Journal of Astrophysics and Astronomy最新文献

The cross-correlation of two-dimensional digital images is fundamental to solar adaptive optics computations. It can be used in a simple tip-tilt correction system to identify the relative shift between consecutive images and correlating sub-aperture images of a Shack–Hartmann wave-front sensor. The typical frequency of computation is about 1 kHz. While the software-based optimized cross-correlations may be sufficient when a small number of sub-apertures are used in a wave-front sensor, hardware-accelerated (FPGA), correlations may be required when a large number of sub-aperture images are involved, e.g., in the case of the proposed National Large Solar Telescope in India. This paper presents SolarAccel: An FPGA-based acceleration of a basic two-dimensional cross-correlation of two images. We accelerate the FPGA-based design by pipelining the individual components of the cross-correlation process. We implemented our RTL logic on a few sets of (128times 128) pixel images and (32times 32) pixel images on a Xilinx Zynq Ultrascale(+) MPSoC on the ZCU104 FPGA evaluation platform. SolarAccel performs a 2D FFT on a (128times 128) image faster than existing work. The cross-correlation on a (32times 32) image is also faster than the existing work. This demonstrates that FPGA acceleration is beneficial in solar adaptive optics applications.

We have spectroscopically studied the last six stars in the northern sky from our preliminary list of candidates for wide non-coeval pairs, and we have found no evidence of non-coevality. Thus, considering our previous research, which found one such binary system, we confirm that our preliminary estimate of the fraction of binaries in the solar neighborhood formed by capture is no more than  0.03%.

Solar activity, such as sunspots and flares, has a great impact on humans, living beings, and technologies in the whole world. Changes in sunspots will influence high-frequency and space-navigation radio communications. Based on the full-disk, southern and northern hemispheres sunspot areas (SAs) data in 1874–2023 from the Royal Observatory, Greenwich (RGO) USAF/NOAA, extreme value theory (EVT) is applied to predict the trend of the 25th and 26th solar cycles (SCs) in this work. Two methods with EVT, the block maxima (BM) approach and the peaks-over-threshold (POT) approach, are employed to research solar extreme events. The former method focuses on each block’s maximum sunspot areas value and is applied for the generalized extreme value (GEV) distribution. The latter method aims to select the extreme values exceeding a threshold value and is used to obtain the generalized Pareto (GP) distribution. It is the first time that the EVT is applied on the sunspot areas data from the Royal Observatory, Greenwich (RGO) USAF/NOAA. The analysis indicates that the estimated 8-year return levels for sunspot areas are 5701 and 6258 using the two methods, while the estimated 19-year return levels are all 7165. This suggests that the trends of the 25th and 26th solar cycles will be stronger than that of the 24th solar cycle.

Collisionless shocks are generated via the magnetic field mediated by Weibel instability in astrophysical systems. In this work, by performing particle-in-cell (PIC) simulations, Weibel instability-mediated magnetic field amplification is investigated for initially unmagnetized, spatially uniform, counter-streaming electron–positron (e⁻/e⁺) plasma flows and compared with the magnetic amplification for nonuniform counter-streaming e⁻/e⁺ plasma flows by considering their drift velocity of (0.5 c). Our simulation results show that initially, the magnetic field grows exponentially in the linear regime and then decays further after saturation for homogeneous e⁻/e⁺ plasma flows. However, in the case of inhomogeneous counter-streaming e⁻/e⁺ plasma flow, the magnetic field re-amplifies in the post-saturation region after the first saturation. It is found that the amplification magnitude of magnetic field energy in the post-saturation region is related to the density fluctuations for upstream plasma. Our calculations show that temperature anisotropy is the reason behind the second saturation of the magnetic field energy in the case of inhomogeneous plasma distribution. Such inhomogeneous media in astrophysical systems like Gamma-ray bursts are common. Therefore, this study will be useful for understanding collisionless shocks' formation and their effects.

The issue of radiation mechanisms triggered in 1950–60s the first applications of plasma physics to understand the nature of radio galaxies. This interplay has steadily intensified during the past five decades due to the premise of in-situ acceleration of relativistic electrons occurring in the lobes of radio galaxies. This article briefly traces the chain of these remarkable developments, largely from an observational perspective. We recount several observational and theoretical milestones established along the way and the lessons drawn from them. We also present a new observational clue about in-situ acceleration of the relativistic particles radiating in the lobes of radio galaxies, gleaned by us from the very recently published sensitive radio observations of a tailed radio source in the galaxy cluster Abell 1033.

