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15 pages, 1034 KiB

Open AccessArticle

Light Variability from UV to Near-Infrared in the Ap Star CU Vir Induced by Chemical Spots

by Yury Pakhomov, Ilya Potravnov and Tatiana Ryabchikova

Galaxies 2025, 13(4), 97; https://doi.org/10.3390/galaxies13040097 - 21 Aug 2025

Multiwavelength modelling of the light variations in the chemically peculiar star CU Vir is presented. The modelling is based on the recent Doppler Imaging of CU Vir, which provides maps of the surface distribution of Si, Fe, He, and Cr. Intensity maps in [...] Read more.

Multiwavelength modelling of the light variations in the chemically peculiar star CU Vir is presented. The modelling is based on the recent Doppler Imaging of CU Vir, which provides maps of the surface distribution of Si, Fe, He, and Cr. Intensity maps in both individual photometric filters and in the wide wavelength range from UV to NIR were calculated, taking into account the individual chemical abundances on the stellar surface. Comparison with observations revealed good agreement of both the light curves and their amplitude along the spectrum. Additionally, we analysed changes in the photometric period of the CU Vir from 1955 to 2022, including TESS measurements. The data of the last decades clearly indicate a gradual decrease in this period. Measurements of the CU Vir period over the next two decades will be crucial for verifying or refuting the periodic nature of its variations. Full article

(This article belongs to the Special Issue Stellar Spectroscopy, Molecular Astronomy and Atomic Astronomy)

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10 pages, 343 KiB

Open AccessArticle

Distant Resolved Spectroscopic Binaries: Orbital Parallaxes Contradict Trigonometric Parallaxes

by Oleg Y. Malkov and Arseniy M. Sachkov

Galaxies 2025, 13(4), 96; https://doi.org/10.3390/galaxies13040096 - 21 Aug 2025

Viewed by 52

Abstract

Resolved spectroscopic binaries (RSB) are the only way (besides trigonometric parallax) to determine the dynamical, hypothesis-free distances to the stars of the galaxy. Analyzing the most comprehensive up-to-date data on RSB, we found that trigonometric parallaxes of all distant (

d > \approx

[...] Read more.

Resolved spectroscopic binaries (RSB) are the only way (besides trigonometric parallax) to determine the dynamical, hypothesis-free distances to the stars of the galaxy. Analyzing the most comprehensive up-to-date data on RSB, we found that trigonometric parallaxes of all distant (

d > \approx

0.5 kpc) binaries overestimate the distance by 10–50%. Such objects appear as single stars in Gaia and Hipparcos data, but their binarity can be detected/suspected by comparing trigonometric parallaxes in different data releases from these space missions. Full article

(This article belongs to the Special Issue Stellar Spectroscopy, Molecular Astronomy and Atomic Astronomy)

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22 pages, 5394 KiB

Open AccessArticle

Unveiling the Variability and Chemical Composition of AL Col

by Surath C. Ghosh, Santosh Joshi, Samrat Ghosh, Athul Dileep, Otto Trust, Mrinmoy Sarkar, Jaime Andrés Rosales Guzmán, Nicolás Esteban Castro-Toledo, Oleg Malkov, Harinder P. Singh, Kefeng Tan and Sarabjeet S. Bedi

Galaxies 2025, 13(4), 93; https://doi.org/10.3390/galaxies13040093 - 14 Aug 2025

Viewed by 222

Abstract

In this study, we present analysis of TESS photometry, spectral energy distribution (SED), high-resolution spectroscopy, and spot modeling of the

α^{2}

CVn-type star AL Col (HD 46462). The primary objective is to determine its fundamental physical parameters and investigate its surface activity [...] Read more.

In this study, we present analysis of TESS photometry, spectral energy distribution (SED), high-resolution spectroscopy, and spot modeling of the

α^{2}

CVn-type star AL Col (HD 46462). The primary objective is to determine its fundamental physical parameters and investigate its surface activity characteristics. Using TESS short-cadence (120 s) SAP flux, we identified a rotational frequency of 0.09655

d^{- 1}

(

P_{rot} = 10.35733

d). Wavelet analysis reveals that while the amplitudes of the harmonic components vary over time, the strength of the primary rotational frequency remains stable. A SED analysis of multi-band photometric data yields an effective temperature (

T_{eff}

) of 11,750 K. High-resolution spectroscopic observations covering wavelengthrange 4500–7000 Å provide refined estimates of

T_{eff}

= 13,814 ± 400 K,

log g

= 4.09 ± 0.08 dex, and

υ sin i

= 16 ± 1 km s⁻¹. Abundance analysis shows solar-like composition of O ii, Mg ii, S ii, and Ca ii, while helium is under-abundant by 0.62 dex. Rare earth elements (REEs) exhibit over-abundances of up to 5.2 dex, classifying the star as an Ap/Bp-type star. AL Col has a radius of

