http://hdl.handle.net/2248/2 2026-07-18T13:03:58Z 2026-07-18T13:03:58Z Mishra, Wageesh Agarwal, Anjali Srivastava, N http://hdl.handle.net/2248/9012 2026-07-16T06:32:30Z 2026-07-01T00:00:00Z

Three-phase evolution of aspect ratio in fast and slow CMEs from the Sun to 1 au Mishra, Wageesh; Agarwal, Anjali; Srivastava, N Coronal mass ejections (CMEs) undergo significant geometric evolution as they propagate from the Sun to 1 au, influencing their radial size, expansion, and space weather impact. We investigate the evolution of CME aspect ratio (κ) and expansion dynamics for four fast and four slow Earth-directed CMEs. Using multipoint coronagraphic observations with the graduated cylindrical shell model and corrected in situ measurements of associated magnetic clouds at 1 au, we track the evolution of κ from the low-middle corona to interplanetary space. We find that κ does notremain constant but exhibits a systematic three-phase evolution: a rise phase in the low-middle corona ( 10–15 R), a saturation phase at intermediate heights, and then a decline phase in the interplanetary space. The ratio of radial expansion speed to leading-edge speed (Vexp/VLE) decreases substantially from the corona to 1 au, indicating a reduction in radial expansion efficiency during interplanetary propagation. The consistent evolution of κ and Vexp/VLE suggests a transition from magnetically dominated expansion in the corona to a regime increasingly controlled by the heliospheric environment. We note that fast CMEs show stronger early expansion and evolve into larger, more radially extended structures, whereas slow CMEs exhibit a more gradual rise and a steeper decline. These results demonstrate that CME geometry evolves significantly during propagation and highlight the need to incorporate aspect ratio evolution in models to improve predictions of CME size, arrival time, and geoeffectiveness. Open Access; This is an Open Access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.

2026-07-01T00:00:00Z Mahavarkar, Prasanna Sriram, S Joshi, Bhagyashree Hasan, Amirul Remya, B. S Chandra, Sarvesh http://hdl.handle.net/2248/9011 2026-07-16T06:29:41Z 2023-12-01T00:00:00Z

Designing a sky-scanning Fabry–Perot interferometer system with a large size integrating sphere Mahavarkar, Prasanna; Sriram, S; Joshi, Bhagyashree; Hasan, Amirul; Remya, B. S; Chandra, Sarvesh Integrating spheres can be manufactured at sizes ranging from 1 mm to 3 m in diameter. It has been agreed widely by manufacturers that fitting a large-sized integrating sphere as per the customer requirement is a complex process. Thus, these spheres due to its large beam divergence from the exit port, have never been deployed for the calibration of aeronomy applications. In this article a optical system is described to integrate a large-sized integrating sphere with the Fabry–Perot etalon and thus devise a set-up to generate the concentric ring pattern and record it on the detector. The experimental set-up was verified by optical simulation using ZEMAX (OpticStudio) so as to validate the system’s performance in the laboratory. The important parameter finesse is calculated and its accuracy is found to be 80%. Open Access; This is an open access article under the CC BY license.

2023-12-01T00:00:00Z Goswami, P. P Goswami, A http://hdl.handle.net/2248/9009 2026-07-16T06:26:05Z 2026-07-01T00:00:00Z

Three extremely metal-poor stars: Discovery of a new CEMP-no star Goswami, P. P; Goswami, A We have conducted detailed high-resolution spectroscopic studies on three extremely metal-poor (EMP) stars HE 0401−0138, HE 1153−0518, and HE 1246−1344. For the stars HE 0401−0138 and HE 1246−1344, we have estimated the abundances of C, Na, Mg, Ca, Sc, Ti, Cr, Mn, Co, Ni, Sr, and Ba along with the upper limits for Li, O, La, Ce, Pr, Nd, Sm, and Eu. For HE 1153−0518, abundances of seven light elements from C through Ni and two heavy elements, Y and Ba, have been derived, together with upper limits for Li, O, and La. Based on their observed abundance patterns, HE 0401−0138 and HE 1246−1344 are classified as normal EMP stars, whereas HE 1153−0518 is identified as a newly discovered CEMP-no star. HE 1153−0518 shows strong carbon enhancement with a high absolute carbon abundance, extreme sodium enrichment, very low neutron-capture element abundances, and a very low carbon isotopic ratio (12C/13C = 2.0). Its spectral energy distribution shows clear infrared excess, indicating the presence of circumstellar dust. The abundance pattern of HE 1153−0518 suggests enrichment by early nucleosynthetic processes, such as faint core-collapse supernovae with mixing and fallback, while the possibility of binary interaction and subsequent internal mixing cannot be ruled out. The discovery and detailed study of HE 1153−0518 add an important object to the small population of highA(C) CEMP-no stars and provide valuable constraints on early chemical enrichment pathways and the nature of the first generations of stars. Open Access; This is an Open Access article distributed under the terms of the Creative Commons Attribution License which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.

2026-07-01T00:00:00Z Vashisht, Tarang Beri, Aru Ghosh, Tanuman Upadhyay, Aman Rana, Vikram http://hdl.handle.net/2248/9008 2026-07-16T06:24:08Z 2026-07-01T00:00:00Z

Probing spectral variability in NGC 4490 ULX-8 over 24 yr of XMM–Newton, Chandra, and Swift-XRT observations Vashisht, Tarang; Beri, Aru; Ghosh, Tanuman; Upadhyay, Aman; Rana, Vikram We present a spectral variability study of the ultraluminous X-ray source NGC 4490 ULX-8 based on 14 Chandra, 6 XMM– Newton, and 19 Swift-XRT observations obtained between 2000 and 2024. The X-ray spectra are modelled using absorbed power-law and absorbed multicolour disc blackbody models. The best-fitting photon indices span 0.9–2.7, while the inferred inner disc temperatures lie in the range kTin 1.0–1.6 keV. We detect pronounced long-term variability in the unabsorbed X-ray luminosity on multiyear time-scales, while variability within individual observations is comparatively modest. A hardness–intensity Diagram of the source shows no clear transition between hard and soft states; however, two recent observations taken on 2022 December 1 and 2024 May 4 show a sharp increase in brightness. The spectra across all observations are dominated by smooth, single-component curvature in the 0.3–10 keV band, consistent with the broadened-disc regime of ultraluminous X-ray sources. A correlation analysis reveals a weak positive LX– trend that remains statistically supported after controlling for absorption-related degeneracies, indicating that it is not driven solely by fitting covariance. The LX–Tin relation is only weakly constrained, but remains compatible, within uncertainties, with both thin-disc and slim-disc scalings. Using disc parameters derived from higher quality XMM–Newton spectra, we obtain model-dependent estimates of the characteristic inner disc radius and compact-object mass asfunctions of inclination and spin. The reported results are consistent with a stellar-mass black hole accretor operating at or near the Eddington limit. Open Access; This is an Open Access article distributed under the terms of the Creative Commons Attribution License which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.

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