Journal of Astrophysics and Astronomy最新文献

A detailed study of stellar populations in Milky Way (MW) satellite galaxies remains an observational challenge due to their faintness and fewer spectroscopically confirmed member stars. We use unsupervised machine learning methods to identify new members for nine nearby MW satellite galaxies using Gaia data release-3 (Gaia DR3) astrometry, the Dark Energy Survey (DES) and the DECam Local Volume Exploration Survey (DELVE) photometry. Two density-based clustering algorithms, DBSCAN and HDBSCAN, have been used in the four-dimensional astrometric parameter space ((alpha _{2016}), (delta _{2016}), (mu _{alpha } cos delta ), (mu _delta )) to identify member stars belonging to MW satellite galaxies. Our results indicate that we can recover more than 80% of the known spectroscopically confirmed members in most satellite galaxies and also reject 95–100% of spectroscopic non-members. We have also added many new members using this method. We compare our results with previous studies using photometric and astrometric data and discuss the suitability of density-based clustering methods for MW satellite galaxies.

The ionosphere’s dynamic fluctuations are a persistent challenge to satellite navigation and communication. The total electron content (TEC) information from global navigation satellite system (GNSS) signals provides the status of the ionosphere for fail-safe transionospheric communication. The equatorial ionization anomaly (EIA) and equatorial plasma bubble (EPB) dominate in low latitude and equatorial ionosphere. The low solar activity's fast varying pre-reversal enhancement is low, and slow varying gravity waves can seed ionospheric disturbances. This study analyses the vertical TEC (VTEC) variations using a ground-based global positioning system (GPS) receiver at Thanjavur (10.72° N, 79.02° E), Tamil Nadu, India, for the years 2019 and 2020, with specific emphasis on the Equinox and Solstice conditions during low solar activity. The suitability of global ionospheric models such as IRI-Plas and NeQuick2 models is investigated with low solar activity GPS VTEC observations. VTEC variations are more during the Vernal Equinox compared to other seasons. The NeQuick2 model underestimates the VTEC content during the night hours and overestimates the day's evening hours regardless of the month, perhaps due to higher ITU-R coefficients. The results help us improve IRI-Plas and NeQuick prediction models' accuracy.

This paper presents a report on the activities and the proposed action plan of the Education and Public Outreach Working Group (EPO WG) of Square Kilometre Array–India Consortium (SKAIC). Details of a set of flagship programs as well as supporting activities are presented, in consonance with the scale of India’s involvement in Square Kilometre Array Observatory (SKAO), as well as the educational and science literacy contexts in the country. Ongoing independent EPO activities by some of the member institutions are also included.

Phosphorus (P) is one of the important elements for the formation of life and plays a crucial role in several biochemical processes. Recent spectral line surveys have confirmed the existence of P-bearing molecules, especially PN and PO, in the star-formation regions, but their formation mechanisms are poorly understood. The P-bearing molecule phosphorus nitride (PN) is detected in several star-forming regions, but this molecule has been poorly studied at high gas densities ((ge )10(^{6}) cm(^{-3})) hot molecular cores. In this paper, we presented the detection of rotational emission line of PN with transition (J = 3)–2 towards the hot molecular cores G10.47(+)0.03 and G31.41(+)0.31, using the Atacama Compact Array (ACA). The estimated column densities of PN for G10.47(+)0.03 and G31.41(+)0.31 using the local thermodynamic equilibrium model are ((3.60pm 0.2)times 10^{13}) cm(^{-2}) and ((9.10pm 0.1)times 10^{12}) cm(^{-2}) with an excitation temperature of (150pm 25) K. The fractional abundance of PN relative to H(_{2}) is (2.76times 10^{-10}) for G10.47(+)0.03 and (5.68times 10^{-11}) for G31.41(+)0.031. We computed the two-phase warm-up chemical model of PN to understand the chemical evolution in the environment of hot molecular cores. After chemical modeling, we claimed that PN is created in the gas phase via the neutral–neutral reaction between PO and N in the warm-up stage. Similarly, PN is destroyed via the ion–neutral reaction between H(_{3})O(^{+}) and PN.

Influence of magnetic field on the propagation of shock waves in radiation gasdynamics is analysed by using wavefront analysis method. We examined behavior of the waves propagated into the two-dimensional (2-D) steady supersonic magnetogasdynamic flow of non-ideal gas with radiation. The transport equations are derived, which determine the condition for the shock formation. The effect of non-idealness and thermal radiation and their consequences under the influence of magnetic field is studied and examined how the flow patterns of the disturbance vary with respect to the variation in the parameters of the flow. It is found that the presence of a magnetic field plays an essential role in the wave propagation phenomena. Nature of the solution with respect to Mach number is analysed, and it is examined how the shock formation distance changes with an increase or decrease in the value of Mach number. Also, the effect of non-idealness on the shock formation distance is elucidated and examined how the shock formation affects the increase in the value of non-ideal parameter in the presence of magnetic field with thermal radiation.

Impact of p-capture reactions on the abundances of neon and magnesium considering the nuclear reaction chain, Neon–Sodium–Magnesium–Aluminum (hereafter extended Ne–Al) for stellar conditions of temperature range of (0.02times 10^{9})–(0.10times 10^{9}) K and typical density of 100 g cc({}^{-1}) has been studied. Then, we have estimated abundances of Ne and Mg, which are of a little special importance. The estimated abundances of these aforesaid elements are then compared with their counterparts, which have been observed in some B-type stars. For those B-type stars, we have discovered a significant agreement in the abundances between the estimated and observed values with a correlation coefficient >0.8.

