Hodges, S.E.; (2012) A multi-wavelength study of fast winds from central stars of planetary nebulae. Doctoral thesis , UCL (University College London).

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Abstract

Structure has been observed in the stellar outflows of hot, luminous OB stars through the temporal spectral analysis of UV data: the absorption troughs of wind-accelerated P-Cygni profiles of certain UV ‘super-ions’, particularly the Pv λλ 1118, 1128 doublet, have revealed the presence of additional absorption components which have been observed to migrate through the wind. Similar P-Cygni profiles have also been observed in the the UV spectra of Central Stars of Planetary Nebulae (CSPNs), but detailed temporal analysis of CSPN outflows has been frustrated due to a lack of substantial time-series data. However, the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite has provided high-resolution time-series data for CSPNs, and therefore the nature of the time-variance of UV P-Cygni profiles can be investigated. To this end FUSE spectroscopic data has been obtained, and certain key UV resonance lines, as found in the stellar wind, have been subjected to various time-series analysis tools including Time Variance Spectra (TVS) and Fourier-based periodicity analysis. Also, optical time-series data of young CSPNs has been obtained via the ESO High-Accuracy Radial velocity Planetary Searcher (HARPS) spectrograph, and therefore similar temporal analysis has been carried out into the possible appearance of time-varying structure of Helium lines found in the deep photospheric regions of the atmosphere with the aim of detecting the presence of modulated structure at the base of the stellar wind – with the aim of discovering a causal mechanism for the higher wind-related phenomena. The presence of such structure in the stellar outflows of CSPNs (and likewise, OB stars) suggests that non-LTE stellar atmosphere analysis techniques – such as the Sobolev with Exact Integration (SEI) method used within this thesis – which assume a spherically smooth wind may provide inaccurate levels of mass loss from the stellar atmosphere; also, the possible non-smooth nature of the wind is considered from the viewpoint of possessing a more porous ‘clumped’ material which would also have an affect upon mass loss determinations, a key factor in the understanding of the latter stages of stellar evolution.

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