Galaxies

13 pages, 542 KiB

Open AccessArticle

A List of the Most Prospective Eclipsing Cataclysmic Variables According to the TESS

by Gulnur Subebekova, Makhabbat Adil, Serik Khokhlov, Aldiyar Agishev and Almansur Agishev

Galaxies 2025, 13(4), 92; https://doi.org/10.3390/galaxies13040092 (registering DOI) - 14 Aug 2025

Eclipsing cataclysmic variables (CVs) are key targets for determining binary system parameters through photometric modeling, yet many of them remain poorly characterized. In this work, we present a list (catalog) of 37 confirmed eclipsing CVs selected based on high-quality and publicly available TESS [...] Read more.

Eclipsing cataclysmic variables (CVs) are key targets for determining binary system parameters through photometric modeling, yet many of them remain poorly characterized. In this work, we present a list (catalog) of 37 confirmed eclipsing CVs selected based on high-quality and publicly available TESS photometric data. The sample includes both long-period systems (with orbital periods exceeding 4 h), such as Z Cam, U Gem, and nova-like variables, as well as a significant number of SW Sextantis stars. Selection criteria required the presence of clearly defined eclipses and sufficient signal-to-noise ratios for reliable analysis. The catalog provides a foundation for phase-folded light curve studies and future modeling efforts aimed at deriving key physical parameters such as component masses, radii, inclinations, and accretion geometries. Notably, several systems, such as V482 Cam, OZ Dra, ASASSN-14ix, and others, have no previously published physical parameters. Our list is accessible via a dedicated website, where each system will have a separate page, including data from TESS, AAVSO, and ZTF. This resource is intended to support detailed follow-up studies. It may encourage other research groups with observational and modeling expertise to contribute to the investigation of these promising but understudied systems. Full article

11 pages, 3500 KiB

Open AccessArticle

Wind and Eruptive Mass Loss near the Eddington Limit

by Stan Owocki

Galaxies 2025, 13(4), 91; https://doi.org/10.3390/galaxies13040091 (registering DOI) - 13 Aug 2025

Abstract

Luminous, hot, massive stars can lose mass both through quasi-steady winds driven by line-scattering of the star’s continuum luminosity, and through transient eruptions identified as Luminous Blue Variables (LBVs). This paper compares and contrasts the processes involved in steady vs. eruptive mass loss, [...] Read more.

Luminous, hot, massive stars can lose mass both through quasi-steady winds driven by line-scattering of the star’s continuum luminosity, and through transient eruptions identified as Luminous Blue Variables (LBVs). This paper compares and contrasts the processes involved in steady vs. eruptive mass loss, with an emphasis on their dependence on the star’s proximity to the classical Eddington limit. For winds, I examine the role of the iron opacity bump in initiating a quasi-continuum-driven outflow, which can induce atmospheric turbulence in O-stars, an envelope inflation cycle in LBVs, or enhanced wind mass loss in WR stars. In contrast, the giant eruptions of eruptive LBVs like

η

Carinae require a sudden addition of energy to the stellar envelope, like that which can occur from stellar mergers. The positive net energy imparted to a substantial fraction (>10%) of the stellar mass leads to sudden ejection that closely follows an analytic exponential similarity solution. Moreover, the rapid rotation and enhanced luminosity of the post-merger star drive a super-Eddington wind. Due to equatorial gravity darkening, this wind is stronger over the poles, sculpting a bipolar structure in the ejected mass, consistent with observations of

η

Carinae’s Homunculus nebula. Full article

(This article belongs to the Special Issue Circumstellar Matter in Hot Star Systems)

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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 24

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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21 pages, 795 KiB

Open AccessReview

Cosmic Magnification of High-Redshift Submillimeter Galaxies

by Marcos M. Cueli, Joaquín González-Nuevo, Laura Bonavera and Andrea Lapi

Galaxies 2025, 13(4), 89; https://doi.org/10.3390/galaxies13040089 - 11 Aug 2025

Viewed by 66

Abstract

Weak lensing magnification probes the correlation between galaxies and the underlying matter field in a similar fashion to galaxy–galaxy lensing shear. Although it has long been sidelined in favor of the latter on the grounds of poorer performance in terms of statistical significance, [...] Read more.

