Theory and Observation of Active B-type Stars

Dear Colleagues,

Active B-type stars are defined by the presence of emission lines formed in a dense environment, often in the form of a circumstellar disk. Among them are the classical Be stars, which are stars surrounded by an ionized gaseous disk, and B[e] stars, whose disks are so dense that even molecules and dust can form within them. In either case, the disks are the source of characteristic infrared excess continuum emission and linear polarization. Active B-type stars often exhibit signatures of variability on different temporal and spatial scales. Of particular importance are variations associated with the formation and dissipation of the gaseous, molecular and dusty disks around the various types of objects that occur on time scales spanning from years to decades. Although mechanisms such as radiation, rotation, pulsation, binarity and magnetic fields and the role they might play in pulling material off the stars were explored in detail over the past decades, the relevant physical processes involved in the formation of sustainable disks and their dynamical evolution are still unclear and a matter of debate.

This Special Issue intends to provide a comprehensive update on the status of the art in the field of active B-type stars. It aims to combine reviews and selected contributions on recent groundbreaking advances in the knowledge of these peculiar objects from both a theoretical and an observational perspective. Latest observations from high-resolution, ground-based facilities and from satellite missions, collected over a wide wavelength range, reveal fascinating details about the shape and structure of circumstellar disks and their interaction with interstellar matter. At the same time, the progress in numerical models combined with ever-increasing computer power facilitate the analysis of complex, multi-dimensional models for a more realistic representation and treatment of the mechanisms behind mass ejection phases and the realistic estimation of the amount of mass lost during some eruptive events. These new insights, from both theory and observations, provide a basis for exploring complex phenomena such as pulsation–wind connections, the transport of angular momentum, viscosity, internal rotation law, and mass loss, and for verifying the various scenarios proposed for the origin, evolution and variability of the circumstellar environment of the diverse classes of active B-type stars.

Potential topics include, but are not limited to:

• Observational properties of active B-type stars. Surveys, catalogues, tools and novel techniques;
• Stellar and fundamental parameters;
• Chemistry and physical structure of ejected material;
• Outflows and mass loss events; 
• Wind structure and properties;
• Rotation, pulsation and pulsation–wind connections;
• Magnetic fields, magnetospheres and magnetic activity;
• Binarity and multiple systems;
• Stellar evolution and evolutionary phases;
• Decretion disks and circumstellar disk formation;
• Dynamical evolution of disk, disk growth and dissipation;
• Evolutionary links among related objects.

References:

Baade et al. 2016, A&A, 588, 56.
Cochetti, Y. R. ; Arias, M. L. ; Kraus, M; et al.  2021, A&A, 647, 164C.
Ghoreyshi et al. 2018, MNRAs, 479, 2214
Halonen, R. & Jones, C. 2013, APJS. 208, 3
Hofmann, K. et al. 2022, A&A, 658,81
Kraus, M. 2019, Galax, 7, 83K
Kriz, S. & Harmanec, P. 1975, Bull. Astron. Inst. Czech., 26, p. 65
Porter, J & Rivinius, T 2003, PASP, Vol. 115, pp. 1153-1170.
Rivinius, T. 2013, ASSP, 31, 253R

Previous proceedings books:

• The B[e] Phenomenon: Forty Years of Studies: Proceedings of a Conference Held at Charles University, Prague, Czech Republic, 27 June- 1 July 2016, Volume 508 of Astronomical Society of the Pacific conference series. Eds.: Anatoly S. Miroshnichenko, Sergey Zharikov, Daniela Korčáková, Marek Wolf.
• New windows on massive stars: asteroseismology, interferometry, and spectropolarimetry, Proceedings of the International Astronomical Union, IAU Symposium, 2015, Volume 307, pp. 154-164.
• Bright Emissaries: Be Stars as Messengers of Star-Disk Physics, Proceedings of a Meeting held at The University of Western Ontario, in London, Ontario, Canada, 11-13 August 2014. Edited by T. A. A. Sigut and C. E. Jones. San Francisco: Astronomical Society of the Pacific, 2016, p.175
• Circumstellar Dynamics at High Resolution. Proceedings of a Joint ESP/Brazilian Workshop held at Foz do Iguacu, Brazil, 27 February-2 March, 2012. ASP Conference Proceedings, Vol. 464. Edited by A. Carciofi and Th. Rivinius. San Francisco: Astronomical Society of the Pacific, 2012.
• Active OB stars: structure, evolution, mass loss, and critical limits, Proceedings of the International Astronomical Union, IAU Symposium, Volume 272, 2011. 

Dr. Lydia Sonia Cidale
Dr. Michaela Kraus
Dr. María Laura Arias
Guest Editors

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