Journal of Astrophysics and Astronomy最新文献

In this study, we apply the dual-component model of (gamma )-ray emission to assess the validity of the unified scheme for high-luminosity radio sources, specifically, Fanaroff–Riley Type II radio galaxies (FR IIs) and Flat-Spectrum Radio Quasars (FSRQs). We analyse a combined dataset comprising 220 FSRQs detected by the Fermi Large Area Telescope (Fermi-LAT) and 107 non-Fermi detected FR IIs. Utilizing the concept of relativistic beaming, we compute both the extended and core (gamma )-ray emissions and used the (gamma )-ray beaming factor ((g_gamma (beta , psi ))) to estimate the (gamma )-ray core-dominance. Our main findings are as follows: (1) Radio ((R_r)) and (gamma )-ray ((R_gamma )) core-dominance parameters (in logarithmic scale) range from −2.40 to 4.32 and −1.63 to 9.73, respectively, for FSRQs, with mean values of 1.36 and 2.52. In contrast, for FR IIs, (R_r) and (R_gamma ) span −3.30 to 0.27 and −1.82 to 3.79, with mean values of 0.16 and 0.23, respectively. The significantly lower core-dominance of FR IIs compared to FSRQs, supports the unified model, wherein FR IIs represent the misaligned counterparts of FSRQs. (2) (gamma )-ray emission in FSRQs is predominantly core-dominated, exceeding the contribution from the extended region by approximately three orders of magnitude. Strong anti-correlations between (R_r), (R_gamma ) and their respective emission components further indicate that (gamma )-ray production is substantially influenced by relativistic beaming effects. (3) Distribution of FR IIs in the parameter space of (R_r) and (R_gamma ) vs. (gamma )-ray emission suggests the presence of varying beaming effects across different regions. These findings indicate that (gamma )-ray emission in FSRQs originates primarily from the core and reveals the contributions of relativistic beaming effect to the unified model of high luminosity samples of FSRQs and FR IIs.

Open clusters (OCs) in the Galaxy are excellent probes for tracing the structure and evolution of the Galactic disk. We present an updated catalog of the fundamental and kinematic parameters for 1145 OCs, estimated using the data from Gaia DR3 earlier listed in Cantat-Gaudin et al. (2020). This sample is complemented by 3677 OCs with astrometric solution from the catalog by Hunt & Reffert (2023). Using the Galaxy potential and the space velocities, orbits of 4006 OCs were computed, and we provide a catalog with orbital parameters such as eccentricity, perigalactic and apogalactic distance, and the maximum vertical height traced by OCs from the Galactic disk. The OCs in the sample are found to be distributed between 5 and 16 kpc from the Galactic center, with older OCs showing a radially extended distribution. The low number of old OCs in the inner region of the Solar circle will likely suggest their destruction in this area. Using the orbital estimations, we explored the maximum vertical height ((Z_{max })) OCs can reach. We derive a quantitative expression for the dependency of (Z_{max }) with the cluster’s age and Galactocentric radius for the first time. The young (age < 50 Myr) and the intermediate age (50 Myr < age < 1 Gyr) OCs show similar values of (Z_{max }) till 9 kpc, with the latter group higher values beyond. OCs older than 1 Gyr show larger values of (Z_{max }) at all Galactocentric radii and significantly larger values beyond 9 kpc. Higher values of (Z_{max }) are found in the third Galactic quadrant, suggesting the link between the higher values and the Galactic warp. This large sample shows that young OCs are also involved in the diagonal ridge formation in the solar neighborhood.

We compare solar wind parameters and storm conditions for two geomagnetic storms recorded during solar cycles 24 and 25 – 17 March 2013 and 23 April 2023. We select these events since they are isolated coronal mass ejection (CME) events with a two-step storm profile, which occurs because both the sheath and magnetic cloud of the CME are geoeffective. We predict the storm profile by implementing five Dst forecast models, Burton et al. (1975), Fenrich & Luhmann (1998), O’Brien & McPherron (2000), Wang et al. (2003), and Temerin & Li (2006) – on the in situ observations obtained at L1. We study the SYM/H profiles in the sheath and cloud regions by comparing the actual SYM/H index recorded in the OMNI database with predictions from the models by evaluating the difference in the recorded and predicted SYM/H minima and the time difference between the storm minima. Our study demonstrates that among the five models evaluated, the Temerin & Li (2006) model excels in predicting the overall storm profile and peak time of geomagnetic storms. In contrast, Fenrich & Luhmann (1998) provides a more precise forecast of the intensity in the storm’s peak. In this study, we defined a new metric, CI, the ‘storm coupling integral’, by integrating a solar wind coupling function over a time interval to quantify its geoeffectiveness. In addition to indicating the geoeffectiveness, CI can be used as a tool to assess and improve the overall performance of forecast models.

