Journal of Astrophysics and Astronomy最新文献

Ultra-Violet Imaging Telescope (UVIT) on board AstroSat is an active telescope capable of high-resolution far-ultraviolet imaging (<1.5('')) and low-resolution ((lambda /delta lambda approx 100)) slitless spectroscopy with a field-of-view as large as (sim ) 0.5(^{circ }). Now almost a decade old, UVIT continues to be operational and generates valuable data for the scientific community. UVIT is also capable of near-ultraviolet imaging (<1.5('')); however, the near-ultraviolet channel stopped working in August 2018 after providing data for nearly 3 years. This paper gives an overview of the latest version (7.0.1) of the UVIT pipeline and UVIT data release version 7. The high-level products generated using pipeline versions having a major ver. no. 7 will be called ‘UVIT data release version 7’. The latest pipeline version overcomes two limitations of the previous version (6.3), namely: (a) inability to combine all episode-wise images; and (b) failure of the astrometry module in a large fraction of the observations. The procedures adopted to overcome these two limitations as well as a comparison of the performance of this new version over the previous one, are presented in this paper. The UVIT data release version 7 products are available at the Indian Space Science Data Center of the Indian Space Research Organization for archival and dissemination from 1 June 2024. New pipeline version is open source and made available on GitHub.

Most reliable parameters are derived when the eclipsing binaries show totality in their light curves. The results of the first photometric studies of seven totally eclipsing marginal contact binaries, conducted using data from ground-based observations and the Transiting Exoplanet Survey Satellite mission are presented in this work. All the binaries are found to be short period ((le )1 d), low mass ratio ((q sim 0.13)–0.25), later spectral class (F, G, K), low total mass ((lesssim )3.0 M(_odot )) and totally eclipsing marginal contact binaries. Spectroscopic studies conducted on three marginal contact binaries, using spectra from the Himalayan Chandra Telescope and Large Sky Area Multi-Object Fibre Spectroscopic Telescope, provide evidence of chromospheric magnetic activity. Period variation studies on three marginal contact binaries (MCBs) indicate mass transfer from secondary to primary components. Characteristic studies conducted using various observed and derived parameters for a comprehensive database of 139 MCBs resulted in grouping the binaries into two classes. The classification characterizes them and explains their evolution in two distinct channels following thermal relaxation oscillation/angular momentum loss (TRO/AML).

We present results of a comprehensive analysis of the polarization characteristics of GRB 200503A and GRB 201009A observed with the Cadmium Zinc Telluride Imager (CZTI) on board AstroSat. Despite these Gamma-ray bursts (GRBs) being reasonably bright, they were missed by several spacecrafts and so far had not been localized well, hindering polarization analysis. We present positions of these bursts obtained from the Inter-Planetary Network and the newly developed CZTI localization pipeline. We then undertook polarization analyses using the standard CZTI pipeline. We cannot constrain the polarization properties for GRB 200503A, but found that GRB 201009A has a high degree of polarization.

This study investigates the response of the horizontal component of the geomagnetic field (H) during the geomagnetic storm of 23–24 April 2023, which was triggered by an Interplanetary Coronal Mass Ejection (ICME). This storm provides a unique opportunity to evaluate the responses in H corresponding to the passage of shock, sheath, and magnetic cloud (MC) structures associated with the ICME. To fulfill this objective, the latitudinal profiles of H-variation are presented for the two distinct cases of the Indian ((75^circ )E) and American ((75^circ )W) sectors. It is found that: (i) latitudinal variances in the phase, amplitude and modulations of H-variation are significant, with amplitude decreasing from mid- to low-latitude, (ii) even though the two longitude sectors had distinct local times throughout the passage of the ICME structures (shock, sheath, and MC), significant storm-induced H-variations of ionospheric/magnetospheric origin are seen, and (iii) H-variation during the passage of sheath and MC region are anomalous, particularly over the Indian longitude sector. The observations showed a reduction of amplitude 350 nT (20:00 UT, April 23) in H-variation at mid-latitude station NVS in the Indian sector during the passage of the CME sheath compared to a reduction of an amplitude of 125 nT (02:45 UT, April 24) during the passage of the MC. These aspects are discussed, and important insights on the response of the terrestrial H-component corresponding to the arrival of different structures in ICME are presented.

From a careful visual scrutiny of the radio structures of a well-defined sample of 2428 sources in the LoTSS-DR2 survey made at 144 MHz with a (6'') beam, we have selected a subset of 25 (i.e., 1%) sources showing highly unusual radio structures, mostly not conforming to the prevalent radio morphological classification. Here, we present and briefly discuss the basic properties of these rare morphological outliers and attempt to dissect their morphological peculiarities based on multi-wavelength radio images and radio-optical overlays. Also, we underscore the need to accord due importance to such anomalous radio sources, considering the challenge they pose to the standard theoretical models and simulations of extragalactic double radio sources.

