Abstract: Publication date: Available online 14 January 2020Source: New AstronomyAuthor(s): Anirudh Pradhan, Vipin Chandra Dubey, Umesh Kumar SharmaAbstractIn this paper, we have obtained general exact solutions of the Einstein’s field equations from the use of conharmonically flat space in relation to a isotropic and spatially homogeneous Friedmann-Robertson-Walker(FRW) model by taking Granda and Oliveros IR cut-off and also by considering the cosmological scale factor in the form of hybrid expansion law (HEL). We investigated the derived model with the help of evolutionary trajectories of deceleration parameter, equation of state (EoS) parameter, energy densities of matter and dark energy, energy density parameters of matter and dark energy, for which model shows suitable behaviour. We also study classical stability of the model by analyzing the squared sound speed, which shows that the model is stable initially. For dynamical analysis of the model, the statefinder diagnostic and ωD−ωD′ pair analysis were performed. Additionally, we also plan to reconcile the dark energy by a method of reconstructing the evolution of the scalar field potential. For this analysis, we take into account the quintessence field for this reconstruction.

Abstract: Publication date: Available online 14 January 2020Source: New AstronomyAuthor(s): N. Hulke, G.P. Singh, Binaya K. Bishi, Ashutosh SinghAbstractA flat FLRW (Friedmann-Lemaitre-Robertson-Walker) cosmological model with perfect fluid comprising of variable Chaplygin gas (VCG) has been studied in the context of f(R, T) gravity with particle creation. The solutions of the modified field equations are obtained through three different considered form of scale factors. The effective pressure is negative throughout the evolution of universe, which leads to accelerated expansion of the universe. In addition to that we have also discussed the importance of particle creation pressure on the cosmological parameters, energy conditions and state-finder diagnostic parameters. It is noticed that the time evolution of source function yields almost constant particle production at late times.

Abstract: Publication date: Available online 14 January 2020Source: New AstronomyAuthor(s): Yehia Abdel-Aziz, A.M. Abdelaziz, S.K. Tealib, Gamal Attia, Igor Molotov, Sergei SchmalzAbstractIn March 2019 the first dedicated of optical observation of space debris and artificial satellites (Optical Satellites Tracking Station (OSTS)) in Egypt has been performed by National Research Institute of Astronomy and Geophysics (NRIAG) at Kottamia Observatory. The 0.28 m Telescope is used for tracking and surveying debris and operational satellites at Low Earth Orbit (LEO), High ellipse orbit (HEO) and the Geosynchronous Earth Orbit (GEO). OSTS has also collaborated with International Scientific Optical Network (ISON) for optical observation. The necessary programs to control the telescope, camera and monitoring process are configured. Coordinate corrected metric data is provided with the time information. The system has validated and calibrated processing. The first results of the observations with image processing using Apex-2 software are presented. The optical observations using OSTS are being used to help characterize the debris environment in LEO, HEO and GEO to assist in the modeling projections for space debris database, real population and distribution, detection and orbital determination, and conjunction analysis between operational satellites and/or dangers debris.

Abstract: Publication date: Available online 13 January 2020Source: New AstronomyAuthor(s): Dinesh Chandra MauryaAbstractIn this paper, we have investigated a flat FLRW (Friedmann Lemaitre Robertson Walker metric) cosmological model in f(R, T) gravity with specific Hubble parameter. We have considered f(R,T)=f(R)+2f(T) where f(R)=R+αR2, f(T)=λT and R is Ricci scalar, T the trace of energy momentum tensor. To obtain exact solutions of modified Einstein’s field equation, we have considered a specific Hubble parameter H(a)=l(a−n+k) which gives the scale factor a(t)=[ekln(t+m)−1k]1n where n > 0, k, l, m are arbitrary constants called model parameters. With this scale factor, we have obtained a transit phase cosmological model with variable deceleration parameter (DP). We have compared our results with observational constraints obtained from various observations by using the curve-fitting techniques and found that the derived model is a transit dark energy model quintessence (ω>−1) at present (ω0≈−0.7406) and approaches to cosmological constant value (ω=−1) at late time universe. The transition point is found as ztc≈0.676 which is in good agreement with the recent observations. Also, the derived model explains formation of different structures in the universe from past to present scenarios.

