Galaxies

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

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

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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

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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 289

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 231

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 184

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, 3536 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

Viewed by 269

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 289

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 480

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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