brief summary about yourself and your achievements
I focus on a very small group of peculiar B-type stars called FS CMa stars (Miroshnichenko 2007). These stars show the B[e] phenomenon, i.e., the presence of the forbidden emission lines and infrared excess. These observed properties point to the extended region of the circumstellar gas and dust. The amount of the circumstellar matter is so huge that it can not be explained by the evolution of a single star, however, the secondaries have been detected only in about 1/3 stars. This is the same percentage as it is observed in ordinary main-sequence late B-type stars, the range of most FS CMa stars. The huge amount of the circumtellar matter complicates the data analysis and prevent the usage of standard methods. Therefore, the FS CMa stars are the last stellar group that evolutionary status is still disputable. None of the possible theories, binarity, post-AGB stars, extreme case of the Be stars, fits the observations well.
Our recent discovery of a very strong magnetic field in one of these objects, IRAS 17449+2320 (Korčáková et al. 2022), points to the new scenario for some of FS CMa stars – the post- merger origin. Other properties of IRAS 17449+2320 confirmed this guess. The post-merger hypothesis explains all the observed phenomena that we discovered in last twenty years during our observation campaign:
In order to confirm the post-merger hypothesis, we start with N-body and magneto-hydro-dynamical simulations. 2.5D magneto-hydrodynamical simulations can explain many of the observed phenomena (Moranchel-Basurto et al. 2023). The magnetic field significantly changes the disc structure, creates the jets from the stellar poles and the inner edge of the disc, hot plasmoid, and currents from the disk towards the star. It is also responsible for the formation of a hot corona. The N-body simulations of N. Dvořáková and F. Dinnbier show that 50% of merger product is a B-type star. This is a natural consequence of the initial mass function, the distribution of the binary parameters according to the mass of the binaries, and a fact that the range of masses of B-type stars is large. These simulations confirmed that the probability of finding of a B-type post-merger is relatively large. However, they also revealed that the largest channel of mergers is currently overlooked, because the community focuses itself rather to the very massive binaries or magnetic Ap stars.
The post-merger hypothesis is very promising for several FS CMa stars. However, it can not be the explanation for all of them. The reason is the pure classification of objects, because the huge amount of the circumstellar matter prohibits the accurate determination of the stellar parameters. Therefore, the current list of FS CMa stars contains also Be/X-ray binary, B[e] supergiant, post-AGB stars, young planetary nebula, even some symbiotics may be there. This is currently the most serious problem in the study of the intermediate-mass post-mergers hidden among FS CMa stars.
These intermediate-mass mergers deserve definitely more attention. They may change our view on the chemical evolution of the galaxy. They may even contribute to the enrichment of the intergalactic matter because N-body simulations of N. Dvoˇr ́akov ́a and F. Dinnbier show that the merger events may occur also out of the galaxy. Mergers observed as FS CMa type objects are still out of the hydrostatic equilibrium, therefore their detailed studies can improve the stellar structure and evolutionary models. Some of them are probably a progenitors of the magnetic Ap stars. They may also offer the explanation of strange young strongly magnetic white dwarfs.
How did your career benefit from the ERASMUS project?
Generally, projects like ERASMUS are very useful programs, but this time it helped me very much. We are only two in the world who systematically study these objects. Therefore, there is no broad discussion and also new data and numerical simulations are obtained very slowly. Thanks to the ERASMUS project, I gave the talk “FS CMa stars – overlooked channel of mergers” at the Instituto de Astrof ́ısica de Canarias (IAC) and could point to the importance of the study of FS CMa stars that are completely overlooked even if they can move the stellar astrophysics significantly forward. After the talk, one colleague from IAC contacted me and showed me the possibilities and limits of UV spectroscopy for the study of FS CMa stars. Moreover, the talk was recorded1 and may reach more broader audience.
How did the ERASMUS program support your personal development?
It was the first time when I was on the island and in a famous touristic place. I was very surprised how poor is the life of the ordinary people in some areas. Instead of the improving the life of people, the tourism pushed it down. The local people are not owners of hotels and other profitable activities, but work in hotels, restaurants, . . . for minimal salaries, while house prices and other services rose.
Can you share some experience from your ERASMUS exchange?
I can recommend the ERASMUS program, everything worked well.
References
Jeřábková, T., Korčáková, D., Miroshnichenko, A., et al. 2016, A&A, 586, A116
Korčáková, D., Sestito, F., Manset, N., et al. 2022, A&A, 659, A35
Korčáková, D., Shore, S. N., Miroshnichenko, A., et al. 2019, in Astronomical Society of the Pacific Conference Series, Vol. 519, Radiative Signatures from the Cosmos, ed. K. Werner, C. Stehle, T. Rauch, & T. Lanz, 155
Kučerová, B., Korčáková, D., Polster, J., et al. 2013, A&A, 554, A143
Kříček, R., Korčáková, D., Jeřábková, T., et al. 2017, in Astronomical Society of the Pacific Conference Series, Vol. 508, The B[e] Phenomenon: Forty Years of Studies, ed. A. Miroshnichenko, S. Zharikov, D. Korčáková, & M. Wolf, 411–412
Miroshnichenko, A. S. 2007, ApJ, 667, 497
Moranchel-Basurto, A., Korčáková, D., & Chametla, R. O. 2023, MNRAS, 523, 5554
Polster, J., Korčáková, D., & Manset, N. 2018, A&A, 617, A79
Polster, J., Korčáková, D., Votruba, V., et al. 2012, A&A, 542, A57
5.9.2023