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Circumstellar Matter in Hot Star Systems

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A special issue of Galaxies (ISSN 2075-4434).

Deadline for manuscript submissions: 20 May 2025 | Viewed by 4904

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Special Issue Editors

Prof. Dr. Anatoly Miroshnichenko

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Guest Editor

Department of Physics and Astronomy, University of North Carolina Greensboro, Greensboro, NC 27412, USA
Interests: circumstellar matter; binary systems; radiative transfer
Special Issues, Collections and Topics in MDPI journals

Dr. Sergei Zharikov

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Guest Editor

Instituto de Astronomía, Universidad Nacional Autónoma de Mexico, AP 106, Ensenada 22800, BC, Mexico
Interests: cataclysmic binaries; circumstellar matter; evolutionary modeling

Dr. Serik Khokhlov

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Guest Editor

Faculty of Physics and Technology, Al-Farabi Kazakh National University, Al-Farabi Avenue, 71, 050040 Almaty, Kazakhstan
Interests: circumstellar matter; binary systems

Special Issue Information

Dear Colleagues,

The Special Issue contains the papers of the international conference "Hot Stars—Life with Circumstellar Matter” (https://conf.astrokaznu.kz/), which took place on October 14−19, 2024, in the city of Almaty, Kazakhstan, on the campus of the Al-Farabi Kazakh National University.

The conference focused on stellar objects at any evolutionary stage, including early-type stars with signs of circumstellar gaseous and dusty material. This definition includes classes of objects such as Herbig Ae/Be, classical Be, Vega-type, Wolf–Rayet stars, proto-planetary nebulae, luminous blue variables, other objects containing the B[e] phenomenon, and more. The exploration of the evolutionary connections between the mentioned classes has led to a better understanding of the interaction between stellar systems and circumstellar matter and, ultimately, of the long-term evolution of galaxies.

This Special Issue aims to inform a broad audience of recent results in the field of the evolution of intermediate-mass and massive stars. As we analyze the information from large-scale and long-term surveys, as well as from recent space missions such as Gaia, new objects that belong to these classes are constantly being discovered and better constraints are being placed on the properties of individual objects and their groups. New data analysis methods and the application of existing methods to various datasets are advancing our knowledge of this exciting research field.

In particular, new data on the variability of Be stars has led to new insights on the mechanisms of the formation and structure of their disks; recent discoveries and long-term studies of objects containing the B[e] phenomenon and post-AGB binaries resulted in new hypotheses about their nature and evolutionary details; other results, from star formation to interstellar mediums, will be presented too.

This Special Issue will be of interest to specialists working in various fields of astrophysics, such as in the evolution of stars and galaxies, interacting binary systems, radiation transfer, dynamics and the evolution of circumstellar matter, and large-scale surveys of astronomical objects.

There is no maximum length, and the suggested minimum is approx. 4000 words. Submitted papers should contain enough novel content (except for reviews, which are acceptable from senior contributors). Please note that the three paper types recommended for this Special Issue are Article, Review, and Communication (limited number). For more details, including the various article types, please visit the following link: https://www.mdpi.com/about/article_types.

Prof. Dr. Anatoly Miroshnichenko
Dr. Sergei Zharikov
Dr. Serik Khokhlov
Guest Editors

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Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Galaxies is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

circumstellar matter
binary stars
pre-main-sequence stars
post-AGB stars
Be stars
B[e] phenomenon
mass loss
mass transfer
observations
theory

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Published Papers (14 papers)

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Jump to: Review

10 pages, 539 KiB

Open AccessArticle

Fundamental Parameters and Evolutionary Scenario of HD 327083

by Nadezhda L. Vaidman, Anatoly S. Miroshnichenko, Sergey V. Zharikov, Serik A. Khokhlov, Aldiyar T. Agishev and Berik S. Yermekbayev

Galaxies 2025, 13(3), 47; https://doi.org/10.3390/galaxies13030047 - 22 Apr 2025

Viewed by 182

Abstract

In this study, we present refined orbital and fundamental parameters of the Galactic B[e] supergiant binary system HD 327083 using the Bayesian Markov Chain Monte Carlo (MCMC) method applied to the radial velocities data of HD 327083. We found that the system is [...] Read more.

q = 1.15 \pm 0.07

. We modeled the evolutionary history of the system using MESA code. Initially, the system was formed by a binary with the orbital period of

