The termination of the slow neutron capture process (s-process) in the Pb--Bi mass region plays a key role in shaping the abundances of the heaviest stable nuclei produced in stellar environments. In this work, we revisit the classical description of the s-process termination developed by Clayton and co-authors, incorporating modern experimental neutron capture cross sections and exploring the sensitivity of the results to variations in neutron irradiation parameters. The reaction network describing the Pb--Bi--Po termination cycle is reformulated as a system of Bateman equations and solved numerically using the burn-up matrix formalism combined with the Pad\'e approximation for the matrix exponential. We investigate the influence of updated $(n,\gamma)$ cross sections for Pb and Bi isotopes, as well as variations in the shape and scale parameters of the neutron exposure distribution, on the isotopic abundances, the timescale required to reach equilibrium, and the behavior at maximum neutron exposure. Our results confirm the robustness of the quasi-stationary equilibrium condition $\sigma_A N_A = \mathrm{const}$ under modern nuclear data, while demonstrating that updated cross sections lead to a noticeable redistribution of isotopic abundances and modify the timescale for reaching the equilibrium plateau. The contribution of the s-process termination to the total abundances of Pb and Bi isotopes is further examined using different neutron exposure distributions. We find that the resulting s-process abundances are largely insensitive to the neutron capture cross section of $^{209}\mathrm{Bi}$ over the investigated range, confirming that $^{208}\mathrm{Pb}$ effectively acts as the termination point of the s-process. Among the considered exposure models, the exponential neutron exposure distribution provides the best overall description of the final s-process abundances. These results are in good agreement with observational abundance constraints and demonstrate that the main qualitative features of the classical Clayton scheme remain valid, while quantitative predictions are significantly refined by modern nuclear data and irradiation models.

In this work, the light curve of the Seyfert galaxy Mrk 6 constructed from photometric observations in the B, V, and $R_{\mathrm{c}}$ filters over the period from 5 April 2016 to 1 February 2026 is presented and analyzed. Over the entire monitoring interval (2016–2026), the variability amplitude of the light curve reaches $\mathrm{\Delta }B=1.9$ mag, $\mathrm{\Delta }V=1.5$ mag, and $\mathrm{\Delta }{R}_{\mathrm{c}}=1.4$ mag. During 2024–2026, the galaxy exhibits synchronous photometric variability in the B, V, and $R_{\mathrm{c}}$ filters with an amplitude of ∼0.3 mag. The study also uses spectroscopic observations obtained on 15 and 22 November 2025 and 16 February 2026 at the Shamakhy Astrophysical Observatory (Azerbaijan), as well as on 9 January 2026 at the Fesenkov Astrophysical Institute (Kazakhstan). The fluxes in the H$\beta$ emission line were calibrated using the [O III] $\lambda 5007$ Å line, ensuring consistent relative calibration of the spectral data. A comparison of the optical spectra reveals a pronounced transformation of the H$\beta$ line profile between November 2025 and January 2026. The broad component, clearly present in November 2025, becomes strongly suppressed and nearly disappears in January 2026, while the narrow emission lines remain stable. This behavior is consistent with a changing-look transition, indicating a temporary weakening of the broad-line region emission. The radius of the broad-line region $R_{\mathrm{BLR}}$ was taken to be equal to the average time delays (lags), amounting to ≈20 light days for the H$\beta$ emission and ≈28 light days for the H$\alpha$.

We examine cyclic nuclear reactions in the lead–bismuth (Pb–Bi) system near the s-process termination point. We present a numerical investigation of the isotopic evolution and decay heat generation in an extended 60-isotope nuclear reaction network under continuous 30 keV neutron irradiation (${10}^{14}$–${10}^{28}$ n cm⁻² s⁻¹) using the Chebyshev Rational Approximation Method (CRAM). The network accounts for 88 transitions, utilising a hybrid data approach that combines neutron capture cross-sections from EAF-2010 and TALYS with fundamental decay properties from the ENDF/B-VIII.0. Our simulations reveal two distinct evolutionary regimes. At moderate fluxes (${10}^{14}$–${10}^{20}$ n cm⁻² s⁻¹), the system establishes a steady cyclic loop driven by the $\alpha$-decay of ${}^{210}\mathrm{Po}$, successfully reproducing the s-process termination isotopic distribution (${}^{208}\mathrm{Pb}{\gg }^{209}\mathrm{Bi}{>}^{207}\mathrm{Pb}{>}^{206}\mathrm{Pb}$), characteristic of low-metallicity AGB stars. As the flux exceeds ${10}^{22}$ n cm⁻² s⁻¹, the classical balance breaks down, propelling mass flow toward heavier trace isotopes and suggesting a potential transition into the intermediate neutron capture (i-process) regime. Heat density calculations demonstrate that while the energy release of the core cycle plateaus near ${10}^5$ W cm⁻³, the extended chain drives an energy surge to over ${10}^8$ W cm⁻³ at ${10}^{24}$ n cm⁻² s⁻¹ before the system enters an unstable transient state at extreme fluxes.

This paper presents the architecture of the Kazakhstani National Virtual Observatory (KazVO)—an International Virtual Observatory Alliance (IVOA) compliant node that unifies the heterogeneous observational datasets of the Fesenkov Astrophysical Institute (FAI). The architectural foundation of the system is built upon a partitioned Data Lake, a German Astrophysical Virtual Observatory (GAVO) Data Center Helper Suite (DaCHS) publishing backend, and a PostgreSQL database in which metadata for published observational products are mapped to IVOA ObsCore, while catalogs and simulation grids use dedicated relational tables. We follow Open Science principles by introducing a metadata-only showcase model based on a four-class data embargo mechanism. Machine-to-Machine services deployed via IVOA protocols are exposed through the KazVO publishing registry registered in the global Registry of Registries (RofR), enabling analysis of Kazakhstani observational assets within external clients such as Tool for OPerations on Catalogues And Tables (TOPCAT), Aladin, and PyVO. The current implementation combines operational VO publication services and targeted photometric processing with scheduled, batch-mode data ingestion, supporting access to published historical and modern observational holdings. Replication has been validated on pilot datasets, while routine deployment at the observing sites and automated reduction of modern spectroscopic streams remain under development. The architecture provides a framework for progressively integrating these components into a complete data lifecycle.

In this work, the light curve of the Seyfert galaxy Mrk 6 constructed from photometric observations in the B, V, and Rc filters over the period from 5 April 2016 to 1 February 2026 is presented and analyzed. Over the entire monitoring interval (2016–2026), the variability amplitude of the light curve reaches ΔB=1.9 mag, ΔV=1.5 mag, and ΔRc=1.4 mag. During 2024–2026, the galaxy exhibits synchronous photometric variability in the B, V, and Rc filters with an amplitude of ∼0.3 mag. The study also uses spectroscopic observations obtained on 15 and 22 November 2025 and 16 February 2026 at the Shamakhy Astrophysical Observatory (Azerbaijan), as well as on 9 January 2026 at the Fesenkov Astrophysical Institute (Kazakhstan). The fluxes of the Hβ emission line were calibrated using the [O III] λ5007 Å line, ensuring consistent relative calibration of the spectral data. The radius of the broad-line region RBLR was taken to be equal to the average time delays (lags), amounting to ≈20 light-days for the Hβ line and ≈28 light-days for the Hα line.