Revista Mexicana de Astronomía y Astrofísica,
Accepted Papers for Volume 60 Number 2 (ADVANCE ACCESS)

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February 2024

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Abstract: In this study we analyzed TESS data of detached eccentric binary system DT Cam and the first physical parameters of the components were obtained. We found that out of eclipse variation of the system shows a small amplitude periodic variation. Most of the frequencies obtained are related with the orbital variation except one which the period was determined as ∼0.605 days. The masses and radii of the primary and secondary components were calculated as M₁=1.793 M_☉, M₂=1.414 M_☉, R₁=1.355 R_☉, and R₂=1.522 R_☉, respectively. Considering the physical properties of the primary component we conclude that it is a rotational variable. We found that the massive component is smaller than the low-mass component. It seems that the secondary component is a pre-main sequence star which is very important for understanding of stellar structure and evolution.

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March 2024

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Abstract: This paper investigated two scalar field cosmological models in f(R,T) gravity with cosmic transit and varying cosmological constant Λ(t). The cosmological constant tends to have a tiny positive value at the current epoch. The scalar field pressure p_φ shows a sign flipping for normal scalar field. For the phantom field, the scalar potential V(φ) is negative and the energy density ρ_φ=E_{_k}+V takes negative values when the equation of state parameter &omega:_φ is less than −1. The WEC, ρ=∑_iρ_i≥ 0 and p_i+ρ_i≥ 0, is not violated but with an instability for the second model at late-times. For a scalar field φ, the condition ρ_φ+p_φ=ρ_φ (1+ω_φ)=2E_k≥ 0 allows for ρ_φ< 0 if ω_φ< −1. The causality and energy conditions have been discussed for both models. The cosmology in both models was studied using a given function a(t) derived from the desired cosmic behavior which is the opposite of the traditional view.

Abstract: We have developed a method to determine the most reliable distances for a large group of planetary nebulae. For this purpose, we analyze the distances obtained from Gaia parallaxes and three determinations of statistical distances. The most reliable distance is derived for 2211 objects, and uncertainties for these distances are calculated in a homogeneous way. Using our most reliable distances, we compare the distributions of Galactic heights of hydrogen-poor and hydrogen-rich central stars of planetary nebulae. We find that [WR] central stars are closer to the Galactic plane than hydrogen-rich central stars and than other hydrogen-poor central stars. The latter have a similar distribution to hydrogen-rich central stars, which is significantly different from the one of [WR] central stars. This result disagrees with the proposed evolutionary sequence for hydrogen-poor central stars.

Abstract: In accordance with the AGN Unified Model, observed polarization can be related to the orientation of the line of sight with respect to the torus. AGN X-ray emission arises from the central region and carries the imprints of the obscuring material. We aim to test a unified scheme based on optical polarization using X-ray absorption. Using the XMM-Newton data of 19, optically polarized Seyfert 1 sources, we developed a systematic analysis by fitting a baseline model to test the presence of X-ray neutral or ionized (warm) absorption. We find that 100% of the polar-polarized sources show the presence of absorption, with 70% favoring the presence of a warm absorber. In contrast, the equatorial-polarized sources show a fraction of absorbed spectra of 75%, with only 50% consistent with the presence of a warm absorber.