P o r b = 108

day, which contained stars with 13.00

\pm 0.05

M_{⊙}

and

11.50 \pm 0.05

M_{⊙}

masses. They had a relatively slow rotation

υ_{r o t} = 0.40 \pm 0.13 υ_{c r i t}

and provided a strong stellar wind. The current system age is

13.6 \pm 0.1

Myr, and the state of the system corresponds to a close filling of the high massive component’s Roche lobe and a beginning of the mass transfer. The mass-transfer event will occur in a short interval of ≲0.1 Myr only. After that, the mass of the post-primary drops to ≈5

M_{⊙}

, the post-secondary mass grows until ≈20

M_{⊙}

, and the binary will convert to a detached system with a long orbital period of ≈700 days. Full article

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

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6 pages, 228 KiB

Open AccessArticle

Stellar Wind Parameters of Massive Stars in Accretion-Powered High-Mass X-Ray Binary Pulsars

by Nina Beskrovnaya, Nazar Ikhsanov and Vitaliy Kim

Galaxies 2025, 13(2), 37; https://doi.org/10.3390/galaxies13020037 - 5 Apr 2025

Viewed by 157

Abstract

The process of mass exchange between the components of High-Mass X-ray Binary (HMXB) systems with neutron stars undergoing wind-fed accretion is discussed. The X-ray luminosity of these systems allows us to evaluate the mass capture rate by the neutron star from the stellar wind of its massive companion and set limits on the relative velocity between the neutron star and the wind. We found that the upper limit to the wind velocity in the orbital plane during the high state of the X-ray source is in the range of 120–1000

km s^{- 1}

, which is by a factor of 2–4 lower than both the terminal wind velocity and the speed of the wind flowing out from the polar regions of massive stars for all the objects under investigation. This finding is valid not only for the systems with Be stars, but also for the systems in which the optical components do not exhibit the Be phenomenon. We also show that the lower limit to the radial wind velocity in these systems can unlikely be smaller than a few percent of the orbital velocity of the neutron star. This provides us with a new constraint on the mass transfer process in the outflowing disks of Be-type stars. Full article

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

11 pages, 2062 KiB

Open AccessArticle

IRAS 17449+2320: A Possible Binary System with the B[e] Phenomenon and a Strong Magnetic Field

by Sergey Zharikov, Anatoly Miroshnichenko, Inna Reva, Raushan Kokumbaeva, Chingis Omarov, Steve Danford, Alicia Aarnio, Nadine Manset, Ashish Raj, S. Drew Chojnowski and Joseph Daglen

Galaxies 2025, 13(2), 32; https://doi.org/10.3390/galaxies13020032 - 31 Mar 2025

Viewed by 239

Abstract

We report the recent results of a long-term spectroscopic and photometric monitoring of IRAS 17449+2320, a member of the least studied group of objects with the B[e] phenomenon called FS CMa-type objects. The main hypothesis for explaining the strong emission-line spectra and infrared excesses of these objects assumes an ongoing or past mass transfer between the components in binary systems. The object is the only star with a gaseous and dusty envelope, where a strong and variable magnetic field (5.5–7.2 kG) was found through the splitting of some spectral lines. Additionally, we discovered the regular appearance of a red-shifted absorption component in spectral lines of neutral hydrogen, helium, and oxygen as well as one of ionized silicon with a period of 36.13 ± 0.20 days. We show that the magnetic field strength also followed this period. The process was accompanied by increasing emission component strengths for the hydrogen lines as well as the helium and metallic absorption lines. We refined the fundamental parameters of the optical counterpart of IRAS 17449+2320 (

T_{eff} = 9800 \pm 300

K, log L/

L_{⊙} = 1.86 \pm 0.06

v sin i = 9 \pm 2

km s⁻¹) and concluded that the star was slightly metal-deficient and viewed nearly pole-on. No signs of a secondary component were found. Possible interpretations of the observed phenomena are suggested, and some earlier findings about the object’s nature are revised. Full article

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

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11 pages, 520 KiB

Open AccessArticle

The Photometric Variability and Spectrum of the Hot Post-AGB Star IRAS 21546+4721

by Natalia Ikonnikova, Marina Burlak and Alexander Dodin

Galaxies 2025, 13(2), 31; https://doi.org/10.3390/galaxies13020031 - 31 Mar 2025

Viewed by 233

Abstract

We present the results of photometric and spectroscopic observations of a poorly studied B-type supergiant with infrared excess, the hot post-AGB star IRAS 21546+4721. Based on our photometric observations in the

U B V R_{C} I_{C}

bands, we detected rapid, night-to-night, [...] Read more.

