Galaxies

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

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

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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17 pages, 320 KiB

Open AccessArticle

CMB Multipole Expansion in a Frame Dragging-Sustained Milky Way

by Federico Re, Marco Galoppo and Massimo Dotti

Galaxies 2025, 13(3), 71; https://doi.org/10.3390/galaxies13030071 - 13 Jun 2025

Abstract

We study the impact on the cosmic microwave background (CMB) landscape of peculiar rotational general relativistic effects. These effects, on galactic scales, do not possess a Newtonian analogue, and therefore could a priori impact CMB analysis. We find that the velocity inferred from [...] Read more.

We study the impact on the cosmic microwave background (CMB) landscape of peculiar rotational general relativistic effects. These effects, on galactic scales, do not possess a Newtonian analogue, and therefore could a priori impact CMB analysis. We find that the velocity inferred from the CMB dipole, under the kinematic interpretation, coincides with that measured by a stationary observer within the Milky Way and not with the one measured by the zero angular momentum observer. We show that the galaxy peculiar frame-dragging effects do not impact the standard CMB analysis, as these modify the multipole coefficients only at higher orders with respect to the dominant terms. Moreover, we prove that no general relativistic framework at the galactic scale patched within the standard cosmological model can account for the current tension on the CMB quadrupole amplitude. Full article

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

7 pages, 1181 KiB

Open AccessCommunication

The Enigmatic, Highly Variable, High-Mass Young Stellar Object Mol 12: A New Extreme Herbig Be (Proto)star

by Mauricio Tapia, Paolo Persi, Jesús Hernández and Nuria Calvet

Galaxies 2025, 13(3), 70; https://doi.org/10.3390/galaxies13030070 - 13 Jun 2025

Abstract

We report new medium-resolution spectroscopy covering the wavelength range from 0.6 to 2.4

μ

m, as well as multi-epoch, multi-wavelength photometry, of the Class I high-mass embedded young stellar object Mol 12 (IRAS 05373+2349). It is embedded (

A_{V} ≃ 12

) [...] Read more.

We report new medium-resolution spectroscopy covering the wavelength range from 0.6 to 2.4

μ

m, as well as multi-epoch, multi-wavelength photometry, of the Class I high-mass embedded young stellar object Mol 12 (IRAS 05373+2349). It is embedded (

A_{V} ≃ 12

) in the centre of a dense core at a distance of 1.59 kpc from the Sun and has a total luminosity of

1.74 \times 10^{3} L_{⊙}

. The spectra show a large number of permitted atomic emission lines, mostly for Fe, H, C, N, and Ca, that originate in the inner zones of a very active protoplanetary disc and no photospheric absorption lines. Conspicuously, the He I line at 1.0830

μ

m displays a complex P-Cygni profile. Also, the first overtone CO emission band-heads at 2.3

μ

m are seen in emission. From the strengths of the principal emission lines, we determined the accretion rate and luminosity to be

\dot{M} \sim 10^{- 5} M_{⊙}

y⁻¹ and

L_{acc} \sim 10^{3} L_{⊙}

, respectively. Decade-long light curves show a series of irregular brightness dips of more than four magnitudes in r, becoming shallower as the wavelength increases and disappearing at

λ > 3 μ

m. The colour–magnitude diagrams suggest the occurrence of a series of eclipses caused by the passage of small dust cloudlets in front of the star, producing more than 10 magnitudes of extra extinction. Full article

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

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28 pages, 1004 KiB

Open AccessArticle

Numerical Solutions and Stability Analysis of White Dwarfs with a Generalized Anisotropic Factor

by Ayazhan Orazymbet, Aray Muratkhan, Daniya Utepova, Nurzada Beissen, Gulzada Baimbetova and Saken Toktarbay

Galaxies 2025, 13(3), 69; https://doi.org/10.3390/galaxies13030069 - 12 Jun 2025

Abstract

This study examines the equilibrium structure and stability of white dwarfs, incorporating both isotropic and anisotropic pressure distributions. The Tolman–Oppenheimer–Volkoff (TOV) equation is numerically solved using the Chandrasekhar equation of state (EoS) to analyze the effects of pressure anisotropy. A general anisotropy function [...] Read more.

