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Atmospheric characteristics of white dwarfs
Krejčová, Kateřina ; Kawka, Adéla (advisor) ; Mayer, Pavel (referee)
We have analyzed the ultraviolet spectra of 40 hydrogen-rich (DA) white dwarfs. These spectra have been obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite and are publicly available via the MAST FUSE database. We derived the effective temperature and surface gravity by fitting the hydrogen Lyman spectral lines with model spectra. By applying white dwarf evolutionary models, we were able to determine the white dwarf mass, cooling age and absolute magnitude. These then allowed us to determine the distance to each star and its predicted gravitational redshift. We have identified several chemical elements in the white dwarf spectra. We determined the abundances of C, Si, P and S by measuring the equivalent widths of selected lines of these elements. Finally, we studied the spectra of J0623-376 and LM Com in more detail.
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High accuracy O-18(p, alpha)N-15 reaction rate in the 8 . 10(6)-5 . 10(9) K temperature range
La Cognata, M. ; Spitaleri, C. ; Mukhamedzhanov, A. ; Banu, A. ; Cherubini, S. ; Coc, A. ; Crucilla, V. ; Goldberg, V. ; Gulino, M. ; Irgaziev, B. ; Kiss, G. G. ; Lamia, L. ; Mrázek, Jaromír ; Pizzone, R. G. ; Puglia, S. M. R. ; Rapisarda, G. G. ; Romano, S. ; Sergi, M. L. ; Tabacaru, G. ; Trache, L. ; Tribble, R. E. ; Trzaska, W. ; Tumino, A.
The O-18(p, alpha)N-15 reaction is of great importance in several astrophysical scenarios, as it influences the production of key isotopes such as F-19, O-18 and N-15. In this work, a high accuracy O-18(p, alpha) N-15 reaction rate is proposed, based on the simultaneous fit of direct measurements and of the results of a new Trojan Horse experiment. In particular, we have focused on the study of the broad 660 keV 1/2(+) resonance. Since Gamma similar to 100 - 300 keV, it strongly influences the nearly-zero-energy region of the cross section by means of the low-energy tail of the resonant contribution and dominates the cross section at higher energies. Here we provide a factor of 2 larger reaction rate above T similar to 0.510(9) K based over our new improved determination of its resonance parameters.
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Atmospheric characteristics of white dwarfs
Krejčová, Kateřina ; Kawka, Adéla (advisor) ; Mayer, Pavel (referee)
We have analyzed the ultraviolet spectra of 40 hydrogen-rich (DA) white dwarfs. These spectra have been obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite and are publicly available via the MAST FUSE database. We derived the effective temperature and surface gravity by fitting the hydrogen Lyman spectral lines with model spectra. By applying white dwarf evolutionary models, we were able to determine the white dwarf mass, cooling age and absolute magnitude. These then allowed us to determine the distance to each star and its predicted gravitational redshift. We have identified several chemical elements in the white dwarf spectra. We determined the abundances of C, Si, P and S by measuring the equivalent widths of selected lines of these elements. Finally, we studied the spectra of J0623-376 and LM Com in more detail.
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