Jupiter family comets, having an orbital period <20 years, allow us to observe their activity and analyze the homogeneity in their coma composition over multiple apparitions. Comet 46P/Wirtanen, with its exceptionally close approach to Earth during its 2018 apparition, offered the possibility for long-term spectroscopic observations. We used a 1.2 m telescope equipped with a low-resolution spectrograph to monitor the comet’s activity and compute the relative abundances in the coma as a function of heliocentric distance. We report the production rates of four molecules CN, C(_2), C(_3) and NH(_2,) and Af(rho ) parameter, a proxy to the dust production, before and after perihelion. We found that 46P has a typical coma composition with almost constant abundance ratios with respect to CN across the epochs of observation. Comparing the coma composition of comet 46P during the current and previous apparitions, we conclude the comet has a highly homogeneous chemical composition in the nucleus with an enhancement in ammonia abundance compared to the average abundance in comets.

Comets are the most primordial objects in our solar system. Comets are icy bodies that release gas and dust when moving close to the Sun. The C/2020 F3 (Near-Earth Object Wide-field Infrared Survey Explorer: NEOWISE) is a nearly isotropic comet moving near-parabolic orbit. The C/2020 F3 (NEOWISE) was the brightest comet in the northern hemisphere after comet Hale–Bopp in 1997 and comet McNaught in 2006. This paper presents the first interferometric high-resolution detection of the comet C/2020 F3 (NEOWISE) using the Giant Metrewave Radio Telescope (GMRT). We detected the radio continuum emission from the comet C/2020 F3 (NEOWISE) with a flux density level 2.84 (±0.56)–3.89 (±0.57) mJy in the frequency range of 1050–1450 MHz. We also detected the absorption line of atomic hydrogen (HI) with a signal-to-noise ratio (SNR) (sim )5.7. The column density of the detected HI absorption line is (N_{textrm{HI}} = (3.46pm 0.60)times (T_{s}/100)times 10^{21},hbox {cm}^{-2}), where we assume the spin temperature (T_{s} = 100) K and filling factor (f = 1). The significant detection of continuum emission from the comet C/2020 F3 (NEOWISE) at (sim )21 cm wavelength indicated that it arose from the large icy grains halo (IGH) region.

Model orbits have been fitted to 27 physical double stars listed in a 1922 catalog. A Markov Chain Monte Carlo technique was applied to estimate best-fitting values and associated uncertainties for the orbital parameters. Dynamical masses were calculated using parallaxes from the Hipparcos mission and are presented in this paper with the estimates of the orbital parameters for the 27 systems. The resulting mass estimates of the current study are in good agreement with a recently published study, as are comparisons with the orbital parameters listed by the Washington Double Star catalog, confirming the validity of the optimization methodology.

A 10–12 m class national large optical-IR telescope (NLOT) is envisaged to meet the growing scientific requirements in astronomy and astrophysics. Telescopes of such dimensions can only be made by segmenting the primary mirror, as it eases a more prominent primary mirror’s fabrication, transportation, operation, and maintenance process. This paper presents the various optical designs analyzed for NLOT that can be fabricated using the India TMT Optics Fabrication Facility (ITOFF) at the Centre for Research and Education in Science and Technology (CREST) campus. We present the primary mirror segmentation details, its ideal optical performance, and study each design’s advantages and technical complexities. Based on the above analysis, we have narrowed it down to an optimal design, and its performance analysis is also discussed.

We studied the timing and spectral properties of the Be/X-ray pulsar Swift J1626.6−5156 using the NICER observations of its 2021 outburst. The most important observation is the positive correlation of the centroid energy of the fundamental cyclotron line with the luminosity. This observation agrees with the usual positive correlation of the centroid energy cyclotron line with luminosity in the sub-critical regime. The correlation between the two quantities is verified using two different continuum models. The photon index decreases with an increase in flux. Thus, the spectrum is softer when the flux is low, which may be due to a decrease in the optical depth of the accretion column with a decrease in the flux.