This study examines the equilibrium structure and stability of white dwarfs, incorporating both isotropic and anisotropic pressure distributions. The Tolman–Oppenheimer–Volkoff (TOV) equation is numerically solved using the Chandrasekhar equation of state (EoS) to analyze the effects of pressure anisotropy. A general anisotropy function is introduced to close and solve the system of differential equations. The results indicate that anisotropy remains negligible at the center and increases toward the stellar surface. Stability is assessed using the speed of sound criterion,

v_{s}^{2} = d p / d ρ

, and the Buchdahl bound,

2 M / R < 8 / 9

, confirming that white dwarfs remain within stability limits. We performed a sensitivity analysis to examine how variations in the anisotropy parameter

α_{0}

and central density affect the mass, radius, and compactness of white dwarfs. Additionally, we calculated the gravitational redshift at the stellar surface and found that it varies with anisotropy, ranging from

z_{s} \sim 3.15 \times 10^{- 3}

in isotropic cases to

z_{s} \sim 0.2 \times 10^{- 3}

in highly anisotropic models. These results link anisotropy to potentially observable features. The findings suggest that while anisotropy does not significantly affect the overall equilibrium structure, it may play a role in astrophysical scenarios involving strong magnetic fields, rotational deformations, or accretion processes in binary systems. Full article

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10 pages, 1248 KiB

Open AccessArticle

Post-AGB Binaries as Interacting Systems

by Hans Van Winckel

Galaxies 2025, 13(3), 68; https://doi.org/10.3390/galaxies13030068 - 12 Jun 2025

Abstract

We present recent progress in our understanding of the physical interaction mechanisms at work in evolved binaries of low-to-intermediate initial mass, which are surrounded by a stable disc of gas and dust. These systems are known as post-asymptotic giant-branch (post-AGB) binaries, but recently, [...] Read more.

We present recent progress in our understanding of the physical interaction mechanisms at work in evolved binaries of low-to-intermediate initial mass, which are surrounded by a stable disc of gas and dust. These systems are known as post-asymptotic giant-branch (post-AGB) binaries, but recently, it has been shown that some systems are too low in luminosity and should be considered as post-red-giant branch (post-RGB) instead. While the systems are currently well within their Roche lobe, they still show signs of active ongoing interaction between the different building blocks. We end this contribution with some future research plans. Full article

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

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15 pages, 922 KiB

Open AccessArticle

Searching for New Objects with the B[e] Phenomenon

by Aisha Zh. Naurzbayeva, Nazgul Sh. Alimgazinova, Anatoly S. Miroshnichenko, Corinne Rossi, Inna V. Reva, Raushan I. Kokumbayeva, Chingis T. Omarov, Sergei V. Zharikov, Nadine Manset, Ashish Raj, Arti Joshi, Richard J. Rudy, Richard C. Puetter, Raleigh B. Perry and Kunduz M. Turekhanova

Galaxies 2025, 13(3), 67; https://doi.org/10.3390/galaxies13030067 - 11 Jun 2025

Abstract

Objects with the B[e] phenomenon, whose defining features are the presence of forbidden emission lines and infrared excess coming from circumstellar dust, represent a broad range of evolutionary stages from pre-main-sequence to planetary nebulae. They are important for understanding mechanisms of the circumstellar [...] Read more.

Objects with the B[e] phenomenon, whose defining features are the presence of forbidden emission lines and infrared excess coming from circumstellar dust, represent a broad range of evolutionary stages from pre-main-sequence to planetary nebulae. They are important for understanding mechanisms of the circumstellar matter formation and evolution. However, it is not easy to discover them, especially among faint stars, as forbidden emission lines are usually weak and hardly noticeable in low-resolution spectra. We developed photometric criteria to search for candidate objects with this phenomenon based on a combination of optical and near-infrared color indices and found nearly 40 objects that satisfy these criteria. Spectroscopy of the candidates allows us to make more confident conclusions on their classification. We present the results of our photometric and spectroscopic observations of six objects, which are part of a large list of ∼40 objects that satisfy our photometric selection criteria for candidate objects with the B[e] phenomenon. Forbidden lines of neutral oxygen were clearly detected in the optical spectrum of one object (VES 683) and suspected in three others. One object, AS 415, is most likely a binary system with components that exhibit partial eclipses but without the B[e] phenomenon, while IRAS 20402 + 4638 may be a luminous member of the FS CMa objects group. Full article

