Journal of Astrophysics and Astronomy最新文献

Accurately determining the origin of radio emissions is essential for numerous scientific experiments, particularly in radio astronomy. Conventional techniques, such as antenna arrays, encounter significant challenges, especially at very low frequencies, due to factors like the substantial size of the antennas and ionospheric interference. To address these challenges, we employ a space-based single-telescope that utilizes co-located antennas complemented by goniopolarimetric techniques for precise source localization. This study explores a novel and elementary machine learning technique to improve and estimate direction of arrival (DoA), leveraging a tri-axial antenna arrangement for radio source localization. Employing a simplistic emission and receiving antenna model, our study involves training an artificial neural network (ANN) using synthetic radio signals. These synthetic signals can originate from any location in the sky and cover an incoherent frequency range of 0.3–30 MHz, with a signal-to-noise ratio between 0 and 60 dB. A large synthetic data set was generated to train the ANN model catering to the possible signal configurations and variations. After training, the developed ANN model demonstrated exceptional performance, achieving loss levels in the training (({sim }0.02)), validation (({sim }0.23%)), and testing (({sim }0.21%)) phases. The machine learning-based approach, remarkably, exhibits substantially quicker inference times (({sim }5) ms) in contrast to analytically derived DoA methods, which typically range from 100 ms to a few seconds. This underscores its practicality for real-time applications in radio source localization, particularly in scenarios with a limited number of sensors.

There are different categories of Indian astronomical texts ranging from theoretically complex ones to simple practical manuals. The texts pertaining to vākya system are the ones which provide simplified algorithms to compute different astronomical quantities using vākyas. Vākyas (or mnemonics) are simple phrases/sentences in which numerical values—associated with an astronomical parameter–are encoded. Since these are meaningful phrases, it is very easy to memorize them and reproduce the numerical values quickly–without any errors. In this paper, by taking an example of Bhūpajñādi-vākyas, we shall demonstrate that the system is very efficient in terms of practical utility without compromising the accuracy.

Although the star-formation process has been studied for decades, many important aspects of the physics involved remain unsolved. Recent advancements in instrumentation in the infrared, far-infrared, and sub-millimeter-wavelength regimes have contributed to a significantly improved understanding of processes in the interstellar medium (ISM) leading to star formation. The future of research on the ISM and star formation looks exciting with instruments like the JWST, ALMA, etc., already contributing to the topic by gathering high-resolution high-sensitivity data and with several larger ground- and space-bound facilities either being planned or constructed. India has a sizable number of astronomers engaged in research on topics related to the ISM and star formation. In this white paper invited by the Astronomical Society of India to prepare a vision document for Indian astronomy, we review the Indian contributions to the global understanding of the star-formation process and suggest areas that require focused efforts both in creating observing facilities and in the theoretical front in India, to improve the impact of our research in the coming decades.

Since recent years, mass segregation driven by two-body relaxation in star clusters has been proposed to be measured by the so-called dynamical clock, (A^+), a measure of the area enclosed between the cumulative radial distribution of blue straggler stars and that of a reference population. Since star clusters spend their lifetime immersed in the gravitational potential of their host galaxy, they are also subject to the effects of galactic tides. In this work, I show that the (A^+) index of a star cluster depends on both its internal dynamics in isolation and the effects of galactic tides. Mainly, I focused on the largest sample of open clusters harboring blue straggler stars with robust cluster membership. I found that these open clusters exhibit an overall dispersion of the (A^+) index in diagnostic diagrams, whereas Milky Way globular clusters show a clear linear trend. However, as also experienced by globular clusters, (A^+) values of open clusters show some dependence on their galactocentric distances, in the sense that clusters located closer or farther than (sim )11 kpc from the Galactic center have larger and smaller (A^+) values, respectively. This different response to two-body relaxation and galactic tides in globular and open clusters, which happen concurrently, can be due to their different masses. More massive clusters can protect their innermost regions from galactic tides more effectively.

The mega-parsec scale radio relics at the galaxy cluster periphery are intriguing structures. While textbook examples of relics posit arc-like elongated structures at the clusters’ peripheries, several relics display more complex structures deviating from the conventional type. Abell 115 is a galaxy cluster hosting an atypical radio relic at its northern periphery. Despite the multi-wavelength study of the cluster over the last decades, the origin of the radio relic is still unclear. In this paper, we present a multi-frequency radio study of the cluster to infer the possible mechanism behind the formation of the radio relic. We used new 400 MHz observations with the uGMRT, archival VLA 1.5 GHz observations, and archival LOFAR 144 MHz observations. Our analysis supports the previous theory on the relic’s origin from the passage of a shock front due to an off-axis merger, where the old population of particles from the radio galaxies at the relic location has been re-energized to illuminate the 2 Mpc radio relic.

Phosphorus (P) is an important element for the chemical evolution of galaxies and many biochemical reactions. Phosphorus is one of the crucial chemical compounds in the formation of life on our planet. In an interstellar medium, phosphine ((hbox {PH}_{3})) is a crucial biomolecule that plays a major role in understanding the chemistry of phosphorus-bearing molecules, particularly phosphorus nitride (PN) and phosphorus monoxide (PO), in the gas phase or interstellar grains. We present the first confirmed detection of phosphine ((hbox {PH}_{3})) in the asymptotic giant branch (AGB) carbon-rich star IRC(+)10216 using the Atacama Large Millimeter/Submillimeter Array (ALMA) band 6. We detect the (J = 1_{0}-0_{0}) rotational transition line of (hbox {PH}_{3}) with a signal-to-noise ratio (SNR) of (ge )3.5(sigma ). This is the first confirmed detection of phosphine ((hbox {PH}_{3})) in the ISM. Based on LTE spectral modeling, the column density of (hbox {PH}_{3}) is ((3.15pm 0.20)times 10^{15}) (hbox {cm}^{-2}) at an excitation temperature of (52pm 5) K. The fractional abundance of (hbox {PH}_{3}) with respect to (hbox {H}_{2}) is ((8.29pm 1.37)times 10^{-8}). We also discuss the possible formation pathways of (hbox {PH}_{3}), and we claim that (hbox {PH}_{3}) may be created via the hydrogenation of (hbox {PH}_{2}) on the grain surface of IRC(+)10216.

