Measurements of physical parameters of accreting white dwarfs and characterization of accretion discs around them using optical spectroscopy
1University of Oulu, Faculty of Science, Astronomy
|Online Access:||PDF Full Text (PDF, 10.1 MB)|
|Persistent link:|| http://urn.fi/URN:NBN:fi:oulu-202108048811
Oulu : J. Hedemäki,
|Publish Date:|| 2021-08-06
|Thesis type:||Master's thesis
Cataclysmic variables (CV) are compact binaries, where a white dwarf (WD) accretes mass from a low-mass companion. For a non-magnetic (or weakly magnetic) WD this accretion of mass creates an accretion disc around it. UV spectroscopy of CV systems allows the easiest way to measure the spectrum of a WD, thus it is widely used. The downside of UV spectroscopy is the limited sample of objects. Using optical spectroscopy, a greater amount of CVs can be studied.
To this end, we set out to study CVs by modelling observed optical spectra, in order to assess two stellar parameters: effective temperature Teff and surface gravity log g of the WD. We first show that we were able with sufficient accuracy to model single WD spectra. We then show that we were able to recover the parameters of modified theoretical single WD spectra, where the modification can be e.g. the addition of noise or the cutting of absorption linecores. We also show that rotational broadening and zeeman-splitting had a negligible effect on our modelling procedure.
Lastly, we show the modelling results of 11 CVs in total, for which the stellar parameters are obtained and accretion disc spectra are extracted. For four objects we compare our obtained parameter values to those obtained by UV spectroscopy. Finally, the contribution of the accretion disc luminosity to the total luminosity of the system is shown.
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