U B V R_{C} I_{C}

bands, we detected rapid, night-to-night, non-periodic brightness variations in the star with peak-to-peak amplitudes up to

0 .^{m} 3

in the V band, as well as color–color and color–brightness correlations. Based on its variability characteristics, IRAS 21546+4721 appears similar to other hot post-AGB stars. Possible causes of the photometric variability are discussed. Additionally, we acquired low-resolution spectra in a wavelength range from 3500 to 7500 Å. The spectrum contains absorption lines typical of an early B-type star, along with a set of emission lines of H I, He I, [O I], [O II], [N II], [S II], and C II originating from an ionized circumstellar envelope. An analysis of the emission spectrum allowed us to estimate the parameters of the gas envelope (

N_{e}

∼ 10⁴ cm⁻³,

T_{e}

∼ 10,000 K) and the star’s temperature (∼26,500 K). The radial velocity measured from the emission lines was

V_{r} = - 141 \pm 7

km s⁻¹. Full article

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

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18 pages, 1207 KiB

Open AccessArticle

Multiplicity of Luminous Blue Variable Stars

by A. Lobel and N. Gorlova

Galaxies 2025, 13(2), 29; https://doi.org/10.3390/galaxies13020029 - 28 Mar 2025

Viewed by 272

Abstract

The study of Luminous Blue Variables (LBVs) is critical to understanding the mechanisms behind their recurring S Dor-like outbursts, which can span decades and feature dramatic spectral changes. These outbursts may result from atmospheric instability or interactions with a companion star, but their causes remain poorly understood. Detecting binarity in LBVs through long-term radial velocity (RV) measurements, which can identify orbital motion via shifts in absorption lines, is a promising method. Periodic line shifts and variability can reveal the presence of a companion star. We report on the monitoring of four LBVs and two candidate LBVs (cLBVs), observing high-resolution spectra from 2009 to 2024. Although we do not find a clear periodic RV signal for LBVs MWC 930, P Cyg, or HD 168607, our long-term monitoring campaign previously detected the binarity of cLBV MWC 314 in 2013. For the first time, we detected a periodic signal in the RV data of the cLBV Schulte 12. In addition, in LBV HD 168607, we observed Discrete Absorption Components, indicative of large-scale structures in a rotating wind. These findings advance our understanding of the binary nature of LBVs and their complex outburst behaviors. Full article

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

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11 pages, 479 KiB

Open AccessArticle

HR 4049: A Spectroscopic Analysis of a Post-AGB Object

by Shakhida T. Nurmakhametova, Nadezhda L. Vaidman, Anatoly S. Miroshnichenko, Azamat A. Khokhlov, Aldiyar T. Agishev, Berik S. Yermekbayev, Stephen Danford and Alicia N. Aarnio

Galaxies 2025, 13(2), 26; https://doi.org/10.3390/galaxies13020026 - 22 Mar 2025

Viewed by 233

Abstract

A new spectroscopic study of HR 4049, a post-AGB star in a binary system, based on échelle spectra taken between 2019 and 2025 with the 0.81 m telescope of the Three College Observatory (North Carolina, USA) at a resolution of R ≈ 12,000 is reported. A cross-correlation analysis of 73 spectra of a single C i multiplet in the 4760–4780 Å range yielded the following orbital parameters: the orbital period

P = 428.474 \pm 0.002

days, eccentricity

e = 0.29 \pm 0.01

, argument of periastron

ω = {242.3}^{\circ} \pm {0.3}^{\circ}

, epoch of periastron

T_{0} = 2,458,383.2 \pm 0.6

, heliocentric systemic radial velocity

γ = - 30.12 \pm 0.09

km s⁻¹, and semi-amplitude of the radial velocity curve

K_{1} = 15.52 \pm 0.13

km s⁻¹. Phase-dependent variations of the Hα line profile indicate dynamic processes in the circumstellar environment. The luminosity of HR 4049 was refined using the Gaia EDR3 parallax (

0.71 \pm 0.10

mas), corresponding to a distance of

1397 \pm 170

pc, and the average visual magnitude in the brightest state (

m_{V} = 5.35

mag). The derived luminosity,

log (L / L_{⊙}) = 4.22 \pm 0.12

, suggests an initial mass of 3.0–4.0

M_{⊙}

. Analysis of the mass function and most probable orbital inclinations (60°–75°) leads to current masses of

\sim 0.75 M_{⊙}

for the primary and

0.70

–

0.82 M_{⊙}

for the secondary component. The results confirm the system’s long-term orbital stability and provide further insights for future research into the nature of post-AGB binaries. Full article

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

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10 pages, 551 KiB

Open AccessArticle

AS 314: A Massive Dusty Hypergiant or a Low-Mass Post-Asymptotic Giant Branch Object?

by Aigerim Bakhytkyzy, Anatoly S. Miroshnichenko, Valentina G. Klochkova, Vladimir E. Panchuk, Sergey V. Zharikov, Laurent Mahy, Hans Van Winckel, Aldiyar T. Agishev and Serik A. Khokhlov

Galaxies 2025, 13(2), 17; https://doi.org/10.3390/galaxies13020017 - 28 Feb 2025

Viewed by 445

Abstract

AS 314 (V452 Sct) is a poorly studied early-type emission-line star, which exhibits an infrared excess at wavelengths longer than 10

μ

m. Its earlier studies have been limited to small amounts of observational data and led to controversial conclusions about its fundamental [...] Read more.