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

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19 pages, 2881 KiB

Open AccessReview

Red Supergiants in the Milky Way and Nearby Galaxies

by Alceste Z. Bonanos

Galaxies 2025, 13(3), 66; https://doi.org/10.3390/galaxies13030066 - 5 Jun 2025

Abstract

Identifications of red supergiants (RSGs) in the Milky Way and nearby galaxies have experienced an exponential increase in recent years, driven by advancements in selection techniques, the continued expansion of archival datasets, and a steady increase in spectroscopic data. This review describes the [...] Read more.

Identifications of red supergiants (RSGs) in the Milky Way and nearby galaxies have experienced an exponential increase in recent years, driven by advancements in selection techniques, the continued expansion of archival datasets, and a steady increase in spectroscopic data. This review describes the advances in methodologies and selection criteria for identifying RSGs and presents the current census of these stars in our own Galaxy and nearby galaxies. It also describes the insights gained from resolving nearby RSGs and their complex circumstellar material in the Milky Way and from the growing samples of RSGs being discovered in the Local Group and beyond. These advances impact the Humphreys–Davidson limit in the cool part of the Hertzsprung–Russell diagram. Furthermore, they provide insight into extreme RSGs and the role of photometric variability and, in particular, of the newly discovered phenomenon of dimming events. Recent observations have enabled the determination of the binarity fraction among RSGs, offering new constraints to stellar evolution. Looking ahead, the synergy between large-scale surveys, high-resolution observations, and emerging machine-learning tools promises to further transform our understanding of the final evolutionary stages of massive stars in the coming decade. Full article

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

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16 pages, 1893 KiB

Open AccessReview

Estimating Hubble Constant with Gravitational Observations: A Concise Review

by Rosa Poggiani

Galaxies 2025, 13(3), 65; https://doi.org/10.3390/galaxies13030065 - 4 Jun 2025

Abstract

The Hubble constant is of paramount importance in astrophysics and cosmology. A large number of methods have been developed with different electromagnetic probes to estimate its value. The most recent results show a tension between values obtained from Cosmic Microwave Background observations and [...] Read more.

The Hubble constant is of paramount importance in astrophysics and cosmology. A large number of methods have been developed with different electromagnetic probes to estimate its value. The most recent results show a tension between values obtained from Cosmic Microwave Background observations and supernovae. The simultaneous detection of gravitational waves and electromagnetic radiation from GW170817 provided a direct estimation of the Hubble constant that did not depend on the astronomical distance ladder. This concise review will present the methods to estimate the Hubble constant with the gravitational observations of compact binary mergers, discussing both bright and dark sirens and reporting the state of the art of the results. Full article

(This article belongs to the Special Issue Gamma-Ray Bursts in Multiwavelength: Theory, Observational Correlations and GRB Cosmology)

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32 pages, 2523 KiB

Open AccessReview

Dust at the Cosmic Dawn

by Yuri A. Shchekinov and Biman B. Nath

Galaxies 2025, 13(3), 64; https://doi.org/10.3390/galaxies13030064 - 23 May 2025

Abstract

Observations provided by the Hubble Space Telescope (HST) and James Webb Space Telescope (JWST) have revealed a surprising abundance of galaxies at the “cosmic dawn” epoch,

z > 7

. Some of them are found even in a more distant universe at z [...] Read more.

