arXiv subjects

Manas Khassanov

Publications and source records attributed to Manas Khassanov.

3 recordsLinked to original sources

arXiv2026

ArxSP: A Python-Based Modular Application for the Reduction of Digitized Archival Spectra

We present a methodology for the reduction of archival spectral data together with the description of a newly developed Python-based software package featuring an interactive graphical interface. The work is primarily aimed at processing spectra obtained with electron-optical converters (EOCs), which are characterized by geometric distortions induced by the magnetic field of the registration system. Such data are preserved, in particular, in the archive of the Fesenkov Astrophysical Institute (FAI), which contains about 10,000 photographic plates. These distortions, along with the need to transform the optical density of the photographic material into relative intensity, cannot be corrected by standard astronomical packages such as IRAF and therefore require a dedicated approach. Historically, reductions at FAI were performed using a program written in the Microsoft QuickC language for computing platforms of the 1990s, rendering it incompatible with modern operating systems. The new package is implemented with the PyQt5 framework, retaining the logic of the original code while extending its functionality. The implemented algorithms include image rotation and cropping, geometric distortion correction, construction of the characteristic curve linking optical density and intensity, and direct conversion of pixel values in object spectra. The developed software ensures reproducible reduction of archival spectra and provides a cross-platform environment with potential for further extensions.

astro-ph.IM↗

arXiv2026

Thin accretion-disc transfer functions in the q-metric spacetime: quadrupolar lensing signatures

We study geometrically thin equatorial disc images in the static, axisymmetric q-metric spacetime using backward ray tracing. The Schwarzschild solution is recovered at $q=0$; for the nonzero deformations considered here, $r=2M$ is a curvature singularity rather than an event horizon. For a distant nearly face-on observer, we construct the first three equatorial transfer functions $r_m(b;q)$. In the {Schwarzschild} limit, the resolved third-crossing interval contains the critical impact parameter $b=3\sqrt{3}M$. As $q$ increases from $-0.3$ to $0.3$, the branch center shifts from $b_{3,c}/M\simeq3.716$ to $6.702$. In units of the physical monopole mass $\mathcal M=(1+q)M$, it instead decreases from $b_{3,c}/\mathcal M\simeq5.309$ to $5.156$. Much of the displacement in metric-parameter units therefore reflects the changing monopole scale. At fixed $\mathcal M$, the inclined first-intersection maps show that the contour dimensions increase with $q$, with larger relative changes near the inner disc. A prescribed power-law emissivity and relativistic frequency-shift weighting yield direct images whose integrated flux differs from the Schwarzschild value by at most $2.4\%$. Between the endpoint models, the horizontal median-flux position increases by $8.8\%$ and the interquartile width by $14.5\%$. Within this emission prescription, the residual deformation dependence appears mainly as a displacement and broadening of the brightness distribution. Higher-order radiative contributions are not included.

gr-qc↗

arXiv2026

Shadow, Emission, and Strong-Field Lensing of Dilatonic Black Holes

We study the shadow and strong-field optical properties of a static, spherically symmetric dyon-like dilatonic black hole. The photon sphere radius, critical impact parameter, and shadow radius are obtained and analyzed in terms of the charge $Q$ and the dilatonic coupling parameter $a$. We show that increasing these parameters decreases the photon sphere and shadow radii, leading to a smaller apparent shadow. The predicted angular diameter is compared with the observational data for M87$^{*}$ and SgrA$^{*}$, and the model parameters are constrained. We also estimate the high-frequency energy emission rate in the geometric-optics approximation and derive the leading Bozza coefficient $\bar{a}$, which characterizes the logarithmic behavior of the deflection angle in the strong-field regime. Astrophysical implication of the obtained outcomes are discussed.

gr-qc↗