Journal of Astrophysics and Astronomy最新文献

This article addresses key open questions in the Milky Way and neighboring galaxies, focusing on utilizing stars and stellar populations to trace galaxy formation and evolution processes. It offers an overview of the current landscape based on community-contributed white papers and outlines emerging research avenues alongside specific observational strategies relevant to the Indian context. Recent advancements in observations, such as precision astrometry from Gaia and asteroseismology enabled by Kepler, have reinvigorated interest in stellar physics, including its role in characterizing exoplanet atmospheres and understanding planet formation and evolution. Upcoming projects like the Rubin Observatory (LSST) and future large spectroscopic surveys will significantly enhance our ability to study stellar populations across various galaxies. These efforts will improve our understanding of dark matter distribution in galaxies, galaxy formation, and their evolution. Furthermore, by studying galaxies within the local volume, researchers can delve into the history of the formation of low-mass dwarf galaxies, the most common type of galaxy in the Universe. The local volume presents an excellent opportunity to test theories of hierarchical galaxy formation and assembly, especially since high-redshift observations of these galaxies’ formation epochs are beyond the reach of current telescopes. Therefore, this article seeks to summarize the current understanding and chart a path forward for the field.

A revised catalogue of 310 Galactic supernova remnants (SNRs) and some statistics on their properties are presented. 21 SNRs have been added to the catalogue since the previously published version from 2019, and 5 entries have been removed, as they have been identified as H ii regions. Also discussed are some basic statistics of the remnants in the catalogue, the selection effects that apply to the identification of Galactic SNRs and their consequences.

We attempt to find the impact of a modified Tolman Oppenheimer Volkoff (TOV) system of equations on the luminosities of direct photons and axions for a specific axion mass in the presence of a magnetic field. We employ two different equation-of-states (EoSs), namely APR and FPS, to generate the profiles of mass and pressure for spherically symmetric and non-rotating neutron stars (NSs). We then compute the axions emission rates by the Cooper-pair-breaking and formation (PBF) process in the core using the NSCool code. We also examine the possibility of an axion-to-photon conversion in the magnetosphere of NSs. Furthermore, we investigate the impact of the magnetic field on the actual observables, such as the energy spectrum of axions and axion-converted photon flux for three different NSs. Our comparative study indicates that the axion energy spectrum and axion-converted photon flux change significantly due to an intense magnetic field.

Gas volume density is one of the critical parameters, along with dispersions in magnetic field position angles and non-thermal gas motions, for estimating the magnetic field strength using the Davis–Chandrasekhar–Fermi (DCF) relation or through its modified versions for a given region of interest. We present VolDen an novel python-based algorithm to extract the number density map from the column density map for an elongated interstellar filament. VolDen uses the workflow of RadFil to prepare the radial profiles across the spine. The user has to input the column density map and pre-computed spine along with the essential RadFil parameters (such as distance to the filament, the distance between two consecutive radial profile cuts, etc.) to extract the radial column density profiles. The thickness and volume density values are then calculated by modeling the column density profiles with a Plummer-like profile and introducing a cloud boundary condition. The cloud boundary condition was verified through an accompanying N-PDF column density analysis. In this paper, we discuss the workflow of VolDen and apply it to two filamentary clouds. We chose LDN1495 as our primary target owing to its nearby distance and elongated morphology. In addition, the distant filament RCW57A is selected as the secondary target to compare our results with the published results. Upon publication, a complete tutorial of VolDen and the codes will be available via https://github.com/aa16oaslak/volden.

A time series of high-resolution spectra in the optical wavelength region was used to examine the variability of physical parameters of the early-stage post-AGB star IRAS 22272(+)5435. Excitation balance analysis for a sample of iron (Fe), cerium (Ce), and neodymium (Nd) lines confirms effective temperature changes from about (5100pm 150) to (5750pm 100) K during the 132-day pulsation cycle. Using the method of ionization balance, we observed a minor change in surface gravity between (log g= 0.5) and (0.7pm 0.3) (cgs). The microturbulent velocity does not change within the uncertainty limits, (xi _t=4.5pm 0.5) km s(^{-1}). Large macroturbulence in the range of 20–25 km s(^{-1}) was found. We observed variable intensity of the oxygen (O) infrared triplet at 7771-5 Å  which is most likely due to changes in luminosity during the pulsation cycle.

In this study, cosmic rays (CR) data from the King Abdulaziz University muon detector in Jeddah (Rc  = 14.8 GV), Saudi Arabia, were utilized to investigate the amplitude and phase components of diurnal variations in CR muons. The data covered the period from 2007 to 2012 and were fitted using a single cosine function with a 24-h period and two cosine functions with periods of 24 h and 12 h, respectively. The distributions of the phases and amplitudes resulting from these fits were analyzed across different time spans.