Weak lensing magnification probes the correlation between galaxies and the underlying matter field in a similar fashion to galaxy–galaxy lensing shear. Although it has long been sidelined in favor of the latter on the grounds of poorer performance in terms of statistical significance, the provision of a large sample of high-redshift submillimeter galaxies by the Herschel observatory has transformed the landscape of cosmic magnification due to their optimal physical properties for magnification analyses. This review aims to summarize the core principles and unique advantages of the cosmic magnification of high-redshift submillimeter galaxies and discuss recent results applied to cosmological inference. The outlook and challenges of this observable are also outlined, with a focus on the ample scope for exploration and its potential to emerge as a competitive independent cosmological probe. Full article

(This article belongs to the Special Issue The Observation and Detection of Dusty Star-Forming Galaxies)

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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 227

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 204

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 246

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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14 pages, 3378 KiB

Open AccessArticle

The pcGR Within the Hořava-Lifshitz Gravity and the Wheeler-deWitt Quantization

by Peter O. Hess, César A. Zen Vasconcellos and Dimiter Hadjimichef

Galaxies 2025, 13(4), 85; https://doi.org/10.3390/galaxies13040085 - 1 Aug 2025

Viewed by 266

Abstract

We investigate pseudo-complex General Relativity (pcGR)—a coordinate-extended formulation of General Relativity (GR)—within the framework of Hořava-Lifshitz gravity, a regularized theory featuring anisotropic scaling. The pcGR framework bridges GR with modified gravitational theories through the introduction of a minimal length scale. Focusing on Schwarzschild [...] Read more.

We investigate pseudo-complex General Relativity (pcGR)—a coordinate-extended formulation of General Relativity (GR)—within the framework of Hořava-Lifshitz gravity, a regularized theory featuring anisotropic scaling. The pcGR framework bridges GR with modified gravitational theories through the introduction of a minimal length scale. Focusing on Schwarzschild black holes, we derive the Wheeler-deWitt equation, obtaining a quantized description of pcGR. Using perturbative methods and semi-classical approximations, we analyze the solutions of the equations and their physical implications. A key finding is the avoidance of the central singularity due to nonlinear interaction terms in the Hořava-Lifshitz action. Notably, extrinsic curvature (kinetic energy) contributions prove essential for singularity resolution, even in standard GR. Furthermore, the theory offers new perspectives on dark energy, proposing an alternative mechanism for its accumulation. Full article

(This article belongs to the Special Issue Cosmology and the Quantum Vacuum—2nd Edition)

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44 pages, 8269 KiB

Open AccessArticle

Contribution of AGN to the Morphological Parameters of Their Host Galaxies up to Intermediate Redshifts of z ∼ 2

by Tilahun Getachew-Woreta, Mirjana Pović, Jaime Perea, Isabel Marquez, Josefa Masegosa, Antoine Mahoro and Shimeles Terefe Mengistue

Galaxies 2025, 13(4), 84; https://doi.org/10.3390/galaxies13040084 - 1 Aug 2025

Viewed by 385

Abstract

The presence of Active Galaxy Nuclei (AGN) can affect the morphological classification of galaxies. This work aims to determine how the contribution of AGN affects the most-used morphological parameters down to the redshift of z ∼ 2 in COSMOS-like conditions. We use a [...] Read more.

The presence of Active Galaxy Nuclei (AGN) can affect the morphological classification of galaxies. This work aims to determine how the contribution of AGN affects the most-used morphological parameters down to the redshift of z ∼ 2 in COSMOS-like conditions. We use a sample of >2000 local non-active galaxies, with a well-known visual morphological classification, and add an AGN as an unresolved component that contributes to the total galaxy flux with 5–75%. We moved all the galaxies to lower magnitudes (higher redshifts) to map the conditions in the COSMOS field, and we measured six morphological parameters. The greatest impact on morphology occurs when considering the combined effect of magnitude, redshift, and AGN, with spiral galaxies being the most affected. In general, all the concentration parameters change significantly if the AGN contribution is >25% and the magnitude > 23. We find that the GINI coefficient is the most stable in terms of AGN and magnitude/redshift, followed by the moment of light (M20), Conselice–Bershady (CCON), and finally the Abraham (CABR) concentration indexes. We find that, when using morphological parameters, the combination of CABR, CCON, and asymmetry is the most effective in classifying active galaxies at high-redshift, followed by a combination of CABR and GINI. Full article