The evolution of the Universe together with galaxies, is one of the fundamental issues that we humans are most interested in. Both the observations of tidal streams from SDSS and the theory of (Lambda )CDM support the hierarchical merging theory. The study of high redshift celestial bodies contributes to a more in-depth study of cosmology. The LAMOST low-resolution search catalog DR11 v1.0 has released 11,939,296 spectra, including 11,581,542 stars, 275,302 galaxies and 82,452 quasars, and so on. The data of 28,780 stellar population synthesis of galaxies and some high redshift quasars are used to do a preliminary statistical research. We selected the data with small errors for analysis and obtained some basic statistical conclusions. Older galaxies have relatively larger stellar velocity dispersions. The larger the metallicity, the greater the stellar velocity dispersion. These statistical results are reasonable and consistent with previous work. Because the stellar velocity dispersion is driven by the total mass of a galaxy at the first order and more massive galaxies have older ages and greater metallicities. The spectra of high redshift quasars show clear Gunn–Peterson trough and Lyman-(alpha ) forest. The identified emission lines and high redshift celestial spectra released by LAMOST, can be used for cosmological research.

Our solar system, consisting of the Sun, planets, Moons, asteroids, and comets, along with gas, dust, ice, and radiation, is a very complex and dynamic system. Globally, planetary, astronomy, and small-body exploration programs have made great strides in understanding the formation and evolution of stellar systems while also providing detailed views of individual bodies. The forthcoming decades offer immense opportunities for planetary exploration from space and observations from ground telescopes that portend to very significantly expand not only the horizons of human exploration but also provide a more fundamental understanding of the evolutionary pathways that led to the myriad diversity in our Solar System. The past, present, and future of the solar system also serve as a Rosetta stone to decipher the physics, chemistry, and biology of the exo-planetary systems. Here, we recommend solar system exploration objectives for the decade and beyond in the context of current global developments in the field and research groups in India.

We study the effect of gravitational clustering at small scales on larger scales by studying mode coupling between virialized halos. We build on the calculation by Peebles (1974), where it was shown that a virialized halo does not contribute any mode coupling terms at small wave numbers k. Using a perturbative expansion in wave number, we show that this effect is small and arises from the deviation of halo shapes from spherical and also on tidal interactions between halos. We connect this with the impact of finite mass resolution of cosmological N-Body simulations on the evolution of perturbations at early times. This difference between the expected evolution and the evolution obtained in cosmological N-Body simulations can be quantified using such an estimate. We also explore the impact of a finite shortest scale up to which the desired power spectrum is realized in simulations. Several simulation studies have shown that this effect is small compared to the effect of perturbations at large scales on smaller scales. It is nevertheless important to study these effects and develop a general approach for estimating their magnitude. This is especially relevant in the present era of precision cosmology. We provide basic estimates of the magnitude of these effects and their power spectrum dependence. We find that the impact of small-scale cutoff in the initial power spectrum and discreteness increases with ((n+3)), with n being the index of the power spectrum. In general, we recommend that cosmological simulation data should be used only if the scale of non-linearity, defined as the scale where the linearly extrapolated rms amplitude of fluctuations is unity, is larger than the average inter-particle separation.

Galaxies, clusters, and the intergalactic medium (IGM) are the essential and interconnected components of the cosmic ecosystem. Galaxies, with their diverse morphologies and stellar populations, are the building blocks of cosmic structure, harboring stars, gas, dust, cosmic rays, magnetic fields, and dark matter. Galaxy clusters, immense gravitational unions of galaxies, offer profound insights into galaxy formation, cosmology, and the nature of dark matter. Bridging these cosmic islands is the IGM, a vast expanse of primordial gas enriched with traces of heavy elements. It harbors the majority of cosmic baryons distributed within an intricate network of filaments and voids. Together, galaxies, clusters, and the IGM offer a holistic view of the cosmic architecture, each playing a unique role in shaping the universe’s grand design. Indian scientists have made substantial contributions to research on galaxies, clusters, and the IGM, both theoretical and observational. To pursue and advance such contributions at par with the international level, the astronomical community emphasizes the urgent requirement for access to cutting-edge ground-based and space-based observatories and computing facilities. Access to state-of-the-art observational and computing facilities will sustain ongoing endeavors and enable Indian scientists to remain at the forefront of advancements in these fields, fostering continued relevance and innovation in astronomy research.

Radio detection of cosmic rays investigates the electromagnetic component of extensive air showers. It is possible to obtain the most critical properties of a cosmic ray, including the depth of shower maximum, energy, and type of primary particle, from radio measurements. Semnan University Radio Array is a new experiment that strives to detect radio emissions from extensive air showers induced by ultra-high energy cosmic rays. To fully harness the potential of the radio detection method in a self-trigger setup, it is essential to have artificial digital and analog filters to eliminate major unwanted emissions, analog-to-digital converters with appropriate specifications for accurate signal reconstruction, and data processing units capable of implementing software-based analysis alongside advanced digital signal processing techniques. This paper describes the design and implementation of a self-triggering approach in SURA-4 as the first phase of the SURA experiment to preserve cosmic ray candidates while removing unwanted emissions by utilizing the capabilities of analog and digital elements and incorporating a custom software framework for radio signal analyses. The ultimate validation of this approach for reliably distinguishing cosmic rays from anthropogenic radio frequency interferences will be pursued in future experiment phases, including cross-verification with three particle detectors.