Journal of Astrophysics and Astronomy最新文献

Spatial, kinematic, and orbital properties, along with ages and chemical compositions of the thin disc, thick disc, and various stellar substructures in the halo, are studied based on data from the LAMOST and Gaia surveys. The star formation in the Galactic thin and thick disc, with peak metallicities of − 0.20 and − 0.45 dex, is found to have peaked about 5.5 and 12.5 Gyr ago, respectively. The thin disc is also found to have experienced an initial star formation burst about 12.5 Gyr ago. The pro-grade population Splash and hot-disc (HD), with peak metallicity of about − 0.60 and − 0.43, are found to be about 13.03 and 12.21 Gyr old, respectively, with peak eccentricity of 0.70 and 0.35, are understood to be of in situ origin. The Gaia-Enceladus/Sausage (GE/S), Thamnos and Sequoia, with peak metallicity of about − 1.31, − 1.36, and − 1.56, are found to be about 11.66, 12.89, and 12.18 Gyr, respectively, and are understood to be remnants of dwarf galaxies merged with the Milky Way. The HD, Splash, and Thamnos have experienced chemical evolution similar to the thick disc, while GE/S, Sequoia, and Helmi stream have experienced distinct chemical enrichment of iron and (alpha )-process elements.

Determination of cosmological parameters is a major goal in cosmology at present. The availability of improved data sets necessitates the development of novel statistical tools to interpret the inference from a cosmological model. In this paper, we combine the principal component analysis (PCA) and Markov Chain Monte Carlo (MCMC) method to infer the parameters of cosmological models. We use the No U-Turn Sampler (NUTS) to run the MCMC chains in the model parameter space. After determining the observable by PCA, we replace the observational and error parts of the likelihood analysis with the PCA reconstructed observable and find the most preferred model parameter set. To demonstrate our methodology, we assume a polynomial expansion as the parametrization of the dark energy equation of state and plug it into the reconstruction algorithm as our model. After testing our methodology with simulated data, we apply the same to the observed data sets, the Hubble parameter data, Supernova Type Ia data, and the Baryon acoustic oscillation data. This method effectively constrains cosmological parameters from data, including sparse data sets.

This paper presents a comprehensive analysis of 30 ks Chandra and 46.8 ks (13 h) 1.4 GHz GMRT radio data on the cool-core cluster RXCJ0352.9(+)1941 to investigate AGN activities at its core. This study confirms a pair of X-ray cavities at projected distances of about 10.30 and 20.80 kpc, respectively, on the NW and SE of the X-ray peak. GMRT L band (1.4 GHz) data revealed a bright radio source associated with the core of this cluster hosting multiple jet-like emissions. The spatial association of the X-ray cavities with the inner pair of radio jets confirms their origin due to AGN outbursts. The 1.4 GHz radio power (7.4 pm 0.8 times 10^{39}) erg s(^{-1}) is correlated with the mechanical power stored in the X-ray cavities (({sim }7.90times 10^{44}) erg s(^{-1})), implying that the power injected by radio jets in the ICM is sufficient enough to offset the radiative losses. The X-shaped morphology of diffuse radio emission seems to be comprised of two pairs of orthogonal radio jets, likely formed due to a spin-flip of jets due to the merger of two systems. The X-ray surface brightness analysis of the ICM in its environment revealed two non-uniform, extended spiral-like emission structures on either side of the core, pointing towards gas sloshing due to a minor merger. It might have resulted in a cold front at (sim )31 arcsec (62 kpc) with a temperature jump of 1.44 keV.

We have studied two manuscripts as commentaries called Laghu Mānasa Vyākhyā and titled grahaṇānayanam. Our attempts to decipher the contents have revealed that they are commentaries in Sanskrit (the script is Kannada) on the 9th century manuscript called Laghu Mānasa by Munjalācarya. These two manuscripts have solved examples of eclipses of śaka 1528 (1606CE) and 1549 (1627CE); the procedure gives all the details to get the mean positions of the Sun, the Moon, and the nodes and subsequently, the timings and magnitude of eclipses. The first text is incomplete; the second has complete calculations. With the details provided for the procedure, we find that the method for finding the sine is unique and differs from that of Bhaskarācārya and Ganeśha Daivajnya. We present the calculations, verify them, and compare them with online software computations. The agreement is within the error limits of observations.