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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 354

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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27 pages, 18125 KiB

Open AccessReview

Molecules and Chemistry in Red Supergiants

by Lucy M. Ziurys and Anita M. S. Richards

Galaxies 2025, 13(4), 82; https://doi.org/10.3390/galaxies13040082 - 21 Jul 2025

Viewed by 516

Abstract

The envelopes of Red Supergiants (RSGs) have a unique chemical environment not seen in other types of stars. They foster an oxygen-rich synthesis but are tempered by sporadic and chaotic mass loss, which distorts the envelope and creates complex outflow sub-structures consisting of [...] Read more.

The envelopes of Red Supergiants (RSGs) have a unique chemical environment not seen in other types of stars. They foster an oxygen-rich synthesis but are tempered by sporadic and chaotic mass loss, which distorts the envelope and creates complex outflow sub-structures consisting of knots, clumps, and arcs. Near the stellar photosphere, molecules and grains form under approximate LTE conditions, as predicted by chemical models. However, the complicated outflows appear to have distinct chemistries generated by shocks and dust destruction. Various RSG envelopes have been probed for their molecular content, mostly by radio and millimeter observations; however, VY Canis Majoris (VY CMa) and NML Cygni (NML Cyg) display the highest chemical complexity, and also the most complicated envelope structure. Thus far, over 29 different molecules have been identified in the envelopes of RSGs. Some molecules are common for circumstellar gas, including CO, SiO, HCN and H₂O, which have abundances of ∼10⁻⁶–10⁻⁴, relative to H₂. More exotic oxides have additionally been discovered, such as AlO, AlOH, PO, TiO₂, and VO, with abundances of ∼10⁻⁹–10⁻⁷. RSG shells support intricate maser emission in OH, H₂O and SiO, as well. Studies of isotope ratios in molecules suggest dredge-up at least into the H-burning shell, but further exploration is needed. Full article

(This article belongs to the Special Issue The Red Supergiants: Crucial Signposts for the Fate of Massive Stars)

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15 pages, 1982 KiB

Open AccessReview

Stellar Evolution Through the Red Supergiant Phase

by Sylvia Ekström and Cyril Georgy

Galaxies 2025, 13(4), 81; https://doi.org/10.3390/galaxies13040081 - 17 Jul 2025

Viewed by 502

Abstract

Massive stars less massive than ∼30

M_{⊙}

evolve into a red supergiant after the main sequence. Given a standard IMF, this means about 80% of all single massive stars will experience this phase. RSGs are dominated by convection, with a radius that [...] Read more.

Massive stars less massive than ∼30

M_{⊙}

evolve into a red supergiant after the main sequence. Given a standard IMF, this means about 80% of all single massive stars will experience this phase. RSGs are dominated by convection, with a radius that may extend up to thousands of solar radii. Their low temperature and gravity make them prone to losing large amounts of mass, either through pulsationally driven wind or through mass-loss outburst. RSGs are the progenitors of the most common core-collapse supernovae, type II. In the present review, we give an overview of our theoretical understanding about this spectacular phase of massive star evolution. Full article

(This article belongs to the Special Issue The Red Supergiants: Crucial Signposts for the Fate of Massive Stars)

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11 pages, 5078 KiB

Open AccessArticle

Doppler Tomography of the Be Star HD 698

by Ilfa A. Gabitova, Sergey V. Zharikov, Anatoly S. Miroshnichenko, Alex Carciofi, Azamat A. Khokhlov, Aldiyar Agishev and Peter Prendergast

Galaxies 2025, 13(4), 80; https://doi.org/10.3390/galaxies13040080 - 16 Jul 2025

Viewed by 564

Abstract

We present a Doppler tomography study of the Be star HD 698, recently resolved via interferometry as a post-mass-transfer binary system consisting of a Be star and a stripped, pre-subdwarf companion. Based on 76 high-resolution optical spectra obtained between 2014 and 2023, we [...] Read more.