Observations provided by the Hubble Space Telescope (HST) and James Webb Space Telescope (JWST) have revealed a surprising abundance of galaxies at the “cosmic dawn” epoch,

z > 7

. Some of them are found even in a more distant universe at z ≃ 14–16. Most of these galaxies appear to be intriguing: they are found to be either super-bright in the rest-frame ultraviolet (UV) band or super-dusty with a heavily reddened stellar population. The transition from the super-bright and super-dusty regimes seems to occur in the redshift range from z∼10.5 to z∼9.5 within a time range of ∼50 Myr. If confirmed, then the origin of this transition is far from being clear. In the review, we discuss possible mechanisms that can make

z > 10

galaxies free of dust and also explain the origin of apparently excessive dust in galaxies at intermediate and lower redshifts

z < 10

. Full article

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

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11 pages, 682 KiB

Open AccessArticle

A Spectroscopic and Photometric Study of MWC 342 and Its B[e] Phenomenon over the Last 40 Years

by Aigerim Zh. Akniyazova, Anatoly S. Miroshnichenko, Sergey V. Zharikov, Hans Van Winckel, Nadine Manset, Ashish Raj, Stephen Drew Chojnowski, Serik A. Khokhlov, Inna V. Reva, Raushan I. Kokumbaeva, Chingis T. Omarov, Konstantin N. Grankin, Aldiyar T. Agishev and Nadezhda L. Vaidman

Galaxies 2025, 13(3), 63; https://doi.org/10.3390/galaxies13030063 - 20 May 2025

Abstract

MWC 342 (V1972 Cyg) was discovered nearly 90 years ago as an early-type emission-line star. It was among the first hot stars whose strong infrared excess was detected in the early 1970s. Several mostly short-term photometric and spectroscopic studies resulted in contradictory conclusions [...] Read more.

MWC 342 (V1972 Cyg) was discovered nearly 90 years ago as an early-type emission-line star. It was among the first hot stars whose strong infrared excess was detected in the early 1970s. Several mostly short-term photometric and spectroscopic studies resulted in contradictory conclusions about the nature and evolutionary status of MWC 342. It has been classified as a pre-main-sequence Herbig Be star, an evolved suspected binary system, and a long-period variable star. Suggestions on the nature of the secondary component to this B0/B1 primary included a cool M-type giant and an X-ray source. We collected medium- and high-resolution optical spectra of MWC 342 taken in 1994–2024 as well as optical photometric data taken in 1986–2024. Analysis of these data shows strong variations in the object’s brightness and spectral line properties at various time scales, but no strictly periodic phenomena have been found. Inparticular, such a long-term dataset allowed us to reveal the optical brightness variations over a nearly 20-year-long quasi-period, as well as their anti-correlation with the H

α

emission-line strength. Also, we did not confirm the presence of He ii emission lines and absorption lines of the star’s atmosphere that were suspected in previously published studies. Full article

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

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31 pages, 2268 KiB

Open AccessArticle

Early Optical Follow-Up Observations of Einstein Probe X-Ray Transients During the First Year

by Siyu Wu, Ignacio Pérez-García, Alberto J. Castro-Tirado, Youdong Hu, Maria Gritsevich, María D. Caballero-García, Rubén Sánchez-Ramírez, Sergiy Guziy, Emilio J. Fernández-García, Guillermo García Segura, Carlos Pérez-del-Pulgar, Dingrong Xiong and Bin-Bin Zhang

Galaxies 2025, 13(3), 62; https://doi.org/10.3390/galaxies13030062 - 19 May 2025

Abstract

We present early follow-up observations of Einstein Probe (EP) X-ray transients, following its first year of operation. EP is a dedicated wide-field X-ray observatory that is transforming our understanding of the dynamic X-ray universe. During its first year, EP successfully detected [...] Read more.