Abstract: Publication date: May 2020Source: New Astronomy, Volume 77Author(s): P.K. Sahoo, S. BhattacharjeeAbstractThe energy densities of dark matter (DM) and dark energy (DE) are of the same order at the present epoch despite the fact that both these quantities have contrasting characteristics and are presumed to have evolved distinctively with cosmic evolution. This is a major issue in standard ΛCDM cosmology and is termed “The Coincidence Problem” which hitherto cannot be explained by any fundamental theory. In this spirit, Bisabr (2010) reported a cosmological scenario in f(R) gravity where DM and DE interact and exchange energy with each other and therefore evolve dependently. We investigate the efficiency and model independancy of the technique reported in Bisabr (2010) in addressing the Coincidence problem with the help of two f(R) gravity models with model parameters constrained from various observations. Our result confirm the idea that not all scalar-tensor gravity theories and models can circumvent the Coincidence Problem and any cosmological scenario with interacting fluids is highly model dependent and hence alternate model independent theories and ideas should be nominated to solve this mystery.

Abstract: Publication date: May 2020Source: New Astronomy, Volume 77Author(s): V.P. KozhevnikovAbstractI performed photometric observations of the poorly studied cataclysmic variable IPHAS J013031.89+622132.3 and discovered very deep eclipses. I obtained observations over 14 nights for a total time of 50 hours during a time span of 6 months. Thanks to the long observation interval, I determined the orbital period with high precision, Porb=0.14935014±0.00000020 d. I derived the eclipse ephemeris, which, thanks to the precision of the orbital period, has a formal validity of 300 years. The average eclipse depth was 1.88 ± 0.07 mag. The prominent parts of the eclipses were smooth and symmetrical. The average eclipse width, including extended asymmetric eclipse wings, was 0.18 ± 0.01 phases or 40 ± 2 min. The average orbital light curve did not show a prominent orbital hump. Because no dwarf nova outburst occurred during the 6 months of monitoring, this cataclysmic variable is likely to be a nova-like variable.

Abstract: Publication date: Available online 30 December 2019Source: New AstronomyAuthor(s): Koijam Manihar Singh, Sanjay Mandal, Longjam Parbati Devi, P.K. SahooAbstractAbstract: Taking up four model universes we study the behaviour and contribution of dark energy to the accelerated expansion of the universe, in the modified scale covariant theory of gravitation. Here, it is seen that though this modified theory may be a cause of the accelerated expansion it cannot totally outcast the contribution of dark energy in causing the accelerated expansion. In one case the dark energy is found to be the sole cause of the accelerated expansion. The dark energy contained in these models come out to be of the ΛCDM type and quintessence type comparable to the modern observations. Some of the models originated with a big bang, the dark energy being prevalent inside the universe before the evolution of this era. One of the models predicts big rip singularity, though at a very distant future. It is interestingly found that the interaction between the dark energy and the other part of the universe containing different matters is enticed and enhanced by the gauge function ϕ(t) here.

Abstract: Publication date: Available online 27 December 2019Source: New AstronomyAuthor(s): Diana P. Kjurkchieva, Velimir A. Popov, Nikola I. PetrovAbstractPhotometric observations of four totally-eclipsing W UMa binaries, NSVS 6673994, NSVS 4316778, PP Lac and NSVS 1926064, are presented. Their global parameters were determined from the light curve solutions and GAIA distances. The main results are as follows: (i) NSVS 6673994, NSVS 4316778 and PP Lac are of W subtype while NSVS 1926064 is of A subtype; (ii) The mass ratios of NSVS 4316778 and NSVS 1926064 are close to the lower mass-ratio limit; (iii) NSVS 4316778 has double contact configuration while NSVS 1926064 is in deep contact; (iv) The changes of the PP Lac period seem cyclic and are accompanied with episodes of essentially constant value; (v) The relations between the global parameters of the four W UMa stars differ considerably from those of Main Sequence (MS) stars. The deviations of the radii, temperatures and luminosities of the stellar components from those of MS stars with the same masses are bigger for the two targets with extremely small mass ratio.