We report the measurement of X-ray polarization in the high synchrotron peaked blazar 1ES 1959(+)650. Of the four epochs of observations from the Imaging X-ray Polarimetry Explorer, we detected polarization in the 2–8 keV band on two epochs. From the model-independent analysis of the observations on 28 October 2022, in the 2–8 keV band, we found the degree of polarization of (Pi _X = 9.0 pm 1.6)% and an electric vector position angle of (Psi _X = 53 pm 5) deg. Similarly, from the observations on 14 August 2023, we found (Pi _X) and (psi _X) values as (12.5 pm 0.7)% and (20 pm 2) deg, respectively. These values are also in agreement with the values obtained from spectro-polarimetric analysis of the I, Q, and U spectra. The measured X-ray polarization is larger than the reported optical values, ranging between 2.5% and 9% when observed from 2008 to 2018. Broadband spectral energy distribution constructed for the two epochs is well described by the one-zone leptonic emission model with the bulk Lorentz factor ((Gamma )) of the jet larger on 14 August 2023 compared to 28 October 2022. Our results favor the shock acceleration of the particles in the jet, with the difference in (Pi _X) between the two epochs being influenced by a change in the (Gamma ) of the jet.

Pulsating variables play a significant role in shaping modern astronomy. Presently it is an exciting era in observational study of variable stars owing to surveys like OGLE and TESS. The vast number of sources being discovered by these surveys is also creating opportunities for 1–2-m class telescopes to provide follow-up observations to characterize these. We present some initial observations of type-II cepheids from the Mt. Abu observatory and highlight the need for dedicated observing runs of pulsating variables. We also present optical designs for several suggested instruments for the Mt. Abu observatory that will contribute towards this goal. We present designs that are fairly simple and yet take due benefit of the unique telescopes and facilities present at the observatory.

Torsional Alfvén waves (TAWs) play a significant role in the dynamics of the solar atmosphere. A detailed study of the TAWs can provide valuable insights into various aspects of the internal structure of the solar atmosphere, and the coronal heating problem. In this paper, the effect of longitudinal structuring (such as gravitational stratification, temperature inhomogeneity, radiative cooling, and background plasma flow) on the characteristics of the standing TAWs in coronal plasma loops, which can be exploited in both temporal and spatial coronal seismology applications, is investigated. The governing equation for TAWs in a dynamic and stratified coronal plasma is reduced to a time-dependent partial differential equation. Analytical dispersion relations of the differential equation are extracted and solved numerically under various scenarios by imposing the necessary and sufficient boundary conditions. The numerical results indicate that the fundamental and first overtone mode frequencies and their ratios and the spatial anti-node shift of the first overtone mode are sensitive functions of gravitational stratification and scaled time of radiative cooling. The magnitude values of these quantities are strongly influenced by the magnitude of the temperature inhomogeneity parameter and are slightly affected by the scaled background plasma flow speed. Tuning the parameters that affect the oscillatory properties of the standing TAWs and matching them with observations can enhance our understanding of the coronal structures and their evolution and serve as a diagnostic tool in coronal seismology.

Several powerful flare events have been recorded because of long-term monitoring on the RT-22 radio telescope (Simeiz) of the galactic source G25.65(+)1.05 from 2000 to 2024. The amplitude of the most powerful flare increased rapidly and reached a record level for this source of 130 kJy. The orbital (7.5 years) and precessional (60 years) periods in the binary system of massive O5 class stars responsible for the occurrence of flares based on monitoring data have been presumably determined. Individual short flares, lasting no more than a month, presumably belonged to a maser in an unsaturated state. The shape of the central part of the maser line, near the maximum phase, suggests a single-component source responsible for the bulk of the increase in flux density. Thus, the most powerful kilomaser G25.65(+)1.05 in the water vapor line at frequency 22.2 GHz has been registered in the Galaxy. The possibility of detecting gravitational waves (GWs) coming from the massive stellar binary system is considered.

The active galactic nucleus S 0528(+)134 was discovered in a search survey at a frequency of 8550 MHz in 1969 using the radio telescope RT-22 (Simeiz) at the Crimean Astrophysical Observatory—the study aimed to search for new active galactic nuclei (AGN). In this article, the goal was to determine the physical characteristics of the close binary system S 0528(+)134 for the subsequent assessment of the level of gravitational radiation coming from it. During long-term monitoring of the object at a frequency of 8 GHz, some powerful flares of flux density occurred, which made it possible to consider the source the most powerful emitter in the Universe. The presence of selected harmonic components in the flux density variations of S 0528(+)134 allowed obtaining the main physical characteristics of a binary system of supermassive black holes (SMBHs), which placed S 0528(+)134 in the rank of one of the most massive SMBHs. This AGN can also be considered the most powerful source for detecting GWs by using International Pulsar Timing Array gravitational wave detectors.