We present a Doppler tomography study of the Be star HD 698, recently resolved via interferometry as a post-mass-transfer binary system consisting of a Be star and a stripped, pre-subdwarf companion. Based on 76 high-resolution optical spectra obtained between 2014 and 2023, we analyze the H

α

and H

β

emission lines and apply Doppler tomography to map the structure of the circumstellar disk. The H

α

line reveals an asymmetric, multi-component velocity distribution, with an emission feature closely following the orbital motion of the companion. V/R variations in both H

α

and H

β

lines are phase-locked with the companion’s orbital motion, indicating a tidally induced disk asymmetry. We discuss possible origins of the companion-centered H

α

emission, including a circumsecondary disk, a transient mass-transfer stream, and stellar wind. Full article

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15 pages, 395 KiB

Open AccessArticle

1PN Effective Binary Lagrangian for the Gravity–Kalb–Ramond Sector in the Conservative Regime

by Vegard Undheim, Eirik Eik Svanes and Alex B. Nielsen

Galaxies 2025, 13(4), 79; https://doi.org/10.3390/galaxies13040079 - 8 Jul 2025

Viewed by 523

Abstract

Within the framework of string theory, a number of new fields can arise that correct the Einstein–Hilbert action, including the Kalb–Ramond two-form field. In this work, we derive explicitly first-order relativistic corrections to conservative dynamics in the presence of a Kalb–Ramond field using [...] Read more.

Within the framework of string theory, a number of new fields can arise that correct the Einstein–Hilbert action, including the Kalb–Ramond two-form field. In this work, we derive explicitly first-order relativistic corrections to conservative dynamics in the presence of a Kalb–Ramond field using the effective field theory approach. The resulting additional terms in the Lagrangian governing conservative binary dynamics are presented explicitly. Full article

(This article belongs to the Special Issue Cosmology and the Quantum Vacuum—2nd Edition)

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11 pages, 1002 KiB

Open AccessArticle

Unveiling the Evolution of MWC 728: Non-Conservative Mass Transfer in an FS CMa Binary

by Nadezhda L. Vaidman, Serik A. Khokhlov and Aldiyar T. Agishev

Galaxies 2025, 13(4), 78; https://doi.org/10.3390/galaxies13040078 - 7 Jul 2025

Viewed by 547

Abstract

We combine corrected Gaia DR3 astrometry with non-conservative MESA modelling to retrace the evolution of the FS-CMa binary MWC 728. The revised parallax sets the distance at

d = 1.2 \pm 0.1

kpc, leading—after Monte-Carlo error propagation—to luminosities of [...] Read more.

We combine corrected Gaia DR3 astrometry with non-conservative MESA modelling to retrace the evolution of the FS-CMa binary MWC 728. The revised parallax sets the distance at

d = 1.2 \pm 0.1

kpc, leading—after Monte-Carlo error propagation—to luminosities of

log {(L / L_{⊙})}_{acc} = 2.6 \pm 0.1

and

log {(L / L_{⊙})}_{don} = 1.5 \pm 0.1

, corresponding to the accretor and donor, respectively. A fiducial binary track that starts with

M_{don} = 3.6 \pm 0.1 M_{⊙}

,

M_{acc} = 1.8 \pm 0.1 M_{⊙}

, and

P_{0} = 21.0 \pm 0.2

d reproduces the observations provided the Roche-lobe overflow, which is moderately non-conservative: only

39 %

of the transferred mass is retained by the accretor, while the remainder leaves the system via (i) a fast isotropic wind from the donor (

α = 0.01

), (ii) isotropic re-emission near the accretor (

β = 0.45

), and (iii) outflow into a circumbinary torus (

δ = 0.15

, lever arm

γ = 1.3

). These channels remove sufficient angular momentum to expand the orbit to the observed

P_{obs} = 27.5 \pm 0.1

d while sustaining the dusty circumbinary outflow. At

t ≃ 223

Myr, the model matches every current observable:

M_{don} = 1.30 \pm 0.05 M_{⊙}

,

M_{acc} = 2.67 \pm 0.05 M_{⊙}

, mass ratio

q = 2.0 \pm 0.1

, and an ongoing transfer rate of

\dot{M} ≃ (1 \pm 0.3) \times 10^{- 6} M_{⊙} {yr}^{- 1}

. MWC 728 thus serves as a benchmark intermediate-mass binary for testing how non-conservative outflows regulate angular-momentum loss and orbital growth. Full article

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16 pages, 1360 KiB

Open AccessReview

Mass Loss in Be Stars: News from Two Fronts

by Alex C. Carciofi, Guilherme P. P. Bolzan, Pâmela R. Querido, Amanda C. Rubio, Jonathan Labadie-Bartz, Tajan H. de Amorim, Ariane C. Fonseca Silva and Vittória L. Schiavolim

Galaxies 2025, 13(4), 77; https://doi.org/10.3390/galaxies13040077 - 7 Jul 2025

Viewed by 661

Abstract

Be stars are characterized by the presence of a circumstellar Keplerian disk formed from material ejected from the rapidly rotating stellar surface. This article presents recent observational and theoretical progress on two central aspects of this phenomenon: the mechanisms driving mass loss, and [...] Read more.

Be stars are characterized by the presence of a circumstellar Keplerian disk formed from material ejected from the rapidly rotating stellar surface. This article presents recent observational and theoretical progress on two central aspects of this phenomenon: the mechanisms driving mass loss, and the fate of the ejected material. Using simultaneous TESS photometry and ground-based spectroscopy, we examine the short-term variability associated with discrete mass ejection events, or “flickers”, and review strong evidence linking them to pulsational activity near the stellar surface. Complementary 3D hydrodynamic simulations reproduce key observational signatures and establish that disk formation requires compact and asymmetric ejection sites with sufficient angular momentum to overcome re-accretion. In systems with binary companions, new high-resolution simulations resolve the outer disk for the first time and identify five dynamically distinct regions, including a circumsecondary disk and a circumbinary spiral outflow. Together, these results provide a coherent framework that traces the full life cycle of disk material from pulsation-driven ejection near the stellar surface to its final destination, whether re-accreted by the companion or lost from the system entirely. Full article

(This article belongs to the Special Issue Circumstellar Matter in Hot Star Systems)

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18 pages, 2282 KiB

Open AccessArticle

Quantifying the Unwinding Due to Ram Pressure Stripping in Simulated Galaxies

by Rubens E. G. Machado, Caroline F. O. Grinberg and Elvis A. Mello-Terencio

Galaxies 2025, 13(4), 76; https://doi.org/10.3390/galaxies13040076 - 7 Jul 2025

Viewed by 639

Abstract

Galaxies moving through the gas of the intracluster medium (ICM) experience ram pressure stripping, which can leave behind a gas tail. When a disk galaxy receives the wind edge-on, however, the characteristic signature is not a typical jellyfish tail, but rather an unwinding [...] Read more.

Galaxies moving through the gas of the intracluster medium (ICM) experience ram pressure stripping, which can leave behind a gas tail. When a disk galaxy receives the wind edge-on, however, the characteristic signature is not a typical jellyfish tail, but rather an unwinding of the spiral arms. We aim to quantify such asymmetries both in the gas and in the stellar component of a simulated galaxy. To this end, we simulate a gas-rich star-forming spiral galaxy moving through a self-consistent ICM gas. The amplitude and location of the asymmetries were measured via Fourier decomposition. We found that the asymmetry is much more evident in the gas component, but it is also measurable in the stars. The amplitude tends to increase with time and the asymmetry radius migrates inwards. We found that, when considering the gas, the spiral arms extend much further and are more unwound than the corresponding stellar arms. Characterizing the unwinding via simulations should help inform the observational criteria used to classify ram pressure stripped galaxies, as opposed to asymmetries induced by other mechanisms. Full article

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19 pages, 601 KiB

Open AccessArticle

The I-Love Universal Relation for Polytropic Stars Under Newtonian Gravity

by Rui Xu, Alejandro Torres-Orjuela and Pau Amaro Seoane

Galaxies 2025, 13(4), 75; https://doi.org/10.3390/galaxies13040075 - 2 Jul 2025

Viewed by 538

Abstract

The moment of inertia and tidal deformability of idealized stars with polytropic equations of state (EOSs) are numerically calculated under both Newtonian gravity and general relativity (GR). The results explicitly confirm that the relation between the moment of inertia and tidal deformability, parameterized [...] Read more.