Abstract: Publication date: Available online 21 November 2019Source: New AstronomyAuthor(s): Kamsali Nagaraj, Praveen Kumar Basuvaraj, S.C. Chakravarty, Praveen Kumar KAbstractThe exospheric composition data of Mars for the period 2014-15 has been extracted and analysed using the observations carried out by the MENCA (Mars Exospheric Neutral Composition Analyser) payload on-board the Mars Orbiter Mission (MOM) launched by India. The latitude, longitude, altitude and solar zenith angle coverage of the partial pressure values of different exospheric constituents are determined and assigned to create a new data-set with orbit-wise data assimilation particularly between 260 and 600 km altitude range. Apart from getting the results on mean individual orbits’ partial pressure profiles, the variations of the total as well as partial pressures are studied with respect to the distribution of the major atmospheric constituents and their dependence on solar activity. In particular, CO2 and O variations are considered together for any differential effects due to photolysis and photo-ionisation. The results on the gradual reduction in densities due to decreasing daily mean sunspot numbers and strong response of CO2 and O pressures to solar energetic particle events like that of 24 December, 2014 are presented.

Abstract: Publication date: Available online 6 November 2019Source: New AstronomyAuthor(s): Jacques P ValléeAbstractThe density wave theory predicted some physical offsets among different tracers of star formation. To test this prediction, here we compiled data on 40 galaxies searched observationally for a physical offset between spiral arm tracers, and found that 24 of them have a positive offset. In a spiral arm, an arm tracer in a region with a given temperature may be at a different location (offset) than an arm tracer in a region with a colder temperature.Some conditions are found to be necessary or sufficient in order to detect an offset between two arm tracers. To find the offset of a tracer from another tracer, one needs a proper linear resolution. Starting in the dust lane and going across the spiral arm, we seek the observed physical width of the star-forming zone (offset). In our sample of 24 galaxies with measured offsets, we find offsets with a median value near 326 pc and a mean near 370 pc. These offsets are comparable to those found in our Milky Way galaxy, between the cold diffuse CO 1-0 gas set at 0 pc, and the hot dust near 350 pc.Preliminary statistics are performed on the angular velocity of the gas and stars and angular velocity of the spiral pattern. Their observed orbital velocity of 200 km/s at a typical galactic radius near 4 kpc yields an angular speed of the gas and stars near 60 km/s/kpc. Their deduced angular rotation for the spiral pattern averages 36 km/s/kpc. These observational results are close to the results predicted by the shock-induced star-forming density wave theory. These mean or median property values will be useful for finding other galaxies that can support density waves.

Abstract: Publication date: Available online 6 November 2019Source: New AstronomyAuthor(s): Bin Zhang, Sheng-Bang Qian, Miloslav Zejda, Jing-Jing Wang, Qi-Jun Zhi, Ai-Jun Dong, Wei Xie, Li-Ying Zhu, Lin-Qiao JiangAbstract1SWASP J204932.94-654025.8 (hereafter J2049) is a newly discovered eclipsing binary system with an orbital period of 0.2299103 days. BVRc light curves (LCs) are presented and analyzed by using the 2013 version of the Wilson-Devinney (W-D) program. Because the observed LCs are asymmetric, a hot star-spot was employed on the secondary component during our analysis. We found that J2049 is a W-subtype shallow contact eclipsing binary system with an orbit inclination of 62∘.69 ± 0∘.95 and a mass ratio of q =1.326 ± 0.056. More importantly, we found the presence of a strong third light, with an average luminosity contribution of 31.3% of the total light. Based on times of the light minima, the orbital period changes of J2049 are studied for the first time, and there is no evidence for any significant dp/dt now. Considering the presence of the third light and the short time span of the eclipse times, more observations are needed in the future.

Abstract: Publication date: Available online 5 November 2019Source: New AstronomyAuthor(s): M. Wolf, M. Mašek, P. Zasche, H. Kučáková, K. HornochAbstractA dozen of new precise times of eclipses were measured for the eclipsing binary DX Cygni as a part of our long-term observational project for studying neglected eclipsing binaries with a short orbital period. Based on a current O−C diagram, we found for the first time that its period is increasing (dP/P=1.68×10−7 day/years) and that times of minima show also significant cyclical changes with a period of about 16 years, caused very probably by a third body orbiting the eclipsing pair. The minimal mass of this companion is 0.49 M⊙. The light curve solution in Phoeberesults to the typical Algol-type semidetached configuration where the secondary fills its Roche lobe. The temperature of primary component was fixed to T1=5300 K according to its spectral type, which gives us T2=3330±20 K for the secondary. The photometric mass ratio was estimated q=0.504±0.012.We also compare orbital parameters of selected known Algol-type eclipsing binaries with proven mass transfer and a third body.