R = 3.74 \pm 0.48 R_{⊙}

, with its H–R diagram position estimating a mass of

M = 4.2 \pm 0.2 M_{⊙}

and an age of

0.12 \pm 0.01

Gyr, indicating that the star has slightly evolved from the main sequence. The TESS light curves were modeled using a three-evolving-spot configuration, suggesting the presence of differential rotation. This star is a promising candidate for future investigations of magnetic field diagnostics and the vertical stratification of chemical elements in its atmosphere. Full article

(This article belongs to the Special Issue Stellar Spectroscopy, Molecular Astronomy and Atomic Astronomy)

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20 pages, 9155 KiB

Open AccessArticle

Long-Term Stability of Chemical Spots and Reasons for the Period Variations in Ap Star CU Vir

by Ilya Potravnov, Tatiana Ryabchikova, Leonid Kitchatinov and Yuri Pakhomov

Galaxies 2025, 13(4), 90; https://doi.org/10.3390/galaxies13040090 - 12 Aug 2025

Viewed by 297

Abstract

We present the results of Doppler Imaging of the Ap star CU Vir in the silicon lines over the 1985–2011 time span, as well as multi-element imaging in the 2009/2011 epoch. The surface distribution of silicon in CU Vir exhibits stability over the [...] Read more.

We present the results of Doppler Imaging of the Ap star CU Vir in the silicon lines over the 1985–2011 time span, as well as multi-element imaging in the 2009/2011 epoch. The surface distribution of silicon in CU Vir exhibits stability over the approximately 26 years studied: the number, shape, and mutual distribution of the overabundance spots have remained unchanged. The modelling of the light curve based on the surface elemental distribution obtained with DI did not reveal any significant changes in the shape of the light curve that could explain the photometric phase shift observed in CU Vir. Consequently, the phase shifts and changes in the photometric period of CU Vir are caused by the rigid longitudinal drift of the surface-abundance structures. We performed simulations of the Tayler instability of the background magnetic field of CU Vir, and discuss the possibility of explaining the period variations by the drift of surface instability modes. Full article

(This article belongs to the Special Issue Stellar Spectroscopy, Molecular Astronomy and Atomic Astronomy)

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15 pages, 6509 KiB

Open AccessArticle

Abundance Analysis of the Spectroscopic Binary α Equulei

by Anna Romanovskaya and Sergey Zvyagintsev

Galaxies 2025, 13(4), 88; https://doi.org/10.3390/galaxies13040088 - 6 Aug 2025

Viewed by 336

Abstract

We present the results of a detailed spectroscopic analysis of the double-lined spectroscopic binary system

α

Equulei. High-resolution spectra obtained with the SOPHIE spectrograph at various orbital phases were used to disentangle the composite spectra into individual components using the spectral line deconvolution [...] Read more.

We present the results of a detailed spectroscopic analysis of the double-lined spectroscopic binary system

α

Equulei. High-resolution spectra obtained with the SOPHIE spectrograph at various orbital phases were used to disentangle the composite spectra into individual components using the spectral line deconvolution (SLD) iterative technique. The atmospheric parameters of each component were refined with the SME (spectroscopy made easy) package and further validated by following methods: SED (spectral energy distribution), the independence of the abundance of individual Fe i–ii lines on the reduced equivalent width and ionisation potential, and fitting with the hydrogen line profiles. Our accurate abundance analysis uses a hybrid technique for spectrum synthesis. This is based on classical model atmospheres that are calculated under the assumption of local thermodynamic equilibrium (LTE), together with non-LTE (NLTE) line formation. This is used for 15 out of the 25 species from C to Nd that were investigated. The primary giant component (G7-type) exhibits a typical abundance pattern for normal stars, with elements from He to Fe matching solar values and neutron-capture elements showing overabundances up to 0.5 dex. In contrast, the secondary dwarf component displays characteristics of an early stage Am star. The observed abundance differences imply distinct diffusion processes in their atmospheres. Our results support the scenario in which chemical peculiarities in Am stars develop during the main sequence and may decrease as the stars evolve toward the subgiant branch. Full article

(This article belongs to the Special Issue Stellar Spectroscopy, Molecular Astronomy and Atomic Astronomy)

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10 pages, 335 KiB

Open AccessArticle

On the Probability of the Astrometric Resolution of Spectroscopic Binaries into Components

by Dugasa Belay Zeleke, Alexey Yu. Sytov, Seblu Humne Negu, Arseniy M. Sachkov, Solomon Belay Tessema and Oleg Yu. Malkov

Galaxies 2025, 13(4), 87; https://doi.org/10.3390/galaxies13040087 - 5 Aug 2025

Viewed by 301

Abstract

Resolved spectroscopic binaries (RSBs) are an extremely valuable class of objects, being the only (apart from trigonometric) supplier of dynamical stellar parallaxes. This circumstance, as well as the comparative paucity of studied RSBs, makes the problem of identifying binary systems potentially capable of [...] Read more.

