Spectroscopic diagnosis of extended circumstellar regions about early type stars
| Thesis title in Czech: | Spektrální diagnostika látky v okolí ranných hvězd |
|---|---|
| Thesis title in English: | Spectroscopic diagnosis of extended circumstellar regions about early type stars |
| Key words: | B[e] jev, protoplanetární mlhovina, zakázané čáry, nebulární diagnostika |
| English key words: | B[e] phenomenon, protoplanetary nebula, forbidden lines, nebular diagnostics |
| Academic year of topic announcement: | 2016/2017 |
| Thesis type: | diploma thesis |
| Thesis language: | angličtina |
| Department: | Astronomical Institute of Charles University (32-AUUK) |
| Supervisor: | doc. Mgr. Daniela Korčáková, Ph.D. |
| Author: | hidden - assigned and confirmed by the Study Dept. |
| Date of registration: | 31.05.2017 |
| Date of assignment: | 07.06.2017 |
| Confirmed by Study dept. on: | 19.06.2017 |
| Date and time of defence: | 05.09.2019 10:00 |
| Date of electronic submission: | 19.07.2019 |
| Date of submission of printed version: | 19.07.2019 |
| Date of proceeded defence: | 05.09.2019 |
| Opponents: | doc. RNDr. Petr Zasche, Ph.D. |
| Advisors: | prof. Steven Neil Shore, Ph.D. |
| Guidelines |
| The focus of the diploma thesis is stars showing the B[e] phenomenon. These stars are distinctive by the presence of emission lines from forbidden transitions, dust emission, and very high Balmer line emission. The emission/absorption lines from permitted transition of neutral or singly ionised species are also found in the spectra. Spectral lines, formed close to the central object, show night-to-night variability, emission lines are variable on time-scale of months, while the emission lines from forbidden transitions show changes in order of years.
These spectral features indicate extended and dynamic circumstellar region, which complicates the determination of the properties of the central object. The connection of high temperature dense medium with low, collisional less outer regions situated into the complicated geometry leads to extreme cases of the radiative transfer problem. Especially, a subgroup of the stars showing the B[e] phenomenon - compact planetary nebulae, suffers with this complication. In contrast to classical planetary nebulae, the nebula is still too close to the central star in this case, that both are linked together. The analysis of such objects requires sophisticated models. The restriction of input parameters and conditions for such a high-level modelling is the main aim of the thesis. Based on the high-resolution archival spectra of a selected object (MWC 939), the student will determine the density and temperature in different regions of the circumstellar medium using the standard nebula diagnostic. Using the ionisation and excitation stage of atoms and ions, and modelling, the properties of the central star will be recovered, to be used as input for more detailed analysis using interpolation from the public grids, or its calculation using stellar atmosphere modelling codes. The work will include a detailed comparison of MWC 939 with other objects from the B[e] compact planetary nebulae sub-group and FS CMa sub-group. Such results will certainly be used for the further work, especially since only a few such objects have studied in detail to date. |
| References |
| Osterbrock, D. E. & Ferland, G. J. 2005, "Astrophysics Of Gaseous Nebulae And Active Galactic Nuclei" (University Science Books, 2nd edition)
Dopita, M.A., Sutherland, R.S. Astrophysics of the Diffuse Universe (Springer), 3rd edition, 2003 Shore, S.N.The Tapestry of Modern Astrophysics (Wiley Interscience), 2003 Mihalas, D. Stellar atmosheres (San Francisco: Freeman), 2nd edition, 1978 |