AS 314 (V452 Sct) is a poorly studied early-type emission-line star, which exhibits an infrared excess at wavelengths longer than 10

μ

m. Its earlier studies have been limited to small amounts of observational data and led to controversial conclusions about its fundamental parameters and evolutionary status. Comparison of high-resolution spectra of AS 314 taken over 20 years ago with those of Luminous Blue Variables and other high-luminosity objects suggested its observed properties can be explained by a strong stellar wind from a distant (D∼10 kpc) massive star, possibly in a binary system. However, a recent assessment of its low-resolution spectrum along with a new distance from a Gaia parallax (∼1.6 kpc) resulted in an alternative hypothesis that AS 314 is a low-mass post-asymptotic giant branch (post-AGB) star. The latter hypothesis ignored the high-resolution data, which gave rise to the former explanation. We collected over 30 mostly high-resolution spectra taken in 1997–2023, supplemented them with results of long-term photometric surveys, compared the spectra and the spectral energy distribution with those of post-AGB objects and B/A supergiants, and concluded that the observed properties AS 314 are more consistent with those of the latter. Full article

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

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Review

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24 pages, 629 KiB

Open AccessReview

Symbiotic Stars in the Era of Modern Ground- and Space-Based Surveys

by Jaroslav Merc

Galaxies 2025, 13(3), 49; https://doi.org/10.3390/galaxies13030049 - 23 Apr 2025

Viewed by 114

Abstract

Symbiotic stars, interacting binaries composed of a cool giant and a hot compact companion, exhibit complex variability across the electromagnetic spectrum. Over the past decades, large-scale photometric and spectroscopic surveys from ground- and space-based observatories have significantly advanced their discovery and characterization. These datasets have transformed the search for new symbiotic candidates, providing extensive time-domain information crucial for their classification and analysis. This review highlights recent observational results that have expanded the known population of symbiotic stars, refined classification criteria, and enhanced our understanding of their variability. Despite these advances, fundamental questions remain regarding their long-term evolution, mass transfer and accretion processes, or their potential role as progenitors of Type Ia supernovae. With ongoing and upcoming surveys, the coming years promise new discoveries and a more comprehensive picture of these intriguing interacting systems. Full article

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

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14 pages, 3588 KiB

Open AccessReview

Intermediate-Mass Mergers: A New Scenario for Several FS CMa Stars

by Daniela Korčáková, Nela Dvořáková, Iris Bermejo Lozano, Gregg A. Wade, Alicia Moranchel Basurto, Pavel Kroupa, Raul Ortega Chametla, Colin Peter Folsom and Ondrej Juhás

Galaxies 2025, 13(3), 46; https://doi.org/10.3390/galaxies13030046 - 22 Apr 2025

Viewed by 205

Abstract

We summarise the properties and nature of a peculiar group of B-type stars called FS CMa stars. These stars show the B[e] phenomenon, i.e., their spectra exhibit both forbidden emission lines and infrared excess. Such properties point to an extended circumstellar gas and dust component. Although the phenomenon has been explained in most B[e] stars, the origin and nature of FS CMa stars is disputed. Here, we focus on the merger hypothesis, for which evidence has recently been discovered. Full article

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

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15 pages, 507 KiB

Open AccessReview

Spectropolarimetry for Discerning Geometry and Structure in Circumstellar Media of Hot Massive Stars

by Richard Ignace, Kenneth G. Gayley, Roberto Casini, Paul Scowen, Christiana Erba and Jeremy Drake

