New Astronomy最新文献

In 2012, Brazil began the studies to send its first deep space exploration mission, ASTER, which would be the first mission to orbit a triple asteroid system, 2001 SN263. We aim to contribute to the ASTER mission by defining the parameters of a multispectral camera system that will be used to study the asteroid system 2001 SN263, through software simulations that should help planning the data collection. We inserted the shape model of the objects in the software POV-Ray and modeled two cameras, a Wide Angle (WAC) and a Narrow Angle (NAC). We inserted the asteroid's parameters and simulated the satellite position. We created various scenes so we could obtain a good view of the asteroid. Alpha is entirely visible only in the WAC images, while the NAC is expected to reveal surface details. Beta seems relatively small in the WAC images, whereas we obtain a broad view from the NAC at 100 km distance. Gamma, smaller than Beta, should provide more detailed images through the NAC, whereas the WAC images should be able to show its inclined orbit around Alpha. To see Gamma behind Alpha in its revolution movement, we would have to elevate the camera's orbit. The method employed to simulate images generated by satellite cameras can be applied to other scenarios where the target requires imaging, extending beyond the field of planetary geology.

In this paper, we study the curved Krori–Barua spacetime geometry to describe compact stars with two components: dark and ordinary matter, using a two-fluid model approach. We choose the equation of state derived from the rotational curves of galaxies for dark matter and the polytropic equation of state for ordinary matter. The physical requirements for a realistic compact star are satisfied using specific parameters. For the polytropic index $\eta =2$, we find the values of observed masses, reported in our previous investigation (Mafa et al., 2020).

Recent observational evidence confirms the weak-collision dynamics of hot optically thin accretion flows around Sgr A${}^{\ast }$ and other nearby galactic nuclei. As a result, thermal conduction as a diffusion process can transfer the heat by electrons in a collisionless magnetized plasma. While most of the previous analytical studies consider the azimuthal viscosity, the recent studies indicated that the radial viscosity strongly affects the properties of the advection dominated accretion discs. So, in this paper, we explore the roles of two parts of anisotropic thermal conduction (parallel and perpendicular) and radial viscosity in the hot accretion disc by considering axisymmetric and steady state assumptions in the presence of outflows that can transport energy from accretion disc outward. We use the set of self-similar solutions to solve the basic equations in our present model. Our solutions reveal that transverse thermal conduction as a cooling mechanism, leads to reductions in gas temperature, disc thickness, and accretion velocity of the disc, whereas the disc rotates at a fast rate. Moreover Our solutions indicate that the perpendicular thermal conduction and the radial viscosity have opposite behavior in the physical variables of the disc. Also, our results have indicated that the anisotropic thermal conduction is significant in the parameter space of radial viscosity, outflow in the regions that the physical constraints $t_{in}\ge t_{\perp ,con}$ and $q_{\parallel ,con}⩽q_{\perp ,con}$ are satisfied.

We present spectroscopic observations of Nova Cas 2020 (V1391 Cas) obtained using the Russian Turkish Telescope during different stages of its 2020 outburst. We followed the spectral evolution of the nova until it entered the nebular phase. The expansion velocity of the ejecta reached $\sim 780{\mathrm{km\; s}}^{-1}$. The fluxes of the neutral [O I] lines at wavelengths 6300, 6364, and 5577 $\text{̊A}$ were used to calculate the electron temperature and the mass of neutral oxygen in the ejecta. We found average values $T_e=\mathrm{4890}K$, $M_{\mathrm{OI}}=\mathrm{2.54}\times {\mathrm{10}}^{\mathrm{-5}}{M}_{\odot }$ which are consistent with the values calculated for other novae. We modeled the nova’s ejected envelope 515 days after its discovery and found that the log elemental abundances by number relative to Hydrogen of the envelope are He = −0.7, C = −5.5, O = −2.5, N = −2.0 and Ne = −4.0.

we explored the holographic dark energy model using Hubble’s Horizon as the infrared (IR) cut-off in Locally Rotationally Symmetric (LRS) Bianchi type-I, considering the $f\left(R\right)$ gravity framework in our analysis. In order to solve the field equations, we assume a relation $F\propto a^m$ and volumetric power law expansion (where $m$ is constant). we have expressed various crucial cosmological parameters in terms of the redshift $z$ and depicted them graphically to enhance our understanding of the expansion and evolution of the universe like holographic dark energy density (${\rho }_{\Lambda }$), holographic dark energy pressure ($p_{\Lambda }$), equation of state parameter ($\omega$) , total energy density parameter ($\Omega$) etc. Also, we analyzed the stability of the universe in our model through the squared speed of sound test and its validity by energy conditions. Ultimately, our model indicates that the universe is currently in an expanding phase, exhibiting an accelerating phase, closely approaching a flat geometry, and its behavior resembles that of a quintessence dark energy model.

