arXiv subjects

V. V. Tsymbal

Publications and source records attributed to V. V. Tsymbal.

3 recordsLinked to original sources

arXiv2026

Cosmological Observational Tests in the JWST Era. II: The Tolman Test

In this work, we investigate a classical cosmological test - the dependence of galaxy surface brightness on redshift z (the Tolman test). We analyzed 6 860 galaxies with reliably determined spectroscopic redshifts from the ASTRODEEP-JWST photometric catalogue. We find that (a) the mean surface brightness of galaxies indeed decreases with increasing distance, and (b) the observed trend shows a significant departure from the prediction of the standard cosmological model, which expects the mean surface brightness to decline as ~ (1 + z)^-4.

astro-ph.CO↗

arXiv2025

Cosmological observational tests in the JWST Era. I: angular size - redshift

This study is devoted to the cosmological "angular size - redshift" test. An analysis is performed of the angular and linear sizes of galaxies from the new ASTRODEEP-JWST catalogue, which contains over 500,000 objects at high redshifts (up to ~20 photometrically determined and up to ~14 spectroscopically determined). For the calculations, 6 860 galaxies with reliably determined spectroscopic redshifts and 319,771 galaxies with known photometric redshifts were used. The linear sizes of galaxies were computed within the framework of two cosmological models - the standard (ΛCDM) model and one of the static models (the so-called "tired light" model). We have shown that within the framework of the ΛCDM model, a significant evolution of the linear sizes of galaxies is observed, with the rate of the evolution closely matching the rate of the cosmic expansion. In contrast, in the static model, the characteristic linear sizes of galaxies exhibit almost no evolution with increasing z.

astro-ph.CO↗

arXiv1998

Doppler-Zeeman mapping of magnetic CP stars: The case of the CP star HD 215441

When using a recently developed method of Doppler-Zeeman mapping (Vasilchenko et al., 1996) for analysis of a real star and real observational data, we are confronted with limitations due to the model simplifications and unavoidable errors in observed spectra. We discuss the errors introduced by probable inaccurracies of the mathematical model: analytical fit of the local Stokes parameters, influence of magneto-optical effect, ignorance of the true atmosphere model to compute local Stokes profiles, non-uniform surface brightness. The magnetic field configuration is found in the form of arbitrarily shifted dipole and sum of dipole and quadrupole, along with the distribution of Si, Ti, Cr and Fe over the surface of the star. Lines of different elements lead to the same magnetic field configuration, which is reliably determined for the part of the stellar surface which faces the observer. This allows to compare the magnetic field and chemical maps of the surface of HD 215441. A large-scale ring structure with the magnetic pole at its center is clearly seen on the abundance maps. Si, Cr and Ti are highly deficient where the magnetic field lines are vertical (near the magnetic pole) while Fe is highly overabundant there.

astro-ph↗