The moment of inertia and tidal deformability of idealized stars with polytropic equations of state (EOSs) are numerically calculated under both Newtonian gravity and general relativity (GR). The results explicitly confirm that the relation between the moment of inertia and tidal deformability, parameterized by the star’s mass, exhibits variations up to

1 %

and

10 %

for different polytropic indices in Newtonian gravity and GR, respectively. This indicates a more robust I-Love universal relation in the Newtonian framework. The theoretically derived I-Love universal relation for polytropic stars is subsequently tested against observational data for the moment of inertia and tidal deformability of the eight planets and some moons in our solar system. The analysis reveals that the theoretical I-Love universal relation aligns well with the observational data, suggesting that it can serve as an empirical relation. Consequently, it enables the estimation of either the moment of inertia or the tidal deformability of an exoplanet if one of these quantities, along with the mass of the exoplanet, is known. Full article

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14 pages, 3543 KiB

Open AccessArticle

The BSN Application-I: Photometric Light Curve Solutions of Contact Binary Systems

by Ehsan Paki, Atila Poro and Minoo Dokht Moosavi Rowzati

Galaxies 2025, 13(4), 74; https://doi.org/10.3390/galaxies13040074 - 30 Jun 2025

Cited by 1 | Viewed by 572

Abstract

Light curve analysis of W UMa-type contact binary systems using MCMC or MC methods can be time-consuming, primarily because the repeated generation of synthetic light curves tends to be relatively slow during the fitting process. Although various approaches have been proposed to address [...] Read more.

Light curve analysis of W UMa-type contact binary systems using MCMC or MC methods can be time-consuming, primarily because the repeated generation of synthetic light curves tends to be relatively slow during the fitting process. Although various approaches have been proposed to address this issue, their implementation is often challenging due to complexity or uncertain performance. In this study, we introduce the BSN application, whose name is taken from the BSN project. The application is designed for analyzing contact binary system light curves, supporting photometric data, and employing an MCMC algorithm for efficient parameter estimation. The BSN application generates synthetic light curves more than 40 times faster than PHOEBE during the MCMC fitting process. The BSN application enhances light curve analysis with an expanded feature set and a more intuitive interface while maintaining compliance with established scientific standards. In addition, we present the first light curve analyses of four contact binary systems based on the TESS data, utilizing the BSN application version 1.0. We also conducted a light curve analysis using the PHOEBE Python code and compared the resulting outputs. Two of the target systems exhibited asymmetries in the maxima of their light curves, which were appropriately modeled by introducing a cold starspot on one of the components. The estimated mass ratios of these total-eclipse systems place them within the category of low mass ratio contact binary stars. The estimation of the absolute parameters for the selected systems was carried out using the

P - a

empirical relationship. Based on the effective temperatures and masses of the components, three of the target systems were classified as A-subtype, while TIC 434222993 was identified as a W-subtype system. Full article

(This article belongs to the Special Issue Study on Contact Binary Stars)

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15 pages, 1991 KiB

Open AccessArticle

ALMA Observations of G333.6-0.2: Molecular and Ionized Gas Environment

by Aruzhan Omar, Aidana Abdirakhman, Nazgul Alimgazinova, Meiramgul Kyzgarina, Aisha Naurzbayeva, Zhomartkali Islyam, Kunduz Turekhanova, Aizat Demessinova and Arailym Manapbayeva

Galaxies 2025, 13(4), 73; https://doi.org/10.3390/galaxies13040073 - 27 Jun 2025

Viewed by 565

Abstract

We present high-angular resolution observations, conducted with the Atacama Large Millimeter/Submillimeter Array (ALMA) in Band 6, of high-excitation molecular lines of

{CH}_{3} CN

, CH₃OH, and the H29

α

radio recombination line, towards the G333.6-0.2 ultracompact (UC) H ii region. [...] Read more.

