Journal of Astrophysics and Astronomy最新文献

The study of exoplanets is one of the fastest-growing areas in astronomy. The number of known exoplanets has increased dramatically, providing new insights into the galaxy’s diversity and abundance of planetary systems. The field has progressed significantly from discovery and characterization to various new areas, including exploring the demographics of exoplanets, examining their atmospheres, investigating the process of planetary formation and evolution, studying the interactions between stars and planets, and searching for signs of life beyond our solar system. These advances are made by drawing expertise from astrophysics, planetary science, atmospheric science, and astrobiology. Recently, there has been a steady growth in the number of Indian astronomers involved in exoplanet research. This exoplanet vision document, prepared under the aegis of ASI, summarizes the field’s current status globally. It also highlights the efforts of various research groups in the country and identifies potential directions for future research. To be able to do competitive exoplanet science within the country, we suggest implementing capacity-building measures in the areas of modeling and theory, establishing new observational facilities, and fostering collaboration within the country and abroad. Specific recommendations of the exoplanet working group are as follows: (1) We identify RV follow-up observations of exoplanets discovered by ongoing and future space-based surveys such as TESS, Gaia, and PLATO as the highest priority areas for the community. We recommend a 4-m class (or large) telescope mounted with a high resolution ((R > rsim 100) K) spectrograph for the RV follow-up and transit spectroscopy studies in the long-term (10–15 yr). In the interim, sufficient time should be made available to the community on the PARAS-2/PRL facility and the upcoming high-resolution spectrograph on DOT/ARIES for these studies. (2) Developing new technology and building state-of-the-art exoplanet instruments for the future 10 m facility class National Large Optical Telescope (NLOT). (3) Leveraging ISRO’s strength in the space program to plan and develop small (e.g., UV, optical, and IR transit payloads) and big space missions (e.g., ExoWorlds) for exoplanet science. (4) Setting up a 1 m class transit telescope for survey and follow-up studies and to have synergy with other observatories for continuous and time-critical observations across different longitudes. (5) Expanding computational resources and augmenting modeling/simulation efforts. (6) Taking the excitement of exoplanet discoveries to the public by integrating it with various outreach and educational activities of the institutes.

Wormholes are hypothetical shortcuts through spacetime, have fascinated cosmologists and theoretical physicists for decades. In this paper, traversable wormholes were studied in the static as well as dynamic backgrounds, with particular stress on cosmic time-dependent wormhole. A concerted effort is made to provide an evolving wormhole shape function, which is both radially (r) and cosmic time (t) dependent. Also, wormholes, which appear as special solutions to the EF equations, are now being viewed as viable interstellar objects. A new matter source, which supplies fuel to construct wormhole spacetime, is provided. Exact wormhole solutions were found in the model under static and dynamic background geometries. It is shown that the exotic matter, which is the necessary ingredient for wormhole physics violate the null and strong energy conditions, but obey the weak and dominant energy conditions marginally in the static case. However, in the dynamic case, the exotic matter, which is the necessary ingredient for wormhole physics, violates the dominant energy conditions, satisfies the null and weak energy conditions partially and fully satisfies the strong energy conditions. Further, stability analysis in each case suggests that the wormhole is traversable in both the cases. Some physical features are briefly discussed in this paper.

A high-precision polarimeter for simultaneous multi-line spectropolarimetric Sun observations is under development at Indian Institute of Astrophysics. Towards this end, we plan to use liquid-crystal retarders as the polarization modulators. A prototype liquid-crystal variable retarder (LCVR) is fabricated and characterized. A solution-processed method is adapted to fabricate the LCVR using commercially available E7 nematic liquid-crystal material. Thickness of the alignment layer of the LC retarder was optimized to achieve uniformity. The fabricated LCVR demonstrates spatial uniformity of retardance comparable to a commercial waveplate. The device is found to have a low-range of operational voltage of <20 V and a very short response time of <1 ms. Also, the device shows consistent operational stability.

By applying a particular kind of modified gravity, we study inflation. Precisely, we extend our investigations beyond Einstein’s gravity to explore the natural inflation model via the term, (F(phi )T). We compute the inflation dynamics to derive the slow-roll parameters, i.e., the tensor-to-scalar ratio r and the scalar spectral index (n_s). This modified form of gravity yields not only the predictions of the original models, but also better fitting with the Planck/BICEP/Keck data.

Time Domain Astronomy (TDA) has ushered in a new era of cosmic exploration. This has been possible with the advanced sensitive surveys that have allowed the discovery and classification of transients to reach unprecedented levels. Over the past decades, numerous classes of stellar transients, including various types of Supernovae (SNe), Novae, Gamma Ray Bursts (GRBs), Electromagnetic counterparts of Gravitational Wave (EMGW) events, Tidal Disruption Events (TDEs), Fast Radio Bursts (FRBs) and many more have been discovered. Of these, detecting the first EMGW event (GW170817/GRB 170817A) and the associated kilonova (AT2017gfo) resulting from a compact object merger stands out as a groundbreaking achievement. A coordinated multi-wavelength approach is crucial for studying these transients, as they exhibit unique behaviours across the different bands of the EM spectrum. This chapter presents an overview of the current understanding and open questions of a few select classes of transients. We highlight the focus areas of TDA in terms of their scientific merit based on existing and future facilities, as well as nationwide and international collaborations. The recommendations made in this chapter are aligned to meet the requirements of all TDA studies.

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.