Share This Special Issue

Special Issue Editor

Prof. Dr. Renada Konstantinova-Antova

E-Mail Website
Guest Editor

Institute of Astronomy and NAO, Bulgarian Academy of Sciences, 72 Tsarigradsko Shosse Blvd., 1040 Sofia, Bulgaria
Interests: stellar magnetic fields; dyanmo driven activity; stellar structure and evolution; late-type stars

Special Issue Information

Dear Colleagues,

Magnetic fields are present everywhere in the Universe. Stars are magnetic from the early stages of their life because they are formed by the plasma in the interstellar clouds. Recent progress in spectropolarimetry, spectroscopy, and interferometry has revealed exciting revelations regarding the magnetic fields and their structure in stars of different mass and at different evolutionary stages. It appears that magnetic fields exist in stars during their whole life, but they are amplified and maintained by different mechanisms with the change of the stellar structure as a star evolves. These recent findings are useful for the theoreticians in the fields of dynamo theory and stellar evolution and prompt further investigation. For example, the influence of the magnetic field on the evolution of a star is still poorly studied. Moreover, the mechanisms generating and maintaining the magnetic fields of stars in very advanced evolutionary stages are still unclear. The activity signatures of these stars, along with many other important topics, remain to be explored.

With these brief thoughts, I invite you to contribute to this topic by submitting your new papers in the field to this Special Issue. Your papers will be peer-reviewed and made available to the public in open access when accepted. For more information, please see the Instructions for Authors on the journal webpage.

Prof. Dr. Renada Konstantinova-Antova
Guest Editor

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.

Keywords

stars
magnetic fields
dynamo
stellar structure
stellar evolution

Published Papers (2 papers)

Download All Papers

Research

Jump to: Review

7 pages, 1424 KiB

Open AccessArticle

R-Process with Magnetized Nuclei at Dynamo-Explosive Supernovae and Neutron Star Mergers

by Vladimir N. Kondratyev

Universe 2021, 7(12), 487; https://0-doi-org.brum.beds.ac.uk/10.3390/universe7120487 - 10 Dec 2021

Cited by 9 | Viewed by 1803

Abstract

Nucleosynthesis at latge magnetic induction levels relevant to core-collapse supernovae and neutron star mergers is considered. For respective magnetic fields of a strength up to ten teratesla, atomic nuclei exhibit a linear magnetic response due to the Zeeman effect. Such nuclear reactivity can be described in terms of magnetic susceptibility. Susceptibility maxima correspond to half-filled shells. The neutron component rises linearly with increasing shell angular momentum, while the contribution of protons grows quadratically due to considerable income from orbital magnetization. For a case j = l + 1/2, the proton contribution makes tens of nuclear magnetons and significantly exceeds the neutron values which give several units. In a case j = l − 1/2, the proton component is almost zero up to the g shell. A noticeable increase in the generation of corresponding explosive nucleosynthetic products with antimagic numbers is predicted for nuclei at charge freezing conditions. In the iron group region, new seeds are also created for the r-process. In particular, the magnetic enhancement of the volume of ⁴⁴Ti isotopes is consistent with results from observations and indicates the substantial increase in the abundance of the main titanium isotope (⁴⁸Ti) in the Galaxy’s chemical composition. Magnetic effects are proven to result in a shift of the r-process path towards smaller mass numbers, as well as an increase in the volume of low-mass nuclides in peaks of the r-process nuclei. Full article

(This article belongs to the Special Issue Magnetic Fields and Activity through Stellar Evolution)

► Show Figures

Figure 1

Review

Jump to: Research

16 pages, 455 KiB

Open AccessReview

Is Core Angular Momentum Key to the Giant Dynamo?

by Klaus-Peter Schröder and Renada Konstantinova-Antova

Universe 2022, 8(8), 411; https://0-doi-org.brum.beds.ac.uk/10.3390/universe8080411 - 05 Aug 2022

Viewed by 891

Abstract

The pros and cons of core angular momentum dissipation into the convective envelopes of giants as a driver of giant activity is discussed in face of the observational evidence, which points to two ”magnetic strips“, in the HRD, where in the first, at the base of the RGB, activity of moderate mass stars is freshly started and rejuvenated in the second strip, ascending along the mid-AGB. It remains unclear, though, which depths the giant dynamo is operating. Both concentrations of active giants in the HRD are related to stellar evolution phases with core contraction and spin-up, and presumably the dissipation of angular momentum into the convective envelope above. At the same time, the latter has a small Rossby number by virtue of its increasing convective turn-over time—i.e., favourable conditions to run an alpha-omega dynamo. Since coronal X-ray emission appears to give an incomplete picture of stellar activity across the HR diagramme, we here focus on the observed chromospheric emissions across the giant branches and find good agreement with the magnetic field Zeeman-detections there. Stable evolution phases—solar-type main sequence stars with central hydrogen burning and moderate mass, central Helium burning K giants—by contrast demonstrate a decline in activity, apparently imposed by magnetic braking, as such stars are also slower rotators. In that sense, the observed picture of two magnetic activity strips across the HR diagramme could empirically be explained as an interplay of magnetic braking during the stable phase of core helium burning and supply by internal angular momentum during episodes of fast core contraction with core spin-up and angular momentum dredge-up, while meeting dynamo-friendly envelope conditions. At the same time, the sporadic external supply of angular momentum by the engulfment events of a planet, in the course of the evolutionary envelope expansion, may explain some cases of exceptional activity outside the here-described general picture. Full article

(This article belongs to the Special Issue Magnetic Fields and Activity through Stellar Evolution)

► Show Figures