The Sun is the only star that harbours a planet known to host life. Our home, the Earth, and other solar system planets reside within the heliosphere – the sphere of influence of the Sun. Within this domain, the Sun’s radiation, energetic particles, plasma wind, magnetic fluxes, and dynamic events, such as flares and coronal mass ejections influence planetary environments. While the Sun provides the basis for life, it also produces severe space weather that is hazardous to humanity’s space-based technologies. Long-term solar variations also influence planetary evolution and habitability. Dynamic solar variability originates in magnetohydrodynamic processes in its interior and atmosphere that provide a window to the plasma universe. Therefore, exploring the origin, impact, and overarching astrophysical implications of the Sun’s activity is of fundamental importance to humanity. In this vision for solar and heliospheric physics – contributing to the vision document of the Astronomical Society of India – we provide a brief synopsis of the current status of the field, focus on outstanding challenges that are expected to drive the field over the next decade or so, and based on an assessment of the expertise available within India, we provide specific recommendations that the Indian community is well poised to address.

This study investigates the open clusters SAI 72 and SAI 75 using Gaia DR3 data, employing the Automated Stellar Cluster Analysis (ASteCA) tool to determine their structural and fundamental properties, including centre coordinates, size, age, distance, mass, luminosity and kinematics. Based on membership probabilities ((Pge 50%)), we identified 112 and 115 stars as probable members of SAI 72 and SAI 75, respectively. Radial density profile (RDP) analysis yielded cluster radii of 2.35 arcmin for SAI 72 and 2.19 arcmin for SAI 75. The spectral energy distribution (SED) fitting was performed to refine metallicity, distance and colour excess parameters, ensuring consistency within 1(sigma ) of isochrone-based estimates. Isochrone fitting of the colour–magnitude diagram (CMD) suggests ages of 316 and 302 Myr, with corresponding distances of (3160 pm 80) and (3200 pm 200) pc. We derived their galactic positions, projected distances ((X_odot ,Y_odot )), and vertical displacements ((Z_odot )). Mass function analysis estimates cluster masses of (612 pm 174) M(_odot ) for SAI 72 and (465 pm 90) M(_odot ) for SAI 75. Kinematic studies indicate that both clusters have reached dynamical equilibrium. The AD diagram method provided convergent point coordinates of ((A,~D)_o = (97^{circ }.016 pm 0^{circ }.09,4^{circ }.573 pm 0^{circ }.05)) for SAI 72 and ((99^{circ }.677 pm 0^{circ }.10,1^{circ }.243 pm 0^{circ }.09)) for SAI 75. Orbital analysis confirms that both clusters follow nearly circular trajectories with low eccentricities and minor variations in apogalactic and perigalactic distances. Furthermore, we determine that SAI 72 and SAI 75 originated beyond the solar circle at (R_{textrm{Birth}} = 10.825pm 0.068) and (R_{textrm{Birth}} = 9.583pm 0.231) kpc, respectively. Their maximum heights above the galactic plane, (Z_{textrm{max}}) are (109 pm 9) pc for SAI 72 and (232 pm 24) pc for SAI 75, reinforcing their classification as part of the young stellar disc population.

Photons emitted during the formation of primordial hydrogen and helium atoms over the Epoch of Recombination are expected to be preserved as additive distortions to the Cosmic Microwave Background (CMB) spectrum. The ‘ripple’ like spectral features from Cosmological Recombination Radiation (CRR) have never been detected, and are expected to be 9 orders of magnitude fainter than the CMB. Array of Precision Spectrometers for the Epoch of Recombination (APSERa) is an upcoming ground-based experiment to detect the CRR signal over 2–6 GHz. While astrophysical foregrounds may be theoretically separated from the CRR signal using their inherently different spectral characteristics, instrument-generated systematics present a practical problem. We present the first-ever study to detect the CRR lines in the presence of a non-ideal antenna, adopting a toy model for antenna beam chromaticity. Using Euclidean distance and Pearson correlation coefficient as metrics to distinguish between CRR signal presence and absence in a simulation pipeline, we demonstrate that it is indeed possible to detect the signal using a chromatic antenna. Furthermore, we show that there are different tolerances to the antenna non-ideality based on the type of chromaticity, observing location, and LST. These can inform antenna and experiment design for a practical detection.

We report results on the radial velocity dispersion profile built out to the outskirts of NGC 4147, a Milky Way globular cluster with detected strong tidal tails. The cluster was chosen to probe, from an observational point of view, recent simulations that suggest that rising velocity dispersion profiles at large distances from the clusters’ centers would be seen in globular clusters without tidal tails. From GEMINI@GMOS spectra, centered in the infrared Ca II triplet region, of selected stars located along the onset of NGC 4147’s tidal tails, we measured their radial velocities and overall metallicities. The derived metallicities were used to ultimately assess the highly-ranked cluster candidates of 9 stars, located between (sim )7 and 33 pc from the cluster’s center, suitable for testing the aforementioned simulation. We complemented the present radial velocities with others available in the literature for the cluster’s members, and built a cluster velocity dispersion profile, which suggests a mostly flat or slightly rising profile at large distances from the cluster’s center. This outcome confirms that kinematically hot outermost cluster stars are seen in NGC 4147, which disproves the recent model predictions. Nevertheless, the mean velocity dispersion of the outermost cluster’s stars agrees with NGC 4147 being formed in a (10^8)–(10^9) (hbox {M}_odot ) dwarf galaxy with a cored dark matter profile that was later accreted to the Milky Way.