Resolved spectroscopic binaries (RSBs) are an extremely valuable class of objects, being the only (apart from trigonometric) supplier of dynamical stellar parallaxes. This circumstance, as well as the comparative paucity of studied RSBs, makes the problem of identifying binary systems potentially capable of being added to the list of known RSBs extremely urgent. In this paper, we propose a methodology for estimating the probability of a spectroscopic binary system to be resolved into components, perform the first step of its application to the SB9 catalogue, and present preliminary results, in particular, a list of the most promising RSB candidates. Full article

(This article belongs to the Special Issue Stellar Spectroscopy, Molecular Astronomy and Atomic Astronomy)

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13 pages, 1787 KiB

Open AccessArticle

A New Activity Cycle of V1413 Aql

by Anna Tatarnikova, Andrey Tatarnikov, Nataliia Maslennikova, Alexander Dodin, Marina Burlak, Natalia Ikonnikova, Alexander Belinski and Georgy Nikishev

Galaxies 2025, 13(4), 86; https://doi.org/10.3390/galaxies13040086 - 4 Aug 2025

Viewed by 320

Abstract

V1413 Aql is an anomalous classical symbiotic star that has remained in an active state almost continuously. After failing to return to quiescence following the 2020 outburst, it underwent a new flare in 2025. We present an analysis of new photometric and spectroscopic [...] Read more.

V1413 Aql is an anomalous classical symbiotic star that has remained in an active state almost continuously. After failing to return to quiescence following the 2020 outburst, it underwent a new flare in 2025. We present an analysis of new photometric and spectroscopic observations, which provide estimates for the binary components at different stages of activity:

L_{cool} = 1700

L_{⊙}

,

R_{cool} = 130

R_{⊙}

;

L_{hot} = 800

L_{⊙}

,

R_{hot} = 28

R_{⊙}

during minimum;

L_{hot} = 7000

L_{⊙}

,

R_{hot} = 64

R_{⊙}

at the 2025 maximum. The significant increase in the luminosity of the hot component during the 2025 outburst deviates from the typical behavior observed in classical symbiotic stars, where outbursts are generally attributed to a redistribution of spectral energy rather than intrinsic changes in luminosity. Full article

(This article belongs to the Special Issue Stellar Spectroscopy, Molecular Astronomy and Atomic Astronomy)

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20 pages, 1666 KiB

Open AccessArticle

Looking for Signs of Unresolved Binarity in the Continuum of LAMOST Stellar Spectra

by Mikhail Prokhorov, Kefeng Tan, Nikolay Samus, Ali Luo, Dana Kovaleva, Jingkun Zhao, Yujuan Liu, Pavel Kaygorodov, Oleg Malkov, Yihan Song, Sergey Sichevskij, Lev Yungelson and Gang Zhao

Galaxies 2025, 13(4), 83; https://doi.org/10.3390/galaxies13040083 - 30 Jul 2025

Viewed by 437

Abstract

We describe an attempt to derive the binarity rate of samples of 166 A-, F-, G-, and K-type stars from LAMOST DR5 and 1000 randomly selected presumably single stars from Gaia DR3 catalogs. To this end, we compared continua of the observed spectra [...] Read more.

We describe an attempt to derive the binarity rate of samples of 166 A-, F-, G-, and K-type stars from LAMOST DR5 and 1000 randomly selected presumably single stars from Gaia DR3 catalogs. To this end, we compared continua of the observed spectra with the continua of synthetic spectra from within 3700

< λ < 9097

Å. The latter spectra were reduced to the LAMOST set of wavelengths, while the former ones were smoothed. Next, we searched for every observed star of the nearest synthetic spectrum using a four-parameter representation—

T_{eff}

,

log g

,

[Fe / H]

, and a range of interstellar absorption values. However, rms deviations of observed spectra from synthetic ones appeared to be not sufficient to claim that any of the stars is a binary. We conclude that comparison of the intensity of pairs of spectral lines remains the best way to detect binarity. Full article

(This article belongs to the Special Issue Stellar Spectroscopy, Molecular Astronomy and Atomic Astronomy)

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11 pages, 498 KiB

Open AccessArticle

LAMOST Spectroscopy and Gaia Photo-Astrometry for an Interstellar Extinction Study

by Oleg Malkov, Aleksandra Avdeeva and Dana Kovaleva

Galaxies 2024, 12(5), 65; https://doi.org/10.3390/galaxies12050065 - 17 Oct 2024

Viewed by 1031

Abstract

The aim of this work is to establish the present accuracy and convergence of available estimates of galactic extinction. We determine the galactic interstellar extinction in selected high-latitude areas of the sky based on Gaia DR3 astrometry and photometry and spectroscopic data from [...] Read more.

The aim of this work is to establish the present accuracy and convergence of available estimates of galactic extinction. We determine the galactic interstellar extinction in selected high-latitude areas of the sky based on Gaia DR3 astrometry and photometry and spectroscopic data from the LAMOST survey. For this purpose, we choose 42 northern high-latitude sky areas surrounding supernovae that allowed establishing the accelerated expansion of the universe. We compare our results with the estimates accepted in that paper and find that they agree well, within observational errors. Simultaneously, the estimates for galactic extinction by other authors along the same sightlines show systematic differences, which can cause the distance to the extragalactic object to change by ±3–5%. Full article

(This article belongs to the Special Issue Stellar Spectroscopy, Molecular Astronomy and Atomic Astronomy)

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