Solar loops are hot and magnetic structures that often have transverse displacements. In this research, we study the characteristics of three solar loops using the images observed in the radiation region with the Hinode/XRT telescope on 11 September 2017. Fluctuations of solar loops can be traced using two methods: image and spectral processing. In the first method, displacements and disturbances are measured in images, while in the second method, periodic patterns are searched in Doppler shifts by spectrometers. Our analysis method is based on image processing and solar loop seismology. In this method, the time slices can be prepared from the images and then analyzed using the wavelet method. The measurement results of time series for three loops with lengths of 113040, 79128, and 62800 km were obtained in the range of 3–18, 3–6, and 3–16 min, respectively. The phase velocity of these oscillations was calculated in the range of 209–1256, 438–879.2, and 130–697.7 km s⁻¹ for three loops, respectively. Also, Alfven speeds were determined as 150–1012, 316–708.8, and 94–562.5 km s⁻¹. The magnetic field related to these fluctuations was calculated by the seismological method with the approximation of the thin cylindrical model for the loops measuring 2.47–16.52, 3.6–11.56, and 1.1–9.18 Gauss. Our findings suggest that oscillating movements in the loops can be interpreted as Kink transverse oscillations.

In an earlier paper, we determined the morphological types of galaxies in the Coma Cluster using data from the HST/ACS Coma Cluster treasury survey. Of the 132 members, 51 are non-dwarfs and 81 are dwarfs. We define dwarfs to have an absolute luminosity (M_{textrm{F814W}}ge -18.5) as in Marinova et al. (2012). In this paper, we identify the morphological types of these dwarf galaxies and conduct a detailed study of their properties. Using GALFIT, we determined the structural properties of our sample, and with spectroscopic redshifts, we determined memberships and distances to identify dwarfs. A visual examination of the residual images reveals that our sample of 78 dwarf galaxies comprises dwarf lenticular (dS0) 22%, dwarf elliptical (dE) 69%, dwarf spirals (dSp) 4%, dwarf ring (dring) 1%, dwarf barred spirals (dSBp) 3% and dwarf irregular (dIrr) 1% galaxies. The bulge-disk decomposition (Sérsic (+) exponential) fits are only good for the dS0 galaxies. The remainder of the sample gives good fits only for single Sérsic fits. The color-magnitude relation (CMR) shows that the dEs are redder and fainter than the rest of the sample (except one dIrr galaxy). The Kormendy relation reveals that dE galaxies have lower surface brightness than the rest of the sample. Our research leads us to conclude that dwarf galaxies appear to have a different formation and evolution process than non-dwarf galaxies.

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.

The cross-correlation of two-dimensional digital images is fundamental to solar adaptive optics computations. It can be used in a simple tip-tilt correction system to identify the relative shift between consecutive images and correlating sub-aperture images of a Shack–Hartmann wave-front sensor. The typical frequency of computation is about 1 kHz. While the software-based optimized cross-correlations may be sufficient when a small number of sub-apertures are used in a wave-front sensor, hardware-accelerated (FPGA), correlations may be required when a large number of sub-aperture images are involved, e.g., in the case of the proposed National Large Solar Telescope in India. This paper presents SolarAccel: An FPGA-based acceleration of a basic two-dimensional cross-correlation of two images. We accelerate the FPGA-based design by pipelining the individual components of the cross-correlation process. We implemented our RTL logic on a few sets of (128times 128) pixel images and (32times 32) pixel images on a Xilinx Zynq Ultrascale(+) MPSoC on the ZCU104 FPGA evaluation platform. SolarAccel performs a 2D FFT on a (128times 128) image faster than existing work. The cross-correlation on a (32times 32) image is also faster than the existing work. This demonstrates that FPGA acceleration is beneficial in solar adaptive optics applications.