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Universe
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Stellar Astrophysics
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Stellar Astrophysics

A special issue of Universe (ISSN 2218-1997). This special issue belongs to the section "Solar and Stellar Physics".

Deadline for manuscript submissions: closed (10 March 2022) | Viewed by 21070

Special Issue Editor

Prof. Dr. Roberto Mignani

E-Mail Website
Guest Editor
INAF, Institute for Space Astrophysics, 20133 Milan, Italy
Interests: stellar astrophysics; compact objects; multi-wavelength observations
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Stellar astrophysics is key to understanding the evolution of stars and planetary systems, understanding the formation of some of the most extreme objects, such as neutron stars and black holes, and tracing back the evolution of our universe, including the history of star formation in the first galaxies. Traditionally the most ancient branch in astronomy, stellar astrophysics has become a trait d’union to many other branches, from cosmology to planetology. In this Special Issue, we will focus on the role of stellar astrophysics in the global framework of modern astronomy, review the main achievements in stellar astrophysics, and outline the aims and strategies for future development in this crucial field.

This Special Issue will develop a number of subjects:

  • The life cycle of stars;
  • Brown dwarfs and hot jupiters;
  • Endpoints of stellar evolution;
  • Evolution of stars in binary systems;
  • Planetary systems in the local galaxy;
  • Stellar explosions, novae and supernovae, and stellar winds;
  • Stellar magnetic fields;
  • The most extreme objects in the universe, such as black holes and neutron stars;
  • Stars in the early universe;
  • Star formation across cosmic time;
  • Stellar dynamics and the galactic structure;
  • Star formation in starburst galaxies;
  • Stellar associations—open clusters and globular clusters;
  • Observational facilities and techniques;
  • Multi-wavelength synergies;
  • Stellar astrophysics with future facilities.

Prof. Dr. Roberto Mignani
Guest Editors

Manuscript Submission Information

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. Universe is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. 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.

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Related Special Issue

Published Papers (5 papers)

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Research

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23 pages, 1137 KiB  
Article
The Effect of Age on the Grouping of Open Clusters: II—Are There Old Binary Clusters?
by Juan Casado
Universe 2022, 8(7), 368; https://doi.org/10.3390/universe8070368 - 4 Jul 2022
Cited by 2 | Viewed by 1636
Abstract
In the present study, we continue testing the Primordial Group hypothesis (Casado 2022), which postulates that only sufficiently young open clusters can be binary or multiple, and old clusters are essentially single. To this end, we revisit all the remaining binary cluster candidates [...] Read more.
In the present study, we continue testing the Primordial Group hypothesis (Casado 2022), which postulates that only sufficiently young open clusters can be binary or multiple, and old clusters are essentially single. To this end, we revisit all the remaining binary cluster candidates in the Galaxy having at least one cluster older than 100 Myr through Gaia data and careful revision of the literature. We found no convincing case for an old binary system among the 120 pairs/groups revised. Most of the pairs are optical pairs or flyby encounters. However, we found three dubious pairs that could falsify the title hypothesis upon further research. We also found two possible primordial pairs older than expected. Our results confirm that the vast majority of binary/multiple OCs in the Galaxy, if not all, are of primordial origin and are not stable for a long time. This finding is in line with similar studies of the Magellanic Clouds and theoretical N-body simulations in the Galaxy. The pairs of OCs in these groups are generally not binary systems since they are not gravitationally bound. We also point out some inconsistencies in previous works and databases, such as false open clusters and duplicities. Full article
(This article belongs to the Special Issue Stellar Astrophysics)
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19 pages, 794 KiB  
Article
Radio Stars of the SKA
by Bin Yu, Albert Zijlstra and Biwei Jiang
Universe 2021, 7(5), 119; https://doi.org/10.3390/universe7050119 - 22 Apr 2021
Cited by 6 | Viewed by 1880
Abstract
Radio emission from stars can be used, for example, to study ionized winds or stellar flares. The radio emission is faint and studies have been limited to few objects. The Square Kilometer Array (SKA) brings a survey ability to the topic of radio [...] Read more.
Radio emission from stars can be used, for example, to study ionized winds or stellar flares. The radio emission is faint and studies have been limited to few objects. The Square Kilometer Array (SKA) brings a survey ability to the topic of radio stars. In this paper we investigate what the SKA can detect, and what sensitivity will be required for deep surveys of the stellar Milky Way. We focus on the radio emission from OB stars, Be stars, flares from M dwarfs, and Ultra Compact HII regions. The stellar distribution in the Milky Way is simulated using the Besançon model, and various relations are used to predict their radio flux. We find that the full SKA will easily detect all UltraCompact HII regions. At the limit of 10 nJy at 5 GHz, the SKA can detect 1500 Be stars and 50 OB stars per square degree, out to several kpc. It can also detect flares from 4500 M dwarfs per square degree. At 100 nJy, the numbers become about 8 times smaller. SKA surveys of the Galactic plane should be designed for high sensitivity. Deep imaging should consider the significant number of faint flares in the field, even outside the plane of the Milky Way. Full article
(This article belongs to the Special Issue Stellar Astrophysics)
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Review

