Time-series analysis of B[e] supergiant stars

Thesis

B[e] supergiant stars (B[e]SGs) are a rare and unusual class of massive evolved stars which are poorly understood. I demonstrate how studying \sgBeshorthand s by analysing time-series observations reveals key information about this stellar class which may help to build a common picture and determine the origin of their phenomena. I utilise spectroscopic data from the Global Jet Watch, which is able to observe astronomical objects with sustained high time-resolution, and describe my contributions to the data reduction pipeline. I access and analyse high-resolution FEROS spectra, and photometry from the ASAS, ASAS-SN, OMC, and TESS surveys.

I take an in-depth case study of the B[e]SG binary GG Carinae, which has been widely studied but poorly understood. I demonstrate that previous determinations of the binary's orbital solution were incorrect and accurately measure it for the first time, finding that the binary is significantly eccentric (e=0.50+/-0.03) and that the system is brightest at periastron. I discovered a pulsation mode in the system from photometric and spectroscopic variability, and analysed it in depth for the first time. The variability has a period of 1.583156+/-0.0002 days and displays amplitude modulation over the binary's orbital period, such that the amplitude of the detected variability is largest just after periastron. The variability is most likely due to an l=2 f-mode pulsation in the primary which is modulated by the time-varying tidal potential in the eccentric orbit. I study the two atomic circumbinary rings of GG Carinae and find evidence of subtle variability of the line centres and the blue-peak to red-peak ratios of the emission lines arising from the inner circumbinary ring over the FEROS observations. I show these variations may be caused due to the binary exciting the circumbinary rings to higher eccentricities over the observation timescales.

A preliminary study utilising TESS and ASAS-SN data of the Galactic B[e]SG sample reveals signatures of binarity in a further three specimens. This increases the ratio of confirmed or suspected binaries in the Galactic B[e]SG population from 4/9 to 7/9, indicating that binarity may be key in understanding the phenomenon. Pulsations similar to those seen in GG Carinae are also detected in at least two further objects for the first time, demonstrating that pulsations may also be a commonality of the class.

Authors: Porter, A

• DOI: 10.5287/ora-qxzydxavr
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: binary star; stellar physics; astrophysics; GG Carinae; B[e] supergiant