Galaxies 2025, 13(2), 40; https://doi.org/10.3390/galaxies13020040 - 11 Apr 2025

Viewed by 237

Abstract

Spectropolarimetric techniques are a mainstay of astrophysical inquiry, ranging from Solar System objects to the Cosmic Background Radiation. This review highlights applications of stellar polarimetry for massive hot stars, particularly in the context of ultraviolet (UV) spaceborne missions. The prevalence of binarity in the massive star population and uncertainties regarding the degree of rotational criticality among hot stars raises important questions about stellar interactions, interior structure, and even the lifetimes of evolutionary phases. These uncertainties have consequences for stellar population synthesis calculations. Spectropolarimetry is a key tool for extracting information about stellar and binary geometries. We review methodologies involving electron scattering in circumstellar envelopes; gravity darkening from rapid rotation; spectral line effects, including the (a) “line effect”, (b) Öhman effect, and (c) Hanle effect; and the imprint of interstellar polarization on measurements. Finally, we describe the Polstar UV spectropolarimetric SMEX mission concept as one means for employing these diagnostics to clarify the state of high rotation and its impacts for massive stars. Full article

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

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8 pages, 1341 KiB

Open AccessReview

Chemical Synthesis in the Circumstellar Environment

by Sun Kwok

Galaxies 2025, 13(2), 36; https://doi.org/10.3390/galaxies13020036 - 3 Apr 2025

Viewed by 213

Abstract

We discuss the spectral distinctions between B[e] stars and compact planetary nebulae. The differentiation between proto-planetary nebulae, transition objects between the asymptotic giant branch and planetary nebulae, and reflection nebulae in binary systems is also discussed. Infrared and millimeter-wave observations have identified many inorganic and organic molecules, as well as solid-state minerals, in the circumstellar environment. There is evidence that complex organics in the form of mixed aromatic/aliphatic nanoparticles (MAONs) are synthesized during the proto-planetary nebulae phase of evolution. Their ejection into the interstellar medium may have enriched the primordial Solar System, and the complex organics found in comets, asteroids, and planetary satellites could be stellar in origin. Full article

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

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13 pages, 4528 KiB

Open AccessReview

Hot Stars in Stellar Populations of Galaxies

by Claus Leitherer

Galaxies 2025, 13(2), 20; https://doi.org/10.3390/galaxies13020020 - 7 Mar 2025

Viewed by 494

Abstract

Star-forming galaxies are hosts of dominant populations of recently formed, hot, massive stars, which give rise to conspicuous stellar spectral features and provide the ionizing fluxes. Strong outflows of these stars shape their properties. These winds affect the evolution and the output of ionizing radiation, as well as the energy and momentum input in the interstellar medium and the chemical enrichment. Many properties of massive stars become even more extreme at a low metallicity. Owing to the pioneering observations of young, metal-poor stellar populations, both locally with HST and large ground-based facilities and at high redshift with JWST, we are at a key moment to assess our understanding of hot massive stars in these galaxies. Stellar population synthesis is a key tool. I will demonstrate how population models of hot, massive stars help to address some issues at the forefront of current research. The recent advent of new evolutionary and atmosphere models of massive stars probing new parameter space allows us to characterize the properties of nearby and distant populations. Full article

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

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10 pages, 426 KiB

Open AccessReview

The Blue Supergiant Problem and the Main-Sequence Width

by Jorick S. Vink and Rene D. Oudmaijer

Galaxies 2025, 13(2), 19; https://doi.org/10.3390/galaxies13020019 - 6 Mar 2025

Viewed by 397

Abstract

Using Gaia DR3 we derive new distances and luminosities for a sample of Galactic B supergiants which were thought to be post main-sequence (MS) objects from their HR diagram location beyond the terminal-age MS (TAMS). When applying the newer Gaia distances in addition to enhanced amounts of core-boundary mixing, aka convective overshooting, we show that these Galactic B supergiants are likely enclosed within the MS band, indicating an evolutionary stage of steady core hydrogen burning. We discuss the importance of considering enhanced overshooting and how vectors in the mass-luminosity plane (ML-plane) can be used to disentangle the effects of wind mass loss from interior mixing. We finish with the key message that any proposed solution to the BSG problem should consider not only an explanation for the sheer number of B supergiants inside the Hertzsprung gap, but should at the same time also account for the steep drop in rotation rates identified at spectral type B1—corresponding to an effective temperature of ∼21 kK, and for which two distinct families of solutions have been proposed. Full article

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

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7 pages, 215 KiB

Open AccessReview

Going Forward to Unveil the Nature of γ Cas Analogs

by Yaël Nazé

Galaxies 2025, 13(1), 8; https://doi.org/10.3390/galaxies13010008 - 24 Jan 2025

Viewed by 459

Abstract

The star

γ

The star

γ

Cas and its analogs are a subset of Be stars that display particularly hard and bright thermal X-ray emission, which has no equivalent among other massive stars. Here, I will review their characteristics and present the latest results of our optical and X-ray monitoring campaigns, including an assessment of the links between the circumstellar environment and the high-energy properties. Possible scenarios to explain this phenomenon will be presented in light of these observational results. Full article

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

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