The findings of this analysis provided valuable insights into the diurnal characteristics of CR muons. The mean amplitude and phase obtained from the single fit were reported as −0.11 ± 0.51% and 11:00 ± 4.30 UT, respectively. Furthermore, employing the two-cosine fit revealed that the first phase had a mean occurrence time of 06:00 ± 6.90 UT, accompanied by an amplitude of −0.10 ± 0.62%. The second phase occurred at 13:00 ± 3.51 UT, with an amplitude of 0.11 ± 0.25%. The study observed diverse distributions and trends in amplitude and phase values across different time scales, including months, seasons, and years.

Additionally, the study investigated the influences of five solar activity parameters on the diurnal CR components using Pearson linear, non-parametric Spearman, and Kendall correlations. These parameters included the interplanetary magnetic field, solar wind speed, Kp index, Dst index, and solar radio flux at 10.7 cm. The results revealed that the relationships between solar activity variables and the diurnal CR parameters were not uniform. There were varying degrees of correlation, with differences in strength and magnitude depending on the specific variable and correlation coefficient being examined.

Sūryasiddhānta is an important astronomical treatise, which is very popular even now in the entire Indian sub-continent. Like other astronomical texts, Sūryasiddhānta describes the procedure to compute different astronomical parameters. However, the procedure to compute the planetary true positions for a given day (as per mid-night reckoning system) and place need to be applied independently for different planets. In this study, we are presenting a mathematical model for the computation of the true positions (nirāyana longitudes) of the planets at any given instant of time of the day for any desired place. This mathematical model is based on the algorithm presented in the Sūryasiddhānta with some modifications such as the usage of the fractional part of the ahargaṇas. The planetary positions or the longitudes of the planets are computed for the Sunrise of Mandi, Himachal Pradesh, and are compared with the Stellarium values (nirāyana – Nirāyana longitude values are obtained by applying the Precision of Equinox correction to the Stellarium Ecliptic (sāyana) longitudes.) to study the accuracy of the results obtained from the mathematical model.

Forbush decreases (Fd) are transient, short-term reductions in the intensity of galactic cosmic rays that reach the Earth’s surface. When this reduction is observed at multiple locations simultaneously, it is referred to as simultaneous Forbush decreases (SFd). Identifying Fd events in daily averaged cosmic ray (CR) raw data is always tedious, but the task has gone minimal through an algorithm (automated Fd detection). We deployed an automated Fd location algorithm on daily-averaged CR data from five neutron monitor stations covering 1998–2006. We identified 80 days with the most simultaneous events. While there exists extensive research on the subject using a case study approach, the current study is statistical. Whereas most of the previous investigations employed a small sample of Fds manually selected from a single CR station, large samples of Fds selected after disentangling the Sun’s influence on CR data from multiple neutron monitors (NMs) are used. The connection between the Fds and many solar-terrestrial variables is tested. The beautiful and consistent results obtained between the space weather variables and Fds at the five NM stations call the attention of space weather researchers to the need for rigorous, detailed, and accurate cataloging of Fds. Solar cycle oscillation significantly impacts the amplitude and timing of Fds. Its influence should be removed before Fd selection.

Active galaxies hosting radio jets can exhibit distinct active phases marked by two sets of radio lobes. Typically, these episodic radio sources have been identified through morphological observations. In addition, spectral characteristics-based methods are also employed wherever multi-frequency deep radio observations are available. However, these methods are inefficient in detecting restarted radio sources that do not exhibit a clear morphology. To address this, a method of using the spectral curvature (({{textrm{SPC}}} = alpha ^{1400~{textrm{MHz}}} _{150~{textrm{MHz}}}-alpha ^{150~{textrm{MHz}}} _{74~{textrm{MHz}}})) to identify restarted radio sources is presented. This is based on the fact that restarted radio sources with significant remnant emission are expected to have concave spectra in contrast to the convex or straight spectra observed in most radio sources. We use available wide area radio surveys in the range of frequencies from 74 MHz to 1.4 GHz to search for episodic radio sources and to shortlist 9,405 sources based on the criteria of ({textrm{SPC}} ge 0.5 ). The candidates thus identified can be followed up for detailed morphological and spectral index studies. This method will find application in the automated identification of episodic radio sources in large radio sky surveys from telescopes like LOFAR and SKA.

Contributions from the Indian gravity community have played a significant role in shaping several branches of astronomy and astrophysics. This document reviews some of the most important contributions and presents a vision for gravity research in the context of astronomy and astrophysics in India. This is an expanded version of one of the chapters in the recently released Vision Document of the Astronomical Society of India.