We present high-angular resolution observations, conducted with the Atacama Large Millimeter/Submillimeter Array (ALMA) in Band 6, of high-excitation molecular lines of

{CH}_{3} CN

, CH₃OH, and the H29

α

radio recombination line, towards the G333.6-0.2 ultracompact (UC) H ii region. Our observations reveal three hot molecular cores: A, B, and C, where emission is detected in ten components of the

J = 14 \to 13

rotational ladder of

{CH}_{3} CN

and in the CH₃OH

J = 5_{1, 4} \to 4_{1, 3}

transition. Rotational diagram analysis of

{CH}_{3} CN

reveals excitation temperatures ranging from 380 to 430 K. First-order moment maps of

{CH}_{3} CN

and CH₃OH reveal distinct velocity gradients in all cores, suggesting rotating structures, with core A also showing evidence of expansion motions. The H29

α

recombination line shows a linewidth of

30.2 \pm 0.12

km s⁻¹, dominated by dynamical and thermal broadening, indicative of large-scale motions in ionized gas. Analysis of the ionized gas properties yields an electron density of

(4.8 \pm 0.4) \times 10^{5}

cm⁻³, an emission measure of

(1.23 \pm 0.06) \times 10^{9}

pc cm⁻⁶, and a Lyman continuum photon flux consistent with an O5–O6 V (Zero-Age Main Sequence; ZAMS) star. Our results suggest that G333.6-0.2 is in an intermediate evolutionary stage between hypercompact (HC) and ultracompact (UC) H ii regions, hosting active high-mass star formation with rotating hot cores and ionized gas dynamics. Full article

(This article belongs to the Special Issue Circumstellar Matter in Hot Star Systems)

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26 pages, 4473 KiB

Open AccessReview

Red Supergiant Mass Loss and Mass-Loss Rates

by Jacco Th. van Loon

Galaxies 2025, 13(4), 72; https://doi.org/10.3390/galaxies13040072 - 20 Jun 2025

Viewed by 953

Abstract

This review discusses the causes, nature, importance and observational evidence of mass loss by red supergiants. It arrives at the perception that mass loss finds its origin in the gravity which makes the star a star in the first place, and is a [...] Read more.

This review discusses the causes, nature, importance and observational evidence of mass loss by red supergiants. It arrives at the perception that mass loss finds its origin in the gravity which makes the star a star in the first place, and is a mechanism for the star to equilibrate. This is corroborated by a careful examination of various popular historical and recent empirical mass-loss rate prescriptions and theoretical works, and which provides no evidence for an explicit dependence of red supergiant mass loss on metallicity though dust-associated mass loss becomes less prevalent at lower metallicity. It also identifies a common problem in methods that use tracers of mass loss, which do not correct for varying scaling factors (often because there is no information available on which to base such correction) and as a result tend to underestimate mass-loss rates at the lower end. Conversely, dense, extended chromospheres in themselves do not translate into high mass-loss rates, and the significance of stochastic mass loss can be overstated. On a population scale, on the other hand, binary interaction acts as a stochastic agent of mass loss of great import. In all, evidence is overwhelming that points at red supergiants at the lower mass end losing mass at insufficient rates to shed their mantles before core collapse, but massive (at birth) red supergiants to be prone to intense, dusty mass loss which sees them become hotter stars before meeting their fate. This is consistent with the identified progenitors of hydrogen-rich supernovae. Supernova evolution holds great promise to probe the mass loss but we caution against confusing atmospheres with winds. Finally, promising avenues are looked into, which could forge step-change progress in what has been a long and arduous search for the holy grail of red supergiant mass loss. We may yet find it! Full article

(This article belongs to the Special Issue The Red Supergiants: Crucial Signposts for the Fate of Massive Stars)

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Galaxies, Volume 13, Issue 4 (August 2025) – 21 articles

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