Behaviour of physical parameters in extended gravity with hyperbolic function

In this paper, we have constructed the cosmological model of the universe in f(R, T) theory of gravity in a Bianchi type \(\mathrm{VI}_h\) universe for the functional f(R, T) in the form \(f(R,T)=\mu R+\mu T\), where R and T are respectively Ricci scalar and trace of energy momentum tensor and \(\mu \) is a constant. We have made use of the hyperbolic scale factor to find the physical parameters and metric potentials defined in the space-time. The physical parameters are constrained from different representative values to build up a realistic cosmological model aligned with the observational behaviour. The state finder diagnostic pair is found to be in the acceptable range. The energy conditions of the model are also studied.     

High-precision stellar abundances of the elements: methods and applications

Efficient spectrographs at large telescopes have made it possible to obtain high-resolution spectra of stars with high signal-to-noise ratio and advances in model atmosphere analyses have enabled estimates of high-precision differential abundances of the elements from these spectra, i.e. with errors in the range 0.01–0.03 dex for F, G, and K stars. Methods to determine such high-precision abundances together with precise values of effective temperatures and surface gravities from equivalent widths of spectral lines or by spectrum synthesis techniques are outlined, and effects on abundance determinations from using a 3D non-LTE analysis instead of a classical 1D LTE analysis are considered. The determination of high-precision stellar abundances of the elements has led to the discovery of unexpected phenomena and relations with important bearings on the astrophysics of galaxies, stars, and planets, i.e. (i) Existence of discrete stellar populations within each of the main Galactic components (disk, halo, and bulge) providing new constraints on models for the formation of the Milky Way. (ii) Differences in the relation between abundances and elemental condensation temperature for the Sun and solar twins suggesting dust-cleansing effects in proto-planetary disks and/or engulfment of planets by stars; (iii) Differences in chemical composition between binary star components and between members of open or globular clusters showing that star- and cluster-formation processes are more complicated than previously thought; (iv) Tight relations between some abundance ratios and age for solar-like stars providing new constraints on nucleosynthesis and Galactic chemical evolution models as well as the composition of terrestrial exoplanets. We conclude that if stellar abundances with precisions of 0.01–0.03 dex can be achieved in studies of more distant stars and stars on the giant and supergiant branches, many more interesting future applications, of great relevance to stellar and galaxy evolution, are probable. Hence, in planning abundance surveys, it is important to carefully balance the need for large samples of stars against the spectral resolution and signal-to-noise ratio needed to obtain high-precision abundances. Furthermore, it is an advantage to work differentially on stars with similar atmospheric parameters, because then a simple 1D LTE analysis of stellar spectra may be sufficient. However, when determining high-precision absolute abundances or differential abundance between stars having more widely different parameters, e.g. metal-poor stars compared to the Sun or giants to dwarfs, then 3D non-LTE effects must be taken into account.     

PS Vir:a short-period solar-like contact binary

We present multi-color photometric observations and a one-dimensional spectrum, acquired from March 2016 to May 2017, for the short-period eclipsing binary PS Vir, by using the 2.16-m,85-cm and 60-cm telescopes at Xinglong station, which is administered by National Astronomical Observatories, Chinese Academy of Sciences. The spectral type was determined as G2V from the onedimensional spectrum. The photometric solution was reduced from BV Rc light curves. The results imply that PS Vir is a W-subtype contact binary with a mass ratio of q = 0.305(±0.008) and a fill-out factor of f = 14.4(±1.8)%. The orbital period may be undergoing a cyclic oscillation with an amplitude of A = 0.0027(±0.0001) d and a modulated period of 11.7(±0.2) yr, which may result from the light-time effect due to a third body. The lower limit on mass for the assumed component is 0.12 M⊙.Moreover, the more massive component of PS Vir may be a bit more evolved star as determined from the mass-luminosity diagram.     

Probing Magnetic Fields with Square Kilometre Array and its Precursors

Origin of magnetic fields, its structure and effects on dynamical processes in stars to galaxies are not well understood. Lack of a direct probe has remained a problem for its study. The first phase of Square Kilometre Array (SKA-I), will have almost an order of magnitude higher sensitivity than the best existing radio telescope at GHz frequencies. In this contribution, we discuss specific science cases that are of interest to the Indian community concerned with astrophysical turbulence and magnetic fields. The SKA-I will allow observations of a large number of background sources with detectable polarization and measure their Faraday depths (FDs) through the Milky Way, other galaxies and their circum-galactic mediums. This will probe line-of-sight magnetic fields in these objects well and provide field configurations. Detailed comparison of observational data (e.g., pitch angles in spirals) with models which consider various processes giving rise to field amplification and maintenance (e.g., various types of dynamo models) will then be possible. Such observations will also provide the coherence scale of the fields and its random component through RM structure function. Measuring the random component is important to characterize turbulence in the medium. Observations of FDs with redshift will provide important information on magnetic field evolution as a function of redshift. The background sources could also be used to probe magnetic fields and its coherent scale in galaxy clusters and in bridges formed between interacting galaxies. Other than FDs, sensitive observations of synchrotron emission from galaxies will provide complimentary information on their magnetic field strengths in the sky plane. The core shift measurements of AGNs can provide more precise measurements of magnetic field in the sub parsec region near the black hole and its evolution. The low band of SKA-I will also be useful to study circularly polarized emission from Sun and comparing various models of field configurations with observations.     