We present early follow-up observations of Einstein Probe (EP) X-ray transients, following its first year of operation. EP is a dedicated wide-field X-ray observatory that is transforming our understanding of the dynamic X-ray universe. During its first year, EP successfully detected a diverse range of high-energy transients—including gamma-ray bursts (GRBs), tidal disruption events (TDEs), and fast X-ray transients (FXTs), besides many stellar flares, disseminating 128 alerts in the aggregate. Ground-based optical follow-up observations, particularly those performed by our BOOTES telescope network, have played a crucial role in multi-wavelength campaigns carried out so far. Out of the 128 events, the BOOTES Network has been able to follow up 58 events, detecting 6 optical counterparts at early times. These complementary optical measurements have enabled rapid identification of counterparts, precise redshift determinations (such as EP250215a at

z = 4.61

), and detailed characterization of the transient phenomena. The synergy between EP’s cutting-edge X-ray monitoring and the essential optical follow-up provided by facilities, such as the above-mentioned BOOTES Global Network or other Spanish ground-based facilities we have access to, underscores the importance and necessity of coordinated observations in the era of time-domain and multi-messenger astrophysics. Full article

(This article belongs to the Special Issue Gamma-Ray Bursts in Multiwavelength: Theory, Observational Correlations and GRB Cosmology)

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11 pages, 887 KiB

Open AccessArticle

Investigation of the Nature of the B[e] Star CI Cam in the Optical Range

by Elena A. Barsukova, Vitaly P. Goranskij, Aleksandr N. Burenkov and Ilya A. Yakunin

Galaxies 2025, 13(3), 61; https://doi.org/10.3390/galaxies13030061 - 19 May 2025

Abstract

The B[e] phenomenon is observed in a wide range of stars at various evolutionary stages. Its nature remains uncertain. The B[e] phenomenon is defined as the simultaneous presence of low-excitation forbidden line emission and strong infrared excess in the spectra of early-type stars. [...] Read more.

The B[e] phenomenon is observed in a wide range of stars at various evolutionary stages. Its nature remains uncertain. The B[e] phenomenon is defined as the simultaneous presence of low-excitation forbidden line emission and strong infrared excess in the spectra of early-type stars. Here, we present new spectral observations of a representative of this class: the star CI Cam. A monitoring campaign was carried out for the He II 4686 Å emission line, which serves as an indicator of binarity in this system. The aim was to detect variations in this line not only due to orbital motion but also those associated with the pulsations of the system’s primary component, the B[e] star. Two maxima in the equivalent width were detected over the pulsation period, during which the equivalent width increased by a factor of three. We refine the classification of CI Cam, assigning it to the FS CMa group of B[e] stars by all criteria, and we refer the secondary component of the system to a group of recently discovered “stripped” stars. Full article

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

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15 pages, 2471 KiB

Open AccessArticle

Spectral and Photometric Studies of NGC 3516 in the Optical Range

by Saule Shomshekova, Alexander Serebryanskiy, Ludmila Kondratyeva, Nazim Huseynov, Samira Rahimli, Vitaliy Kim, Laura Aktay and Yerlan Aimuratov

Galaxies 2025, 13(3), 60; https://doi.org/10.3390/galaxies13030060 - 16 May 2025

Abstract

This paper presents the results of the photometric and spectral monitoring of the galaxy NGC 3516, which is an active galactic nucleus (AGN) of type Sy

1.5

with a changing look. Observations were carried out at the Fesenkov Astrophysical Institute (FAI, Almaty, Kazakhstan) [...] Read more.

This paper presents the results of the photometric and spectral monitoring of the galaxy NGC 3516, which is an active galactic nucleus (AGN) of type Sy

1.5

with a changing look. Observations were carried out at the Fesenkov Astrophysical Institute (FAI, Almaty, Kazakhstan) and the Shamakhy Astrophysical Observatory (ShAO, Shamakhy, Azerbaijan). Spectral monitoring of this galaxy in the wavelength range 4000–7000 Å began in 2020, while photometric observations have been conducted since 2014. During the observation period, estimates of the galaxy’s brightness in the B, V and

R c

filters were obtained, as well as measurements of the emission line and continuum fluxes. The light curve shows increased brightness of NGC 3516 in 2016 and 2019. The increase of emission line fluxes of H

β

and H

α

and continuum began in 2019 and continued until spring 2020, when these characteristics reached their maximal values. A powerful X-ray flare took place on 1 April 2020. A new phase of brightening began in 2021 and has continued until 2025. After reaching their maxima in 2020, the emission fluxes of H