In attempts to resolve the neutron lifetime puzzle, there was suggested a hypothetical decay of neutrons into some unspecified dark matter (DM) particles. Later there were performed studies on how the hypothetical decay of neutrons would affect neutron stars. Recently it was shown that with the allowance for the second solution of Dirac equation for hydrogen atoms, the theoretical branching ratio (BR) for the two-body decay of neutrons (compared to their three-body decay) is amplified by a factor of 3300 from 0.000004. So, the BR becomes about 1.3% in the excellent agreement with the “experimental” BR = (1.15 ± 0.27)% required for reconciling the two distinct experimental values of the neutron lifetime: one from the beam experiments, another from the trap experiments. This meant that the two-body decay of neutrons in the beam experiments (that count only the protons) plays a much more sizable part in the overestimation of the lifetime of neutrons in these experiments than previously thought. Hydrogen atoms corresponding to the second solution of Dirac equations are called the second flavor of hydrogen atoms (SFHA) by the analogy with the flavors of quarks. The existence of the SFHA is evidenced by four different types of atomic/molecular experiments. The primary feature of the SFHA is that due to having only the s-states, they do not emit or absorb the electromagnetic radiation (except for the 21 cm line): they are practically dark. The SFHA became a candidate for a part of DM for the first time after the SFHA-based successful qualitative and quantitative explanation of the perplexing observation by Bowman et al. of the anomalous absorption in the redshifted 21 cm line from the early Universe. In the present paper we analyzed how this neutron decay into the SFHA affects neutron stars. We showed that old neutron stars could very slowly generate the new specific, described in detail baryonic DM in the form of the SFHA. Some old neutron stars would release it into their tiny atmospheres, while some other old neutron stars would release it into the interstellar medium. Besides, mergers of a neutron star with another neutron star or with a black hole, accompanied by the ejection of neutron-rich material, can also lead to the formation of SFHA as the ejecta cools down. This is another interesting aspect of the multi-messenger astronomy focused on studying these mergers through the gravitational waves they generate. These mechanisms of generating new baryonic DM in the universe should have the fundamental importance. We point out the indirect observational evidence of the continuing generation of new baryonic DM. We hope that our results will stimulate a further research in this direction.

The objective of this article is to study topologically charged Eddington-inspired Born–Infeld (briefly, EiBI) gravity spacetime. It is proved that the topologically charged EiBI spacetime executes different types of pseudosymmetry, viz. Ricci generalized pseudosymmetry as $R\cdot R=Q(S,R)$, Ricci generalized projectively pseudosymmetry as $P\cdot R=\frac{2}{3}Q(S,R)$, pseudosymmetry due to conformal curvature as $C\cdot C=-\frac{(r^2{\alpha }^2+2ϵ{\alpha }^2-r^2)}{6r^4}Q(g,C)$ and pseudosymmetry due to conharmonic curvature as $K\cdot K=-\frac{({\alpha }^2-1)}{2r^2}Q(g,K)$. Also, we have exhibited the linear dependence of $Q(g,C)$ and $Q(S,C)$ on the difference $(C\cdot R-R\cdot C)$. Moreover, it is exhibited that the topologically charged EiBI spacetime is an Einstein manifold of level 3, 2-quasi Einstein, conformal 2-forms are recurrent, Ricci 1-forms are recurrent and generalized Roter type. As a special case, we have acquired the geometric structures of point-like global monopole (briefly, PGM) spacetime and topologically charged Ellis Bronnikov Wormhole (briefly, TCEBW) spacetime. Also, we have explored that the topologically charged EiBI spacetime possesses almost $\eta$-Ricci-Yamabe soliton, almost $\eta$-Ricci soliton, and for a certain condition it admits almost Ricci soliton. Further, it is also verified that such a spacetime reveals generalized curvature inheritance and for a particular condition it admits