Circumstellar Matter of B-type Stars
| Název práce v češtině: | Circumstellar Matter of B-type Stars |
|---|---|
| Název v anglickém jazyce: | Circumstellar Matter of B-type Stars |
| Klíčová slova: | spektrální diagnostika|látka v okolí hvězd|horké hvědy |
| Klíčová slova anglicky: | spectroscopic diagnosis|circumstellar matter|hot stars |
| Akademický rok vypsání: | 2022/2023 |
| Typ práce: | disertační práce |
| Jazyk práce: | angličtina |
| Ústav: | Astronomický ústav UK (32-AUUK) |
| Vedoucí / školitel: | doc. Mgr. Daniela Korčáková, Ph.D. |
| Řešitel: | skrytý - zadáno a potvrzeno stud. odd. |
| Datum přihlášení: | 02.08.2022 |
| Datum zadání: | 02.08.2022 |
| Datum potvrzení stud. oddělením: | 20.09.2022 |
| Zásady pro vypracování |
| A small sample of B-type stars shows forbidden emission lines in their spectra and strong infrared excess due to the presence of circumstellar gas and dust. Such type of spectra has been found among supergiants, Herbig Ae/Be stars, compact planetary nebulae, and symbiotic stars (Lamers et al., 1998). However, there is a group called FS CMa stars, whose nature and evolutionary status has not been determined.
The focus of the thesis is the later one, FS CMa group. Currently, the most favourable scenario is the binarity. However, not sufficient binaries have been found among FS CMa stars. Moreover, almost every sigh of the binarity may be explained by another physical process or inappropriate observational technique. Recently, very strong magnetic field was discovered in IRAS 17449+2320 (Korčáková et al., 2022). This opened the possibility that some of the FS CMa stars are post-merger systems. This hypothesis is supported by large space velocity toward the galactic pole indicating that the star escaped from the birth cluster. The conservation of the momentum supports the companion merging. One of the key tasks is to identify the candidates of post-mergers. Due to the huge amount of the circumstellar matter, the classification of the individual objects is very difficult. The list of the FS CMa stars is highly probably polluted by post-AGB objects, symbiotic stars, and Be/X-ray binaries. Currently, the amount of data is sufficient to study physical processes that take place in these objects, e.g. material ejecta or pulsations. |
| Seznam odborné literatury |
| Dopita, M.A., Sutherland, R.S. Astrophysics of the Diffuse Universe (Springer), 3rd edition, 2003
Emerson, D., 1999, "Interpreting Astronomical Spectra", John Wiley & Sons Gray, D.F., ``The Observation and Analysis of Stellar Photospheres'', Cambridge University Press, 2005 Jaschek, C., Andrillat, Y., Jaschek, M., 1996, A&AS 117, 281 Lamers, H.J.G.L.M., Zickgraf, F.J., de Winter, D., Houziaux, L., Zorec, J., 1998, A&A 340, 117 Mihalas, D. Stellar atmosheres (San Francisco: Freeman), 2nd edition, 1978 Miroshnichenko, A. S. 2007, ApJ, 667, 497 Miroshnichenko, A. S., Manset, N., Kusakin, A. V., et al. 2007, ApJ, 671, 828 Osterbrock, D. E. & Ferland, G. J. 2005, "Astrophysics Of Gaseous Nebulae And Active Galactic Nuclei" (University Science Books, 2nd edition) Rivinius, T., Carciofi, A., & Martayan, C. 2013, A&ARv, 21, 69 Stars with the B[e] Phenomenon. ASP Conference Series, Vol. 355, M. Kraus & A. Miroshnichenko eds., San Francisco: Astronomical Society of the Pacific, 2006 The B[e] Phenomenon: Forty Years of Studies. ASP Conference Series, Vol. 508., A. Miroshnichenko, S. Zharikov, D. Korčáková & M. Wolf San Francisco: Astronomical Society of the Pacific, 2017 Zickgraf, F.J., Wolf, B., Stahl, O., Leitherer, C., & Klare, G. A&A, 143, 421 |
| Předběžná náplň práce v anglickém jazyce |
| Among B-type stars are observed stars surrounded by the gas, eventually also by dust. The gas reveals itself in the spectra as emission lines, while the dust is responsible for the infrared excess. These stars are very variable and many unsoved questions are related with them. The best studied are classical Be stars (see, e.g. review Rivinius, 2013). The gas emission comes from the decretion disk. Material outflow is supported by the fast rotation of the star and pulsations. However, the exact principle is not yet known. More complex circumstellar matter is around B[e] stars. The forbidden emission lines, pointing to very low density material in outer parts, and the infrared excess are detected. Such spectral properties show stars of different types and at different evolutionary stages. The B[e] stars have been found among supergiants, young planetary nebulae, Herbig Ae/Be stars, and symbiotic stars (Lamers et al., 1998). The B[e] phenomenon is natural for young planetary nebulae and symbiotic stars. There has to be a phase during the expansion of the envelope when such spectral properties are observed. In Herbig Ae/Be stars, the accretion of the material is responsible for the B[e] phenomenon. The B[e] supergiants have the geometrically thick slowly expanding disk, surrounded by the dusty ring in the equatorial region, while the fast radiatively driven wind is around poles (Zickgraf et al., 1985). However, there are B[e] stars whose evolutionary status is not known, FS CMa stars (Miroshnichenko, 2007). These stars are the main topic of the proposed project.
Recently, it has been shown that one of the FS CMa stars is a post-merger system. The crucial question is whether this star was misclassified or whether all FS CMa stars are all post-merger systems. In the latter case, FS CMa stars provide an evolutionary sequence of the merging process. Understanding the merger process helps, among others, to understand the formation, evolution, and chemical composition of stars and interstellar matter. Recently, it has been shown that mergers played an important role in the formation of first stars and properties of young galaxies. |