β

and H

α

decreased by a factor of 1.5–2 and remained at a low level until 2022–2023, when they began to increase again. Medium-resolution spectra obtained on 20 April 2020, with the 1-meter “West” telescope (TSHAO) were used to study the broad components of the H

β

and H

α

emission line profiles. Model calculations showed that the broad profile of the H

α

line consists of a central unshifted component and two (blue and red) components shifted symmetrically relative to the central component by a velocity of

v = 980 \pm 20

km

s^{- 1}

. The H

β

emission line was relatively weak, so the radial velocity of its components was determined with a large uncertainty:

900 \pm 600

km

s^{- 1}

. Full article

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13 pages, 5876 KiB

Open AccessArticle

V694 Mon: A Recent Event of Mass Transfer in the Dynamical Mode

by Vitaly P. Goranskij, Elena A. Barsukova, Aleksandr N. Burenkov, Natalia V. Metlova, Alla V. Zharova and Ilya A. Yakunin

Galaxies 2025, 13(3), 59; https://doi.org/10.3390/galaxies13030059 - 14 May 2025

Abstract

The phenomenon of runaway mass transfers between components of binary systems on a dynamical timescale has been theoretically predicted. However, this phenomenon has been observed for the first time in the history of astronomy just now in a symbiotic system V694 Mon. We [...] Read more.

The phenomenon of runaway mass transfers between components of binary systems on a dynamical timescale has been theoretically predicted. However, this phenomenon has been observed for the first time in the history of astronomy just now in a symbiotic system V694 Mon. We employed medium- and high-dispersion spectroscopy, along with multicolor photometry, to study this event in detail. Over 6 years, beginning in 2018, we observed the cessation of disk accretion, the filling of the accretor’s Roche lobe, and the subsequent formation of an A-type star within it. The pulsating envelope of the M giant donor was transferred to the accretor down to its base. Thus, the products from the hydrogen-burning layer appeared on the donor’s surface, and a flash of an emission-line spectrum enriched with s-process elements was detected. We discuss discrepancies between theoretical predictions and observations, as well as other phenomena potentially related to dynamical mass transfer. Full article

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

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8 pages, 246 KiB

Open AccessArticle

Studies of Hot Stars and Other Observational Programs Using the 1-Meter Optical Telescope Zeiss-1000 of SAO RAS

by Vladimir V. Komarov, Victoria N. Komarova and Alexander S. Moskvitin

Galaxies 2025, 13(3), 58; https://doi.org/10.3390/galaxies13030058 - 13 May 2025

Abstract

Here, we briefly describe the current state of the Zeiss-1000 telescope of the Special Astrophysical Observatory of Russian Academy of Sciences (SAO RAS). Principal attention is given to research programs from recent years. The observations made according to allocated requests both by researchers [...] Read more.

Here, we briefly describe the current state of the Zeiss-1000 telescope of the Special Astrophysical Observatory of Russian Academy of Sciences (SAO RAS). Principal attention is given to research programs from recent years. The observations made according to allocated requests both by researchers from the observatory and scientists from other institutions and organizations are planned within a half-year schedule. The instrumental facilities provide a wide range of methods for studying objects of interest. They include standard photometry, moderate- and high-resolution spectroscopy, and polarimetry, along with unique “guest” methods (e.g., emission line imaging). The research programs cover different fields of astrophysics. The topic of “hot stars” and other important developments have become possible due to the introduction of new research methods at the telescope. Blazars, gamma-ray burst optical transients, massive supernovae, cataclysmic variables, magnetic stars, white dwarfs, luminous blue variables, red dwarfs, and many others are among its targets. Full article

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

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57 pages, 2185 KiB

Open AccessReview

Exploring the GRB–Supernova Connection: Does a Superluminous Hypernova Population Exist?

by Achille Fiore, Ludovica Crosato Menegazzi and Giulia Stratta

Galaxies 2025, 13(3), 57; https://doi.org/10.3390/galaxies13030057 - 6 May 2025

Abstract

Observations of several gamma-ray bursts (GRBs) that are temporally and spatially compatible with energetic supernovae (hypernovae) have established their common origin. In one case (GRB 111209A/SN 2011kl), the associated supernova was classified as superluminous (SN 2011kl). The exceptional duration of the observed gamma-ray [...] Read more.

