modified holographic Ricci dark energy for homogeneous hypersurface in the scalar tensor theory of gravitation, proposed by Saez–Ballester (Phys. Lett. A, 113, 467 (1986)). The hybrid expansionlaw (Akarsu et al., JCAP, 01, 022 (2014)) has been used to get a determinate solution. The physical condition that is shear scalar proportional to the expansion scalar is used to obtain the solution of the field equations. Thevarious physical and geometrical aspects of the model are also discussed.

• Study of the cosmic ray intensity in relation to geomagnetic storms and solar interplanetary parameters for solar cycles 21 and 23

This paper comprises the comparative study of the behavior of CRI with geomagnetic storms, southward component of IMF, i.e. $|Bz|$, IMF $B$, solar wind speed ($V$) and $V \cdot |Bz|$ for two consecutive odd solar cycles 21 (1976–1985) and 23 (1996–2008). Our examination arrived at an interesting result that the strongest decrement in CRI occurs around the same time when Dst achieve their minima. The correlation coefficient of Dst with CRI is observed high for both the solar cycles. We have moreover contrasted the profiles of CRI with$B$, $|Bz|$ and $V$ and came to the resolution that the strongest increment in $B$, $|Bz|$ and $V$ happens on the same day when CRI reaches its minimum peak. During the study of CRI with the solar wind speed, we have observedodd behavior for the year 1977 and 2003 with a time lag of one day. We have also found that CRI is highly anti-correlated with $V\cdot |Bz|$ when contrasted with $V$ or $|Bz|$ alone. The correlation coefficient between CRI and $V · |Bz|$ is found to be high and the same ($−$0.8) for the solar cycles.

• Numerical study of singular fractional Lane–Emden type equations arising in astrophysics

The well-known Lane–Emden equation plays an important role in describing some phenomena in mathematical physics and astrophysics. Recently, a new type of this equation with fractional order derivative in the Caputo sense has been introduced. In this paper, two computational schemes based on collocation method with operational matrices of orthonormal Bernstein polynomials are presented to obtain numerical approximate solutions of singular Lane–Emden equations of fractional order. Four illustrative examples are implemented inorder to verify the efficiency and demonstrate solution accuracy.

• # Journal of Astrophysics and Astronomy

Volume 41, 2020
All articles
Continuous Article Publishing mode

• # Continuous Article Publication

Posted on January 27, 2016

Since January 2016, the Journal of Astrophysics and Astronomy has moved to Continuous Article Publishing (CAP) mode. This means that each accepted article is being published immediately online with DOI and article citation ID with starting page number 1. Articles are also visible in Web of Science immediately. All these have helped shorten the publication time and have improved the visibility of the articles.

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019