Three-dimensional orbits near the interior Lagrange point (L₁) of the Sun–Earth barycentre system are being considered for multiple missions. Trajectories at these Lagrange points are intrinsically unstable, necessitating spacecraft to utilize trajectory control to sustain proximity to their designated orbits. This research examines the station keeping of halo orbits around the Sun–Earth Lagrange point L₁ within the circular-restricted three-body problem (CRTBP) utilizing two control strategies: target point approach (TPA) and linear quadratic regulator (LQR) methods. Halo orbits with out-of-plane amplitudes of 120,000, 150,000 and 250,000 km were generated using a differential correction method. Random initial errors in the state vector of the satellite were introduced to simulate realistic perturbations, and a genetic algorithm (GA) was applied to optimize maneuver intervals in the TPA. The TPA was tested with different numbers of future target points (2, 3, 4 and 5). Results from different simulations indicate that the TPA is more fuel-efficient for small perturbations, while the LQR approach is more effective for larger initial dispersions. Additionally, a transformation from the Sun–Earth barycentric frame to the Earth-centred J2000 inertial frame is established. These findings provide valuable insights for designing efficient station-keeping strategies that balance maneuver costs with mission longevity. This study offers a comprehensive strategy for maintaining spacecraft near the desired halo orbit trajectories.

The study of exoplanets is one of the fastest-growing areas in astronomy. The number of known exoplanets has increased dramatically, providing new insights into the galaxy’s diversity and abundance of planetary systems. The field has progressed significantly from discovery and characterization to various new areas, including exploring the demographics of exoplanets, examining their atmospheres, investigating the process of planetary formation and evolution, studying the interactions between stars and planets, and searching for signs of life beyond our solar system. These advances are made by drawing expertise from astrophysics, planetary science, atmospheric science, and astrobiology. Recently, there has been a steady growth in the number of Indian astronomers involved in exoplanet research. This exoplanet vision document, prepared under the aegis of ASI, summarizes the field’s current status globally. It also highlights the efforts of various research groups in the country and identifies potential directions for future research. To be able to do competitive exoplanet science within the country, we suggest implementing capacity-building measures in the areas of modeling and theory, establishing new observational facilities, and fostering collaboration within the country and abroad. Specific recommendations of the exoplanet working group are as follows: (1) We identify RV follow-up observations of exoplanets discovered by ongoing and future space-based surveys such as TESS, Gaia, and PLATO as the highest priority areas for the community. We recommend a 4-m class (or large) telescope mounted with a high resolution ((R > rsim 100) K) spectrograph for the RV follow-up and transit spectroscopy studies in the long-term (10–15 yr). In the interim, sufficient time should be made available to the community on the PARAS-2/PRL facility and the upcoming high-resolution spectrograph on DOT/ARIES for these studies. (2) Developing new technology and building state-of-the-art exoplanet instruments for the future 10 m facility class National Large Optical Telescope (NLOT). (3) Leveraging ISRO’s strength in the space program to plan and develop small (e.g., UV, optical, and IR transit payloads) and big space missions (e.g., ExoWorlds) for exoplanet science. (4) Setting up a 1 m class transit telescope for survey and follow-up studies and to have synergy with other observatories for continuous and time-critical observations across different longitudes. (5) Expanding computational resources and augmenting modeling/simulation efforts. (6) Taking the excitement of exoplanet discoveries to the public by integrating it with various outreach and educational activities of the institutes.

Wormholes are hypothetical shortcuts through spacetime, have fascinated cosmologists and theoretical physicists for decades. In this paper, traversable wormholes were studied in the static as well as dynamic backgrounds, with particular stress on cosmic time-dependent wormhole. A concerted effort is made to provide an evolving wormhole shape function, which is both radially (r) and cosmic time (t) dependent. Also, wormholes, which appear as special solutions to the EF equations, are now being viewed as viable interstellar objects. A new matter source, which supplies fuel to construct wormhole spacetime, is provided. Exact wormhole solutions were found in the model under static and dynamic background geometries. It is shown that the exotic matter, which is the necessary ingredient for wormhole physics violate the null and strong energy conditions, but obey the weak and dominant energy conditions marginally in the static case. However, in the dynamic case, the exotic matter, which is the necessary ingredient for wormhole physics, violates the dominant energy conditions, satisfies the null and weak energy conditions partially and fully satisfies the strong energy conditions. Further, stability analysis in each case suggests that the wormhole is traversable in both the cases. Some physical features are briefly discussed in this paper.