Doctor of Philosophy (PhD)
Physics and Astronomy
The existence of extended, cold dust envelopes surrounding R Coronae Borealis (RCB) stars has been known about for over 30 years. RCB stars are an exotic group of extremely hydrogen-deficient, carbon-rich supergiants that are known for their spectacular declines in brightness (up to 8 mags) at irregular intervals. There are three possible origins of these envelopes: (1) they are fossil planetary nebulae (PNe), indicating that RCB stars formed via a final Helium-shell flash; (2) they are the remnant material from the merger of a CO and a He white dwarf binary, (3) they have been constructed from dust ejection events during the current phase of the central stars. In the first scenario we expect to find the shell H--rich, while in the remaining two scenarios the shell is H--poor. I have directly investigated the hydrogen abundance of the envelope surrounding R Coronae Borealis, itself, with archival observations from the Galactic Arecibo L-band Feed Array HI (GALFA-HI) Survey. Further, I have examined new and archival Spitzer Space Telescope and Herschel Space Observatory images in the far infrared and submillimeter of these envelopes to examine the morphology of these dusty shells. Herschel has, in particular, revealed the first ever bow shock associated with an RCB star with its observations of SU~Tauri. I have also put together some of the most comprehensive spectral energy distributions (SEDs) of these stars ever made with multi--wavelength data from the ultraviolet to the submillimeter. I will discuss all these results and their implications for the origins of the circumstellar material of RCB stars and the origins of RCB stars themselves.
Document Availability at the Time of Submission
Release the entire work immediately for access worldwide.
Montiel, Edward Joseph, "Circumstellar Dust Shells: Clues to the Evolution of R Coronae Borealis Stars" (2016). LSU Doctoral Dissertations. 3683.