http://hdl.handle.net/2248/2 Fri, 18 Sep 2026 20:26:14 GMT 2026-09-18T20:26:14Z http://hdl.handle.net/2248/9050 Title: Properties of faint X-ray activity of XTE J1908+094 in 2019 Authors: Chatterjee, Debjit; Jana, Arghajit; Chatterjee, Kaushik; Bhowmick, Riya; Nath, Sujoy Kumar; Chakrabarti, S. K; Mangalam, A; Debnath, Dipak Abstract: We study the properties of the faint X-ray activity of Galactic transient black hole candidate XTE J1908+094 during its 2019 outburst. Here, we report the results of detailed spectral and temporal analysis during this outburst using observations from Nuclear Spectroscopic Telescope Array (NuSTAR). We have not observed any quasi-periodic-oscillations (QPOs) in the power density spectrum (PDS). The spectral study suggests that the source remained in the softer (more precisely, in the soft–intermediate) spectral state during this short period of X-ray activity. We notice a faint but broad Fe Kα emission line at around 6.5 keV. We also estimate the probable mass of the black hole to be 6.5−0.7+0.5M☉, with 90% confidence. Description: Open Access; This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/4.0/). Tue, 01 Jun 2021 00:00:00 GMT http://hdl.handle.net/2248/9050 2021-06-01T00:00:00Z http://hdl.handle.net/2248/9049 Title: Photometric metallicity of galactic RR lyrae stars in the gaia DR3 era Authors: Prakash, Mahiguhappriya; Das, Susmita; Singh, H. P; Kumar, Nitesh Abstract: RR Lyrae stars are pulsating variables crucial for distance determination and galactic structure studies. Metallicities of fundamental-mode (RRab) RR Lyrae stars are commonly derived from photometry using empirical relations involving the Fourier parameter ϕ31 and the pulsation period. We present a new, calibrated G-band relationship between pulsation period P, Fourier parameter ϕ31, and metallicity [Fe/H] for galactic RR Lyrae stars from the Gaia survey. A set of 72 fundamental mode RR Lyrae stars were identified for deriving the relation in the G-band after visual examination of their light curves. Unlike recent large-scale calibrations, our relation prioritizes calibration purity by anchoring exclusively to a homogeneously analyzed sample of high-resolution spectroscopic metallicities from the literature. Our best fit relation is [Fe/H] = (−6.93 ± 0.58) − (6.04 ± 0.37)P + (1.65 ± 0.11)ϕ31. We compare the [Fe/H] predicted by our relation for the stars in our calibration sample with that obtained from previously established relations in the G-band using different approaches. Our calibrated G-band P-ϕ31-[Fe/H] relationship demonstrates high reliability when validated against spectroscopic data, achieving a negligible bias of 0.00 dex and an empirical RMS scatter of 0.26 dex. Furthermore, by applying an Orthogonal Distance Regression (ODR) routine that fully propagates parameter covariance, we establish a mathematically strict empirical baseline whose theoretical uncertainties perfectly align with this observed dispersion. We find that the inclusion of the R21 Fourier parameter offers no significant improvement in metallicity estimation. Comparisons with literature confirm that our linear relation aligns closely with other Gaia DR3-based studies, while offering improved precision over older DR2-based relations. Description: Open Access; This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license. Mon, 01 Jun 2026 00:00:00 GMT http://hdl.handle.net/2248/9049 2026-06-01T00:00:00Z http://hdl.handle.net/2248/9048 Title: Constraining neutron-capture nucleosynthesis from surface chemical composition of chemically peculiar stars: The puzzling case of HE 1005-1439 Authors: Goswami, A; Choplin, Arthur; Goswami, P. P; Siess, L; Goriely, S Abstract: The chemical composition of stellar atmospheres provides a valuable window into the complex processes of stellar nucleosynthesis. Among chemically peculiar cool stars, many objects are the products of mass transfer in binary systems, including most carbon stars, CH stars, and CEMP-s and CEMP-r/s stars. Accurate and precise determinations of heavy-element abundances in these systems serve as powerful tracers of neutron-capture nucleosynthesis operating in the slow (s) and intermediate (i) regimes. Such measurements also place important constraints on binary evolution, mass-transfer mechanisms, the onset of early s-process enrichment, and the astrophysical sites and production pathways associated with the i-process. In this work, we investigate the origin of the extremely metal-poor star HE 1005-1439, which has previously been suggested to exhibit a surface composition enriched by a combination of s- and i-process nucleosynthesis. Using new multi-zone, detailed AGB models for both the s- and i-processes, we find that a mixed i + s scenario provides a plausible explanation for the observed abundance pattern of HE 1005-1439, although a pure i-process AGB model yields an almost equally satisfactory fit. Description: Open Access; This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license. Mon, 01 Jun 2026 00:00:00 GMT http://hdl.handle.net/2248/9048 2026-06-01T00:00:00Z http://hdl.handle.net/2248/9047 Title: Bar-driven gas redistribution suppresses star formation in spiral galaxies: Evidence from dust lanes in NGC 3351 Authors: George, K; Subramanian, S Abstract: We present observational evidence, based on high-resolution imaging from HST, ALMA, and AstroSat/UVIT, that the redistribution of gas driven by the bar in the face-on spiral galaxy NGC 3351 results in suppressed star formation in its central regions. Dust and molecular gas coexist in galaxies, allowing dust lanes observed in galaxies to be used to probe the distribution of gas. In the central regions of NGC 3351, covered by the stellar bar, dust lanes are visible in the HST F438W–F814W colour map, but surprisingly, these areas lack molecular gas and recent star formation. The inward orientation of the dust lane morphology towards the galaxy’s centre suggests that molecular gas was once present in this region but was redistributed to the centre due to the stellar bar’s action. The direction of the dust lanes therefore indicates the past inflows of gas towards the galaxy centre, with their morphology consistently oriented inwards along the bar. These findings support a scenario in which the stellar bar has efficiently channelled molecular gas into the nucleus, building the central reservoir while suppressing star formation along the bar. Description: Open Access; Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Mon, 01 Jun 2026 00:00:00 GMT http://hdl.handle.net/2248/9047 2026-06-01T00:00:00Z