Observations of several gamma-ray bursts (GRBs) that are temporally and spatially compatible with energetic supernovae (hypernovae) have established their common origin. In one case (GRB 111209A/SN 2011kl), the associated supernova was classified as superluminous (SN 2011kl). The exceptional duration of the observed gamma-ray prompt emission of GRB 111209A (about 7 h) is widely considered key to unlocking the physics behind the still mysterious origin of superluminous supernovae (SLSNe). We review the main observational and theoretical findings that may link some ultra-long GRBs to SLSNe. Specifically, we examine notable events and the role of progenitors and host galaxies in shaping these phenomena and focus on the proposed models. While a magnetar central engine is a plausible mechanism for both luminous and long-duration GRBs, a conclusive answer remains elusive, as alternative explanations are still viable. Further observational and theoretical work is required to clarify progenitor pathways and explosion mechanisms, potentially extending the classical GRB-SN connection to rare superluminous hypernovae. Full article

(This article belongs to the Special Issue Gamma-Ray Bursts in Multiwavelength: Theory, Observational Correlations and GRB Cosmology)

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12 pages, 3593 KiB

Open AccessArticle

Spectral Variability of Herbig Ae Star V1295, Aquila

by Hemayil Adigozalzade, Silva Jarvinen, Swetlana Hubrig, Ulviyya Bashirova and Nariman Ismailov

Galaxies 2025, 13(3), 56; https://doi.org/10.3390/galaxies13030056 - 6 May 2025

Abstract

This article presents the results of long-term spectral studies of the unusual Herbig Ae star V1295 Aql. The variability in the spectrophotometric parameters of the emission and absorption components of the hydrogen lines Hα, Hβ, and D Na I—and of various metallic lines—is [...] Read more.

This article presents the results of long-term spectral studies of the unusual Herbig Ae star V1295 Aql. The variability in the spectrophotometric parameters of the emission and absorption components of the hydrogen lines Hα, Hβ, and D Na I—and of various metallic lines—is studied. The periodic variability in these parameters over a period of 51.7 days, recently established using mean longitudinal magnetic field measurements, is confirmed. The obtained average value of the radial velocities of metal absorption lines is Vr = 0.75 ± 1.85 km/s. According to our long-term observations, the radial velocities of the star do not change over time. This indicates the absence of a close stellar-mass companion. Full article

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

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17 pages, 1201 KiB

Open AccessArticle

Time Dilation Observed in Type Ia Supernova Light Curves and Its Cosmological Consequences

by Václav Vavryčuk

Galaxies 2025, 13(3), 55; https://doi.org/10.3390/galaxies13030055 - 3 May 2025

Abstract

The cosmic time dilation observed in Type Ia supernova light curves suggests that the passage of cosmic time varies throughout the evolution of the Universe. This observation implies that the rate of proper time is not constant, as assumed in the standard FLRW [...] Read more.

The cosmic time dilation observed in Type Ia supernova light curves suggests that the passage of cosmic time varies throughout the evolution of the Universe. This observation implies that the rate of proper time is not constant, as assumed in the standard FLRW metric, but instead is time-dependent. Consequently, the commonly used FLRW metric should be replaced by a more general framework, known as the Conformal Cosmology (CC) metric, to properly account for cosmic time dilation. The CC metric incorporates both spatial expansion and time dilation during cosmic evolution. As a result, it is necessary to distinguish between comoving and proper (physical) time, similar to the distinction made between comoving and proper distances. In addition to successfully explaining cosmic time dilation, the CC metric offers several further advantages: (1) it preserves Lorentz invariance, (2) it maintains the form of Maxwell’s equations as in Minkowski spacetime, (3) it eliminates the need for dark matter and dark energy in the Friedmann equations, and (4) it successfully predicts the expansion and morphology of spiral galaxies in agreement with observations. Full article

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

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