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39 pages, 4082 KiB  
Review
Stellar Chromospheric Variability
by Richard de Grijs and Devika Kamath
Universe 2021, 7(11), 440; https://doi.org/10.3390/universe7110440 - 15 Nov 2021
Cited by 10 | Viewed by 6062
Abstract
Cool stars with convective envelopes of spectral types F and later tend to exhibit magnetic activity throughout their atmospheres. The presence of strong and variable magnetic fields is evidenced by photospheric starspots, chromospheric plages and coronal flares, as well as by strong Ca [...] Read more.
Cool stars with convective envelopes of spectral types F and later tend to exhibit magnetic activity throughout their atmospheres. The presence of strong and variable magnetic fields is evidenced by photospheric starspots, chromospheric plages and coronal flares, as well as by strong Ca ii H+K and Hα emission, combined with the presence of ultraviolet resonance lines. We review the drivers of stellar chromospheric activity and the resulting physical parameters implied by the observational diagnostics. At a basic level, we explore the importance of stellar dynamos and their activity cycles for a range of stellar types across the Hertzsprung–Russell diagram. We focus, in particular, on recent developments pertaining to stellar rotation properties, including the putative Vaughan–Preston gap. We also pay specific attention to magnetic variability associated with close binary systems, including RS Canum Venaticorum, BY Draconis, W Ursae Majoris and Algol binaries. At the present time, large-scale photometric and spectroscopic surveys are becoming generally available, thus leading to a resurgence of research into chromospheric activity. This opens up promising prospects to gain a much improved understanding of chromospheric physics and its wide-ranging impact. Full article
(This article belongs to the Special Issue Stellar Astrophysics)
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32 pages, 635 KiB  
Review
Architecture of Hierarchical Stellar Systems and Their Formation
by Andrei Tokovinin
Universe 2021, 7(9), 352; https://doi.org/10.3390/universe7090352 - 21 Sep 2021
Cited by 50 | Viewed by 3014
Abstract
Accumulation of new data on stellar hierarchical systems and the progress in numerical simulations of their formation open the door to genetic classification of these systems, where properties of a certain group (family) of objects are tentatively related to their formation mechanisms and [...] Read more.
Accumulation of new data on stellar hierarchical systems and the progress in numerical simulations of their formation open the door to genetic classification of these systems, where properties of a certain group (family) of objects are tentatively related to their formation mechanisms and early evolution. A short review of the structure and statistical trends of known stellar hierarchies is given. Like binaries, they can be formed by the disk and core fragmentation events happening sequentially or simultaneously and followed by the evolution of masses and orbits driven by continuing accretion of gas and dynamical interactions between stars. Several basic formation scenarios are proposed and associated qualitatively with the architecture of real systems, although quantitative predictions for these scenarios are still pending. The general trend of increasing orbit alignment with decreasing system size points to the critical role of the accretion-driven orbit migration, which also explains the typically comparable masses of stars belonging to the same system. The architecture of some hierarchies bears imprints of chaotic dynamical interactions. Characteristic features of each family are illustrated by several real systems. Full article
(This article belongs to the Special Issue Stellar Astrophysics)
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26 pages, 4656 KiB  
Review
“In-System” Fission-Events: An Insight into Puzzles of Exoplanets and Stars?
by Elizabeth P. Tito and Vadim I. Pavlov
Universe 2021, 7(5), 118; https://doi.org/10.3390/universe7050118 - 22 Apr 2021
Cited by 1 | Viewed by 7000
Abstract
In expansion of our recent proposal that the solar system’s evolution occurred in two stages—during the first stage, the gaseous giants formed (via disk instability), and, during the second stage (caused by an encounter with a particular stellar-object leading to “in-system” fission-driven nucleogenesis), [...] Read more.
In expansion of our recent proposal that the solar system’s evolution occurred in two stages—during the first stage, the gaseous giants formed (via disk instability), and, during the second stage (caused by an encounter with a particular stellar-object leading to “in-system” fission-driven nucleogenesis), the terrestrial planets formed (via accretion)—we emphasize here that the mechanism of formation of such stellar-objects is generally universal and therefore encounters of such objects with stellar-systems may have occurred elsewhere across galaxies. If so, their aftereffects may perhaps be observed as puzzling features in the spectra of individual stars (such as idiosyncratic chemical enrichments) and/or in the structures of exoplanetary systems (such as unusually high planet densities or short orbital periods). This paper reviews and reinterprets astronomical data within the “fission-events framework”. Classification of stellar systems as “pristine” or “impacted” is offered. Full article
(This article belongs to the Special Issue Stellar Astrophysics)
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