In this paper, we report the results of the detailed temporal and spectral studies of the BeXRB J21347(+)4737 based on the data from the nuclear spectroscopic telescope array (NuSTAR) and Swift/XRT in a wide energy range of 0.5–50 keV. Coherent pulsation with a period of (322.738pm 0.018) s was found in the light curve, implying the source pulsation has spun down by 0.341 s yr(^{-1}) when compared with the coherent pulsation estimated from XMM Newton >7 years ago. The pulse profile of the source demonstrates energy dependence and has evolved with time. The pulse fraction of the source observed by NuSTAR initially decreases with energy up to (sim )15 keV, followed by a non-monotonic increasing trend above 15 keV. The source spectrum can be well approximated by an absorbed power-law model with modification by an exponential cutoff at high energies. The absorbed flux of the source is (4times 10^{-11}) erg cm(^{-2}) s(^{-1}) and its corresponding luminosity is (3.5times 10^{35}) erg s(^{-1}). The study of pulse-phase resolved spectroscopy shows a strong variation of spectral parameters on the phase. No additional emission or absorption features in the form of Fe line or cyclotron lines were observed both in the phase-averaged and phase-resolved spectra of IGR J21347(+)4737.

We considered a modified gravity theory through a special kind of ghost-free bimetric gravity, where one massive spin-2 field interacts with a massless spin-2 field. In this bimetric gravity, the late-time cosmic acceleration is achievable. Alongside the background expansion of the Universe, we also studied the first-order cosmological perturbations and probe the signature of the bimetric gravity on large cosmological scales. One possible probe is to study the observational signatures of the bimetric gravity through the post-reionization 21-cm power spectrum. We considered upcoming SKA1-mid antenna telescope specifications to show the prospects of the detectability of the ghost-free bimetric gravity through the post-reionization 21-cm power spectrum. Depending on the values of the model parameter, there is a possibility to distinguish the ghost-free bimetric gravity from the standard (Lambda )CDM model with the upcoming SKA1-mid telescope specifications.

Optical spectroscopy offers the most direct view of the stellar properties and the accretion indicators. Standard accretion tracers, such as H(beta ), H(alpha ) and Ca II triplet lines, and most photospheric features fall in the optical wavelengths. However, these tracers are not readily observable from deeply embedded protostars because of the large line of sight extinction ((A_v sim 50)–100 mag) toward them. In some cases, however, it is possible to observe protostars at optical wavelengths if the outflow cavity is aligned along the line-of-sight that allows observations of the photosphere, or the envelope is very tenuous and thin, such that the extinction is low. In such cases, we not only detect these protostars at optical wavelengths, but also follow up spectroscopically. We have used the HOPS catalog (Furlan et al. in 2016) of protostars in Orion to search for optical counterparts for protostars in the Gaia DR3 survey. Out of the 330 protostars in the HOPS sample, an optical counterpart within 2('') is detected for 62 of the protostars. For 17 out of 62 optically detected protostars, we obtained optical spectra (between 5500 and 8900 Å) using nt Object Spectrograph and Camera (ADFOSC) on the 3.6-m Devasthal Optical Telescope (DOT) and Hanle Faint Object Spectrograph Camera (HFOSC) on 2-m Himalayan Chandra Telescope (HCT). We detect strong photospheric features, such as the TiO bands in the spectra (of 4 protostars), hinting that photospheres can form early in the star-formation process. We further determined the spectral types of protostars, which show photospheres similar to a late M-type. Mass accretion rates derived for the protostars are similar to those found for T-Tauri stars, in the range of 10(^{-7})–10(^{-8}) (M_odot ) yr(^{-1}).

N-body numerical simulations code for the orbital motion of asteroids/planetesimals within the asteroid belt under the gravitational influence of the Sun and the accreting planets, has been developed. The aim is to make qualitative, and to an extent a semi-quantitative argument, regarding the possible extent of radial mixing and homogenization of planetesimal reservoirs of the two observed distinct spectral types, viz., the S- and C-types, across the heliocentric distances due to their dynamical orbital evolution, thereby, eventually leading to the possible accretion of asteroids with chemically diverse constituents. The spectral S- and C-type asteroids are broadly considered as the parent bodies of the two observed major meteoritic dichotomy classes, namely the non-carbonaceous (NC) and carbonaceous (CC) meteorites, respectively. The present analysis is performed to understand the evolution of the observed dichotomy and its implications due to the nebula and early planetary processes during the initial 10 Myr (million years). The homogenization across the two classes is studied in context to the accretion timescales of the planetesimals with respect to the half-life of the potent planetary heat source, ²⁶Al. The accretion over a timescale of ~1.5 Myr, possibly resulted in the planetary-scale differentiation of planetesimals to produce CC and NC achondrites and iron meteorite parent bodies, whereas the prolonged accretion over a timescale of 2–5 Myr resulted in the formation of CC and NC chondrites. Our simulation results indicate a significant role of the initial eccentricities and the masses of the accreting giant planets, specifically, Jupiter and Saturn, in triggering the eccentricity churning of the planetesimals across the radial distances. The rapid accretion of the giant planets with appropriate eccentricities, critically influences the triggering of the orbital resonances that are in turn responsible for the radial mixing of the two distinct chemical reservoirs across early solar system. This would influence the chemical composition and mixing of the various planetary reservoirs. The observed dichotomy among the NC and CC reservoirs can be preserved within the initial 5 Myr in the early solar system in case the accretion of the two giant planets is prolonged. The present work provides a semi-quantitative formulation in terms of radial homogenization. A rigorous computational formulation of the evolving ensemble of distinct chemical reservoirs is beyond the scope of the present computational work.