Name: Thomas R. Geballe

Institution: Gemini-N

e-mail: tgeballe(no-spam)gemini.edu

Partner Contry: GS

Science Meeting: Yes

User Meeting: Yes

NGO Staff Meeting: None Selected

Presentation: Yes

Format: Poster

Title: 18O and the formation of R Coronae Borealis and Hydrogne-deficient Carbon Stars

Co-author: G. C. Clayton (1), F. Herwig (2), C. Fryer (3), M. Asplund (4)

Co-authors' Institutions: (1) Louisiana State University, (2) Los Alamos National Laboratory and Keele University, (3) Los Alamos National Laboratory, (4) Mount Stromlo Observatory

Abstract:

We have found that at least seven hydrogen-deficient carbon (HdC) and R Coronae Borealis (RCB) stars, have 16O/18O ratios close to and in some cases less than unity, values orders of magnitude lower than other stars (the Solar value is 500). Greatly enhanced 18O is evident in every HdC and RCB star cool enough to have detectable 2um CO bands. The three HdC stars measured have 16O/18O<1, lower values than in any of the RCB stars. We have explored the idea that HdC and RCB stars originate in the mergers of CO- and He-white dwarfs, and conclude that nucleosynthesis during the merger may not only may provide a suitable environment for copious production of 18O, leading to low values of 16O/18O, but also may account for other observed isotopic and elemental abundance ratios.