Correlations among color,morphology, and luminosity for the luminous red galaxy (LRG) sample of the SDSS data release 5

We have investigated the correlations among color, morphology and luminosity for all LRGs, cut I LRGs, cut II LRGs, and Main galaxies that are also classified as LRGs. It is found that the morphology of LRGs is tightly correlated with luminosity. The rest-frame u-g color of cut I LRGs and cut II LRGs is nearly independent of luminosity, but the color of Main galaxies is correlated with luminosity. For cut I LRGs and Main galaxies, the early type proportion apparently changes with color: at the rest-frame u-g < 1.3 it increases strongly with increasing color, while at the rest-frame u-g > 1.3 it decreases with increasing color. We also notice that the morphology of cut II LRGs is only a weak function of color. Published in Astrofizika, Vol. 50, No. 3, pp. 335–345 (August 2007).     

Lie group variational integrators for the full body problem in orbital mechanics

Equations of motion, referred to as full body models, are developed to describe the dynamics of rigid bodies acting under their mutual gravitational potential. Continuous equations of motion and discrete equations of motion are derived using Hamilton’s principle. These equations are expressed in an inertial frame and in relative coordinates. The discrete equations of motion, referred to as a Lie group variational integrator, provide a geometrically exact and numerically efficient computational method for simulating full body dynamics in orbital mechanics; they are symplectic and momentum preserving, and they exhibit good energy behavior for exponentially long time periods. They are also efficient in only requiring a single evaluation of the gravity forces and moments per time step. The Lie group variational integrator also preserves the group structure without the use of local charts, reprojection, or constraints. Computational results are given for the dynamics of two rigid dumbbell bodies acting under their mutual gravity; these computational results demonstrate the superiority of the Lie group variational integrator compared with integrators that are not symplectic or do not preserve the Lie group structure.     

Morphologies of AGN host galaxies using HST/ACS in the CDFS-GOODS field

Using HST/ACS images in four bands F435W, F606W, F775W and F850LP, we identify optical counterparts to the X-ray sources in the Chandra Deep Field South in the GOODS South field. A detailed study has been made of these sources to study their morphological types. We use methods like decomposition of galaxy luminosity profiles, color maps and visual inspection of 192 galaxies which are identified as possible optical counterparts of Chandra X-ray sources in the CDFS-GOODS field. We find that most moderate luminosity AGN hosts are bulge dominated in the redshift range (z≈0.4–1.3), but not merging/interacting galaxies. This implies probable fueling of the moderate luminosity AGN by mechanisms other than those merger driven.     

Forecasting the Peak Amplitude of the 24th and 25th Sunspot Cycles and Accompanying Geomagnetic Activity

Forecasting solar and geomagnetic levels of activity is essential to help plan missions and to design satellites that will survive for their useful lifetimes. Therefore, amplitudes of the upcoming solar cycles and the geomagnetic activity were forecasted using the neuro-fuzzy approach. Results of this work allow us to draw the following conclusions: Two moderate cycles are estimated to approach their maximum sunspot numbers, 110 and 116 in 2011 and 2021, respectively. However, the predicted geomagnetic activity shown to be in phase with the peak of the 24th sunspot cycle will reach its minimum three years earlier, then it will rise sharply to reach the 25th maximum a year earlier (i.e., 2020). Our analysis of the three-century long sunspot number data-set suggests that the quasi-periodic variation of the long-term evolution of solar activity could explain the irregularity of the short-term cycles seen during the past decades.     

Evidence of Traveling Waves in Filament Threads

High-resolution Hα filtergrams (0.2″) obtained with the Swedish 1-m Solar Telescope resolve numerous very thin, thread-like structures in solar filaments. The threads are believed to represent thin magnetic flux tubes that must be longer than the observable threads. We report on evidence for small-amplitude (1 – 2 km s⁻¹) waves propagating along a number of threads with an average phase velocity of 12 km s⁻¹ and a wavelength of 4″. The oscillatory period of individual threads vary from 3 to 9 minutes. Temporal variation of the Doppler velocities averaged over a small area containing a number of individual threads shows a short-period (3.6 minutes) wave pattern. These short-period oscillations could possibly represent fast modes in accordance with numerical fibril models proposed by Díaz et al. (Astron. Astrophys. 379, 1083, 2001). In some cases, it is clear that the propagating waves are moving in the same direction as the mass flows.     

Origin of magmatic sulfides in a Proterozoic island arc—an example from the Portneuf–Mauricie Domain,Grenville Province,Canada

The Portneuf–Mauricie Domain (PMD), located in the south-central part of the Grenville province, contains Mesoproterozoic Ni–Cu ± platinum-group element (PGE) prospects hosted in a variety of plutonic intrusions (layered, with simple structures, or zoned) and emplaced in a mature island arc setting. A two-stage model is envisaged to explain the formation of magmatic sulfides. An early loss of a small amount of sulfides in the conduits of primitive, hydrous mantle-derived melts under high fO₂, resulted in depletion of the magmas in chalcophile and precious metals (Cu/Pd ratios vary from initial mantle values up to 1.6 × 10⁶). Then, nearer the mineralized zones, the magmas interacted with sulfide-bearing country rocks, resulting in felsification of the magmas, assimilation of crustal sulfur (δ ³⁴S values up to +5.5‰), and the formation of an immiscible sulfide liquid. Liquid-sulfide formation was followed by variable interactions between the silicate and sulfide magmas, which were responsible for the enrichment of sulfides in Ni, Cu, and, locally, PGE. Indeed, low R factors are found for prospects hosted in intrusions with a simple internal structure and in layered intrusions whereas high R factors are found for prospects hosted in zoned intrusions. Finally, sulfide melt may have been partly incorporated into later pulses of magma and injected into shallow magma chambers to form the PMD prospects. The PMD prospects share common characteristics with other well-known deposits (Aguablanca, Vammala, Stormyrplunen, and deposits in Alaskan/Ural-type intrusions), attesting to the Ni, Cu, and PGE potential of deposits associated with subduction-zone settings.