Abstract: Publication date: Available online 25 October 2019Source: New AstronomyAuthor(s): A. Narayan, A. Chakraborty, A. DewanganAbstractThis paper deals with the stability analysis of the triangular equilibrium points for the generalized problem of the photogravitational restricted three body where both the primaries are radiating. The problem is generalized in the sense that the eccentricity of the orbits and the oblateness due to both the primaries and infinitesimal are considered. The stability in the case of linear resonance are analyzed based on the Floquet’s theory for finding the characteristic exponent for a system containing periodic coefficients. It was found that the critical value of μ for the stability boundary for parametric excitation is dependent on the oblateness of the primaries as well as infinitesimal.

Abstract: Publication date: Available online 18 October 2019Source: New AstronomyAuthor(s): Emad. A.-B. Abdel-Salam, Mohamed I. NouhAbstractLane –Emden differential equation of the polytropic gas sphere could be used to construct simple models of stellar structures, star clusters and many configurations in astrophysics. This differential equation suffers from the singularity at the center and has an exact solution only for the polytropic index n=0,1and5. In the present paper, we present an analytical solution to the fractional polytropic gas sphere via accelerated series expansion. The solution is performed in the frame of conformable fractional derivatives. The calculated models recover the well-known series of solutions whenα=1. Physical parameters such as mass-radius relation, density ratio, pressure ratio and temperature ratio for different fractional models have been calculated and investigated. We found that the present models of the conformable fractional stars have smaller volume and mass than that of both the integer star and fractional models performed in the frame of modified Rienmann Liouville derivatives.

Abstract: Publication date: Available online 12 October 2019Source: New AstronomyAuthor(s): Soumyodipta Karmakar, Surajit Chattopadhyay, Irina RadinschiAbstractThe present paper reports a study of the reconstruction of f(R) gravity from holographic Ricci dark energy, a specific case of Nojiri-Odintsov holographic DE (ref Nojiri and Odintsov (2005a), S. Nojiri, S. D. Odintsov, Phys. Rev. D 72 023003 (2005)), in the presence of bulk viscosity. The reconstructed equation of state (EoS) parameter wR was found to have a transition from quintessence to phantom in the absence of the bulk viscosity. Thus, the behaviour of wR for this reconstruction scheme was identified as “quintom” in the absence of the bulk viscosity. However, in the case of the bulk viscous scenario wR behaves like “quintessence”. Furthermore, the generalized second law of thermodynamics was tested in the case of the reconstructed f(R) gravity. Finally, the stability of this model against small perturbations was demonstrated with the aid of squared speed of sound.

Abstract: Publication date: Available online 28 August 2019Source: New AstronomyAuthor(s): F. Davoudi, S.J. Jafarzadeh, A. Poro, O. Basturk, S. Mesforoush, A. Fasihi Harandi, MJ. Gozarandi, Z. Zare Mehrjardi, P.D. Maley, S. Khakpash, K. Rokni, A. SarostadAbstractPhotometric observations of exoplanet transits can be used to derive the orbital and physical parameters of an exoplanet. We analyzed several transit light curves of exoplanets that are suitable for ground-based observations whose complete information is available on the Exoplanet Transit Database (ETD). We analyzed transit data of planets including HAT-P-8 b, HAT-P-16 b, HAT-P-21 b, HAT-P-22 b, HAT-P-28 b and HAT-P-30 b using the AstroImageJ (AIJ) software package. In this paper, we investigated 82 transit light curves from ETD, deriving their physical parameters as well as computing their mid-transit times for future Transit Timing Variation (TTV) analyses. The Precise values of the parameters show that using AIJ as a fitting tool for follow-up observations can lead to results comparable to the values at the NASA Exoplanet Archive (the NEA). Such information will be invaluable considering the numbers of future discoveries from ground and space-based exoplanet surveys.