Reid, Andrew Harold Noble; (1994) The variability of three O-type stars: zeta Ophiuchi; zeta Puppis; and HD 93521. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Analysis of time-resolved optical spectroscopy of the rapidly rotating O-stars: ζ Ophiuchi (O9.5 V); ζ Puppis (O4 I(n)f); and HD 93521 (O9.5 V), is presented. Extensive datasets were acquired for the first two stars, including coordinated, multi-observatory observations; these stars represent the principal subjects for investigation. For HD 93521, the data are more fragmentary; however, the echelle nature of the spectra and the similar spectral classification to ζ Oph, justify their inclusion. For all three stars, the optical observations show line profile variations (1pv) in the form of 'bumps' and 'dips' migrating from blue to red on typical timescales of several hours. Strong changes in line shape and equivalent width are also observed for ζ Pup. The strength of these variations is dependent upon line species and line strength in all cases. For the two principal stars, the morphology of the lpv is investigated by using a Fourier time-series technique which incorporates the CLEAN deconvolution algorithm. The lpv of the HD 93521 is investigated by comparison with synthetic data generated by a non-radial pulsation (NRP) stellar model. The origin of the lpv in O-stars is controversial; a major aim of this work is to discriminate between photospheric non-radial pulsation, rotational modulation, and variability at the base of the stellar wind, as the cause of the optical variability. In addition to the optical spectroscopy, narrow-band photometry was available for the primary stars, and, for all three stars, time-resolved IUE ultraviolet spectroscopy (some simultaneous with the optical data). The simultaneous UV data are of particular importance as they allow an investigation of a possible 'photospheric connection' between the lpv and the development of enhancements in optical depth within the stellar wind seen as discrete and narrow absorption components in the UV resonance lines. As a collateral study, the analysis techniques which have been applied to the optical data have been tested on a series of synthetic profiles generated by NRP stellar models. The results from the synthetic data allow a comparison with those obtained on observational data, both given here and in previous studies.

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