Journal of Astrophysics and Astronomy最新文献

Molecular clouds are the prime locations of star formation. These clouds contain filamentary structures and cores which are crucial in the formation of young stars. In this work, we aim to quantify the physical properties of structural characteristics within the molecular cloud L1251 to better understand the initial conditions for star formation. We applied the getsf algorithm to identify cores and filaments within the molecular cloud L1251 using the Herschel multi-band dust continuum image, enabling us to measure their respective physical properties. Additionally, we utilized an enhanced differential term algorithm to produce high-resolution temperature maps and column density maps with a resolution of ({13.5}''). We identified 122 cores in the region. Of those, 23 are protostellar cores, 13 are robust prestellar cores, 32 are candidate prestellar cores (including 13 robust prestellar cores and 19 strictly candidate prestellar cores), and 67 are unbound starless cores. getsf also found 147 filament structures in the region. Statistical analysis of the physical properties (mass (M), temperature (T), size and core brightness (hereafter, we are using the word luminosity (L)) for the core brightness) of obtained cores shows a negative correlation between core mass and temperature and a positive correlation between (M/L) and (M/T). Analysis of the filaments gives a median width of 0.14 pc and no correlation between width and length. Out of those 122 cores, 92 are present in filaments ((sim ) 75.4%) and the remaining were outside them. Out of the cores present in filaments, 57 ((sim ) 62%) cores are present in supercritical filaments ((M_textrm{line}>16 M_{odot }/textrm{pc})).

In this work, an exact solution of Einstein’s field equations in isotropic coordinates for anisotropic matter distribution is obtained by considering a particular metric choice of metric potential (g_{rr}). To check the feasibility of the model, we have investigated all the physical characteristics of a realistic star. It is found that the model is potentially stable, and the adiabatic index is greater than (frac{4}{3}). The model has been analyzed for compact star 4U 1538-52.

Molecular clouds are prime locations to study the process of star formation. These clouds contain filamentary structures and cores, which are crucial sites for the formation of young stars. The star-formation process has been investigated using various techniques, including polarimetry, for tracing magnetic fields. In this small review-cum-short report, we put together the efforts (mainly from the Indian community) to understand the roles of turbulence and magnetic fields in star formation. These are two components of the ISM competing against gravity, which is primarily responsible for the collapse of gas to form stars. We also include attempts made using simulations of molecular clouds to study this competition. Studies on feedback and magnetic fields are combined and listed to understand the importance of the interaction between two energies in setting the current observed star formation efficiency. We have listed available and upcoming facilities with the polarization capabilities needed to trace magnetic fields. We have also stated the importance of ongoing and desired collaborations between Indian communities and facilities abroad to shed more light on the roles of turbulence and magnetic fields in the process of star formation.

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.

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.